[Gasification] Why is nitrogen dilution bad?

Sun Jan 28 23:47:30 CST 2007

Jonathon,

>> The retort will produce a gas free of nitrogen and will mainly be a mix
>> of
>> methane, H2 and CO and a bunch of other hydrocarbons in small
>> percentages.

According to http://www.woodgas.com/gasification.htm:

"Producer Gas" made with air:       (CO 22%; H2 18%; CH4 3%, CO2 6% and N2
51%).
"Synthesis Gas" made with O2:    (CO 40%,  H2 40%, CH4 3% and CO2 17%)

Meanwhile the UN FAO gives the following analysis for "Retort Gas":

"Retort Gas"  (CO 23%, H2 2%, CH4 17%, CO2 38%, O2 2%, N2 18%)

See
http://www.fao.org/docrep/X5555E/x5555e07.htm#6.10%20using%20retort%20or%20converter%20gas

The problem with retort gas is the hydrogen deficiency for the methanol
synthesis reaction:  CO + 2H2 ---> CH3OH.

Using straight retort gas I doubt one would improve on the 'natural'
methanol yield of 2% from destructive distillation.  The hydrogen balance
needs improving by some means, whether Steam Methane Reformation, water gas
shift or both.  A regular gasifier will yield a better balanced CO-H2 gas
and be easier to build.

>>The Riche style retort is essentially a long
>> vertical tube heated from the bottom,

This retort I built accomplishes everything a Riche gas producer does, but
without the firebrick masonry flue of the stock Riche, and with far less
fuel consumption:

http://gasifiers.bioenergylists.org/?q=gallmeierretort

>>the gasses generated in the retort
>> pass through the glowing char formed at the bottom and to some extent
>> breaktown the tars and other constituents in the raw pyrolysis gas.

Even the higher temperatures obtainable in a retort won't do much tar
cracking.

Mark

> ----- Original Message ----- 
> From: "Jonathan F. Pratt" <jonpratt76 at hotmail.com>
> To: <gasification at listserv.repp.org>
> Sent: Sunday, January 28, 2007 11:30 PM
> Subject: [Gasification] Why is nitrogen dilution bad?
>
>
>> Jim,
>>
>> For the simplest type of "Producer Gas to Synfuels" setup, your probably
>> best attempting some kind of retort with good scrubbing and filtration
>> and
>> the most common iron catalysts used in the big fischer-tropsch plants.
>> You
>> could start with pure fine rust or iron oxide fines.
>>
>> The retort will produce a gas free of nitrogen and will mainly be a mix
>> of
>> methane, H2 and CO and a bunch of other hydrocarbons in small
>> percentages.
>>
>> Some of the literature from the late 40's didn't mention using retorts
>> for
>> the raw syn gas but did mention acheiving very good yields of
>> hydrocarbons
>> in the range suitable for producting synthetic gasoline in the lab by
>> using
>> a 1 inch vertical column "iron pipe" filled with iron oxide spaced at 8
>> cm
>> intervals or so with small screens to enable the fluidization of the iron
>> oxide as the gas was injected from the bottom under pressure of 10-25
>> atmospheres if memory serves me correctly.  temperature of the column was
>> maintained around 300C
>>
>> Good first pass throughput and temperature stability was attained using
>> this
>> setup which is a small scale "fluidized bed reactor".  The output is
>> mainly
>> hydrocarbon vapors that is condensed.  Raw biomass may produce a higher
>> CO
>> to H2 ratio than is optimal, but the yield should still be pretty good
>>
>> Generally a retort will produce a lot of tar and nasty constituents that
>> would probably plug up the catalyst however if you use a "Riche" type
>> retort
>> and very good filtration this might actually work for a small scale
>> biomass-synfuel setup.  The Riche style retort is essentially a long
>> vertical tube heated from the bottom, the gasses generated in the retort
>> pass through the glowing char formed at the bottom and to some extent
>> breaktown the tars and other constituents in the raw pyrolysis gas.
>> Filter
>> the gas through a cyclone and sawdust filter and run it through a
>> compressor
>> (optional) then through the "fluidized bed" of iron oxide.  Just make
>> sure
>> you have a pressure release valve on the retort!
>>
>> Jonathan
>>
>>>
>>> Message: 8
>>> Date: Sun, 28 Jan 2007 02:45:40 -0800
>>> From: "jim mason" <jimmason at whatiamupto.com>
>>> Subject: [Gasification] why do liquifaction proceses require
>>> nitrogen-less synthesis gas?
>>> To: gasification at listserv.repp.org
>>> Message-ID:
>>> <31a4f6f00701280245t3134f70fpb1f0c2218e2756ea at mail.gmail.com>
>>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>>
>>> i'm reviewing the literature on methanol and fischer-tropsch based
>>> liquifaction processes, with an interest in seeing if any of these are
>>> realistic to consider as DIY sorts of efforts.
>>>
>>> despite lots of details on catalysts and temp and pressure, i can't
>>> seem to answer a very basic question: why is the nitrogen such a
>>> problem in these processes?
>>>
>>> all the processes assume starting with a synthesis gas that is only CO
>>> and H2.  no tars and co2 is scrubbed out.  so usually you start with
>>> an oxygen blown gasifier, or a external combustor dual FLB sort of
>>> system, so that the produced gas is without nitrogen.  which is lots
>>> of work, obviously.
>>>
>>> is the problem that the nitrogen will tend to reform to ammonia (NH3)
>>> in the presence of cataylsts under temp and pressure.  or will it form
>>> NoX and poison the various catalysts?  or is there another problem?
>>>
>>> can someone here clarify this for me?
>>>
>>> j
>>>
>>
>>
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