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marcuss
23rd September 2004, 16:07
I am investigating different methods to on-line measure the massflow of powders in pneumatic transport. I want to measure the massflow of wood and peatpowder transported to a combined heat and powerplant. I have not found any non-intrusive techniques that can detect the absolute massflow when the moisture content of the powder is changing. In my case the humidity can fluctuate between 4-10%.
Do you have any suggestions?

Best regards

Marcus Svanberg

DRHewson
30th September 2004, 10:12
I don't have any experience with the company (see link below) or their equipment but I found them while surfing today. They mention that there is minimal impact of changes in moisture content. Although it's designed for free fall conveyor transfer point applications it may be adaptable to your pneumatic conveying application.

http://www.berthold.com.au/industrial_pages/free%20fall%20bulk%20flow.html

Gerhard Kappler
18th October 2004, 7:53
Originally posted by marcuss
Dear Lyn

I am investigating different methods to on-line measure the massflow of powders in pneumatic transport. I want to measure the massflow of wood and peatpowder transported to a combined heat and powerplant. I have not found any non-intrusive techniques that can detect the absolute massflow when the moisture content of the powder is changing. In my case the humidity can fluctuate between 4-10%.
Do you have any suggestions?

Best regards

Marcus Svanberg

dirkvanderg
22nd February 2005, 7:40
Marcuss, giday

I read your request for a system that meausres the mass flow in pneumatic conveying lines: I also am looking for a system with an accuracy of say 1-1.5% (moisture is not an issue here). Anyone of my fellow Bulkies who knows about such a system or can help me with a solution.

Thanks, Dirk van der Galien, The Netherlands.

marcuss
22nd February 2005, 7:44
I have found a system from Promecon that measures the mass flow of pulverised coal. I will test this equipment in a biofuel application this spring. You are welcome to contact me in this matter. I am not sure you can get an accuracy of 1 % but in what application is this necessary?

Regards

Marcus Svanberg

Michael Reid
22nd February 2005, 22:10
Maybe what you need is an impact weigher, installed either at the feed point to the system (ahead of the rotary valve) or at the receival point, above the silo.

Michael Reid.

Gerhard Kappler
23rd February 2005, 14:34
A mass flow measurement at Mass flow measurement of pneumatically conveyed powder is possible. The system consists of a radiometric density measurement and a speed measurement.
The limit is the density of the conveyed product in the pipe. If this value is too low a measurement is mot possible.
Please let me know
- pipe diameter and material
- mass flow in t/h
- expected speed of the powder

With these data I will be able to check the application.

Best Regards

Gerhard Kappler
Berthold Technologies
Gerhard.Kappler@ Berthold.com

Dr M Bradley
28th February 2005, 10:18
At The Wolfson Centre we've been working on this problem, in collaboration with many others around the globe, for about twenty years. We have tested just about every principle ever thought of.

As the other respondent says, you need a velocity measurement and a density measurement. The velocity measurement is easy - electrostatic or capacitive are good enough, others are equally possible.

However, getting the density measurement is very difficult. Anything electrical for measurement of density (e.g. capacitance tomography, electrostatic measurement, microwave absorption etc) is bady affected by moisture content. Audio (e.g. sound attenuation or reflection) is badly affected by small changes in particle size. The only method NOT affected by moisture or particle size (or both) is radiometeric (e.g. X-ray attenuation) but you need a high density in the flow for it to work - it's fine at say 200 kg of solids per cubic metre of air (local value, not cross-sectional average), but at 10 forget it! So basically, no good for your application. Also, it's expensive if you use an X-ray generator, whereas if you use a radioactive source (Strontium 90 isotope for instance) you have a safety issue.

The only really reliable method of determining the flow rate is to measure it by loss in weight at the feeder. A second best might be to calibrate the feeder if it is a volumetric system such as a screw, but the accuracy can be poor if the density varies.

Notwithstanding all of the above, you have to look at the reason fror wanting the measurement, in the context of the overall system. You may be aware that the other thing which is a problem when feeding a combuster with a biomass fuel is the water content - even if you know the mass fed, this isn't the whole answer to your control problems because what you are really trying to control is the heat generation rate and this is determined by the feed rate of dry solids, modified by the change in nett calorific value as a result of moisture content. These problems compound each other - if you feed at a higher moisture content, the heat you are feeding reduces because in a given mass, there is less dry solids, but reduces even further because the nett CV is also less! So with the typical wide moisture content of biomass fuels, even if you had a reliable mass flow measurement system, it really wouldn't help you very much!

There are other means of control which could be more helpful, for example based on measurement of heat generation rate. The problem with this is the time lag - which can make the control dynamics difficult. I would suggest a study of the fuel variation (density and moisture content) would be a good starting point to understanding what can be achieved in the way of both open-loop control of feeding and also the dynamics of closed-loop control through heat generation.

I hope this helps. Email me if you want more info, bm08@gre.ac.uk.

Bob Driskell
1st November 2006, 17:03
I wanted to know if anyone has tried measuring a pneumatically conveyed powder stream using a coriolis meter. It would have to be a "strainght tube" type. In theory it should give a velocity and a density regardless of electrical characteristics?
I am trying to avoid using a measuring pot and weigh cells to confirm flow.

Jon Scarrott
2nd November 2006, 9:22
Hi Bob Driskell, (apologies to Marcuss)

why are your trying to avoid a weighing solution when its probably the most accurate and repeatable solution? You would generally need to feed from some sort of vessel into the pneumatic conveying system so why not use a loss in weight system?

We were involved in feeding from a high pressure vessel into a conveying system which was feeding sand for E grade glass. The system achieved an overall accuracy of better than 1%.

We have tried in the past using radiometric systems using Cs137 but the material velocity, moisture and rapid fluctuation in flow defeated this method.

We also did some work at the Wolfson centre based on particle impact noise. The results were variable depending on particle size and distribution, however we did discover it was very good at sensing when a compressor on the roof turned on and off. This system was originally developed by BP to measure grinding efficiency in ball mills.

Jon Scarrott
Lodestone Electronics Ltd

Thomas Feldhaus
31st December 2006, 13:58
Dear Marcus,

I have not read the entire correspondence and do not know if my comment is of use for you. In brief, we had - among other things - the problem at ThyssenKrupp Steel that there was no way to measure the mass flow in a reliable and precise way.

The task: Magnesium Granulate had to be transported against 5-6 bars into the melt. Two further desulphurisation agents were conveyed through the same pipeline. Problem: The typical sawtooth pattern.

In response to that we implemented the technology that is described on the attachment. The advantage here is that there is no need to measure as you know exactly the amount you convey. If you are interested in obtaining more details send me an email under tfeldhaus@feldhaus-technik.de

Regards, Thomas