The effectiveness of heat pumps as part of CCGT-190/220 Tyumen CHP-1

The article considers the possibility of increasing the energy efficiency of CCGT-190/220 Tyumen CHP-1 due to the utilization of lowgrade heat given off in the condenser unit of the steam turbine. To assess the effectiveness of the proposed system, the indexes of thermal efficiency are given. As a result of a research the following conclusions are received: The heat-transfer agent heat pump, when heated uses low-grade heat TPP and increases heat output, but consumes the electricity. Using a heat pump is effective for a small temperature difference between the condenser and the evaporator. Good example is heating water before chemical treatment. This method is more efficient than using a replacement boiler and it is used in steam selection.


Introduction
Thermal power plants (TPP) are the main source of heat and electricity in Russia. The natural gas is the main fuel for thermal power plants. The consumption of natural gas will change significantly [1] by 2030 and the share of thermal power plants in Russia will be approximately 67% of the overall total of fossil fuel thermal power plants [2]. Therefore, intensive use of non-renewable sources of energy will determine the need to improve the efficiency of their use. There are many ways to achieve this goal, one of them is to use heat pumps at the power station.
Studies have shown that heat losses of TPP capacitors reach approximately 40 percent in some cases. The one of the possibilities to reduce heat loss is to use combined cycle power plant (CCGT). The data reported calculated potential of 190/220 for improving efficiency of CCGT with the use of heat pumps.
There is alsouse of chimney which allows separate operations of gas turbine power plant (GTPP) and a steam turbine power plant (STPP) in the arrangement of CCGT-190/220 ( Figure 1) [4].

Materials and Methods
The following method of calculation of thermal balance ( Figure 2) was applied to the study [5].

Fig.2.The heat balance of combined-cycle plant
The heat of the fuel supplied to the working fluid in the cycle CCGT, MW: (1) Where: pc Q -consumption of heat in the CCGT, perceived in the steam cycle of the products of combustion, MW: Where: -consumption of fuel in the steam and gas parts of combined-cycle plant, kg / s;  Additional production of thermal energy and the power consumption in the compressor is calculated as follows [6]:  (13) To determine the degree of the influence on temperature difference and the main indicator of the efficiency of heat pumps (the coefficient of performance), we calculated the characteristics of heat pump for the heat pump with a compressor on the same shaft as the PSU, intercooled and subcooler [7]. As a working agents, the R134a, R152a, R600 and R600a.were selected.
Initial data for the calculation of the heat pump is shown ( The heat generation / electric output ratio can be considered as a reverse value of electric / heat output ratio (equivalent of the conversion ratio of heat pumps) [8,9]: Where: -enthalpy of steam input and enthalpy of water leaving network heater, kj/kg ℃;

Results
According to the method we listed above we were in compliance with thermal balance and were able to calculate the efficiency of the existing CCGT -190/220.
The source of low-grade heat is a water cooling system. However, we reject the tower in this case, because capacitor plays a role of the evaporator of heat pump.
The main impact on efficiency of the thermal pump is exerted by a difference in temperatures of evaporation and condensation of Freon. Therefore, it depends on temperature of the low-potential heat carrier after the thermal pump and temperature of the high-potential heat carrier (hot water) at the exit from the thermal pump. The results indicate that the COP of a heat pump mainly depends on the temperature difference between the receiver and the source of heat, and the type of working fluid to a small degree.
The dependence of COP of a heat pump's temperature difference between the evaporator and condenser for Freon can be expressed by the formula: The results of calculation of CCGT efficiency with heat pump for heating water for domestic hot water (DHW), and before the chemical water treatment are presented in Table  2.  Using the heat pump is most effective when small temperature difference occurs between the condenser and evaporator.
We estimated a ratio of under produced electrical energy and generated thermal energy of unit CCGT-190/220.
When comparing the COP of a heat pump and the underproduction of generated thermal energy, we can conclude that the use of the heat pump is more efficient than the use of steam extraction and vice versa [10].
The steam consumption in CCGT-190/220 condenser is 56.19 kg / s, the absolute pressure in turbine condenser is 0.063 kgf / cm2, and the loss of heat in the steam turbine condenser is 35.4 MW. This thermal energy can be used for various purposes: to heat water before chemical water treatment, replace the regenerative heating, heating hot water for one's own needs, and to heat the coolant for third-party users [11][12][13]. For water purification it is necessary to heat the water from 10 to 30 0C, and for DHW from 5 to 650 0C.
This method allows comparison of efficiency of the heat pump and steam extraction for heating water CHP. Table 3. Options for the use of heat pumps to the power station.

Options
Chemical water treatment DHW The temperature difference in the evaporator and condenser 25 70 The coefficient of performance 7.55 3.31 Enthalpy of steam input network heater, kj/kg; 2539 Enthalpy of water leaving network heater, kj/kg; 267.9 The enthalpy of steam in the condenser of the steam turbine 2282.7 Internal relative, mechanical and electrical efficiencies of the steam turbine 0.833 Underproduction of the electric power of to generated thermal energy 10.64 Comparison of the COP of heat pump and underproduction of to generated thermal energy 3.083 7.3 Overall, Table 3shows that for the chemical water treatment it is more efficient to use heat pumps.

Discussion
This method allows comparison of efficiency of the heat pump and steam extraction for heating water CHP, but it does not consider the possibility of thermal or electric energy from the replacement's source.
We consider two options for water heating for DHW [8,9]: 1 -Electricity generation replacement IES spent on a heat pump (CCGT with a heat pump + IES); 2 -Generated heat development in the boiler room (CCGT with waste heat boiler). Under generation electricity in the comparison version is the cost of electricity in the compressor of the heat pump -15.19 MW. As a source of electrical energy used PGU-IES. Usually, such plants have about 50-52% efficiency.
In the case of CCGT with boiler, heat generation will be Qtnu -51.49 MW. Then additional flow of heat in the boiler will be The difference between the total cost of fuel options under consideration is 24.03 MW and shows savings (deficit) of one embodiment of fuel in relation to another. The use of this criterion allows us to objectively identify strengths of matched types of thermal circuits cogeneration plant with heat pump, without the use of fuel dividing methods and type of energy produced.
Using heat pumps for chemical water treatment is most effective when considering the heat balance of PSU. But the use of heat pumps for heating the heat transfer medium to higher temperatures as effective when considering a substitute source of heat and electrical energy.

Conclusions
The heat-transfer agent heat pump, when heated uses low-grade heat TPP and increases heat output, but consumes the electricity. Using a heat pump is effective for a small temperature difference between the condenser and the evaporator. Good example is heating water before chemical treatment. This method is more efficient than using a replacement boiler and it is used in steam selection. Further study assumes economic кationale use this technology to calculate capital costs and payback periods.