Methane is the main component of biogas. Biogas is composed of 50% - 80% methane (CH4), 20% - 40% carbon dioxide (CO2), 0% - 5% nitrogen (N2), less than 1% hydrogen (H2), less than 0.4% oxygen (O2) and 0.1% - 3% hydrogen sulfide (H2S). Because biogas contains a small amount of hydrogen sulfide, it is slightly smelly. Its characteristics are similar to that of natural gas. If there is 8.6-20.8% (by volume) of biogas in the air, explosive mixture gas will be formed.

The harmful substances contained in biogas combustion products are mainly as follows:

 

(1) Carbon monoxide. When the biogas combustion is incomplete, carbon monoxide is contained in the flue gas. Carbon monoxide can easily replace oxygen and combine with heme in human blood. When people breathe more carbon monoxide, they will suffocate due to lack of oxygen.

 

(2) , sulfur dioxide. Biogas contains a small amount of hydrogen sulfide and organic sulfur. In the process of combustion, sulfur dioxide is oxidized to form sulfur dioxide, which will strongly stimulate human respiratory organs.

 

(3) , nitrogen oxides. When biogas is burned at high temperature, it will promote the reaction of nitrogen and oxygen in the air to generate nitrogen oxides (including nitric oxide and nitrogen dioxide). Nitrogen oxides have a strong stimulating effect on human respiratory organs, and the concentration above 0.25% can lead to death.

Advantages of biogas combustion

 

(1) The heat generated by biogas combustion can generate electricity and produce direct economic benefits.

 

(2) The toxic gases, such as nitrogen oxide, carbon monoxide and sulfur dioxide, produced after biogas combustion, can be treated again to avoid environmental pollution.

 

 

 

Accounting table for economic benefits of biogas feed system

 

Serial number

 

Item value 1 value 2 value 3 value 4

 

1 waste quantity (T / D) 1000 1000 1000

 

2. Leachate accounts for 20% 18% 18% 16%

 

3. Total amount of leachate (T / D) 200 180 180 160

 

4. COD content of leachate (mg / L) 50000 50000 50000

 

5uasb digestibility 80% 80% 80% 80%

 

6cod conversion methane ratio (Nm3 / kg) 0.35 0.35 0.35 0.35

 

7 methane amount (Nm3 / h) 116.67 105.00 105.00 93.33

 

8 methane content in biogas 60% 60% 60% 60%

 

9 methane calorific value kJ / m3 35900 35900 35900 35900

 

10 increase boiler heat value kW 1939.04 1745.14 1745.14 1551.23

 

11 thermal efficiency of the whole plant 25% 25% 20% 25%

 

12 self consumption 10% 10% 10% 10%

 

13. Power on grid per hour kW 436.28 392.66 314.13 349.03

 

14 years operation time h 8000 8000 8000

 

15 feed in tariff yuan / kW 0.65 0.65 0.65 0.65

 

16 year maintenance cost (RMB 10000) 22 22

 

17 year income (RMB 10000) 224.87 202.18 161.35 179.49