FOR

IMPROVED WATER EXTRACTION PROCESS FROM VEGETATIVE MATERIAL

CROSS-REFERENCE TO RELATED APPLICATIONS

This is an international application filed under 35 U.S.C. § 363 claiming priority, under 35 U.S.C. § 119(e)(1), of provisional application Serial No. 61/727,440, previously filed November 16, 2012, under 35 U.S.C. § 111(b).

BACKGROUND OF THE INVENTION

Various types of seed and vegetable product (hereafter, product) are used to produce a variety of substances usable for food, feed, and manufacturing activities. These substances include ethanol, sugars, and oils. Some types of produce usable for this purpose include corn and soya (soybeans).

A multi-stage installation operating in a continuous mode can extract these substances from the product. For example, a series of stages that extract the oil from corn might include grinding the product, separating the oil-bearing portion of the product from the remainder of the mixture, dissolving the oil in a solvent, removing the oil-solvent solution from the entire mass, and then separating the oil from the solvent.

The remaining product may comprise a liquid aqueous solution of water, ethanol, various types of water-soluble organic compounds (WSO), and fibrous material. The term "liquid" here includes both freely flowing liquids as well slurries that flow and can be pumped but have relatively high viscosity.

In many cases, the organic compounds are sugars of various types. These sugars, when free of the ethanol and a portion of the water, have commercial value. An installation comprising a number of interconnected processing elements or components may further process this aqueous solution in a continuous mode to extract nearly all of the ethanol and a substantial percentage of the water. Complete or nearly complete ethanol removal is important to meet requirements for the remaining products.

These processing elements each perform one or more steps in a series that extracts some of the water and nearly all of the ethanol to produce a liquid solution with a concentration of sugar that may range from 30 - 75%. Intermediate materials may be sent to upstream elements for various reasons.

Such an installation usually comprises a number of relatively large components that use substantial amounts of power and take a significant amount of space. To avoid the need for very large stages and for greater energy efficiency, a larger number of smaller stages is usually preferable. This means that a typical installation requires a number of stages to achieve the desirable higher concentrations of organic compounds such as sugar.

A so-called stripping column is in the form of tank that serves as a later stage of one such installation to remove a portion of the ethanol from the slurry and to reduce the percentage of water in the material under processing. A stripping column has a vertically oriented tubular housing defining an enclosed internal space. A number of perforated trays are horizontally oriented and vertically spaced from each other within the internal space. A stripping column is often quite large, perhaps 20 - 30 feet high and several feet in diameter.

A stripping column has an inlet close to the top of the housing and above the topmost tray. The inlet receives a liquid solution containing water, ethanol, and organic compounds such as sugar. A stripping column operates in a continuous mode, with a constant flow of material into the inlet and a sugar-containing slurry flowing from the bottom of the stripping column. In the conventional system, the slurry exiting the stripping column has almost no ethanol.

The slurry that exits the stripping column then flows to final processing equipment shown in phantom in Fig. 1 at 23, for removing the remaining ethanol and further removal of water to produce the concentration of organic compound desired in the final product. This final processing equipment 23 has a significant number of components that occupy substantial space in the plant, and require significant energy to operate. Eliminating equipment 23 would be ideal, but to date this has not seemed possible due to clogging of pipes and ducts upstream of the equipment 23.

Further, the higher temperature is of the steam used in the various heat exchangers, the more likely clogging becomes. Other factors can sometimes also cause clogging.

BRIEF DESCRIPTION OF THE INVENTION

An installation for removing water and volatile water-soluble organic compounds from a liquid aqueous solution uses a reduced number of components relative to earlier installations. The installation includes a tank for accumulating liquid aqueous solution therein at a tank pressure, and further includes a pump. The pump receives the liquid aqueous solution from the tank at a pump input and provides the liquid aqueous solution at a pump output with a selected pump pressure higher than the tank pressure. A heater, typically a heat exchanger using steam as a source of heat energy, receives at an inlet, liquid aqueous solution from the pump. The heater heats the liquid aqueous solution passing though the heater to a selected outlet temperature at an outlet. The liquid aqueous solution exits the heater with an outlet pressure between the pump and tank pressures.

A first nozzle within the tank receives the heated liquid aqueous solution from the heater, and discharges the solution into the tank. The nozzle creates a pressure drop in the liquid aqueous solution substantially equal to the difference of the outlet pressure and the tank pressure.

The pump and the nozzle cooperate to set the outlet pressure at a level exceeding the vaporization pressure of water at the selected outlet temperature. By so doing, the water in the liquid aqueous solution will not flash into vapor.

As the water vaporizes, dissolved materials such as sugar present in the liquid will precipitate from the water as solid particles. These precipitated particles from the liquid often adhere to the adjacent walls. Over time these particles build up, eventually clogging the passage through the heater. Avoiding this vaporizing reduces clogging, allowing the system to extract an amount of water and volatile water-soluble organic compounds from the liquid aqueous solution similar to that possible with earlier installations having a substantially larger number of components.

One preferred embodiment includes a heater supplying an amount of heat to the liquid aqueous solution that depends on a first heating control signal. This embodiment includes at least a first temperature sensor past which the liquid aqueous solution flows from the heater to the nozzle. This first temperature sensor providing a first temperature signal encoding the temperature of the liquid aqueous solution passing thereby.

A controller receives the first temperature signal and provides the first heating control signal as a function of the first temperature signal.

The installation may also include a second temperature sensor past which the liquid aqueous solution flows from the pump to the heater. This second temperature sensor providing a second temperature signal encoding the temperature of the liquid aqueous solution passing thereby. The controller receives the second temperature sensor, and provides the first heating control signal as a function of the first and second temperature signals.

The installation may further include a second nozzle at the top of the tank receiving pressurized intermediate liquid aqueous solution from an external source and spraying said intermediate material into the tank. A port at the top of the tank allows vapors formed by evaporation from the intermediate material to pass. This version may also include a flow divider receiving liquid aqueous solution from the pump and supplying a portion thereof to the heater and the remaining portion to an external receptacle. The specifications for the installation may be selected so that material sent to the external receptacle have desired ratio of water to solids.

The installation may be designed so that the pump has a flow rate of liquid aqueous solution that produces at least a predetermined flow velocity through the heater and at the exit thereof. Maintaining a sufficiently high flow velocity further reduces sticking of material to the heater walls and the clogging that results from this sticking. In certain installations, this predetermined flow velocity may be at least approximately 3 - 5 feet per second and preferably 5 fps.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a block diagram of a portion of a larger system for removing water and volatile organic compounds from a precursor material having dissolved volatile organic compounds in the nature of an aqueous solution having appreciable viscosity.

Fig. 2 is a block diagram of a level controller that maintains an appropriate level of material within various containers forming parts of the block diagram of Fig. 1.

Fig. 3 is a block diagram showing details of a flash tank assembly forming a part of the block diagram of Fig. 1.

Fig. 4 is a block diagram showing details of a stripping column assembly forming a part of the block diagram of Fig. 1.

Fig. 5 is a block diagram level controller that maintains an appropriate

temperature level within a heat exchanger forming a part of the block diagram of Fig. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The block diagram of Fig. 1 broadly shows apparatus 10 for removing nearly all of the ethanol and a part of the water from precursor material in the form of a liquid aqueous solution having dissolved organic compounds such as one or more sugars as well as ethanol or other volatile hydrocarbons, and the water. Such a solution may be in the nature of a slurry or liquid having appreciable viscosity and should be pumpable. The concentration of the organic compounds in the final material may often range from 30 - 75%. That is, the fraction of water may range from 75 - 30%.

The invention is implemented in a flash tank assembly 20 and a stripping column assembly 50. The final material is an aqueous solution of the dissolved organic material such as the sugar indicated, and provided in an output pipe or duct 87. Any volatile hydrocarbons that dissolve in water such as ethanol present in the precursor material flow in a separate stream of water and condensed hydrocarbon material in a path 21.

Precursor material continuously flows into flash tank assembly 20 in duct 27 from preprocessor units 13. Assemblies 20 and 50 include multiple pumps that move the material to various processing components inside and outside of these assemblies.

The apparatus forming assemblies 20 and 50 make a final processor 23 (shown in phantom) unnecessary. Processor 23 has in the past been necessary to achieve the desired concentration of organic compounds. A processor 22 comprises a number of pumps, heat exchangers, separation vessels, and the associated plumbing. These take space and are costly to install, maintain, and operate, adding cost to the overall process. The invention provides an identical final material.

In Fig. 1, flash tank assembly 20 and stripping column assembly 50 cooperate to remove the ethanol from the precursor material in duct 27, and to concentrate the organic compounds in the final material. Extracted ethanol and water continuously flows to ethanol tank 25 from flash tank assembly 20. The ethanol solution in tank 25 may be used by various components in preprocessor units 13.

Flash tank assembly 20 receives a continuous flow of hot ethanol solution vapors in duct 47 from stripping column assembly 50. These vapors heat intermediate materials and in doing so, condense and flow to tank 25 as a liquid solution of ethanol and water. Assemblies 20 and 50 each process and reprocess the intermediate material, eventually removing essentially all of the ethanol from the intermediate material to form the flow to solvent (ethanol- water) tank 25.

Intermediate material flows to stripping column assembly 50 from flash tank assembly 20 in a duct 41. This intermediate material is a liquid comprising the organic compounds, a reduced concentration of ethanol, and water. For example, the

intermediate material may comprise 20 - 30% organic compounds, 15% ethanol, and the remainder water.

The intermediate material in duct 41 is processed by the stripping column assembly 50 to complete the removal of ethanol and to remove additional water from the duct 41 intermediate material. Intermediate material for which processing is complete flows as finished material from stripping column assembly 50 in a duct 87.

As one example, final material may comprise a slurry that is 30 - 70% sugars by weight, with the remainder almost completely water. The proportions of sugars and water can be controlled by setting operating parameters for stripping column assembly 50, which will be discussed below.

Fig. 1 also shows a controller 30 that manages the settings of various components in assemblies 20 and 50 to implement the overall operation. While controller 30 controls settings for components in the entire system 10, implementing the invention requires that certain components of assemblies 20 and 50 have particular settings to accomplish the purposes of the invention. Fig. 2 shows a level controller 30a forming a portion of controller 30. Controller 30a manages the level of materials in processing elements of assemblies 20 and 50.

Fig. 3 shows details of flash tank assembly 20. Precursor material flows on path 27 to a heat exchanger 32 that heats the precursor material, which then flows to flash tank 22 on duct 44. In one preferred embodiment, vapors from the stripping column flow through heat exchanger 32 on path 47, increasing thermal efficiency of operation.

The precursor material sprays out within flash tank 22 through a nozzle 43 that serves as a throttling valve. Nozzle 43 reduces the pressure of the precursor material and cause a part of the ethanol in the precursor material to vaporize. The ethanol vapors that form in flash tank 22 flow to a duct 34 and are drawn by a vapor pump 29 through a heat exchanger 26.

Cold water flowing through heat exchanger 26 condenses a portion of the ethanol in the ethanol vapors. The mix of vapors and liquid from heat exchanger 26 flow in a duct 32 where the ethanol- water vapors continue on path 32b to the vapor pump 29 and the liquid ethanol- water solution falls through duct 32a to eventually, solvent tank 25.

Flash tank 22 operation removes some but not all of the ethanol from the precursor material, forming an intermediate material that accumulates in the bottom of flash tank 22 as a pool 51. This intermediate material in pool 51 flows under gravity to a pump 35 which pumps the intermediate material under pressure to the input of a flow diverter 24.

Flow diverter 24 diverts a percentage of the incoming flow to a first, or return outlet 38, and the remainder of the incoming flow to duct 41. The percentage of the flow diverted to outlet 38 and duct 41 depends on the value of a first diverter percentage signal received on a signal path 24a from the level controller 30a of Fig. 2. The flow of intermediate material through outlet 38 merges with incoming precursor material flowing in duct 27. Thus, the intermediate material that flows to outlet 38 is reprocessed within flash tank 22.

Flash tank 22 includes a first level sensor 31 that provides a first level signal on a path 37. Level controller 30a (Fig. 2) receives the first level signal and provides the first diverter percentage signal as a function of the first level signal value.

In one simple scenario, when the surface of pool 51 is below first level sensor 31, the value of the first diverter percentage signal causes flow diverter 24 to divert to return outlet 38, all of the flow into the inlet of flow divider 24. When the surface of pool 51 touches first level sensor 31, level controller 30a provides to flow diverter 24, a first diverter percentage signal on path 24a whose value specifies that a preselected percentage of the intermediate material flow from pump 35 diverts to first outlet 38 and the remainder of the flow diverts to duct 41. Level controller 30a may then maintain this value of the first diverter percentage signal for some specified period of time.

The mass flow rate in duct 27 less the mass flow rate in duct 41 should approximately equal the mass flow rate through duct 34 to assure that the level of pool 51 stays approximately constant. The time that flow diverts to outlet 41 should be set short enough to assure that a pool 51 of at least a minimum size is always present. Material flowing from outlet 41 will typically have a concentration of 10 - 20 % ethanol, 15 - 25% organic compounds, and the remainder water.

Fig. 4 shows details of the stripping column assembly 50. A tank comprising stripping column 53 performs the final extraction of ethanol from the intermediate materials flowing to assembly 50 in duct 41, and also removes a further amount of water from the intermediate material.

Stripping column 53 conventionally comprises a vertically oriented cylindrical housing 82 enclosing a vertically extending series or array of horizontally oriented trays or shelves 38. A topmost shelf 38t defines the bottom of a top space 65 of housing 82. A bottom shelf 38b defines the top of a bottom space 64 of housing 82. A stripping column 53 may be several feet in diameter and 20 or more feet tall.

Each shelf 38 occupies a substantial portion of the housing 82 cross section. A number of perforations in each shelf 38 allow vapors to rise through the materials flowing across the shelves 38. The material itself flows or drips downwards under the influence of gravity through a hole in each of the shelves 38. As the intermediate material flows across shelves 38, volatile materials such as ethanol and water vaporize, and being lighter than air, flow upwards within housing 82.

Stripping column 53 includes an outlet 59 through which intermediate material flows or sprays into the top space 65. Stripping column 53 also includes a lower nozzle 61 through which at least partially processed intermediate material flows or sprays into the bottom space 64.

Hot ethanol and steam exit stripping column 53 through duct 47 attached to an opening at the top of stripping column 53. Duct 47 carries the hot ethanol and steam to a heater shown as a heat exchanger 33 in Fig. 3. In general, a heat exchanger using a heated fluid to heat a liquid flowing in separate ductwork is most thermally efficient. However, any type of heater such as an electrical heater may provide similar

functionality. The hot ethanol and steam heat the precursor material flowing through heat exchanger 33, in the course of which the ethanol and steam cool and condense. The cooled and condensed ethanol and steam then flow to the ethanol tank 25 through a path 21. Using the already hot ethanol and steam improves the overall speed and efficiency of the process.

Intermediate material flowing from outlet 41 of flow divider 24 (Fig. 3) passes through a heat exchanger 56, which raises the material's temperature substantially, in one installation to 100 °C. The heated intermediate material sprays from outlet 59 into top space 65.

The intermediate material spraying from outlet 59 slowly flows downwardly through the various shelves 38, eventually reaching bottom space 64. The intermediate material reaching bottom space 64 forms a pool 99. Pool 99 material typically is in the form of a slurry.

As the intermediate material flows downwards through shelves 38, essentially all of the ethanol and some of the water in the intermediate material vaporize and flow upwardly to duct 47. The flow through shelves 38 serve to mix and agitate the intermediate material, increasing the vaporization of the ethanol. For this reason, the material in pool 99 has almost no ethanol.

The material in pool 99 continuously flows to a pump 77 that pressurizes the material flowing from pool 99. The pressurized pool 99 material flows to a flow diverter 84. The flow to diverter 84 splits to an exit outlet duct 87 and a return outlet duct 97 under the control of a diverter percentage signal carried on path 84a. A fraction of the material entering flow diverter 84 flows to outlet duct 87 and the remainder flows on outlet duct 97 past a temperature sensor 91. Temperature sensor 91 provides a signal on a data path 91a encoding the temperature of the material flowing from outlet 97.

The material from flow diverter 84 that flows in duct 97 reaches an inlet 71a of a heat exchanger 71 that heats the material flowing from duct 97. In one installation operating according to this invention, heat exchanger 71 heats the material flowing through it to a temperature in the range of 118 - 122 °C.

Material exits heat exchanger 71 in a duct 71b and flows past a second temperature sensor 95. Sensor 95 provides a second temperature signal on a data path 95a encoding the temperature of the material flowing from outlet71b. Although sensors 91 and 95 are shown as flow-through types, sensors 91 and 95 may also mount on the interior or exterior walls of ducts 71a and 71b respectively.

Heat exchanger 71 receives saturated steam for heating the material that flows through heat exchanger 71 from inlet 7 la to outlet 7 lb. The amount of steam that heat exchanger 71 receives is controlled by a valve 67. Valve 67 receives steam from a steam source and controls the flow rate of the steam through valve 67 responsive to a steam flow rate control signal carried on path 67a. Controlling the steam flow rate controls the temperature rise of the material flowing through heat exchanger 71. Other sources, such as electricity may also provide heat for the heat exchanger 71.

Material from heat exchanger 71 flows to a nozzle 61. Upon exiting nozzle 61, additional water and any remaining volatile ethanol in the material vaporize. The vapors flow upwards, further heating the downwardly flowing intermediate material on trays 38 and exit through duct 47 to heat exchanger 33 in flash tank assembly 20. A pump may be needed to pull these vapors from stripping column 53. The remainder of the material flowing from nozzle 61 joins the pool 99 of material at the bottom of housing 82. Pump 77 continues to recycle the material in pool 99, with sufficient pool 99 material exiting through outlet 87 as set by diverter percentage signal on path 84a to maintain pool 99 at an appropriate level.

A level sensor 81 senses the level of pool 99 and provides on path 81a a second level signal that indicates the level of pool 99. Level controller 30a (Fig. 2) receives the second level signal on path 81a, and provides a diverter percentage signal on path 84a to flow diverter 84. Controller 30a may use any suitable algorithm to select the value that it provides on path 84a to control the setting of flow diverter 84 and the level of pool 99.

It is in heat exchanger 71 that problems have arisen in prior art installations. The relatively high temperature of the material and the high concentration of organic compounds such as sugar often result in material adhering to the interior walls of the ductwork carrying the materials. In essence the materials has such a high concentration of organic compounds that these compounds bake on the interior walls in the same way that food sticks to a pan or skillet if the utensil is too hot.

The conventional installations use a final processor that avoids high temperatures in the heat exchangers. Such an approach requires many more components, as previously mentioned.

The characteristics and design of pump 77, heat exchanger 71, outlet 71b, and nozzle 61 should be chosen to control the velocity and pressure of the material as it flows through heat exchanger 71. The pressure in the material should be great enough within heat exchanger 71 and outlet 71b to prevent any vaporization of water or ethanol within these components. Vaporization of water precipitates sugar dissolved in that water , and some of that precipitated sugar will adhere to the adjacent wall.

The vaporization point of water of course, depends on the temperature and pressure, so maintaining pressure above the vaporization point for the temperature involved will prevent vaporization of the water. This information is readily available in steam tables. Thus, if the highest temperature of the mixture within heat exchanger 71 and particularly at outlet 71b is 120 °C (248 °F), then pressure above about 14 psig at that point will prevent the water from flashing into steam. The presence of dissolved materials such as sugar actually reduces the vaporization pressure for the water in the material in pool 99.

A similar analysis is true for ethanol, although since the concentration of ethanol in the pool 99 material is very low, vaporization of the ethanol is a much smaller problem.

For suitable thermal efficiency, a typical heat exchanger 71 has a large number of smaller tubes that carry the material. These smaller tubes combined with the relatively high viscosity of the material result in substantial pressure drop through heat exchanger 71. Thus, pressure within heat exchanger 71 is normally lowest near and also within outlet 71b, which is where the slurry temperature is highest as well. It is at this point that material is more likely to attach or burn on to the interior surfaces of heat exchanger 71 and outlet 71b. Pressure in heat exchanger 71 and outlet 71b should be sufficiently high to limit or eliminate vaporization of the liquids in the material within these vessels at the outlet . Minimum pressure within heat exchanger 71 and outlet 71b depends on the pressure rise that pump 77 generates, and the pressure drop across nozzle 61. Of course, heat exchanger 71 and outlet 71b must be of sufficient strength to prevent leakage or failure. Selecting pump 77 and nozzle 61 properly, creates an appropriately high pressure within heat exchanger 71 and outlet 71b that prevents within these components, vaporization of liquids in the material.

Velocity of the material flow through heat exchanger 71 is also important. Local hot spots within heat exchanger 71 can cause slowly moving material to adhere at these hot spots. As velocity increases, material passes such local hot spots more quickly, and thus is less likely to adhere. Further, higher velocity of the material can often scrub or flush lightly adhering material from these hot spots.

This effect is not dissimilar to stirring the food in a hot pan to prevent it sticking to the pan surface. Testing suggests that a minimum velocity of 5 feet per second of the material within heat exchanger 71 and outlet 71b will minimize or even eliminate the amount of material adhering to interior surfaces in these vessels. This preferred flow velocity though this ductwork depends to some extent on the concentration of organic compounds in the material. Lower concentrations may allow lower flow velocity, in the 3 feet per second range.