COMBINED CYCLE POWER PLANT

Abstract

The invention relates to a combined cycle power plant that includes, a gas turbine plant, a heat recovery steam generator heated by hot waste gases of a gas turbine plant, and a steam turbine plant driven by the steam produced, and a waste gas purification plant, arranged downstream of the heat recovery steam generator in which carbon oxides in the waste gases can be absorbed by an absorber fluid, which is subsequently regenerated at an elevated temperature in a regenerating section while giving up the carbon oxides for supplying to a storage. The regenerating section has a heater for maintaining a necessary elevated temperature for regeneration. The heater operates with steam from the heat recovery steam generator or from the steam turbine plant. The steam condenses and the resulting hot condensate can be supplied to a flash boiler where it, at low pressure, immediately at least partially evaporates. This steam can be supplied to an appropriate stage of the steam turbine plant according to the steam pressure.

Description

TECHNICAL FIELD

The present invention relates to a combined cycle power plant (CCPP) comprising a gas turbine plant, a heat recovery steam generator (HRSG) heated with hot exhaust gases from the gas turbine plant, and a steam turbine plant driven by the generated steam.

BACKGROUND

Such a CCPP is shown in U.S. Pat. No. 5,839,269. In this known CCPP a steam turbine plant is provided with a high pressure turbine, a medium pressure turbine and a low pressure turbine, whereby high pressure and medium pressure steam is produced in the steam generator for driving the high pressure or medium pressure turbine, and the steam expanded in the medium pressure turbine is used to drive the low pressure turbine. In the CCPP of U.S. Pat. No. 5,839,269 it is also provided that steam with reduced low pressure can be channeled off from a sufficiently hot feed water tank of the steam generator and fed into a medium stage of the low pressure turbine through appropriate steam inlets.

In addition U.S. Pat. No. 5,839,269 discloses a range of measures for optimizing the design of gas turbine plants and for optimizing the operation of gas turbines.

Gas turbine plants and other large combustion plants are typically operated with fuels based on hydrocarbons. This inevitably generates carbon oxides during operation, especially carbon dioxide, which is a green house gas and harmful to the environment, and should therefore be separated from the waste gases of the gas turbine plant. In principle, known waste gas purification plants can be used which are arranged downstream of the respective combustion process and which have an absorbing section and a regenerating section. Carbon dioxide which is carried along within the absorbing section, through which the particular waste gases are flowing, can be absorbed at relatively low temperature using an amine-H₂O-system with the formation of a relatively concentrated amine carbonate solution. The concentrated amine carbonate solution can be subsequently converted in a regeneration section at high temperature into a relatively weak concentration amine-carbonate-solution, whereby carbon dioxide is released and led away and subsequently collected and stored. In lieu of such amine systems other waste gas purification systems, for example systems using chilled ammonia, can also be used.

From US 2011/0314815 A1 it is generally known to equip a CCPP as described above with a downstream waste gas purification plant. in US 2011/0314815 A1 it is shown that a waste gas purification plant with relatively small capacity can be sufficient, if the gas turbine plant is operated with exhaust gas recirculation in such a way that during combustion substantially only completely oxidized hydrocarbons, that is, carbon dioxide and water (and N₂) remain. Otherwise, there is no indication towards an optimal integration of the waste gas purification plant into a CCPP.

SUMMARY

The purpose of the invention is thereby to connect a CCPP with a waste gas purification plant in an optimized way to supply the necessary thermal energy for heating the regeneration section of the purification plant and to use the residual heat for increasing the performance of the steam turbine plant.

In particular, according to the invention, a waste gas purification plant is provided downstream of the gas turbine plant and the heat recovery steam generation plant, the gas purification plant comprising an absorbing section and a regenerating section, whereby inside the absorbing section, through which the waste gases flow, carbon dioxide which is carried in the waste gases is absorbed by an amine-H₂O-system at relatively low temperature forming (relatively) high concentrations of amine carbonate solution, and whereby the concentrated amine carbonate solution is converted into a relatively weak amine carbonate solution in the regeneration section at an elevated temperature giving off carbon dioxide which is led away, whereby the regeneration section can be heated with steam, and the relatively weak amine carbonate solution generated in the regeneration section having an elevated temperature can be supplied via a heat exchanger back into the absorbing section for reuse, and thermal energy can be exchanged in the heat exchanger between the relatively weak concentration of amine carbonate solution and the relatively high concentration of amine carbonate solution being supplied to the regeneration section.

According to a first aspect of the invention the heat for the regeneration of the amine solution is introduced into the regeneration section by way of steam from the steam turbine and/or the steam generator, and the heat from the regenerated amine solution, having an elevated temperature, is used for preheating the high concentration amine carbonate solution led away from the absorbing section. The thermal energy required for regeneration of the amine solution can thereby be substantially reduced.

According to a preferred embodiment, the regeneration section is heated with saturated steam at a specified temperature. It is advantageous that the temperature level is only dependent on the steam pressure, so that the desired temperature can be regulated with the steam pressure.

In the case of a steam turbine plant with a high pressure steam turbine, a medium pressure steam turbine and a low pressure steam turbine, the steam for heating the regeneration section can be taken from the connection between the outlet of the medium pressure turbine and the inlet of the low pressure turbine.

According to an advantageous embodiment of the invention, the hot condensate generated from heating the regeneration section can be supplied to an evaporator of the heat recovery steam generator in order to produce additional steam with low pressure, the steam can then be supplied to a stage of the low pressure turbine, whereby this steam can, if necessary, be channeled through a superheater of the steam generator before being introduced into the low pressure turbine, in order to increase its power output.

Advantageously, the thermal energy, which may need to be conducted away from the absorbing section, can be used to preheat the feed water for the steam generator.

The steam circuits therefore only need to be slightly modified, according to the invention, to supply the necessary thermal energy for the waste gas purification plant and/or to use resulting residual heat for increasing the performance of the steam turbine plant, i.e. the hot condensate is used in a new, additional pressure level (compared to the standard water-steam cycle.

According to a particularly advantageous embodiment of the invention the regeneration of the amine solution in the regeneration section can be carried out at a temperature of 126° C. as opposed to a possible process temperature of about 145° C., whereby the separation of the carbon dioxide out of the high concentration amine carbonate solution supplied to the regeneration section happens at a less than optimal process temperature. This is accepted here because the necessary thermal energy for heating the regeneration section is thereby disproportionally reduced, so that the performance of the CCPP and its efficiency can be substantially increased. As a result, only a relatively small loss of performance must be tolerated compared to a CCPP without downstream waste gas purification.

According to another aspect of the invention the hot condensate or pressurized water is supplied to at least one flash evaporator and allowed at least partly to evaporate there at low pressure so that additional steam is released for operating the steam turbine plant, in particular for the low pressure steam turbine of the steam turbine plant.

Usable steam for operating the low pressure turbine of the steam turbine plant is produced with little effort by introducing hot condensate or pressurized water into the at least one flash boiler, where it boils due to a fast reduction in pressure and evaporates. The physical effect is thereby exploited whereby the boiling point of a liquid is dependent on pressure, and accordingly a hot liquid starts to boil suddenly when it is introduced into a space having low pressure and therefore at least partially evaporates.

According to a preferred embodiment of the invention, where appropriate, a series of flash boilers can be provided, whereby pressurized water or condensate from a first flash boiler is supplied to a second flash boiler which has a lower inner pressure compared to the first flash boiler, so that the pressurized water or condensate, coming out of the first flash boiler, can at least partially evaporate here. If necessary, further flash boilers can be arranged in a cascade. The flash boilers in the flash boiler cascade thereby produce steam with accordingly different pressure levels, whereby the steam of each flash boiler is supplied to an appropriate stage of the turbine, in particular to the low pressure turbine of the steam turbine plant.

The steam coming from a flash boiler can, if necessary, be superheated with the heat recovery steam generator plant of the CCPP in order to drive the respective turbine section more effectively.

Preferred features of the invention can be found in the claims and in the following description of the drawings by way of which particularly preferred embodiments of the invention are described in more detail.

Protection is not only claimed for the indicated or shown combination of features but also for any combination of the shown or indicated individual features.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings show in:

FIG. 1 a highly schematized representation of a CCPP according to the invention,

FIG. 2 a schematized representation of a waste gas purification plant according to the invention,

FIG. 3 a representation of an advantageous connection of the regeneration section of the waste gas purification plant to a CCPP or its steam generator or its low pressure steam turbine of the steam turbine plant

FIG. 4 a schematized representations for the use of a hot condensate or pressurized water from the power plant or waste gas purification plant, and

FIG. 5 an advantageous variation of the arrangement shown in FIG. 3.

DETAILED DESCRIPTION

According to FIG. 1 the CCPP according to the invention comprises a gas turbine plant 1, which can have a generally known construction, for example as in the above mentioned U.S. Pat. No. 5,839,269, and having a compressor 11, at least one combustion chamber 12 and a gas turbine 13. The hot waste gases 100 of the gas turbine plant 1 then flow through a heat recovery steam generator 2. Arranged downstream of the heat recovery steam generator 2 is a waste gas purification plant 4, which is described below. The steam produced in the heat recovery steam generator 2 drives a steam turbine plant 5. The gas turbine plant 1 and the steam turbine plant 5 can drive generators 3 or the like respectively, whereby it is possible in principle to couple the rotor shafts R of the gas turbine plant 1 with those of the steam turbine plant 5 and use a common generator 3.

For driving the steam turbine plant 5 a steam circuit can be provided as described in the following:

Water is fed by a pump 7 from a feed water tank 6 into a heater 8, which is arranged inside of a heat recovery steam generator 2 in the waste gas path. At the outlet of the heater 8 there is high pressure water with, for example, a pressure of 160 bar and a temperature of 300° C. In a tube register 9 downstream of the heater 8 the high pressure water is evaporated and superheated, so that high pressure steam is available at the outlet of the tube register 9. This superheated, high pressure steam is supplied to a high pressure steam turbine 51 of the steam turbine plant 5, whereby the high pressure steam expands inside the high pressure turbine 51. The steam expanded in this way, CRH (Cold Reheat), is subsequently supplied through a further tube register 10, so that this steam is reheated. The steam from the tube register 10 is supplied to a medium pressure turbine 52 of the steam turbine plant 5, whereby the steam expands in the medium pressure turbine 52 so that there is low pressure steam downstream of it, which, if necessary, can be further heated in a tube register (not shown) and supplied to a low pressure turbine 53 of the steam turbine plant 5. The steam expanded in the low pressure turbine 53 subsequently flows into an air- or water-cooled condenser 109. The condensate produced there is then supplied by a pump 111 back to the feed water tank 6.

According to FIG. 2, the waste gas purification plant 4 comprises an absorbing section 41 through which the waste gas flows, and a regeneration section 42 in order to regenerate the absorbing medium from section 41 and to supply it back to the absorbing section 41. At the outlet of the absorbing section 41 there are waste gases 1000 free of carbon oxides.

Inside the absorbing section 41 the waste gases 100 flow through a bath of water and amine solution, whereby the carbon dioxide in the waste gases 100 is bonded by the water to form carbonic acid, which with the amines then forms a relatively high concentration of amine carbonate solution. This relatively high concentration of amine carbonate solution is supplied to the regeneration section 42 by a pump 113. Inside the regeneration section 42 a high temperature is maintained, for example a temperature from about 120° to 145° C., at which the relatively high concentration of amine carbonate solution is converted into a relatively weak concentration of amine carbonate solution, giving off carbon dioxide in the process, whereby the carbon dioxide is supplied by a compressor 114 to a store or the like (not shown).

The temperature necessary for the regeneration process in the regeneration section 42 can be maintained by circulating the relatively weak concentration of amine carbonate solution, produced in the regeneration section 42, in a circuit through a heater 115, which is itself heated with steam as described below.

The relatively weak concentration of amine carbonate solution is supplied back to the absorbing section 41 by a pump 116, whereby on returning the solution flows through a heat exchanger 112 through which the relatively high concentration of amine carbonate solution being supplied to the regeneration section 42 also flows (in opposite directions), so that the high concentration of amine carbonate solution supplied to the regeneration section 42 is pre-heated and the heater 115 requires a relatively low thermal input for maintaining the necessary temperature for the regeneration process.

The heater 115 of the regeneration section 42 is preferably heated with steam, in particular saturated steam, which can be diverted off at point A in FIG. 1 in the steam path between the medium pressure steam turbine 52 and the low pressure steam turbine 53 of the steam turbine plant 5. This channeled off steam condenses at or in the heater 115 whilst giving up heat to the relatively low concentration amine carbonate solution. The thereby generated condensate K, the temperature of which is around the operating temperature of the regeneration section 42, i.e. at a temperature between about 120° C. and 145° C., can then be supplied according to FIG. 3 to an evaporator 118 and therein heated with heat from the heat recovery steam generator 2. The steam generated there, the pressure of which is below the pressure of the steam supplied to the inlet of the low pressure steam turbine, can be subsequently superheated and supplied via appropriate steam inlets to an intermediate stage of the low pressure steam turbine 53.

Alternatively, the steam produced by the evaporator 118 can be supplied to the heater 115 together with the steam channeled off from point A, preferably superheated. The dotted line in FIG. 3 shows such option.

Alternatively, the condensate K from the heater 115 can also be introduced into the feed water tank 6 so that, on the one hand, the feed water is accordingly heated.

As a result the condensate K from the heater 115 is used for producing steam having a very low pressure for introducing into an intermediate stage of the low pressure steam turbine 53. The waste gas purification plant is therefore used to generate a fourth steam pressure level, in addition to the steam pressure levels for the high, middle, and low pressure steam turbines of the steam turbine plant 5. The steam turbine plant 5 and the heat recovery steam generator 2 are only slightly modified by the waste gas purification plant 4.

It has proved advantageously to operate the regeneration section 42 of the waste gas purification plant 4 at a relatively low temperature, which is actually suboptimal for the regeneration process. The thermal energy requirement of the heater 115 is thereby disproportionally reduced, with the result that the loss of performance of the CCPP, due to the necessary removal of thermal energy during the operation of the waste gas purification plant 4, is kept low.

The absorbing section 41 of the waste gas purification plant, through which the hot waste gases 100 flow, must be cooled in order to maintain the necessary low temperature for the absorption process. This temperature is about 40° C. in case of the amine system, and about 5° C. in case of the chilled ammonia process.

According to an embodiment, shown in FIG. 4, the hot condensate K from heater 115 is supplied by a pump 116 to the inlet of a flash boiler 117, whereby a regulating valve 118 is arranged at the inlet of the flash boiler 117 in order to maintain a pressure in the line between the flash boiler 117 and the pump 116, whereby the pressure is above the boiling pressure of water at the prevailing temperature of the condensate K. In the flash boiler 117 there is a lower pressure compared to the pressure in the line between the pump 116 and the flash boiler 117, so that the condensate K introduced into the flash boiler 117, to a greater or less extent, immediately evaporates (flashes to steam). The very low pressure steam produced, the pressure of which is below the steam pressure at A in the steam path between the medium pressure turbine and the low pressure turbine, can now be supplied to an intermediate stage of the low pressure turbine 53. By increasing the pressure of the hot condensate K using pump 116, the pressure and the quantity of the flashed steam, produced in the boiler 117, can be increased.

According to a preferred variation of this embodiment the very low pressure steam from the flash boiler 117 can be superheated in a heater 119 before it is introduced into the low pressure turbine 53. The heater 119 can itself be heated with steam from the outlet of the high pressure turbine (CRH) or preferably by flue gas in the heat recovery steam generator (HRSG). In principle any other heat source could also be used.

According to another embodiment of the invention, as shown in FIG. 5, in place of a single flash boiler 117, there can be a cascade of flash boilers 117, 117′, 117″, whereby the condensate coming from each flash boiler 117, 117′ is supplied to a subsequent flash boiler 117′, 117″ through a further regulating valve 118′, 118″, whereby the pressure in the subsequent flash boiler 117′, 117″ is lower than the pressure in the preceding flash boiler 117, 117′, so that the condensate supplied to it partially evaporates quickly. For example, the cascade may comprise three flash boilers 117, 117′, 117″, as shown in FIG. 5.

As mentioned above, the pump 116 in FIGS. 4 and 5 can be used for increasing the hot condensate (K) pressure, so as to increase the pressure and quantity of the flashed steam.

In this way, steam flows having subsequently decreasing pressures can be directed from the flash boilers of the flash boiler cascade 117, 117′, 117″ and be supplied to appropriate different stages of the low pressure steam turbine 53.

In this embodiment the steam flows, supplied to the low pressure steam turbine, can also be superheated in appropriate heaters 119, before they are introduced into the low pressure steam turbine 53. The heater 119 may be heated by steam from any suitable source.

This embodiment is based on the general idea that condensed water exiting at relatively high temperature can be (partially) evaporated in flash boilers at low pressure, and the steam produced can be used for driving the steam turbine.

Claims

1. A combined cycle power plant (CCPP) comprising, a gas turbine plant,a heat recovery steam generator through which hot waste gases from the gas turbine plant flow,a steam turbine plant driven by steam from the heat recovery steam generator, anda waste gas purification plant, arranged downstream of the heat recovery steam generator, having an absorbing section in which carbon dioxide in the waste gases is absorbed by an absorber fluid, whereby the waste gas purification plant comprises a regeneration section which is supplied with the absorber fluid loaded with carbon dioxide, whereby the absorber fluid can be regenerated at an elevated temperature while giving up the carbon dioxide for supplying to a storage, and whereby the regenerated absorber fluid is supplied back into the absorbing section for absorbing the carbon dioxide in the waste gases, whereby the regeneration section comprises a heater which is heatable with the steam from the heat recovery steam generator or from the steam turbine plant, whereby the supplied steam condenses in or at the heater and the resulting hot condensate is supplied to at least one evaporator, where it is at least partially evaporated to steam and whereby this steam is introduced into a stage of the steam turbine plant, in particular into an intermediate stage of the low pressure turbine of the steam turbine plant.

2. The combined cycle power plant according to claim 1, further comprising a heat exchanger is arranged between the absorber section and the regeneration section, whereby the absorber fluid from the regeneration section being led back into the absorbing section, and the absorber fluid from the absorbing section being supplied to the regeneration section through the heat exchanger.

3. The combined cycle power plant according to claim 1, wherein the thermal energy extracted from the absorbing section is used for preheating fuel for the gas turbine plant or for preheating feed water for the steam turbine plant.

4. The combined cycle power plant according to claim 1, wherein a part of the steam generated by the at least one evaporator is added to the steam supplied to the heater of the regeneration section.

5. The combined cycle power plant according to claim 1, wherein the steam generated by the at least one evaporator is superheated in a heater of the heat recovery steam generator and then supplied to a middle stage of the low pressure turbine of the steam turbine plant.

6. The combined cycle power plant according to claim 1, wherein the steam turbine plant comprises a high pressure steam turbine, a medium pressure steam turbine and a low pressure steam turbine, whereby steam is taken from a point between the outlet of the medium pressure steam turbine and the inlet of the low pressure steam turbine for heating the heater of the regeneration section.

7. The combined cycle power plant according to claim 1, wherein the condensate is supplied to a cascade of flash boilers, whereby pressurized water or condensate from a first flash boiler is supplied to a second flash boiler which has a lower inner pressure relative to the first flash boiler, so that the pressurized water or condensate from the first flash boiler can at least partially evaporate, whereby the steam produced by the flash boilers is supplied to one or more stages of the steam turbine plant, in particular to the low pressure steam turbine, corresponding to their different pressures.

8. The combined cycle power plant according to claim 7, wherein the steam from the at least one flash boiler is superheated, e.g. with the heat recovery steam generator, before being introduced into a stage of the steam turbine plant.

9. The combined cycle power plant according to claim 7, wherein the steam from the at least one flash boiler is superheated by the steam, coming from the outlet of the high pressure steam turbine of the steam turbine plant.

10. The combined cycle power plant according to claim 1, wherein the remaining condensate from the at least one evaporator is supplied to the feed water tank of the steam turbine plant.