Combined plants efficiency

Even for this simplest CCGT plant, iterations on such a calculation are required, with various values of p, in order to meet the requirements set on T, the steam turbine entry temperature, and 7s (the calculated value of 7s has to be such that the dewpoint temperature of the gas (7jp) is below the economiser water entry temperature (7b) and that may not be achievable). But with the ratio /i satisfactorily determined, the work output from the lower cycle Wl can be estimated and the combined plant efficiency obtained from... 

With the fuel energy input known from the calculation of the gas turbine plant performance, F = Aff[CV]o, the combined plant efficiency is determined as... 

Most modem CCGT plants use open air cooling in the front part of the gas turbine. An exception is the GE MS9001H plant which utilises the existence of the lower steam plant to introduce steam cooling of the gas turbine. This reduces the difference between the combustion temperature T ot and the rotor inlet temperature The effect of this on the overall combined plant efficiency is discussed in Ref. [1] where it is suggested that any advantage is small. 

The coupled nuclear-hydrogen plant investigated in this paper was studied in earlier work (Vilim, 2007). There the full power condition and the combined plant efficiency were estimated. The plant appears in Figures 1 through 3 as three modules - the primary system, the power conversion system and the high-temperature electrolysis plant. The interface between the nuclear side and the chemical plant appears in these figures in the form of the flow paths that connect these three modules. 

The performance of the reference interface is characterised in Vilim (2007). In that work the GPASS/H code was used to determine the full power condition, the combined plant efficiency and the partial power load schedule. The values of the main operating parameters are summarised in Table 1. 

The next generation of gas turbine-based, combined-cycle power plants, under constmction in many parts of the world, is to feature net plant efficiencies in the 60% range based on LHV of fuel input. These faciUties, scheduled for start-up in the latter 1990s, are anchored by large gas turbines capable of simple-cycle efficiencies >40% LHV in some cases. To develop these machines, manufacturers have scaled up and improved upon designs that have already proved to be highly rehable. 

At least two manufacturers have developed and installed machines rated to produce more than 210 MW of electricity in the simple-cycle mode. In both cases, the machines were designed and manufactured through cooperative ventures between two or more international gas turbine developers. One 50-Hz unit, first installed as a peaking power faciUty in France, is rated for a gross output of 212 MW and a net simple-cycle efficiency of 34.2% for natural-gas firing. When integrated into an enhanced three-pressure, combined-cycle with reheat, net plant efficiencies in excess of 54% reportedly can be achieved. 

A comparison of the effect of the various cycles on the overall thermal efficiency is shown in Fig. 29-40. The most effective cycle is the Brayton-Ranidne (combined) cycle. This cycle has tremendous potential in power plants and in the process industries where steam turbines are in use in many areas. The initial cost of the combined cycle is between 800- 1200 per kW while that of a simple cycle is about 300- 600 per kW. Repowering of existing steam plants by adding gas turbines can improve tne over plant efficiency of an existing steam turbine plant by as much as 3 to 4 percentage points. 

In the area of performance, the steam turbine power plants have an efficiency of about 35%, as compared to combined cycle power plants, which have an efficiency of about 55%. Newer Gas Turbine technology will make combined cycle efficiencies range between 60-65%. As a rule of thumb a 1% increase in efficiency could mean that 3.3% more capital can be invested. However one must be careful that the increase in efficiency does not lead to a decrease in availability. From 1996-2000 we have seen a growth in efficiency of about 10% and a loss in availability of about 10%. This trend must be turned around since many analysis show that a 1% drop in the availability needs about 2-3% increase in efficiency to offset that loss. 

The thermal efficiency of the combined plant is greater than that of the upper cycle alone, by an amount 7Jl(1 — tjh). 

The arbitrary overall efficiency of the combined plant (Eq. (7.12)) may then be written... 

For a mass flow of air (Mg) to the compressor of the gas turbine plant, a mass flow Mf of fuel (of specific enthalpy hfo) is supplied to the two combustion chambers (Mf = (Mf)ff + (Mf)f). The overall efficiency of the combined plant is then... 

After allowing for the performance penalties arising from the CO2 removal, Lozza and Chiesa estimated an efficiency of 46.1%, for a maximum gas turbine temperature of 1641 K and a pressure ratio of 15 (compared with the basic CCGT plant efficiency of 56.1%). They concluded that the plant cannot compete, in terms of electricity price, with a semi-closed combined cycle with CO2 removal (Cycle A2). 

The Siemens Westinghouse TSOFC commercialization plan is focused on an initial offering of a hybrid fuel cell/gas turbine plant. The fuel cell module replaces the combustion chamber of the gas turbine engine. Figure 1-8 shows the benefit behind this combined plant approach. Additional details are provided in Section 8. As a result of the hybrid approach, the 1 MW early commercial unit is expected to attain -60% efficiency LHV when operating on natural gas. 

Determine the thermodynamic efficiency and the net power output of the Braysson combined plant. Plot the sensitivity diagram of rj (cycle efficiency) versus (pressure at state 6) and sensitivity diagram of r] (cycle efficiency) versus pg (pressure at state 8). 

Determine the mass flow rate of air through the Brayton cycle, and the thermodynamic efficiency and net power output of the Brayton/ Rankine combined plant. 

The data obtained from coal analyses (Table 1.1) establish the price of the coal by allocation of production costs as well as to control mining and cleaning operations and to determine plant efficiency. However, the limitations of the analytical methods must be recognized (Rees, 1966). In commercial operations, the price of coal not only reflects the quantity of coal but also invariably reflects the relationship of a desirable property or even a combination of properties to performance of coal under service conditions (Vorres, 1993). 

Today, the largest solar power plant in the United States is the 22-year-old thermal plant in California s Mojave Desert, which has a combined total capacity of 354 mW. At Kramer Junction, California, nine solar power plants, each 30 mW or larger, have been in operation for two decades. The yearly insolation in the area is 2,940 kWh/m2. Plant efficiencies range from 10 to 17%, and their capital costs range from 2,500 to 3,500 per kWp The cost of generated electricity from these plants drops as their size increases, and ranges from 10 to 17 /kWh. 

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