Waste-Heat Water Distillation System

CROSS REFERENCES

This application claims priority to U.S. provisional patent application 61/838,066, filed 21 June 2013.

BACKGROUND

As the global demand for potable water continues to stress current water supplies, the need for systems that can convert non-potable water sources into potable or distilled water is vital.

Population growth will increase the stress on water supplies, increasing the need for systems that can address current and future water demand. There are abundant sources of non-potable water available, including seawater and/or other water sources containing biological contaminants and/or undesirable dissolved solids. These sources of non-potable water are also referred to as raw water or raw feedwater.

Filter and filtration systems can improve quality of near-potable fresh water; however they can't be used for desalinization of seawater. Reverse osmosis systems can be used for

desalinization of seawater, but reverse osmosis systems have many disadvantages, including high operating costs and necessary replacement of costly membranes. Operating by forcing seawater through a membrane at high pressure, these systems must overcome the naturally high osmotic pressure of seawater to freshwater, which requires operating pressures as high as 70 atmospheres. Future innovations to reduce energy cost are limited by this high pressure requirement, and these systems are likely already fully optimized in energy efficiency. Moreover, reverse osmosis systems do not remove all solids from the non-potable water source; therefore applications that require pure, distilled water can't use them.

Distillation systems operate by changing the phase of the raw water from a liquid to a vapor, then condensing the vapor, leaving behind solids and biological contaminants. These systems require more energy than reverse osmosis systems; however they provide the best method to ensure the removal of dissolved solids and other contaminants from the raw water. Commonly used methods of distillation include vapor-compression and multi-flash or multi- effect distillation. These systems have evolved to use significantly less energy than traditional distillation to vaporize raw water; however they are still energy intensive. Because these systems are already highly optimized, the opportunity for additional improvements in energy efficiency is limited.

Waste-heat distillation systems utilize waste heat normally rejected to the environment to drive distillation, significantly reducing the energy cost. The true energy cost of a waste-heat distillation system must also include any adverse affects, such as reduced power output of the integrated system supplying the waste heat. Furthermore, a system's ability to utilize available waste heat throughout the entire dynamic operating range of the system with which it integrates determines the overall effectiveness of the waste-heat distillation system.

PRIOR ART

Conventional distillation systems use a source of energy such as an electric heating element or combustion to boil the raw water into vapor. U.S. Pat. No. 6,830,661 describes a conventional distiller that uses electrical heating elements to boil the raw water into vapor. Because of the high latent heat of vaporization of raw water, this type of distillation is not energy efficient and is typically found on small or portable devices.

Vapor-compression distillation uses a pump or other means to increase the pressure of the steam leaving a boiling chamber, before entering a condensing chamber. This allows condensation to occur at a higher temperature than the boiling of the raw water, which allows the heat of formation released during condensation to be recycled and used to boil the raw water. Vapor- compression distillation reduces the energy required for distillation; however, a compressor or pump is required to move the steam from the lower pressure boiling chamber to the higher pressure condensing chamber. This requires energy, adding to the energy cost of vapor

compression. Additionally heaters are required on many systems to achieve and maintain the desired operating temperature and pressure, increasing the energy cost. Although waste heat can be used to preheat the raw water, a compressor or pump is still required, another energy cost.

Multi-flash or multi-effect distillation utilizes a series of chambers, each having a lower temperature and pressure than the preceding chamber. The raw water evaporates in increments as it travels from the highest-temperature chamber to lowest-temperature chamber. Cooling fluid passes through each chamber, condensing the water vapor while increasing in temperature. The exiting cooling fluid is used as the source of raw water for distillation, allowing the heat released during condensation to be used to preheat the raw water. Additional heating of the exiting cooling fluid is required before it can be used as a source of raw water, adding to the energy required for distillation.

Multi-flash systems require narrow, predefined mass-flow and temperature ranges for all fluids used in distillation, requiring fine control to maintain, a drawback of these systems. They also operate in a steady- state condition and do not accommodate fluctuations in mass-flow rates or temperatures of any of the fluids used in the distillation process, which is a further disadvantage.

Vacuum or sub-atmospheric pressure distillation systems operate with an internal pressure below atmospheric pressure. This allows the raw water to boil at lower temperatures, reducing the heat required to preheat the raw water and build up of scale and other solids on the boiling surfaces. An initialization process is required to reduce the internal pressure and remove the air and other non-condensable gases from the system.

One method to generate the desired sub-atmospheric internal pressure in a sub-atmospheric distillation system is to employ a high water column. This method requires a very large minimum- size system and still requires a source of heat for distillation or other means to drive the distillation. U.S. Pat. No. 7,597,785 describes a sub-atmospheric distillation system using tall columns filled with liquid to create the sub-atmospheric internal pressure. It also requires either a compressor in a vapor-compression configuration or a raw water temperature above the flash temperature inside the boiling chamber.

Another method to create a sub-atmospheric internal pressure is to implement an expanding volume in the boiling chamber. A batch of raw water is introduced to a chamber, where the volume is increased, reducing the internal pressure. U.S. Pat. No. 7,670,463 describes a sub- atmospheric distillation system that employs a variable volume as part of the raw water flow path. This method requires additional mechanical devices, such as pistons, and therefore additional energy to operate.

Another method utilizing sub-atmospheric distillation is to employ a refrigeration system. U.S. Patents 6,926,808 and 4,880,504 disclose vacuum distillation systems that use the heating and cooling coils from an integrated refrigeration system to drive the distillation. While the energy to operate this system is lower than conventional distillation, this method still requires a refrigeration system and the energy to drive the refrigeration cycle. Accordingly, refrigeration-based systems are not energy efficient.

Another method of sub-atmospheric distillation is to perform distillation in batches. A batch of raw water is reduced in pressure, removing non-condensable gases, then preheated to the desired operating temperature or range. A portion of the raw water is boiled off into steam and condensed. The remaining raw water is discharged, a new batch of raw water is introduced, and the process is repeated. The buildup of dissolved solids and other contaminants requires frequent batch steps, With each batch requiring time and energy for initialization, batch distillation is inefficient and undesirable for most applications. U.S. Pat. No. 4,985,122 describes a continuous- flow vacuum-distillation system; however, this system uses batch processing in the preheating part of the distillation process and retains the disadvantages of batch processing.

U.S. Pat. No. 6,010,599 describes a vacuum distillation apparatus that uses a heater to preheat the raw water, along with a refrigeration cycle. This system also employs batch distillation and has the disadvantages of both refrigeration distillation and batch processing, as previously described.

U.S. Patents 5,242,548, 5,922,174, and 5,211,816 describe vacuum-distillation systems that recirculate the raw water out of the boiling chamber, through a heat exchanger, then back into the the boiling chamber. In addition to the resources required by the hot side of the heat exchanger, additional pumps and energy are required to drive the recirculation of the raw water. The distilled water is also pumped out of the condensation chamber, cooled, and returned back into the condensation chamber. This also requires additional pumps and the energy to drive the circulation of the distilled water. These systems do not ensure the raw water is introduced at or above the flash temperature of the system, allowing sensible heating and phase-change heating to mix together, another disadvantage of these systems.

With energy consumption a major drawback of most distillation systems, utilizing waste heat to drive distillation provides the best opportunity for low-energy distillation. The majority of terrestrial and maritime power is generated from thermodynamic processes that reject enormous unused heat to the environment as waste. Along with many other processes that require cooling, a vast resource of waste heat is available from these thermodynamic processes that can be used to drive a distillation process.

Multi-flash systems can also operate as waste-heat distillation systems, using condensing vapor, such as spent steam from an integrated power-generation system, to complete the required preheating of raw water before it enters the series of flash chambers. Because the raw water is already preheated during condensation, the steam must be received at a higher temperature and pressure than that of a condenser that uses cooling fluid at a temperature determined by

environmental conditions. This results in a reduced pressure drop available for the integrated power system, increases the true energy cost of the steam.

U.S. Pat. No. 5,511,388 describes a distillation system that uses the waste heat from the hot coils of an integrated refrigerator to preheat the raw water. An additional heater, requiring energy, is also used to boil the raw water. The condenser is contained within the refrigerator; therefore the heat removed during condensation is rejected within the refrigerator, requiring additional energy to drive the refrigeration system.

U.S. Pat. No. 4,525,243 describes a sub-atmospheric distillation system that uses the waste heat from an integrated vacuum pump to preheat the raw water. The vacuum pump is also used to move the steam from the boiling chamber to the condensing chamber, operating as a vapor- compression distillation system. This requires energy to pump the lower-pressure steam from the boiling chamber to the higher-pressure condensing chamber, as required for vapor compression.

U.S. Pat. No. 8,545,681 describes a combined-cycle power generation system that also generates distilled water as a byproduct. This apparatus includes a gas turbine, uses two additional heat sources, and super heats the steam so it can be used to provide additional power. This process does recycle waste heat that can be used for distillation or desalination by reverse osmosis;

however, it includes power-generation components not covered or included in any of the embodiments presented.

U.S. Patents 6,309,513 and 5,853,549 describe desalinization systems that utilize waste heat to drive the distillation of raw water. The boiling of the raw water occurs on the inside of an array of vertically oriented tubes, an orientation which has limitations. As water vapor is generated in the tubes, the tube walls are exposed to a mixture of water vapor and liquid. As more heat is introduced into the evaporator, the ratio of water vapor to liquid raw water inside the tubes goes up, which can result in a reduction in the amount of heat transferred to the boiling raw water and/or undesirable acceleration of the brine/vapor mix exiting the tube ends.

To operate as intended, U.S. Patents 6,309,513 and 5,853,549 require a narrow, predetermined operating range as defined in the specifications, which state the Delta-T and liquid evaporation rate must occur at a stated or desired capacity. The specifications also state the temperature of the waste-heat fluid must be received at a predetermined value, another limiting factor reducing the ability to utilize available waste heat throughout the dynamic operating range of the integrated system supplying the waste heat. Additionally the raw water received inside the evaporator of these systems is not preheated above the flash temperature inside the evaporator. Sensible heating of raw water has a significantly lower heat-transfer rate than the phase-change heat-transfer rate experienced by boiling on a heating surface. Mixing in raw water below the flash temperature of the boiling chamber can result in undesirable fluctuations, pulses, or ceasing of the boiling on the heating surface. These and other systems overcome this condition by adding additional circulation pumps to assist the mixing, requiring additional energy for distillation.

The known prior art also contains systems that cannot accommodate either transient conditions or fluctuations in heating resource mass-flow rates or temperatures. Narrow, predefined operating conditions and/or required steady- state operations adversely affect the ability of a waste- heat distillation system to seamlessly integrate with a system rejecting waste heat. When utilizing waste heat to drive distillation, adverse effects on the integrated system supplying the waste heat must be considered when determining the true energy cost. Additionally, the amount of available heat rejected throughout the entire dynamic operating range of the integrated system supplying the waste-heat source used for distillation determines the overall effectiveness of waste-heat distillation system.

Waste-heat distillation systems observed in the known prior art operate within a predefined, narrow operating range. If the waste-heating resources fall below the desired operating range in mass-flow rate and/or temperature, additional heat is needed to make up for the difference, requiring additional components and energy. If waste heat available exceeds the operating limits, the waste heat is diverted and not used. This could require other resources to remove the heat from the integrated system supplying the waste heat, which complicates controls and operations.

Other waste-heat distillation systems known in the prior art are inflexible and cannot accommodate the dynamic operating range associated with many sources of waste heat. This inflexibility is a result of one or more of the following: narrow predefined operating range; steady- state operation; inability to accommodate transient conditions; inability to accommodate fluctuations in heating-resource temperatures; inability to accommodate fluctuations in heating- resource mass-flow rates; mixing of sensible preheating and phase-change heating; fine-tuned recirculating pumps and mass flow for recirculation of raw water within boiling chamber; fine- tuned recirculating pumps and mass flow for recirculation of distilled product within condensing chamber. Any of these disadvantages results in one or more of the following limitations: additional heating resources are required during reduced availability of waste heat, increasing energy requirements; complicated controls are required to accommodate conditions above or below defined operating range; during periods of maximum rejected heat, available heat is not completely utilized; other resources are required to remove excess heat from integrated system during periods of maximum rejected heat.

ADVANTAGES

Accordingly, several advantages of one or more aspects of the present invention are as follows: to provide distilled water with minimal power requirements, to provide a method to utilize waste heat that is normally rejected to the environment, to provide a method that can utilize a wide range of heating-fluid sources, to provide a method that can operate on the heating resources available, to provide a method that can accommodate fluctuations in heating resources and transient conditions, to provide improved integration with systems rejecting waste heat, to provide a system that can operate in parallel with or in replacement of a heat exchanger or a steam condenser. Other advantages of one or more aspects will be apparent from a consideration of the drawings and ensuing description.

SUMMARY

A waste-heat distillation system that converts a source of non-potable water into potable and/or distilled water, utilizing waste heat to perform all preheating and phase-change heating requirements is presented. The waste heat used for distillation is also referred to as "heating fluid," and can be in a liquid, vapor, or condensing- vapor state, depending on the embodiment used. Using the waste heat to perform all heating of the raw water eliminates the need for heating resources, providing improved energy efficiency. Additionally, the present invention operates on the temperature difference between the heating fluid and the cooling fluid, with a temperature determined by environmental conditions. Normal operation occurs when a nominal temperature difference between these fluids is encountered, along with nominal mass-flow rates of the heating and cooling fluids. This results in an improvement over prior art, as a system that can operate on a wider range of heating-fluid temperatures and better accommodate the normal dynamic operating range associated with an integrated power system.

The present invention receives the raw water inside the boiling chamber at or above the flash temperature inside the boiling chamber, which is determined by the heating and cooling fluids used. The raw water enters the boiling chamber and flows down a flow ramp, where a portion flashes into vapor. The raw water cools as it boils, until it reaches the flash temperature of the boiler, which is determined by the internal pressure inside the boiling chamber. The raw water flows off of the flow ramp and enters the boiling chamber, mixing with the raw water in the boiling chamber at the flash temperature, even if the heating-fluid mass-flow rate and/or temperature fluctuates or experiences transient conditions. This results in the improvement benefit of maximizing the heat transfer from the heating fluid occurring by phase-change boiling, while minimizing heat transfer that could occur by sensible heating or unnecessary vapor bubbles generated by flashing. This results in a higher throughput of heat from the waste-heat source, even during transient or fluctuating conditions commonly encountered by the waste-heat source, which has it own independent operating requirements. This further provides the benefit of minimizing any adverse impact or restriction on the integrated system supplying the waste heat.

In accordance with one embodiment of the present invention, raw water can be received from a source, including the same source as the waste heat, which is already sufficiently preheated. In other embodiments, the raw water can be obtained from a source, such as the cooling fluid, where it is not sufficiently preheated, requiring preheating from the heating fluid until it reaches or exceeds the flash temperature inside the boiling chamber. Should the temperature of the raw water drop below the flash temperature, the high heat-transfer rate would be reduced to sensible heating, and the system would operate slowly or enter a sleep-but-ready state.

The present invention utilizes simple system controls that maintain a liquid level or range within the boiler. High heat levels result in rapid boiling, requiring more make-up raw water to maintain the liquid level. As heat levels decrease, the need for make-up raw water also decreases. When heat resources shut down, no action is required by the level-control system. The system remains in a sleep state but rapidly resumes boiling once heating resources are returned. The liquid-level controls also remove raw water from the boiling chamber at a fraction proportional to the amount of raw water introduced into the boiling chamber. This results in a limited, predetermined increase of dissolved solids and other contaminants within the boiling chamber. Simplifying the controls to focus on the liquid level, coupled with the previously described advantage of raw water maintained at the flash temperature, results in a system that reacts to heat loads by changing boiling rates and producing distilled water proportional to the heat removed. This provides the improved capability to accommodate dynamic and transient conditions and higher utilization of waste heat available throughout the dynamic operating range of the integrated system supplying the waste heat. In accordance with other embodiments of the present invention, the heat removed from the heating fluid in the boiling chamber, and resulting exiting temperature of the heating fluid, can be controlled by controlling the cooling-fluid flow rate. This, combined with the increased dynamic range and ability to accommodate transient conditions, allows the system to perform the duties of a heat exchanger, thus providing the improved benefit of operating in parallel with and/or in replacement of a standard heat exchanger, producing distilled water proportional to the heat removed by the system.

In accordance with other embodiments of the present invention, heating fluids received as a condensable vapor, such as spent steam, can be used. Condensing on the inside of a tube array that also provides a drainage path for the condensate allows free boiling on the outside of the tube array inside the boiling chamber. This allows for an improved dynamic range and better response to transient conditions, as previously discussed. Additionally, exposing steam to lower-temperature cooling fluid with a temperature determined by environmental conditions provides the improved benefit of the reduced steam cost and improved integration with the system providing the waste heat.

Additional features and advantages will be apparent in the description and drawings provided herein.

DRAWINGS

FIG. 1 is a sectional schematic view of embodiment 1, which utilizes a single source for both heating fluid and non-potable water.

FIG. 2 is a sectional schematic view of embodiment 2, which uses a source of non-potable water that is not preheated, adding the capability to preheat the non-potable water.

FIG. 3A is a sectional schematic view of embodiment 3, which utilizes a phase-changing heating fluid, such as steam.

FIG. 3B is a detailed sectional schematic view of the vapor heating-fluid system of embodiment 3 illustrated in FIG. 3A.

FIG. 4 is a detailed sectional schematic view of embodiment 4, which adds to embodiment 2 the capability to control the cooling-fluid mass-flow rate, based on the temperature of the heating fluid entering the system.

REFERENCE NUMERALS

18 cooling-fluid system

20 cooling-fluid supply pipe

22 cooling-fluid inlet junction

24 cooling-fluid heat-exchange tubes

26 cooling-fluid exit junction

28 cooling-fluid exit pipe

40 product liquid-level sensor

42 product-sensor wire

44 product control unit

46 product power wire

48 product level pipe

50 product level pump

120 condenser high-density vacuum pump 122 condenser high-density gas tube

124 condenser low-density vacuum pump

126 condenser low-density gas tube

130 vapor connection pipe

132 splashguard

134 splash-drain tube

140 condensing chamber

144 condensing chamber accumulator separator

146 condenser accumulator communication port

148 condenser-product accumulator

160 boiling chamber

162 feedwater flow ramp

80 boiler liquid-level sensor

82 boiler sensor wire

84 feedwater control unit

86 transmission power wire

88 transmission electric motor

90 transmission motor drive shaft

92 feedwater pump drive shaft

94 rotary gearbox transmission

96 brine-pump drive shaft

98 brine pipe

100 brine pump

102 product-pump drive shaft

104 product pump pipe 106 distilled-product pump

192 feedwater inlet pipe

194 feedwater pump

196 boiler feedwater pipe

198 feedwater pressure valve

200 boiler interface pipe

174 feedwater inlet pipe

176 feedwater preheater pipe

178 heat-exchanger feedwater pipe

280 feedwater heat exchanger

282 heat-exchanger heating-fluid inlet

284 heat-exchanger heating-fluid exit

286 heat-exchanger raw-feed inlet

288 heat-exchanger raw-feed exit

60 heating-fluid inlet pipe

62 heating-fluid supply pipe

61 heating-fluid pipe T-junction

263 heating-fluid system

63 heating-fluid boiler inlet

64 heating- fluid inlet junction

66 heating-fluid tubes

68 heating-fluid exit junction

70 heating-fluid exit pipe

360 vapor heating-fluid system

362 vapor boiler-inlet pipe 364 vapor inlet-supply pipes

366 inlet-condensate collection tubes

368 vapor condensing tubes

370 vapor boiler pipe

372 vapor supply pipes

374 condensate-collection tubes

376 vapor low-density-boiler-gas tube

378 vapor-condensate accumulator

392 vapor-condensate return pipe

394 vapor-condensate return pump

396 accumulator liquid-level sensor

398 accumulator sensor wire

400 accumulator control unit

402 accumulator control power wire

403 accumulator high-density gas tube

404 accumulator diverter valve

405 vacuum pump high-density gas tube

406 accumulator high-density vacuum pump

408 accumulator low-density gas tube

410 accumulator low-density vacuum pump

500 heating-fluid temperature sensor

502 heating-fluid sensor wire

504 heating-fluid temperature controller

506 heating-fluid power wire

508 cooling-fluid flow valve 150 di stilled water

152 accumulator- minimum liquid level

154 accumulator "pump-off liquid level

156 accumulator "pump-on" liquid level

158 accumulator- maximum liquid level

412 condensate-minimum liquid level

414 condensate-maximum liquid level

164 water vapor

166 raw feedwater

168 boiler feedwater

170 boiler- minimum liquid level

172 boiler- maximum liquid level

DETAILED DESCRIPTION

Embodiments presented provide a method and apparatus for distilling a source of non- potable water into potable water or distilled water and concentrated discharge (also called brine waste). The embodiments require a heating fluid and a cooling fluid to drive the boiling and condensing required for distillation, which is driven by the difference in temperature between the heating fluid and the cooling fluid. Because the embodiments are driven by a temperature differential, a wide range of heating fluids can be used, even heating fluids below 100° Celsius, the boiling temperature of water at standard atmospheric pressure. The embodiments presented require small amounts of electrical power to pump liquids, but no power is required for heating; therefore the power requirements are substantially lower than other prior art systems.

The system can utilize a variety of sources for non-potable water and cooling fluid. Some of the sources of non-potable water include: salt water, lake water, river water, and brackish water. The non-potable water source is also referred to as "raw water" or "raw feedwater" or "feedwater" and is labeled in the diagrams as 166. The cooling fluid used by the system can be the same cooling fluid commonly used in heat exchange processes. Some of these cooling fluids include: salt water, lake water, river water, brackish water, and air.

Embodiment 1

FIG. 1 illustrating embodiment 1, utilizing a single source for both heating fluid and raw feedwater 166, is described below.

A condensing chamber 140 is used to condense water vapor 164 received from an attached vapor connection pipe 130 into distilled water 150. A plurality of cooling-fluid heat-exchange tubes 24 passes through the internal volume of the condensing chamber 140, providing the capability to condense the water vapor 164 inside condensing chamber 140. The condensing chamber 140 is a sealed-pressure vessel capable of positive and negative near-vacuum internal pressures. A condenser-product accumulator 148 is located below condensing chamber 140. A condensing chamber accumulator separator 144 separates product accumulator 148 and condensing chamber 140. Accumulator separator 144 is the floor of condensing chamber 140 and the top of product accumulator 148. Accumulator separator 144 has a condenser

accumulator communication port 146, which allows the condensing chamber 140 and product accumulator 148 to communicate freely. Communication port 146 is large enough to allow both liquids and vapors to communicate freely. Product accumulator 148 is a sealed-pressure vessel capable of positive and negative near- vacuum internal pressures.

The cooling fluid used to remove heat from the water vapor 164 inside condensing chamber 140 flows through a cooling-fluid system 18, comprising: a cooling-fluid supply pipe 20, a cooling-fluid inlet junction 22, the plurality of cooling-fluid heat-exchange tubes 24, a cooling- fluid exit junction 26, and a cooling-fluid exit pipe 28.

The cooling-fluid supply pipe 20 is connected to the cooling-fluid inlet junction 22. The inlet junction 22 is connected to the plurality of cooling tubes 24. Inlet junction 22 is attached to condensing chamber 140 in a sealed manner, allowing the plurality of cooling tubes 24 to connect to inlet junction 22 from inside the condensing chamber 140. The cooling tubes 24 pass through the internal volume of condensing chamber 140 and are attached to the cooling-fluid exit junction 26 on the opposite side of condensing chamber 140. Exit junction 26 is attached to condensing chamber 140 in a sealed manner, allowing the plurality of cooling tubes 24 to connect to exit junction 26 from inside the condensing chamber 140. The exit junction 26 connects to the cooling-fluid exit pipe 28.

Air and other gases that are not water vapors can enter the system. These gases may be capable of condensing; however within the operating temperature and pressure ranges of the system, they will not condense, and are herein referred to as "non-condensable gases".

To operate the system properly, these non-condensable gases must be removed, so that the cooling system 18 is generally exposed to water vapor and not non-condensable gases. Vacuum pumps 124 and 120 are employed to initiate and maintain this condition.

A condenser low-density gas tube 126 is connected to the inlet of a condenser low-density vacuum pump 124 and the top of condensing chamber 140, providing vacuum pump 124 with the capability to remove low-density gases from the upper region of condensing chamber 140. A condenser high-density gas tube 122 is connected to the inlet of a condenser high-density vacuum pump 120 and the product accumulator 148 above an accumulator-maximum liquid level 158. This provides vacuum pump 120 with the capability to remove high-density gases from the product accumulator 148. High-density gases in condensing chamber 140 flow down into product accumulator 148 through communication port 146. This also provides vacuum pump 120 with the capability to remove the high-density non-condensable gases from the condensing chamber 140. A boiling chamber 160 is a sealed-pressure vessel capable of positive and negative near- vacuum internal pressures and is also referred to as boiler 160. Boiler 160 contains a volume of raw feedwater for evaporation, labeled as boiler feedwater 168 in the diagrams. Boiler feedwater 168 is maintained between a boiler-minimum liquid level 170 and a boiler-maximum liquid level 172. A plurality of heating-fluid tubes 66 passes through the internal volume of the boiler 160 below the minimum liquid level 170 and is submerged under the boiler feedwater 168. The heating-fluid tubes 66 provide the capability to heat and boil the boiler feedwater 168 into water vapor 164. Vapor connection pipe 130 is attached to boiler 160, providing a flow path for water vapor 164 generated in the boiler 160 to flow into condensing chamber 140.

Raw feedwater 166 is received into boiler 160 from a boiler interface pipe 200. Pipe 200 is attached to boiler 160 in a sealed manner, allowing the raw feedwater 166 flowing inside pipe 200 to enter the internal volume of boiler 160. A feedwater flow ramp 162 is located inside boiler 160 and is attached to boiler 160. Flow ramp 162 is oriented in a manner allowing the raw feedwater 166 exiting boiler interface pipe 200 to flow onto flow ramp 162. Flow ramp 162 is open, allowing the raw feedwater 166 received at a temperature above the flash temperature inside the boiler 160, to flash boil and cool as it flows over the flow ramp 162. Flow ramp 162 is sloped to assist the flow of the raw feedwater 166 down flow ramp 162. The end of flow ramp 162 is open, allowing the raw feedwater 166 to spill freely off the end of flow ramp 162 and into boiler 160, where it mixes with and becomes boiler feedwater 168. The end of flow ramp 162 is positioned furthest from a brine pipe 98, and as close to a heating-fluid exit junction 68 as is practical. The flash boiling on the flow ramp also generates water vapor 164 that flows onto condensing chamber 140 through vapor connection pipe 130.

The heating fluid used to heat and boil the boiler feedwater 168 inside boiler 160 flows through a heating-fluid system 263, comprising: a heating-fluid boiler inlet 63, a heating-fluid inlet junction 64, the plurality of heating-fluid tubes 66, the heating-fluid exit junction 68, and a heating-fluid exit pipe 70.

The heating fluid enters a heating-fluid inlet pipe 60. A heating fluid pipe T-junction 61 is connected to the inlet pipe 60, a heating-fluid supply pipe 62, and a feedwater inlet pipe 192. Supply pipe 62 connects to the heating-fluid boiler inlet 63. Supply pipe 62 is attached to boiler 160 in a sealed manner, allowing boiler inlet 63 to connect to and communicate with supply pipe 62 from inside the internal volume of boiler 160. Inlet junction 64 is connected to boiler inlet 63 and the plurality of heating-fluid tubes 66. The heating-fluid tubes 66 pass through the internal volume of boiler 160 below the boiler-minimum liquid level 170 and are attached to the heating- fluid exit junction 68 on the exit side of boiler 160. The heating-fluid exit junction 68 connects to the heating-fluid exit pipe 70. Exit pipe 70 is attached to boiler 160 in a sealed manner, allowing heating-fluid exit junction 68 to connect to and communicate with exit pipe 70 from inside the internal volume of boiler 160.

The vapor connection pipe 130 connects to boiler 160 and condensing chamber 140, providing a sealed-flow path for water vapor 164 leaving boiler 160 to enter condensing chamber 140. Pipe 130 is attached to the top of boiler 160. Pipe 130 is also attached to condensing chamber 140, near the top of condensing chamber 140. Pipe 130 is capable of positive and negative near-vacuum internal pressures, and is sized sufficiently to allow vapor to flow freely and accommodate condensation that occurs within it. Pipe 130 provides the capability to convey water vapor and non-condensable gases from boiler 160 through pipe 130 and into condensing chamber 140. A splashguard 132 is located inside boiler 160 and attached to boiler 160 at the inlet of pipe 130. Splashguard 132 is oriented in a manner that forces the water vapor 164 leaving boiler 160 to turn sharply as it exits the boiler 160, causing liquid and water droplets to strike the splashguard 132 and drain into an attached splash-drain tube 134. Drain tube 134 extends from splashguard 132 downward, allowing the liquid to drain into the boiler feedwater 168. Drain tube 134 is oriented in a manner to best eliminate water vapor 164 from flowing upward into the drain tube 134.

During Normal Operation, raw feedwater entering boiler 160 is at or above the temperature of the boiler feedwater 168. The temperature of the boiler feedwater 168 fluctuates between the temperature of the heating fluid and cooling fluid. Using the heating fluid as the source of raw feedwater ensures that the temperature of the raw feedwater is above the temperature of the boiler feedwater 168. (Other embodiments require preheating of the raw feedwater, and T- junction 61 is replaced by a heat exchanger in those other embodiments.)

Feedwater inlet pipe 192 is connected to the T-junction 61, where some of the heating fluid is received as raw feedwater 166. Inlet pipe 192 connects to the inlet of a feedwater pump 194. A boiler feedwater pipe 196 connects to the outlet of feedwater pump 194 and a feedwater pressure valve 198. Feedwater pump 194 is a shaft-driven positive-displacement pump driven by an attached feedwater pump drive shaft 92. Pressure valve 198 is attached to boiler interface pipe 200. Pipe 200 is attached to boiler 160, allowing raw feedwater 166 flowing inside pipe 200 to enter the internal volume of boiler 160. Pressure valve 198 is used to increase the pressure of raw feedwater 166 leaving feedwater pump 194 and flowing through feedwater pipe 196, which prevents the feedwater 166 from boiling upstream from pressure valve 198.

A brine pump 100 is used to remove boiler feedwater 168 from boiler 160, limiting the amount of salt, dissolved solids, biological contents, and other impurities in boiler feedwater 168. The brine pipe 98 connects to the inlet of brine pump 100 and boiler 160 just above the bottom of boiler 160, providing brine pump 100 with the capability to remove boiler feedwater 168 from inside boiler 160. Brine pump 100 is a shaft-driven positive-displacement pump driven by an attached brine-pump drive shaft 96.

A distilled-product pump 106 is used to remove the majority of distilled water 150 from the product accumulator 148. A product pump pipe 104 connects to the inlet of product pump 106 and the product accumulator 148, just above the bottom of product accumulator 148, providing product pump 106 with the capability to remove distilled water 150 from product accumulator 148. Product pump 106 is a shaft-driven positive-displacement pump driven by an attached product-pump drive shaft 102.

A rotary gearbox transmission 94 connects and synchronizes rotary drive shafts: feedwater pump drive shaft 92, brine-pump drive shaft 96, and product-pump drive shaft 102. All pumps driven by transmission 94 are positive-displacement pumps, pumping non-compressible fluids, resulting in a near-linear mass-flow relationship of the fluid flowing between the feedwater pump 194, brine pump 100, and distilled-product pump 106.

For this embodiment, transmission 94 is geared such that feedwater pump drive shaft 92 and brine-pump drive shaft 96 spin at the same rotational rate. Product-pump drive shaft 102 is geared to spin at 80% of the rotational rate of feedwater pump drive shaft 92 and brine-pump drive shaft 96.

Transmission 94 is powered by a transmission electric motor 88, through an attached transmission motor drive shaft 90. Transmission 94 is geared in a manner that best matches the predetermined maximum operational rotational rate of feedwater pump 194 and brine pump 100, with the maximum operational rotational rate of electric motor 88. Product pump 106 is geared to operate at 80% the rotational rate of brine pump 100 and feedwater pump 194. Electric motor 88 has sufficient power to drive transmission 94 and all connected pumps at the predetermined maximum operational rotational rate when full electrical power is supplied to electric motor 88.

The sizing of the positive-displacement pumps, coupled with the drive-shaft rotation ratios, defines the near-linear mass-flow relationship between pumps (feedwater pump 194, brine pump 100, and product pump 106). Feedwater pump 194 is sized to accommodate the predetermined maximum mass-flow rate of raw feedwater 166 flowing into boiler 160 required to maintain the liquid level of boiler feedwater 168 between minimum liquid level 170 and maximum liquid level 172.

A mass-flow ratio of two to three units of raw feedwater 166 through feedwater pump 194 to one unit of brine waste through brine pump 100 is used. This provides the capability to remove a predetermined amount of boiler feedwater 168, limiting the amount of salt, dissolved solids, biological contents, and other impurities in boiler feedwater 168. Higher mass-flow ratios can be used, but will increase the percentage of dissolved solids and other impurities of the boiler feedwater 168, requiring more frequent maintenance and cleaning of the internal contents of boiler 160. Other applications, such as maritime brine refrigeration systems, can utilize the rejected brine-waste water reducing the need for rock salt.

To achieve the two-to-one ratio of raw feedwater 166 to brine waste, the displacement of feedwater pump 194 should be twice the displacement of brine pump 100. This results in a one- to-one mass-flow ratio of brine waste to distilled water 150 generated in condensing chamber 140. The displacement of product pump 106 should be the same displacement as brine pump 100. With product-pump drive shaft 102 geared to spin at 80% of the rate of feedwater pump drive shaft 92 and brine-pump drive shaft 96, product pump 106 will pump out 80% of the distilled water 150 generated in product accumulator 148.

To achieve the three-to-one ratio of raw feedwater 166 to brine waste, the displacement of feedwater pump 194 should be three times the displacement of brine pump 100. This results in a one-to-two mass-flow ratio of brine waste to distilled water 150 generated in condensing chamber 140. The displacement of product pump 106 should be twice the displacement of brine pump 100. With product-pump drive shaft 102 geared to spin at 80% of the rate of feedwater pump drive shaft 92 and brine-pump drive shaft 96, product pump 106 will pump out 80% of the distilled water 150 generated in product accumulator 148.

The raw feedwater 166 entering the inlet of feedwater pump 194 by inlet pipe 192 can be at a higher pressure than the fluid exiting the feedwater pump 194 into feedwater pipe 196. Feedwater pump 194 can therefore generate shaft power that is transferred to transmission 94 by feedwater pump drive shaft 92. (The combined work required to power brine pump 100 and product pump 106 through transmission 94 exceeds the work generated by shaft 92; therefore transmission 94 does not enter a runaway state.)

A boiler sensing and control system is employed to maintain the liquid level of the boiler feedwater 168 inside boiler 160 between the predetermined minimum and maximum liquid levels. A boiler liquid- level sensor 80 connects to boiler body 160 and monitors the liquid level of the boiler feedwater 168 inside boiler 160. When level sensor 80 detects that the liquid level in boiler body 160 is at the boiler-minimum liquid level 170, level sensor 80 sends an "activate" signal to a feedwater control unit 84 by a boiler sensor wire 82. When level sensor 80 detects that liquid level in boiler body 160 is at the boiler-maximum liquid level 172, sensor 80 sends a shutdown signal to control unit 84 by sensor wire 82. When control unit 84 receives an activate signal from sensor 80, it sends full operational power to the transmission electric motor 88 by a transmission power wire 86. When control unit 84 receives a shutdown signal from level sensor 80, it shuts down power to electric motor 88, utilizing a simple pump-up control system approach.

The method described to maintain the liquid level of boiler feedwater 168 inside boiler 160 is a pump-up control system approach. This control system may be the simplest control system that can be used to maintain the liquid level between the minimum level 170 and the maximum level 172. For someone skilled in the art of level-control systems, a more preferred but more complex proportional-integral-derivative controller (PID controller) can be used. This would result in a continuous flow of raw feedwater 166 that is roughly proportional to the heat transferred into the boiler feedwater 168 through the heating fluid. A PID controller would also maintain a narrower range of boiler feedwater 168 maximum and minimum liquid levels in boiler 160.

Product pump 106 is configured to pump out 80% of the distilled water 150 produced in the product accumulator 148. The remaining distilled water 150 is pumped out by a product level pump 50. Pump 50 is an electrically driven positive-displacement pump. Pump 50 is sized and powered to pump at least 50% of the maximum operational mass-flow rate of condensed distilled water 150 produced in the product accumulator 148 when full electrical power is supplied. The combined capacity of product pump 106 and pump 50 exceeds the maximum operational mass-flow rate of condensed distilled water 150 produced in the product accumulator 148.

A product liquid-level sensor 40 connects to the product accumulator 148 and monitors the liquid level inside the product accumulator 148. When level sensor 40 detects that liquid level in product accumulator 148 is at an accumulator "pump-on" liquid level 156, sensor 40 sends an activation signal to a product control unit 44 by a product-sensor wire 42. When level sensor 40 detects that the liquid level in product accumulator 148 is at an accumulator "pump-off liquid level 154, sensor 40 sends a "shutdown" signal to control unit 44 by product-sensor wire 42. When control unit 44 receives an activation signal from sensor 40, it sends full power to electrically driven pump 50 by a product power wire 46. When control unit 44 receives a shutdown signal from sensor 40, it shuts down power to product level pump 50, utilizing a simple pump-out control system approach. A product level pipe 48 connects to the inlet of product- level pump 50 and the product accumulator 148, just above the bottom of product accumulator 148, providing pump 50 with the capability to remove distilled water 150 from product accumulator 148.

Using the pump-out control system in the product accumulator 148, and the pump-up control system in the boiler 160, the liquid level of distilled water 150 inside the product accumulator 148 can go above the accumulator "pump-on" liquid level 156 to the accumulator- maximum liquid level 158. The liquid level can also go below the accumulator "pump-off liquid level 154 to an accumulator-minimum liquid level 152. The location of the accumulator- maximum liquid level 158 above the accumulator "pump-on" liquid level 156 should be positioned such that the volume of distilled water 150 between these levels should be equal to the volume of boiler feedwater 168 between the minimum and maximum liquid levels (170 and 172) inside boiler 160. The location of the accumulator-minimum liquid level 152 should be positioned below "pump-off liquid level 154, such that the volume of distilled water 150 between these levels should also be equal to the volume of boiler feedwater 168 between the minimum and maximum liquid levels (170 and 172) inside boiler 160. The accumulator- minimum liquid level 152 should be positioned above the bottom of product accumulator 148, at a location such that the volume of distilled water 150 between the bottom of product

accumulator 148 and accumulator-minimum liquid level 152 also equals the volume of boiler feedwater 168 between the minimum and maximum liquid levels (170 and 172) inside boiler 160. The accumulator-maximum liquid level 158 is used to position the vacuum pump 120 such that it does not ingest liquid distilled water 150. The accumulator-minimum liquid level 152 is used to ensure that the product pump 106 does not ingest vapors or gases. The method to calculate these levels is conservative, ensuring that the liquid level never varies outside these ranges. If needed, a tighter range can be calculated for liquid level 152, if the mass-flow ratio between feedwater pump 194 and product pump 106 is included in the calculation. A tighter range can also be calculated for liquid level 158 if the distilled water 150 removed by pump 50 is included in the calculation.

The pump-out method as described may be the simplest control system that can be used to maintain the liquid level of distilled water 150 between the minimum liquid level 152 and the maximum liquid level 158. For someone skilled in the art of level-control systems, a more preferred but more complex PID controller can be used. This would result in a more continuous flow of distilled water 150. It would also result in a more constant level of distilled water 150 in product accumulator 148 and a tighter range between accumulator-minimum liquid level 152 and accumulator-maximum liquid level 158.

Embodiment 1 utilizes a source of heating fluid and cooling fluid to drive the distillation of raw feedwater into distilled water. Embodiment 1 uses the heating fluid as the source of the raw feedwater, which ensures the raw feedwater is always preheated above the temperature of the boiler raw water 168 inside boiler 160. The mass-flow rate of the heating fluid must exceed a minimum predetermined amount. The mass-flow rate of the cooling fluid must also exceed a minimum predetermined amount. When the heating fluid is received at a temperature above the temperature of the cooling fluid by a predetermined minimum threshold amount, embodiment 1 uses the temperature difference between the heating fluid and the cooling fluid to drive the distillation of the raw feedwater.

Because the system is driven by the temperature difference between the heating fluid and cooling fluid, heating fluids that are below 100° Celsius (the boiling temperature of water at standard atmospheric pressure) can be used. Embodiment 1 can use rejected cooling fluid from a heat-exchange process, even though it is well below 100° Celsius. As long as the heating fluid and cooling fluid mass-flow rates exceed the minimum predetermined amounts and the heating- fluid temperature is above the cooling-fluid temperature by the minimum predetermined threshold amount, embodiment 1 can operate within a wide range of fluctuating mass-flow rates and temperatures of both heating and cooling fluids. Embodiment 1 further operates on the heating resources available, producing less or more distilled water, depending on the resources provided.

When the temperature difference between the heating fluid and cooling fluid drops below the predetermined minimum threshold amount, embodiment 1 operates slowly or enters an idle condition, but remains ready to resume Normal Operation. When the heating fluid and cooling fluid temperature difference exceeds the predetermined threshold amount, the system resumes Normal Operation. The same slow or idle condition occurs if the mass-flow rate of the heating fluid drops below the minimum predetermined amount or if the mass-flow rate of the cooling fluid drops below the minimum predetermined amount.

Embodiment 1 utilizes heat that is normally rejected to the environment with no useful benefit to drive the distillation of non-potable water into distilled water. The heating fluid is most commonly received as discharged cooling fluid from a heat-exchange process.

Operation - embodiment 1

Initialization and start up from a "Cold Start" condition: Initially the temperature of the system is at or near ambient temperature. The internal volume of the system is at or near ambient pressure and filled with air and non-condensable gases. This initial condition is called a "Cold Start" condition.

To prepare the system for distillation, the plurality of cooling-fluid heat-exchange tubes 24 in the internal volume of condensing chamber 140 must be surrounded by water vapor 164. The plurality of heating-fluid tubes 66 in the internal volume of boiler 160 must be submerged under the boiler feedwater 168. The boiler feedwater 168 and the water vapor 164 must exist in equilibrium; this condition requires the internal pressure to be adjusted such that the boiler feedwater 168 is at boiling temperature, and the water vapor 164 is at condensation temperature. For a typical Cold Start condition, this requires a sub-atmospheric, near-vacuum internal pressure. Once these conditions are satisfied, the system is ready to begin distillation when supplied with a source of heating fluid, cooling fluid, raw feedwater, and electrical power for the control systems and pumps. This condition is herein referred to as a "Ready" condition.

To prepare the system requires access to raw feedwater and distilled water. The steps required to change the system from a Cold Start condition to a Ready condition are described below. Boiler 160 is filled with raw water to boiler-maximum liquid level 172. Condenser high- density vacuum pump 120 is activated for a predetermined time, which initially reduces the internal pressure inside boiler 160. Further pumping of vacuum pump 120 during this predetermined time causes the boiler feedwater 168 to boil into water vapor 164. This water vapor 164 generated from boiler feedwater 168 in boiler 160 flows through vapor connection pipe 130 and into condensing chamber 140. The water vapor 164 forces the high-density non- condensable gases from the lower region of the condensing chamber 140 through the

communication port 146 and into the condenser-product accumulator 148. This is where the high-density, non-condensable gases are removed by vacuum pump 120. The pumping continues until the heat-exchange tubes 24 are not exposed to any high-density non-condensable gases.

The condenser low-density vacuum pump 124 is activated for a predetermined time. This also results in boiling of boiler feedwater 168 into water vapor 164, which replaces low-density non-condensable gases from the upper region of the condensing chamber 140, until the heat- exchange tubes 24 are not exposed to any low-density non-condensable gases. Condenser- product accumulator 148 is filled with distilled water to accumulator-minimum liquid level 152. The activation of the vacuum pump 120 and vacuum pump 124 is repeated in reverse order. The low-density vacuum pump 124 is re-activated for a predetermined time, followed by the reactivation of vacuum pump 120 for a predetermined time. This ensures that the heat-exchange tubes 24 are surrounded by water vapor 164. This further ensures the boiler feedwater 168 and the water vapor 164 exist in equilibrium, and the system is now in a Ready condition. The system remains Ready, even if the surrounding ambient temperature changes.

Normal Operation: When the system is in a Ready condition, it will begin "Normal

Operation" when it receives the following resources: Heating fluid and cooling fluid with a temperature difference and mass-flow rates above a predetermined amount, a source of raw feedwater, and electrical power to drive the various pumps and controls. Normal Operation further requires that the temperature of the raw feedwater 166 entering boiler 160 is at or above the temperature of the boiler feedwater 168. For embodiment 1, the heating fluid is also used for the source of raw feedwater 166, which is generally at a temperature above the temperature of the boiler feedwater 168.

During Normal Operation, the system maintains the liquid level of the boiler feedwater 168 inside boiler 160 between the boiler-minimum liquid level 170 and the maximum liquid level 172. The system also maintains the level of the distilled water 150 between the accumulator- minimum liquid level 152 and the accumulator-maximum liquid level 158. Heating fluid flows through the heating-fluid system 263, causing the boiler feedwater 168 to boil into water vapor 164. Cooling fluid flows through cooling-fluid system 18, condensing the water vapor 164 received from the boiler 160 into distilled water 150 in condensing chamber 140. The system also outputs concentrated discharge (also called brine waste). Distillation will occur even if the heating fluid is below the boiling temperature of water at standard pressure (100° Celsius). The internal pressure and temperature of the connected system will adjust based on the heating-fluid and cooling-fluid temperatures. A more detailed description of Normal Operation is provided below.

The heating fluid enters the heating-fluid inlet pipe 60, passes through T-junction 61, and into the heating-fluid supply pipe 62. The heating fluid enters the heating-fluid system 263 through the heating-fluid boiler inlet 63, where it also enters the internal volume of boiler 160. The heating fluid flows through heating-fluid inlet junction 64 and into the plurality of heating- fluid tubes 66, which are submerged under the boiler feedwater 168. The heating fluid is at a higher temperature than the boiler feedwater 168, which is already at the boiling point due to the internal pressure inside of boiler 160. This configuration results in heat transferring from the heating fluid, through the walls of the heating-fluid tubes 66, and into the boiler feedwater 168, causing boiler feedwater 168 to boil into water vapor 164. This heat transfer results in cooling of the heating fluid. The heating fluid exits the plurality of heating-fluid tubes 66, flows into heating-fluid exit junction 68 and into heating-fluid exit pipe 70, where the heating fluid exits the internal volume of boiler 160. The heating fluid exits the system through exit pipe 70.

The water vapor 164 flows up through boiler 160, around splashguard 132, and into vapor connection pipe 130. The sharp turn in flow of the water vapor 164 around splashguard 132 causes liquid and water droplets to strike splashguard 132 and drain back into the boiler feedwater 168 through the splash-drain tube 134. This ensures that the water vapor 164 contains little or no liquid or water droplets as it flows through connection pipe 130 and into condensing chamber 140.

While the heating fluid is boiling the boiler feedwater 168 into water vapor 164 in the boiler 160, the cooling fluid is flowing through the cooling-fluid system 18, condensing the water vapor 164 into distilled water 150. The cooling fluid enters the cooling-fluid supply pipe 20 and flows into the cooling-fluid inlet junction 22 and into the plurality of cooling-fluid heat- exchange tubes 24, where it enters the internal volume of condensing chamber 140. The temperature of the cooling fluid flowing inside the plurality of heat-exchange tubes 24 is below the temperature required to condense the water vapor 164 surrounding the heat-exchange tubes 24. This results in the water vapor 164 condensing on the outer surface of the heat-exchange tubes 24, creating distilled water 150, which falls from the heat-exchange tubes 24 to the bottom of condensing chamber 140 and onto the accumulator separator 144. The distilled water 150 drains through the communication port 146 and into the condenser-product accumulator 148.

The latent heat of formation released during the condensing of the water vapor 164 transfers through the walls of the heat-exchange tubes 24, and into the cooling fluid flowing inside the heat-exchange tubes 24. This results in sensible heating of the cooling fluid inside heat-exchange tubes 24. The cooling fluid flows into the cooling-fluid exit junction 26, where it leaves the internal volume of the condensing chamber 140, and into the cooling-fluid exit pipe 28, where it exits the system.

The heating fluid enters feedwater inlet pipe 192 from T-junction 61 and is used as raw feedwater 166. The heating fluid is at a higher temperature than the boiler feedwater 168, satisfying the requirement for Normal Operation. Raw feedwater 166 flows from inlet pipe 192, through feedwater pump 194, through boiler feedwater pipe 196, through pressure valve 198, through boiler interface pipe 200, and into boiler 160. (Other embodiments require the use of heat exchangers to preheat the raw feedwater. T-junction 61 is replaced by a heat exchanger to accomplish some of preheating in the other embodiments.)

Raw feedwater 166 enters boiler 160 through boiler interface pipe 200 and flows onto feedwater flow ramp 162. The raw feedwater 166, received at a higher temperature than the flash temperature inside the boiler 160, will flash and partially boil into vapor as it flows over flow ramp 162. This results in cooling of the remaining raw feedwater 166, but never below the temperature of the boiler feedwater 168 determined by the internal pressure of the boiler 160. The raw feedwater 166 flows off the end of flow ramp 162 and mixes with the boiler feedwater 168.

The raw feedwater 166 that enters feedwater pump 194 is at a higher pressure than the raw feedwater 166 leaving feedwater pump 194. Pump 194 therefore functions as a flow-metering device and can generate shaft power. This power is used by rotary gearbox transmission 94, which also synchronizes the mass-flow rate of raw feedwater entering and leaving boiler 160, limiting the increase in impurities of the boiler feedwater 168.

As the boiler feedwater 168 is replenished by raw feedwater 166, a portion of the mixed boiler feedwater 168 is removed by brine pump 100, limiting the increase of dissolved solids and other impurities of the boiler feedwater 168. Brine pump 100 removes boiler feedwater 168 at a predetermined mass-flow ratio to the raw feedwater 166 introduced into boiler 160. This is accomplished by the sizing ratio of the feedwater pump 194 to the brine pump 100, and the gearing ratio of these pumps established through transmission 94. With a mass-flow ratio of two to three units of raw feedwater 166 flowing into boiler 160 for every unit of raw water 168 removed from boiler 160, the increase in dissolved solids and other impurities of the boiler feedwater 168 to the raw feedwater 166 varies around 100% for the two-to-one ratio and around 200% for the three-to-one ratio.

A boiler sensing and control system is employed on the boiling chamber to maintain the liquid level of the boiler feedwater 168 inside boiler 160 between the boiler-minimum liquid level 170 and the maximum liquid level 172, as required for Normal Operation. Applying power to the transmission electric motor 88 drives transmission 94, which drives feedwater pump 194 and brine pump 100. Pump 194 is coupled to brine pump 100, and pumps more fluid into boiler 160 than brine pump 100 pumps out of boiler 160. This provides the control system the ability to replenish the boiler feedwater 168 that leaves boiler 160 as water vapor 164.

The transmission 94 also drives the distilled-product pump 106, which is configured to pump out 80% of the distilled water 150 produced in the condenser-product accumulator 148. Product pump 106 is coupled with transmission 94, ensuring that transmission 94 does not enter a runaway state caused by shaft power generated by feedwater pump 194. The remaining 20% of distilled water 150 is pumped out by product level pump 50, which is powered and controlled by the product sensing and control system. This product sensing and control system also maintains the liquid level of the distilled water 150 in product accumulator 148 between the accumulator- minimum liquid level 152 and the accumulator-maximum liquid level 158, as required for Normal Operation.

By maintaining the liquid level of the boiler feedwater 168 inside boiler 160, the system can operate with fluctuations in both flow rate and temperature of heating fluid. A higher mass-flow rate or temperature of the heating fluid will result in a higher boiling rate of the boiler feedwater 168, resulting in more distilled water 150 being produced. Conversely, a lower mass-flow rate or temperature of the heating fluid will result in a lower boiling rate of the boiler feedwater 168, and less distilled water 150 being produced. The system operates on the difference in

temperature of the heating and cooling fluids. The temperature of the boiler feedwater 168 inside boiler 160 varies between these temperatures and will fluctuate up or down along with the heating and cooling fluid temperatures.

Slow operation and ready state: If the heat available from the heating fluid decreases, the system will continue to operate although at a slower rate, producing less distilled water 150. If the heating fluid or cooling fluid stops flowing, the system will enter the Ready state. As long as the feedwater pump 194 remains primed with raw feedwater, the system will remain Ready and resume Normal Operation when the heating fluid and cooling-fluid mass-flow rates and temperature difference return to the normal predetermined values.

Periodic tasks during normal operation: While the start-up procedure removes the majority of non-condensable gases sufficient to prepare the system for a Ready condition, some non- condensable gases can exist in the boiler 160, and over time, additional non-condensable gases can accumulate in the system. Periodic activation of the low-density vacuum pump 124 for a predetermined time removes the low-density, non-condensable gases from the upper region of the condensing chamber 140. Periodic activation of the high-density vacuum pump 120 for a predetermined time removes the high-density non-condensable gases from the lower region of the product accumulator 148, ensuring that the cooling-fluid heat-exchange tubes 24 are surrounded by water vapor 164.

DETAILED DESCRIPTION - Embodiment 2

FIG. 2 is a sectional schematic view of embodiment 2, which does not use a single source for the heating fluid and raw feedwater. Embodiment 2 receives raw feedwater that has not been preheated and can be the same temperature as the cooling fluid. During Normal Operations, the temperature of the raw feedwater entering boiler 160 must be at or above the temperature of the boiler feedwater 168; therefore embodiment 2 requires additional functionality to preheat the raw feedwater. To accomplish this, T-junction 61 in embodiment 1 is replaced with a feedwater heat exchanger 280. The modifications and additions to embodiment 1 required to make embodiment 2 are described below. The raw feedwater enters a feedwater inlet pipe 174. Inlet pipe 174 is connected to a feedwater preheater pipe 176. Pipe 176 passes through the internal volume of condensing chamber 140 and is the first heat-exchange pipe to be exposed to the water vapor 164 entering condensing chamber 140 from vapor connection pipe 130. Water vapor 164 condenses on the outer surface of preheater pipe 176, which results in sensible heating of the raw feedwater inside pipe 176. Inlet pipe 174 is attached to condensing chamber 140 in a sealed manner that allows pipe 176 to connect to inlet pipe 174 from inside condensing chamber 140. Pipe 176 connects to a heat-exchanger feedwater pipe 178. Feedwater pipe 178 is attached to condensing chamber 140 in a sealed manner that allows pipe 176 to connect to feedwater pipe 178 from inside condensing chamber 140.

The T-junction 61 in embodiment 1 is replaced with heat exchanger 280, which uses the heating fluid to heat the raw feedwater. The mass-flow rate of the heating fluid is significantly higher than the mass-flow rate of the raw feedwater, and heat exchanger 280 must accommodate the flow differential. Heat exchanger 280 is sized to best ensure the raw feedwater is preheated above the temperature of the boiler feedwater 168 in boiler 160. If heat exchanger 280 overheats the raw feedwater, the raw feedwater 166 will flash boil and cool as it flows down flow ramp 162, which is acceptable for Normal Operations.

Feedwater pipe 178 connects to a heat-exchanger raw-feed inlet 286, allowing the raw feedwater to flow into and through heat exchanger 280. The raw feedwater exits heat exchanger 280 through a heat-exchanger raw-feed exit 288, which is connected to the feedwater inlet pipe 192. The raw feedwater entering inlet pipe 192 has been heated by the heating fluid in heat exchanger 280. Inlet pipe 192 connects to the inlet of feedwater pump 194 and continues through the system as described in embodiment 1.

Inlet pipe 60 connects to a heat-exchanger heating-fluid inlet 282, allowing the heating fluid to flow into and through heat exchanger 280, where it heats the raw feedwater. The heating fluid exits heat exchanger 280 at a heat-exchanger heating-fluid exit 284, which is connected to supply pipe 62. The heating fluid flows through supply pipe 62 and continues through the system as described in embodiment 1.

Embodiment 2 adds the capability to use a source of raw feedwater that has not been preheated. The heating fluid is used to preheat the raw feedwater above the temperature of the boiler feedwater 168 inside the boiler 160. Embodiment 2 extends the sources of heating fluids that can be used from embodiment 1. Some of these sources of heating fluids include:

recirculating cooling fluid (commonly found in combustion engines and other processes that use a heat exchanger), flue and exhaust gases, and wet exhaust gases (found in marine propulsion systems).

Operation - Embodiment 2

Unlike embodiment 1, embodiment 2 does not use the heating fluid as the source for raw feedwater. Embodiment 2 uses a source of raw feedwater that is not sufficiently preheated, requiring additional functionality to preheat the raw feedwater before it enters boiler 160. The operational changes and additions from embodiment 1 required for embodiment 2 are described below.

Initialization and start up from a Cold Start condition: During start up, the only difference between embodiment 1 and embodiment 2 is the different source of raw feedwater used to fill boiler 160. The steps required to prepare embodiment 2 from a Cold Start condition to a Ready condition are the same steps described for embodiment 1.

Normal Operation: Embodiment 2 adds a preheater to embodiment 1 to ensure that the feedwater 166 entering boiler 160 is at or above the temperature of the boiler feedwater 168 required for Normal Operation. If the temperature of the raw feedwater 166 is below the temperature of the boiler feedwater 168, the boiling will be reduced or even stopped, as some of the heat may be used for sensible heating. The system will not operate efficiently; therefore this condition is not part of the Normal Operation, but is still in a Ready condition. Additional operations are performed by embodiment 2 from those already described for Normal Operation of embodiment 1. These additional operations are described below.

In embodiment 2, the raw feedwater enters inlet pipe 174 and flows through the feedwater preheater pipe 176. Pipe 176 passes through condensing chamber 140 and is exposed to water vapor 164, which condenses on preheater pipe 176. This results in sensible heating of the raw feedwater flowing inside preheater pipe 176. The raw feedwater exits preheater pipe 176 and condensing chamber 140 and flows into heat-exchanger feedwater pipe 178.

The T-junction 61 in embodiment 1 is replaced in embodiment 2 by the feedwater heat exchanger 280. The heating fluid and raw feedwater flow paths through T-junction 61 in embodiment 1 are modified for heat exchanger 280. These modifications and additional operations required by embodiment 2 are described below. The raw feedwater flows from feedwater pipe 178, into the heat exchanger 280, through the heat-exchanger raw-feed inlet 286. The raw feedwater is heated and exits the heat exchanger 280 through heat-exchanger raw-feed exit 288. The raw feedwater is now preheated and flows into feedwater inlet pipe 192 as raw feedwater 166. The raw feedwater 166 continues through inlet pipe 192, as in embodiment 1.

The heating fluid enters heating-fluid inlet pipe 60 and flows into the heat exchanger 280 through heat-exchanger heating-fluid inlet 282. The heat exchanger 280 provides the capability for the heating fluid to heat the raw feedwater. The heating fluid leaves the heat exchanger 280 through heat-exchanger heating-fluid exit 284 and enters heating-fluid supply pipe 62. The heating fluid continues on through supply pipe 62, as in embodiment 1.

During Normal Operation, the raw feedwater 166 entering boiler 160 must be at or above the temperature of the boiler feedwater 168, or the system will operate very slowly or enter a Ready condition. Methods to increase the preheating capability of the raw feedwater 166 include: 1) Increasing the size and/or capacity of heat exchanger 280; 2) Adding additional pipe length to preheater pipe 176; or 3) Increasing the length and/or quantity of the cooling-fluid heat-exchange tubes 24, which results in a cooler boiler feedwater 168 temperature, reducing the amount of preheating required for the raw feedwater.

Slow operation and Ready state: Because embodiment 2 receives raw feedwater that requires preheating, decreases in the heating-fluid flow rate or temperature can cause the temperature of the raw feedwater 166 entering boiler 160 to drop below the temperature of the boiler feedwater 168. The system functions, but very slowly, and is not considered Normal Operation. This condition is considered to be a Ready condition, even though some distilled water 150 is produced. The system will resume Normal Operation when the heating-fluid flow rate or temperature is increased such that the raw feedwater 166 can be heated to a temperature above the temperature of the boiler feedwater 168.

A shutdown of the heating or cooling fluid will cause the system to stop but remain in a Ready condition. When the heating and cooling fluid are returned to normal predetermined levels, the system will resume Normal Operation.

Periodic tasks during Normal Operation: There are no differences between embodiment 1 and embodiment 2 for periodic tasks. The periodic steps required for embodiment 2 are the same steps described for embodiment 1. DETAILED DESCRIPTION - Embodiment 3

FIG. 3 A is a sectional schematic view of embodiment 3. Embodiment 3 utilizes a phase- changing heating fluid such as steam for the heating fluid source. FIG. 3B is sectional schematic view of the heating-fluid system used in embodiment 3. Like embodiment 2, embodiment 3 uses a source of raw feedwater that is not preheated. Embodiment 3 requires modifications and additions to embodiment 2 to accommodate a phase-changing heating fluid. The additions and modifications to embodiment 2 required to make embodiment 3 are described below.

Heating-fluid system 263 used to heat and boil the boiler feedwater 168 in embodiment 2 is replaced by a vapor heating-fluid system 360. The vapor heating fluid flows through the new heating-fluid system 360, comprising: a vapor boiler-inlet pipe 362, a plurality of vapor inlet- supply pipes 364, a plurality of inlet-condensate collection tubes 366, a plurality of vapor condensing tubes 368, a plurality of vapor supply pipes 372, a vapor boiler pipe 370, a plurality of condensate-collection tubes 374, a vapor low-density-boiler-gas tube 376, a vapor-condensate accumulator 378, and a vapor-condensate return pipe 392. FIG. 3B is sectional schematic view of embodiment 3, showing the heating-fluid system 360 in greater detail.

Air and other gases that are not heating fluid vapors can enter the heating fluid flow path. These gases may be capable of condensing; however, within the operating temperature and pressure ranges of the system, they will not condense, and are herein referred to as "non- condensable gases".

The vapor heating fluid enters heating-fluid inlet pipe 60, flows into heat exchanger 280 through inlet 282, through heat exchanger 280, out of heat exchanger 280, through exit 284, and into supply pipe 62, as in embodiment 2. Embodiment 3 requires this flow path to be capable of accommodating a vapor heating fluid with some heating fluid in a liquid state. The flow path through heat exchanger 280 must also accommodate condensing heating fluid. Heating fluid in either liquid and/or vapor states can flow freely through heat exchanger 280 and onto the vapor heating-fluid system 360.

Supply pipe 62 in embodiment 3 connects to the new vapor heating-fluid system 360 at inlet pipe 362. Supply pipe 62 is attached to boiler 160 in a sealed manner, allowing inlet pipe 362 to connect to and communicate with supply pipe 62 from inside the internal volume of boiler 160.

The heating-fluid system 360, with the exception of accumulator 378 and return pipe 392, is submerged under the boiler feedwater 168, below the minimum liquid level 170. The latent heat of formation released from the condensing heating fluid inside heating-fluid system 360 provides the heating capability to heat and boil the boiler feedwater 168 into water vapor 164 inside boiler 160.

The plurality of vapor inlet-supply pipes 364 is sloped downward, providing gravity drainage for condensed heating fluid. Inlet pipe 362 connects to the upper end of each of the supply pipes 364 on the inlet side of boiler 160. The plurality of vapor supply pipes 372 is located on the opposite side of boiler 160 from the supply pipes 364. The plurality of vapor condensing tubes 368 connects the plurality of supply pipes 364 to the plurality of vapor supply pipes 372. The plurality of vapor condensing tubes 368 is sloped, providing gravity drainage for condensed heating fluid. The lower end of each of the supply pipes 364, located furthest from attached inlet pipe 362, is connected to the plurality of vertically stacked inlet-condensate collection tubes 366, in a manner that allows condensed heating fluid in the supply pipes 364 to drain into the plurality of collection tubes 366.

The plurality of vapor supply pipes 372 is sloped downward, providing gravity drainage for condensed heating fluid. Boiler pipe 370 connects to the upper end of each of the supply pipes 372. The lower end of each of the supply pipes 372 is connected to the plurality of vertically stacked condensate-collection tubes 374, in a manner that allows condensed heating fluid in the supply pipes 372 to drain into the plurality of collection tubes 374. The vapor low-density gas tube 376 connects to the top of boiler pipe 370 at the highest region of the heating-fluid system 360.

The vapor-condensate accumulator 378 is a sealed-pressure vessel capable of positive and negative near- vacuum internal pressures. Accumulator 378 is located below the boiler 160, such that the top of accumulator 378 is the bottom of boiler 160. The bottom of the vertically stacked collection tubes 366 connects to the top of accumulator 378, allowing vapor and liquid to communicate from collection tubes 366 into accumulator 378, exiting the internal volume of boiler 160. The bottom of vertically stacked collection tubes 374 connects to the top of accumulator 378, allowing vapor and liquid to communicate from collection tubes 374 into accumulator 378, exiting the internal volume of boiler 160.

The vapor heating-fluid system 360 provides the capability (using gravity) for condensed heating fluid that occurs at any location in the heating-fluid system 360 to drain into the accumulator 378. It further provides the capability for any condensed heating fluid that enters the heating-fluid system 360 at inlet pipe 362 to drain into the accumulator 378. The heating- fluid system 360 provides the capability for non-condensable gases that are denser than the vapor heating fluid to accumulate in the accumulator 378. Non-condensable gases that are less dense than the vapor heating fluid accumulate in the low-density gas tube 376 at the highest region of the heating-fluid system 360.

An accumulator low-density gas tube 408 connects to the low-density gas tube 376 and the inlet of an accumulator low-density vacuum pump 410. Tube 408 is attached to boiler 160 in a sealed manner, allowing the low-density gas tube 376 to connect to and communicate with tube 408 from inside the internal volume of boiler 160. This provides vacuum pump 410 the capability to remove the low-density, non-condensable gases from the top of the heating-fluid system 360.

Condensed heating fluid drains into the vapor-condensate accumulator 378 through attached collection tubes 366 and 374. An accumulator liquid-level sensor 396 connects to the accumulator 378 and monitors the liquid level of the condensed heating fluid inside the accumulator 378. When level sensor 396 detects the liquid level in accumulator 378 is at a condensate-maximum liquid level 414, level sensor 396 sends an activate signal to an accumulator control unit 400 by an accumulator sensor wire 398. When level sensor 396 detects that the liquid level in accumulator 378 is at a condensate-minimum liquid level 412, level sensor 396 sends a shutdown signal to control unit 400 by sensor wire 398. When control unit 400 receives an activation signal from level sensor 396, it sends full power to an electrically driven vapor-condensate return pump 394 by an accumulator control power wire 402. When control unit 400 receives a shutdown signal from level sensor 396, it shuts down power to return pump 394. Return pump 394 is an electrically driven positive-displacement pump. When full electrical power is supplied to return pump 394, the pump is sized and powered to remove at least 120% of the maximum predetermined mass-flow rate of condensed heating fluid received in accumulator 378.

The method described above is a pump-out control system approach. This control system may be the simplest control system that can be used to maintain the liquid level of condensed heating fluid between the maximum liquid level 414 and the minimum liquid level 412. For someone skilled in the art of level-control systems, a more preferred but more complex, feedback-control system such as a PID controller can be used. This would result in a continuous flow of condensed heating fluid pumped from vapor-condensate accumulator 378 that roughly matches the accumulation rate of condensing heating fluid in accumulator 378. It would also maintain a tighter range of maximum and minimum liquid levels of condensed heating fluid inside accumulator 378.

The vapor-condensate return pipe 392 connects to and interfaces with accumulator 378, just above the bottom of accumulator 378. Return pipe 392 connects to the inlet of return pump 394, providing return pump 394 with the capability to remove the condensed heating fluid from accumulator 378.

An accumulator high-density gas tube 403 connects to the accumulator 378 above the condensate-maximum liquid level 414. Gas tube 403 connects to an accumulator diverter valve 404. Valve 404 provides the capability to open the heating-fluid system 360 to the ambient environment. Valve 404 connects to a vacuum pump high-density gas tube 405, which connects to the inlet of an accumulator high-density vacuum pump 406, providing vacuum pump 406 the capability to remove the high-density, non-condensable gases that accumulate in accumulator 378 when valve 404 is closed.

Embodiment 3 adds to embodiment 2 the capability to use a phase-changing heating fluid, such as condensing steam, as the heating fluid source. Embodiment 3 utilizes the latent heat of formation of the condensing vapor, which is normally rejected into the environment with no useful benefit, to drive the distillation of a source of non-potable water into distilled water.

Embodiment 3 can operate in parallel with or even replace a commonly used steam condenser, if sized sufficiently.

OPERATION - Embodiment 3

Embodiment 3 uses a condensing vapor, such as steam, as the source of heating fluid to drive the distillation. The operational additions and changes to embodiment 2 required to operate embodiment 3 are described below.

Initialization and start up from a Cold Start condition: For embodiment 3 to be in a Ready condition, a new requirement is added: the inner surface of the vapor heating-fluid system 360 must be generally exposed to heating fluid, and not the non-condensable gases that fill the heating-fluid system 360 during a typical Cold Start condition. For embodiment 3, the majority of non-condensable gases must be removed from the heating-fluid system 360. The additional steps required to transform embodiment 3 from a Cold Start condition to a Ready condition are described below.

To complete this process, vapor heating fluid must be available to the heating-fluid system 360. If the vapor heating fluid is available at pressures greater than the ambient pressure, the accumulator diverter valve 404 is opened. This allows the vapor heating fluid received into heating-fluid system 360 to flow through the system, forcing non-condensable gases out of the system. The diverter valve 404 is closed after a predetermined time period.

If the vapor heating fluid is below ambient pressure, the accumulator high-density vacuum pump 406 is activated for a predetermined time. This removes the majority of high-density, non- condensable gases from the lower region of the heating-fluid system 360 inside the vapor- condensate accumulator 378. The accumulator low-density vacuum pump 410 is activated for a predetermined time, removing the majority of the low-density, non-condensable gases from the upper region of the heating-fluid system 360. The working surface area inside heating-fluid system 360 is effectively evacuated of non-condensable gases, and embodiment 3 is now in a Ready condition. (Note: these steps are in addition to the steps required to prepare embodiment 2 for a Ready condition.)

Normal Operation: Embodiment 3 replaces the heating-fluid system 263 used in

embodiment 2 with a vapor heating-fluid system 360. The heating fluid flowing into inlet pipe 60, through heat exchanger 280, through supply pipe 62, though heating-fluid system 263, and out through exit pipe 70 in embodiment 2 for Normal Operation is replaced by the operations described below.

The vapor heating fluid enters inlet pipe 60 and flows into the heat exchanger 280 through heat-exchanger heating-fluid inlet 282. Cooling of the vapor heating fluid occurs if the vapor is above saturation temperature. Condensing of the vapor heating fluid occurs as the vapor heating fluid flows through the heat exchanger 280, heating the raw feedwater also flowing through the heat exchanger 280. The vapor heating fluid flows out of the heat exchanger 280 and into supply pipe 62 with some heating fluid condensed into a liquid state. The heating fluid, mostly vapor, flows into the vapor heating-fluid system 360 at vapor boiler-inlet pipe 362.

The vapor heating fluid condenses inside the portion of the heating-fluid system 360 that is inside boiler 160, submerged under the boiler feedwater 168. The latent heat released by the condensing vapor heating fluid transfers through the walls of the heating-fluid system 360 and into boiler 160, causing boiler feedwater 168 to boil into water vapor 164. The condensed heating fluid drains through the heating-fluid system 360 and into the vapor-condensate accumulator 378.

Embodiment 3 also adds a new requirement for Normal Operation: the system must remove condensed heating fluid from condensate accumulator 378 while maintaining the liquid level of condensed heating fluid between minimum liquid level 414 and maximum liquid level 412. A sensing and control system is employed to maintain and remove the condensed heating fluid. This sensing and control system employs an electrically driven return pump 394 to pump out the condensed heating fluid.

Periodic tasks during Normal Operation: In addition to the periodic steps required for embodiment 2, embodiment 3 requires the following additional steps to ensure that the inner surface of the heating-fluid system 360 is generally exposed to heating fluid and not air or other non-condensable gases. The additional periodic steps are described below.

While the start-up procedure removes the majority of non-condensable gases from the heating-fluid system 360 sufficient to prepare the system for a Ready condition, some non- condensable gases can exist in the heating-fluid system 360. Over time, additional non- condensable gases can accumulate in the heating-fluid system 360. Periodic activation of the accumulator high-density vacuum pump 406, for a predetermined time, removes the high- density, non-condensable gases from the lower region of the heating-fluid system 360. Periodic activation of the accumulator low-density vacuum pump 410, for a predetermined time, removes the low-density, non-condensable gases from the upper region of the heating-fluid system 360, ensuring the inner surfaces of the vapor condensing tubes 368 are exposed to heating fluid and not undesirable non-condensable gases.

DETAILED DESCRIPTION - Embodiment 4

FIG. 4 is a sectional schematic view of embodiment 4. Embodiment 4 adds to embodiment 2 the capability to control the cooling-fluid flow rate based on the temperature of the heating fluid. Embodiment 4 requires additions to embodiment 2 to accommodate the flow control. The additions to embodiment 2 required to make embodiment 4 are described below.

A heating-fluid temperature sensor 500 connects to the inlet pipe 60 and monitors the heating-fluid temperature entering the system at pipe 60. Sensor 500 converts the temperature to an electrical voltage and sends the voltage to a heating-fluid temperature controller 504 by a heating-fluid sensor wire 502. Controller 504 converts the received voltage from sensor 500 to a power setting that is sent to a cooling-fluid flow valve 508, causing valve 508 to open to a predetermined opening position. Controller 504 sends the power to valve 508 by a heating-fluid power wire 506.

Controller 504 establishes a near-linear relationship between the heating-fluid temperature and the opening position of valve 508 such that: 1) A minimum temperature threshold equates to a maximum closed position of valve 508; and 2) A maximum temperature threshold equates to a maximum open position of valve 508. When the heating fluid temperature is below the minimum temperature threshold, valve 508 remains in the maximum closed position. When the heating fluid temperature is above the maximum temperature threshold, valve 508 remains in the maximum open position. The predetermined maximum and maximum temperature thresholds used by controller 504 are adjustable by controller 504. The opening and closing of valve 508 provides the capability to control the cooling fluid mass-flow rate through cooling system 18.

The method described to control the cooling fluid mass-flow rate based on the heating fluid temperature may be the simplest method to achieve this goal. A more efficient method to adjust the mass-flow rate of the cooling fluid is to control the power to the pump that drives the cooling fluid. To achieve this, a cooling fluid pump, which is not shown or described in any

embodiment, is moved to replace valve 508. The cooling-fluid pump must be capable of variable mass-flow output based on the power supplied to the pump. Controller 504 must then be capable of supplying the required power to achieve the desired cooling fluid mass flow, which is predetermined by the temperature of the heating fluid entering pipe 60.

Embodiment 4 adds to embodiment 2 the capability to regulate the heat removed from the heating fluid, based on the temperature of the heating fluid. Embodiment 4 utilizes waste heat, which is normally removed from a high-temperature process by a heat exchanger, to drive the distillation of non-potable water into distilled water. The heating fluid for embodiment 4 is also the cooling fluid for a heat-exchange process. By regulating the temperature of this fluid ("heating fluid" for embodiment 4, "cooling fluid" for another heat-exchange process), embodiment 4 can operate in parallel with or even replace the heat exchanger if sized sufficiently.

Operation - Embodiment 4 Embodiment 4 adds to embodiment 2 the capability to control the cooling-fluid mass-flow rate, based on the temperature of the heating fluid entering the system at inlet pipe 60.

Embodiment 4 requires all the operations as previously described in embodiment 2, plus the additional operations described below.

Initialization and start up from a Cold Start condition: During start up, there is no difference between embodiment 2 and embodiment 4. The steps required to prepare embodiment 4 from a Cold Start condition to a Ready condition are the same steps described for embodiment 2.

Normal Operation: Embodiment 4 adds to embodiment 2 the capability to control the cooling-fluid mass-flow rate, based on the temperature of the heating fluid. During Normal Operation, the heating fluid flows into pipe 60. As the temperature of the heating fluid flowing through pipe 60 increases above the minimum predetermined threshold temperature, flow valve 508 begins opening from its predetermined minimum opening, allowing more cooling fluid to flow through cooling system 18. Further increases in heating fluid temperature causes flow valve 508 to open further, until the heating-fluid temperature reaches the maximum threshold temperature. At this temperature, valve 508 is fully open, and any further increase in heating fluid temperature has no effect on valve 508. Conversely, if the heating fluid temperature drops below the maximum threshold temperature, valve 508 begins closing until the heating fluid temperature reaches the minimum threshold temperature. At this temperature, flow valve 508 is at a maximum closed position. Valve 508 remains at maximum closed position as long as the heating fluid temperature is at or below the minimum threshold temperature.

Opening and closing of valve 508 provides the capability to control the cooling-fluid mass- flow rate through cooling system 18. This results in less distilled water being generated and less heat removed from the heating fluid. Restricting the cooling fluid will at some point cause the system to enter an idle state; however the system remains in a Ready condition. This also allows embodiment 4 to function as a heat exchanger, with ability to control the amount of heat removed from the heating fluid in a cooling system. It further allows the distillation system to work in parallel with or even in replacement of a heat exchanger.

The remainder of the Normal Operation for embodiment 4 is the same as embodiment 2.

Periodic tasks during Normal Operation: There are no differences between embodiment 2 and embodiment 4 for periodic tasks. The periodic steps required for embodiment 4 are the same steps described for embodiment 2.