The firebox belongs to the group of Counter flow fireboxes; such construction enables the combustion of very wet fuels over 60%. It consists of the hydraulically driven stepped grate. The grate consists of the cast bars made of alloy steel resistant to high temperatures. The carrier of grid is made of steel elements and profiles of high thickness and consists of three completely separate parts, allowing to different parts of the grid to move independently of each others. This construction enables the combustion of fuel of different quality, even of very poor quality. The construction also enables that different combustion phases occur in certain zones of the grid - the phases are as follows: the heating of the fuel, the moisture evaporation, the combustion of volatiles and the combustion of solid residue. The frame of the grate is cooled by water from the heat exchanger through special pumps, and this part is the only part of the firebox that contains the water. Primary combustion air is fed under the grate into three completely separate zones each of which is separately controlled. The secondary air is fed into three zones: above the grid, on the first turn of the flue gas and the back side of the boiler. The tertiary combustion air is fed into immediately before the heat exchanger. The firebox is a two-pass structure, which means that the flue gas passes through two zones of hot bricks.


Such construction allows to flue gas to pass through the secondary combustion zone, resulting in a low content of carbon monoxide and high combustion efficiency. Both zones of the firebox are made of fireproof brick with a high content of aluminum. There are thick layers of insulating thermal concrete on the external side of the thick fireproof wall. The temperature of the firebox, during the normal operation of the boiler, is 800-1000°C; while the external side of the boiler is insulated with fireproof panels, which guarantees the surface temperature less than 40°C. At the bottom of the furnace there is the system of hydraulically driven pushers that drains the ash that has passed through a moving grate, which allows easier handling of the entire system. The external – supporting construction of the firebox is made of I and U steel profiles of high thickness. The complete steel construction is very robust and guarantees the safety and long life expectancy of the whole boiler. The temperature in the firebox is controlled at three points through three thermocouple temperature probes; the underpressure in the boiler is measured by the differential pressure transducer. The flow of cooling water in the frame of the grate is measured by the flow sensor. The temperature of the input and output of the cooling water in the frame of the grid are also measured. The level of fuel in the grate is measured at two points by two infrared probes.




Heat exchanger is made of boiler steel and is a three-pass construction. In this type of construction, the flue gases from the firebox pass for three times through different exchanger components, thus increasing the efficiency of the boiler system. The position the exchanger is at the top of the firebox, thereby reducing heat loss due to radiation from the firebox. Heat exchanger regime is 119/110°C. The exchanger is thermally insulated with rock wool and its outer cover consists of fireproof thermal insulation panels, reducing the heat loss to a minimum.

The exchanger is equipped with an automatic deashing system. At the front door of the exchanger a considerable number of special soot blowers are mounted, which occasionally let the air under the high pressure through the pipes of the exchanger, through which the ash is transported to multycyclone. This system requires significantly smaller number of personnel involved in cleaning and maintenance of the plant. This system consists of the following components:


-          Blowers

-          Control cabinet with integrated control

-          Compression vessel

-          Electrical cables for connection of valves to control cabinet

-          Clamps 6/4"

-          Flexible hose 4.6" (to connect blower and nozzles)

-          Steel pipe frame for connection of blowers to compressive vessel



Hydraulic silo with movable floor. The silo consists of the following components:


-          Hydraulic aggregate with complete fittings

-          Two hydraulic cylinders to start the pusher

-          Control unit

-          Two rows of pushers, welded at HEB profiles

-          Level probe


Stoker is a conveyor that takes biomass from the silo and transports it to the first row of bars of the grate. The stoker is made of large steel profiles which are, for the purpose of the strength, pour out in the concrete base. It consists of a series of triangular pushers, of which the last two have the built-in special blades made ​​of tool steel. This construction of silos and stoker allows the use of granulated biomass of G100. The stoker is consisted of the following components:


-          Hydraulic aggregate with complete fittings

-          Two hydraulic cylinders to start the pusher

-          One row of triangular pushers, strengthened by internal profiles, welded at HEB profile

-          Control unit

-          Steel structure of the stoker made of UPN and HEB profiles

-          Level probe




The electrical cabinet with integrated touch screen PLC has the task of automatic control of the combustion process by the set upper and lower boiler water temperature. PLC monitors the conditions in the firebox by measuring and maintaining the vacuum and temperature at different points, as well as dosing of fuel by the stoker. PLC also regulates the fan of primary, secondary, tertiary air and the recirculation fan, all this by frequency regulators. Together with the electrical cabinet, PC is also supplied through which it is possible to completely monitor the installation and to control via the Internet. PLC has the option of GSM alarm messages to four phone numbers.