Method for generating steam and steam generation device

Abstract

The invention relates to a method for generating steam using condensate (4) returned in the form of feed water (11). So that higher efficiency can be achieved, the invention proposes that the feed water (11) is evaporated in a steam generator (17) with the formation of process steam (3), the process steam (3) is at least partially condensed in a consumer device (V) with the dissipation of heat and formation of a condensate (4), the condensate (4) is at least partially supplied to a feed water treatment apparatus (7) for treatment, the feed water (11) treated in the feed water treatment apparatus (7) is separated in a flash tank (12) into a steam phase (13) and a liquid phase (14), the liquid phase (14) of the feed water (11) is supplied to the steam generator (17) and in the steam generator (17) is evaporated with the formation of process steam (18) and the steam phase (13) of the feed water (11) is supplied to a compressor (15) for compressing and forming a process steam (19).

Description

[0001] The invention relates to a method for generating steam using condensate returned in the form of feedwater. Furthermore, the invention relates to a steam generating device for generating steam using condensate returned in the form of feedwater, preferably using such a method, comprising a steam generator for generating process steam, a delivery device to a consumer device for forming a condensate by condensing the process steam, a return device for supplying condensate, and a feedwater treatment system for treating the condensate to form feedwater.

[0002] Steam generation facilities are regularly used to generate process steam, which can drive a steam turbine or be used to heat an industrial process. Such industrial processes can be chemical processes or other manufacturing processes that require heat at specific points or to carry out specific process steps. These can be, for example, drying processes or the like.

[0003] Documents DE4022544A1, CN115751268A and WO2015 / 068531A1 disclose steam generating devices according to the state of the art.

[0004] Steam generation facilities typically comprise one or more steam generators in the form of so-called steam boilers, which are fired with fossil or renewable fuels. The resulting hot flue gas is used to evaporate feedwater supplied to the steam boiler. In industrial steam boilers, the feedwater is usually supplied at overpressure via pipes, so that process steam can be continuously and efficiently supplied to a connected consumer device at essentially constant pressure and temperature. As previously discussed, the type of consumer device can vary greatly. However, regardless of its design, the process steam is condensed in the consumer device, releasing heat.The condensate is usually returned via a recirculation device and fed into a feedwater treatment system of the steam generation equipment, where the condensate is degassed. The feedwater thus produced is then re-evaporated in the steam boiler and fed back to the consumer equipment as process steam.

[0005] In order to utilize the energy of the flue gases in the steam generator as effectively as possible and transfer it to the feedwater, it is desirable to supply the feedwater to the steam generator at the lowest possible temperature. Otherwise, the flue gas leaves the steam generator at a relatively high temperature, and thus with a relatively high amount of unused heat. However, in the case of thermal degassing in the feedwater treatment system, the feedwater is produced at a temperature level of slightly above 100 °C. To reduce the feedwater temperature after degassing, economizers are known. These are designed as heat exchangers in which the feedwater is cooled, for example, by fresh water, which can then be fed to the feedwater treatment system to compensate for condensate losses.Condensate losses can occur, for example, when a portion of the condensate is drained to remove non-volatile contaminants that accumulate in the water circuit. Alternatively, a portion of the feedwater can be evaporated by reducing the pressure to extract heat from the feedwater. However, there is still a need to improve the existing processes and steam generation systems with regard to the achievable efficiency and effectiveness.

[0006] Therefore, the object of the present invention is to design and further develop the method and the steam generating device of the type mentioned at the outset and explained in more detail above in such a way that a higher efficiency can be achieved.

[0007] This object is achieved according to claim 1 by a method for steam generation using condensate returned in the form of feed water, in which the feed water is evaporated in a steam generator to form process steam, in which the process steam is at least partially condensed in a consumer device to release heat and form a condensate, in which the condensate is at least partially fed to a feed water treatment system for treatment, in which the feed water treated in the feed water treatment system is separated into a vapor phase and a liquid phase in a flash tank, in which the liquid phase of the feed water is fed to the steam generator and evaporated in the steam generator to form process steam, and in which the vapor phase of the feed water is fed to a compressor for compression and formation of process steam.

[0008] The above object is further achieved in a steam generating device according to the preamble of claim 9 in that a flash tank is provided for separating the feed water from the feed water treatment into a vapor phase and a liquid phase, a return line for feeding the liquid phase of the feed water into the steam generator and a compressor for compressing the vapor phase of the feed water.

[0009] According to the process, feedwater is evaporated in at least one steam generator to form process steam, which is then delivered to a consumer device where the process steam condenses, releasing heat. The condensate formed is then returned and treated in a feedwater treatment plant so that it can subsequently be used for further evaporation in at least one steam generator. During the treatment of the feedwater, impurities, which can be gases, liquids or solids, are removed. Before the treated feedwater is evaporated in the steam generator, it is first partially expanded in a so-called flash tank. In this process, part of the feedwater evaporates, forming a vapor phase and extracting heat from the remaining liquid phase of the feedwater, which is then cooled in the flash tank.The liquid phase of the feedwater is then evaporated in the steam generator by flue gas, which allows more heat to be extracted than without prior cooling of the feedwater in the flash tank. It is particularly useful and therefore already common practice for the feedwater to be conducted through the steam generator in a pipe system, where the feedwater is evaporated indirectly, particularly in countercurrent, by the flue gas.

[0010] The vapor phase of the feedwater, which has also been cooled by evaporation in the flash tank, is fed to a compressor, where the vapor phase is compressed and heated in the process. The compression and heating of the vapor phase of the feedwater is so extensive that process steam is also produced in this way. The pressure level and / or temperature level of this process steam can at least substantially correspond to the pressure level and / or temperature level of the process steam generated in the steam generator. However, this is not required. The process steam generated by the compressor will, however, preferably be used to heat an industrial process or in another beneficial way, so that a higher overall degree of efficiency and a higher level of effectiveness of the entire process can be achieved.

[0011] The steam generator device for generating process steam using feedwater requires, in particular for carrying out the method described above, at least one steam generator and a feedwater treatment system for processing condensed process steam into feedwater for re-evaporation in at least one steam generator. The steam generator device comprises a discharge device for discharging the process steam to a consumer device, wherein in a simple case, the discharge device may be a line or the like. Furthermore, the steam generator device also has a return device for returning condensate formed by the condensation of process steam in the consumer device to the steam generator device, in particular to the feedwater treatment system. During feedwater treatment, at least one degassing of the condensate preferably takes place.Alternatively or additionally, liquid or solid impurities could also be separated from the condensate, if necessary together with a portion of the condensate, which can then be replaced with fresh water.

[0012] In addition, the steam generation system features a flash tank into which treated feedwater is fed. There, the feedwater is split into a liquid phase and a vapor phase, with the vapor phase being formed by the evaporation of a portion of the feedwater as a result of a pressure reduction in the flash tank. The evaporation of a portion of the treated feedwater lowers the temperature of the liquid phase and the vapor phase relative to the original feedwater. The liquid phase can then absorb a larger portion of the flue gas heat in the steam generator, leading to greater steam generation efficiency. Furthermore, the vapor phase of the feedwater is not discarded as an energy loss but fed to a compressor for compression. This creates process steam at a high pressure and temperature level, so that this process steam can also be used energetically to operate the industrial process.It is also conceivable that the same industrial process is used in which the process steam generated by the steam generator is used. However, the two process steams can also be used in different industrial processes.

[0013] In this case, all known types of compressors are suitable. These include, in particular, turbo compressors, piston compressors, and screw compressors.

[0014] The method and the steam generating device are described together below, without necessarily distinguishing between the method and the steam generating device in detail. However, the person skilled in the art will recognize from the respective context which features are particularly preferred with regard to the method and the steam generating device.

[0015] In a first particularly preferred embodiment of the process, the condensate is at least partially degassed in the feedwater treatment. Gases contained in the feedwater can damage the steam generator. Oxygen (O2) and / or carbon dioxide (CO2), in particular, can pose a problem or be present in large quantities in the condensate of the process steam. Therefore, in many cases, oxygen (O2) and / or carbon dioxide (CO2) are preferably expelled from the condensate in the feedwater treatment.

[0016] For degassing the condensate in feedwater treatment, it may be appropriate, regardless of the gases to be expelled, to feed the condensate to the feedwater treatment system together with heating steam. The heating steam heats the condensate, particularly directly. Due to the high temperature, the gases are expelled from the feedwater and are preferably removed from the feedwater treatment system together with the vapor from the heating steam and / or evaporated condensate.

[0017] To ensure energy efficiency in the treatment of condensate for feedwater production and the heating of industrial processes with process steam, it is advisable to feed the condensate into the feedwater treatment system at a temperature between 60°C and 100°C, preferably between 70°C and 80°C, in particular at least substantially above 80°C. The higher the condensate temperature, the less heating steam is required for its treatment. The lower the condensate temperature, the greater the amount of heat that can be transferred to the industrial process being heated. Heat losses along the pipe lengths must also be taken into account.

[0018] Alternatively or additionally, for the same reasons, the condensate can be treated in the feedwater treatment system at a pressure between 1 bar and 2 bar, preferably between 1.1 and 1.5 bar, in particular at least substantially 1.2 bar. The lower the pressure, the more heat can be transferred to the industrial process. However, a certain pressure is required to adequately degas the condensate and to ensure sufficient expansion of the feedwater in the flash tank. Therefore, the temperature of the feedwater in the feedwater treatment system is preferably above 100 °C, with little heating steam being required at a temperature between 102 °C and 108 °C, in particular at least substantially 105 °C. At the same time, sufficient expansion and temperature reduction can be ensured in the flash tank.

[0019] To adequately cool the liquid phase of the feedwater in an overall economical manner, it is generally advisable to operate the flash tank at an absolute pressure between 0.07 bar and 1.0 bar. The lower the pressure, the lower the temperature at which the feedwater can be fed to the steam generator. However, the corresponding negative pressure must be generated with considerable equipment and energy expenditure. Therefore, it is particularly preferred to operate the flash tank at a pressure between 0.2 bar and 1.0 bar, although in many cases a pressure of at least 0.4 bar will represent a fairly good compromise.For the reasons previously mentioned in connection with pressure, and given that the pressure and temperature in the flash tank are interdependent, it will be advisable, alternatively or additionally, to operate the flash tank at a temperature between 40 °C and 100 °C, preferably between 60 °C and 100 °C. A reasonably good and economical compromise will in many cases be a temperature of at least substantially 75 °C.

[0020] To reduce the pressure in the flash tank to a level below the pressure level in the feedwater treatment system, and especially below ambient pressure, it is recommended for simplicity if the compressor creates a corresponding negative pressure in the flash tank. The pressure in the flash tank should be set so low that it is at least below the pressure in the feedwater treatment system. Otherwise, partial evaporation of the feedwater while simultaneously cooling it in the flash tank cannot be ensured.

[0021] Regardless, for many applications, it is expedient for the steam generator to produce process steam at a temperature between 100 °C and 450 °C. In these cases, the aforementioned advantages of the process are particularly evident. This is even more true when the process steam temperature is between 100 °C and 250 °C. A good compromise that allows for efficient use of the steam generation system will, in many cases, be a process steam temperature of essentially 130 °C and 200 °C.

[0022] Efficient use of the process steam generated by the compressor can also be achieved if this process steam has a temperature between 100 °C and 450 °C. This applies particularly to temperatures between 100 °C and 250 °C, although a good compromise is often achieved for this process steam if the vapor phase of the feed water in the compressor is heated to essentially 100 °C and 200 °C.

[0023] To achieve efficient use of process steam, the process steam obtained in the compressor from the vapor phase of the feedwater can be at least partially combined with the process steam from the steam generator. The combined process steam can then be easily used jointly in a subsequent process in the consumer facility. This can be further enhanced if the combined process vapors from the steam generator and the compressor have at least essentially the same temperature and / or at least essentially the same pressure. However, this is not mandatory.

[0024] Depending on the requirements of the consumer device, it may also be conceivable that the process steam obtained in the compressor from the vapor phase of the feedwater is delivered to the consumer device at least partially as separate process steam. This is particularly useful if the consumer device has a heat demand at different temperature levels, and especially if different amounts of heat are required at the different temperature levels.

[0025] However, the process steam obtained from the vapor phase of the feedwater in the compressor can also be used, at least in part, directly as heating steam and fed into the feedwater treatment system. This may potentially prevent conversion losses, for example, through additional throttling.

[0026] In principle, however, the heating steam can be recovered at least partially, regardless of the source of the process steam, by reducing the pressure of the process steam via a throttle. This allows the feedwater treatment system to be operated simply and at a precisely adjustable temperature.

[0027] The advantages of this process are particularly evident when a steam boiler is used as the steam generator for simplicity. Alternatively, or additionally, the condensate can be fed to the feedwater treatment system in a targeted and controlled manner using a condensate pump.

[0028] For simple and efficient partial evaporation of the feedwater in the flash tank, it is advisable to connect the feedwater treatment system to the flash tank via a throttle. Alternatively or additionally, the liquid phase of the feedwater can be fed to the steam generator via a feedwater pump. This can also be achieved reliably and precisely in this way.

[0029] In a first particularly preferred embodiment of the steam generation device described above, a heating steam supply line for heating the condensate is assigned to the feedwater treatment system. In this way, the feedwater treatment system can be operated simply and efficiently. This applies in particular when the condensate is heated directly by the heating steam supplied via the heating steam line. In particular, but not necessarily only in such a case, it may also be advisable for the feedwater treatment system to be assigned a vapor discharge line for discharging gas expelled from the condensate. The vapor discharge line can discharge heating steam not condensed in the feedwater treatment system or steam formed in the feedwater treatment system, together with the gases expelled from the condensate. In principle, however, it would also be possible for only gas expelled from the condensate and no steam, i.e. vapors, to be discharged via the vapor discharge line.However, this will not be preferred in most cases, which is why the term vapor discharge is used here anyway.

[0030] In the case of a heating steam supply line, a throttle can be assigned to it for simplicity, generating heating steam by throttling process steam. This allows for defined operation of the feedwater treatment system and is easy to implement.

[0031] In order to combine and use the process steam generated by the steam generator and the compressor, a combination of process steam from the compressor and the steam generator can be provided. Alternatively or additionally, two separate process steam lines can be provided for separately supplying process steam to the consumer equipment. In this case, the process steam from the steam generator can be used separately from the process steam generated by the compressor. Alternatively or additionally, the compressor can also be connected to the heating steam supply line. The corresponding process steam can then be used easily and efficiently to operate the feedwater treatment system.

[0032] It is also simple in terms of equipment and process if the steam generator is a steam boiler. These are cost-effective and reliable to operate. From an energy and equipment perspective, it may be expedient to connect the feedwater treatment system to the flash tank via a throttle. The same applies if a feedwater pump is assigned to the return line to supply the feedwater to the steam generator. To ensure that the required amount of condensate is always returned to the feedwater treatment system, a condensate pump can be assigned to the feedwater treatment system to supply condensate to the feedwater treatment system.

[0033] The invention is explained in more detail below with reference to a drawing which merely represents an exemplary embodiment. Fig. 1 shows an industrial plant for carrying out an industrial process with a steam generating device according to the invention in a schematic view and Fig. 2 shows the steam generating device from Fig. 1 in a schematic detailed representation.

[0034] In the Fig. 1 An industrial plant A for carrying out an industrial process P is shown by way of example. The illustrated and, to this extent, preferred industrial plant A is a paper production plant in which the industrial process P of paper production is carried out. Alternatively, many other industrial plants A for carrying out different industrial processes P could also be considered in connection with the invention, whereby the industrial processes P are in particular those that have a not insignificant heat requirement. Paper production is characterized by a particularly high heat requirement, since paper production is fundamentally quite energy-intensive.

[0035] In the Fig. 2 a steam generating device 1 is shown which provides the required heat to a consumer device V of the industrial plant A via a delivery device 2. The heat is used in the form of process steam 3 in the industrial process P of paper production. By using the process steam 3 as a heat source in the corresponding consumer device V of the industrial process P, the process steam 3 is at least partially condensed and the resulting condensate 4 is returned to the steam generating device 1 via a return device 5. The process steam 3 or the condensate 4 is therefore at least substantially circulated, albeit in different states of aggregation. In the illustrated and in this respect preferred steam generating device 1, the delivery device 2 and the return device 5 are designed in the form of a line, specifically a delivery line and a return line.The consumer facility V is in the . Fig. 2 not shown, since the specific design of the consumer facility V is not of particular importance in this case.

[0036] The condensate 4 returned via the recirculation device 5 is fed via a condensate pump 6 into a feedwater treatment system 7, where the condensate 4 is heated by direct heat transfer with the heating steam 8 that is also supplied, in this case from 80 °C to 105 °C. The pressure in the feedwater treatment system 7 is such that a vapor phase 9 prevails in the feedwater treatment system 7, into which gases dissolved in the condensate, in particular oxygen (O 2 ) and carbon dioxide (CO 2 ), are expelled. The vapor phase 9 is discharged together with the expelled gases via a vapor discharge line 10. A correspondingly treated condensate 4 remains in the feedwater treatment system 7 in the form of feedwater 11.The feedwater 11 is discharged from the feedwater treatment system 7 to a flash tank 12, in which the feedwater 11 is expanded via a throttle 21 in such a way that a portion of the treated feedwater 11 evaporates in the flash tank 12, thus cooling the feedwater 11. In this way, a vapor phase 13 of the feedwater 11 and a liquid phase 14 of the feedwater 11 are formed in the flash tank 12, both of which have a significantly lower temperature than the treated feedwater 11 in the feedwater treatment system 7.

[0037] In the illustrated and thus preferred steam generation device 1, a negative pressure is drawn in the flash tank 12 by means of a compressor 15, with the flash tank 12 being located on the suction side of the compressor 15. The pressure in the flash tank 12 is not only below the pressure in the feedwater treatment system 7, but also below the ambient pressure. This is an absolute pressure of less than 1 bar. The liquid phase 14 of the feedwater 11 remaining in the flash tank 12 is then pumped by a feedwater pump 16 in a return line 22 into a steam generator 17, in which the feedwater 11 is evaporated in a manner known per se. Of course, two or more steam generators 17 can also be provided, which are then preferably operated in parallel.

[0038] The steam generator 17 is a steam boiler in which a fuel is burned to form flue gas. The flue gas is guided along pipes in which the feedwater 11 flows countercurrently to the flue gas, thus first being heated and then evaporated and, if necessary, superheated. The feedwater 11 is under absolute overpressure, so that the feedwater 11 is converted in the steam generator 17 into process steam 18, which can be conveniently used as a heat source for heating the industrial process P in the consumer device V.

[0039] In the illustrated and thus preferred method, a process steam 19 is fed via a junction 24 to the process steam 18 formed in the steam generator 17, which is formed by compressing the vapor phase 13 of the feedwater 11 in the compressor 15 following the flash tank 12. In the illustrated and thus preferred method, the process steam 18 from the steam generator 17 and the process steam 19 from the compressor 15 have approximately the same pressure. The temperatures can also be approximately the same. A portion of the correspondingly combined process steam 3 can be fed via a throttle 20 and a heating steam supply line 23 in the form of heating steam 8 into the feedwater treatment system 7 in order to heat the condensate 4 therein.The part of the process steam 3 not required to form heating steam 8 is then discharged to the consumer device V via the discharge device 2 in the form of a discharge line, before the condensed process steam 3 is later returned as condensate 4 via the return device to the steam generation device 1. List of reference symbols

[0040] 1 Steam generation device 2 Discharge device 3 Process steam 4 Condensate 5 Return device 6 Condensate pump 7 Feedwater treatment 8 Heating steam 9 Steam phase 10 Vapor discharge 11 Feedwater 12 Flash tank 13 Steam phase 14 Liquid phase 15 Compressor 16 Feedwater pump 17 Steam generator 18 Process steam Steam generator 19 Process steam Compressor 20 Throttle 21 Throttle 22 Return line 23 Heating steam supply line 24 Merging A Industrial plant P Industrial process V Consumer device

Claims

1. Method for steam generation using condensate (4) recycled in the form of feed water (11), - in which the feed water (11) is vaporized in a steam generator (17) while forming process steam (3), - in which the process steam (3) is at least partially condensed in a consumer device (V) while releasing heat and forming a condensate (4), - in which the condensate (4) is at least partially fed to a feed water treatment (7) for treatment, - in which the feed water (11) treated in the feed water treatment (7) is separated into a vapor phase (13) and a liquid phase (14) in a flash tank (12) - in which the liquid phase (14) of the feed water (11) is fed to the steam generator (17) and is vaporized in the steam generator (17) while forming process steam (18), and - in which the vapor phase (13) of the feed water (11) is fed to a compressor (15) for compression and formation of a process steam(19).

2. Method according to claim 1, - in which the condensate (4) is at least partially degassed in the feed water treatment (7), in particular by separating off oxygen (O2) and / or carbon dioxide (CO2), and - in which, preferably, the condensate (4) is fed to the feed water treatment (7) together with a heating steam (8) for, in particular direct, heating of the condensate (4).

3. Method according to claim 1 or 2, - in which the condensate (4) is fed to the feed water treatment (7) at a temperature of between 60° and 100°C, preferably between 70°C and 80°C, in particular of at least substantially 80°C, and / or - in which the condensate (4) is degassed in the feed water treatment (7) at a pressure of between 1 bar and 2 bar, preferably between 1.1 and 1.5 bar, in particular of at least substantially 1.2 bar and / or at a temperature of greater than 100 °C, preferably between 102 °C and 108 °C, in particular of at least substantially 105 °C.

4. Method according to any one of claims 1 to 3, - in which the flash tank (12) is operated at a pressure of between 0.07 bar and 1.0 bar, preferably between 0.2 bar and 1.0 bar, in particular of at least substantially 0.4 bar, and / or - in which the flash tank (12) is operated at a temperature of between 40 °C and 100 °C, preferably between 60 °C and 100 °C, in particular of at least substantially 75 °C.

5. Method according to any one of claims 1 to 4, - in which the compressor (15) draws a negative pressure in the flash tank (12) at least in comparison with the pressure in the feed water treatment (7) and / or - in which the steam generator (17) and / or the compressor (15) generates a process steam (3, 18, 19) at a temperature of between 100 °C and 450 °C, preferably between 100 °C and 250 °C, in particular at least substantially 200 °C.

6. Method according to any one of claims 1 to 5, - in which the vapor phase (13) of the feed water (11) compressed in the compressor (15) is combined with the process steam (18) from the steam generator (17) and / or is delivered as separate process steam (19) to the consumer device (V) and / or is fed to the feed water treatment (7) as heating steam (8) and / or - in which the heating steam (8) is at least partially provided by process steam (3, 19) throttled via a throttle (20).

7. Method according to any one of claims 1 to 6, - in which a steam boiler is used as the steam generator (17) and / or - in which the condensate (4) is fed to the feed water treatment (7) by means of a condensate pump (6).

8. Method according to any one of claims 1 to 7, - in which the feed water treatment (7) is connected to the flash tank (12) via a throttle (21) and / or - in which the liquid phase (14) of the feed water (11) is fed to the steam generator (17) by means of a feed water pump (16).

9. Steam generating device (1) for generating steam using condensate (4) recycled in the form of feed water (11), preferably with a method according to one of claims 1 to 8, with a steam generator (17) for generating a process steam (3, 18), with a discharge device (2) to a consumer device (V) for forming a condensate (4) by condensation of the process steam (3), with a return device (5) for supplying condensate (4) and with a feed water treatment (7) for treating the condensate (4) to form the feed water (11), characterized in that a flash tank (12) for separating the feed water (11) from the feed water treatment (7) into a vapor phase (13) and a liquid phase (14), a return line (22) for feeding the liquid phase (14) of the feed water (11) into the steam generator (17) and a compressor (15) for compressing the vapor phase (13) of the feed water (11) are provided.

10. Steam generating device according to claim 9, characterized in that a heating steam supply line (23) for heating the condensate (4), in particular directly, and / or a vapour discharge line (10) for discharging gas expelled from the condensate (4) is assigned to the feed water treatment (7) and in that, preferably, a throttle (20) for forming heating steam (8) by throttling process steam (3) is assigned to the heating steam supply line (23).

11. Steam generating device according to claim 9 or 10, characterized in that a merging junction (24) is provided for process steam (19) from the compressor (15) and process steam (18) from the steam generator (17) or that two separate process steam lines are provided for the separate supplying of process steam (18, 19) to the consumer device (V) or that the compressor (15) is connected directly to the heating steam supply line (23).

12. Steam generating device according to any one of claims 9 to 11, characterized in that the steam generator (17) is a steam boiler and / or that the feed water treatment (7) is connected to the flash tank (12) via a throttle (21) and / or that the return line (22) is assigned a feed water pump (16) for supplying the feed water (11) to the steam generator (17) and / or that the feed water treatment (7) is assigned a condensate pump (6) for supplying condensate (4) to the feed water treatment (7).

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