KR101529130B1 - A multi-stage membrane process and an upgrading apparatus for the production of high purity methane gas using low operation pressure and temperature conditions - Google Patents

Abstract

The present invention relates to a separating method of high purity methane gas from biogas, comprising: a step (step 1) of compressing and cooling the biogas to make a pressure of 3 bar to 11 bar and to make the temperature of the biogas from -20 to 10 deg. C; a step (step 2) of separating methane and carbon dioxide while maintaining a penetration portion of the first polymer separation membrane, a penetration portion of the second polymer separation membrane, and a penetration portion of the third polymer separation membrane in a decompression condition of 0.2 bar to 0.9 bar, wherein the area ratio of a first polymer separation membrane, a second polymer separation membrane, and a third polymer separation membrane is 1 : 1 : 1 to 1 : 5 : 1, the stream of a residual portion of a first polymer separation membrane is connected to a second polymer separation membrane, the stream of a penetration portion of the first polymer separation membrane is introduced in a three-stage polymer separation membrane for separating gas connected to the third polymer separation membrane; and a step (step 3) of maintaining decompression of the penetration of the second polymer separation membrane, and recirculating along with the residual portion of the third polymer separation membrane before a compression process of the step 1. The polymer separation membranes have 100 GPU to 1,000 GPU of carbon dioxide transmission and have 20 to 34 of carbon dioxide/methane selectivity. The present invention enables to produce the high purity methane from the biogas produced from a food waste and an organic material.

Description

TECHNICAL FIELD [0001] The present invention relates to a multi-stage membrane separation and purification apparatus and method for separation of high purity methane gas characterized by low-temperature and low-pressure operating conditions,

In order to increase methane recovery rate by maximizing methane / carbon dioxide selectivity of the polymer separator adopted from the biogas, the supply temperature of the biogas including the methane gas to be purified is set to a low temperature, The present invention relates to a method for separating a high purity methane gas and a methane gas purification apparatus, which are operated under optimized conditions of a membrane area ratio of a polymer membrane under an operating condition of low operating pressure for enhancing safety. More specifically, Ammonia, desiloxane, and dehumidified biogas were investigated for the low temperature and low pressure operating conditions using polymer membranes with high carbon dioxide permeability and moderate methane / carbon dioxide selectivity, and by adjusting the membrane area ratio for each stage, Three-stage Recycle Membrane Process and Liquid for Biomethane Purification It is about the whole condition.

Biogas generated by anaerobic digestion of food waste, organic waste, livestock wastewater, etc. is mainly composed of about 50 to 75% by volume of methane and about 25 to 50% by volume of carbon dioxide, and about 0.1% by volume or less of impurities Air, about 7,000 to 8,000 ppm of hydrogen sulfide, and about 40 ppm of siloxane. Methane, a major component of biogas, has a 20% contribution to global warming compared to carbon dioxide. It is designated as a greenhouse gas with a contribution of about 18%, which is about 49% by volume, followed by carbon dioxide. However, methane gas has an amount of energy of 5,000 kcal / m ³ , which is regarded as a renewable energy resource that can be recycled.

Methods for recovering and recycling biogas include direct combustion, electricity production, supply to city gas, and use as fuel for automobiles. Various methods of utilization are being developed in accordance with the background and economics of methane gas generation. Among these, the most economical and energy efficient technology is to refine the methane concentration, that is, the energy content of the biogas to a high purity, and to use the high purity methane gas fuel of 95 vol% or more which can be used as city gas or automobile fuel It is a high-purity fuel for power generation in Sweden, Germany and other parts of the world. High purity methane gas can be applied to existing urban gas appliances and natural gas automobiles without replacing existing equipment. It is accepted as the next generation of clean bio energy. Sweden Germany, which is a developed country of renewable energy, It is establishing national policy to replace natural gas with biogas.

A variety of techniques have been developed for the separation process for making the biogas highly purified, the plant, and the operation conditions thereof. The high purity technology of biomethane consists of pretreatment technology to remove siloxane, ammonia, hydrogen sulfide, water and so on in biogas, where various components remain as impurities, and de-carbon dioxide separation technology to separate the remaining carbon dioxide and methane. Among them, the de-carbonating and separating technology is largely divided into a cryogenic method, a physical or chemical absorption method using water or amines, a pressure swing adsorption method using zeolite and a carbon molecular sieve, , Membrane separation using high methane-selective polymer membranes, and so on.

Biogas High purity refining technology is being developed and commercialized mainly in USA and Europe. Representative companies that have biogas refining technology are absorbing method using water, polyethylene glycol, amine and so on as absorbent. Prometheus Energy of America, Polyimide Membrane or Polysulfone Membrane, Evonik of Germany, Air-liquides of France, Acrion Technology of Austria, etc., and zeolite or carbon molecular sieve Schmack in Germany, Carbotech in Germany, and Xebec in Canada. Separately, a lot of research and development has been carried out on the hybrid process of separation membrane adsorption, seawater cooling and absorption.

In the case of the absorption method, for example, Korean Patent Laid-Open No. 10-2010-0037249 discloses a high purity biogas purification system and a biogas purification method. More particularly, the present invention relates to a method for removing carbon dioxide by absorbing carbon dioxide through a pretreatment unit for removing water, a hydrogen sulfide component, and a siloxane component so that the biogas generated in the anaerobic digestion unit can be used as a gaseous fuel and a gas adsorbing unit for removing carbon dioxide through an adsorbent, And a method of purifying the biogas.

Korean Patent Publication No. 10-2012-0083220 also discloses a methane recovery method and methane recovery apparatus. Specifically, the siloxane in the biogas is adsorbed on the adsorbent to remove it. In the reaction removing step, hydrogen sulfide is reacted with the metal oxide to remove it as metal sulfide, and oxygen in the biogas is reacted with copper- And a method for concentrating methane by separating carbon dioxide in the biogas through a pressure swing adsorption process in a concentration process.

However, the methane purification method of the above-mentioned invention uses a carbon dioxide absorption process or a PSA adsorption process to increase the installation cost of the plant, to cause a large amount of process operation costs, to make a device of a small scale impossible, The process is complicated and energy is consumed much.

Therefore, we tried to use the separation membrane method which is suitable for domestic biogas refining facilities and which is easy to maintain and has high methane purity. Among them, separation membrane method can be operated by dry method compared with other separation method, so it is advantageous in winter, environmentally friendly because it does not use toxic absorber, plant cost is low, operation cost is low, and scale up-scale down is easy It is expected to occupy a unique position in future biomethane purification technology.

Methane concentration and recovery rate are the most important targets in the separation membrane process, and the recovery rate is usually 60 ~ 75% in the first separation membrane process. In order to increase the recovery rate of methane, the separation membrane is connected in series in two stages, the permeate of the first separation membrane is incinerated and the permeate portion of the second separation membrane is recirculated, and the separation membrane is separated into two stages A three-stage membrane recycling process has been developed which recirculates the permeate of the membrane into the three-stage membrane and recycles the untransmitted methane gas of the two-stage membrane.

First, Korean Patent Laid-Open No. 10-2011-0037921 discloses a low-temperature biogas separation method as an example of performing a single-stage separation membrane process. In detail, the biogas generated in the anaerobic condition is passed through a desulfurization process, a desulfurization process, a desulfurization process, a compression process, a dehumidification process, and a biogas compressed to 7 bar is subjected to a single stage separation membrane process using a hollow fiber membrane module made of polystyrene To a technique for purifying methane from biogas.

In the method of separating methane and carbon dioxide from the biogas through the separation membrane process, the recovery rate of methane contained in the biogas is only about 70% or less in the conventional one-stage separation membrane process, And the energy consumed by the system is excessively high, resulting in a low energy efficiency of the system.

In order to solve such a problem, a technique relating to a multistage separation membrane process for purifying methane from biogas has been developed.

For example, in Japanese Patent Application Laid-Open No. 2007-254572, a methane-enriched two-stage system and its operating method have been disclosed. Specifically, the present invention relates to a process for supplying a mixed gas to a first separation membrane, supplying a non-permeable gas to a separation membrane at a subsequent stage in a pressurized state, and further, recovering methane gas at a high concentration by passing carbon dioxide through a second separation membrane. It is described that the membrane is preferably a DDR type zeolite membrane which is an inorganic material.

Japanese Patent Application Laid-Open No. 2008-260739 discloses a two-stage methane concentration apparatus and methane concentration method. Specifically, the method includes the steps of: passing a mixed gas through a first separation membrane made of an inorganic porous material; And passing the non-permeable gas through the second separating membrane made of an inorganic porous material to concentrate the methane gas. At this time, an inorganic porous material is used as a separation membrane to be used.

The US patent US 2004/0099138 discloses a membrane separation process. More specifically, 98% or more methane was recovered from the landfill gas using a carbon dioxide absorption tower and a two-stage separation membrane process. The fed gas was subjected to a first compression process, a dehumidification process, a second compression process, a heat exchange process, The feed gas was compressed to 21 bar in the first compressor, compressed to 60 bar through a second compressor and a heat exchanger to facilitate the operation of the carbon dioxide adsorption tower, and heated to a temperature of 30 ° C. The gas is concentrated to a gas containing 90% of carbon dioxide and 10% of methane and impurities through the permeate portion of the first separation membrane and recycled to the top of the carbon dioxide absorption tower. The gas permeated to the permeate portion of the second separation membrane is supplied to the second compressor, To increase the recovery rate. In addition, the two-stage recirculation membrane process is based in Ecuolon Technology, Austria, which uses a polyamide-imide membrane from Air Liquide, France. The two-stage separation membrane processes known from the prior art use various membranes. The disadvantages of these processes are summarized as follows. The purification methane gas has a disadvantage that the recovery rate is as low as 90% or less at a purity of 95% or more.

Japanese Patent No. 2009-242773 discloses a three-stage separation membrane process. Specifically, the methane concentration apparatus disclosed in the above-mentioned prior art is a methane gas concentration apparatus for separating carbon dioxide from a mixed gas containing at least methane gas and carbon dioxide and concentrating methane gas, and a separation membrane which is preferentially permeable to carbon dioxide A second concentration device for further concentrating the methane gas by a separation membrane that has preferentially permeated carbon dioxide from the non-permeable gas of the first concentration device; and a second concentration device for concentrating methane gas, And a recovery device for recovering the methane gas by the separation membrane that has preferentially permeated the carbon dioxide from the separation membrane. It is described that polyimide is most preferably used as the separation membrane. However, since the area ratio of the first stage and the second stage is similar in the patent scope and the area of the third stage separation membrane is simply lower than that of the first stage, the process conditions for the temperature and the membrane area are not specified, It is considered that the specific feasibility of achieving high methane purity and recovery rate is low.

Evonik, Germany's first commercialization of the three-stage membrane process in 2010, has been actively developing the membrane process for polyimide (P84) hollow fiber membranes developed in Germany since 2008, It has commercialized a step-by-step 3-step process patent for the stepwise arrangement and recompression of the permeate from the second stage in the first stage and second stage in-stream permeate through the retentate (PCT / EP2011 / 058636). Adopted membranes employ materials with a methane / carbon dioxide of at least 35 or more, and many of Evonik's announcements for a three-stage membrane process show that polyimide membranes have a selectivity of about 50 as compared to polysulfone membranes In the case of the polysulfone membrane adopted in the embodiment of the present invention at the same recovery rate as the excellent separation characteristic of the methane concentration of 98% at the recovery rate of 99% at the high pressure of 16 to 20 bar at the high pressure of 16 to 20 bar, It is known that the mid-membrane has a recirculation rate of 50% or less.

However, as shown in the following Table 1, since a conventional polyimide material has a high film cost and high film production cost and a high carbon dioxide / methane selectivity of about 50, the permeability of carbon dioxide is as low as several barrel or less, A high pressure operating condition is desirable to use less separator. However, when used under such high-pressure operating conditions, the plant costs are high in piping, measurement equipment, and membrane including high-pressure compressors, increased energy consumption caused by high-pressure compression, possibility of plant failure, and risk of methane explosion There is a limitation in the installation site, and there is a disadvantage that the membrane replacement cost due to contamination of the membrane during the operation is high, which makes it difficult to develop the market.

In the case of polysulfone film, cellulose acetate, polycarbonate, etc., as shown in Table 1, the film material is usually much cheaper than the polyimide film and the carbon dioxide / methane selectivity is slightly lower, but the permeability of carbon dioxide is very high The advantages of the membrane module are low cost and high permeability, which means that the required number of membranes is relatively low, which lowers the cost of the fabrication of the plant and low replacement costs for membrane contamination. When a separation membrane using a polymer membrane material having a selectivity of 20 or less is used in a process, a large amount of gas is recycled in order to obtain high purity methane, which causes a problem that energy required is large. On the other hand, membrane materials such as polyimide having a selectivity of at least 50 tend to have a very low permeability. When the separator using such a material is used in the process, the amount of high purity methane produced is small and the amount of recycled is large Which requires a large number of membranes and high-pressure operating conditions, which increases the scale of the process. For this reason, polysulfone, cellulose acetate, polycarbonate, etc., having a moderate carbon dioxide / methane selectivity of from 20 to 34 can be used as long as it is possible to obtain suitable operating conditions for recovering high purity methane at high recovery rates for high- Preferably, a separation membrane material is used, and a separation membrane having a high carbon dioxide permeability of 100 GPU to 1,000 GPU developed as a hollow fiber membrane or a composite flat membrane having an asymmetric layer structure is preferable. Particularly, it is desirable to select polysulfone (PS) whose selectivity is slightly lower than that of polyimide but has a higher permeability to carbon dioxide and a higher resistance to plasticization of carbon dioxide due to a higher supply side pressure than that of polyimide. In particular, polysulfone has merits of replacing the membrane when the membrane is damaged due to hydrogen sulfide, compaction, and membrane contamination because the membrane cost is only 1/20 of that of the expensive polyimide. In particular, unlike the high-pressure process of Ebonic, polysulfone has high permeability, so if low-pressure operating conditions are applied, separation membrane costs and piping costs are reduced, operating conditions are safe, and costs for compressors and related equipment are reduced Have.

Types of Polymers P _CO2
(Barrer) P _CO2 / P _CH4
Polytrimethylsilylpropyne 33100 2.0

Low selectivity
High transmittance Silicone rubber 3200 3.4 Natural rubber 130 4.6 Polystyrene 11 8.5 Polyamide (Nylon 6) 0.16 11.2 Poly (vinyl chloride) 0.16 15.1 Polycarbonate (Lexan) 10.0 26.7
Medium selectivity
Intermediate permeability Polysulfone 4.4 30.0 Polyethyleneterephthalate (Mylar) 0.14 31.6 Cellulose acetate 6.0 31.0 Poly (ether imide) (Ultem) 1.5 45.0 High selectivity
Low permeability Poly (ether sulfone) (Victrex) 3.4 50.0 Polyimide (Kapton) 0.2 64.0 1 Barrer = 10 ^{- 10} cm ^{3 -} cm ^- cm ^{- 2 -} s ^{- 1 -} cmHg ^-1
* P _CO2 = Carbon dioxide permeability
* P _CO2 / P _CH4 = carbon dioxide / methane selectivity
* Basic principles of Membrane Technoloogy (second edition),
Kluwer Academic Publishers, Marcel Mulder.

Korean Patent No. 10-1086798 discloses a method for separating high purity methane gas from a landfill gas and a methane gas purification apparatus in terms of a patented multi-stage membrane separation process in Korea. In particular, a high purity methane is recovered by a combination of the pretreatment step, which is carried out at a comparatively low pressure and temperature (7 to 15 bar, -10 to 50 ° C), a two-stage separation membrane process and pressure swing adsorption, And the like. However, since the above-mentioned process is limited to the gas generated in the landfill, it is a separation membrane operation condition for the supply gas containing gas which is almost not contained in the biogas such as nitrogen and oxygen in the supply gas, Since the PSA treatment process is included in the post-treatment of the remaining gas after passing, it is not suitable for the biogas purification process which does not contain nitrogen or oxygen from the beginning and has a low concentration of hydrogen sulfide and a high methane concentration.

Korean Patent No. 10-1100321 discloses a purification / solidification and compression system of biogas. In detail, the biogas produced from the anaerobic digestion biogas facility is solidified by using a siloxane removing device, a desulfurizing device, a compression device, a gas heater, and a two-stage separation membrane device. Is heated to 50 캜 through a gas heater before it is compressed and supplied to the separation membrane. However, such a high temperature operation condition promotes the plasticization of the polymer membrane to lower the selectivity of methane / carbon dioxide, and it is considered that the upper / lower pressure ratio is low and the temperature on the supply side is too high.

Further, Korean Patent Laid-Open No. 10-2014-0005846 discloses a method of separating gas using a gas separation membrane module having a selectivity of 35 or more, which can produce high efficiency at a high pressure of 9 to 75 bar on the feed side and 3 to 10 bar on the permeation side A device and a separation method have been disclosed. In addition, separation results for pressure ratio and selectivity are presented, and the disadvantages of various arrangements of membrane separation processes from the first stage to the third stage are described. However, most of these processes are operated at high pressures and thus have a disadvantage of high energy costs and high plant costs.

Korean Patent No. 10-1327337 discloses a multistage membrane system and method for producing biomethane and recovering carbon dioxide. In detail, the separation membrane structure is formed in a multi-stage so that biogas can be primarily separated, and the recovered carbon dioxide can be separated again to recover high purity carbon dioxide. Particularly, the temperature of the compressed gas is controlled at 20 to 30 ° C to prevent the generation of condensed water after removing water, and a method of pressurizing the biogas to pressurize it to 10 to 20 bar. However, in the case of FIG. 3 shown in the embodiment, the recirculation process is described at the rear end of the compressor, and it is predicted that technically efficient process operation is difficult.

The methane refining method through the above two-stage or three-stage methane refining process can be applied to an expensive polymer membrane material having an excessively high operating temperature or operating pressure, an area ratio, an upper / lower pressure ratio, It is considered that only one or two of the above-described process conditions are considered and the feasibility of the process is low due to problems such as the recovery rate of the processes because the results of the examples are not properly shown Loses.

Therefore, the inventors of the present invention have been studying a method of separating methane gas by membrane separation, and have found that a polymer material such as polysulfone, which has a higher permeability to carbon dioxide than a polyimide and has methane / carbon dioxide selectivity lower than that of polyimide, In order to optimize the conditions such as operation temperature, low pressure operating condition, and upper / lower pressure ratio, the specific selectivity of the polymer membrane is maximized and the total area ratio of the gas membrane By optimizing the area ratio of each stage, a method of separating 95% or more of high purity methane gas at a high recovery rate of 90% or more has been developed and the present invention has been completed.

It is an object of the present invention to provide a separation method of high purity methane gas and a methane gas purification apparatus by controlling the area ratio of each stage of the separation membrane process using a polymer membrane having high carbon dioxide permeability and selectivity under low temperature and low pressure operation conditions from biogas There is.

In order to achieve the above object,

Compressing and cooling the biogas to a pressure of 3 bar to 11 bar and a temperature of the biogas to -20 ° C to 10 ° C (step 1);

The biogas compressed and cooled in step 1 is mixed with the first polymer membrane separation membrane area, the second polymer membrane separation membrane area, and the third polymer membrane separation membrane area ratio of 1: 1: 1 to 1: 5: 1, The first polymer membrane permeate stream is introduced into the third polymer membrane for gas separation connected to the third polymer membrane, and the permeate portion of the first polymer membrane, the permeate portion of the second polymer membrane, and the third polymer Separating methane and carbon dioxide by maintaining the permeate portion of the membrane at a reduced pressure of 0.2 bar to 0.9 bar (Step 2); And

(Step 3) of recycling the permeate portion of the second polymer separation membrane to the compression process of Step 1 together with the remaining portion of the third polymer separation membrane while maintaining the reduced pressure, wherein the polymer separation membrane has a carbon dioxide permeability of 100 GPU 1,000 GPU and a carbon dioxide / methane selectivity of 20 to 34. The present invention also provides a method for separating high purity methane gas from a biogas.

In addition,

A supply part of the biogas;

A compression and cooling unit for compressing and cooling the biogas supplied from the supply unit of the biogas to a pressure of 3 bar to 11 bar and a temperature of -20 ° C to 10 ° C;

1 to 1: 5: 1 ratio of the area of the first polymer membrane area, the area of the second polymer membrane area and the area of the third polymer membrane area for removing carbon dioxide from the compressed and cooled gas in the compression and cooling part, 1 polymer separator membrane residual stream is connected to the second polymer separator and the first polymer separator membrane permeate stream is connected to the third polymer separator; And

And a recycle line for introducing the permeate portion of the second polymer separation membrane and the remaining portion of the third polymer separation membrane into the compression and cooling portion,

Wherein the polymer separation membrane is a polymer separation membrane having a carbon dioxide permeability of 100 GPU to 1,000 GPU and a carbon dioxide / methane selectivity of 20 to 34.

Further,

Methane gas having a purity of 95% or more separated by the above method is provided.

Further,

And provides automobile fuel and city gas containing the high purity methane gas.

The method of separating high purity methane gas from biogas according to the present invention has an effect of producing high purity methane from biogas generated from food waste and organic matter. In addition, it is possible to increase the production rate of methane by recycling the remaining trace amount of methane through the three-stage separation membrane process so as to be refined again. Further, the temperature of the biogas is lowered before the step of separating the carbon dioxide by injecting the biogas into the polymer membrane, and the supply side pressure and the permeation side pressure are adjusted to a low level, and the area ratio of the membrane It has an excellent effect of separating methane gas by a high recovery rate of high purity methane, a reduction in operation energy cost (methane refinery installation cost, methane refinery operation cost), and safe operation compared with conventional methane refining methods , It is effective to provide a new methane separation and purification technology.

1 is a schematic diagram showing an example of a methane gas purifying apparatus according to the present invention.

The present invention

Compressing and cooling the biogas (step 1);

The biogas compressed and cooled in step 1 is mixed with the first polymer membrane separation membrane area, the second polymer membrane separation membrane area, and the third polymer membrane separation membrane area ratio of 1: 1: 1 to 1: 5: 1, Introducing the first polymer separation membrane permeate stream into the third separation membrane for gas separation connected to the third polymer separation membrane to separate carbon dioxide (step 2); And

(Step 3) of recirculating the permeate of the second polymer separator and the remaining portion of the third polymer separator before the compression step of step 1,

Wherein the polymer separation membrane is a polymer separation membrane having a carbon dioxide permeability of 100 GPU to 1,000 GPU and a carbon dioxide / methane selectivity of 20 to 34, and a method for separating methane gas of high purity from the biogas.

Hereinafter, a method for separating high purity methane gas from the biogas according to the present invention will be described in detail for each step.

First, in the method for separating high-purity methane gas from a biogas according to the present invention, step 1 is a step of compressing and cooling the biogas to a pressure of 3 bar to 11 bar and a temperature of the biogas to -20 ° C to 10 ° C to be.

The step 1 is a step of compressing and cooling the biogas, and compressing and cooling the biogas to an appropriate pressure and temperature to perform a separation membrane process for separating methane gas of high purity from the biogas.

At this time, it is preferable that the compression and the cooling of the step 1 are performed such that the temperature of the biogas becomes -20 캜 to 10 캜. If the temperature of the compressed and cooled biogas in step 2 is lowered to less than -20 ° C, the selectivity of the polymer separator is greatly increased, but the cooling cost of the entire separator is increased. In particular, If the temperature is higher than the temperature of 10 ° C, the selectivity of the polymer separator is significantly lowered, so that the recovery rate and purity of methane are lowered and the separator may be damaged due to heat.

It is preferable that the compression and cooling of step 1 are performed such that the pressure of the upper biogas is 3 to 11 bar and the pressure of the lower biogas is 0.2 to 0.9 bar at the same time. If the pressure of the compressed and cooled biogas is less than 3 bar in the step 2, the purity and recovery rate of the methane is significantly lowered due to the limitation of utilization of the polymer separator due to the lowering of the upper / lower pressure ratio of the separation membrane process , And even if it exceeds 11 bar, the purity and recovery rate of the final methane may be lowered due to the decrease of selectivity due to the plasticization due to carbon dioxide in the separation membrane process, or the membrane may be damaged.

Further, the biogas of step 1 may contain 0.0001% to 0.1% moisture, hydrogen sulfide, ammonia, siloxane, nitrogen and oxygen as impurities. The composition of the biogas supplied in the step 1 is, for example, about 65% to 75% by volume of methane, about 25% to 35% by volume of carbon dioxide, and most of the methane and carbon dioxide accounts for about 250 ppm to about 2500 ppm of hydrogen sulfide, About 90 ppm to about 100 ppm, and about 3500 ppm to about 4500 ppm moisture.

At this time, the biogas of the step 1 may be pre-treated such as dehumidification, desulfurization, deammonia and desiloxane treatment.

The biogas of the step 1 may be the one subjected to the pretreatment, and it is preferable that the dehumidifying treatment is performed first during the pretreatment of the biogas. The dehumidification treatment is performed first to protect the desulfurizing agent and the desiloxane when the dry desulfurization and the desiloxane are pretreated. This is because it is possible to prevent the performance of the various adsorbents from being prematurely terminated or deteriorated have. When the wet desulfurization or wet ammonia removal process is introduced, the dehumidification process of the biogas is preferably installed at the downstream end of the wet process in order to protect the permeation characteristics of the separation membrane. The dehumidifying process may be performed by passing a raw material biogas through a cylindrical dehumidifier having a tube in which cooling water supplied from an external chiller is circulated, but the present invention is not limited thereto.

In addition, it is preferable that the dehumidification treatment is performed so that the dew point temperature of the gas becomes 0 캜 or lower. More preferably, it is preferably carried out at -15 캜 to -50 캜. If the dew point temperature of the dehumidified gas exceeds 0 캜, the apparatus may be corroded in a continuous process, and there is a problem that the various adsorbents are entangled in the subsequent compression process and the performance is lowered. There is a problem that the finally produced methane gas can not be used as an automobile fuel.

Further, the desulfurization treatment can be performed by dry desulfurization or wet desulfurization. Hydrogen sulphide contained in the biogas generates odor and causes corrosion of the machine, so it needs to be removed. At this time, the dry desulfurization process is environmentally friendly as compared with the wet desulfurization process, and an additional wastewater treatment process is unnecessary, thereby providing excellent process economics.

The desulfurization treatment may be performed by an iron oxide tower, and the desiloxane treatment may be performed by an impregnated activated carbon tower and a silica gel tower. The siloxane is combusted in the engine when it is used as a fuel for automobiles because of the high temperature generated in the cylinder of the compressor used in the purification process or because silica (SiO ₂ ) is generated on the surface for a long time, So that the life of the parts of the refining process apparatus or the engine can be shortened. Therefore, a pretreatment step is required to remove the parts. The iron oxide-based adsorbent adsorbs a large amount of hydrogen sulfide, whereas the ammonia that has not been adsorbed is adsorbed using an impregnated activated carbon adsorbent, and some siloxane is also adsorbed. Finally, the siloxane is adsorbed and removed from the silica gel column. As described above, the desulfurization and desiloxane process can be operated without degrading desulfurization and desiloxane performance even in an urgent situation, compared with a general desulfurization process composed of a single adsorbent, and each adsorbent can complement each other's functions.

It is preferable that the desulfurization and desiloxane treatment is performed so that the concentration of hydrogen sulfide in the treated gas is 20 ppm or less and the concentration of siloxane is 0.1 ppb or less. When the hydrogen sulfide is contained in the final product at a concentration exceeding 20 ppm, there is a problem that the product may generate bad odor and cause corrosion of the apparatus used when it is used as fuel. Also, when the concentration of siloxane exceeds 0.1 ppb, the high temperature generated in the compressor cylinder used in the refining process, or when the finally produced methane gas is used as automobile fuel, it is burned in the engine, SiO ₂ ) is generated on the surface and solid matters are adhered thereto, which may shorten parts life of the purification processing apparatus or the engine.

Further, in addition to the desulfurization and desiloxane treatment, the deammonia treatment can be performed. The biogas supplied in step 1 may contain ammonia, and ammonia can be removed through deammonia treatment.

Next, in the method for separating high-purity methane gas from the biogas according to the present invention, step 2 is a step of separating the biogas compressed and cooled in step 1 from the first polymer membrane area, the second polymer membrane area and the third polymer membrane area Is 1: 1: 1 to 1: 5: 1, the first polymer separation membrane residual stream is connected to the second polymer separation membrane, and the first polymer separation membrane permeation part stream is connected to the third polymer separation membrane, Separating the methane and the carbon dioxide by separating the permeate portion of the first polymer separator, the permeate portion of the second polymer separator, and the permeate portion of the third polymer separator under a reduced pressure of 0.2 bar to 0.9 bar.

Specifically, the material used in the separation membrane process for separating carbon dioxide in step 2 is preferably a polymer material having a carbon dioxide / methane selectivity of 20 to 34, more preferably an amorphous or semi-crystalline polymer. For example, Polysulfones, polycarbonates, polyethylene terephthalates, cellulose acetates, polyphenylene oxides, polysiloxanes, polyethylene oxides, polypropylene oxides and mixtures thereof are most preferred. In addition, polymer materials designed to have low selectivity in order to increase the permeability of carbon dioxide in the manufacturing process of the membrane material may be included.

At this time, in the case of a separation membrane in which a selective layer is processed into a thin film by a phase transfer method or a thin film coating method using an asymmetric composite membrane or a hollow fiber membrane, the carbon dioxide permeability is preferably 100 GPU to 1,000 GPU. The unit of area (cm ² ), the unit pressure (mmHg) of the separation membrane, and the unit pressure (mmHg) of the separation membrane are represented by the gas permission unit (1 GPU = (10 ^-6 cm m ³ ) / (cm ² sec sec mm mmHg) And the volume (cm < ³ >) of carbon dioxide permeated per unit time (sec).

Generally, polyisocyanurates and polyimides used in separator materials have high selectivity. In the present invention, however, polysulfone having intermediate selectivity but superior plasticization resistance against carbon dioxide is used. When a separator material having a very low selectivity is used, there is a problem that a large amount of recirculated gas is required to obtain high purity methane, which requires a large amount of energy. On the other hand, when a material having a high selectivity is used, the permeability tends to be low. In this case, the separation membrane process using such a material requires a small amount of high purity methane produced and a large amount of recycled material, And there is a problem that the scale of the apparatus of the process becomes large. For the above reasons, a separator material having a selectivity higher than that of the intermediate layer is preferable. Among them, it is preferable to use a polymer material such as polysulfone which is more resistant to plasticization due to pressure than polyimide.

As a result of studying the membrane process, it can be seen that the methane recovery rate and purity depend not only on the selectivity of the membrane, but also on the pressure ratio between the high and low pressure sides of the membrane. That is, the higher the pressure, the higher the plasticity of the carbon dioxide, and the lower the selectivity, the worse the separation results. Further, the larger the upper pressure and the lower pressure ratio, the better the maximum separation result can be achieved, and even if the selectivity is higher in the lower pressure ratio range, the methane purity or separation result is lowered as a result.

When the permeability of the membrane material is studied by the temperature, the lower the temperature of the supplied gas, the higher the selectivity and the lower the permeability. Accordingly, in order to compensate for the drawbacks of relatively low selectivity in the case of materials such as polysulfone or cellulose acetate, which have higher permeability than polyimide and lower selectivity, if the operating temperature of the low-temperature feed gas is adopted, It is possible to utilize the characteristics of the separator which obtains high purity methane at a high recovery rate.

Considering the process efficiency such as the concentration of residual carbon dioxide and the recovery rate, the polymer separator is a three-stage separator. The ratio of the first polymer separator area, the second polymer separator area, and the third polymer separator area is 1: 1: 5: 1. When carbon dioxide is separated into a single separation membrane, there is a problem that the concentration of residual carbon dioxide is high and the recovery rate is low. If the ratio of the first polymer membrane area, the second polymer membrane area, and the third polymer membrane area is less than 1: 1: 1 in step 2, the recovery rate and methane purity are lowered due to the low selectivity of the polymer membrane, If the ratio of the area of the first polymer membrane, the area of the second polymer membrane, and the area of the third polymer membrane exceeds 1: 5: 1, there is a problem that the recovery rate and methane There is a problem that the purity is lowered and the cost required for the separation membrane and related piping is increased.

In addition, it is preferable that the permeated portion of the first polymer separator, the second polymer separator, and the third polymer separator in the step 2 maintain a reduced pressure of 0.2 bar to 0.9 bar. If the permeability of the first polymer separator, the second polymer separator, and the third polymer separator is maintained under a reduced pressure of less than 0.2 bar in the step 2, there is a problem that the price and operation cost of the reduced pressure pump increase, , The upper / lower pressure ratio is lowered to 10 or less, so that the selectivity of the separation membrane can not be utilized to the maximum, which lowers the recovery rate and purity.

Next, in the method for separating methane gas of high purity from the biogas according to the present invention, in step 3, the permeation part of the second polymer separation membrane, together with the residual part of the third polymer separation membrane, And recirculating.

It is preferable that the end of the three-stage polymer separation membrane, that is, the permeation portion of the second polymer separation membrane and the remaining portion of the third polymer separation membrane, are recycled to the compression and cooling steps in order to improve the methane gas recovery rate of the final product gas Do.

Thus, in order to improve the recovery rate of the methane gas, the permeate portion of the second polymer separator and the remaining portion of the third polymer separator are recycled to the compression and cooling stages, and the separation membrane process is preferably repeated. At this time, the gas passing through the transmitting portion of the third polymer separator is burnt. The concentration of carbon dioxide in the gas passing through the step of separating the carbon dioxide is preferably 1 vol% or less. When the concentration of carbon dioxide in the final product gas exceeds 1 vol.%, The purity of the produced methane gas becomes low, making it difficult to use it as automobile fuel or city gas energy.

In addition,

A supply part of the biogas;

A compression and cooling unit for compressing and cooling the biogas supplied from the supply unit of the biogas;

1 to 1: 5: 1 ratio of the area of the first polymer membrane area, the area of the second polymer membrane area and the area of the third polymer membrane area for removing carbon dioxide from the compressed and cooled gas in the compression and cooling part, 1 polymer separator membrane residual stream is connected to the second polymer separator and the first polymer separator membrane permeate stream is connected to the third polymer separator; And

And a recycle line for introducing the permeate portion of the second polymer separation membrane and the remaining portion of the third polymer separation membrane into the compression and cooling portion,

Wherein the polymer separation membrane is a polymer separation membrane having a carbon dioxide permeability of 100 GPU to 1,000 GPU and a carbon dioxide / methane selectivity of 20 to 34.

1 shows an example of the methane gas purifying apparatus according to the present invention,

Hereinafter, the methane gas congestion device according to the present invention will be described in detail with reference to FIG.

In the methane gas purifying apparatus 100 according to the present invention, the biogas supplying unit 10 for supplying the biogas may be a biogas generating unit such as a biogas generated in a food waste treatment plant, a sewage sludge treatment plant, a landfill, The device introduced into the purification device may be a known device such as a blower.

Further, the methane gas purifying apparatus 100 according to the present invention may include a dehumidifying unit 20 and a pretreatment unit 30 for removing sulfur, ammonia, and siloxane from the dehumidified gas. The dehumidifying part 20 is not limited to a specific configuration, and may be, for example, a cylindrical dehumidifying device having a tube in which cooling water supplied from an external cooler is circulated.

The pretreatment unit 30 for removing sulfur, ammonia, and siloxane from the dehumidified gas in the dehumidifying unit 20 may include a desulfurization unit and a desiloxane unit. The desulfurization unit may include an iron oxide tower, The desiloxane device may include an iron oxide column, an impregnated activated carbon column, and a silica gel column. At this time, each device for the desiloxane may be connected in series or in parallel. The iron oxide-based adsorbent adsorbs a large amount of hydrogen sulfide. The hydrogen sulfide that has not been adsorbed is adsorbed by using an impregnated activated carbon adsorbent, and at this time, a part of the siloxanes are also adsorbed. Such desulfurization and desiloxane units can be operated without degradation of desulfurization and desiloxane performance even under urgent conditions, as compared with general desulfurization and desiloxane units composed of a single adsorbent. Each of the adsorbents complements each other's functions, And the siloxane can be efficiently removed.

In the methane gas purifying apparatus 100 according to the present invention, the compression and cooling unit 40 is not particularly limited as an apparatus for compressing and cooling the biogas such that the biogas is suitable for the separation membrane process, And any device capable of cooling can be used.

The compression and cooling unit 40 is composed of a compression unit 41 and a cooling unit 42. The compression unit 41 compresses the pretreated biogas into a bio- In this case, the pressure of the compressed biogas is preferably 3 to 11 bar. If the pressure of the biogas compressed by the compression unit is less than 3 bar, the purity and recovery rate of the methane due to the lowering of the upper pressure / lower pressure ratio of the separation membrane process is greatly reduced due to the low selection of the polymer separation membrane. Even when the pressure exceeds 11 bar, there is a problem that the purity and recovery rate of the final methane may be lowered or the membrane may be damaged due to the decrease in selectivity due to the plasticization due to carbon dioxide in the separation membrane process.

The cooling unit 42 is configured to cool the temperature of the biogas to match the inlet temperature for the separation process of the biogas, and the temperature of the cooled gas is preferably -20 ° C to 10 ° C. If the temperature of the biogas cooled by the cooling unit is lower than -20 ° C, the selectivity of the polymer separation membrane becomes extremely high, but the cooling cost of the entire separation membrane apparatus becomes high. Particularly, And if the temperature is higher than 10 ° C, the selectivity of the polymer separator is greatly lowered, so that the recovery rate and purity of methane are lowered and the separator may be damaged due to heat.

The cooling unit 42 prevents the temperature of the biogas from being heated due to the heat of compression generated during the compression of the biogas in the compression unit 41 and increases the efficiency of the separation membrane of the biogas by cooling the proper temperature Thereby increasing the production efficiency of methane produced.

In the methane gas purification apparatus 100 according to the present invention, the purification unit 50 includes a first polymer separator 51 connected in series with the biogas compressed and cooled by the compression and cooling unit 40, The polymer separator 52 and the third polymer separator 53 to be separated into methane and carbon dioxide.

The ratio of the area of the first polymer separator 51, the area of the second polymer separator 52, and the area of the third polymer separator 53 is preferably 1: 1: 1 to 1: 5: 1. When carbon dioxide is separated into a single separation membrane, there is a problem that the concentration of residual carbon dioxide is high and the recovery rate is low. If the ratio of the first polymer membrane area, the second polymer membrane area, and the third polymer membrane area is less than 1: 1: 1, the lower selectivity of the polymer membrane lowers the recovery rate and purity of methane, When the ratio of the first polymer membrane area, the second polymer membrane area, and the third polymer membrane area is more than 1: 5: 1, there is a problem that the energy required for compression is high. There is a problem that the purity is lowered and the cost required for the separation membrane and related piping is increased.

In addition, the material used in the separation process for separating carbon dioxide is preferably a polymer material having a carbon dioxide / methane selectivity of 20 to 34, more preferably an amorphous or semi-crystalline polymer. For example, polysulfone, poly Most preferred are carbonates, polyethylene terephthalates, cellulose acetates, polyphenylene oxides, polysiloxanes, polyethylene oxides, polypropylene oxides, and mixtures thereof. In addition, polymer materials designed to have low selectivity in order to increase the permeability of carbon dioxide in the manufacturing process of the membrane material may be included.

At this time, in the case of a separation membrane in which a selective layer is processed into a thin film by a phase transfer method or a thin film coating method using an asymmetric composite membrane or a hollow fiber membrane, the carbon dioxide permeability is preferably 100 GPU to 1,000 GPU. The unit of area (cm ² ), the unit pressure (mmHg) of the separation membrane, and the unit pressure (mmHg) of the separation membrane are represented by the gas permission unit (1 GPU = (10 ^-6 cm m ³ ) / (cm ² sec sec mm mmHg) And the volume (cm < ³ >) of carbon dioxide permeated per unit time (sec).

Generally, polyisocyanurates and polyimides used in separator materials have high selectivity. In the present invention, polysulfone, which has intermediate selectivity but is superior in plasticization resistance against carbon dioxide to polyimide and low in resin price, Cellulose acetate or the like is used. When a separator material having a very low selectivity is used, there is a problem that a large amount of recirculated gas is required to obtain high purity methane, which requires a large amount of energy. On the other hand, when a material having a high selectivity is used, the permeability generally tends to be low. In the separation membrane process using such a material, the amount of gas to be permeated is small and the processing capacity is insufficient. And there is a problem that the scale of the apparatus of the process becomes large. For such reasons, it is preferable to use a separator material having a selectivity of medium or higher but high permeability to carbon dioxide. Among them, it is preferable to use a polymer material such as polysulfone which is more resistant to plasticization due to pressure than polyimide Do.

In the methane gas purifying apparatus according to the present invention, the purifying section 50 is provided with a permeating section of the second polymer separating membrane 52 and a part for recirculating the remaining portion of the third polymer separating membrane 53 to the compression and cooling section 40 1 recirculation line 61 and a second recirculation line 62, as shown in FIG. By recycling the methane present in the permeate portion through the recycle, the recovery rate of the methane gas can be improved.

Hereinafter, a method for separating high-purity methane gas from a biogas will be described with reference to the methane gas purifier 100. The biogas is supplied from the biogas supply unit 10 and the dehumidifying unit 20 and the pre- 30, the water, sulfur, ammonia, and siloxane are removed, and the biogas pretreated in the compression and cooling section 40 is compressed and cooled at an appropriate pressure and temperature. Next, the carbon dioxide contained in the biogas is supplied to the third polymer separator (53) through the permeate portion of the first polymer separator when supplied to the first polymer separator (51) of the purifier (50) And passes through the remaining portion of the polymer membrane. At this time, a certain amount of carbon dioxide that is not permeable to the gas passing through the remaining portion of the first polymer separator is included, and the biogas containing the carbon dioxide is supplied to the second polymer separator 52 again. Most of the supplied biogas passes through the second polymer separator, and the biogas passing through the remaining portion of the second polymer separator has high purity (95% or more) of methane . Meanwhile, the carbon dioxide contained in the biogas supplied to the third polymer separator through the permeate of the first polymer separator permeates through the third polymer separator, and the third polymer separator permeate gas is directly combusted, or carbon dioxide Can be connected to the process of recovering the water. At this time, the carbon dioxide concentration of the gas passing through the third polymer membrane permeation portion is preferably 90% or more, more preferably 95% to 99%. If the concentration of carbon dioxide in the gas is less than 90%, the production efficiency of methane gas may be lowered. In addition, the gas that has passed through the first polymer membrane permeable portion is supplied to the compression and cooling portion through the second recirculation line (62) connected to the third polymer membrane remnant portion.

The pressure of the gas supplied to the first polymer separator 51, the second polymer separator 52 and the third polymer separator 53 is preferably 3 bar to 11 bar, and the pressure of the permeable portion is 0.2 bar to 0.9 bar It is preferable to maintain the decompression condition and keep the ratio of the upper and lower pressures to 10 to 50 as appropriate. The pressure of the gas supplied to the first polymer separator, the second polymer separator, and the third polymer separator is regulated by the compression unit 41, and a vacuum pump or a blower (not shown) is used to regulate the pressure of the transmission unit .

Further,

Methane gas having a purity of 95% or more separated by the above method is provided.

The methane gas according to the present invention produced methane gas having a purity of 95% or more, methane gas having high purity from biogas generated from food waste and organic matter by the methane gas separation method according to the present invention. At this time, the methane gas separation method according to the present invention is excellent in the methane production rate by recycling the remaining trace amount of methane to be purified again through the three-step separation membrane process.

In addition,

And provides automobile fuel and city gas containing the high purity methane gas.

According to the present invention, it is possible to efficiently separate and utilize high purity methane by purifying biogas discharged from a food waste disposal site, a sewage sludge disposal site, a landfill site, an animal wastewater treatment site, etc., and the separated methane gas is 95% And the recovery rate is 90% or more, so that it is separated into low energy cost, low plant cost, and low operation cost. The methane gas fuel having a purity of 95% or more as described above can be used as city gas or automobile fuel.

Hereinafter, the present invention will be described in detail with reference to the following examples and experimental examples.

It should be noted, however, that the following examples and experimental examples are illustrative of the present invention, but the scope of the invention is not limited by the examples and the experimental examples.

<Experimental Example 1> Determination of methane gas separation efficiency according to operating pressure

Confirmation of methane gas separation efficiency of methane gas separation method of the present invention depending on operating pressure

In order to confirm the methane gas separation efficiency according to the operation pressure of the biogas compression process of the methane gas separation method according to the present invention, the following experiment was performed.

The methane gas was purified using biogas from a food waste treatment facility located in the Paju Facilities Management Corporation and a module made of a polysulfone separator (carbon dioxide / methane selectivity 30, carbon dioxide permeability 120 GPU). The composition of the supplied biogas was about 65% to 75% by volume of methane, about 25% to 35% by volume of carbon dioxide, about 1500 ppm to 2500 ppm of hydrogen sulfide, about 90 ppm to 100 ppm of siloxane and about 3500 ppm to 4500 ppm of moisture. The supplied biogas was pretreated to remove hydrogen sulfide in an amount of 20 ppm or less and siloxane in an amount of 0.1 ppb or less and dehumidified to a dew point temperature of -15 ° C and maintained at a temperature of 10 ° C. The pressure of the pre-treated biogas supplied to the purification part was adjusted to be 2 to 14 bar, the permeation part pressure of the first polysulfone hollow fiber membrane was 3 bar, the permeation part pressure of the second polysulfone hollow fiber membrane and the third polysulfone hollow fiber membrane Was maintained at 0.8 bar. The separation membrane process was performed by feeding biogas at a rate of 100 L / min at an area ratio of the first polysulfone hollow fiber membrane, the second polysulfone hollow fiber membrane and the third polysulfone hollow fiber membrane at a ratio of 1: 1: 1, Are shown in Table 2 below.

In the following Table 2, the recovery rate was calculated by the following equation (1) in terms of the amount of purified methane of 90% to 99% with respect to the amount of lower methane charged.

&Quot; (1) &quot;

Operating temperature
(° C)
supply
flux
(L / min)
supply
pressure
(bar) The first polysulfone
Hollow fiber membrane area: second polysulfone
Hollow fiber membrane area: third polysulfone hollow fiber membrane area
The second polysulfone
Hollow fiber membrane
Residual portion
Third polysulfone
Hollow fiber membrane
Transmission portion

Recovery rate
(%)





10





100
2





1: 1: 1 Flow rate (L / min) 80.0
87.7 Methane concentration (%) 89.4 7.1 Carbon dioxide concentration (%) 10.6 92.9
3 Flow rate (L / min) 71.2
98.1 Methane concentration (%) 96.4 5.5 Carbon dioxide concentration (%) 3.6 94.5
8 Flow rate (L / min) 69.9
97.5 Methane concentration (%) 97.1 4.6 Carbon dioxide concentration (%) 2.9 95.4
11 Flow rate (L / min) 66.3
92.0 Methane concentration (%) 97.8 2.7 Carbon dioxide concentration (%) 2.2 97.3
14 Flow rate (L / min) 61.1
82.7 Methane concentration (%) 99.3 1.2 Carbon dioxide concentration (%) 0.7 98.8

As shown in Table 2, at the same operating temperature and at a supply flow rate of 10 ° C. and 100 L / min, high-purity methane having a purity of 95% or more at an operating pressure of 3 bar to 11 bar was separated at a high recovery rate of 90% . The purity of the methane finally produced tends to increase as the pressure increases, and the recovery rate decreases as the flow rate of the second polysulfone hollow fiber membrane residue decreases.

<Experimental Example 2> Separation efficiency of methane gas according to permeation pressure of the first polysulfone hollow fiber membrane and the second polysulfone hollow fiber membrane

1st Polysulfone  The hollow fiber membrane and the second Polysulfone  Hollow fiber membrane Transmission portion  Confirmation of methane gas separation efficiency of the methane gas separation method of the present invention by pressure

The following experiments were carried out to confirm methane gas separation efficiency according to the permeation pressure of the first polysulfone hollow fiber membrane and the second polysulfone hollow fiber membrane of the methane gas separation method according to the present invention.

A methane gas separation method was carried out by installing a blower to confirm methane gas separation efficiency depending on whether the pressure of the first polysulfone hollow fiber membrane and the second polysulfone hollow fiber membrane permeation was reduced.

Methane gas was purified using biogas from a food waste treatment facility located in the Paju Facilities Management Corporation and a module made of a polysulfone separator (carbon dioxide / methane selectivity 34, CO2 permeability 200 GPU). The composition of the supplied biogas was about 65% to 75% by volume of methane, about 25% to 35% by volume of carbon dioxide, about 1500 ppm to 2500 ppm of hydrogen sulfide, about 90 ppm to 100 ppm of siloxane and about 3500 ppm to 4500 ppm of moisture. The supplied biogas was pretreated to remove hydrogen sulfide in an amount of 20 ppm or less and siloxane in an amount of 0.1 ppb or less and dehumidified to a dew point temperature of -15 ° C and maintained at a temperature of 0 ° C. The pressure of the pre-treated biogas supplied to the purification part was adjusted to be 8 bar, and the permeation part pressure of the first polysulfone hollow fiber membrane and the second polysulfone hollow fiber membrane was adjusted to be 0.5 bar to 1 bar. The separation membrane process was performed by supplying biogas at a rate of 100 L / min at an area ratio of 1: 2: 1 of the first polysulfone hollow fiber membrane, the second polysulfone hollow fiber membrane, and the third polysulfone hollow fiber membrane. Are shown in Table 3 below.

Operating temperature
(° C)
supply
flux
(L / min)
supply
pressure
(bar) The first polysulfone hollow fiber membrane
Of the second polysulfone hollow fiber membrane
Permeate pressure
(bar)
The second polysulfone
Hollow fiber membrane
Residual portion
Third polysulfone
Hollow fiber membrane
Transmission portion

Recovery rate
(%)



0



100



8
0.5 Flow rate (L / min) 53.3
98.4 Methane concentration (%) 99.7 1.4 Carbon dioxide concentration (%) 0.3 98.6
0.8 Flow rate (L / min) 66.9
97.2 Methane concentration (%) 97.9 3.0 Carbon dioxide concentration (%) 2.1 97.0
One Flow rate (L / min) 69.9
89.2 Methane concentration (%) 97.1 4.6 Carbon dioxide concentration (%) 2.9 95.4

As shown in Table 3 above, when the experiment was conducted at the same operating temperature and supply flow rate of 0 ° C and 100 L / min, the operating pressure was 8 bar and the permeate pressure of the first polysulfone hollow fiber membrane and the second polysulfone hollow fiber membrane was It was observed that 95% or more of high purity methane at 0.5 bar and 0.8 bar was separated at a high recovery of 90% or more. The purity and recovery rate of the methane produced at the end was higher as the permeate pressure was lower.

<Experimental Example 3> Determination of methane gas separation efficiency according to operating temperature

Determination of methane gas separation efficiency of methane gas separation method of the present invention according to operating temperature

In order to confirm the methane gas separation efficiency according to the operating temperature of the methane gas separation method according to the present invention, the following experiment was performed.

The methane gas was purified using biogas from a food waste treatment facility located in the Paju Facilities Management Corporation and a module made of a polysulfone separator (carbon dioxide / methane selectivity 30, carbon dioxide permeability 120 GPU). The composition of the supplied biogas was about 65% to 75% by volume of methane, about 25% to 35% by volume of carbon dioxide, about 1500 ppm to 2500 ppm of hydrogen sulfide, about 90 ppm to 100 ppm of siloxane and about 3500 ppm to 4500 ppm of moisture. The supplied biogas was pretreated to remove hydrogen sulfide in an amount of 20 ppm or less and siloxane in an amount of 0.1 ppb or less, and the dew point temperature was adjusted to -15 ° C, followed by adjusting the temperature to -15 ° C to 35 ° C. The pressure of the pretreated biogas supplied to the purification part was adjusted to be 11 bar, and the permeation part pressure of the first polysulfone hollow fiber membrane and the second polysulfone hollow fiber membrane was maintained at 0.5 bar. The separation membrane process was performed by supplying biogas at a rate of 100 L / min at an area ratio of 1: 2: 1 of the first polysulfone hollow fiber membrane, the second polysulfone hollow fiber membrane, and the third polysulfone hollow fiber membrane. Are shown in Table 4 below.

Operating temperature
(° C)
supply
flux
(L / min)
supply
pressure
(bar) The first polysulfone
Hollow fiber membrane area: second polysulfone
Hollow fiber membrane area: third polysulfone hollow fiber membrane area
The second polysulfone
Hollow fiber membrane
Residual portion
Third polysulfone
Hollow fiber membrane
Transmission portion

Recovery rate
(%)
-15




100




11




1: 2: 1 Flow rate (L / min) 73.7
98.6 Methane concentration (%) 97.2 9.2 Carbon dioxide concentration (%) 2.8 90.8
10 Flow rate (L / min) 71.5
96.2 Methane concentration (%) 96.7 5.9 Carbon dioxide concentration (%) 3.3 94.1
15 Flow rate (L / min) 68.0
89.6 Methane concentration (%) 95.6 4.2 Carbon dioxide concentration (%) 4.4 95.8
35 Flow rate (L / min) 57.8
81.9 Methane concentration (%) 91.3 1.6 Carbon dioxide concentration (%) 8.7 98.4

As shown in Table 4, it was observed that 95% or more of high purity methane was separated at a high recovery rate of 90% or more when the temperature of the compressed biogas was 10 ° C or lower. Methane purity tended to decrease as the operating temperature increased to 35 ° C. As the operating temperature increased, the permeability of the polysulfone hollow fiber membrane was improved and the recovery rate of the second polysulfone hollow fiber membrane decreased, .

Experimental Example 4 Methane gas separation efficiency was determined according to the ratio of the first polysulfone hollow fiber membrane area, the second polysulfone hollow fiber membrane area and the third polysulfone hollow fiber membrane area

1st Polysulfone  Hollow fiber membrane area, 2nd Polysulfone  Hollow fiber membrane area and third Polysulfone  Determination of methane gas separation efficiency of the methane gas separation method of the present invention according to the ratio of the hollow fiber membrane area

In order to confirm methane gas separation efficiency according to the ratio of the first polysulfone hollow fiber membrane area, the second polysulfone hollow fiber membrane area and the third polysulfone hollow fiber membrane area of the methane gas separation method according to the present invention, the following experiment was performed Respectively.

Methane gas was purified using a biogas generated from a food waste treatment facility located in the Paju Facilities Management Corporation and a module made of a polysulfone separator (carbon dioxide / methane selectivity of 25, carbon dioxide permeability of 100 GPU). The composition of the supplied biogas was about 65% to 75% by volume of methane, about 25% to 35% by volume of carbon dioxide, about 1500 ppm to 2500 ppm of hydrogen sulfide, about 90 ppm to 100 ppm of siloxane and about 3500 ppm to 4500 ppm of moisture. The supplied biogas was pretreated to remove hydrogen sulfide in an amount of 20 ppm or less and siloxane in an amount of 0.1 ppb or less, and the dew point temperature was dehumidified to -15 캜 and maintained at a temperature of 10 캜. The pressure of the pretreated biogas supplied to the purification section was adjusted to be 8 bar, and the permeate pressure of the first polysulfone hollow fiber membrane and the second polysulfone hollow fiber membrane was maintained at 1 bar. Also, biogas was supplied at a rate of 100 L / min to adjust the area ratio of the first polysulfone hollow fiber membrane and the second polysulfone hollow fiber membrane to 2: 1: 1 and 1: 1: 1 to 1: 7: 1, And the results are shown in Table 5 below.

Operating temperature
(° C)
supply
flux
(L / min)
supply
pressure
(bar) The first polysulfone
Hollow fiber membrane area: second polysulfone
Hollow fiber membrane area: third polysulfone hollow fiber membrane area
The second polysulfone
Hollow fiber membrane
Residual portion
Third polysulfone
Hollow fiber membrane
Transmission portion

Recovery rate
(%)






10






100






8
2: 1: 1 Flow rate (L / min) 77.6
84.6 Methane concentration (%) 92.3 3.2 Carbon dioxide concentration (%) 7.7 96.8
1: 1: 1 Flow rate (L / min) 69.9
92.2 Methane concentration (%) 97.1 4.6 Carbon dioxide concentration (%) 2.9 95.4
1: 3: 1 Flow rate (L / min) 70.0
98.3 Methane concentration (%) 96.8 1.9 Carbon dioxide concentration (%) 3.2 98.1
1: 4: 1 Flow rate (L / min) 68.9
95.1 Methane concentration (%) 97.1 1.8 Carbon dioxide concentration (%) 2.9 98.2
1: 5: 1 Flow rate (L / min) 68.4
93.7 Methane concentration (%) 97.4 2.4 Carbon dioxide concentration (%) 2.6 97.6
1: 7: 1 Flow rate (L / min) 60.9
81.6 Methane concentration (%) 98.3 6.8 Carbon dioxide concentration (%) 1.7 93.2

As shown in Table 5 above, as the ratio of the first polysulfone hollow fiber membrane area, the second polysulfone hollow fiber membrane area, and the third polysulfone hollow fiber membrane area increases from 1: 1: 1 to 1: 3: 1, The purity and recovery rate of the final methane gas recovered from the remaining part of the polysulfone hollow fiber membranes gradually increases and the purity of the final methane gas increases as the ratio increases from 1: 4: 1 to 1: 5: 1, but the recovery rate gradually decreases Respectively. Accordingly, in order to separate high purity methane having a purity of about 95% or more at a high recovery rate of 90% or more, it is confirmed that the ratio of the first polysulfone hollow fiber membrane area to the second polysulfone hollow fiber membrane area should be 1: 1: 1 to 1: 5: 1 I could.

100: methane gas purification apparatus
10:
20: Dehumidification part
30:
40: Compression and cooling unit
41:
42:
50:
51: First polymer membrane
52: Second polymer membrane
53: Third polymer membrane
61: first recirculation line
62: second recirculation line

Claims (10)

Compressing and cooling the biogas to a pressure of 3 bar to 11 bar and a temperature of the biogas to -20 ° C to 10 ° C (step 1);
The biogas compressed and cooled in step 1 is mixed with the first polymer membrane separation membrane area, the second polymer membrane separation membrane area, and the third polymer membrane separation membrane area ratio of 1: 1: 1 to 1: 5: 1, The first polymer membrane permeate stream is introduced into the third polymer membrane for gas separation connected to the third polymer membrane, and the permeate portion of the first polymer membrane, the permeate portion of the second polymer membrane, and the third polymer Separating methane and carbon dioxide by maintaining the permeate portion of the membrane at a reduced pressure of 0.2 bar to 0.9 bar (Step 2); And
(Step 3) of recycling the permeate portion of the second polymer separation membrane to the compression process of Step 1 together with the remaining portion of the third polymer separation membrane while maintaining the reduced pressure, wherein the polymer separation membrane has a carbon dioxide permeability of 100 GPU 1,000 GPU, and the selectivity of carbon dioxide to methane is 20 to 34. A method for separating methane gas from a biogas.
The method according to claim 1,
Wherein the biogas of step 1 comprises at least one selected from the group consisting of water, hydrogen sulfide, ammonia, siloxane, nitrogen and oxygen in an amount of 0.0001 to 0.1 vol% as an impurity. Separation method.
The method according to claim 1,
The polymer separator is one kind of polymer separator selected from the group consisting of polysulfone, polycarbonate, polyethylene terephthalate, cellulose acetate, polyphenylene oxide, polysiloxane, polyethylene oxide, polypropylene oxide and mixtures thereof A method for separating methane gas from a biogas.
The method according to claim 1,
Wherein the biogas of step 1 is subjected to at least one pretreatment selected from the group consisting of dehumidification, desulfurization, deammonia and desiloxane treatment.
A supply part of the biogas;
A compression and cooling unit for compressing and cooling the biogas supplied from the supply unit of the biogas to a pressure of 3 bar to 11 bar and a temperature of -20 ° C to 10 ° C;
1 to 1: 5: 1 ratio of the area of the first polymer membrane area, the area of the second polymer membrane area and the area of the third polymer membrane area for removing carbon dioxide from the compressed and cooled gas in the compression and cooling part, 1 polymer separator membrane residual stream is connected to the second polymer separator and the first polymer separator membrane permeate stream is connected to the third polymer separator; And
And a recycle line for introducing the permeate portion of the second polymer separation membrane and the remaining portion of the third polymer separation membrane into the compression and cooling portion,
Wherein the polymer separator is a polymer separator having a carbon dioxide permeability of 100 GPU to 1,000 GPU and a selectivity of carbon dioxide to methane of 20 to 34.
6. The method of claim 5,
Wherein the methane gas purifier includes a dehumidifier for removing moisture from the biogas supplied by the biogas supply unit; And a pretreatment unit for removing sulfur and siloxane from the dehumidified gas in the dehumidifying unit.
6. The method of claim 5,
Wherein the methane gas purifying apparatus is capable of separating 95% by volume or more methane gas at a recovery rate of 90% by volume to 99% by volume.
The method of claim 1, wherein the methane gas is separated into at least 95 vol% of purity.
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