AIR ENERGY STORAGE WITH INTERNAL COMBUSTION ENGINES

Abstract

The present invention relates to a method and system for increasing power output and enhancing efficiency of an internal combustion engine, which comprises: cooling exhaust gas of the engine in a recuperating heat exchanger by transferring heat to stored air; compressing the exhaust gas to a pressure requisite for admission into the engine utilizing a compander module powered by expanding previously compressed and stored air in an expander without parasitic power consumption; mixing the exhaust gas with expanded air; and cooling or heating the exhaust gas to a suitable temperature in a final trim cooler or heater and supplying the exhaust gas to the engine at a pressure requisite at an admission point, without the need for additional compression and concomitant parasitic power consumption needed for exhaust gas recirculation. Extra electric power output and higher thermal efficiency is facilitated by using the excess power generation from the compander in a synchronous AC generator.

Claims

1. A method for increasing power output and enhancing efficiency of an internal combustion engine, which comprises: (a) cooling exhaust gas of the engine in a recuperating heat exchanger by transferring heat to stored air; (b) compressing the exhaust gas to a pressure needed for admission into the engine utilizing a compander module powered by expanding previously compressed and stored air in an expander without parasitic power consumption; c) mixing the exhaust gas with expanded air; and d) cooling or heating the exhaust gas to a suitable temperature in a final trim cooler or heater and supplying the exhaust gas to the engine at a pressure requisite at an admission point, without the need for additional compression and concomitant parasitic power consumption needed for exhaust gas recirculation.

2. The method as recited in claim 1, wherein surplus power from a carbon-free generation resource is used to compress an ambient air stream in an intercooled, multi-stage process compressor to storage pressure, which is then cooled in an aftercooler with moisture removal to storage temperature.

3. The method as recited in claim 2, wherein the carbon-free generation resource is solar or wind energy.

4. The method as recited in claim 2, wherein the storage pressure is 100 bar.

5. The method as recited in claim 2, wherein the storage temperature is 50° C.

6. The method as recited in claim 2, wherein a surplus power source is a fossil fuel-fired generation asset.

7. The method as recited in claim 6, wherein the fossil fuel-fired generation asset is a gas fired combined cycle power plant running overnight, or a nuclear power plant running at full load.

8. The method as recited in claim 2, wherein up to 100% (v) H.sub.2 combustion is enabled for carbon-free power generation.

9. The method as recited in claim 1, wherein the compander is self-balanced or designed to generate excess power to be used in a generator.

10. The method as recited in claim 1, wherein the gas is natural gas or a mixture of H.sub.2 and methane (CH.sub.4), or a syngas.

11. The method as recited in claim 1, wherein the internal combustion engine is a reciprocating internal combustion engine.

12. The method as recited in claim 1, wherein the internal combustion engine is a gas turbine.

13. The method as recited in claim 1, wherein compressed air energy storage enables up to 100% (v) H.sub.2 combustion in the internal combustion engine, with enhanced efficiency and reduced NOx emissions.

14. The method as recited in claim 1, wherein liquefied air energy storage enables up to 100% (v) H.sub.2 combustion in the internal combustion engine, with enhanced efficiency and reduced NOx emissions.

15. The method as recited in claim 1, wherein extra electric power output and higher efficiency is facilitated by using excess power generation from the compander in a synchronous AC generator.

16. A system for increasing power output and enhancing efficiency of an internal combustion engine, which comprises: (a) cooling exhaust gas of the engine in a recuperating heat exchanger by transferring heat to stored air; (b) compressing the exhaust gas to a pressure needed for admission into the engine utilizing a compander module powered by expanding previously compressed and stored air in an expander without parasitic power consumption; c) mixing the exhaust gas with expanded air; and d) cooling or heating the exhaust gas to a suitable temperature in a final trim cooler or heater and supplying the exhaust gas to the engine at a pressure requisite at an admission point, without the need for additional compression and concomitant parasitic power consumption needed for exhaust gas recirculation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a schematic diagram of energy storage with hydrogen, i.e., prior art with hydrogen stored as compressed gas in a reservoir (very high pressure, moderate temperature).

[0019] FIG. 2 is a schematic diagram of a generic compressed air energy storage (CAES) process.

[0020] FIG. 3 is a schematic diagram of a generic liquid air energy storage (LAES) process.

[0021] FIG. 4 is a schematic diagram of a preferred embodiment of the present invention, i.e., CAES with Reciprocating ICE (RICE) and Exhaust Gas Recirculation (EGR), providing a detailed, quantitative description of the invention.

[0022] FIG. 5 is a diagram of a RICE with a turbocharger module, equipped with a generator for operation within the present invention.

[0023] FIG. 6 is a diagram of a RICE with exhaust turbine and generator, for operation within the present invention.

[0024] FIG. 7 displays a further embodiment of the present invention, i.e., CAES with gas turbine (GT) and EGR.

[0025] FIG. 8 is a diagram representing an alternative admission point (gas turbine compressor discharge—combustor inlet) for a recirculated gas and air mixture.

[0026] FIG. 9 illustrates a further embodiment of the present invention, i.e., LAES with gas turbine (GT) combined cycle and EGR.

DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention is described in FIG. 4 using one embodiment, i.e., RICE with EGR and CAES. This particular embodiment is used for the detailed, quantitative description of the present invention. Surplus power from a carbon-free generation resource such as solar or wind energy (100) is utilized to compress an ambient air stream (10) in an intercooled, multi-stage process compressor (301) to the storage pressure (100 bar), which is then cooled in an aftercooler with moisture removal (302) to storage temperature (50° C.). Pressurized and cooled air stream (11) is delivered to the storage reservoir (303). This completes the “charge” phase of the energy storage process.

[0028] Note that the surplus power source (100) can be a fossil fuel-fired generation asset as well. One example would be a gas fired combined cycle power plant running overnight (in order not to shut down for fast load ramp up next morning and avoid thermal stresses) and generating power at very low prices (or even a “negative” price, i.e., the storage facility is paid to use the generated surplus power). Another example is a nuclear power plant that must run at full load at all times, whether there is a demand for power or not. This would create an arbitrage opportunity, i.e., the ability to make a profit by discharging stored air and generating power when electricity prices are much higher. The type of the surplus power source is immaterial to the present invention.

[0029] During the “discharge” phase of the process, compressed air stream (12) is sent through a pressure control valve (304) to a recuperating heat exchanger (305) and heated to a temperature of 250° C. by cooling the recirculated portion of the RICE (500) exhaust gas stream 24 from the discharge temperature (327° C.) to 70° C. It should be emphasized that the numbers cited herein are meant to be representative of the process based on a particular RICE for illustration purposes and thus subject to change and optimization, particularly by the engine OEM, for actual field deployment. Compressed air stream (14) at 50 bar and 250° C. is expanded through the expander section (601) of a “compander” (combined compressor-expander) (600), which drives the compressor (602) of the same. The compander (600) can be self-balanced (i.e., no net power generation or consumption) as depicted in FIG. 4 or it can be designed to generate excess power to be used in a generator. The particular configuration is subject to optimization during the detailed design phase.

[0030] Compressor (602), which is on the same shaft as expander (601), increases the pressure of the recirculated portion of the exhaust gas (24) from 1 bar to 5 bar. Recirculated and pressurized exhaust gas stream (25) mixes with the expanded air stream (26) and is cooled in the trim cooler (307) to a temperature of 50° C. Mixed air-gas stream (27) at 5 bar and 50° C. comprises the charge air for the RICE (500), which is ideally designed to burn 100% H.sub.2 fuel gas (stream 34).

[0031] Exhaust gas stream (21) of the RICE (500) at 1 bar and 325° C. is separated into two streams, 22 and 23. Stream 22 is sent to the stack whereas stream 23 is sent to the recuperator (305). Based on the assumption that recirculated gas stream 23 flow rate is 40% of the RICE exhaust flow stream 21, selected stream properties are summarized in Table 1.

TABLE-US-00001 TABLE 1 Air and gas stream data 10 21 23 27 34 Air Gas Gas Air + Gas Fuel Flow rate, kg/h 64,760 109,300 43,720 108,100 1,180 Temperature, ° C. 15.0 327.0 327.0 50.0 25.0 Pressure, bar 1.0 1.0 1.0 1.0 20.7 O.sub.2, %(v) 20.74 6.86 6.86 14.88 0.00 H.sub.2O, %(v) 1.01 23.37 23.37 10.12 0.00 H.sub.2, %(v) 100

[0032] The engine selected for the sample calculation has the following performance: 18.9 MWe generator output; 48% net LHV efficiency, and; 1,180 kg/h H.sub.2 consumption (LHV of 120,068 kJ/kg).

[0033] The engine is loosely based on MAN 18V51/60 with performance calculated using Thermoflow, Inc.'s THERMOFLEX heat and mass balance simulation software. The base unit is a medium speed (500 rpm), 18-cylinder gas engine available in 18.7 and 20.4 MW electric output versions (MAN 51/60G). Although no detailed information is available on the turbocharger, using typical values of 5 bar charge air pressure and single-stage charge compressor, based on 30 kg/s charge air flow rate, compressor power consumption is estimated as 7.5 MW, which is supplied by the exhaust gas turbine of the turbocharger unit.

[0034] According to the present invention, as illustrated in FIG. 5, if the turbocharger (505) of the RICE (500) is modified (i) to include a clutch/coupling (504) between the compressor (501) and turbine (502) and (ii) a generator (507) attached to the turbine by another clutch/coupling (506), during the discharge phase of the energy storage process, the compressor (501) can be deactivated (clutch 504 disengaged), and 5 bar charge air is directly supplied to the engine (engine cylinder 503). At the same time the generator (507) is activated (clutch 506 engaged) and electric power is supplied to the grid. As a result, with the same amount of fuel consumption, net output increases to 18.9+7.5=26.4 MW and the engine efficiency becomes 26.4/18.9×48%=67%.

[0035] Alternatively, if the RICE is to be deployed exclusively in an energy storage mode, the turbocharger module can be modified by permanently removing the compressor and adding a generator (FIG. 6).

[0036] Power consumption of the intercooled compressor (301) during the charge phase of the process is calculated as 11 MW (including the power consumed by the fin-fan coolers for inter- and aftercoolers—not shown in FIG. 4). Engine heat consumption during the discharge phase is:

(1,180/3,600)kg/s×120,068 kJ/kg=39.4 MWth.

[0037] Arguably, the most useful measure of CAES performance is the “primary energy efficiency” (PEE), which is the ratio of generated energy to consumed energy, i.e.,

[00001]$\begin{array}{cc}\mathrm{PEE}=\frac{t_g.Math.{\stackrel{.}{W}}_E}{t_c.Math.{\stackrel{.}{W}}_C+t_g.Math.\stackrel{\_}{\eta }.Math.\stackrel{.}{Q_F}}& 1\end{array}$

where: [0038] {dot over (W)}.sub.E=RICE (in this case) net power output during discharge, MWe or kWe [0039] {dot over (W)}.sub.C=Total power consumption during charging, MWe or kWe [0040] {dot over (Q)}.sub.F=Total fuel consumption of the RICE, MWth or kWth [0041] t.sub.g=Time of generation, hours [0042] t.sub.c=Time of charging, hours [0043] η=Average power plant efficiency

[0044] This equation provides an electricity-to-electricity roundtrip efficiency that isolates the energy losses in the conversion of electricity to compressed air and back to electricity. The second term in the denominator of the PEE formula represents the electric energy that could have been generated with the same amount of fuel input with average power plant efficiency (45.5% for natural gas-fired, 32.7% coal-fired power plants in the U.S. in 2015 based on U.S. Energy Information Administration data). Assuming t.sub.g=t.sub.c and η=50%, the PEE of the present invention becomes:

[00002]$\mathrm{PEE}=\frac{26.4}{11+50\%.Math.39.4}=86\%.$

Thus, the present invention increases the base engine output by 7.5/18.9=40% in energy storage mode at the same fuel consumption as in base operation mode; improves the heat rate (efficiency) by the same factor; and enables (or, at the very least, contributes significantly to enabling) 100% H.sub.2 combustion for carbon-free power generation.

[0045] It should be noted that the present invention can also be applied to operation with natural gas or a mixture of H.sub.2 and methane (CH.sub.4), or a syngas (mainly, a mixture of H.sub.2 and CO). Exhaust gas recirculation is beneficial to reduction of NOx emissions with any gaseous fuel by the same mechanism, i.e., reduction of flame temperature by dilution with an inert gas component (e.g., H.sub.2O and/or CO.sub.2). However, unlike the case with combustion of 100% H.sub.2, exhaust gas will include CO.sub.2.

Description of the Preferred Embodiments

[0046] There are multiple embodiments of the present invention, including: CAES with RICE (simple or combined cycle) and EGR; CAES with gas turbine (simple or combined cycle) and EGR; LAES with RICE (simple or combined cycle) and EGR; and LAES with gas turbine (simple or combined cycle) and EGR.

[0047] The invention is described quantitatively using a preferred embodiment, i.e., CAES with RICE (simple cycle) and EGR (FIG. 4). It should be noted that simple cycle means that the exhaust gas of the internal combustion engine (RICE or gas turbine) is not used in a “bottoming cycle” for additional power generation. The bottoming cycle can be a steam Rankine cycle or an “organic” Rankine cycle (ORC), or any type of heat engine cycle where the heat content of the internal combustion engine exhaust gas can be utilized as cycle heat input.

[0048] A further embodiment of the present invention, CAES with gas turbine and EGR, is shown in FIG. 7. The charge process is the same. During the discharge phase of the process, compressed air stream (12) is sent through a pressure control valve (304); the cold stored air (13) is then sent to a recuperating heat exchanger (305) and heated to a suitably high temperature by cooling the recirculated portion of the gas turbine (510) exhaust gas stream (23). It should be noted that the actual numbers are subject to determination and optimization, particularly by the gas turbine OEM, for actual field deployment. Compressed air stream (14) is expanded through the expander section (601) of the compander (610), which drives the booster fan (603) of the same. The compander (610) is designed to generate excess power to be used in a generator. Recirculated and pressurized exhaust gas stream (25) mixes with the expanded air stream (26) and cooled in the trim cooler (307) to a temperature suitable for mixing with atmospheric air to form stream (27) and admission into the compressor inlet of the gas turbine (510).

[0049] Another possible admission point for the mixed stream is at the compressor discharge of the gas turbine (510). In that case, stream (27) mixes with the compressed air from the gas turbine compressor discharge and enters the combustor. In order to minimize the temperature discrepancy, recirculated gas and air mixture is heated in the heat exchanger (305) utilizing GT exhaust gas (a portion of it) or working fluid (e.g., steam or water) from the bottoming cycle (700, in the case of a combined cycle configuration). In this case, however, the compander (610) includes the component (603), which is a compressor (i.e., higher pressure ratio and power consumption) instead of a booster “fan.” This is the case because the pressure at the admission point is higher (e.g., 20 bara or more for modern advanced class heavy duty industrial gas turbines) than atmospheric (i.e., 1 bara). In that instance, the likelihood of excess power generation from the compander is unlikely (but not impossible). The particular configuration and performance is subject to optimization during the detailed design phase.

[0050] In a further embodiment of the present invention, LAES with gas turbine (in combined cycle) and EGR is shown in FIG. 9. In the charge process, air (10) is drawn from the atmosphere and cleaned of dust and other non-gaseous pollutants in an inlet filter (260). Clean air is first compressed to a high pressure in an intercooled compressor (261). Compressed air is cooled to a cryogenic temperature and liquefied in a liquefier (262). This liquid air is kept stored in thermally insulated tanks (263) at low pressure. During discharge, liquid air is compressed in a cryogenic pump (264) and then heated in one or more heat exchangers (265) utilizing stored heat within the LAES facility (250) or merely ambient air.

[0051] Cryogenically stored air stream (13) from the LAES (250) is heated in the heat exchanger (305) utilizing the exhaust gas (21) from the gas turbine (510). Heated air stream (14) is expanded through the expander section (601) of the compander (610), which drives the booster fan (603) of the same. The compander (610) is designed to generate excess power to be used in a generator. After heating the stored air, gas turbine exhaust gas stream is divided into two branches. Stream (24) goes through the compander (610) and constitutes the circulated portion of the exhaust gas stream (21). Stream (22) goes into the bottoming cycle (700), where it heats the working fluid (steam, hydrocarbon, or another fluid) for additional power generation. The particular configuration is subject to optimization during the detailed design phase.

[0052] From the three embodiments shown in FIGS. 4, 7 and 9, it would be apparent to one of ordinary skill in the art how the remaining five embodiments can be constructed by mixing and matching the CAES, LAES, RICE, and GT components.