Starting up a thermal power plant is an incredible experience, one that every power engineer looks forward to. The process of breathing life into a massive mechanical giant that produces several megawatts of power that powers millions of households. The boiler light up process is an engineering marvel that demands skills, precision, and deep understanding of how all of the parts of the plant works together. A smooth and efficient light-up process not only ensures safe operation of the boiler, but also sets the tone for the entire power generation process. And if not done properly, it can lead to issues ranging from incomplete combustion to some serious equipment damage.
For power plant engineers and operators, mastering the boiler light-up process is a mark of experience and expertise. It’s a test of their ability to control and balance numerous parameters, such as various pressures & temperatures. The entire process is a blend of science and art, where precision timing and careful monitoring make all the difference.
In this article, we’ll take a closer look at some of the important pre-operational checks required to be performed prior to boiler light-up process.
General Checks Required for Boiler Light-Up
Following are some of the various checks needed to be performed before initiating the light-up process.
- Electrical Supply System Charged: During non-operational phase, thermal power plant relies on electrical supply from the grid to operate its electrical equipment and auxiliaries. It is required to check and maintain the healthiness of electrical supply and ensure all unit bus are charged.
- Fuel Oil System Readiness: Fuel oil such as Heavy Fuel Oil (HFO) and Light Diesel Oil (LDO) is used in boiler for combustion before the coal is introduced. It is required to check the availability of sufficient fuel oil and ensuring that the line of the fuel oil is charged up to the oil station of the boiler burners.
- Instrument And Service Air: Compressed Instrument air is used to operate various pneumatic devices & control valves, and compressed service air is used for various operations like line scavenging, cleaning, ash transportation, purging filters, etc. It is required to check the availability of continuous supply of compressed air from Compressor House.
- DMCW & ACW System: Demineralized Cooling Water (DMCW) is used for cooling purpose in various auxiliaries. It is a Close Cycle Cooling System which circulates in a closed loop. It is divided into two parts, Steam Generator (SG) side and Turbine Generator (TG) side. Ensuring healthiness of SGDMCW & TGDMCW pumps and maintaining storage tank level is necessary to avoid tripping of any auxiliary due to insufficient cooling. The Auxiliary Cooling Water, unlike DMCW, is an Open Cycle Cooling System. The Auxiliary Cooling Water is used in various heat exchangers like PHE for cooling down the DMCW. After absorbing the heat in PHE, ACW is dumped into cooling tower for cooling. Maintaining sufficient ACW flow is necessary in order to operate DMCW system.
- Auxiliary PRDS Charging: Auxiliary Pressure Reducing and De-Superheating (APRDS) system is used to provide steam for turbine auxiliaries, boiler auxiliaries, Heating and Atomizing of Heavy Fuel Oil (HFO), during startup and low loads condition.
- Furnace Readiness: Ensuring no foreign material exists in the boiler furnace, all manholes and inspection doors of the boiler should be closed tightly. All wall blowers and Long Retractable Soot Blowers (LRSB) should be in home position.
- Ash Handling System & ESP: Bottom ash hopper (BAH) should be available in service. HP & LP Water Pumps for De-ashing & Slurry pumps for transferring ash slurry should be ready. Electro-Static Precipitator (ESP) should be ready with all inspection doors closed & all flue gas dampers open.
- System Readiness: Make sure all permits issued are cancelled prior to light-up and all maintenance work should be completed. Trial of all auxiliaries should be taken before light-up. All instruments and control system should be in DCS mode. Boiler protection test should be carried out.
Upon performing all of the necessary checks, the boiler light-up process can be initiated. Making sure that the required operation and maintenance staff is available round the clock during light-up process.
Cold Start-Up Checklist
Cold starting is a condition meaning that starting off the boiler in the state of comparatively lower pressure and temperatures. In simple words, cold starting is the procedure to start off the boiler for the first time, or after a relatively long shutdown. Cold startup is a very critical operation because variation in the pressure and temperature may cause thermal stress resulting in cracks and damages of the boiler tubes.
Following are some checks to be performed before initiating cold startup:
- The differential temperature between Feed water and Boiler Metal must not exceed specified maximum value. If the difference is high, minimum fill rate should be used.
- The unit has been chemically cleaned, Re-Heater and Superheater lines have been steam blown, and all the safety valves have been set.
- All instrumentation and associated mechanical equipment has been checked out and is available for service.
- All Control systems have been checked and are available for service.
- All Safety Interlock systems must be checked prior to Startup to ensure proper functioning.
- Exercise the systems by creating the actual interlock actuating conditions.
- Simulate the activating condition if the actual condition cannot be created.
- The Auxiliary Fuel firing equipment has been checked out to ensure it is properly functioning. Recheck the following items to make sure that:
- Auxiliary Fuel available at required pressure.
- All quick disconnect couplings properly assembled.
- All Manual Valves are open.
- All Control Valves are closed.
- The Pulverizers and Feeders have been checked out and are available for service. Recheck the following items to ensure that:
- All Pulverizer Discharge Gates are open.
- All Hot Air Gates are closed and all Hot Air Control Dampers are closed.
- All Cold Air Gates are closed and the Cold Air Control Dampers are open no more than 5%. If the PA Fans have been off for more than 5 minutes, the Cold Air Dampers are driven to a 100% Air flow position.
- All Bunker Outlet Valves are open and Coal is available to the Feeders.
- All Pulverizer & Feeder Seal Air Valves are open.
- The Pulverizer Lube Oil systems are available for service.
- The Windboxes have been checked for proper Damper positioning and the tilts are set at horizontal.
- The Feedwater system and at least one Boiler Feed Pump (BFP), including the instrumentation & equipment, has been checked out and is available for operation. During a Startup, the Feedwater flow should be controlled in automatic mode for best results.
- The Deaerator Auxiliary Steam supply is operational and deaerated feedwater at desired temperature is available. To avoid oxygen corrosion in the Boiler, the use of deaerated feedwater with a temperature of greater than 102 °C (215 °F) is recommended.
- The Boiler Recirculation Pump (BRP) has been checked out, the Suction & Discharge Isolation Valves are open, and all Pump instrumentation is available for service. The Pump differential pressure monitoring must be in service. Ensure that the proper trip settings have been made.
- The Startup system’s Drain Transfer system is ready for operation. This system includes the Flash Tank, Receiving Tank, and Drain Transfer Pumps.
- Auxiliary Steam is available from another operating Boiler or common system for supplying the Deaerator and Feed water tank.
- Cooling Water system is in operation.
- All air & gas handling equipment are checked and is available for service.
- The Scanner / Ignitor Air Fans are ready for operation.
- Furnace Draft must be maintained within safe limits at all times. Extreme care should be taken when Draft and Air flow controls are in the manual mode.
- The APHs have been prepared for service and adequate means of extinguishing an APH fire is available and ready for use.
- The Soot blowing equipment are checked for proper operation and the system is in the Startup mode with all Soot blowers retracted and the main Supply Valve closed.
- The HP / LP Bypass stations are available for service, and hydraulic stations are in operation. The Water supply for De-Superheating has been established with any Isolation Valves open.
- The Condenser is available for service, with circulation Water flow, and vacuum has been established to accept Water flow from the Drain Transfer Pumps and LP Bypass.
- The Condensate Polishing Unit (CPU) is available for operation.
- The Turbine Generator has been prepared and is available for service.
- The SSC / Bottom Ash Hopper is filled with water to operating level and the seal trough is full to operating level to provide a furnace seal.