CN1274648C - Production and apparatus for producing methane from refuse embedded gas - Google Patents

Abstract

The invention relates to a method and equipment for preparing methane from landfill gas, and belongs to the fields of waste treatment and renewable energy. The method includes compressing the extracted landfill gas, freeze-drying, multi-stage filtration, and then performing a pretreatment process of adsorption drying; and then performing a pressure swing adsorption cycle production process of high-pressure adsorption, parallel flow equalization, and normal pressure regeneration; The equipment includes a compressor, a cold dryer, a filter and a drying tower connected in sequence, and a pressure swing adsorption cycle system is composed of 2 to 6 adsorption columns connected in parallel. The invention has the advantages of simple equipment, convenient process operation, low investment, less land occupation and good flexibility. In addition to landfill gas, the raw material gas can also be a variety of biogas; the product gas can be directly used as compressed natural gas (CNG) for vehicles after compression, and city gas, chemical raw material gas, etc. can also be produced by changing the process parameters.

Description

A method and equipment for producing methane from landfill gas

technical field

The invention belongs to the field of garbage treatment and renewable energy, and is characterized in that it relates to a resource utilization method of landfill gas and other biogas with similar components.

technical background

Landfill gas (Landfill Gas, LFG) contains 40-70% CH ₄ and 30-50% CO ₂ respectively, and its calorific value is about 4500-5500kcal/Nm ³ , that is, the energy produced by burning LFG per cubic meter is about the same It is better than 0.45 liters of diesel or 0.6 liters of gasoline, so it is a clean fuel with high utilization value. About 22-36 million tons of CH ₄ from landfills are discharged into the atmosphere every year in the world, polluting the environment and wasting a lot of renewable energy. Take China as an example. In 2000, the volume of urban waste removal in China reached 130 million tons. The statistical data of the past 20 years show that the amount of urban waste in China is increasing at a rate of 8-10% per year, and the current main treatment method is still sanitary filling. According to this, it can be speculated that the production of LFG in China is increasing day by day. It is predicted that by 2010 China's landfill methane production will reach 6.6 billion m ³ , based on a utilization rate of 30%, equivalent to saving 2.4 million tons of standard coal, equivalent to about 2.23 billion m ³ of natural gas. Therefore, LFG is one of the biomass energy to be developed and utilized.

The four main components of landfill gas are CH ₄ , CO ₂ , N ₂ and O ₂ . Currently, there are three ways to purify CH ₄ from landfill gas: absorption separation, adsorption separation and membrane separation. Since CO ₂ is a weakly acidic gas, most of CO ₂ in landfill gas can be removed by absorption separation using alkaline solution as absorbent, but the solubility of N ₂ and O ₂ in the solution is very small, and the separation effect is not obvious. Membrane separation uses the different permeability of the membrane to carbon dioxide and methane to realize the separation of CO ₂ /CH ₄ , but the membrane separation process needs to be completed under a high pressure of 1.7-5.5Mpa, and the technical and economic costs are relatively high. Adsorption separation adopts temperature swing adsorption, which requires heating, consumes a lot of energy, and takes a long time to complete a cycle. It is generally used in small-scale industrial production.

Contents of the invention

The purpose of the present invention is to solve the problem that landfill gas is discharged into the atmosphere and pollute the environment while wasting a lot of energy. A new method for producing methane from LFG is proposed, and methane is produced by separating and purifying LFG to make LFG Become a renewable clean energy, and has the characteristics of simplicity and high efficiency.

A method for producing methane from landfill gas proposed by the present invention includes a pretreatment process and a pressure swing adsorption cycle production process;

The pretreatment process includes the following steps:

1) Compress the extracted landfill gas, the compressed gas pressure is 0.08-0.2MPa;

2) Freeze-dry the compressed gas to remove part of the water vapor, and the freezing temperature is -10～-25°C;

3) Filter the compressed and condensed gas to remove various impurity gases such as particulate matter and H ₂ S;

4) The filtered gas is then adsorbed and dried with activated alumina to remove the remaining water vapor;

The pressure swing adsorption cycle production process specifically comprises the following steps:

5) High-pressure adsorption, the gas after adsorption and drying is passed into the first adsorption unit for high-pressure adsorption, the adsorption pressure is 0.3-0.6Mpa, the adsorption time is 30-120s, and the product gas enriched in methane is obtained. From the first adsorption unit Collect at the outlet valve;

6) Co-current pressure equalization, the first adsorption unit that completes the high-pressure adsorption closes the outlet valve, and then communicates with the subsequent second adsorption unit, so that the pressure of the two adsorption units is the same;

7) Atmospheric pressure regeneration, after the first adsorption unit completes pressure equalization, its outlet valve is opened to communicate with the atmosphere to discharge the residual gas in it, and the product gas is introduced from the inlet for back blowing, the back blowing flow rate is 0.8-2.0Nm ³ / h, to regenerate the adsorbent of the adsorption unit;

8) The second adsorption unit performs steps 5-7 in sequence to complete high-pressure adsorption, co-current pressure equalization and regeneration, and so on, each adsorption unit performs steps 5-7 in sequence; the adsorption system completes a pressure swing adsorption cycle.

The present invention also proposes the equipment for realizing the above method, including a pretreatment unit and a production unit connected thereto; the pretreatment unit includes a compressor, a cold dryer, a filter and a drying tower connected in sequence; to remove particulate impurities in the LFG, Moisture, H ₂ S gas and other impurity gases, and stabilize the gas flow and pressure entering the production unit; the production unit uses 2 to 6 adsorption columns connected in parallel to form a pressure swing adsorption cycle system to realize the separation and purification of methane.

Features and effects of the present invention:

The pretreatment unit is to remove particulate impurities, moisture, H ₂ S gas and other impurity gases in the LFG, and to stabilize the gas flow and pressure entering the production unit at a certain level, so as to ensure the subsequent pressure swing adsorption (Pressure SwingAdsorption, PSA) production unit runs normally and stably (among them, alumina adsorption drying is a key step, which ensures that the gas entering the pressure swing adsorption tower is dry, while protecting the adsorbent in the adsorption tower from damage, it also ensures that the product gas Meet the requirements for water dew point in the national CNG standard for vehicles.);

The adsorption tower of the production unit can be filled with 3A, 4A, 5A and 13X zeolites and various long and short carbon molecular sieves; the pressure swing adsorption time is 30-120s, and the adsorption pressure is 0.3-0.6Mpa; The product gas is blown back to the adsorption tower, the blowback flow rate is 0.8-2.0Nm ³ /h; the system gas production rate is 4-10m ³ /h (pressure 0.3MPa).

The pretreatment unit of the present invention removes particulate impurities, moisture, _H2S gas and other impurity gases in the LFG by means of compression condensation, multi-stage filtration and alumina adsorption drying, and makes the gas entering the system reach a stable flow rate and pressure. The production unit completes the separation of methane and carbon dioxide, the main components in LFG, by means of pressure swing adsorption, provides methane product gas with a purity of more than 96%, and achieves a methane recovery rate of more than 55%.

The invention has simple equipment, convenient operation, low investment, less land occupation and good flexibility. In addition to landfill gas, the raw material gas can also be a variety of biogas; the product gas can be directly used as compressed natural gas (CNG) for vehicles after compression, and city gas, chemical raw material gas, etc. can also be produced by changing the process parameters.

Description of drawings

Fig. 1 is the whole process flowchart of the method of the present invention.

Detailed ways

The specific process of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

The embodiment of the method and equipment of the present invention is shown in Figure 1, wherein the solid line represents the feed gas, the dotted line represents the product gas, and the dotted line represents the tail gas. The equipment of the system used in this embodiment comprises:

The inlet of the 200m ³ /h air pump is connected to the gas collection system of the landfill site, the outlet is connected to the gas storage tank 2 with an effective volume of 25m ³ through the valve, the outlet of the gas storage tank 2 is connected to the compressor 3 through the valve, and the power of the compressor 3 It is 500kW and can compress the raw gas to 1MPa. The compressor 3 is directly connected to the cold dryer 4. The cold dryer 4 is directly connected to the filter 5. The filter is filled with natural quartz sand, and the filter outlet passes through the flow meter in turn. 1. The thermometer is connected to the drying tower 6, which is filled with activated alumina, and the outlet of the drying tower 6 is connected to the adsorption tower 7, and the adsorption tower 7 has a tail gas outlet and a product gas outlet.

The above-mentioned gas storage tank 2, compressor 3, cold dryer 4, and filter 5 of the present embodiment are directly connected, and the filter and the drying tower 6 all adopt conventional chemical equipment, and activated alumina is filled in the drying tower; the adsorption tower 7 is also Belonging to conventional equipment, the adsorption tower 7 of this embodiment consists of two adsorption columns A and B connected in parallel to form a pressure swing adsorption system. The inner diameter of the adsorption column is 0.30m, and the filling height of the adsorbent in the adsorption column is 0.66m.

The method for producing methane from landfill gas by using the equipment of this embodiment comprises the following steps:

1) Air extraction pump 1 extracts the raw material gas from the air extraction well of the landfill, sends it to the gas storage tank 2 for buffering, and then compresses it through the compressor 3. The compressed gas pressure is 0.08-0.2 MPa;

2) The compressed gas is sent to the cold dryer 4 to freeze and dry to remove part of the water vapor, and the cooling temperature is -10 to -25°C, preferably around -15°C;

3) The freeze-dried gas is sent to the filter 5 to filter out various impurity gases such as particulate matter and H ₂ S. The impurity particle size in the filtered gas is less than 5 μm, the impurity content is ≤0.03g/Nm ³ , and the H ₂ S content is ≤ 20mg/ ^Nm3 ;

4) Reenter the drying tower 6 and utilize the activated alumina in the tower to remove the remaining water vapor, and the relative humidity of the gas is <35% (under the condition of 0.2MPa);

5) After the pretreated gas enters the adsorption tower 7 composed of two adsorption columns and filled with 4A zeolite, it is firstly subjected to high-pressure adsorption, and the raw material gas enters the adsorption column A, pressurized to above 0.3Mpa, and the pressure swing adsorption time is 30s ( Including the time of boosting process);

6) After the high-pressure adsorption of the adsorption column A is completed, the adsorption column A and the adsorption column B are connected to carry out parallel current pressure equalization (in this embodiment, the pressure of the adsorption column A drops to about 0.15 MPa, and the pressure of the adsorption column B rises from normal pressure to about 0.15 MPa. MPa, parallel current pressure equalization time 5s);

7) After the co-current pressure equalization is completed, the outlet valve of the adsorption column A is connected to the atmosphere, the residual gas in the column is removed, and the product gas is introduced for purging (the flow rate of the product gas blowback in this embodiment is 0.8Nm ³ /h), and the adsorption is completed. Atmospheric pressure regeneration of the adsorbent of column A;

8) At the same time that adsorption column A is regenerated under normal pressure, adsorption column B performs high-pressure adsorption, which is the same as the high-pressure adsorption of adsorption column A; after adsorption column B completes high-pressure adsorption, adsorption columns A and B are connected for parallel flow and pressure equalization, One pressure swing adsorption cycle of the adsorption tower 7 is completed. The gas production rate of the system is 4m ³ /h.

In another embodiment, the configuration of the system equipment is the same as that of the above embodiment. The adsorption tower 7 consists of four adsorption columns connected in parallel to form a pressure swing adsorption system, and the adsorption columns are filled with 13X zeolite. Step 2) The temperature of the cold dryer is -20°C. Step 5) The pressure swing adsorption time is 105s, the adsorption pressure is 0.6MPa, the product gas blowback flow rate is 2.0Nm ³ /h, and the system gas production rate is 10m ³ /h.

Claims (3)

1. a method of producing methane from garbage loading embeading gas is characterized in that, comprises pretreatment technology and transformation sorption cycle production technique;

This pretreatment technology may further comprise the steps:

1) the garbage loading embeading gas that extracts is compressed, compression back gaseous tension is 0.08～0.2MPa;

2) will compress back gas and carry out lyophilize and remove portion water steam, freezing temp-10～-25 ℃;

3) gas behind the compression condensation is filtered filtering particulate matter and H wherein ₂Various foreign gases such as S;

4) the gas reusing activated alumina after the filtration carries out adsorption dry removal surplus water steam;

Described transformation sorption cycle production technique specifically may further comprise the steps:

5) high pressure absorption will the gas after adsorption dry feeds first absorbing unit and carries out high pressure absorption, and adsorptive pressure is 0.3～0.6Mpa, and adsorption time is 30～120s, obtains the enrich methane product gas, collects from this first absorbing unit outlet valve;

6) co-current and pressure equalization is finished first absorbing unit of high pressure absorption and is closed outlet valve, is communicated with thereafter second absorbing unit again, makes two absorbing unit pressure identical;

7) after normal pressure regeneration, first absorbing unit were finished and all pressed, its outlet valve was opened with atmosphere and is communicated the discharge of the residual gas in it, and introduced product gas from import and carry out blowback, and the blowback flow is 0.8～2.0Nm ³/ h makes the adsorbent reactivation of this absorbing unit;

8) second absorbing unit process of carrying out step 5-7 is successively finished high pressure absorption, co-current and pressure equalization and regeneration, and each absorbing unit carries out the process of step 5-7 successively by that analogy; This adsorption system is finished a transformation sorption cycle.

2. an equipment of producing methane from garbage loading embeading gas is characterized in that: comprise pretreatment unit and coupled productive unit; This pretreatment unit comprises compressor, cooling driers, filter and the drying tower that connects successively; To remove granule foreign, moisture, the H in the landfill gas ₂S gas and other foreign gas, and make gas flow, the pressure-stabilisation that enters productive unit; This productive unit adopts 2～6 adsorption columns formation in parallel transformation sorption cycle system, to realize separation, the purification of methane.

3. according to the described equipment of claim 2, it is characterized in that: the weighting material in the described pressure-swing absorber is selected one or more of 3A, 4A, 5A, 13X zeolite and length carbonaceous molecular sieve.

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