Moisture content in steam increases with high TDS levels in the feedwater tank due to water carry over. Wet steam reduces the process efficiency thereby increasing fuel consumption.
As the pressure of steam reduces, turbulence at the water surface increases, thereby increasing the moisture carryover in the steam. To ensure high dryness fraction of steam, the boiler should be operated close to design pressure.
The quality of boiler feedwater is an important determinant of safe boiler operations and it should be monitored to maintain the quality within safe working limits.
A majority of the boiler related accidents occur because of water level falling below the low level. For safe boiler operations it should be ensured that the boiler low water level alarm is functional at all times.
About 80% of boiler failures can be attributed to the either low water condition or operator error. Low water level being more controllable of the two, for safe boiler operations it must be ensured that boiler is not operated at low water level.
Most of the boiler failures can be attributed to the either low water condition. For safe boiler operations both of these areas must be kept under check.
Large drop in the furnace draught pressure is a good indicator of clinker formation. Clinker formed inside the boiler reduces the heat transfer area for the flue gases and increases the electrical consumption of the ID & FD fans.
To ensure safe boiler operations, in between burner trips, complete air purge should be allowed to ensure fuel-rich atmosphere is not formed.
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To safeguard boilers against fuel explosion in the furnace, operators must ensure that especially during startup and shutdown a fuel rich environment is not created in the furnace.
Solid fired boilers should regularly be checked for clinker and the same should be removed. Clinker may reduce the boiler operating efficiencies.
For larger steam loads it is advisable to opt for a battery of boilers instead of one large boiler to ensure optimum fuel consumption.
Increasing the inlet air temperature by 30-40degC increased the boiler efficiency by about 0.6%
High negative draft in a solid fuel fired boiler carries away the unburnt fuel along with the flue gas. This leads to wastage of fuel.
Generating steam at higher pressure facilitates meeting peak steam demands on fluctuating loads.
The TDS inside a boiler should be maintained at recommended levels else it can lead to scaling of the boiler tubes and eventually failure of the tubes which is a safety hazard.
Dissolved oxygen eats into iron and corrodes it. Thus dissolved oxygen should be removed from the feedwater tank else it can lead to corrosion of the tank and of the boiler tubes leading to a safety hazard.
Shell type steam boilers offer better fuel efficiencies as compared to coil type boilers.
Co-generation plant operations should be decided only after comparing the running cost to cost of electricity.
Injection of flash steam and condensate into the feedwater tank should be via a deaerator head. A deaerator ensures mixing of make-up water, condensate and flash steam to deliver uniform temperatures.
Opting for shell type boilers over coil type boilers leads to availability of good quality steam and reduces the process steam requirements.
Air to fuel ratio should be monitored and controlled to minimize unburnts. Presence of 1% unburnts represents 2.5% excess fuel consumption.
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With coil type steam boiler, condensate cannot be recovered. Condensate contains 20% of the energy in steam.
Referencing the boiler efficiency to the GCV of the fuel rather than the NCV gives a more accurate picture and draws our attention to the enthalpy losses.
Higher moisture content in fuel leads to higher enthalpy loss. Efforts should be made to minimize addition of surface moisture content in fuel.
Maintaining the right level of water in the feedwater tank reduced the overall boiler feedwater TDS. This leads to reduced blowdown and the associated blowdown loss.
To deliver the same amount of energy, the flowrate of hot water will have to be 45 times than that of steam necessitating higher pumping costs. Use steam in place of hot water where ever possible.
A mere 20deg c deviation of flue gas temperatures from optimum value result in 1% excess fuel consumption – monitor flue gas temperatures to control stack loss.
Co-generation plant operations should be decided only after comparing the running cost to cost of electricity.
For the same rate of heat transfer, the surface area of heat exchanger required with thermic fluid greater that what is required with steam. With larger heating surfaces the radiation losses also proportionally increase.
Flue gas temperatures depend on steam temperature, excess air and heat transfer efficiency. Monitoring this parameter gives a good indication of the boiler operating conditions.
Boilers do not operate at rated efficiencies and the running efficiencies are found to be 3%-12% lesser than rated efficiencies. Boilers efficiency should be monitored.
In plants where multiple boilers are used to meet the steam demand, at part loads the most efficient boilers should be used.
Attention should be given to ingress of moisture during fuel handling and storage. Poor quality of fuel leads to poor boiler efficiency.
Radiation loss of a boiler enclosure is 1% at full load and 4% at quarter load. Operating boiler closer to full load improves efficiency.
The configuration of the co-generation system is important to ensure high efficiency and better return on investment.
The cost of generation of steam using solid fuel fired boilers today is greater than an oil fired boiler 10yrs ago. Energy conservation is the only avenue to reduce fuel bills.
Chemical treatment of make up water increases the TDS levels in the boiler, leading to increased blowdown. Returning condensate reduces the TDS levels and thus blowdown, leading to fuel savings.
Frequent changes to the boiler fuel firing system destabilize combustion, resulting in higher fuel consumption. This leads to poor boiler efficiencies and higher fuel bills.
Higher feedwater temperature increases the boiler output with reduced fuel consumption.
Saturated steam has a higher heat transfer coefficient than super heated steam. Thus use saturated steam for indirect heat transfer applications.
One kg of steam is equivalent to 27 Kg of thermic fluid to deliver the same heat content. For heating applications less than 200degc, steam is preferable to thermic fluid as heating media.
Maintaining high TDS levels in the boiler drum results in water carryover and foaming. This leads to wet steam and lower heat transfer efficiencies to the process.
Avoid over sizing the boiler. Over sizing leads to frequent on-off cycles in a boiler which lowers boiler efficiency.
Boiler operation parameters should be monitored continuously to correct operations. An S: F variation of even 0.25 translates into 1.85% excess fuel consumption.
As a rule of thumb, feedwater tank should be sized to be 1.5 times the peak steam demand.
Fuel waste due to boiler scale may be 2% for water-tube boilers and upto 5% in fire-tube boilers. Pretreatment of feedwater, adequate blowdown and boiler cleaning minimize scaling.
Dissolved oxygen eats into iron and corrodes it leading to steam leaks. High feedwater temperature drives out dissolved oxygen, thus preventing leaks and saving fuel.
Measuring specific fuel consumption gives a true reflection of your plant efficiencies. With steadily climbing fuel prices, monitoring plant efficiencies is integral to sustain energy savings.
Excess air in the boiler combustion leads to losses. Flue gas temperatures are a good indicator of excess air and should be monitored.
A correctly selected and sized steam trap reduces process time and simultaneously saves energy.
Condensate forms at steam temperatures. If it is returned to the feed water tank, every 6oC rise in temperature reduces the fuel bill by 1%.
Black or white smoke emitted from the boiler chimney indicates inadequate combustion leading to excess fuel consumption. Check boiler parameters and settings
During a cold start, the temperature of the boiler should be raised gradually. Improper warm-up of the boiler severely harms the boiler health.
Over heating the Furnace Oil Day tank can create a hazardous condition in the boiler house. Thus the temperature of this tank should be regulated.