Combination plants

Interest has continued in on-site manufacture of hydrogen peroxide from the elements, particularly for remote sites located considerable distances from wodd-scale anthraquinone processes. However, no commercial-scale direct combination plants have been constmcted as of this writing. 

In this chapter, a short review of the thermodynamics of CCGTs is given. However, the author recommends readers to refer to two books which deal with combined plants in greater detail [1,2]. 

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

A combined plant with heat loss between two cyclic plants in series... 

The overall thermal elficiency of the combined plant is by definition... 

Fig. 7.3. Open circuit gas lurbine/closed steam cycle combined plant (CCGT). No supplementary firing...

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... 

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 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). 

Figure 5.5a depicts a combined plant in which a closed Brayton helium nuclear plant releases heat to a recovery steam generator, which supplies heat to a Rankine steam plant. The generator is provided with a gas burner for supplementary additional heat when the demand of steam power is high. The Rankine plant is a regenerative cycle. 

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. 

Schneider, H. J., E. Honold, and T. Masuhr. Treatment of benign prostatic hyperplasia. Results of a surveillance study in the practices of urological specialists using a combined plant-based preparation (Sabal extract WS 1473 and Urdca extract WS 1031). Fortschr Med 1995 113(3) 37-40. 

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. 

Figure 1 Combined plant with reference interface...

Figure 5 Combined plant with alternate interface...

The alternate interface still requires a high temperature heat source to power the heat exchanger HX2 in Figure 2. However, this heat source is now envisioned to be electrical heaters or a hydrogen or natural gas combustor in place of reactor heat. The link to the reactor has been broken allowing for improved temperature control and limiting HX2 to a role as an accident initiator in the chemical plant rather than the combined plant. 

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