SNOX process
The SNOX process is a process which removes sulphur dioxide, nitrogen oxides and particulates from flue gases. The sulphur is recovered as concentrated sulphuric acid and the nitrogen oxides are reduced to free nitrogen. The process is based on the well-known WSA process Wet sulfuric acid process a process for recovering sulfur from various process gasses in the form of commercial quality sulfuric acid (H2SO4) [1][2][3]
The SNOX process is based on catalytic reactions and does not consume water or absorbents. Neither does it produce any waste, except for the separated dust.
In addition the process can handle other sulphurous waste streams. This is highly interesting in refineries, where e.g. H2S gas, sour water stripper gas and Claus tail gas can be led to the SNOX plant, and thereby investment in other waste gas handling facilities can be saved.
The 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- cooling of the gas to about 100ºC whereby the H2SO4 condenses and can be withdrawn as concentrated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
Applications
The SNOX process developed by Haldor Topsoe has been specifically developed for power and steam generation plants to remove sulphur and nitrogen oxides from combustion of heavy residuals, petroleum coke, sour gasses or other waste products from refineries
SNOX for flue gas desulphurisation
The SNOX process can be applied for treatment of flue gases from combustion of primarily high-sulphur fuels in power stations, refinery and other industrial boilers and for treatment of other waste gases containing sulphur compounds and nitrogen oxides.
The first full scale plant treating 1,000,000 Nm³/h flue gas from a 300 MW coal fired power plant in Denmark was started up in 1991.
The largest SNOX plant in operation treats 1,200,000 Nm³/h flue gas from four petroleum coke fired boilers at a refinery in Sicily, Italy.
The process catalytically reduces both the SO2 and the NOx in flue gases by more than 95% and with integration of the recovered heat from the WSA Condenser it is reported to have lower operating costs than conventional technologies [4][5]
SNOX - for enhanced sulphuric acid production
In several places there is a need for both electric power and sulphuric acid. A cheap high-sulphur fuel such as petroleum coke can be used for power generation, while the flue gas is cleaned in SNOX plant under production of sulphuric acid. Elemental sulphur is fired in the SNOX plant in order to produce the desired amount of sulphuric acid.
References
- ^ Sulphur recovery; (2007). The Process Principles in sulphur recovery by the WSA process.). Denmark: Jens Kristen Laursen, Haldor Topsoe A/S. Reprinted from Hydrocarbonengineering August 2007
- ^ Power Plant Engineering/Larry Drbal/ISBN-10/ASIN: 0412064014
- ^ Processes for sulfur recovery, regeneration of spent acid, and reduction of nox emissions/Springer New York/ISSN 0009-2355 (Print) 1573-8329 (Online)[/http://www.springerlink.com/content/57351150l6074366]
- ^ Gas purification. 5th ed./Kohl, Arthur, L./ISBN 0-88415-220-0
- ^ Handbook of pollution control processes/Robert Noyes/ISBN 0-8155-1290-2