The wet sulfuric acid process (WSA process) is a gas

desulfurization Desulfurization or desulphurisation is a chemical process for the removal of sulfur from a material. This involves either the removal of sulfur from a molecule (''e.g.'' A=S → A:) or the removal of sulfur compounds from a mixture such as oil refin ...

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 of commercial quality

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...

(H₂SO₄) with the simultaneous production of high-pressure steam. The WSA process can be applied in all industries where the removal of sulfur is an issue. The wet catalysis process is used for processing sulfur-containing streams, such as: * H₂S gas from e.g.

amine gas treating Amine gas treating, also known as amine scrubbing, gas sweetening and acid gas removal, refers to a group of processes that use aqueous solutions of various alkylamines (commonly referred to simply as amines) to remove hydrogen sulfide (H2S) and c ...

unit * Off-gas from sour water stripper (SWS) gas *Off-gas from

Rectisol 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 combus ...

*Spent acid from an

alkylation unit An alkylation unit (alky) is one of the conversion processes used in petroleum refineries. It is used to convert isobutane and low-molecular-weight alkenes (primarily a mixture of propene and butene) into alkylate, a high octane gasoline componen ...

Claus process The Claus process is the most significant gas desulfurizing process, recovering elemental sulfur from gaseous hydrogen sulfide. First patented in 1883 by the chemist Carl Friedrich Claus, the Claus process has become the industry standard. Th ...

tail gas *Heavy residue or

petcoke 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 utility boiler off-gas *Boiler flue gases from various processes SNOX flue gas desulfurization *

Metallurgical Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are known as alloys. Metallurgy encompasses both the sc ...

process gas *Production of sulfuric acid

The process

;The main reactions in the WSA process *

Combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...

: 2 H₂S + 3 O₂ 2 H₂O + 2 SO₂ (-1036 kJ/mol) *

Oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

: 2 SO₂ + O₂ 2 SO₃ (-198 kJ/mol)

vanadium (V) oxide Vanadium(V) oxide (''vanadia'') is the inorganic compound with the formula V2 O5. Commonly known as vanadium pentoxide, it is a brown/yellow solid, although when freshly precipitated from aqueous solution, its colour is deep orange. Because ...

catalyst] *Hydration reaction, Hydration: SO₃ + H₂O H₂SO₄ (g) (-101 kJ/mol) *Condensation: H₂SO₄ (g) H₂SO₄ (l) (-90 kJ/mol) The energy released by the above-mentioned reactions is used for steam production. Approximately 2–3 tons of high-pressure steam are produced per ton of acid.

Industrial applications

Industries where WSA process plants are installed: * Refinery and

petrochemical industry The petrochemical industry is concerned with the production and trade of petrochemicals. A major part is constituted by the plastics (polymer) industry. It directly interfaces with the petroleum industry, especially the downstream sector. Compan ...

Metallurgy Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are known as alloys. Metallurgy encompasses both the sc ...

industry * Coal-based industry (

coking Coking is the heating of coal in the absence of oxygen to a temperature above 600 °C to drive off the volatile components of the raw coal, leaving a hard, strong, porous material of high carbon content called coke. Coke consists almost ent ...

and

gasification Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (). This is achieved by reacting ...

) *

Power industry The electric power industry covers the electricity generation, generation, electric power transmission, transmission, electric power distribution, distribution and electricity retailing, sale of electric power to the general public and industry. ...

Viscose Rayon is a semi-synthetic fiber, made from natural sources of regenerated cellulose, such as wood and related agricultural products. It has the same molecular structure as cellulose. It is also called viscose. Many types and grades of viscose ...

industry * Sulfuric acid industry

WSA for gasifiers

The acid gas coming from a

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. By ...

or similar unit installed after the gasifier contains H₂S, COS and

hydrocarbons In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...

in addition to CO₂. These gases were previously vented to the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

, but now the acid gas requires purification in order not to affect the environment with SO₂ emission. The WSA process provides a high sulfur recovery and recovers heat for steam production. The heat recovery rate is high and the cooling water consumption low, which saves resources.

Examples of WSA process for gasification

Example 1: *Feed-gas flow: 14,000 Nm³/h *Composition

ol % OL may refer to: Arts and entertainment * Orphaned Land, an Israeli progressive metal band * Old Lace (comics) Old Lace (often nicknamed as OL''Runaways'' #9) is a super-powered fictional dinosaur character appearing in American comic books p ...

5.8% H₂S, 1.2% COS, 9.7% HC and 77.4% CO₂ *SOx concentration

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 Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

plant, producing 500 kilotons/year of ammonia for fertilizer production

Spent acid regeneration and production of sulfuric acid

The WSA process can also be used for the production of sulfuric acid from sulfur burning or regeneration of the spent acid from e.g.

alkylation Alkylation 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 (or their equivalents). Alkylating agents are reagents for effecting ...

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 trioxide Sulfur trioxide (alternative spelling sulphur trioxide, also known as ''nisso sulfan'') is the chemical compound with the formula SO3. It has been described as "unquestionably the most important economically" sulfur oxide. It is prepared on an ind ...

formed by

catalytic oxidation Catalytic oxidation are processes that rely on catalysts to introduce oxygen into organic and inorganic compounds. Many applications, including the focus of this article, involve oxidation by oxygen. Such processes are conducted on a large scale ...

of the

sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...

reacts instantly with the moisture to produce sulfuric acid in the vapor phase to an extent determined by the

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

. Liquid acid is subsequently formed by condensation of the sulfuric acid vapor and not by the 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 is 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 In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...

to water-soluble forms. according to the Fertilizer Manual published jointly by the

United Nations Industrial Development Organization The United Nations Industrial Development Organization (UNIDO) (French: Organisation des Nations unies pour le développement industriel; French/Spanish acronym: ONUDI) is a specialized agency of the United Nations that assists countries in e ...

(UNIDO) and the

International Fertilizer Development Center The International Fertilizer Development Center (known as IFDC) is a science-based public international organization working to alleviate global hunger by introducing improved agricultural practices and fertilizer technologies to farmers and by li ...

.
(July 2008). IFDC FOCUS ON FERTILIZERS AND FOOD SECURITY,Issue 4; Global Shortage of Sulfuric Acid Contributes to Rising Fertilizer Costs

References

{{Reflist Oil refining Chemical processes Air pollution control systems