Hydrothermal Power Plant

Cross Reference to Related Applications

[0001 ] The present application claims priority to the US Provisional Patent application of the same titled filed on April, 28, 2009, having application serial no. 61/173,498, which is incorporated herein by reference.

Background of Invention

[0002] The present invention relates to an improved means of electric power generation via the oxidation of various organic materials in a Supercritical

Water Oxidation Reactor (SCWOR).

[0003] Prior methods of using SCWOR to generate electric power are disclosed in the following US Patents no. 5,485,728, US Pat. No. 5,000,099 and US Pat. No.7,640, 745, which are incorporated herein by reference.

[0004] SCWOR have an inherent utility as the most of efficient means to completely oxidize organic waste of all types, including toxic chemical, as well as wet biomass, such as sludge.

[0005] However, while an SCWOR can also use conventional fuels without creating harmful by-products, other than CO2, the conventional fuels need not be heavily refined and can even be contaminated with water, organic and organo- inter-metallic and metallic compounds.

[0006] However, prior to the current invention, SCWOR have had poor efficiencies that have not made commercially viable to produce energy. Accordingly, the actual implantation of SCWOR designs in the patent literature is scant and largely in academic research laboratories and government end use to date.

[0007] Bio fuels, in particular ethanol, has gained popularity as an automotive gasoline additive in the US, as well as a direct fuel in other countries. AS ethanol is generally produced from corn or such cane, a significant non- fermentable biomass is created in these processes. These biomasses are sometimes burnt as fuel, but being somewhat wet, are an inefficient and particulate polluting heat source.

[0008] It would be desirable to utilize mixed biomasses of varying water contents as a fuel with the utmost efficiency to produce power with an entirely clean combustion process, that is only producing CO2 as the only gaseous by product, other than water as steam. Achieving such an objective would reduce the dependence on fossil fuels and reduce the overall "carbon footprint" of power production by turning biomass that might otherwise be burnt without generating power into power. In addition, such an improvement in technology would facilitate the clean up and disposal of toxic wastes and allow safe disposal of waste at many manufacturing facilities without the expense and risk of storing and transporting waste.

[0009] It is therefore a first object of the present invention to provide such a SCWOR of improved efficiency in which moist organic materials can be efficiently combusted without expending additional energy to pre-dry the fuel, and without chemical conversion of the wet fuel into another fuel that is more suitable for combustion in existing combustion apparatus.

[001 0] It is a further object of the invention to provided such power plant in which the SCWOR provides complete combustion without undesirable by-products.

[001 1 ] It is still another object of the invention to provide such a plant is capable of accept multiple and diverse fuel sources for the recovery of useful energy with high thermal efficiency. Summary of Invention

[001 2] In the present invention, the first object is achieved by providing a power generating plant that comprises a super critical water oxidation reactor (SCWOR) having a feed port for reactants and an exit port for exhaust, a brine separator having an inlet for receiving the exhaust of the SCWOR and at least one outlet for gases, two or more pairs of air compressors and expanders coupled in rotary motion by a common axle, at least one heat exchanger associated with each of said one or more pairs of compressors and expanders, wherein the hot exhaust gas exiting the brine separator enters a first expander, and the cooled exhaust gas exiting the first expander enters a first heat exchanger that cools hot compressed air from the air compressor while reheating the cooled exhaust gas exiting the first expander prior to a second stage of expansion, and the cooled air exiting the heat exchanger enters a downstream compressor stage in said 2 or more pairs of air compressor and expanders, a motor or motor/generator with a rotary coupling to at least one common drive mechanism of the air compressor-expander pairs, wherein the rotary motion of the drive mechanism supplies mechanical power driving the motor generator for both electric power and driving the air compressors.

[001 3] The above and other objects, effects, features, and advantages of the present invention will become more apparent from the following description of the embodiments thereof taken in conjunction with the accompanying drawings.

Brief Description of the Drawings

[001 4] FIG. 1 is a schematic diagram the generically discloses the operative principles of the HTPP in a first embodiment.

[001 5] FIG. 2 is a schematic diagram of the power generation system in the HTPP of FIG. 1.

[001 6] FIG. 3 is a schematic diagram of a second embodiment of the HTPP.

[001 7] FIG. 4 is a schematic diagram of a third embodiment of the HTPP.

[001 8] FIG. 5 is a schematic diagram of a fourth embodiment of the HTPP.

[001 9] FIG. 6 is a schematic diagram of a firth embodiment of the HTPP.

Detailed Description

[0020] Referring to FIGS. 1 through 6, wherein like reference numerals refer to like components in the various views, there is illustrated therein a new and improved Hydro-Thermal Power Plant (HTPP) generally denominated 100 herein.

[0021 ] In accordance with the present invention, FIG. 1 illustrates a HTPP 100 that comprises a super critical water oxidation reactor (SCWOR) 110. At the super critical conditions the organic materials that enter the SCWOR 110 are oxidized, as are described for example in US Pat. No. 5,558,783 issued to McGuinness on Sep.24, 1996) and 5,384,051 (issued to McGuinness on Jan.

24, 1995) which are incorporated herein by reference. This oxidation reaction generates heat that is used to generate electrical power in the HTTP 100 as described further below. SCWOR 100 preferably incorporates a permeable- wall or transpiring wall 115. The SCWOR 110 may be operated at pressures above or below the critical pressure or water.

[0022] In a currently preferred mode of operation, various combinations of biomass and organic materials are co-injected with water or in an aqueous suspended state into the top of the SCWOR 110 at the injector 1405. Hot exhaust and reaction products are controllably cooled in the quench cooler 120 at the exit of the SCWOR 110 by direct mixing with cooled re-circulated brine that circulates in line 1300 from the bottom of the gravity separator 130, into which the cooled reaction product is then received from the quench cooler 120.

[0023] It should be appreciated that an important aspect of the current invention is the extracts of heat from the hot liquid recirculation stream of the brine. This is more both a more efficient way to extract heat from gases as proposed in US Pat. no. 5,485,728 issued to Norman L. Dickinson on Jan. 23, 1996 for "EFFICIENT UTILIZATION OF CHLORINEAND MOISTURE- CONTAINING FUELS" and US Pat. no. 5,000,099 (which is a continuation in part of a series of patents to Dickinson), but also enables other routes for heat and energy recovery that would otherwise be lost in a prior art system.

[0024] This technology can be applied to all types of pumpable organic sludges and raw biomass slurries. A process using Waste water treatment facility (WWTF) sludge is now described for illustration purposes, as it will be apparent to one of ordinary skill in the art that other sources of organic material can also be used in the same HTTP 100. For example, many high moisture renewable fuel sources and non-renewable fuel sources such as coal may be used to generate power in the inventive HTPP 100. Wastewater sludge will preferably be taken off the bottom of the existing WWTF gravity thickeners at approx 3% biosolids (BS) concentration. The sludge can be ground as necessary to improve pumpability, and then pumped at low pressure to the HTPP 100. The sludge is preferably centrifuged to approx 10% biosolids concentration. Filtrate water from the centrifuge is sent back to the WWTF headworks.

The concentrated sludge is then pumped to combustor pressure via pump 260.

[0025] When the fuel to the SCWOR is sludge it is pre-heated by heater 265 to approx 200 ⁰ C before injection into SCWOR 110, which is preferably a hydrothermal transpiring-wall combustor (such as are disclosed in US Pat. No. 5,558,783 and 5,384,051) where it is turbulently combined with a preheated mixture of superheated steam and compressed air. The combustor will normally operate at subcritical pressures (below the critical pressure of water), but may also be designed to operate above the critical pressure of water. Spontaneous oxidation of the sludge occurs upon mixing within the combustor. Superheated reaction products (CO ₂ , N ₂ , excess O ₂ , water vapor and inorganic residuals) exit the bottom of the combustor and enter the quench cooler 120

[0026] The quench cooler 120 partially cools the stream, thereby forming a saturated

2- phase vapor-liquid mixture. This 2-phase stream then enters a gravity separator 130 for separation into liquid and vapor streams. This gravity separator 130 operates below the local saturation temperature of water and will contain what will be referred to as a brine, as it contains some dissolved inorganic slats. As shown in the embodiments of FIG. 1 and 3-6, the hot liquid phase or brine leaves the bottom of the separator 130 via line 1300 carrying with it all of the suspended and dissolved inorganic constituents of the sludge.

[0027] In the embodiment of FIG. 3-6, the stream in line 1300 passes through a steam generator 270, such as a shell & tube heat exchanger for example, before being recycled back to the quench cooler 120 via pump 121. The steam generator 270 is thus designed to extract useful heat from the liquid brine recirculation loop 1300. The brine circulation quench pump 121 supports the continued flow of brine in loop 1300.

[0028] Inorganic solids are continuously removed from this stream via hydrocyclone filtration at filter 500, and then removed from the system via blowdown for solids dewatering and disposal at 505. A hydrocyclone 500 is optionally replaced with a filter or other means known in the art to separate and remove free solids from the liquid in brine recirculation loop 1300 . "Blowdown" refers to a liquid stream leaving the process for disposal. This stream would contain any separated solids from the hydrocyclone or filter, but might only contain dissolved solids to control the total amount of dissolved solids in the brine recirculation loop. This technique is routinely used in steam boilers to prevent total dissolved solids from reaching saturation and precipitating out on the walls of the equipment as scale. Blowdown water containing the dissolved solids is directed back to the WWTF headworks. Blowdown is a small percentage of the total flow through the recirculation loop.

[0029] In the embodiment of FIG. 1 , 3 and 4 the hot vapor mixture of CO ₂ , N ₂ , O ₂ and water vapor exits the 2-phase separator 130 and enters a condenser 220, where the water vapor is condensed and separated from the non-condensable gases. [0030] It should be appreciated that the condensed water output from condenser 220 at port 242 is generally free of inorganics and organics; it is essentially distilled water but may require additional polishing. Such excess condensed water is drained from the process and returned to the WWTF, such as at moisture condenser 240, via outlet 242. The remaining condensed water is heated and vaporized for mixing with the compressor air (from compressor 3317) via valve 1403 prior to injection into the combustor. Thus, a portion of this condensed water is optionally recycled back to the combustor or SCWOR 110 (via circulation pump 107) for liner transpiration via liner 115 at inlet port 1406 (where it is delivered outside the permeable-wall or transpiring wall 115.) However, the water before returning to the either the injector 1405 or the side port 1406 is preferably reheated by injector trim heaters 1401.

[0031 ] Therefore, two 3 -way flow control valves 1402 and 1403 are provided for dividing the total flow of compressed air and transpiration water to separate destinations. Such flow control valves might use multiple 2-way valves instead of a single 3 -way valve to achieve same end. Flow control valve 1402 divides liquid transpiration water into two streams. One stream going to the boiler to be vaporized for use in transpiration service and the balance going to the boiler to be vaporized for use in injection/mixing service with the feed. Flow control valve 1403 divides the compressed air into two streams. The other stream going to the reactor annulus at port 1406 for use in transpiration service and the balance going to the feed injector 1405 for injection/mixing with the feed from pump 265. The injector trim heaters 1401 are also useful in reactor start-up and control.

[0032] In the embodiments of FIG. 1-4, the non-condensable gases are used to generate power in generation train 3000 by being fed to one or more gas expanders wherein they drive a rotary mechanism. As shown in FIG. 1, in stage 3300 of train 3000 each of the air compressor stages 3317 are coupled in rotary motion to one or more gas expansion stages 3315 by a common drive mechanism 160. One or more of such coupled compressor-expander pairs or stages are arranged in a train of two or more pairs to achieve higher overall compression ratio and expansion ratio than possible with pair. Two or more compressor and expander stages may be coupled in rotary motion at different rotational speeds by means of a common gearbox, as done in integrally-geared compressors known in the art. The cooperative operation of the other stages of train 3000 is shown in more detail in FIG. 2. The non-condensable gases leaving the condenser 240 are heated in a pre -heater 3318 by heat from the hot brine recirculation loop 1450 and then reduced to atmospheric pressure via a multi-stage hot gas expander cascade train 3000. Each stage of the expander cascade drives one of the compressor stages. Should it be desired to recover carbon dioxide from this stream of non-condensable gases, it would best be done upstream of the high-pressure expander preheater at unit 245, wherein the carbon dioxide by removal is represent by the exciting arrow 246.

[0033] The power train 3000 preferably deploys 3 or 4 stages of compression with intercooling, while the expansion likewise requires 3 or 4 stages of expansion with interstage reheat. FIG. 2 illustrates a preferred aspect of the invention with three separate expander-compressor pairs 3100, 3200 and 3300 cascaded in series. In this aspect, heat from each compressor intercooler is used to heat and expand the noncondensable gases upstream of each interstage reheater. This reduces the total preheat required upstream of each stage of expansion, providing more efficient product of energy from the biomass. This allows each expander-compressor train to operate more closely to its optimum speed for maximum efficiency. Thus, at least 2 of the 3 coupled expander - compressor pairs 3100, 3200 and 3300 have at least one associated heat exchanger 3110 and 3210 (for 3100 and 3200 respectively) that receives the compressor output as a heat source and to increase the enthalpy of the exhaust of the preceding expander in the chain.

[0034] Thus, in operation the output gas from the first compressor 3117 is fed to the next compressor 3217 in pair 3200, and the output of compressor 3217 is feed to the next compressor 3317. An intercooler such as 3110 for compressor - expander pair 3100 cools the gas before the next stage of compression. However, intercooler receives the cooler exit gas from each expander as the heat transfer fluid such that heat or enthalpy in the gas from compression is transferred to the gas before the next stage of expansion.

[0035] In addition, the input to the last expander 3115 in coupled compressor- expander pair 3100 is heated first by the output of compressor 3117 via air compressor intercooler 3110 that acts as a heat exchanger.

[0036] Further, the input of the second expander 3215 in coupled pair 3200 is heated first by the output of compressor 3217 via air compressor intercooler 3210 that acts as a heat exchanger.

[0037] In addition, heat from the brine separator 130 liquid effluent stream supplies additional higher temperature heat to the exhaust gases of an expander prior to a first or subsequent expansion stage downstream of s air compressor intercoolers. Thus, preferably as shown each of expanders 3150, 3250, and 3350 are thus associated with a heat exchangers 3118, 3218 and 3318 respectively that receives either the re-circulating brine, or a heat transfer fluid heated therefrom, as a heat source and further increase the enthalpy of the exhaust of the preceding expander.

[0038] The final low-pressure expander-compressor pair 3100 is connected to a motor/generator 3001. During plant start up from a cold condition motor operation is generally required drive the air compressors. As the system comes up to temperature, the low-pressure expander will gradually supply power to the compressor and eventually produce enough power to generate surplus electric power to the grid. The intermediate-pressure and high-pressure expander-compressor trains 3300 and 3200 may or may not have a connected motor/generator 3002 and 3003 respectively.

[0039] While US Pat. No. 5,485,728 and 5,000,099 similarly use a SCWOR in a power generation scheme they do not appear to teach or suggest the "brine" heat or the heat of compression to reheat the expanded gas before it is feed to the next turbine. These patents all refer to preheating the gas before the expander by extracting heat from a hot gaseous stream. The present invention extracts heat from the hot liquid recirculation stream.

[0040] Thus, in the present invention the integrated combination of air compression, constant pressure hydrothermal combustion and gas expansion with energy recovery thereby completes a Hydrothermal Brayton Power Cycle.

[0041 ] As shown in FIG. 3-6, another aspect of the invention is the steam generator 270 located in the hot brine recirculation loop 1300 generates steam supplying a conventional steam turbine system 300 for additional power recovery. The steam turbine 314 may drive a dedicated electric generator 312, or may be connected to the low pressure expander-compressor-motor/generator train via a conventional overrunning clutch, these alternative coupling means being designated 1450 in FIG. 5-6. The effluent from the steam powered turbine 314 then enter the steam condenser 311, which has a water cooling inlet 313. The steam turbine re-circulation pump 106 is used to return the output of the moisture separator 240 to the heat exchanger 220 that pre-cool that mixture entering the moisture condenser 240, while a second recirculation pump 105 return the water exiting this heat exchanger 220 to the steam generator 270.

[0042] The total net power produced by the HTPP 100 is roughly evenly split between the expander-compressor cascade 3000 and the steam turbine system

300. Overall HTPP thermal efficiency is approximately 38% based on higher heating value of the wet feed. Thus, while the present invention will always incorporate a Brayton power generation cycle it may or may not include an optional Rankine (steam) co-generation cycle.

[0043] In FIG. 4 and 6, an optional steam superheater 400 is disposed at least partially within the SCWOR 110 to further improve the efficiency of the steam turbine system 300.

[0044] In another embodiment of the invention there is a mode of operation whereby a condenser 240 need not be disposed in the vapor outlet from the brine separator 130 to directly inject the hot vapor mixture into the expander- compressor. These embodiments are illustrated in FIG. 5 and FIG. 6 by the optional bypass line 5001 having valves valve around the condenser, which allows HTPP operation without the condenser in the loop. The reason for condensing and cooling the hot vapor exhaust stream is to cool the gas to facilitate removal of CO ₂ from the high-pressure exhaust gas stream, which is most easily done cool.

[0045] In other aspects of the invention, it may be preferable to provide for in-situ cleaning of the combustor liner and feed injector by injection of a suitable cleaning agent into the feed injector assembly and into the annular space between the pressure vessel wall and permeable liner. Water treatment systems as known in the art to control corrosion and fouling of process equipment.

[0046] Also, in the embodiments shown in FIG. 5 and 6 a dashed line 166 is intended to illustrate the optional gear box or clutch coupling between the generators

3001 and 312, or a common shaft to a single generator.

[0047] It should be appreciate that in alternative embodiments the oxidizer to the SCWOR 1000 may be air, oxygen enriched air, or oxygen. Air separation technology may optionally be installed upstream of the SCWOR 110 to separate air into oxygen-rich and nitrogen-rich streams. The nitrogen-rich stream may optionally be used to drive a gas expander as part of the power generation train 3000. Such oxidizer may or may not be mixed with the transpiration water entering at portal 1401.

[0048] In power train 3000, additional motors 3002 and 3003, or may not be required at all depending on the application. For example, the motor 3003 might be required for start-up, but then once the system is up to pressure and temperature, the compressor is driven solely by the expander. We will endeavor to start the system up without using motors on the higher pressure expander-compressors. A clutch coupling 3116 and 3216, typically an overrunning clutch, such that when the expander-compressor comes up to speed it automatically disengages from the motor 3003 allowing the motor to be switched off. Such clutches are commonly employed in industry. Although a hydrodynamic centrifugal or axial type compressor is shown in the diagram, for smaller plants a reciprocating compressor as known in the art may also be similarly employed in which all stages are driven via a common drive mechanism and motor/generator. Likewise, although hydrodynamic centrifugal or axial gas expanders are shown in the diagram, for smaller flows a reciprocating or other positive displacement type expansion engine may also be similarly employed whereby all stages of expansion may be connected via a common drive mechanism.

[0049] In other embodiments of the invention the air compressor stages may be driven independently from the gas expander stages. Gas expander stages are capable of generating mechanical power to directly drive electric generators, air compressors, pumps, chillers or any other type of driven equipment.

[0050] While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be within the spirit and scope of the invention as defined by the appended claims.