After anaerobic treatment in the process of resource utilization of organic waste, the biogas produced contains a variety of gases, among which CH4 is a very good clean energy, However, H2S is a kind of malodorous corrosive gas, which has strong corrosivity to the following pipelines, biogas tanks, gas combustion equipment, etc., and the concentration of SO2 produced by the combustion of H2S is very high, which seriously pollutes the natural environment. Therefore, before the utilization of biogas, it is necessary to remove the H2S in biogas to avoid the corrosion of later equipment.
At present, we have undertaken a number of domestic biogas desulfurization projects. According to the gas volume, composition and use of biogas in the project, we have designed desulfurization processes that meet the needs of customers, such as dry chemical desulfurization, acid biological desulfurization, alkali biological desulfurization, complex iron desulfurization, etc., and provided targeted solutions for customers from the perspectives of design, construction and operation.
01 alkaline biological desulfurization
The basic biological desulfurization process is divided into two steps
One step: the methane is converted from gas phase to liquid phase by desulfurization reaction tower. Desulfurization reaction tower is a washing tower, biogas enters from the bottom of the tower and passes through the filter bed. The micro alkaline circulating water enters from the top of the tower, disperses through the nozzle, and freely falls through the filter bed. The filter material can further disperse the biogas and the circulating water, prolong the contact time, and improve the washing effect. The circulating water containing sulfide flows into the regeneration tank from the bottom of desulfurization reaction tower.
Chemical equation in desulfurization reaction tower: H2S (g) + OH - → HS (L) + H2O
The second step: the regeneration pool completes the process of sulfide oxidation in the circulating water. A large number of desulfurization bacteria (mainly colorless sulfur bacteria, etc.) in the circulating water will feed on the sulfide, convert the sulfide into their own nutrients, enter the microbial self circulation process, and discharge elemental sulfur and hydroxyl from the bacteria, so as to achieve the purpose of degradation. The heat exchanger in the regeneration pool provides heat for the circulating water to ensure that the temperature of the circulating water is about 33-34 ℃. The aeration head provides oxygen for the circulating water to ensure proper dissolved oxygen in the circulating water. By digesting sulfide in circulating water, desulfurizing bacteria produce elemental sulfur and sulfate (about 5%). Sulfate will reduce pH value of circulating water, and it is necessary to add some alkali liquor to neutralize the 5% sulfate through dosing system.
Chemical equation in regeneration tank: HS (L) + 1 / 2O2 → S + Oh-
These two steps are very important for biogas desulfurization system.
In one step, H2S is removed and oh - is consumed,
In the second step, sulfide is oxidized to elemental sulfur by desulfurizing bacteria in the regeneration tank, and oh - is regenerated. The elemental sulfur is precipitated by the sedimentation tank, and the sulfur sludge is discharged from the bottom, and the supernatant of the sedimentation tank returns to the circulating water system.
02 acid biological desulfurization
The process of acid biological desulfurization is divided into three steps
One step: the biogas passes through the desulfurization reactor, in which the filter material is installed, and the surface of the filter material is covered with water layer. After contacting with the filter material, the chemical substance in the biogas dissolves in the surface layer, and transforms from the gas phase to the liquid phase, so as to facilitate the further absorption and decomposition of the cells in the filter material.
Second step: the odor components in the aqueous solution are absorbed by microorganisms, and H2S is transferred from the water to the microorganisms.
Three steps: the specific bacteria (mainly Thiobacillus ferrooxidans, Thiobacillus denitrificans, Thiobacillus thiooxidans, Thiobacillus thiooxidans) in the filter media will feed on the pollutants, transform the pollutants into their own nutrients, make the H2S from the form of compounds into free state, enter the self circulation process of microorganisms, so as to achieve the purpose of degradation. At the same time, obligate bacteria and other microorganisms can achieve their own reproduction process, when the food pollution compounds and obligate bacteria nutrition needs to achieve a balance.
Desulfurization: 2h2s + O2 → 2S + 2H2O
Regeneration: 2S + 3O2 + 2H2O → 2h2so4
Biogas alkali and acid biological desulfurization are self-developed and mature desulfurization technologies, that is, by using the regeneration of desulfurization microorganisms and controlling biochemical reaction conditions, H2S in biogas can be transformed into elemental s or sulfate, so as to achieve the purpose of removing H2S. Using this technology, in the process of project operation, only a small amount of nutrients and alkali need to be added to ensure the activity of microorganisms, which can improve the desulfurization efficiency. It is a very economic and stable biogas desulfurization technology.