GB2351323A

GB2351323A - Heat and power generation plant.

Info

Publication number: GB2351323A
Application number: GB9914483A
Authority: GB
Inventors: A Karabasov
Original assignee: NEWTONVILLE Ltd
Current assignee: NEWTONVILLE Ltd
Priority date: 1999-06-21
Filing date: 1999-06-21
Publication date: 2000-12-27
Also published as: GB9914483D0

Abstract

Steam or gas turbine electricity and heat generating plants wherein working fluid is heated 1, (71 Fig. 4) and expanded in a turbine 3 (62) producing shaft work driveing a generator 7 (63). Turbine exhaust gas ( w ) or bleed steam a, b, c is fed to heat exchangers 18, 19, 20 (64) wherein heat may be extracted for heat consumer 100 (H1). Working fluid may be fed to the heater via the heat exchanger by closing valves 22, 23, 27, (70 76, 77) to provide heated feedwater or, to maximise heat exchanger output to the heat consumer at times of demand, the heat exchangers are bypassed by a duct 26 (70) by closing valves 17, 21 (72, 73). Steam cycle has feed heaters 11-13, deaerator 14 and exchangers 37,41,45 for second heat load DH. Gas cycle has refrigerator (69) and second load (H2) heated jointly by compressor intercooler (68) and further exhaust gas heat exchanger (65).

Description

2351323 Power Generation Plant The present invention relates to power

generation (including nuclear powered generating plant), and is directed towards energy and resource-saving technologies and may be used in steam and gas turbine plants, where using any type of fuel, both electric and heat energy are produced.

In conventional electricity generation installations, a generator is driven by a heat engine, typically a gas turbine or steam turbine. In the case of gas turbines, fuel is burnt in the turbine to produce rotation of a drive shaft to drive the generator, and hot exhaust gases are emitted from the turbine. In the case of steam turbine plant, water is heated in a boiler by either fossil fuel or nuclear energy to produce steam, which is then led to a turbine where the steam is expanded to produce shaft work to drive the generator. The steam leaving the turbine still contains useful quantities of energy however.

An objective of the present invention is to increase the efficiency of a power generating plant which provides both electric energy and heat outputs to consumers. In preferred forms of the invention there is a decrease in the value of the plant's heat energy production when this 2 is not required by or otherwise not supplied to consumers, this allows an increase in electric energy production to fulfil the electric energy demand of electric energy consumers. The electric energy consumer is not necessarily the same as the heat energy consumer.

A first aspect of the invention provides an installation for generating electricity and for supplying heat to a heat consumer, the installation comprising:

heating means for heating a first working fluid; means for expanding the first working fluid to produce shaft work; means to convert the shaft work into electricity; heat exchanger means for extracting heat from the expanded first working fluid; means for selectively conducting a second working fluid through the heat exchanger means in thermal contact with the expanded first working fluid to heat the second means for leading the second working fluid to the heat consumer; means for conducting the first working fluid through the heat exchanger in thermal contact with the expanded first working fluid, prior to leading the first working fluid to the heating means; and characterised by further comprising means for conducting the first working fluid to the 3 heating means without passing through the heat exchanger; and control means for controlling the flow of the first and second working fluids so that all, part, or none of the flow of first working fluid to the heating means passes through the heat exchanger means.

In a second aspect, there is provided a method for operating such an installation, wherein when the heating demand from the heat consumer is large control means is operative to route working fluid to the heating chamber principally or exclusively via the bypass duct, and wherein when the heating demand from the heat consumer is small then the control means is operative to route working fluid to the heating chamber principally or exclusively via the first duct.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 illustrates schematically a steam turbine generating plant capable of providing electrical energy and heat energy to consumers; Figure 2 shows the heat cycle of the plant of Figure 1 in a first operating mode; Figure 3 illustrates the heat cycle of the plant of 4 Figure 1 in a second operating mode; Figure 4 is a schematic diagram of a gas turbine generating plant; Figure 5 illustrates the heat cycle of the gas turbine plant of Figure 4 in a first operating mode; Figure 6 illustrates the heat cycle of the gas turbine plant of Figure 4 in a second operating mode; Referring now to Figure 1, there is seen a generating plant comprising a boiler 1, a turbine assembly 3 comprising a high-pressure turbine 2, a medium pressure turbine 5 and a low-pressure turbine 6. The three turbines are arranged to drive a generator 7.

Water is fed to the boiler 1, which supplies steam to the first, highpressure, turbine 2. The boiler may be fuelled by coal, gas, oil or other suitable means such as nuclear to produce steam with parameters required.

The steam is then fed to the turbine assembly 3, where the process of its expansion is effected. The result is that the turbine 3 actuates a mechanical device, for example, the electric generator 7. Expanded steam from the high-pressure turbine 2 is passed to an intermediate superheater 4, after which it is directed to the medium pressure turbine 5 and then to the low-pressure turbine 6 and then to a condenser 8.

In the condensor 8 the steam is cooled by an external heat-transfer medium and is thus converted to liquid water. The liquid is then directed into a series of low pressure heat exchangers 11, 12 and 13 by a pump 10. The liquid is then passed into a deaerator 14. The deaerator 14, and the second and third heaters 12 and 13 may not be present in all embodiments of the invention. The liquid is then directed by, for example a pump 15, to the heating side of a series of high pressure heat exchangers 18, 19 and 20. The liquid is then directed into the boiler or steam generator 1 of the plant.

The heat source for the low-pressure heat exchangers 11, 12 and 13 is partially expanded steam drawn from a pressure tapping g in the lowpressure turbine 6, and a pressure tapping f and a pressure tapping e in the medium-pressure turbine 5, respectively. When expanded steam from these pressure tappings has been fed through the heat exchangers 11, 12 and 13, the cooled and expanded steam is led to the condenser 8.

The heat source for the high-pressure heat exchangers 18, 19 and 20 is partially expanded steam drawn from a 6 pressure tapping c in the medium-pressure turbine 5, a pressure tapping b in the medium-pressure turbine 5, and a pressure tapping a in the high- pressure turbine 2, respectively. When partially expanded steam from these pressure tappings has been fed through the heat exchangers 18, 19 and 20, respectively, the cooled partial ly-expanded steam is led to the deaerator 14.

Thus, water pumped from the condenser 8 by the pump 10 is initially heatec in the heat exchangers 11, 12 and 13 and passes to the deaerator 14. Water pumped from the deaerator 14 by the pump 15 to the high-pressure heat exchangers 18, 19 and 20 is heated therein, and then flows to the boiler 1. 15 In addition to supplying the low-pressure heat exchangers with part i a 1 ly-expanded steam as a heat source, the installation further includes a second series of lowpressure heat exchangers 37, 41 and 45. Partially- expanded steam may be fed to the heat exchangers 37, 41 and 45 from pressure tappings d, e and f in the mediumpressure turbine 5, the respective flows being controlled by valves 36, 40 and 44. A heat transfer fluid is pumped through the heat exchangers 37, 41 and 45 by a pump 49, so that the f luid may transport heat to a f irst heat consumer DH via the heating circuit 48. As demand in the heating circuit 48 rises and falls, the valves 36, 40 and 7 44 may be opened and closed to provide more or less part i a 1 ly- expanded steam to the heat exchangers 37, 41 and 45 to meet this varying demand.

The installation shown in figure 1 also provides for the supply of heat to a second heat consumer 100, heated fluid being provided to the heat consumer 100 via a valve 23 situated downstream of high-pressure heat exchanger 20. Fluid is returned from the heat consumer 100 via a circuit 24 including a pump 25 and a valve 22, the fluid being returned to the flow upstream of the high-pressure heat exchanger 18.

A valve 16 downstream of the pump 15 controls the supply of heated fluid from the deaerator 14. Immediately downstream of the valve 16, a bypass B branches from the main flow path, to provide a fluid pathway which cuts out the high-pressure heat exchangers 18, 19 and 20. The bypass B is controlled by a valve 27, and by adjusting the valve 27 and a valve 17 situated downstream of the branch, the heated fluid from the deaerator 14 may be caused to pass through the high- pressure heat exchangers, or alternatively may be diverted round them.

From the valve 16, water may be directed to the boiler 1 the through the valve 17, the heat exchangers 18, 19 and 20, and through a final control valve 21.

8 Alternatively, if the valve 17 and the f inal control valve 1 are closed, then water is fed to the boiler I via the bypass B. Simultaneously, if valves 23 and 22 are opened, water can circulate to the second heat consumer 100 and through the high-pressure heat exchangers.

With the valve 27 controlling the bypass B closed, then by controlling the degree of opening of the valves 23 and 22, and the degree are opening of the valves 1 and 17, the water flow through the high-pressure heat exchangers may be divided between a recirculating flow supplied to the second heat consumer 100 and a flow to the boiler 1.

If the valve 27 controlling the bypass B is opened, then the f low of water from the valve 16 to the boiler 1 may be divided between the heat exchangers 18, 19 and 20 and the bypass B. By simultaneous regulation of all five of the valves 17, 21, 22, 23 and 27, the water flowing through the valve 16 may be divided between an unheated boiler feed flow through bypass B and valve 27, a recirculating flow through the second heat consumer 100, and a heated boiler feed flow through the valve 21 to the boiler 1. The proportions of these flows may be controlled relative to each other by appropriate setting of the five valves.

By closing valves 17 and 21, and opening valves 22 and 9 23, the heated sides of the said heat exchangers 18-20 and the heat exchange circuit 24 which provides the second heat consumer 100 with heat energy can be isolated from the boiler supply flow.

As the ratios of the flows through the heat exchangers 18, 19 and 20 and the bypass B are changed, the proportion of boiler feed water which is heated by the heat exchangers will clearly vary. To enable the boiler to produce steam of the appropriate parameters to operate the turbine assembly 3, the heat input to the boiler 1 will have to be regulated in accordance with the temperature of the incoming boiler feed water and the boiler throughput.

In order to regulate the amount of heat energy directed to the second heat consumer 100 from the high pressure heat exchangers, it is possible to change the amounts of steam extracted from the turbine into the heating sides of the given heaters by means of the valves 31, 32 and 33. When this is done, the heating side of, at least, one of the said heat exchangers 18- 20 can be controlled to provide the regulated extraction of steam at higher pressure using valves 31, 32 and 33.

When operating a combined heat and electrical power generating plant, the heating requirements of the second heat consumer 100 is likely to varying on a daily cycle, as well as on a seasonal cycle. In the installation of the present invention, when the demand for heat energy by the second heat consumer 100 is large, then the boiler 5 feed flow is directed exclusively through the bypass B. The circulating flow in the heating circuit 24 is then the only flow extracting heat from the heat exchangers 18, 19 and 20 and thus the maximum heat output to the second heat consumer 100 is achieved. Since the boiler feed water does not pass through the heat exchangers 18, 19 and 20, the boiler feed water temperature is lowest and greater heat input to the boiler is necessary to produce steam at the appropriate temperature and pressure.

At times of intermediate heat demand by the second heat consumer 100, a portion of the boiler feed water flow is led via the bypass B and a portion is sent through the heat exchangers 18, 19 and 20, so that the temperature of the boiler feed water is raised to an intermediate level. Since the boiler feed water is extracting heat from the heat exchangers, less heat is available for the second heat consumer 100 but since demand is lower, then that demand can be satisfied.

When the second heat consumer 100 has a low or zero demand, then the valves 22 and 23 can be closed to produce a low or zero f low rate round the circuit 24. The valve 27 is also closed, so that all of the boiler feed water is directed through the heat exchanger is 18, 19 and 20 to raise the temperature of the boiler f eed water to a maximum level. The heat input requirement of the boiler is thus minimised and the efficiency of the installation increased.

Figures 2 and 3 are diagrams illustrating the 10 thermodynamic cycle of the installation of figure 1. In the figures, the cycle starts at point j downstream of the condenser 8, and follows the heating of the fluid to point m at the entrance to the high-pressure turbine. The f luid is then expanded to point n, and returned to the super heater 4 to be raised to point p. The partially-expanded steam which is tapped from the turbines to feed the heat exchangers is illustrated at the lower right-hand part of the graph, and the extraction of heat in the condenser is represented by the generally horizontal lower extremity of the graph.

In f igure 2, the bypass B is not operating, since the valve 27 is closed. Thus, the temperature of the boiler feed water is seen at point 1, the same temperature as the partially-expanded steam exiting from the highpressure turbine at point a. The feed water must be raised f rom point 1 to point m in the boiler, and thus 12 the heating requirement for the boiler 1 is ql.

In f igure 3, the valve 17 is closed and the entire supply of boiler feed water is being provided via the bypass B. This corresponds to the situation in which the second heat consumer 100 is operating at maximum demand. The boiler feed water is thus being supplied at the temperature of the partial ly-expanded steam exiting from the medium-pressure turbine at tapping d, and is represented on the graph of f igure 3 at point k. The heating requirement of the boiler 1 in this situation is Q1, since the feed water must be raised from point k to point m. It can clearly be seen that the heating requirement Q, for the cycle of figure 3 is greater than that (ql) f or t he cycle of figure 2, to maintain the same properties at point m in the cycle.

As an alternative to using steam for the working fluid of the closedcircuit installation, an inert gas such as nitrogen, helium, neon or argon may be used. The inert gas may be mixed with an ionisable additive such as caesium, and before expansion in the turbine the heated gas may be expanded in a magnetohydrodynamic generator to produce electrical energy. in a closed-circuit installation the working fluid may be heated by means of combustion of fossil fuel or gas, or by means of a 13 nuclear reactor. The heating, cooling, compression and expansion of the working fluid may or may not involve a change of state from liquid to gas or vapour phase.

Referring now to figure 4, there is seen an open-cycle gas turbine generating plant comprising first and second compressors 60 and 61, a turbine 62, and a generator 63. The compressors 61 and 62 and the generator 63 are driven by the turbine 62. The exhaust gas from the turbine 62 10 is led through a first heat exchanger 64, a second heat exchanger 65, and may then be discharged through valve 66 or led to a third heat exchanger 67 through valve 78. In operation, air is drawn in f rom the atmosphere and 15 warmed in the heat exchanger 67, and the warmed air is then fed to the first compressor 60. The air passes through the first compressor 16 and is heated and compressed. This heated air is then cooled in a heat exchanger 68, and is passed through a refrigerator 69 20 before entering the second compressor 61. The compressed air from the second compressor 61 may be led directly through a valve 70 to a combustion chamber 71 where the air is heated. Alternatively, the valve 70 may be closed and the air from the second compressor 61 may be led 25 through a valve 72 to the heating side of the f irst heat exchanger 64, where the airflow is further heated using heat from the turbine exhaust. The heated air may then 14 be led via the valve 73 to the combustion chamber 71.

In the combustion chamber 71, the air is heated by burning fuel to increase its temperature and pressure, and the air is then fed to the turbine 62 to drive the compressors 60 and 61 and the generator 63, with the turbine exhaust being fed to the first heat exchanger 64.

In the heat exchanger 64, heat is extracted from the turbine exhaust and may be used to preheat the air before it enters the combustion chamber 71. Alternatively, if the valves 72 and 73 are closed and the valve 70 is open, the first heat exchanger 64 may be used to provide heat to a heat consumer Hl by circulating a heat transfer fluid through a pump 75, valve 76, heat exchanger 64, valve 77, and the heat consumer Hl. By varying the amount of opening of the valve 70, the valves 72 and 73, and the valves 76 and 77, the heated compressed air leaving the compressor 61 may be divided into two streams, one of which is led directly to the combustion chamber 71, and the other of which is led to the combustion chamber 71 via the heat exchanger 64. Simultaneously, a circulating flow of air may act as a heat transfer medium to supply heat to the heat consumer Hl.

The turbine exhaust gas emerging from the first heat exchanger 64 may be led to a second heat exchanger 65, linked to a heat transfer circuit to supply heat to a further heat consumer H2. In the heat exchanger 65 heat is drawn out of the turbine exhaust gas to the supplied to the heat consumer H2. In the third heat exchanger 68, heat is removed from the compressed air leaving the first compressor stage 60, to be supplied to the heat consumer H2.

When the heating demand at the first heat consumer H1 is large, the valves 72 and 73 are closed and the compressed air from compressor 61 is supplied directly to the combustion chamber 71 without pre-heating in the first heat exchanger 64. This arrangement ensures that the maximum heat transfer capacity of the first heat exchanger 64 is available to heat the heat transfer fluid in the circuit of the first heat consumer H1, and thus ensures maximum heat output for the consumer.

When the heating demand at the first heat consumer H1 is minimal, then the valves 76 and 77 are closed down to reduce the circulation of the transfer fluid in the consumer circuit. Simultaneously, valve 70 is closed and valves 72 and 73 are opened so that the air compressed in the compressor 61 is heated in the first heat exchanger 64 before passing to the combustion chamber 71. This minimises the fuel requirement in the combustion 16 chamber to produce high-energy gas for the turbine 62.

At intermediate values of heating demand for the first heat consumer H1, the valve 70, valves 72 and 73, and valves 76 and 77 are set at intermediate positions, in order to provide a circulation of heated fluid sufficient to supply the demand of the consumer H1, and to pre-heat a partial stream of air to be f ed to the combustion chamber through the valves 72 and 73, while a further partial stream of air passes through valve 70 to the combustion chamber 71 directly.

The installation shown in figure 4 is an open-circuit gas turbine plant wherein the exhaust gas from the turbine 62 passes first to heat exchanger 64, wherein heat is extracted either to preheat the combustion gas or to supply the heat consumer HI, or both. From the heat exchanger 64, the turbine exhaust gas passes to second heat exchanger 65, wherein further heat is extracted to supply heat consumer H2. The turbine exhaust gas is then either discharged to atmosphere through valve 66, or passed through valve 78 to heat exchanger 67, which preheats the entering the first compressor 60. Heated air the leaving the compressor 16 passes through heat exchanger 68, where heat is extracted to supply the second heat consumer H2. The system is thus extremely efficient, since very little heat is allowed to escape 17 with the turbine exhaust gas.

Referring to figures 5 and 6, the heat cycle of the gas turbine plant of figure 4 is illustrated.

The characteristic points of physical condition change of the working medium (inlets and outlets from the main unit elements) are marked on Figure 4 using the letters a, b, c,.... The corresponding characteristic points on the T-S charts for ideal operation cycles of the above mentioned for the two modes of operation are marked with the same letters.

Fig. 5 is a TS chart of the ideal operation cycle for 15 the installation of Figure 4 in a warm season, when heat demand of consumers is lower. The chart uses the following designations:

Q, - (specific) heat brought to the cycle combustion chamber 71; Qper regeneration heat supplied by heat exchanger 64 inside the cycle (the direction is marked with an arrow); QT2 - heat provided to the consumer though heat exchanger 65; Qyz - heat given out to the environment with the emitted gas; 18 QT3 - heat provided to consumer through heat exchanger 68; Qx - heat emitted to the environment through refrigerator 69; A,b,c, are characteristic physical change points of the working medium in this mode of operation.

The operation of the installation of Figure 4 when the heat requirement of the heat consumer is below a predetermined threshold will now be described.

In this operation mode for instance, in the warm season, etc, the positions of valves of the working medium and heat carrier circuits are the following: valves 70, 76, 77 are closed, valves 72, 73 are open, valves 66, 78 are partially open or at least one of them is open; and valve 79 is partially open.

The electrical generator 63 operating at start up as an actuating electrical engine actuates the compressors 60 and 61 and the turbine 62. Thus compressor 60 intakes air (for instance, with the temperature T = 300C) and compresses it to a certain pressure level. As a result the temperature of the air rises for example to the level T = 2100C. The air is then cooled in heat exchanger 68 for example to the temperature T = 1100C and supplied to the consumer for instance for district heating. From the 19 heating side of heat exchanger 68 the air moves into refrigerator 69 by the action of the compressor 60. There it is further cooled for example to T = 300C by giving out heat Qx to the environment. The cooled air is then further compressed in compressor 61 for example to 26,8 atm, and heated up to for example T = 2100C. The air then moves into the heated side of heat exchanger 64 for instance into the space between the pipes through the open valve 72. In this operation mode the heat exchanger serves as a regenerator. In the heat exchanger 64 the air is heated for example to T = 5100C using the heat of the gas coming from turbine 61 in this example the temperature of the gas is T = 5300C. The air then enters the combustion chamber 71 through valve 73. Gaseous or liquid organic fuel is supplied to combustion chamber 71 and mixed with the air. The fuel is combusted in combustion chamber 71 at an increased pressure thus supplying heat. Combustion products actuate the gas turbine 62 as a result of expansion by means of their kinetic energy. The turbine can then drive compressors and 61 and the electrical generator 63 thereby producing electrical energy which can be supplied to consumers. As a result of the expansion in the turbine 62 the temperature of the working medium goes down in this example from 12500C to 5300C. The gaseous working medium exiting the turbine 62 enters the heated side of heat exchanger 64. There the working medium is cooled for example to T = 2300C as a result of regenerative heating of the gas compressed in compressor 61 (Q,,,. This temperature is sufficient to provide for heating. Thus gas with the temperature T,, as mentioned enters the heat exchanger 65 and serves as a heating agent. The gas is cooled by giving out heat QT2 by the heat carrier of the consumer's heat supply current to normal temperature of for example T = 1100C. After passing through the heat exchanger 65 the working medium is cooled giving out a quantity a quantity of heat Qyx to the minimum cycle temperature Td by emitting gas into the atmosphere through the open valve 66 or through the open valve 78 or through both partially open valves 66 and 78. The open position of valve 7B is utilised in a case where it is necessary to produce additional heat for consumers when the ambient temperature is low this does result in a lower electrical efficiency. In this mode of operation a part of the emitted gas passing through the open valve 78 heats the air taken in by the compressor 60 to an initial temperature of Td. This temperature enables the air passing into the heating side of the heat exchanger 67 to be heated up to T = 2100C, which is sufficient to increase the quality of heat produced by heat exchanger 68. In order to cool the working medium and provide the consumer with the quantity heat (QT3 and QT2) water is pumped through the heated side of heat exchangers 68 and 21 by a pump 80. The temperature of the water entering the heat exchangers is ≥700C. Valve 79 is required to make the capacities of heat exchangers 68 and 65 correspond, so as to have the outgoing network water at a temperature of 150-1800C. As a result of this the district heating unit H2 of the consumer is provided with network water with optimal parameters (see the book "District Heating SystemC by L.S. Khrilev, Moscow, Energoatomizdat, 1988, pp. 179-181).

Fig. 6 represents T-S chart of the ideal operation cycle for variant 1 of the energy unit in the maximum operation mode (for instance, during the heating season - approximately 7 months per year). Additional designations used on the chart are as follows: Q, - heat brought to the cycle (in combustion chamber 8); QT1 - heat supplied to consumer through the heat exchanger 6.

Based on the temperature levels of the working medium as mentioned above for the sake of illustration, see Fig.6, the operating mode with a minimum/reduced supply of heat to consumers in the warm season may be described as follows:

Absolute electrical efficiency of the plant is 44%.

22 The heating capacity of the combustion chamber in this operating mode is 600 Mwt (h).

The electrical capacity of the energy unit will amount 5 to 264 Mwt (el).

The heating capacity supplied to consumers by gas coolants 2 and 13 is 156 Mwt (h).

The ratio of fuel heat use is 70%.

The ratio of thermodynamic efficiency of the cycle is 53,1%.

That operation of the present invention when the heat requirement of the heat consumer is at or above the threshold, i.e, when a greater amount of heat is supplied to consumers, is as follows:

The valves 70, 76 and 77 are in an open position, whereas valves 72 and 73 are closed. As a result the gaseous working medium compressed in the compressor 61 and is supplied directly to the heater or combustion chamber 71, by-passing the heat exchanger 64. The capacity of the combustion chamber must be increased, for example by supplying additional heat, in order to compensate for the working fluid being at a lower initial temperature. For 23 the given example to get T, = 12500C it is heated from the starting Ti = 2100C, not from Tk = 5100C as is the case in the first operating mode. Thus, the flow rate of the working medium passing through gas turbine 11 is the same as in the previous operation mode with the same incoming temperature and pressure. The electrical generator 63 therefore produces the same electrical power (N,l = const). As in the previous operation mode the gas coming out of turbine 62 passes through the heating side of heat exchangers 64 and 65 and is further emitted in the atmosphere via valve 66.

The differences in the operation of the heat exchanger 64 in this mode of operation will now be described. The heat carrier (water/steam or gas) is pumped through the heat exchanger 64 using the pump 75 of the consumer's heat exchanger circuit using valves 76 and 77. Thus, in this mode of operation the consumer H1 can be supplied with additional heat of higherpotential (the working medium is cooled by supplying heat to the consumer H1 from for example Tb = 5300C to T, = 230OC) without using an additional heat exchanger. The parameters of the heating energy produced can satisfy the needs of more consumers, than in the first mode of operation. The analysis of heat consumption of main industry sectors provides an estimate that over 60% of consumed heat is 24 supplied as steam. Depending on the character and conditions of the technological process the parameters of the steam consumed may vary from for example 150 to 5000C. Most technological processes use steam with a 5 pressure 0,5-4,0 MPa.

For steam heating both one- and two-pipe systems with a recirculation of condensate may be employed. These systems typically comprise: steam heating units on a dependent scheme; water heating units on independent scheme; hot water supply units; technological units consuming steam and other units.

The following is an assessment of this mode of operation in comparison with the previous operation mode.

The absolute electrical efficiency is 32%.

Due to a wider temperature range of the heated gas the capacity of combustion chamber must be increased from 600 Mwt to 824 Mwt.

The electrical capacity is 264 Mwt (el) - const.

The amount of heat output supplied to the consumer by heat exchangers 65 and 68 is 156 Mwt (h) - The amount of additional heat output of a higher potential supplied to consumers by the heat exchanger 64 is 224 Mwt (h).

The total heat output is 380 Mwt (h). 5 The ratio of fuel heat use is 78, 1%.

The ratio of thermodynamic efficiency of the cycle is 59,9%.

Thus comparing the two modes of operation we find that the electrical capacity of the generator remains the same, whereas the ratio of fuel heat use goes up from 70 to 79.1%, an absolute increase of 8,1%. Furthermore, the ratio of thermodynamic efficiency of the cycle increases from 53.1 to 53. 9%, an absolute increase of the 0.8%. Additionally, total heat output is increased by 2.43 times, in this example by 224 Mwt.

In order to meet a periodically increased need of consumers for heat energy the present invention enables an avoidance of the construction and operation of an additional boiler installation. Taking into consideration the fact that the efficiency ratio of modern organic fuel boilers amounts to 90%, the nominal capacity of the heater of the additional boiler should be 11% higher than the additional heat power supplied form a plant 26 producing electrical energy using the present invention. That is, in order to produce the same amount of additional heat as in a plant according to the present invention, the heater of the additional boiler would inefficiently burn up more fuel than the proposed unit by approximately 11%.

In connection with the mentioned above under variant 1 the capital cost economy is (152 -135/152)100%=11,2% of capital costs required for the construction of an energy unit and an additional boiler based on existing know-how.

with the estimated 11% economy of fuel burnt in the additional boiler, the annual economy of operational costs after the implementation of the present invention is estimated to be no less than 25% of the annual operational costs of a heat and power station using an additional boiler to supply heat to consumers.

Thus the present invention produces electrical and heating energy and gives a number of positive production and economic effects in that the same quantity of electrical energy produced compared to prior art plants the present invention efficiently operates in both modes of operation.

Claims

27 Claims

1. An installation for generating electricity and for supplying heat to a heat consumer, the installation comprising: heating means for heating a first working fluid; means for expanding the first working fluid to produce shaft work; means to convert the shaft work into electricity; heat exchanger means for extracting heat from the expanded first working fluid; means for selectively conducting a second working fluid through the heat exchanger means in thermal contact with the expanded first working fluid to heat the second working fluid; means for leading the second working fluid to the heat consumer; means for conducting the first working fluid through the heat exchanger in thermal contact with the expanded first working fluid, prior to leading the first working fluid to the heating means; and characterised by further comprising means for conducting the first working fluid to the heating means without passing through the heat exchanger; and control means for controlling the flow of the first and second working fluids so that all, part, or none of 28 the f low of f irst working f luid to the heating means passes through the heat exchanger means.

2. An installation according to claim 1 wherein the means to produce shaf t work is a steam turbine, and the means to convert shaft work into electricity is an electricity generator.

3. An installation according to claim 2, wherein the first and second working fluids are water.

4. An installation according to claim 2 or claim 3, comprising a boiler for heating the working fluid, a turbine for expanding the heated working fluid, and a heat exchanger receiving partially expanded working f luid from the turbine, the installation further comprising a condenser receiving fully expanded steam from the turbine, a f irst duct f or conducting water f rom. the condenser through the heat exchanger to the boiler, a bypass duct for conducting water from the condenser to the boiler without passing through the heat exchanger, and valve means for controlling the flow of water through the first and the bypass ducts.

5. An installation according to claim 4, wherein the first duct includes a supply branch downstream of the heat exchanger leading to the heat consumer, and a return 29 branch upstream of the heat exchanger f or returning water from the heat consumer to the first duct.

6. An installation according to claim 5 wherein the supply branch includes a supply valve for controlling the flow of working fluid in the supply branch.

7. An installation according to claim 5 or claim 6, wherein a pump is provided to circulate working fluid from the return branch, through the first duct to the supply branch and through the heat consumer.

8. An installation according to claim 4, wherein the turbine is a multistage turbine and wherein the heat exchanger comprises a plurality of heat exchanger units, each of which receives partial ly-expanded working fluid from a respective stage of the turbine.

9. An installation according to claim 8, wherein the flow of part ia 1 lyexpanded working fluid to each heat exchanger unit is controllable by a respective control valve.

10. An installation according to claim 1 wherein the means to produce shaf t work is a gas turbine, and the means to convert shaft work into electricity is an electricity generator.

11. An installation according to claim 10, wherein a compressor is operable to provide intake gas to heating means of the gas turbine.

12. An installation according to claim 10 or claim 11, comprising a heating chamber for heating the working fluid, a turbine for expanding the heated working fluid, and a heat exchanger receiving expanded working fluid from the turbine, the installation further comprising a first duct for conducting intake gas for the heating chamber through the heat exchanger, a bypass duct for conducting intake gas to the heating chamber without passing through the heat exchanger, and valve means for controlling the flow of intake gas through the first and the bypass ducts.

13. An installation according to any of claims 10 to 12, wherein the first duct includes a supply branch downstream of the heat exchanger leading to the heat consumer, and a return branch upstream of the heat exchanger for returning working fluid from the heat consumer to the first duct.

14. An installation according to claim 13, wherein the supply branch includes a supply valve for controlling the flow of working fluid in the supply branch.

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15. An installation according to claim 13 or claim 14, wherein a pump is provided to circulate working fluid from the return branch, through the first duct to the supply branch and through the heat consumer.

16. A method of operating a combined heat and electricity generating installation according to any preceding claim, wherein when the heating demand from the heat consumer is large control means is operative to route working fluid to the heating chamber principally or exclusively via the bypass duct, and wherein when the heating demand from the heat consumer is small then the control means is operative to route working fluid to the heating chamber principally or exclusively via the first duct.

17. A method according to claim 16 wherein the operating parameters of the heating means are controlled in dependence upon the proportions of the working fluid flowing to the heating means through the first and the bypass ducts, respectively.

18. A combined heat and electrical power generating installation substantially as described herein with reference to figures 1 to 3, or figures 4 to 6 of the accompanying drawings.

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19. A method of operating a combined heat and electrical power generating installation, substantially as described herein.