Advantages of Desulfurization in Biogas Plants

While biogas plants are often considered to be a step toward a cleaner future because of their nature as a renewable energy source, biogas itself contains contaminants such as sulfur, so desulfurization of biogas plants can provide substantial advantages in this direction.

This energy source is produced using the anaerobic decomposition of organic matter

Biogas plants provide a renewable energy source produced from organic matter decomposition without oxygen. The nature of the organic matter can be of plant or animal origin and is typically a biproduct of wastewater, agriculture, or food industries. Biogas itself is made up of primarily methane (CH4) and carbon dioxide (CO2) as well as small amounts of other gases such as nitrogen (N2), hydrogen (H2) and hydrogen sulfide (H2S).

Plants use cutting edge technology to produce the fuel that is used for heat and electricity generation.  They use a process known as anaerobic digestion to break down the organic materials in a digester without the presence of oxygen. There, bacteria break down the organic compounds and produce methane gas and other products. These are stored or used in generators that convert them into usable energy. The solid waste byproduct of this process can be used as organic agricultural fertilizer.

Desulfurization of biogas plants that produce hydrogen sulfide (H2S)

As mentioned earlier, this process naturally results in the production of hydrogen sulfide (H2S), which is a corrosive, toxic gas that is harmful to the environment. Therefore, to ensure that this renewable energy remains promising in a cleaner, decarbonized future, desulfurization in biogas plants offers a promising path ahead. 

Desulfurization is used in biogas plants for the removal of the hydrogen sulfide. It can reduce or eliminate the sulfur compounds – particularly those from hydrogen sulfide and sulfur dioxide – found in liquids and gases such as biogas, making it a strong option.

The sulfur itself is naturally found within the source organic materials.  It is released during the process of making biogas but can cause environmental and technical problems if allowed to be combined with other compounds or released into the atmosphere on its own. Desulfurization overcomes that issue.

Methods of desulfurization in biogas plants

There are many different ways for desulfurization to occur in biogas plants. These include:

• Chemical
• Biological
• Physical

Each comes with its advantages and drawbacks, depending on the product being treated, the amount of sulfur to be removed, and the overall operating conditions.

Chemical

This is a process in which chemicals are used for the conversion of hydrogen sulfide into a compound that is no longer corrosive.

Following the reaction with the hydrogen sulfide, the result is a solid precipitate that can be removed from the biogas.  

Advantages of this method include speed and efficiency, though they also require large amounts of energy, produce solid waste, and require certain controlled operating conditions.

Biological

Biological desulfurization in biogas plants uses microorganisms that break down the hydrogen sulfide. Those microorganisms consume H2S as a source of energy and oxidize it to either sulfate (SO4) or elemental sulfur (S). 

Advantages of this method include that it is both economical and ecological. That said, the drawbacks include low reaction rate, microorganism temperature or pH variation sensitivity, or potential inhibition of other biogas compounds.

Physical

Physical desulfurization in biogas plants is the most commonly used method and involves absorption and adsorption.

In absorption, biogas is passed through a liquid with an H2S affinity, such as an alkaline solution, organic solution, or water. The H2S dissolves into the liquid, separating it from the biogas. The liquid can be converted into another compound or can be regenerated using thermal or chemical treatment to recover the H2S.

Adsorption has to do with passing biogas through a solid with a high H2S surface retention capacity. Examples of such a solid include sponge iron, activated carbon and zeolite. The H2S adheres to the surface of the solid, separating it from the biogas.

Advantages of using physical methods of desulfurization in biogas plants include versatility and simplicity. Disadvantages include issues with liquid or solid saturation, pressure loss, and possible contamination from other biogas compounds.

Another option that could be included in the adsorption methods is the desulphurisation inside the biogas reactor itself, carried out by means of desulphurisation within the biogas reactor itself, carried out by means of iron oxide-hydroxide compounds and other functional oxides specially developed to be added directly into the fermentation reactor.

This methodcaptures the hydrogen sulphide in the digester and reacts it to generate iron sulphide and sulphur. Among its advantages are the following –
• It avoids toxicity and physical risks
• No risk of explosive mixtures
• Minimises corrosion damage as H2S is removed before leaving the reactor.
• Safe and clean handling
• Cheaper and more efficient desulphurisation
• Improved compost characteristics

FAQs About Biogas Plants

1. What is a biogas plant? A biogas plant is a facility that produces renewable energy through the anaerobic decomposition of organic matter, which can be of plant or animal origin. This organic matter typically comes from wastewater, agriculture, or food industries.

2. How does a biogas plant work? Biogas plants use a process known as anaerobic digestion to break down organic materials in a digester without oxygen. Bacteria break down the organic compounds and produce methane gas and other products, which are then stored or used in generators that convert them into usable energy.

3. What is desulfurization in biogas plants? Desulfurization is a process used in biogas plants for the removal of sulfur compounds, particularly those from hydrogen sulfide and sulfur dioxide, found in liquids and gases such as biogas. It helps to ensure that the renewable energy produced remains clean and environmentally friendly.

4. Why is desulfurization necessary in biogas plants? Desulfurization is necessary because the process of making biogas naturally results in the production of hydrogen sulfide (H2S), a corrosive, toxic gas that is harmful to the environment. Removing this sulfur makes the biogas safer and more sustainable.

5. What methods of desulfurization are used in biogas plants? There are several methods of desulfurization used in biogas plants, including chemical, biological, and physical methods. The choice of method depends on the product being treated, the amount of sulfur to be removed, and the overall operating conditions.

6. What is the chemical method of desulfurization in biogas plants? The chemical method involves using chemicals to convert hydrogen sulfide into a compound that is no longer corrosive. This typically involves the use of ferric salts, such as ferric chloride or iron sulfate, in combination with oxygen. The result is a solid precipitate that can be removed from the biogas.

7. What are the advantages and drawbacks of the chemical method of desulfurization? The chemical method of desulfurization is fast and efficient. However, it requires large amounts of energy, produces solid waste, and requires certain controlled operating conditions.