[Gasification] Gasification Digest, Vol 35, Issue 12

[doug.williams]

Hi Peter,
Sorry but only brief answers to your questions:
 
> Looking at your excellent report and photo's on your archives page (yes 
> we have bowed to pressure and are organising someone to do something 
> similar for our own work, will post a link to list in due course) I note 
> the flare colours are similar to what we used to get from our early 
> models, though if the operation was at the 320Nm3/hr level for the 
> daylight photos  then we have to get better gas flow measurements 
> ourselves as the flare volumes depicted are what we would expect from 
> the system with the fan at low speed. Perhaps you did not have the 
> gasifier at full flow when the pictures were taken?

Open flare testing was conducted at low levels due to the fire hazards present in California. Water sprays were used to wet the area of the tests.

The two daylight photos were to show the first cold start-up gas, first at ignition, then a little later as the exothermic heat began to return to the gas making, not heat soaking. Cold start-ups are never conducted at high flows, because you will consume all the char before the raw fuel can be carbonized.
The night photos were done to show at a higher rate, how the exiting combustible gas changes in volume, as the amount of pyrolysis gas from the raw fuel over the bed either fails to flow or in our case, not fed quickly enough to keep up with the required gas making quality. Night photos provide the best view of these changes. The colors of the gas relate to a known % of clean gas free from hydrocarbons, and a particulate level consistent with prior testing. 

 > Just a clarification: When you talk about air blown you are referring to 
> the fan forcing air in rather than drawing gas out? 

The short answer is yes, but fans are not appropriate for commercial gasifiers. You need a Roots blower which is a positive displacement pump (suction or blown) then you will see how your gasifier really behaves. Fans just spin and you cannot have any control over any obscure changes in pressure or suction.

>We did play with 
> this at one stage and whilst it looked promising the level of instrument 
> control required was beyond our skills and resources at the time and 
> negated our advances in "open core" operation. Though it did make an 
> interesting Updraft/Downdraft hybrid blowing gas out both ends when the 
> top lid was opened! 

When you are forced to use only manual refueling, many design issues do not have to be addressed, but go automation, you will start to need all those $$$.

>I see you have addressed this somewhat with a 
> divorced feed system via a cross flow auger. We also looked at ram type 
> plug feeders as a auger alternative, but all these things increase 
> complexity, cost, maintenance requirements and parasitic electric loads, 
> the opposite of our core philosophy of KISS. Though we would stress this 
> in no way negates their validity or value where the situation warrants.

Unless the inflow refueling point is at ground level, fuel has to be lifted and that take energy. You just cannot open the top of a gasifier to atmosphere as the ingoing fuel will displace gas, this requires a fuel lock. Screw augers cannot provide a reliable plugging effect blown or on suction, that is if you are using say woody biomass, and ram types are not appropriate for linear hearths. Not sure how you would consider any of the known basic automated components as redundant in the search for KISS.
 
> We are now (finally!) moving to a full commercial design suited to ease 
> of replication, having spent much of the last 2years on this aspect 
> rather than gasifier operation itself which has been more than 
> satisfactory. We are now planning the fabrication of a 250kg/hr model 
> and +500kg/hr model, 

>From what you say, you had better get that refueling system sorted first. Moving the fuel and it's type in the volume required will stretch mechanical skills.

>the former for retro fitting and dual fueling 
> diesels and the latter for matching to an optimised low btu gas engine 
> 500kWe genset from our new Malaysian partners later this year. The large 
> throat size again a concession to material handling of lighter mixed 
> biomass feed stocks rather than a need to build a single module for the 
> scale of job, who knows what other break through s this change might 
> lead to?

Well we will look forward to seeing your creations shortly when you get organized. 

 > I know I am occasionally to frustrated in my writings, the negative 
> experiences with industry peers in the fair land of Oz coloring my 
> outlook to a degree, but I remain as others have in their long careers, 
> eternally optimistic that a new age of gasification is dawning, and even 
> if it isn't we are enjoying the journey anyway!

When I used to teach my girlfriends how to drive, I told them look for potholes down the road, not when they are in front of the wheels. Keep an eye on where gasification may take you, because the destination is going to be set by the small details, not the potential grandeur of it's application(;-)

This is all I can offer for a while, but glad some found it interesting.

Doug Williams,
Fluidyne.









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