Steam Generator (Boiler) Part-3 boiler efficiency.ppsx
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The document discusses the efficiency of steam generators, focusing on various aspects such as heat loss, combustion air control, and factors affecting boiler efficiency like feed water temperature and condensate recovery. It highlights the significance of maintaining optimal operating conditions and practices to minimize energy losses and improve overall efficiency. Additionally, it provides methods for calculating boiler efficiency, emphasizing the importance of proper monitoring and maintenance to optimize performance.
![EFFICIENCY CALCULATION
The direct method for calculating boiler efficiency is a quick
way to determine a boiler's performance by comparing the
percentage of total heat output to heat input. The formula for
calculating boiler efficiency using the direct method is:
Boiler efficiency = (Energy output / Energy input) x 100
This formula can be broken down further to:
E = [Q (H-h) / q*GCV] x 100
Q = Quantity of steam generated (kg/hr)
H = Enthalpy of steam (Kcal/kg)
h = Enthalpy of water (kcal/kg)
GCV = Gross calorific value of the fuel
Mohammad
Shoeb
Siddiqui](https://image.slidesharecdn.com/steam-generator-boiler-part-3-250104131633-d36d154c/85/Steam-Generator-Boiler-Part-3-boiler-efficiency-ppsx-32-320.jpg)
Steam Generator (Boiler) Part-3 boiler efficiency.ppsx
- 1. Steam Generator (Boiler) Part 3 Mohammad Shoeb Siddiqui
- 2. IMPROVEING EFFECIENCIES OF STEAM GENERATION SYSTEM ENERGY CONSERVATION USE OF ECONOMISER USE OF WASTE HEAT Mohammad Shoeb Siddiqui
- 3. ENERGY LOSSES HEAT CARRIED OUT WITH STACK FLUE GASES HEAT CARRIED OUT WITH STACK IN THE FORM OF WATER VAPOUR UNBURNED FUEL, INCOMPLETE COMBUSTION HEAT LOSSES FROM BOILER HEAT WASTE THROUGH BLOW DOWN Mohammad Shoeb Siddiqui
- 4. Heat losses Having discussed combustion in the boiler furnace, and particularly the importance of correct air ratios as they relate to complete and efficient combustion, it remains to review other potential sources of heat loss and inefficiency. Heat losses in the flue gases This is probably the biggest single source of heat loss The losses are attributable to the temperature of the gases leaving the furnace. Clearly, the hotter the gases in the stack, the less efficient the boiler. Mohammad Shoeb Siddiqui
- 5. Heat losses The gases may be too hot for one of two reasons: The burner is producing more heat than is required for a specific load on the boiler: This means that the burner(s) and damper mechanisms require maintenance and re-calibration. The heat transfer surfaces within the boiler are not functioning correctly, and the heat is not being transferred to the water: This means that the heat transfer surfaces are contaminated, and require cleaning. Mohammad Shoeb Siddiqui
- 6. Heat losses Some care is needed here - Too much cooling of the flue gases may result in temperatures falling below the ‘dew point’ and the potential for corrosion is increased by the formation of: 1. Nitric acid (from the nitrogen in the air used for combustion). 2. Sulphuric acid (if the fuel has a sulphur content). 3. Water. Mohammad Shoeb Siddiqui
- 7. Radiation losses Because the boiler is hotter than its environment, some heat will be transferred to the surroundings. Damaged or poorly installed insulation will greatly increase the potential heat losses. A reasonably well-insulated shell or water-tube boiler of 5 MW or more will lose between 0.3 and 0.5% of its energy to the surroundings. This may not appear to be a large amount, but it must be remembered that this is 0.3 to 0.5% of the boiler’s full- load rating, and this loss will remain constant, even if the boiler is not exporting steam to the plant, and is simply on stand-by. Mohammad Shoeb Siddiqui
- 8. Boiler Net Efficiency % Mohammad Shoeb Siddiqui
- 9. FACTORS AFFECTING BOILER EFFICIENCY EXCESS AIR RATE BURNERS FIRING RATE FLUE GAS TEMPERATURE FEED WATER TEMPERATURE CONDENSATE RECOVERY COMBUSTION AIR TEMPERATURE FOULING OF HEAT TRANSFER SURFACE BLOW DOWN Mohammad Shoeb Siddiqui
- 10. Combustion Air Control Excess or Less Air Accurate control of the amount of air is essential to boiler efficiency: Too much air will cool the furnace, and carry away useful heat. Too little air and combustion will be incomplete, unburned fuel will be carried over and smoke may be produced. In practice, however, there are a number of difficulties in achieving perfect (stoichiometric) combustion: The conditions around the burner will not be perfect, and it is impossible to ensure the complete matching of carbon, hydrogen, and oxygen molecules. Some of the oxygen molecules will combine with nitrogen molecules to form nitrogen oxides (NOx). Mohammad Shoeb Siddiqui
- 11. To ensure complete combustion, an amount of ‘excess air’ needs to be provided. This has an effect on boiler efficiency. The control of the air/fuel mixture ratio on many existing smaller boiler plants is ‘open loop’. That is, the burner will have a series of cams and levers that have been calibrated to provide specific amounts of air for a particular rate of firing. Clearly, being mechanical items, these will wear and sometimes require calibration. They must, therefore, be regularly serviced and calibrated. On larger plants, ‘closed loop’ systems may be fitted which use oxygen sensors in the flue to control combustion air dampers. Air leaks in the boiler combustion chamber will have an adverse effect on the accurate control of combustion. Mohammad Shoeb Siddiqui
- 12. Burner The ability to burn fuel oil efficiently requires a high fuel surface area-to-volume ratio. Experience has shown that oil particles in the range 20 and 40 μm are the most successful. Particles which are: Bigger than 40 μm tend to be carried through the flame without completing the combustion process. Smaller than 20 μm may travel so fast that they are carried through the flame without burning at all. Mohammad Shoeb Siddiqui
- 13. Burner An important function of burners is turndown. This is usually expressed as a ratio and is based on the maximum firing rate divided by the minimum controllable firing rate. The turndown rate is not simply a matter of forcing differing amounts of fuel into a boiler, it is increasingly important from an economic and legislative perspective that the burner provides efficient and proper combustion, and satisfies increasingly stringent emission regulations over its entire operating range. Mohammad Shoeb Siddiqui
- 14. Flue gas control "Flue gas control" in a boiler refers to the process of monitoring and adjusting the composition and temperature of the exhaust gases (flue gas) leaving the boiler to optimize combustion efficiency, minimize emissions, and ensure safe operation, typically achieved by regulating the amount of combustion air supplied to the burner based on real- time flue gas analysis data Flue gas analysis: Regularly measuring the composition of the flue gas, including carbon dioxide (CO2), oxygen (O2), carbon monoxide (CO), and nitrogen oxides (NOx), to determine the combustion efficiency and identify potential issues. Mohammad Shoeb Siddiqui
- 15. Flue gas control Excess air control: Adjusting the amount of combustion air supplied to the burner to maintain an optimal level of excess air, which is necessary for complete combustion but should be minimized to maximize efficiency. Flue gas temperature control: Monitoring and regulating the temperature of the flue gas to ensure proper heat transfer and avoid excessive heat loss. Improved boiler efficiency: By maintaining optimal combustion conditions, flue gas control can significantly increase the boiler's thermal efficiency and reduce fuel consumption. Mohammad Shoeb Siddiqui
- 16. Feed Water Temperature A steam boiler plant must operate safely, with maximum combustion and heat transfer efficiency. To help achieve this and a long, low- maintenance life, the boiler water can be chemically treated. A higher feed water temperature directly improves boiler efficiency by reducing the amount of heat needed to convert water into steam, resulting in less fuel consumption and better overall thermal performance; essentially, the boiler doesn't have to work as hard to heat the water to the desired temperature when the feed water is already hot. Mohammad Shoeb Siddiqui
- 17. Feed Water Temperature Freedom from scale - If hardness is present in the feedwater and not controlled chemically, then scaling of the heat transfer surfaces will occur, reducing heat transfer and efficiency - making frequent cleaning of the boiler necessary. In extreme cases, local hot spots can occur, leading to mechanical damage or even tube failure. Freedom from corrosion and chemical attack - If the water contains dissolved gases, particularly oxygen, corrosion of the boiler surfaces, piping and other equipment is likely to occur. As the feed water temperature increases, the boiler efficiency generally increases as well. Mohammad Shoeb Siddiqui
- 18. Feed Water Temperature Reduced fuel consumption: Higher feed water temperature means less heat is required from the fuel to reach the desired steam temperature, leading to lower fuel usage. Heat recovery systems: Utilizing heat recovery systems like economizers as well as feed water heaters to preheat the feed water is a common method to improve boiler efficiency by raising the feed water temperature. Mohammad Shoeb Siddiqui
- 19. CONDENSATE RECOVERY Condensate recovery significantly improves boiler efficiency by allowing the reuse of hot condensate as feed water, which means less energy is needed to heat the water to its boiling point, resulting in reduced fuel consumption and increased overall boiler efficiency; in some cases, this can lead to When condensate is recovered and returned to the boiler, it carries a significant amount of latent heat which can be reused to generate steam, reducing the need for additional heat input from fuel combustion. a 10-20% reduction in fuel requirements. Mohammad Shoeb Siddiqui
- 20. CONDENSATE RECOVERY Factors affecting condensate recovery efficiency: Condensate piping design: Proper piping layout and insulation are essential to minimize heat loss during condensate transport. Condensate collection system: Efficient collection of condensate from all steam using equipment is crucial. Condensate treatment: Treating condensate to remove impurities can improve boiler water quality and prevent issues. Mohammad Shoeb Siddiqui
- 21. Combustion Air Temperature A higher combustion air temperature directly increases boiler efficiency, as the preheated air contributes more heat to the combustion process, resulting in less heat loss through the flue gas and a higher overall efficiency; typically, a 40°F increase in combustion air temperature can lead to around a 1% improvement in boiler efficiency. An often-stated rule of thumb is that boiler efficiency can be increased by 1% for each 15% reduction in excess air or 40°F reduction in stack gas temperature. Boilers often operate at excess air levels higher than the optimum. Mohammad Shoeb Siddiqui
- 22. Combustion Air Temperature Key points about combustion air temperature and boiler efficiency: Heat transfer: When combustion air is preheated, it enters the furnace at a higher temperature, leading to more efficient heat transfer to the water within the boiler. Reduced flue gas temperature: By utilizing more of the heat from the combustion process, the flue gas leaving the boiler is cooler, minimizing heat loss up the chimney. Mohammad Shoeb Siddiqui
- 23. Combustion Air Temperature Excess air control: Proper air preheating can help optimize the air-to- fuel ratio, reducing the need for excessive excess air which can lower efficiency. How to preheat combustion air: Air preheaters: Most modern boilers use a dedicated heat exchanger to preheat the combustion air using the heat from the flue gas. 1. Steam Coil Air Pre Heater (SCAPH) 2. Regenerative Air Pre Heater Mohammad Shoeb Siddiqui
- 24. FOULING OF HEAT TRANSFER SURFACE Fouling of a heat transfer surface in a boiler significantly reduces its efficiency by increasing the thermal resistance, which hinders the transfer of heat from the combustion gases to the water, ultimately requiring more fuel to achieve the desired steam production; this results in higher energy consumption and increased operating costs. Key points about fouling and boiler efficiency: Reduced heat transfer coefficient: When a fouling layer builds up on the heat transfer surface, it acts as a thermal barrier, lowering the rate of heat transfer and decreasing the heat transfer coefficient. Mohammad Shoeb Siddiqui
- 25. Key points about fouling and boiler efficiency: Increased thermal resistance: The fouling layer adds additional resistance to heat flow, making it harder for heat to move from the hot gases to the water, impacting the overall heat transfer process. Higher fuel consumption: To compensate for the reduced heat transfer due to fouling, the boiler needs to burn more fuel to reach the desired steam temperature, leading to higher energy consumption. Local hot spots: Fouling can create uneven heat distribution on the heat transfer surface, leading to potential hot spots that can damage the boiler components. Mohammad Shoeb Siddiqui
- 26. Factors contributing to fouling in boilers: Water chemistry: High mineral content in boiler water can lead to scale formation on the heat transfer surfaces. Fuel impurities: Ash and other particulates from the fuel can deposit on the heat transfer surfaces. Operating conditions: High boiler water temperatures and slow flow rates can promote fouling. Mohammad Shoeb Siddiqui
- 27. How to mitigate fouling in boilers: Water treatment: Properly treating boiler water to remove minerals and control pH levels. Fuel quality control: Using fuel with low ash content. Optimized operating conditions: Maintaining proper flow rates and operating temperatures. Regular cleaning: Implementing scheduled cleaning procedures to remove fouling deposits. Mohammad Shoeb Siddiqui
- 28. BLOW DOWN A "blow down" operation on a boiler, while necessary to remove impurities and maintain proper water chemistry, can negatively impact boiler efficiency if done excessively, as it essentially wastes heated water and energy by removing a portion of the boiler water, which needs to be replaced with fresh, cold feed water; therefore, the optimal blowdown rate is crucial to balance cleanliness with energy conservation. Mohammad Shoeb Siddiqui
- 29. Key points about blowdown and boiler efficiency: Negative impact of excessive blowdown: Too much blowdown leads to significant energy loss due to the constant need to heat up fresh feedwater to replace the blown-down water, thereby reducing overall boiler efficiency. Importance of controlled blowdown: Maintaining a proper blowdown rate based on factors like water quality and boiler operation ensures that only the necessary amount of water is removed, minimizing energy loss while still preventing issues like scale formation and carryover. Impact on steam quality: Improper blowdown can also affect steam quality by allowing too many impurities to enter the steam system if not managed correctly. Mohammad Shoeb Siddiqui
- 30. How to optimize blowdown for efficiency: Monitor TDS levels: Regularly monitor the Total Dissolved Solids (TDS) levels in the boiler water to determine the appropriate blowdown frequency and rate. Use automatic blowdown systems: Automated blowdown systems can precisely control the blowdown rate, minimizing unnecessary water waste. Consider heat recovery options: In some cases, heat recovery systems can be installed to capture some of the energy from the blowdown water, further mitigating energy losses. Mohammad Shoeb Siddiqui
- 31. EFFICIENCY CALCULATION Boiler efficiency is the percentage of energy that goes into heating a home and isn't wasted. It depends on many factors, including combustion and thermal efficiencies, as well as radiation, convection, and blow down losses. There are two common methods for calculating boiler efficiency: Direct method This quick method calculates boiler efficiency by dividing the total energy output by the total energy input. Indirect method This method calculates boiler efficiency by finding and subtracting the sum of all the individual losses from 100% Mohammad Shoeb Siddiqui
- 32. EFFICIENCY CALCULATION The direct method for calculating boiler efficiency is a quick way to determine a boiler's performance by comparing the percentage of total heat output to heat input. The formula for calculating boiler efficiency using the direct method is: Boiler efficiency = (Energy output / Energy input) x 100 This formula can be broken down further to: E = [Q (H-h) / q*GCV] x 100 Q = Quantity of steam generated (kg/hr) H = Enthalpy of steam (Kcal/kg) h = Enthalpy of water (kcal/kg) GCV = Gross calorific value of the fuel Mohammad Shoeb Siddiqui
- 33. EFFICIENCY CALCULATIONS The direct method is also known as the "input-output method" because it only requires the useful output (steam) and the heat input (fuel) to calculate efficiency. Direct efficiency values are generally closer to reality than indirect efficiency values because they account for uncovered losses like radiation losses and on-off losses. However, direct efficiency calculations only provide information about the overall loss magnitude, not the magnitudes of individual losses. To check the efficiency rating of a new boiler (made since 2015), you can find the Energy-related Products (ErP) rating on the boiler or on the paperwork from installation. Mohammad Shoeb Siddiqui