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Boiler Thermal Efficiency

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. [Pg.51]

Boiler Thermal Efficiency Traditionally, boiler thermal efficiency is calculated pour/pm, where in is the LHV (lower heating value) of the fuel. A rule of thumb for economizers is that boiler efficiency increases by 1 percent for every 22°C (40°F) drop in temperature of the dry flue gas. These two statements do not reveal the considerable quantity of additional heat, available to be recovered through condensation of the water vapor in the flue gas, which is lost to atmosphere with hot flue gas. Based on fuel HHV (higher heating value), the total latent heat loss can be substantial an additional 9.6 percent (natural gas), 8.0 percent (propane), 6.5 percent (heating ou). [Pg.52]

For gas-side materials, one available technology employs Teflon-covered metal tubing and Teflon tube sheets. This technology is often operated across both the acid and water dew points, and can accept inlet gas temperatures to 533 K (260°C). Typical applications may achieve a cold-end AT below 45 C (80 F), improve the boiler thermal efficiency by 10 percent (LHV basis), and have a simple payback of 2 to 3 years, based on fuel avoidance (Figs. 24-58 and 24-59). [Pg.52]

FIG. 24-59 Characteristic curves for boiler thermal efficiency as a function of flue gas effluent temperature and flue gas water dew points. Based on the LHV of a fuel, and stoichiometric reaction, 100 percent efficiency would be achieved if sufficient combustion heat were recovered and removed, so that the temperature of the effluent flue gas was reduced to 25°C. For a flue gas with a 55°C dew point, recovering additional heat via condensation by cooling from 175 to 35°C (as shown) would increase the overall efficiency by more than 13 percent. Courtesy Combustion b- Energy Systems, Ltd. www.condexenergy.com.)... [Pg.53]

Steam Injection (SI) and Water Injection (WI). SI and WI are commonly applied to gas turbines to limit NO emissions. SI reduces the PFT by diluting oxygen near the burner front and directly removing heat from the burner flame. WI functions in a similar way, but removes even more heat from the burner flame due to its heat of vaporization. Both SI and WI lower boiler thermal efficiency—typically by no more than 1 or 2 percent. Most industrial boilers can handle these losses, although utility units cannot. SI or WI may be the lowest-cost option for reducing NO to less than 40 ppmvd, if simple combustion modifications are not successful. [Pg.283]

Test No. Firing Rate MW /hr (10 Btu/hr) Petroleum Coke %, heat input basis C") Excess O2 (%) Boiler Thermal Efficiency (%)... [Pg.53]

There has been increased interest in firing wood waste as a supplement to coal in either pulverized coal (PC) or cyclone boilers at 1—5% of heat input. This appHcation has been demonstrated by such electric utilities as Santee-Cooper, Tennessee Valley Authority, Georgia Power, Dehnarva, and Northern States Power. Cofiring wood waste with coal in higher percentages, eg, 10—15% of heat input, in PC and cyclone boilers is being carefully considered by the Electric Power Research Institute (EPRI) and Tennessee Valley Authority (TVA). This practice may have the potential to maximize the thermal efficiency of waste fuel combustion. If this practice becomes widespread, it will offer another avenue for use of fuels from waste. [Pg.59]

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. [Pg.1210]

Figure 3-19 shows the thermal efficiency of the gas turbine and the Brayton-Rankin cycle (gas turbine exhaust being used in the boiler) based on the LHV of the gas. This figure shows that below 50% of the rated load, the combination cycle is not effective. At full load, it is obvious the benefits one can reap from a combination cycle. Figure 3-20 shows the fuel consumption as a function of the load, and Figure 3-21 shows the amount of steam generated by the recovery boiler. [Pg.140]

Because fuel costs are high, the search is on for processes with higher thermal efficiency and for ways to improve efficiencies of existing processes. One process being emphasized for its high efficiency is the gas turbine combined cycle. The gas turbine exhaust heat makes steam in a waste heat boiler. The steam drives turbines, often used as lielper turbines. References 1, 2, and 3 treat this subject and mention alternate equipment hookups, some in conjunction with coal gasification plants. [Pg.340]

The condensing steam turbine has a relatively low thermal efficiency because about two-thirds of the steam enthalpy is lost to cooling water in the condenser. Expensive boiler feedwater treatment is required to remove chlorides, salts, and silicates, which can be deposited on the blades causing premature failure. The blades are already under erosion conditions because of water drops present in the condensing steam. Even with these disadvantages, the condensing turbine is still selected, especially in a process that requires very large compressor drivers and relatively low amounts of process steam. [Pg.283]

For (a), calculations showed that the presence of feed heating made little difference to the overall efficiency. Essentially, this is because although feed heating raises the thermal efficiency %, it leads to a higher value of and hence a lower value of the boiler efficiency, tjb- The overall lower cycle efficiency (t o)l = Vb Hl expected to... [Pg.120]

A second criterion of performance sometimes used is an artificial thermal efficiency (tja) in which the energy in the fuel supply to the CHP plant is supposed to be reduced by that which would be required to produce the heat load (Qu) in a separate heat only boiler of efficiency (tjb). i e- by (Qu/ b)- The artificial efficiency (tja) is then given by... [Pg.170]

Large power stations use complex feed heating systems before the boiler feed pumps (LP) and after the boiler feed pumps (HP), which can give high overall thermal efficiencies of 39 per cent. However, for the smaller machine, it becomes uneconomic to consider multiple bleeds from the turbine, and the final choice is dictated by the extra cost for the additional complexity against lower running costs due to increased efficiency. As a minimum, a contact type de-aerator is often employed which would extract a small bleed of around 2-3bar from the turbine. [Pg.181]

The radiant section of an industrial boiler may typically contain only 10 per cent of the total heating surface, yet, because of the large temperature difference, it can absorb 30-50 per cent of the total heat exchange. The mean temperature difference available for heat transfer in the convective section is much smaller. To achieve a thermally efficient yet commercially viable design it is necessary to make full use of forced convection within the constraint of acceptable pressure drop. [Pg.347]

Most plants have boilers producing steam for space heating many need steam for other purposes as well. Boiler water requirements for boilers have changed radically over recent years. The old Lancashire and Economic boilers had large heating surfaces and low heat transfer rates scale deposits would do no more harm than reduce their thermal efficiency. [Pg.476]


See other pages where Boiler Thermal Efficiency is mentioned: [Pg.107]    [Pg.2617]    [Pg.2596]    [Pg.107]    [Pg.2617]    [Pg.2596]    [Pg.58]    [Pg.59]    [Pg.423]    [Pg.367]    [Pg.189]    [Pg.483]    [Pg.259]    [Pg.1208]    [Pg.139]    [Pg.340]    [Pg.111]    [Pg.117]    [Pg.267]    [Pg.373]    [Pg.1180]   
See also in sourсe #XX -- [ Pg.155 ]




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