Feed Effluent Exchanger Recommendations

[sshep]

I would greatly appreciate some advice on alternatives to replace an undersized shell and tube feed-effluent exchange for a UOP Pacol Process. This process is used to make olefins from normal paraffins. It is similar to a vapor phase hydrotreating process in that feed paraffins C10 to C14 are mixed with H2 and fully vaporized in the feed effluent exchanger, then heated to approx 900F, passed through the reactor and condensed in the feed-effluent exchanger. The pressure is less than 60psig. Because essentually the same material is being vaporized and condensed on the respective sides of this exchanger, a temperature pinch occures inside the exchanger. One alternative we are considering is a Packinox exchanger made by alfalaval (see

http://www.alfalaval.com

and find Packinox under the product pulldown). This equiment is a platefin exchanger inside a pressure vessel. It addresses getting past the pinch by having alot of surface area, low pressure drop, and designed to minimize liquid-vapor slip.

I think this type equipment would work great but the cost is very high. It is made in Europe and the exchange rate alone has pushed up the cost significantly since I first considered it. I would be most grateful for alternative recommendations of similar function equipment so as to get some competitive quotes. Any help is appreciated. -sshep

 

[StoneCold]

sshep
I have seen Packinox exchangers on other UOP processes but I don't know that I have ever seen on on a Pacol design. Did you ask UOP? I assume that the "undersized exchanger" is actually just the limiting piece of equipment that is keeping you from running more than the design flowrate, because I am pretty sure your product quality and feed rate were guaranteed in the design. The only thing I have heard bad about a Packinox is the obvious. If it plugs, and they have, you are all done. But I would ask UOP they would probably know best.

 

[sshep]

Hey StoneCold,
As you obviously know something about this I will give a bit more info. Pacol is the UOP paraffin to olefin conversion process. Globally my company owns several Pacol units. Of the two in the USA, the newest (year 2001) includes a Packinox, the other (year 1980) does not. Packinox is also used at some of our European Pacols, but I am not sure the history of those. Packinox is basically the latest exchanger technology which UOP has incorporated into the Pacol design. At this point most of the problems with Packinox in these applications have been ironed out. Filters and spray bar backflush ancillaries protect the exchanger. The cleaning (if/when required) is via an air decoke procedure, and my own experience with the vaporizing side laydown is a not very dense carbon layer for which this procedure seems likely to work.

Our 1980 plant had an original design capacity of 150MMlb/yr, but now runs at over 250MMlb/yr. Our fired charge heater operates at its permited maximum firing rate. Although I have based Packinox retrofit economics soley on the basis of energy recovery, it is obvious that such a change will be redirected to additional capacity the instant it comes on line. Basically you have concluded correctly.

My problem at this point is how to improve on the capital cost of a retrofit in the face of an apparently single source equipment supplier. Even with a 1.25Cr-0.5Mo material of construction, this is not cheap piece of heat transfer equipment. If there are other suppliers of similar or competitive designs then I would like to learn about those alternatives. Any help is appreciated. - sshep

 

[StoneCold]

sshep
You are correct that the Packinox exchangers are pricey. Sounds like you know that you can retrofit your older unit based on some newer units you already have. I don't think there are other suppliers of a Packinox type exchanger. I was told that they are made by explosion forming in a mold. Each plate for the exchanger being made in one shot. You might look for other plate and frame exchanger companies that due large explosion formed plates, but I am guessing they are very few and the cost savings might not outweigh the risk. It appears that Packinox has added several cleaning mechanisms into the exchanger to overcome some of the cleaning problems experienced by earlier units.
Good Luck
StoneCold

 

[ApC2Kp]

sshep,
The description of "platefin exchanger inside a pressure vessel" got my attention. The internal installation could offset the pressure design problems of a plate exchanger. There might be some factors for evaluating a MONPLEX unit. Most are large gas-to-gas heat exchangers on SO2 converters in sulphuric acid plants. Some previous applications had been power plant recuperators by North American Technologies (originators). See webpage,

http://www.enviro-chem.com/plant-tech/3rdtier/monplxtop.html

Contact: John Burk