Carbon Dioxide Meter in a kiln?

[Chalgravesteve]

OK, in the course of a visit from the local water authority, checking on our mains connections and backflow valves to the boiler, the commercial plumber I'm dealing with has suggested that drying wood using hot air through a kiln will warm the wood and it will release Carbon Dioxide in the same way that it would when its burnt in a stove. This seems a reasonable hypothesis.

 

He suggested that we have a warning sensor in the kiln to show the levels, as the doors are closed most of the time.

 

I am of the opinion that any levels that might exist will quickly dissipate when we open the main doors to move stuff about, so the risk is almost non existent. I'm quite happy to put a sensor in there anyway, so that's not an issue, I just wondered if anyone else had considered this before or had any issues with Carbon Dioxide emissions in a kiln? 

[Gary Prentice]

No kiln knowledge or experience, but I'd be surprised if kiln drying releases significant volumes of CO2. Someone will probably be along to explain why I'm wrong, but as it's the moisture content of the wood that is being changed, the wood isn't being chemically altered by decomposition or burning etc, then where is the carbon coming from? 

[openspaceman]

7 hours ago, Chalgravesteve said:

OK, in the course of a visit from the local water authority, checking on our mains connections and backflow valves to the boiler, the commercial plumber I'm dealing with has suggested that drying wood using hot air through a kiln will warm the wood and it will release Carbon Dioxide in the same way that it would when its burnt in a stove. This seems a reasonable hypothesis.

 

As Gary says there are not likely to be high levels of CO2 and there will be oxygen present so asphyxiation is unlikely  even in a recirculating kiln with no fresh air entering.

 

In sealed ship's holds there have been cases of the air being used up by microbes living off the wood and even with extremely dry wood in pellets lethal levels of  carbon monoxide have built up where the volatile organic compounds have only partially oxidised.

 

The other case where  people have been asphyxiated is in sealed grain stores and possibly silage towers where all the oxygen has been used up by the respiration of the grain or microbes eating the silage.

 

CO detectors are cheap enough if you are worried.

[Rough Hewn]

Unless the wood is heated to a reactionary temperature, no CO2 will be released. Drying = removal of water below 100c.
Vacuum kilns aside.
To extract CO2 and other volatile gasses you have to heat to at least 250-300+oC.
Co2 is nasty stuff, 2percent is dangerous but carbon monoxide is worse.
Above 1 percent CO is very toxic by 10% it's nearly lethal.
But same in regards to heating it to extract gasses.
How hot is your kiln?
[emoji106]

[Paul in the woods]

If you search there's reports of deaths due to CO being given off by wood pellets at room temperature*, so I wouldn't be confident CO2 wouldn't be given off in a kiln.

 

*this was the first thing I came across: https://academic.oup.com/annweh/article/56/7/755/172902

 

 

[openspaceman]

2 hours ago, Rough Hewn said:

To extract CO2 and other volatile gasses you have to heat to at least 250-300+oC.
Co2 is nasty stuff, 2percent is dangerous but carbon monoxide is worse.
Above 1 percent CO is very toxic by 10% it's nearly lethal.
But same in regards to heating it to extract gasses.
How hot is your kiln?

We seem to be having differences today Saul.

 

CO2 can be given off from a number of pathways but it's not toxic unless it has displaced all the oxygen.

 

CO is lethal at 0.3% within 30 minutes as it binds up all the haemoglobiin in the red blood cells.

[Rough Hewn]

If you search there's reports of deaths due to CO being given off by wood pellets at room temperature*, so I wouldn't be confident CO2 wouldn't be given off in a kiln.
 
*this was the first thing I came across: https://academic.oup.com/annweh/article/56/7/755/172902
 
 

That's scary.
Why are pellets doing that?
When log cabins don't?

[Rough Hewn]

We seem to be having differences today Saul.
 
CO2 can be given off from a number of pathways but it's not toxic unless it has displaced all the oxygen.
 
CO is lethal at 0.3% within 30 minutes as it binds up all the haemoglobiin in the red blood cells.

Everyday is a school day [emoji3]
but if that article is to be believed, should I build a wooden shed? Or just not fill it with pellets?
[emoji848]

[openspaceman]

28 minutes ago, Rough Hewn said:

That's scary.
Why are pellets doing that?
When log cabins don't?

As I said wood gives off volatile organic compounds, they give it its smell, these compounds react with oxygen to break down and one of the products is CO, CO2 is also formed but as it is not toxic its not a problem. Pellets are made with fresh wood, this gives off more VOCs than aged wood, they also have a very large surface area and their dust makes more, so  there's lots of substrates for reactions to take place. It's likely these VOCs and other volatile solids that the microbes eat and make a woodchip pile hot, after a while the heap cools down and in the same way over time the pellets would stop producing CO.

 

It came as a frightening revelation to me as a firm I snagged boilers for fitted a pellet store which contained 20tonnes in a 2 storey room above the boiler, Above that was the control room and buffer tanks. The manhole above the pellets was not sealed and potentially I was exposed to CO when I was working in the control room. I was only there a few hours but worse was that the control room opened out onto a landing with 3 flats.

 

This was a prestigious development opened by the London Mayor but like many green initiatives it went tits up after 5 years (long story) and the pellet boiler was ripped out and gas combis installed in the twelve flats.

[Chalgravesteve]

Like everyone else, I hadn't really given it any thought. Clearly, with pellets, there is a substantial surface area exposed, whereas with logs, its tiny by comparison. The build up of CO also requires an airtight room, where the kiln is venting air all the time.

 

There appear to be absolutely no instances reported where logs are involved, its entirely based around pellets and their storage and the heat that they are stored at. 

 

Just for my own peace of mind, I'll be putting a sensor in there, just to see if it kicks off or not.