Date:         Wed, 17 Jul 2002 17:03:31 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Running on Tap Water (was Re: Attention California
              Vanagonites)
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At 01:23 PM 7/17/2002, Harmon Seaver wrote:
>    There is none. There must be a vacuum on the engine end to suck the
> air into
>the pyrolysis area of the gasifier.

Ah!  So simple!

>  Turn off the engine, the gasifier goes out
>and must be relit before you start off again. The gasifier is quite
>self-regulating in that respect -- when the engine demands more gas, it
>has more
>vacuum, thus the gasifier creates more gas, let off the throttle, it stops
>producing. There's always an "overlap", of course, but the gasifier body is
>fairly large compared to the actual burn area so can hold a good bit of gas.

So there's a check valve on the air inlet to prevent it burping back?  And
how do you establish air flow to light the device before the engine is
running?  What happens to those startup gases?

> >
> > And how do folks deal with the rather astounding toxicity of the stuff?
>
>    It's not that bad, no worse than natural gas, for instance.

Here I have to Disagree Very Strongly.  Natural Gas is essentially
non-toxic -- it's almost entirely methane CH4 (non-toxic) and ethane C2H6
(practically non-toxic).  It will asphyxiate you if you breathe enough of
it, just like nitrogen, helium etc.   While CO on the other hand is the
reason people used to stick their heads in the oven to commit suicide --
that was producer gas...

0.08% concentration will possibly knock you out it two hours;
0.16% WILL knock you out and may kill you in two hours;
0.32% will knock you out and may kill you in half an hour;
0.64% will knock you out and may kill you in 10-15 minutes;
0.128% will knock you out and may kill you in 1-3 minutes.
ANY of those concentrations will eventually kill you dead, dead,
dead.  Hemoglobin has an affinity for CO roughly ten times its affinity for
O2, and the CO will be preferentially taken up by your hemoglobin until
there isn't enough left to support your personal combustion, and you
die.  The warning curves for CO detectors in the US are set to allow about
ten per cent of your hemoglobin to have already taken up CO before they
issue an alarm.
3% natural gas won't bother you in the slightest -- it won't even burn.  It
takes almost 4% concentration before it will burn.

Here's fao.org on the subject:
>Fortunately normal producer gas installations work under suction, so that
>even if a minor leak in the installation occurs, no dangerous gases will
>escape from the equipment during actual operation. The situation is
>different however during starting-up and closing down of the installation.
>
>During starting-up the gas is generally vented, and it is necessary to
>ensure that the gases produced cannot be trapped in an enclosed room. As a
>rule a suitable chimney will provide sufficient safety.
>
>During closing-down of the installation a pressure buildup in the gasifier
>will occur, caused by the still hot and pyrolysing fuel. As a result gases
>containing carbon monoxide will be released from the installation during a
>relatively short period. It is because of the danger from those gases that
>it is generally recommended that a gasified installation be located in the
>open air, if necessary covered by a roof.


*NOTE* that they don't even contemplate deliberately pressurizing the stuff...



>It's just that it
>doesn't have stinky stuff added to warn you, like natural gas or propane
>does. When dealing with any gaseous fuel you have to take precautions, of
>course, make sure there are no leaks, etc. A carbon monoxide monitor is cheap
>and effective.

However those monitors are meant to monitor byproducts of normal
combustion, with expected space concentrations in the neighborhood of
0.01-0.05%.  They really don't contemplate a leak in a pressurized system
venting 20% CO into the space.  ISTM that for a system using this gas under
pressure as you describe, a different class of monitors are necessary, with
greatly expanded range and a graduated series of warning including  one
that sets off an air-raid siren and a recording of George Thorogood singing
"Run Like Hell"

>    And have you ever looked at the dangers of gasoline? The military makes
>horrific bombs out of gasoline.

Er...straw man...though I grant you that the extremely low caloric content
and flame temperature of producer gas don't lend it to military
applications. <g>

>  Not to mention the serious dangers of just
>getting it on your skin.

You could take a bath in the stuff and aside from stinging your naughty
bits not come to any great immediate harm.  If you kept on doing it no
doubt there would be serious consequences down the road.  Gasoline vapor is
an anesthetic -- if you took a lungful of straight vapor it would make you
woozy, and if you did *that* very often it would certainly make you very
sick.  But a lungful of straight producer gas would quite possibly kill you
stone dead on the spot.

I think you need to re-evaluate the order of magnitude of the dangers
involved.  ISTM that these quotes from fao.org are useful and interesting:


>2.8.3 Explosion hazards
>
>Explosions can occur if the gas is mixed with sufficient air to form an
>explosive mixture.
>
>This could occur for several reasons:
>
>- air leakage into the gas system;
>- air penetration during refuelling;
>- air leakage into a cold gasifier still containing gas which subsequently
>ignites;
>- backfiring from the fan exhaust burner when the system is filled with a
>combustible mixture of air and gas during starting-up.
>
>Air leakage into the gas system does not generally give rise to
>explosions. If a leakage occurs in the lower part of the gasifier (as is
>generally the case) this will result in partial combustion of the gas
>leading to higher gas outlet temperatures and a lower gas quality.
>
>When the pyrolytic gases in the bunker section are mixed with air (as is
>bound to happen during refuelling) an explosive mixture can be formed. It
>is not unusual for this to result in small and relatively harmless
>explosions, especially when the fuel level in the bunker is relatively low.
>
>Risk to the operator can be obviated if the gases in the bunker section
>are burnt off through the introduction of a piece of burning paper or the
>like, immediately after opening the fuel lid. Another possibility is to
>install a double sluice type filling system.
>
>Air leakage into a cold gasifier and immediate ignition will lead to an
>explosion. Cold systems should always be carefully ventilated before
>igniting the fuel.
>
>During the start-up of an installation, the gases are as a rule not passed
>through the entire filter section, in order to avoid blocking the filters
>with the tars produced during start-up. The filter may thus still contain
>air, and after an inflammable gas is produced and led through the
>sometimes quite voluminous - filter section an explosive mixture can
>result. If the gas is now ignited at the fan outlet a backfire can occur,
>leading to a violent explosion in the filter section. It is fox this
>reason that it is advisable to fit the fan outlet with a water lock.

Note that the hazards peculiar to small-scale producer-gas systems are
primarily because the operator has to open the gas-filled bunker in order
to refuel, a frequent operation.



>1.4 What to expect from a wood gasifier system
>
>Operation of modern spark ignition or compression ignition stationary
>engines with gasoline or diesel fuel is generally characterized by high
>reliability and minor efforts from the operator. Under normal
>circumstances the operator's role is limited to refuelling and
>maintenance. There is little need for action and virtually no risk of
>getting dirty. Start and operation can in fact be made fully automatic.
>
>Anybody expecting something similar for wood gas operation of engines will
>be disappointed. Preparation of the system for starting can require half
>an hour or more. The fuel is bulky and difficult to handle. Frequent
>feeding of fuel is often required and this limits the time the engine can
>run unattended. Taking care of residues such as ashes, soot and tarry
>condensates is time-consuming and dirty.
>
>It is a common mistake to assume that any type of biomass which fits into
>the opening of the refuelling lid can be used as fuel. Many of the
>operational difficulties which face inexperienced users of gasifiers are
>caused by the use of unsuitable fuels. In order to avoid bridging in the
>fuel bunker, reduced power output because of large pressure losses, or
>"weak" gas, slag cakes, tar in the engine and damage to the gasifier
>caused by overheating, it is necessary for most designs that the fuel
>properties are kept within fairly narrow ranges. This is not necessarily a
>more serious limitation than the need to use gasoline of super grade for
>high compression spark ignition engines rather than regular gasoline or
>diesel fuel. But in the case of gasifier operation, more of the
>responsibility for quality control of the fuel rests with the operator.
>The need for strict fuel specifications is well documented in the
>experiences reported from the Second World War (43). It is unfortunate
>that some commercial companies, with little practical experience, but
>trying to profit from the renewed interest in gasification, have
>advertised the possibility of using almost any kind of biomass even in
>gasifiers which will work well only with fuels meeting fairly strict
>standards. This has in some cases created unrealistic expectations and has
>led to disappointments with the technology.
>
>Operation of wood gas engines can also be dangerous if the operator
>violates the safety rules or neglects the maintenance of the system.
>Poisoning accidents, explosions and fires have been caused by unsafe
>designs or careless handling of the equipment. It may be assumed that
>modern systems are designed according to the best safety standards, but it
>is still necessary to handle the equipment in a responsible manner.
>
>Finally, it must be realised that the current technology is generally
>based on the designs of the mid-1940's. Only a few persons have retained
>detailed practical knowledge of design, material selection and operation
>and maintenance procedures. Many of the currently active manufacturers
>have no access to the experience of such persons and base their designs on
>information available in the literature, and on recent and comparatively
>limited experience. There has been some improvement of the technology, for
>instance of filter designs based on new materials, but the practical
>operating experience with these improved systems is limited. A consequence
>of this is that equipment failures caused by design mistakes, choice of
>the wrong materials, or incomplete instructions to the user on operation
>and maintenance, must be expected in the first period of reintroduction of
>wood gasifiers.
>
>The reports on operational difficulties presented in this publication and
>elsewhere must be evaluated with this in mind. It can safely be assumed
>that second generation systems will show improved performance.
>
>Those interested in the technology must accept that it demands hard work
>and tolerance of soiled hands by a responsible operator, and that it is
>not yet perfect. But as will be shown, it is both serviceable and economic
>in many applications in spite of its inconveniences.


david


--
David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"