[Gasification] raising H2 concentration in downdraft gasification

Thomas Reed tombreed2010 at gmail.com
Mon Dec 23 21:18:10 CST 2013


Dear Rex

By hydrogenating biodiesel 

C17H35COOH. (DH = (18x420 + 36x120 - 36) = 11,824 kJ/mole    11,844

To C18H38 (DH = (18x420+38x120) = 12,120

 2.3% higher.  
<><><>
You only increase the energy content by 2.3%!  

I'll bet the burning  velocity drops because the straight hydrocarbon is more difficult to burn than the oxygenated compound.  (Eg, alcohols vs their corresponding paraffins).  

The solubility for varnishes etc. drops, so that hydrogenating could be a negative in a dirty system, or a positive in a clean system because it will stay clean.  

<><><>

I made and burned a lot of biodiesel in tests in the early 1990s at the Colorado School of Mines, CSM.  

No problems in city buses.

Yours truly

Tom Reed

Thomas B Reed 
280 Hardwick Rd
Barre, Ma 01005
508-353-7841

> On Dec 22, 2013, at 1:26 AM, "Rex Zietsman" <rex at whitfieldfarm.co.za> wrote:
> 
> Dear Tom and the List,
> 
> Happy holidays to all and merry Christmas for the 25th. 
> 
> Believe it or not, but we are going via liquefaction and catalytic cracking
> aided by in situ hydrotreating and deoxygenation of long chain hydrocarbon
> molecules all in one reactor. We produce a decent deoxygenated oil, not
> pyrolysis oil. Low yield - only about 250 litres/ton of 15% MC biomass. When
> tested via the ASTM tests for diesel, it has a longer tail at both high and
> low boilers - easily fixed with fractionation. But, if the starting
> feedstock contains sulphur, the residual sulphur is about 10% of the
> incoming. This can be as high as 500ppm in the oil which is fine for
> "standard" diesel. To make ultralow sulphur diesel we have to hydrotreat.
> Hence the hydrogen requirement. 
> 
> In one of our projects, we have waste vegetable oil at a good price. The
> idea is to deoxygenate this oil to produce a diesel similar to that from
> crude oil. Here the hydrogen requirement is high in the range of 30kg/ton.
> As it is still relatively small ie 1200 litres/hour, we need 30kg/hour of
> H2. Hence the post.
> 
> All the best
> Rex 
> 
> -----Original Message-----
> From: Thomas Reed [mailto:tombreed2010 at gmail.com] 
> Sent: 21 December 2013 12:07 AM
> To: Discussion of biomass pyrolysis and gasification
> Cc: <gasification at lists.bioenergylists.org>; John M. Bradley; Chuck
> Stevenson
> Subject: Re: [Gasification] raising H2 concentration in downdraft
> gasification
> 
> Dear Rex and All; 
> 
> Merry Xmas and happy synthesizing.  
> 
> Rex must be a chemical engineer because he has outlined the problem nicely
> below.
> 
> A partial solution is reaction of only the 80% cellulose in the wood to make
> a synthesis gas:  
> 
> C6H10O5 + 1/2 O2 ===> 6 CO + 5 H2 
> 
> And leaving the 20% lignin behind as charcoal (Biochar) for soil enrichment
> and atmospheric CO2 reduction.  
> 
> Reaction of part of the CO with water reduces the unbalance to an excellent
> synthesis gas:
> 
> 6 CO + 5 H2 + 3 H2O ===> 3 CO + 8 H2. ||   ==> 3CH2 (oil)  + 3 H2
> 
> Leaving enough excess H2 to drive the reaction forward.  Toplit Updraft
> gasification consumes the cellulose , leaving the lignin as Biochar.
> 
> <><><>
> 
> I am an expert in molecular sieves, and have made a quantity of a Fischer
> Tropsch catalyst with one isolated Fe atom per unit cell.  Should make a low
> MW diesel.  
> 
> <><><>
> 
> If anyone has the means, and would like to pursue this, contact me privately
> with an offer.  
> 
> Tom Reed
> 
> Dr. Thomas B Reed
> 280 Hardwick Rd
> Barre, Ma 01005
> 508-353-7841
> 
>> On Dec 16, 2013, at 2:56 AM, "Rex Zietsman" <rex at whitfieldfarm.co.za>
> wrote:
>> 
>> Hi All,
>> 
>> We are looking at a system that will hydrotreat bio oils from 
>> pyrolysis, catalytic cracking and vegetable oil. For this we need in 
>> the region of 30kg hydrogen/ton oil. At small scale ie 1 ton oil/hour, 
>> this works out at, you guessed it, 30kg of hydrogen/hour. As this is a 
>> small amount in the overall scheme of things, we are looking at 
>> gasifying wood chips and to recover the hydrogen using pressure swing 
>> absorption. What I would like to know is whether we can increase the 
>> H2 concentration in syngas by tweaking the gasifier. Clearly we can 
>> look at the water gas shift reaction but, as the syngas has to be 
>> cooled, washed, pressurised and reheated, it is quite an additional 
>> investment for the scale we are looking at. If we could simply up the 
>> H2 content, we would go straight from washing to PSA. Residual gas 
>> would be piped to a diesel generator where CO and the like will be
> combusted prior to exhaust to atmosphere.
>> 
>> For easy mental arithmetic, let us assume a 33% H2 concentration in 
>> dry syngas. 30kg/hour of H2 is 15kmol/hour or 15/0.33 = 45kmol/hour of 
>> syngas. A kmol of gas has a volume of 22.4 Nm3. So, to get 30kg/hour 
>> requires 22.4 x
>> 45 = 1000 Nm3 syngas/hour (mental arithmetic here, go with the flow).
>> Assuming an 80% PSA recovery this means that we need 1250Nm3/hour of
> syngas.
>> Not a bad sized downdraft gasifier! Assuming 6MJ/Nm3, this is around a 
>> 2MW thermal unit. If we can get the H2 concentration up to say 40%, 
>> then the syngas requirement would be 37.5kmol/hour or 37.5/45 x 1250 = 
>> roughly 80% of
>> 1250 or roughly 1000 Nm3 syngas/hour. This reduces the size of 
>> gasifier to 1.6MW thermal and more sensible in size.
>> 
>> 
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> 
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