RU2143638C1 - Circuit arrangement for steam generators to recover low-potential heat of stack gases - Google Patents

Abstract

FIELD: thermal engineering. SUBSTANCE: circuit includes air heater 21 placed between fan 22 and steam generator 17, convection stage 13 providing communication between deaerator 14 and condensate pump 7 by means of condensate pipeline 16 through makeup condenser 8, and also two similar parallel auxiliary circuits of series-connected condenser 8, vacuum pump 9, evaporation stage 26 whose blowdown pump 6 ensures drain to sludge tank 2, and condenser stage 27 which connect, respectively, raw water pipeline 28 to distillate pipeline 1 for make-up of steam generator 17 and to secondary steam line 11 downstream of vacuum pump 9 introduced in deaerator 14, and also process water pipeline 33 to distillate line 1; gas line of steam generator 17 communicates with draft fan 25 through parallel-connected air heater 21, convection stage 13, evaporation stage 26, and through respective condensing stages 26; condensate pumps 7 are connected to raw water pipeline 28 and process water line 23; circulating water pump 29 downstream of turbine condenser 19 is included in addition in parallel with makeup condenser 8 and recovery condenser 3. EFFECT: improved efficiency of reuse of low-potential heat of stack gases. 1 dwg

Description

 The invention relates to heat power facilities of thermal power plants.

 A well-known thermal diagram of a condensation power plant (Ryzhkin V. Ya. Thermal power plants. - M .: Energia, 1967, p. 399, Fig. 12-3), consisting of a steam generator that generates steam for a turbine, after which the condensate is condensed by a condensate pump fed through a system of low pressure heaters to the deaerator.

 Replenishment of water losses is carried out with chemically purified water, which is deaerated in a low pressure deaerator before being fed to the evaporators. To obtain the distillate, steam from the turbine offsets is used. The heated condensate of the exhaust steam of the turbine, the condensate of the steam entering the high pressure heaters, the distillate obtained from the chemically purified water are sent to the high pressure deaerator. The thermodynamic cycle is closed by high-pressure heaters, in which deaerated water, due to the heat from the turbine offsets, acquires a higher temperature potential and enters the water economizer of the steam generator.

 The considered thermal scheme of the condensation power plant is optimal in the steady-state temperature limits of the flue gases. Feasibility studies have shown that to heat the condensate it is more efficient to use the heat of steam from the turbine offsets than the heat of the exhaust gases.

It should be noted that the temperature of the exhaust gases after the steam generator is 110-120 ^o C. From a thermodynamic point of view, their temperature potential is quite sufficient to heat the condensate in low-pressure heaters and to make up for boiler water losses.

 The use of low-potential heat of the exhaust gases automatically increases the amount of generated electric energy through the use of steam extraction energy, which is supplied to low-pressure heaters, evaporators, and low-pressure deaerators.

 The noted drawbacks are eliminated by the fact that an air heater located between the fan and the steam generator, a convective step connecting the condensate pipe through the deaerator and condensate pump, as well as two similar parallel process chains consisting of a series condenser, a vacuum pump, are additionally introduced into the thermal circuit of a condensing power plant , an evaporation stage having, by means of a purge pump, a discharge into the slurry tank, and a condensation stage, respectively connecting the raw water pipe to the steam generator feed distillate pipe and to the secondary steam pipe after the vacuum pump, introduced into the deaerator, and the production water pipe to the distillate pipe, and on the gas side the steam generator is connected through parallel-connected air heater, convective, evaporative stages and through appropriate condensing stages with a smoke exhaust, condensate pumps that are connected to the raw and process pipelines water, in addition, the circulation water pipe after the turbine condenser is introduced in parallel into the feed and processing condensers.

 The drawing shows the proposed scheme for the utilization of low potential heat of the exhaust gases for power steam generators, where 1, 10, 11, 16, 28, 29, 33 are pipelines of distillate, distillate to feed the steam generator, secondary condensate vapor, crude, circulating and process water, 2 is slurry tank, 3, 8 - technological and make-up condensers, 4, 6 - purge pumps, 5, 9 - vacuum pumps, 7, 23, 30, 34 - condensate pumps, 12 - feed pump, 13 - convection stage, 14 - deaerator, 15 - high pressure heaters, 17 - steam generator, 18 - turbine generator, 19 — turbine condenser, 20 — circulation pump, 21 — air heater, 22 — fan, 24 — greenhouses, 25 — smoke exhauster, 26, 31 — evaporation stages, 27, 32 — condensation stages.

 Steam generator 17, turbogenerator 18, turbine condenser 19, condensation pump 23, circulation pump 20, deaerator 14, feed pump 12, high pressure heaters 15, smoke exhaust 25, fan 22, pumps 4, 6, 7, 20, 23, 30, 34 - are standard equipment. They are selected based on appropriate calculations.

The design of the convective stage 13, the air heater 21, the evaporation stages 26, 31, the condensation stages 27, 32 are made in one housing. The fraction of perceived heat at each stage is determined by thermal calculation. Based on this amount of heat, thermal, aerodynamic and hydraulic calculations of each stage are carried out. In the evaporation stages 26 and 31, the exhaust gases reduce their temperature to 70-80 ^o C. They carry out the implementation of the process of boiling water at a temperature of 40-50 ^o C and overheating of steam. The heat transfer coefficient of the steps reaches 70-80 W / (m ² • ^o C). The main advantage of this design of the evaporator is a non-scale operation. Due to overheating and washing with water in the resulting vapor, salt entrainment is minimized. The removal of salts from the water volume is carried out by the pump 6 in the sludge tank 2.

Condensation stages 27 and 32 bring the temperature of the flue gases to 20-30 ^o C. In this case, the heat transfer coefficient is 200-250 W / (m ² • ^o C). Condensate of water vapor from the exhaust gases by condensate pumps 30 and 34 is fed into the pipelines of raw and process water in front of the evaporation stages 26 and 31.

 The type and technical data of vacuum pumps 5 and 9 are not specified in the considered scheme, but are selected on the basis of specific initial data and calculations.

 The proposed scheme for the utilization of low potential heat of flue gases works as follows.

The exhaust gases after the steam generator 17 with a temperature of 110-170 ^o depending on the type of fuel burned (natural gas or fuel oil) enter the air heater 21, convective stage 13 and evaporation stages 26 and 31. Of the latter, they are sent to the condensation stages 27 and 32. Smoke exhaust 25 pumps off flue gases with a temperature of 20-30 ^o C from the air heater 21 and the condensation stages 27 and 32. The fan 22 pumps air through the air heater 21 and delivers it to the combustion in the steam generator 17. The condensate of the turbine 18 is pumped by a pump 23 first through a condenser 8, and then through a convective stage 13, in which it is heated before entering the deaerator.

 Water treatment of raw water, necessary to make up for losses, is carried out by preheating it in the condensation stage 27 and evaporation in the evaporation stage 26. The vacuum is created by a vacuum pump 9, which pumps the steam out of the vaporization volume of the evaporation stage (not shown) and pumps it into the condenser 8 , and partially sent directly to the deaerator. The distillate of feeding the steam generator with pump 7 is poured into deaerator 14. In the water volume of the evaporation stage (not shown in the drawing), an increase in the concentration of salts dissolved in the water occurs and, therefore, to maintain its value below the critical value of pump 6, part of the water is drained into tank 2.

 The amount of heat emitted with the flue gases is much greater than the amount that may be required to heat the air, condensate and to make up for water losses. As one of the possible options for covering the excess of this heat, it is the production of distillate from process water according to the scheme described above. Technological water is understood as water that was previously used in any technological process. As a rule, it contains components that negatively affect the ecology of the environment. Therefore, it is most rational to evaporate this water with low-grade waste heat. In order to close the ecological chain, it is necessary to consider concentrated sludge from tank 2 as feedstock for the corresponding production. This application is not considered within the application.

The circulation water after the turbine condenser is 30 ^o C, and in condensers 3 and 8 it increases to 40-60 ^o C. This water can be used (as an option) to heat the greenhouse before being fed to the cooling tower.

Thus, the proposed disposal scheme has the following advantages:
1) increase in thermal efficiency due to the use of low-grade heat of the exhaust gases instead of steam extraction from the turbine to low-pressure heaters;
2) the replacement of chemical water treatment to obtain a distillate from raw water;
3) the use of the emitted heat of the heat power plant to restore process water with environmentally friendly properties;
4) the use of a solution of purge water of evaporators as feedstock for the corresponding production;
5) commercial sale of the heat of heated circulating water.

Claims (1)

 The scheme of utilization of low potential heat of the flue gases for power steam generators, including a turbine generator, a turbine condenser connected by means of a condensate pump, a deaerator, a feed pump and a high pressure heater with a steam generator, characterized in that an air heater located between the fan and the steam generator, an convective stage is additionally introduced into it connecting the condensate pipe through the feed condenser deaerator and condensate pump, also two ana logical parallel process chains consisting of a successively placed condenser, a vacuum pump, an evaporation stage, which has a drain into the sludge tank by means of a purge pump, and a condensation stage, respectively connecting the raw water pipeline to the steam generator feed distillate pipeline and to the secondary steam pipeline after the vacuum pump to the deaerator, and the production water pipeline to the distillate pipeline, and on the gas side the steam generator is connected through steam Along with the included air heater, convection, evaporation stages and through the corresponding condensation stages with a smoke exhaust, condensate pumps that are connected to the raw and process water pipelines, in addition, the circulation water pipeline after the turbine condenser is parallelly introduced into the feed and processing condensers.