The conditioning of the synthesis gas is an important link between gas generation and utilization, for example in a combined heat and power plant. The treatment of the gas is tailored to the purity requirements of the downstream processes.
The gas already produced in the AHT Twin-fire reactor is very clean and can be used in thermal processes without further treatment. Simple cleaning of the gas using hot gas filters is also possible depending on the application.
If a very high gas purity is required (such as <20mg/Nm3), the generated synthesis gas undergoes a combined wet gas scrubbing and cooling in the gas conditioning. In the last cleaning step, the remaining interfering aerosols are removed in a downstream, specially developed wet Electrostatic precipitator (ESP).
This offers the possibility of using the cleaned gas in ovens and combined heat and power plants. The high gas purity ensures safe gas transport over long distances and highly efficient utilization in the CHP. The cleaned gas is also the basis for further processes such as gas liquefaction or other chemical processes.
AHT Gas Conditioning
Gas cooling and washing
Although the synthesis gas produced by the AHT process is already very clean, it still contains small amounts of saturated tar and ash. In wet gas conditioning, it is cooled and unwanted by-products are removed.
These are the individual steps:
- In the cyclone separator, dust particles are removed. The product gas is forced into a circulating stream, so that the centrifugal forces cause the particles to be separated.
- In the hot gas filter, dust is reliably removed, which simplifies the maintenance and operation of the plants.
- In the gas precooler, the gas is sprayed with water, which lowers the temperature. Dust particles are bound and washed out of the gas.
- In the gas scrubber, the washing water is atomized into the smallest water droplets (about 1 µm), on which particles can deposit and be subsequently removed.
- In the main gas cooler, the gas is sprayed with water in counterflow, which is led through packing material to increase the active surface area. Finest dirt particles and water-soluble substances are bound by water droplets.
- In the electrostatic precipitator (electrofilter), fine aerosols are discharged through an electric field from spray electrodes and remain in the washing water.
- In the cold gas heat exchanger, the gas is further cooled so that water and tar still present in the gas can condense. The closed secondary cold water circuit is cooled by a compression refrigeration system.
Other unwanted impurities such as sodium, potassium, and sulphur can also be removed in this way. In other standard applications, these are precipitated or neutralized in the washing water. The result is now a clean synthesis gas for further use.
In order to operate the washing water in a closed loop, flocculating agents are dosed into the washing water depending on the degree of contamination, so that suspended substances can be dissolved from the water. A flocculation aid causes the particles to agglomerate into larger flocs. This water-floc mixture is pumped from below into the flotation tank. The air dissolved in the water-floc mixture enters the flotation tank and drives the flocs to the surface, where they are removed with a surface scraper and transferred to corresponding containers. This enables a highly efficient separation of solids from the water without the use of filters. These sludges can now be disposed of or reintroduced into the gas generation process.
The wash water in the gas conditioning plant needs to be cleaned and cooled to be reused. The water treatment consists of four functional units:
- Flocculant dosing system
- Pressure release flotation units with dissolved air
- Heat recovery
The purified water drains down over a rim and is pumped through a wash water heat exchanger to return the heat to a low-temperature circuit. This low-temperature heat can be used for drying the feedstock.