SNOX Flue gas desulphurisation
Encyclopedia
The SNOX process is a process
which removes sulfur dioxide
, nitrogen oxide
s and particulates from flue gases. 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 WSA process
, a process for recovering sulfur from various process gasses in the form of commercial quality sulfuric acid (H2SO4)
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
(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.
has been specifically designed for power and steam generation plants to remove sulfur and nitrogen oxides from combustion of heavy residuals, petroleum coke
, 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 H2S gas, SWS gas, Claus tail gas and elemental sulfur, potentially turning this technology into a complete sulfur management system.
Possible configurations:
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
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 CO2 emission.
can be used for power generation, while the flue gas is cleaned in SNOX plant under production of sulfuric acid. Elemental sulfur is fired in the SNOX plant in order to produce the desired amount of sulfuric acid.
Industrial process
Industrial processes are procedures involving chemical or mechanical steps to aid in the manufacture of an item or items, usually carried out on a very large scale. Industrial processes are the key components of heavy industry....
which removes sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
, nitrogen oxide
Nitrogen oxide
Nitrogen oxide can refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds:* Nitric oxide, also known as nitrogen monoxide, , nitrogen oxide* Nitrogen dioxide , nitrogen oxide...
s and particulates from flue gases. The sulfur is recovered as concentrated sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
and the nitrogen oxides are reduced to free nitrogen. The process is based on the well-known WSA process
Wet sulfuric acid process
The wet sulfuric acid process is one of the key gas desulfurization processes on the market today. Since the Danish catalyst company Haldor Topsoe introduced and patented this technology in the late 1980s, it has been recognised as an efficient process for recovering sulfur from various process...
, a process for recovering sulfur from various process gasses in the form of commercial quality sulfuric acid (H2SO4)
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
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
(H2S) gas, sour water stripper gas
Sour gas
Sour gas is natural gas or any other gas containing significant amounts of hydrogen sulfide . Natural gas is usually considered sour if there are more than 5.7 milligrams of H2S per cubic meter of natural gas, which is equivalent to approximately 4 ppm by volume...
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 100 °C whereby the H2SO4 condenses and can be withdrawn as concentrated sulfuric acid product
Applications
The SNOX process developed by Haldor TopsoeHaldor Topsoe
Haldor Topsøe is a Danish catalyst company. The company was founded in 1940 by Dr. Haldor Topsøe. The company also develops process technology for petroleum refining, ammonia production, methanol production, and other industries....
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
Petroleum coke is a carbonaceous solid derived from oil refinery coker units or other cracking processes. Other coke has traditionally been derived from coal....
, sour gasses
Sour gas
Sour gas is natural gas or any other gas containing significant amounts of hydrogen sulfide . Natural gas is usually considered sour if there are more than 5.7 milligrams of H2S per cubic meter of natural gas, which is equivalent to approximately 4 ppm by volume...
, 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
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
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 H2S gas, SWS gas, Claus tail gas and elemental sulfur, potentially turning this technology into a complete sulfur management system.
Possible configurations:
Flue gas desulfurisation
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
Petroleum coke is a carbonaceous solid derived from oil refinery coker units or other cracking processes. Other coke has traditionally been derived from coal....
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
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 CO2 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 cokePetroleum coke
Petroleum coke is a carbonaceous solid derived from oil refinery coker units or other cracking processes. Other coke has traditionally been derived from coal....
can be used for power generation, while the flue gas is cleaned in SNOX plant under production of sulfuric acid. Elemental sulfur is fired in the SNOX plant in order to produce the desired amount of sulfuric acid.