[Gasification] Gasification Digest, Vol 35, Issue 12

[Peter & Kerry Davies]

Hi Doug,

Good to hear you continue hard at it as well. Congratulations on your 
success so far.

We moved to an active grate system in our linear design back in early 
2010, based on the reality that real world fuels often contained 
contamination in the form of small stones or nails which alas defied any 
attempt to vaporise them with the wood or mixed sewerage biosolids we 
were working with...:) What then originally was a change wrought by the 
need to manage a feed stock issue ended in being an incredibly flexible 
package and since have been able to make similar observations to your 
own over the positive benefits to consistent gas flows over extended 
operating hours, lifting the original packed bed limit from 12hrs to 
true 24/7 capable without the need to get down and dirty cleaning out 
the gasifier every day.

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?

Real world is so much different to what many envision and it was great 
to see pictures in a working environment.

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

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, 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?

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!

Cheers,
Peter



On 22/07/2013 4:00 AM, gasification-request at lists.bioenergylists.org wrote:
> Operation of Shasta 1 over the annual seasonal changes while hooked up to a online gas analyzer, highlighted the variations that can be experienced by the gas making process, some of which are almost impossible to detect, let alone control. The stability and natural evolution of the packed bed oxidation and reduction chars has always been considered the most important aspect to our gas making philosophy, so a new design feature of Shasta Class, is adjustment of the bed during operation in responce to gas quality changes. Char extraction is not used in any way to maintain the process, but some char does exit the reduction zone naturally with soot's entrained in the gas, and the dropped larger fraction augured out the bottom. The cyclone then removes most of the char entrained in the gas stream.