Problem with Propane Condensers!!

[nong]

We have problem in summer with propane condensers (Air Colled H/X), outlet temp is over than design little bit( 115==> 125F) because inlet air temp is higher (90==>105F). What 'd we fix it? I heard there are some chemical that can reduce temp of propane or increase fan speed will help ?

Thank you

 

[Rich2001]

I worked on a simillar project. This is some of what we implemented:

1. Cleaned the Air-cooled Condenser with the hose from the fire system - weekly.

2. Adjusted the pitch on the fan blades to increrase air flow.

3. Constructed a shade to keep sunlight

Get a set of baseline field data:
- Ambient Air temperature
- Barometric pressure
- %RH
-Time of date
- Get a grid system up to the condensor and monitor the the air temperature as it passes the HX.
- Temperature,Presuure and flowrates of the propane.

 

[TD2K]

There's no chemical to change essentially the condensing temperature of the propane. Now, if you can allow some heavier material in the propane like butane, that will decrease the condensing temperature and make the cooler perform better from a heat transfer point of view but may not be acceptable from a product quality standpoint.

With actual inlet air temperatures of 105F versus a design of 90F, you've sort of hit the problem on the head. As Rich suggested, keep the tubes clean and make sure the fan pitch are at maximum to increase air flow as much as possible is going to help. You could also look at different fans or increasing the existing fans' speed, that would increase the air flow through the bundle (motor upgrade might be necessary in this case). However, with a 15F mismatch on inlet air temperatures, I doubt it will fix the problem.

Check for any sign of air recirculation, that will hurt you, especially in this case.

If you have low relative humidity, you could look at an evaporative water cooler to humidify and cool the inlet air. You can also just run water over the top of the tube bundles to increase the amount of cooling (fire monitors work) but fouling is a potential problem depending on the water quality.

Putting another set of coolers in might be something you want to consider depending what the effect of the high inlet air temperatures are on your process/operation and how long these temperatures last for. High temperatures 5 days a year is a lot different when it comes to justifying new equipment or changes versus 2 months.

 

[KernOily]

As TD2K said, watch out about spraying your tube bundles with water. An operator in this area did it, and it worked GREAT - for about two weeks. Then they noted that in between sprayings that the fin-fan was performing even worse than it did before the fire hose trick. So they went up there to look and - the tubes were totally scaled up from the nasty water quality.

One trick I've heard of on forced-draft coolers, although I've not seen this but I'm dying to try it, is to build a shallow dam to contain a few inches of water right under the unit. So where you normally have a concrete pad or ag-base under the unit, for dust control, you have a shallow pond. The air drawn across the pond will evaporate some of the water, thus cooling it a few degrees and helping the cooler performance. I learned this from an old piping designer who had worked in the middle east for a long time. TD2K - you ever heard of this? Wonder how effective it is? Thanks!
Pete
pjchandl@prou.com

 

[TD2K]

Pete, I heard of it over in Saudi but I think the one I heard about was on a shut-down plant. I also seem to remember it did not work that well from 2nd hand feedback I did get though getting any hard data on things over there was about impossible unless you could get into the plant and get it yourself.

I did check with one contact of mine who worked in the Abqaiq plants where I thought it was used, he doesn't remember it but that's a big plant and he didn't work in all of it. Sorry I couldn't be of more help.

You definitely would not want to spray ground water on air coolers over there, most of the ground water was pretty dubious quality, lots of TDS.

 

[nong]

Yes TD2K. We used to sprayed water for others coolers. Gas leak from some tubes casing 1-2 weeks shutdown.
I'm considering to change belt/pulley (speed reducer) from 6 to 3 ratio to gain more air flow. Do u think this 'll work?
Another problem is we lose propane from our system a lot!!! than expected, but I don't know how and where they'r gone. Pls suggest.

 

[TD2K]

A change from 6:3 ratio using the fan laws is going to double your fan speed which will double the air flow, increase the head by 4x and increase the power demand by 8x. Of course, the actual increase will depend on the system resistance curve imposed by the cooler tube bundle, have you checked your motors that they can handle this additional load?

Also, the tip speed is going to double, are the fans blades designed for this speed? Turn a fan too fast and blades can fail which is not something you want to happen.

As far as propane losses, it's going somewhere obviously. I'd check first any drains/vents/PSVs to flare. You can get ultrasonic meters designed to 'hear' the high frequency sound these leaks make and you simply put the probe up against the valve and listen (a screwdriver and your ear is a lower tech version). Alternatively, if the leaks are with liquid propane, the leaks are easy to spot due to frosting on the outside of the line on the low pressure side. Depending how your flare system is purged, you might have some success taking samples of the flare gas at each leg and seeing if any show high levels of propane. After that, you'll need to check for leaks either to atmophere to possibly to the process if the propane pressure is higher than the process pressure. It's a slow process, BTDT.