Wet sulfuric acid process
Encyclopedia
The wet sulfuric acid process (WSA 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 gasses in the form of commercial quality sulfuric acid
(H2SO4), with simultaneous production of high pressure steam. The WSA process is applied in all industries where removal of sulfur is an issue.
The wet catalysis process is especially suited for processing one or more sulfur containing streams such as.:
The energy released by the above mentioned reactions is used for steam production. Approximately 2–3 ton high-pressure steam per ton of acid produced.
-, Selexol
-, amine gas treating
or similar installed after the gasifier contains H2S, COS and hydrocarbons in addition to CO2. These gases were previously often flared and vented to the atmosphere, but now the acid gas requires purification in order not to affect the environment with SO2 emission.
Not only can the WSA process meet the demands of SO2 removal, the process also accepts a wide range of feed-gas compositions.
The WSA plant provides a high sulfur recovery and the heat recovered causes a substantial steam production. The heat recovery rate is high and the cooling water consumption low, resulting in superior cost performance of this process.
Example 2:
A sulfur plant in China will be built in connection with an ammonia plant, producing 500 kilotons/annum of ammonia for fertilizer production
formed by catalytic oxidation of the sulfur dioxide
reacts instantly with the moisture to produce sulfuric acid in the vapour phase to an extent determined by the temperature. Liquid acid is subsequently formed by condensation of the sulfuric acid vapour and not by absorption of the sulfur trioxide in concentrated sulfuric acid, as is the case in contact processes based on dry gases.
The concentration of the product acid depends on the H2O/SO3 ratio in the catalytically converted gases and on the condensation temperature.
The combustion gases are cooled to the converter inlet temperature of about 420–440 °C. To process these wet gases in a conventional cold-gas contact process (DCDA) plant would necessitate cooling and drying of the gas to remove all moisture. Therefore the WSA process is in many cases a more cost-efficient way of producing sulfuric acid.
About 80% to 85% of the world’s sulfur production is used to manufacture sulfuric acid. 50% of the world’s sulfuric acid production is used in fertilizer production, mainly to convert phosphates to water-soluble forms, according to the Fertilizer Manual, published jointly by the United Nations Industrial Development Organization (UNIDO) and IFDC.
Haldor 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....
introduced and patented this technology in the late 1980s, it has been recognised as an efficient process for recovering sulfur from various process gasses in the form of commercial quality 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...
(H2SO4), with simultaneous production of high pressure steam. The WSA process is applied in all industries where removal of sulfur is an issue.
The wet catalysis process is especially suited for processing one or more sulfur containing streams such as.:
- H2S gas from e.g. amine gas treatingAmine gas treatingAmine gas treating, also known as gas sweetening and acid gas removal, refers to a group of processes that use aqueous solutions of various alkylamines to remove hydrogen sulfide and carbon dioxide from gases...
unit - Off-gas from sour water stripper (SWS gas)Sour gasSour 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...
- Off-gas from RectisolRectisolRectisol is the trade name for an acid gas removal process that uses methanol as a solvent to separate acid gases such as hydrogen sulfide and carbon dioxide from valuable feed gas streams. By doing so, the feed gas is made more suitable for combustion and/or further processing...
- Spent acid from e.g. AlkylationAlkylationAlkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion or a carbene . Alkylating agents are widely used in chemistry because the alkyl group is probably the most common group encountered in...
- Claus processClaus processThe Claus process is the most significant gas desulfurizing process, recovering elemental sulfur from gaseous hydrogen sulfide. First patented in 1883 by the scientist Carl Friedrich Claus, the Claus process has become the industry standard....
tail gas - Heavy residue or petcoke-fired utility boiler off-gas
- Boiler flue gases from various processes SNOX flue gas desulfurisation
- Metallurgical process gas
- Production of sulfuric acid
The process
The main reactions in the WSA process- Combustion: H2S + 1.5 O2 = H2O + SO2 + 518 kJ/mole
- Oxidation: SO2 + ½O2 = SO3 + 99 kJ/mole (in the presence of a vanadium (V) oxideVanadium(V) oxideVanadium oxide is the chemical compound with the formula V2O5. Commonly known as vanadium pentoxide, this brown/yellow solid is the most stable and common compound of vanadium. Upon heating it reversibly loses oxygen...
catalyst) - Hydration: SO3 + H2O = H2SO4 (g) + 101 kJ/mole
- Condensation: H2SO4 (g) = H2SO4 (l) + 90 kJ/mole
The energy released by the above mentioned reactions is used for steam production. Approximately 2–3 ton high-pressure steam per ton of acid produced.
Industrial applications
Industries where WSA process plants are installed:- Refinery and petrochemical industry
- Metallurgy industry
- Coal-based industry (coking and gasification)
- Power industry
- Viscose industry
- Sulfuric acid industry
WSA for gasifiers
The acid gas coming from a RectisolRectisol
Rectisol is the trade name for an acid gas removal process that uses methanol as a solvent to separate acid gases such as hydrogen sulfide and carbon dioxide from valuable feed gas streams. By doing so, the feed gas is made more suitable for combustion and/or further processing...
-, Selexol
Selexol
Selexol is the trade name for an acid gas removal solvent that can separate acid gases such as hydrogen sulfide and carbon dioxide from feed gas streams such as synthesis gas produced by gasification of coal, coke, or heavy hydrocarbon oils...
-, amine gas treating
Amine gas treating
Amine gas treating, also known as gas sweetening and acid gas removal, refers to a group of processes that use aqueous solutions of various alkylamines to remove hydrogen sulfide and carbon dioxide from gases...
or similar installed after the gasifier contains H2S, COS and hydrocarbons in addition to CO2. These gases were previously often flared and vented to the atmosphere, but now the acid gas requires purification in order not to affect the environment with SO2 emission.
Not only can the WSA process meet the demands of SO2 removal, the process also accepts a wide range of feed-gas compositions.
The WSA plant provides a high sulfur recovery and the heat recovered causes a substantial steam production. The heat recovery rate is high and the cooling water consumption low, resulting in superior cost performance of this process.
Why use the WSA process in connection with gasification?
- flexibility in feed composition
- more than 99% of the sulfur is recovered as concentrated sulfuric acid of commercial grade
- attractive operating economy
- simple layout, simple operation
Examples of WSA process for gasification
Example 1:- Feed-gas flow: 14,000 Nm3/h
- Composition [vol %]: 5.8% H2S, 1.2% COS, 9.7% HC and 77.4% CO2
- SOx concentration [vol %]: 1.58%
- H2SO4 production: 106 MTPD
- Steam production: 53 ton/h
- Cooling water consumption: 8 m3/ton acid (delta T = 10°C)
- Fuel consumption: 1,000 Nm3/h (LHV = 2,821 kcal/Nm3)
Example 2:
A sulfur plant in China will be built in connection with an ammonia plant, producing 500 kilotons/annum of ammonia for fertilizer production
Spent acid regeneration and production of sulfuric acid
The WSA process can also be used for production of sulfuric acid from sulfur burning or for regeneration of the spent acid from e.g. alkylation plants. Wet catalysis processes differ from other contact sulfuric acid processes in that the feed gas contains excess moisture when it comes into contact with the catalyst. The sulfur trioxideSulfur trioxide
Sulfur trioxide is the chemical compound with the formula SO3. In the gaseous form, this species is a significant pollutant, being the primary agent in acid rain. It is prepared on massive scales as a precursor to sulfuric acid.-Structure and bonding:Gaseous SO3 is a trigonal planar molecule of...
formed by catalytic oxidation of the 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...
reacts instantly with the moisture to produce sulfuric acid in the vapour phase to an extent determined by the temperature. Liquid acid is subsequently formed by condensation of the sulfuric acid vapour and not by absorption of the sulfur trioxide in concentrated sulfuric acid, as is the case in contact processes based on dry gases.
The concentration of the product acid depends on the H2O/SO3 ratio in the catalytically converted gases and on the condensation temperature.
The combustion gases are cooled to the converter inlet temperature of about 420–440 °C. To process these wet gases in a conventional cold-gas contact process (DCDA) plant would necessitate cooling and drying of the gas to remove all moisture. Therefore the WSA process is in many cases a more cost-efficient way of producing sulfuric acid.
About 80% to 85% of the world’s sulfur production is used to manufacture sulfuric acid. 50% of the world’s sulfuric acid production is used in fertilizer production, mainly to convert phosphates to water-soluble forms, according to the Fertilizer Manual, published jointly by the United Nations Industrial Development Organization (UNIDO) and IFDC.