JP5669835B2 - Gas separator - Google Patents

Description

  The present invention relates to a gas separation device.

The so-called biogas generated in sewage treatment plants, livestock manure, garbage, and fermenters that produce alcoholic beverages is mainly composed of methane (CH ₄ ) gas and carbon dioxide (CO ₂ ) gas. Thus, highly efficient energy recovery becomes possible, and if carbon dioxide gas is separated and purified, it can be effectively used for various industrial raw materials such as food additives. Biogas has a methane content of approximately 55 to 65% and a carbon dioxide content of approximately 35 to 45%, although it varies depending on the composition of the organic material from which it is generated.

JP 2004-300035 A

  One method for separating and recovering methane and carbon dioxide from biogas is a PSA (Pressure Swing Adsorption) method. When this method is used, biogas is passed through a tower packed with physical adsorbents (molecular sieves) such as synthetic zeolite, activated alumina, ceramics, porous glass, porous resin, etc., and methane is separated and purified. Carbon dioxide and water are adsorbed and desorbed by using the difference in adsorption capacity with respect to the pressure of water. In addition, a plurality of adsorption towers are prepared, and biogas is continuously processed by switching to an adsorption process and a regeneration process, or an adsorption process, a depressurization process, a regeneration process, and a pressure equalization process. However, when regenerating the adsorption tower at normal pressure, it is necessary to use a part of the product gas (for example, about 15 to 20%) as the regeneration gas, and the recovery efficiency is poor.

  In addition to the PSA method, a TSA (Thermal Swing Adsorption) method can be considered. When using this method, a biogas is passed through a tower filled with an adsorbent that supports a chemical adsorption component such as potassium carbonate or amine on a support such as activated carbon or porous resin, and only methane is exhausted. Carbon dioxide and water are adsorbed and desorbed using the difference in adsorption capacity with respect to the temperature of the agent. Also in this case, similarly to the PSA method, a plurality of adsorption towers are prepared and the biogas is continuously processed. In the case of the TSA method, operation at a low pressure is possible, but heat energy is wasted because it is necessary to blow in high-temperature gas or steam for regeneration of the adsorption tower, and also for heating and cooling. Since much time is required, the efficiency is poor.

  In addition, in order to use methane and carbon dioxide separated from biogas as various industrial raw materials for various fuels and food additives, it is necessary to reliably remove impurities such as hydrogen sulfide, ammonia and water contained in biogas. There is. In this case, a high removal rate can be obtained by adopting a high-pressure water washing system using alkaline water, but a large number of various devices are required, and there is a great problem in terms of cost.

  Then, this application makes it a subject to provide the gas separation apparatus which isolate | separates a specific component efficiently from mixed gas, reducing a component apparatus conventionally.

  In order to solve the above problems, in the present application, a plurality of adsorption towers are prepared, and at the time of regeneration, regeneration is performed at a pressure lower than that at the time of adsorption and at an ambient temperature or lower, and the heat transfer tubes of the adsorption tower being adsorbed A heat medium is circulated between the heat transfer tubes of the adsorption tower being regenerated. This heat medium effectively uses the heat of adsorption as the heat of desorption. Further, in order to compensate for the heat shortage necessary for heat radiation and desorption generated by adsorption, the adsorption tower being adsorbed and the adsorption tower being regenerated are exchanged with air outside the tower.

  Specifically, a gas separation device that separates a specific component from a mixed gas composed of a plurality of components, wherein the specific component in the mixed gas is adsorbed, a plurality of adsorption towers including heat transfer tubes, A heat medium circulation path for circulating a heat medium between the heat transfer pipe of the adsorption tower being adsorbed and the heat transfer pipe of the adsorption tower being regenerated among the plurality of adsorption towers, and the heat medium circulation path is at least outside The adsorption heat of the adsorption tower that is higher than the temperature is transferred to the adsorption tower that is being regenerated by the heat medium, and the adsorption tower that is being regenerated is at least lower in pressure than the adsorption tower that is being adsorbed. In addition, regeneration is performed at a temperature lower than the outside air temperature, and heat exchange is performed with the outside air outside the adsorption tower that is being regenerated.

  The specific component to be separated by the gas separation device is a gas composed of components contained in the mixed gas, and is a gas composed of at least components that can be physically adsorbed by the adsorption tower. In the gas separation apparatus, the temperature of the adsorption tower during adsorption becomes higher than the outside air temperature, and the adsorption tower being regenerated is set to regenerate at least at a pressure lower than the adsorption tower during adsorption and below the outside air temperature. . Since the adsorption temperature is higher than the outside air temperature and the regeneration temperature is lower than the outside air temperature, the mixed gas provided from the upper process is continuously operated by operating the adsorption tower and the regeneration tower side by side. The heat generated by the adsorption action can be used as the heat of the desorption action only by circulating the heat medium passing through the heat transfer tubes in the adsorption tower while realizing the typical treatment.

  Here, the heat medium circulating through the heat medium circulation path is a medium capable of transporting the heat of each adsorption tower, and examples thereof include water. Since the adsorption temperature is higher than the regeneration temperature, the heat of adsorption can be transferred by circulating a heat medium between the tower being adsorbed and the tower being regenerated. Further, since the regeneration temperature is lower than the outside air temperature, the heat corresponding to the temperature drop caused by the pressure drop when transitioning from the adsorption state to the regeneration state can be compensated by the heat exchange of the adsorption tower with the outside air. As a result, the heat of adsorption is used without leakage and a heat source is not required. Therefore, it is possible to efficiently separate the specific component from the mixed gas while reducing the number of components compared to the related art.

  The adsorption tower during adsorption may adsorb at least at a temperature higher than the outside air temperature and exchange heat with the outside air outside the adsorption tower during adsorption. According to this, heat dissipation of adsorption heat is promoted, and adsorption performance can be enhanced.

  Further, the mixed gas is biogas, the specific component is carbon dioxide, and the gas separation device removes impurities contained in the biogas upstream of the plurality of adsorption towers. A pretreatment tower may be further provided. Such a mixed gas may contain various impurity components. However, by providing a pretreatment tower for removing impurities on the upstream side of the adsorption tower, carbon dioxide can be produced from biogas without complicating the components. It can be separated efficiently.

  The specific component can be efficiently separated from the mixed gas while reducing the number of components compared to the conventional one.

It is a lineblock diagram of the biogas separation recovery system concerning an embodiment. It is a block diagram of the biogas isolation | separation collection system which concerns on a modification.

  FIG. 1 is a configuration diagram of a biogas separation and recovery system 1 (corresponding to a gas separation device in the present invention) 1 according to an embodiment. The biogas separation and recovery system 1 according to the present embodiment separates and recovers methane, carbon dioxide, water, and the like from so-called biogas generated in a sewage treatment plant, livestock manure, garbage, fermenters that produce alcoholic beverages, and the like. Then, the separated methane is sent out as various fuel gases, and the separated carbon dioxide is sent out as a raw material for industrial gas such as food additives. The biogas processed by the biogas separation and recovery system 1 according to the present embodiment assumes that the methane content is approximately 55 to 65% and the carbon dioxide content is approximately 35 to 45%. . Note that the biogas separation system 1 according to the present embodiment is not applied only to such biogas separation. For example, the present invention can be applied to a case where carbon dioxide, water, etc. are separated and recovered from combustion exhaust gas such as factory exhaust gas. Further, carbon dioxide separated from biogas does not necessarily need to be effectively used as a raw material for industrial gas, and may be discarded, for example.

  Biogas is produced by fermenting with fungi after transitioning high molecular organic substances contained in organic waste or the like to low molecular organic substances. The biogas generated in the fermenter for the purpose of reducing organic waste is recovered by the biogas separation and recovery system 1 and the methane and carbon dioxide contained in the biogas are separated, thereby reducing the waste energy and the biomass energy. Effective commercialization and commercialization of gas for various uses are planned.

  The biogas separation and recovery system 1 according to the present embodiment is a two-system adsorption tower 2A filled with an adsorbent such as molecular sieve or activated carbon in order to continuously separate impurities such as methane, carbon dioxide and water in the biogas. , B. The tower may be filled with an adsorbent that adsorbs carbon dioxide or water, or an adsorbent that adsorbs water on the upstream side of the tower and adsorbs carbon dioxide on the downstream side. It may be a two-layer structure filled with an adsorbent. Then, by switching these adsorption towers 2A and 2B to an adsorption process and a regeneration process, or an adsorption process, a depressurization process, a regeneration process, and a pressure equalization process, the difference in gas adsorption characteristics of the adsorbent is utilized. The carbon dioxide and water adsorbed at a relatively high pressure are desorbed at a relatively low pressure. In addition, although the adsorption tower which comprises each system | strain here is called adsorption tower 2A, B, the adsorption tower which comprises one system | strain is not limited to what is single body, It divides | segments into plurality. It is good also as a structure. The number of adsorption towers is appropriately determined according to the target adsorption amount, on-site installation conditions, and the like.

  In addition, the biogas separation and recovery system 1 improves the adsorption / desorption performance by exchanging heat between the adsorption side and the regeneration side while using the PSA method as a keynote. That is, the biogas separation / recovery system 1 uses a circulating water tank, a circulating water pump, or the like to effectively use the heat generated when adsorbing carbon dioxide as heat when desorbing and regenerating carbon dioxide. A device 3 is provided. By this water circulation device 3, the adsorption temperature is in a relatively low temperature range of approximately 0 to 60 ° C and the regeneration temperature is approximately in the range of -10 to 50 ° C. The circulation route only needs to be able to transfer the heat of adsorption as circulating water as an intermediate heat medium, and may circulate the adsorption towers in parallel or in series, or may switch the flow direction as necessary. When the temperature of circulating water falls below freezing point due to outside air temperature, use antifreeze such as ethylene glycol solution. As the intermediate heat medium, for example, a medium excellent in heat transport such as Freon gas or ammonia gas can be applied. When these heat medium gases are used as the intermediate heat medium, the circulating water pump and the circulating water tank can be omitted and left to natural convection. As the heat medium is circulated by the water circulation device 3, the adsorption heat is removed on the adsorption side so as to suppress a decrease in adsorption performance due to a temperature rise. On the regeneration side, heat lost by regeneration and pressure swing (reduced pressure) is compensated to suppress a decrease in desorption performance, and the adsorption / desorption performance is improved. By carrying out heat transport between the adsorption side and the regeneration side by the water circulation device 3, energy-saving and efficient operation can be expected.

  In particular, when the carbon dioxide concentration of the gas to be processed is relatively high, such as the biogas processed by the biogas separation and recovery system 1 according to the present embodiment, a large amount of heat of adsorption is generated. For this reason, if there is no heat exchange function such as an adsorption tower structure equipped with heat transfer tubes and a water circulation device 3, it is difficult to treat the adsorption heat by the adsorption process alone. A combination with a pretreatment process capable of processing up to 1 to 2% is required. In the present biogas separation and recovery system 1, not only can the adsorption process be performed alone, but also the effective utilization of the heat of adsorption by the water circulation device 3 for the regeneration heat can be realized. For this reason, thermal energy is utilized very effectively.

  Here, the system is designed such that each process value is in the order of adsorption temperature, outside air temperature (ambient temperature), and desorption temperature in descending order of temperature. By setting each process value in this way, the heat of adsorption can be used as the heat of desorption without performing special control. That is, by setting the regeneration temperature lower than the adsorption temperature, the heat of adsorption can be used as heat for regeneration only by transferring the heat of adsorption using a heat medium. In addition, each process value of the whole system will shift naturally according to the change of outside temperature, without performing special operation.

  The heat of adsorption and heat of desorption are theoretically equal, but the temperature drops with a pressure swing. In the biogas separation and recovery system 1, since each process value is set as described above, a part of the regenerative heat including the temperature drop is obtained from the outside air by actively exchanging heat with the outside air. Can compensate for heat. In other words, since the desorption temperature is set lower than the outside air temperature, regeneration by suppressing the temperature drop of the gas generated at the time of depressurization during regeneration by active heat exchange between the outer surface of the adsorption tower and the outside air. Reduction in rate is prevented. For this reason, compared with the case where a separate heat source is provided, the apparatus can be simplified and configured compactly, and heat dissipation loss can be eliminated.

  In addition, the biogas separation / recovery system 1 includes a pressure equalizing buffer tank 4 for stabilizing gas components and pressure to flow in a downstream process, a vacuum pump 5 used for regeneration of the adsorption towers 2A and B, and a drain separator as others. 6, an off-gas KO drum (a steam separator) 7, and various valves.

  Here, the adsorption towers 2 </ b> A and 2 </ b> B are in the shape of a fixed tube plate type heat exchanger in order to realize heat transport by the water circulation device 3. The biogas, which is the raw material gas, passes through the cylinder side filled with the adsorbent, and a heat medium such as water or an aqueous ethylene glycol solution flows through the pipe side connected to the water circulation device 3. In addition, as described above, in order to positively exchange heat with the outside air and supplement the heat, the heat insulating material is not attached to the shell outer surfaces of the adsorption towers 2A and 2B, and heat exchange with the outside air is performed. Vertical or brim-shaped heat transfer fins are provided as necessary.

  In the adsorption towers 2A and 2B having such a structure, in order to adsorb carbon dioxide and water, an appropriate amount of adsorbent is filled to secure a channel area in the tower for ensuring a certain contact time. It is required to secure a heat transfer area for efficient heat exchange of heat of adsorption / desorption with the medium. Of these, the flow area in the tower is uniquely determined by the gas flow rate, and the heat transfer area is uniquely determined by the amount of gas, the amount of gas components to be adsorbed and desorbed, and the pressure operation conditions. Although the amount of adsorbent can be reduced by shortening the switching time, it leads to an increase in the capacity of the vacuum pump used for regeneration and a decrease in separation efficiency, so that a certain amount of volume is still required.

In order to secure the contact time in the tower, the biogas separation and recovery system 1 is designed so that the gas flow rate in the adsorption towers 2A and 2B is operated at 1 m / s or less, as in the case of a general adsorption tower. Has been. In this case, even if the heat transfer effect by the adsorbent filled is taken into consideration, the gas side film heat transfer coefficient remains at about 10 to 100 W / m ² K, and there is a large difference from the pipe side film heat transfer coefficient. Produce. Therefore, in order to solve this problem, the adsorption towers 2A and 2B according to the present embodiment employ a fin tube as a heat transfer tube to ensure a large heat transfer area. In order to make the filling of the adsorbent relatively easy, it is preferable to employ a low fin tube.

  The biogas separation and recovery system 1 configured as described above operates as follows. The biogas separation and recovery system 1, when biogas which has been pressurized to some extent from the upper process is supplied, after removing the droplets in the biogas with the drain separator 6, the biogas is supplied to one of the adsorption towers 2 A and B. Allow to vent.

  FIG. 1 shows a state where the adsorption tower 2A is in the adsorption process and the adsorption tower 2B is in the regeneration process. As shown in FIG. 1, on the side of the adsorption tower 2A in the adsorption process, a valve V1A that can open and close a pipe path that leads from the drain separator 6 to the adsorption tower 2A, and a pipe that leads from the adsorption tower 2A to the pressure equalization buffer tank 4 By opening the valve 4A capable of opening and closing the path, the biogas sent from the upper process is vented.

On the other hand, as shown in FIG. 1, on the side of the adsorption tower 2B in the regeneration process, the ventilation of the biogas is stopped by closing the valve 1B and the valve 4B, and the pipe connecting the adsorption tower 2B to the vacuum pump 5 When the valve 2B capable of opening and closing the path is opened, the vacuum pump 5 evacuates the adsorption tower 2B. The adsorption heat generated in the adsorption tower 2A is transferred to the adsorption tower 2B by the water circulation device 3 and used as desorption heat in the adsorption tower 2B. Further, heat for compensating for the temperature drop due to the pressure swing (decompression) is taken in from the ambient outside air. Thereby, the desorption action in the adsorption tower 2B is promoted, and the adsorbent is regenerated. The carbon dioxide desorbed in the adsorption tower 2B passes through the vacuum pump 5 and the off-gas KO drum 7, and can also be used as product CO ₂ gas by being treated as off-gas by a carbon dioxide purification facility outside the system. is there.

  In addition, since the biogas separation and recovery system 1 according to the present embodiment is based on normal temperature and low pressure, the adsorption process is performed under atmospheric pressure to a low pressure of about 0.06 MPa (G) (more preferably 0.02 MPa (G ) And the like, and the regeneration step is basically based on regeneration using a vacuum pump 5 under a vacuum of 100 torr or less (under negative pressure). However, the biogas supplied from the upper process is already pressurized, and a certain pressure (for example, 0.2 MPa (G) or more) is already applied, and the biogas is adsorbed at that pressure. In the case of venting into the tower, the regeneration pressure may be any pressure from a vacuum of -0.1 MPa to a normal pressure region of about 0.01 MPa. In the case of normal pressure regeneration, the vacuum pump 5 can be omitted.

  The adsorption towers 2 </ b> A and 2 </ b> B alternately manage the adsorption process and the regeneration process in this way, whereby the biogas supplied from the upper process is continuously processed. When transitioning from the adsorption process to the regeneration process, the valves 1A (B) and 4A (B) are closed from the state where both towers are in the adsorption process, and then the valve 2A (B) is opened and the vacuum pump 5 is turned on. to start. The period from when the vacuum pump 5 is started until the pressure drop in the adsorption tower settles can be regarded as a depressurization process from the adsorption process to the regeneration process. On the other hand, when making a transition from the regeneration process to the adsorption process, the valve 2A (B) is closed and the vacuum pump 5 is stopped, and then the valves 1A (B) and 4A (B) are opened. At this time, until the pressure in the adsorption tower 2A (B) becomes equal to the pressure in the adsorption tower 2B (A), a part of the purified biogas flowing downstream of the adsorption tower 2B (A) is absorbed in the adsorption tower. It will flow into 2A (B). However, the pressure equalization buffer tank 4 suppresses fluctuations in the flow rate of the gas flowing in the flow paths downstream of the adsorption towers 2A and 2B. After closing the valve 2A (B), the valve 3A (B) is opened to equalize the pressure in both towers, and then the valve 1A (B) and the valve 4A (B) are opened to close the valve 3A (B). Thus, a pressure equalization step may be performed between the regeneration step and the transition to the adsorption step. Operations of the series of valves and pumps are sequentially controlled by control devices (not shown).

  The biogas separation and recovery system 1 according to the present embodiment can directly receive high-concentration carbon dioxide gas, eliminates the need for a large pretreatment facility such as a high-pressure water washing process, and greatly reduces the number of components.

  In addition, the biogas separation / recovery system 1 can increase the treatment capacity per weight of the adsorbent because the adsorption / desorption heat is appropriately used while performing vacuum regeneration. The recovery rate of methane gas is about 65% to 85% due to loss outside the system in the prior art, but is 95% or more in the present embodiment.

  Further, not only the purity of the recovered methane gas but also the recovered carbon dioxide gas has a purity of 95% or more. Therefore, even if it does not perform a large-scale process in the downstream process, it can be used as various industrial raw materials such as food additives for the purpose of adding impurities and other refining processes.

  In the biogas separation / recovery system 1, since the adsorption / desorption heat and the outside air heat are effectively used by the water circulation device 3 and a separate heat source is not necessary, the power energy used for driving the circulation pumps and the control power source is sufficient. Sufficient and energy saving. In particular, since the biogas separation and recovery system 1 is a low-pressure process, power consumption of a rotating machine or the like is suppressed.

  Thus, since the biogas separation and recovery system 1 can save energy while reducing the number of components, the recovery cost of methane and carbon dioxide contained in the biogas can be greatly reduced. . In trial calculation, it can be reduced to at least one third of the conventional method. In addition, since the gas that can be effectively used can be recovered even though it is an energy saving and resource saving type system, it can directly contribute to the reduction of environmental load.

  In the biogas separation / recovery system 1 according to the above embodiment, a blower that covers the pressure loss in the system is not provided in the path through which the biogas flows. However, the biogas separation / recovery system 1 is based on a low pressure, and the biogas supplied from the higher-level process may be sent at a very low pressure from atmospheric pressure to a slight positive pressure. For this reason, in such a case, in order to compensate for the pressure loss in the system, as shown in FIG. You may provide the equipment which compensates for loss as needed. When the gas compressor 9 is downstream of the adsorption towers 2A and B, the pressure equalization buffer tank 4 is branched from the main path (that is, the branch returning to the adsorption towers 2A and B downstream of the gas compressor 9). If it is provided in the path), it is possible to effectively suppress flow rate fluctuations during pressure equalization.

  In addition, the biogas separation and recovery system 1 according to the above embodiment employs a configuration in which the exhaust from the vacuum pump 5 is sent directly to the lower process. However, the biogas separation and recovery system 1 may adopt a configuration in which a part of the exhaust of the vacuum pump 5 returns to the adsorption tower being regenerated. In this case, since the regeneration of the adsorption tower is promoted, the carbon dioxide recovery efficiency can be increased. As a specific configuration for returning a part of the exhaust of the vacuum pump 5 to the regenerating adsorption tower, for example, a path between the adsorption tower 2A (B) and the valve V3A (B), the off-gas KO drum 7, A route having a valve in the middle is provided. By opening and closing the valve together with the valve V1A (B), a path for returning a part of the exhaust of the vacuum pump 5 to the adsorption tower is formed.

  In general, biogas contains a trace amount of impurity components such as nitrogen, oxygen, moisture, siloxane, hydrogen sulfide, and ammonia. Siloxane, hydrogen sulfide, ammonia, and the like are harmful components for use in fuels and food additives, and thus need to be removed. Therefore, when directly receiving and processing biogas, as shown in FIG. 2, depending on the necessity of the product, a pretreatment tower 10 filled with an adsorbent such as activated carbon is installed in front of the adsorption towers 2A and 2B. By adsorbing and removing these components in advance, impurities can be contained in the carbon dioxide gas separated and recovered in addition to the purified biogas, and a high value-added gas can be provided.

  In the biogas separation and recovery system 1 according to the above embodiment, the adsorption temperature and the regeneration temperature are set so as to sandwich the outside air temperature. For example, the heat medium circulating in the water circulation device 3 is fixed by a heater or a cooler. The temperature may be controlled within a temperature range (for example, 35 to 40 ° C., etc.), and the adsorption temperature may be set higher than this temperature range and the regeneration temperature may be set lower than this temperature range. In this case, in order to suppress loss of thermal energy, each adsorption tower may be provided with a heat insulating material for preventing heat exchange with the outside air. Even if the biogas separation and recovery system 1 according to the above-described embodiment is configured in this way, at least the heat of adsorption can be used as the desorption heat, so that the heat energy can be used effectively.

1 ・ ・ Biogas separation and recovery system 2A, B ・ ・ Adsorption tower 3 ・ ・ Water circulation device

Claims (3)

A gas separation device for separating a specific component from a mixed gas of biomass gas or combustion exhaust gas composed of a plurality of components,
A plurality of adsorption towers containing heat transfer tubes that adsorb the specific components in the mixed gas;
A heat medium circulation path for circulating a liquid heat medium with a pump between the heat transfer pipe of the adsorption tower being adsorbed and the heat transfer pipe of the adsorption tower being regenerated among the plurality of adsorption towers,
The heat medium circulation path transfers the adsorption heat of the adsorption tower that is at least at a temperature higher than the outside air temperature to the adsorption tower that is being regenerated with the heat medium,
The adsorbing tower being regenerated is regenerated at least at a lower pressure and lower than the outside air temperature than the adsorbing tower being adsorbed, and exchanges heat with the outside air outside the adsorption tower being regenerated
Gas separation device. The adsorption tower during adsorption adsorbs at least at a temperature higher than the outside air temperature, and exchanges heat with the outside air outside the adsorption tower during adsorption.
The gas separator according to claim 1. The specific component is at least one of carbon dioxide and water,
The gas separation device further includes a pretreatment tower for removing impurities contained in the mixed gas upstream of the plurality of adsorption towers.
The gas separator according to claim 1 or 2.

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