Utilizing the coupling of liquefied natural gas and liquid ammonia fuel to build a zero-carbon clean energy system

Abstract

The present invention belongs to the field of comprehensive energy utilization and zero-carbon environmental protection. It proposes a zero-carbon clean energy system that uses liquefied natural gas and liquid ammonia fuel to couple. The natural gas after LNG gasification is mixed with NH3 as fuel, which can significantly improve the fuel combustion conditions and greatly reduce CO2 emissions. At the same time, the rich cold capacity of LNG is used to separate the oxygen in the air and use it to increase the oxygen concentration in the combustion oxygen supply air, realizing LNG / NH3 oxygen-enriched cycle combustion, increasing the CO2 concentration in the exhaust gas, and reducing NO during the combustion process. x The NH3-SCR system is used to reduce NO in the exhaust gas. x Near-zero emissions. Furthermore, CO2 in flue gas can be absorbed to produce ammonium bicarbonate, which can be sold as a product or decomposed and regenerated. The regenerated CO2 can be used to produce dry ice using some of the refrigeration capacity of LNG. Compared to existing technologies, this invention offers a compact overall structure, high energy efficiency, low carbon emissions, and low pollutant emissions. It is economical and practical, and has promising application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of environmental protection technology, mainly aims at the treatment of flue gas denitrification and decarbonization, and involves a zero-carbon clean energy system constructed by coupling liquefied natural gas and liquid ammonia fuel. Technical Background

[0002] In 2020, the global maritime fleet reached approximately 100,000 vessels, generating approximately 820 million tons of CO2 annually. Currently, the shipping industry accounts for approximately 2.3% of global carbon emissions and is projected to contribute 3.5% by 2050. From 2008 to 2050, the shipping industry is only expected to reduce carbon emissions by approximately 33%. Therefore, in the context of the global response to climate change, the shipping industry's greenhouse gas emissions have attracted global attention. Compared to other industries, ocean shipping's energy and power systems are difficult to electrify, resulting in a higher reliance on petroleum-based fuels, making carbon reduction more challenging. There is an urgent need to strengthen the research and development of low-carbon fuel substitution, the rational use of zero-carbon / non-fossil fuel alternatives, and end-of-pipe carbon capture technologies.

[0003] Currently, ships are still primarily powered by petroleum-based fuels. Clean alternative fuels include low-carbon fuels such as liquefied natural gas (LNG), methanol, and biomass-based blends, as well as zero-carbon alternatives such as hydrogen and ammonia. As the most common alternative to traditional fuel oil, LNG has been widely used as a marine propulsion fuel. However, when used alone, its carbon emissions remain high, only decreasing by approximately 25% compared to conventional fuels, a significant gap from the 50% reduction target. Furthermore, the nitrogen oxides and CO produced by methane combustion require further control. Furthermore, direct combustion using air as oxygen requires a high air-to-fuel ratio, and the resulting CO2 is excessively diluted by the nitrogen, making subsequent carbon capture difficult and costly. The potential application of ammonia as a fuel in the marine sector has recently garnered widespread attention. Pure ammonia fuel is expensive, its combustion conditions are difficult to control, and it easily generates nitrogen oxides. Furthermore, specialized combustion equipment is currently lacking. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method for constructing a zero-carbon clean energy system by coupling liquefied natural gas and liquid ammonia fuel with high comprehensive utilization rate, low cost and no secondary pollution.

[0005] The object of the present invention can be achieved by the following technical solution: a zero-carbon clean energy system is constructed by coupling liquefied natural gas and liquid ammonia fuel, comprising: an LNG storage tank, a liquid ammonia storage tank, an air separation system and a combustion device;

[0006] The LNG in the LNG storage tank passes through the primary heat exchange system, the secondary cold recovery system and the tertiary heat exchange system in sequence before entering the combustion device, where it is used together with NH3 as fuel.

[0007] The oxygen separated from the compressed air by the air separation system and the supplementary air are used as the oxygen supply source and are fully burned with the fuel in the combustion device;

[0008] After the flue gas after combustion is cooled by the high-temperature waste heat boiler, part of it is sent back to the combustion device as recycled flue gas, and the other part of the non-recirculating flue gas enters the multi-effect SCR denitrification reduction reactor. The flue gas after denitrification then passes through the air preheater, the first-stage flue gas cooler, and the flue gas deep cooler in sequence; the flue gas deep cooler is connected to the second-stage cooling recovery system, and the first-stage flue gas cooler is connected to the third-stage heat exchange system.

[0009] The method of utilizing the above-mentioned zero-carbon clean energy system mainly includes the following steps:

[0010] 1) Utilizing the inherent cold energy of LNG, the system, through a liquid nitrogen cycle and a primary heat exchange system involving a compression turbine, delivers this cold energy to the air separation system, where it cools the pre-treated compressed air. This condenses and liquefies the majority of the oxygen, separating it from the nitrogen. The separated oxygen is then vaporized and its cold energy recovered, used to increase the oxygen concentration in the air required for fuel combustion. The remaining low-temperature nitrogen is then heated and its cold energy recovered before being used as a product or directly released. The cold energy carried by the vaporized oxygen and low-temperature nitrogen is recovered and used to pre-cool the compressed air in the air separation system.

[0011] 2) After the aforementioned treatment, LNG is converted into low-temperature gaseous natural gas. The refrigeration contained in the gas is recovered through a secondary refrigeration recovery system with circulating refrigerant. This refrigeration is then used to deep-cool the post-combustion flue gas, solidifying and separating the carbon dioxide contained therein. The remaining low-temperature nitrogen is then heated and its refrigeration recovered before being used as a product or directly released. The refrigeration it carries is then recovered and used for primary pre-cooling of the combustion flue gas.

[0012] 3) The natural gas undergoes tertiary cooling recovery, using a three-stage heat exchange system with circulating refrigerant. The higher temperature flue gas is used to raise the temperature of the natural gas to above 0°C, and the flue gas is also significantly cooled to facilitate subsequent CO2 capture.

[0013] 4) After the liquid ammonia is vaporized, the cold energy generated can be used to cool the hot flue gas. Afterwards, NH3 and natural gas are mixed in a certain proportion and fed together as fuel into the combustion device (the two fuels can be pre-mixed or fed separately in stages). The separated oxygen and supplementary air are used as the oxygen supply required for combustion, so that the fuel can be fully burned in the combustion device. After the flue gas after combustion is cooled by the high-temperature waste heat boiler (G1), part of it is used as recycled flue gas and returned to the combustion device by the fan. Through reasonable fuel grading and flue gas recycling, the generation of nitrogen oxides in the flue gas is reduced, and an appropriate amount of ammonia is used at the end of the combustion to perform selective non-catalytic reduction of nitrogen oxides.

[0014] 5) The other part of the non-reflow flue gas discharged from the high-temperature waste heat boiler enters the multi-effect SCR denitrification reduction reactor, using an appropriate amount of ammonia as a reducing agent to fully reduce and remove the nitrogen oxides therein, and at the same time fully oxidize and remove CO.

[0015] 6) The flue gas denitrified by the SCR unit then passes through the air preheater (G2), where the heat collected is used to preheat the air required for combustion. This flue gas is then used to preheat the natural gas in the three-stage preheating system, further reducing the flue gas temperature to below 20°C.

[0016] 7) Based on available cooling capacity, CO2 can be captured from the cooled flue gas using a combination of condensation and absorption methods. 30% of the flue gas is treated using condensation and enters the flue gas deep cooling system, where the flue gas temperature is reduced to below -80°C. The CO2 is condensed and liquefied or converted into dry ice. The remaining non-condensable nitrogen is recovered through cooling capacity and can be incorporated into the nitrogen system generated by the air separation system for utilization or release.

[0017] 8) The remaining 70% of the flue gas (already cooled to below 20°C) undergoes a low-temperature ammonia absorption decarbonization process. The CO2 is circulated and absorbed in a high-efficiency gas-liquid reactor. The resulting ammonium bicarbonate is recovered as a solid product through cooling and crystallization. After secondary scrubbing to remove ammonia, the decarbonized flue gas can be directly discharged.

[0018] Furthermore, the LNG should be stored in a constant temperature pressure tank maintained at -160°C or below and at a pressure greater than 1.0 MPa. Liquid ammonia should be stored in a tank maintained at a temperature below 40°C and at an operating pressure greater than 2.5 MPa. The LNG storage tank is an insulated pressure tank maintained at -160°C or below and at a pressure greater than 1.0 MPa. The liquid ammonia storage tank is maintained at a temperature below 40°C and at an operating pressure greater than 2.5 MPa.

[0019] Furthermore, the refrigeration provided by LNG during storage is utilized. After it leaves the storage tank, it passes through a primary refrigeration recovery system, using circulating liquid nitrogen as a cooling medium for refrigeration exchange. The compression-turbine cycle of the liquid nitrogen reduces the temperature of the circulating liquid nitrogen to -205°C to -200°C, which is used to liquefy the oxygen in the compressed air and separate the nitrogen from the liquid oxygen. The remaining refrigeration of the circulating liquid nitrogen, the refrigeration from the regasification of the liquid oxygen, and the refrigeration recovered from the low-temperature nitrogen are used for pre-cooling and dehydration of the compressed air. After passing through the primary refrigeration recovery system, the LNG is fully vaporized, with its temperature rising to -115°C to -110°C.

[0020] Furthermore, the secondary cold recovery system utilizes Freon and other circulating refrigerants to supply cooling to the flue gas deep cooling system, ultimately cooling the flue gas to -95°C to -90°C. After liquefaction and separation of the CO2, the gas can be directly bottled or further compressed into dry ice for cryogenic storage. The remaining cooling capacity of the circulating refrigerant and the cooling capacity recovered from the low-temperature nitrogen are used for primary pre-cooling of the flue gas. After passing through the secondary cold recovery system, the natural gas temperature rises to -30°C to -20°C.

[0021] Furthermore, the three-stage heat exchange system uses a solution such as ethylene glycol as a cold circulation carrier to deeply cool the hot flue gas, reducing its temperature to below 20°C, while preheating the natural gas to above 20°C before feeding it into the combustion device.

[0022] Furthermore, the flue gas cooled by the flue gas primary cooler can be divided into two routes, of which 20-40% of the flue gas enters the flue gas primary cooler and is finally cooled to below -100°C through graded cooling, so that the CO2 therein is liquefied and separated, and then canned or made into dry ice. The remaining flue gas comes into contact with 20% of the cold ammonia circulating liquid, which absorbs the CO2 therein and converts it into ammonium bicarbonate. The ammonia circulating liquid is cooled by the circulating refrigeration liquid recovered from the above-mentioned cold capacity, so that it is maintained at 15-20°C, so that the CO2 absorption efficiency reaches more than 90%. When the ammonium bicarbonate concentration accumulates to 20%, it is reduced to 0°C by the circulating refrigeration liquid, so that the ammonium bicarbonate crystals are precipitated, and its solid product is recovered.

[0023] Furthermore, the liquid ammonia in the liquid ammonia storage tank is heated and vaporized in a vaporization heat exchanger before being fed into the combustion device. The volume ratio of ammonia to natural gas is 0.2 to 1:1. The two can be pre-mixed before combustion or added to the burner in stages.

[0024] Furthermore, the oxygen source for combustion within the combustion device is oxygen-enriched air, which is a mixture of pure oxygen separated by the air separation system and air, wherein the oxygen content is 40-80% by volume, with the remainder being nitrogen. After combustion, the residual oxygen concentration in the flue gas is controlled to be 1-3%, the carbon dioxide concentration is greater than 30%, and the remainder is nitrogen and water vapor.

[0025] Furthermore, the flue gas discharged from the combustion device passes through a high-temperature waste heat boiler to reduce its temperature from 700-900°C to 350-400°C. Afterwards, 50-70% of the flue gas returns to the combustion device through the induced draft fan for flue gas recirculation. The remaining 30-50% of the flue gas is denitrified by a multi-effect SCR catalytic reduction denitrification reactor (SCR). The ammonia required for denitrification is injected from the tail of the combustion device and the inlet of the SCR device respectively. Through the joint action of the SNCR non-catalytic reduction denitrification reactor (SNCR) at the tail of the furnace and the SCR device, the concentration of nitrogen oxides in the flue gas is reduced to 5mg / m 3 The following is to achieve near-zero emission of flue gas nitrogen oxides. The molar ratio of the added ammonia to the nitrogen oxides in the original flue gas is 1.0-1.2:1.

[0026] Furthermore, the mixed fuel combustion device is one or a combination of an internal combustion engine, a gas turbine or a gas boiler, and reduces the concentration of nitrogen oxides in the exhaust flue gas by partially recirculating and burning the flue gas.

[0027] Through the above treatment, LNG and liquid ammonia containing cold energy can be effectively utilized to achieve near-zero emissions of nitrogen oxides and CO2, and build an effective zero-carbon clean energy system.

[0028] Compared with the prior art, the present invention has the following characteristics:

[0029] 1) The present invention overcomes the problems existing in the exhaust emission process of traditional combustion methods, and proposes a method for constructing a zero-carbon clean energy system by coupling liquefied natural gas and liquid ammonia fuel, which mainly includes the steps of cascade recovery of cold capacity, air cooling separation, flue gas cooling separation, combustion air oxygen enrichment and lifting, combustion exhaust cascade denitrification, flue gas cooling and decarbonization. This process method is simple to prepare and has low cost. Ammonia not only has the zero-carbon function of fuel, but also plays an important role in reducing nitrogen oxide emissions and capturing and recycling CO2, and has good application prospects. The present invention realizes the comprehensive utilization of liquefied natural gas cold capacity and reduces the operating cost of the system.

[0030] 2) The ammonia in the present invention not only has the function of zero-carbon fuel, but also achieves the reduction of terminal tail gas nitrogen oxides and the capture and resource utilization of CO2 without any secondary pollution.

[0031] 3) The present invention uses the natural gas after LNG gasification and NH3 as fuel. Under the condition of obtaining the same heat energy, it can significantly improve the fuel combustion conditions and greatly reduce CO2 emissions compared to the case of burning each of them separately. At the same time, the oxygen in the air is separated by the cold energy rich in LNG, and is used to increase the oxygen concentration in the combustion oxygen supply air, realizing the LNG / NH3 oxygen-enriched cycle combustion and increasing the CO2 concentration in the exhaust gas. In addition, the combination of ammonia and natural gas can reduce NO during the combustion process. x The production of NO in the exhaust gas is achieved by using the NH3-SCR system x Nearly zero emissions. Furthermore, the remaining cooling capacity of LNG can be used to cool flue gas and ammonia solution, and the CO2 in the flue gas can be absorbed to produce ammonium bicarbonate, which can be sold as a product or decomposed and regenerated. The regenerated CO2 can be used to make dry ice using part of the cooling capacity of LNG.

[0032] 4) This invention features a compact overall structure, high energy efficiency, low carbon emissions, and low pollutant emissions. It is economical and practical, with high decarbonization efficiency, and has promising application prospects. Hybrid fuel energy systems combining LNG low-carbon fuel with zero-carbon fuel will be a future development trend. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the process flow of the system of the present invention.

[0034] In the figure: LNG storage tank 1, liquid ammonia storage tank 2, air separation system 3, combustion device 4, primary heat exchange system 5, secondary cold recovery system 6, tertiary heat exchange system 7, gasification device 8, high-temperature waste heat boiler 9, multi-effect SCR denitrification reduction reactor 10, air preheater 11, flue gas primary cooler 12, flue gas deep cooler 13. DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to specific examples. This example is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following examples.

[0036] like Figure 1 As shown, the present invention relates to a zero-carbon clean energy system constructed by coupling liquefied natural gas and liquid ammonia fuel, comprising: an LNG storage tank 1, a liquid ammonia storage tank 2, an air separation system 3 and a combustion device 4;

[0037] The LNG in the LNG storage tank 1 passes through the primary heat exchange system 5, the secondary cold recovery system 6 and the tertiary heat exchange system 7 in sequence and then enters the combustion device 4. The liquid ammonia in the liquid ammonia storage tank 2 is gasified by the gasification device 8 and then enters the fuel device 4. In the combustion device 4, natural gas and NH3 are used together as fuel.

[0038] The oxygen separated from the compressed air by the air separation system 3 and the supplementary air are used as the oxygen supply source and are fully burned with the fuel in the combustion device 4;

[0039] After the flue gas after combustion is cooled by the high-temperature waste heat boiler 9, part of it is sent back to the combustion device 4 as recycled flue gas, and the other part of the non-recirculating flue gas enters the multi-effect SCR denitrification reduction reactor 10. The flue gas after denitrification then passes through the air preheater 11, the flue gas primary cooler 12, and the flue gas deep cooler 13 in sequence; the flue gas deep cooler 13 is connected to the secondary cooling recovery system 6, and the flue gas primary cooler 12 is connected to the tertiary heat exchange system 7.

[0040] Here’s how to use the zero-carbon clean energy system described above:

[0041] The first step is to recover and utilize the system's cold energy. Utilizing the cold energy contained in the LNG, the primary heat exchange system 5, consisting of a liquid nitrogen cycle and a compression turbine, delivers this cold energy to the air separation system 3, where the pre-treated compressed air is cooled and cooled. Most of the oxygen is condensed and liquefied, and then separated from the nitrogen. The separated oxygen then passes through a vaporization cold recovery unit 14, an air preheater 11, and a mixing unit 4, where it is used to increase the oxygen concentration in the air required for fuel combustion. The remaining low-temperature nitrogen is then heated and cold-recovered before being used as a product or released directly. The cold energy carried by the vaporized oxygen and low-temperature nitrogen is recovered and used to pre-cool the compressed air in the air separation system 3. After the above treatment, the LNG is vaporized into gaseous low-temperature natural gas. The cold energy contained in the gas is recovered by a secondary cold recovery system 6 with circulating refrigerant. This recovered cold energy is then used to deep-cool the post-combustion flue gas, liquefying and separating the carbon dioxide contained therein. The remaining low-temperature nitrogen is then heated and cold-recovered before being used as a product or released directly. The cold energy it carries is recovered and used for primary pre-cooling of the flue gas after combustion. The natural gas then undergoes tertiary cold recovery. Using a three-stage heat exchange system with circulating refrigerant, the higher-temperature flue gas is used to raise the natural gas temperature to above 0°C. The flue gas is also significantly cooled, facilitating subsequent CO2 capture.

[0042] In the second step, a mixed fuel of LNG low-carbon fuel and NH3 zero-carbon fuel is burned. After the liquid ammonia in the liquid ammonia storage tank 2 is gasified by the gasification device 8, the cold energy generated can be used to cool the hot flue gas. Afterwards, NH3 and natural gas are fed into the combustion device as fuel in a certain proportion (the two fuels can be pre-mixed or fed in separately in stages), and the separated oxygen and supplementary air are used as the oxygen supply source required for combustion, so that the fuel is fully burned in the combustion device 4. After the flue gas after combustion is cooled by the high-temperature waste heat boiler 9 (G1), part of it is returned to the combustion device 4 as recycled flue gas by the fan. Through reasonable fuel grading and flue gas recycling, the generation of nitrogen oxides in the flue gas is reduced, and an appropriate amount of ammonia is used at the end of the combustion to carry out selective non-catalytic reduction treatment of nitrogen oxides.

[0043] The third step is exhaust gas purification. The remaining non-recirculated flue gas discharged from the high-temperature waste heat boiler 9 enters the multi-effect SCR denitrification reduction reactor 10, where an appropriate amount of ammonia is used as a reducing agent to fully reduce and remove nitrogen oxides and simultaneously oxidize and remove CO. The flue gas denitrified by the multi-effect SCR denitrification reduction reactor 10 then passes through the air preheater (G2) 11, where the heat collected is used to preheat the air required for combustion. This flue gas is then used to preheat natural gas in the three-stage natural gas preheating system, further reducing the flue gas temperature to below 20°C. Depending on the available cooling capacity, the cooled flue gas can be used to capture CO2 using a combination of two methods. 30% of the flue gas is treated by condensation and enters the flue gas deep cooler 13, where the flue gas temperature is reduced to below -80°C. The CO2 is condensed and liquefied or converted into dry ice 15. The remaining non-condensable nitrogen, after cooling capacity recovery, can be incorporated into the nitrogen system generated by the air separation system for utilization or release. The remaining 70% of the flue gas (which has been cooled to below 20°C) is decarbonized with low-temperature ammonia water. The CO2 is then recycled and absorbed in a high-efficiency gas-liquid reactor 16. The resulting ammonium bicarbonate 17 is recovered as a solid product through crystallization. After a secondary scrubbing process to remove ammonia, the decarbonized flue gas can be directly discharged.

[0044] Example 1:

[0045] (1) Primary recovery and utilization of LNG cooling capacity.

[0046] LNG is stored in 2.0MPa insulated pressure tanks at a storage temperature of -161°C. LNG liquid is then injected into the primary refrigeration recovery system as needed. Using a liquid nitrogen circulation system with a compression system, refrigeration is extracted from L1a. The circulating liquid nitrogen is then cooled to -200°C through the compressor-turbine action before being fed into L1b. The air is then cryogenically separated. Compressed air (2-5MPa) is introduced into the cooled side of the air separator at a certain ratio, cooling the air and condensing most of the oxygen into liquid oxygen. After passing through the simple distillation tower built into the air separator, the liquid oxygen is discharged from the bottom of the tower. Unliquefied gaseous nitrogen is discharged from the top of the tower, and the refrigeration it contains is recovered and used to re-cool the flue gas after combustion.

[0047] (2) Secondary recovery and utilization of LNG cooling capacity.

[0048] The LNG discharged from the air separation system is basically vaporized, and it still contains a lot of residual cold energy. The temperature rises to -115℃. The cold natural gas then enters the secondary cold energy recovery system. Using Freon as a circulating cold carrier, the cold energy is taken out from L2a and sent to L2b to deeply cool the flue gas (N2 / CO2) after combustion. The carbon dioxide in it is liquefied and separated to obtain pure CO2, which is directly made into dry ice, and the temperature is reduced to -90℃.

[0049] (3) Three-level recovery and utilization of LNG cooling capacity.

[0050] After passing through the secondary cooling recovery system, the temperature of the natural gas rises to -35°C. The remaining cooling energy contained in the vaporized natural gas is then exchanged with the flue gas after combustion through the tertiary heat exchange system L3a-b, using an ethylene glycol solution as the cooling medium. This preheats the gas to 20°C and cools the flue gas. The preheated gas then enters the combustion device for combustion. The oxygen required for combustion is provided by the liquid oxygen separated by the air separation system in step (1). The liquid oxygen is vaporized and heated by the heat exchanger, and the cooling energy obtained is used to cool the flue gas.

[0051] (4) Combustion of mixed fuels.

[0052] The CH4 / NH3 mixture is used for gas turbine combustion, internal combustion engine combustion, or furnace combustion, with ammonia accounting for approximately 30% of the mixed fuel. To reduce the production of nitrogen oxides, ammonia is injected in a staged manner, and a functional zone with SNCR denitrification is established at the tail of the burner. Due to the use of oxygen-enriched combustion and CO2 enrichment, the flue gas from the combustion device is cooled to 350°C after heat recovery in the waste heat boiler G1. A portion of the flue gas then re-enters the combustion device driven by a high-temperature fan for gas recirculation, with a recirculation reflux ratio of 60%.

[0053] (5) Flue gas purification.

[0054] The flue gas not recycled is discharged. It first passes through an SCR catalytic unit, using ammonia as a reducing agent to reduce nitrogen oxides in the flue gas to nitrogen. This flue gas (N2 / CO2 / H2O) then passes through a heat exchanger, where its heat is used to preheat the LNG vaporization gas. After cooling, the flue gas temperature drops to 85°C. Refrigeration recovered from the air-cooled nitrogen, liquid oxygen regasification, and liquid ammonia evaporation steps is then used to further cool the flue gas to 20°C, condensing and removing most of the H2O. The CO2 in the flue gas is then captured and further cooled to -10°C using the recovered excess refrigeration using a condensation separation method to remove water. The flue gas then enters the N2 / CO2 separation condenser, where the refrigeration of the LNG gas after air separation cools the N2 / CO2 mixture to -90°C, liquefying and separating the CO2, which is then compressed into dry ice.

[0055] Compared with the existing technology, the CO2 emission in the coupled clean energy system of the present invention is reduced by more than 80%, and the concentration of nitrogen oxides in the exhaust gas is less than 10mg / m 3 .

[0056] Example 2:

[0057] (1) First-level recovery and utilization of LNG cooling capacity.

[0058] LNG is stored in 4.0MPa insulated pressure tanks at a storage temperature of -161°C. LNG liquid is then injected into the primary refrigeration recovery system as needed. Using a liquid nitrogen circulation system with a compression system, the refrigeration is extracted from L1a. The circulating liquid nitrogen is then cooled to -200°C through the compressor-turbine action before being fed into L1b. The air is then cryogenically separated. Compressed air (2-5MPa) is introduced into the cooled side of the air separator at a certain ratio to cool the air, condensing most of the oxygen into liquid oxygen. After passing through the simple distillation tower built into the air separator, the liquid oxygen is discharged from the bottom of the tower. The unliquefied gaseous nitrogen is discharged from the top of the tower, and the refrigeration it contains is recovered and used to re-cool the flue gas after combustion.

[0059] (2) Secondary recovery and utilization of LNG cooling capacity.

[0060] The LNG discharged from the air separation system is basically vaporized, and its temperature rises to -110℃. The cold natural gas then enters the secondary cold recovery system, using Freon as a circulating cold carrier to extract the cold energy from L2a and send it to L2b to deeply cool the flue gas (N2 / CO2) after combustion, liquefy and separate the carbon dioxide to obtain pure CO2, and directly make dry ice with the temperature reduced to -96℃.

[0061] (3) Three-level recovery and utilization of LNG cooling capacity.

[0062] After passing through the secondary cooling recovery system, the temperature of the natural gas rises to -30°C. The remaining cooling energy contained in the vaporized natural gas is then exchanged with the flue gas after combustion through the heat exchange system L3a-b, with the selected cooling medium being ethylene glycol solution. This preheats the gas to 25°C and cools the flue gas. The preheated gas then enters the combustion device for combustion. The oxygen required for combustion is provided by the liquid oxygen separated by the air separation unit in step (1). The liquid oxygen is vaporized and heated by the heat exchanger, and the cooling energy obtained is used to cool the flue gas.

[0063] (4) Combustion of mixed fuels.

[0064] The natural gas / NH3 mixture is used for gas turbine combustion, internal combustion engine combustion, or furnace combustion, with ammonia accounting for approximately 40% of the mixed fuel. To reduce the production of nitrogen oxides, ammonia is injected in a staged manner, and a functional zone with SNCR denitrification is established at the tail of the burner. Due to the use of oxygen-enriched combustion and CO2 enrichment, the flue gas from the combustion device is cooled to 320°C after heat recovery in the waste heat boiler G1. A portion of the flue gas then re-enters the combustion device driven by the high-temperature fan for gas recirculation, with a recirculation reflux ratio of 55%.

[0065] (5) Flue gas purification.

[0066] The flue gas not recycled is discharged. It first passes through an SCR catalytic unit, using ammonia as a reducing agent to reduce nitrogen oxides in the flue gas to nitrogen. This flue gas (N2 / CO2 / H2O) then passes through a heat exchanger, where its heat is used to preheat the LNG vaporization gas. After cooling, the flue gas temperature drops to 80°C. The flue gas is then further cooled to 15°C using the recovered cooling energy from air-cooled nitrogen, liquid oxygen regasification, and liquid ammonia evaporation, condensing and removing most of the H2O. The CO2 in the flue gas is then captured using a low-temperature ammonia absorption process with 20% ammonia water, where both the gas and liquid phase temperatures are below 10°C. When the resulting ammonium bicarbonate concentration reaches 15%, the temperature of the partially recycled absorption liquid is cooled to below 2°C, causing the ammonium bicarbonate to crystallize. Filtration and dehydration are then performed to produce a solid ammonium bicarbonate product, which can be used as an industrial raw material. The make-up water required by the absorption unit can be replenished by condensed water in the flue gas. Due to the low-temperature absorption and the subsequent ammonia removal unit, problems such as ammonia escape are avoided.

[0067] By optimizing the operating parameters of the coupled clean energy system, the emission of CO2 in the exhaust gas was reduced by more than 90%, and the concentration of nitrogen oxides in the exhaust gas was less than 5mg / m 3 .

[0068] The description of the above embodiments facilitates understanding and use of the present invention by those skilled in the art. Those skilled in the art can readily modify the embodiments and apply the general principles thereof to other embodiments without requiring creative effort. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should fall within the scope of protection of the present invention.

Claims

1. A zero-carbon clean energy system constructed by coupling liquefied natural gas and liquid ammonia fuel, characterized in that: include: LNG storage tanks, liquid ammonia storage tanks, air separation systems and combustion units; The LNG in the LNG storage tank passes through the primary heat exchange system, the secondary cold recovery system, and the tertiary heat exchange system in sequence before entering the combustion device, where it is used together with NH3 as fuel. The volume ratio of ammonia to natural gas entering the combustion device is 0.2 to 1:

1. The oxygen separated from the compressed air by the air separation system and the supplementary air are used as the oxygen supply source and are fully burned with the fuel in the combustion device. The oxygen source in the combustion device is oxygen-enriched air composed of a mixture of pure oxygen separated by the air separation system and air, wherein the oxygen volume content is 40-80% and the rest is nitrogen. The residual oxygen concentration in the flue gas after combustion is controlled at 1-3%, the carbon dioxide concentration is greater than 30%, and the rest is nitrogen and water vapor. After the flue gas after combustion is cooled by the high-temperature waste heat boiler, part of it is sent back to the combustion device as recycled flue gas, and the other part of the non-recirculating flue gas enters the multi-effect SCR denitrification reduction reactor. The flue gas after denitrification then passes through the air preheater, the flue gas primary cooler, and the flue gas deep cooler in sequence; the flue gas deep cooler is connected to the secondary cooling recovery system, and the flue gas primary cooler is connected to the tertiary heat exchange system; The flue gas discharged from the combustion device passes through the high temperature waste heat boiler to reduce its temperature from 700-900 o C dropped to 350-400 o C. Afterwards, 50-70% of the flue gas returns to the combustion device through the induced draft fan for flue gas recirculation; the remaining 30-50% of the flue gas passes through the multi-effect SCR denitrification reduction reactor for denitrification treatment. The ammonia required for denitrification is injected from the tail of the combustion device and the inlet of the multi-effect SCR denitrification reduction reactor respectively. Through the combined action of the SNCR and SCR devices at the tail of the furnace, the nitrogen oxide concentration in the flue gas is reduced to 5mg / m 3 The following is to achieve near-zero emission of flue gas nitrogen oxides; the molar ratio of the added ammonia to the nitrogen oxides in the original flue gas is 1.0-1.2:

1.

2. The method of constructing a zero-carbon clean energy system by coupling liquefied natural gas and liquid ammonia fuel according to claim 1, characterized in that: The LNG storage tank is -160 o C below, the pressure is greater than 1.0MPa insulation pressure tank, the temperature of the liquid ammonia storage tank is lower than 40 o Below C, the working pressure is greater than 2.5MPa.

3. The method of constructing a zero-carbon clean energy system by coupling liquefied natural gas and liquid ammonia fuel as claimed in claim 1, wherein: The cooling energy contained in the LNG storage tank during storage passes through the primary cooling energy recovery system to liquefy the oxygen in the compressed air and separate the nitrogen and oxygen in the air. After passing through the primary cooling energy recovery system, the LNG is fully gasified and the temperature rises to -115 o C ~ -110 o C; The first-stage cooling recovery system uses circulating liquid nitrogen as a cooling medium to exchange cooling capacity, and under the circulation of liquid nitrogen compression-turbine, the temperature of the circulating liquid nitrogen is reduced to -205 o C ~ -200 o C. The remaining cooling capacity of the circulating liquid nitrogen, the cooling capacity of the liquid oxygen regasification and heating, and the cooling capacity recovered from the low-temperature nitrogen are used for pre-cooling and dehydration of the compressed air.

4. The method of claim 1 for constructing a zero-carbon clean energy system by coupling liquefied natural gas and liquid ammonia fuel, wherein: In the secondary cooling capacity recovery system, Freon is used as a circulating cooling medium to supply cooling to the flue gas deep cooler, and finally the flue gas is cooled to -95 o C~ -90 o C. After the CO2 is liquefied and separated, it is directly bottled or further compressed into dry ice for low-temperature storage; The remaining cooling capacity of the circulating cooling medium and the cooling capacity recovered by the low-temperature nitrogen are used for the primary pre-cooling of the flue gas; after the natural gas passes through the secondary cooling capacity recovery system, the temperature rises to -30 o C~ -20 o C.

5. The method of constructing a zero-carbon clean energy system by coupling liquefied natural gas and liquid ammonia fuel as claimed in claim 1, wherein: The three-stage heat exchange system uses ethylene glycol solution as a cold circulation carrier to cool the hot flue gas to a temperature of 20 o Below 30°C, and preheat the natural gas to 20 o C and above and then sent to the combustion device.

6. The method of constructing a zero-carbon clean energy system by coupling liquefied natural gas and liquid ammonia fuel as claimed in claim 1, wherein: The flue gas cooled by the flue gas primary cooler is divided into two paths, of which 20-40% of the flue gas enters the flue gas primary cooler and is finally cooled to -100°C through graded cooling. o Below 300°C, the CO2 is liquefied and separated, and then canned or made into dry ice; The remaining flue gas is in contact with the cold ammonia circulating liquid, which absorbs the CO2 and converts it into ammonium bicarbonate; the ammonia circulating liquid is cooled by the circulating refrigeration liquid recovered from the above cold capacity to keep it at 15-20 o C, so that the CO2 absorption efficiency reaches more than 90%. When the concentration of ammonium bicarbonate accumulates to 20%, it is reduced to 0 by circulating the refrigerant. o C, ammonium bicarbonate is crystallized and its solid product is recovered.

7. The method of claim 1 for constructing a zero-carbon clean energy system by coupling liquefied natural gas and liquid ammonia fuel, wherein: Ammonia and natural gas can be premixed before combustion or added to the combustion device in stages.

8. The method of constructing a zero-carbon clean energy system by coupling liquefied natural gas and liquid ammonia fuel as claimed in claim 1, wherein: The combustion device is one or a combination of an internal combustion engine, a gas turbine or a gas boiler, and reduces the concentration of nitrogen oxides in the exhaust flue gas by partially recirculating and burning the flue gas.

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