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SOP Plants

Sulphur oxidation Process

Desulphurization is a chemical process for the removal of sulphur from a material. This can involve either the removal of sulphur from a molecule or the removal of sulphur compounds from a mixture such as petrochemicals or flue gases. Mostly also heat recovery is included to use it in this or other processes. This results in a very short return on invest.

P&P desulphurization plants are high efficient and allows our customers to save energy and raw-materials.


Many of these processes are of great industrial and environmental importance as they provide the bulk of sulphur used in industry and also reduce the release of harmful sulphur compounds into the environment (hydro-desulphurization, flue-gas desulphurization); particularly sulphur dioxide (SO2) which leads to acid rain.

The SOP (sulphur oxidation process) is one of the key gas desulphurization processes on the market today. It has been recognised as an efficient process for recovering sulphur from various process gases in the form of commercial quality sulphuric acid (H2SO4), with simultaneous production of high pressure steam. The SOP process is applied in all industries where removal of sulphur is an issue.

The SOP is especially suited for processing one or more sulphur containing streams such as:

  • H2S gas from e.g. amine gas treating unit
  • Off-gas from sour water stripper (SWS gas)
  • Off-gas from Rectisol
  • Spent acid from an Alkylation unit
  • Claus process tail gas
  • Heavy residue or petcoke-fired utility boiler off-gas
  • Boiler flue gases from various processes SNOX flue gas desulphurization
  • Metallurgical process gas
  • Production of sulphuric acid

The main reactions in a SOP:

Combustion: H2S + 1.5 O2 = H2O + SO2 + Energy

Oxidation: SO2 + ½O2 = SO3 + Energy (in the presence of e.g. a vanadium (V) oxide catalyst)

Hydration: SO3 + H2O = H2SO4 (g) + Energy

Condensation: H2SO4 (g) = H2SO4 (l) + Energy

The energy released by the above-mentioned reactions is recovered by our P&P heat exchanger systems used e.g. for steam production or for heating in other processes. E.g. approximately 2–3 ton high-pressure steam per ton of acid can be produced.

Industrial applications

Industries where SOP plants are installed:

  • Refinery and petrochemical industry
  • Metallurgic industry
  • Coal-based industry (coking and gasification)
  • Power industry
  • Viscose industry
  • Sulphuric acid industry

SOP for gasifiers

The acid gas 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 SOP process meet the demands of SO2 removal, the process also accepts a wide range of feed-gas compositions.

The SOP-plant provides a high sulphur recovery and the heat recovered causes e.g. 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 SOP process in connection with gasification?

  • flexibility in feed composition
  • more than 99% of the sulphur is recovered as concentrated sulphuric acid of commercial grade
  • attractive operating economy
  • simple layout, simple operation

Spent acid regeneration and production of sulphuric acid

The SOP process can also be used for production of sulphuric acid from sulphur burning or for regeneration of the spent acid from e.g. alkylation plants. Wet catalysis processes differ from other contact sulphuric acid processes in that the feed gas contains excess moisture when it comes into contact with the catalyst. The sulphur trioxide formed by catalytic oxidation of the sulphur dioxide reacts instantly with the moisture to produce sulphuric acid in the vapour phase to an extent determined by the temperature. Liquid acid is subsequently formed by condensation of the sulphuric acid vapour and not by absorption of the sulphur trioxide in concentrated sulphuric 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. 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 SOP process is in many cases a very cost-efficient way of producing sulphuric acid.

About 80% to 85% of the world’s sulphur production is used to manufacture sulphuric acid. 50% of the world’s sulphuric 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 the International Fertilizer Development Centre.