Drying logs and waste paper?

[Chipy]

I'm considering putting an Anaerobic Digester in and I need ways of using the heat up. I currently use envirobed (waste paper) to bed my cows with which has been kiln dried. I also have a 200kw log boiler which already heats houses etc so not much spare heat with that. I can buy the envirobed not kiln dried for a quarter of the price and get paid to dry it. I can also dry my logs for my biomass boiler. My question is is there such a drier that will dry logs and envirobed which is like sawdust?

[cornish wood burner]

I'm currently looking at an Alvan Blanch batch dryer to dry chip and peat. It will obviously take a while to dry logs but it might be OK to finish them.

Edited April 17, 2016 by cornish wood burner

[Chipy]

I'm currently looking at an Alvan Blanch batch dryer to dry chip and peat. It will obviously take a while to dry logs but it might be OK to finish them.

 

Have a rough price?

[cornish wood burner]

All the info is at work but I think the one I looked at was around £23k. It was a while ago and I've not really had the time to go into it deeply yet but there is a lot of choices in size and presumably price. They also do continuous conveyor dryers but more money.

[cornish wood burner]

£20k plus a heat exchanger for 7.5 tonne capacity in 2013. Heat input 300 kW.

That is the biggest single batch machine they make. Doubles are available with 15 tonne capacity. Smaller machines with 2.5 or 5 tonnes capacity are available. They must be busy as the salesman hasn't got back to me to answer some queries I asked 10 days ago

Pto, lister or electric powered.

[openspaceman]

I'm considering putting an Anaerobic Digester in and I need ways of using the heat up. I currently use envirobed (waste paper) to bed my cows with which has been kiln dried. I also have a 200kw log boiler which already heats houses etc so not much spare heat with that. I can buy the envirobed not kiln dried for a quarter of the price and get paid to dry it. I can also dry my logs for my biomass boiler. My question is is there such a drier that will dry logs and envirobed which is like sawdust?

 

How much spare heat do you have, after all you'll need to keep the digester warm?

 

You have two very different types of material to dry, the limit on the rate of drying of the sawdust like stuff will be how much heat you can deliver to it, because its rate of receiving heat at its surface will be less than its rate of internal conduction, so it can deliver the heat into water in the middle of the particle before the surface gets too hot.

 

Logs are different, as the outside gets drier it cannot conduct heat into the interior to volatilise water deep inside, so you have to deliver lower temperature heat to the surface over a much longer period.

 

Logs will air dry, sawdust probably won't to any sensible depth.

 

Logs present little resistance to air flow, air won't easily flow through sawdust.

 

Even with a deep bed chip dryer using 40C waste heat the electricity costs for running the fans was significant.

 

It cost us about 1 kWh of heat to extract 1 kg of water from logs in our dryer, we reckoned we could half that at the cost of much more expensive equipment. If one could maintain a clean burn by direct combustion of wood chip the losses in the flue stack even at 50%mc wwb are much less than a dryer in the absence of heat recovery.

 

Given some of the above and if you are going to use the biogas produced in a spark ignition engine then a co current dryer for the sawdust like stuff using the hot (500C+) exhaust may be worth looking at, a rotary valve metering the envirobed into the exhaust and collecting the resulting material in a cyclone. The feedback loop being maintaining the cyclone at ~110C by varying the feed rate of the rotary valve. This would be more problematic with a diesel exhaust as there would be more chance of combustion.