Overall efficiency and specific work

The (arbitrary) overall efficiency and specific work quantities obtained from these calculations are illustrated as carpet plots in Fig. 4.11. It is seen that the specific work is reduced by the turbine cooling, which leads to a drop in the rotor inlet temperature and the turbine work output. Again this conclusion is consistent with the preliminary analysis and calculations made earlier in this chapter. 

Fig. 5,4. Overall efficiency and specific work for [CBTli<-i plant with single-step cooling of NGVs, with combustion temperature and pressure ratio as parameters (after Ref. [5], Chapter 4).

Fig, 6.17. Overall efficiency and specific work of dry and wet cycles compared. 

Fig. 7.9. Overall efficiency of CCGT plant compared with overall efficiency and specific work of CBT plant...

Fig. 5.4 shows a carpet plot of overall efficiency against specific work for the cooled [CBTJici plant (single step) with pre.ssure ratio and combustion temperature as parameters. As shown earlier, by the preliminary air standard analysis and the subsequent calculations in Chapter 4, there are relatively minor changes of thermal efficiency compared with the uncooled plant [CBT]iuc, but there is a major effect in the reduction of specific work. 

Macchi et al. provided a similar comprehensive study of the more complex RWI cycles as illustrated in Fig. 6.19, which shows similar carpet plots of thermal efficiency against specific work for maximum temperatures of 1250 and 1500°C, for surface intercoolers. The division of pressure ratio between LP and HP compressors is again optimised within these calculations, leading to an LP pressure ratio less than that in the HP. For the RWI cycle at 1250°C the optimisation appears to lead to a higher optimum overall pressure ratio (about 20) than that obtained by Horlock [5], who assumed LP and HP pressure ratios to be same in his study of the simplest RWI (EGT) cycle. His estimate of optimum pressure ratio... 

Calculation of the specific work and the arbitrary overall efficiency may now be made parallel to the method used for the a/s cycle. The maximum and minimum temperatures are specified, together with compressor and turbine efficiencies. A compressor pressure ratio (r) is selected, and with the pressure loss coefficients specified, the corresponding turbine pressure ratio is obtained. With the compressor exit temperature T2 known and Tt, specified, the temperature change in combustion is also known, and the fuel-air ratio / may then be obtained. Approximate mean values of specific heats are then obtained from Fig. 3.12. Either they may be employed directly, or n and n may be obtained and used. 

For the ISTIG cycle, Fig. 6.18 shows thermal efficiency plotted against specific work for varying overall pressure ratios and two maximum temperatures of 1250 and 1500°C. Peak efficiency is obtained at high pressure ratios (about 36 and 45, respectively), before the specific work begins to drop sharply. Note that the pressure ratios of the LP and HP compressors were optimised within these calculations. 

Intermolecular metallo-ene reactions have received until now virtually no attention as a method in target-oriented organic synthesis despite the extensive work and interesting prospects. Problems of regio-and stereo-selectivity and overall efficiency seem to limit their applicability to specifically activated eno-philes. 

An example is that a large pump is driven by a steam turbine operating between ISOpsig and atmospheric condition. 3800 Ib/h steam is measmed online. The pump power requirement is estimated by equation (8.1) as 72 hp. On the other hand, the theoretical power supplied by the steam mrbine can be estimated from the theoretical steam table. The steam table indicates the specific steam rate of 18.22 Ib/kWh, which indicates the steam turbine can deliver 208.6 kW (38001b/h/18.221b/kWh) or 279.6 hp. Thus, the overall efficiency of the turbine and pump is only 26% (72/279.6). This efficiency is much lower than design. It was found that steam turbine blades were severely eroded over time and no inspection and maintenance work was ever done on the turbine for a long time. 

With HR-steam as the heat source and anunonia as the working fluid the pressure of the NH3-gas before the turbine could be approx. 90 bar(a) and the temperature 120 °C, that is quite near the critical point. The condensation pressure of the NHj would be approx. 12 bar(a). The relatively high pressures lead to elevated plant costs. Other working fluids, such as isobutane or isopentane, can be used to get lower pressure levels. The critical point of isobutane is approx. 36 bar(a) and 135 °C and of isopentane approx. 34 bar(a) and 187 °C. With isopentane as working fluid flie pressure in the evaporator could be approx. 13 bar(a) at 130 °C and in the condenser approx. 1.1 bai(a) at 30 C. With an overall efficiency of 14 % for the electricity production the generated power would be 1.8 MW. With a specific plant cost of 2000 euros/kWh the investment would be 3.6 million euros and the cost of electricity 0.04 euros/kWh with an annuity ctor of 0.16. 

Any large-scale resin-handling system has three basic subsystems, for unloading, storage, and transfer. For a complete system to work at peak efficiency, processors need to write specifications that fiilly account for the unique requirements of each subsystem. The least efficient component, no matter how inconsequential it may seem, will limit the overall efficiency of the entire system. 

The work required to compress the gas to the high pressures adds to the overall cost and complexity of the compressed hydrogen energy solution and can exceed 20% of the specific energy content of the compressed hydrogen itself. This greatly reduces the overall well-to-wheel efficiency of the fuel cell system. 

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