EP0724683A1

EP0724683A1 - Integration construction between a steam boiler and a steam turbine and method in preheating of the supply water for a steam turbine

Info

Publication number: EP0724683A1
Application number: EP94928907A
Authority: EP
Inventors: Ilmari MÄKILÄ; Markku Raiko; Sasu Valkamo; Jarmo Tuominen
Original assignee: Imatran Voima Oy
Current assignee: Fortum Power and Heat Oy
Priority date: 1993-10-19
Filing date: 1994-10-11
Publication date: 1996-08-07
Anticipated expiration: 2014-10-11
Also published as: DE69425064T2; WO1995011370A1; EP0724683B1; AU7814694A; DE69425064D1; FI934603A0; ATE194208T1; FI934603A; GR3034073T3; FI101163B; DK0724683T3; PT724683E; EE03219B1; ES2148346T3

Abstract

The invention concerns an integration construction between a steam boiler and a steam turbine and a method for preheating of the supply water. In the integration construction the steam is passed from the steam boiler (10) along the duct (24a) into the steam turbine (11) so as to rotate the electric generator (12) which generates electricity. The economizer (23) consists of at least two parts, comprising at least one first economizer part (23') and at least one second economizer part (23''). The supply water is passed from the cold economizer part (23') to a supply-water preheater, which consists of a heat exchanger (24) in which thermal energy is transferred from bled steams of the steam turbine, either directly or through a medium, preferably water, into the supply water. After this, the supply water, which had been preheated by means of bled steams from the steam turbine, is passed in the steam boiler (10) into the hot economizer part (23'') and further to the vaporizer (240) and into the superheater (24) and through the superheater into the steam turbine.

Description

Integration construction between a steam boiler and a steam turbine and method in preheating of the supply water for a steam turbine

The invention concerns an integration construction between a steam boiler and a steam turbine and a method in preheating of the supply water for a steam turbine.

The last heat face of a steam boiler before the smokestack is either a flue-gas/air heat exchanger or an economizer. In the present application, a flue-gas/air heat exchanger is understood as a heat exchanger between flue gas and combustion air, in which the heat is transferred from flue gas to combustion air to preheat the combustion air. In the present application, an economizer is understood as a heat exchanger in which thermal energy is transferred from the flue gases to the supply water.

When a flue-gas/air heat exchanger is used, the supply water for the boiler can be preheated by means of bled steam from the steam turbine, whereby the efficiency of the steam turbine process is improved. A flue-gas/air heat exchanger, i.e. a heat exchanger in which thermal energy is transferred from the flue gases directly into the combustion air, is usually not used in small steam power plants because of its high cost.

When a flue-gas/air heat exchanger is not used, the flue gases of the steam boiler are cooled, before they are passed into the smokestack, by means of an economizer. In such a case, the supply water cannot be preheated by means of bled steam from the steam turbine, because the preheating would raise the ultimate temperature of the flue gases and would thereby lower the efficiency of the boiler.

From the prior art, also the mode described in the patent DE 2 243 380 is known for integration of a steam boiler and a steam turbine. In the method, the supply water is divided into two parts, i.e. into a duct passing to the boiler and into a duct passing to the high-pressure preheating plant. It is an advantage of said invention that the flue-gas/air heat exchanger can be substituted for by means of this solution. On the other hand, the complexity of the system is a drawback.

From the prior art, also the solution described in DE 3 111 Oil Al is known, in which the supply water is preheated, out of control-technical reasons, both by means of bled steam and by means of flue gases. Further, the solution also includes a flue- gas/air heat exchanger. A drawback is the complexity and the high cost of the system of integration.

In the economizer of a steam boiler, heat is transferred from the flue gases to the supply water. The change in the temperature of the supply water in the economizer is lower than the change in temperature at the flue gas side. The increase in the temperature of the supply water is, as a rule, 40...50 % of the corresponding lowering of the temperature at the flue gas side. Therefore, the difference in temperature at the hot end of the economizer is considerably higher than at the cold end. It follows from this observation that, besides the heat obtained from the flue gases, also other heat can be transferred to the supply water. In a steam turbine process, it is advantageous to utilize bled steam for preheating of the supply water.

The idea of the present invention is to divide the economizer of the steam boiler of a steam power plant into two or more parts, the supply water being preheated in the preheaters of the high-pressure side fitted between said economizer parts by means of bled steam from the steam turbine.

By means of the invention, integration of the steam boiler and of the steam turbine process is made more efficient. By means of the arrangement in accordance with the invention, the flue gases of the steam boiler can be cooled efficiently at the same time as the efficiency of the steam turbine process is improved. The investment cost is lower than that of an alternative provided with a flue-gas/air heat exchanger: improved controllability and boiler efficiency smaller boiler building - lower cost of the boiler.

When a flue-gas/air heat-exchanger solution is unprofitable, by means of the present invention it is possible to achieve an improved process when the use of bled steam can be increased.

The invention is advantageous especially when the combustion air of the steam boiler is heated in one or several steam/air heat exchangers that are connected in series and that utilize bled steam.

The integration construction in accordance with the invention between a steam boiler and a steam turbine is mainly characterized in that the economizer consists of at least two parts, comprising at least one first economizer part and at least one second economizer part, whose supply water is hotter, and that the supply water is passed from the first economizer part to a supply-water preheater, which consists of a heat exchanger in which thermal energy is transferred from bled steams of the steam turbine, either directly or through a medium, preferably water, into the supply water, after which the supply water, which had been thus preheated by means of bled steams from the steam turbine, is passed in the steam boiler into the second economizer part and further through the vaporizer into the superheater and through the superheater into the steam turbine.

The method in accordance with the invention in steam turbine operation is mainly characterized in that, in the method, the supply water is, before the vaporizer, preheated in at least three steps, the preheating involving at least two economizer parts and the first preheating of the supply water taking place by means of thermal energy taken out of the flue gases in the first economizer part, and that there is at least one second preheating stage between the economizer parts, in which stage the preheating of the supply water is carried out by means of bled steams or by means of thermal energy taken out of said steams, the supply water that has been preheated in the method by means of bled steam being thereupon passed into the second economizer part, in which the supply water is hotter, and further into the vaporizer and into the superheater and further, in the form of steam, into the steam turbine so as to rotate an electric generator and to generate electricity.

The invention will be described in the following with reference to some preferred embodiments of the invention illustrated in the accompanying figures, the invention being, yet, not supposed to be confined to said embodiments alone.

Figure 1 shows a first preferred embodiment of the integration construction in accordance with the invention, in which the boiler construction comprises an economizer for preheating the supply water by means of thermal energy taken out of the flue gases, which economizer is divided into two parts, the supply water duct between said economizer parts being provided with a supply-water preheater, which consists of a heat exchanger in which heat is transferred from bled steams to preheating of the supply water.

Figure 2 shows an embodiment of the invention in which the economizer is divided into two parts, between which there are two preheaters of supply water, which consist of heat exchangers in which the supply water is preheated in two steps by means of bled steams from the steam turbine.

Figure 3 is a temperamre/thermal-capacity graph of an economizer operation as per the embodiment of Fig. 1.

Figure 4 is a temperature/thermal-capacity graph of the economizer of a steam boiler as per Fig. 2.

Figure 5 is a temperature/thermal-capacity graph of an economizer operation in which the economizer consists of three parts and in which preheating of the supply water is carried out between die parts of the economizer by means of bled steams.

Fig. 1 shows a first preferred embodiment of the invention. In the embodiment of Fig. 1, the steam boiler is denoted with the reference numeral 10, the steam turbine with the reference numeral 11, and the electric generator that is rotated by the turbine and that generates electricity with the reference numeral 12. In the embodi¬ ment of Fig. 1, the combustion air is introduced (arrow I^) by means of the fresh- air blower 14 of the boiler 10 along the duct 13 into the furnace M of the boiler 10. The fuel is introduced along the duct 15 as is indicated by the arrow 1^.

The frame constructions of the boiler 10 are denoted with the reference R. The flue gases are passed from the boiler 10 into the smokestack 16.

In the embodiment of Fig. 1, the condenser is denoted with the reference numeral 17 and the supply water tank with the reference numeral 18. From the condenser 17, which is a heat exchanger, there is, for example, a district heating duct 17a for utilization of the condensing heat. The condensate pump is denoted with the refer¬ ence numeral 19.

To the supply- water tank 18, there is a bled-steam duct 20 from the steam turbine. The steam duct 21a from the steam turbine 11 communicates with the inlet side of the condenser 17, and the condensate- water duct 21b communicates with the outlet side of the condenser 17, while the condensate- water pump 19 circulates the conden¬ sate water into the supply water tank 18.

From the supply water tank 18 there is a supply water duct 22a to the economizer 23', i.e. to the heat exchanger, which is placed inside the frame construction R of the boiler 10 as one heat face in connection with the flue gas duct D. In this connection, heat is transferred from the flue gas S before the smokestack 16, by means of the heat exchanger 23, to the supply water. The heated supply water is made to flow by means of the pump 190 along the duct 22b to the supply- water preheater, i.e. the heat exchanger 26, to which a bled-steam duct 27a passes and from which heat exchanger 26 there is a duct 27b for condensate water to the supply water tank 18. Thus, in the heat exchanger 26, preheating of the supply water that flows in the duct 22b is carried out by means of the thermal energy obtained from bled steams. The supply water is passed further along the duct 22b, after it has been brought to a higher temperature, into the second part 23" of the economizer 23, i.e. of the flue-gas/supply- water heat exchanger, and further from the economizer 23" through the vaporizer 240 to the superheater 24 and, in the form of steam, along the duct 24a, to the steam turbine 11.

Fig. 2 shows an embodiment of me invention which is in the other respects similar to that shown in Fig. 1, except that combustion-air preheaters 25a, 25b, i.e. steam/air heat exchangers, are placed in the duct 13. They are heat exchangers in which bled- steam heat is transferred to the combustion air. It is a further difference in compari¬ son with the embodiment shown in Fig. 1 that, between the first part 23' and the second part 23" of d e economizer of the boiler, the supply water is heated in two stages by means of thermal energy recovered from bled steams.

In Fig. 2, as is also the case in the embodiment of Fig. 1, the steam boiler is denoted with the reference numeral 10, the steam turbine with the reference numeral 11, and me electric generator that generates electricity and that is rotated by the turbine with the reference numeral 12. The combustion air is introduced (arrow L_j) by means of the fresh-air blower 14 of the boiler 10 along the duct 13 into the furnace M of the boiler 10. The fuel is supplied along die duct 15 in d e way indicated by the arrow I^.

The frame constructions of the boiler 10 are denoted with me letter R. The flue gases are passed from me boiler 10 into the smokestack 16.

The condenser is denoted with the reference numeral 17, and me supply water tank with the reference numeral 18. The condenser 17 is a heat exchanger. It comprises a cooling- water duct 17a for removal of the condensate heat. Thus, condensate heat is transferred from the exhaust steam of the turbine to the cooling water. The condensate pump is denoted with the reference numeral 19.

From the steam turbine 11 there is a bled-steam duct 20 to the supply water tank 18. The exhaust-steam duct 21a from the steam turbine 11 communicates with the inlet side of d e condenser 17, and me condensate- water duct 21b communicates with the outlet side of die condenser 17 while die condensate- water pump 19 circulates the condensate water into me supply water tank 18. From the supply water tank 18 there is a supply-water duct 22a to die heat exchanger 23.

In the embodiment of Fig. 2, me supply water is made to flow by means of the pump 190 along the supply- water duct 22a to the economizer 23', i.e. to the flue- gas/supply-water heat exchanger, in which thermal energy of the flue gas is trans¬ ferred into die supply water through tubular heat faces of equivalent placed in me heat exchanger 23' in the flue-gas duct D. Along die duct 22b, die supply water which has been preheated in accordance widi the invention is passed further into a first heat exchanger 26a, to which there is a bled-steam duct 27a from the steam turbine 11 and from which mere is an outlet duct 27b for condensate/steam into the supply water tank 18.

After this, ie supply water that was preheated by means of bled steam from the steam turbine in the first heat exchanger 26a is transferred into a second heat exchanger 26b, to which there is a bled-steam duct 28a from the higher-pressure steam turbine side and from which there is an outlet duct 28b. The duct 28b passes to die heat exchanger 26a, so that the condensate is transferred further through die outlet duct 27b into the supply water tank 18. Thus, the supply water tiiat was preheated in two stages by means of bled steams is transferred into die second part 23" of the two-part economizer of the boiler 10, from which part 23" the supply water is passed further into the vaporizer 240 placed next to die furnace of the boiler and into die superheater, and drrough its heat exchanger constructions along the duct 24a, in die form of steam into the steam turbine 11.

In the embodiment of Fig. 2, it is preferable that die bled-steam duct 27 includes a branch point C₂ for passing a bled-steam duct 29a to die heat exchanger 25a for preheating of the combustion air, and mat die bled-steam duct 28a includes a branch point C₃ for passing a bled-steam duct 30a to me heat exchanger 25b. From the heat exchangers 25a,25b tiiere are ducts 29b,30b to d e branch point C₄ for passing the condensate to d e duct 27b and further into the supply water tank 18.

Within die scope of d e invention, an embodiment is also possible in which bled steam of the same pressure level is passed into one or several supply-water pre¬ heaters and/or into one or several combustion-air preheaters.

Thus, in the construction illustrated in Fig. 2, die preheating of the supply water is carried out by means of bled steams from the steam turbine between the two parts of the two-part economizer. Further, in the construction, by means of the thermal energy recovered from the bled steams, combustion air is also heated, which is passed along die duct 13 into the furnace M of the boiler 10.

Fig. 2 illustrates a preferred mode of carrying out the invention. The supply water is passed into die first economizer package 23' of the steam boiler at a temperature of about 100°C from the supply water tank. The supply water is heated in the first economizer package to about 150°C. After this the supply water is passed to the high-pressure side bled-steam preheater, i.e. to the heat exchanger 26a, in which the supply water is preheated by means of bled steam to about 175°C. From the high- pressure side supply-water preheater, d e supply water is passed to the second preheater, to die heat exchanger 26b, where the supply water is heated to about 200°C, and further into the second economizer package 23", where the supply water is heated by further 50...100°C. At the same time, the combustion air is preheated, likewise by means of bled steam, in one or several steps, preferably to a temperature of about 200°C. In the preheaters of air and supply water, it is preferable to use die same bleeding points C₂ and C₃ of die steam turbine.

Fig. 3 shows a temperature/thermal-capacity graph of an economizer which corre¬ sponds to die embodiment of Fig. 1. The temperature is indicated in d e vertical system of coordinates, and the thermal capacity in the horizontal system of coordinates. In die figure, the temperature increase line 1-2 illustrates a conventional prior-art solution, in which the supply water is heated from the state 1 to the state 2 and die flue gases are cooled from the state 3 to die state 4. Further, in the figure, the solution of Fig. 1 is illustrated, in which, from the stams point 5 to me stams point 6, preheating of the supply water is carried out by means of bled steams, after which the supply water is heated further in the latter part 23" of the economizer from the stams point 6 to the stams point 7.

Fig. 4 is a temperature/thermal-capacity graph of an economizer corresponding to the embodiment of Fig. 2. The embodiment of the figure is in the other respects similar to the illustration in Fig. 2 except that from the stams point 5 to the stams point 6 the preheating of the supply water is carried out in two steps, first from the point 5 to the point 5a and from the point 5a to the point 6. From the point 5 to the point 5a, the preheating of the supply water is carried out by means of bled steams at a lower pressure of steam, and from the stams point 5a to the stams point 6 the preheating of the supply water is carried out by means of bled steams at a higher pressure of steam. Thus, in the illustration in Fig. 2, the preheating of the supply water takes place in four steps: from the stams point 1 to the stams point 5 by means of the first part 23' of the economizer; from the stams point 5 to the stams point 5a and from me stams point 5a to the stams point 6 by means of bled steams by means of the heat exchangers 26a, 26b, and from the stams point 6 to the stams point 7 by means of the second part 23" of the economizer.

Within the scope of the invention, of course, an embodiment is possible in which the economizer comprises more than two parts, between which parts preheating of the supply water is carried out separately by means of bled steams. An operation of an economizer in three parts is illustrated by d e temperamre/thermal-capacity graph of an economizer in Fig. 5. Preheating of the supply water by means of bled steams takes place between the economizer parts 23 ',23" from the status point 5 to the stams point 5a, and between me economizer parts 23" and 23"' from the stams point 5b to the stams point 6.

Claims

1. An integration construction between a steam boiler and a steam turbine, in which integration construction the steam is passed from the steam boiler (10) along the duct (24a) into die steam turbine (11) so as to rotate the electric generator (12) which generates electricity, and in which integration construction the supply water that has been circulated through d e steam boiler (10) is vaporized in the vaporizer (240) placed in d e steam boiler (10) and superheated in the superheater (24), into which vaporizer and superheater the supply water is passed through an economizer (23), which is a heat exchanger in which heat is transferred from the flue gases into the supply water, c h a r a c t e r i z e d in that the economizer (23) consists of at least two parts, comprising at least one first economizer part (23') and at least one second economizer part (23"), whose supply water is hotter, and tiiat the supply water is passed from the first economizer part (23') to a supply-water preheater, which consists of a heat exchanger (24) in which thermal energy is transferred from bled steams of the steam turbine, eitiier directly or tiirough a medium, preferably water, into the supply water, after which the supply water, which had been thus preheated by means of bled steams from the steam turbine, is passed in the steam boiler (10) into the second economizer part (23") and further to the vaporizer (240) and into the superheater (24) and through the superheater into the steam turbine.

2. An integration construction as claimed in claim 1, c h a r a c t e r i z e d in diat the heat exchanger faces of the economizer (23) are placed in the flue-gas duct (D) of me steam boiler (P), and diat the supply water is first made to flow in me economizer part (23') that is placed at die trailing side of die flue-gas flow, seen in the flow direction (S) of me flue gases, and only thereafter, through bled-steam preheating, into the second economizer part (23"), which is placed, in relation to the first-mentioned economizer part (23'), at the inlet side of the flue-gas flow, seen in die flow direction (S) of die flue gases.

3. An integration construction as claimed in claim l or 2, c h a r a c t e r i z e d in that die supply- water preheater consists of two heat exchanger parts, into the first one of which bled steams are passed at a lower pressure, and into the latter one of which, seen in the flow direction (23) of die supply water, bled steams are passed at a higher pressure, the preheating of the supply water passed to die steam boiler (11) taking place in two steps.

4. An integration construction as claimed in any of die preceding claims, c h a r ¬ a c t e r i z e d in that, besides for preheating of supply water, bled steams are also used for preheating of combustion air (L_j), the integration construction comprising a bled-steam duct to a combustion-air preheater (25a,25b), which preheater consists of heat exchangers through which bled steams are passed, which bled steams, after they have delivered their heat to the combustion air, are passed as condensate water into the supply water tank (18).

5. An integration construction as claimed in the preceding claim, c h a r a c t e r - i z e d in that die combustion air is preheated by means of bled steams in at least two steps, bled steams at a lower steam pressure being passed into the first step, into its heat exchanger (25a), and bled steam at a higher steam pressure being passed into the latter step (seen in the air flow direction Li), into its heat exchanger (25b), and mat from the bled-steam duct (27a), which passes to the first preheater (26a) of supply water, from its branch point (C₂), a bled-steam duct (29a) is passed to the first combustion-air preheater (25a), to its heat exchanger, and tiiat from the second bled-steam duct (28a), which passes to the second preheater (26b) of supply water, tiirough the branch point (C₃), a bled-steam duct (30a) is passed to die second combustion-air preheater (25b), to its heat exchanger.

6. A method in preheating of the supply water for a steam turbine, in which steam turbine construction the supply water is passed into the economizer (23) of the steam boiler (10), in which economizer heat is transferred in a heat exchanger from the flue gases into the supply water, and tiiat said economizer is fitted so tiiat its heat faces are at least partly placed in the flue-gas duct (D) of d e steam boiler (11), c h a r a c t e r i z e d in that, in the method, the supply water is, before the vaporizer (240), preheated in at least three steps, the preheating involving at least two economizer parts (23 ',23") and die first preheating of die supply water taking place by means of thermal energy taken out of the flue gases in the first economizer part (23'), and tiiat there is at least one second preheating stage between the economizer parts (23 ',23"), in which stage the preheating of the supply water is carried out by means of bled steams or by means of thermal energy taken out of said steams, the supply water that has been preheated in the method by means of bled steams being thereupon passed into the second economizer part (23"), in which the supply water is hotter, and further into the vaporizer (240) and into the superheater (24) and further, in the form of steam, into the steam turbine (11) so as to rotate an electric generator (12) and to generate electricity.

7. A method as claimed in the preceding claim, c h a r a c t e r i z e d in tiiat, besides die supply water, die combustion air is also preheated by means of energy taken out of bled steams.

8. A method as claimed in die preceding claim, c h a r a c t e r i z e d in that, in the method, bled steam is passed, at die same pressure level, besides to preheating of supply water, also to preheating of combustion air, and that bled steam is passed at die same pressure from the same duct both to preheating of combustion air and to preheating of supply water.