RU2285808C2 - Method for operation of cooling system for thermal and nuclear power stations with cooling water bodies - Google Patents

Abstract

FIELD: power engineering, possible use in cooling systems of thermal and nuclear power stations.

SUBSTANCE: in accordance to method, water is taken from water bodies and fed via pipelines into heat exchangers for draining heat from station equipment with following discharge of used water back into body of water and supplying body of water with water for covering losses. Water is additionally taken from cooling body of water for cleaning it from salts by means of evaporation. Produced distillate is returned to cooling body of water, remaining brine is evaporated until salts form as cubic remainder, while volumetric flow of water fed for evaporation is determined in accordance to expression:

where S_D - salt content of distillate (parameter of evaporation plant); S_w - required salt content of water in cooling water body, gram/liter; S_n - salt content of water used for covering losses connected to natural vaporization, gram/liter; D_u -water vaporization per hour, m³/hour.

EFFECT: maintained salt balance of cooling water bodies at acceptable level to prevent salt precipitation on heating surfaces, resulting in decreased heat transfer coefficient and causing increased losses of cooling water.

Description

The invention relates to energy and can be used in cooling systems of thermal and nuclear power plants.

At any power plant, there is a cooling system, including cooling ponds. These are cooling ponds and spray pools.

In spray pools of nuclear power plants, water is used to remove heat from various primary equipment.

In the cooling ponds, the water used to condense the steam in the turbine condensers is cooled.

The prototype is taken as a method of operation of a cooling system of thermal and nuclear power plants with reservoirs of chillers used to remove heat from various equipment of the station, in which they take water from these reservoirs, direct it through pipelines to heat exchangers to remove heat from the station’s equipment with subsequent discharge of used water back into the reservoir and replenishing it with water to cover water losses [1].

The cooling systems based on spray pools and cooling ponds have the following disadvantages.

Since water evaporation is constantly carried out from the surface of cooling ponds, and in spray pools this process is most intensive, the salt content of cooling water gradually increases in them, which, when the water circulation is closed, causes salt deposition on the heating surfaces of the equipment and, thus, negatively affects the state of heat exchange heat removal circuit equipment. Due to this, the heat transfer coefficient decreases and, as a result, there is a need to increase the flow rate of cooling water. In addition, with an increase in the salt content in the cooling pond, it is difficult to maintain a deep operational vacuum (the pressure in the condenser increases), therefore, the economic performance of the power plant deteriorates (the electric power of the turbine decreases, and therefore, the efficiency decreases). When using ball cleaning with abrasives, the service life of the cooling surfaces of the condensers is reduced. In addition, microscopic leaks are almost always present in the condenser, which, with an increased salt content of cooling water, leads to an increased load on the condensate-cleaning unit due to the cooling water entering the vapor space of the condenser. In addition, an increase in the concentration of salts in the cooling pond to 1.1-1.2 g / l is the limit value according to the condition of organizing commercial fish farming in the pond.

Due to leaks in the heat exchange equipment (for example, due to stuffing box seals), a weak transfer of radioactivity to cooling water is possible for nuclear power plants. The salts contained in the cooling water of the spray pools of nuclear power plants are capable of accumulating long-lived radionuclides and, even if weakly radioactive salts get into water bodies, radionuclides are concentrated [2, 3]:

in foam - 100-10000 times;

in phytoplankton - 500-75000 times;

in green algae - 800-50000 times;

in insect larvae - 100-100000 times;

in fish - 100-30000 times.

Since the spray pool is an isolated water system, that is, there is no flow of water from it into the surrounding water bodies, over time, the spray pool of a nuclear power plant itself becomes a weak source of radioactivity. The operational experience of NPPs with VVER-1000 showed that the total activity of ¹³⁴ Cs, ¹³⁷ Cs can be up to 22 ÷ 38 Bq / kg, respectively.

It is not possible to reduce the salinity of cooling water in the spray pool by draining saline water, since even weakly radioactive salts can enter the water bodies and radionuclides can be concentrated [2, 3]. Reducing the salt content in the water of the cooling pond by draining saline water while ensuring good water exchange, namely at a sufficient distance from the discharge point of purge water from the dam and shallow water, as shown by preliminary calculations by the Institute of Geology and Geophysics of SSU, can only be recommended as a temporary method applicable only for an urgent solution to the problem of lowering salinity.

The objective of the present invention is to maintain at an acceptable level of salt balance of the reservoirs of coolers of thermal power plants and nuclear power plants.

To achieve the named technical result in the proposed method of operation of the cooling system of thermal and nuclear power plants, including cooling ponds, in which they take water from these reservoirs, direct it through pipelines to heat exchangers to remove heat from the plant’s equipment and then discharge the used water back to the pond and replenishing it with water to cover water losses, additional water is taken from the cooling pond to clean it from salts by evaporation, the resulting distillate is rotate into a cooling pond, the remaining brine is evaporated to form salts in the form of a still bottom, the resulting distillate is also sent to a cooling pond. The volumetric flow rate of water directed to evaporation is determined in accordance with the expression:

where S _DOU - salt content of the distillate obtained in the evaporation installation (installation parameter);

S _in - the required salinity of the water in the reservoir cooler, g / l;

S _n is the salt content of water used to cover losses associated with natural evaporation (in the case of covering losses with water from natural reservoirs, it is determined from the reference literature or analytically, and in the case of covering losses with distillate or chemically purified water, it is a parameter of the evaporation plant or chemical water treatment), g / l;

D _u - the amount of water evaporated from the reservoir-cooler water, m ³ / h,

and the amount of water needed to feed the reservoir is determined from the expression:

where D _to - the amount of VAT residue formed per unit time, m ³ / h

The authors chose a desalination plant with horizontal tube film evaporators to evaporate the purge water from the cooling pond, which provides low scale formation, high concentration ratio, high heat transfer coefficient and, as a result, low metal consumption [4, 5], as well as low temperature of the obtained distillate (approximately 30 ° C) allows you to submit it to the cooling pond with slight cooling in the open air and to ensure its acceptable low temperature.

The invention is illustrated in figure 1, which shows a diagram of the implementation of the method.

The method is as follows. Purge water with a volume flow of D _pr comes from the cooling pond 1 for evaporation to a desalination plant with horizontal pipe film evaporators (DOW GTPA) 2, in which the brine is concentrated about 200 times [4] due to the evaporation of water, which occurs under vacuum in a thin liquid film, which ensures low scale formation on the heating surfaces, and therefore, a high heat transfer coefficient in evaporators and, as a consequence, low metal consumption of the installation [4, 5]. The distillate formed in the distillation unit in an amount of D is returned to the cooling pond. The amount of brine (D _ol -D) enters the limit evaporation unit 3, where distillate in the amount of D1 is obtained, which is returned back to the cooling pond 1. This method thus allows due to the low temperatures of the obtained distillate (approximately 30 ° C) ) to submit it to a cooling pond with slight cooling in the open air and to ensure an acceptable low temperature regime of the reservoir. The bottoms of the evaporators of the limit evaporation unit are sent for temporary storage and further processing, which may include bituminizing, cementing, vitrification and obtaining salt melt. The loss of water due to natural evaporation of D _u and the loss of water with still bottoms of salts D _k in the case of a spray pool is compensated by feeding distillate from the evaporation plant (in the case of using the thermal method of preparing make-up water at nuclear power plants) or chemically purified water from chemical water treatment (in case the use of a chemical method for the preparation of make-up water at nuclear power plants), and in the case of using a cooling pond, only make-up from a natural reservoir.

The heating steam required for the operation of distillation desalination plants is taken from turbine selections.

The volumetric flow rate taken from the spray pool for evaporation is determined by the formula (1). The loss of water due to natural evaporation D _u , which is equal to water consumption, is taken from the data given in table 1. The salinity of the distillate was taken equal to S _doU = 0.005 g / l [4, 5].

The results of calculating the volumetric flow rate of water supplied for evaporation are shown in the graph (Fig. 2), according to which this parameter can be calculated based on the required salinity of the water in the pool.

The volumetric flow rate taken from the cooling pond for evaporation is determined by the formula (1). The loss of water due to natural evaporation D _u , which is equal to water consumption, is taken from the data given in table 1. The salinity of the distillate was taken equal to S _DOU = 0.005 g / l [4, 5], the salinity of the makeup water was taken for the Volga River to be S = 0.1972 g / l, according to [6].

The calculation results are shown in the graph of the volumetric flow rate of water supplied to the evaporation, according to which this parameter can be calculated based on the required salinity of the water in the cooling pond.

The effect of the application of this method is to improve the environmental situation on the territory of the nuclear power plant by reducing the number of sources of radioactivity, which is a spray pool of nuclear power plants, as well as the absence of the need to build a second pool during the construction of the second stage of the station. In addition, by reducing the salinity of the cooling water of the cooling ponds, the heat transfer coefficient increases and, as a result, the vacuum increases (the pressure in the condenser decreases), therefore, the economic indicators of the power plant improve (the electric power of the turbine increases, and therefore, the efficiency improves) reduces the use of ball cleaning with abrasives and, as a result, increases the service life of the cooling surfaces of the condensers. The load on the condensate treatment unit is reduced due to a decrease in the salinity of cooling water entering through the leakage of the pipe system into the vapor space of the condenser. Also, a decrease in the concentration of salts in the cooling pond is a favorable factor for the condition of organizing commercial fish farming in the pond. In addition, an improvement in the environmental situation in and around the station leads to a significant reduction in environmental charges.

Information sources

1. Margulova T.X. Nuclear Power Plants: A Textbook for High Schools. - 3rd ed. reslave. and add. - M .: Higher. School, 1978. - 360 S. s.

2. Khonikevich A.A. Treatment of radioactive contaminated water in laboratories and research nuclear reactors. Ed. 3rd, rev. and add. M .: Atomizdat, 1974, 312 p.

3. The basics of water purification from radioactive contamination. / Kuznetsov Yu.V., Schebetkovsky V.N., Trusov A.G., ed. tsp - box. USSR Academy of Sciences V.M. Vdovenko, ed. 2nd, break and add., M., Atomizdat, 1974, 360 pp.

4. Installations distillation desalination horizontal pipe film. ZAO NPP "MASHPROM", Yekaterinburg, 2000.

5. DOU with film horizontal - tube evaporators (DOU GTPA-700), NPO Ecohim VNIPI industrial technology, 1999.

6. Heat engineering reference. Ed. 2nd, rev. Ed. Yureneva and P.D. Lebedev. T.1. M., "Energy", 1975, 775 pp.

Claims (1)

The method of operation of the cooling system of thermal and nuclear power plants, including cooling ponds, in which they take water from these ponds and send it to heat exchangers to remove heat from various equipment of the station with the subsequent discharge of water back into the reservoir and its recharge with water to cover losses, characterized the fact that additionally water is taken from the cooling pond for purification from salts by evaporation, the resulting distillate is returned to the cooling pond, the remaining brine is evaporated to brine statka, and the resulting distillate is also sent to a cooling pond, while the volumetric flow rate of water supplied for evaporation is determined in accordance with the expression:

where S _dow - salinity of the distillate (evaporation unit parameter); S _in - the required salinity of the water in the reservoir cooler, g / l; S _p - salt content of water used to cover losses associated with natural evaporation, g / l; D _and - the amount of evaporated water per hour, m ³ / h

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