Dahlman OLGA

Aqueous absorption scrubbers

After OLGA the product gas is tar free. Classic aqueous scrubbers can be used without struggling with tar contaminated water.

First goal is the condensation of water. Usually the gas is cooled to approximately 30 ºC. Condensation of water enhances the calorific value of the gas, which improves the utilisation in a gas engine or gas turbine.

Second goal is the removal of inorganic impurities. The presence of inorganic impurities are dependent on the composition of the biomass/waste feedstock. Some impurities are already reduced significantly in the condensation stage, for other impurities (like NH₃ or H₂S) more effort is necessary. Several options can be considered, for example for NH3 removal:

• A chemical scrubber, multiple staged with acid injection. This system is relatively simple and straightforward, but acid is required and salt waste water is formed which could result in considerable operational costs, dependant upon the impurity concentrations.
• A water condenser / scrubber in combination with a stripper. Research showed that this is in particular interesting for the removal of NH₃. The NH₃ is stripped from the scrubber water and is recycled to the gasifier where the NH₃ is reduced to N₂. The stripper does requires steam, which costs should be considered.
• A water scrubber with a biological water treatment. This process could be very interesting but needs to be checked carefully. The bacteria might be affected by toxic components present in the product gas.
• A combination of the above options, optimised for your specific situation.

Our packed bed scrubbers are custom designed to meet the client specifications and gas absorption requirements. Our process specialists will look at your wishes, requirements and site circumstances, after which we propose an optimal designed scrubbing system. Our possibilities include:

• Several construction materials, e.g. polypropylene, HDPE, stainless steel or alloy.
• Skid mounted systems complete with tanks, pumps, instrumentation, and piping.
• Turn key delivery of systems including fans, ductwork, installation & commissioning.