Dry Desulfurization

How it works

Dry desulfurization is to fill a cylindrical desulfurization tower with a certain height of desulfurizer. The biogas passes through the desulfurizer from bottom to top, and H₂S is removed to achieve the desulfurization process. The desulfurizer commonly used in sewage treatment plants is iron oxide, which is cylindrical in shape. The principle of iron oxide desulfurization is as follows：

Fe₂O₃H₂O+3H₂S=Fe₂S₃H₂O+3H₂O

It can be seen from the above reaction equation that Fe2O3 absorbs H2S and turns into Fe2S3. As biogas continues to be produced, iron oxide absorbs H2S. When the absorbed H2S reaches a certain amount, the H2S removal rate will be greatly reduced until it fails.

Advantages

1. Simple Structure and Easy Operation: The system has no complex moving parts, requiring minimal maintenance, making it suitable for low-cost operation and maintenance of small and medium-sized biogas projects (processing capacity <500 m³/h).

2. Low Investment Cost and Outstanding Economic Performance with Simple Equipment: The desulfurization tank itself is simple in structure and does not require extensive auxiliary equipment (such as a circulation pump or heating system). The initial equipment investment is significantly lower than that of complex processes such as wet desulfurization. Small Footprint: The entire system is compact and requires minimal space, making it ideal for projects with limited space.

3. High Desulfurization Accuracy and Strong Reliability: Conventional iron oxide desulfurizers can reduce H₂S to below 20 mg/m³, meeting the standards for biogas power generation and residential gas.

4. Simple Operation and Maintenance, with Manageable Operating Costs: Operating at room temperature and pressure, no heating or pressurizing equipment is required, resulting in low energy consumption and operating costs limited to desulfurizer replacement (approximately 0.1-0.3 RMB/m³ of biogas). 5. Strong Safety: The desulfurization reaction is mild, without flammability or explosion risks. The desulfurizer (such as iron oxide) is non-toxic and can be disposed of as ordinary solid waste (or elemental sulfur can be recovered) after disposal.

6. No secondary pollution, environmentally friendly, dry process: The desulfurization reaction is a gas-solid phase reaction, and the product is solid sulfur or sulfide (such as iron sulfide), which remains in the filler. No wastewater is generated, avoiding complex wastewater treatment issues and being more environmentally friendly.

7. Flexibility and adaptability, modular design: Single or multiple tanks can be flexibly configured (in series or parallel) according to the biogas volume, making expansion easy. Highly resistant to load fluctuations: Highly adaptable to fluctuations in biogas production and concentration, particularly suitable for intermittent production or unstable gas volume (such as farms and seasonal production plants).

Key operating parameter control

1. To ensure desulfurization efficiency and system stability, the following operating parameters must be strictly controlled:

Biogas residence time: The residence time of biogas in the desulfurization tower must be ≥10 seconds (adjusted based on H2S concentration; higher concentrations require longer) to ensure sufficient reaction between H2S and the desulfurizer. This is usually achieved by controlling the biogas flow rate (using variable frequency drive).

2. Biogas moisture content: The moisture content of biogas entering the desulfurization tower must be <80% (dew point <15°C) to prevent the desulfurizer from absorbing water and agglomerating. This moisture content can be reduced using a precooler or adsorption dryer.

Desulfurizer filling height: The desulfurizer bed height is typically 2-3 times the tower diameter (e.g., a 1m tower diameter requires a 2-3m bed height) to ensure sufficient contact area for reaction. Filling should be uniform to avoid "channeling" (localized short-circuiting of biogas, preventing it from reacting with the desulfurizer).

3. H2S concentration monitoring: Install an H2S detector online (one at the inlet and one at the outlet). When the outlet H2S concentration exceeds the set value (e.g., 20 mg/m³), replace the desulfurizer in a timely manner. It is recommended to record data once an hour to trace the desulfurization efficiency.

Application Scenario

Large sewage treatment plants, large-scale livestock and poultry farms, large food factories, restaurant kitchen waste treatment plants, landfills and other places that produce large amounts of biogas. 

Product Case