Multistage one pack system refrigeration natural gas liquefaction system and method
Technical field
The present invention relates to a kind of natural gas liquefaction process, especially relate to a kind of multistage one pack system refrigeration natural gas liquefaction system and method.
Background technology
Liquefied natural gas (LNG) has the performance of clean environment firendly, promotes rapidly in many applications such as middle samll cities and towns gas, industrial fuel, gas peak regulation and the accident emergency of no natural gas line arrival area, gas combustion automobile, high-grade porcelain processing.But receive the influence of International Crude Oil, Gas Prices is constantly soaring, and natural gas liquefaction plant's benefit natural gas liquefaction plant cost of material constantly increases, thereby causes the liquefaction plant profit margin constantly to descend.Natural gas liquefaction plant develops to maximization, scale direction both at home and abroad in recent years, and the maximum liquefying power of single at present cover has arrived 7,800,000 tons/year.Energy consumption is low, construction cost is relatively low, can be applied to the developing direction that large-scale liquefaction process is China's liquefaction technology in future again.
Natural gas liquefaction process is broadly divided into following three kinds both at home and abroad at present:
1) stepwise kind of refrigeration cycle; 2) azeotrope kind of refrigeration cycle is subdivided into band again or does not circulate with circulation of the single-stage mixing cryogen of precooling and multistage azeotrope; 3) swell refrigeration is subdivided into band again or does not freeze with the single-stage expansion of precooling refrigeration and multiple expansion.
Above technology is adapted to the natural gas liquefaction plant of different disposal scale because of characteristics separately.The natural gas liquefaction process of band swell refrigeration circulation is too high because of plant energy consumption, and single covering device treating capacity is little, is substituted by the mixing cryogen refrigerating cycle liquefied technology of single-stage gradually in recent years.Single-stage mixing cryogen refrigerating cycle liquefied technology is present domestic and international 50 * 10
4The main flow technology of the liquefaction factory of the following treatment scale of t/a.And the mixing cryogen refrigerating cycle liquefied technology (C3/MRC) and the multistage azeotrope refrigeration liquefying flow path of the precooling of band propane are used for the above medium-and-large-sized base load type natural gas liquefaction device of natural gas more.The refrigerating cycle liquefied flow process energy consumption of stepwise is low, be applicable to 100 * 10
4The above ultra-large type natural gas liquefaction device of t/a.
As seen from the above analysis, mixing cryogen refrigerating cycle liquefied technology (C3/MRC), multistage azeotrope refrigeration liquefying flow path and the refrigerating cycle liquefied flow process of stepwise of the precooling of band propane can be applicable to large-scale or the ultra-large type natural gas liquefaction process.But receive the monopolization of foreign natural gas liquefaction technology and key equipment, Chinese large-sized liquefaction factory construction cost can't be effectively controlled.Develop and a kind ofly can be applicable to that the large-scale natural gas liquefaction process that can use China's autonomy-oriented equipment again is very necessary.
Summary of the invention
In order to overcome the above-mentioned shortcoming of prior art; The invention provides a kind of multistage one pack system refrigeration natural gas liquefaction system and method; In conjunction with traditional stepwise refrigeration process advantage, from the key equipment production domesticization technology of traditional stepwise refrigeration process has been carried out improving and innovation simultaneously, except that having traditional stepwise refrigeration process characteristics; Also have the characteristics of cryogen compressor, heat exchanger production domesticization, convenient buying, investment more economize.
The technical solution adopted for the present invention to solve the technical problems is: a kind of multistage one pack system refrigeration natural gas liquefaction system comprises propane chilldown system, ethene liquefying refrigerating system and ethene liquefying refrigerating system; Said propane chilldown system comprises propane compressor, propane tank, high pressure propane evaporimeter, middle pressure propane evaporator and the low-pressure propane evaporimeter that connects successively; Said ethene liquefying refrigerating system comprises ethene storage tank, high-pressure ethylene evaporimeter, middle pressure ethene evaporimeter, low pressure ethylene evaporimeter and the ethylene compressor that connects successively; Said ethene liquefying refrigerating system comprises natural gas subcooler and the methane compressor that connects successively; Said ethene storage tank is connected with the low-pressure propane evaporimeter, and said ethylene compressor is connected with the high pressure propane evaporimeter, and said methane compressor is connected with the high pressure propane evaporimeter.
The present invention also provides a kind of multistage one pack system refrigeration natural gas liquefaction, comprises the steps:
1) the propane chilldown system carries out precooling to natural gas, methane and ethylene agent:
After natural gas, methane and ethene at first are cooled to-35 ℃ through three grades of propane device sweat coolings, get into the heat exchange cooling of ethene liquefying refrigerating system; The propane steam that comes out from three grades of propane evaporators through propane cooler water-cooled to 40 ℃, gets into propane tank and stores after propane compressor is pressurized to 1.32MPa.g; Cold-producing medium propane from propane tank passes through the throttling of one-level J-T valve, and pressure gets into the high pressure propane evaporimeter after reducing to 0.735MPa.g, and natural gas, methane and ethene are cooled off; The gaseous propane of high pressure propane evaporator evaporation is got back to the propane compressor supercharging, and LPG is through the throttling of secondary J-T valve, and pressure is pressed propane evaporator in reducing to and getting into behind the 0.305MPa.g, and natural gas, methane and ethene are cooled off; The middle gaseous propane of propane evaporator evaporation of pressing is got back to the propane compressor supercharging; LPG is through the throttling of three grades of J-T valves; Pressure gets into the low-pressure propane evaporimeter after reducing to 0.011MPa.g; Natural gas, methane and ethene are cooled off, and the gaseous propane of low-pressure propane evaporator evaporation is got back to the propane compressor supercharging and is circulated;
2) ethene liquefying refrigerating system is cooled to-95~-85 ℃ with natural gas, methane:
Ethene through ethylene chiller water-cooled to 40 ℃, gets into the propane chilldown system and is cooled to-35 ℃ and liquefaction after ethylene compressor is pressurized to 1.9MPa.g, gets into the ethene storage tank stores then; Through the throttling of one-level J-T valve, pressure gets into the high-pressure ethylene evaporimeter after reducing to 0.95MPa.g, and natural gas and methane are cooled off from-35 ℃ of liquid ethylenes of ethene storage tank; The ethene of high-pressure ethylene evaporator evaporation is got back to the ethylene compressor supercharging, and liquid ethylene is through the throttling of secondary J-T valve, and pressure is pressed the ethene evaporimeter in reducing to and getting into behind the 0.23MPa.g, and natural gas and methane are cooled off; The middle ethene of ethene evaporator evaporation of pressing is got back to the ethylene compressor supercharging; Liquid ethylene is through the throttling of three grades of J-T valves; Pressure gets into the low pressure ethylene evaporimeter after reducing to 0.017MPa.g; Natural gas and methane are cooled off, and the ethene of low pressure ethylene evaporator evaporation is got back to the ethylene compressor supercharging and is circulated;
3) to cross cooling system be the cold excessively cold that provides of natural gas and methane self to methane:
Methane is crossed cooling system and the natural gas of ethene liquefying refrigerating system liquefaction is crossed through the natural gas subcooler is chilled to-150 ℃, cross the natural gas throttling after cold after temperature reduce to-162 ℃, get into the LNG storage tank stores; Simultaneously; Cold-producing medium methane is cooled in this one-level about-150 ℃; Through the choke valve decrease temperature and pressure, pressure is reduced to 100KPa, temperature gets into the heat exchange of natural gas subcooler after reducing to-152.9 ℃ more then, and temperature goes out the natural gas subcooler after being upgraded to-100 ℃~-120 ℃ again; And directly get into the methane compressor supercharging, after accomplishing, supercharging gets into the circulation of propane chilldown system.
Compared with prior art, good effect of the present invention is: purified natural gas temperature in six heat exchangers (evaporimeter) and a plate-fin heat exchanger (natural gas subcooler) reduces gradually, until liquefaction; The required cold of liquefaction process is provided by propane, ethene, three systems of methane, and this system's regulating measure is abundant, can the cold that be complementary be provided for gas deliquescence process, thereby embodies this method in operational flexibility with to the adaptability of raw material.Compared with prior art, have the following advantages:
One, the gas deliquescence process energy consumption is low.
For natural gas liquefaction, the principal element that influences energy consumption is the heat transfer temperature difference of cryogenic temperature and refrigeration heat transfer process.Under identical cryogenic temperature operating mode, heat transfer temperature difference is big more, and the energy consumption of refrigeration system is high more.
Adopt multistage one pack system of the present invention to carry out natural gas liquefaction, propane, ethene evaporate under 3 different evaporating pressures, are divided into 3 temperature grade cooled natural gas, and the vaporized refrigerant under each pressure gets into corresponding compressor compresses.Adopting methane at last is that natural gas and the cooling of self provide cold as crossing cryogen.The whole heat transfer process temperature difference is comparatively even, no heat transfer bottleneck, and the available energy loss is little, and is energy-conservation obvious.Than the C3/MRC process energy consumption that generally uses at present low about 5%.
Two, the cryogen compressor is the one pack system compressor, and it is easier to design, and purchases more conveniently, and compressor operating is more stable, and can adopt production domesticization equipment, effectively reduces the construction investment of liquefaction factory.
The cryogen compressor comprises propane compressor; Ethylene compressor, methane compressor, wherein the minimum suction temperature of propane compressor is-40~-35 ℃; The minimum suction temperature of ethylene compressor is-101 ℃; For propane compressor and ethylene compressor low temperature industry extensively utilization at home, so this compressor is easy to buying, the realization production domesticization.The minimum suction temperature of methane compressor in traditional stepwise refrigeration process is-150 ℃, and home equipment can't use, and has limited the popularization of this technology.
Adopt natural gas liquefaction process of the present invention, the minimum suction temperature of methane compressor is brought up to-120 ℃, adopts the one-level air inlet, and the compressor of this operating mode is existing ripe achievement in the low temperature industry at home, has solved the bottleneck of domestic Large LNG factory production domesticization.
Three, liquefaction process heat exchanger range of choice is big, can adopt the ice chest structure, also can adopt tube shell type structure, or both structure combining.
Both at home and abroad the main heat exchanger equipment of LNG factory mainly is around heat exchange of heat pipe and plate-fin heat exchanger, has only APCI and LINDE two families around the existing world production merchant of heat exchange of heat pipe, and price is higher, and plate-fin heat exchanger manufacturer at home is more.Main heat exchanger in the external Large LNG factory all adopt around pipe.Adopt natural gas liquefaction process of the present invention, main heat exchanger adopts tube shell type structure and plate-fin heat exchanger, and large-scale liquefaction plant production domesticization is limited by the form of main heat exchanger no longer.
Description of drawings
The present invention will explain through example and with reference to the mode of accompanying drawing, wherein:
Fig. 1 is a system principle sketch map of the present invention.
The specific embodiment
A kind of multistage one pack system refrigeration natural gas liquefaction system; As shown in Figure 1, comprising: propane compressor 1, ethylene compressor 2, methane compressor 3, high pressure propane evaporimeter 4, middle pressure propane evaporator 5, low-pressure propane evaporimeter 6, high-pressure ethylene evaporimeter 7, middle pressure ethene evaporimeter 8, low pressure ethylene evaporimeter 9, natural gas subcooler 10, propane cooler 11, ethylene chiller 12, methane cooler 13, propane tank 14, ethene storage tank 15.Wherein:
Propane compressor 1, propane cooler 11, propane tank 14, high pressure propane evaporimeter 4, middle pressure propane evaporator 5 are connected with low-pressure propane evaporimeter 6 successively, constitute the propane chilldown system, are used for natural gas, methane and ethylene agent are carried out precooling.
Ethene storage tank 15, high-pressure ethylene evaporimeter 7, middle pressure ethene evaporimeter 8, low pressure ethylene evaporimeter 9, ethylene compressor 2 are connected with ethylene chiller 12 successively, constitute ethene liquefying refrigerating system, are used for natural gas, methane are cooled to-95 ~-85 ℃.
Natural gas subcooler 10, methane compressor 3 and methane cooler 13 are connected successively, constitute methane and cross cooling system, are used to the cold excessively cold that provides of natural gas and methane self.
A kind of multistage one pack system refrigeration natural gas liquefaction comprises the steps:
1) the propane chilldown system carries out precooling to natural gas, methane and ethylene agent:
Natural gas, methane and ethene at first after high pressure propane evaporimeter 4, middle pressure propane evaporator 5 and 6 three grades of propane sweat coolings of low-pressure propane evaporimeter are cooled to-35 ℃, get into the heat exchange cooling of ethene liquefying refrigerating system.
The propane steam that comes out from three grades of propane evaporators through propane cooler 11 water-cooleds to 40 ℃, gets into propane tank 14 and stores after propane compressor 1 is pressurized to 1.32MPa.g; Cold-producing medium propane from propane tank 14 passes through the throttling of one-level J-T valve, and pressure gets into high pressure propane evaporimeter 4 after reducing to 0.735MPa.g, and natural gas, methane and ethene are cooled off; The propane of high pressure propane evaporimeter 4 evaporation is got back to propane compressor 1 supercharging, and operative liquid propane is through the throttling of secondary J-T valve, and pressure is pressed propane evaporator 5 in reducing to and getting into behind the 0.305MPa.g, and natural gas, methane and ethene are cooled off; The middle propane of propane evaporator 5 evaporations of pressing is got back to propane compressor 1 supercharging; Operative liquid propane is through the throttling of three grades of J-T valves; Pressure gets into low-pressure propane evaporimeter 6 after reducing to 0.011MPa.g; Natural gas, methane and ethene are cooled off, and the propane of low-pressure propane evaporimeter 6 evaporations is got back to propane compressor 1 supercharging and is circulated.
2) ethene liquefying refrigerating system is cooled to-95~-85 ℃ with natural gas, methane:
Ethene through ethylene chiller 12 water-cooleds to 40 ℃, gets into the propane chilldown system and is cooled to-35 ℃ and liquefaction after ethylene compressor 2 is pressurized to 1.9MPa.g, gets into ethene storage tank 15 and stores; Through the throttling of one-level J-T valve, pressure gets into high-pressure ethylene evaporimeter 7 after reducing to 0.95MPa.g, and natural gas and methane are cooled off from-35 ℃ of liquid ethylenes of ethene storage tank 15; The ethene of high-pressure ethylene evaporimeter 7 evaporation is got back to ethylene compressor 2 superchargings, and operative liquid ethene is through the throttling of secondary J-T valve, and pressure is pressed ethene evaporimeter 8 in reducing to and getting into behind the 0.23MPa.g, and natural gas and methane are cooled off; The middle ethene of ethene evaporimeter 8 evaporations of pressing is got back to ethylene compressor 2 superchargings; Operative liquid ethene is through the throttling of three grades of J-T valves; Pressure gets into low pressure ethylene evaporimeter 9 after reducing to 0.017MPa.g; Natural gas and methane are cooled off, and the ethene of low pressure ethylene evaporimeter 9 evaporations is got back to ethylene compressor 2 superchargings and is circulated.
3) to cross cooling system be the cold excessively cold that provides of natural gas and methane self to methane:
Methane is as the cold-producing medium of super cooled sect; The natural gas that liquefaction stages (ethene liquefying refrigerating system) has been liquefied is chilled to-150 ℃ excessively through natural gas subcooler 10 (plate-fin heat exchanger); Temperature is reduced to-162 ℃ after crossing the natural gas throttling after cold, gets into the LNG storage tank stores; Simultaneously, cold-producing medium methane is cooled in this one-level about-150 ℃, and through the choke valve decrease temperature and pressure, pressure is reduced to 100KPa then, and temperature is reduced to-152.9 ℃, gets into natural gas subcooler 10 again, is natural gas and self cold excessively cold that provides.The temperature that methane after the throttling goes out natural gas subcooler 10 is-100 ℃~-120 ℃, and this gas directly gets into methane compressor 3 superchargings, through methane cooler 13 water-cooleds, gets into the circulation of propane chilldown system then after supercharging is accomplished.
The basic principle of multistage one pack system refrigeration natural gas liquefaction process is: the circulation of adjacent higher temperature level is given to heat in the circulation of lower temperature level.The circulation of first order propane refrigeration provides cold for natural gas, cold-producing medium ethene and cold-producing medium methane; Second level ethylene refrigeration circulation provides cold for natural gas and cold-producing medium methane; Third level methane refrigeration cycle is natural gas and self cold is provided.Through six heat exchangers (evaporimeter 4 to 9) and a plate-fin heat exchanger (natural gas subcooler 10) cooling, the temperature of natural gas reduces gradually, until liquefaction.