Explosion protection of the pulverized-coal system of a coal-fired combined heat power plant

16 September 2021

The pulverized-coal system at coal-fired combined heat power plant is designed for grinding and drying of supplied coal and consists of storage, a raw-coal feeder and a coal pulverizer. Coal dust with a size of 40-200 µm obtained in the process of pulverizing is combustible and can explode in the form of a dust-air mixture.

Explosive concentrations of coal dust are usually observed in the coal pulverizer and the air classifier, which returns large particles back to the coal pulverizer. It is worth noting that process routings of pulverizing are being developed for specific equipment and fuel specification. Under normal operation and compliance with process routings, the concentration of coal dust usually exceeds the upper explosion limit and thus does not pose a threat.

Under certain circumstances, the concentration of dust can fluctuate, for example, when stopping or starting coal pulverizers, interruptions in the supply of raw coal, various process non-conformances. The presence of an ignition source in the form of glowing particles or heated surfaces in such a situation with a high probability leads to an explosion.

Traditionally, to ensure the explosion safety of coal pulverizers, explosion venting devices are used; excess pressure and explosion products are vented through them into the environment, thereby maintaining the integrity of the equipment. The explosion accidents in the pulverized coal system experience show that passive explosion protection is effective in terms of protecting equipment, but does not ensure the safety of personnel. A person can get into the area affected by vented explosion products and get seriously injured or even die. This is typical for coal-fired combined heat power plants and coal-steam plants, where the design provides for the venting of explosion pressure into the plant main building.

An effective technical solution for the explosion protection of such equipment is the installation of an active explosion suppression system. The most important advantage of this system compared to explosion venting devises is the isolation and suppression of the explosion in the equipment at the stage of emergence. In this case, the explosion products do leave the body of the protected equipment, and the explosion pressure does not reach dangerous for the equipment values.

Active explosion suppression system manufactured by the company RSBP spol. s.r.o for one coal pulverizer consists of:

  • highly sensitive pressure sensor DetEx that detects an explosion at an early stage
  • control unit CONEX I
  • HRD container unit for explosion suppression and isolation.

The volume of containers with an explosive suppressant is selected individually based on the volume of protected equipment and the characteristics of coal dust 

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This technical solution for the explosion protection of the pulverized-coal system is recommended for use as the main or additional measure to ensure explosion safety during the equipment update of existing coal-fired boiler plants, as well as the design and construction of new electrical generating unit for coal-fired combined heat power plants and coal-steam plants. Detailed information about the active explosion suppression system can be found in the product section.

You can find more detailed information about the active explosion suppression system in the Product Catalogue section.