If you use propane, you have a gas flow regulator. Via a knob, you can control much gas can pass thru the regulator, measured in kilo pascals. Turn the knob to open more, bigger hole, more kPa, more gas exiting the burner all leads to more heat.

So your not thinking, "Ok, I gotta cut back the heat to 200 degrees." Your thinking, "Ok I gotta go down to 1 kPa."

Fantastic project! Have you been following the efforts of a group of Harvard students to creates the perfect BBQ smoker for brisket?

http://www.nytimes.com/2015/07/19/busin ... .html?_r=0

Inspirational!!

hipporun wrote:If you use propane, you have a gas flow regulator. Via a knob, you can control much gas can pass thru the regulator, measured in kilo pascals. Turn the knob to open more, bigger hole, more kPa, more gas exiting the burner all leads to more heat.

So your not thinking, "Ok, I gotta cut back the heat to 200 degrees." Your thinking, "Ok I gotta go down to 1 kPa."

Would it be possible to integrate a closed loop electronic control system into the machine, whereby if I were to select the desired temp the system would automatically adjust the pressure accordingly?

Yes. There are (many) commercial gas roasters that have that, but I have no idea how to accomplish that.

As long as its possible, I reckon if I talk to the right professors, should be able to do it

Good Luck to you. I am meeting a gentleman next week who has designed a 5lb, gas fired drum roaster. I met him at the Oregon City farmers market last week. He had a booth and some good coffee to taste, but no sign of the roaster. I would love to see it in action, maybe pick his brain or get some pics.

If you 'mine' this site and the Homeroasters site, you'll find a wealth of information. What you propose has been done both by home builders and commercially. For the fluid bed roaster you initially mentioned there are a number of choices.
-- all-in-one or separate air source? Some, especially home-built, use a separate blower...not sure why, perhaps to keep the electric sparks away from the propane.
-- propane ignition...probably from a BBQ.
-- blower source. Generally, vacuum cleaner blowers are used, as they have plenty of capacity to go up to a couple of kilos and are not expensive. But there are plenty of other blowers.
--blower control is usually done with a triac, similar to a light dimmer. Lots of people buy router speed controllers...same thing. Either could be adapted to automatic control.
-- air control. Changing the motor speed is OK for fine-tuning, but if you want to roast variable quantities you'll also need to be able to control the air flow. You either block on the suction side, or use a waste gate to bleed off excess air. This might best be a manual setting.
-- electric or propane. Generally, once one gets over a half pound or so a regular 15-amp/120-Volt circuit won't give enough heat. Some go to 20-amp/120-Volt; most that stay electric go up to 240-Volt. But, most large roasters fuel with propane.
-- burners from camp stoves, pig cookers and the like all work. You'll need to determine how many max BTU you need for a given charge of beans...you can find this on the suggested web sites. Burners can be modified to give more heat by drilling out the orifice. Probably, for the size you're planning on, you'll need a 20# regulator as a rough control. Again, you might want to leave this as a manual setting, dependent on batch size. After that, you'll need a needle valve or some such for a fine control. Industrial controls are available that you should be able to rig to a computer.
-- your stack diameter will be somewhat dependent on planned range of batch sizes. Too narrow and the bean column will be too tall, too wide and you'll have trouble lofting the beans.
-- don't forget to include some sort of window to view the beans. Industrial high temp tubing is available and probably best. Some home builders use butane lantern glass or 'Bake-a-round' which was a bread cooker gadget popular many years ago.
-- you'll need at least a Bean Temp (BT) probe. Look for posts by EricS, who supplies the DIY roaster community with these; his posts are a font of information, but mostly for drum roasters. On a drum roster, you also need an MET probe, so that you can see small changes in source heat. This is less used on air roasters as one can see changes more readily on the BT, due to the huge amount of hot air, but this might be a good area for you to do some original research and experimentation.
-- computer control, if you want to do this, is very popular. Artisan software is free and interfaces easily. Most people like the Arduino boards for the interface.
--bean cooling is important. The simplest way with an air roaster is to bump up the air and cut the heat; it's sub-optimum though as the device has residual heat that will slow the cooling process. Think about how you might get the beans out rapidly and into a separate cooler for best results. Also, if you cool outside you can roast more batches in succession.
--don't forget that you need a way to separate and catch chaff. If you leave it in the roaster it can catch fire or at least carbonize and impart off-tastes. There are tons of designs for this.
--I was thinking that it might be interesting to have some sort of diverter plate at the top of the stack. Flipped one way it would keep the beans in and pass chaff. Flipped the other way, the beans could be blown out the top and into the cooler by bumping the blower up to max.
-- don't forget that roasters have to be cleaned, especially downstream from the bean mass!

That's about all I can think of...have fun!

Maurice

Many thanks for the reply and wealth of information you have provided. You have given me a lot to think about and areas to research. Now I know what topics I'm looking to read up on, should make this project high quality!

Cheers,
AK

P.S. Do you know much on PLC control, and how it relates directly to coffee roasting machines. Can I program the system, for example to be at one temperature 'X' minutes into the roast and be at another temperature 'Y' minutes into the roast?

A plc would be overkill for that, but you could do it. Any sort of embedded system would work really provided you know how to program it.

What is your major?

We don't really major here in the UK. Elective modules are available (in addition to compulsory modules). I have picked the following as preferences
ELECTIVE:
-Contact Mechanics Tribology
-Additive Manufacturing
-Polymer Engineering- Processing and Manufacture
- Internal Combustion Engines
COMPULSORY;
-Individual project
-Computer control and instrumentation
-International design project
-Engineering management