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Resin build-up in dust extraction pipework (OSB plant)

Resin build-up in dust extraction pipework (OSB plant)

Resin build-up in dust extraction pipework (OSB plant)

(OP)
The dust extraction system in question is in place in a large-scale continuous-operation OSB production facility. The problem section is the extraction from the OSB blenders & formers.

In the blenders wood strands are blended with resin binders (MDI & LPF) and a small amount of wax. In the formers strands go through the forming line where cross-directional layers are formed. Following these stages the layers of cross-directional strands are pressed under intense heat and pressure to form a rigid, dense structural panel of oriented strand board (OSB). Due to these processes, there is present at both stages an amount of dust, resin vapour and resinated dust.

The aim is simply to keep the formers under negative pressure, to prevent release of dust / vapour to the rest of the plant.

The air extracted from the blenders / formers is conveyed through the dust extraction piping (welded/flanged steel pipework)- where it mixes with unresinated dust from other areas of the plant- to the baghouse filter. At the baghouse, the dust is filtered out and the clean air is released to the atmosphere.

There are problems with the current realisation of this system.

Initially it was found that not all the resin vapour and resinated dust from the formers was not conveying through the pipework with the rest of the dust. Instead, this material was sticking to the inside of the pipework. The material continued to stick, with the effect of continuously reducing the inner diameter of the effected pipework, eventually blocking it entirely. Apart from the obvious lack of suction at the formers, this also meant that the rest of the system became unbalanced and did not function as designed. Furthermore, this build-up necessitated shutting down the process and clearing the pipes, with associated costs of downtime and maintenance.

To solve this problem, various different types of pre-filter have been installed in the extraction hoods (as shown in the diagram). Some of the filters work to keep all resin and dust out of the lines, while allowing enough extraction to keep the formers under negative pressure; this is what was hoped for. However, the problem with these filters is that they quickly become clogged with dust and resin, and need to be replaced. This again leads to downtime and maintenance.

A good solution to this problem is required, to eliminate the issue of resin sticking to the inside of the dust extraction pipework. Looking at possible solutions, the following questions arise:

-    Is there a key conveying velocity to prevent build-up of resin in the pipework?

-    Do suitable pre-filters exist that will prevent resin from entering the pipework?

-    Can the filters be installed on the formers so that they will not become clogged during normal operation? Does a pre-filter system exist that allows continual regeneration of the filter? Automatic indexing roll filters would appear to be an option, however we have no experience with such a system.

RE: Resin build-up in dust extraction pipework (OSB plant)

I've done a few of these systems , you can check our web site, and the problem you describe usually occurs in the older systems.  The biggest problem is with conveying velocity ( must be within 4800 5200 fpm )not being adequate do to modification made by plant personnel after the installation or changes required during same.  Static pressure, cfm and the velocities are all a delicate balance and any changes to one will effect the others, all these things I'm sure you're already aware of....so to answer your question the only suggestion I might make would be to use the rolled media you mentioned as a fix untill maybe revamping of the overall system could be made.  Good luck having been in this field for about 16 years there is no easy answer.

John J Almeda
Aircon Corporation
http://www.aircon-corporation.com

RE: Resin build-up in dust extraction pipework (OSB plant)

I like the roll filter idea too. It could be built to index automatically or by hand. I'm surprised that John in previous post indicates that these systems can be self cleaning at 4800 FPM to 5200 FPM. Can anyone verify that?

Peter Ott

RE: Resin build-up in dust extraction pipework (OSB plant)

I would think if the air velocity in the roll filter was reduced (by expanding duct size) which may be required by the size of the filter unit anyway then you would be OK.  The filter media is not self cleaning it would need to be disposed as you use it.  Still lot cheaper than roto rooting duct work.

Another thought what if you use water wash such as those used in large kitchen hoods or those that used to be used in spray booths.  Granted the uncured resin and other filtered contaminants will lead to some kind of gooey god awful sludge and that has to be disposed of (more EPA regulations to read) but again do you really like roto rooting duct work??

Dan Bentler

RE: Resin build-up in dust extraction pipework (OSB plant)

Dan

I wasn't clear in my post. I meant to ask if the DUCTWORK is self-cleaning at velocities of 4800 to 5200 CFM.

Peter Ott

RE: Resin build-up in dust extraction pipework (OSB plant)

Vent guy

I dont have the books anymore, but transport velocity of 4800 to 5200 seems to be for very heavy particulate concrete dust metal dusts etc.  Even with that high velocity (noisy duct work and added erosion in bends) I would think uncured resin would still stick to the ducting.  I think the guy with 16 years in the business said it all "no easy answer no magic fix"

Dan Bentler

RE: Resin build-up in dust extraction pipework (OSB plant)

Do you have trouble cleaning the fabric in the baghouse?  Does the addition of more dust, or change in temperature make it less sticky?  Maybe adding dilution air to drop the temp, or feeding more dust in up front would help.  Maybe this could be done in a pretreatment section which could be cleaned easily.  Have you considered a wet ESP or a water impingement filter?  The pH would probably be important.  You could purge the water to a waste fuel boiler.

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