Water-injected gas compressor and method for controlling the water supply |
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申请号 | EP14171207.5 | 申请日 | 2014-06-04 | 公开(公告)号 | EP2811165A2 | 公开(公告)日 | 2014-12-10 |
申请人 | Gardner Denver Deutschland GmbH; | 发明人 | Klaus, Frank Georg; | ||||
摘要 | The application relates to a method for controlling the water supply of a water-injected gas compressor which has a cooling water circuit into which is injected, as fresh water, demineralized water and non-demineralized water. The method according to the application comprises the following steps: determination of the electrical conductivity of the non- demineralized water; determination of a proportion of the demineralized water that must be added to the non-demineralized water, to provide a resulting mixture with a desired conductivity; addition of the specified proportion of demineralized water to the non-demineralized water and supplying the resulting mixture as the fresh water for the cooling water circuit; supply of the fresh water to the cooling water circuit in a desired amount. Further, the application relates to a Water-injected gas compressor comprising a compression stage, a cooling water circuit, and a water mixing unit. | ||||||
权利要求 | |||||||
说明书全文 | The invention relates to a method for controlling the water supply of a water-injected gas compressor. Furthermore, the invention relates to a water-injected gas compressor adapted to perform such a method. Water injected compressors are used for compressing gaseous media such as air in order to make them available as a gas. Water is used for sealing, lubrication and cooling of the compressor. The injected cooling water is separated from the compressed gas after exiting the compressor. The cooling water heated by the compressor is fed to a cooling device. The cooled cooling water is then filtered and fed back into the compressor. If the cooling water reaches a high conductivity as a result of the heating (above 50°C), then calcification significantly increases, thus causing dirt/debris to occur that impairs functioning (jamming of valves, altering spaces). In such compressors, there may be variation of several parameters of the cooling water due to evaporation of the cooling water and/or absorption of atmospheric humidity into the cooling water. Evaporation of cooling water causes the relative mineralization of the cooling water to increase, thereby increasing sediment that can lead to compressor damage. In the opposite case, if the mineral content of the cooling water decreases due to atmospheric humidity absorption, then this has a negative effect on the buffer capacity of the cooling water to absorb free carbonic acid. Free carbonic acid in the cooling water that is not bound, is very aggressive and promotes corrosion. The pH of the cooling water may be altered by evaporation of cooling water, absorption of atmospheric humidity into the cooling water, or absorption of copper or iron ions, so that the cooling water has a corrosive effect. A task of the present invention is to provide an improved method for controlling the water supply to a water-injected gas compressor. The cooling water supplied to the compressor should always has a quality with respect to the conductivity, and preferably also regarding further parameters as the content of calcium carbonate, and the PH. In this case, the cost and complexity of the sensors to be installed in the cooling circuit should be minimized. This task is fulfilled by the method according to claim 1 and a gas compressor according to claim 9. The method according to the invention controls the water supply of a water-injected compressor based on an understanding that the measurement of the conductivity of the cooling water in the cooling circuit does not provide sufficiently precise information about the amount of dissolved ions present in the cooling water. To obtain more precise information from measuring the cooling water circuit, much more sophisticated measurements would be needed, but these cannot be obtained from a corresponding gas compressor at a reasonable cost. The addition of demineralized (distilled) water, insofar as such addition is governed only by the conductivity values determined in the cooling circuit, can thus lead to an undesired cooling water quality leading to an increased corrosion of the metallic parts of the compressor, thereby drastically reducing the lifetime of such systems. In contrast, the quality of drinking water (non-demineralized water) provided on-site may be easily determined, and it may be assumed that this basic quality is not generally subject to fluctuations. The types of drinking water provided on-site could be well water, river or lake water, tanked in water, or municipal water. Although drinking water is preferred, non-demineralized water not rising to the standards of drinking water may be provided on-site. This water can be well water, river or lake water, tanked in water, or municipal water, such as recycled municipal water used for irrigation. The non-demineralized water available on site, such as drinking water, can be locally available non-demineralized water. The invention recognizes that, based on the quality of the locally available water, such as drinking water, the proportion of demineralized water may be easily determined by measurement or calculation, in order to determine the amount of demineralized water that needs to be added to the drinking water to obtain a mixture of optimal quality water, fresh water, for the compressor, i.e. the conductivity values and the water hardness are so adjusted that sedimentation and corrosion are minimized. It is presumed drinking water would require the least measurement and calculation and non-drinking water would require more measurement and testing, all within the skill of the artisan. A difference of the method according to the invention compared to the prior art is that one does not use the conventional measurement and control of the conductivity taking place in the cooling water circuit, but rather that one adjusts the conductivity of the supplied fresh water to a desired value by changing the proportions of the demineralized and non-demineralized water depending on the conductivity. In the simplest case, the measurement of the conductivity of the cooling water in the cooling water circuit may be completely dispensed with, although this remains possible in modified embodiments. In comparison to the previously known methods, the method according to the invention provides the compressor with fresh water having a much more consistent conductivity and a much more consistent calcium content. The result is that, according to the invention, the water quality of the cooling water in the cooling circuit has a similar conductivity and the same desired content of calcium carbonate. This ensures that the cooling water injected during the compression process always has a consistent, optimized quality in terms of conductivity, calcium carbonate content and pH during the compression process. In contrast to the prior art method, the conductivity of the cooling water present in the cooling water circuit will not affect the composition of the supplied fresh water. Therefore, there is no longer any risk that, for example, an increase in conductivity caused by corrosion processes in the cooling water circuit could be misinterpreted as being due to an increased calcium carbonate content. By the method according to the invention, calcification and corrosion processes inside the compressor may be effectively prevented and/or minimized. According to an advantageous embodiment, the proportions of demineralized and non-demineralized water in the fresh water are determined by means of a control unit. The control unit monitors the conductivity of the demineralized and non-demineralized water. The conductivities may in this way be manually entered as a fixed parameter by the operating personnel. This is easily possible in most cases, since the conductivity of the drinking water normally used (non-demineralized water) and the thus obtained demineralized water (distilled water) are not subject to seasonal fluctuations and are therefore almost constant. The properties of the drinking water used are normally known through local water analysis or can be determined using analysis devices. With additional knowledge of the demineralization plant, the conductivity of the demineralized water that is obtained from the drinking water may be calculated by the control unit. Measurements have shown that the conductivity of water, which has been demineralized, for example by means of a reverse osmosis system, is lower than the conductivity of the drinking water by a factor of about 10. In alternative embodiments, the controller monitors the conductivity values of the demineralized and non-demineralized water obtained by means of conductivity sensor measurement. The non-demineralized and demineralized water is preferably supplied from a water supply source. The water supply source may include a demineralization plant for the production of demineralized water. The water supply source may be, for example, a public water supply or a private water source. In a preferred embodiment, the amount of non-demineralized and demineralized water supplied is metered by means of corresponding valves. It has proven useful in this context, that the opening times of the valves may be determined as a function of the conductivity of the non-demineralized and demineralized water. This type of regulation can be implemented with little effort and cost-effectively. To minimize contamination of the cooling water by bacteria and other contaminants, the cooling water in the cooling water circuit should be regularly drained and completely or partially replaced by fresh water. This is particularly important when the compressor provides compressed air, since the injected cooling water comes into direct contact with the compressed air. In this respect, the conductivity of the cooling water is used as an indicator of the degree of contamination of the cooling water, because conductivity is known to increase due to corrosion processes. The determination of the conductivity of the cooling water is preferably carried out continuously by means of a conductivity sensor. When a given conductivity value is exceeded, the cooling water in the cooling water circuit is completely or partially replaced by fresh water. In alternative embodiments, the cooling water may also be replaced by fresh water at predefined time intervals. Further advantages, details and developments of the invention will become apparent from the following description of a preferred embodiment with reference to the drawings. The compressor system 01 includes a compressor 02 into which the cooling water 03 is injected. The cooling water 03 is used for cooling, lubrication and sealing of the compressor 02. The injected cooling water 03 is separated from the compressed gas 04 after exiting the compressor 02 by means of the separator 05. The compressed gas 04 released from the cooling water 03 flows into a compressed air system. The separated cooling water 03, which has been heated to a temperature of e.g. 65°C in the compressor 02 is passed through an internal heat exchanger 07 and is thereby cooled down to the desired temperature level for re-injection. The cooled cooling water 03 is optionally fed to a filtration unit and returned to the suction side of the compressor 02. Mixing with fresh water 09 follows in order to improve the water quality of the cooling water 03 and/or compensate for any water loss that occurs. The fresh water 09 supplied consists of a mixture of non-demineralized water 10, which is supplied as a rule via a drinking water pipeline, and demineralized water 12, which is preferably obtained via a demineralization plant (not shown) from the non-demineralized water 10. The proportion of the demineralized and non- demineralized water 10, 12 in the fresh water 09 is dependent on the conductivity of the demineralized and non-demineralized water 10, 12. The proportion of the demineralized and non-demineralized water 10, 12 is determined with the help of a control unit 13 on the basis of given conductivity values and by means of conductivity sensors (not shown), for example, by calculation through implemented routines or determined from tables of stored values. The so determined quantities of liquid are metered via two valves 14 based on corresponding opening times of the valves 14. A mixing unit 15, comprising the valves 14, mixes the necessary amount of demineralized and non-demineralized water to adjust the quantity of fresh water which is fed into the compressor 02. The fresh water 09 thus produced and supplied to the compressor 02 has a consistent conductivity, a consistent amount of calcium carbonate and a pH value suitable for the application. As a result, the cooling water 03 in the cooling water circuit also has optimum water quality. In practice it has been shown that a water-injected compressor 02 works well when the conductivity of the cooling water 03 lies between 100 and 200 µS/cm. On the one hand, there is little precipitation of calcium carbonate at conductivity in this range, while, on the other hand, the remaining water hardness acts as a buffer capacity for the absorption of dissolved carbonic acid during the compression, which would otherwise act aggressively. Thus, the pH of the cooling water 03 injected during the compression also lies between 6.5-8 and thus in a relatively neutral to slightly alkaline range. In this way, the corrosion and sedimentation processes induced by the cooling water 03 may be effectively reduced in the cooling water 03. In the cooling water circuit, a conductivity sensor (not shown) may be arranged to determine the conductivity of the cooling water 03 continuously. When a given conductivity value is exceeded, the cooling water 03 in the cooling water circuit is replaced completely or partially by fresh water 09. The conductivity increases, for example as a result of corrosion processes. By this measure, it may be ensured that the contamination of the cooling water 03 is kept low. Alternatively, the cooling water 03 may be partially or completely replaced by fresh water 09 at predefined time intervals. In this case, conductivity measurement in the cooling water circuit may be entirely dispensed with. List of reference numerals
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