[Stoves] Understanding TLUDs, MPF and more. (was Re: Bangladesh TLUD )

Thu Dec 14 13:47:03 CST 2017

Dear Frank

Your mention of the rapid heating affecting the result is mentioned in one of the papers I referenced. There is a difference in what happens and you have confirmed it.

If the biomass is heated rapidly through 360, let's say from outside through the wall of a steel tube, then the release of heat will en enough to cause thermal runaway until all the biomass is processed, say at 390 C.

Your description of the experiment is exactly what will demonstrate what the TGA analysis did: that the temperature inside the pipe will rise above the temperature in the oven.

As you said, this can only happen if there is heat generated by a process inside. That necessarily involves re-ordering the chemistry.

At different temperatures different things happen‎. Note the spike at 800 C on one chart. That is a big energy release so something is being converted to something else.

It is also interesting that there is a significant absorption of energy by the biomass at 320. I have never heard of that phenomenon before. Food absorbs quite a bit of energy when cooked, usually between 85 and 105 C. Just right for boiling water. How convenient.

Crispin

Andrew,

A pipe filled with sand, purged with N2 and temperature probe placed inside  and placed in a furnace,- the temperature should lag behind the oven temperature as the heat slowly goes into the pipe. The temperature of biomass inside the pipe should also lag behind  unless heat is produced inside from the biomass. I will not be permitted to drill two holes through the furnace wall to test this out. But I think the experiment would show if Oxygen in the biomass structure already reacted with surrounded C and H would free up and increase heat as a secondary 'structure shift'(?) occurs.

When charring biomass at increasing temperatures (450c to 900c in 50deg increments) it needs to be done very slowly or fire happens and a run-a-way temperature ruining the experiment. The char produced is used to plot Activity to find the optimum temperature for highest activity char. This heated slowly to allow the gases to escape and dilute below concentrations supporting combustion.

I don't have equipment for gas analysis. The lab I now work in is very small using cheap equipment. It can do all I would want for biomass testing (Box-1) and a lab like it could be set up anywhere.

Regards

Frank

On 12/14/17 8:28 AM, Andrew Heggie wrote:

On 13 December 2017 at 05:43, Frank Shields <franke at cruzio.com<mailto:franke at cruzio.com>> wrote:

This is an interesting topic and one i have wondered about. When packing hard a pipe with biomass then flushing with N2 then placing in an oven to heat from the outside to a temperature to 550c a lot of gases come out the small hole at the end.  That will ignite if the door is opened and O2 contact. I have wondered if any heat is being produced in the pipe itself? or all from external heat? If there is it can't be much because the temperature advances at a continuous rate. Should you see the temperature jump well above 550c its because air leaked in to the furnace and there is a flame.

Frank it is interesting  what you seem to be showing when opening the door is that the pyrolysis offgas coming out of the hole is above its auotignition point.  What would be relevant to the current discussion is :
1 the temperature variation inside the tube

2 the varying analysis of the composition of offgas as the tube heats up.

Andrew

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