CN102226627B - Equipment and process for liquefying and separating coal bed methane - Google Patents

Abstract

The invention belongs to the field of liquefaction and separation of mixed gas, and in particular relates to a liquefaction and separation equipment and process for coal bed gas, especially low CH ₄ gas content coal bed gas. The liquefaction and separation process of the present invention independently liquefies and separates CO ₂ and CH ₄ successively by controlling the cooling temperature step by step, avoiding the problem that _{CO 2 is} first liquefied or even sublimated in the process of CH liquefaction to block equipment. It not only solves the potential safety hazard in the coalbed methane mining process, but also collects pure CH ₄ , which can be used for other industrial applications.

Description

Equipment and process for liquefaction and separation of coal bed gas

technical field

The invention belongs to the field of liquefaction and separation of mixed gas, and in particular relates to a liquefaction and separation equipment and process for coal bed gas, especially low CH ₄ gas content coal bed gas.

Background technique

Coalbed methane, commonly known as "gas", is an unconventional natural gas associated with coal and stored in the coal seam in an adsorbed state. Its calorific value is 2-5 times that of general-purpose coal, and its main component is methane. There are two extraction methods for coalbed methane: one is surface extraction, which has high methane purity (about 98%) and high utilization value. It can be directly pressurized for pipeline network transportation, and can also be directly liquefied for storage and transportation. But much more widely is extraction under mines where coal mining is already in production. The methane content of coalbed methane extracted in this way is relatively low, usually between 30% and 70%. The main purpose of coal mining in my country has always been coal mining, and the drainage of coal bed methane (gas) is only carried out for the requirements of coal mine safety production. Separating and purifying methane from mine coalbed methane is of great significance for expanding and improving the effective utilization rate and economic value of coalbed methane. However, my country's coalbed methane has the characteristics of huge quantity, scattered production areas, small scale of single well, low gas concentration and oxygen content in underground extraction. Generally, there is no other effective way of utilization except for nearby use, and the situation of venting and waste is very serious. If the methane and air in coalbed methane are separated and the purified methane is liquefied and filled, it will greatly facilitate transportation and utilization.

At present, the methods that can be applied to the separation and purification of methane from coalbed methane generally include low-temperature liquefaction separation, pressure swing adsorption and membrane separation, each of which has its own characteristics and application range. However, for processes such as pressure swing adsorption and membrane separation, it is necessary to pressurize the raw material gas in the separation process, which obviously expands the explosive concentration range of coalbed methane. , safety issues must be considered in all separation techniques.

According to the combustion theory, when combustible gases such as methane explode in the air, there is a minimum explosion oxygen concentration, and the corresponding point is called the critical point of explosion, which forms a triangle with the upper and lower limit concentration points of the explosion of combustible gases, usually called It is the Coward explosion triangle, when the concentration range of the mixture is within the explosion triangle, the system is very likely to explode.

As shown in Figure 1, area Ⅰ is an explosion triangle area; area Ⅱ is an oxygen-deficient area, that is, adding oxygen (air) can explode; area Ⅲ is a low-methane area, that is, increasing methane can explode; area Ⅳ is a safe area, where no explode. At normal temperature and pressure, the concentration range of methane mixed with air is 5%-15%. This range will change with the change of pressure and temperature, and both the increase of temperature and the increase of pressure will expand the range of explosive concentration. Separation and purification of methane from mine coalbed methane (a mixture of air and methane), no matter how high the methane concentration in the initial mixture is, as the separation of methane decreases, it will pass through the explosive concentration range in the system, which is very important for any separation and purification systems are very dangerous. Therefore, in the process of processing coalbed methane, it is necessary to always consider possible safety issues and control the content of methane and air to achieve absolute safety in the mining process.

Chinese patent CN100404988C discloses a process and equipment for the liquefaction and separation of air-containing coalbed methane. The process described in the patent first cools the preliminarily treated coalbed methane and passes it into the middle of the fractionation tower. The condensation of the condenser, the gas fraction and the liquid fraction in the tower are fully exchanged in quality and heat, and high-purity nitrogen is obtained at the top of the fractionation tower, and high-purity liquid natural gas is obtained at the bottom of the fractionation tower. A part of clean air is drawn between the coal bed gas inlets and passed into the heat exchanger. The entire liquefaction and separation steps in this process are carried out under low temperature conditions, with high separation purity and good safety performance. Liquefied natural gas can be produced at the same time as separation, which not only avoids air pollution caused by emissions, but also effectively utilizes air coalbed methane resources.

However, the liquefaction process described in this patent also has certain defects: in the process of condensing and liquefying air-containing coalbed methane, the temperature is directly lowered to the liquefaction temperature of methane -168°C. At this time, methane is liquefied, but other gases such as O ₂ and N ₂ are still in gaseous state, although methane can be separated, but because the air contains some CO ₂ , and CO ₂ has been liquefied or even directly condensed into solid dry ice at -168°C, it is easy to block the fractionation tower and affect the fractionation effect. Obviously, this scheme does not take into account the adverse effects of this potential factor, which may easily lead to incomplete separation of methane and oxygen, and there are still safety problems. On the other hand, this scheme first lowers the temperature of the coalbed methane as a whole, so that part of the gas is liquefied and then passed into the fractionation tower, and then uses evaporation and condensation to exchange mass and heat to achieve the purpose of separation. This scheme consumes a lot of energy, and there is obviously a waste of resources. question.

Chinese patent CN101270952A discloses an air recovery type mine gas separation and liquefaction method and equipment. The patent first compresses and purifies the mine gas raw material gas, removes impurities in the raw material gas, and obtains compressed and purified mine gas; The mine gas is passed into the heat exchanger to cool the temperature below -82.5°C; the cooled mine gas is passed into the middle of a fractionation tower, and high-purity low-temperature gas is obtained at the top of the fractionation tower, and at the bottom of the fractionation tower High-purity liquefied natural gas is obtained; the low-temperature air sorted out from the top of the fractionation tower is introduced into a heat exchanger as a refrigerating gas to recover cooling capacity. The scheme described in this patent adopts the method of air reheating, which reduces energy consumption and reduces costs.

However, in the scheme described in the patent, the purpose of first cooling the coalbed methane raw material gas to below -82.5°C is mainly to reduce the required cooling energy consumption by means of gradient cooling and supplemented by cold air recirculation, but there is still no Consider the problem that CO ₂ will liquefy or even turn into solid dry ice to block equipment during the cooling process, and because the cooling process at this time is carried out in a heat exchanger, even considering the possible CO ₂ liquefaction problem, it is still could not be resolved.

Contents of the invention

For this reason, the technical problem to be solved by the present invention lies in the problem of incomplete gas separation caused by _CO2 blockage of equipment during the coalbed gas liquefaction and separation process in the prior art, and further provides a liquefaction separation equipment with better separation effect and energy saving.

Further, the present invention also provides a process for the liquefaction separation process.

In order to solve the above-mentioned technical problems, the equipment for coalbed methane liquefaction and separation according to the present invention includes sequentially connected:

Compression and purification equipment: used to pretreat the coalbed methane raw material gas;

Multiple series-connected cold separators: the primary cold separator cools the incoming coalbed methane raw material gas, so that the gas with the lowest boiling point is liquefied and collected, and other unliquefied gases enter the latter stage cold separator, and continue to condense the remaining mixed gas The gas with the lowest boiling point is liquefied and collected; the temperature controlled by the cold separator in the latter stage is lower than the temperature controlled by the cold separator in the upper stage; the liquefied product in the cold separator in the latter stage is input to any one of the front In the cold separator of the first stage, it is used as a cold medium fluid to exchange cooling capacity; the unliquefied gas in the cold separator of the last stage is re-introduced into the cold separator of the previous stage as a cold medium fluid to exchange cold capacity; The cold divider of the stage controls the temperature through the auxiliary refrigeration equipment.

There are also heat exchangers adapted to it in series before the cold separators at each level;

The coal bed gas enters the heat exchanger for pre-cooling and cooling before entering the cold separators at all levels;

The liquid collected in the cold separators of each stage is re-introduced into the heat exchanger adapted to it as a cold medium fluid for exchanging cooling capacity.

The cold divider is equipped with:

Cold medium channel: the cold medium fluid is input into the cold medium channel, which is used to provide the cooling capacity required for the cooling and liquefaction of the coalbed gas;

Heat exchange device: the heat exchange device includes a heat exchange chamber, the lower part of the heat exchange chamber is connected with a coalbed methane input pipeline and a liquefied product discharge pipeline, and its upper part is connected with a spiral exhaust pipe. The flow direction of the coalbed gas is opposite to the flow direction of the cold medium fluid in the cold medium channel.

The coalbed methane is input into the heat exchange device to exchange mass and heat with the cold medium fluid in the cold medium channel, so that the coalbed methane is cooled and cooled, and after heat exchange, the gas with the lowest boiling point in the coalbed methane is realized Liquefaction to achieve separation from other gas components; the liquefied liquid in the coalbed methane is discharged through the liquefied product discharge pipeline, and other unliquefied gas is discharged through the exhaust pipeline.

The heat exchange chamber is also provided with a tray 6, the tray 6 is arranged on the upper part of the heat exchange chamber, and the tray 6 is provided with through-flow holes, and the coal bed gas and the liquefied liquid are in the Gas-liquid heat exchange is carried out at the above-mentioned tray 6.

The heat exchange chamber also includes a drain plate and a liquid collector arranged below the tray 6, the liquefied liquid enters the liquid collector through the drain plate, and the liquefied product discharge pipe is the same as the liquid collector bottom connection.

The device also includes a liquid level sensor for controlling the liquid level of the liquid collector, and the discharge volume is adjusted by controlling a valve arranged on the liquefied product discharge pipeline.

The cold separators at each stage are also equipped with an auxiliary refrigeration system, which is used to compensate the cooling capacity required for the liquefaction of the coal bed gas.

The auxiliary refrigeration system is a gas expansion refrigeration system or a mixed refrigerant refrigeration system.

The outside of the cold divider is covered by a polyurethane insulation layer.

The cold separator includes a _{CO cold} separator capable of liquefying CO and a CH _cold separator capable of liquefying CH that are connected in sequence, and the heat exchanger includes a CO _cold separator and a _CH cold separator respectively connected to each other. The primary heat exchanger and secondary heat exchanger adapted to the _CH cold separator; the gas channels of the primary heat exchanger are respectively connected to the output pipeline of the purification compression equipment and the coal seam of the _CO cold separator The gas input pipeline is connected, the first cold medium passage of the _CO2 cold separator is connected with the first cold medium passage of the primary heat exchanger, and the second cold medium passage of the _CO2 cold separator is connected with the The auxiliary refrigeration system is connected, the gas channel of the secondary heat exchanger is respectively connected with the exhaust pipe of the _CO2 cold separator and the coalbed gas input pipeline of the _CH4 cold separator, and the secondary heat exchanger The cold medium channel of the heater communicates with the exhaust pipe of the CH ₄ cold separator and the first cold medium channel of the CO ₂ cold separator respectively, and the cold medium channel of the CH ₄ cold separator communicates with the auxiliary Refrigeration system connection;

The liquid collector of the _CO2 cold separator and the liquid collector of the _CH4 cold separator communicate with the first cold medium passage and the second cold medium passage of the primary heat exchanger through the liquefied product discharge pipe respectively .

The control temperature of the CO ₂ cold separator is -85~-80°C; the control temperature of the CH ₄ cold separator is -170~-160°C.

The invention also discloses a coalbed gas liquefaction separation process, which includes the following steps:

(1) Pretreatment of raw gas: purify the raw gas of coalbed methane and compress it at low pressure to remove water vapor, dust and sulfur-containing substances contained in coalbed gas;

(2) Liquefaction and separation of CO ₂ : the pretreated CBM is pre-cooled by the primary heat exchanger, and then passed into the CBM input pipeline at the bottom of the CO ₂ cold separator, and continues to cool down to -85~-80°C. Make the coalbed methane reach the liquefaction temperature of _CO2 , liquefy the _CO2 in it, and collect the liquefied _CO2 liquid at the same time, and other unliquefied coalbed gas components continue through the exhaust pipe at the top of the _CO2 cooler into the secondary heat exchanger;

( ₃ ) Liquefaction and separation of CH : the _coalbed methane separated from CO is passed into the secondary heat exchanger for pre-cooling, and then passed into the coalbed gas input pipeline at the bottom of the CH ₄ cold separator, and the auxiliary refrigeration system continues to force cooling Lower the temperature to -170~-160°C, so that the coalbed methane reaches the liquefaction temperature of CH ₄ , liquefy the CH ₄ in it, and collect the liquefied CH ₄ at the same time; other unliquefied coalbed gas components are cooled by the CH ₄ Exhaust pipe at the top of the distributor;

(4) Treatment of O ₂ and N ₂ : the unliquefied O ₂ and N ₂ in the coal bed gas are passed into the secondary heat exchanger as a cold medium fluid to exchange cooling capacity or to be emptied.

In the step (2), the collected CO ₂ is introduced into the first cold medium passage of the primary heat exchanger for cold exchange.

In the step (3), the collected CH ₄ is introduced into the second cold medium channel of the primary heat exchanger for heat exchange and used as power energy for other equipment.

In the step (4), unliquefied O ₂ and N ₂ are sequentially passed into the cold medium passage of the secondary heat exchanger, the first cold medium passage of the CO ₂ cold separator and the cold medium fluid as the cold medium fluid. Exchange cooling capacity through the first cold medium channel of the primary heat exchanger.

The cooling and cooling of the primary heat exchanger, secondary heat exchanger, _CO2 cold separator and _CH4 cold separator are controlled by an auxiliary refrigeration system.

Compared with the prior art, the above-mentioned technical solution of the present invention has the following advantages: 1. The cold divider of the present invention is provided with a hot medium channel and a cold medium channel at the same time, and the hot medium channel and the cold medium channel spiral in a spiral shape Arrangement, so that the cold gas can directly exchange heat with the coalbed methane through the cold medium channel, and the temperature can be lowered in the cold separator without deliberately adding a condenser to provide external cooling. This structure can greatly reduce the external cooling. 2. A page sensor is set in the liquid collection device, and when the liquid reaches a certain height, the valve opens to discharge the collected liquid, while retaining a certain amount of liquid to ensure the unliquefied product 3. The liquefaction separation equipment can select a plurality of cold separator combinations according to the coalbed gas of different components, and only need to control the cooling temperature of different cold separators to separate the substances of each component; 4. The present invention The liquefaction and separation process independently liquefies and separates _CO2 and _CH4 successively by controlling the cooling temperature step by step, avoiding the problem that _CO2 is first liquefied or even sublimated to block the equipment during the _CH4 liquefaction process; 5. Reintroducing the separated and collected liquid CO ₂ and CH ₄ into the cold medium channel of the heat exchanger can save energy; 6. The unliquefied O ₂ and N ₂ can be repeatedly introduced into the cold medium channel of the heat exchanger as the heat exchange medium , save energy.

Description of drawings

In order to make the content of the present invention more easily understood, the present invention will be described in further detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein

Fig. 1 is a schematic diagram of the explosion triangle theory;

Fig. 2 is a schematic diagram of the coalbed gas liquefaction separation process equipment according to the present invention.

The reference signs in the figure are expressed as: 1-compression purification equipment, 2-first-stage heat exchanger, 3-CO ₂ cold separator, 4-secondary heat exchanger, 5-CH ₄ cold separator, 6-tray , 7-liquid level sensor, 8-auxiliary refrigeration system, 9-cryogenic expansion system.

Detailed ways

As shown in Figure 2, the equipment for coalbed methane liquefaction and separation according to the present invention includes sequentially connected:

Compression purification equipment 1: including dust removal equipment, sulfur removal equipment and water removal equipment, used for pretreatment of the coalbed methane raw material gas. The selected dust removal equipment is a water curtain or a return tank; the sulfur removal equipment is a dry alkaline catalyst filter tank or a wet copper sulfate washing tank; the water removal equipment is an organic silica gel adsorption and desorption tank. The coalbed methane only contains gases such as O ₂ , N ₂ , CH ₄ and CO ₂ .

A plurality of series-connected cold separators: the cold separator regulates its own temperature control according to the properties of each component gas in the coalbed methane, so that the various component gases in the coalbed methane are cooled and cooled in the cold separators at each level. get liquefied. The primary cold separator lowers the temperature of the incoming coalbed methane raw material gas, so that the gas with the lowest boiling point is liquefied and collected, and other unliquefied gases enter the subsequent stage of cold separator to continue to liquefy and collect the gas with the lowest boiling point in the remaining mixed gas; The temperature controlled by the cold separator of the first stage is lower than the temperature controlled by the cold separator of the previous stage; the liquefied product in the cold separator of the latter stage is input into the described cold separator of any previous stage as The cold medium fluid exchanges the cooling capacity; the unliquefied gas of the cold separator in the last stage is reintroduced into the cold separator in the upper stage as the cold medium fluid to exchange the cooling capacity; the cold separator in the last stage passes through the auxiliary refrigeration The device controls the temperature.

Multi-stage heat exchangers respectively adapted to the cold separators at each stage: the heat exchanger is connected in series with the cold separators, and the coalbed gas enters the cold separators at each stage before entering the The adapted heat exchanger performs pre-cooling and cooling. At the same time, the liquid collected in the cold separators of each stage is reintroduced into the matched heat exchanger as a cold medium fluid to exchange cold capacity.

The compression and purification equipment is connected to the heat medium channel of the raw material gas of the primary heat exchanger, and the raw material gas of coalbed methane enters the heat exchanger after being purified by the compression and purification equipment, and the heat that enters the cold separator after being cooled is The liquefaction and separation of coalbed methane is carried out in the exchange device, the temperature of the cold medium fluid in the latter stage of cold separator is lower than the temperature of the cold medium fluid in the previous stage of cold separator, and the temperature of the cold medium fluid in each stage of cold separator The fluid promotes the liquefaction of one of the gases in the coalbed methane.

The cold separator is arranged vertically, and the heat medium channel of the heat exchanger adapted to it is introduced into the gas input pipe at the bottom of the cold separator.

The cold divider includes:

Cold medium channel: the cold medium fluid is input into the cold medium channel, which is used to provide the cooling capacity required for the cooling and liquefaction of coalbed methane;

Heat exchange device: the coalbed gas is input into the heat exchange device to exchange heat with the cold medium fluid in the cold medium channel, so that the coalbed gas is cooled and cooled, and after the heat exchange, a gas in the coalbed gas is liquefied. Achieve separation from other gas components;

The heat exchange device includes a heat exchange chamber. The lower part of the heat exchange chamber is connected with a coalbed methane input pipe and a liquefied product discharge pipe, and its upper part is connected with a spiral exhaust pipe. After heat exchange, the coalbed methane The liquefied liquid is discharged through the liquefied product discharge pipe, and the unliquefied gas is discharged through the exhaust pipe;

The cold medium passage has a spiral structure, spirals outside the heat exchange device, and spirals with the spiral exhaust pipe. The flow direction of the coalbed gas in the heat exchange device is the same as that of the cold medium in the cold medium passage. The flow direction of the fluid is opposite, so that the cold gas and the coalbed methane have sufficient contact space for sufficient heat exchange;

The heat exchange chamber is also provided with a tray 6 placed on the upper part of the heat exchange chamber and a drain plate and a liquid collector arranged below the tray 6, and the tray 6 is provided with a flow hole, so that The coalbed gas and the liquefied liquid undergo gas-liquid heat exchange at the tray 6, the liquefied gas enters the liquid collector through the diversion plate, and the liquefied product discharge pipe is the same as that of the liquid collector. The bottom end is connected, and the liquid collection device also includes a liquid level sensor for controlling the liquid level of the liquid collector, and the discharge volume is adjusted by controlling a valve arranged on the liquefied product discharge pipeline.

Auxiliary refrigeration system: when the cooling capacity provided by the refrigerant-containing gas cannot meet the temperature control requirements of the cooler, the auxiliary refrigeration system is used to compensate for the cooling capacity required by the cooler; The auxiliary refrigeration system is a gas expansion refrigeration system or a mixed refrigerant refrigeration system.

When in use, the cold separator needs to be installed vertically, and the coalbed gas enters the cold separator from the bottom of the cold separator to be liquefied. At this time, the liquefied liquid flows downward under the action of its own gravity, and the gas flowing upward Can be fully contacted for mass and heat exchange.

The outside of the cold divider is covered by a multi-layer polyurethane insulation layer to ensure the heat preservation and sealing of the entire cold divider.

The cold separator includes a _CO cold separator 3 that can liquefy _CO and a CH _cold separator ₅ that can liquefy CH that are connected in sequence, and the heat exchanger includes a cold separator that is connected with the _CO respectively. The first-stage heat exchanger 2 and the second-stage heat exchanger 4 that are adapted to the device 3 and the CH ₄ cold separator 5; The coalbed methane input pipeline of the _CO2 cold separator 3 is connected, and the first and second cold medium passages of the _CO2 cold separator 3 are respectively connected with the first cold medium passage of the primary heat exchanger 2 and the Auxiliary refrigeration system 8 is connected, and the gas channel of the secondary heat exchanger 4 is respectively connected with the exhaust pipe of the _CO2 cold separator 3 and the coalbed gas input pipeline of the _CH4 cold separator 5, and the The cold medium channel of the secondary heat exchanger 4 communicates with the exhaust pipe of the CH ₄ cold separator 5 and the first cold medium channel of the CO ₂ cold separator 3 respectively, and the CH ₄ cold separator 5 The cold medium channel communicates with the cryogenic expansion system 9 . The control temperature of the CO ₂ cold separator 3 is -85~-80°C; the control temperature of the CH ₄ cold separator 5 is -170~-160°C.

The liquid collector of the CO ₂ cold separator 3 and the liquid collector of the CH ₄ cold separator 5 communicate with the first and second cold medium passages of the primary heat exchanger through liquefied product discharge pipes respectively.

The _CO2 cold separator 3 is also provided with an auxiliary refrigeration system 8. When the energy provided by _N2 and _O2 to the _CO2 cold separator 3 cannot meet the requirements of the _CO2 liquefaction temperature, the auxiliary refrigeration of the _CO2 cold separator The system 8 is started, and the refrigerant-containing working fluid is passed into the cold medium channel of the CO ₂ cold separator 3 to meet the temperature requirements required by the cold separator.

The temperature in the CH ₄ cold separator 5 must reach the liquefaction temperature of CH ₄ , the temperature is mainly due to the expansion and gasification of the working fluid to absorb the heat energy in the cold separator, so that the temperature in the cold separator drops to reach the liquefaction temperature of CH ₄ . The expansion tube of the cryogenic expansion system 9 surrounds the outside of the condensing tube, and the refrigerant-containing working medium is passed into the cold medium channel to provide the cooling capacity required for the cooling of the CH ₄ cold separator 5, which is used outside the entire system Covered with multiple layers of polyurethane insulation.

Both the _CO2 cold separator 3 and the CH _cold separator 5 contain a liquid collection device 7, and the liquid collection device includes a diversion plate and a liquid collector for guiding flow, and the liquid collector and the liquid storage The gas tank is connected to collect the liquid, or connected to the cold medium channel of the heat exchanger, and used as the cold medium to provide the cooling capacity required by the cold separator.

The liquid collecting device also includes a liquid level sensor for controlling the liquid level of the liquid collector, and the discharge volume is adjusted through a control valve. When the liquid reaches a certain height, the valve opens to discharge the collected liquid, while leaving a certain amount of liquid to ensure the sealing of the unliquefied product body.

The cooling of the primary heat exchanger 2, secondary heat exchanger 4, _CO2 cold separator 3 and _CH4 cold separator 5 is controlled by the refrigeration system.

The coalbed gas liquefaction separation process of the present invention comprises the following steps:

(1) Pretreatment of raw material gas: The raw material gas of coalbed methane is pressurized by Roots pump at low pressure and entered into high-efficiency dust removal, water removal and sulfur removal equipment for purification to remove a large amount of water vapor, dust and sulfur-containing substances in the gas. The selected dust removal equipment is a water curtain or a return tank; the sulfur removal equipment is a dry alkaline catalyst filter tank or a wet copper sulfate washing tank; the water removal equipment is an organic silica gel adsorption and desorption tank. The coalbed methane only contains gases such as O ₂ , N ₂ , CH ₄ and CO ₂ .

(2) Liquefaction and separation of CO ₂ : put the coalbed methane containing residual gases such as O ₂ , N ₂ , CH ₄ , and CO ₂ into the first-stage heat exchanger for cooling and precooling treatment. In this step, the temperature should be controlled so that CO ₂ The temperature of liquefaction. Pass the pre-cooled gas from the bottom into the gas input pipeline of the CO ₂ cold separator installed vertically. The control temperature in the CO ₂ cold separator is -85～-80°C. Since the cold medium channel is spiral It hovers outside the heat exchange chamber and hovers with the exhaust pipe, so the cold energy contained in the cold medium fluid can cool the coal bed gas to -85~-80°C. On the one hand, the auxiliary refrigeration system is used Detect the temperature in the CO ₂ cold separator, and on the other hand, when the cooling capacity of the cooling medium fluid cannot bring the temperature of the coal bed gas to the approved temperature, start the auxiliary refrigeration system, including the refrigerant into the cold medium channel to provide cold energy, and force the temperature of the CO ₂ cooler to drop. Since cooling and cooling is a continuous process, when the mixed gas passes through a long enough helical exhaust pipe during the rising process, at the CO ₂ condensation temperature, the CO ₂ gas begins to liquefy in the exhaust pipe of the cold separator, Condensation on the inner wall of the pipe. Under the double action of updraft disturbance and condensate gravity, _CO2 droplets slide down the wall of the spiral tube, and finally fall into the liquid collector under the spiral tube. Due to the exhaust pipe with sufficient length, all the _CO2 contained in the coal bed gas can be liquefied and collected. The liquid collector is equipped with a liquid level sensor, and when the liquid reaches a certain height, the valve opens to discharge the collected CO ₂ liquid, while leaving a certain amount of liquid to ensure the sealing of the unliquefied product body. The CO ₂ outlet can be connected to the gas storage tank to collect it, or it can be directly connected to the first cold medium channel of the primary heat exchanger to perform primary cooling treatment on the incoming coalbed methane raw material gas, and CO ₂ itself is converted into gas. At this time, the coalbed methane mixture only contains N ₂ , O ₂ and CH ₄ . The cold medium fluid in the cold medium channel of the CO ₂ cold separator is mainly N ₂ and O ₂ discharged from the CH ₄ cold separator.

(3) Liquefaction and separation of CH ₄ : The coalbed methane containing N ₂ , O ₂ , CH ₄ and other gases is passed into the heat medium channel of the secondary heat exchanger for secondary cooling and pre-cooling treatment. The temperature of this part should be controlled at methane The temperature at which liquefaction can occur. Then the pre-cooled coalbed gas is passed into the coalbed gas input pipeline of the vertically arranged _CH4 cold separator from the _bottom , and the control temperature in the _CH4 cold separator is -170～-160°C. The separator is the last-stage cold separator, and there is no cooling gas with lower temperature for cold exchange and cooling. Therefore, the CH ₄ cold separator adopts a cryogenic expansion auxiliary system for forced cooling. The refrigerant containing refrigerant is passed into the cold medium of the CH ₄ cold separator to forcibly lower the temperature of the coal bed gas in it to the approved temperature. Because the cold medium channel spirals outside the heat exchange chamber and spirals with the exhaust pipe, and because cooling is a continuous process, the mixed gas rises through a long enough spiral tube and condenses in CH ₄ At higher temperatures, condensation will form on the inner wall of the spiral tube. Under the dual effects of updraft disturbance and condensate gravity, CH ₄ droplets flow down the wall of the spiral tube, and finally fall into the liquid collector under the spiral tube. A liquid level sensor is installed at the liquid collector to control the opening of the valve to control the outflow of CH ₄ . The purpose is to leave a certain amount of CH ₄ liquid to seal the unliquefied gas. The outlet of CH ₄ can be directly connected to the gas storage tank for filling into liquefied natural gas, or it can be connected to the cold medium channel of the primary heat exchanger to cool down the incoming coalbed methane raw material gas, and at the same time, the CH ₄ liquid is reheated through heat exchange For gas, the gas outlet is directly connected to the gas storage tank for collection or used as power energy for other equipment. The temperature in the CH ₄ cold separator must reach the liquefaction temperature of CH _4. The temperature is mainly due to the expansion and vaporization of the working fluid to absorb the heat energy in the cold separator, so that the temperature in the cold separator drops to reach the liquefaction temperature of CH ₄ . The expansion tube of the cryogenic expansion system is wrapped around the outside of the condenser tube, and the outside of the entire system is covered with polyurethane insulation.

(4) Treatment of O ₂ and N ₂ : The remaining O ₂ and N ₂ can be directly connected to the cold medium channel of the primary heat exchanger and the secondary heat exchanger for heat exchange, and CO ₂ can also be introduced The cold medium channel of the cold separator provides energy for the liquefaction of _CO2 . The temperature of the CO ₂ cold separator mainly depends on the temperature of N ₂ and O ₂ from the CH4 cold separator to meet the liquefaction requirements of CO _2. When the energy provided by N ₂ and O ₂ to the CO ₂ cold separator cannot meet the CO ₂ liquefaction When the temperature is required, the auxiliary refrigeration system of the CO ₂ cold separator will start to meet the temperature requirements of the cold separator. The refrigeration system is a gas expansion refrigeration system or a mixed refrigerant refrigeration system.

Finally, N ₂ , O ₂ and CO ₂ used for exchanging cooling capacity are discharged through the outlet of the primary heat exchanger or collected into the gas storage tank.

The equipment and process for the liquefaction and separation of coalbed methane according to the present invention can also set different stages of cold separators and heat exchangers according to the composition and content of the coalbed methane to be separated, so that the different components in the coalbed methane Liquefaction, separation and collection in turn.

Apparently, the above-mentioned embodiments are only examples for clear description, rather than limiting the implementation. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. And the obvious changes or changes derived therefrom are still within the scope of protection of the present invention.

Claims (16)

1. A coal bed gas liquefaction separation equipment is characterized in that, comprising sequentially connected: Compression and purification equipment (1): used to pretreat the raw material gas of coalbed methane; Multiple series-connected cold separators: the primary cold separator cools the incoming coalbed methane raw material gas, so that the gas with the lowest boiling point is liquefied and collected, and other unliquefied gases enter the latter stage cold separator, and continue to condense the remaining mixed gas The gas with the lowest boiling point is liquefied and collected; the temperature controlled by the cold separator in the latter stage is lower than the temperature controlled by the cold separator in the upper stage; the liquefied product in the cold separator in the latter stage is input to any one of the front In the cold separator of the first stage, it is used as a cold medium fluid to exchange cooling capacity; the unliquefied gas in the cold separator of the last stage is re-introduced into the cold separator of the previous stage as a cold medium fluid to exchange cold capacity; The cold divider of the stage controls the temperature through the auxiliary refrigeration equipment. 2. The equipment for liquefaction and separation of coalbed methane according to claim 1, characterized in that: There are also heat exchangers adapted to it in series before the cold separators at each level; The coal bed gas enters the heat exchanger for pre-cooling and cooling before entering the cold separators at all levels; The liquid collected in the cold separator at each stage is input into the matched heat exchanger as a cold medium fluid to exchange cooling capacity. 3. The equipment for liquefaction and separation of coalbed methane according to claim 1 or 2, characterized in that, the cold separator is provided with: Cold medium channel: the cold medium fluid is input into the cold medium channel, which is used to provide the cooling capacity required for the cooling and liquefaction of the coalbed gas; Heat exchange device: the heat exchange device includes a heat exchange chamber, the lower part of the heat exchange chamber is connected with a coalbed methane input pipeline and a liquefied product discharge pipeline, and its upper part is connected with a spiral exhaust pipe. The flow direction of the coalbed gas is opposite to the flow direction of the cold medium fluid in the cold medium channel. 4. The equipment for liquefaction and separation of coalbed methane according to claim 3, characterized in that: The heat exchange chamber is also equipped with a tray (6), the tray (6) is arranged on the upper part of the heat exchange chamber, and the tray (6) is provided with through-flow holes, and the coal bed gas and The liquefied liquid undergoes gas-liquid heat exchange at the tray (6). 5. The equipment for liquefaction and separation of coalbed methane according to claim 4, characterized in that: The heat exchange chamber also includes a drain plate and a liquid collector arranged under the tray (6), the liquefied liquid enters the liquid collector through the drain plate, and the liquefied product discharge pipe is the same as the collector. Connect to the bottom of the liquid tank. 6. The equipment for liquefaction and separation of coalbed methane according to claim 5, characterized in that: It also includes a liquid level sensor for controlling the liquid level of the liquid collector, and adjusts the discharge volume by controlling a valve arranged on the liquefied product discharge pipeline. 7. The equipment for liquefaction and separation of coalbed methane according to claim 6, characterized in that: The cold separators at each stage are also equipped with an auxiliary refrigeration system, which is used to compensate the cooling capacity required for the liquefaction of the coal bed gas. 8. The equipment for liquefaction and separation of coalbed methane according to claim 7, characterized in that: The auxiliary refrigeration system is a gas expansion refrigeration system or a mixed refrigerant refrigeration system. 9. The equipment for liquefaction and separation of coalbed methane according to claim 8, characterized in that: The outside of the cold divider is covered by a polyurethane insulation layer. 10. The equipment for liquefying and separating coalbed methane according to any one of claims 7-9, characterized in that: The cold separator includes a sequentially connected _CO2 cold separator (3) capable of liquefying _CO2 and a _CH4 cold separator (5) capable of liquefying _CH4 , and the heat exchanger includes a The primary heat exchanger (2) and secondary heat exchanger (4) adapted to the CO ₂ cold separator and the CH ₄ cold separator; the gas channels of the primary heat exchanger (2) are respectively connected to the purification The output pipeline of the compression equipment (1) is connected with the coalbed methane input pipeline of the CO ₂ cold separator (3), and the first cold medium channel of the CO ₂ cold separator (3) is connected with the primary heat exchanger The first cold medium channel of (2) is connected, the second cold medium channel of the CO ₂ cold separator (3) is connected with the auxiliary refrigeration system, and the gas channels of the secondary heat exchanger (4) are respectively It communicates with the exhaust pipe of the CO ₂ cold separator (3) and the coalbed methane input pipe of the CH ₄ cold separator (5), and the cold medium channel of the secondary heat exchanger (4) is connected with the The exhaust pipe of the CH ₄ cold separator (5) communicates with the first cold medium passage of the CO ₂ cold separator (3), and the cold medium passage of the CH ₄ cold separator (5) communicates with the auxiliary Refrigeration system connection; The liquid collector of the CO ₂ cold separator (3) and the liquid collector of the CH ₄ cold separator (5) are respectively connected to the first cooler of the primary heat exchanger (2) through the liquefied product discharge pipeline. The medium channel communicates with the second cold medium channel. 11. The equipment for coalbed methane liquefaction and separation according to claim 10, characterized in that: The control temperature of the CO ₂ cold separator (3) is -85~-80°C; the control temperature of the CH ₄ cold separator (5) is -170~-160°C. 12. A process for liquefying and separating coalbed methane, characterized in that it comprises the following steps: (1) Pretreatment of raw gas: purify the raw gas of coalbed methane and compress it at low pressure to remove water vapor, dust and sulfur-containing substances contained in coalbed gas; (2) Liquefaction and separation of CO ₂ : the pretreated CBM is pre-cooled by the primary heat exchanger, and then passed into the CBM input pipeline at the bottom of the CO ₂ cold separator, and continues to cool down to -85~-80°C. Make the coalbed methane reach the liquefaction temperature of _CO2 , liquefy the _CO2 in it, and collect the liquefied _CO2 liquid at the same time, and other unliquefied coalbed gas components continue through the exhaust pipe at the top of the _CO2 cooler into the secondary heat exchanger; ( ₃ ) Liquefaction and separation of CH : the _coalbed methane separated from CO is passed into the secondary heat exchanger for pre-cooling, and then passed into the coalbed gas input pipeline at the bottom of the CH ₄ cold separator, and the auxiliary refrigeration system continues to force cooling Lower the temperature to -170~-160°C, so that the coalbed methane reaches the liquefaction temperature of CH ₄ , liquefy the CH ₄ in it, and collect the liquefied CH ₄ at the same time; other unliquefied coalbed gas components are cooled by the CH ₄ Exhaust pipe at the top of the separator; (4) Treatment of O ₂ and N ₂ : the unliquefied O ₂ and N ₂ in the coal bed gas are passed into the secondary heat exchanger as a cold medium fluid to exchange cooling capacity or to be emptied. 13. The process of coalbed methane liquefaction and separation according to claim 12, characterized in that: In the step (2), the collected CO ₂ is introduced into the first cold medium passage of the primary heat exchanger for cold exchange. 14. The process of coalbed methane liquefaction and separation according to claim 12, characterized in that: In the step (3), the collected CH ₄ is introduced into the second cold medium channel of the primary heat exchanger for heat exchange and used as power energy for other equipment. 15. The process of coalbed methane liquefaction and separation according to claim 12, characterized in that: In the step (4), unliquefied O ₂ and N ₂ are sequentially passed into the cold medium passage of the secondary heat exchanger, the first cold medium passage of the CO ₂ cold separator and the cold medium fluid as the cold medium fluid. Exchange cooling capacity through the first cold medium channel of the primary heat exchanger. 16. The process of coalbed methane liquefaction and separation according to any one of claims 12-15, characterized in that: The cooling and cooling of the primary heat exchanger, secondary heat exchanger, _CO2 cold separator and _CH4 cold separator are controlled by an auxiliary refrigeration system.

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