Boiler Control

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Instrumentation and controls in a boiler plant encompass an enormous range of equipment from simple industrial plant to the complex in the large utility station.?

????????????? The boiler control system is the means by which the balance of energy & mass into and out of the boiler are achieved. Inputs are fuel, combustion air, atomizing air or steam &feed water. Of these, fuel is the major energy input. Combustion air is the major mass input, outputs are steam, flue gas, blowdown, radiation & soot blowing.

Control loops

Boiler control systems contain several variable with interaction occurring among the control loops for fuel, combustion air, & feedwater . The overall system generally can be treated as a ?series of basic control loops connected together. for safety purposes, fuel addition should be limited by the amount of combustion air and it may need minimum limiting for flame stability.

Combustion controls

????????????? Amounts of fuel? and air must be carefully regulated to keep excess air within close tolerances-especially over the loads. This is critical to efficient boiler operation no matter what the unit size, type of fuel fired or control system used.

Feedwater control

Industrial boilers are subject to wide load variations and ?require quick responding control to maintain constant drum level. Multiple element feed water control can help faster and more accurate ?control response.

BLOCK DIAGRAM DESCRIPTION

????????????? The block diagram of boiler control is shown in figure 1.the output from the boiler ie, the steam outputs and the level of water is given to transmitters. The output of transmitter is given to the controller which act as level indicator controller and flow indicator controller. If there is any error corresponding to desired set point, the signal from controller is given to the converter which will open or close the valve and the water will be drained out or filled? according to required steam.

????????????? The major loops in boiler control are

  1. Combustion control
  2. ?Feedwater control

COMBUSTION CONTROL

????????????? A combustion control system is broken down into (a) fuel control and (b) combustion air control subsystems. The interrelationship between these two subsystems necessitate the use of fuel air ration controls.

????????????? The primary boiler fuels are coal, oil and gas. The control of gas and oil fuels requires simplest controls- ie, a control valve in the fuel line.

????????????? The steam drum pressure is an indication of balance between the inflow and outflow of heat. Therefore by controlling the steam supply one can establish balance between the demand for steam (process load ) and supply of water.

 

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