RU2528452C2 - Method of heating at steam heat exchangers and plant to this end - Google Patents

Abstract

FIELD: power engineering.

SUBSTANCE: invention relates to power engineering. Method of heating at steam heat exchangers by means of stepwise heating of medium in heat exchangers at several steps by steam with pressure increased at every step and fed to heat exchangers via steam lines and steam condensate discharge from heat exchangers via pipes of every step via condensate discharge devices. Note here that boiler room or thermal power station stem is used at every stage for heating of said heat exchangers. Before feeding to heat exchanger said steam is mixed by injection in jet compressor with steam resulted from condensate self-evaporation. Note here that condensate is discharged from heating first stage condensate discharge while a portion of discharged condensate is injected into steam after jet injection. Invention covers also the plant for implementation of said method.

EFFECT: lower steam consumption, production of high-purity condensate and longer life of heat exchange pipes.

4 cl, 1 dwg

Description

The invention relates to heat engineering and can be used in the chemical, metallurgical, energy and food industries for heating various media with steam.

One of the most important problems that arise during the processing of various media and their heating with steam is the reduction of heat consumption. To do this, if there is such a possibility, stepwise heating of the heated medium is used, when the medium is heated at the first stages with lower pressure steam, and at high pressure with subsequent steps. In this case, the low-pressure steam is, as a rule, the secondary steam formed during the primary processing of the medium. The use of secondary steam for heating can significantly reduce the cost of high-pressure steam, which is produced at a boiler house or a thermal power plant and has a high cost, while secondary steam is quite cheap. At the same time, in many industries there is no secondary steam, therefore, in the vast majority of cases, for heating, it is necessary to use high-pressure steam supplied from a boiler house or thermal power plant. At the same time, due to the specifics of the operation of boiler houses or thermal power plants, the pressure of this steam is significantly higher than that required for heating, and therefore it must be reduced in reduction plants. However, in them the excess steam potential is lost, as a result of which the steam consumption for heating is excessively high.

The use for steam heating of a boiler house or CHP with a high pressure having a high temperature leads to the appearance of high temperature stresses in the heat exchanger (which in most cases shell-and-tube heat exchangers are used) that lead to tube ruptures. As a result, the devices have to be stopped for repair and replacement of tubes. When the tubes break, the mixture of the heated medium and steam condensate of the boiler house or thermal power plant is mixed, leading to contamination of the latter. Dirty condensate cannot be returned to the boiler room or CHP, as is usually done during normal operation. As a result of the above, the heat consumption increases even more, since the heat that it possesses is lost with the condensate. In addition, additional costs are required for the chemical cleaning of the condensate-replacing water before it is fed into the boiler of a boiler house or a thermal power plant instead of condensate.

A known method and installation for heating in a steam heat exchanger (Kichigin MA, Kostenko GN Heat exchangers and evaporators. - M.-L.: Gosenergoizdat, 1955. - P.14, Fig.1-3). According to this method, implemented on a known installation, steam from a boiler room steam generator (or from a thermal power plant) is fed to a steam heat exchanger, in which the heated medium is heated. At the same time, the flow rate and pressure of the steam are regulated using fittings installed on the steam line. When the heated medium is heated in the heat exchanger, the steam condenses, giving off its heat. The steam condensate from the heat exchanger is removed through the exhaust device and returned to the steam generator (to the boiler room or to the CHP).

The disadvantages of the known method and installation include:

- high heat consumption, due to the fact that the entire heating of the medium is carried out by steam with constant pressure and in one heat exchanger;

- the boiler room steam generator (or CHP) produces steam of a certain pressure, which in most cases is significantly greater than that required for heating the medium. Therefore, the steam pressure must be reduced by reducing it before it is fed to the heat exchanger. As a result, the heat exchanger is heated by superheated (relative to the saturation temperature) steam. This leads to the appearance of additional temperature stresses in the heat exchanger, causing tube ruptures, as well as to the mixing of the heated medium with condensate and its contamination.

A known method and apparatus for evaporating solutions in an evaporator (Kasatkin A.G. Basic processes and apparatuses of chemical technology. - M .: Chemistry, 1971. - P.374-375, Fig. IX-18). According to this method and installation, the evaporation of the solution is carried out in an evaporator. The initial solution is fed into it and the stripped off solution is removed. When evaporating from the solution, the secondary vapor evaporates. To heat the device, primary steam with high pressure is used. This steam is brought to the jet compressor (injector), into which the secondary steam of lower pressure is injected. In the compressor, the primary and secondary pairs are mixed, and the mixture with intermediate pressure is divided into two parts. Most of it is fed into the heating chamber, and the rest is diverted to the side to other consumers.

The main disadvantages of the known method and installation are:

- mixing of primary and secondary steam. Due to the fact that the secondary vapor evaporates from the evaporated solution, it contains small drops of the latter. As a result of mixing, the condensation of steam leaving the heat exchanger chamber of the evaporator is contaminated. Such condensate can no longer be returned to the boiler room or to the CHP. Therefore, the cost of heat for obtaining primary steam increases, as well as the cost of preparing water for boilers;

- the mixed vapor stream exiting the compressor has a high temperature significantly exceeding the vapor saturation temperature. This is mainly due to the high temperature of the primary vapor. As a result, high temperature stresses arise in the heat exchanger chamber of the evaporator, which lead to tube ruptures, as a result of which the apparatus must be stopped for repair and tube replacement. Tube ruptures also lead to mixing of the evaporated solution with steam condensate of the CHP and contamination of the latter.

A known method and installation for utilization of low potential heat of hot water (Steam-compressor for utilization of low potential heat of hot water. - URL: http://www.ejector.ru./3022r.shtml, accessed: 20.11.2012). According to the method and installation of steam from a boiler room or a thermal power plant, it is supplied to a steam-jet compressor, which also receives steam from self-evaporation of condensate from process plants collected in a device for collecting and removing condensate. In a steam-jet compressor, primary steam and self-evaporation steam are mixed to produce the required pressure steam for supplying the consumer. The use of well-known solutions allows the use of low-grade heat, which is possessed by condensate removed from process plants. Due to this, there is a reduction in the cost of steam boiler or CHP.

The main disadvantages of the known method and installation are:

- inconsistency in the work of steam consumers and condensate sources, which are various technological installations. As a result of this, the condensate flow rate or its pressure can be such that the amount of vapor from self-evaporation will be small for the operation of a steam-jet compressor. This will increase the cost of steam boiler or CHP;

- the temperature and pressure of the condensate can be such that self-evaporation of steam will not occur. As a result, the steam-jet compressor will not be able to work, and the steam consumption of the boiler room or CHP will increase.

Closest to the claimed technical solution is a two-stage heating method in steam heat exchangers and an installation for its implementation (Kichigin MA, Kostenko G.N. Heat exchangers and evaporators. - M.-L.: Gosenergoizdat, 1955. - P. 15, FIGS. 1-5). This method includes the stepwise heating of the heated medium in steam heat exchangers in two stages with steam increasing at each stage the pressure and the removal of steam condensate from the heat exchangers at each stage through intended for this device. In this case, the first stage is heated by low steam, and the second by high pressure. The installation for implementing this method consists of two sequentially installed steam heat exchangers connected by pipelines of a heated medium, steam pipelines of high and low pressure steam, connected to each heat exchanger and pipelines allocated from them with condensate drainage devices. These method and installation for its implementation are taken as a prototype. The disadvantages of the known method and installation include:

- high heat consumption for heating the heated medium. This is because the condensed high-pressure steam is removed from the heat exchanger in the form of a condensate with a high temperature, with which a large amount of unused heat is removed from the heating installation. In this case, pumping such condensate is fraught with the danger of boiling it with a possible decrease in pressure;

- heating the heat exchanger in the second stage of steam heating with a high temperature exceeding the saturation temperature. This is due to the peculiarities of the operation of the CHP, from which steam is supplied. The pressure of this vapor is usually much higher than that required for heating, so it must be reduced. The use of steam with high temperature leads to the appearance of high temperature stresses in the heat exchanger, which lead to tube ruptures. As a result, the devices are stopped for repair and replacement of tubes. When the tubes rupture, the heated medium is mixed with the condensate of the steam of the thermal power station, polluting the latter. Such condensate can no longer be returned to the CHP, as is usually done during normal operation. As a result of the above, there is an increase in the cost of heat for heating, since the heat that it possesses is lost with the condensate. In addition, additional costs are required for the chemical cleaning of the condensate replacement water before it is fed to the CHP boiler instead of condensate;

- the need to reduce high-pressure steam supplied from the CHPP for heating. In this case, the excess steam potential is lost, as a result of which the steam consumption for heating increases.

These disadvantages of known methods and installations in this field of technology have stimulated the search for new technical solutions.

The proposed technical solution is aimed at solving the problem of reducing steam costs, obtaining high purity steam condensate and increasing the life of the heat exchange tubes.

The solution to the technical problem is achieved by the fact that in the method of heating in steam heat exchangers, comprising the stepwise heating of the heated medium in several steam heat exchangers with increasing pressure at each stage and the removal of steam condensate from the heat exchangers at each stage through the condensate drain devices, according to the invention, for heating the heat exchangers on each stage uses steam from a boiler house or thermal power plant, which before entering the heat exchanger is mixed by means of jet injection in a jet compressor with arom samoispareniya of condensate withdrawn from the same heat exchanger to the condensate drain device, moreover, the condensate derived from the installation of the device the first condensate preheating stage, and part of the withdrawn condensate is sprayed into the vapor jet after injection.

In the proposed method of heating in steam heat exchangers, steam condensate can sequentially flow through the condensate drainage devices from the heat exchangers in the direction from the last to the first stage.

The solution to the technical problem is achieved by the fact that in the installation for heating in steam heat exchangers, including several successively installed heat exchangers connected by pipelines of the heated medium, steam pipelines connected to each heat exchanger and diverted from piping heat exchangers with condensate drain devices, according to the invention, steam pipelines connected to heat exchangers , are connected to the common collector for steam supply of a boiler house or a thermal power plant for installation, on a steam pipe connected to the corresponding To each heat exchanger, a jet compressor is installed at each stage, to which a steam extraction pipe is connected from the condensate drain device from this heat exchanger, a device for injecting condensate into the steam stream is connected to each jet compressor, and each condensate injection device is connected by a pipeline to a common condensate drain pipe from installation.

In the installation for implementing the inventive method, devices for removing condensate from heat exchangers at all stages in the direction from the last to the first can be connected by condensate overflow pipelines.

Next, we consider in more detail the need and sufficiency of both each of the distinguishing features of the claimed technical solutions, and their entirety to achieve a technical result.

The claimed combination of features of the proposed technical solutions allows for the stepwise heating of the heated medium using only high-pressure CHP steam, in the absence of low-pressure steam. Thanks to the use of jet compressors on steam pipelines in heat exchangers at each stage of heating, a significant reduction in steam costs of a boiler house or a high-pressure CHP is achieved. This effect occurs due to the fact that in each compressor the steam of the boiler house or CHP is mixed with steam from self-evaporation of condensate discharged from the same heat exchanger, which is secondary steam. In this case, steam from a boiler house or CHP plant having a high pressure injects steam into the compressor from self-evaporation of condensate, the pressure of which is much lower than the steam pressure of a boiler house or CHP plant heating the heat exchanger. As a result, steam comes out of the jet compressor with the pressure required to supply the stage in question to the heat exchanger. Moreover, at the first stage of heating, a lower pressure is maintained in the heat exchanger than in the next, and in the same way it occurs until the very last stage. Accordingly, the secondary vapor pressures from self-evaporation of the condensate and heating vapors in all stages of heating are likewise correlated.

The use of jet compressors on steam pipelines to heat exchangers allows to reduce the steam consumption of the boiler room or CHP entering them. This is due to the fact that the flow rate of steam entering the heat exchangers (determined by the necessary heating of the heated medium) consists of two cost components: steam from a boiler house or a thermal power plant and secondary steam from self-evaporation of condensate. In this case, the total steam consumption of the boiler room or CHP is less than the total steam consumption for heating the heat exchangers by the total secondary steam consumption from all devices. It should also be noted that due to a decrease in the pressure of the secondary vapor from self-evaporation of the condensate from the last stage of heating to the first, there is an increase in the injection coefficients of jet compressors in stages. Accordingly, they reduce the steam costs of the boiler room or CHP, supplied to the respective heat exchangers.

According to the claimed technical solution, condensate drainage devices are used in the condensate drainage pipelines from each heat exchanger, in which the condensate self-evaporates as a result of pressure reduction. The possibility of self-evaporation of the condensate provides the connection of the condensate drain with the jet compressor, due to its injectable ability, determined by the design. Moreover, in the noted signs of the claimed solution, a new property is revealed that is not characteristic of the known condensate drainage devices - self-evaporation of the condensate to a pressure determined by the injected ability of the jet compressor. As a result of the above, there is a reduction in steam costs of the boiler house or CHP, determined by the amount of secondary steam from self-evaporation of condensate leaving the heat exchangers.

As already noted, in jet compressors, the steam pressure of the CHPP decreases to the values required at each stage. Moreover, the marked decrease in pressure occurs without reduction, and as a result of steam injection of a boiler house or thermal power plant with a high vapor pressure from self-evaporation of condensate having a lower pressure. At the same time, the high steam potential of the boiler house or thermal power plant is not lost, as during reduction, but is used to obtain the desired heating steam pressure for each heat exchanger. That is, through the use of the high potential of the steam boiler or CHP, its consumption is reduced. As a result of this, a new property of the compressor is manifested as a device for reducing the pressure of the primary steam of a boiler house or thermal power plant.

Heat exchangers are heated at all stages of heating by steam from a boiler house or CHP, which has a temperature significantly higher than the temperature of steam saturation. The use of compressors does not lead to a significant decrease in the temperature of the steam entering the heat exchangers. In order to prevent overheated steam from entering the heat exchangers, excessive steam overheating must be removed. To this end, the claimed technical solution provides for the injection of a part of the condensate discharged from the first heating stage into the steam after the jet compressors, for which purpose condensate injection devices are used as part of the proposed installation. The amount of condensate injected is determined in each case, depending on the temperature of the superheated steam. Due to the supply of condensate to the vapor, it evaporates, as a result of which the vapor temperature decreases to values close to the saturation temperature. The supply of such steam to the heat exchangers eliminates the appearance of temperature stresses in them, leading to tube ruptures. This extends the life of the heat exchanger tubes. In addition, contamination of steam condensate in the boiler room or CHPP with a heated medium is excluded, which allows returning this condensate to the boiler room or CHPP along with its heat. This leads to lower heat costs for heating, as well as lower costs for the preparation of water for boiler feed.

The claimed technical solution provides for a sequential flow of condensate through the condensate drainage devices from the heat exchangers from the last to the first heating stage. This feature makes it possible to provide an increase in the amount of secondary steam from self-evaporation of the condensate in the marked sequence. Thus, in each subsequent condensate drainage device, the amount of secondary steam that is injected by the jet compressor of this stage will be increased. As a result, the steam consumption of the boiler house or CHP is reduced even more, i.e. steam costs are reduced even more.

The technical result of the application of the claimed technical solution is to significantly reduce the cost of steam boiler or CHP to heat the heated medium, to obtain condensate of high purity and increase the life of the heat transfer tubes.

A search conducted in the sources of scientific, technical and patent information, as well as the above analysis of analogues, did not reveal technical solutions that coincided with the claimed combination of distinctive features. This, combined with obtaining a technical result, allows us to conclude that the proposed invention meets the criteria of "novelty" and "inventive step".

The invention is industrially applicable and can be used in various industries for heating various environments in steam heat exchangers. All features of the invention are feasible and reproducible. They are used to achieve a technical result in full.

The invention is illustrated by drawings, where figure 1 shows a diagram of a two-stage installation for implementing the proposed method.

The installation consists of a heat exchanger of the first stage 1 and a heat exchanger of the second stage 2, which are connected by pipelines of the heated medium 3, 4 and 5. Steam exchangers 6 and 7 are connected to the heat exchangers 1 and 2, respectively, which are connected to a common collector 8 for supplying steam to the boiler house or thermal power station for the installation. Pipelines 9 and 10 with condensate drainage devices 11 and 12 are allocated from heat exchangers 1 and 2, respectively. On the pipelines 6 and 7, jet compressors 13 and 14 are installed, respectively, to which are connected the pipelines 15 and 16 for taking steam from the condensate removal devices 11 and 12 from the heat exchangers 1 and 2. The steam pipe 17 is connected to the jet compressor 13, and the steam pipe 18 is connected to the jet compressor 14 Devices for injecting condensate 19 and 20 into the steam stream, respectively, are connected to the jet compressors 13 and 14, to which pipelines 21 and 22 are connected from the common condensate drain pipe 23 from the installation. The condensate drain 11 and 12 are connected by a condensate overflow pipe 24. A condensate drain pipe 25 from the installation is connected to the condensate drain 11. A pump 26 is installed on the common pipe 23.

The claimed method of heating in steam heat exchangers is carried out in the described installation as follows.

The heated medium through the pipeline 3 is supplied to the heat exchanger 1 of the first heating stage. The medium heated in it through pipeline 4 enters the heat exchanger 2 of the second heating stage, after heating in which it is discharged from the installation through pipeline 5.

Steam from a boiler room or CHP plant is supplied through a common collector 8. In this case, the total flow is divided into two parts. One part enters the jet compressor 13 for heating in the first stage. Secondary steam is injected into the compressor 13 through the steam line 15 from self-evaporation of the condensate leaving the heat exchanger 1.

A mixture of steam from a boiler house or CHP and secondary steam from a compressor 13 with the pressure necessary to heat the heated medium in the first stage enters the device 19 for injecting condensate into the steam stream to remove steam overheating. Condensate is supplied to the device 19 through the pipe 21. The cooled steam from the device 19 through the steam pipe 6 enters the heat exchanger 1 of the first heating stage.

In the heat exchanger 1, the medium passing through it is heated by the heat of vapor condensation. Condensate from the heat exchanger 1 is discharged through a pipe 9 to the condensate drain 11, in which condensate self-evaporates when the pressure decreases due to the injection effect of the compressor 13. Condensate from the condensate drain 12 from the heat exchanger 2 also enters the device 11. Secondary steam released from the drain condensate 11 is discharged through the steam line 15. The remaining condensate is discharged from the installation through the pipeline 25, from which the common condensate drain pipe 23 is often taken from the installation l condensate to cool the steam. This condensate is pumped by a pump 26 through pipelines 21 and 22 to devices 19 and 20 for injecting condensate into the steam stream to relieve steam overheating.

The steam from the boiler house or CHPP intended for the second stage of heating through steam line 18 enters the jet compressor 14, into which secondary steam is injected through steam line 16 from self-evaporation of condensate leaving the heat exchanger 1. A mixture of steam from the CHP and secondary steam from compressor 14 with the pressure necessary for heating the heated medium in the second stage, enters the device 20 for injection of condensate into the steam stream in order to cool the steam. Condensate is supplied to the device 20 through the pipe 22. The cooled steam from the device 20 through the steam pipe 7 enters the heat exchanger 2 of the second heating stage.

In the heat exchanger 2, condensation of steam occurs, the heat of which is transferred to the heated medium. Condensate from the heat exchanger 2 is discharged through the pipeline 10 to the condensate drain 12, in which condensate self-evaporates when the pressure decreases due to the injection effect of the compressor 14. Secondary steam from the condensate drain 12 is discharged through the steam line 16 to the compressor 14. The remaining condensate from the device 12 through the pipeline condensate flow 24 enters the condensate drain 11.

An example of a specific implementation of the claimed method.

The heated medium is a chloride solution of sodium and potassium with a flow rate of 40 m / h is heated in a two-stage installation from 70 to 125 ° C. In the first stage heat exchanger, the solution is heated to 90 ° C.

The plant receives steam from a thermal power plant with a pressure of 1.0 MPa and a temperature of 220 ° C. Part of this steam with a flow rate of 1.16 t / h is supplied to the first stage jet compressor, into which 250 kg / h of secondary steam is injected from self-evaporation of condensate leaving the first stage heat exchanger. 1.41 t / h of steam comes out of the compressor with a pressure of 0.12 MPa and a temperature of 200 ° C. This steam enters the condensate injection device, in which PO l / h of condensate is injected into the steam stream. Then the steam with a temperature of 108 ° C enters the heating of the heat exchanger of the first stage.

Condensed steam from this heat exchanger in the form of condensate flows into the condensate drainage device, in which the pressure of 0.33 MPa is maintained due to the injection effect of the first stage jet compressor. Steam condensate of the second stage is supplied to the same device. As a result of the pressure reduction, self-evaporation of the condensate occurs and 250 kg / h of secondary steam is released from it, which enters the compressor. The remaining condensate with a temperature of 70 ° C is discharged from the unit. A part of the condensate discharged from the installation is taken and pumped into the device for injecting condensate into the steam stream in order to cool the steam.

Steam CHP is also supplied to the second stage jet compressor with a flow rate of 2.25 t / h. 160 kg / h of secondary steam are injected into the compressor from self-evaporation of the condensate leaving the heat exchanger of the second stage. 2.41 t / h of steam leaves the compressor with a pressure of 0.44 MPa and a temperature of 214 ° C. This steam enters the condensate injection device, in which 140 l / h of condensate is injected into the steam stream. After that, steam with a temperature of 150 ° C enters the second stage heat exchanger.

The condensate from the heat exchanger of the second stage flows into the condensate drain, in which the pressure of 1.47 MPa is maintained due to the injection effect of the jet compressor of the second stage. Due to the pressure reduction, self-evaporation of the condensate occurs and 160 kg / h of secondary steam are released from it, which enters the compressor. The remaining condensate with a temperature of 110 ° C is discharged to the condensate drain device of the first stage.

The application of the proposed technical solutions allows us to solve the technical problem - to reduce the cost of steam for heating the solution, which in the considered example is reduced by 25% compared with the prototype. In addition, the cooling of the steam after the compressors makes it possible to avoid the supply of superheated steam to the heat exchangers, which leads to an increase in the service life of the heat exchange tubes by 2.5 times. An increase in the service life of the heat exchange tubes leads to the fact that the steam condensate does not mix with the heated solution during tube ruptures. Therefore, the condensate discharged from the installation is constantly diverted to the CHPP, thereby reducing the cost of heat and water treatment for boilers.

Claims (4)

1. The method of heating in steam heat exchangers, including the stepwise heating of the heated medium in several steam heat exchangers with increasing pressure at each stage and the removal of steam condensate from the heat exchangers at each stage through condensate drainage devices, characterized in that boiler room steam is used to heat the heat exchangers at each stage or CHP, which before entering the heat exchanger is mixed by jet injection in a jet compressor with steam from self-evaporation of condensate discharged from of the same heat exchanger into the condensate drainage device, and the condensate is removed from the installation from the condensate drainage device of the first heating stage, and part of the condensate drained is injected into the steam after jet injection. 2. The heating method in steam heat exchangers according to claim 1, characterized in that the steam condensate flows sequentially through the condensate drainage devices from the heat exchangers from the last to the first stage. 3. Installation for heating in steam heat exchangers, including several series-installed heat exchangers connected by pipelines of the heated medium, steam pipelines connected to each heat exchanger and diverted from piping heat exchangers with condensate drainage devices, characterized in that the steam pipelines connected to the heat exchangers are connected to a common collector steam supply of a boiler house or CHP plant to the installation, on the steam pipe connected to the corresponding heat exchanger at each stage is installed with a jet compressor, to which a steam extraction pipe is connected from the condensate drain device from this heat exchanger, a device for injecting condensate into the steam stream is connected to each jet compressor, and each condensate injection device is connected by a pipeline to a common condensate drain pipe from the installation. 4. Installation for heating in steam heat exchangers according to claim 3, characterized in that the condensate drainage devices from the heat exchangers at all stages from the last to the first are connected by condensate overflow pipelines.

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