Project informations:
Biogas Plant, waste is citric acid
Qingdao City, Shandong Province of China
Biogas is converted to CNG for vehicle
Designed capacity: 30,000 Nm³/day
Dry chemical desulphurization + Membrane separation decarburization
After two-stage desulphurization processes, then go through our GasDec system for carbon removal, biogas could be upgraded to make CNG, for vehicle or going into national pipeline network.
The gas quality after upgrading as below:
| Item | Quality Index | Comments | |
| High thermal value | MJ/m3 | >31.4 | In the specific geographical area for vehicle driving, under the highest operation pressure, the water dew point shouldn't be higher than -13 degree.C; When lowest ambient temperature lower than -8 degree.C, the water dew point should be 5 degree.C lower than the lowest temperature. |
| CO2 | % | ≤3.0 | |
| Total Sulfur | mg/Nm3 | ≤200 | |
| H2S | mg/Nm3 | ≤15 | |
| O2 | % | ≤0.5 |
The Flowchart of biogas upgrading system
Procedures of our biogas upgrading system
1, Biogas Generation
Biogas is generated in anaerobic reactor and stored in gas holder in low pressure. Boosted by biogas blower, biogas is delivered to wet desulphurization tower;2, Wet Desulphurization
Wet chemical desulphurization technology is mainly structured as a single tower. Chemicals adopted is Na2CO3 with addition of catalysts (oxygen carrier). Chemicals is dissolved in the water, contact rightabout with biogas in the tower. More than 95% hydrogen sulfide, a small amount of carbon dioxide and other acidic substances can be absorbed by the liquid. The pregnant solution (the liquid) would be boosted by pump to a special groove, sprayed and oxidized by means of air suction for regeneration. Meanwhile elemental sulfur is precipitated out of the liquid, to be recycled for sale.
3, Dry Desulphurization
Dry chemical desulphurization technology is for the purpose of fine desulphurization, mainly structured as double towers, can be used alternately or operated in parallel or in series. Chemicals adopted is usually ferric oxide. Hydrogen Sulfide is converted to solid sulfide.4, Gas Cleaning
The gas is boosted by biogas compressor, then after procedures of cooling, water and impurities removal, to be delivered to decarburization unit.5, Biogas Decarburization
The decarburization technology we adopt is chemical absorption. Chemical solution contacts with biogas rightabout in the absorption tower, to absorb carbon dioxide till its content lower than 3%. The upgraded gas is discharged from top of absorption tower, to be cooled by cooler and cleaned by separator for the removal of condensate water and chemical solution. Then gas is delivered to compressor.
The pregnant solution (the liquid) returns to the regeneration tower. The precipitation of carbon dioxide is achieved through steam stripping. The precipitated carbon dioxide gets through cooler and separator, can be discharged into atmosphere directly. The barren solution from the bottom of regeneration tower is pumped through automatic flow monitoring pipeline into absorption tower for circulatory use.
This is our GasDec system.
1, NG Compressor
The gas after decarburization procedure we can call it natural gas now. Its pressure rises to 22MPa or other pressure levels by natural gas compressor.2, NG Cleaning
The compressed natural gas would be dried and cleaned further by automatic NG drier. The working principle of drier is pressure swing absorption, taking 4A molecular sieve as absorbent.3, CNG Metering
CNG metering device is required when gas is for sale. Measuring method we usually adopt mass measurement. Eg. The mass flowmeter of our project in Henan Province of China is Emerson CNG050, accuracy could reach 0.5 magnitude. Gas is filled into CNG tank lorry through gas dispenser machine, to be delivered to standard CNG station (or Primary CNG station) as fuel for vehicle.Main equipment list of our upgrading system
| No. | Item | Comments |
| Biogas Desulphurization System | ||
| 1 | Wet Desulphurization Tower | |
| 2 | Groove,Pregnant Solution | |
| 3 | Groove,Barren Solution | |
| 4 | Groove,regeneration | |
| 5 | Separator | |
| 6 | Dry Desulphurization Tower | |
| 7 | Regeneration Pump | |
| 8 | Pump,Desulphurization | |
| 9 | Pump,Sulfur Foam | |
| 10 | Biogas Blower | |
| 11 | Electrical Monitoring | |
| 12 | Alarming System | |
| Biogas Decarburization System | ||
| 1 | Pump,barren Solution | |
| 2 | Decarburization Tower | Methane Recovery: ≥99%, Gas quality satisfies GB18047-2000 standard |
| 3 | On-line Analyzer | |
| 4 | On-site control box | |
| 5 | PLC System | |
| 6 | Operator Station | |
| 7 | On-line UPS | |
| 8 | Automatic flowmeter | |
| 9 | Motorized Valve | |
| 10 | Pressure Transmitter | |
| 11 | On-site Pressure Gauge | |
| 12 | On-site Temperature Gauge | |
| 13 | Liquid level Gauge | |
| 14 | Frequency Converter | |
| 15 | Filter | |
| 16 | Storage Tank | |
| 17 | Underground Groove | |
| 18 | Underwater Pump | |
| 19 | Biogas Compressor | |
| 20 | Power Distribution Cabinet | Assembling Unit |
| CNG Compressing, drying and metering Unit | ||
| 1 | CNG Compressor | |
| 2 | Dryer | |
| 3 | Gas Dispenser Machine | |
| Circulatory Cooling Water Unit | ||
| 1 | Circulatory water system |
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