The pulverisation system in coal-fired power plants is designed for pulverisation and drying of incoming coal and consists of a hopper, a raw coal feeder and a mill. Coal dust with a size of 40-200 microns that is obtained in the process of crushing is combustible and in the form of a dust-air mixture can explode.
Explosive concentrations of coal dust are usually observed in the mill and in the air separator that brings coarse particles back to the mill. It is worth noticing that process flow charts are developed for specific equipment and fuels. In normal operation, and in compliance with the process charts, the concentration of coal dust is normally above the upper explosive limit, i.e. does not constitute a hazard.
Under certain circumstances, the dust concentration can fluctuate, e.g. during shutdown or start-up of the mills, interruptions in the raw coal supply, and various process disruptions. The presence of an ignition source in the form of smouldering particles or heated surfaces in such a situation is highly likely to result in an explosion.
Explosion protection valves are traditionally used to ensure the safety of mills, the overpressure and products of the explosion are released through them into the environment, thereby maintaining the integrity of the equipment. Experience from explosion accidents in dust preparation systems shows that passive explosion protection is effective in terms of equipment protection, but does not ensure the safety of personnel. A person can enter the area affected by the released explosion products and be seriously injured or even killed. This is characteristic of coal-fired thermal power plants and thermal power stations where the design provides for release of explosion pressure into the main room of the plant.
An effective technical solution for the explosion protection of such equipment is to install an active explosion suppression system. The most important advantage of this system as compared to explosion venting is the localisation and suppression of an explosion in the equipment at its incipient stage. This prevents explosions from escaping from the enclosure of the protected equipment and prevents explosions from reaching dangerous levels.
The RSBP spol. s r.o. active explosion suppression system for a single mill consists of:
- A highly sensitive pressure sensor DetEx that detects an explosion at an early stage;
- A CONEX control panel;
- A group of HRD cylinders for suppressing and shutting off an explosion.
The volume of explosive suppressant cylinders is individually selected based on the volume of the equipment to be protected and the characteristics of the coal dust.
This technical solution for the explosion protection of the dust suppression system is recommended for use as a basic or supplementary explosion protection measure in the modernisation of existing coal-fired CHPPs as well as the design and construction of new power units of coal-fired TPPs. Detailed information on the active explosion suppression system can be found in the product section.
More information about the active explosion suppression system can be found in the product section.