Any tips on drying wood chip?

[Doing it for the kids]

We couldn't stack it any higher than about 0.5m when we dry on our floor otherwise the bottom gets all crispy while the top hasnt dried at all.

Interesting, thanks. What rh and temp are you pushing through, how big a fan and what floor?

 

[scotston]

type in 'equilibrium moisture content of wood' into google and select images. Number 12 image in is my particular favourite. The concept is to continually dry at the same RH, anything below 40% should return chip around 10%MC. If you keep drying at a constant RH, the lower chip dries immediately to 10% but doesn't get any drier as it has reached its equilibrium. The upper layers then do the same. Ignore temperature as it does not tell you what the RH is and it is only how dry the air is that matters.This is how I dry for my gasiifer, sometimes go for 30% RH if I want it closer to 8% MC. My fans are spec'd for drying grain at 6ft; this depth works fine for the chip, just need to wait longer. I normally go for 4ft. Here endeth the lesson.

 

[Doing it for the kids]

type in 'equilibrium moisture content of wood' into google and select images. Number 12 image in is my particular favourite. The concept is to continually dry at the same RH, anything below 40% should return chip around 10%MC. If you keep drying at a constant RH, the lower chip dries immediately to 10% but doesn't get any drier as it has reached its equilibrium. The upper layers then do the same. Ignore temperature as it does not tell you what the RH is and it is only how dry the air is that matters.This is how I dry for my gasiifer, sometimes go for 30% RH if I want it closer to 8% MC. My fans are spec'd for drying grain at 6ft; this depth works fine for the chip, just need to wait longer. I normally go for 4ft. Here endeth the lesson.

Whooow the end of class bell hasn't rung yet!

There Are lots of charts but hard to work out which is 12! What I can see is to get chip to 20-25% the relative air humidity doesn't seem to need to be much below 75% and air temp doesn't seem to make much differance.

You are drying to a much lower MC so your RH has to be lower which makes sense.

Based on this lesson the single biggest factor is air puff (fan size) followed by RH below 80% then possible air temp at 30 degrees. Would you agree sir!?

 

[Courier]

What I can see is to get chip to 20-25% the relative air humidity doesn't seem to need to be much below 75% and air temp doesn't seem to make much differance.

If you heat the air then you reduce it's RH.

Get yourself one of these and it may help your understanding -

http://www.thermometersdirect.co.uk/mason's-wet-dry-bulb-hygrometer-thermometer.html

Explanation beneath -

https://www.avogadro-lab-supply.com/item/Masons_Wet_Dry_Bulb_Hygrometer/1001

 

[scotston]

fan size relates to air pressure in the duct and therefore air speed through the crop. This is a function of how much air is present at any given RH to either take or add moisture to the chip. around 80%RH should get you the chip you need (I dry wheat at 65% to make it 14.5%MC), but depending on the air flow, to an extent, depends on the speed of drying ie how much chip can you dry per day.

yes heating the air is reducing the RH and yes a hygrometer is a good idea. The question is are you going to dry chip using constant humidity or do you not have that facility? If you only have a temperature probe you are using a calculated ratio between the air temp and air humidity to give you an RH value that is only valid at that point in time. As soon as the ambient air and ambient RH changes, you need to change the parameters in order to get constant RH. If we assume you set the drier at 30degC fixed temp control on a fine sunny day say 65%RH, 5degC, then the humidity (RH) in the duct could be as low as 30%RH. But then it rains and the ambient goes to 99%RH at the same temp, the RH in duct will be more like 65%RH - at a constant heat input. This would produce overly dry chip at the floor and perhaps wet at the top depending on how consistent the weather is. A rule of thumb is a 7degC uplift in ambient temperature using heating will produce a 35% drop in humidity in the duct. Floor drying is quite efficient in terms of heat input, just costs to run the bloody fans. All of this info was taught to me by both Richard Flach of Flach and Leroy drying systems and a 200 page book written in the 70's that Richard gave me!

 

[Doing it for the kids]

All very interesting, thank you.

We will only be using about 20-30% of the whole drying floor to dry a load so the air capacity / pressure should be very high, is very high, we will get good penetration.

They system is designed for grain, I can control the max air temp to some degree but not low temp. I can control humidity two ways, the first is on the fans that can be set to what ever I want, the second is on the biomass which turns the pump on and off depending on high low parameters. On a sunny day I don't need the biomass at all and even then may struggle to keep the RH above 70%.

I can get the air RH way down in any weather, if anything it's hard to keep it high, even when the pump is off, natural circulation is enough on cloudy days

What sort of air pressure do you need to get a consistant dry through the whole depth? I need to keep an eye that we don't cook the bottom but leave the top too wet....

 

[Courier]

Probably better to use more floor area and a thinner layer.

 

[Doing it for the kids]

What sort of depth?

 

[shakerator]

fan size relates to air pressure in the duct and therefore air speed through the crop. This is a function of how much air is present at any given RH to either take or add moisture to the chip. around 80%RH should get you the chip you need (I dry wheat at 65% to make it 14.5%MC), but depending on the air flow, to an extent, depends on the speed of drying ie how much chip can you dry per day.

yes heating the air is reducing the RH and yes a hygrometer is a good idea. The question is are you going to dry chip using constant humidity or do you not have that facility? If you only have a temperature probe you are using a calculated ratio between the air temp and air humidity to give you an RH value that is only valid at that point in time. As soon as the ambient air and ambient RH changes, you need to change the parameters in order to get constant RH. If we assume you set the drier at 30degC fixed temp control on a fine sunny day say 65%RH, 5degC, then the humidity (RH) in the duct could be as low as 30%RH. But then it rains and the ambient goes to 99%RH at the same temp, the RH in duct will be more like 65%RH - at a constant heat input. This would produce overly dry chip at the floor and perhaps wet at the top depending on how consistent the weather is. A rule of thumb is a 7degC uplift in ambient temperature using heating will produce a 35% drop in humidity in the duct. Floor drying is quite efficient in terms of heat input, just costs to run the bloody fans. All of this info was taught to me by both Richard Flach of Flach and Leroy drying systems and a 200 page book written in the 70's that Richard gave me!

But they didn't have fan inverters in the 1970's.
The affinity laws. Run fan at 50%. Consume only 12% of full power. High heat, air flow to match back pressure. Stirrers if possible. Makes the electric bill more viable

 

[Doing it for the kids]

Fans are either on or off...

 

[shakerator]

Fans are either on or off...

Project killed then imo

 

[Sunco Machinery]

can use rotary wood chips dryer machine.