A process load is usually a high-pressure steam load. A process load pertains to manufacturing operations, where heat from steam or hot water is used in the process. A process load is further defined as either continuous or batch. In a continuous load, the demand is fairly constant - such as in a heating load. The batch load is characterized by short-term demands. The batch load is a key issue when selecting equipment, because a batch-type process load can have a very large instantaneous demand that can be several times larger than the rating of the boiler. For example, based on its size, a heating coil can consume a large amount of steam simply to fill and pressurize the coil. When designing a boiler room for a process load with instantaneous demand, a more careful boiler selection process should take place.
Loads vary, and a power plant must be capable of handling the minimum load, the maximum load, and any load variations. Boiler selection is often dictated by the variation in load demand, rather than by the total quantity of steam or hot water required. There are three basic types of load variations: seasonal, daily, and instantaneous.
Stack temperature is the temperature of the combustion gases (dry and water vapor) leaving the boiler. A well-designed boiler removes as much heat as possible from the combustion gases. Thus, lower stack temperature represents more effective heat transfer and lower heat loss up the stack. The stack temperature reflects the energy that did not transfer from the fuel to steam or hot water. Stack temperature is a visible indicator of boiler efficiency. Any time efficiency is guaranteed, predicted stack temperatures should be verified.
Stack loss is a measure of the amount of heat carried away by dry flue gases (unused heat) and the moisture loss (product of combustion), based on the fuel analysis of the specific fuel being used, moisture in the combustion air, etc.
Condensing boilers can achieve up to 98% thermal efficiency, compared to 70%-80% with conventional designs (based on the higher heating value of fuels). Typical models offer efficiencies over 90% when the return water temperature is at 110 ºF or less; the lower the return water temperature, the higher the efficiency gain.
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.
Package boiler is a boiler that had been fabricated and available as a complete package. The entire pressure parts have been assembled in the workshop and ready to be sent to the field or site where power plant is located. On the field/site requires only connection and integration of course work in electrical connections, water pipes, steam pipes and fuel piping system to operate. Package boiler is one of classification of boiler based on erection. Design package boilers in general are the type of Fire Tube Boiler and have made up shell and tubes. This type has high heat transfer both radiation and convection.
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.
