AU2006284266A1 - Condensation method - Google Patents

Description

DECLARATION 1, Mrs MARINA ANGELIKA BREWIS, a sworn translator of Hahn Forum, 222 Richard Street, Hatfield 0083, Pretoria, Republic of South Africa do solemnly and sincerely declare that I have a competent knowledge of the English and German languages and that the following is a true and accurate translation of PCT/DE2006/001097 (International Publication WO 2007/022738 Al) entitled: "Condensation Method". DATED AT PRETORIA THIS 21st DAY OF AUGUST 2007 MRS M A BREWIS MANUNA ANGEUKA BREWIS SWORN iRAWSATOR EEDIGDE VERTALE

PRETORLA

WO 2007/022738 1 PCT/DE2006/001097 Condensation Method The invention relates to a condensation method having the features as set out in the generic clause of patent claim 1. The efficiency of a power station is a factor which, in particular when planning new power stations, has a decisive influence on the economic viability. Numerous efforts have thus been made to optimise steam power processes in thermal power stations. In this context, particular emphasis is also placed on the condensation system. Especially in the case where such air-cooled condensers are employed as are frequently used at the location of a power station in the event of water shortage, the potential with regard to the efficiency of a power station has not yet been optimally exploited. Air-cooled condensers suffer from the basic drawback that only the dry air temperature can be used. In addition, when operated at particularly low waste steam pressures, excessive cooling of the condensate is likewise greater than in the case of water-cooled surface condensers. Air-cooled condensers normally have two condensation stages. In a first condensation stage about 80-90% of the waste steam of a turbine is condensed. A 100% condensation in the first condensation stage is virtually impossible due to the process-related parameters, such as e.g. the fluctuating outside temperatures, so that a second condensation stage is in any case required for the condensation of residual steam. For this reason, air-cooled condensers installed in condensation or dephlegmatisation mode are frequently combined, mariia\trie\ CM Condensationi Method GFA PC 2 108 2007 WO 2007/022738 2 PCT/DE2006/001097 the condensation with dephlegmatisation being provided for residual steam condensation, i.e. forming the second condensation stage. Normally, the condensate obtained is fed directly to a condensate collection tank. The condensate is subsequently supplied to a degasifier, in which treated additional water is admixed, serving to replace losses which have occurred as a result of leakage, in order to be then fed again to an evaporator connected upstream of the turbine by means of a feed pump. Since the condensate in the degasifier must again be brought to boiling temperature for degasification purposes, it is a drawback for the energy balance if the condensate has previously been supercooled too much, since ultimately an increased energy supply must be realised by employing primary fuels. The aim is, therefore, to keep the excessive cooling of the condensate as low as possible in order to minimise the employment of primary fuels. The aim is at the same time to keep the amount of energy to be employed for the condensation of the turbine waste steam likewise at a minimum. It is the object of the invention to provide a condensation method, wherein the excessive cooling of the condensate may be minimised in order to improve the efficiency of the power station. This object is attained by a condensation method having the features of patent claim 1. It is an essential feature of the method according to the invention that the condensate flow obtained in the condenser, prior to its introduction into a condensate collection tank, is heated in a condensate heating stage specifically provided for this purpose. Heating of the condensate flow is performed by the turbine waste steam during the condensate heating stage. The partial flow of steam emerging from the condenser is simultaneously fed to a degasifier, in marina\trIc\ CM Condensation Medhod GEA PCT 2 108 2007 WO 2007/022738 3 PCT/DE2006/001097 which the partial flow of the steam heats colder additional feed water and is itself fully condensed. In the installation mode according to the invention a condensate heating stage, provided in addition to a degasifier, allows to significantly minimise the excessive cooling of the condensate and, as a result, to reduce the use of primary fuels. Model calculations have confirmed that excessive cooling of the condensate observable in air-cooled condensers of conventional construction, may be reduced in a range of about 1 - 6 K to about 0,5 K, as compared with the temperature in the saturation state behind the turbine. The power station efficiency increases according to the reduction of excessive cooling. In a 600 MW power station the thermal efficiency may be improved by up to about 0,25%, which, in view of the dimensions of the power plant, must not be seen as a negligible quantity. In the method according to the invention, the thermal energy of the turbine waste steam flow is utilised substantially more effectively, because it is not released into the environment by the condensers, but to a large extent flows into the condensate, i.e. is preserved to the largest possible extent in the thermal circuit. The reduced energy losses bring about the intended improvement of the power station efficiency. By heating the supercooled condensate, a simultaneous condensation of a portion of the turbine waste steam flow is attained so that less waste steam enters the condenser. As a result, the condensers may possibly be designed in smaller dimensions. Advantageous embodiments of the inventive concept form the subject of the subsidiary claims. In the method according to the invention it suffices if the first condensation stage, i.e. the air-cooled condenser, is installed exclusively in dephlegmatisation mode, since a degasifier, required in any case in steam power processes, may be used mariaa\IrIc\ CM Condensation Method GEA PCT 21 08 2007 WO 2007/022738 4 PCT/DE2006/001097 as the second condensation stage for condensing the excess steam. The construction of the air-cooled condenser is thus simplified. The method according to the invention is, of course, also applicable to condensers which include heat exchanger elements installed both in condensation as well as in dephlegmatisation mode. In condensers installed entirely in dephlegmatisation mode, a great portion of the waste steam of the turbine is already condensed. Nevertheless, for thermodynamic reasons the partial steam flow emerging from the condenser so adjusts itself automatically that an adequate volume flow is available in the degasifier. In the case of the installation of the condensers in dephlegmatisation mode, the turbine waste steam flow is passed, as it were, to the degasifier via the condenser, emerging as partial steam flow. If the partial steam flow emerging from the condenser is, in certain circumstances, not sufficient to adequately heat the colder additional feed water, it is possible to feed a further partial steam flow of the turbine waste steam flow directly, i.e. without making use of the condenser. An increased heat demand within the degasifier exists in particular, if relatively large amounts of treated additional feed water are fed into the material cycle. Since the additional feed water regularly exhibits a distinctly lower temperature than the condensate, it has, in this case as well, an advantageous effect on the energy balance of a condensation power station, if the partial waste steam flow from the condenser is used to degasify the additional feed water or to at least thermally promote the degasification. The degasification of the additional feed water is performed primarily, preferably exclusively, in the degasifier provided for this purpose. Due to the heating of the condensate flow in the condensate heating stage, gases, produced by the process, may escape in this case as well; however, the heated condensate has a very low inert gas content so that only low volumes of gas arise during the condensate heating stage. The gases may be removed by suction, just like in the case of a dephlegmator and a degasifier. mnarina\trle\ CM Condensation Method GEA PCT 21 08 2007 WO 2007/022738 5 PCT/DE2006/001097 If it is observed that due to the suction of air from the degasifier excess steam is sucked off as well, it is possible, in an advantageous further development of the invention, to condense this excess steam likewise by additional water. This as well causes the additional water to be heated. The heated additional feed water from the degasifier is preferably also supplied to the condensate heating stage, so that the additional feed water is heated in two stages. Although the condensate flow from the condenser suffices to condense a portion of the turbine waste steam flow, full condensation of the partial steam flow emerging from the condenser is, however, not possible in practice for reasons of the energy balance. A condensation of the partial steam flow can be ensured in any event by an adequate amount of colder additional feed water. In order to improve the thermal transition during the condensate heating stage, it is provided to bring the condensate into contact with the turbine waste steam flow in droplet form. This can be done in that the condensate is guided over shaped bodies and brought into contact with the turbine waste steam flow by way of the counter-flow method. The shaped bodies may for this purpose be arranged in cascade-like fashion. A cascade-like arrangement of steel sheets without using shaped bodies is, in principle, likewise conceivable. The decisive factor is the optimisation of the thermal transition from the turbine waste steam flow to the supercooled condensate. In this context, it is considered to be particularly advantageous to atomise the condensate in order to form drops. The condensate can thus be fed to the condensate heating stage by means of nozzles. The drops of the supercooled condensate form low-temperature condensation seeds during the condensate heating stage, thereby accelerating the condensation of the turbine waste steam flow, while simultaneously increasing the temperature of the condensate in an advantageous manner in terms of energy. marina\trle\ CM Condensaion Method GEA PCT 2 08 2007 WO 2007/022738 6 PCT/DE2006/001097 The invention is elucidated in more detail in what follows by way of the embodiments illustrated schematically in the figures. Figure 1 shows a very simplified steam power process of a thermal power station, wherein from a turbine 1 a turbine waste steam flow 2 is fed to a condenser 3 via a duct. The condenser 3 is represented by an air-cooled condenser with heat exchanger elements 4 installed in condensation mode as well as heat exchanger elements 5 installed in dephlegmatisation mode. A large portion of the turbine waste steam flow condenses inside the condenser 3. Starting from the condenser 3, the condensate K obtained is fed to a condensate heating stage 6, during which the supercooled condensate K comes into contact with the turbine waste steam flow 2. The condensate K is heated in such a manner that a partial steam flow of the turbine waste steam flow 2 is already condensed prior to the entry of the turbine waste steam flow K into the condenser 3 via the duct 7 and is reintroduced directly to the material cycle as part of the condensate K3. In addition, a degasifier 8 is provided, to which a partial steam flow T, emerging from the condenser 3, is fed. The partial steam flow T is condensed by supplying colder additional feed water W. In doing so, the additional feed water W is heated and simultaneously degasified. The degasifier 8 serves, as it were, as a second condensation stage set up downstream. The condensate K1 from the degasifier 8 is fed to the condensate heating stage 6, wherein the excessive cooling of the condensates K, K1 is utilised for the condensation of a portion of the turbine waste steam flow 2. The embodiment according to Figure 2 differs primarily from that according to Figure 1 in that the condenser 9 is installed exclusively in dephlegmatisation mode. This can be seen from the entry of the steam in the lower edge region of the condenser 9. marina'tri CM Condcnsation Method GEA PCT 2 108 2007 WO 2007/022738 7 PCT/DE2006/001097 A further difference resides in that, apart from the degasifier 8, there is provided, likewise as a second condensation stage, an excess steam condenser 11. The excess steam condenser 11 serves to fully condense, i.e. by additional feed water W, excess steam T2, which is already considerably enriched by inert gases from the condenser 9. This has the effect that the additional feed water W heats up and mixes with the condensate from the excess steam. The mixture is fed to the condensate heating stage 6 as condensate flow K2. In both embodiments an air-suction device 10 is provided in order to remove gases from the material flow. The air-suction device 10 is connected both to the condenser 9 installed exclusively in dephlegmatisation mode or, respectively, to the heat exchanger elements 5 installed in dephlegmatisation mode, as well as to the condensate heating stage 6 as well as to the degasifier 8 or, respectively, the excess steam condenser 11. The entire condensate K3 is returned to a condensate collection tank, not shown in more detail. Figure 3 shows the calculated change in the thermal efficiency of the process (in %), plotted against the condensate excessive cooling (in K). The basis for the values stated in this diagram is a calculation according to the formula ilth=P/(Qin+AQin), i 1 th denoting the efficiency, P denoting the turbine output, Qin denoting the thermal feed and AQin denoting the additional heat for heating the condensate. The following values arise in a 600 MW power station: Condensate tK *C 38,50 38,00 37,00 36,00 35,00 34,00 33,00 temperature Excessive AtK K 0,50 1,00 2,00 3,00 4,00 5,00 6,00 cooling of condensate Condensate hK kJ/kg 161,28 159,19 155,01 150,83 146,65 142,47 138,29 enthalpy Waste heat Qab MW 800,26 801,03 802,57 804,11 805,66 807,20 808,74 Additional heaorsate AQin MW 0,00 0,77 2,31 3,86 5,40 6,94 8,48 heating Efficiency Tith % 42,85 42,83 42,78 42,73 42,68 42,64 42,59 Change in Aqth % 0,00 0,02 0,07 0,12 0,16 0,21 0,26 efficiency L marinw\trIe\ CM Condcisation Method GEA PCI 2 08 2007 WO 2007/022738 8 PCT/DE2006/001097 The following parameters are constant in this calculation: turbine output 600 MW, waste steam mass flow 369 kg/s, waste steam enthalpy 2330 kJ/kg, waste steam pressure 7 kPa, saturation steam temperature 39"C, heat supply 1400,26 MW. The advantage of the method according to the invention resides in that the excessive cooling of the condensate may be reduced considerably, resulting in the improvement of the efficiency. marila\0re\ CM Condeisation Method GEA PCT 21 08 2007 WO 2007/022738 9 PCT/DE2006/001097 Reference numerals: 1 - turbine 2 - turbine waste steam flow 3 - condenser 4 - heat exchanger element installed in condensation mode 5 - heat exchanger element installed in dephlegmatisation mode 6 - condensate heating stage 7 - duct 8 - degasifier 9 - condenser 10 - air-suction 11 - excess steam condenser K - condensate K1 - condensate K2 - condensate K3 - condensate T - partial steam flow T1 - partial steam flow T2 - excess steam W - additional feed water niarinaitrle\ CM1 Condcusation Method GEA PCT 2 08 2007

Claims (7)

1. Condensation method, wherein water is fed to an evaporator connected upstream of a turbine (1) of a condensation power station, the turbine waste steam flow (2) being fed to an air-cooled condenser (3, 9) for condensation, characterised in that the condensate flow (K) obtained in the condenser (3, 9) is heated in a condensate heating stage (6) prior to being introduced into a condensate collection tank, heating of the condensate flow (K) being performed by a turbine waste steam flow (2) during the condensate heating stage (6) and a partial steam flow (T, T1) emerging from the condenser (3, 9) being fed to a degasifier (8), in which colder additional feed water (W) is heated by the partial steam flow (T, T1).

2. Condensation method according to claim 1, characterised in that the air cooled condenser (9) is installed in dephlegmatisation mode.

3. Condensation method according to claim 1, characterised in that the air cooled condenser (3) includes heat exchanger elements (4, 5) installed both in condensation mode as well as in dephlegmatisation mode.

4. Condensation method according to any one of claims 1 to 3, characterised in that the condensate (K, K1) is brought into contact with the turbine waste steam flow (2) in drop form in the condensate preheating stage (5).

5. Condensation method according to claim 4, characterised in that the condensate (K, K1) is guided over shaped bodies in order to form drops.

6. Condensation method according to claim 5, characterised in that the shaped bodies are arranged in cascade-like fashion. marina\0rle\ CM Condnstiioin Method GEA PCT 21 08 2007 WO 2007/022738 11 PCT/DE2006/001097

7. Condensation method according to claim 4, characterised in that the condensate (K, K1) is atomised in order to form drops. martin ric\ CM Condensation Mcll,,d GEA PCT 2 10 2007