[Stoves] Stove gas testing
frank
frank at compostlab.com
Fri Sep 14 20:19:45 EDT 2007
Thanks for this info.
The semiconductor I am using is made of a coating of tin dioxide SnO2
. It is very sensitive down to less than 1uL CH4 when injected into my
10 ml cell.
Another thing I found out that could be very important to our group is
that these SnO2 semesters -need- oxygen and the sensitivity is oxygen
dependent. A change in O2 = a change in sensitivity to CH4, CO and H
readings. So the oxygen concentration in the gas must be present and
constant. Perhaps when pulling air from the stack (that may have no O2)
we should mix in a stream of oxygen (air). That I noticed was being done
at Stove Camp.
Perhaps the LaCoO3 will show promise in the future for cheap equipment
to read methane.
Frank
B.C. Romero Orellana wrote:
>
> Maybe it can help....
>
> *Sensors and Actuators B: Chemical*
> <http://www.sciencedirect.com/science/journal/09254005>
> Volume 57, Issues 1-3
> <http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235283%231999%23999429998%23152811%23FLA%23&_cdi=5283&_pubType=J&view=c&_auth=y&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=048249f3f76392877ae8d2b325845176>,
> 7 September 1999, Pages 108-114
>
> Abstract
>
> Technology associated with both catalytic and semiconductor-based gas
> sensors has been combined to produce hybrid devices capable of
> detecting low levels of combustible gases. First-generation
> non-selective sensors, which respond to a wide range of reducing gases
> including hydrogen, carbon monoxide, lower hydrocarbons and ethanol
> vapour, were obtained by coating narrow diameter platinum wire coils
> with a low resistivity tin dioxide-based formulation. As in the case
> of catalytic sensors, /semi/conductor-based pelli/stors/ (semistors)
> are typically operated in a bridge-type circuit. However, in contrast
> to catalytic sensors, which are used to detect percentage levels of
> combustible gases, semistors are responsive to sub-100 ppm
> concentrations. Optimisation experiments have been carried out on
> factors affecting performance, such as sensing layer composition, coil
> pitch and firing time. A further study on the effects of incorporating
> an additional catalyst-containing surface filter layer has led to the
> development of a second-generation methane-selective sensor.
> Undesirable humidity and ambient temperature effects, normally
> associated with tin dioxide-based sensors, can be eradicated by
> operating a semistor in conjunction with a compensating element. This
> utilises a filter layer, which removes all target gas response while
> retaining the same humidity and temperature dependence as the sensor
>
>
> *Sensors and Actuators B: Chemical*
> <http://www.sciencedirect.com/science/journal/09254005>
> Volume 117, Issue 2
> <http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235283%232006%23998829997%23629515%23FLA%23&_cdi=5283&_pubType=J&view=c&_auth=y&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=1ab6e22437088cdd3f05be2f8f4fd33d>,
> 12 October 2006, Pages 420-425
> Transducers '05 - Selected Papers from TRANSDUCERS '05. The 13th
> International Conference on Solid-State Sensors, Actuators and
> Microsystems
>
> In the present study, LaCoO_3 perovskite was used as an active filter
> to suppress the sensitivity of a Pt/SnO_2 sensor to CO and C_2 H_5 OH.
> A sol–gel procedure was used for the preparation of SnO _2 fine
> powder, which was impregnated with hexachloroplatinic acid to obtain
> 1.0 wt% Pt on SnO_2 . The LaCoO_3 perovskite fine powder was prepared
> by citrate method, using nitrate precursors of La and Co. LaCoO _3 is
> an effective oxidation catalyst for oxidation of both carbon monoxide
> and ethanol at temperatures lower than 250 °C. However, the catalyst
> does not convert methane at temperatures as high as 400 °C. The Pt/SnO
> _2 is highly sensitive to ethanol and shows a significant sensitivity
> to CO. The perovskite filter eliminates the sensitivity of the sensor
> to CO and C_2 H_5 OH, making the sensor highly selective to methane in
> the presence of CO and ethanol in air.
>
>
>
> On 9/14/07, *frank* <frank at compostlab.com
> <mailto:frank at compostlab.com>> wrote:
>
> Stovers,
>
> FYI
> I purchased both a CO, CH4 detector planned for measuring the
> pyrolysis
> gases from the primary combustion in a TLUD (along with CO2, and O2).
> After about a thousand dollar of equipment and set up equipment (and
> hours of work) I discovered the CO, CH4 and H2 detectors are all the
> same with, perhaps the difference being the temperature the detector
> chamber goes to. I had them assembled in a series and when I injected
> CH4 both the CO and CH4 indicated a reading. Injecting the CO
> and both
> gave a reading. So there is no way I know of when using these type
> detectors to make specific gas readings. I do not have a H
> detector but
> found out that it is also same detector so cannot be used. The
> only ones
> that seem to work well is the CO2 and O2 detectors. Using any one
> of the
> others to measure a mix of CO, CH4 and H.
>
> Not sure yet but I think the FT-IR is the way to go ???? but
> that is
> way out of my R&D budget range.
>
> Anyone have any other suggestions?
>
> Thanks
> Frank
>
>
>
>
>
>
> --
> Frank Shields
> Soil Control Lab
> 42 Hangar way
> Watsonville, CA 95076
> (831) 724-5422 tel
> (831) 724-3188 fax
> frank at compostlab.com <mailto:frank at compostlab.com>
> www.compostlab.com <http://www.compostlab.com>
>
>
>
>
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>
> --
> Carolina Romero
--
Frank Shields
Soil Control Lab
42 Hangar way
Watsonville, CA 95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at compostlab.com
www.compostlab.com
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