The SNOX process is a
process
A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic.
Things called a process include:
Business and management
*Business process, activities that produce a specific se ...
which removes
sulfur dioxide,
nitrogen oxides and particulates from
flue gases
Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. Quite often, the flue gas refers to the combustion exhaust gas produced ...
. The sulfur is recovered as concentrated
sulfuric acid and the nitrogen oxides are reduced to free nitrogen. The process is based on the well-known
wet sulfuric acid process
The wet sulfuric acid process (WSA process) is a gas desulfurization process. After Danish company Haldor Topsoe introduced this technology in 1987, it has been recognized as a process for recovering sulfur from various process gases in the form ...
(WSA), a process for recovering sulfur from various process gasses in the form of commercial quality sulfuric acid (H
2SO
4).
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 sulfurous waste streams. This is highly interesting in refineries, where e.g.
hydrogen sulfide (H
2S) 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.
Process
The SNOX process includes the following steps:
*Dust removal
*Catalytic reduction of NO
x by adding NH
3 to the gas upstream of the SCR DeNO
x reactor
*Catalytic oxidation of SO
2 to SO
3 in the oxidation reactor
*Cooling of the gas to about 100 °C whereby the H
2SO
4 condenses and can be withdrawn as concentrated sulfuric acid
Applications
The SNOX process developed by
Haldor Topsoe has been specifically designed for power and steam generation plants to remove sulfur and nitrogen oxides from combustion of heavy residuals,
petroleum coke
Petroleum coke, abbreviated coke or petcoke, is a final carbon-rich solid material that derives from oil refining, and is one type of the group of fuels referred to as cokes. Petcoke is the coke that, in particular, derives from a final cracki ...
,
sour gasses, or other waste products from refineries.
Today, refineries are struggling to find ways to dispose of their increasing amount of sulfurous streams and waste products. Large amounts of high-sulfur residuals, particularly heavy oil and petroleum coke, are being produced and sold as fuel to the marine market or the cement industry. These off-take markets are, however, changing due to environmental constraints, and new markets have to be identified. One attractive option would be to use these residual fuels to produce power and steam, leaving behind the issue of emissions to be addressed. The SNOX technology is especially suitable for cleaning flue gases from combustion of high-sulfur fuels in refineries. The SNOX process is a very energy-efficient way to convert the NOx in the flue gas into nitrogen and the SOx into concentrated
sulfuric acid of commercial quality without using any absorbents and without producing waste products or waste water. Along with the flue gases, other sulfurous waste streams from a refinery can be treated, such as H
2S gas, sour water stripping (SWS) gas, Claus tail gas and elemental sulfur, potentially turning this technology into a complete sulfur management system.
Possible configurations:
Flue-gas desulfurization
The SNOX process can be applied for treatment of flue gases from combustion of primarily high-sulfur fuels in power stations, refinery and other industrial boilers and for treatment of other waste gases containing sulfur 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
Petroleum coke, abbreviated coke or petcoke, is a final carbon-rich solid material that derives from oil refining, and is one type of the group of fuels referred to as cokes. Petcoke is the coke that, in particular, derives from a final cracki ...
fired boilers at a refinery in
Sicily, Italy
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.
The process catalytically reduces both the SO
2 and the NO
x 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.
Recycling of hot combustion air from the SNOX plants to the boilers in combination with high pressure steam production in the SNOX plants increase the thermal efficiency and output of the boilers, resulting in a proportional reduction in CO
2 emission.
Enhanced sulfuric acid production
In several places there is a need for both electric power and sulfuric acid. A cheap high-sulfur fuel such as
petroleum coke
Petroleum coke, abbreviated coke or petcoke, is a final carbon-rich solid material that derives from oil refining, and is one type of the group of fuels referred to as cokes. Petcoke is the coke that, in particular, derives from a final cracki ...
can be used for power generation, while the flue gas is cleaned in an SNOX plant producing sulfuric acid. Elemental sulfur is fired in the SNOX plant in order to produce the desired amount of sulfuric acid.
See also
*
Flue-gas desulfurization
References
{{Reflist
Oil refining
Chemical processes