Heating index for combined-cycle

The technique of the analysis of combined-cycle power plants with binarity coefficient which is less than one is offered. The technique enters a heating indicator. The index characterizes warmth anneafling by combined-cycle power plant. Plant is equipped with the steam turbine with heating selection of steam. Plants with afterburning and dual-fuel plants are considered. Interference of again entered index, degrees of binarity, various efficiencies is at each other shown in this article. The heat balance diagrams and the power streams’s integrated charts of combined-cycle plants on the basis of the gas-turbine unit V64.3 are submitted. The calculated quantitative values of an efficiency on power generation on thermal consumption, coefficient of binarity, a heating index, the relative annealing of warmth and other characteristics for some of the actual or being in a stage of the project combined-cycle plants are given.


Introduction
Increasing the efficiency of fuel using in power plants is a relevant problem. One of the ways to increase the energy generation efficiency is using of combined-cycle power plants (CCPP) with binarity coefficient which is less than one. Through this, using of solid fuel in combined-cycle is possible [1][2][3][4]. Binarity coefficient is determined by the following equation: where GTU ; STU , MWenergy supplied to the combined-cycle plant through the combustion chamber of the gas turbine and the steam boiler, respectively. This index characterizes the amount of energy supplied to the installation through the gas turbine relative to the total energy supplied

Combined-cycle power plant with a coal afterburning
In contrast to the gas turbine combustion chamber where gas is burned, for generating steam of high parameters in the steam boiler can be used any type of fuel, including coal. In the combined cycle technology coal is involved with the efficiency of using unattainable in other technologies of energy generation where coal is used.
The thermodynamic feature of a combined-cycle with binarity less than one is described below. Energy is supplied in two places (Figure 1a). The first onethrough the combustion chamber of the gas turbine GTU = gas ) to ensure work of the gas turbine cycle (1-2-3-4-1, Figure 1a). The second onethrough the steam power boiler ( CCPP = coal to ensure high parameters of the generated steam in the steam turbine cycle. The heat flow worked in the gas turbine ( out GTU ) is also transferred to the watersteam circuit through the waste-heat boiler. Useful product in the form of electricity are obtained both IOP Publishing doi:10.1088/1757-899X/1019/1/012012 2 in the gas turbine and in the steam turbine units of the combined cycle. In addition, the steam turbine unit has a heat selection that provides heat supply to the consumer h (Figure 1a).
The technological scheme describing thermodynamic approach is presented in Figure 1b. The air enters the compressor of a gas turbine unit (GTU), is compressed and enters with high pressure into the combustion chamber, where its temperature is increased due to the combustion of gas. After this the hot air and the products of combustion of the fuel enter the gas turbine, where they provide the electricity output ( GTU ). After gas turbine the exhaust gases is sent to a waste-heat boiler (WHB), where it is used to generate steam of average parameters for a steam turbine unit (STU) with power generation ( STU ). At the same time, high parameters of a sharp steam ensure the combustion of fuel (in particular, coal) in a steam boiler (SB), and an additional stream combined with reheating steam (process R-RR, Fig. 1a) and sent to the middle part of the steam turbine unit is generated in the waste heat boiler. Thus, the steam turbine has a wheel space where with steam expansion a flow of steam increases, even if there are bleeds (not shown in Figure 1b). The exhausted steam after the steam turbine enters the condenser (C), where it weeps (process K-K ', Figure 1a) and then is transferred to a waste-heat boiler and a steam boiler by the condensate pump (CP) and the feed-water pump (FWP). The regeneration system on the cycle arrangement is represented by a deaerator. In addition, the steam turbine has heat extraction, steam from which is sent to the heating system (HS) to provide heat supply h to the consumer. The presence of the heat recovery boiler and steam boiler in the thermal scheme, which provide parallel steam generation of high and average parameters, determine the name of the installation, as a parallel-type CCPP [5].
Obviously, the binarity coefficient is less than one (γ <1) provided by the combustion of additional fuel in a steam boiler relative to the combustion chamber of a gas turbine. Such units are called combined-cycle power plants with afterburning of fuel. And units where gas is used as fuel in the combustion chamber of a gas turbine and coal in a steam boiler are called dual-fuel units.
The efficiency of the gas turbine unit of the CCPP can be determined by the following equation: Taking into account the energy conservation law and using the approaches [6], the amount of heat, which is lost in GTU, will be: out GTU = GTU − GTU .
(11) At the same time, the combined-cycle power plants can work not only by electrical but also by thermal load curve ( h > 0). In this case the efficiency of the steam turbine unit is: Therefore Heating degree β characterizes the heat supply by the combined-cycle power plant: Where from after generations Considering that theoretically, in the studied installation 0 < h CCPP  1, the Heating degree β can take the values β <0 (Figure 2). For technically implemented combined-cycle power plants the heating degree β depends on the binary coefficient γ and for plants close to the binary type can take values β > 1. Due to heat flows can be obtained for the needs of heating only in this case (Figure 2a). For plants with a low binary coefficient, in particular for plants with predominant combustion of coal with γ ≤ 0.5, β may take values (Figure 2b, shown by hatching) 0 < β  1.
(22) The relationship between the heating degree (β) and the binary coefficient (γ) of the CCPP is linear and depends on the relative heat supply of the CCPP (the value of the heat extraction). In general, β grows with γ ( Figure 3).
Heating CCPP is characterized by the operation of a steam turbine unit in a heat-extraction mode. It is apparent that with the growth of combined electricity generation, characterized by the efficiency of a steam turbine unit increasing (STU), the heating degree (β) of the CCPP (Figure 4) also grows. At the same time, to ensure high efficiency of the CCPP, should not tend to high  values.
The effect of the gas turbine unit efficiency on the CCPP efficiency is less noticeable than the effect of the heating degree β. The greater the quantity of heat extraction (β grows), the higher the  Figure 5). In general, we can say that for the high thermodynamic efficiency of the dual-fuel CCPP, there is should be a powerful gas turbine unit with a relatively small steam turbine, but at the maximum heat extraction. Questions of economic efficiency are not considered in this paper.

Calculation results
The following are the results of some CCPP schemes calculations with heat extractions (Figures 6-9). During calculations according to the JSC "VTI" and JSC "ENKO-center" schemes it was taken into account that heat is supplied to the consumer after the waste-heat boiler does not enter the steam turbine unit (table 1).
In general, examples of calculations show that the heating degree can be used for the analysis of CCPP with the heat supply to the consumer.