Boilers Steam Generation

Steam generators, commonly called boilers, are used by industrial manufacturers to produce steam. Steam is used to drive turbines and provide heat to process equipment. Steam generators are classified as fire-tube or water-tube boilers. High-pressure, medium-pressure, and low-pressure steam is 

A fired heater or furnace is a device used primarily to heat large quantities of hydrocarbons. These systems are very expensive and complex and require a well-trained and dedicated staff. A process technician assigned to these units studies the basic components of the system, traces out each major flow path, and works closely with senior technicians until he or she is qualified to operate the equipment. Modern control instrumentation and high-tech control rooms are designed to monitor and control all vital processes. 

As with most industrial applications, fired heaters come in a wide variety of designs. 

Cabin—direct fired Cylindrical—direct fired Box—direct fired A-frame—direct fired Fire-tube—indirect fired 

A furnace or fired heater can be classified as natural, induced, forced, or balanced draft. The pressure inside a warm furnace is typically lower because of buoyancy differences in the cooler outside air. A natural-draft furnace can operate using this approach however, when fans are used to push or pull the air through the furnace, greater heat transfer rates can be achieved. A natural-draft fired heater is severely limited in contrast to these systems. 

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Cast iron sectional boilers Steel boilers Electrode boilers Steam generators Vertical shell boilers Horizontal shell boilers Watertube boilers Waste heat boilers Fluid bed boilers... 

Utility operators may choose from several technologies to generate electricity, although the most common approach is via the use of high-temperature, fossil fuel boiler plants. In this case, the boiler (steam generator) itself may be of several different design types. 

The boiler steam generation system primarily covers the boiler itself, the boiler surfaces (the primary heat-transfer and steam-generating surfaces within the boiler proper), and all necessary appurtenances. 

Essentially, except for once-through boilers, steam generation primarily involves two-phase nucleate boiling and convective boiling mechanisms (see Section 1.1). Any deposition at the heat transfer surfaces may disturb the thermal gradient resulting from the initial conduction of heat from the metal surface to the adjacent layer of slower and more laminar flow, inner-wall water and on to the higher velocity and more turbulent flow bulk water. 

Off gas from furnace is introduced into the combustion chamber to burn its remaining combustibles, and to decompose its pollutant and other odor components. Excess air is automatically controlled by the oxgen concentration at the exit of the combustion chamber. Heat of off gas from the combustion chamber is recovered by the waste heat boiler. Steam generated in the boiler is supplied to the indirect steam dryer. When the amounts of steam generated is not sufficient for drying dewatered cake, auxiliary fuel is used to generate the additional steam. 

Power Production. Steam cycles for generation of electric power use various types of boilers, steam generators, and nuclear reactors operate at subcritical or supercritical pressures and use makeup and often also condensate water purification systems as well as chemical additives for feedwater and boiler-water treatment. These cycles are designed to maximize cycle efficiency and reliability. The fuel distribution of sources installed in the United States from 1990—1995 are as follow coal, 45% combined cycle, 27% miscellaneous, 14% nuclear, 11% solar, oil, and geothermal, 1% each and natural gas, 0.3%. The 1995 summer peak generation in the United States was 620 GW (26). The combined cycle plants are predominantly fired by natural gas. The miscellaneous sources include bagasse, black liquor from paper mills, landfill gas, and refuse (see Fuels frombiomass Fuels fromwaste). 

When some of the HP steam generation is unknown, a bottom-up approach may be the right one for setting up a steam balance. This approach is applied to the same example above, but assuming the boiler steam generation is unknown and to be determined from the steam balance. 

The deaerator balance (Table 16.12) has two unknowns, namely, treated water as makeup and condensate return. Boiler feed water is provided for three boilers, steam generation in convection sections of furnaces H-9001, F6001 and F-5001 as well as two WHB s. Assume blowdown rate of 2% in average, the total amount of BFW can be calculated as BFW rate = (394 + 64 + 54+18 + 63) x 1.02 = 605klb/h. 

There are several cost components contributing to boiler steam generation ... 

Thus, the specific total cost Cst for boiler steam generation can be expressed as... 

Initial Point and Convergence Criteria The recommended commutation strategy is to use total boiler steam generation as initial trial rate and repeated until the convergence criteria is met ... 

The steady state model is based on the mass and energy balances which were carried out over the furnace, heat exchanger area, economising section, dolezal, drum, generating section and superheaters. A set of nonlinear algebraic equations were used to accurately predict changes in the physical state of each system. Fig. 1 shows a simplified PFD for recovery boiler steam generation cycle. 

Fig. 1-A simplified PFD for recovery boiler steam generation cycle.

BAAQMD 9-10, NOx and CO from Boilers, Steam Generators, and Process Heaters in Petroleum Refineries, Jan. 5,1994 H.R. 4503, 862... 

Power generation Cooling-water heat exchangers, flue gas desulfurization systems, fossil fuel boilers, steam generator tubes (nuclear), air heaters, steam turbine systems, vaults, atmospheric corrosion, gasification systems, mothballing... 

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