Compared with the pulverized coal boiler, the CFB boiler is similar with it on the controlling method on steam-water side. But they two own great difference on the combustion controlling. And the biggest difference is the monitoring, adjusting of recycle material and the interlock protection which is special for the CFB boiler.
Talking to the CFB boiler, it is of low-temperature combustion, its flame characteristic is greatly worse than the pulverized coal boiler, So it would not equipped with the furnace flame monitor system (except for the under-bed ignition device), but it pay great attention to the controlling of furnace bed temperature and bed pressure, and the monitoring of the rate of air and coal, the adjusting and interlock protection, it woks hard on the material fluidization, recycle, the monitor of the air volumes, so that a stable recycle volume could be established and the ash balance, heat balance of boiler combustion could be guaranteed.
On the aspect of thermal controlling, the main difference between the CFB boiler and other pulverized coal boiler are listed in the following:
1. The following ones are added in the closed-loop controlling system:
(1) Bed-temperature adjusting system;
(2) Bed-pressure adjusting system;
(3) SO2 emission system;
2 The following functions are added in the interlock protection system:
(1) Under the following circumstance, the main-fuel trip would be caused because of the damage of material recycle: the added primary air volume caused by main-fuel trip interlock is lower than the min. data (the fluidization and loss of furnace bed material); the outlet pressure of back-feeding air is lower than the min. data (the fluidization and loss of material in back-feeding valve); the rate between air and fuel is 2min (or even worse) than the min. value.
(2) The bed-temperature interlock function for fuel in-and-out is added (be equal to the support condition of the nozzle ignition energy of pulverized coal boiler).
(3) When the inlet, outlet smoke temperature of separator is higher than 480℃, the trip is caused becase the drum water level is too low, the effect of waterwall cooling would not be good as many heat material are existing in CFB boiler inside. If the superheater flow is less than 10% and the inlet, outlet steam pressure is reduced to be smaller than 11Kpa, the effect of superheater cooling would not be good. Both of the two conditions would caused the overheat protection act. It means that the inlet vane of the primary air fan would point to 0, and the main controlling of air volume would be turned to manual.
(4) As there is so many sets of air fan, the air fan interlock of CFB boiler would be much complex.
3. It is very difficult to measure out the following parameters of the monitor system:
(1) The measuring of bed temeprature;
(2) The measuring of bed pressure;
(3) The measuring of the air volumes for fluidization or combustion.
4 Basic principle for the adjusting of boiler combustion system are listed: adjust the coal-feeding volume according to the load requirements; the principle for coal-adjusting is “ increase coal before the coal is added, decrease air after the coal is reduced; adjust the primary air, the secondary air, the total air volume according to the load, coal and oxygen. The primary air can garantee the material fluidization and maintain a certain material recycle volume. The furnace temperature could be controlled by adjusting the ratio between the primary air and the secondary air. The negative pressure on furnace outlet could be controlled by the adjusting of the opening degree of the induced draft fan.                
5 Except for the automatic protection or interlock protection device of normal pulverized coal boilerm the following requirements are added according to the characteristic of CFB boiler.
(1) Differential pressure of material layer ---- the pressure of air room which is below the air distributor and the top pressure of dense are should be connected into the differential pressure meter, and it could be regarded as a parameter of the combustion controlling and the slag discharging.
(2) Differential pressure of the suspension section ---- The top pressure of dense area and the furnace outlet pressure should be connected into the differential pressure meter, and it could be regarded as a parameter of the controlling of boiler recycle material.
(3) The thermocouple with the anti-wear sleeve should be installed in the dense area to monitor the temperature, the exposed length of the thermocouple is 100~150mm, and the temperature is shown with numbers in the controlling room.