[Stoves] Gasifier without chopping the fuel into small pieces

Thu Jun 30 17:55:32 CDT 2022

Crispin, Ron, 

Saravanakumar is still active in research. This was an attempt to gasify
Prosopis without chipping it. I major Prosopis project in Kenya failed a few
years ago partly because they kept wearing out knives in their Finnish
chipper. It was designed as a cross draft gasifier which was intended to
produce gas. 

There have been various cross gas gasifiers including one developed here to
generate power from coffee husks. My favorite cross draft design was
developed by Foster Wheeler in Hartlepool, UK, in 1980 for gasifying tires.
It was called "Tyrolysis". The intent was to pyrolyze the tires and make a
heating oil product. It did not survive. Thermal conversion of tires is a
challenge in any direction. 

Tom 

From: Stoves <stoves-bounces at lists.bioenergylists.org> On Behalf Of Crispin
Pemberton-Pigott
Sent: Thursday, June 30, 2022 1:33 PM
To: Stoves <stoves at lists.bioenergylists.org>
Subject: Re: [Stoves] Gasifier without chopping the fuel into small pieces

Dear Ron

I thought it was a cross draft stove because the primary air enters
horizontally and the gases exit horizontally on the other side. 

I see an air channel going to the right and up. I doubt that is an essential
part of the combustion. When building a crossdraft stove it is necessary
either to blow air down from the top of the fuel, or to vent gases produced
in the fuel hopper. 

I haven't decided if Saravanakumar is trying to make and collect char, of it
he is focussed on getting a combustible gas as the main product. He is
certainly not trying to cook. 

I found his PhD thesis and his research is focussed on innovative combustion
processes. What I found unusual with this paper was the intention to get
good quality gas from chopped branches. 

The 10 KW power rate is not a surprise given the fuel size. It is hard to
get a small number of branches to easily easily. Making it bigger will
definitely make the result more predictable. 

It is nice to see that Tom Reed was a co-author. It must have been one of
his last journal articles. 

Regards 

Crispin 

From: rongretlarson at comcast.net <mailto:rongretlarson at comcast.net> 

Crispin and list: 

   Yes - an interesting paper.  New to me, although a few years old.

One could also describe this as a bottom lit updraft (BLUD) stove - which is
usually down played. as desirable.  And it has some relationships also to
Rockets.- which are similarly bottom lit

I doubt of much use to anyone working on family sized cook stoves - with its
rating around 10 kWth.  Users at that level won't mind the needed blower.  

This apparently does a good job in minimizing time spent tending the fire
(as does Kevin;'s and TLUDs).

What I found most interesting is better understanding the term "cross draft"
- which is inherent also in Kevin McLean's "Sun24".   But not TLUds using
chips or pellets or holey briquettes or ball-shaped fuel..   

 "Cross draft" here meaning horizontal - neither "up", nor down"".  But
there is clearly also updraft here along two of the four sides

The word "cross". meaning that pyrolysis of the central portion of the long
(60+ cm) fuel pieces occurs using hot O2 coming from each end of the gaps
between 3 (or 4) round horizontal cylindrical pieces of tree "trunks" (maybe
limbs).

Being close together it seems much easier for the O2 to get to the pyrolysis
region with inner inner horizontal air, not inner vertical air.

This is the situation also in Kevin's stove.  Big difference is that Kevin's
O2 starts moving radially in after flowing (pushed) downward, not being
pushed upward.

I have looked for and never found data on pressure differences at a
pyrolysis front.  This paper tells me that the pressure is lower at the
inside glowing-flaming pyrolysis front.  Complicated also by pyrolysis
occurring  with flames above and below logs and probably some flame motion
inward (or outward.

So it would seem that then air flow is fairly complicated where the
pyrolysis gases are exiting the horizontal tree trunks.  Hot gases are
exiting, but O2 also has to be entering.

I don't see this as helping make for cheaper cooking.  Certainly not for
making char (although a lot more could be made if desired I presume.)

TDR probably pretty good since there is a blower.

Anyone able to add to the air flow near the horizontally exiting pyrolysis
gases?   Both here and in Kevin's char-making stove?

Ron

On Jun 29, 2022, at 12:46 PM, Crispin Pemberton-Pigott
<crispinpigott at outlook.com <mailto:crispinpigott at outlook.com> > wrote:

Dear Friends

There is a paper by A. Saravanakumar, T.M. Haridasan, Thomas B. Reed which I
would like to bring to your attention.

A frequent complaint about gasifiers is that the fuel ahs to be chipped or
reduced to mall pieces.  This paper explores the gasification of stick wood
in a rather interesting manner.  It will not be of interest to everyone, but
is worth a look and has some solid theory and construction advice. 

It is called Flaming pyrolysis model of the fixed bed cross draft long-stick
wood gasifier.

You can see it (free) for research and discussion purposes at

<https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.acade
mia.edu%2F4295996%2FFlaming_pyrolysis_model_of_the_fixed_bed_cross_draft_lon
g_stick_wood_gasifier&data=05%7C01%7C%7C5097d47386b746b1ce9208da5acac250%7C8
4df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637922124136666827%7CUnknown%7CTWF
pbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%
7C3000%7C%7C%7C&sdata=BaB4F8ZhCVutsmOrfnWmmVGZtQN65E964CE1fIgKZh4%3D&reserve
d=0>
https://www.academia.edu/4295996/Flaming_pyrolysis_model_of_the_fixed_bed_cr
oss_draft_long_stick_wood_gasifier

Abstract:

The future industrial development of biomass energy depends on the
application of renewable energy

technology in an efficient manner. Of all the competing technologies under
biomass, gasifiers are considered

to be one of most viable applications. The use of biomass fuel, especially
biomass wastes, for distributed

power production can be economically viable in many parts of the world
through gasification of biomass.

Since biomass, is a clean and renewable fuel, gasification gives the
opportunity to convert biomass into clean

fuel gas or synthesis gas for industrial uses. The preparation of feedstock
for a gasifier requires time, energy

and labour and this has been a setback for gasifier technology development.
The present work is focused on

gasification of long-stick wood as a feed material for gasifiers. This
application makes reduction not only in

the cost but also on the power consumption of feed material preparation. A
50 m3/h capacity gasifier was

fabricated in the cross draft mode. The cross draft mode makes it possible
to produce low tar content in

producer gas. This cross draft mode operates with 180W of blower supply for
air to produce 10 kW of

thermal output. The initial bed heights of the long-stick wood and charcoal
are 58 cm and 48 cm respectively.

Results were obtained for various flow conditions with air flow rates
ranging from 20 to 30 m3/h. For modelling,

the flaming pyrolysis time for long-stick wood in the gasifier is calculated
to be 1.6 min. The length of the flaming

pyrolysis zone and char gasification zone is found to be 34 cm and 30 cm
respectively. The rate of feed was

between 9 and 10 kg/h. Continuous operation for 5 h was used for three runs
to study the performance. In this

study we measured the temperature and pressure in the different zones as a
function of airflow. We measured the

gas flow and efficiency of the gasifier in order to determine its commercial
potential for process and power

industries.

Regards

Crispin

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