[Gasification] Bob's system, and general comments about making gas

[Zietsman, Rex]

Hi Drew,

I agree with you. I am an engineer and come from a plant design
background. So process control is part of running a system. Reading
through the list submissions has made me realise that automation is put
down because Listers don't understand what is possible, through no fault
of their own. 
>From an automation point of view, I agree that gravity feeding is
madness due to the bridging likelihood: you cannot afford not to tend to
the gasifier all day. So, how does one control a gasifier? This is not a
trivial question. Let me put it this way: let us say you are off grid
and run a power generation system that must deliver power in a manner
similar to an on grid system ie you can switch on equipment or power
using devices (fridges come on automatically) and need to balance the
power requirement with an engine. In a gravity fed gasifier, the engine
throttle will open to maintain the engine output speed at the greater
load. This will automatically pull more gas from the gasifier and more
fuel will be gasified. As the hopper is gravity fed, the fuel will slide
down on demand. Similarly, if your power demand drops, the engine will
throttle back and pull less gas. This will slow gasification down and
reduce the rate of conversion of the fuel. Simple control. 
So, if you take away the gravity feed, how will you control the rate of
feed to the gasifier? I have some ideas but would like to hear what you
and the list would suggest would be a good control system.

Kind regards
Rex

-----Original Message-----
From: gasification-bounces at listserv.repp.org
[mailto:gasification-bounces at listserv.repp.org] On Behalf Of drew
Sent: 07 March 2007 23:15 PM
To: Bob Stuart; gasification at listserv.repp.org
Subject: [Gasification] Bob's system, and general comments about making
gas

Hi Bob,

    I have corresponded with these guys who do what you are 
suggesting.   Their setup is quite good and they appear on the list 
occasionally.  The issue is one of scale, at a large scale almost 
anything is possible and many things are economic.   


    I think that you are on a good track.    I believe the axiom  "doing

the same thing over and over, and expecting different results is crazy" 
so I tend to ask myself a few questions in regards to gasification

1.  What worked, and on what scales? and what about it was the part that

"worked" and what was problematic?
2.  What's different now that we can apply?


http://www.cleanfuels.nl/Biomass%20energy%20technologies/biomass%20energ
y%20technologies.htm


Few technologies scale down well, or cheaply and _*historically* 
_especially this is true of controls.   Remember 30 years ago if you 
wanted to build an "intelligent" system that could vary 3 or 4 inputs in

accordance with the data from 3 or 4 sensors it would require a small 
crew of engineers, a computer room worth more than 10 years wages, ect 
.....    It's different now, very different.


I think the imbert system has proven to be the best "low tech" system 
going, but it is so fuel specific and tricky to operate that it wasn't 
practical for most users (look at how quickly it disappeared even though

gas prices remained astronomical after WWII).    Why is it fuel 
specific?    In my mind it's because it relies on gravity feed to keep 
it's reduction tube optimally packed.   It's reduction tube is it's key 
feature.   That is to a certain extent a simplification but largely it 
seems true.   
Must we continue to rely on gravity feed?  I don't think so.    I am not

talking about adding a fuel auger to the top of an imbert, I am asking 
why use a hopper in an imbert, isn't it mostly a place for fuel to 
bridge?    People relied on gravity feed because of it's simplicity, but

it can be clearly shown that as the system is reduced in size it becomes

more fuel specific and more likely to bridge. 

Historically these systems required skilled operators and worked best 
when the whole system was agitated (bumpy roads), today Doug (the most 
knowledgeable person on the matter) will insist that they still require 
skilled operators.    The operator would adjust engine load, air intake,

water spray (more for cooling an overheated reduction tube than for the 
extra H) and most importantly reject inappropriate fuel!!!!!.....  

What's different now that wasn't available then,  computer based 
controls certainly.     Right now I can by a very simply programmable 
PLC  capable of simutanously running 3 position reporting  servomotors 
as per program requirements, and simultaneously reading 4 data input 
devices.    So if you wanted feed to be a function of gas output 
pressure, with conditional air controls running on a data logged 
system......   350.00   bucks including the motors and some 
sensors......    Never before has this sort of thing been available for 
this sort of money.    Integration of small controls is happening so 
fast in some industries, why not here????  

All the best
Drew

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