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equipped with heat accumulator shows optimal thermal efficiency, high
reliability and economic exploitation of the system. The heat accumulator
tank also allows flexible fuel charging and boiler’s operation – see figure
4.5, where a heating system with heat accumulator is installed;
5.4.
Operation of the boiler in “stand-by” mode
During the exploitation of the of the heating system, the fuel consumption rate
varies in wide range even in a period of 24 hours. The thermal capacity of the
boiler is result of the thermo-chemical processes, organized in the fuel hopper
chamber and the combustion chamber as well – in case the fuel has been
consumed, the thermal capacity of the boiler will be decreased, also after the
fuel hopper has been charged, after approximately 30 minutes the wood logs
start to release volatile gases (which is highly intensive process) and leads to
increased thermal capacity of the boiler. The efficiency of the boiler also varies
along the fuel consumption and time. The practice shows that the boiler and the
heating system are seldom balanced – in most case the thermal capacity of the
boiler will be higher or lower than the heat consumption rate by the heating
system. In case the thermal capacity of the boiler is higher than the heat demand,
the temperature of the circulating water will be increased and will be reached the
set-point of the operating thermostat of the boiler – in such a case the flue gas
fan will be switched off and the boiler will go into stand-by mode, the thermal
capacity of the boiler will be decreased to higher extent. In stand-by mode the
air is naturally driven in the boiler and the char oxidation in the fuel hopper
chamber is sustained. The measurements show that in stand-by mode the
thermal capacity of the boiler is approximately 10% of the nominal thermal
capacity of the unit. In case that the temperature of the circulating water is
decreased, the flue gas fan will be switched on and in a period of 3 - 5 minutes
the combustion process will be in nominal operating conditions, the boiler’s
thermal capacity will be increased as well.
EXPLANATION: in case the wood logs, placed in the fuel hopper have been
consumed, then the thermal capacity as well as the temperature of the flue gases
of the boiler will be decreased. In such a case the flue cases thermostat will be
activated (when the flue gases temperature is below the set-point of the flue gas
thermostat) and the boiler will be switched into stand-by mode (i.e. the flue gas
fan will be switched off) and thus the char layer in the fuel hopper chamber will
be preserved. After the fuel hopper is charged with new quantity, the boiler will
go into nominal operation mode.
