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Plate And Frame Heat Exchanger
Started by Guest_Guest_Maita Garcia_*, May 07 2003 07:07 PM
11 replies to this topic
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#1
Guest_Guest_Maita Garcia_*
Posted 07 May 2003 - 07:07 PM
Hey everyone,
I have another question about plate and frame heat exchangers. As previously discussed, we had problems about leaks on the exchangers after they were put back together.
The solution of our maintenance guys is to put a circulating caustic solution in the exchanger to clean out stuck polymer (polyethylene chips) and additives (primarily amides). Do you think this will work? Also, do you think it may affect the integrity of the rubber gaskets for the exchanger?
Thanks!
I have another question about plate and frame heat exchangers. As previously discussed, we had problems about leaks on the exchangers after they were put back together.
The solution of our maintenance guys is to put a circulating caustic solution in the exchanger to clean out stuck polymer (polyethylene chips) and additives (primarily amides). Do you think this will work? Also, do you think it may affect the integrity of the rubber gaskets for the exchanger?
Thanks!
#2
Posted 07 May 2003 - 11:23 PM
No...this probably won't work. If the gaskets are EPDM, the NaOH will most likely not harm them (so long as you're operating at relatively low concentrations and temperatures). If you have polymer chips in the stream, caustic is not going to help this. You need to get them out of the stream prior to entry into the heat exchanger. To do this, my first choice would be a duplex basket strainer. If this is cost prohibitive for you, contact the manufacturer of the unit and ask for a port strainer to capture the chips.
#3
Guest_Guest_Maita Garcia_*
Posted 08 May 2003 - 06:16 PM
Thanks for the reply. Actually, the upstream bucket strainers have not helped in capturing the polyethylene chips. Any other ideas?
#4
Guest_Guest_Art Montemayor_*
Posted 09 May 2003 - 09:26 AM
Maita:
Using Caustic solution makes no common sense in your application. Your maintenance guys are either too lazy to do their job correctly or have no working knowledge of what they are confronted with.
As Chris Haslago has said, Caustic will damage the rubber gaskets. There is no logic that caustic will dislodge (or breakdown) polyethylene better than a more benign fluid like water. So, why use a corrosive fluid like caustic? It will attack rubber.
Now for the more practical question: Why resort to using chemical treatment on a PHE type heat exchanger that is readily designed for dis-assembly when cleaning? That is one of the strongest features of a PHE - the ability to totally disassemble the unit and provide a thorough, manual cleaning. This is what should be taking place, complete with a 100% gasket replacement. If your company is too cheap and considers the gaskets too expensive to replace, then you applied the wrong type of exchanger for the job. The PHE is probably the most economical type on a first-cost, capital comparison. One of the trade-offs it has, however, is that the gaskets have to be replaced when the unit is dissassembled. That is why this type of exchanger is primarily used in clean fluids applications.
If you don't want to replace gaskets, the only other idea is: replace the PHE - which is even more expensive at this stage in the game.
Sorry that there is no easy answer if the application was not well thought out at the outset.
Art Montemayor
Using Caustic solution makes no common sense in your application. Your maintenance guys are either too lazy to do their job correctly or have no working knowledge of what they are confronted with.
As Chris Haslago has said, Caustic will damage the rubber gaskets. There is no logic that caustic will dislodge (or breakdown) polyethylene better than a more benign fluid like water. So, why use a corrosive fluid like caustic? It will attack rubber.
Now for the more practical question: Why resort to using chemical treatment on a PHE type heat exchanger that is readily designed for dis-assembly when cleaning? That is one of the strongest features of a PHE - the ability to totally disassemble the unit and provide a thorough, manual cleaning. This is what should be taking place, complete with a 100% gasket replacement. If your company is too cheap and considers the gaskets too expensive to replace, then you applied the wrong type of exchanger for the job. The PHE is probably the most economical type on a first-cost, capital comparison. One of the trade-offs it has, however, is that the gaskets have to be replaced when the unit is dissassembled. That is why this type of exchanger is primarily used in clean fluids applications.
If you don't want to replace gaskets, the only other idea is: replace the PHE - which is even more expensive at this stage in the game.
Sorry that there is no easy answer if the application was not well thought out at the outset.
Art Montemayor
#5
Posted 09 May 2003 - 06:54 PM
Sounds like you may be dealing with plastic "fines" rather than "chips". Art did a good job is covering the scaling/fouling issue that you're having. As I see it, you should probably examine the free channel spacing in this unit. It's probably 2.5 mm to 4.0 mm. If it's 2.5 mm, I'd start by examining the possibility of replacing these plates with ones that have a deeper pressing depth (4.0 mm). Be aware that this change will affect your thermal performance and pressure drop through the unit. You'll need to work with the supplier of the unit if you chose to explore this option.
#6
Guest_Guest_Maita Garcia_*
Posted 12 May 2003 - 02:20 AM
Dear Chris and Art,
Thank you for your insights on this matter. Hopefully, we can sway the guys from applying the caustic cleaning solution. It's like making a bad situation worse.
Just another question for all you guys out there with PHE experience. When you clean the PHE, you obviously have to loosen the bolts and pull the plates away from each other. The question is : do you actually take the plates off when you clean them OR do you keep them hanging on the bolts and wash between the plates with a brush or high-pressure washer (steam or water)?
I think some wrong cleaning practices resulted in premature plate failure (the exchanger is only five years old and has only been used 20% of the time).
Thank you for your insights on this matter. Hopefully, we can sway the guys from applying the caustic cleaning solution. It's like making a bad situation worse.
Just another question for all you guys out there with PHE experience. When you clean the PHE, you obviously have to loosen the bolts and pull the plates away from each other. The question is : do you actually take the plates off when you clean them OR do you keep them hanging on the bolts and wash between the plates with a brush or high-pressure washer (steam or water)?
I think some wrong cleaning practices resulted in premature plate failure (the exchanger is only five years old and has only been used 20% of the time).
#7
Guest_Guest_Art Montemayor_*
Posted 12 May 2003 - 12:49 PM
Maita:
I believe you have reason to be concerned. When maintenance thinks they have to use a caustic solution to clean equipment they also have cause for concern because of the safety procedures they must pay attention to due to the hazards involved should the caustic leak, spray or douse someone.
I have had considerable experience dealing with caustic cleaning of equipment during plant operations and maintenance while Chris also has the experience of OEM design and instructions on maintenance of PHE type exchangers. Perhaps between us both we can come up with some constructive comments to alleviate what must be an understandable problem for you. I don’t know the make and model of your PHE and I’ll let Chris comment on recommendations for maintenance and cleaning methods as an OEM sees it.
I identify with this problem because I labored for many years, organizing my plant operations and maintenance personnel in order to avoid what is always a typical situation here in the USA and overseas. Project engineers often neglect to give importance to the critical documents and manuals that are shipped with special-designed equipment such as PHEs, process filters, compressors, etc. They fail to include instructions and communications for the OEM and their own warehouse and maintenance people regarding the custody of the equipment and the documents when they arrive at plant site. I have seen this repeated many times because of communication failure or simple ignorance. What happens is that the OEM manuals over operating, maintenance and spare parts are often removed from the crates by ordinary plant labor while the project engineer who ordered the equipment is either unavailable or having coffee. More often than not, the documentation is thrashed, wasted, or simply discarded in a dumpster together with the slats, packing material, and other waste.
Subsequently, when the equipment is already installed, maintenance is called to inspect or to repair the new equipment, there are no maintenance instructions and the maintenance guys are left to inquire, assume, or figure out as best they can over what they have to do to complete their assignment. Many maintenance people are good, experienced technicians and know a lot about disassembling machines without relying on detailed instructions. However, in the case of a very specific and different kind of animal, they often are forced to make decisions based on generalizations of their experience – which may not apply.
This is why project engineers working for me often didn’t take kindly to my demands of their participation in preliminary inspection and participation of planning the disassembly and assembly of critical equipment. They simply felt they ought to let maintenance “do its thing” and arrive on the scene after all the hard planning and work was completed. I keep insisting that maintenance departments can only do as good a job as the engineering department does in keeping the maintenance department updated with the correct, state-of-the-art tools, training, and accurate information.
My point here is not to preach, but to emphasize (again, and again) that maintenance department personnel never want to work with hazardous chemicals. They are too smart and clever to accept such a situation without a good, technical reason and necessity. I am sure Chris will concur that it is unnecessary to apply caustic solution to a PHE to remove solid, inert particles. However, proper and detailed instructions should be passed on to maintenance for them to do a proper job. I have also had similar experiences with PHE units where the gaskets kept failing in warm water service. It turned out that maintenance had never received the gasket replacement instructions and was trying to do a good job the way they envisioned the gaskets should work. Of course, their idea was erroneous, since they had no prior PHE experience. Even working with good intentions, what seems to be a very simple operation often isn’t.
My experience is that once you have a trained and instructed maintenance on the PHE, you will not have any future leakage or other problems with the units. PHEs, when installed and maintained according to design, will operate literally years without problems. I wouldn’t recommend it, but I’ve run PHEs for over 3 years without inspection or maintenance. I’ll turn this over now to Chris, who I hope will offer some expert advice on how to maintain your unit.
I believe you have reason to be concerned. When maintenance thinks they have to use a caustic solution to clean equipment they also have cause for concern because of the safety procedures they must pay attention to due to the hazards involved should the caustic leak, spray or douse someone.
I have had considerable experience dealing with caustic cleaning of equipment during plant operations and maintenance while Chris also has the experience of OEM design and instructions on maintenance of PHE type exchangers. Perhaps between us both we can come up with some constructive comments to alleviate what must be an understandable problem for you. I don’t know the make and model of your PHE and I’ll let Chris comment on recommendations for maintenance and cleaning methods as an OEM sees it.
I identify with this problem because I labored for many years, organizing my plant operations and maintenance personnel in order to avoid what is always a typical situation here in the USA and overseas. Project engineers often neglect to give importance to the critical documents and manuals that are shipped with special-designed equipment such as PHEs, process filters, compressors, etc. They fail to include instructions and communications for the OEM and their own warehouse and maintenance people regarding the custody of the equipment and the documents when they arrive at plant site. I have seen this repeated many times because of communication failure or simple ignorance. What happens is that the OEM manuals over operating, maintenance and spare parts are often removed from the crates by ordinary plant labor while the project engineer who ordered the equipment is either unavailable or having coffee. More often than not, the documentation is thrashed, wasted, or simply discarded in a dumpster together with the slats, packing material, and other waste.
Subsequently, when the equipment is already installed, maintenance is called to inspect or to repair the new equipment, there are no maintenance instructions and the maintenance guys are left to inquire, assume, or figure out as best they can over what they have to do to complete their assignment. Many maintenance people are good, experienced technicians and know a lot about disassembling machines without relying on detailed instructions. However, in the case of a very specific and different kind of animal, they often are forced to make decisions based on generalizations of their experience – which may not apply.
This is why project engineers working for me often didn’t take kindly to my demands of their participation in preliminary inspection and participation of planning the disassembly and assembly of critical equipment. They simply felt they ought to let maintenance “do its thing” and arrive on the scene after all the hard planning and work was completed. I keep insisting that maintenance departments can only do as good a job as the engineering department does in keeping the maintenance department updated with the correct, state-of-the-art tools, training, and accurate information.
My point here is not to preach, but to emphasize (again, and again) that maintenance department personnel never want to work with hazardous chemicals. They are too smart and clever to accept such a situation without a good, technical reason and necessity. I am sure Chris will concur that it is unnecessary to apply caustic solution to a PHE to remove solid, inert particles. However, proper and detailed instructions should be passed on to maintenance for them to do a proper job. I have also had similar experiences with PHE units where the gaskets kept failing in warm water service. It turned out that maintenance had never received the gasket replacement instructions and was trying to do a good job the way they envisioned the gaskets should work. Of course, their idea was erroneous, since they had no prior PHE experience. Even working with good intentions, what seems to be a very simple operation often isn’t.
My experience is that once you have a trained and instructed maintenance on the PHE, you will not have any future leakage or other problems with the units. PHEs, when installed and maintained according to design, will operate literally years without problems. I wouldn’t recommend it, but I’ve run PHEs for over 3 years without inspection or maintenance. I’ll turn this over now to Chris, who I hope will offer some expert advice on how to maintain your unit.
#8
Guest_Guest_jom_*
Posted 13 May 2003 - 06:17 AM
Why do so many engineers have queries about plate heat exchanger operations?
These machines are always purpose designed by the supplier for the job.
If you have a problem - do the obvious. Refer to the supplier. They will have the best advice possible. It's so easy.
John.
These machines are always purpose designed by the supplier for the job.
If you have a problem - do the obvious. Refer to the supplier. They will have the best advice possible. It's so easy.
John.
#9
Posted 13 May 2003 - 03:31 PM
Ah....just back from a nice vacation in Orlando, FL.....
Now, Art (as usual) gave you some extremely valuable advice. Addressing the cleaning problem:
If this heat exchanger is going to have to be mechanically cleaning on a regular basis, do two things:
If the gaskets are not glued on, purchase a new plate pack with glued gaskets. Glued gaskets will stand up much better to the 1000 psi power washing (with water) that I'll recommend for cleaning.
Monitor the condition of the plate pack carefully. When the gaskets need to be replaced, you'll have to have the manufacturer do this (the disadvantage of glued gaskets). Schedule this for a shutdown or around your production schedule since you're only using the unit 20% of the time.
PHE's are great heat exchangers, so long as they're used in the right services and they're maintained properly.
Now, Art (as usual) gave you some extremely valuable advice. Addressing the cleaning problem:
If this heat exchanger is going to have to be mechanically cleaning on a regular basis, do two things:
If the gaskets are not glued on, purchase a new plate pack with glued gaskets. Glued gaskets will stand up much better to the 1000 psi power washing (with water) that I'll recommend for cleaning.
Monitor the condition of the plate pack carefully. When the gaskets need to be replaced, you'll have to have the manufacturer do this (the disadvantage of glued gaskets). Schedule this for a shutdown or around your production schedule since you're only using the unit 20% of the time.
PHE's are great heat exchangers, so long as they're used in the right services and they're maintained properly.
#10
Guest_Guest_Maita Garcia_*
Posted 14 May 2003 - 04:12 AM
Dear Art and Chris,
Thank you for your input on this subject. Rest assured that I'll relay this to our Maintenance guys so that we can be guided on this. Art, you're absolutely right about documentation being thrown out like yesterday's trash -- seen it happen often enough here. At least though, our process engineers here are intimately involved in a lot of the maintenance activities (hence my questions). =)
Dear John,
We did consult the supplier for this -- unfortunately, they recommended that we purchase a new heat exchanger (surprise, surprise). Then again, this is after all, a business so I guess I can't blame them. But thanks for the reminder.
This website is an EXCELLENT idea. Keep up the good work guys!
Maita
Thank you for your input on this subject. Rest assured that I'll relay this to our Maintenance guys so that we can be guided on this. Art, you're absolutely right about documentation being thrown out like yesterday's trash -- seen it happen often enough here. At least though, our process engineers here are intimately involved in a lot of the maintenance activities (hence my questions). =)
Dear John,
We did consult the supplier for this -- unfortunately, they recommended that we purchase a new heat exchanger (surprise, surprise). Then again, this is after all, a business so I guess I can't blame them. But thanks for the reminder.
This website is an EXCELLENT idea. Keep up the good work guys!
Maita
#11
Guest_Guest_jom_*
Posted 22 May 2003 - 07:18 AM
Maita,
Perhaps you've solved your problems by now, but here's a few more thoughts.
My first job as an engineer was designing PHEs. I left that work long, long ago, but I don't suppose the machines have changed much.
I guess you've already figure out that the proper solution is to keep the solids from reaching the exchanger. If the strainers are not effective, do you need finer sieves? At the moment your exchanger is acting as the filter.
I think it is scandalous that the supplier cannot give you advice, other than replace the unit. That only makes sense if the original design has no hope of meeting your current duty. Very shortsighted, as it seems you would not buy another PHE.
As to caustic cleaning - caustic soda is the universal detergent used to descale PHEs in the dairy, brewery and other food industries. The dairy has more PHEs than any other industry. Any milk pasteuriser has to be cleaned every 6 or 7 hours and this is done by circulating NaOH. The rubber gaskets don't suffer, if they are the right formulation.
But caustic is a dangerous material. Food plants are properly equipped to use it routinely. If you do it on a once-off basis, are you ready to manage the hazards? If you mix it up from solid flakes, watch out for boiling. How will you dispose of it?
From memory, users had no difficulty regasketting, even if glued. You have to burn and scrape off the old gaskets with a low temp flame.
When you disassmeble you will soon see if you need to remove the plates from the frame to clean them. If you can just hose them down to remove the fines, then leave them on the frame. If you need to scrub them, they'll have to come off.
Removing them from the frame is trivial, but they must go back in the correct order. There should be a number stamped on each plate to help. You should also have a plate arrangement drawing.
Cheers,
John.
Perhaps you've solved your problems by now, but here's a few more thoughts.
My first job as an engineer was designing PHEs. I left that work long, long ago, but I don't suppose the machines have changed much.
I guess you've already figure out that the proper solution is to keep the solids from reaching the exchanger. If the strainers are not effective, do you need finer sieves? At the moment your exchanger is acting as the filter.
I think it is scandalous that the supplier cannot give you advice, other than replace the unit. That only makes sense if the original design has no hope of meeting your current duty. Very shortsighted, as it seems you would not buy another PHE.
As to caustic cleaning - caustic soda is the universal detergent used to descale PHEs in the dairy, brewery and other food industries. The dairy has more PHEs than any other industry. Any milk pasteuriser has to be cleaned every 6 or 7 hours and this is done by circulating NaOH. The rubber gaskets don't suffer, if they are the right formulation.
But caustic is a dangerous material. Food plants are properly equipped to use it routinely. If you do it on a once-off basis, are you ready to manage the hazards? If you mix it up from solid flakes, watch out for boiling. How will you dispose of it?
From memory, users had no difficulty regasketting, even if glued. You have to burn and scrape off the old gaskets with a low temp flame.
When you disassmeble you will soon see if you need to remove the plates from the frame to clean them. If you can just hose them down to remove the fines, then leave them on the frame. If you need to scrub them, they'll have to come off.
Removing them from the frame is trivial, but they must go back in the correct order. There should be a number stamped on each plate to help. You should also have a plate arrangement drawing.
Cheers,
John.
#12
Posted 02 July 2003 - 10:07 AM
Hi everyone,
I would like to add something here too as a lot of people have joined in. The box up job after the replacement of the gaskets is very important and mechanical staff who dont have previous experience in doing so are probably going to damage these new ones too. The proper and even tightening in the trick..look for it that it is done properly when assembling it back
Hasani
I would like to add something here too as a lot of people have joined in. The box up job after the replacement of the gaskets is very important and mechanical staff who dont have previous experience in doing so are probably going to damage these new ones too. The proper and even tightening in the trick..look for it that it is done properly when assembling it back
Hasani
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