industrial dryer (for dog chews)

[knighty]

anyone have any experience with / info about industrial dryers for dog chews / dried fruit etc.. ?


I bid on one in an auction when a big food company went bust... but there's some sort of problem with the finance which was outstanding on the machine and I'm starting to assume I won't be able to buy it... (it's been a month already)

this (http://www.afosgroup.com/products/DRYERS.pdf) is the same as the one I bid on

new ones are out of my price range... (£35k+)

I've seen other makes etc.. cheaper but I'm worried about quality/reliability.. assuming you get when you pay for... (mostly cheap imports)

the one I bid on was previously used to dry strawberries, it dried out 110kg at a time at 40'C

I've been told because I'm drying meat I could run at 90'C and it would be a lot quicker...
(there is an option for an exterior heat source, I could use hot water from our generator for free heat)


as I see it... it's basically a big heated box with a dehumidifier ontop...

so I don't see why I couldn't build one then have a refrigeration engineer sort out the dehumidification... only problem is I don't see how a dehumidifier will work at all well at 90'C ?

anyone know how they work ?

I guess they must use an air to air heat exchanger to dump the heat from the room before the air is dehumidified ?

using 2 air to air heat exchangers, the air could be cooled by the air returning into the box, and then my outside air.... that way the returning air would be pre-heated ?

I made a couple of (very simple) diagrams to explain what I mean....

http://img265.imageshack.us/img265/4066/boxl.png

http://img822.imageshack.us/img822/2259/airflow.png
(green is fresh air)


this gives max airflow over the product

without having to have all the airflow go through the dehumidifier (which I assume would otherwise be overwhelmed with hot air)

the fresh air to air heat exchanger could have an inverter controlled fan on it to give a consist air temp into the evap.


I've searched all over the place for info... but can't find anything...
this is the only way I can see it working...

unless either the evap doesn't have to be so cold... just cold relative to the room temp ?

or if the compressor/evap would be able to cope with 90'C air over it ?


I'd really appreciate any info/input here.... I'd talk to the refrigeration engineer I use (the only one I've every known locally who's any good) but he's recovering from a knee operation right now!

[desA]

You may want to research tunnel-type driers. May be fairly simple to build...

[mad fridgie]

Drying, one of my favorites!!!!!!!!!
Start at the beginning
How much product do you want to dry. (Start KG)
How long do you want it to take (Hrs)
What is the water content of the product at the start (% per Kg)
What water content do you want at the end (% of final KG)
Is a critical product (dog chew "NO")
What is the maximum temp you can get away with for drying.
What are physical attributes of the product ( how fat)
At what rate can you raise the temp of the product (does it distort) in this case I suspect a bit of distortion is not that important)
From this you can determine what is required. " how ever this type of drying is not an exact science, each design calculation method is correct to a about 85%, so allowance of 20% is normally made for the inconsistencies of the process

[Magoo]

have you concidered vacuum driers, cheap to operate.

[knighty]

hi, thanks for the replies

*I'd like to be able to put about 300kg of meat etc.. in and have it done in about 20 hours so I can empty it and fill it up again the next day
(or... I could make a much larger machine, and put some more product in Monday to Friday day and then empty it the following Monday... or any combination of that)

*moisture content is about 70%

*no idea about final moisture content... I guess pretty low ? - enough so the product is hard, and won't go mouldy... I've googled and found between 10 to 12%.. do you know if this sounds about right ?

*I've been told I can go to 110'C for drying... but 90'C is better

*I'll mostly be making tripe sticks, and liver sticks etc.. which will be thinly sliced to start with.. 2 or 3mm thick... I might do some other thicker things (3cm ish) but would be happy to leave them in for longer

*not sure how much it will distort with heating... but I don't think it will be much, and it won;t really be a problem anyway


hope these answers help...

quick bit of background... we're a family business making raw dog food, we've been going for 120 years... and dry treats will be something new for us :-)

[Magoo]

Basically comes down to how much do you want to spend. Investment capital verus running cost, low investment and heat the hell out of product to remove moisture, versus dehumidify [ costly ] low running costs. Check Munters Rotaire dehumidifiers.
I have done a few deer velvet driers, as in room dehumidifiers and vacuum driers, they are batch process tonnes at a time.

[mad fridgie]

At 90C
you need a 10Kw heater element (PID control via solid state relay), you need approx 100M3/hr fresh air (that is nothing) (air to air would heat ex-changer would save 1.5kw, would you bother!) However I would use the waste energy to preheat water for other process!
The fresh air and exhaust I would use 100mm dampened spigots (manual to be cheap) either side of the main fan. (blow a bit out suck a bit in)
Stack velocity of 5-6M/S
Best have a belt driven fan (motor out side the main air stream)
I would look at a "one hour ramp" room temp to 90C.
Make sure the box is well insulated (at with the right rated insulation)

[knighty]

awesome !

that's pretty easy to do then :-)

will there be any benefit to having the incoming air ducting through a couple of industrial portable de-humidifiers ?
(I could get some cheap on ebay?)


do you know if I could buy some refrigerated panels which will be ok up to 90'C ?

I'm having a new freezer build soon... so could have this done at the same time ?



I didn't like the idea of the extra running cost at first.... but then they money I save on not buying a pre-build unit will pay for a lot of electricity !


p.s. sorry for the slow reply, I had some problems logging in :o

[mad fridgie]

No need for any extra dehumidifiers, no benefit.
Check your local panel manufactures for high temp options.
the 10Kw is slightly bigger than you need.
If you want to go very cheap running costs then you do need to go low temp drying (max for your local guy to design say 50C), I would not bother on that size, if you can use the waste energy to heat water.
Basically a pre-heat tank for your main water heating system.
Just a very deep coil mounted in your exhaust air, depending upon your daily hot water use, (normally a lot in your industry) there is no reason why you could not just about recover all the vented energy. So need not be expensive to run

[knighty]

yeah, we use tons of hot water, so I'll do it like that then


I'm planning to set up a generator in a few months running on the fat we cut off the meat and render down to lard... to cut down on the electric bill and use the engine coolant to heat water to cut down on the gas bill....

there should be enough heat there that I could run a radiator of engine coolant in front of the intake to the electric heater and save some more money there :-)


thanks for all the info.... I googled my ass off but couldn't find anything apart from people trying to sell machines

I'll easily be able to built a setup as you described, and could easily build another later on for more capacity etc.. :-)

thanks again

Alan.

[mad fridgie]

If you are using a generator, normally water is around the mid 80C in the coolant system, you could just use a heat exchanger (rad) in side the main air stream, OK drying temp will be a bit lower, slightly more fresh air would be required, but gut feeling is that it still would dry your product. and you cold still recover the exhaust heat