UNDERFEED STOKER UNIT and RECIPROCATING GRATE STOKER

Nominal power of the boilers: from 100 kW to 20.000 kW

The Underfeed Stoker units and Underfeed grate firing system are suitable for
following fuel-types:

Fuel division underfeed stoker unit
Fuel division grate firing system  

System of firewood feeding and loading

Fuel can be discharged from

• square and rectangular hoppers (tip down bunker) – see hydraulic fuel discharge and spring care chamber discharge
• round silo (high silo) – see silo fuel discharge diagonal, silo fuel discharge horizontal with pneumatic pushing forward and silo discharge horizontal with hydraulic pushing forward
• storage reservoir – see storage reservoir with hydraulic fuel discharge

Combustion system 'underfeed stoker unit/underfeed grate firing system'

Underfeed stoker unit and underfeed grate firing system especially was designed for dry and
small granular fuel.

Feeding from fuel depends on the kind of fuel and local conditions by worm conveyors
or by hydraulic feed systems.

For optimal combustion and complete ash-removal a movable burn out grate for ash-removal, manufactured with heat-resistant steel is attached at the underfeed stoker unit of the com-
bustion hollow.

For supervision, control and regulation of the quantity of fuel and ash in furnace room
measuring of level are installed as well as above the furnace-hollow and above the
moved ash grate.

View into the furnace room of an underfeed stoker unit

Ash that is removed above the grate afterwards falls through a fall chamber either into an
ashes container that is directly positioned below the firing or is moved outside the firing with an ash removal snail.
With optimal mixture of combustion gases with oxygen frequency controlled combustion air fans enable complete combustion. In different combustion zones the necessary quantity is
calculated by means of control (load control).

combustion air fans

As a sign for permanent innovative research a calorifier of the initial heating of fuel
and drying was installed for further improvement of efficiency run with unused heat
of exhaust gases.

The combustion gases are burned completely  due to stepped combustion and permanent
control of the remaining value of oxygen and conducted into the heat exchanger situated
there.

Heat exchanger

Transmission of energy of hot waste gases into the system for use of heat is carried out
with the heat exchanger, which shows utmost comfort for operating at cleaning and
maintenance.

Automatic compressed air cleaning unit for boiler tubes

The following media for heat carrier can be used for it:

• warm water up to 95ºC
• hot water up to 120ºC
• hot water more than 120ºC
• thermo oil up to 300ºC
• low pressure steam up to 1 bar
• steam up to 36 bar
• hot steam up to 450ºC

Flue gas dedusting

In principle flue gas dedusting is carried out by an attached multi-cyclone for trapping
of flying ash. A lower residual content of dust is required by legislation for bigger plants.
For keeping this level there will be used systems like

• electrostatic filter
• tissue filter
• condensation plant

multi-cyclone	electrostatic filter

For holding up the degree of effectiveness in each point of operation a part of flue gas
is resupplied to the heating through flue gas recycling.

The rest of the cleaned waste gases is conducted through exhaust gas fans to chimney
plant.

Computer-controlled regulation

Full-automatic control and regulation of the complete firing plant on biomass is
carried out from a SPS (programmable memory-control).

Influence of oxygen, furnace temperature, flue gas recycling, flue gas temperature,
temperature of combustion air, quantity of material, humidity of material, flow pipe
and return pipe temperature and consumption of individual consumers (net) can be
projected in full-automatic control and regulation of SPS and further processed
into instruction signals by an integrated oxygen and capacity regulation.

Heating operation works full automatically, from supplying of biomass, control
and regulation of combustion up to control of the pumps.

On request all these parameters can be processed with a process-visualisation and
saved in single figures or comprehensive diagrams and statistics.

The components of the plant recorded schematic and saved thus enabling us to have a summary of the status and the functions of single parts of the plant and of the complete
plant in a simple and clear manner. Each little difference to the predefined parameters are
displayed and automatically led back into the set condition.

Because of this kind of visualisation it is not only possible recording on the monitor
or memory but also with a PC and a modem it is possible to see a change and differences
in the set point of all parameters anytime.