EP1245795A2 - Method for avoiding depositions in vapour-systems - Google Patents

Abstract

Process for preventing deposition of impurities in steam systems comprises preventing the steam solubility of the impurities present in certain concentrations from being exceeded as a result of changes in temperature and/or pressure ratios within the steam system. An Independent claim is also included for a steam system for carrying out the above process. Preferred Features: The impurity is silicon dioxide. The steam system consists of steam cooling or steam injection of a gas turbine system. The temperature and/or pressure of the steam flowing through the steam system is adjusted to prevent the steam solubility of the impurities present in steam in certain concentrations from being exceeded.

Description

TECHNICAL AREA

The present invention relates to a method for preventing the deposition of contaminants in steam systems in which the steam flowing therein has the given steam quality Is subject to temperature and / or pressure changes. The invention also relates to a steam system to carry out the process.

STATE OF THE ART

For cooling thermally highly stressed components of energy machines, for example one Gas turbine plant, steam is increasingly being used for efficiency reasons use as a coolant. This steam can be used as a steam but also as a steam-air mixture, the components to be cooled in an open, semi-open or closed system flow through.

In an open steam system, the steam is supplied by a steam supply device (Waste heat boiler, steam turbine system, auxiliary steam generator, ...) to the device for Use of steam, for example, led to a gas turbine system to its components To cool warming. The cooling steam arrives after flowing through the cooling system for example gas turbine system in the working fluid of the gas turbine system and with it ultimately into the atmosphere.

In a semi-open steam system, the steam is supplied by a steam supply device (Waste heat boiler, steam turbine system, auxiliary steam generator, ...) to the device for Use of steam, for example, led to a gas turbine system to its components To cool warming. The cooling steam is after flowing through the cooling system Gas turbine system of a device for steam extraction (waste heat boiler, steam turbine system, technological process, ...).

In a closed steam system, the device for providing steam (steam cooler, Steam blower, steam filter, ...) identical to the device for steam extraction. Through the device for providing steam, the device for using steam is in in our case the gas turbine plant, steam with the appropriate parameters available posed. After flowing through the cooling system of the gas turbine system, the Steam is returned to the steam supply device for maintenance purposes of the circuit necessary pressure increase, cooling, cleaning u. Like. Make.

In steam injection to increase performance, steam is used as an additional Work equipment to increase the mass flow of the work equipment in the gas turbine plant injected. This can in turn take the form of direct injection of steam into the Work equipment or indirectly after the flow through gas turbine components to be cooled respectively. The steam can also be in the form of a steam-air mixture, i.e. H. in combination with cooling air via an open air cooling system, again indirectly, d. H. after the flow of gas turbine components to be cooled, into which working fluid is injected.

The steam injection method is used. H. the steam introduction into the work equipment the gas turbine system also in the Cheng Cycle. The Cheng Cycle is used to avoid a steam turbine system and the one required to operate the steam turbine system Systems of steam generated in the waste heat boiler completely into the gas turbine plant injected.

Impurities in the steam are characterized by a certain solubility in steam. With regard to possible deposits, silicon dioxide (SiO ₂ ) is of particular importance because of the problems with the cleaning of make-up water and condensate as well as the difficulties in measuring. Representing the large number of possible contaminants, SiO ₂ is therefore used as an example below.

The high-precision components of a gas turbine system, the small dimensions of the cooling channels, the high demands on the flow conditions and the like result in the need to guarantee high steam quality. Without this purity it comes to deposits within the steam systems, the performance of the systems is reduced and revisions with corresponding downtimes of the systems are required. This is particularly important for the open and semi-open steam systems because in these systems the cooling steam has to be made available again and again, and thus new impurities can always get into the system.

Last but not least, this results in the steam generator technology used numerous constraints, for example with regard to component design (steam drying in drums and separators), steam temperature control through water injection or steam mixing, chemical driving, etc.

Attempts are currently being made through appropriate concepts of steam provision and Steam cleaning is a steam quality that avoids deposits with great reliability sure. Thus, numerous methods of steam mixing are known to control the steam temperature without being able to regulate water injection. Furthermore, special steam filters, especially recommended for closed steam systems.

All of these approaches rely on such disadvantageously high steam applications technical and thus also financial effort to produce very pure water guarantee to further improve the quality of this water through condensate cleaning systems, contamination of the steam by appropriate methods of steam generation and steam parameter control to avoid the steam through suitable filters of Free contaminants and chemical interactions in the systems concerned z. B. Prevent corrosion by choosing a suitable material.

PRESENTATION OF THE INVENTION

The invention is therefore based on the object of a method for preventing deposition of contaminants in steam systems, in which the Disadvantages of the prior art can be avoided.

The solution to the above object according to the invention is, in such steam systems, in which the steam of given steam quality flows in temperature and / or Is subject to pressure changes through a corresponding constructive design and design of steam systems to prevent changes in the Temperature and / or pressure conditions within the steam system the steam solubility of the impurities present in the steam in certain concentrations becomes.

The essence of the invention is therefore not, as previously according to the prior art Quality d. H. the purity of the steam on a certain, very low and deposits with a high probability of bringing preventive value, but rather under the conditions given in practice for the steam quality and accordingly prevent the solubility behavior of the impurities from separating the Contamination in the steam system can occur at all. Surprisingly, it shows namely, that the total "pre-cleaning" of the water or steam is actually done is not necessary, but that it is sufficient to reach critical parameters in the Avoiding the steam system means separating contaminants to avoid pulling parameters of the steam.

This happens because the parameters temperature and pressure by a suitable Choice of design parameters and / or by appropriate guidance of the steam in the system, or if necessary by ensuring the temperature accordingly, never assume values that allow the separation of impurities. With in other words, it is about an excessive drop in temperature and / or pressure to prevent a critically low value. This can be done in a variety of ways be it that a critical drop in temperature caused by an increase in Steam mass flow, and / or a reduction in cooling external influences prevented is, and / or also by the steam, especially in critical areas of the Steam system, experiences a corresponding temperature increase. In terms of pressure can be influenced by the fact that the flow conditions by the type and Design of the steam duct in the steam system should be designed in such a way that pressure losses, especially in critical areas.

A first embodiment of the method according to the invention is characterized in that the impurities are silicon dioxide (SiO ₂ ).

In a further embodiment of the method, the method involves steam cooling or a steam injection of a gas turbine system is used. These are two special ones significant applications of steam in gas turbine plants.

An additional measure to prevent deposits can also be provided the temperature and / or pressure of the steam flowing in the steam system be set so that in the steam system the steam solubility in a particular The concentration of impurities present in the steam is not exceeded. Usually there is scope for the parameters of temperature and / or pressure in steam systems flowing steam sufficiently large to be able to select or optimize at least one of these parameters to further reduce the risk of deposits.

The method can be designed particularly advantageously by using both values are monitored at the same time, and the value pair of pressure and temperature of the steam in the Steam system never takes on a critical value, and that particularly critical areas the steam system with significant pressure drops can be avoided. In particular, can this also happens by a drop in pressure such that the Vapor solubility of the impurities present in the vapor in certain concentrations would be compensated for by a corresponding rise in temperature becomes.

With steam-air mixtures it should be noted that the partial pressure is now used for the steam pressure of the steam in the mixture is to be considered as the pressure variable.

Another embodiment of the invention is characterized in that the only one critical pressure drop in the steam system to the point where the steam exits the device is placed for steam use. So at most in the easy-to-clean exit region Deposits are made. The flow velocities are also at the exit point the steam high, a self-cleaning effect can occur.

The invention also includes a steam system for performing one of those described above Method.

BRIEF EXPLANATION OF THE FIGURES

Fig. 1

ein schematisches Löslichkeitsdiagramm für SiO₂ in Wasser und Dampf,

Fig. 2

ein schematisches h-s-Diagramm mit Linien konstanter Dampflöslichkeit von SiO₂ und

Fig. 3

ein schematisches h-s-Diagramm nach Figur 2 mit dem Parameterverlauf in einem halboffenen Dampfsystem.

The invention will be explained in more detail below using exemplary embodiments in conjunction with the drawings. Show it:

Fig. 1

a schematic solubility diagram for SiO ₂ in water and steam,

Fig. 2

a schematic hs diagram with lines of constant vapor solubility of SiO ₂ and

Fig. 3

3 shows a schematic hs diagram according to FIG. 2 with the course of parameters in a semi-open steam system.

WAYS OF CARRYING OUT THE INVENTION

The vapor solubility of contaminants depends essentially on the parameters of pressure and temperature. With increasing temperature and increasing pressure their vapor solubility generally increases and vice versa, the pressure influence being dominant. Figure 1 shows an example of all impurities, a diagram for the solubility of SiO ₂ in water or steam as a function of temperature at pressures of 1 bar, 6 bar, 19 bar and 50 bar. It can be seen that SiO ₂ is soluble in steam at a pressure of 6 bar and a temperature of 400 ° C up to a concentration of approx. 1 mg / kg (1000 ppb).

Despite this behavior, which is known per se, it has always been concluded for the prevention of deposits in steam systems that only by ensuring the conditions corresponding to the worst case and thus by the lowest concentration of SiO ₂ or another impurity, deposition thereof can be effectively prevented can be. To avoid SiO ₂ deposits in steam systems, concentrations of less than 0.02 mg / kg (SiO ₂ <20 ppb) are given as guidelines.

Because the provision of such pure steam, especially with open and semi-open ones Steam systems, is expensive, the inventive approach relies on critical in the system Avoid values of pressure and temperature at which deposits of Impurities could come.

Rule in steam systems of gas turbine plants (steam cooling, steam injection, etc.) typically temperatures in the range of 250 to 580 ° C and pressures in the range from 20 to 40 bar.

A gas turbine system is subsequently a system consisting of at least understood a compressor, at least one combustion chamber and at least one gas turbine. Air is drawn in and compressed by the compressor, then as combustion air fed to a combustion chamber, and the hot gas produced there in a work-performing manner Gas turbine relaxes. The at least one gas turbine and the at least one compressor are on a wave.

Due to the variety of the combination of steam systems, the task of Steam system, the components through which steam flows. The like in a gas turbine plant resulting possibilities, it can be in the device for steam use in a Gas turbine plant around the entire plant but also, for example, only around one component of the Act housing or a row of blades.

The problem of preventing deposits is not only interesting for steam systems, where the steam heats up, as exemplified by the steam cooling system of gas turbine systems explained, but also when using steam for heating purposes, in which the steam experiences a drop in temperature. Under the concept of the steam system steam cooling systems are generally understood, but also steam heating systems.

In FIG. 1, various parameter changes with the resulting effects on vapor solubility are again shown using the example of silicon dioxide (SiO ₂ ).

First, arrow I shows an isobaric transition from a state A with p = 6 bar and T = 400 ° C. to a state B with p = 6 bar and T = 300 ° C. It is easy to see that such a pressure reduction can already result in SiO _{2 being} deposited. If the maximum SiO ₂ concentration soluble in steam at point A was 1.0 mg / kg (1000 ppb), this decreased to a value of 0.14 mg / kg (140 ppb) at point B.

Arrow II shows an isothermal transition from state B to state C with p = 1 bar and T = 300 ° C. It can again be seen that such a drop in temperature can also result in SiO _{2 being} deposited. If the maximum SiO ₂ concentration soluble in steam at point B is 0.14 mg / kg (140 ppb), this decreases to a value of 0.11 mg / kg (110 ppb) at point C.

The arrow III shows an isobaric transition from state C to state D with p = 1 bar and T = 500 ° C. It can again be seen that, in contrast to the previous changes in state, such an increase in temperature now leads to an increase in the vapor solubility of SiO ₂ . If the maximum vapor-soluble SiO ₂ concentration at point C is 0.11 mg / kg (110 ppb), this increases to a value of 0.18 mg / kg (180 ppb) at point D. An increase in temperature is therefore suitable to a Counteracting or compensating for the reduction in the steam solubility of contaminants due to pressure drop.

• man die Auslegungsparameter für Druck und/oder Temperatur ausreichend hoch wählt,
• dafür gesorgt wird, dass durch Druck- und/oder Temperaturabfall die Dampflöslichkeit von Verunreinigungen nie erreicht bzw. überschritten wird oder
• indem die sinkende Dampflöslichkeit infolge Druckabfall durch einen Temperaturanstieg teilweise oder vollständig kompensiert wird.

Taking advantage of the solubility behavior of impurities, deposits in steam systems can now be avoided by

• the design parameters for pressure and / or temperature are chosen to be sufficiently high,
• it is ensured that the vapor solubility of contaminants is never reached or exceeded due to a drop in pressure and / or temperature or
• by partially or completely compensating for the decreasing vapor solubility due to a drop in pressure due to an increase in temperature.

• im Falle der Notwendigkeit der Beherrschung grösserer Druck- und/oder Temperaturabfälle die Auslegungsparameter für Druck und/oder Temperatur ausreichend hoch gewählt werden,
• eine kritische Kombination von Druck- und Temperaturabfall vermieden wird,
• ein kritisches Absinken der Dampflöslichkeit infolge grösserer Druckabfälle durch eine entsprechende Erwärmung des Dampfes und damit einen Temperaturanstieg kompensiert wird.

According to the invention, parameter configurations in steam systems that are critical with regard to possible separation of impurities are now avoided by ensuring in terms of process technology and flow technology that the limit for possible separations is never reached or exceeded. This is achieved by the system design

• if it is necessary to control major pressure and / or temperature drops, the design parameters for pressure and / or temperature are chosen to be sufficiently high,
• a critical combination of pressure and temperature drop is avoided,
• a critical decrease in steam solubility due to larger pressure drops is compensated for by a corresponding heating of the steam and thus a rise in temperature.

Gas turbine plants come into connection in many ways, almost without exception in power generation with waste heat boilers. Waste heat boilers have up to three Pressure levels and possibly overheating. So there are many of ways to influence the parameters of a corresponding steam system.

Larger pressure and / or temperature drops in steam systems can be reduced by a corresponding one Design of the flow cross sections, choice of steam mass flows u. like. avoid.

If the steam serves to cool components, as shown in the example of the gas turbine system, the steam is heated up by the absorption of heat. Is constructive now Make sure that before and / or in areas with a significant drop in pressure there is an appropriate one The cooling steam is heated.

FIG. 2 shows an hs diagram with lines of constant SiO ₂ solubility in steam. Again one sees the decreasing vapor solubility as the pressure and temperature decrease. Interestingly, the lines of constant SiO ₂ vapor solubility correspond approximately to the bisector between the lines of constant pressure and the lines of constant temperature. The limit value (GW) for steam turbines is also shown.

In addition to FIG. 2, FIG. 3 shows the state changes of the steam within a steam system, in the present case a semi-open steam cooling system of a gas turbine system, in the form of an hs diagram (x-axis: entropy, y-axis: enthalpy). The cooling steam has a pressure of 30 bar and a temperature of 360 ° C at point E (exit from the device for providing steam). Up to the gas turbine system or the component to be cooled (device for steam use), for example a blade, pressure losses of approximately 8 bar and temperature losses of approximately 5 K occur. The steam therefore has a pressure of approx. 22 bar and a temperature of 355 ° C at point F (entry into the device for steam use). This pressure loss is accompanied by a large decrease in the vapor solubility. When the component to be cooled (device for steam use) flows through, further pressure losses of the order of 4 bar occur. However, the steam heats up by approx. 200 K. The steam thus has a pressure of 18 bar and a temperature of 560 ° C at the outlet of the component to be cooled at point G (outlet from the device for steam use). With these parameters, the steam is now fed to a device for steam removal. As a result of the rise in temperature, there is a significant increase in the steam solubility of SiO ₂ within the device for steam use. To prevent SiO ₂ deposits, it would be sufficient for the process shown to adhere to a limit value for the SiO ₂ concentration of 3000 ppb (3 mg / kg). It can also be seen that the area critical for deposits is the entry area of the steam into the component to be cooled (device for steam use). However, the limit value GW usually used for steam systems and specified for steam turbine systems is only 20 ppb.

The situation is somewhat different for steam-air mixtures. For the vapor pressure is now take into account the partial pressure of the steam, which is dependent on the steam concentration. This means that there are low partial pressures, especially at low steam concentrations of the steam, which in turn leads to very low steam solubility of the respective impurity can lead. This can be remedied by adhering to a minimum vapor concentration bring.

Under the conditions mentioned, it is advantageous to have a significant pressure drop in the Steam system at the point where the steam emerges from the component to be cooled or to provide the device for steam use and the highest possible exit speed to realize the steam. This would increase the build-up of contaminants, for example due to exceptional operating conditions Concentrate easily accessible areas and therefore easy-to-clean areas. By the The self-cleaning effect which develops with increasing steam speed can Deposition of contaminants can be prevented in the best case.

Claims (10)

Method for preventing the deposition of contaminants in steam systems, in which the steam flowing therein, given the steam quality, is subject to temperature and / or pressure changes,
characterized in that
Appropriate design and layout of the steam systems prevents the steam solubility of the impurities present in the steam in certain concentrations from being exceeded as a result of changes in the temperature and / or pressure conditions within the steam system. A method according to claim 1, characterized in that the impurities are silicon dioxide (SiO ₂ ). Method according to one of the above claims, characterized in that the steam system is a steam cooling or a steam injection of a gas turbine system. Method according to one of the above claims, characterized in that additionally by adjusting the temperature and / or pressure of the steam flowing in the steam system it is prevented that the steam solubility of the impurities present in certain concentrations in the steam is exceeded. Method according to one of the above claims, characterized in that the structural design and layout of the steam systems acts in such a way that the value pair of pressure and temperature of the steam in the steam system never assumes a value at which the steam solubility of the impurities present in certain concentrations in the steam is exceeded , and that in particular critical areas with significant pressure drops without a simultaneous equivalent temperature increase of the steam are avoided. A method according to claim 5, characterized in that a drop in pressure such that the steam solubility of the impurities present in certain concentrations would be exceeded is compensated for by a corresponding increase in temperature. Method according to one of the above claims, characterized in that in the case of steam-air mixtures the partial pressure of the steam in the mixture is to be taken into account as the pressure variable. Method according to one of the above claims, characterized in that the only critical pressure drop in the steam system is placed in the place of the exit of the steam from the device for steam use. A method according to claim 8, characterized in that at the exit point of the steam from the device for steam use, the flow rate of the steam is so high that a self-cleaning effect occurs at the exit point. Steam system for carrying out a method according to one of claims 1 to 9.

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