EffiMax 4000 for FBC/Grate Boilers

Why Effimax 4000?

  • Reduces unburnt losses by ensuring negative draft in furnace is maintained between set limits: (Desired limit is -2 to -5mmWC)
  • Ensures safety from backfire by maintaining draft pressure in furnace below atmospheric at all loads
  • Trims excess air in flue gas to maintain optimum stack O2%
  • Ensures sufficient air residence time in boiler for effective combustion and heat transfer
  • Maintains an ideal air:fuel ratio at all loads
  • Ensures optimum combustion air flow corresponding to the fuel firing rate
  • Proper fluidization of bed takes place such that the combustion air flow is always greater than the minimum fluidization velocity

Unique Features

Boiler Master

The boiler master control loop receives the drum pressure signal from the drum pressure transmitter and compares it to the operator-entered set-point. The controller modulates its output in order to eliminate any difference between the signal and the set-point. The output of the controller represents the boiler demand for steam, and is sent to the variable frequency drives on the feeders or distributors if automatic feed control is used. It is also sent to the fuel/air ratio station.

The operator may adjust the set-point in automatic or place the controller in manual to fire the boiler manually. The controller rejects to Manual on bad signal quality. A high/low pressure alarm is shown.

Fuel/Air Ratio Adjustment

The fuel-air ratio is determined by a lookup table entered into the controller during commissioning once the combustion test has been performed. The means of trimming, or fine-tuning, the fuel-air ratio is provided via a faceplate display on the controller which allows the operator to enter a value for the fuel-air ratio, based on observation and/or a sample from a portable combustibles or O2 analyzer. This value will modify the demand for air-flow by multiplying the position signal from the boiler master with a correction factor, limited to +/-10% for safety. The signal is sent to the fuel-air ratio lookup table and then to the VFD on the FD Fan. It is also sent to the furnace pressure control loop as a feed-forward adjustment.

Furnace Pressure

The furnace pressure control loop receives the signal from the furnace pressure transmitter, compares it to the operator-entered set-point and generates a correction signal. The result is sent to the VFD on the ID Fan.

Fuel firing modulation

Modulating control is a basic improvement in controlling combustion. A continuous control signal is generated by a controller monitoring the steam. Reductions in steam pressure or hot water temperature leads to an increase in firing rate.
The advantages of introducing fuel firing modulation in combustion control include-
  • Fuel and air requirements are continuously matched to the combustion demand
  • Steam pressure is maintained within closer tolerances
  • Greater boiler efficiency
  • Weighted average flue gas temperature is lower

Excess air regulation

In actual practice, solid fuel fired burning do not do a perfect
job of mixing the fuel and air even under the best
achievable conditions.

Additionally, complete mixing may be a lengthy process.
Figure alongside shows that in order to ensure complete
combustion and reduce heat loss, excess air has to be kept
within a suitable range.

The regulation of excess air provides:

  • A better boiler heat transfer rate
  • An ‘advance warning’ of flue gas problems (excess air coming out of the zone of maximum efficiency)
  • Substantial savings on fuel
Oxygen trim

When a measurement of oxygen in the flue gas is available, the combustion control mechanism can be vastly improved (since the percentage of oxygen in flue is closely related to the amount of excess air) by adding an oxygen trim control module, allowing:

  • Tighter control of excess air to oxygen set-point for better efficiency
  • Faster return to set-point following disturbances
  • Tighter control over flue emissions
  • Compliance with emissions standards
  • Easy incorporation of carbon monoxide or opacity override.