Fire detection and sprinklers control system for inclined coal conveyors

WOLFF GROUP

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Krzysztof Tetla
Fire detection and sprinklers control system for inclined coal conveyors

Problem:

  • how to adapt the inclined coal conveyors system to the legal regulations concerning fire protection
  • how to design a fire detection, alarm and extinguishing system resistant to false alarms caused by very difficult operating conditions (high dust content, vibrations, changing temperature, humidity)

Solution:

  • preparation of an engineering design for the system in accordance with the applicable regulations and standards, including the PN EN54-22 standard
  • application of linear temperature detectors (sensor cables) resistant to interference resulting from very difficult operating conditions
  • activation of the system on the basis of at least two coinciding alarm states

Check the details for equipment and services in the field of fire protection installations:

  • preparation of an engineering design for a fire alarm system
  • design of an early detection system for flameless fires
  • design of a sprinklers installation with control system
  • fire alarm central unit
  • linear, addressable thermal detectors
  • manual call points (MCP)
  • sprinkler system

On the basis of the analysis carried out in order to protect the inclined coal conveyor against fires, we designed a fire detection, alarm and extinguishing control system (FDAECS). The protection extends along the inclined coal conveyors system, within which we used linear thermal detectors (sensor cables) and manual call points. Furthermore, we applied fixed extinguishing devices in the form of a sprinkler installation for extinguishing the inclined coal conveyor. What is important, we have provided two modes of sprinkler system activation: automatic and manual. Automatic activation is carried out on the basis of a confirmed fire alarm signal (group coincidence of at least two events).

Fire detectors for harsh operating conditions

The operating conditions within the conveyor system were very difficult for the correct operation of most fire detectors. These conditions include: high dust content, vibrations, humidity and changing temperatures. An improper selection of the detectors would have serious consequences. For example, a false activation of the fire protection system would lead to stopping the fuel supply process and a costly reduction in the power capacity of the power plant. There would also be a risk that water from the sprinkler system could wash off large amounts of coal, which, by running down the inclined conveyor, would destroy elements of the system – similar to a mudslide.

On the basis of the experience of the project engineers, it was decided to use detection based on temperature measurement carried out by fire detectors compliant with the PN-EN 54-22 standard, which at the same time have a national certificate of compliance with this standard and IP65 protection.

How to guarantee a reliable fire alarm signal

Automatic activation of the fire protection system is based on a certain fire alarm signal, which is generated as a result of the coincidence of two alarm states – two-group coincidence was selected. The protected conveyor system will be equipped with two independent lines of sensor cables with detectors spaced every 3 m, which allows for the implementation of coincidence and ensure compliance with the requirements resulting from environmental conditions.

Manual activation of the sprinkler system

Manual control of the sprinkler system is possible using the „start extinguishing” buttons located in front of the top and bottom entries to the inclined conveyor system.

It is possible to stop the extinguishing during the first category alarm and within emergency escape time. The „stop extinguishing” buttons are used for this purpose. After starting the extinguishing process, the “stop extinguishing” buttons are deactivated.

Detection of flameless fires and pre-emergency conditions

This installation is a technological system, accepted for industrial installations where normative requirements do not exist or where existing systems do not function properly and effectively.

Limiting the possibility of using only certified and approved devices in industrial installations means that the fire detection system in such an installation will be formally correct, but due to the exclusion of custom design and tested technological detection systems, it may not function properly and may therefore be dangerous for the protected installation.

As a result of joint studies after a series of severe failures in unprotected fuel supply systems in power plants, an effective technology for early detection of flameless fires was developed, followed by temperature monitoring. It was assumed that in order to effectively protect the system against the effects of fires, the fire should be detected at the earliest possible stage, i.e. in the case of fires of coal, biomass, organic fuels – at the moment of starting a flameless fire, i.e. smouldering. Experience in many installations in Poland has shown that frequently detected fire hazards can be alleviated manually or by basic means, without the use of fire extinguishing systems and without the participation of the fire service, often through internal procedures, inspections and preventive repairs. The system used by us is a proven solution ensuring reliable fire detection where traditional fire detection technologies are not sufficient or it is very difficult to detect a fire using such technologies.

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