Heat Exchangers & Linings / Coatings

[kerrg]

Any one with experience of tubeside lined heat exchangers?

If so, what were your experiences?

 

[Montemayor]

kerrg:

What, exactly, do you mean by "lining"? Do you propose to "protect" the channels, nozzles, tubesheets, tubes'interior walls (I wouldn't) by applying a coating to the metal surface?

If so, I presume you are aware that you will definitely alter the conductive heat transfer characteristics of your exchanger. You will have added yet another resistance for the heat transfer to defeat and just made it tougher on your application. I've used explosive-applied rare metal surfaces on taxing heat transfer surfaces like nitric acid reboilers - but have never heard of nor read about anyone coating (or lining) heat transfer surfaces. Titanium and other such metals are ultra expensive; but they don't produce an insulating surface while protecting against corrosion as a liner would. Could you be more specific in your basic data and explanations (at least a little bit more than a condensed sentence)? Perhaps I'm missing something here.


Art Montemayor
Spring, TX

 

[phex]

We have used heat exchangers coated with a protective layer in water service. Don't know if it is still done, most customers by now require duplex steel. The exchangers were running perfectly for 10 years and still do, so I presume this is a viable option if cost of duplex steel is a matter.

hth,
chris

PS: The german name for that covering is "Saekaphen", try to look that up as a first hint, if your application is low-temperature water service.

 

[kerrg]

phex, your spot on, its Sakaphen and the likes of heresite thin film linings which I am trying to get experience on.

I am led to believe that by applying this type of lining the heat transfer although initially reduced is better during the longer life of the exchanger i.e. reduces fouling etc.

 

[phex]

I can only communicate our customers experience on this. They never had any problems with these heat exchangers. I am led to believe that the increased heat transfer resistance due to the coating is negligible as it is applied in a very thin layer. As I said in my last post above, they (the customer in question) never had problems with these hx, when we moved in to revamp the plant, they initially asked to apply the saekaphen also to the new hx we needed. Later they modified this (also because the difference in cost has become minimal) to duplex steel, mainly due to the fact that the new exchangers had untreated water on both sides, shell and tube, which would have made the coating even a little more expensive than the duplex version.

The use of saekaphen was widely done in the nineties, but most customers by now - as I mentioned above - require duplex steels. I can't give you a definitive suggestion on this. If the requirement for coating is only on tube side, you might save a little money. My recommendation would be to ask your preferred manufacturer for their opinion and prices.

hth,
chris

 

[pkpbip]

We have had good experience with these coatings in two different services:

1) in water cooling exchangers we have applied the coating to reduce the fouling with great success on problem coolers (even in spots where the cooling water return temp is high, like 135-140F, where many foulants drop out of solution). Initially we were also worried about heat transfer problems due to another layer, but we have not seen a significant loss of duty and since they foul less they get more heat transfer in the long run. The way it has been explained to me is that as long as conduction heat transfer is not your limiting resistance then the extra layer will not make you lose much duty.

2) another application is in lubes dewaxing plants on scraped surface chillers. The chillers cool a waxy lube oil stream and wax forms on the wall which is scraped by a scraper. Pressure drop builds up on the equipment which reduces run length and requires hot washes. The internals of this exchanger (the scrapers and shafts) are coated which reduces the amount of hot washings required.

 

[rmw]

Plastocor does thin coat low solids epoxy linings, as well as tubesheet and waterbox (channel) linings. Google will find them.

rmw