Sulphuric acid from hydrosulphuric gas by "wet" catalysis DC-DA process

The flowsheet for the production of sulphuric acid from hydrosulphuric gas or from hydrosulphuric gas + waste sulphuric acid by “wet” catalysis double conversion-double absorption (DC-DA) process was developed.

The developed technology of the required capacity can be used to produce sulphuric acid from hydrosulphuric gas and waste acids at gas processing plants that obtain hydrosulphuric gas, which is a by-product of oils and oil derivatives purification.

The developed process includes the following units:

  • furnace unit with a waste heat boiler;
  • conversion unit;
  • absorption unit;
  • acid storage;
  • stack;
  • cooling water unit.

Technology description

Atmospheric air, hydrosulphuric gas and waste sulphuric acid are fed into the furnace pos. 2 for burning. Air is supplied to the furnace by centrifugal blower pos. 1. In the furnace, hydrogen sulfide is burned by an exothermic reaction and waste sulphuric acid is decomposed.

Process gas, generated in the furnace, containing 8.5 - 9.0% vol. SO2 and 10 - 11% vol. water vapor, is cooled to a temperature of ~ 425°C in a waste heat boiler pos. 3 and enters the first catalyst layer in a four-layer converter pos. 6, pre-cleaned from ash impurities in the gas filter pos. 5. The converter operates in DC-DA (3 + 1) mode.

Catalytic oxidation of SO2 to SO3 takes place in the converter in two successive stages. After the converter, the process gas is cooled to the required temperature, thereafter SO3 formed as a result of the catalytic conversion of SO2 is sequentially captured in two absorbers with packing pos. 9, 13 with product sulphuric acid manufacture.

To cool the gas after the first stage of conversion before absorption, an economizer of a special design pos. 4 is used, ensuring the cooling of the gas mixture to the required temperature without condensation of sulphuric acid vapor on its tubes.

Sulphuric acid mist, formed during the first absorption in large quantities, is captured in a special pos. 9, mist eliminator.

Power steam with P = 4.0 MPa; T = 440°C is obtained in a waste heat boiler with a built-in superheater and an external economizer.

The plant is equipped with all necessary instrumentation and equipment to ensure continuous operation, remote control or start-up. In case the established permissible parameters are exceeded, visual and sound alarm of the most important process operations is provided. In order to avoid operational errors and protect the plant’s units, a blocking system, that takes into account the features of the process, is provided. Sulphuric acid concentration is automatically controlled, registrated and regulated during absorption tower cycles.

The developed flowsheet for sulphuric acid production from hydrosulphuric gas meets the following requirements:

  • space-saving placement of apparatuses at the production site;
  • the use of energy-efficient technological equipment;
  • minimal emissions of harmful impurities with off-gases into the atmosphere (SO2, SO3, H2SO4, NxOy);
  • minimum of liquid effluents and the absence of solid waste;
  • increased share of recoverable heat generated at various stages of the process;
  • highly automated process using modern control and regulation systems.

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Resulting products:

  • commercial grade sulphuric acid with a minimum 92.5% concentration per GOST 2184-77;
  • the process allows to get part of the products in the form of 98.5-99.5% sulphuric acid.

By-products:

A feature of the proposed production method is the high degree of heat recovery during the hydrosulphuric gas burning and the catalytic oxidation of sulphur dioxide to sulphur trioxide to obtain power steam P = 4 MPa, T = 440°C in the amount of 1.35-1.45 tons per ton of H2SO4. Steam can be used to generate electricity or other industrial site needs.