---------- Forwarded message ----------
From:
Thomas Koch <tk@tke.dk> Date: Sat, Nov 30, 2013 at 6:34 AM
Subject: Re: [Gasification] Fluidised bed reactor
To: Discussion of biomass pyrolysis and gasification <
gasification@lists.bioenergylists.org>, Kevin <
kchisholm@ca.inter.net>
Tom
I agree very much to your description of the status of FB gasifiers.
Not real upscaleable to an interesting size - to many operations problems - too big carbon or thermal losses and too dirty gas to real interesting !
The 2 Danish FB biomass gasifier - Pyroneer and Skive are struggling a real lot with gas cleaning.
Do you have any idea of the status of the Viking gasifier development?
I have asked several times if it is possible to visit the plant for over 2 years - or if there is a public report available with a little data?? but no luck sofar.
The last information I have from the project is from linked-in where saw that the only engineer I knew on the project have left this summer.
Best regards
Thomas Koch
-----Oprindelig meddelelse-----
Fra: Gasification [mailto:
gasification-bounces@lists.bioenergylists.org] På vegne af Tom Miles
Sendt: 30. november 2013 07:01
Til: 'Kevin'; 'Discussion of biomass pyrolysis and gasification'
Emne: Re: [Gasification] Fluidised bed reactor
If you want to use the engine exhaust in a gasifier you must consider the heat and material balance for a gasifier and IC engine.
Fuel input 100%
Heat loss in FB gasifier 5%
(Sensible) Heat loss to cooling the gas 25% Cold clean gas efficiency to engine 70% (20% C0, 20% H2, 2% CH4, 12% CO2, 44% N).
Heat conversion in engine ~25%
33% to power (~14-17% fuel to power)
33% to engine jacket heat (17% net)
33% to exhaust. (17% net, mostly CO2 and N)
By injecting exhaust into the gasifier you are recycling a lot of inert gas (CO2, N2) and very little heat. The best use of the exhaust gas heat may be in preconditioning the fuel. Danish Technological University (DTU Viking gasifier, 1990-2010, that is now being commercialized by Weiss) and later All Power Labs (Power Pallet, 2009) have used heat from the exhaust to indirectly dry and pyrolyze incoming fuel. The dried and partially devolatilized wood, along with preheated combustion air, appears to contribute to a stable oxidation zone. Both units make a very good quality gas. These are both fixed bed downdraft gasifiers with pre-pyrolysis zones.
Peak temperatures reach 1000 C-1200 C in the oxidation zone and 800-900C in the reduction zones.
http://www.btgworld.com/en/references/publications/handbook-biomass-gasifica
tion-second-edition We have worked with many fluidized bed gasifiers in research and in industrial applications, for producer gas, and for synthesis gas. The fluidized bed is an intriguing reactor that has its use in industrial applications but they are expensive to build and operate.
Fluidized bed (FB) gasifiers are unique because distributor plates or nozzles in the bed uniformly distribute the reactant (air, steam) in the sand (or media) bed. It is therefore imperative that the fuel be distributed uniformly for good gasification. This good distribution affords good temperature control as the fuel goes through the exo- and endo- thermic reactions that Kevin described. The ideal arrangement is to feed the fuel into the bed and allow sufficient time (depth) for it to completely react before breaking the surface into the vapor space above the bed. Of course there are variations on fluidized bed reactors such as spouted beds, fast beds, or entrained flow reactors. The latter are used for fast pyrolysis to liquid fuels by companies like Ensyn. I think that Dynamotive is the only company that uses a bubbling bed for pyrolysis. Many of the biomass to liquid reactors consumes the char to drive the process so there is no excess char
When used for gasification fluidized beds can be pretty stable in the
650-750 C range. The higher temperatures are needed to provide thermal inertia when wetter fuel (>20% MC) is used. Higher temperatures are generated by adding oxidants as Kevin has described. Higher vapor space temperatures (750 C) can be achieved by adding air above the bed. The partial oxidation can reduce NOx precursors in the fuel gas. You can think of the heat balance as consuming between 25% and 33% of the fuel to convert the remainder to chemical (producer gas or syngas) and sensible energy.
Producer gas is burned directly in a boiler or reformed for use in engines.
Synthesis gas is usually made using enriched air or oxygen as the reactant or by indirect heating, as in a dual fluid bed. The variety of catalytic reformers used to make synthesis gases can be seen online in the presentations at the TC Biomass 2011 and 2013 conferences.
http://www.gastechnology.org/tcbiomass2013/Pages/2013-Presentations.aspx There are a few small commercial (50-100 tpd) fluidized bed/entrained flow pyrolyzers that are making specialized products (liquid smoke) for the food industry. In general there are no commercial small scale fluidized bed gasifiers or combustors.
Attempts by US boiler makers and several small entrepreneurs have failed to sustain commercial operation of fluidized bed gasifiers or combustors at the small scale.
Tom Miles
-----Original Message-----
From: Gasification [mailto:
gasification-bounces@lists.bioenergylists.org] On Behalf Of Kevin
Sent: Friday, November 29, 2013 9:23 AM
To: Discussion of biomass pyrolysis and gasification
Subject: Re: [Gasification] Fluidised bed reactor
Dear Rex
----- Original Message -----
From: "Rex Zietsman" <
rex@whitfieldfarm.co.za>
To: <
gasification@lists.bioenergylists.org>
Sent: Friday, November 29, 2013 4:18 AM
Subject: [Gasification] Fluidised bed reactor
> Kevin,
>
> What you say is correct. However, there is benefit in returning some
> exhaust
> back to gasification as you force a higher production of CO relative to
> CO2
> production. I suspect it is an equilibrium thing...
# For a gasifier having a relatively high exit temperature, then engine
exhaust additions to the gasifier intake air could indeed be a way to both
lower the gasifier exit temperature, and to raise the CO level.
There is a CO/CO2 equilibrium consideration, and also a kinetics or "speed
of reaction" consideration.
Best wishes,
Kevin
>
> Rex
>
>
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