Available energy accounting

To compare the values of steam at various pressures for design studies or accounting once the plant is built, the AB method is useful. The maximum available energy in a working fluid can be determined from... 

Accessible work potential is called the exergy that is the maximum amount of work that may be performed theoretically by bringing a resource into equilibrium with its surrounding through a reversible process. Exergy analysis is essentially a TA, and utilizes the combined laws of thermodynamics to account the loss of available energy. Exergy is always destroyed by irreversibilities in a system, and expressed by... 

Table I gives the distribution of the energy input to the deep-basin still as determined from the results of the 3-day energy balance. As shown, 32% of the available energy was utilized for useful output of the still. The largest single loss, 25%, was heat radiation from the basin water. The remainder of the heat losses, taken separately, are relatively moderate collectively, however, they account for about 43% of the incoming solar energy.

Wepfer, W.J., "Applications of Available Energy Accounting," Thermodynamics Second Law Analysis, A.C.S. Symposium... 

Second Law quantities such as available-energy and negentropy need not be introduced explicitly into the optimization although their effects are evaluated (indirectly) by the shadow and marginal prices. Furthermore, any required Second Law based prices can be obtained by using Equations 17 and 18 or by way of a thermoeconomic accounting technique (5,15). 

Gaggioli, R. A. Wepfer, W. J., "Available-Energy Accounting— A Cogeneration Case Study," paper presented at the 85th AIChE Meeting, Philadelphia, June, 1978. 

It is important to note that the accumulated available energy does not take into account the actual energy collected by each reactor. In fact, the actual collected energy is a function of concentration ratio, as concentrating collectors are able to capture only a 1 /Cr fraction of the diffuse radiation. In order to reflect this, another quantity can be defined called the accumulated collected energy... 

In an energy-producing process, the differences in energy quality can be accounted for by the concept of available energy (availability) using the second law of thermodynamics. To perform a second-law NEA, availability is defined as... 

China s oil fields are widely located in the countiy s 14 provinces. The total number of oil fields put into service by the end of 1990 is 238, of which 84% of reserves is recovered by the injection of water and the enh ced recovery in average is accounted for at about 32.5% of the oil originally in place, then, 60 to 70% of the oil in the reservoir can not be recovered. Oil and water do not mix interfaces are formed which must be forced by the available energy. Therefore the injection of miscible agents to recover additional oil is needed. Development of a least-cost option as an environmental sound way for enhanced oil recovery is an issue the petroleum industry sector must address. 

The cycle is not optimized yet, especially with respect to intermediate pressures. Also, the expanders effectivenesses might be higher than those used in the calculation (0.85). That means, that some potential still exists for efficiency increase which could offset some small losses, not taken into account. The energy balance in the recuperators is fulfilled when the recuperator effectiveness Sfgg is taken equal to 0.98. Indeed, the available heat is ... 

Reistad, G.M. and Gaggioli, R.A., "Available Energy Accounting", this volume. 

The error in energy analyses is that they attribute all the inefficiencies to losses, and then mis-calculate those. As was demonstrated for the coal-fired boiler, the first law efficiency (85%) was a poor approximation to the true efficience (33.8%). (Furthermore, perturbation studies show that the trends in first and second law efficiencies can move in opposite directions. For the coal-fired boiler problem, if the steam conditions were changed to 811°K/6.87 MPa (1000°F/1000 psia) and if the first law efficiency were decreased to 83%, the result would be an increase to 34.3% in second law efficiency.) The major inefficiencies were due to heat transfer (njj = 47.3%) and combustion (Hjj = 73.8%), with the stack losses accounting for only 5.5% of the available energy input with the coal. In contrast, an energy analysis shows the combustion process to be 100% efficient and... 

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