[Gasification] Gasification Digest, Vol 23, Issue 15

[Peter & Kerry]

On 18/07/2012 5:00 AM, gasification-request at lists.bioenergylists.org wrote:
> From: Thomas Koch<tk at tke.dk>
>
> Subject: Re: [Gasification] BIOCOAL - THE WOOD FUEL OF THE FUTURE
>
> But it will cost 50 % of the heating value of the wood

Thomas, I am unsure where this number comes from could you give more detail?

In straight energy recovery terms it really depends on a number of 
factors including level of torrefaction as determined by temperature and 
residence times. We would expect 90% retained energy for the product we 
are aiming for, though the overall energy efficiency of the process will 
be lower as a % of the original wood delivered to the plant is used to 
run the process. The trade off is a "specified" fuel with much higher 
utility, far better transport economy (not carting energy robbing 
water), problem free storage and handling with existing coal equipment 
and uniform very low emission combustion performance vs raw wood fuel. 
When the first commercial pilot is complete then we will do a energy 
balance measurement (to compare with the theoretical calculation).

Although in our circumstance this more for academic interest and as a 
benchmark to judge future process improvements as in any case the the 
argument is somewhat moot, current practice (burning waste in Beehive 
burners) recovers 0% of the embodied waste wood energy for a negative 
cost to the business. The potential clients they have are not interested 
in straight wood chip or sawdust as the low energy density and higher 
handling requirements preclude their "raw" use in their existing coal 
fired boiler plant at anything like a reasonable co-firing rate 
(sawdust/chip is usually limited to <5% of fuel feed). New biomass 
optimised boilers have been ruled out because of their very high cost.

In one case that we have been asked to consider the fuel spec is so 
tight in terms of energy density and form that it can only be met by 
making a blended torrefied wood/charcoal pellet (one approach to achieve 
this is tweaking the operating parameters of the gasifier in favour of 
more char production and combining this with the fines from TW retort 
through a densification plant). Technically this can be done, making it 
work economically is the bigger challenge.

Leland also makes a interesting point:
> There is a company formed to make torrified wood. I am terrified of the prospects as it would be a lot easier to gasify wood at the site of coal use.
We have tried hard over the years arguing the same case. The reality 
though is what we call technology inertia, businesses stay with the 
energy technology they know (straight combustion of solid fuels in the 
cases we are talking about), they will accept an "improved" solid fuel 
that does not require much in the way of change to "business as usual" 
so long as the decision can be easily reversed if it doesn't work out. 
Interestingly if they are already using a gas fuel, such as LPG then 
they can much more easily be persuaded to consider an on site gasifier.

Which raises an interesting future scenario in those countries where 
large scale fracking is taking place and "cheap" abundant gas supplies 
are becoming available. Changing over from coal to another fossil fuel, 
in this case Coal seam or Oil shale gas is a straight forward economic 
decision by businesses with boilers, particularly where industry price 
competition is also driving the change. Once this occurs then "step 
change" to on site gasifiers will become easier in the future a the 
vastly expanded gas industry gets past its first flush, new energy 
players fail & or merge to form more monopolistic entities and the gas 
prices inevitably rise.

Cheers,

Peter