Improvement in Plant Availability, Load Factor, and Efficiency
In any power plant our aim is to have 100% availability of the plant but practically it is not possible since all equipment needs periodical maintenance.
- In any power plant our aim is to have 100% availability of the plant but practically it is not possible since all equipment needs periodical maintenance which is to be planned properly which is known as a planned maintenance. Sometimes equipment fails/trips due to some unplanned reason and causes plant outage. This outage is called a forced outage.
- The planned outage is taken as per the recommendation of OEM (Original equipment manufacturer) to carry out maintenance to achieve reliable operation of the unit.
- This planned outage period is decided so we know the reduction in % availability of the unit.
- A forced outage is due to failure of some equipment or tripping of some equipment on protection. This is a matter of concern since it affects the availability of the unit and in turn reduction in power generation and hence plant load factor and increased oil consumption due to re-startup and thereby the increased cost of generation.
- Boiler tube leakage is the major reason for the forced outage in a coal-fired power plant.
Boiler tube leakage occurs due to following reasons:
- Fireside erosion
- Waterside corrosion
- Overheating of tubes
- Creep life exhaustion
- Hydrogen embrittlement
- Thermal shocks
- Improper operation practices
- Poor maintenance
- Welding defects
- Erosion by ash and erosion by secondary air leakages are a significant cause of boiler tube failure.
To minimize the boiler tube leakage following measures may be adopted:
- During annual overhaul thorough visual inspection of boiler heating surfaces is be done also tube thickness survey and thickness mapping is to be done to identify eroded tubes and if the thickness is reduced more than 25% of a normal thickness such tubes are to be replaced.
- In highly erosion-prone areas in the second pass to reduce erosion, shielding of tubes/bends is to be done.
- Welding in the boiler is to be done only with welding electrodes recommended by OEM and welding is to be carried out only by IBR certified welders and 100% welding joints are to be inspected and radiography to be done.
- Alignment of all the coil assemblies and tubes to be checked and correction to be done
- A thorough inspection of refractory and corrections where ever necessary to be done
- Root cause analysis of failed tube from experts and metallurgical lab to be done
- Chemical cleaning of the boiler to be done
- There is a significant scope for improving Plant load factor. Key technical problem areas are as follows:
- The poor condition of boiler pressure parts due to high erosion, overheating, oxide deposits, weak headers, pressurized furnace
- Poor water chemistry affects the condition of boiler and turbine
- The poor performance of air heaters due to blocked elements and high seal leakage
- The poor performance of coal mills resulting in too high unburnt carbon
- The poor performance of E.S.P. resulting in the high emission
- Problems of the high axial shift, vibrations, differential expansion in the turbine
- The low vacuum condenser due to dirty/plugged tubes, air ingress, and tube leakage
- Passing of BFP/CEP recirculation valve resulting in low discharge
- High-pressure heaters not in service directly impacting energy efficiency
- Deficiencies in electrical systems including HT/LT motor failure
- The poor condition of D.C. system
- The poor condition of balance of plant resulting into underutilization of unit capacity
Major reasons for high station operating heat rate are as follows:
- Low combustion efficiency lead to high carbon loss
- Failure of boiler tube leading to the forced outage and thereby more startup
- The poor performance of milling system due to lack of maintenance planning and spares planning
- High dry gas losses due to high unwanted excess air
- Poor sealing and heat transfer in air heaters
- High air ingress in the boiler and high heat loss due to poor insulation
- The poor performance of ESP causes failure of ID fan and low availability
- Nonavailability of quality and quantity of coal
- High auxiliary power consumption due to high heart rate and outages
- High boiler erosion and corrosion lead to high force outage
- Air-fuel velocity is not same for all coal burners which causes unbalanced flame and change the temperature profile
- Inefficient soot blowing leads to lower heat transfer to boiler tubes and wastage of thermal energy by way of higher flue gas exit temperature affecting boiler efficiency adversely
- Inefficient air heaters due to worn out/chocked heating element, improper seal clearances, damaged sector plates, side sealing plates, air ingress due to damaged expansion bellow, improper sealing of inspection holes, leads to low-temperature inlet hot air to coal mills and affect the coal drying and in turn reduces mill capacity. This also leads to higher aux. the power consumption of ID, FD, PA fan due to the handling of a high quantity of unutilized air.
- High superheater/reheater spray reduces boiler efficiency since it is designed for almost zero sprays at full load with design coal
- Low turbine efficiency due to high seal clearances and salt deposit due to poor water chemistry
- Low condenser vacuum due to air ingress, cooling water temperature, quantity, and quality, the Poor performance of cooling water pumps, chocking of condenser tubes
- High cooling water temperature due to the poor performance of the cooling tower
- Passing of BFP/ CEP recirculation valves limits flow and increases aux. power consumption
- Low superheat and reheat temperature
- HP/LP Heaters out of service
- Partial load operation
- Tripping/Forced outage
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