[Gasification] Drying

[AJH]

On Thu, 14 Dec 2006 10:36:46 -0000, Adam Carr, Renergy wrote:

>As a rule of thumb in most heat applications higher grade heat (i.e. from gas cooling and engine exhaust) has a greater commercial value than low-grade (water jacket) heat. 

OK but this depends on a number of things, the chp scheme I see
utilises its waste heat at below 100C simply because the heat main is
unpressurised water.


>This is certainly true of the project we are currently working on, so for me the key drying issue is can we dry ~one tonne an hour continuously using ~500KW of hot water at 90C thereby enabling us to derive revenue from the higher grade heat.

You need to define how wet to start with and how dry at finish. What
you also have to consider is that the engine may be rejecting its
coolant heat at 90C but its radiator is probably only rejecting this
heat at 20deg C above ambient. If you choose to have your drying air
higher than this then you have to use a much bigger radiator.

Having said that it does look like your coolant has enough energy to
remove 3/4 tonne of water an hour, so at 50% COP you could dry
1.4tonnes of 35% mc wwb down to 1 tonne of 10% mc wwb per hour but
this would probably involve pumping 5m3/sec of air through it. What it
won't do is dry any single piece of your wood in that time as the
residence time would need to be greater than an hour.

So whilst it may look better not to use your higher temperature heat
for the drying there are good reasons to consider it, higher
throughput, less residence time and smaller equipment being just some.

AJH