EP1917422B1 - Condensation method - Google Patents

Description

The invention relates to a condensation method having the features in the preamble of claim 1. Such a method is known from WO 90/07633 known.

Power plant efficiency is a factor that has a decisive influence on economic efficiency, especially when new power plants are planned. There are therefore many efforts to optimize steam power processes in thermal power plants. Particular attention is paid to the condensation system. In particular, the potential in terms of power plant efficiency is not yet optimally utilized when using air-cooled condensers, such as those often used in water shortages at the power plant site. Air-cooled condensers have the inherent disadvantage that only the dry air temperature can be used. In addition, when operating with particularly low evaporation pressures, the condensate subcooling is greater than with water-cooled surface condensers:

Air-cooled condensers usually have two condensation stages. In a first condensation stage, about 80-90% of the exhaust steam of a turbine is condensed. A 100% condensation in the first condensation stage is due to the process-related parameters, such as the fluctuating outside temperatures virtually impossible, so that in any case a second condensation stage for the residual steam condensation is required. For this reason, condensed and dephlegmatorily switched air-cooled condensers are often combined with each other, wherein the dephlegmatoric condensation is provided for residual vapor condensation, thus forming the second condensation stage.

Usually, the recovered condensate is fed directly to a condensate collection tank. Subsequently, the condensate is fed to a degasser, is added in the treated as a replacement for loss of leakage processed water, to then be fed via a feed pump again upstream of the turbine evaporator. Since the condensate must be brought back to boiling temperature in the deaerator for degassing, it is detrimental to the energy balance if the condensate was previously overcooled, since ultimately an increased energy supply must be realized through the use of primary fuels. It is therefore desirable to minimize the overcooling of the condensate to minimize the use of primary fuels. At the same time, the aim is also to keep the amount of energy to be used for the condensation of the turbine exhaust steam as low as possible.

From the WO 90/07633 A For example, a condensation process is known in which a small portion of the turbine effluent stream is introduced into a condensate collection tank to warm the condensate. This is to avoid condensate supercooling. The order of magnitude of the turbine effluent flow to be used for condensate heating is about 1% of the amount of steam passed through the main exhaust steam line.

From the DE 22 57 369 A1 is provided as a second stage of a condensation device instead of a dephlegmator an injection capacitor. Condensate recovered from the condensation process is sprayed within the injection condenser. To increase the efficiency of the injection condenser, the condensate is pumped into heat exchanger elements to further cool it down. In this way, the cycle process lost a lot of energy, which adversely affects the power plant efficiency.

The invention has for its object to provide a condensation method in which the supercooling of the condensate can be minimized and at the same time the power plant efficiency is further improved.

This object is achieved in a condensation method with the features of claim 1.

It is essential in the method according to the invention that the condensate stream obtained in the condenser is heated prior to introduction into a condensate collection tank in a condensate reheating stage specially provided for this purpose. The heating of the condensate stream takes place within the Kondensatwärwärstufestufe by the turbine exhaust steam. At the same time, the partial steam flow emerging from the condenser is fed to a degasser, in which the partial steam flow heats colder additional feed water and completely condenses itself.

In addition, a condensate heating stage provided in addition to a degasser makes it possible, in the switching mode according to the invention, to significantly minimize condensate subcooling and thus to reduce the use of primary fuels. Model calculations have confirmed that a condensate supercooling observed in air-cooled condensers of conventional design can be reduced in a range of about 1-6 K to about 0.5 K from the saturation temperature behind the turbine. Depending on the reduction in subcooling, the power plant efficiency increases. With a 600 MW power plant, the thermal efficiency can be improved by up to approx. 0.25%, which, considering the dimensions of the power plant, should be considered as a non-negligible factor.

In the method according to the invention, the thermal energy of the turbine exhaust steam flow is used much more effectively, since it is not discharged through the capacitors to the environment, but flows to a large extent in the condensate, so the heat cycle is largely retained. The reduced energy losses lead to the desired improvement in power plant efficiency. By heating the supercooled condensate, a condensation of a part of the turbine exhaust steam flow is achieved at the same time, so that less exhaust steam enters the condenser. Under certain circumstances, the capacitors can be made smaller.

Advantageous embodiments of the inventive concept are the subject of the dependent claims.

In the method according to the invention, it is sufficient if the first condensation stage, that is the air-cooled condenser, is connected exclusively dephlegmatorily, since a deaerator, which is anyway required in steam power processes, can be used as the second condensation stage for condensing the excess steam. The structure of the air-cooled condenser is simplified. Of course, the fiction, contemporary method is also applicable to capacitors, both Have condensing and dephlegmatorisch switched heat exchange elements.

In completely dephlegmatorisch switched capacitors, a high proportion of the exhaust steam of the turbine is already condensed. Nevertheless, for thermodynamic reasons, the partial steam flow emerging from the condenser automatically adjusts itself so that a sufficient volume flow is available in the degasser. In the dephlegmatorisch circuit of the capacitors Turbineabdampfstrom is effectively passed through the condenser to the degasser and exits as a partial steam flow. If, under certain circumstances, the partial vapor stream emerging from the condenser is insufficient to adequately heat the colder additional feed water, it is possible for another partial steam stream of the turbine waste steam stream to flow directly, i. without the way through the capacitor is supplied. An increased heat demand within the degasser exists in particular when larger amounts of treated additional feed water are added to the material cycle. Since the additional feed water regularly has a significantly lower temperature than the condensate, it also has an advantageous effect on the energy balance of a condensation power plant, if the Teilabdampfstrom is used from the condenser to degas the feed water or at least contribute thermally to the degassing.

The degassing of the additional feed water is first and foremost, preferably exclusively, in the designated degasser. Due to the heating of the condensate stream in the condensate warm-up stage, gases can also escape here as a result of the process, but the heated condensate is very poor in inert gases, so that only small amounts of gas are produced within the condensate-warming stage. The gases can be removed by suction just like a dephlegmator and, like a degasser.

If it should be determined that excess air is sucked out of the deaerator by the air extraction, it is in an advantageous Development of the invention possible to condense this excess steam also by additional water. This also warms the make-up water.

The heated additional feed water from the degasifier is preferably also supplied to the condensate warm-up stage, so that the additional feed water is heated in two stages. Although the condensate stream from the condenser is sufficient to condense a portion of the turbine effluent stream, complete condensation of the partial steam effluent exiting the condenser is virtually impossible for energy balance reasons. A condensation of the partial steam flow can be ensured by a sufficient amount of colder additional feed water in each case.

In order to improve the heat transfer within the Kondensatwärwärmstufe, it is intended to bring the condensate in droplet form with the turbine exhaust steam in contact. This can be done by passing the condensate over moldings and bringing it in countercurrent contact with the turbine effluent stream. For this purpose, the shaped bodies can be arranged in cascade. Basically, a cascade-like arrangement of sheets without the use of moldings is conceivable. The decisive factor is the optimization of the heat transfer from the turbine waste steam to the supercooled condensate. In this context, it is considered particularly expedient to atomize the condensate for droplet formation. The condensate can therefore be introduced by means of nozzles in the Kondensatwärwärmstufe. The droplets of supercooled condensate form condensation nuclei of low temperature within the condensate warm-up stage, thereby accelerating the condensation of the turbine effluent stream while at the same time raising the temperature of the condensate energetically.

The invention will be explained in more detail with reference to the embodiments schematically illustrated in the figures.

The FIG. 1 shows a highly simplified steam power process of a thermal power plant, in which a Turbineabdampfstrom 2 is fed from a turbine 1 via a line 2 to a condenser 3. The condenser 3 is an air-cooled condenser with condenser-connected heat exchanger elements 4 and dephlegmatorily connected heat exchanger elements 5. A majority of the turbine waste steam flow condenses inside the condenser 3.

The recovered condensate K is supplied from the condenser 3, starting from a condensate warm-up stage 6, within which the supercooled condensate K comes into contact with the turbine waste steam stream 2. The condensate K is heated so that a partial vapor stream of the turbine waste steam stream 2 is condensed into the condenser 3 via line 7 before the turbine waste steam stream 2 enters, and is recirculated directly into the material cycle as part of the condensate K3.

Furthermore, a degasser 8 is provided, to which a partial steam flow T exiting from the condenser 3 is supplied. The partial steam flow T is condensed by supplying colder additional feed water W. In this case, the additional feed water W is heated and degassed at the same time. The degasser 8 serves as a sort of downstream second condensation stage. The condensate K1 from the degasser 8 is fed to the condensate warm-up stage 6, in which the subcooling of the condensates K, K1 is used to condense a part of the turbine effluent stream 2.

The embodiment of FIG. 2 is different from the one of FIG. 1 primarily in that the capacitor 9 is switched exclusively dephlegmatorisch. This can be seen at the steam inlet at the lower edge region of the condenser 9.

Another difference is that, in addition to the degasser 8, a surplus steam condenser 11 is also provided as the second condensation stage. The excess steam condenser 11 is used to excess vapor T2, which is already heavily enriched with inert gases from the condenser 9, completely to condense by adding feed water W. This has the effect that the additional feed water W is heated and mixed with the condensate from the excess steam. The mixture is fed as condensate stream K2 to the condensate warm-up stage 6.

In both embodiments, an air exhaust 10 is provided to remove gases from the material flow. The air exhaust 10 is connected both to the exclusively dephlegmatorisch switched capacitor 9 and the dephlegmatorisch connected heat exchanger elements 5, as well as to the Kondensataufwärmstufe 6 and to the degasser 8 and the excess steam condenser 11. The entire condensate K3 is fed in a manner not shown a condensate collection tank.

FIG. 3 shows the calculated change of the thermal efficiency of the process (in%), plotted by condensate supercooling (in K). The basis for the values given in this diagram is a calculation according to the formula η1th = P / (Qin + ΔQin), where ηth is the efficiency, P is the turbine power, Qin is the heat input and ΔQin is the additional heat for condensate heating. For a 600 MW power plant, the following values result: condensate temperature tK ° C 38.50 38,00 37,00 36,00 35,00 34,00 33,00 Condensate condensate supercooling ΔtK K 0.50 1.00 2.00 3.00 4.00 5.00 6.00 Kondensatenthalpie hk kJ / kg 161.28 159.19 155.01 150.83 142.47 142.47 138.29 waste heat qab MW 800.26 801.03 802.57 804.11 805.66 807.20 808.74 Additional heat for condensate heating ΔQin MW 0.00 0.77 2.31 3.86 5.40 6.94 8.48 efficiency ηth % 42.85 42.83 42.78 42.73 42.68 42.64 42.59 Efficiency change Δηth % 0.00 0.02 0.07 0.12 0.16 0.21 0.26

The following parameters are constant in this calculation: turbine output 600 MW, exhaust steam mass flow 369 kg / s, exhaust steam enthalpy 2330 kJ / kg, evaporating pressure 7 kPa, saturated steam temperature 39 ° C, heat input 1400.26 MW. The advantage of the method according to the invention is expressed by the fact that the supercooling of the condensate can be greatly reduced, which affects the improvement of the efficiency.

Reference numerals:

1 -

turbine

2 -

turbine exhaust steam

3 -

capacitor

4 -

Condenser switched heat exchanger element

5 -

dephlegmatorisch switched heat exchanger element

6 -

Condensate heating stage

7 -

management

8th -

degasser

9 -

capacitor

10 -

air extraction

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

Claims (7)

1. Condensation method according to which water is fed to an evaporator connected upstream of a turbine (1) of a condensation power station, the turbine exhaust steam flow (2) being supplied to an air-cooled condenser (3, 9) for condensation, while the condensate flow (K) obtained in the condenser (3, 9), prior to being introduced into a condensate collecting tank, is preheated in a condensate pre-heating stage (6) by means of the turbine exhaust steam flow (2), and in which a partial vapour flow (T, T1) emerging from the condenser (3, 9) is supplied to a degasifier (8), characterised in that the turbine exhaust steam flow (2) supplied to the air-cooled condenser (3, 9) is firstly passed through the condensate pre-heating stage (6) to heat the condensate flow (K) and in that colder additional feed water (W) is heated by the partial vapour flow (T,T1) in the degasifier.
2. Condensation method according to claim 1, characterised in that the air-cooled condenser (9) is connected according to the dephlegmatory principle.
3. Condensation method according to claim 1, characterised in that the air-cooled condenser (3) has heat exchange elements (4, 5) which are connected both in a condensing fashion and also according to the dephlegmatory principle.
4. Condensation method according to one of claims 1 to 3, characterised in that the condensate (K, K1) is brought into contact with the turbine exhaust steam flow (2) in the condensate pre-heating stage (5) in the form of drops.
5. Condensation method according to claim 4, characterised in that the condensate (K, K1) is passed over shaped bodies in order to form drops.
6. Condensation method according to claim 5, characterised in that the shaped bodies are arranged in the form of a cascade.
7. Condensation method according to claim 4, characterised in that the condensate (K, K1) is atomised to form droplets.

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