Biochar Systems

This page will present various systems of biochar formation and discuss the intricacies of each as they become apparent. The text will proceed in the order of the attachments:

There are many variations of this partial burn technology, the most common is the TLUD stove, Top Lit Up Draft, that uses external air to oxidize psrt of the fuel value of the feed stock to  raise the temperature of the new or next in line to be converted material to a level high enough for combustion to begin.  This is discussed below under various combinations of orientation of the lighting and draft.  See below.

Another more efficient, but less popular or researched configuration is the combination of a TLUD and a heat recovery / concentration system to quickly reduce the externally applied oxygen to zero as the exothermic portion of the pyrolysis process is enabled.  This is described below under the title EXOFD, Exothermic Flexible Draft. To be added 121216.


SLSD - or- Side Load Side Draft:  This unique little prototype may be the next simplest biochar processor that seems to be scalable with little technical modification.  This statement has yet to be validated as of June 24, 2010.  Really the ideal configuration of this design might better be called SLnoDfX but "slnod" is such a neat name that I bet it will stick (but what do I know?). 



This device comes from an idea offered in the NEUSA by Dr. Hugh McLaughlin.  Hugh formed a version of the TLUD stationary cooking and space heating device (if he did not invent it originally?).  My engineer friend Robert Essert has modified the TLUD design to lie on its side and incorporate a simple feed system and char collection area with a control mechanism to keep the pyrolysis zone in about the right place.  He presented the design at the last meeting of the Pioneer Valley Biochar Initiative on Tuesday, June 22, 2010. 

The pyrolysis zone is the area in red/orange in the design as shown in the SLSD pictuer above and the attachment below.  The feed system is controlled by a thermal switch located near the end of the feed auger.  Please honor the CC release on this site by crediting Bob Essert in any implementation of this design.

We will be experimenting with simple scale ups of this in the near future.  It would seem that this could be run by hand if there were no power alternatives available.  Details will be added as more experience is gained.  You can add comments to this page to let Bob know how you are doing with your tests.  

A brief discussion of "SLnoD": the unit is mounted horizontally and the feed stock flows from one side (thus the "SL" for side load) and the unheated material proceeds from the feed area into the pyrolysis region from the force of the auger pushing it forward.  Once the tube is full to the char release area with unignited feedstock it is lighted by whatever means is convenient.  One way that works on this size device is to just lift it up a little and drip some candle wax on the exposed end and lighting it.  one could also start the charge with a small amount of alcohol mixed with the initial feed stock and lighting it when it is near the drop off point.  The "noD" part of the name comes from the understanding that the most char will be produced when the charring is done only with the oxygen that comes in with or as part of the feed stock (thus the "noD" for no Draft), the additional "fX" might stand for front exhaust.

It will be neat to see this system combined with Frank Jeffers cracking system so that the gas comes out clean and usable directly in a variety of producer or water gas compatible systems.

The next scale up will probably involve cascading these systems to be able to handle wet material - we are not there yet.

See the comments below for an ongoing discussion of what we have found as we work through the reality of char formation.

NOTE: The ABCD file shows three drawings of the Essert efforts.  The bottom drawing should have a line drawn at about 35 degrees below the horizontal  to represent the base or horizontal floor for that final design.  The question remains whether extending the tube beyond the current pyrolysis zone would solve any of these issues.  ABCD stands for "angled burn counter draft" as Bob explains in the comment.

True Pyrolysis:
The TLUD concept is based on use of combustion of part of the feed stock to supply the endothermic heat required gasify the volatile compounds.  The early combustion is facilitated by addition of sufficient outside oxygen (normally from air) to oxidize the most volatile compounds.  In the process the BTU content of the volatile gases and partially oxidized carbon (CO) is diluted by the portion of the air that is not usable. 

Pyrolysis of organic material occurs in the absence of added air.  Pyrolysis does involve oxidation of a portion of the volatiles and carbon but is limited to the oxidation that can occur by shifting the oxygen around among the atoms that have various affinities for (bond energies) each other.  This shifting occurs once the molecular structures are broken by the addition of outside heat.

There is a significant amount of energy that is released in this readjustment of oxygen carriers that can be used for preheating of new feed stocks, but this heat is not collected and stored for this preheating in the normal TLUD configuration.  The following drawings sketch out the differences:

The TLUD uses primary and secondary air to separate the gasification process from the full / final combustion of the majority of the gases released.  The deficiency in primary air allows most of the carbon in the feedstock to remain unconsumed after the burning front has moved below the pure carbon region.  This results in a batch process from which char can be recovered if the temperature of the char is reduced below the kindling temperature when the initial burning process is completed.
 

Real pyrolysis can happen either in a completely enclosed container that is heated with fuels burned outside of the container.  Gas will have to be vented or the container will explode.  An alternative procedure is to start the pyrolysis in the normal TLUD fashion and then push the char above the burning front up and over the side of the supply tube as shown on the left.  Over time the hot char will build up around the supply tube and will continue to "cook" itself and provide the exothermic heat to the newly added feed stock. 
Several things happen as the feed stock moves from the cool supply container up through the TLUD inner tube. 
1) The feedstock is heated and the moisture (up to three times the dry weight of the feed stock) is evaporated,
2) This water vapor moves wherever it can go - various design possibilities could allow the moisture to be vented or to be reintroduced into the fuel later as a component of the water shift reaction,
3) As the feed stock moves up the TLUD tube it is either heated to kindling temperature from the heat provided by hot char around the outside (if any exists) or it is simply moved up toward the region at which normal TLUD burning occurs.  NOTE: the thermocouple ports on the right side of the the TLUD tube.  These sensors control the position of the burning front by turning the feed screw on and off at appropriate times.  Over time the char produced overflows the TLUD tube and the char builds up around the outside.  The auger at the bottom of the outer container controls the height of the external char.

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Alan Page,
Jul 20, 2010, 6:03 AM
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Alan Page,
Jun 24, 2010, 12:16 PM
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