[Gasification] Charcoal Gasification No. 5

[Mark & Elena Gallmeier]

To Doug and All,

> The bottom line of my presentation stated:  If the quality of charcoal 
> could not be controlled to ensure that all volatiles were carbonized, then 
> the gasification process had to have a tar cracking capability.<

This answers my question about char 'quality', at least for charcoal 
gasifiers for internal combustion engines.

Table 4 in this reference:  http://www.fao.org/docrep/X5328e/x5328e05.htm 
provides some data about different 'quality' chars.  The results there 
mostly parallel my own experience operating my volatiles afterburning 
charcoal retort:  http://gasifiers.bioenergylists.org/gallmeierretort

Regards,

Mark

> Message: 2
> Date: Fri, 24 Aug 2007 12:44:44 +1200
> From: "doug.williams" <Doug.Williams at orcon.net.nz>
> Subject: [Gasification] Charcoal Gasification No. 5
> To: "GASIFICATION" <GASIFICATION at listserv.repp.org>
> Message-ID: <001101c7e5e7$f6c65e70$0201a8c0 at dougspc>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Gasification Colleagues,
>
> While this discussion is to encourage the beginner to make producer gas in 
> the most simplistic manner, there are very sound arguments against making 
> charcoal at cost to the environment.
> I missed out a very important issue which Mark questioned regarding 
> residue volatiles, and remembered that I had written about this years ago 
> on file, relating to designing reliable charcoal gasifiers
>
> Thanks to a timely visit from my daughter to type out some extracts,(and 
> $20), you get to see what I said about charcoal gasifiers 18 years ago to 
> people on the ground in developing countries, and fully engaged in 
> gasification activity. Nothing has changed, but a wider appreciation of 
> global warming emphasises the need to use our biomass resources in less 
> wasteful practice, than making charcoal for gasifier fuel.
>
> The bottom line of my presentation stated:  If the quality of charcoal 
> could not be controlled to ensure that all volatiles were carbonized, then 
> the gasification process had to have a tar cracking capability. In this 
> respect, the design had to be the same as for a wood gasifier, therefore 
> it was a waste of the fuel resource to make charcoal, and loose the energy 
> content of the volatiles.
> The arguments against this, continually return to the cost of labour, to 
> cut the wood into fuel blocks by hand, which last week, I did myself at 
> the rate of 50-60 kgs/hr, the equivalent of about 16 litres of diesel 
> fuel. (worth $1.05/ltr)
>
> Even in New Zealand, that is a good return for a worker with no skills to 
> be employed for the job, and if done on contract, rural people will bury 
> you in blocks given the opportunity to earn cash money. This leads onto 
> the simple fact, that if a gasifier is not being used to conduct an 
> activity that creates a financial return, then there is no point in using 
> the technology.  Alternatively, if you wish to create a standard of living 
> that is currently provided by fossil fuels, then you need to reallocate 
> your time to become a survivor, and face the realities, and 
> responsibilities it takes, to cut the mustard! There is a price to pay to 
> join the "Black Hands Gang"  (:-)
>
> Doug Williams,
> Fluidyne.
>
>
>
> Extracts from a Paper I wrote on conceptual designing of charcoal 
> gasifiers in 1989.
>
> INTRODUCTION
>
> In preparation of the material for this workshop, most of the modern 
> papers on engine gasification have been reviewed.  This modern material is 
> of course based on historical work by earlier investigators of the 
> technology, adding to, but rarely improving on the quality of knowledge 
> available.
>
> For whatever reason, researchers papers concentrate on the theoretical 
> mathematical modelling of each and every aspect of the various chemical 
> processes.  None to my knowledge make reference to the physical phenomena 
> that accompany the chemical equations.
>
> Gasification is a continuous process of staged phenomena that can be 
> managed to perform consistently given that the phenomena is created in the 
> correct sequence.
>
> It is this physical behaviour that determines gasifier design, and the 
> design which provides the conditions to handle the phenomena.
>
> While the knowledge of gasification is widespread, the understanding of 
> converting it into a reliable technology appears to be missing from the 
> comprehension of many involved with the technology.
>
> It has been written that gasification is not an art but a science.  While 
> this may be true, what has not been appreciated is that the fabrication of 
> steel to manufacture a gasifier is an art form unto itself.
>
> This material pays particular attention to the gas cooling, cleaning 
> systems.
>
> No formulas are offered in this work which is based on the collection of 
> information from Fluidyne wood gasifiers over many thousands of operating 
> hours.
>
> Doug Williams
> March 1989
>
>
>
> 1.    The Choice
>
> The gasification of biomass is going to play an ever increasing role in 
> providing energy for developing economies.
>
> Given the right conditions, gasification is a powerful economic tool, but 
> the wrong conditions can create an ecological disaster.
>
> To implement gasification projects in any country, the choice of 
> gasification fuel has to be determined by availability.  Most projects 
> will use wood or charcoal, and this is the choice that has to be made 
> before a project begins.
>
> The Greenhouse Effect is now starting to affect the world climates as a 
> result of fossil fuel combustion and atmospheric pollution.  Can the 
> manufacture of charcoal continue to be encouraged?
>
> Rapid depletion of tropical rain forest continues unabated and soil 
> erosion contaminates rivers, ruining water supplies.
>
> As designers and builders of gasifiers, our choice of whether to carbonise 
> 3 - 5 tonnes of wood to yield one tonne of charcoal, has long term 
> environmental repercussions.  Taking the easy route to problem solving, 
> has historically proven to be the most costly in the long run.
>
> Can we afford the cost?
>
>
> 2.    DEVELOPING THE CONCEPT
>
> 2.1  Purpose of the design
>
> Before any gasifier design can be formulated, the purpose of the design 
> must first be derived.
>
> When a gasifier is used in one place with a single fuel and source of 
> supply, the operating parameters of the gasifier can be determined and 
> closely controlled.  From a design point of view this has proven to be the 
> greatest weakness, since most of the design and manufacture has evolved in 
> the safety of a developed country.  Even the fuel woods and charcoals used 
> for development are those readily available and rarely are similar or 
> compatible to those found in the countries that have to use the gasifier.
>
> Most of the problems that are experienced with the gasifiers can be 
> tracked right back to the beginning of the project by the objectives being 
> founded on the wrong concept.
>
> Because a gasifiers use cannot be guaranteed to be restricted to one set 
> of operating parameters, the design must be compromised and provision made 
> for variability.
>
> 2.2    Variability
>
> Variability is a specification in itself for it has to cover the 
> uncontrollable aspects of gasifier operating conditions.  These can be 
> summarised as follows:
>
> Location
> Altitude
> Ambient Temperature
> Humidity
> Fuel Species
> Moisture content of the fuel
> Quality of fuel preparation
>
> For any gasifier to operate without problems within these variables, the 
> design must be able to handle them all in the very worst situation.
>
>
> End of extract.