Boiler Boiler control and control and operationoperation

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Boiler control and operation

Control techniques are capable of reducing operating costs while providing greater flexibility in plant management and control

Overview

Boiler control and operation

Air Flow Control/Oxygen Trim *Air Flow Control/Oxygen Trim * Steam - Pressure *Steam - Pressure * Steam - Temperature *Steam - Temperature * Feed Water and Drum Level *Feed Water and Drum Level * Fuel Oil Flow ControlFuel Oil Flow Control Fuel Gas Flow ControlFuel Gas Flow Control

CombustionCombustion controlcontrol

Tools for burner combustion Tools for burner combustion

control generally include regulation control generally include regulation of excess air, oxygen trim, burner of excess air, oxygen trim, burner modulation, air/fuel cross-limiting modulation, air/fuel cross-limiting and total heal control. The better and total heal control. The better burner control systems include all of burner control systems include all of these elements. these elements.

Air Flow Control/Oxygen Air Flow Control/Oxygen TrimTrim

Excess-air regulationExcess-air regulation Oxygen trimOxygen trim Optimize excess airOptimize excess air Burner modulationBurner modulation Air/fuel cross-limitingAir/fuel cross-limiting

CombustionCombustion controlcontrol

Figure 1: Excess air must be kept within a suitable range to ensure complete combustion and reduce heat loss.

CombustionCombustion controlcontrol

Figure 2: A cross-limiting combustion circuit allows firing multiple fuels simultaneously without risking excess fuel.

Steam – PressureSteam – Pressure ControlControl sometimes called “boiler master”sometimes called “boiler master” Maintain steam pressureMaintain steam pressure By adjusting fuel and combustion air By adjusting fuel and combustion air

flowsflows When the pressure drops, the flows When the pressure drops, the flows

are increased.are increased. Steam pressure sensor acts directly on Steam pressure sensor acts directly on

fuel and air flow controls.fuel and air flow controls. Final control devicesFinal control devices

Fuel: pulverizerFuel: pulverizer Air: forced draft fanAir: forced draft fan

Steam – PressureSteam – Pressure ControlControl

Steam – TemperatureSteam – Temperature ControlControl

Factors affecting the steam temperatureFactors affecting the steam temperature Boiler loadBoiler load Excess airExcess air Feedwater temperatureFeedwater temperature Cleanliness of heating surfaceCleanliness of heating surface

Steam temperature controlSteam temperature control Gas bypassGas bypass Buner controlBuner control AttemperationAttemperation Gas recirculationGas recirculation Excess airExcess air Divided furnaceDivided furnace

Too low a level may expose boiler Too low a level may expose boiler tubes, which overheats and tubes, which overheats and damages themdamages them

Too high a level may interfere Too high a level may interfere with separating moisture from with separating moisture from steamsteam

The optimum ,half of sight glass The optimum ,half of sight glass outside the drumoutside the drum

Feed Water and Drum Feed Water and Drum LevelLevel

Boiler drum-level controlBoiler drum-level control

drum-level control single-drum-level control single-elementelement

drum-level control two-element drum-level control two-element drum-level control three-drum-level control three-

elementelement

drum-level control drum-level control single-elementsingle-element

Figure : Figure : Drum-level control with a single-Drum-level control with a single-element module.element module.

drum-level control two-drum-level control two-elementelement

Figure : Figure : Drum-level control with a two-Drum-level control with a two-element moduleelement module

drum-level control three-drum-level control three-elementelement

Figure : Figure : Drum-level control with a three-Drum-level control with a three-element module.element module.

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