[Stoves] the 150 gasifier in operation in Vietnam
Kevin
kchisholm at ca.inter.net
Tue Mar 6 09:39:39 CST 2012
Dear Paul
----- Original Message -----
From: Paul Olivier
To: Discussion of biomass cooking stoves
Sent: Tuesday, March 06, 2012 4:09 AM
Subject: Re: [Stoves] the 150 gasifier in operation in Vietnam
Kevin,
I understand what you mean by an oxidizing atmosphere.
# Note also that while "pure air" is clearly oxidizing, a mixture of "air + combustibles" is also oxidizing. Additionally, pure CO2, with or without water vapor, as a product of combustion, with no excess air, can also be oxidizing, depending on temperature and the metals involved.
I do not know what quality of stainless steel is used in the strainer that I have been using.
But it is definitely stainless steel, and it lasted three runs.
I would assume that stainless steel is better than mild steel.
Would you agree?
# I just don't know. It is not at all a simple issue. In point of fact, most non-iron ingredients in stainless steel are actually more reactive and "corrodible" or "oxidizable" than the iron content of the SS. SS relies on the stability of an oxidized film for its durability. If "operatijng conditions" are such that a stable oxide film forms, then you will get great life. However, if localized combustion conditions are such that the oxide film is attacked, or is prevented from forming, then there is probably little to no benefit from using SS.
Ordinary grades of stainless steel becomes brittle when subjected to this kind of heat.
446 stainless steel might have a chance.
# Again, it is more than heat... for example, in addition to the possibility of oxygen attack, there may also be the possibility of "alkali attack", where the Na and K oxides, that may be fumed off from the ash, attack the oxide coating on the SS.
Silicon carbide cloth is much cheaper than stainless steel,
and it is far more resistant to heat than stainless steel.
# Again, while simple temperature resistance is probably a very much reduced concern with SiC cloth, it also may be subject to other conditions that may cause it to fail easier. Given that it is cheap, many questions can be answered at low cost with a test run.
But I am not sure at what temperatures it emits the most thermal radiation.
# This is a really interesting issue or subject. Very complex also. :-) There are two issues here: 1: The emissivity of teh material, and 2: its temperature. With a surface of a given emissivity, the radiant heat transfer will inrease with the difference between 4th powers of the absolute temperatures of the hot and cold surfaces. Emissivities can vary greatly, say from .03 (for polished metals) to about .90 to .95 (for most materials with a dull surface.)
# Note that Dr. Tom Reed is a wizard at high temperature measurement, among other things. If he could tell us how to do reliable and accurate high temperature measurements, we should be able to readily determine the actual emissivity, simply by using a radiation pyrometer, and noting teh error between "True Temperature" and "Radiation Pyrometer Temperature." SImply turn "the knob on the pyrometer" to the emissivity position that gives the right reading, and then you know the actual emissivity.
Best wishes,
Kevin
Paul
On Tue, Mar 6, 2012 at 1:23 PM, Kevin <kchisholm at ca.inter.net> wrote:
Dear Paul
----- Original Message -----
From: Paul Olivier
To: Discussion of biomass cooking stoves
Sent: Tuesday, March 06, 2012 1:00 AM
Subject: Re: [Stoves] the 150 gasifier in operation in Vietnam
Kevin,
I do not think that normal mild steel wire mesh would make it through a single gasifier run.
# Certainly, "red hot mild steel" in an oxidizing air atmosphere will scale up and fail quickly. However, you don't have that.... you have a combustion zone atmosphere. It is very simple and cheap[ to try. Try it, and let the screen itself tell you that it needs to be of higher quality.
I'm afraid that it has to be something "exotic".
# Let the system prove to you that it needs to be exotic. :-)
This wire mesh really gets hot.
# "Hot" is one thing, but "oxdizing atmosphere" is another. If the atmosphere the screen "sees" is "adequately reducing", then mild steel might be an economically good solution. On the other hand, as the atmosphere becomes increasingly oxidizing, then the more exotic materials are required.
Someone measured the temperature about 4 inches above the dome.
When the probe reached 500 C, he stopped.
# A material that would fail in air at 500 C might be quite acceptable in a reducing atmosphere at 500 C
# The problem is one of Temperature AND Atmosphere. You could probably reduce costs safely, with a test program that confirmed the minimum quality screen material that would do an acceptable job.
Best wishes,
Kevin
Thanks.
Paul
On Tue, Mar 6, 2012 at 11:39 AM, Kevin <kchisholm at ca.inter.net> wrote:
Dear Paul
Why not start with simple mild steel screen, of various sizes, and test them to see how long they last?
Exotic materials will probably last longer, but at a very much higher cost.
Once you have cost and "lifetime" information, then you can make the best decision about what materials to use.
Best wishes,
Kevin
----- Original Message -----
From: Paul Olivier
To: Discussion of biomass cooking stoves
Sent: Tuesday, March 06, 2012 12:12 AM
Subject: Re: [Stoves] the 150 gasifier in operation in Vietnam
446 stainless can handle temperatures as high as 1,200 C.
Silicon carbide is quite cheap, and it can handle temperatures as high as 1,650 C.
http://accuratus.com/silicar.html
Thanks.
Paul
On Tue, Mar 6, 2012 at 11:02 AM, Anand Karve <adkarve at gmail.com> wrote:
Dear Paul,
I have not worked with that grade of stainless steel and also not worked with silicon carbide mesh.
Yours
A.D.Karve
On Tue, Mar 6, 2012 at 11:58 AM, Paul Olivier <paul.olivier at esrla.com> wrote:
A.D.,
I am looking for a 446 stainless steel wire mesh.
Have you ever worked with silicon carbide mesh?
It is used as an emitter in thermophotovoltaics.
Paul
On Tue, Mar 6, 2012 at 10:54 AM, Anand Karve <adkarve at gmail.com> wrote:
Dear Paul,
even stainless steel is no good. At high temperature, it corrodes and crumbles into pieces.
Yours
A.D.Karve
On Mon, Mar 5, 2012 at 4:03 PM, Steve Taylor <steve at thetaylorfamily.org.uk> wrote:
On 5 March 2012 02:56, Paul Olivier <paul.olivier at esrla.com> wrote:
I know that a tungsten wire mesh exists.
But no doubt this would be too expensive.
Tungsten will oxidise to nothing very quickly. Probably Incoloy would be ideal
Steve
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Paul A. Olivier PhD
27C Pham Hong Thai Street
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Mobile: 090-694-1573 (in Vietnam)
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Paul A. Olivier PhD
27C Pham Hong Thai Street
Dalat
Vietnam
Louisiana telephone: 1-337-447-4124 (rings Vietnam)
Mobile: 090-694-1573 (in Vietnam)
Skype address: Xpolivier
http://www.esrla.com/
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Paul A. Olivier PhD
27C Pham Hong Thai Street
Dalat
Vietnam
Louisiana telephone: 1-337-447-4124 (rings Vietnam)
Mobile: 090-694-1573 (in Vietnam)
Skype address: Xpolivier
http://www.esrla.com/
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Paul A. Olivier PhD
27C Pham Hong Thai Street
Dalat
Vietnam
Louisiana telephone: 1-337-447-4124 (rings Vietnam)
Mobile: 090-694-1573 (in Vietnam)
Skype address: Xpolivier
http://www.esrla.com/
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