Re: Basic Calcs
Try
G E Klinzing et al book "Pneumatic conveying of solids - A theoretical and practical approach" pub:- Chapman & Hall ■
Book Recommendation
Dear Mantoo
Thankyou very much , I am going try and source the book.
Cheers Peter ■
Coffee Beans
Deear Peter1111,
You have nor mentioned whether the blower in question is a positive displacement blower or a regenerative blower-lets get that out of the way first. Roots blowers can run at lower revolutions per minute than a regenerative blower as it is moving atmosperic air under regulated low presure
where a regenerative blower uses atmosperic air only.
What is the available power? 480 volt three phase
is best 220 volt single phase is second best.
What is the distance that the beans are to be conveyed? what are you going to use for piping? Are you blowing them into a bagging hopper? what size piping are you going to use?, two and one half inch is typical in small frame rotary lobe Roots type blowers.
Or are you looking at calculations and then going to the blower supermarket?-if so the rotary lobe blower /being positive displacement is the better buy as it has a more useable power range in a smaller package where the regenerative is limited by resistance as it acts exactly like a centrifugal pump.
The better option is to vacuum the beans through a decelerator cone to reduce damage to the bean itself as it has a huge amount of surface area in relation to the coffee bean to slow it down by gravity to a full stop.
Have the beans been roasted prior to movement by air to the receiving area? I ask this because hor beans will affect the air calculations simply because they are a heat source and this will have an effect on blower performance calculations due to moisture entering the system unless your flow is very small.
You should also go in haste to a rotary lobe blower manufacturers web site to get their respective blower performance charts as this will
provide you with a world of information and help for sizing the blower in question.
Do not forget to factor in a deceleration cone on the receiving end unless you plan on breaking the beans anyway.
On a simular note you should also be factoring in Boyles law calculations for gasses including the working altitude etc. ■
Beans
Dear lzaharis
Thankyou for your reply. This design is, for the time being, only theoretical and forms as an introduction into the ways and means of pneumatic conveying for myself. That said obviously I'd like to implement the best idea possible (all advice & criticism invited).
In essence I am to convey the beans from a vertical hopper into an offset roasting chamber (through a pipe) where within the beans will be continually circulated and roasted using heated air.
So far I have calcd the velocity & airflow required to suspend the bean in a bed of air. From here I have worked it back to the transfer pipe conveying the beans. My mass ratio of solids (kg/s) / air (kg/s) is roughly 0.13 in the pipe. does this seem ok? The only problem is that using a bean loading rate of 0.73Kg/s
I get a air mass flow rate of 4.95 Kg/s or (vol = 4.12m3/s). Which seems quite large? AND it's at room temp so if i work it out according to the roasting temp of 260 deg C I get an even bigger volumetric flow rate of 5.7m3/s.
Is there not a correlation between the hopper-feed flow rate (and the bean density) and the blower deliver flow rate (and the air density)?? The above flow rates seem far too large for such a small application i.e. if the delivery pipe is 0.25m in diameter an air velocity of 84m/s exists within -- which seems well too high. Ofcourse I could enlarge the diameter but it seems silly to have a bigger bore pipe (0.52m) just to bring that vel down to 20m/s especially for the short stretch of piping 5m (or is that the route to go? - what is the best velocity with which to convey solids?).
All of the preceeding calcs have been done on a vertical pipe which isn't accurate for my horizontal pipe which bends into the vertical below the chamber. Apparently there are alot more influences to take into consideration with regards to a horizontal design. The formulae I have managed to find are very wishy washy and rely on data which is only obtainable post installation ... or from the mythical pneumatic conveying charts which I am battling to lay my grubby student hands on.
Sorry I haven't been very precise in my description.... Basically I have 25 Kg of Coffee beans (density = 620kg/m3) which I need to convey (as quick as possible within reason) into the roast chamber where they will cycle while roasting at 260deg C. I can charge the system at room temp then once the beans are cycling start heating the air flow. For starters to get a feeling for it I will use a positive pressure blower (of some sort .. will look into your suggestions) to charge the system.
Could you in any means aid me through the basics of correlating the two flow rates (solid and fluid). I did try and locate the book which was recommended to me in an earlier posting but technical librarians give me that look which insinuates that there is no such book.... the only other way would be to import it at a cost of +R3000 to get it from the states. Its a bit out of my budget.
Thanks for your time and interest.
Regards,
Peter ■
Details
Positive displacement
Prefer single phase 220V but if the pros far out weigh it I can use 480V
Distance : 5m
materials selection will come after I done the other system calcs (what is a decent cost effective stainless that can be utilised in the above scenario?).
Discharging into a roasting chamber.
would like to keep the piping as small as possible +- 0.25m but that seems to be causing unfortunately high velocities.
Yes will finish off calcs and then hit the market to see whats available.
How much damage would occur to the beans in the above mentioned arrangement? If i keep 90 deg bends out of it wouldn't the damage be minimal?
Roasting takes place post conveyance.
How needed is a deceleration cone in the above scenario if within the roaster I am diffusing the flow enough to allow the bean to drop out of the air flow (perhaps with a little nudge from a well placed deflector plate) ■
Coffee Quest
Peter 1111,
Do not even bother with pnuematics for a distance and volume that small!!!!!!!
A small grain auger or "Little giant" brand grain elevator is all you need to do this as the air driven system would be nothing but a money waster. and reduce your damage to almost zero from impact and abrasion.
The little giant elevators are 110 volt single phase with a V belt drive through a pulley to the head of the chain driven elevator. the elevator has rubber paddles connected to a chain drive to move material from A to B and they come in many lengths with a narrow trough to move the beans.
Solve your problem before it starts and keep it simple by using a pendant control to start and stop the flow into the roaster.
The little giant elevators are small and light so placement is easy.
www.newhollandelevator.com ■
Re: Basic Calcs
lzaharis
Thanks man I agree that for transporting the beans the recommended elevator is a much better choice however a blower of some sort will still be needed to circulate the beans within the roasting chamber as using hot air to roast the beans is the main concept behind the design (sorry I may not have specified this) ... I just thought perhaps some how I could use the air flow to charge my system as well without having an additional loading system to worry about. Do you think its a valid route to follow?
Is a solid to fluid mass flow ratio of 0.2 acceptable? what are the limits?
Thankyou for your ideas and help
cheers ■
Coffee Troubles
Dear Peter1111,
If my memory serves coffee roasters have paddles for mixing, blending and to prevent over heating/hot spots/burning the beans while roasting.
Also you will end up ruining the blower bearings and all has they will not handle the temps-air is blown in through the heat source/a fuirnace blower for example and heated in a heat exchanger and then blown to the roaster drum. unless the heater is directly under the drum with some roasters-the small tabletop ones come to mind which is why beans get burned -yuck
If the atmosperic oxygen is hot enough it will catch fire-I am sure you dont want that.
The roasting process is heating up the natural oils in the beans in additon to the shell of the bean.
I am sure you do not want a blast furnace for a coffee roaster which is what you will have as you are inadvertantly providing combustion air with the delivery system.
I am sure you would prefer french roast to french roasted coffee bean ash. ■
Thanks Bulk-Online
Hello
Sorry I haven't replied but I've been away from a while. All in all I made adjustments to my design and its going on fairly well.
I'd just like to say that this forum is truly a great help and means of sharing vital information. It is wonderful that people are so willing to share their knowledge and advice. A special thanks goes to Amrit T. Agarwal for his help with the pneamatic conveying calcs which he emailed as well as to Izaharis for his help interest.
Hope b-o continues to grow.
Regards,
Peter ■
Basic calcs
Hello All.
This forum thing is new to me but hopefully it works out. I am a student who is having serious problems in relating the (density and mass flow) of the solid(coffee beans) to the (density and mass flow) of the conveying fluid (air). It is a simple setup with the beans being gravity fed from a hopper into a horizontal pipe through which air is flowing. (are there charts available to find these relationships?)
I would be hugely appreciative of anyone who could possibly assist me with these "basic" formula / calcs / charts or where to find them.
Thankyou.
Reards,
Peter
frostp@satweb.co.za ■