Problems with compressed air purging of process pipelines
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Specifically, air is used for purging the process pipelines by compressing it with a compressor having a capacity of 23,000 NM3/H; the outlet pressure of the compressor is 0.8 MPa, while the inlet pressure is at atmospheric level. The issue is that some people argue that the air becomes saturated or nearly saturated after compression, and that condensate water will form during the purging of the process pipelines, thereby affecting subsequent production. Is this concern valid? Could you provide the specific calculation process to determine whether condensate will form? I can list the parameters required. This post was last edited by hw197358 on 2009-2-8 13:58.]
Take it on yourself first; you can also provide the calculation steps
First, check the air humidity at that time to calculate the water vapor content. Calculate the vapor pressure of water after compression again, and determine the corresponding saturation temperature; if this saturation temperature is higher than the lowest temperature that can be achieved after compression, then condensation water will form.
I’m not quite sure. The buffer tank of the compressor should be able to drain water, right? There shouldn’t be much pressure in the pipes that are being purged. So how can condensate water form in those pipes? Is the pressure in those pipes also 0.8 MPa?
1. Although there is a buffer tank, gases with high flow rates may carry small liquid droplets. 2. In environments with high humidity, calculations must be performed. 3. Some of the pipelines to be purged have very strict requirements regarding water content.
Just calculate it using Aspen or Pro/II and you’ll know
Does it have to be this complicated? Can’t we add a dryer to the pipeline?
If the minimum ambient temperature during pipeline purging is higher than the normal pressure dew point of the compressed air used, there is no need to worry about the formation of condensation water in the compressed air. For reference!
There should be no problem. First, when air is compressed, it passes through a cooler, which causes some of the free water to precipitate. Even if the air is saturated upon leaving the compressor, as it flows through the piping, its temperature rises and its pressure drops, turning it into unsaturated air; in this case, no water will precipitate.
Haha, the pressure has dropped, it’s been throttled, expansion has occurred, the temperature has fallen, water has precipitated, and now it’s unobstructed
Is there a low-point drain in the process design? If not, it’s fine to let in a little moisture.
It shouldn’t happen; the condensate has already separated out in the gas collection pipe, so it’s sufficient to drain it regularly
No problem. Usually, a short receiving pipe is installed at the end of the pipeline, pointing downward, to allow for regular drainage
The chemical industry has high requirements regarding water content; it should be calculated
Our system is purged in winter; the air pressure after passing through the screw compressor is 0.7 MPa, and the pipes through which air flows are prone to freezing once the air supply is stopped. The air becomes saturated after compression, as the buffer tank at the compressor outlet can release a large amount of water. Although the pressure may drop as the air flows through the pipes, firstly there are liquid droplets present, and secondly, the rapid flow of air causes the temperature in the pipes to drop, leading to the condensation of water vapor. Therefore, I believe it’s a combination of pressure reduction and temperature drop, with one of these effects being more dominant.
When purging with compressed air (at a pressure of 1.6 Mpa) at a rate of 35,000 NM3/H, if the compressed air is not cooled and of its moisture is not removed in advance, water droplets will form at the valves after purging the pipes. This is especially true in the winters in the northern regions, where temperatures are low; the compressed air is hot and contains saturated moisture, which will definitely cool down and turn into water when it comes into contact with the cold pipes. To reduce the amount of moisture in the pipes without affecting subsequent production, it is necessary to use heat exchangers and steam-water separators after compression； If the requirements are not met, it is necessary to invest in an additional refrigerated dryer, which can significantly reduce the moisture content in the compressed gas. :lol
No problem; a little water can be removed through the initial cycle of drying.