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.
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.
The operating objectives for steam boiler plant include:
Safe operation.
Maximum combustion and heat transfer efficiency.
Minimum maintenance.
Long working life.
The quality of the water used to produce the steam in the boiler will have a profound effect on meeting these objectives.
System load is measured in either BTUs or tons of steam (at a specific pressure and temperature). It would be nearly impossible to size and select a boiler(s) without knowing the system load requirements. Knowing the requirements leads to the following information:
The boiler(s) capacity, taken from the maximum system load requirement.
The boiler(s) turndown, taken from the minimum system load requirement.
Conditions for maximum efficiency, taken from the average system load requirement.
Determining the total system load requires an understanding of the type(s) of load in the system. There are three types of loads: heating, process, and combination.
The primary purpose of the boiler is to supply energy to the facility's operations – for comfort heating, manufacturing process, laundry, kitchen, etc. The nature of the facility's operation will dictate whether a steam or hot water boiler should be used. Hot water is commonly used in heating applications, with the boiler supplying water to the system at 120°F to 220°F. The operating pressure for hot water heating systems usually is 30 psig to 125 psig (hydrostatic). Under these conditions, there is a wide range of hot water boiler products available. If system requirements are for hot water of more than 250°F, a high-temperature water boiler should be considered.
This is because, under normal circumstances, the exhaust temperature of the boiler cannot completely condense the water in the flue gas, and the difference between the low calorific value and the high calorific value is mainly in the part of the latent heat of vaporization, so the low heat is used. The value is calculated to reflect the true efficiency of the boiler. However, there will be some special circumstances. For example, if the boiler is a condensing boiler, the calculation of the condensed water portion should be calculated using the high calorific value.
The combustion air preheater is definitely one of heat exchanger applications. Based on Figure 1 below, flue gas simply leaves steam boiler and passes via air preheater. The combustion air is passed through this equipment too to increase its temperature before being combined with boiler fuel.
Because the temperature of combustion air is lower than the temperature of flue gas, combustion air receive heat transfer from flue gas through combustion air preheater in the process of convection heat transfer. The heat transfer make temperature of flue gas lower and consequently minimizes its heat loss and also decreases the air temperature to stack.
Economizer is one of steam boiler’s equipment which is used to heat feedwater before it is supplied into steam drum. Economizer is the heat exchanger equipment to increase boiler efficiency by absorbing heat recovery of flue gases. The lower temperature of flue gas out from stack, the heat loss will be less and the fuel which is needed to convert water into steam will be also less in certain circumstances. So it can be said that economizer can save the fuel efficiently. Economizer will make temperature of feedwater higher, so steam boiler can produce steam easily.
Gas fired boiler is a boiler which uses gas as its fuel. Gas fired boiler consists of some important components such as flame ignition, gas metering system, air compressor, air piping, gas piping, burner nozzles, and the others. Combustion process of gas fired boiler should be maintained and operated properly to produce efficient combustion result.
