RU2355895C1 - Condensation method - Google Patents

Abstract

FIELD: electricity, mechanical engineering.

SUBSTANCE: invention is related to turbine steam condensing method. Exhausted turbine steam is supplied for condensing to air-cooled condenser. Condensate accumulated in condenser is preliminary heated in condensate heating stage before directing it to turbine preevaporator. Condensate is heated by means of turbine steam partial flow. Degasifier for makeup water degasifying treatment is included in parallel to condensate heating stage.

EFFECT: invention allows to minimise condensate overcooling and at the same time to raise power station efficiency.

7 cl, 3 dwg

Description

The invention relates to a condensation method with the features of the restrictive part of paragraph 1 of the formula.

C.p.d. power plants is a factor which, in particular, with the new planning of power plants, has a decisive influence on efficiency. Therefore, various efforts are being made to optimize steam-power processes in thermal power plants. Of particular importance is also the condensation system. In particular, the potential for efficiency power plants are still insufficiently used if air-cooled condensers are used, as they often find application when there is a shortage of water at the location of the power plant. Air-cooled condensers have the disadvantage caused by the principle that only dry air temperature can be used. In addition, during operation with particularly low exhaust vapor pressures, condensate overcooling is greater than that of water-cooled surface condensers.

Air-cooled condensers, as a rule, have two stages of condensation. At the first stage of condensation, 80-90% of the turbine exhaust steam is condensed. 100% condensation in the first stage of condensation is almost impossible due to process-related parameters such as, for example, fluctuating external temperatures, so in any case a second stage of condensation of the residual vapor is required. For this reason, air-cooled condensers included in the condenser and reflux condenser are often combined with each other, and reflux condensation is provided for condensation of the residual vapor, i.e. forms the second stage of condensation.

Typically, the condensate obtained is fed directly to the collection tank. Then the condensate is sent to a degasser, in which make-up water prepared as a replacement for leakage losses is mixed, after which the condensate is again fed to the evaporator upstream of the turbine using a feed pump. Since the condensate in the degasser again has to be brought to a boiling point for degassing, damage to the energy balance is caused by the fact that the condensate was previously too much supercooled, since an increased supply of energy due to the use of primary fuels is required. Therefore, attempts are being made to keep condensate subcooling as low as possible in order to minimize the use of primary fuels. At the same time, attempts are being made to maintain at the lowest possible level the amount of energy used to condense the turbine exhaust steam.

A condensation method is known from WO 90/07633 A, in which a small part of the turbine exhaust steam stream is sent to a condensate collector to heat the condensate. Due to this, condensation subcooling should be eliminated. The turbine exhaust steam stream to be used to heat the condensate is approximately 1% of the amount of steam sent through the main steam outlet.

In DE 2257369 A1, a contact capacitor is provided as a second stage of the condensation device instead of a reflux condenser. The condensate obtained during the condensation process is sprayed inside the contact capacitor. To increase the efficiency of the contact condenser, the condensate is pumped into the heat exchange elements to further subcool it. Thus, the circulation process loses a lot of energy, which negatively affects the efficiency power plants.

The basis of the invention is the task of creating a condensation method that would minimize condensation of the condensate and at the same time increase the efficiency power plants.

This problem is solved in the condensation method with the characteristics of paragraph 1 of the formula.

It is essential for the method according to the invention that the condensate stream obtained in the condenser is heated at the condensate heating stage specially provided for this before entering the condensate collector. The condensate stream is heated inside the condensate heating stage by means of a turbine exhaust steam stream. At the same time, a partial steam stream leaving the condenser is fed to a degasser, in which a partial steam stream heats the colder make-up water and condenses itself.

The condensate heating stage, provided in addition to the degasser, can significantly minimize the condensate overcooling and thereby reduce the use of primary fuels. Model calculations have confirmed that the condensate subcooling observed with traditionally designed air-cooled condensers can be reduced in the range from 1-6 K to about 0.5 K compared with the temperature in the saturation state behind the turbine. Depending on the reduction in subcooling, the efficiency power plants rises. At a power plant with a capacity of 600 MW thermal efficiency can be increased to about 0.25%, which, in view of the size of the power plant, should be considered a value that cannot be neglected.

In the method according to the invention, the thermal energy of the turbine exhaust steam stream is used much more efficiently, since it is not given off by the capacitors to the surrounding space, but mostly flows into the condensate, i.e. to a large extent is stored in the thermal circuit. Reduced energy loss leads to the desired increase in efficiency power plants. By heating the supercooled condensate, at the same time, condensation of a part of the turbine exhaust steam stream is achieved, so that less exhaust vapor enters the condenser. Capacitors can be due to this, under certain circumstances, calculated smaller.

Preferred embodiments of the invention are the subject of the dependent claims.

The method according to the invention is sufficient if the first stage of condensation, i.e. the air-cooled condenser is turned on exclusively reflux, since the degasser, which is already necessary in steam-powered processes, can be used as a second condensation stage to condense excess steam. The design of the air-cooled condenser is thereby simplified. Of course, the method is also applicable to capacitors containing both condenser and reflux heat exchange elements.

For fully switched on reflux condensers, a large proportion of the exhaust turbine steam is already condensing. However, for partial thermodynamic reasons, the partial steam stream exiting the condenser is spontaneously set so that a sufficient volume flow is available in the degasser. When the condensers are refluxed, the exhaust steam of the turbine is to a certain extent passed through the condenser to the degasser and exits in the form of a partial steam stream. If the partial steam stream leaving the condenser under certain circumstances is insufficient for the required heating of the colder make-up water, then it is possible to supply another partial stream of exhaust turbine steam directly, i.e. bypassing the path through the capacitor. An increased need for heat inside the degasser arises, in particular, if larger quantities of prepared make-up water are introduced into the material circuit. Since make-up water has a constantly noticeably lower temperature than condensate, the energy balance of the condensing power plant is also positively affected by the fact that a partial flow of exhaust steam from the condenser is used to degass make-up water or at least thermally facilitate degassing.

Decontamination of make-up water occurs, first of all, mainly exclusively in the degasser provided for this. As a result of heating the condensate stream in the condensate heating stage, gases can also escape here, although the heated condenser is very poor in inert gases, so that only small amounts of gases appear inside the condensate heating stage. Gases can be removed both at the reflux condenser and at the degasser due to suction.

If it is determined that as a result of suction of air from the degasser, excess steam is sucked out, then in one preferred embodiment of the invention, this excess steam can also be condensed by make-up water. Due to this, makeup water is also heated.

The heated make-up water from the degasser is also mainly supplied to the condensate heating stage, so that the make-up water is heated in two stages. The condensate stream from the condenser is sufficient to condense part of the turbine exhaust steam stream, however, the full condensation of the partial steam stream leaving the condenser due to energy balance reasons is practically impossible. The condensation of the partial steam flow can in any case be guaranteed by a sufficient amount of colder make-up water.

In order to improve the heat transfer inside the condensate heating stage, it is provided to bring the condensate in the form of droplets into contact with the exhaust stream of the turbine steam. This can occur due to the fact that the condensate is directed through the molded body and in countercurrent contact with the flow of exhaust steam from the turbine. For this, molded bodies can be cascaded. In principle, cascading of sheets is also possible without using molded bodies. The decisive factor is the optimization of heat transfer from the flow of the exhaust steam of the turbine to the supercooled condensate. In this regard, it is considered especially advisable to spray condensate for dropping. Condensate can be introduced into the condensate heating stage by means of nozzles. Drops of supercooled condensate form low-temperature condensation centers inside the condensate heating stage, as a result of which the condensation of the exhaust steam of the turbine is accelerated, while the temperature of the condensate is energetically favorable.

The invention is explained in more detail below using schematically depicted in the drawings examples of its implementation.

Figure 1 in a very simplified form depicts a steam-power process of a thermal power plant, in which a turbine exhaust steam stream 2 is supplied from a turbine 1 through a pipeline to a condenser 3. The condenser 3 is an air-cooled condenser with condenser-connected heat-exchange elements 4 and reflux-connected heat-exchange elements 5. Most of the turbine exhaust steam stream condenses inside the condenser 3.

The obtained condensate K is supplied from the condenser 3 to the condensate heating stage 6, inside which the supercooled condensate K comes into contact with the turbine exhaust steam stream 2. Condensate K is heated, so that even before the flow of turbine exhaust steam 2 enters the condenser 3 through pipeline 7, the partial turbine exhaust steam stream 2 condenses and returns directly to the material circuit as part of condensate K3.

Further, a degasser 8 is provided, to which a partial steam stream T exiting from the condenser 3 is supplied. A partial stream T of steam condenses due to the supply of colder make-up water W. In this case, the make-up water W is heated and simultaneously degassed. The degasser 8 serves to a certain extent as the downstream second condensation stage. Condensate K1 from the degasser 8 is fed to the condensate heating stage 6, in which condensate K, K1 is supercooled, used to condense part of the turbine exhaust steam stream 2.

The example in figure 2 differs from the example in figure 1, primarily in that the capacitor 9 is turned on exclusively reflux. This is seen at the steam inlet in the lower edge region of the condenser 9.

Another difference is that in addition to the degasser 8, an excess steam condenser 11 is also provided as a second condensation stage. It serves to completely condense the excess steam T2, already highly enriched with inert gases from the condenser 9, namely due to the make-up water W. This has the effect that the make-up water W is heated and mixed with the condensate of the excess steam. The mixture is supplied as a condensate stream K2 to the condensate heating stage 6.

In both examples, an air exhaust 10 is provided to remove gases from the substance stream. The air exhaust 10 is connected to both the exclusively reflux condenser 9 and the reflux condenser 5 connected to the condensate heating stage 6, as well as to the degasser 8 and the excess steam condenser 11. All K3 condensate is supplied to a collector (not shown).

Figure 3 shows the calculated change in thermal efficiency the process (in%), applied depending on the subcooling of the condensate (in K). The values indicated in this diagram are based on the calculation using the formula ηth = P / (Qin + ΔQin), where ηth denotes the efficiency, P is the turbine power, Qin is the heat input, and ΔQin is the additional heat for heating the condensate. A power plant with a capacity of 600 MW has the following values:

Condensate temperature tK ° C 38.50 38.00 37.00 36.00 35.00 34.00 33.00 Condensation Subcooling ΔtK K 0.50 1.00 2.00 3.00 4.00 5.00 6.00 Condensate enthalpy hK kJ / kg 161.28 159.19 155.01 150.83 146.65 142.47 138.29 Waste heat Qab MW 800,26 801.03 802.57 804.11 805.66 807.20 808.74 Additional heat to heat condensate ΔQiη MW 0.00 0.77 2,31 3.86 5.40 6.94 8.48 C.p.d. ηth % 42.85 42.83 42.78 42.73 42.68 42.64 42.59 Change in efficiency Δηth % 0.00 0.02 0,07 0.12 0.16 0.21 0.26

The following parameters are constant in this calculation: the turbine power is 600 MW, the mass flow of the exhaust steam is 369 kg / s, the enthalpy of the exhaust vapor is 2330 kJ / kg, the pressure of the exhaust steam is 7 kPa, the temperature of saturated steam is 39 ° C, the heat input is 1,400.26 MW. The advantage of the method according to the invention is due to the fact that the hypothermia of the condensate can be sharply reduced, which affects the increase in efficiency

List of Reference Items

1 - turbine

2 - turbine exhaust steam flow

3 - capacitor

4 - included condenser heat exchange element

5 - included reflux heat exchange element

6 - condensate heating stage

7 - pipeline

8 - degasser

9 - capacitor

10 - air exhaust

11 - excess steam condenser

K - condensate

K1 - condensate

K2 - condensate

K3 - condensate

T - partial steam flow

T1 - partial steam flow

T2 - excess steam

W - make-up water.

Claims (7)

1. A condensation method in which water is supplied to an evaporator upstream of a condensing power plant turbine (1), the turbine exhaust steam stream (2) being supplied for condensation to an air-cooled condenser (3, 9) and a stream (K) obtained in the condenser (3, 9) ) the condensate before entering the condensate collector is heated in the condensate heating stage (6) by means of a turbine exhaust steam stream (2), characterized in that the turbine exhaust vapor stream (2) supplied to the air-cooled condenser (3, 9) is first directed through the stage (6 ) heating the condensate, moreover, the partial steam stream (T, T1) exiting the condenser (3, 9) is supplied to the degasser (8), in which the colder make-up water (W) is heated through the partial stream (T, T1). 2. The method according to claim 1, characterized in that the air-cooled condenser (9) is included reflux. 3. The method according to claim 1, characterized in that the air-cooled condenser (3) contains heat exchange elements (4, 5), included as a condenser and reflux condenser. 4. The method according to one of claims 1 to 3, characterized in that the condensate (K, K1) in the form of droplets is brought into contact in the condensate heating stage (5) with the exhaust turbine steam stream (2). 5. The method according to claim 4, characterized in that the condensate (K, K1) is sent for dropping through the molded body. 6. The method according to claim 5, characterized in that the shaped bodies are arranged in cascade. 7. The method according to claim 4, characterized in that for droplet formation, the condensate (K, K1) is sprayed.

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