Fuel energy saving ratio

A third performance criterion developed for combined heat and power plant involves compari.son between the fuel required to meet the given loads of electricity and heat in the CHP plant with that required in a reference system . The latter involves conventional plants that meet the same load demands (indicated by subscript D), for example, in a conventional electric power station and in a heat only boiler. 

A CHP system meeting the same power and heat demands (I, A ) is shown in Fig. 9.3b it is implied that this cogeneration plant is perfectly matched, delivering the required (I, An) precisely, using a WHR. 

The total fuel energy required in the reference system is 

Chapter 9. The as turbine as a cogeneration (combined heat and power) plant 

MATCHED PLANT WITH WASTE HEAT BOILER 

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The fuel energy savings ratio (FESR) is then defined as the ratio of the saving (AF) to the fuel energy required in the conventional plants,... 

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... 

Figure 19.1 indicates the flue losses to be expected for different temperatures and excess air. It is seen that considerable savings can be made, particularly at higher temperatures, by reducing excess air levels to a practical minimum. It is also evident that a reduction in air/gas ratio to below stoichiometric will cause a rapid deterioration in efficiency caused by the energy remaining in the incomplete combustion of fuel. 

The boiler itself should be very efficient to generate steam and for this preparation of oil, air to fuel ratio, stack temperature of flue gases, conversion of furnace oil to LSHS oil, maximum condensate recovery, cleaning of the fire side, replacement of old boilers etc. are the various important factors to be taken care-of. Factors responsible for optimum consumption of steam such as supply of steam at correct pressure, provision of pressure reducing valves, water separators in steam lines for supply of dry steams at requisite pressure, selection of trap of right type and size for efficient recovery of condensate etc. should be considered for the saving of thermal energy. 

In its energy predictions for 2030, the Finnish National Research Council shows that despite environmental issues the internal combustion engine has been actually saved from obsolescence by changes to the engine itself. These changes include exhaust gas recirculation, multipoint fuel injection, closed-loop air ratio... 

Economics of residential fuel cells is more complex. Here the purchase price must be justified with sufficient savings in expenditures for energy over the lifetime of the power system. One method that may be used to evaluate feasibility of residential fuel cell power systems is a simple payback time. This is simply a ratio between purchase price and annual savings in electricity expenditures. The result suggests to the potential user... 

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