Re: Airflow Versus Productflow During Pneumatic Conveying
Attrition is one of the major drawbacks of pneumatic conveying. I think your palletised product is very fragile and under high lean phase velocities the pellets break. In low velocity dense phase you will get less attrition but there will be still fines generated. Is there a maximum permissible limit for fines in the final product?
You have net mentioned the pellet size and details of your dense phase trials as not all materials can be dense phased. Using inverters on blowers is not normal for lean phase conveying but they have been used. There is a minimum air flow required for conveying and going below that limit will not convey the material in lean phase. But in your case you will probably need a compressor rather a blower to convey in dense phase. As at lower velocity the material is conveyed at higher SLR & conveying pressures. ■
Re: Airflow Versus Productflow During Pneumatic Conveying
hello,
For an in depth answer not enough data are given.
Product data s.a. material, material density, particle size distribution and suspension velocity.
Also the performance results of the test are important.
The pellets, you are referring to have a bulk density of 1100 kg/m3.
Reducing the bulk density to 700 kg/m3 means that the voids between the particles should increase, due to the pneumatic conveying breakage.
I find that hard to believe. An I crease in bulk density is more likely as the voids will be filled up with smaller particles.
Further:
22 kW for 15 m3/min at 1 bar delta p seems a bit low.
Applying a Volt/Hertz regulator in combination with a blower is no problem as long as the following is considered:
Lower rpm causes a lower volumetric efficiency and higher outlet temperature.
When the outlet temperature becomes to high, then the pressure has to be reduced
Consult the manufacturer for the lowest allowable rpm in relation to the lubrication.
Testing in your installation is OK.
Then you are using your installation as a 1 to 1 scale laboratory.
Can also be done with a bulk truck if the volume is suitable
However, the interpretation of the various test results will be very difficult without a proper calculation program.
This program can reveal the hidden changes in the pneumatic conveying regime.
From each test a product loss factor can be derived and a regression formal can be derived, showing the relation between the loss factor and the loading ratio and the turbulence and the division between the pressure drops for acceleration, air, suspension, elevation and collisions.
From the tests it should then be possible to decide the (eventual) modifications necessary to make the system work for the new product
Testing can create the problem of getting too much figures that cannot be related to eachother in a mathematical system.
You then don’t see the trees anymore because of the forest.
success
Teus ■
Teus
Re: Airflow Versus Productflow During Pneumatic Conveying
Hello,
Teus had a good point. Your power requirement should be near 33KW at the operating conditions you stated. What is the motor rating?
Slowing down the blower via a variable speed drive should not be a problem. It would be best to let your blower supplier recommed a drive and the operating limits for you. This way you will not overheat the blower or the motor. Most motors are VSD ready, but in some instances shielded / grounded bearings are a must to prevent bearing damage due to current running through the rolling elements. As a rule of thumb you can usually expect half the maximum flow at maximum operating conditions. Please make sure to select a drive that is set up for constant speed / torque. Will 7.5m3/min do the trick?
If you need to experiment with the same flow but higher pressure you could try renting a oil free screw from e.g. A.I.R Air International Rental (HQ in the Netherlands). I am not sure if this trial and error method is worth it though. ■
Re: Airflow Versus Productflow During Pneumatic Conveying
Hello,
thank you all for your replies. the product flow is about 4 tons per hour. we did the successfull test with the blower as mentioned before. We dont use a special method for measuring density. we just take a bucket of 10 liters en measure the weight. before we make pallets of the product its weight is about 400kg/m^3. after a machine made pallets of this product, we measure with the same bucket 1100kg/m^3. the pallet size is about 8mm long and the width is about 4mm. when the blower is running it shows us about 650mbar pressure difference.
the test wich failed, the pressure was about 3 bars. this system transports was partial dense phase. after each piece of material a certain amount of are is blown. because of the different sizes in of material in the tube.
the air velocity and collisions causes breakage of the pallets. also the air is responsible for fluidisation of this product. so if we use lots of air, and we measure again, the density decreases.
it blower is not running at 1 bar, it is limited to 1 bar. normally the blower shows the figure about 600mbar.
For all responses, I can conlude, it can't hurt to use a frequenty converter. I wondered if it really can influence the density (the way we measure)
I have to take in account the higher outlet temperature.
I am curious, because there are lots of different parameters to take in account, and sometimes, systems don't react as you thought they would be. I think the best way is to try it, so I can verify my simple thought: try to find the point when the tubes are (just not) blocking with product, to get as less air in the end product and to reach the least damage to the pallets and so to reach the highest density ■
Re: Airflow Versus Productflow During Pneumatic Conveying
Hi Coe,
That has always been an approach to any given issue. As a minimum I would strongly recommend to start a spread sheet that captures all of your system conditions, (pressures, flow rates, densities, etc.) as well as a schematic and scaled sketch of your conveying system. This way could can log your feed rates and gauge trends, success and failures better.
Also, this would be the fundamental data set any conveying expert would hope to be able to obtain from you. GIGO= Garbage In, Garbage Out. The more accurate you can deliver said data, the faster, more accurate, and cheaper your expert solution gets. ■
Frequency Converter ?
hello
i think the blower you used is roots blower, the air flow but not the pressure for roots blower can be changed of outlet if using converter, so if the rmp is not high, it is not recommended to using the frequecny converter.
but for dense conveying , if the laval of orfice nozzle is used for air flow control , air flow is affected by the pressure of air supply, so frequency converter can not change the pressure , why use it?
i think the pressure drop is a little low, the air flow is also low for dense conveying , becasue the air flow is related to pressure , if you wanna dense conveying, i think the high pressure roots should be need.
the above is only my view.
■
Airflow versus productflow during pneumatic conveying
hello,
we have a blower of 22kW, 900m^3 air per hour, and a maximum transportpressure of 1 bar. pipeline 4" length pipeline is 40 meters. density of the product normally is 400kg/m^3
normally, this layout is good enough for our applications.
however, we want to transport a new product in our application.
this is a unstable granulate, it is a pellet made of fine powder , and during transports it falls apart easily. the new density is about 1100kg/m^3. after transportation we hope to have a density about 700kg/m^3
so, its need to be transported with less air as possible.
a test with the application above was successfull. but a test with dense phase transport failed.
however I want to transport this product with less air as possible.
my simple thought was to use a frequency converter for the blower, so less air can be given and a certain ratio air/product can be searched for, just before transportations stops.
can somebody tell me if this is the right strategy? Is there anyone who has experience with frequency converter on a blower?
thanks, ■