The vital toxin in biogas is hydrogen sulfide, and this contaminant is corrosive and poisonous. When not addressed immediately, degreaser formulation, hydrogen sulfide can cause irreparable damage to the equipment, instrumentation, and piping. The presence of various components in biogas can impact its efficiency and end-use. When internal engines can perform the best in less than 100 ppm hydrogen sulfide or H2S concentration, boilers can survive in 1000 ppm concentration. However, there are many ways to remove H2S from biogas. The most common methods for hydrogen sulfide removal from biogas are biological desulphurization and iron chloride dosing. We will cover both these methods in the following.
This method uses microorganisms to remove hydrogen sulfide from biogas. Most sulfide oxidizing microorganisms come from the Thiobacillus family. You will need stoichiometric amounts of oxygen for microbiological oxidation to remove hydrogen sulfide from biogas. You will have to add this much oxygen to the biogas, and it needs to be two to six percent air, depending on the hydrogen sulfide concentration.
You will find this method easy and cost-effective. You can add air or oxygen directly to the storage tank or digester surfactant. As Thiobacilli is ubiquitous, the system will not require inoculation. It will grow on the digester surface while providing necessary microaerophilic and essential nutrients at the same time. It will form yellow clusters and can have a significant impact on the sulfide level. This addition can reduce the amount of sulfide concentration up to 95% or even less than 50 ppm based on the reaction time and temperature. However, the process will require some safety measures.
You will have to add a proper amount of oxygen or air. Overdosing can offer adverse results. Additionally, biogas is explosive in the air in the 6 and 12% range. Any mistake might lead to pump failures. If you use a steel digester, there might be a risk of corrosion at the liquid or gas interface. You can avoid this with rust protection in digesters.
Iron Chloride Dosing
The usage of the iron chloride method is also straightforward. You can feed the iron chloride to the substrate or digester slurry directly. The chloride will react with the hydrogen sulfide fast. As a result, it will form iron sulfide particles. You might find this method extremely effective since it can reduce high hydrogen sulfide levels. However, it is not much effective to attain a stable and low level of hydrogen sulfide. Therefore, it might not be the best method all the time. You can use it as a partial removal process water-based surfactant. The benefit is that it will avoid corrosion in the upgrading process. You will need another removal process to reduce the concentration in biogas.
Both these methods for hydrogen sulfide removal from biogas are easy to follow and effective. However, there will be some limits and benefits. Know your requirements before considering any removal method. Moreover, both these processes are cost-effective, and you will not have to spend on tools. For example, you will need only a storage tank and dosing pump for the iron chloride dosing method.
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