Patent Application
20190063685
Not Applicable
Not Applicable
The present invention relates to the field of energy storage technologies, and more specifically to the methods enabling an improvement in the technologies intended for large-scale conversion and storage of liquefied natural gas (LNG) fuel and electrical energy. It further relates to the methods making possible to profitably integrate the Liquefied Natural Gas Storage and Re-gasification (LNGSR) and Liquid Air Energy Storage (LAES) technologies, as the first step to creation of a highly efficient Liquid Air and Gas Energy Storage (LAGES) technique. Such method may be preferably used in design of the Floating LNGSR units integrated with the barge-mounted Power Generation units, which are intended for highly efficient operation both in the base-load and load-following modes.
A planned and started transfer to the decarbonized power grids is based first of all on increased use of the fossil fuels with reduced carbon content, such as natural gas in gaseous and liquefied states. In the latter case an implication of the LNGSR terminals is constantly growing. As described in “Handbook of Liquefied Natural Gas” (by Saeid Makhatab, et al., Elsevier, Oxford, 2014), they perform the unloading and storage of the imported liquefied natural gas (LNG) and its on-demand pumping, regasification and injection into transmission pipeline. According to report of the LNG-Worldwide Ltd. “Current Outlook for Global LNG to 2020 and European LNG Prospects” (September 2014), in 2013 the 104 existing LNGSR terminals in 29 countries have imported 237 MTPA of LNG fuel, providing at the time approximately 10% of the global gas consumption. Thereby, a volume of imported LNG is expected to grow by 2025 up to 500 MTPA.
Recently the floating storage and regasification units (FSRU) have been introduced in the LNG market. Moreover, the concepts of FSRU integrated with barge-mounted power plants (BMPP) are intensively now developed by the Wison, BWSC, TGE-Marine Gas Engineering, Samsung and Hyundai Heavy Industries and other companies. These near-shore Floating Storage, Regasification and Power production Units (FSRPU) may be the flexible and economic alternative to building the land-based LNG regasification terminals and stationary power plants, since they can avoid the long lead time and high cost of building the land-based facilities and offer quick deployment to a range of potential locations. Being connected to the local land-based electrical and gas networks they may provide the seasonal or intermittent deliveries to smaller and remoted gas and power customers with the significantly reduced CAPEX and OPEX indexes.
The developers of a FSRPU concept claim the benefit of recovering a high-grade waste heat from the power generators installed at the BMPP for regasification of LNG instead of using the air, sea water or intermediate carrier-based LNG evaporators for this purpose. However such technical solution does not make possible to use the mentioned waste heat for increase in fuel efficiency of power generation processes and does not obviate a need for use of the said LNG evaporators during operation of the power generators at low loads. In addition, dissipation of cold thermal energy of the LNG being regasified eliminates a possibility of its profitable use in the integrated energy conversion processes, contrary to proposed, for example, operation of the land-based LNGSR terminal in conjunction with the co-located Liquid Air Energy Storage (LAES) system (see the U.S. patent application Ser. No. 16/109,884). Here a cold thermal energy of LNG converted into cold thermal energy of liquid air is profitably used for reliquefying up to 35% of send-out natural gas during LAES facility discharge. What is more, availability of liquid air as an intermediate product of the LAEStechnology makes possible to gain the other benefits from its harnessing: provision of zero-carbon emitting exhaust of LAES facility through a cryogenic capture of CO2 component (as described in the published U.S. Patent Application No. US 20180221807) or an increase in power output and efficiency of the LAESfacility equipped with the semi-closed CO2 bottoming cycle (as described in the provisional U.S. Patent Application No. 62/554,053).
By this means there is a need for improvement in design of the FSRPU. A basis for such improvement could be an integration between the FSRPU and LAES into floating Liquid Air and Gas Energy Storage (LAGES) and elaboration of such method for its operation which would provide: a) full obviation of the need for usage of the air, sea water or intermediate carrier-based LNG evaporators; b) an effective recovery of high-grade waste heat from power generators for increase in its output and fuel efficiency; c) a further improvement in performance of the LAESsystem through reducing the energy intensity of air liquefaction; and d) widening the applicability of the LAGES system through an efficient its operation both in the load-following regime with energy storage capability and in base-load mode.
In one or more embodiments, a proposed method for liquid air and gas energy storage (LAGES) may comprise in combination: pumping the LNG stream from the storage tanks into a co-located Liquid Air Energy Storage (LAES) system for continuous regasifying the LNG in the said system including its preheating, evaporation and superheating with injection of send-out gas into gas networks; continuous producing a liquid air with consuming a required power by the compressors of air liquefier of the LAESsystem and interchanging a waste thermal energy between the LNG being regasified and the process air being produced; storing a liquid air only in the periods of low demand for energy in the grid; on-demand producing the on-peak and mid-peak power by at least one power train comprising a fueled and supercharged reciprocating engine-based generator with upstream installed high-pressure air expander and down-stream installed low-pressure exhaust gas expander through consuming both a stored and directly produced liquid air at a rate exceeding a rate of its continuous production; and recovering a cold thermal energy released by regasified liquid air for performing the operation of the LAESsystem in one of the modes selected from the group comprising: reliquefaction of a part of send-out natural gas, cryogenic capture of CO2 component from exhaust of power train and integration of power train with a semi-closed CO2 bottoming cycle.
In so doing the improvements in method may further comprise in combination: driving the compressors of air liquefier during off-peak hours by at least one reciprocating engine-based generator of the power train through consumption of the fuel and air delivered from atmosphere by a standard turbocharger and required for combustion of said fuel in the said engine; driving the compressors of air liquefier during on-peak and mid-peak hours by at least one said reciprocating engine-based generator of the power train through consumption of a fuel and regasified liquid air produced at that instant by air liquefier and required for combustion of said fuel in the said engine; producing the on-demand power by at least one said power train with its delivery into electrical grid during on-peak and mid-peak hours through consumption of a fuel and liquid air stored and produced at that instant by air liquefier; recovering a part of cold thermal energy inherent in the produced pressurized liquid air in the process of its liquefaction in the air liquefier; and recovering a cold thermal energy of LNG being regasified for cooling a process air at the inlet of compressor stages of air liquefier down to (−60° C.)-(−80° C.) using a closed cooling loop with an intermediate heat carrier between the air and LNG.
For production of liquid air the proposed method may further combine the following processes in air liquefaction (AL) train: pressurizing a feed air stream in the first stage of feed air compressor with its following cooling in the first feed air cooler, drying and freeing from the atmospheric CO2 contaminants and an additional cooling in the second feed air cooler; following pressurizing a feed air stream in the second stage of feed air compressor up to a bottom charge cycle pressure with its following cooling in the third feed air cooler; forming a process air stream as a mixture of the said pressurized and cooled feed air stream and a stream of boil-off air recirculating from the air separator at a bottom charge cycle pressure; following pressurizing the process air stream up to top charge cycle pressure in two-stage process air compressor with its intercooling in the first process air cooler and aftercooling in the second process air cooler; further reducing in temperature of process air in the second air-to-LNG heat exchanger with following its liquefying through a said recovery of a part of cold thermal energy inherent in the produced pressurized liquid air; subsequent reducing a temperature of the liquefied process air in the first air-to-LNG heat exchanger; final cooling the liquefied process air by the recirculating stream of boil-off air escaping the air separator; depressurizing the liquefied process air in the liquid air expander, resulting in formation of deeply cooled two-phase process air escaping the said expander at a bottom charge cycle temperature and a bottom charge cycle pressure; separating the liquid and gaseous phases of process air with a said recirculation of boil-off air stream; pressurizing a liquid air stream escaping a separator up to a low pressure required for its following storage or direct use in the power train; recovering a part of cold thermal energy of low pressure liquid air for the said liquefying a process air; and delivering a low pressure liquid air into a storage or its direct use in the power train for production of on-demand power over the mid-peak and on-peak hours.
In so doing, recovering the cold thermal energy of regasified LNG for cooling a process air at the inlet of compressor stages of air liquefier may be performed through: collection of compression heat by the streams of intermediate heat carrier circulating through a set of the mentioned air coolers installed in parallel at the outlet of heat carrier pump; pooling all said steams at the outlet of coolers; additional heating of a pooled stream of intermediate heat carrier in the main cooler of at least one reciprocating engine with use a low-grade waste heat of said engine; and using a collected heat for regasification and superheating of the LNG stream escaping the second air-to-LNG heat exchanger.
Finally, the proposed method may be applied to storage an excessive energy from the grid through its using for driving the compressors of air liquefier during off-peak hours and said additional heating of a pooled stream of intermediate heat carrier at that instant with an accumulated waste heat of cooling system of at least one reciprocating engine operated during mid and on-peak hours.
Embodiments will hereinafter be described in detail below with reference to the accompanying drawings, wherein lie reference numerals represent like elements. The accompanying drawings have not necessarily been drawn to scale. Where applicable, some features may not be illustrated to assist in the description of underlying features.
The practical realization of the proposed method for liquid air and gas energy storage (LAGES) may be performed through the integration between the LNGSR terminal and LAES system into combined LAGES facility. At such facility the interchanging of a waste thermal energy between the LNG being regasified and the process air being liquefied and regasified provide a drastic increase in performance of the LAES system and a marked decrease in the LAGES capital costs. The invented method may be especially promising for design of the Floating LNGSR units integrated with the barge-mounted Power Generation units, making such integrated facility capable to highly efficient operate both in the base-load and load-following modes.
The
The LNG stream is continuously delivered from the storage 6 by the LP and HP pumps 7 and 8 into air liquefier of the LAGES facility, wherein it is initially heated in the first air-to-LNG heat exchanger 9 by a stream of highly pressurized liquefied process air and thereafter in the second air-to-LNG heat exchanger 10 by a stream of highly pressurized process air. The further evaporation and final reheating of LNG is going in the LNG regasifier 11 at the expense of heat transfer with an intermediate heat carrier. The regasified LNG is injected into pipeline 12 of gas network.
The atmospheric feed air 13 is pressurized in the first stage 14 of feed air compressor, cooled in the first feed air cooler 15, dried and freed from atmospheric CO2 contaminants in the adsorber 16, additionally cooled in the second feed air cooler 17, pressurized in the second compressor stage 18 up to a bottom charge cycle pressure and aftercooled in the third feed air cooler 19.
At the inlet of process air compressor 20 the pressurized and aftercooled feed air is mixed with the boil-off air 21 recirculating from the air separator at the same bottom charge cycle pressure. The process air, as a mixture of feed and boil-off air streams, is pressurized in the first stage 20 of process air compressor, intercooled in the first process air cooler 21, further pressurized in the second compressor stage 22 up to a top charge cycle pressure and aftercooled in the second process air cooler 23.
Further deep cooling a highly pressurized process air is performed in the said second air-to-LNG heat exchanger 10 by the LNG stream, after which the air is liquefied in the process air liquefier 24 through its cooling by a stream of liquid air escaping the air separator. A temperature of the pressurized liquefied process air is additionally reduced in two heat exchangers installed in tandem: in the said first air-to-LNG heat exchanger 9 by the LNG stream and in the air-to-air heat exchanger 25 by the recirculating stream of boil-off air escaping the air separator. The following depressurizing the liquefied process air in the liquid air expander 26 leads to formation of deeply cooled two-phase process air escaping the said expander at a bottom charge cycle temperature and a bottom charge cycle pressure.
The liquid and boil-off phases of process air are separated in the separator 27 with a said recirculation of boil-off air stream through heat exchanger 25 into inlet of process air compressor 20. In its turn, a pressure of liquid air stream escaping a separator is increased by a pump 28 up to a low value required for its following storage or direct use in the power block, after which this stream is directed to air liquefier 24, wherein a part of its cold thermal energy is used for the said liquefying a process air. The LP liquid air escaping the liquefier 24 is directed through a control valve 29 into a liquid air storage 30 during off-peak hours or to the power block for production of on-demand power over the mid-peak and on-peak hours.
Collection of compression heat and its recovery for LNG regasification is performed with use of intermediate heat carrier circulating in the closed loop and directed by the pump 31 through a set of said air coolers 15, 17, 19, 21 and 23 placed in parallel at the outlet of said pump. To reach a temperature required for injection of regasified LNG into NG network, a pooled stream of the intermediate heat carrier streams escaped the said air coolers is additionally heated in the heat exchanger 32 by a low-grade waste heat extracted from the cooling system of the gas engine 1 being used for driving the compressors of air liquefier. In the said LNG regasifier 11 the collected compression heat of air liquefier and low-grade heat of gas engine cooling system are transferred from an intermediate heat carrier to the LNG, resulting in its regasification and superheating.
The described above mode of air liquefier operation is applied to storage of excessive power produced by the BMPP facility integrated with SRGU. However the invented method may be also adapted to storage of excessive energy in the grid. For this purposes, an excessive power from the grid is consumed during off-peak hours for driving the compressors of air liquefier, whereas a gas engine 1 is taken out of service for this time-period and is put into operation during mid and on-peak hours. A low-grade waste heat of its cooling system is accumulated in this time interval and used in the heat exchanger 32 for an additional heating of the intermediate heat carrier during off-peak hours.
The improvements in operation of the power block of the LAGES facility are not subject of the present invention. Because of this its schematic view in the
In the
The performances of liquid air and gas energy storage (LAGES) facility using the proposed method of operation are tabulated below for the case of a possible send-out capacity of FSRU at a level of ˜0.5 MTPA. At such LAGES facility production of a liquid air in the LAESsystem is performed during 24 h per day and on condition that relationship between the flow-rates of LNG (pure methane) and liquid air streams is equal to 1.1:1. The production of power in the LAESsystem may be also performed both in the base-load operation mode during 24 h/d and in the load-following regime. In the las case the durations of off-peak and on-peak hours have been selected identical, but may be varied from 0 to 12 hours per day with operation during rest of daily hours in mid-peak regime. At the duration equal to 0 h/d, the LAGES facility is operated in base-load mode. For each operation mode a sought value of facility fuel-to-power conversion efficiency is determined.
In calculation performed the top charge cycle pressure of process air stream and the top discharge cycle pressure of pumped liquid air stream are set at a level of 67 barA and 140 barA correspondingly. The power block of the LAESsystem comprises a set of two power trains with reciprocating gas engines and expanders. The first engine operated continuously is equipped with the standard turbocharger being used only during off-peak hours at ˜65% of engine nominal output. The second engine is operated only during on-peak hours. A charging of the reciprocating engines with combustion air is performed at a pressure of ˜4 barA, whereas the discharging of exhaust gases is performed at a pressure of ˜3.5 barA and a temperature of ˜570° C. The mentioned temperature of engine exhaust gases and an amount of fuel combusted in the duct burner of the power train provide the maximum admissible temperatures of ˜540° C. and 760° C. for regasified air at the inlets of the modified steam turbine being used as HP expander and power turbine being used as LP expander. The general data of equipment installed in the Air Liquefier (AL) train and Power Production (PP) train are listed in Table 1.
For regasification of discharged liquid air with recovery of its cold thermal energy a system providing integration of the power trains with the semi-closed CO2 bottoming cycle has been selected, because such system makes possible to reach a highest level of fuel efficiency of the LAGES facility. As an intermediate heat carrier in the air liquefier the propane has been selected. The main results of performed calculations are presented in the Tables 2.-4 They have clearly demonstrated a very high daily fuel efficiency of the LAGES facility which is equal to 59.7% during facility operation in base-load regime and 57.3-58.8% during its operation in load-following regime with storage of excessive power produced by facility.
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. For example, the invented method may be applied to design and operation of the near-shore Floating Storage, Regasification and Power Units (FSRPU) connected with the national electric and natural gas networks and intended for storage of excessive grid power.
This application claims the benefits of U.S. Provisional Patent Application No. 62/550,704 titled “Method for Liquid Air and Gas Energy Storage” and filed on Aug. 28 2017.
| Number | Date | Country | |
|---|---|---|---|
| 62550707 | Aug 2017 | US |
