Chemical Absorption Type Biogas Desulfurization and Upgrading System to Natural Gas (CNG)

Treated gas type: biogas produced from food waste waste biogas plant

Technology process: After de-moisture, de-dust, pressure rising, removing organic sulfur , removing inorganic sulfur, decarburization ,High pressure compressing,drying and so on, the production is CNG for vehicle using.

Daily CNG output: 12,000Nm³

Anaerobic digestion + Dry chemical desulphurization + Chemical absorption 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: Comments: The above data is subject to clients' actual requirements.

The Flowchart of biogas upgrading system



Procedures of our biogas upgrading system
  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;
  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.
  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.
  The gas is boosted by biogas compressor, then after procedures of cooling, water and impurities removal, to be delivered to decarburization unit.
  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.
  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.
  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.
  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