BOG and LNG cold energy comprehensive recycling system
Technical Field
The utility model belongs to LNG (liquefied natural gas) receiving station energy comprehensive recovery utilizes the field, concretely relates to BOG and LNG cold energy comprehensive recovery utilizes system.
Background
As last half year of 2019, domestic built and put into production LNG stations reach 21 seats, but cold energy generated in the LNG receiving and unloading process is not well utilized. Meanwhile, a large amount of BOG (LNG vaporized gas) is generated in the operation process of the LNG receiving station, and the LNG receiving station cannot be well recycled, only a small amount of BOG (flash gas) is recycled at present, and most of BOG is combusted and discharged through a torch system, so that energy waste is caused. The two parts cause a great deal of energy waste, and further cause great economic loss. Therefore, the design of a proper LNG cold energy utilization and BOG recycling method has important significance.
The Chinese patent document with the publication number of CN109386316A and the name of a combined utilization system and method of LNG cold energy and BOG combustion energy discloses a combined utilization system of LNG cold energy and BOG combustion energy, wherein high-temperature steam generated by BOG combustion is used for generating electricity through a generator, one part of waste heat steam is used for heating a circulating medium cooled by LNG, and the other part of waste heat steam is used for providing heat energy for a heat supply subsystem, so that the purpose of improving the power generation efficiency of the system is achieved. However, the technology is limited by the load range of the BOG gas turbine, has low flexibility, and cannot well process the BOG gas turbine when the BOG load fluctuation of the LNG receiving station is large.
Chinese patent document CN109404079A entitled BOG recondensing and LNG cold power generation integrated system for LNG receiving station discloses a method for using LNG cold power generation for BOG recondensing process. However, the efficiency of converting the cold energy of the low-temperature Rankine cycle into the electric energy is low, so the utilization efficiency of the method is not high.
Therefore, a process with high energy recovery rate and high operational flexibility, which can well cope with the BOG load fluctuation of the LNG receiving station, is required to recover the cold energy of the LNG receiving station and the generated BOG. The process takes a peak-adjusting LNG receiving station as an example, LNG cold energy utilization and BOG recycling are skillfully combined, BOG production fluctuation in different periods is considered to be large, BOG is cooperatively recovered by adopting condensation regasification, combustion power generation and direct compression processes, and hot water generated by flue gas waste heat after BOG combustion power generation is used for providing a heat source for LNG cold energy power generation, so that the process has strong cooperativity and good operation elasticity, and the waste of BOG is reduced while LNG cold energy power generation is fully realized.
SUMMERY OF THE UTILITY MODEL
An object of the utility model is to above-mentioned proposition, BOG and the LNG cold energy recycle system that is applicable to the LNG receiving station is not carried out fine recycle to BOG and the LNG cold energy that the function in-process produced to present LNG receiving station to reach the recovery in coordination to the LNG receiving station complementary energy, improve the energy utilization of LNG receiving station. According to the difference of LNG external output and BOG output in the LNG receiving station base load non-unloading period, the LNG unloading period, the peak regulation non-unloading period and the peak regulation unloading period, condensation regasification, combustion power generation and direct compression processes are respectively arranged to cooperatively recover the BOG, and meanwhile, hot water generated by waste heat of flue gas generated after the BOG combustion power generation is used for providing a heat source for LNG cold energy power generation, so that the efficiency of a cold energy power generation system is improved.
The utility model discloses at least, one of following technical scheme realizes.
A BOG and LNG cold energy comprehensive recycling system comprises a BOG condensation regasification system, a BOG direct compression output system, a BOG cogeneration system and an LNG cold energy power generation system;
the BOG condensation regasification system comprises an LNG storage tank, an LNG immersed pump, an LNG pressure pump, a BOG buffer tank, a condensation regasification system BOG compressor, a pressurization LNG-BOG pre-cooler and a BOG re-condenser, wherein the pressurization LNG-BOG pre-cooler and the BOG re-condenser are connected with the LNG pressure pump; the LNG storage tank, the BOG buffer tank, the BOG compressor of the condensation regasification system, the pressurization LNG-BOG precooler and the BOG recondenser are sequentially connected; the LNG immersed pump divides natural gas in the LNG storage tank into two parts, and the LNG booster pump and the BOG recondenser are both connected with the LNG immersed pump; the LNG pressurization pump divides the pressurized LNG into two streams, one stream is sent to a pressurization LNG-BOG precooler to precool the BOG from the BOG buffer tank, and the other stream is mixed with the precooled LNG and then sent to a downstream external transportation and LNG cold energy power generation system;
the BOG direct compression output system comprises a BOG seawater preheater, a BOG direct compression output system BOG compressor and a BOG seawater cooler, wherein the BOG seawater preheater, the BOG direct compression output system BOG compressor and the BOG seawater cooler are connected with the BOG buffer tank; the BOG seawater preheater, the BOG direct compression output system BOG compressor and the BOG seawater cooler are sequentially connected;
the BOG cogeneration system comprises a thermoelectric system BOG compressor connected with the BOG seawater preheater, BOG pressure regulating and metering equipment, a first gas turbine generator set, a flue gas waste heat boiler and a second gas turbine generator set connected with the BOG pressure regulating and metering equipment; the BOG compressor of the thermoelectric system, the BOG pressure regulating and metering device, the first gas turbine generator set and the flue gas waste heat boiler are sequentially connected;
the LNG cold energy power generation system comprises an LNG raw seawater vaporizer, a natural gas metering system connected with the LNG raw seawater vaporizer, an LNG-mixed working medium heat exchanger, an LNG seawater reheater connected with the LNG-mixed working medium heat exchanger, a mixed working medium storage tank, a mixed working medium booster pump, a mixed working medium reheater connected with a flue gas waste heat boiler and an expansion generator connected with the LNG-mixed working medium heat exchanger; the LNG-mixed working medium heat exchanger, the mixed working medium storage tank, the mixed working medium booster pump, the mixed working medium reheater and the expansion generator are sequentially connected.
Further, in the BOG condensation regasification system, LNG at the temperature of-164 to-161 ℃ and 1.15bar in an LNG storage tank is pressurized to 4-6 bar by an LNG immersed pump and then divided into two parts, one part is conveyed to the LNG pressurizing pump, and the other part enters a BOG recondenser to condense BOG;
the LNG pressurized by the LNG pressurization pump is divided into two streams, one stream is sent to a pressurization LNG-BOG precooler to precool the BOG from the BOG buffer tank, and the other stream is mixed with the LNG returned after precooling and then sent to a downstream external transportation and LNG cold energy power generation system.
Furthermore, the mixed working medium of the LNG cold energy power generation system is a combination of at least two of the organic working media.
Furthermore, a mixed working medium reheating heat source of the LNG cold energy power generation system is hot water generated by a flue gas waste heat boiler.
And furthermore, a feedback regulating valve is arranged at the LNG shunting position in front of the LNG-mixed working medium heat exchanger, the LNG-mixed working medium heat exchanger is regulated according to the fluctuation of the use amount of downstream natural gas, and when the demand of the natural gas is too large or too small, the LNG raw seawater vaporizer is opened to vaporize, and then the LNG-mixed working medium heat exchanger is conveyed to downstream after pressure regulation and metering.
Furthermore, the BOG condensation and regasification system, the BOG direct compression output system and the BOG cogeneration system are used for processing the generated BOG, aiming at four different conditions mainly existing in the LNG receiving station, namely a base load non-unloading period, a base load unloading period, a peak regulation non-unloading period and a peak regulation unloading period.
Further, in the period of basic load output and non-unloading, the BOG production is minimum, at the moment, a gas turbine is started to carry out recovery combustion on the BOG, and condensation, regasification and compression are not adopted to enter a medium-low pressure pipe network facility.
Further, during the period of basic load export and ship unloading, the LNG export amount is unchanged, the BOG generation amount is increased due to the ship unloading reason, the export LNG is liquefied by a BOG condensation regasification system, two gas turbines are started to recover the BOG, and the rest BOG is treated by a compression and retraction pipe network.
Further, in the peak-shaving external transportation and non-ship unloading period, the LNG external transportation amount is increased rapidly, the BOG generation amount is further increased, the BOG treatment amount of the BOG condensation regasification system is also increased along with the increase of the LNG external transportation amount, at the moment, two gas turbines are started to recover, burn, generate power, condense and regasify the BOG, and the rest BOG enters a medium-low pressure pipe network after being compressed.
Further, during peak load regulation export and ship unloading periods, the LNG export amount is increased rapidly, the BOG production amount is the maximum, at the moment, the BOG condensation regasification system, the BOG direct compression export system and the BOG combined heat and power generation system are started at full load, and the rest BOG is combusted through a flare.
Compared with the prior art, the utility model discloses following beneficial effect has:
1. the utility model discloses BOG burning power generation system, condensation regasification system, compression advance the pipe network system and come to retrieve BOG for technology has very strong cooperativity and good elasticity of operation.
2. The waste heat of the flue gas after BOG combustion power generation is utilized to generate hot water for providing a heat source for LNG cold energy power generation, and the waste of BOG is reduced while the LNG cold energy power generation is fully realized.
3. The problem of the too big recovery difficulty of BOG production fluctuation is solved, LNG cold energy generating efficiency and the energy utilization of receiving station have been improved.
Drawings
Fig. 1 is a schematic view of a system for comprehensively recycling BOG and LNG cold energy according to an embodiment of the present invention;
the figures show that: 1-LNG storage tank, 2-LNG immersed pump, 3-LNG booster pump, 4-LNG raw seawater vaporizer, 5-natural gas metering system, 6-BOG buffer tank, 7-condensation regasification system BOG compressor, 8-pressure LNG-BOG precooler, 9-BOG recondenser, 10-BOG seawater preheater, 11-BOG direct compression export system BOG compressor, 12-BOG seawater cooler, 13-LNG-mixed working medium heat exchanger, 14-LNG seawater reheater, 15-mixed working medium storage tank, 16-mixed working medium booster pump, 17-mixed working medium reheater, 18-expansion generator, 19-thermoelectric system BOG compressor, 20-BOG pressure regulating metering equipment, 21-flue gas waste heat boiler, 22-first gas turbine generator set, 23-second gas turbine genset.
Detailed Description
For a better understanding of the present invention, the following description is given in conjunction with the accompanying drawings and examples, but the scope of the invention is not limited to the examples.
Construction scale of 500 multiplied by 10 of certain peak regulation type LNG receiving station4t/a, the LNG external basic load is kept at 150 x 104Sm3D (45 t/h), and the peak-shaving output is 1800 x 104Sm3And d (585 t/h), the temperature of the LNG discharged from the storage tank is-161 ℃, and the gasification pressure is 8 MPa. Maximum gasification output capacity of 6000 x 104Sm3/d。
The BOG output of the LNG receiving station during the external transportation without unloading the base load is 6.12-6.36 t/h, the BOG output of the LNG receiving station during the external transportation without unloading the base load is 22.94-23.10 t/h, the BOG output of the LNG receiving station during the external transportation without unloading the peak regulation is 43.81-44.68 t/h, and the BOG output of the LNG receiving station during the external transportation without unloading the base load is 60.39-63.46 t/h. The station is provided with a BOG condensation regasification system, the treatment capacity is 20t/h, and two BOG compressors with 9000 sides (the total treatment capacity is 12.16t/h) can compress BOG into a 0.4MPa pipe network. Furthermore, the utility model discloses to increase two sets of design scale and adjust BOG recovery system for 6 t/h's gas turbine generator group.
The comprehensive BOG and LNG cold energy recycling system shown in FIG. 1 comprises a BOG condensation regasification system, a BOG direct compression export system, a BOG cogeneration system and an LNG cold energy power generation system;
the BOG condensation and regasification system comprises an LNG storage tank 1, an LNG immersed pump 2, an LNG booster pump 3, a BOG buffer tank 6, a condensation and regasification system BOG compressor 7, a pressurization LNG-BOG pre-cooler 8 and a BOG re-condenser 9, wherein the pressurization LNG-BOG pre-cooler 8 and the BOG re-condenser 9 are connected with the LNG booster pump 3; the LNG storage tank 1, the BOG buffer tank 6, the BOG compressor 7 of the condensation regasification system, the pressurization LNG-BOG precooler 8 and the BOG recondenser 9 are sequentially connected; the LNG immersed pump 2 divides natural gas in the LNG storage tank 1 into two parts, and the LNG booster pump 3 and the BOG recondenser 9 are both connected with the LNG immersed pump 2; the LNG pressurization pump 3 divides the pressurized LNG into two streams, one stream is sent to a pressurization LNG-BOG precooler 8 to precool the BOG from the BOG buffer tank 6, and the other stream is mixed with the precooled LNG and then sent to a downstream external transportation and LNG cold energy power generation system;
the BOG direct compression output system comprises a BOG seawater preheater 10, a BOG direct compression output system BOG compressor 11 and a BOG seawater cooler 12 which are connected with the BOG buffer tank 6; the BOG seawater preheater 10, the BOG direct compression output system BOG compressor 11 and the BOG seawater cooler 12 are sequentially connected;
the BOG cogeneration system comprises a thermoelectric system BOG compressor 19 connected with the BOG seawater preheater 10, BOG pressure regulating metering equipment 20, a first gas turbine generator set 22, a flue gas waste heat boiler 21 and a second gas turbine generator set 23 connected with the BOG pressure regulating metering equipment 20; the BOG compressor 19, the BOG pressure regulating and metering device 20, the first gas turbine generator set 22 and the flue gas waste heat boiler 21 of the thermoelectric system are sequentially connected;
the LNG cold energy power generation system comprises an LNG raw seawater vaporizer 4, a natural gas metering system 5 connected with the LNG raw seawater vaporizer 4, an LNG-mixed working medium heat exchanger 13, an LNG seawater reheater 14 connected with the LNG-mixed working medium heat exchanger 13, a mixed working medium storage tank 15, a mixed working medium booster pump 16, a mixed working medium reheater 17 connected with a flue gas waste heat boiler 21 and an expansion generator 18 connected with the LNG-mixed working medium heat exchanger 13; the LNG-mixed working medium heat exchanger 13, the mixed working medium storage tank 15, the mixed working medium booster pump 16, the mixed working medium reheater 17 and the expansion generator 18 are connected in sequence.
The BOG and LNG cold energy comprehensive recycling system comprises the following processes:
BOG condensation regasification system: LNG at the temperature of-161 ℃ and 1.15bar in an LNG storage tank 1 is pressurized to 5.5bar by an LNG immersed pump 2, the LNG is divided into two parts, one part is conveyed to an LNG pressurizing pump 3, and the other part enters a BOG recondenser 9 to condense BOG;
the LNG pressurized by the LNG pressurizing pump 3 is divided into two streams, one stream is sent to a pressurizing LNG-BOG precooler (8) to precool the BOG from the BOG buffer tank 6, and the other stream is mixed with the LNG sent back after precooling and then sent to a downstream external transportation and LNG cold energy power generation system;
BOG at-150 ℃ and 1.15bar is led out from the top of an LNG storage tank 1, enters a BOG buffer tank 6 for pressure stabilization, is compressed to 5.5bar by a BOG compressor 7 of a condensation regasification system, is cooled to-100 ℃ and then enters a BOG recondenser 9 to be directly contacted with one LNG stream coming out of an LNG immersed pump 2 for heat exchange and condensation after being heated to-67.49 ℃, is mixed with the other LNG stream coming out of the LNG immersed pump 2 after being discharged from the BOG recondenser 9, is cooled to-139.19 ℃, enters a pressurization pump 3 for pressurization to 65bar, and is heated to-134.76 ℃. And a part of pressurized LNG precools BOG again, and the mixed temperature of the other part of LNG and precooled heat-exchanged LNG at-131.78 ℃ is increased to-132.38 ℃ and then enters the downstream. According to the technical scheme, 1t of BOG can be liquefied by every 6.86t of LNG.
BOG direct compression export system: BOG which is led out from an LNG storage tank 1 and has the temperature of-150 ℃ and the pressure of 1.15bar enters a BOG buffer tank 6, is preheated to-55 to-50 ℃ by a BOG seawater preheater 10, then enters a BOG compressor 11 of a BOG direct compression output system to be compressed to 4bar, is cooled by a BOG seawater heat exchanger 12 and then is output to a medium-low pressure pipeline.
The BOG cogeneration system: BOG (boil off gas) of-150 ℃ and 1.15bar, which is led out from an LNG (liquefied natural gas) storage tank 1, enters a BOG buffer tank 6, flows through a BOG seawater preheater 10 to be preheated to-55 ℃, is compressed to 18bar through a BOG compressor 19 of a thermoelectric system, enters a first gas turbine generator set 22 and a second gas turbine generator set 23 through a pressure regulating metering device 20 to generate electricity, tail gas is introduced into a flue gas waste heat boiler 21 and exchanges heat with cold water of 30 ℃, and the generated hot water of 70 ℃ is used as a circulating heat source of an LNG cold energy power generation system.
LNG cold energy power generation system: the 65bar LNG coming out of the BOG condensation regasification system is divided into two paths at the temperature of-132.38 ℃, one path of LNG is output outwards along the original LNG original seawater vaporizer 4 of the station, the other path of LNG exchanges heat with a mixed working medium through an LNG-mixed working medium heat exchanger 13, and the mixed working medium is C2C3 (mixed ethane and propane). The natural gas after heat exchange is heated to 0 ℃ by an LNG seawater reheater 14, passes through an original natural gas metering system 5 of an LNG receiving station and passes through a natural gas output main pipe and an external conveying pipe network;
the liquid C2C3 with the pressure of 0.2MPa and the temperature of-61 ℃ coming out from a mixed working medium refrigerant storage tank 15 (in the embodiment, the mixed working medium is C2C3, namely the mixture of ethane and propane) is pressurized to 1.1MPa by a mixed working medium booster pump 16, the temperature is increased to-60 ℃, then the liquid C2C3 passes through a mixed working medium reheater 17, is heated to 40 ℃ (gaseous state) by hot water with the temperature of 70 ℃ and normal pressure generated in a flue gas waste heat boiler 21, enters an expansion generator 18 for expansion power generation, is expanded to 0.2MPa, the temperature is reduced to-19 ℃, enters an LNG-mixed working medium heat exchanger 13 for heat exchange, and the temperature is reduced to. The LNG cold energy power generation system can generate about 20kW for 1t of LNG, and the power generation power is 16kW without hot water reheating, so that the LNG cold energy power generation system can improve the LNG cold energy power generation efficiency by about 25%.
In the period of basic load output and non-unloading, the LNG output is 45t/h, the BOG output is 6.12 t/h-6.36 t/h, and at the moment, a gas turbine can be started to burn to recover and burn the BOG, and condensation regasification and compression are not adopted to enter a medium-low pressure pipe network.
During the period of base load export and ship unloading, the LNG export amount is 45t/h, the BOG generation amount is about 23t/h, 6.56t/h of BOG can be treated by condensation and regasification, two gas turbines are started to burn at the moment to recover the BOG (12t/h), and the residual 4.44t/h of BOG is treated by compressing and retracting a pipe network.
During the peak load-shifting period and the non-unloading period, the LNG load-shifting amount is increased to 585t/h, the BOG production amount is about 44t/h, and 20t/h of BOG can be treated by condensation and regasification. At the moment, two gas turbines can be started to recover and burn the BOG for power generation and start a BOG condensation and regasification system, and the remaining 12t/h of BOG is compressed and enters a medium-low pressure pipe network.
During peak-shaving export and ship unloading periods, the LNG export amount is increased to 585t/h, the BOG production amount is 60.39-63.46 t/h, at the moment, two gas turbines can be started at full load to recover, burn and generate power for BOG, a BOG condensation regasification system, a BOG direct compression export system and a BOG cogeneration system are started, hot water is generated by residual BOG combusted smoke through the smoke waste heat boiler 21 and is used for reheating mixed working media in the LNG cold energy power generation process, and the LNG cold energy power generation efficiency is improved by about 25%.
The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.