Sulphuric acid from elemental sulphur by DC-DA process

DС-DA sulphuric acid production technology from sulphur was developed at JSC NIUIF (RF patent No. 2201393 dated September 18, 2001) and implemented on an industrial scale at several chemical plants in the Russian Federation.

Among the latest implementations of this technology:

1. In 2009, a new sulphuric acid plant with a 740 MTPY capacity was put into operation at OJSC Ammophos, Cherepovets.

2. In 2010, a new sulphuric acid plant with a 650 MTPY capacity was put into operation at BB JSC Apatit, Balakovo.

3. In 2013, a new sulphuric acid plant with a 620 MTPY capacity was put into operation at LLC Kazphosphate, Taraz, Republic of Kazakhstan.

4. In 2020, a new DС-DA sulphuric acid plant with a 1,1 MMTPY capacity was put into operation at JSC Apatit, Cherepovets.

Production method

Sulphuric acid production is carried out according to a "short" environmentally friendly, energy-saving flowsheet with Double Conversion and Double Absorption (DC-DA), which is used by modern sulphuric acid production plants around the world.

Process parameters

Process parameter


production capacity of one process line

from 20 to 1100 MTPY *

Operating regime

continuous, not less than 330 per year;

Raw materials

sulphur solid (lumpy, granular) or liquid, grade not lower than 99.90

Sulphur consumption per 1 ton of H2SO4 (from nozzles)

0,328 t/t;

Final product

commercial-grade sulphuric acid with concentration of 92.5 - 98.5% w/w and special, improved grades of sulphuric acid for caprolactam, synthetic fibers and other products;


power steam (P = 4 MPa, T = 440°C) up to 1.24 tons per ton of H2SO4.

* At customer’s request, a sulphuric acid plant of any capacity within the specified capacity range can be developed

The advantages of the proposed sulphuric acid system:

  • quickly reaches its design capacity;
  • reliable and easy in operation;
  • guarantees the minimum emission of harmful gases into the atmosphere;
  • has a minimal power consumption;
  • supplied with simple and reliable equipment;
  • SO2 conversion rate, not less than 0.998;
  • overall absorption of SO3 - 0.9999.

This technology can be used in both revamp of existing sulphuric acid systems with the maximum use of existing equipment, and in the construction of new DC-DA systems from sulphur. The flowsheet of the new sulphuric acid plant is shown in Fig. 1.

The main difference between the new DC-DA flowsheet from the existing flowsheets is the use of a new RKS type water-tube waste heat boiler with external elements installed in the converter section of the system. The new boiler makes it possible to significantly increase the degree of useful heat recovery, released during production process and increase power steam generation in the sulphuric acid system.

The converter section uses gas heat exchangers, developed by JSC NIUIF, both of a diffuser type, and with ring and plate baffles.

The drying-absorption department uses cost-effective and efficient equipment and apparatuses manufactured both in the Russian Federation and abroad. For proficient distribution of sulphuric acid onto the packing in absorption towers, trough type distributors (troughs), developed by JSC NIUIF, are used.

Shell-and-tube heat exchangers, developed by JSC NIUIF, have high heat removal efficiency and low hydraulic resistance and are used to cool sulphuric acid. The upper and lower segments of such heat exchanger tubesheets are not filled with tubes, which increases heat removal efficiency, reduces its metal consumption and hydraulic resistance to the sulphuric acid flow in the tube side.


Figure 1. NIUIF sulphuric acid technology flowsheet

DT - drying tower; WHB - RKS boiler; B - blower; HE 1, HE 2, HE 3 - heat exchangers; C - converter; A1 - first monohydrate absorber; A2 - second monohydrate absorber; E1 + SH1 - primary superheater and economizer; E2 - secondary economizer; SH2 – secondary superheater

NIUIF sulphuric acid department new laboratory has a modern, automated system for determining the catalytic activity of fresh and spent samples of vanadium sulphuric acid catalysts. System’s set up is shown in the photo below. The system equipment allows it to be used in scientific research, because it can simulate various temperature, gas composition and contact time conditions. This, in turn, makes it possible to cover the entire behavior spectrum of vanadium catalysts under the conditions of their industrial application.


Lab system for determining the catalytic activity of sulphuric acid vanadium catalysts

In 2019, NIUIF developed and patented an original flowsheet for obtaining liquid sulphur dioxide based on the use of pure oxygen in the presence of excess sulphur vapor in the combustion zone. The relevance of this topic is due to the fact that at present, in the Russian Federation, liquid sulphur dioxide production is completely non-existent, and the need for this product is fully met through imports. Based on the patented flowsheet, a lab system for the production of liquid sulphur dioxide was set up in NIUIF laboratory for a detailed study of the liquid sulphur dioxide synthesis process per patented invention, in order to obtain data sufficient for the industrial plant development. At present, the system is used to conduct research on various stages of this process. The flowsheet and photo of the lab system for liquid sulphur dioxide production are presented below.


Flowsheet for liquid sulphur dioxide production

E1 - thermostat; E2 - cryostat; Б1 - gas cylinder; F - sulphur filter; KR - combined reactor; K - cryostat; E3 - container for final product storing.


Lab system for the production of liquid SO2 from sulphur and oxygen