Efficiency is the most important requirement for any and every process industry. Efficiency ensures that the process plants are operating smoothly and effectively. However, there are numerous factors to ensure that the efficiency of the steam boilers is attained as warranted by the boiler manufacturers. It is well-known that investing in the steam boiler is merely a fraction of the total cost covered by the process industry. In fact, the primary cost incurred by the industries is that of fuels. In most cases, boiler efficiency is lesser than the rated efficiency from the boiler manufacturers. Various components are responsible for contributing to the overall efficiency of the boilers. Two main factors that affect boiler efficiency are Combustion efficiency and Thermal efficiency.
Types of Fuels Used in Steam Boilers:
Different process plants use different fuels depending on their availability, requirements, and costs. Fuels are mainly classified as solids, liquids, and gaseous forms that have unique chemical properties that may function only with a certain type of steam boiler. Some of the different types of fuels are:
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Solid:
- Coal
- Wood
- Briquettes
- Wood Chips
- Wood Logs
- Bailed Bagasse
- Sawdust
- Rice Husk
- Coffee Husk
- Palm Shell
- Groundnut Shell
- Coconut Shell and many more
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Liquid:
- Light Diesel Oil
- High-Speed Diesel
- Furnace Oil
- Low Sulfur Heavy Stock
- Industrial Diesel Oil
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Gaseous:
- Natural Gas
- Liquefied Petroleum Gas
- Biogas
What is Combustion in Steam Boilers?
Combustion is a chemical process wherein the oxygen from the air is reacted with fuel at high temperature to release the stored energy, better known as thermal energy in the form of flue gases at high temperature. Fuels and fuel quality do indeed play an imperative role in combustion. Fuel combustion in the oxidizing atmosphere takes place when the fuel reaches a certain temperature called ‘flash point’ in the case of liquid fuels and ‘fire point’ in the case of solid fuels.
In combustion, partial energy released by the fuel is utilized in converting the moisture content in fuel into water vapor. Therefore, it can be concluded that the process of combustion also generates water vapor. However, in most cases, the water vapor produced is not used for any applications that lead to the wastage of heat energy contained in it. As the moisture or water content of the fuel increases, a larger part of the energy released by fuel is utilized in converting the moisture into vapor. Consequently, it will reduce the overall energy transferred to the boiler drum for the purpose of steam generation.
Therefore, it is important to pay due attention to the quality of fuels while buying them. Secondly, it is essential to be careful in fuel handling and storage, and must not be stored in open spaces where the chances of getting wet from rain are high.
Optimal fuel consumption is ensured with complete and proper combustion with minimal heat loss. To determine the quality of combustion in a steam boiler, one can check the color of smoke. Emission of white smoke indicates high air to fuel ratio that means that although the combustion was complete, a high amount of air carried excess heat energy. On the other hand, black smoke indicates a low air-to-fuel ratio with oxygen deficiency which means incomplete combustion and high unburnt losses. Grey smoke is an indication for optimum air to fuel combustion with optimal fuel combustion and minimum loss.
Correlation between Fuels and Efficiency in Boilers:
Solid fuels have a tendency of fouling that foul the tubes in the course of time with the flue gases generated. It results in a reduction in heat transfer area and an increase in fuel consumption. It is noteworthy that any changes in the fuel quality would, directly and indirectly, affect the boiler efficiency. Although, boiler manufacturers suggest aiming to bridge the gap between direct and indirect boiler efficiency.
Fuel to steam efficiency is an essential measure for boiler efficiency, but calculating it in an actual situation is difficult. It can be considered as the amount of energy converted into steam. Fuel to steam efficiency depends on conditions such as complete load and specified air and feedwater temperature.
Factors Affecting Fuel Quality:
Fuel specification has a tremendous effect on efficiency. With gaseous fuels, high hydrogen content contributes to increased water vapor in combustion in which the water vapor utilizes energy to change its phase. A high water vapor loss while igniting the fuel leads to lower efficiency.
Accelerated TDS level in feedwater tanks results in water carryover that leads to increased fuel consumption. In a steam generation, dissolved solids become more concentrated, which results in failure in the bursting of steam bubbles formed to reach the water surface, forming foam carried over to steam mains. It eventually results in wastage of fuel because of increased moisture content in steam.
Conclusion:
Since its establishment in 1983, Rakhoh Boilers have strived to deliver world-class quality products to their clients by manufacturing efficient and reliable industrial steam boilers that ensure enhanced productivity and sustainability. Rakhoh manufactures numerous products of ranging product capacity and pressure range for effective combustion with various fuels.