Starch Dust
Starch dust is an explosive material (Class 1 Dust). Its Pmax (pressure rise due to a dust explosion) is about 10 bars. Its Kst is in the range of 100 to 200 bar meters/sec.
To initate a dust explosion, the following conditions are required:
1. Dust concentration above the minimum concentration.
2. Oxygen
3. A source of ignition with energy greater than the energy required to ignite the dust.
4. The dust cloud is contained in a closed vessel.
Since they did not have a dust explosion for the last 10 years, it is likely that one or more of the above conditions are not being met.
From my experience, the most likely source of ignition is a pulse jet bag type dust collector, if this the type that they have.
Regards,
Amrit T. Agarwal
Consulting Engineer
Pneumatic Conveying Consulting
Email: polypcc@aol.com
Ph and Fax: 304 346 5125 ■
Starch Dust Explosion
Starch dust is an explosive material (Class 1 Dust). Its Pmax (pressure rise due to a dust explosion) is about 10 bars. Its Kst is in the range of 100 to 200 bar meters/sec.
To initate a dust explosion, the following conditions are required:
1. Dust concentration (grams/cu meter) above the minimum.
2. Plenty of oxygen.
3. A source of ignition with energy greater than the energy required to ignite the dust.
4. The dust cloud is contained in a closed vessel.
Since they did not have a dust explosion for the last 10 years, it is likely that one or more of the above conditions are not being met.
From my experience, the most likely source of ignition is a pulse jet bag type dust collector, if this the type that they have.
They can still have a dust explosion if all of the above conditions are met, and there is no pressure relief provided.
Regards,
Amrit T. Agarwal
Consulting Engineer
Pneumatic Conveying Consulting
Email: polypcc@aol.com
Ph and Fax: 304 346 5125 ■
Re: Starch Dust
I think the question is particularly refering to the effective of the section of plastic pipe.
If the pipe is conductive plastic and there is continuity at the connections to the steel pipe, then the risk is no greater than if it were metal and I guess that if you thought it was ABS, it was black so it could have carbon in the mix to make the plastic conductive.
If the pipe is non-conductive then it is likely to build up a static charge on it. However as it is non-conductive the energy of the static spark which can form may be relatively low and could be less than the MIE of the product.
It would be more risky if there were two sections of non-conductive pipe with a section of conductive material between. In that case all the static energy which can accumulate on the conductive section can build up and be released in a single high energy spark.
If they really need a section of plastic pipe in for any reason, it may not be as much of a problem as it first appears but making the whole length conductive would appear to me to be very much more preferable.
Don't forget that static may not be the only source of ignition though; a burning ember, a foreign body striking the wall of the steel pipe, a hot bearing on an upstream pipece of equipment, etc. may all be possible causes.
The system should have a proper risk asessment if one hasn't already been carried out. ■
Re: Starch Dust
Many thanks for your helpful and considered replies.
There are people working in the vicinity and it would be better to have conductive pipe material throughout and not continue to invite trouble from unpredictable static. ■
Re: Starch Dust
Dinus,
Also, make sure that all of the piping and all of the connected equipment is bonded and continuously grounded. Without proper grounding, static charge will still accumulate and cause static shock to operating personnel.
Regards,
Amrit T. Agarwal
Consulting Engineer
Pneumatic Conveying Consulting
Email: polypcc@aol.com
Ph and Fax: 304 346 5125 ■
Starch dust
Hi Colleagues
Recently visited a site where waste starch dust and room air is being conveyed to a bag filter with downstream fan. Most of the conveying pipe, ~3" dia, is carbon steel but there is a ~12' section made from plastic,ABS? There is no means of controlling the dust concentration into the system.
Could this be regarded as an explosion/ fire hazard though it has been there 10 years? ■