Patent Application
20180073802
Not Applicable
Not Applicable
The present invention relates to the field of energy conversion technique, and more specifically to the methods enabling an improvement in the technologies intended for conversion and storage of excessive energy and natural gas at the pressure reducing (city gate) stations. More particularly, the present invention relates to the methods making possible to profitably combine the operation of the small scale liquid air energy storage with co-production of liquefied natural gas (LNG) directly at the storage facility and at the co-located city gate station.
In modern times the electrical energy storages are becoming an integral part of the distribution grids, ensuring the on-demand and reliable supply of electricity by the intermittent renewable energy sources and providing a stable and efficient operation of the base-load fossil-fuel fired and nuclear power plants around the clock.
Amongst the known methods for energy storage able to accumulate a lot of energy and store it over a long time-period, the recently proposed methods for Liquid Air Energy Storage (LAES) (see e.c. Patent. FR 2,489,411) are distinguished by a much simpler permitting process and the freedom from any geographical, land and environmental constraints, inherent in other known methods for large-scale energy storage technologies, lice Pumped Hydro Electric Storage (PHES) and Compressed Air Energy Storage (CAES). In the LAES systems liquid air is produced using excessive power from the grid, stored in the small volume tanks between the off-peak and on-peak hours and re-gasified and used as effective working medium for producing a peaking power in the periods of high power demand. However, producing a liquid air during off-peak hours is an energy intensive process and many technical solutions have been proposed for reducing the energy consumption and losses in this process with an increase in the LAES round-trip efficiency.
One of the possible ways for improvement in performance of the LAES facility could be its integration with the natural gas (NG) pressure reducing (city gate) station and recovery an available exergy of the high-pressure (HP) gas being presently wasted in the throttling valves. At the same time, the known proposals on utilization of available HP NG potential can't be used for achievement of the invention goals for the following reasons. Some of these proposals make possible to replace the throttling valves by the turbo-expanders converting a kinetic energy of the motive gas stream into a “green” power. Therewith a thermal energy at a rate of ˜3.5 kWth per each kW of additional mechanical power produced should be consumed to provide the identical temperatures of the high-pressure and low-pressure gas streams, resulting in a low efficiency of thermal energy-to-power conversion efficiency. In addition, recovery of wasted kinetic energy is desirable to perform on the 24/7 basis, whereas the actual need for this power is arising only during on-peak hours. Therefore, during off-peak hours it would be expedient to recover the energy of gas expansion at the CG station for desirable improvement in the performance of integrated LAES facility and to find the more effective ways for use of the mentioned thermal energy.
The other known proposals are devoted to using a high-pressure gas potential for liquefaction of a part of delivered gas at the CG stations (Tianbiao He and Y. L. Ju “A novel process for small-scale pipeline natural gas liquefaction”, Applied Energy, No. 115, pp. 17-24, Febeuary 2014). This makes possible to store and on-demand use the LNG produced, flattening the fluctuations in NG supply caused by daily and seasonal variations in flow and pressure of natural gas at the CG station inlet and outlet. Alternatively the LNG may be distributed as a transport fuel at the adjacent filling stations. In these proposals the whole of the available energy of high-pressure gas stream recovered in the turbo-expanders is spent for increase in the LNG production rate rather than delivering a produced power into the grid. In addition, a proposed LNG production at the CG station is characterized by a very low gas liquefaction ratio. Because of this, the integration between the CG station and LAES facility could make possible to use a high cold thermal energy potential of re-gasified liquid air for increase in common LNG production at the station and facility on the one hand and to provide a peaking power production capability of the CG station on the other hand.
As a whole, the method for energy storage with co-production of peaking power and liquefied natural gas is selected as a subject for an innovative improvement in the present invention. Thereby, the integration between the liquid air energy storage and CG station with exchange and recovery of the waste energy streams of the integrated facilities are found to be the effective means for achievement of the invention's goals.
In one or more embodiments, a proposed method for energy storage with co-production of peaking power and liquefied natural may comprise in combination: a) charging the energy storage facility with liquid air produced through consumption of an excessive power from the grid and/or any co-located energy source; b) discharging the energy storage facility through expanding the re-gasified air with on-demand producing and delivering a peaking power to the grid; and c) reducing a pressure of natural gas at the co-located city gate station from a high inlet value down to a low outlet one with co-producing the LNG from a part of supplied gas through usage of auto-refrigeration of expanded gas stream.
The invented method may differ from the known those in that: a) depressurizing a gas at the said city gate station may be performed with producing a power which may be used for at least partial meeting the demands for power during charging the energy storage facility and may be delivered into grid during discharging the energy storage facility; b) co-producing the LNG at the said city gate station during charging the energy storage facility may be supplemented by simultaneous re-gasifying the whole of LNG produced and using a released cold thermal energy for reducing the facility demands for a power consumed; and) c) producing a peak power during discharging the energy storage facility may be supplemented by a simultaneous using a cold thermal energy of the re-gasified air stream for co-producing the LNG directly at the facility from a part of gas delivered to the city gate station.
In one or more embodiments, charging the energy storage facility with liquid air may include the steps of: a) externally powered compressing the fresh air stream up to a bottom charge pressure with its further freeing from the CO2 and H2O contaminants; b) mixing the streams of treated fresh and recirculating air streams at a bottom charge pressure thus forming a process air stream; c) succeeding externally powered compressing the process air up to a rated charge pressure; d) final self-powered compressing the whole air stream air by at least one booster compressor driven by a cold turbo-expander of open air auto-refrigeration cycle; and e) further processing the process air between the top and bottom charge pressures in the said air auto-refrigeration cycle, resulting in generating a liquefied air from a part of process air at a bottom charge pressure and recirculating a rest of it for mixing with a fresh air; and may further be characterized by: a) providing at least a part of external power required for compressing the fresh and process air at the sacrifice of power produced at the co-located city gate station in the process of gas depressurization; and b) providing a deep cooling of the recirculating air stream before its mixing with a fresh air at the sacrifice of cold thermal energy released in the process of LNG re-gasification.
In one or more embodiments, discharging the energy storage facility with a peaking power production may further include the steps of: a) pumping the liquid air at a top discharge pressure; b) re-gasifying the pumped air with capturing its cold thermal energy; and c) expanding a re-gasified air down to bottom discharge pressure in at least one-stage expander with on-demand producing the bulk of peaking power; and may further be characterized by: a) providing a co-production of the LNG directly at the energy storage facility in addition to the bulk of LNG production at the city gate station at the sacrifice of harnessing a captured cold thermal energy in the process of liquefying the whole of natural gas delivered from the said station; and b) providing a thermal assistance to the air expanding process through an increase in air temperature upstream of each expansion stage at the sacrifice of thermal energy derived from any available source of such energy and selected from the group comprising but not limited to ambient air, industrial waste heat streams, and combusting a part of depressurized natural gas escaping city gate station.
In one or more embodiments, reducing a pressure of natural gas from a high inlet value down to a low outlet one at the co-located city gate station during charging the energy storage facility may further include the steps of: a) pre-cooling the whole of delivered high-pressure gas with a stream of low-pressure gas escaping the said station; b) dividing a pre-cooled high-pressure gas into two streams, first of which is further used for liquefaction of the second one in the open auto-refrigeration cycle; c) succeeding deep cooling and liquefying the second gas stream with a stream of low-pressure gas escaping the city gate station; d) expanding the second liquefied gas stream down to a said low gas pressure accompanied by final cooling the expanded two-phase stream down to the bottom cycle temperature; and e) separating the liquid and vapor phases of the second gas stream, resulting in forming the liquefied part and vapor part of a said stream at a said low gas pressure; and may further be characterized by: a) pumping a liquefied part of the second gas stream up to a said high pressure at which gas is delivered into city gate station; b) exchanging thermal energy between a recirculating air stream from the energy storage facility and a pumped liquefied part of the second gas stream from the city gate station, resulting in said deep cooling a recirculating air stream before its mixing with a stream of treated fresh air and in re-gasifying a pumped part of the second gas stream; c) mixing the first gas stream and a re-gasified part of the second gas stream at a said high gas pressure; d) expanding the mixed gas stream down to a said low gas pressure accompanied by producing a power and deep cooling the said mixed gas stream down to the bottom cycle temperature; e) using a power produced by the expanded mixed gas stream at the city gate station as at least a part of external power required for compressing the fresh and process air at the energy storage facility; f) blending the expanded mixed gas stream with a vapor part of the second gas stream so forming a stream of low-pressure gas escaping the city gate station; and g) using a cold thermal energy of low-pressure gas stream escaping the city gate station for the said deep cooling and liquefying the second gas stream and pre-cooling the whole of delivered high-pressure gas.
In one or more embodiments, reducing a pressure of natural gas from a high inlet value down to a low outlet one at the co-located city gate station during discharging the energy storage facility may further include the steps of a) pre-cooling the whole of delivered high-pressure gas with a stream of low-pressure gas escaping the said station; b) dividing a pre-cooled high-pressure gas into two streams, first of which is further used for liquefaction of the second one in the open auto-refrigeration cycle; c) succeeding deep cooling and liquefying the second gas stream with a stream of low-pressure gas escaping the city gate station; d) expanding the second liquefied gas stream down to a said low gas pressure accompanied by final cooling the expanded two-phase stream down to the bottom cycle temperature; e) separating the liquid and vapor phases of the second gas stream, resulting in forming the liquefied part and vapor part of a said stream at a said low gas pressure; and f) using a liquefied part of the second gas stream as the bulk of LNG produced and stored at a pressure identical to a low pressure of gas escaping the city gate station; and may further be characterized by: a) expanding the first gas stream down to a said low gas pressure accompanied by producing a power and deep cooling the said first gas stream down to the bottom cycle temperature; b) using a power produced by the expanded first gas stream at the city gate station as addition to a peaking power on-demand delivered to the grid by the energy storage facility; c) blending the expanded first gas stream with a vapor part of the second gas stream so forming a stream of low-pressure gas escaping the city gate station; and d) using a cold thermal energy of low-pressure gas stream escaping the city gate station for the said deep cooling and liquefying the second gas stream and pre-cooling the whole of delivered high-pressure gas.
In one or more embodiments, a temperature of low-pressure gas escaping the city gate station during charging the energy storage facility may be increased up to at least permissible minimum through a heat exchange between a stream of process air escaping the externally powered compressor train and a stream of low-pressure gas escaping the city gate station.
In one or more embodiments, producing the LNG at the city gate station during discharging the energy storage facility at a pressure level below a said low pressure of gas escaping the station may include the additional steps of: a) reducing a pressure of liquefied part of the second gas stream down to a required level accompanied by formation of a two-phase stream; b) separating a liquid phase from the two-phase stream with its storing and on-demand delivering as a salable LNG product at a required pressure; c) compressing a vapor phase of the two-phase stream up to a low gas pressure at the city gate outlet or up to a high gas pressure at the station inlet; and d) mixing the compressed vapor stream with a low-pressure gas escaping the station or with a high-pressure gas delivered to the station.
In one or more embodiments, a high-pressure gas at the inlet of city gate station may be on-demand dried and ridded of the water vapor and carbon dioxide contaminants upstream of the pre-cooling step.
Finally, in one or more embodiments a natural gas delivered into city gate station may be on-demand subjected to freeing from the contaminants including the steps of: a) drying the whole of high-pressure gas upstream of the pre-cooling step; b) removing the liquefied and/or solidified CO2 contaminants from the first gas stream downstream of the expanding step; and c) removing the CO2 contaminants from the second gas stream upstream of the deep cooling and liquefying step.
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 energy storage with co-production of breaking power and liquefied natural gas (LNG) may be performed through the operational interaction between the integrated LAES facility and CG station both during storage charge and discharge.
100—compressor train of the LAES facility
200—turbo-expander-booster compressor train of the LAES facility
300—liquefaction, separation and storage equipment of the LAES facility
400—equipment package of the CG station.
According to the present invention, compressor train is designed as two-stage turbomachinery, wherein the first compression stage 102 and second compression stage 106 are driven by the common electric motor 103. A fresh air from atmosphere is delivered through a pipe 101 into the first compression stage 102 and pressurized up to a bottom charge pressure. Train is equipped with intercooler 104 and inter-cleaner (adsorber) 105 for capture of moisture and carbon dioxide from a pressurized fresh air. A removal of compression heat in the intercooler 104 may be performed by an ambient air or water. At the outlet of adsorber (point 107) the cooled and cleaned fresh air is mixed with a recirculating air stream 315 delivered under a bottom charge pressure from a package 300 through a package 400, so forming a process air stream 108, which is further compressed in the second compression stage 106 up to a rated pressure level. During deep cooling a recirculating air stream 315 in the heat exchanger 406 its temperature drops below −100° C., resulting in corresponding drastic decrease in temperature of the mixed air stream 108 upstream of compressor 106 and in power consumed by this compressor. The said deep cooling of recirculating air is performed with a stream of the LNG produced at the city gate station, as described below. Removal of compression heat from a process air escaping the compressor 106 with cooling the air down to −5° C.-−15° C. is performed in the heat exchanger 109 by a stream of low pressure gas escaping the city gate station, as also described below.
Further compressing the entire process air stream up to a top charge pressure is performed in the booster compressor 201 driven by the cold turbo-expander 202 with cooling the air after said compressor in the heat exchanger 203. At given ratio between the top and bottom charge pressures, the mentioned marked cooling the process air at the inlet of booster compressor 201 makes possible to increase a pressure ratio in this compressor without increase in power consumed by it. In its turn, this provides a corresponding decrease in a pressure ratio in the compressor 106, resulting in a further reducing a power consumed by it.
At the said top charge pressure the process air stream is delivered into a deep cooler 301, wherein its temperature decreased substantially below 0° C. with a recirculating air stream. Further air is directed to the point 302, wherein it is divided into two streams 303 and 305. The extracted part of process air (stream 303) is expanding down to a bottom charge pressure in the said cold turbo-expander 202 with an accompanied deep cooling of expanded air stream 304. The rest of process air (stream 305) is additionally cooled and fully liquefied with a recirculating air in the air liquefier 306. The liquefied rest of process air is further directed into a generator-loaded turbine 307, wherein it is expanded down to a bottom charge pressure with an accompanied final cooling of expanded air down to bottom charge temperature. A bottom charge pressure is selected at a level exceeding atmospheric pressure by 1-7 bar. An air separator 308 installed at the outlet of expander 307 is used to separate the liquid and vapor phases of the finally expanded and cooled rest of process air. The liquid air stream 309 is directed to the pressurized liquid air vessels 310, wherein it is stored at The bottom charge pressure and temperature between the energy storage charge and discharge. The air vapor stream 311 is directed to the point 312, wherein its mixing with an expanded and cooled part 304 of process air is performed. This results in formation of a recirculating air stream 313 at a bottom charge pressure. The said recirculating air stream is further used for the final cooling and liquefying the rest 305 of process air in the air liquefier 306, causing the accompanied heating the outgoing stream 314 of recirculating air. This air stream is further used for said cooling the process air in the deep cooler 301, causing the accompanied further heating the outgoing stream 315 of recirculating air. As mentioned above, the recirculating air stream 315 escaping the package 300 is deeply cooled in the heat exchanger 417 before its mixing with a fresh air stream at the point 107.
Operation of the integrated CG station during energy storage charge is run as follows. The stream of natural gas at a rated high-pressure (HP) is delivered from the main pipeline through a pipe 401 into adsorber 402, wherein it is cleaned of the water vapor and carbon dioxide contaminants. The cleaned gas is subjected to pre-cooling in the heat exchanger 403 with a stream of natural gas escaping the city gate station and directed further to the cold turbo-expander 404 shaft-connected with the generator 405. Power produced by the cold-turbo-expander through recovery of the wasted gas pressure drop comprises from 50 to 100% of energy required for driving the compressor train, depending on the pressure ratio in the expander 404. In so doing, the electric motor 103 of compressor train takes its current from the generator 405 only or from the electric grid and generator 405 at one time. The expanding of gas down to a rated low pressure is accompanied by its deep cooling down to a bottom cycle temperature, at which gas is delivering to the said heat exchanger 406, wherein its cold thermal energy is used for a deep cooling of the recirculating air stream 315, as described above. The low-pressure gas escaping the heat exchanger 406 possesses a yet sufficient cold thermal energy to pre-cool the incoming stream of high-pressure gas in heat exchanger 403 and intercool the process air in the heat exchanger 109 between the second stage 106 of compressor train and the booster compressor 201. Resulting from a heat exchange in the said equipment, the stream of low-pressure gas 407 is delivered into a low-pressure main pipeline at a temperature equal to or exceeding a minimum allowable value.
300—liquefaction, separation and storage equipment of the LAES facility
400—equipment package of the CG station
500—LNG production package of the LAES facility
600—expander train of the LAES facility.
Operation of the LAES facility in discharge operation mode is performed as follows. A stream 315 of liquid process air is extracted at a bottom dicharge pressure from the storage 310 and pumped by a pump 316 up to top discharge pressure selected in the range between 10 and 200 bar. The discharged air stream 317 is delivered into a package 500 which is destined for liquefaction of a stream of high-pressure natural gas 423 supplied from a CG station package 400. The feed gas destined for liquefaction at the LAES facility is dryed and purified at the said CG station and is pressure is consistent with a high pressure of gas into CG station from the main HP pipeline. At the LNG production pressure selected in the range between 2 and 12 barA a flow-rate of the LNG produced at the LAES facility may reach 15-55% of a flow-rate of discharged air flow-rate. As this takes place, a LNG production yield may be somewhat increased through a decrease in selected top discharged air pressure at a given high pressure of supplied natural gas. For realization of this approach the appropriate adjustment of the liquid air pump 316 and selection of a proper expander train 600 configuration are required.
To provide the LNG production directly at the LAES facility a pumped discharged air stream 317 is delivered into a gas liquefier—air regasifier 501. Exchange of thermal energy between the discharged liquid air and supplied natural gas in this heat exchanger results in liquefaction of entire gas stream 423 and regasification of entire discharged air stream 317. The latter is directed from the regasifier 501 to the air expander train 600, wherein it first preheated in the recuperator 601, and thereafter superheated in the heat exchanger 602 at a sacrifice of heat exchange with a stream 608 of thermal (preferably wasted) energy. The following expanding the superheated air stream is performed in the at least one-stage expander train 600 whose configuration is selected with regard to a top discharged air pressure provided by a pump 316. At a said pressure exceeding 40-45 barA a two-stage expander train configuration with reheating a discharged air between the stages may be used.
As shown in the
A liquefied natural gas is directed from the heat exchanger 501 to the generator-loaded liquid gas expander 502, wherein its depressurization down to a selected storage pressure with a final cooling are performed. This results in forming the LNG product which is stored in the pressurized storage tank 503 and on-demand delivered to the customers.
Operation of the integrated CG station during energy storage discharge is run as follows. The stream of natural gas at a rated high-pressure (HP) is delivered from the main pipeline through a pipe 401 into adsorber 402, wherein it is cleaned of the water vapor and carbon dioxide contaminants. At the adsorber outlet (point 408) a small part 424 of cleaned gas is extracted and directed to a package 500 for its full liquefaction directly at the LAES facility as described above, whereas the bulk of cleaned gas is subjected to pre-cooling in the heat exchanger 403 with a stream of natural gas escaping the city gate station. At the point 409 the gas stream is divided into parts. The first (greater) part is directed to the generator 405-loaded cold turbo-expander 404, wherein it is expanded down to a rated low pressure (LP) and deeply cooled. A power produced by the cold expander 404 depends on a pressure ratio in it and may be comparable to a power produced by the hot expander train of the LAES facility operated with reasonable superheating and reheating of discharged air stream.
The second (lesser) part of the HP gas is subjected to deep cooling and liquefying in the heat exchanger 410 with a following expansion in the liquid gas expander 411 down to a said rated low pressure. The two-phase gas stream escaping the expander 411 is separated into a liquid phase (properly LNG) and vapor phase in the separator 412. The latter is combined at the point 413 with a stream of gas escaping the expander 404, forming the combined gas stream 414 at a bottom cycle temperature and a rated low pressure. The combined LP gas stream sequentially passes through the liquefier 410 and pre-cooler 403, providing accordingly the liquefaction of the said second part of natural gas and pre-cooling the whole of the gas delivered into CG station. Resulting from a heat exchange in the said equipment, the stream of low-pressure gas 415 is delivered into a low-pressure main pipeline at a temperature equal to or exceeding a minimum allowable value.
A further processing of the LNG produced at the CG station is performed in accordance with a pressure of the LNG storage. If a pressure of pressurized LNG in the tank 503 is equal to a said rated low pressure of natural gas, the produced LNG is directly delivered from a separator 412 into a storage vessel 503 through the open valve 416 and pipe 417 with the closed valve 418. If a pressure of pressurized LNG in the tank 503 is below a said rated low pressure of natural gas, the produced LNG is directed from a separator 412 through the open valve 418 with the closed valve 416 to a Joule-Thomson valve 419, wherein its pressure reduced down to a pressure in the storage tank 503. A gas separator 420 installed at the outlet of JT valve 419 is used to separate the liquid and vapor phases of the partially depressurized gas stream. A greater (liquid) gas stream 417 is directed to the pressurized liquid gas vessel 503, whereas a minor (vapor) gas stream 421 is compressed up to a rated low gas pressure by the auxiliary compressor 422 and directed through a pipe 423 to the LP gas distribution grid. As a whole, amount of the LNG produced directly at the LAES facility makes up between 25% and 45% of the LNG production rate at the CG station.
The performance of small-scale energy storage with co-production of peaking power and liquefied natural gas (LNG) are presented below. The calculation of these performances has been performed as applied to integration between liquid air energy storage (LAES) facility and city gate (CG) station. The latter is exemplified by CG station designed for reducing a pressure of the ˜43,000 m3/h of natural gas (assumed as 100% of methane) from 75 barA down to 15 barA (Alt.1), from 65 barA down to 7 barA (Alt.2) and from 25 barA down to 5 barA (Alt. 3). During LAES charge the whole of obtained gas is delivered from the CG station into a low-pressure gas distribution pipeline, whereby mechanical energy of the expanded gas and its cold thermal energy are recovered at the LAES facility, reducing consumption of external power required for air liquefaction. During LAES discharge from 15 to 30% of obtained gas is liquefied at the CG station and LAES facility, resulting in their combined LNG capacity between 0.02 and 0.03 MTPA. The rest of obtained gas is delivered to the customers at the reduced pressure. Simultaneously mechanical energy of the gas expanded at the CG station and re-gasified air expanded at the LAES facility is converted into 1.3-1.6 MWe of peaking power delivered into electric grid.
In the conducted feasibility study it was assumed that the LAES facility is equipped with the equipment, providing its charge with use of single turbo expander-compressor based open air auto-refrigeration cycle (see
The given and assumed technical data used in numerical simulation of the energy storage performance are listed in the Table 1 below.
In their turn, the main calculated performance of the integrated LAES facility and CG station during LAES charge are presented in the Table 2. Here the following designations are used: GPA and GLA−flow-rates of process air and liquid air produced; WFAC and WMAC−mechanical power consumed by the feed and main air compressors; WLAES-CH−electric power consumed by the LAES facility; ALR=(GLA/GPA)×100%−air liquefaction ratio; GHPG and GLPG−flow-rates of HP gas delivered into CG station and LP gas escaping CG station; PHP−high pressure of gas delivered into CG station; PLP−low pressure of gas escaping CG station; WCTE−electric power produced by cold turbo-expander of the CG station; WCH=WLAES-CH−WCTE−total electric power consumed from the grid during LAES charge; and ωCH=WCH/(GLA×3.6)−specific external power consumed for air liquefaction during LAES charge.
The main calculated performance of the discharge process and combined operational results are presented in the Table 3, wherein the following designations are used: GHPG and GLPG−flow-rates of HP gas delivered into CG station and LP gas escaping CG station; GLNG-CG, GLNG-LAES and GLNG=GLNG-CG+GLNG-LAES−flow-rates of LNG produced correspondingly at the CG station, LAES facility and in combination; GLR=(GLNG/GHPG)×100%−gas liquefaction ratio; PHP−high pressure of gas delivered into CG station; PLP−low pressure of gas escaping CG station; PLNG−pressure of the produced LNG; WCG−electric power produced by the CG station; QTH-SH and QTH-RH−thermal load of air superheater and reheater; WHPAE and WLPAE−mechanical power produced by the high and low pressure air expanders; WLAES-DCH−electric power produced by the LAES facility; ωLAES-DCH=WLAES-DCH/(GLA×3.6)−specific power produced during LAES facility discharge; RTEGRID=(WLAES-DCH/WCH)×100%−grid round trip efficiency of the LAES facility; and WDCH=WLAES-DCH+WCG−total electric power delivered into the grid during LAES discharge.
As may be seen from the data presented in the Tables 2 and 3, the proposed integration of the LAES facility and CG station provides a drastic decrease in consumption of external power during LAES charge and multifold return of the power into grid during LAES discharge throughout the entire diapasons of the gas pressure ratio (π=PHP/PLP) and inlet gas high pressure PHP, at which natural gas enters the CG station. Particularly high RTEGRID values may
be achieved at the enhanced gas pressure ratio, as it is in Alternative C at the π=9.3. However, most of the CG stations are using the lesser gas pressure ratio, allowing nonetheless the impressive RTEGRID values to be attained, as in the Alternatives A and C, wherein at the π=5 RTEGRID values are equal to 160% and 240% correspondingly.
The recent developments in the field of pressure reducing stations have resulted in introducing the natural gas turbo-expanders into their design, making possible to recover a wasted mechanical power of expanded gas for generation of so-called “green” power. Such the turbo-expanders should be equipped with a mandatory pre-heaters of the high-pressure gas to provide a minimum admissible gas temperature in the low pressure pipelines identical to that in the high pressure pipeline. On the one hand, preheating a gas upstream of “warm” turbo-expander increases its output, but on the other hand an extra power is generated with a low thermal energy-to-power conversion efficiency, not exceeding 30%. In the present invention a “warm” turbo-expander is replaced by a “cold” one, wherein inlet temperature of dehumidified natural gas should be sustained at a level significantly below 0° C. A thermal energy being before used for pre-heating the natural gas may be now harnessed for superheating and reheating the expanded air at the LAES facility. Thereby an amount of thermal energy required in this case may be reduced by a factor of 2-3, whereas efficiency of its conversion into additional power of the air expander train may achieve 63-67%.
As also evident from the Tables 2 and 3, an amount of LNG produced directly at the LAES facility (GLNG-LAES) is varied within narrow limits (0.4-0.45 kg/s) for all considered alternatives, but its share in a total amount of LNG produced (GLNG) varies over a wider range from 20 to 30%. This is explained by a strong effect of two factors (gas pressure ratio in the cold turbo-expander and a value of inlet high pressure, at which natural gas enters the CG station) on the LNG production rate (GLNG-CG) of this station. Thereby the second factor makes a greater impact on the GLNG-CG value that must be considered in the integration of the CG station with the LAES facility. For example, design of the CG stations in the alternatives A and C provides the same gas pressure ratio (π=PHP/PLP=5) in the cold turbo-expanders, which however operate at the drastically distinct inlet high pressures (75 barA for Alt. A and 25 barA for Alt. C). This will cause the value of GLNG-CG in the Alt. A to increase by a factor of 1.5 up to 1.43 kg/s, as compared to LNG production of 0.95 kg/s in the Alt. C. At the same time, design of the CG stations in the alternatives A and B provides the comparable levels of the gas inlet high pressure (75 barA for Alt. A and 65 barA for Alt. B), which however operate at the drastically distinct gas pressure ratio in the cold turbo-expanders (π=5 for Alt. A and π=9.3 for Alt. B). This will cause the value of GLNG-CG in the Alt. B to increase only by a factor of 1.26 up to 1.8 kg/s, as compared to LNG production of 1.43 kg/s in the Alt. A. As a whole, it should be noted that a total gas liquefaction ratio at the integrated CG and LAES facility, varied in the range from 17 to 28%, significantly exceeds this value of the competitive technologies and may be achieved with use of the simplest and cheap single expander-based cycles for air and natural gas. Finally, the CG station with the higher values of the inlet gas pressure (PHP) and pressure ratio (π) in the cold turbo-expanders are preferable for integration with the LAES facilities.
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.
This application claims the benefits of U.S. Provisional Application No. 62/393,252 titled “Method for Energy Storage with Co-production of Peaking Power and Liquefied Natural Gas” and filed on Sep. 12th 2016.
| Number | Date | Country | |
|---|---|---|---|
| 62393252 | Sep 2016 | US |
