Concrete needs to be protected
Most contractors who build biogas plants are aware of the negative influence of acids on concrete, which is why they opt for a type of concrete that is ‘acid-resistant’. However, it appears these acid-resistant concretes are not always sufficiently effective. One of the main problems is corrosion of the reinforcement in the concrete (also called concrete cancer) and carbonatation.
Concrete cancer & carbonatation
Carbonatation is a natural process in concrete. During the curing process, calcium hydroxide is formed, which reacts with carbon dioxide. Calcium hydroxide provides an alkaline environment and thus protects the steel reinforcement in the concrete. Due to the carbonatation reaction, pH levels drop below 8/9, which can lead to corrosion of the reinforcement.
H2S Hydrogen sulphide
Together with the presence of organic acids (such as lactic acid and acetic acid), the HS2 factor is one of the most threatening acids for the protection of your concrete structure. Organic acids can be a problem, even at concentrations as low as 1%. At minimum concentrations of oxygen in the biogas, H2S can form sulphuric acid (in the case of condensation in the gas range). H2S, which results from the reduction of sulphureous organic material in the input streams, will form an equilibrium between the digestate and the biogas. The H2S in the biogas will cause concrete damage at the headspace or gas zone.
Protect your biogas plant
A desulphurisation procedure is carried out during the biogas process (by means of a controlled supply of air, among other things) but it is not sufficient to neutralise the negative influence of the H2S. The temperature of the biogas above the material to be fermented is higher than the temperature at the concrete wall. This causes a condensation layer to form on that wall. The presence of H2S will create an acidic environment. During the gas phase, bacteria that produce sulphuric acid of increasingly higher concentrations develop in the acidic condensation layer on the concrete wall. The acid will attack the concrete wall. Over time, the cementitious material loses its cohesion and the concrete crumbles down to the reinforcement, resulting in stability issues.
Rocathaan Hotspray as an ideal finish
This seamless finish protects your plant against the aforementioned influences for years to come. The product is sprayed hot and seamless and cures within 10 seconds. The structure of the system partly depends on the existing substrate. In recent years, Prokol has gained ample experience in applying Hotspray in biogas plants.