Many of us often come across drinking water in our homes that smells like rotten eggs. The same may also happen when water is boiled using boilers and other such devices. The reason for the rotten egg smell could be because of hydrogen sulfide. It is basically a chemical compound. It is a colorless hydride gas and it has that typical foul smell of rotten eggs. Beyond a certain level, it is flammable, corrosive and poisonous. Hence, when it comes to biogas manufacturing units, there are reasons to remove this gas from the biogas. In this article, we will try and learn something more about the ways and means by which hydrogen sulfide removal from biogas is possible.
Why Should It Be Removed?
As mentioned above, hydrogen sulfide is corrosive and poisonous and it could lead to widespread damage to various equipment, piping and instrumentation. The amount and quantum of damage to the piping caused by hydrogen sulfide would depend on its concentration. Boilers are capable of withstanding hydrogen sulfide up to around 1000 ppm and the internal combustion engines work best when this gas is maintained at concentrations below 100 PPM.
How is it removed from Piping?
There are many methods that are used for the removal of this gas from biogas and the most common methods are something known as anaerobic digestion process. This process makes use of oxygen and air to remove biogas and iron chloride dosing is also used for the purpose.
Process Called Biological Desulphurization
It also is possible to remove this gaseous substance from biogas through a process known as biological desulphurization. We need to understand that the various microorganisms of sulphide oxidation elements are from the family known as Thiobacillus. For helping in the process of microbiological oxidation as far as sulphide is concerned, there are a few things that one needs to bear in mind. To begin with it is important to add the right quantities of oxygen to the biogas. The quantum of oxygen required would depend on the levels of concentration of hydrogen sulphide. This could range from 2 to 6% air in case of biogas.
The method is quite simple. You should add oxygen or pure air directly to the digester and once this is done the desulphurization process would be activated. You could also make use of a storage tank and it could work as a gas holder. We also need to understand that the elements known as Thiobacilli are present almost everywhere and therefore there is no need for special inoculation of the substance. They also grow on the digestate surfaces. This helps in offering the required microaerophilic surface. It also is able to provide the required nutrients. Once they are activated, they start forming yellow sulfur clusters. Through this process it is possible to bring down the levels of hydrogen sulphide from biogas from as high as 95% to as low as 50 ppm. However, this would depend on a number of factors such as reaction time, the temperature and the exact place where the air or oxygen is added to hydrogen sulphide.
It is clear from the above that there are quite a few proven and time-tested methods for safe, efficient and thorough removal of hydrogen sulfide from biogas.
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