Flue Gas Desulfurization SNOX Process by Haldor

Application: The SNOX process treats boiler flue gases from the combustion of high-sulfur fuels, such as heavy residual oil and petroleum coke. The SNOX process is a combination of the Topsøe WSA process and the Topsøe SCR DeNOx process. The process removes SO2, SO3 and NOx as well as dust. The sulfur is recovered in the form of concentrated commercial-grade sulfuric acid. The SNOX process is distinctly different from most other flue gas desulfurization processes in that its economy increases with increasing sulfur content in the flue gas.

Description: Dust is removed from the flue gas by means of an electrostatic precipitator or a bag filter. The flue gas is preheated in a gas/gas heat exchanger. Thereafter, it is further heated to approximately 400°C and ammonia is added, before it enters the reactor, where two different catalysts are installed. The first catalyst makes the NOx react with ammonia to form N2 and water vapor, and the second catalyst makes the SO2 react with oxygen to form SO3. The second catalyst also removes any dust traces remaining. During the cooling in the gas/gas heat exchanger, most of the SO3 reacts with water vapor to form sulfuric acid vapor. The sulfuric acid vapor is condensed via further cooling in the WSA condenser, which is a heat exchanger with vertical glass tubes.

Concentrated commercial-grade sulfuric acid is collected in the bottom of the WSA condenser and is cooled and pumped to storage. Cleaned flue gas leaves the WSA condenser at 100°C and can be sent to the stack without further treatment. The WSA condenser is cooled by atmospheric air. The cooling air can be used as preheated combustion air in the boiler. This process can achieve up to 98% sulfur removal and about 96% NOx removal.

Other features of the SNOX process are:
• No absorbent is applied
• No waste products are produced. Besides dust removed from the flue gas, the only products are cleaned flue gas and concentrated commercial-grade sulfuric acid.
• High degree of heat efficiency
• Modest utility consumption
• Attractive operating economy
• Simple, reliable and flexible process.

Licensor: Haldor Topsøe A/S.