Current biogas desulphurisation methods: advantages and disadvantages

Biogas is a renewable energy source obtained through the anaerobic decomposition of organic waste. However, this fuel gas often contains a proportion of hydrogen sulphide (H₂S), a corrosive and toxic compound. Therefore, it is necessary to remove H₂S through desulphurisation processes before biogas can be used as energy. In the following, we describe the current methods for desulphurising biogas, indicating their advantages and disadvantages.

Chemical methods for desulphurisation of biogas

Chemical methods use compounds to convert hydrogen sulphide into inert substances. For example, iron salts such as ferric chloride (FeCl₃) are used. It is also common to inject oxygen to oxidise the H₂S and transform it into solid sulphur or sulphate. This technique is fast acting and removes the corrosive gas efficiently. However, it has significant drawbacks. It consumes a lot of energy and generates solid waste that has to be treated afterwards. In addition, it requires very controlled operating conditions to function properly.

Biological methods of desulphurisation of biogas

These methods use micro-organisms (bacteria) that consume H₂S as an energy source. The bacteria oxidise the sulphur to sulphate or elemental sulphur, removing it from the biogas in a natural way. In addition, it is often an economical and environmentally friendly process because it uses living organisms without the need for aggressive chemical reagents. However, biological desulphurisation is relatively slow compared to other methods. It is also sensitive to changes in temperature, pH or other environmental conditions. Even other substances present in the biogas can inhibit the activity of the bacteria and reduce the efficiency of the process.

At Nalón Minerals we work on solutions adapted to these living environments. Find out more about our sustainable N-Bio Solutions lines.

Physical methods for biogas desulphurisation

Physical methods remove H₂S without direct chemical reactions, by absorption or adsorption processes. In adsorption, the biogas passes through a liquid that traps the H₂S (e.g. water or alkaline solutions). The hydrogen sulphide is thus dissolved in the liquid and separated from the gas. In adsorption, the biogas is passed through a solid material (e.g. activated carbon, sponge iron or zeolite). This material retains the H₂S on its surface, separating it from the gaseous flow. In general, these physical methods are versatile and simple to implement in a biogas plant. However, they have some limitations. Saturation of the liquid or solid adsorbent reduces their efficiency over time. In addition, these systems can cause pressure drop in the gas flow. Another drawback is that they can lose efficiency if the biogas contains other impurities that foul the adsorbent or adsorbent medium.

Desulphurisation within the digester

It is possible to remove H₂S from inside the anaerobic digester, before the gas is released to the outside. This method adds iron compounds (special oxides and hydroxides) directly into the biogas reactor. These additives capture H₂S as soon as it is formed during digestion. The resulting reaction forms iron sulphide (FeS) and elemental sulphur inside the tank. The toxic gas is thus removed before it is released along with the biogas. One of its advantages is that it prevents the accumulation of H₂S outside the reactor. This reduces the risks of corrosion, toxicity and even explosions in the plant. In addition, it is a clean and economical process that simplifies the design of the installation by not requiring additional external equipment. As an additional benefit, sulphur and iron are retained in the digestate (digestate residue), improving its properties as an organic fertiliser.

Conclusions

In short, removing H₂S from biogas is a fundamental step. Only then can this energy source be used safely and sustainably. The various existing methods meet this objective, but each has its own advantages and disadvantages. Therefore, the choice of desulphurisation method depends on factors such as H₂S concentration, available resources and the operating conditions of each project. Applying the right technique ensures cleaner biogas and protects the plant. It also helps to obtain better quality renewable energy.

Quick comparison of methods

At Nalón Minerals, we help companies find the best desulphurisation strategy. Our high purity, low environmental impact products offer safety, performance and sustainability.