Lower heating value thermal efficiency

Many preliminary analyses of gas turbines are based on the assumption of a closed air standard cyclic plant, and for such analyses the use of tj as a thermal efficiency is entirely correct (as discussed in the early part of Chapter 3 of this book). But most practical gas turbines are of the open type and the rational efficiency should strictly be used, or at least its approximate form, the arbitrary overall efficiency tjq. We have followed this practice in the latter part of Chapter 3 and subsequent chapters even though some engineers consider this differentiation to be a somewhat pedantic point and many authors refer to tjo as a thermal efficiency (or sometimes the lower heating value thermal efficiency ). 

The efficiencies of modem thermal power stations using the steam cycle can exceed 40% based on lower heating value, although the average efficiency of the installed stock worldwide is... 

Given a 2.0 MWac fuel cell cycle operating on 700 Ib/hr of methane, what is (a) the HHV thermal input of the methane gas, (b) the LHV thermal input, (c) the HHV electric efficiency, (d) the LHV electric efficiency, and (e) the HHV Heat Rate Assume the higher and lower heating value of methane as 23,881 and 21,526 Btu/lb respectively. 

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). 

The heat released from combustion of the fuel is transferred by radiation and convection to evaporate water and create superheated steam, which is then used to create electricity in a steam turbine. Steam temperatures in state-of-the-art coal-fired boilers are pushing close to 600°C (i.e. above the critical point of water) with net electricity production reaching 45% of the thermal energy of the burned fuel [43]. Modem subcritical boilers are closer to 39% net efficiency in electricity production, but older boilers can have efficiencies as low as 30% on a lower-heating-value basis. 

Association (United States) calculates efficiencies based on the lower heating value (LHV) for gas fuels and the higher heating value for oil fuels. It is general practice to report gas-engine performance in terms of British thermal units per horsepower-hour (LHV) and oil-engine... 

Gasification determines to a large extent the cost of indirect liquefaction. Also, the thermal efficiency of gasification contributes largely to the overall thermal efficiency of the entire process. The thermal efficiency is defined as the lower heating value of the products divided by the lower heating value of the feed... 

The theoretical maximum thermal efficiency for the conversion of methane into paraffins is 78% (based on lower heating values). The practically attainable efficiency is of course much lower. 

The thermal efficiency of a GTG plant depends on the composition of the natural as well as the plant design. The MTG reaction per se has hi energy efficiency, of the order of 95% based on the lower heating value (LHV), with the remaining 5% of chemical energy released as heat of reaction [25]. The LHV is the appropriate basis since internal-combustion engines do not condense... 

For such atmospheric CHP systems, an electrical efficiency of 45-50%, based on lower heating value (LHV) of the fuel, is considered the upper limit [21,26,28], while a total thermal and electrical efficiency of 85-90% is feasible. 

To avoid major modifications of the power plant, the optimal position of a CO2 capture process seems to be in between the flue gas desulfurization unit (FGD) and the stack. Particulate matter as well as SO and NO concentrations are reduced to a large extent, which lowers the requirements regarding chemical resistance and reduces the risk of plugging. To quantify the flue gas condition subsequent to the FGD unit, a model of a state of the art hard coal fired power plant was developed and implemented in Aspen Plus . The considered power plant features a thermal duty of 1210 MW and a net thermal efficiency of 45% (based on lower heating value of the feedstock). 

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... 

A number of benefits of using OEC in MSW incinerators have been cited.8 The economic incentives include increased waste-processing capacity, greater thermal efficiency, increased production in a waste-to-energy facility, reduced demand on the exhaust system, and a smaller air pollution control system. Increased capacity may be particularly important for many waste processors which are at their maximum capacity, since it is usually difficult to obtain permits to build new facilities. The environmental incentives include improved ash burnout, lower hydrocarbon emissions, lower CO, greater flexibility and control, and the ability to bum low-heating-value wastes such as dewatered sludge. 

For convective dryers thermal efficiencies in the range 0.4—0.7 may be expected, the lower values applying to heat sensitive products which require drying air temperatures < 100 °C. Vacuum dryers can have thermal efficiencies as high as 0.9, but their capital costs are also high. 

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