The SNOX™ process effectively removes SO2, SO3, NOx and particulates from flue gases, recovering the sulphur as high quality sulphuric acid and reducing NOx to nitrogen and water vapour.
Features of SNOXTM flue gas desulphurisation
The SNOX™ process displays a number of features:
- process and flue gas heat down to 100°C is recovered and recycled to the boiler to increase steam production
- dust is removed effectively in the process
- SO3 is handled without problems
- no consumption of absorbents and process water
- no production of waste water, slurries, or solids
- no additional CO2 emission
- possibility of handling other sulphur containing off-gases simultaneously
- simplicity and flexibility
In sharp contrast to other flue gas desulphurisation technologies, the SNOX™ plant operating costs decrease with increasing sulphur content in the fuel, and thus high-sulphur fuels can be used in an environmentally friendly and economically attractive way.
The flue gas desulphurisation process
The SNOX™ process includes the following steps:
- dust removal
- catalytic reduction of NOx by adding NH3 to the gas upstream the SCR DeNOx reactor
- catalytic oxidation of SO2 to SO3 in the oxidation reactor
- cooling of the gas to about 100ºC whereby the H2SO4 condenses and can be withdrawn as concentrated sulphuric acid product
Dust removal
Dust removal is an important feature of the SNOX™ technology. Dust (ashes and soot) must be removed to a very low level. This takes place in an electrostatic precipitator or in bag filters. Residual dust will be trapped in the SO2 conversion catalyst from where it can be removed. In this way the cleaned gas will be virtually dust free.
Heat exchange
Since the flue gas is heated up by means of the reacted flue gas after the SO2 converter, the absence of leaks between the two sides of the heat exchanger is important. Topsoe has experience with vendors supplying efficient, large-scale, gas tight heat exchangers.
The SNOX condenser™
The design of the air-cooled, multi-tube SNOX™ condenser allows controlled cooling of the process gas and condensation of the sulphuric acid without formation of acid mist. The vertical glass tubes, the brick-lined bottom section and the coated tube-plates of the condenser are designed for long service life and avoidance of corrosion.
Our proprietary catalyst
Another important element of the SNOX™ process is the proprietary Topsoe catalysts - the DNX series and the VK-W series - developed respectively for the reduction of NOx and for the conversion of SO2 into SO3 in the presence of water vapour. The catalysts feature high activity and stability.