Steam generation method and steam generator

Abstract

A steam generation method using condensed water (4) that is reused in the form of feedwater (11) is described and illustrated. To achieve higher efficiency, the method is provided such that the feedwater (11) is evaporated in a steam generator (17) to form process steam (3), the process steam (3) is at least partially condensed in a consumer device (V) to release heat and form condensed water (4), the condensed water (4) is at least partially supplied to a feedwater treatment device (7) for treatment, the treated feedwater (11) in the feedwater treatment device (7) is separated into a gas phase (13) and a liquid phase (14) in a flash tank (12), the liquid phase (14) of the feedwater (11) is supplied to a steam generator (17) and evaporated in the steam generator (17) to form process steam (18), and the gas phase (13) of the feedwater (11) is supplied to a compressor (15) to compress and form process steam (19).

Description

Technical Field

[0001] The present invention relates to a method for generating steam using condensate that is reused in the form of feed water. Further, the present invention is a steam generation device for generating steam using condensate that is recycled in the form of feed water, preferably using such a method, and includes a steam generator for generating process steam, a discharge device to a consumer device for forming condensate by condensation of the process steam, a recirculation device for supplying the condensate, and a feed water treatment device for treating the condensate to form feed water.

[0002] Steam generation devices are commonly used to generate process steam that can be used to drive steam turbines or for heating industrial processes. Such industrial processes may be chemical processes or other manufacturing processes that require heat at specific locations or to perform specific process steps. As an example, these may be drying processes and the like.

[0003] Typically, a steam generation device includes one or more steam generators in the form of so-called steam boilers, which are fired with fossil fuels or renewable fuels. The resulting high-temperature flue gas is used to evaporate the feed water supplied to the steam boiler. The feed water is usually supplied to an industrial steam boiler under overpressure via pipes, whereby process steam can be continuously and efficiently supplied to the connected consumer device at substantially constant pressure and temperature. As discussed previously, the types of consumer devices can be configured in a very diverse manner. However, the process steam releases heat and condenses within the consumer device regardless of the design of each consumer device. The condensate is usually returned via a recirculation device and supplied to the feed water treatment device of the steam generation device, where it is deaerated. The feed water thus obtained is then evaporated again in the steam boiler and returned to the consumer device as process steam.

[0004] To utilize the energy of the flue gas in the steam generator as effectively as possible and transfer this energy to the feedwater, it is desirable to supply the feedwater to the steam generator at the lowest possible temperature, depending on the circumstances. Otherwise, the flue gas will still be discharged from the steam generator at a relatively high temperature and therefore with a relatively large amount of unused heat. However, in the case of thermal degassing in the feedwater treatment device, the feedwater is obtained at a temperature level slightly above 100°C. To lower the feedwater temperature after degassing, economizers are known, which are configured as heat exchangers, in which the feedwater is cooled by fresh water that can be supplied to the feedwater treatment device, for example, to compensate for condensate loss. Condensate loss can occur, for example, when some of the condensate is discharged to remove non-volatile impurities that accumulate in the water circuit. Alternatively, some of the feedwater may be evaporated by reducing the pressure to extract heat from the feedwater. However, there is still a need to improve known processes and steam generators in terms of the efficiency and effectiveness to be achieved.

[0005] Therefore, the present invention is based on the objective of configuring and further developing methods and steam generators of the type described at the beginning and in more detail above, so as to achieve higher efficiency.

[0006] The objective, according to claim 1, is a method for generating steam using condensed water that is reused in the form of water supply, - The feedwater is evaporated in the steam generator to form process steam. - Process steam is at least partially condensed within the consumer device, releasing heat and forming condensate. - The condensed water is supplied at least partially to the feedwater treatment device for processing. - The feedwater treated in the feedwater treatment device is separated into a gas phase and a liquid phase in the flash tank. - The liquid phase of the feedwater is supplied to the steam generator, where it is evaporated to form process steam. - The gas phase of the feedwater is supplied to the compressor to compress and form process steam. It can be solved by the method.

[0007] The above objective is also solved by providing a steam generator according to the higher conceptual part of claim 9, which includes a flash tank for separating feedwater from a feedwater treatment device into a gas phase and a liquid phase, a return line for supplying the liquid phase of the feedwater to a steam generator, and a compressor for compressing the gas phase of the feedwater.

[0008] According to the method, in at least one steam generator, feedwater is evaporated, thereby forming process steam, which is then discharged into a consumer device where the process steam condenses while releasing heat. The resulting condensate is then returned and processed in a feedwater treatment device, and subsequently used for re-evaporation in at least one steam generator. During the treatment of the feedwater, impurities are removed from this condensate, which may be gaseous, liquid, or solid. Before the treated feedwater is evaporated in the steam generator, it is first partially expanded in a so-called flash tank. This causes part of the feedwater to evaporate, forming a gaseous phase, which extracts heat from the remaining liquid phase of the feedwater, and this liquid phase is then cooled in the flash tank. The liquid phase of the feedwater is then evaporated by the flue gas in the steam generator, and more heat can be extracted from this flue gas than without the prior cooling of the feedwater in the flash tank. Supplying feedwater indirectly through a steam generator in a piping system where the feedwater is evaporated by flue gas, particularly in counterflow, is especially practical and therefore already a common practice.

[0009] The gaseous phase of the feedwater, which is also cooled by evaporation in the flash tank, is supplied to a compressor, where it is compressed and heated. The compression and heating of the gaseous phase of the feedwater proceeds to such an extent that process steam is obtained. The pressure and / or temperature levels of this process steam can, at least substantially, correspond to the pressure and / or temperature levels of the process steam formed in the steam generator. However, this is not necessary. Nevertheless, the process steam generated via the compressor can preferably be used to heat the industrial process or in another useful way, thereby further improving efficiency and the overall process efficiency.

[0010] A steam generator for generating process steam using feedwater requires, in particular to carry out the above method, at least one steam generator and a feedwater treatment device for processing the condensed process steam into feedwater for re-evaporation in at least one steam generator. The steam generator is equipped with a discharge device for discharging the process steam to a consumer device, and in simple cases the discharge device may be piping or the like. In addition, the steam generator also has a return device for returning the condensed water formed by the condensation of process steam in the consumer device back to the steam generator, in particular to the feedwater treatment device. At least one degassing of the condensed water is preferably carried out in the feedwater treatment device. However, alternatively or additionally, liquid or solid impurities can also be separated from the condensed water, along with a portion of the condensed water as needed, and this portion of the condensed water can then be replaced with fresh water.

[0011] In addition, the steam generator has a flash tank to which treated feedwater is supplied. In the flash tank, the feedwater is separated into a liquid phase and a gas phase, the gas phase being formed by the evaporation of a portion of the feedwater as a result of the pressure drop in the flash tank. The evaporation of a portion of the treated feedwater lowers the temperature of the liquid and gas phases relative to the original feedwater. The liquid phase can then absorb a larger proportion of heat from the flue gas in the steam generator, which leads to higher efficiency in steam generation. In addition, the gas phase of the feedwater is not wasted as energy loss but is supplied to the compressor for compression. This generates process steam at high pressure and high temperature levels, and as a result, this process steam can also be used to generate energy to operate industrial processes. It is also conceivable that the process steam generated by the steam generator is used in the same industrial process. However, the two process steams can also be used in different industrial processes.

[0012] In principle, all known types of compressors can be used as compressors of this disclosure. In particular, these include turbo compressors, piston compressors, and screw compressors.

[0013] In the following, the method and the steam generator will be described together without necessarily making a detailed distinction between them. However, it will be clear to those skilled in the art from the context of each that which features are particularly preferred in relation to the method and the steam generator.

[0014] In a particularly preferred first embodiment of the method, the condensate is at least partially degassed in the feedwater treatment device. Gases contained in the feedwater can damage the steam generator. In particular, oxygen (O2) and / or carbon dioxide (CO2) can be problematic or present in large quantities in the condensate of process steam. Therefore, in many cases, oxygen (O2) and / or carbon dioxide (CO2) are preferably removed from the condensate in the feedwater treatment device.

[0015] To degas the condensate within the feedwater treatment apparatus, it may be prudent to supply the condensate to the feedwater treatment apparatus together with heated steam, regardless of the gas to be removed. The heated steam heats the condensate, particularly directly. As a result of the high temperature, the gas is removed from the feedwater and, preferably, is removed from the feedwater treatment apparatus together with the exhaust from the heated steam and / or evaporated condensate.

[0016] To make the treatment of condensate for feedwater and the heating of industrial processes with process steam energy-efficient, it is prudent to supply condensate to the feedwater treatment device at a temperature of 60°C to 100°C, preferably 70°C to 80°C, and especially at least substantially 80°C. The higher the temperature of the condensate, the less heating steam is required to treat it. The lower the temperature of the condensate, the greater the amount of heat that can be transferred to the industrial process to be heated. Furthermore, heat loss along the length of the piping must be taken into consideration.

[0017] Alternatively or additionally, for the same reasons, condensed water can be treated in a feedwater treatment apparatus at a pressure of 1 to 2 bar, preferably 1.1 to 1.5 bar, and especially at least substantially 1.2 bar. Lower pressure allows more heat to be transferred to the industrial process. However, some pressure is necessary to adequately degas the condensed water and ensure sufficient expansion of the feedwater in the flash tank. Therefore, the temperature of the feedwater in the feedwater treatment apparatus is preferably above 100°C, and at temperatures of 102°C to 108°C, especially at least substantially 105°C, little heating steam is required. At the same time, sufficient expansion and temperature reduction can be ensured in the flash tank.

[0018] To adequately cool the liquid phase of the feedwater in an economical manner overall, it is generally prudent to operate the flash tank at an absolute pressure of 0.07 bar to 1.0 bar. The lower the pressure, the lower the temperature at which the feedwater can be supplied to the steam generator. However, the corresponding negative pressure must be generated using equipment and energy. Therefore, it is particularly preferable for the flash tank to operate at a pressure of 0.2 bar to 1.0 bar, but in many cases, a pressure of at least substantially 0.4 bar will be a fairly good compromise. For the reasons previously stated in relation to pressure, and given that the pressure and temperature in the flash tank are interdependent, it would be appropriate, alternatively or additionally, for the flash tank to operate at a temperature of 40°C to 100°C, preferably 60°C to 100°C. In many cases, a fairly good economic compromise would be a temperature of at least substantially 75°C.

[0019] For simplicity, it is advisable for the compressor to generate a corresponding negative pressure in the flash tank to reduce the pressure in the flash tank to a level below the pressure level in the feedwater treatment system, and especially below the ambient pressure. The pressure in the flash tank must be set low enough to be at least below the pressure in the feedwater treatment system; otherwise, partial evaporation of the feedwater in the flash tank and the simultaneous cooling of the feedwater cannot be ensured.

[0020] Regardless, steam generators that produce process steam at temperatures between 100°C and 450°C are useful for many applications. In these cases, the aforementioned advantages of the method are also realized. This is even more true when the process steam temperature is between 100°C and 250°C. A good compromise that allows for the efficient use of steam generators would often be a process steam temperature of substantially 130°C and 200°C.

[0021] The efficient use of process steam generated by the compressor can also be achieved when this process steam has a temperature of 100°C to 450°C. This is especially true for temperatures between 100°C and 250°C, where a good compromise is often achieved for this process steam as well, if the gas phase of the feedwater in the compressor is heated to substantially 100°C and 200°C.

[0022] To achieve efficient use of process steam, process steam obtained from the gas phase of feedwater in the compressor can be combined, at least partially, with process steam from the steam generator. The combined process steam can then be easily used together in subsequent processes in the consumption device. This can be further facilitated if the process steam to be combined from the steam generator and the compressor has at least substantially the same temperature and / or at least substantially the same pressure. However, this is not essential.

[0023] However, depending on the requirements of the consumer device, it is also conceivable that process steam obtained from the gas phase of feedwater in the compressor may be delivered to the consumer device at least partially as separate process steam. This is particularly appropriate when the consumer device has heat demands at various temperature levels, especially when varying amounts of heat are required at different temperature levels.

[0024] The process steam obtained from the gas phase of the feedwater in the compressor can also be used, at least partially, as heating steam and supplied to the feedwater treatment device. In this way, conversion losses may be avoided, for example, by additional throttling.

[0025] However, in principle, heated steam can be recovered, at least partially, independently of the process steam supply source by reducing the pressure of the process steam through a throttle valve. In this way, the feedwater treatment system can be operated at a temperature that is simple and precisely adjustable.

[0026] The advantages of the method are particularly achieved when a steam boiler is used as a steam generator for the sake of simplification. Alternatively or additionally, the condensate can be supplied to the water treatment device in a defined manner using a condensate pump.

[0027] For a simple and efficient partial evaporation of the feed water in the flash tank, it is advisable to connect the water treatment device to the flash tank via a throttle valve. Alternatively or additionally, the liquid phase of the feed water can be supplied to the steam generator by a feed water pump. This can also be done in a reliable and defined manner in this way.

[0028] In a particularly preferred first embodiment of the above steam generating device, a heating steam supply line for heating the condensate is assigned to the water treatment device. In this way, the water treatment device can be operated simply and efficiently. This is particularly true when the condensate is directly heated by the heating steam supplied via the heating steam line. In particular, but not necessarily only in such cases, it may also be useful when the water treatment device is associated with an exhaust discharge line for removing the gases removed from the condensate. The exhaust discharge line can remove the non-condensable heating steam or the steam formed in the water treatment device together with the gases removed from the condensate. However, in principle, it would also be possible for only the gases removed from the condensate to be discharged via the exhaust discharge line without steam, i.e., water vapor. However, since this will hardly be preferred in most cases, the term exhaust discharge line is still used here.

[0029] In the case of the heating steam supply line, for the sake of simplification, a throttle valve can be assigned to this heating steam supply line to form the heating steam by throttling the process steam. This enables a defined operation of the water treatment device and is easy to implement in terms of equipment.

[0030] A confluence can be provided between the process steam from the compressor and the process steam from the steam generator to allow them to be combined and used together. Alternatively or additionally, two separate process steam lines can also be provided for a separate supply of process steam to a consumer device. The process steam from the steam generator can then be used separately from the process steam generated by the compressor. Alternatively or additionally, the compressor can also be connected to a heating steam supply line. The corresponding process steam can then be used simply and efficiently to operate a feedwater treatment device.

[0031] If the steam generator is a steam boiler, the equipment and methods are simple. They are inexpensive and reliable in operation. From an energy and equipment standpoint, it can be useful if the feedwater treatment system is connected to a flush tank via a throttle valve. The same applies if a feedwater pump is assigned to the return line to supply feedwater to the steam generator. To ensure that condensate is always returned to the feedwater treatment system in the desired amount, a condensate pump can be assigned to the feedwater treatment system to supply condensate to it.

[0032] The present invention will be described in more detail below with reference to drawings showing only one embodiment. [Brief explanation of the drawing]

[0033] [Figure 1] This is a schematic diagram of an industrial plant for executing an industrial process using a steam generator according to the present invention. [Figure 2] Figure 1 is a schematic detail diagram of the steam generator.

[0034] Figure 1 shows an example of an industrial plant A for carrying out an industrial process P. An industrial plant A shown and preferred in this respect is a paper mill on which the industrial process P of papermaking is carried out. Alternatively, in connection with the present invention, many other industrial plants A for carrying out various industrial processes P are also conceivable, where the industrial process P has, in particular, a significant heat demand. Papermaking is, in principle, quite energy-intensive and is therefore characterized by a particularly high heat demand.

[0035] Figure 2 shows a steam generator 1 that supplies the heat required for a consumer unit V of industrial plant A via a discharge device 2. The heat is used in the form of process steam 3 in the industrial papermaking process P. By using the process steam 3 as a heat source in the corresponding consumer unit V of industrial process P, the process steam 3 is at least partially condensed, and the resulting condensate 4 is returned to the steam generator 1 via a return device 5. Thus, the process steam 3 or condensate 4 is at least substantially circulated, albeit in various condensation states. In the illustrated and preferred steam generator 1, the discharge device 2 and the return device 5 are configured in line form, specifically in the form of a discharge line and a return line. The specific design of the consumer unit V is not particularly important in this case, and therefore the consumer unit V is not shown in Figure 2.

[0036] The condensed water 4 returned via the return device 5 is supplied to the feedwater treatment device 7 via the condensed water pump 6, where the condensed water 4 is heated to 80°C to 105°C by direct heat transfer with the similarly supplied heated steam 8. The pressure inside the feedwater treatment device 7 is such that the gas phase 9 is dominant, and dissolved gases in the condensed water, particularly oxygen (O2) and carbon dioxide (CO2), are expelled into this gas phase 9. The gas phase 9, along with the expelled gases, is discharged through the exhaust discharge line 10. The properly treated condensed water 4 in the form of feedwater 11 remains inside the feedwater treatment device 7. The feedwater 11 is discharged from the feedwater treatment device 7 to the flash tank 12, where the feedwater 11 is expanded via the throttle valve 21 so that a portion of the treated feedwater 11 evaporates within the flash tank 12, thereby cooling the feedwater 11. In this way, the gas phase 13 and the liquid phase 14 of the feedwater 11 are formed in the flash tank 12, and both the gas phase 13 and the liquid phase 14 of the feedwater 11 have a temperature significantly lower than the treated feedwater 11 in the feedwater treatment device 7.

[0037] In the illustrated, preferred steam generator 1, a negative pressure is drawn in a flash tank 12 by a compressor 15, and the flash tank 12 is correspondingly located on the suction side of the compressor 15. The pressure in the flash tank 12 is not only less than the pressure in the feedwater treatment device 7, but also less than the ambient pressure. Therefore, it 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 through a return line 22 to a steam generator 17, where the feedwater 11 is evaporated in a manner known to itself. Of course, two or more steam generators 17 can be provided, and these two or more steam generators 17 are then preferably operated in parallel.

[0038] The steam generator 17 is a steam boiler in which fuel is burned to form flue gas. The flue gas is guided along a pipe, and within this pipe, the feedwater 11 is guided in a counterflow relative to the flue gas, thus being first heated, then evaporated, and superheated as needed. The feedwater 11 is under absolute overpressure, and as a result, the feedwater 11 is converted into process steam 18 within the steam generator 17, and this process steam 18 can be used as a heat source to heat the industrial process P in the consumer device V.

[0039] The process steam 18 formed in the steam generator 17 is supplied via the confluence 24 together with the process steam 19 formed by the compression of the gas phase 13 of the feedwater 11 in the compressor 15 downstream of the flash tank 12, in a manner preferred in this respect, as illustrated. The process steam 18 from the steam generator 17 and the process steam 19 from the compressor 15 have substantially the same pressure, as illustrated and therefore preferred. The temperatures may also be substantially the same. A portion of the correspondingly combined process steam 3 is supplied to the feedwater treatment device 7 in the form of heated steam 8 via the throttle valve 20 and the heated steam supply line 23, so that the condensed water 4 can be heated in the feedwater treatment device 7. The portion of the process steam 3 not required for the formation of heated steam 8 is then discharged to the consumer device V via the discharge device 2 in the form of a discharge line, and the condensed process steam 3 is subsequently returned to the steam generator 1 as condensed water 4 via the return device. [Explanation of Symbols]

[0040] 1. Steam generator 2 Ejection device 3 Process steam 4. Condensate 5. Return device 6. Condensate pump 7. Water supply treatment equipment 8. Heating steam 9. Gas phase 10 Exhaust line 11 Water supply 12 Flash Tanks 13. Gas phase 14 Liquid phase 15 Compressor 16. Water supply pump 17 Steam generator 18. Process steam (steam generator) 19. Process steam (compressor) 20 throttle valve 21 Throttle valve 22 Return Line 23. Heating steam supply line 24. Confluence A Industrial Plant P Industrial Process V Consumer device

Claims

1. A steam generation method that uses condensed water (4) which is reused in the form of water supply (11), - The feedwater (11) is evaporated in the steam generator (17) to form process steam (3), - The process steam (3) is at least partially condensed in the consumer device (V), releasing heat to form condensed water (4), - The condensed water (4) is at least partially supplied to the water treatment device (7) for processing, - The feedwater (11) processed in the feedwater treatment device (7) is separated into a gas phase (13) and a liquid phase (14) in the flash tank (12). - The liquid phase (14) of the feedwater (11) is supplied to the steam generator (17), and is evaporated within the steam generator (17) to form process steam (18). - The gas phase (13) of the feedwater (11) is supplied to the compressor (15) to compress and form process steam (19). method.

2. - The condensed water (4) contains particularly oxygen (O ２ ) and / or carbon dioxide (CO2) ２ By separating the ) the water is at least partially degassed within the water supply treatment apparatus (7), - Preferably, the condensed water (4) is supplied to the feedwater treatment device (7) together with heated steam (8) in order to directly heat the condensed water (4). The method according to claim 1.

3. - The condensed water (4) is supplied to the water supply treatment device (7) at a temperature of 60°C to 100°C, preferably 70°C to 80°C, and especially at least substantially 80°C, and / or - The condensed water (4) is degassed in the water treatment device (7) at a pressure of 1 to 2 bar, preferably 1.1 to 1.5 bar, particularly at least substantially 1.2 bar, and / or at a temperature greater than 100°C, preferably 102°C to 108°C, particularly at least substantially 105°C. The method according to claim 1 or 2.

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

5. - The compressor (15) generates a negative pressure in the flash tank (12) that is at least compared to the pressure in the feedwater treatment device (7), and / or - The steam generator (17) and / or the compressor (15) generate process steam (3, 18, 19) having a temperature of 100°C to 450°C, preferably 100°C to 250°C, and particularly at least substantially 200°C. The method according to any one of claims 1 to 4.

6. - The gas phase (13) of the feedwater (11) compressed in the compressor (15) is combined with the process steam (18) from the steam generator (17) and / or discharged to the consumer device (V) as a separate process steam (19) and / or supplied to the feedwater treatment device (7) as heating steam (8) and / or - The heated steam (8) is at least partially supplied by process steam (3, 19) that is throttled through a throttle valve (20). The method according to any one of claims 1 to 5.

7. - A steam boiler is used as a steam generator (17), and / or - The condensed water (4) is supplied to the water supply treatment device (7) by the condensed water pump (6). The method according to any one of claims 1 to 6.

8. - The water supply treatment device (7) is connected to the flash tank (12) via a throttle valve (21), and / or - The liquid phase (14) of the water supply (11) is supplied to the steam generator (17) by the water supply pump (16). The method according to any one of claims 1 to 7.

9. A steam generator (1) for generating steam using condensed water (4) that is reused in the form of feedwater (11), preferably using the method according to any one of claims 1 to 8, comprising: a steam generator (17) for generating process steam (3, 18); a discharge device (2) to a consumer device (V) for forming condensed water (4) by condensation of the process steam (3); a return device (5) for supplying condensed water (4); and a feedwater treatment device (7) for processing the condensed water (4) to form the feedwater (11), A steam generator (1) is provided with a flash tank (12) for separating the feedwater (11) from the feedwater treatment device (7) into a gas phase (13) and a liquid phase (14), a return line (22) for supplying the liquid phase (14) of the feedwater (11) to the steam generator (17), and a compressor (15) for compressing the gas phase (13) of the feedwater (11).

10. A heating steam supply line (23) for heating the condensed water (4) in particular directly, and / or an exhaust discharge line (10) for discharging gases removed from the condensed water (4) are assigned to the feedwater treatment device (7), and preferably a throttle valve (20) for forming heating steam (8) by throttling the process steam (3) is assigned to the heating steam supply line (23), characterized in that The steam generator according to claim 9.

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

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

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