Biogas decarbonization and purification scheme
Biogas composition table
| serial number |
Gases |
VOL % |
Remark |
| 1 |
CH4 |
59.41
|
50~65 |
| 2 |
CO2 |
30.82
|
35~40 |
| 3 |
H2O |
8.12
|
0~0.5 |
| 4 |
O2 |
|
|
| 5 |
N2 |
|
|
| 6 |
H2S |
|
< 10mg/l |
| 7 |
NH3 |
1.65 |
≤300PPM |
| 8 |
H2 |
|
|
1.1, the principle of membrane decarburization and purification
The membrane separation and decarburization unit uses advanced hollow fiber membrane separation technology to remove carbon dioxide from biogas or landfill gas.
The working principle of hollow fiber membrane is to separate different gas molecules through different gas penetration rates in the hollow fiber membrane of polymer materials. Among them, the gas with a fast permeation rate is called "fast gas", and the gas with a slow permeation rate is called "slow gas". The water, hydrogen sulfide, carbon dioxide and oxygen in biogas are "fast gas", while nitrogen and methane are "slow gas". Therefore, this selective osmotic adhesion characteristic of the membrane group determines that membrane biogas purification can not only remove a large amount of carbon dioxide, but also remove some hydrogen sulfide and oxygen impurities.
1.2 Description of the process for membrane decarburization
The biogas purification and decarbonization system is designed to run 8000h per year. After desulfurization, the raw material biogas at room temperature and pressure is pressurized by the screw compressor, and the pressurized biogas is then passed through the suction dryer, precooler and filter, and the solid impurities, moisture, hydrocarbons and other substances carried in the biogas are removed to meet the process requirements of pretreatment before membrane. The membrane separation unit is decarburized and purified by a two-stage separation method, and after passing through the membrane separation unit, the CH4 finished gas with a purity greater than 95% is finally generated.
The CO2 exhaust gas separated from the membrane stack can be emitted directly or recycled.
Membrane decarburization technology mainly has the following outstanding advantages:
1. High product purity and high recovery rate;
2. The process flow is simple, the operation and management are simple;
3. The membrane pack itself does not consume energy and has low operating costs;
4. Environmental protection and energy saving, no sewage, no need for chemical additives;
5. Small footprint, standard container integration and modular expansion.
Membrane stack separation schematic
The components of biogas are mainly methane (CH4) and carbon dioxide (CO2), biogas purification and purification is mainly to remove carbon dioxide gas in biogas, it can be seen from the figure that the main gas CO2 penetration rate in biogas is higher than that of CH4 gas, using the characteristics of the gas membrane to quickly separate CH4 gas and CO2 gas in biogas to achieve the purpose of CH4 gas content greater than 95%.
CO2 liquefaction Procee from Biogas after H2S, and water vapour as well as ammonia.
Flow chart of cleaning and purifying tail gas from Biogas
(1) The feed gas first enters the scrubber to remove the particles and organic impurities in the carbon dioxide recovery gas, stabilize and balance the system pressure, and ensure that the compressor unit has good working conditions. After three-stage compression by the compressor, pressurize to 3.0 MPa. G, and then carry on the low-temperature distillation washing process.
(2) The compressed gas enters the low-temperature distillation scrubber to remove the water and other substances which have a higher boiling point than carbon dioxide.
(3) The gas from the low temperature distillation washing process enters the liquefaction process. In the liquefaction process, the main equipment is Freon integrated skid, which have a high refrigeration efficiency.
(4) Liquid phase CO2 from the "liquefaction" section enters the purification tower to remove the impurities of H2, N2, CH4 and other gas phases in liquid CO2. Purification tower is the key equipment of the whole set of equipment. Based the principle of low temperature distillation, we can get CO2 after purifying repeatedly the liquid CO2 by internal circulation.
1. The product liquid CO2 from the bottom of the purifier is sent to the liquid CO2 storage tank for filling. The main features of the process are as follows:
2. The low-temperature distillation washing process is adopted to replace the traditional purifier and dryer. At the same time, the water and other substances which have a higher boiling pointthan than carbon dioxide are removed without replacing the molecular sieve, lower the operation cost of users.
3. The unique design of purification tower ensures a high product quality.
4. Reasonable process design can reduce the operating cost of the device, the performance of device operating/investment and income are the best.
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