Plant with supplementary firing

Plants with supplementary firing allow obtaining higher eflBciencies but lead to increased CO2 (when burning a carbon containing fuel) and NOj emissions. 

Fig. 7.5. Open circuit ga.s turbine/closed steam cycle combined plant (CCGT). With supplementary firing (after...

For a plant with a fired heat boiler, as in Fig. 9.2b, both the work output Wcg ind the main heat supply = F are assumed to be unaltered at 1.0 and 4.0, respectively, but supplementary fuel energy is supplied to the WHB, Fj = 1.5F = 6.0. The useful heat supplied is then assumed to increase to 7.2 and the non-u.seful heat rejected to be 1.8. Thus the parameter A changes to 7.2. 

Thus the FESR is less attraetive when there is a large heat load and a WHB with supplementary firing is used. In general, the FESR is probably the most useful of the CHP plant performanee eriteria as it ean be used direetly in the eeonomie assessment of the plant [1. ... 

There are many gas turbine CHP plants in operation for a range of purposes and applications. Here we describe the salient features of two such plants, each operating with a WHR but also with supplementary firing which can be introduced to meet increased heat demands. 

A) Combined heating and power stations with steam turbines B) Combined heating and power stations with gas turbines C) Combination plant (without supplementary firing) D) Block-type thermal power station with gas engines... 

Finckh, H.H. and Pfost, H. (1992), Development potential of combined cycle [GUD] power plants with and without supplementary firing, ASME J. Engng Power Gas Turbines 114(4), 653-659. 

For the supplementary fired plant of Fig. 9.2b with Aiy = 7.2 and with the parameter tp taken as 1.2, so that Fj = 6, the fuel energy savings ratio is... 

A gas turbine CHP. scheme which operates at Liverpool University, UK, consists of a Centrax 4 MW (nominal) gas turbine with an overall efficiency of about 0.27, exhausting to a WHB. The plant meets a major part of the University s heat load of about 7 MW on a mild winter s day. Supplementary firing of the WHB (to about 15 MW) is possible on a cold day. Provision is al.so made for by-passing the WHB when the heat load is light, in spring and autumn,. so that the plant can operate very flexibly, in three modes viz., power only, recuperative and supplementary firing. 

In the above example, a relatively complex steam generator of the watertube type has been adopted. Where lower-quality steam for process or fuel heating is required, a simpler shell (or firetube) design may be appropriate. In some cases, supplementary firing may be provided for the boiler, so further increasing plant complexity and with it the need for enhanced control and maintenance requirements. 

Refs. [72, 73] are based on the use of Ni- and Fe-based OCs. In Ref. [72], different GT compressor ratios are investigated in order to optimize the performance of the plant. The maximum temperature of the GT is dictated from the maximum temperature acceptable from the solid material in the air reactor. In the study by Wolf [73], a sensitivity analysis is carried out by using an air reactor temperature of 1000 °C and 1200 °C. By increasing the maximum solid temperature, the efficiency increases from around 49% up to 52.4% with a CO2 capture rate of 100%. In the study by Consonni [72], the maximum solid temperature has been varied from 850 to 1050°C with an electrical efficiency of 43-48% and CO2 capture rate of 100% (Figure 5.26). A supplementary natural gas post-firing has been adopted to improve the combined cycle efficiency up to 52.5% (with reduced CO2 capture rate to 54%) by increasing the maximum turbine inlet temperature (TIT). 

Oral communications between the main control room, the supplementary control rooms, other suitable plant locations and ofif-site emergency services are important to safety, particularly under conditions of anticipated operational occurrences or design basis accidents. Such conunuiucations should normally be provided with two, preferably diverse communication Unks and should be electromagneticaUy compatible with the I C systems (self-powered telephones, battery operated telephones, hand held portable radios). These communication links should be routed in such a way that fires, failures of electrical systems or other applicable PlEs cannot incapacitate both systems simultaneously. 

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