Fluid handling – Processes – With control of flow by a condition or characteristic of a...
Reexamination Certificate
2002-06-14
2003-07-08
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Processes
With control of flow by a condition or characteristic of a...
C137S178000, C137S187000, C415S169200
Reexamination Certificate
active
06588443
ABSTRACT:
The subject matter of the present invention is a method of draining condensate from a reservoir of a compressed air or compressed gas system that can be subjected to a pressure above atmospheric, to a subatmospheric pressure or to atmospheric pressure depending on the operating condition of the compressed air or compressed gas system and a device for carrying out this method.
The method of the invention and the device of the invention are more particularly provided for the purpose of draining condensate from a reservoir of a multistage air or gas compressor, which will be termed gas compressor hereinafter. The method of the invention and the device of the invention will be explained hereinafter in the light of their application on multistage gas compressors.
Depending on the operating conditions compressed gas compressors always take in a certain quantity of water vapor that partially condenses after the compression process. This happens to a greater extent when an aftercooler is arranged downstream of a gas compressor, the higher temperatures in the compressed gas resulting from the compression process, which typically may amount to more than 100° C., being reduced to technically sensible values in said aftercooler.
In a multistage gas compressor, compression is carried out step-by-step in compressor stages connected in series. Each compressor stage is hereby typically provided with a compressor unit of its own, an aftercooler and a trap arranged downstream thereof. The condensate produced in aftercooling is separated from the compressed gas stream and is led out of the gas compressor. The pressure of the compressed gas or gravitation generally cause thereby the condensate to be discharged via a drain pipe into a reservoir of any configuration. Said reservoir is thereby either a component part of the gas system or a component part of a condensate drain device by means of which the collected condensate is eventually discharged from the gas compressor.
On account of the particular operating conditions that may occur in multistage gas compressors, the use of previously known condensate drain devices with a pilot operated diaphragm valve for draining collected condensate from a reservoir as they have been described in EP 391 250 for example is possible to a limited extent only. The reason therefore is that, on account of the operating conditions of a gas compressor, both excess pressure and negative pressure as well as atmospheric pressure can prevail.
The use of condensate drain devices with float actuated exhaust valves is not advantageous because they are prone to dirt and grime, dirt and grime being inevitable in compressed gas plants.
For reasons of economy, it does not make any sense to operate a multistage gas compressor at full output power against atmospheric pressure when no compressed gas is demanded by a consumer. Generally, it does not make sense either to switch off the multistage compressor since each process of switching off and of starting implies increased wear of the motor and the compressor. Therefore, in case the demand for compressed gas is reduced, the compressor is often set to idle in such a manner that a sealing device locks the intake side of the first compressor except for a small opening cross-section while an exhaust device located on the pressure side of the last compressor stage is concurrently opened. The exhaust device can be connected to the intake side of the first compressor. A locking device provided on the pressure side of the last compressor prevents the already produced compressed gas from flowing back into the compressor. This arrangement permits the multistage compressor to continue to run without load at low pressure at idle, which considerably saves energy. Increased wear, as it is caused by frequent switching off and on can thus be avoided.
If the compressor is set to the idle condition described, the compressor continues to run without load at low pressure. But a small quantity of compressed gas is delivered, a certain pressure ratio between the various compressor stages being maintained as a result thereof. If the multistage compressor is in this state of control for a longer period of time, pressures below the pressure in the intake gas, more specifically below atmospheric pressure, may develop in the first compressor stages.
If no compressed gas is needed for an extended period of time, the whole multistage compressor can be switched off in order to save the energy still needed for operating at idle. Once all of the compressor units have been stopped, the compressor unit is generally vented with atmospheric pressure via an exhaust device on the pressure side of the last compressor stage. In this case, atmospheric pressure prevails in all the parts of the multistage compressor.
As a result thereof, different operating conditions can occur in a reservoir in which condensate produced in a trap of a compressor unit is collected. At normal operation of the multistage compressor, all of the reservoirs that are arranged on the pressure side of a respective one of the compressors are subjected to pressures above the pressure of the intake gas, more specifically above atmospheric. In this case, collected condensate could be discharged from all the reservoirs by means of condensate drain devices built according to previously known design principles. Drainage thereby is performed either driven by the excess pressure relative to atmospheric pressure prevailing in the compressor stage and/or by gravitation.
The same applies when the multistage compressor is completely turned off. In this case, all of the reservoirs are subjected to atmospheric pressure so that the condensate can be drained by gravitation from all the reservoirs without any problem. In this case too, prior art condensate drain devices can readily be utilized inasmuch as a certain excess pressure is not needed for opening.
As already described herein above though, in the described idle condition when less compressed gas is demanded, some compressor stages located in proximity to the gas intake (i.e., low compressor stages) may be subjected to pressures below the intake pressure, more specifically below atmospheric. In this case, the condensate produced in a trap of such compressor stages is drained into a reservoir, the collected condensate with the gas space located there above being however subjected to a pressure below the initial pressure, more specifically below atmospheric.
In using a condensate drain device as disclosed in EP 391 250 for draining the condensate the problem is that, due to their design, these condensate drain devices open their exhaust valve when a negative pressure develops in the reservoir and the pressure difference between reservoir and exhaust side of the condensate drain device, which is subjected i.a. to atmospheric pressure, reaches a certain value. The negative pressure in the reservoir and in the compressor stage causes ambient air to be drawn into the amplifier stage and condensate may be simultaneously entrained. Various compressor units may thus be vented on their exhaust side, which is not desired, and concurrently slurried with condensate, which may damage the compressor units. This is the reason why the condensate must in any case be prevented from being discharged from a reservoir which is subjected to a pressure below atmospheric.
The same applies when trying to drain the collected condensate from the reservoir subjected to negative pressure under the influence of gravity by means of a conventional condensate drain device.
In principle, it is possible to discharge collected condensate from the reservoirs of a multistage compressor by means of conventional condensate drain devices, by those described in EP 391 250 for example. Additional safety measures must thereby be taken in order to prevent drainage against atmospheric pressure when a reservoir is subjected to negative pressure. For this purpose, a check valve is often arranged behind the condensate drain device, said check valve reliably preventing the condensate drain device from un
Koch Berthold
Schlensker Herbert
Akerman & Senterfitt
Beko Technologies GmbH
Michalsky Gerald A.
LandOfFree
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