Method for Liquid Air Energy Storage with Semi-Closed CO2 Bottoming Cycle

Abstract

A proposed method provides a highly efficient fueled power output augmentation of the liquid air energy storage (LAES) through its integration with the semi-closed CO.sub.2 bottoming cycle. It combines the production of liquid air in air liquefier during LAES charge using excessive power from the grid and an effective recovery of stored air for production of on-demand power in the fueled supercharged reciprocating internal combustion engine (ICE) and associated expanders of the power block during LAES discharge. A cold thermal energy of liquid air being re-gasified is recovered for cryogenic capturing most of CO.sub.2 emissions from the facility exhaust with following use of the captured CO.sub.2 in the semi-closed bottoming cycle, resulting in enhancement of total LAES facility discharge power output and suppressing the thermal NOx formation in the ICE.

Claims

1. A method for liquid air energy storage (LAES) with semi-closed CO.sub.2 bottoming cycle comprising in combination: charging the energy storage with liquid air produced through consumption of an excessive power from the co-located renewable energy sources or from the grid; discharging the energy storage with on-demand producing and delivering a power to the grid through pumping and re-gasifying the stored air and its recovering in the multi-stage expander train and as combustion air for the fueled supercharged internal combustion engine (ICE); recovering the cold thermal energy of discharged liquid air being regasified for cryogenic cooling the LAES facility exhaust with capturing and liquefying at least a part of CO.sub.2 emissions formed by combustion of fuel in the said LAES facility; and wherein the improvement comprises in combination: pumping the said liquid CO.sub.2 up to pressure somewhat exceeding a pressure of the pumped liquid air, injection of the pumped liquid CO.sub.2 into a stream of re-gasified air, resulting in regasification of injected CO.sub.2 and forming a mixed air-CO.sub.2 stream; superheating the mixed air-CO.sub.2 stream in the waste heat recuperator upstream of the high-pressure (HP) turbo-expander stage; recovering the superheated mixed air-CO.sub.2 stream in the said HP expander installed upstream of said supercharged reciprocating ICE; dividing a full air-CO.sub.2 mixed stream escaping the HP expander into a proportion of air-to-CO.sub.2 amounts in the said stream; recovering the bulk of mixed air-CO.sub.2 stream for combustion of fuel in the said supercharged reciprocating ICE; releasing the exhaust gases from the said ICE at the enhanced pressure and temperature; delivering the rest of mixed air-CO.sub.2 stream through a pressure equalizer for the mixing with the exhaust gases escaping the said ICE; increasing a temperature of the formed gaseous mixture through controlled combusting an additional fuel in this mixture; recovering the mixed exhaust gases through their expanding in the low-pressure (LP) turbo-expander stage with following recuperating the waste heat of mixed exhaust gases escaping the LP expander at a pressure near atmospheric for said superheating the mixed air-CO.sub.2 stream upstream of the HP expander; multi-stage treating the mixed exhaust gases including their dewatering and deep cooling first by a stream of treated exhaust gases escaping the facility and then by a stream of re-gasified air prior to said its mixing with CO.sub.2 stream; further cryogenic cooling the mixed exhaust gases by a stream of discharged liquid air, accompanied by regasifying a said liquid air and desublimating and separating at least a part of solid CO.sub.2 component from the stream of mixed exhaust gases being cooled; periodical fusion of the separated solid CO.sub.2 component under a pressure exceeding CO.sub.2 triple point with use of available waste heat streams from the LAES facility; withdrawing and accumulating the separated CO.sub.2 in liquid form prior to its said pumping and mixing with the re-gasified discharged air; and said recovering a cold thermal energy of treated exhaust gases for said dewatering and deep cooling the non-treated mixed gases and following removing the treated exhaust gases with a non-captured part of CO.sub.2 emissions into atmosphere.

2. A method as in claim 1, wherein a minimal amount of the liquid CO.sub.2 mixed with the re-gasified air is established at a level equal to amount of CO.sub.2 formed by combustion of fuel in the LAES facility, whereas a maximum amount of said CO.sub.2 mixed with air does not exceed a level, at which a concentration of oxygen in air-CO.sub.2 mixture at the ICE inlet is achieving a minimal admissible value required for stable combusting a fuel in the said ICE.

3. A method as in claims 1-2, wherein a maximum amount of the liquid CO.sub.2 mixed with the re-gasified air exceeds a minimum amount of such CO.sub.2 by a factor of 2.0-4.0 and preferably by a factor of 2.5-3.0.

4. A method as in claims 1-3, wherein an amount of the liquid CO.sub.2 mixed with the re-gasified air is selected at a level providing a desirable suppressing the formation of NOx emissions in the ICE, but not exceeding a said maximum amount of such liquid CO.sub.2.

5. A method as in claim 1, wherein an amount of the liquid CO.sub.2 mixed with the re-gasified air may be increased through enhancement in pressure of liquid air produced and stored during LAES charge.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Embodiment will hereinafter be described in detail below with reference to the accompanying drawing, wherein lie reference numerals represent like elements. The accompanying drawing has not necessarily been drawn to scale.

[0019] FIG. 1 is a schematic view of the first embodiment for implementing the discharging the energy storage with cryogenic capturing at least a part of the CO.sub.2 emissions from energy storage exhaust and their use in the semi-closed CO.sub.2 bottoming cycle, according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The practical realization of the invented method for Liquid Air Energy Storage (LAES) with semi-closed CO.sub.2 bottoming cycle may be performed through the integration between the liquefier of LAES facility, fueled supercharged reciprocating internal combustion engine (ICE) with associated turbo-expanders package and system for exhaust gas treatment including cryogenic capture of a part of CO.sub.2 emissions from facility exhaust with recovery of the captured CO.sub.2 emissions in the said bottoming cycle. Such the integration makes possible to maximize power output and round-trip efficiency of the energy storage and to significantly suppress the formation of the thermal NOx emissions. The LAES operation includes the modes of its charge and discharge. The charge operation mode is identical to that described in the published U.S. Patent Application No. 2018/0221807 and therefore its detailed explanation is not needed here.

[0021] FIG. 1 shows schematically the first embodiment of the power block of LAES facility for implementing the discharge operation mode with semi-closed CO.sub.2 bottoming cycle. Here the involved equipment packages are designated as: [0022] 100liquid air storage equipment; [0023] 200supercharged reciprocating ICE package; [0024] 300expander train; [0025] 400exhaust dewatering and cryogenic cooling package; and [0026] 500bottoming cycle package.

[0027] Operation of the power block in discharge mode is performed as follows. A stream of liquid air is extracted from the storage 101 at a bottom dicharge cycle pressure exceeding 2 barA and pumped by a pump 102 up to top discharge cycle pressure selected in the range between 100 and 200 bar. The highly-pressurized liquid air stream is delivered into package 400, wherein its regasification is performed in one of two heat exchangers 401 and 402 operated by turns. The regasified air is further subjected to a moderate heating in heat exchanger 403 and mixed in the point 404 with a stream of pumped liquid CO2, resulting in formation of highly-pressurized air-CO.sub.2 mixed stream. A temperature of said mixed stream is further risen in the hot recuperator 301 up to level not exceeding 600 C. The said temperature restriction makes possible to use the commercially available back-pressure steam turbine as a high-pressure (HP) expander 302, wherein partial expanding the superheated air-CO.sub.2 mixed stream is performed down to an intermediate discharge cycle pressure selected in the range from 2 up to 12 barA. The HP expander 302 is coupled with electric generator 303, converting mechanical work of expander into a part of the energy storage electrical output.

[0028] In the point 304 the air-CO.sub.2 mixed stream escaping the expander 302 is divided into two parts. Most of the mixed stream is directed through the optional intercooler 201 to the fueled reciprocating internal combustion engine (ICE) 202 for its supercharging and combustion of fuel delivered into said ICE through pipe 203. This is accompanied by formation of the water (H.sub.2O) vapor and additional gaseous carbon dioxide (CO.sub.2) components in the stream of exhaust gases escaping the ICE under pressure slightly below a selected intermediate discharge cycle pressure. The said engine is loaded by the generator 204 and used to produce from 35 to 65% of total energy storage power output. A minor part of the air-CO.sub.2 mixed stream escaping the expander 302 bypasses the ICE 202 and is directed through pressure equalizer 205 to the point 206, wherein its mixing with exhaust gases from engine 202 is performed.

[0029] A temperature of mixed exhaust gases stream and concentration of the said H.sub.2O and CO.sub.2 components in this stream are further increased, resulting from combustion of a small amount of additional fuel delivered via pipe 207 into the duct burner 208 installed dowstream of the point 206. Amount of additional fuel consumed should be designed so that a stable combustion of this fuel and a temperature of the mixed exhaust stream at the outlet of said burner 208 not exceeding 750 C. would be ensured. The said restriction on the enhancement of the mixed exhaust stream temperature provides two necessary conditions for design and operation of the described scheme. On the one hand, it makes possible to use the commercially available power turbine produced by the engine manufacturer as low-pressure (LP) exhander 305 of this mixed exhaust stream, wherein its pressure is reduced down to a pressure slightly above the armospheric value. On the other hand, it provides the temperatures of mixed exhaust stream at the outlet of expander 305 and inlet of recuperator 301 in the range securing a temperature of superheated air-CO2 mixed stream at the outlet of said recuperator not exceeding 600 C. The generator 306 driven by LP expander 305 produces a part of energy storage power output.

[0030] A further treatment of mixed exhaust gases stream cooled in the recuperator 301 is destined for dewatering these gases and freeing them from most of the CO.sub.2 components. The first step of gases dewatering may be a drainage of water condensate from the recuperator 301 through a coupled drainage device. In the following two-stage cooling process, the exhaust stream is cooled firstly in the first cooler 405 down to a temperature close to 1 C., resulting in further condensing the water vapor and its removal through a coupled drainage device. A succeeding cooling of the mixed exhaust gases down to 70 C.-90 C. is performed in the second cooler 403, resulting in freezing the water component on the tubing surface of this cooler. Since a water vapor mass content in the mixed exhaust gas stream at the inlet of second cooler 403 does not exceed 0.4-0.7%, ice deposition on the tubing surface during energy storage discharge does not lead to a marked increase in pressure drop. This makes possible to postpone the ice removal until starting a process of the energy storage charge. During this process a compression heat from any air intercooler or aftercooler of compressor train may be used to melt the ice on the tubing surface of the cooler 403 with drainage of the formed liquid water through a coupled drainage device.

[0031] A final cryogenic cooling of dewatered mixed exhaust gases stream down to the temperature below 120 C. is performed in one of two heat exchangers 401 and 402 operated by turns and accompanied by de-sublimation of most of the CO.sub.2 component and its deposition on the tubing surface of said heat exchangers in the form of dry ice. Since a mass CO.sub.2 content in the dewatered mixed exhaust gas stream at the inlet of heat exchangers 401 and 402 lies in the range from 17 to 28%, solid CO.sub.2 deposition on the tubing surface of these heat exchangers may lead to a marked increase in pressure drop of mixed exhaust gas stream. To exclude formation of intolerably thick layer of dry ice during energy storage discharge, the said heat exchangers are used in turn for de-sublimation of most of the CO.sub.2 component and its removal in a liquid state. Whereas in one heat exchanger a cryogenic capture of CO.sub.2 component from mixed exhaust gases stream is accompanied by formation of dry ice on its tubing surface, another heat exchanger is disconnected from the mixed exhaust gas duct and liquid air pipe and is freeing from the solid CO.sub.2. The CO.sub.2 is removed in liquid form into pressurized tank 501, for which purpose a shell of disconnected heat exchanger is pressurized up to pressure above critical value 5.2 barA and available waste heat stream from the LAES facility (for example, a stream of cooling water from the gas engine 202) is directed into tubing part of this heat exchanger to fuse the dry ice on the outer surface of tubing part and convert it directly into liquid CO.sub.2.

[0032] It should be stressed that at a selected and fixed top discharge pressure of the pumped liquid air, its temperature at the at the inlet of heat exchangers 401 and 402 is directly dependent on a pressure and temperature of the liquid air produced, stored and delivered to suction of the pump 102. In its turn, for each given concentration of CO.sub.2 in the mixed exhaust gas stream a temperature of liquid air at the inlet of heat exchangers 401 and 402 has a direct impact on a minimal level of the mixed exhaust gas temperature, which may be achieved at the outlet of said heat exchangers and consequently on a share of CO.sub.2 desublimated in them. For example, at the given top discharge pressure of 140.6 barA a temperature of mixed exhaust gas temperature at the outlet of heat exchangers 401 and 402 may reach 181 C.-140 C. in the diapason of produced liquid air pressures from 2.7 to 14.7 barA. This makes possible to capture from 100 to 85% of the CO.sub.2 emissions from the mixed exhaust gas stream without CO.sub.2 recirculation.

[0033] The treated and deeply cooled exhaust gas with significantly reduced CO.sub.2 content escapes the heat exchangers 401 and 402 and is delivered into first cooler 405, wherein its cold thermal energy is used for cooling and dewatering the un-treated mixed exhaust stream. Since a temperature of mixed exhaust stream escaping the cooler 405 is fixed at a level of about 1 C., a temperature of treated exhaust stream 406 is always below 0 C. This makes possible to use this exhaust stream as source of cold for the gas engine cooling system, or to accumulate this cold for following its usage for intercooling the pressurized air during LAES facility charge.

INDUSTRIAL APPLICABILITY

[0034] The comparative analysis of the LAES facility in three configurations is presented below: Alt. 1without any post-combustion exhaust gases treatment; Alt. 2with near-zeroth carbon emitting exhaust; and Alt. 3.with semi-closed CO.sub.2 bottoming cycle. The calculation of these performances has been performed as applied to integration between the air liquefier and power block, including a fueled supercharged reciprocating internal combustion engine (ICE) supplemented by duct burner (DB) installed downstream of gas engine and expander train with HP air expander installed upstream of ICE and LP exhaust expander installed downstream of the DB.

[0035] Using an excessive power of renewable energy sources, the air liquefier produces 15.1 kg/s of liquid air at a pressure of 6.7 barA during 12 off-peak hours. During 12 on-peak hours the stored liquid air is pumped up to 140.5 barA and converted into on-demand power in the power block with fueled augmentation. The ICE is exemplified by fueled gas engine designed for producing 9730 kW of electrical power at Heat Rate of 7779 kJ/kWh or 46.3% of electrical efficiency. In the Alt. 1 and 2 this standard engine is supercharged with 15.1 kg/s of pure regasified liquid air used as combustion air at the pressure of 3.9 barA and temperature of 45 C. In the Alt. 3 the stream of pumped liquid CO.sub.2 at a rate of 3.9 kg/s is mixed with the stream of HP regasified liquid air at a rate of 15.1 kg/s to form the stream of HP air-CO.sub.2 mixture as a working medium of the semi-closed CO.sub.2 bottoming cycle. The concentration of oxygen in this mixed stream is equal to 17.9% (v/v), which is significantly below the oxygen content of 21% (v/v) in pure air used for supercharging the GE in the Alt. 1 and 2. After superheating in the recuperator and partial expansion in the HP expander the mixed air-CO.sub.2 stream is divided into two parts. The bulk of the mixed stream at a rate of 15.1 kg/s is used for supercharging the ICE, whereas a minor part bypasses the GE and combines with the GE exhaust only before the DB. The ICE and DB are supplied with a methaneous fuel, having heat of combustion at a rate of LHV=48632 kJ/kg. Reduced concentration of oxygen in the air-CO.sub.2 mixture at the engine inlet in the Alt. 3 leads to significant suppression of NOx formation in the combustion of fuel in this engine. In all Alternatives the exhaust gases escape the GE at the pressure of 3.6 barA and temperature of 570 C., having in their composition the CO.sub.2 and H.sub.2O components, as products of fuel combustion. Combusting an additional fuel in the duct burner leads to increase in temperature of exhaust gases up to 750-760 C. and to further changes in their flow-rate and composition. The additionally heated exhaust gases are expanded in the LP expander and cooled in the recuperator, after which they are removed into atmosphere in Alt. 1 or subjected to further treatment in the Alt. 2 and 3.

[0036] This treatment includes dewatering and cryogenic cooling of the facility exhaust gases. In the Alt. 2 the treatment process is finalized by cryogenic capture and removal of 98-99% of CO.sub.2 emissions from LAES facility exhaust. In the Alt. 3 up to 72% of CO.sub.2 component (3.9 kg/s) may be cryogenically captured and recirculated to inlet of the power block. The rest of CO.sub.2 components (1.55 kg/s) are emitted into atmosphere at a level of CO.sub.2 emissions from LAES facility without any post-combustion exhaust gases treatment. In so doing this specific level (248 kg/MWh for Alt. 3 and 274 kg/MWh for Alt. 1) is far less than permitted for the large gas-fired power plants established by the new 2015 U.S. Carbon Pollution Standard.

[0037] As confirmed by such leading OEM as Siemens, Alstom and MAN Energy Solutions, the commercially available back-pressure steam turbine may be used as the HP turbo-expander, wherein a pressure of superheated mixture of air and CO.sub.2 is reduced from 140 barA down to 4 barA (see FIG.). Thereby a temperature of said gaseous mixture at the inlet of this expander is maintained at a level of 550-560 C. The industrial expanders produced by the MDT or ABB Turbochargers may be used as the LP turbo-expander, wherein a temperature of mixed exhaust gases at the inlet of such expander is maintained at the admissible level of 760 C. The main calculated performance of the LAES facility during its operation in charge and three different alternative discharge modes are presented in the Table below.

[0038] As evident from the presented calculation results, the use of proposed semi-closed CO.sub.2 bottoming cycle, wherein amount of recirculating CO.sub.2 ranges up to 25% of consumed liquid air, makes possible to increase the discharge power output of LAES facility by 10% and to significantly reduce formation of thermal NOx emissions in gas engine. Both the effects could be further enhanced, if production and storage of liquid air would be performed at a lower pressure with corresponding decrease in temperature of HP liquid air being used for cryogenic CO.sub.2 capture. However care must be exercised to avoid the reducing of O.sub.2 concentration at the gas engine inlet below 16% (v/v).

[0039] The use of semi-closed CO2 bottoming cycle provides also an enhancement of grid round-trip efficiency (RTE) of LAES facility from 118% up to 130% and recasted RTE from 71% up to 79%. At the identical duration of the facility charge and discharge, the grid RTE is determined as simple relationship between the LAES facility discharge power output and power consumed for facility charge. The recasted RTE is determined having regard to grid power equivalent of fuel consumed by the ICE and DB during facility discharge. Since the average grid fuel-to-power conversion efficiency does not exceed 33%, through multiplying of this value by the total heat input in each Alternative a grid power equivalent of fuel consumed may be calculated. Then the recasted facility discharge power is determined through subtraction of the calculated grid power equivalent of fuel consumed from total facility discharge power. In its turn, the recasted RTE is calculated as relationship between the recasted facility discharge power and power consumed for facility charge.

[0040] It should be noted that the term comprising does not exclude other elements or steps and a or an do not exclude a plurality. It should also be noted that reference signs in the claims should not apparent to one of skill in the art that many changes and modifications can be effected to the above embodiments while remaining within the spirit and scope of the present invention.

TABLE-US-00001 Parameters Units Alt. 1 Alt. 2 Alt. 3 LAES charge duration h/d 12 12 12 Charge power from RES MWe 17.28 17.28 17.28 Production of liquid air kg/s 15.1 15.1 15.1 Pressure of liquid air stored barA 6.7 6.7 6.7 LAES discharge duration h/d 12 12 12 Consumption of liquid air kg/s 15.1 15.1 15.1 Pressure of liquid air pumped barA 140.5 140.5 140.5 Temperature of HP liquid air C. 164.5 164.5 164.5 Zero CO2 exhaust No Yes No Semi-closed CO2 bottoming cycle No No Yes CO2 content in untreated exhaust kg/s 1.55 1.55 5.45 flow CO2 content in treated exhaust kg/s 1.55 0.025 1.55 flow CO2 removal efficiency % 0 98.5 0 CO2 recirculation kg/s 0 0 3.9 Pure air flow at the GE inlet kg/s 15.1 15.1 N/A Air-O2 mixed flow at the GE inlet kg/s N/A N/A 15.1 Bypass air-O2 mixed flow kg/s N/A N/A 3.9 O2 concentration at the GE inlet % (v/v) 21 21 17.9 O2 concentration at the DB inlet % (v/v) 10.1 10.1 8.7 Heat input with fuel in GE MWth 21.01 21.01 21.01 Heat input with fuel in DB MWth 3.62 3.62 6.08 Total heat input with fuel MWth 24.63 24.63 27.09 Grid power equivalent of fuel MWe 8.13 8.13 8.94 consumed GE power output MWe 9.73 9.73 9.73 HP expander power output MWe 7.09 7.09 8.60 LP expander power output MWe 3.91 3.91 4.58 Auxiliary power consumption MWe 0.36 0.36 0.38 Total net power produced MWe 20.37 20.37 22.52 A share of CO2 cycle in total % 0 0 9.6 power Fuel-to-power conversion % 83 83 83 efficiency LAES grid round-trip efficiency % 118 118 130 LAES recasted round-trip % 71 71 79 efficiency