Steam boilers efficiency

Energy efficiency of the process. If the process requires a furnace or steam boiler to provide a hot utility, then any excessive use of the hot utility will produce excessive utility waste through excessive generation of CO2, NO, SO, particulates, etc. Improved heat recovery will reduce the overall demand for utilities and hence reduce utility waste. 

Reducing products of combustion from furnaces, steam boilers, and gas turbines by making the process more energy efficient through improved heat recovery. 

Steam costs vary with the price of fuel. If steam is only generated at low pressure and not used for power generation in steam turbines, then the cost can be estimated from local fuel costs assuming a boiler efficiency of around 75 percent (but can be significantly higher) and distribution losses of perhaps another 10 percent, giving an overall efficiency of around 65 percent. 

Metal Cleaning. Citric acid, partially neutralized to - pH 3.5 with ammonia or triethanolamine, is used to clean metal oxides from the water side of steam boilers and nuclear reactors with a two-step single fill operation (104—122). The resulting surface is clean and passivated. This process has a low corrosion rate and is used for both pre-operational mill scale removal and operational cleaning to restore heat-transfer efficiency. 

The thermal efficiency of steam-tube units will range from 70 to 90 percent, if a well-insiilated cylinder is assumed. This does not allow For boiler efficiency, however, and is therefore not direc tly comparable with direct-heat units such as the direct-heat rotaiy diyer or indirect-heat calciner. 

TABLE 25-68 Energy Output and Efficiency for 1000 Metric Ton of Waste/Day Steam-Boiler Turbine-Generator Energy-Recovery Plant Using Unprocessed Industrial Solid Wastes with Energy Content of 12,000 kJ/kg... 

Economizers Economizers improve boiler efficiency by extracting heat from the discharged flue gases and transferring it to feedwater, which enters the steam generator at a temperature appreciably lower than the saturation-steam temperature. 

Energy Efficiency Measures and Estimated Improvement Potentials for Steam Boilers. 

In 1854, the Manchester Steam Users Association was formed to help with the prevention of explosions in steam boilers and to find efficient methods in their use. To achieve this, the Association employed the first boiler inspectors, whose services were then made available to the Association s members. Within a short space of time, the members became convinced that insurance to cover the high cost of repair or replacement of damaged boilers was desirable, and this resulted in the first boiler insurance company (The Steam Boiler Assurance Company) being formed in 1858. The scope of the services for inspection and insurance later extended to include pressure vessels, steam engines, cranes, lifts and electrical plant, the insurance protection in each case being supported by an inspection service carried out by qualified engineer surveyors. 

Boilers are designed to operate within a range of firing levels the greater this range (turndown ratio), the more flexible they are in operation. However, boiler efficiency changes with variation in steam output, and most boilers produce their maximum efficiency at about 80 to 85% of MCR. 

Feedwater regulators are fitted to boilers as a means of controlling the rate of addition of FW. This is necessary to maintain a consistent water level that, in turn, reduces the risks of thermal shock to the boiler, reduces the potential for BW carryover with the steam, and improves boiler efficiency. 

Economizers are one of several types of FW heaters, all of which are designed to provide thermodynamic gains in the steam cycle. They typically are located in the exit gas system, where their use improves overall boiler efficiency, which tends to increase by 1 % for every 40 to 50 °F (22-28 °C) reduction in flue gas temperature... 

A boiler plant raises 5.2 kg/s of steam at 1825 kN/m2 pressure, using coal of calorific value 27.2 MJ/kg. If the boiler efficiency is 75%, how much coal is consumed per day If the steam is used to generate electricity, what is the power generation in kilowatts, assuming a 20% conversion efficiency of the turbines and generators ... 

Make a rough estimate of the cost of steam per ton, produced from a packaged boiler. 10,000 kg per hour of steam are required at 15 bar. Natural gas will be used as the fuel, calorific value 39 MJ/m3. Take the boiler efficiency as 80 per cent. No condensate will be returned to the boiler. 

However, this is not likely to be the case. In this example, the two boilers might have different fuels, with different fuel costs and different efficiencies, and the gas turbine (perhaps, with supplementary firing) will have completely different characteristics from the steam boilers. Thus, there are degrees of freedom created by multiple steam generation devices with different costs of fuels, different boiler efficiencies and different power generation potential. Individual steam boilers and HRSGs will have minimum and maximum flows. 

There are many types of steam boilers, depending on the steam pressure, steam output and fuel type. Blowdown is required to remove the dissolved solids not removed in the boiler feedwater treatment. The efficiency of the boiler depends on its load. 

Energy efficiency of the process. If the process requires a furnace or steam boiler to provide hot utility, then any... 

Natural gas will be used in the steam boilers to obtain steam. It is assumed that the thermal efficiency of a steam-generating plant is around 80%.74... 

Economizers improve boiler thermal efficiency by recovering heat from the combustion flue gases exhausted from the steam boiler section. The recovered heat is used to heat colder streams (heat sinks), before ultimate discharge of the waste gas to atmosphere. This recovered heat displaces the need to bum additional fuel to heat these same streams. 

The heat of combustion in a process heater or steam boiler may liberate 100 X 106 Btu/h. If the heater s efficiency is 78 percent, the heat absorbed by the tubes should be 78 X 106 Btu/h. When observing a heater s operation, it is a good idea to check this heat balance by calculation. 

Rankine Cycle. The sleam-Rankine cycle employing steam turbines has been the mainstay of utility thermal electric power generation for many years. The cycle, as developed over the years, is sophisticated and efficient. The equipment is dependable and readily available. A typical cycle (Fig. 21) uses superheat, reheat, and regeneration. Heat exchange between flue gas and inlet air adds several percentage points to boiler efficiency in fossil-fueled plants. Modern steam Rankine systems operate at a cycle top temperature of about 800 K with efficiencies of about 40%. All characteristics of this cycle are well suited to use in solar plants. 

One additional source conducted a test on performance at a waste-wood boiler burning TDF that included results on steam generated and boiler efficiency using the heat-loss method for varied fuel mixes.2 Although the test summary notes that emissions testing was done, the results were not obtained. Nevertheless, one of the conclusions of the test report was that TDF had no environmental disadvantages when compared with the supplemental coal used during the tests.2... 

The /main modifications took place in the burners. The boiler itself has not been modified. In the tests it achieved 60% of nominal output of steam. With better monitoring of superheater temperatures, it is expected to achieve an output of 90%. The test program will be developed this year (1980) and will include emission analysis, boiler efficiency, corrosion, and other aspects. CESP also plans to analyse smaller boilers which will operate this same year. 

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