CN108151442A - Low-temperature preparation system for L NG in raw material gas - Google Patents

Abstract

The invention relates to the field of gas purification and gas liquefaction, and provides a low-temperature preparation system for LNG in raw gas, which includes an inlet pipe and an LNG storage tank, and also includes a refrigeration assembly and a first rectification tower, and the refrigeration assembly includes a first heat exchanger , the inlet pipe communicates with the feed inlet of the first rectification tower, the feed gas exchanges heat with the first heat exchanger through the inlet pipe, the gas outlet of the first rectification tower communicates with the LNG storage tank through the outlet pipe, and the first rectification tower The distilled gas passes through the outlet pipe to exchange heat in the first heat exchanger, and the bottom distillate of the first rectification tower leads to the carbon dioxide collection box. In the present invention, the raw material gas enters the first heat exchanger through the inlet pipe for heat exchange and cooling, and the carbon dioxide and methane in the raw material gas are fractionated in the first rectification tower, and the purified biomass natural gas is output from the top of the tower kettle , and collected to the LNG storage tank through the outlet pipe, the whole process can not only separate the carbon dioxide in the raw gas, but also produce LNG, the whole process has high production efficiency and good economy.

Description

Low temperature production system of LNG in raw gas

technical field

The invention relates to the fields of gas purification and gas liquefaction, in particular to a low-temperature preparation system for LNG in raw material gas.

Background technique

Natural gas containing carbon dioxide exists widely. Before the liquefaction of natural gas raw material gas, carbon dioxide must be removed to avoid blockage of heat exchangers and pipelines by dry ice formed by carbon dioxide at low temperature.

In particular, for biogas, biogas consists of 50%-80% methane (CH4), 20%-40% carbon dioxide (CO2), 0%-5% nitrogen (N2), less than 1% hydrogen (H2), less than 0.4% Oxygen (O2) and 0.1%-3% hydrogen sulfide (H2S) and other gases. Since the carbon dioxide contained in biogas accounts for a large proportion of components, the combustion calorific value of biogas is significantly lower than that of natural gas, which greatly limits the application scenarios of biogas. In the field of biogas purification to produce natural gas from biomass, the high carbon dioxide content leads to high removal cost, which leads to the lack of economically feasible utilization means for the current large amount of biogas, resulting in waste of resources and environmental pollution. Purifying biogas to produce LNG (liquefied natural gas) is a potential biogas gathering and transportation mode. Under the current technical level and conditions, the conventional method is to first remove the carbon dioxide in the biogas to produce pure biological natural gas, and then pass Refrigeration to produce LNG, this mode has the problem of high cost and poor economy.

Contents of the invention

The purpose of the present invention is to provide a low-temperature production system of LNG in raw gas, which aims to solve the problem of high production cost of LNG in biogas.

The present invention is achieved like this:

An embodiment of the present invention provides a low-temperature production system for LNG in raw gas, which includes an inlet pipe and an LNG storage tank, and also includes a refrigerated refrigeration component and a first rectification tower that can separate components. The refrigeration component includes the first A heat exchanger, the inlet pipe communicates with the feed port of the first rectification tower, the raw material gas exchanges heat in the first heat exchanger through the inlet pipe, and the gas outlet of the first rectification tower It communicates with the LNG storage tank through a gas outlet pipe, and the distillate gas of the first rectification tower exchanges heat in the first heat exchanger through the gas outlet pipe, and the bottom distillation of the first rectification tower The outlet liquid leads to the carbon dioxide collection tank.

Further, it also includes a BOG cold energy collection channel, through which the BOG gas discharged from the LNG storage tank exchanges heat in the first heat exchanger through the BOG cold energy collection channel.

Further, it also includes a second rectification tower, the distilled gas from the first rectification tower is cooled and enters the second rectification tower for secondary rectification, and the gas outlet of the second rectification tower passes through the The gas outlet pipe communicates with the LNG storage tank.

Further, the distillate gas from the first rectification tower exchanges heat in the first heat exchanger before entering the second rectification tower.

Further, the bottom distillate of the second rectification tower is guided to the first heat exchanger for heat exchange.

Further, the gas generated after the heat exchange of the distillate from the second rectification tower is transported to a gas generator for combustion and power generation, or is pressurized and reintroduced into the inlet pipe for secondary treatment or natural gas is merged into the pipe. net or produce CNG.

Further, it also includes a refrigerated second heat exchanger, the overhead distillate gas of the first rectification column is partially condensed in the second heat exchanger and refluxed to the first rectification column as an overhead reflux liquid. Distillation tower, the feed gas passing through the second heat exchanger enters the first heat exchanger for heat exchange.

Further, it also includes a carbon dioxide discharge pipe connected at one end to the bottom of the first rectification tower, and the other end of the carbon dioxide discharge pipe is connected with two branch pipes, one of which is connected to the liquid carbon dioxide collection tank, and the other is connected to the liquid carbon dioxide collection tank. The carbon dioxide in one of the branch pipes exchanges heat in the first heat exchanger.

Further, a heat supply unit is connected in series at the rear side of the condenser of the refrigeration assembly along the direction of the refrigerant flow path, and the heat supply unit supplies heat to the first rectification column by extracting the refrigeration medium of the refrigeration assembly or through The heat transfer cycle transfers heat to the first rectification column.

The present invention has the following beneficial effects:

In the production system of the present invention, the raw material gas enters the first heat exchanger through the inlet pipe for heat exchange and cooling, so that the gas-liquid two-phase fluid is in the inlet pipe, and it is transported to the first rectification tower. The distillation tower fractionates the carbon dioxide and methane in the raw gas through the principle and technology of low-temperature rectification, and the purified biomass natural gas is output from the top of the tower still, and is collected into the LNG storage tank through the gas outlet pipe, and the first rectification tower The distillate gas enters the first heat exchanger through the gas outlet pipe, that is, the separated natural gas can be cooled again through the first heat exchanger, and the liquid carbon dioxide is output from the bottom of the tower, which can be collected into the liquid carbon dioxide collection tank. Through the above-mentioned working method, not only can the carbon dioxide in the raw material gas be separated, but also LNG can be produced. The production efficiency of the whole process is high and the economy is relatively good.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is a schematic structural diagram of a low-temperature production system for LNG in raw gas provided by an embodiment of the present invention;

Fig. 2 is a structural schematic diagram of the low-temperature production system of LNG in the feed gas of Fig. 1 using a heating unit to supply heat to the first rectification tower;

Fig. 3 is the structure schematic diagram of the second rectification tower set in the low-temperature production system of LNG in the feed gas of Fig. 1;

Fig. 4 is a schematic structural view of the second rectification tower of the low-temperature production system of LNG in the feed gas of Fig. 1 provided with an exhaust pipe;

Fig. 5 is a schematic structural view of the low-temperature production system of LNG in the feed gas of Fig. 1 provided with a second heat exchanger;

FIG. 6 is a schematic structural view of the low-temperature production system of LNG from raw material gas in FIG. 1 provided with a carbon dioxide discharge pipe.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Referring to Fig. 1 and Fig. 2, an embodiment of the present invention provides a low-temperature production system for LNG in raw gas, including an inlet pipe 1 and an LNG storage tank 2, wherein the inlet pipe 1 is used to introduce raw gas, and the raw gas is mainly Biogas (water and hydrogen sulfide and other impurities have been removed), the LNG storage tank 2 is used to store the LNG separated from the raw gas, and the production system also includes a refrigeration unit 3 and a first rectification tower 4. The refrigeration unit 3 is used for The first rectification tower 4 achieves the purpose of gas-liquid separation through low-temperature distillation technology, wherein the refrigeration assembly 3 is mainly composed of a compressor 31, a condenser 32, a first heat exchanger 33, a throttling member 34 or an expansion The machine and pipeline form a circulation loop. The refrigerant medium is compressed into a high-temperature and high-pressure gas in the compressor 31, cooled to normal temperature by the condenser 32, then input to the first heat exchanger 33 and cooled to a low temperature, and then passed through the throttling member 34 or Expansion work becomes a low-temperature and low-pressure medium, and the cold energy is released in the first heat exchanger 33 to cool the high-pressure refrigerant medium in the form of heat recovery. The first rectification column 4 includes the bottom of the tower and the bottom of the tower. bottom, and the bottom of the tower kettle is connected with the bottom of the tower, the top of the bottom of the tower is connected with the tower kettle, and the purpose of low-temperature distillation can be achieved through the heating part of the tower kettle, the inlet pipe 1 is connected with the tower kettle, and the feed gas passes through the inlet pipe 1 at The first heat exchanger 33 exchanges heat, the gas outlet of the tower still communicates with the LNG storage tank 2 through the gas outlet pipe 5, and the distilled gas of the first rectification tower 4 enters the first heat exchanger 33 through the gas outlet pipe 5, and in addition The bottom of the first rectification tower 4 is connected with a liquid carbon dioxide collection box 41, which can collect liquid carbon dioxide. In the present invention, after the raw material gas is introduced into the intake pipe 1, and after the first heat exchanger 33 is heat exchanged and refrigerated, the temperature of the raw gas decreases, and the carbon dioxide phase changes into a liquid state, that is, the tower still introduced into the first rectifying tower 4 is Gas-liquid two-phase fluid, the first rectification tower 4 fractionates the carbon dioxide and methane in the feed gas through the low-temperature rectification principle and technology, and the gas outlet of the tower kettle of the first rectification tower 4 outputs purified biomass natural gas , the liquid carbon dioxide is output from the bottom of the tower and is collected into the liquid carbon dioxide collection tank 41, and the biomass natural gas is input into the first heat exchanger 33 through the gas outlet pipe 5, and the LNG that is further refrigerated into a lower temperature is exported to the LNG storage tank 2, and the LNG storage tank 2. Receive and store liquefied LNG. Generally, a valve should be installed on the gas outlet pipe 5 to control the on-off of the gas outlet pipe 5 . In the above process, not only can the carbon dioxide in the raw material gas be separated, but also LNG can be produced. The whole process has high production efficiency and good economy. Usually, the production system also includes a BOG (flash evaporator) collection tank 6, the BOG collection tank 6 communicates with the LNG storage tank 2 through an air duct 61, and the BOG in the LNG storage tank 2 passes through the air duct 61 to exchange heat with the first device 33. In this embodiment, a BOG collection tank 6 is added, so that the BOG in the LNG storage tank 2 can be collected into the BOG collection tank 6 through the air duct 61, and the BOG in the air duct can be recovered when passing through the first heat exchanger 33 cold energy. In addition, for the low-temperature rectification technology of the first rectification tower 4, the refrigeration assembly 3 can be used to supply heat. Specifically, a heat supply unit 35 is connected in series behind the condenser 32 of the refrigeration assembly 3 along the direction of the refrigerant flow path, and The heat supply unit 35 can supply heat to the first rectification tower 4 by extracting the refrigeration medium of the refrigeration assembly 3 or transfer heat to the first rectification tower 4 through a heat transfer cycle. For the heat transfer cycle, the load is mainly driven by a pump. The heat medium absorbs heat at the bottom heat supply structure 42 of the first rectification tower 4 , and then releases heat in the bottom bottom of the first rectification tower 4 .

Referring to Fig. 3, optimize above-mentioned embodiment, preparation system also includes the second rectifying tower 7, the gas outlet of the first rectifying tower 4 is communicated with the bottom of the second rectifying tower 7, the second rectifying tower 7 The gas outlet communicates with the LNG storage tank 2 through the gas outlet pipe 5 . In this embodiment, a second rectification tower 7 is added on the flow path between the first rectification tower 4 and the LNG storage tank 2, and the structure and function of the second rectification tower 7 and the first rectification tower 4 are similar, The three are connected in series in sequence, and the biomass natural gas purified by the first rectification tower 4 is introduced into the second rectification tower 7 for rectification again, which can remove carbon dioxide at a deeper level and obtain purer biomass natural gas for export to the outlet. In the air pipe 5 , LNG is produced after heat exchange and cooling by the first heat exchanger 33 , and is collected into the LNG storage tank 2 .

Referring to FIG. 4 , to continue optimizing the above embodiment, the biomass natural gas exported from the first rectification tower 4 is first led to the first heat exchanger 33 to continue refrigeration, and then led to the second rectification tower 7 after reaching a lower temperature. An exhaust pipe 71 is connected to the bottom of the second rectification tower 7 , and the distillate gas from the second rectification tower 7 is introduced into the first heat exchanger 33 through the exhaust pipe 71 for heat exchange. Usually, most of the carbon dioxide is separated in the first rectification tower 4, and then the liquid discharged from the bottom of the second rectification tower 7 is rich in methane, and the carbon dioxide content is relatively low, and the liquid is discharged through the exhaust pipe 71, And when passing through the first heat exchanger 33 , the liquid methane is transformed into a gaseous state through the heat exchange effect of the first heat exchanger 33 . The gas discharged from the exhaust pipe 71 can be effectively utilized according to needs, for example, it can be transported to a gas generator for combustion and power generation; or after being increased, it can be imported into the intake pipe 1 in parallel, and then introduced into the first rectification tower in sequence through the intake pipe 1 4 Carry out rectification and collection again; or the produced natural gas can be incorporated into the gas plant or CNG (compressed natural gas) can be produced, so that the utilization rate of methane in the raw gas can be improved.

Referring to Fig. 5, further, in another embodiment, the production system also includes a second heat exchanger 8, the second heat exchanger 8 is also used for refrigeration, and the distillate gas from the first rectification tower 4 passes through the outlet The air pipe 5 is inside the second heat exchanger 8 . In this embodiment, the biomass natural gas separated from the first rectification tower 4 is first refrigerated by the second heat exchanger 8 to obtain a lower temperature, then enters the first heat exchanger 33 for heat exchange and refrigeration again, and finally leads to Collected in LNG storage tank 2. In addition, for the structure of the second heat exchanger 8, the second heat exchanger 8 is also provided with a liquid guide pipe, and the liquid guide pipe communicates with the gas outlet pipe 5 and the tower still of the first rectification tower 4. The top of the rectification tower 4 forms a reflux effect, and the purified biomass natural gas vapor is output from the top of the first rectification tower 4, and enters the second heat exchanger 8 at the top of the tower, and the second heat exchanger 8 is supplied by an external cooling medium. cold, or extract a cold fluid from the first heat exchanger 33 for cooling, steam is partially condensed into liquid in the second heat exchanger 8 and returns to the bottom of the first rectification tower 4, and other steam enters the first heat exchanger 33, further freezing and liquefaction into LNG.

Referring to Fig. 6, further, in another embodiment, the production system also includes a section of carbon dioxide discharge pipe 9 connected to the bottom of the first rectification tower 4, and the other end of the carbon dioxide discharge pipe 9 is connected with two branch pipes 91 , one of the branch pipes 91 is connected to the liquid carbon dioxide collection tank 41 , and the other branch pipe 91 passes through the first heat exchanger 33 . In this embodiment, the liquid carbon dioxide output from the bottom of the first rectification tower 4 can be utilized as required. For example, the liquid carbon dioxide can be exported through one of the branch pipes 91 to prepare dry ice, and can also be discharged through another branch pipe 91. During the discharge process, the liquid carbon dioxide enters the first heat exchanger 33 to recover cold energy, and the liquid carbon dioxide phase changes into gaseous carbon dioxide, which can be used to prepare gaseous carbon dioxide products. Of course, each branch pipe 91 should be provided with a valve, through which the on-off of the corresponding branch pipe 91 can be controlled, and then the corresponding branch pipe 91 can be selected to be opened as required.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (9)

1. a kind of system that unstripped gas purifies and produces LNG, including air inlet pipe and LNG storage tank, it is characterised in that：Further including can The cooling assembly of refrigeration and can component separation first rectifying column, the cooling assembly include First Heat Exchanger, the air inlet Pipe is connected with the first rectifying column feed inlet, and unstripped gas is exchanged heat by the air inlet pipe in the First Heat Exchanger, and described the The gas outlet of one rectifying column is connected with the LNG storage tank by air outlet pipe, the first rectifying column distillate gas pass through it is described Air outlet pipe exchanges heat in the First Heat Exchanger, and the bottom of towe distillate of the first rectifying column leads to carbon dioxide collection case.

2. the system that unstripped gas as described in claim 1 purifies and produces LNG, it is characterised in that：Further include the collection of BOG colds Channel, the interior BOG gases discharged of the LNG storage tank are exchanged heat by the BOG colds collection channel in the First Heat Exchanger.

3. the system that unstripped gas as described in claim 1 purifies and produces LNG, it is characterised in that：Further include Second distillation column, The first rectifying column distillates gas and enters the secondary rectifying of Second distillation column progress after cooling, the Second distillation column Gas outlet is connected by the air outlet pipe with the LNG storage tank.

4. the system that unstripped gas as claimed in claim 3 purifies and produces LNG, it is characterised in that：The first rectifying column Gas is distillated to exchange heat in the First Heat Exchanger before into the Second distillation column.

5. the system that unstripped gas as claimed in claim 3 purifies and produces LNG, it is characterised in that：The Second distillation column Bottom of towe distillate is directed in the First Heat Exchanger and exchanges heat.

6. the system that unstripped gas as claimed in claim 5 purifies and produces LNG, it is characterised in that：The Second distillation column evaporates Go out the gas that generates after liquid heat exchange be delivered to gas electricity generator carry out combustion power generation or by be pressurized and again row import described in into Tracheae carries out after-treatment or produces natural gas and be incorporated to pipe network or produce CNG.

7. the system that unstripped gas as described in claim 1 purifies and produces LNG, it is characterised in that：Further include can freeze Two heat exchangers, the tower top distillate gas of the first rectifying column condense in the second heat exchanger inside points and are used as overhead reflux liquid The first rectifying column is back to, the unstripped gas through second heat exchanger, which enters in the First Heat Exchanger, to exchange heat.

8. the system that unstripped gas as described in claim 1 purifies and produces LNG, it is characterised in that：Further include one end with it is described The carbon dioxide exhaust line of the bottom of towe connection of first rectifying column, the carbon dioxide exhaust line other end are connected there are two branch pipe, Wherein one branch pipe connects the liquid carbon dioxide collecting box, and the carbon dioxide in another branch pipe is changed in described first It exchanges heat in hot device.

9. the system that unstripped gas as described in claim 1 purifies and produces LNG, it is characterised in that：Along refrigerant flow direction in It is in series with heating unit on rear side of the condenser of the cooling assembly, the heating unit is by extracting the refrigeration of the cooling assembly Medium is to the first rectifying column heat supply or passes through heat-carrying circulating heat transfer to the first rectifying column.