Pumps – With condition responsive control of coolant or lubricant
Reexamination Certificate
2000-01-07
2001-09-11
Freay, Charles G. (Department: 3746)
Pumps
With condition responsive control of coolant or lubricant
Reexamination Certificate
active
06287084
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention refers to a compressor system with a water-injection cooled compressor in a cooling water circuit.
Such compressor assemblies are employed to compress gaseous media, especially air, and to provide this as a pressure gas. Water is used for sealing, lubricating and cooling the compressor, which has the advantage over oil not to be detrimental to health or the environment. DE 44 47 097 describes a water-cooled compressor system in which the compressor is formed as a screw-type compressor. The cooling water is injected in the area of the rotors of the compressor and reseparated from the compressed gas after leaving the compressor. The water heated in the compressor is then guided towards a cooling means. Then the cooled cooling water is filtered and re-supplied to the compressor. In this process, various parameters of the cooling water can be changed by evaporation of the cooling water or by absorption of humidity from the air into the cooling water: if the relative salinity of the water increases because of evaporation of cooling water, an increased amount of deposit precipitates, which might cause damages and defects in the narrow sealing gaps and to the sealing rings. Deposit formation is kept low by a polarization means, which does not, however, prevent the salinity from rising. If, on the other hand, the salinity of the cooling water decreases because of humidity absorbed from the air, the buffer ability of the cooling water to absorb free carbon dioxide is reduced. Yet free carbon dioxide in the cooling water which is not buffered (bound) is very aggressive and corrosive. The Ph-value of the cooling water might also be changed by evaporation of cooling water, absorption of humidity from the air into the cooling water or absorption of copper or iron ions, so that the cooling water has a corrosive effect.
From DE 821 993 and US 722 524, compressors are known that use distilled water for cooling. Distilled water is rather expensive and is very delicate with a view to its pH value.
SUMMARY OF THE INVENTION
It is the object of the invention to improve the water quality in an injection-cooled compressor system.
In a compressor system according to the invention, the cooling water circuit is provided with a measuring device to determine the values of conductivity of the cooling water and a water supply source to supply non-desalinated water and desalinated water, i.e. non-deionized and deionized water. A controlling means causes the introduction of desalinated water, when the conductivity exceeds an upper conductivity limit, and the introduction of non-desalinated water into the cooling water circuit, when the conductivity falls below a lower conductivity limit. Thus, the salinity of the cooling water is controlled such that the conductivity of the cooling water always remains within a predetermined range. As the conductivity also is an approximation for the pH-value of the water, the pH-value of the cooling water can be controlled such that it does not shift into the acid or alkaline range but remains within the neutral range by controlling the conductivity of the water.
When the conductivity falls below the lower conductivity limit, non-desalinated water is added to the cooling water, thereby increasing the conductivity of the cooling water so that the value of conductivity of the cooling water again rises above the lower conductivity limit. By controlling the conductivity of the cooling fluid to be above a lower conductivity limit, a strong decline in the pH-value of the water is avoided. Thereby, the pH-value of the water is maintained above a pH-value of 6.5, for example. Thus, the cooling water is not aggressive, so that the corrosion because of the cooling water within the coolant circuit is greatly reduced.
When the upper conductivity limit is exceeded, desalinated water is added to the cooling water. Thereby, the conductivity of the cooling water is reduced. After the conductivity falls below the upper conductivity limit, the introduction of desalinated water is stopped again. By means of the salts dissolved in the cooling water, the cooling water can absorb carbon dioxide, which is absorbed when air is compressed and has a very corrosive effect. The salinity of the cooling water, however, is not arbitrary, as the salts start to deposit when a certain concentration of salts is exceeded, i.e., particles form in the cooling water, which can lead to damages in sealing gaps, bearing seals, sliding bearings etc. Therefore, the salinity of the cooling water has to be limited, which is determined by the upper conductivity limit.
Thus, two effects are achieved by controlling the conductivity of the cooling water within a determined range of conductivity: firstly, a super-acidity of the cooling water is avoided, thereby in turn avoiding corrosion within the cooling water circuit. Secondly, the salinity of the cooling water is maintained below a limit so that no deposition occurs, whereby damages or defects of movable parts within the cooling circuit can be avoided. Thereby compressor systems can be put into practice in which less corrosion-resistant materials can be used in the cooling water circuit and in the compressor. As the cooling water is nearly free of deposits, a compressor can be designed with very narrow sealing gaps, and therefore, for example, with sliding bearings. Thus, the cooling water control means according to the invention provides the preconditions for increasing the effectivity and longevity of a gas compressor system.
Preferably, the water supply source comprises a desalinization device which is supplied with non-desalinated water. Furthermore, a bypass is provided bypassing the desalinization device, and valves are provided connecting either the desalinization device or the bypass to the compressor. The valves are switched such that water desalinated in the desalinization device is supplied to the compressor or the cooling circuit when the conductivity falls below a lower limit. If non-desalinated water is to be supplied to the cooling circuit, the valves are switched such that the non-desalinated water is guided past the desalinization device through the bypass and supplied to the compressor or the cooling water circuit in a non-desalinated state. The non-desalinated water supplied to the desalinization device or the bypass can, for example, be drinking water from the public drinking water net. Preferably, the desalinization device is provided as an ion exchanger or a reversed osmosis device.
The overall control of the conductivity can occur in the form of a flicker control or continuously. Preferably, the conductivity can be controlled in a range from 10 to 20 &mgr;S/cm at 25° C.
In a preferred embodiment, there is provided a return pipe from the cooling water circuit to a water supply source inlet through which water of the cooling water circuit can be supplied to the water supply source. The cooling water coming from the cooling water circuit can be desalinated in the desalinization device of the water supply source when needed. This results in a closed coolant circuit the cooling water thereof is desalinated in a leg parallel to the compressor in the desalinization device and resupplied to the cooling water circuit. Thus, the cooling water is recycled. Only little strain is put on the desalinization device by not desalinating water supplied from the outside, e.g. drinking water, as the water of the cooling water circuit generally only has to be desalinated to a relatively small extent.
In a preferred embodiment of the invention, the water of the water supply source is led into a gas take-in duct of the compressor. Thus, water coming from the water supply source is not led into the cooling water circuit, which approximately provides the pressure of the gas compressed by the compressor, but is led into the gas take-in duct of the compressor where there is an approximately atmospheric pressure. In this manner, an introduction of the water of the water supply source into the cooling water circuit can be achi
Diller Ramik & Wight
Freay Charles G.
KT Kirsten Technologie-Entwicklung GmbH
Rodriguez W
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