GAS-L: Downdraft gasifier scalability

["Tom Reed" <tombreed@attbi.com>]

Dear Kollol and all:

 

Kollol said..

I completely agree with you about the DD gasifiers. Its the best proven and commercialised gasifier w.r.t gas quality, ease of operation etc.

However, I think its two major limitations are:-

1.0     It's unit capacity restriction - which means that one has to resort to multiple units operating in parallel when higher capacity is desired.

 

WE DEVELOPED THE "STRATIFIED DOWNDRAFT GASIFIER" (SDG) AT SERI/NREL FROM 1980-1988.  IT DOES NOT USE NOZZLES FOR THE PYROLYSIS PHASE, BUT HAS AN OPEN TOP AND BRINGS THE AIR UNIFORMLY TO THE FUEL.  THIS REMOVES SIZE LIMITATION.  THE LARGEST ONE BUILT WAS A 75 TON/DAY, 1.2 M ID UNIT BUILT BY SYN-GAS CORP. IN 1988.  IT WAS ALSO OPERATED ON PURE OXYGEN AND AT 10 ATMOSPHERES PRESSURE.

 

MORE THAN HALF OF THE DOWNDRAFT GASIFIERS NOW BEING BUILT USE THIS PRINCIPLE.  FOR INSTANCE, ALL THE GASIFIERS OF PROF. MUKUNDA AND TEAM IN BANGALORE USE THIS PRINCIPLE, AND SO DO THOSE BEING DEVELOPED AT THE COMMUNITY POWER CORPORATION (www.gocpc.com).

 

THE PRINCIPLES AND PRACTICE ARE DISCUSSED IN "FUNDAMENTALS, DEVELOPMENT AND SCALEUP OF THE AIR-OBYGEN STRATIFIED DOWNDRAFT GASIFIER" (REED, GRABOSKI, LEVI), AVAILABLE AT THE BEF PRESS (WWW.WOODGAS.COM).

 

(Anyone who can talk of a DD gasifier in operation of higher than 3.0 metre ID?)

 

A 9 M SDG GASIFIER WOULD REQUIRE RAKES TO GUARANTEE A UNIFORM BED DEPTH TO KEEP THE FLAME FRONT HORIZONTAL, BUT IT CAN PROBABLY BE DONE. 

 

2.0    It's limitation w.r.t feed size. Since, it cannot take feed of smaller size, it means, one has to resort to briquetting ! That is not only adding a very costly processing step but also to the best of my knowledge there, as yet, are no known satisfactory briquetting machine which has been working commercially. Thus, using rice husk as it is, without briquetting,  in a DD gasifier is a NO! NO!

 

AGREED THAT RAW RICE HULLS ARE DIFFICULT IN A DD GASIFIER, BUT BRIQUETTING IS QUITE PRACTICAL FOR SAWDUST AND I CAN BUY 6 MM SAWDUST PELLETS IN MY HARDWARE STORE FOR MY PELLET HEATER IN THE U.S.   I BELIEVE RICE HUSK PELLETS AND LOGS HAVE BEEN MADE (WIDELY USED WWII.)

 

I think these are probably some of the major reasons why the emphasis in the Developed countries has been on FB rather than DD gasifiers. After all, cleaning tar from fuel gas is a very very old technology.

 

NOT TAR CLEANING FROM WOOD/BIOMASS.  IT STILL SEEMS TO BE THE MAIN STICKING POINT FOR FLUIDIZED BED GASIFIERS. 

 

Regards

Kollol

 

REGARDS,      TOM REED        BEF GASWORKS

----- Original Message -----

From: Anuradda Ganesh

To: Tom Reed

Cc: Thomas Koch ; Kollol Dey ; Gas - L

Sent: Tuesday, September 17, 2002 9:51 AM

Subject: Re: GAS-L: Tar Standards and Codes

Dear Prof Reed and all,

The fact that we are already saying that FB gasifiers have 10,000-50,000
ppm tar nd DD gasifiers have only 100-1000ppm, shows that one has measured
them. If accuracy or non-accuracy was not the issue, then it becomes very
important to define these figures with reference to a particular method of
sampling and analysis of these tars and particulates.

I will explain this more explicitly. I have just complted a study on
comparison of three of the sampling techniques commomnly used in India for
measurement of tar and particulates. The final report is being made and
is not yet ready for public disclosure. However, I am in a position to
give this example.

On simultaneous measurement of tar and particlaute using two of the
techniques, we found that for the same gasifier-system operating, the tars
measured by one was about 10 times that by the other. The figure for
particulates , however , was found to be of the same range using both the
techniques. This still does not qualify the technique giving higher values
as best or absolute, as we could have something better. Probably what one
needs to know is, w.r.t. one method (could be any) what is the tolerance
of
the end-user-- both numbers and quality/constituents of
tar/particulate. Then with existing co-relations one could have an option
of various techniques.
 

You may also be aware, that India already has very clearly laid out
procedure for testing and certification of updraft and downdraft gasifier
systems,.India also has a procedure for monitoring the performance of
gasifiers on site.

Now in view of the discrepency in values, one needs to set the standards
for amounts of T &P  w.r.t a particular sampling method and analysis
procedure. Otherwise, a gsifier falling into a" good" gasifier class may
be
declared as" bad"  in terms of the T & P  generate , measured by two in
dependent groups using two different techniques.

anuradda


 


Prof.Anuradda Ganesh
Energy Systems Engineering,
I.I.T Bombay, Powai, Mumbai - 400 076.

Phone  (W) 576 7886     (H) 576 8886,  572 0762
FAX    (91)-22-572 6875, 572 3480

On Mon, 16 Sep 2002, Tom Reed wrote:

> Dear Thomas and all:
>
> Thomas puts it very well when he says...
>
> >  The problem about this protocol is that it is initiated by researchers and driven forward by researchers.
>
> A second problem is that the EEC (with tons of money) is mostly focussed on fluidized bed gasifiers which make tars in the raw gas of 10,000-50,000 ppm.  When they reduce them by a factor of 100 they think they are doing well. But downdraft gasifiers have only initially 100-1000 ppm tar in the raw gas when properly operated.  Tar measurements suitable for the first case don't have the sensitivty required for the second case. 
>
> A third problem is that money and time is no object... the more the better.  While those of us in small gasifiers want to find a gas that is clean enough for engines and don't care too much about the exact analysis of the tar. 
>
> So, we should all be interested in high sensitivity, low cost, fast tests and many of us are working on it.  The Bacharach Smoke Meter (cost $75) comes pretty close to a good quality test and I have been trying to make it quantitative with some success. 
>
> Yours truly,                     TOM REED                     BEF GASWORKS
>   ----- Original Message -----
>   From: Thomas Koch
>   To: Kollol Dey ; Gas - L
>   Sent: Monday, September 16, 2002 2:39 AM
>   Subject: Re: GAS-L: Standards and Codes
>
>
>   Dear Kollol
>
>   That is a very relevant subject you discuss.
>
>   In EU there have been a work ongoing on stardadisation on tar measurement going on for some years.
>   Search on "Tar protocol" to get more information.
>   The problem about this protocol is that it is initiated by researchers and drive forward by researchers.
>
>   Do you have the tiem to explain how you are used to conduct performance test?
>
>   New input would be very helpfull for us in the biomass field.
>
>
>   Thomas KOch
>
>
>
>
>     ----- Original Message -----
>     From: Kollol Dey
>     To: Gas - L
>     Sent: Monday, September 16, 2002 9:54 AM
>     Subject: GAS-L: Standards and Codes
>
>
>     Dear ALL,
>
>     1.0    I wish to know the internationally accepted standard codes that are available for conducting the "Performance Test" of a bio gasifier - whether it be moving bed, fluidised bed or entrained bed type. Can anyone help?
>     I understand that ASME has a PTC - 47 which is meant for an IGCC units. But have no idea as to how much of this can be adopted in checking the performance of a biomass gasifier? I also understand that ASME had a code for conducting Performance Tests on a coal based producer gas plant - I think it was PTC - 16, but I believe this code has been with drawn for sometime.
>     If someone is working on such a code - good !
>     But if this is not so, then isn't it time that a PTC for biomass gasifiers be drawn up ?
>
>     2.0    Further, the petroleum and petrochemical industry rely on API for standards, codes and recommended practices. Isn't it time that such things also be introduced in this industry (biomass gasification)  so that there are guidelines for buyers of biomass gasifiers to go by? I am sure this will be interest of the industry and will keep away a lot of "tall claims and counter claims"once the industry sees such internationally accepted standards and codes.
>
>     Comments please !!
>
>     K.Dey.
>
>