Fuel-to-steam efficiency is a measure of the overall efficiency of the boiler. It accounts for the effectiveness of the heat exchanger as well as the radiation and convection losses. It is an indication of the true boiler efficiency and should be the efficiency used in economic evaluations. As prescribed by the ASME Power Test Code, PTC 4.1, the fuel-to-steam efficiency of a boiler can be determined by two methods: the InputOutput Method and the Heat Loss Method.
The term “boiler efficiency” is often substituted for thermal efficiency or fuel-to-steam efficiency. When the term “boiler efficiency” is used, it is important to know which type of efficiency is being represented. Why? Because thermal efficiency, which does not account for radiation and convection losses, is not an indication of the true boiler efficiency. Fuelto-steam efficiency, which does account for radiation and convection losses, is a true indication of overall boiler efficiency. The term “boiler efficiency” should be defined by the boiler manufacturer before it is used in any economic evaluation.
Combustion efficiency is an indication of the burner’s ability to burn fuel. The amount of unburned fuel and excess air in the exhaust are used to assess a burner’s combustion efficiency. Burners resulting in low levels of unburned fuel while operating at low excess air levels are considered efficient. Well designed conventional burners firing gaseous and liquid fuels operate at excess air levels of 15% and result in negligible unburned fuel. Well designed ultra low emissions burners operate at a higher excess air level of 25% in order to reduce emissions to very low levels. By operating at the minimum excess air requirement, less heat from the combustion process is being used to heat excess combustion air, which increases the energy available for the load. Combustion efficiency is not the same for all fuels and, generally, gaseous and liquid fuels burn more efficiently than solid fuels.
The number of passes that the flue gas travels before exiting the boiler has been a good criterion when comparing boilers. As the flue gas travels through the boiler it cools, and therefore changes volume. Multiple pass boilers increase efficiency because the passes are designed to maximize flue gas velocities as the flue gas cools. ZOZEN has developed new design technologies in our WNS series boilers allowing for comparable efficiencies in fewer passes, resulting in smaller boiler systems that will fit in tighter quarters.
Emissions standards for boilers have become very stringent in many areas because of the new Clean Air regulations. The ability of the boiler to meet emissions regulations depends on the type of boiler and burner options. ZOZEN has options to meet 5ppm NOx regulations, as well as 1 ppm CO regulation at 30 ppm NOx out of the box. We can also custom-engineer Selective Catalytic Reduction (SCR) for more rigorous emissions controls.
ASME code – also known by its longer name: ASME Boiler & Pressure Vessel Code – regulates the design, development, and manufacturing of boilers used in a variety of industries and applications.
This code was developed by the American Society of Mechanical Engineers, an organization that has been around for well over 100 years and is focused on establishing safety codes and standards for mechanical equipment.
Within the industrial heating industry, ASME code is the established standard that many pieces of equipment are built to.
Heating systems that adhere to the specifications set forth by ASME code have been constructed according to guidelines intended to promote safety and quality. As such, heating equipment that is ASME code compliant has been thoroughly inspected to assure that it meets high safety and quality standards.
Evaporation phase occurs in water wall tubes. Evaporation is the process to convert water into steam. Therefore water wall tubes should be designed and constructed to provide high heat absorption, minimum excess air level and highest boiler efficiency. Construction of water wall tubes should be also constructed to prevent air leakage into steam boiler, eliminate amount of heat losses and permit high heat release and combustion rate in the furnace.
Construction of water wall tubes must provide high quality of the supporting component such as tubes, casing, refractory, lagging, tile, fin, and so on. Best construction will reduce heat loss and maintenance. Construction of water wall tubes can be classified into four types such as:
The primary objective of an industrial boiler is the generation of steam. Steam is generated by heat transfer at a constant pressure. The fluid, which is initially in a liquid state, is heated, produces a variation in its phase and becomes saturated vapour.
This saturated steam can then be used for different applications such as sterilization, fluid heating or electricity generation.
