[Stoves] Dell-Point gasifier pellet / corn /wheat biomass stove

[Thomas Reed]

Dear Jeff: 

Thanks for the excellent question. 

I have a pellet stove in my lab (Home Depot cheapy) which performs quite 
well on wood pellets.  I have also used it to test corn, cherry pits, 
acai pits and Distillers dried grain pellets (from Coors).  All the 
other fuels perform poorly, with a buildup of ash in the fire box.  Only 
the cherry pits operated for more then 1/2 hour.  I think if I added an 
air jet pulse I could blow the ash out into the larger chamber and run 
much longer.  I think the stove would need an air/fuel adjustment to 
burn some other pellets. 

So the two main problems are getting rid of ash and adjusting A/F ratio.

The stove operates like a close coupled TLUD gasifier - like our wood 
gas stove.  It pyrolyses from below, keeping the temperature around 700 
C and slagging down. It then adds more air above to complete the 
combustion at > 1500 C. 
------------------------------------------------------------------------
I have just read the manufacturers claims and patent information and 
wish I could convert to a Dell Point pellet stove.  Their claims of 
efficiency and fuel tolerance are so impressive as to make me 
skeptical.  However, I looked up USPatent

6,336,449

and liked everything I saw.  I particularly liked ...

"According to a preferred feature, the system includes an oxygen sensor 
so as to substantially increase the overall steady state efficiency 
level by controlling the combustion air level to pellet fuel quantity 
ratio and rate of burn within the chamber. The amount of combustion air 
to the zone in which the gases are burned is regulated by the oxygen 
sensor in proportion to the amount of pellet fuel being combusted. The 
oxygen sensor employs a feedback loop to a main control system for the 
burner, which controls the fan motor speed supplying the induced 
combustion air being drawn through the combustion zone. The oxygen 
sensor measures oxygen concentrations between lean (any oxygen in the 
exhaust system not being utilized to combust pellets) to rich in oxygen 
(when there is not enough oxygen for the amount of fuel present in the 
combustion zone). The oxygen sensor balances the level of air to fuel so 
as to maintain an optimum rate of burn, which in turn effects the 
efficiency level of the combustion process. This oxygen sensor is 
conveniently located in the exhaust system to monitor the exhaust gases."

Being able to operate at the correct A/F ratio permits much cleaner 
combustion and higher efficiency.  I understand that European pellet 
stoves often have O2 (lambda) sensors.  I began working with O2 sensors 
for crystal growth in 1970 at MIT, so have a soft spot in my heart 
(head?) for them. 
------------------------------------------------------------------------
The oxygen sensor on my car costs $30 (two wire) to $60 (four wire).  
For more accurate results the four wire adjusts the temperature of the 
zirconia sensor element for greater accuracy and quick startup.  It is 
my opinion that as fuels become more expensive and emissions more 
important, that most combustion and gasification devices will include 
one or more oxygen sensor.  The signal output is 0-200 mV for lean burn 
and 600-1200 mV for rich.  If I wasn't busy, I'd take my stove apart and 
"remanufacture it" according to this patent.  Or maybe I'll sell it and 
buy a Dell point. 

With Winter coming, I hope your question will earn a lot of practical 
comments.

Yours truly,

TOM REED                      THE BIOMASS ENERGY FOUNDATION






 

Jeff Seibert wrote:
> Tom,
>
> Are you familiar with a company called Dell-Point? They claim to be the
> first (and only?) manufacturer of a biomass gasifier home heating stove. The
> US patent on it 6,336,449 describes a close-coupled gasification combustion
> burner. I think it's a reverse downdraft type (ie updraft?)
> Any info. pro or con would be appreciated. Can you direct me to anyone that
> has experience with this stove?
>
>
> Thanks
> Jeff Seibert
>
>