Design of boiler houses operating on solid fuel – soiled fuel boiler houses

Design of solid fuel boiler houses The solid fuel boiler plants (with unit capacity of one boiler up to 4 MW) are a system of devices and units intended for generation of heat energy, in which processes of heat transfer, fuel combustion and ash disposal take place with minimum costs of hand labour due to automation of the processes.

Fuel for this type boiler houses can be: coal, coke, peat, fire wood and waste wood (chips, bark) both in bulk and in briquets (fuel briquets, fuel pellets).

Solid fuel is a conventional fuel for boiler houses, features high safety and flexibility. Almost all solid fuel is interchangeable, that is why there are no difficulties in purchase of raw materials.

Their basic advantage is low cost of fuel as well as relatively low initial investment (in comparison with gas and liquid fuel boiler houses).

The basic disadvantage of solid fuel boilers is low degree of automation (in comparison with gas and liquid fuel boiler houses), mandatory control and presence of maintenance personnel.

The basic elements of the solid fuel boiler plants are as follows:

  • Fuel storage system
  • Fuel supply system
  • Boiler units actually
  • Ash removal system
  • Pump and heat exchange equipment

Fuel supply of boiler house depends on fuel type. For example, in coal boilers coal is supplied by means of a special feeder to a band conveyer which transfers it to boiler measuring hoppers from where coal is supplied to solid fuel boiler by a shearing plate.

The boilers operating on chips and waste wood needs fuel storage with “live bottom” system (based on movable scraping sections), which does not allow formation of lumps of wood fuel. Fuel supply immediately to boiler is performed by reciprocating screws.

Design of solid fuel boiler houses Fuel for the boilers operating on pellets can be transported from the storage by means of scraping, band, screw conveyors or by pneumatic transport to hoppers located near boilers, and from there fuel is supplied to boiler furnace by screw conveyor. Pellets can be delivered both in bulk by dump trucks and in big bags (soft containers). Big bag discharge to fuel storage and their delivery to fuel supply hopper can be performed by lifting devices of fuel storage and boiler (monorail hoists, beam cranes).

To clean flue gases from solid particles (ash) each boiler is provided with an ash collector (a centrifugal collector). A stack is provided to remove combustion products. Heat supply scheme is selected in accordance with the technical design assignment for the boiler house (close/open, two-pipe/four-pipe). Separation of boiler and network circuits is carried out by means of heat exchangers. Circulation of heat carrier in the circuits is performed by pump equipment. Temperature mode of the boiler circuit is as a rule 105-80°С, of the network heating circuit is 95-70°С, of hot water supply – 60°С.

To compensate temperature variations of water volumes the boiler houses are provided with expansion tanks. The system is equipped with safety valves to emergency pressure relief. Temperature of network water in heat network changes by automatic weather dependent control devices in accordance with temperature schedule. Metering units are installed in the boiler rooms for determination of heat energy supplied to a consumer.

Control of boiler operation, maintenance of design temperature, control of water treatment system, pump operation, etc. is carried out automatically. To this end, each boiler plant except for obligatory boiler automatic devices is equipped with automatic control devices of boiler parameters complete with sensors and controllers. The boiler plant control system is provided with their protection against equipment overload and interlock of emergency operation mode in case of increase of limit values of temperature in furnace, water temperature in the straight line of heat network and in case of decrease of water pressure in the system lower the admissible value.