Sangir has successfully provided yet another specialty solution using the Stud-Liner product for the lining inside the dome of a biogas plant. Biogas Digesters or Bio-digesters made from Cement/Concrete are used for breaking down organic matter, by bio-digestion in anaerobic conditions to generate Biogas, which is a gaseous alternative fuel. The Biogas is a mixture of gases which predominantly includes Methane, Carbon Dioxide and Hydrogen Sulfide. The Concrete Dome of the Biogas plant is the place where the Biogas gets stored. However, the Hydrogen Sulfide present in the Biogas, reacts with the Lime/Calcium carbonate present in the cement surface of the dome, causing deterioration of the concrete.
When the amount of biogas generated is high, its pressure pushes the slurry levels down, there is usually an equalizer chamber where the slurry is pushed into, but when the gas is being used and the pressure tends to fall, the slurry level rises to maintain this pressure. As the Gas is stored in the dome of the digester, the concrete/cement surfaces of the digester are exposed to Hydrogen Sulfide (H2S), which constitutes a part of the Biogas, along with Methane and Carbon dioxide. Hydrogen Sulfide reacts with calcium carbonate & Lime present in the concrete, which leads to concrete corrosion and results in structural degradation and irreparable damages, thinning, and eventual structural failure. Hydrogen Sulfide can eat away the top layers, and once the rebar cage is exposed or the concrete layer becomes porous, the rebar metal reacts fast, and material loss takes place. This can lead to reinforcement failure and could result in a dome collapse.
- Organic Sulphates and Inorganic Sulphide present in slimes of sewerage flows and form the Total Sulphide present in the sewerage. A fraction of the dissolved Hydrogen Sulphide is released.
- A process of bacterial reduction occurs when the H2S, in combination with the other gases, such as CO2 , is progressively oxidized, reducing the pH value, to the point where it splits off with water molecules to form Sulphuric Acid.
- The powerful inorganic H2SO4 reacts with hydrated calcium silicates and lime in the cement structure & reduces it to a soft swelling paste.
- This process has two kinds of effects on the concrete structure: first is thinning and the other is making the concrete layers porous, and the H2S manages to reach the structural steel rebar-cage reinforcement.
The gas is stored in the Concrete Dome portion of the biogas plant. Thereby this is the area which needs to be protected from H2S. Various lining and coating methods have been tried so far, without any lasting effect or success.
Stud-Liner – Permanent Solution:
Sangir has been successful in providing a permanent, effective and cost-optimized solution for the lining of the Bio-Gas Plant domes, by using stud-liners.The Stud-liner sheets were cut to size and shape and laid on the semi-spherical dome-shaped shuttering/formwork. All the edges between individual pieces of stud-liner sheets were welded on site using a hot-air extrusion welding process.After which the steel rebar cage and reinforcement are installed, consisting of structural steel, and concrete was poured over this.
