Coal fired boiler – Guideline for energy efficient operation:

Coal fired boilers are major energy consuming equipment’s for process industry and care to be taken to improve performance of coal fired boiler. Boiler performance depends on various operation parameters and external factors.

Representative picture of coal fired boiler

Listing various ways for energy efficient operation of coal fired boiler :-

  • Coal quality : Properties of coal keeps on varying from place to place. Although various grades has been established for coal costing. Still with combination of various parameter like Gross calorifc value, ash quantity, volatile matter, moisture, carbon contain, hydrogen contain etc. Properties and suitability of coal to boiler differs. which needs to be considered while boiler procurement and operation. Hydrogen contain in fuel will take away major energy produced, hence hydrogen contain in the fuel must be low. Moisture is also another area of loosing heat and it should be minimum. External moisture ingress to be curtailed off for better coal quality.
  • Flue gas temperature: Flue gas temperature to chimney must be as low as possible. Lower temperature in flue gas indicated higher energy conversion in boiler. acid dew point must be considered while lowering temperature. Flue gas heat may be utilized in preheating boiler feed water or combustion air.
  • Excess Air in flue gas: Oxygen in flue gas indicates excess air supplied for combustion. Theoretically we should supply oxygen only required for combustion but practically it is not possible therefore oxygen supplied is higher than combustion requirement. Higher oxygen level means excess air, Excess air in flue gas takes away heat along with flue gases.
  • Improper air supply: Carbon monoxide generation in flue gas indicated improper combustion of fuel and it must be avoided. Fuel used in the boiler should be combusted completely to get complete heat of fuel. Due to low oxygen supply or uneven oxygen supply there may be changes of incomplete combustion of fuel. Incomplete combustion will reduce boiler efficiency drastically, it must be checked regularly and controlled by proper combustion system.
  • Unburnt carbon : unburnt carbon in ash indicates improper combustion of fuel, unburnt carbon to be minimized to gain on efficiency part. Regular monitoring of carbon contain in fly ash, bottom and coarse ash help in identifying unburnt carbon problem in boiler.
  • Insulation of boiler : As heat is exchanged in the boiler at high temperature above 800 Deg C, surface of boiler is the area from which heat may escape to the surrounding environment. Insulation and refractory in the boiler should be maintained properly to reduce heat loss to boiler.
  • Boiler water quality: Boiler water quality if very important for safe and troublefree operation of boiler. Lower TDS feed water reduces boiler blowdown and can save energy venting though boiler blowdown. Also flash heat recovery from boiler can be planned for reducing heat loss to atmosphere.
  • Variable frequency drives: Most of the boiler are designed for peak load requirement but average loading of boiler is normally low, Variable frequency drives helps in reducing power consumption in low load condition.
  • Soot generation and cleaning: Soot generation is common problem in boiler and it reduces heat transfer coefficient of heat exchanges like Economizer & APH. Soot must be cleaned as it starts depositing on the boiler. To avoid this problem flue gas path are normally designed vertical. If vertical design of heat exchanges is not possible or there is soot deposition on the heat exchanger surface. Soot blowers can be used to remove it, Various soot blowers are available in the market based on the requirement compressed air soot blower, steam soot blower or ultrasonic soot blowers can be used.
  • Boiler Automation : As coal is obtained from mother nature. Properties of coal varies from place to place, therefore automation plays higher role in boiler to adopt to the change and maintaining boiler on best efficiency parameters.
  • Boiler Loading: Lower loading of boiler reduces boiler efficiency, considering loading of boiler at design stage multiple furnace or bed design may be selected or designed.

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