Hydrogen Sulfide is the major pollutant in biogas. It is very important to remove hydrogen sulfide from the biogas because of it’s corrosive and poisonous nature. If not removed then it may cause substantial harm to the device, piping, and instrumentation.
The corrosiveness and poisonousness of hydrogen sulfide vary based on its presence in ppm. There is not only one process of hydrogen sulfide removal from biogas, there are many ways from which it can be removed. Many new methods like the removal of hydrogen sulfide by activated carbon, red rock, etc. have been also tested these days.
Here is the process of desulphurization by the biological method.
Desulphurization by biological method
In this desulphurization of biogas by biological methods, micro-organisms perform all the activities. Many of these microorganisms belong to the Thiobacillus family. Oxygen in stoichiometric amounts must be added to biogas to perform microbiological oxidation. This approximates 2-6% air present in biogas relying on the presence of the amount of hydrogen sulfide.
The desulphurization can be simply done by adding air or oxygen directly to the storage tank or the digester performing at the exact time as that of the gasholder. Systems will not need inoculation because the Thiobacilli are omnipresent. They get the essential nutrients and the important microaerophilic surface as they develop on the dig estate surface. They shape clusters of sulfur which are yellow-colored. Relying on the conditions, the time of reaction, the place and proportion of added air in the hydrogen sulfide, it’s engagement can be lessened up to 95% to smaller than 50 ppm.
Overdose of the air can cause the pump to fail thus safety measures be taken primarily to avoid such a situation. If the concentration of air is up to 6-12 % in the biogas then it becomes an explosive substance, being sure of the methane quantity. At the interface of gas and liquid, there’s a little danger of corrosion in the digester which are made of steel and especially those who are without any rust protection.so it is better to keep the causative measure strictly while working in these areas.
Dosing of Iron chloride (FeCl)
Dosing of Iron chloride can stand directly to feed substrate or to digester slurry, then with the obtained hydrogen sulfide, the iron chloride will react to form iron sulfide particles(salt). This process is very beneficial in decreasing massive hydrogen sulfide concentration but not in obtaining a stable and low degree of hydrogen sulfide. So, in this aspect, this process of iron chloride dosing can just be considered as a biased removal method. This process is good for avoiding corrosion which may take place in the remaining upgrading cycle.
The cost involved in all such processes is very limited because all you need to invest is in just a storage tank for the dosing pump and to make and keep an iron chloride solution. But it doesn’t end up here because, on the contrary, the functional expense will be a little high because of the main cost for iron chloride.
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