Boiler Control Systems Overview

Typical Sequence of Operation

• The first step involves checking all permissives and pre-ignition interlocks for safety before proceeding.
• If all checks are satisfactory, the burner management system (BMS) initiates the start of the main burner system.

Ignition and Flame Establishment

• The BMS starts the igniter and opens the pilot shut-off valve (SSOV) when all conditions for ignition are met.
• The pilot trial for ignition period is necessary to verify that a stable pilot flame is established before proceeding to the main flame.
• High airflow detection by the BMS occurs during the pre-ignition phase.
• The purge counter is initiated when there’s a need to clear the combustion chamber of unburned gas.

Shutdown Procedures

• The burner system shutdown sequence is triggered by failure to establish a flame or by exceeding safety limits.
• An action such as a failed flame detection or safety limit violation extinguishes the flame in the burner system.
• The post-purge ensures that residual gases are cleared from the system after shutdown for safety.

Operating Modes

• In standby mode, the programming controller continuously monitors system conditions and remains ready for ignition.
• The startup sequence can be repeated only if all safety conditions and pre-ignition checks are satisfied.

BMS Operations

• When the BMS shuts the pilot SSOV, it locks out the burner system to prevent unsafe operation.
• If the main flame is not established within 10 seconds, the BMS goes into safety shutdown and lockout.
• During the pilot trial for ignition period, if the pilot flame is not proven within 10 seconds, the BMS will execute a shutdown.

Timing and Conditions

• The main SSOV closes during the main flame trial for ignition period if the flame is not detected.
• If a burner safety limit opens during operation, the BMS will initiate a safety shutdown.
• The programming controller begins the safe start check during the startup sequence to ensure all systems are operational.

Lights and Indicators

• The controller returns to standby mode once ignition trials are satisfactorily completed, or safety conditions fail.
• Poor voltage conditions lasting over 4 minutes will prevent energizing the burner and could lead to a system lockout.
• During a safety shutdown and lockout, the programming controller displays an indicator to alert operators.

Boiler Operation Conditions

• A safety shutdown and lockout does not occur during the pilot trial for ignition if the main SSOV is energized with no flame present.
• Fire-tube boilers typically do not require controllers that start draft fans or prove purge conditions.
• The BMS detects internal faults at any operational stage and will perform necessary safety actions.

Common Actions and Conditions

• 'Call for heat' in natural draft gas-fired boilers triggers the ignition sequence.
• The uptake damper is primarily opened by the combustion air blower.
• Gas-fired boilers require adequate fuel and air supply for combustion initiation.
• The boiler ignition sequence begins with the command from the programming controller.

Specific Boiler Considerations

• After confirming the low-fire position, the programming controller prepares for fuel delivery.
• Oil-fired boilers necessitate pre-start checks for fuel viscosity and heater functionality.
• The main SSOV is energized once the air-fuel mixture is confirmed safe and ready for ignition.

Fuel Considerations

• If the boiler uses oil requiring preheating, the preheat condition must be ensured before ignition.
• Dual fuel boilers do not require specific actions to ensure functionality besides basic startup checks.
• The primary function of the pilot SSOV is to control the flow of fuel to the pilot burner.

Safety Measures

• If the pilot fails to ignite within 15 to 90 seconds, the primary controller will execute a safety shutdown.
• Main flame loss during the run period triggers an immediate system shutdown for safety.
• In oil-fired boilers without a pilot, the call for heat is managed directly by the control system.
• An ignition failure during startup results in a halt of operations, followed by troubleshooting protocols.

Starting Conditions

• Before initiating a steam or hot water boiler, all safety limits and operational conditions must be verified.
• A typical programming control in fully automatic boiler systems coordinates start-up, operation, and safety functions.
• More than two main flame failures in a single call for heat cycle may require a 5-minute natural draft purge to ensure safety before restart.

This quiz provides an overview of boiler control systems, focusing on the role of the pilot SSOV, primary control, operating control, and programming control in maintaining the desired steam pressure or water temperature. It also covers the restart process in case of pressure or temperature drops.