Topic: Calculation of the thermal scheme of a geothermal power plant
The geothermal power plant consists of two turbines:
the first one works on saturated water vapor obtained in an expansion
body. Electric power - N ePT = 3 MW;
the second - works on saturated steam of freon - R11, which is used
ryatsya due to the heat of the water removed from the expander. Electrical
power - N eHT, MW.
Water from geothermal wells with temperature t gv = 175 °С post-
goes into the expander. The expander generates dry saturated steam with
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25 degrees cooler t guards This steam is sent to the lane
turbine. The remaining water from the expander goes to the evaporator, where
cooled by 60 degrees and pumped back into the well. Not good-
roar in the evaporation plant - 20 degrees. Working bodies expand -
in the turbines and enter the condensers, where they are cooled by water from
rivers with temperature t xv \u003d 5 ° С. The water heating in the condenser is
10 ºС, and undercooling to saturation temperature 5 ºС.
Relative internal turbine efficiencies ç oi= 0.8. Electromechanical
cal efficiency of turbogenerators çem = 0.95 .
Define:
electric power of the turbine operating on freon - N eChT and
total capacity of GeoTPP;
consumption of working fluids for both turbines;
water flow from the well;
Efficiency of GeoTPP.
Take the initial data from Table 3 according to the options.
Table 3
Initial data for task No. 3
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EXITS
3. Determine the enthalpies at characteristic points:
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4. We calculate the available heat drop in the turbine:
fri fri
5. We find the actual heat drop in the turbine:
NiPT =NIPT ⋅ç oi = 744,6 ⋅ 0,8 = 595,7kJ /kg .
6. Consumption of steam (water from a geothermal well) for water
turbine is found by the formula:
DoPT =
NiPT ⋅ç Em
5,3kg /with .
7. Water flow from the geothermal well to the evaporator and
the entire GeoTPP in general is found from the system of equations:
PT ISP
Solving this system, we find:
7.1 water flow from the geothermal well to the evaporator:
hHW −hp
2745,9 − 733,25
733,25 − 632, 25
7.2 water flow from a geothermal well in general
DGV = 5,3 + 105,6 = 110,9kg /with .
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8. Freon consumption in the second turbine is found from the heat equation
balance sheet:
ISP OUT XT XT
where ç and= 0.98 - Evaporator efficiency.
⋅ç and ⋅
hp −hout
105,6 ⋅ 0,98 ⋅
632,25 − 376,97
114,4kg /with .
9. The electric power of the second turbine, which runs on cooling
Done, is determined by the formula:
where HiXT = (hp −h XT)ç oi- actual heat drop second
XT XT T
10. The total electrical power of the GeoTPP will be equal to:
GeoTES HT
11. Let's find the efficiency factor of GeoTPP:
ç GeoTPP
GeoTPP
D −h
⎜ ⎜D
N eGeoTPP
⎛ ⎛ 5,3 105,6 ⎞ ⎞
⎝ 110,9 110,9 ⎠ ⎠
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CALCULATION OF A GEOTHERMAL POWER PLANT
We will calculate the thermal scheme of a binary type geothermal power plant, according to.
Our geothermal power plant consists of two turbines:
The first works on saturated water vapor obtained in the expander. Electric power - ;
The second one works on saturated steam of R11 freon, which evaporates due to the heat of water removed from the expander.
Water from geothermal wells with pressure pgw and temperature tgw enters the expander. The expander generates dry saturated steam at a pressure of pp. This steam is sent to a steam turbine. The remaining water from the expander goes to the evaporator, where it cools down and ends up back into the well. Temperature difference in the evaporation plant = 20°C. The working fluids expand in the turbines and enter the condensers, where they are cooled by water from the river with a temperature txw. Water heating in the condenser = 10°C, and subcooling to saturation temperature = 5°C.
Relative internal efficiency of turbines. Electromechanical efficiency of turbogenerators = 0.95.
Initial data are given in Table 3.1.
Tab. 3.1. Initial data for GeoPP calculation
Schematic diagram of GeoPP of binary type (Fig. 3.2).
Rice. 3.2.
According to the diagram in Fig. 3.2 and the initial data we carry out calculations.
Calculation of the scheme of a steam turbine operating on dry saturated steam
Steam temperature at the turbine condenser inlet:
where is the temperature of the cooling water at the condenser inlet; - water heating in the condenser; is the temperature difference in the condenser.
The steam pressure in the turbine condenser is determined from the tables of properties of water and steam:
Available heat drop to the turbine:
where is the enthalpy of dry saturated steam at the turbine inlet; - enthalpy at the end of the theoretical steam expansion process in the turbine.
Steam flow from expander to steam turbine:
where is the relative internal steam efficiency turbines; - electromechanical efficiency of turbogenerators.
Geo Expander Calculation thermal water
The equation heat balance expander
where is the flow rate of geothermal water from the well; - enthalpy of geothermal water from the well; - water flow from the expander to the evaporator; - enthalpy of geothermal water at the outlet of the expander. It is determined from the tables of properties of water and water vapor as the enthalpy of boiling water.
Expander Material Balance Equation
By solving these two equations together, it is necessary to determine and.
The temperature of geothermal water at the outlet of the expander is determined from the tables of properties of water and water vapor as the saturation temperature at the pressure in the expander:
Determination of parameters at characteristic points of the thermal circuit of a turbine operating in freon
Freon vapor temperature at the turbine inlet:
Freon vapor temperature at the turbine outlet:
The enthalpy of freon vapor at the turbine inlet is determined by p-h diagram for freon on the saturation line at:
240 kJ/kg.
The enthalpy of freon vapor at the outlet of the turbine is determined from the p-h diagram for freon at the intersection of the lines and the temperature line:
220 kJ/kg.
The enthalpy of boiling freon at the outlet of the condenser is determined from the p-h diagram for freon on the curve for boiling liquid by temperature:
215 kJ/kg.
Evaporator calculation
Temperature of geothermal water at the outlet of the evaporator:
Evaporator heat balance equation:
where is the heat capacity of water. Accept = 4.2 kJ / kg.
From this equation it is necessary to determine.
Calculation of the power of a turbine operating on freon
where is the relative internal efficiency of the freon turbine; - electromechanical efficiency of turbogenerators.
Determining the power of the pump for pumping geothermal water into the well
where - pump efficiency, 0.8 is accepted; - average specific volume of geothermal water.
Practice #6
Target: get acquainted with the principle of operation of GeoTPP and ocean thermal energy conversion technologies (OTEC), as well as with the methodology for their calculation.
Lesson duration- 2 hours
Working process:
1. On the basis of the theoretical part of the work, get acquainted with the principle of operation of the GeoTPP and the technologies for converting the thermal energy of the ocean (PTEC.
2. In accordance with the individual task, solve practical problems.
1. THEORETICAL PART
Use of ocean thermal energy
Ocean thermal energy conversion technology (OTEC) generates electricity from the temperature difference between warm and cold ocean water. Cold water is pumped through a pipe from a depth of more than 1000 meters (from a place where the sun's rays never reach). The system also uses warm water from an area close to the surface of the ocean. heated sunbeams The water passes through a heat exchanger with low boiling point chemicals such as ammonia, which creates a chemical vapor that drives the turbines of power generators. The vapor is then condensed back into liquid form using chilled water from the deep ocean. Tropical regions are considered to be the best place to place PTEC systems. This is due to the greater temperature difference between water in shallow water and at depth.
Unlike wind and solar farms, ocean thermal power plants can produce clean electricity around the clock, 365 days a year. The only by-product of such power units is cold water, which can be used for cooling and air conditioning in administrative and residential buildings near the power generating facility.
Usage geothermal energy
Geothermal energy is energy derived from the natural heat of the earth. This heat can be achieved with the help of wells. The geothermal gradient in the well increases by 1°C every 36 meters. This heat is delivered to the surface in the form of steam or hot water. Such heat can be used both directly for heating houses and buildings, and for the production of electricity.
According to various estimates, the temperature at the center of the Earth is at least 6650 °C. The rate of cooling of the Earth is approximately equal to 300-350 ° C per billion years. The earth emits 42·10 12 W of heat, of which 2% is absorbed in the crust and 98% in the mantle and core. Modern technology does not allow reaching heat that is released too deeply, but even 840000000000 W (2%) of available geothermal energy can provide the needs of mankind for a long time. Areas around the edges of the continental plates are the best place to build geothermal plants because the crust in such areas is much thinner.
There are several ways to get energy at GeoTPP:
· Direct scheme: steam is sent through pipes to turbines connected to electric generators;
· Indirect circuit: similar to the direct circuit, but before entering the pipes, the steam is cleaned of gases that cause the destruction of the pipes;
· Mixed circuit: similar to the direct circuit, but after condensation, gases that have not dissolved in it are removed from the water.
2. PRACTICAL PART
Task 1. Determine starting temperature t2 and amount of geothermal energy E o (J) aquifer thickness h km at depth z km, if the characteristics of the reservoir rock are given: density p gr \u003d 2700 kg / m 3; porosity a = 5 %; specific heat C gr =840 J/(kg K). temperature gradient (dT/dz) in °C / km, select according to the table of task options.
Average surface temperature t o take equal to 10 °C. Specific heat capacity of water From to = 4200 J/(kg K); density of water ρ \u003d 1 10 3 kg / m 3. Calculate with respect to surface area F \u003d 1 km 2. The minimum allowable formation temperature is taken equal to t1=40 ° C.
Determine also the time constant of extraction of thermal energy o (years) when water is injected into the reservoir and its consumption V \u003d 0.1 m 3 / (s km 2). What will be the thermal power extracted initially (dE/dz) τ =0 and after 10 years (dE/dz) τ =10?
Task 1 is devoted to the thermal potential of geothermal energy concentrated in natural aquifers at a depth z (km) from earth's surface. Typically aquifer thickness h (km) less depth its occurrence. The layer has a porous structure - rocks have pores filled with water (porosity is estimated by the coefficient α). Average density hard rock earth's crust p gr \u003d 2700 kg / m 3, and the coefficient of thermal conductivity λ gr \u003d 2 W / (m K). The change in ground temperature towards the earth's surface is characterized by a temperature gradient (dT/dz), measured in °C/km or K/km.
The most common on the globe are areas with a normal temperature gradient (less than 40 ° C / km) with a density of heat fluxes outgoing towards the surface of ≈ 0.06 W / m 2. The economic feasibility of extracting heat from the bowels of the Earth is unlikely here.
In semi-thermal areas, the temperature gradient is 40-80 °C/km. Here it is advisable to use the heat of the bowels for heating, in greenhouses, in balneology.
In hyperthermal areas (near the boundaries of the platforms of the earth's crust) the gradient is more than 80 °C/km. It is expedient to build a GeoTPP here.
With a known temperature gradient, it is possible to determine the temperature of the aquifer before the start of its operation:
T g \u003d T o + (dT / dz) z,
where T o is the temperature on the Earth's surface, K (° C).
In calculation practice, the characteristics of geothermal energy are usually referred to 1 km 2 of the surface F.
The heat capacity of the reservoir C pl (J / K) can be determined by the equation
C pl \u003d [α ρ in C in + (1- α) ρ gr C gr ] h F,
where p in and C in are, respectively, the density and isobaric specific heat
p gr and C gr - density and specific heat capacity of the soil (formation rocks); usually p gr \u003d 820-850 J / (kg K).
If you set the minimum allowable temperature at which you can use thermal energy reservoir T 1 (K), then it is possible to estimate its thermal potential by the beginning of operation (J):
E 0 \u003d C pl (T 2 -T 1)
The time constant of the reservoir τ 0 (possible time of its use, years) in the case of removal of thermal energy by pumping water into it with a volumetric flow rate V (m 3 / s) can be determined by the equation:
τ 0 \u003d C pl / (V ρ in C in)
It is believed that the thermal potential of the reservoir during its development changes according to the exponential law:
E=E 0 e -(τ / τ o)
where τ is the number of years since the start of operation;
e is the base of natural logarithms.
Thermal power of a geothermal reservoir at time τ (years from the start of development) in W (MW):
Task 2 It is believed that the actual efficiency η oceanic thermal power plant, using the temperature difference of surface and deep waters (T 1 -T 2) = ∆T and operating according to the Rankine cycle, is half the thermal efficiency of the plant operating according to the Carnot cycle, η t k . Estimate the possible value of the actual efficiency of the OTES, the working fluid of which is ammonia, if the water temperature on the ocean surface t , °С, and the water temperature at the depth of the ocean t2 , °С. What expense warm water V , m/h will be required for OTES with a capacity of N MW?
Task 2 is devoted to the prospects of using the temperature difference between the surface and deep ocean waters to generate electricity at the OTES operating according to the well-known Rankine cycle. As a working fluid, the use of low-boiling substances (ammonia, freon) is supposed. Due to small temperature differences (∆T=15÷26 o C), the thermal efficiency of a plant operating according to the Carnot cycle is only 5-9%. The real efficiency of a plant operating on the Rankine cycle will be half that. As a result, in order to obtain a share of relatively small capacities at OTES, large consumptions of "warm" and "cold" water are required and, consequently, huge diameters of inlet and outlet pipelines.
Q 0 =p V C p ∆T,
where p is the density sea water, kg / m 3;
C p - mass heat capacity of sea water, J / (kg K);
V - volumetric water flow, m 3 / s;
∆T \u003d T 1 -T 2 - temperature difference between surface and deep waters
(cycle temperature difference) in °C or K.
In an ideal theoretical Carnot cycle, the mechanical power N 0 (W) can be defined as
N 0 \u003d η t k Q o,
or taking into account (1) and the expression for the thermal efficiency of the Carnot cycle η t k:
N 0 \u003d p C p V (∆T) 2 /T 1.
Task 3 Double-circuit steam-water geothermal power plant with electric power N receives heat from water from geothermal wells with a temperature t gs . Dry saturated steam at the outlet of the steam generator has a temperature 20 0 C lower than t gs . The steam expands in the turbine and enters the condenser, where it is cooled by water from environment with temperature t xv . The cooling water is heated in the condenser by 12 0 C. The condensate has a temperature 20 0 C higher than t xv . Geothermal water leaves the steam generating plant at a temperature 15 0 C higher than the condensate. Relative turbine internal coefficient η oi , electrical efficiency of the turbogenerator η e =0.96. Determine the thermal efficiency of the Rankine cycle, steam flow and specific consumption heat, water flow from geothermal wells and from the environment.
In a single-circuit steam turbine GeoTEP, the enthalpy of dry saturated steam after separation is determined by the temperature of geothermal water t gw. From tables of thermodynamic properties of water and water vapor or h-s diagrams. In the case of a double-circuit GeoTEU, the temperature difference in the steam generator Δt is taken into account. Otherwise, the calculation is carried out as for a solar steam turbine TPP.
Steam consumption is determined from the ratio
kg/s,
where η t is the thermal efficiency of the cycle,
η оі - Relative internal efficiency of the turbine,
η e is the electric efficiency of the turbogenerator,
N is the power of the GeoTEU, kW,
The flow rate of hot water from geothermal wells is determined from the formula
, kg/s,
consumption cold water from the environment to steam condensation
, kg/s,
where c = 4.19 kJ/kg∙K is the heat capacity of water,
η pg is the efficiency of the steam generator,
Δt pg – temperature difference of geothermal water in the steam generator, 0 С,
Δt xv - temperature drop of cold water in the condenser, 0 C.
The calculation of GeoTEU with low-boiling and mixed working fluids is carried out using tables of thermodynamic properties and h-s diagrams of the vapors of these liquids.
| Quantities and their units | Task options | |||||||||
| N, MW | ||||||||||
| t min., 0 С | ||||||||||
| t min., 0 С | ||||||||||
| η oi , % |
geothermal energy
Abstract.
Introduction.
The cost of electricity generated by geothermal power plants.
Bibliography.
Abstract.
This paper presents the history of the development of geothermal energy, both throughout the world and in our country, Russia. An analysis was made of the use of the deep heat of the Earth to convert it into electrical energy, as well as to provide cities and towns with heat and hot water in such regions of our country as Kamchatka, Sakhalin, and the North Caucasus. An economic justification for the development of geothermal deposits, the construction of power plants and their payback periods have been made. Comparing the energies of geothermal sources with other types of electricity sources, we obtain the prospects for the development of geothermal energy, which should take important place in the overall balance of energy use. In particular, for the restructuring and re-equipment of the power industry of the Kamchatka region and the Kuril Islands, partly Primorye and the North Caucasus, one should use their own geothermal resources.
Introduction.
The main directions for the development of generating capacities in the country's energy sector in the near future are the technical re-equipment and reconstruction of power plants, as well as the commissioning of new generating capacities. First of all, this is the construction of combined cycle plants with an efficiency of 5560%, which will increase the efficiency of existing thermal power plants by 2540%. The next stage should be the construction of thermal power plants using new technologies for burning solid fuels and with supercritical steam parameters to achieve an efficiency factor of TPPs equal to 46-48%. Nuclear power plants with new types of thermal and fast neutron reactors will also be further developed.
An important place in the formation of the Russian energy sector is occupied by the country's heat supply sector, which is the largest in terms of the volume of consumed energy resources, more than 45% of their total consumption. District heating systems (DH) produce more than 71%, and decentralized sources produce about 29% of all heat. More than 34% of all heat is supplied by power plants, approximately 50% by boilers. In accordance with the energy strategy of Russia until 2020. it is planned to increase heat consumption in the country by at least 1.3 times, and the share of decentralized heat supply will increase from 28.6% in 2000 to up to 33% in 2020
The increase in prices that has occurred in recent years for fossil fuels (gas, fuel oil, diesel fuel) and its transportation to remote regions of Russia and, accordingly, the objective increase in selling prices for electrical and thermal energy fundamentally change the attitude towards the use of renewable energy sources: geothermal, wind, solar.
Thus, the development of geothermal energy in certain regions of the country already makes it possible today to solve the problem of electricity and heat supply, in particular in Kamchatka, the Kuril Islands, as well as in the North Caucasus, in certain regions of Siberia and the European part of Russia.
Among the main directions for improving and developing heat supply systems should be the expansion of the use of local non-traditional renewable energy sources and, first of all, geothermal heat earth. Already in the next 7-10 years with the help of modern technologies local heat supply thanks to thermal heat, significant fossil fuel resources can be saved.
In the last decade, the use of non-traditional renewable energy sources (NRES) has experienced a real boom in the world. The scale of application of these sources has increased several times. This direction is developing most intensively in comparison with other areas of energy. There are several reasons for this phenomenon. First of all, it is obvious that the era of cheap traditional energy carriers has irrevocably ended. In this area, there is only one trend - the rise in prices for all their types. No less significant is the desire of many countries deprived of their fuel base for energy independence. Environmental considerations, including the emission of harmful gases, play a significant role. Active moral support for the use of renewable energy is provided by the population of developed countries.
For these reasons, the development of renewable energy in many states is a priority task of technical policy in the field of energy. In a number of countries, this policy is implemented through the adopted legislative and regulatory framework, which establishes the legal, economic and organizational foundations for the use of renewable energy. In particular, the economic foundations consist in various measures to support renewable energy at the stage of their development of the energy market (tax and credit benefits, direct subsidies, etc.)
In Russia practical use RES significantly lags behind the leading countries. There is no legislative or normative base as well as state economic support. All this makes it extremely difficult to practice in this area. The main reason for the inhibitory factors is the protracted economic trouble in the country and, as a result, difficulties with investments, low solvent demand, lack of funds for the necessary developments. However, some work and practical measures for the use of renewable energy in our country are being carried out (geothermal energy). Steam-hydrothermal deposits in Russia are available only in Kamchatka and the Kuril Islands. Therefore, geothermal energy cannot take a significant place in the energy sector of the country as a whole in the future. However, it is able to radically and on the most economic basis solve the problem of energy supply to these regions, which use expensive imported fuel (fuel oil, coal, diesel fuel) and are on the verge of an energy crisis. The potential of steam-hydrothermal deposits in Kamchatka is able to provide different sources from 1000 to 2000 MW installed electrical power which greatly exceeds the needs of this region for the foreseeable future. Thus, there are real prospects for the development of geothermal energy here.
The history of the development of geothermal energy.
Along with huge resources of fossil fuels, Russia has significant reserves of the earth's heat, which can be multiplied by geothermal sources located at a depth of 300 to 2500 m, mainly in the fault zones of the earth's crust.
The territory of Russia is well explored, and today the main resources of the earth's heat are known, which have significant industrial potential, including energy. Moreover, almost everywhere there are reserves of heat with a temperature of 30 to 200°C.
Back in 1983 in VSEGINGEO an atlas of the resources of thermal waters of the USSR was compiled. In our country, 47 geothermal deposits have been explored with reserves of thermal waters, which allow you to get more than 240 10³ m³ / day. Today in Russia specialists from almost 50 scientific organizations deal with the problems of using the heat of the earth.
More than 3,000 wells have been drilled to use geothermal resources. The cost of geothermal research and drilling work already carried out in this area, in modern prices is more than 4 billion. dollars. So in Kamchatka, 365 wells have already been drilled in geothermal fields with a depth of 225 to 2266 m and spent (back in Soviet times) about 300 million cubic meters. dollars (in current prices).
The operation of the first geothermal power plant was started in Italy in 1904. The first geothermal power plant in Kamchatka, and the first in the USSR, the Pauzhetskaya Geothermal Power Plant was put into operation in 1967. and had a power of 5 mW, subsequently increased to 11 mW. New impetus for development geothermal energy in Kamchatka was attached in the 90s with the advent of organizations and firms (JSC Geoterm, JSC Intergeotherm, JSC Nauka), which, in cooperation with industry (primarily with the Kaluga Turbine Plant), developed new progressive schemes, technologies and types of geothermal-to-electrical energy conversion equipment and secured a loan from the European Bank for Reconstruction and Development. As a result, in 1999 Verkhne-Mutnovskaya GeoTPP (three modules of 4 MW each) was put into operation in Kamchatka. The first block of 25mW is introduced. the first stage of the Mutnovskaya GeoTPP with a total capacity of 50 MW.
The second phase with a capacity of 100 MW can be commissioned in 2004
Thus, the immediate and quite real prospects for geothermal energy in Kamchatka have been determined, which is a positive undoubted example of the use of renewable energy in Russia, despite the serious economic difficulties in the country. The potential of steam-hydrothermal fields in Kamchatka is capable of providing 1000 MW of installed electric power, which significantly covers the needs of this region for the foreseeable future.
According to the Institute of Volcanology, Far Eastern Branch of the Russian Academy of Sciences, the already identified geothermal resources make it possible to fully provide Kamchatka with electricity and heat for more than 100 years. Along with the high-temperature Mutnovskoye field with a capacity of 300 MW(e) in the south of Kamchatka, significant reserves of geothermal resources are known at the Koshelevskoye, Bolshe Bannoy, and in the north at the Kireunskoye deposits. Heat reserves of geothermal waters in Kamchatka are estimated at 5000 MW (t).
Chukotka also has significant reserves of geothermal heat (on the border with the Kamchatka region), some of them have already been discovered and can be actively used for nearby cities and towns.
The Kuril Islands are also rich in the reserves of the earth's heat, they are quite enough to supply heat and electricity to this territory for 100,200 years. Reserves of a two-phase geothermal coolant have been discovered on Iturup Island, with a capacity (30 MW(e)) sufficient to meet the energy needs of the entire island in the next 100 years. Here, wells have already been drilled at the Ocean geothermal field and a GeoPP is being built. There are reserves of geothermal heat on the southern island of Kunashir, which are already being used to generate electricity and heat supply to the city of Yuzhno Kurilsk. The bowels of the northern island of Paramushir are less studied, but it is known that this island also has significant reserves of geothermal water with a temperature of 70 to 95 ° C, and a GeoTS with a capacity of 20 MW (t) is also being built here.
The deposits of thermal waters with a temperature of 100-200°C are much more widespread. At this temperature, it is advisable to use low-boiling working fluids in the steam turbine cycle. The use of double-circuit Geothermal power plants on thermal water is possible in a number of regions of Russia, primarily in the North Caucasus. Geothermal deposits with a reservoir temperature of 70 to 180°C, which are located at a depth of 300 to 5000 m, are well studied here. Geothermal water has been used here for a long time for heat supply and hot water supply. In Dagestan, more than 6 million m of geothermal water is produced annually. About 500 thousand people in the North Caucasus use geothermal water supply.
Primorye, the Baikal region, the West Siberian region also have reserves of geothermal heat suitable for large-scale use in industry and agriculture.
Conversion of geothermal energy into electrical and thermal energy.
One of the promising areas for using the heat of highly mineralized underground thermal waters is converting it into electrical energy. For this purpose, a technological scheme was developed for the construction of a Geothermal power plant, consisting of a geothermal circulation system (GCS) and a steam turbine plant (STP), the scheme of which is shown in Fig.1. Distinctive feature Such a technological scheme from the well-known is that in it the role of an evaporator and a superheater is performed by a downhole vertical counterflow heat exchanger located in the upper part of the injection well, where produced high-temperature thermal water is supplied through the surface pipeline, which, after transferring heat to the secondary coolant, is pumped back into the formation. The secondary coolant from the condenser of the steam turbine plant enters the heating zone by gravity through a pipe lowered inside the heat exchanger to the bottom.
The Rankine cycle is at the heart of the work of vocational schools; t,s is a diagram of this cycle and the nature of the change in the temperatures of heat carriers in the evaporator heat exchanger.
The most important point in the construction of GeoTPP is the choice of the working fluid in the secondary circuit. The working fluid selected for a geothermal installation must have favorable chemical, physical and operational properties under given operating conditions, i.e. be stable, non-flammable, explosion-proof, non-toxic, inert to structural materials and cheap. It is desirable to choose a working fluid with a lower coefficient of dynamic viscosity (less hydraulic losses) and with a higher thermal conductivity (improves heat transfer).
It is practically impossible to fulfill all these requirements at the same time, therefore, it is always necessary to optimize the choice of one or another working fluid.
Low initial parameters of working bodies of geothermal power plants lead to the search for low-boiling working fluids with a negative curvature of the right boundary curve in the t, s diagram, since the use of water and steam leads in this case to a deterioration in thermodynamic performance and to a sharp increase in the dimensions of steam turbine plants, which significantly increases their cost.
It is proposed to use a mixture of isobutane + isopentane in the supercritical state as a supercritical agent in the secondary circuit of binary energy cycles. The use of supercritical mixtures is convenient because the critical properties, i.e. the critical temperature tc(x), the critical pressure pc(x) and the critical density qc(x) depend on the composition of the mixture x. This will allow, by selecting the composition of the mixture, to select a supercritical agent with the most favorable critical parameters for the corresponding temperature of the thermal water of a particular geothermal field.
As a secondary coolant, a low-boiling hydrocarbon isobutane is used, the thermodynamic parameters of which correspond to the required conditions. Critical parameters of isobutane: tc = 134.69°C; pk = 3.629 MPa; qk = 225.5 kg/m³. In addition, the choice of isobutane as a secondary coolant is due to its relatively low cost and environmental friendliness (unlike freons). Isobutane as a working fluid has found wide distribution abroad, and it is also proposed to use it in a supercritical state in binary geothermal energy cycles.
The energy characteristics of the installation are calculated for a wide range of temperatures of produced water and various modes of its operation. In all cases, it was assumed that the condensation temperature of isobutane tcon =30°C.
The question arises about the choice of the smallest temperature differenceêtfig.2. On the one hand, a decrease in êt leads to an increase in the surface of the evaporator heat exchanger, which may not be economically justified. On the other hand, an increase in êt at a given temperature of thermal water ts leads to the need to lower the evaporation temperature ts (and, consequently, the pressure), which will negatively affect the cycle efficiency. In most practical cases, it is recommended to take êt = 10÷25ºС.
The obtained results show that there are optimal operating parameters of the steam power plant, which depend on the temperature of the water entering the primary circuit of the heat exchanger steam generator. With an increase in the evaporation temperature of isobutane tz, the power N generated by the turbine increases by 1 kg/s of the secondary coolant consumption. At the same time, as tg increases, the amount of evaporated isobutane decreases per 1 kg/s of thermal water consumption.
As the temperature of thermal water increases, the optimum evaporation temperature also increases.
Figure 3 shows the graphs of the dependence of the power N generated by the turbine on the evaporation temperature ts of the secondary coolant at various temperatures of thermal water.
For high-temperature water (tt = 180ºС), supercritical cycles are considered, when the initial vapor pressure pн= 3.8; 4.0; 4.2; and 5.0 MPa. Of these, the most effective in terms of obtaining maximum power is the supercritical cycle, close to the so-called "triangular" cycle with an initial pressure pn = 5.0 MPa. During this cycle, due to the minimum temperature difference between the heat carrier and the working fluid, the temperature potential of thermal water is used to the fullest extent. Comparison of this cycle with the subcritical one (pn=3.4MPa) shows that the power generated by the turbine during the supercritical cycle increases by 11%, the flow density of the substance entering the turbine is 1.7 times higher than in the cycle with pn=3 ,4 MPa, which will lead to an improvement in the transport properties of the coolant and a reduction in the size of the equipment (supply pipelines and turbine) of the steam turbine plant. In addition, in the cycle with pH = 5.0 MPa, the temperature of the waste thermal water t, injected back into the reservoir, is 42ºС, while in the subcritical cycle with pH = 3.4 MPa, the temperature tн = 55ºС.
At the same time, an increase in the initial pressure to 5.0 MPa in the supercritical cycle affects the cost of the equipment, in particular, the cost of the turbine. Although the dimensions of the flow path of the turbine decrease with increasing pressure, the number of turbine stages simultaneously increases, a more developed end seal is required, and, most importantly, the thickness of the casing walls increases.
To create a supercritical cycle in the technological scheme of GeoTPP, it is necessary to install a pump on the pipeline connecting the condenser with the heat exchanger.
However, factors such as the increase in power, the reduction in the size of the supply pipelines and the turbine, and the more complete actuation of the thermal potential of thermal water, speak in favor of the supercritical cycle.
In the future, it is necessary to look for coolants with a lower critical temperature, which will make it possible to create supercritical cycles using thermal waters with a lower temperature, since the thermal potential of the vast majority of explored deposits in Russia does not exceed 100÷120ºС. In this regard, the most promising is R13B1(trifluorobromomethane) with the following critical parameters: tk = 66.9ºС; pk = 3.946 MPa; qk= 770kg/m³.
The results of evaluation calculations show that the use of thermal water with a temperature of tk = 120ºС in the primary circuit of the GeoTPP and the creation of a supercritical cycle with an initial pressure of pn = 5.0 MPa in the secondary circuit on freon R13B1 also makes it possible to increase the turbine power up to 14% compared to the subcritical cycle with initial pressure pn = 3.5 MPa.
For the successful operation of the GeoTPP, it is necessary to solve the problems associated with the occurrence of corrosion and salt deposits, which, as a rule, are aggravated with an increase in the mineralization of thermal water. The most intense salt deposits are formed due to the degassing of thermal water and the disruption of carbon dioxide balance as a result of this.
In the proposed technological scheme, the primary coolant circulates in a closed circuit: reservoir - production well - surface pipeline - pump - injection well - reservoir, where conditions for water degassing are minimized. At the same time, it is necessary to adhere to such thermobaric conditions in the surface part of the primary circuit, which prevent degassing and precipitation of carbonate deposits (depending on temperature and salinity, the pressure must be maintained at 1.5 MPa and above).
A decrease in the temperature of thermal water also leads to precipitation of non-carbonate salts, which was confirmed by studies conducted at the Kayasulinsky geothermal site. Part of the precipitated salts will be deposited on the inner surface of the injection well, and the bulk will be carried to the bottomhole zone. The deposition of salts at the bottom of the injection well will contribute to a decrease in injectivity and a gradual decrease in the circular flow rate, up to a complete stop of the GCS.
To prevent corrosion and scaling in the GCS circuit, an effective HEDPK (hydroxyethylidene diphosphonic acid) reagent can be used, which has a long-term anti-corrosion and anti-scale effect of surface passivation. Restoration of the passivating layer of OEDFK is carried out by periodically pulsed injection of a reagent solution into thermal water at the mouth of a production well.
To dissolve the salt sludge that will accumulate in the bottomhole zone, and therefore to restore the injectivity of the injection well, a very effective reagent is NMA (concentrate of low molecular weight acids), which can also be introduced periodically into the circulating thermal water in the area before the injection pump.
Therefore, from the above, it can be suggested that one of the promising directions for the development of the thermal energy of the earth's interior is its conversion into electrical energy by building double-circuit GeoTPPs on low-boiling working agents. The efficiency of such a conversion depends on many factors, in particular, on the choice of the working fluid and the parameters of the thermodynamic cycle of the secondary circuit of the GeoTPP.
The results of the computational analysis of cycles using various heat carriers in the secondary circuit show that the most optimal are supercritical cycles, which allow increasing the turbine power and cycle efficiency, improving the transport properties of the coolant and more fully adjusting the temperature of the initial thermal water circulating in the primary circuit of the GeoTPP.
It has also been established that for high-temperature thermal water (180ºС and above), the most promising is the creation of supercritical cycles in the secondary circuit of the GeoTPP using isobutane, while for waters with a lower temperature (100÷120ºС and above), when creating the same cycles, the most suitable heat carrier is freon R13B1.
Depending on the temperature of the extracted thermal water, there is an optimal temperature for the evaporation of the secondary heat carrier, corresponding to the maximum power generated by the turbine.
In the future, it is necessary to study supercritical mixtures, the use of which as a working agent for geothermal energy cycles is the most convenient, since by selecting the mixture composition, one can easily change their critical properties depending on external conditions.
Another area of use of geothermal energy is geothermal heat supply, which has long been used in Kamchatka and the North Caucasus for heating greenhouses, heating and hot water supply in the housing and communal sector. An analysis of world and domestic experience indicates the prospects of geothermal heat supply. At present, geothermal heat supply systems with a total capacity of 17175 MW are operating in the world, more than 200 thousand geothermal installations are operated in the USA alone. According to the plans of the European Union, the power geothermal systems heat supply, including heat pumps, should increase from 1300 MW in 1995 to 5000 MW in 2010.
In the USSR, geothermal waters were used in the Krasnodar and Stavropol Territories, Kabardino-Balkaria, North Ossetia, Checheno-Ingushetia, Dagestan, Kamchatka Oblast, Crimea, Georgia, Azerbaijan and Kazakhstan. In 1988, 60.8 million m³ of geothermal water was produced, now in Russia it is produced up to 30 million. m³ per year, which is equivalent to 150÷170 thousand tons of reference fuel. At the same time, the technical potential of geothermal energy, according to the Ministry of Energy of the Russian Federation, is 2950 million tons of reference fuel.
Over the past 10 years, the system of exploration, development and exploitation of geothermal resources has collapsed in our country. In the USSR scientific research work Institutes of the Academy of Sciences, Ministries of Geology and gas industry. Exploration, appraisal and approval of deposit reserves were carried out by institutes and regional subdivisions of the Ministry of Geology. Drilling of productive wells, field development, development of technologies for re-injection, treatment of geothermal waters, operation of geothermal heat supply systems were carried out by subdivisions of the Ministry of Gas Industry. It included five regional operational departments, the Soyuzgeotherm scientific and production association (Makhachkala), which developed a scheme for the prospective use of geothermal waters of the USSR. The design of systems and equipment for geothermal heat supply was carried out by the Central Research and Design and Experimental Institute of Engineering Equipment.
At present, comprehensive research work in the field of geothermy has ceased: from geological and hydrogeological studies to the problems of purification of geothermal waters. Exploratory drilling is not carried out, the development of previously explored deposits is not carried out, the equipment of existing geothermal heat supply systems is not modernized. The role of state administration in the development of geothermy is negligible. Geothermal specialists are scattered, their experience is not in demand. Analysis of the current situation and development prospects in new economic conditions Russia, let's do it on the example of the Krasnodar Territory.
For this region, of all renewable energy sources, the most promising is the use of geothermal waters. Figure 4 shows the priorities for the use of renewable energy for heat supply to objects in the Krasnodar Territory.
In the Krasnodar Territory, up to 10 million m³/year of geothermal water with a temperature of 70÷100º C is produced annually, which replaces 40÷50 thousand tons of organic fuel (in terms of conventional fuel). There are 10 fields in operation with 37 wells, 6 fields with 23 wells are under development. Total number of geothermal wells77. 32 hectares are heated by geothermal waters. greenhouses, 11 thousand apartments in eight settlements, 2 thousand people are provided with hot water. Explored operational reserves of geothermal waters of the region are estimated at 77.7 thousand cubic meters. m³/day, or when operating for heating season-11.7 million m³ per season, predicted reserves, respectively, 165 thousand. m³/day and 24.7 mln. m³ per season.
One of the most developed Mostovskoye geothermal field, 240 km from Krasnodar in the foothills of the Caucasus, where 14 wells were drilled with a depth of 1650÷1850m with flow rates of 1500÷3300 m³ / day, a temperature at the mouth of 67÷78º C, a total salinity of 0.9÷1, 9g/l. By chemical composition geothermal water almost meets the standards for drinking water. The main consumer of geothermal water from this field is a greenhouse complex with a greenhouse area of up to 30 hectares, which previously operated 8 wells. Currently, 40% of the greenhouse area is heated here.
For heat supply of residential and administrative buildings of the village. Bridge in the 80s, a geothermal central heating point (CHP) was built with an estimated thermal power of 5 MW, the diagram of which is shown in Fig. 5. Geothermal water in the central heating center comes from two wells with a flow rate of 45÷70 m³/h each and a temperature of 70÷74ºС into two storage tanks with a capacity of 300m³. To utilize the heat of waste geothermal water, two steam-compressor heat pumps with an estimated thermal power of 500 kW were installed. The geothermal water used in heating systems with a temperature of 30÷35ºС before the heat pump unit (HPU) is divided into two streams, one of which is cooled to 10ºС and drained into the reservoir, and the second is heated up to 50ºС and returned to the storage tanks. Heat pump units were manufactured by the Moscow plant "Kompressor" on the basis of A-220-2-0 refrigeration machines.
Thermal power control geothermal heating in the absence of peak reheating, it is carried out in two ways: by passing the coolant and cyclically. With the latter method, the systems are periodically filled with geothermal coolant with simultaneous draining of the cooled one. With a daily heating period Z, the heating time Zn is determined by the formula
Zn = 48j/(1 + j), where is the heat output coefficient; design air temperature in the room, °С; and actual and calculated outdoor air temperature, °С.
The capacity of storage tanks of geothermal systems is determined from the condition of ensuring the normalized amplitude of air temperature fluctuations in heated residential premises (± 3 ° C) according to the formula.
where kF is the heat output of the heating system per 1°C of the temperature difference, W/°C; Z \u003d Zn + Zpp period of operation of geothermal heating; Zp pause duration, h; Qp and Qp is the calculated and seasonally average heat output of the heating system of the building, W; c volumetric heat capacity of geothermal water, J/(m³ ºС); n number of geothermal heating starts per day; k1 is the heat loss coefficient in the geothermal heat supply system; A1 amplitude of temperature fluctuations in a heated building, ºС; Rnom total indicator of heat absorption of heated premises; Vc and Vts capacity of heating systems and heating networks, m³.
During the operation of heat pumps, the ratio of geothermal water flow rates through the evaporator Gi and the condenser Gk is determined by the formula:
Where tk, to, t is the temperature of geothermal water after the condenser, the heating system of the building and HPI evaporators, ºС.
It should be noted the low reliability of the used designs of heat pumps, since their operating conditions differed significantly from the operating conditions of refrigeration machines. The ratio of discharge and suction pressures of compressors when operating in heat pump mode is 1.5÷2 times higher than the same ratio in refrigerating machines. Failures of the connecting rod and piston group, oil facilities, and automation led to the premature failure of these machines.
As a result of the lack of control of the hydrological regime, the operation of the Mostovskoye geothermal field after 10 years, the pressure at the wellhead decreased by 2 times. In order to restore the reservoir pressure of the field in 1985. three injection wells were drilled, a pumping station was built, but their work did not positive result due to the low injectivity of the formations.
For the most promising use of geothermal resources in the city of Ust-Labinsk with a population of 50 thousand people, located 60 km from Krasnodar, a system of geothermal heat supply with an estimated thermal power of 65 MW has been developed. Of the three water-pumping horizons, Eocene-Paleocene deposits were selected with a depth of 2200÷2600m, formation temperature 97÷100ºС, salinity 17÷24g/l.
As a result of the analysis of existing and prospective heat loads in accordance with the scheme for the development of the city's heat supply, the optimal, calculated, thermal power of the geothermal heat supply system was determined. A technical and economic comparison of four options (three of them without peak boilers with a different number of wells and one with reheating in the boiler) showed that the scheme with the peak boiler (Fig. 6) has the minimum payback period.
The geothermal heat supply system provides for the construction of the western and central thermal water intakes with seven injection wells. Operating mode of thermal water intakes with re-injection of cooled coolant. Double-circuit heat supply system with peak reheating in the boiler room and dependent accession existing systems building heating. Capital investment in the construction of this geothermal system amounted to 5.14 million. rub. (in prices of 1984), payback period 4.5 years, estimated savings of substituted fuel 18.4 thousand tons of reference fuel per year.
The cost of electricity generated by geothermal power plants.
The costs of research and development (drilling) of geothermal fields account for up to 50% of the total cost of a GeoTPP, and therefore the cost of electricity generated at a GeoPP is quite significant. Thus, the cost of the entire pilot-industrial (OP) Verkhne-Mutnovskaya GeoPP [capacity 12 (3 × 4) MW] amounted to about 300 million rubles. However, the absence of transportation costs for fuel, the renewability of geothermal energy and the environmental friendliness of electricity and heat production allow geothermal energy to successfully compete in the energy market and, in some cases, produce cheaper electricity and heat than traditional IES and CHP. For remote areas (Kamchatka, Kuril Islands), GeoPPs have an unconditional advantage over thermal power plants and diesel stations operating on imported fuel.
If we consider Kamchatka as an example, where more than 80% of electricity is produced at CHPP-1 and CHPP-2, operating on imported fuel oil, then the use of geothermal energy is more profitable. Even today, when the process of construction and development of new GeoPPs at the Mutnovsky geothermal field is still underway, the cost of electricity at the Verkhne-Mutnovskaya GeoPP is more than two times lower than at the CHPP in Petropavlovsk Kamchatsky. The cost of 1 kWh(e) at the old Pauzhetskaya GeoPP is 2¸3 times lower than at CHPP-1 and CHPP-2.
The cost of 1 kWh of electricity in Kamchatka in July 1988 was between 10 and 25 cents, and the average electricity tariff was set at 14 cents. In June 2001 in the same region, the electricity tariff for 1 kWh ranged from 7 to 15 cents. At the beginning of 2002 the average tariff in OAO Kamchatskenergo was 3.6 rubles. (12 cents). It is clear that the economy of Kamchatka cannot successfully develop without reducing the cost of electricity consumed, and this can only be achieved through the use of geothermal resources.
Now, when restructuring the energy sector, it is very important to proceed from real prices for fuel and equipment, as well as energy prices for different consumers. Otherwise, you can come to erroneous conclusions and forecasts. So, in the strategy for the development of the economy of the Kamchatka region, developed in 2001 in Dalsetproekt, without sufficient justification, the price of 1000m³ of gas was set at $50, although it is clear that the real cost of gas will not be lower than $100, and the duration of development gas fields will be 5÷10 years. At the same time, according to the proposed strategy, gas reserves are calculated for a life of no more than 12 years. Therefore, the prospects for the development of the energy sector in the Kamchatka region should be associated primarily with the construction of a series of geothermal power plants at the Mutnovsky field [up to 300 MW (e)], the re-equipment of the Pauzhetskaya GeoPP, whose capacity should be increased to 20 MW, and the construction of new GeoPPs. The latter will ensure the energy independence of Kamchatka for many years (at least 100 years) and will reduce the cost of electricity sold.
According to the World Energy Council, of all renewable energy sources, the most low price for 1 kWh at GeoPP (see table).
|
power |
use power |
Price installed |
in the last |
||||
| 10200 | 55÷95(84) | 2÷10 | 1÷8 | 800÷3000 | 70,2 | 22 | |
| Wind | 12500 | 20÷30(25) | 5÷13 | 3÷10 | 1100÷ 1700 | 27,1 | 30 |
| 50 | 8÷20 | 25÷125 | 5÷25 | 5000÷10000 | 2,1 | 30 | |
| tides | 34 | 20÷30 | 8÷15 | 8÷15 | 1700÷ 2500 | 0,6 |
From the experience of operating large GeoPPs in the Philippines, New Zealand, Mexico and the USA, it follows that the cost of 1 kWh of electricity often does not exceed 1 cent, while it should be borne in mind that the power utilization factor at GeoPPs reaches 0.95.
Geothermal heat supply is most beneficial with the direct use of geothermal hot water, as well as with the introduction of heat pumps, which can effectively use the heat of the earth with a temperature of 10÷30ºС, i.е. low-grade geothermal heat. In the current economic conditions of Russia, the development of geothermal heat supply is extremely difficult. Fixed assets must be invested in drilling wells. In the Krasnodar Territory, with the cost of drilling 1m of a well 8 thousand rubles, its depth is 1800m, the costs amount to 14.4 million rubles. With an estimated well flow rate of 70 m³ / h, a triggered temperature difference of 30º C, round-the-clock operation for 150 days. per year, the utilization rate of the estimated flow during the heating season is 0.5, the amount of heat supplied is 4385 MWh, or in value terms 1.3 million rubles. at a tariff of 300 rubles/(MWh). At this rate, well drilling will pay off in 11 years. At the same time, in the future, the need to develop this area in the energy sector is beyond doubt.
Findings.
1. Almost throughout Russia there are unique reserves of geothermal heat with coolant temperatures (water, two-phase flow and steam) from 30 to 200º C.
2.In recent years in Russia, on the basis of large fundamental research geothermal technologies have been created that can quickly provide effective application heat of the earth at GeoPP and GeoTS to produce electricity and heat.
3. Geothermal energy should take an important place in the overall balance of energy use. In particular, for the restructuring and re-equipment of the power industry of the Kamchatka region and the Kuril Islands and partly of Primorye, Siberia and North Caucasus you should use your own geothermal resources.
4. Large-scale introduction of new heat supply schemes with heat pumps using low-grade heat sources will reduce fossil fuel consumption by 20÷25%.
5. To attract investments and loans to the energy sector, it is necessary to implement effective projects and guarantee timely repayment of borrowed funds, which is possible only with full and timely payment for electricity and heat supplied to consumers.
Bibliography.
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Geothermal energy resources in Russia have significant industrial potential, including energy. The heat reserves of the Earth with a temperature of 30-40 °С (Fig. 17.20, see color insert) are available almost throughout Russia, and in some regions there are geothermal resources with temperatures up to 300 °С. Depending on the temperature, geothermal resources are used in various sectors of the national economy: electric power, heating, industry, agriculture, balneology.
At temperatures of geothermal resources above 130 ° C, it is possible to obtain electricity on single-circuit geothermal power plants(GeoES). However, a number of regions of Russia have significant reserves of geothermal waters with a lower temperature of about 85 ° C and above (Fig. 17.20, see color insert). In this case, it is possible to obtain electricity at the GeoPP with a binary cycle. Binary power stations are two-circuit stations using their own working fluid in each circuit. Binary stations are also sometimes referred to as single-loop stations that operate on a mixture of two working fluids - ammonia and water (Fig. 17.21, see color insert).
The first geothermal power plants in Russia were built in Kamchatka in 1965-1967: Pauzhetskaya GeoPP, which operates and currently produces the most cheap electricity in Kamchatka, and the Paratunskaya GeoPP with a binary cycle. In the future, about 400 GeoPPs with a binary cycle were built in the world.
In 2002, the Mutnovskaya GeoPP was put into operation in Kamchatka with two power units with a total capacity of 50 MW.
The technological scheme of the power plant provides for the use of steam obtained by two-stage separation of the steam-water mixture taken from geothermal wells.
After separation, steam with a pressure of 0.62 MPa and a degree of dryness of 0.9998 enters a double-flow steam turbine with eight stages. Paired with steam turbine a generator with a nominal power of 25 MW and a voltage of 10.5 kV is operating.
To ensure environmental cleanliness, the technological scheme of the power plant provides for a system for pumping condensate and separating back into the earth's layers, as well as preventing hydrogen sulfide emissions into the atmosphere.
Geothermal resources are widely used for heat supply, especially when using hot geothermal water directly.
Low-potential geothermal heat sources with a temperature of 10 to 30 °C should be used with heat pumps. A heat pump is a machine designed to transfer internal energy from a coolant with a low temperature to a coolant with high temperature using an external force to do work. The principle of operation of a heat pump is based on the reverse Carnot cycle.
The heat pump, consuming) kW of electrical power, produces from 3 to 7 kW of thermal power to the heat supply system. The transformation ratio varies depending on the temperature of the low-grade geothermal source.
Heat pumps are widely used in many countries around the world. The most powerful heat pump plant operates in Sweden with a thermal capacity of 320 MW and uses the heat of the Baltic Sea.
The efficiency of using a heat pump is determined mainly by the ratio of prices for electrical and thermal energy, as well as the transformation ratio, which indicates how many times more thermal energy is produced compared to the electrical (or mechanical) energy consumed.
The most economical operation of heat pumps is during the period of minimum loads in the power system. Their operation can contribute to the alignment of schedules electrical load power systems.
Literature for self-study
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in Russia / Team of authors. St. Petersburg: Nauka, 2002.
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