Here is a slightly modified reactor for the standard GEK that creates an 11" inside hearth diameter, instead of the previous 10".  The reactor shell continues to be 12".  This larger hearth is achieved by changing the way in which the inner insulation tube is done, as well as how the bell mounts to the base of the reactor. The wider hearth allows for a wider nozzle ring and wider tapers to the base of the reduction zone.

Previously the reduction cone could taper out to 6". This new reactor will support tapers out to 7.5". This larger taper potential can be used either to increase residence time in the reduction zone with the standard 3" restriction, or to support larger restriction and related tapers, and thus larger total gas flow rates. Our current testing is suggesting that increased residence time in reduction would be helpful.  The change from 6" to 7.5" diameter at the base of the cone is about a 50% increase in cross-sectional area for gas flow.

The pictures here show a full hourglass hearth made to fit this new 11" reactor. Completing the hourglass instead of leaving the top cone to form passively over the standard inverted V hearth base, seems to result in less bridging, as the fuel is on a slippery metal surface, not charash. As we are now using stainless for these hearth elements, and already fighting out making cones, there is no longer a need to use the ash to passively form the top cone. Purpose forming this top cone also eliminates the need for the tar fence, which previously prevented circulation through this ash formed top cone.  Still keeping this hearth mounted to the base, with lots of open space on the sides, continues to make possible the packing of robust insulating around the hearth, with several stages of "walls within walls" to prevent convective heat flows.

The hearth shown in the pictures has a 4" restriction with 8" height from the restriction to the bottom of the taper. Bottom opening is 7.5". This is a less than ideal taper outwards, but was done to get the max gas flow rate from the standard GEK so as to run a large generator in Costa Rica (where these pictures were taken). With the standard 3" restriction, the same 7.5" bottom opening will create a 1:2.5 taper ratio, which is the direction the accumulated testing is directing towards.   The drawing below shows the standard 3" restriction.  

Here's mounting the hourglass hearth into the reactor, filling char up to 2" above nozzles, then wood blocks to the top. 

Post run we emptied the reactor layer by layer to inspect the condition of the bed.  Notice the progressive size shrinkage in the char as we go lower in the hearth.  Chunk blocks like these maintain a nice void space even when deep in the reduction bell.  Compare this to pictures of the size shrinkage with shells or wood chips, which become extremely small and tend to pack the bed.

Here is what the insides of the ejector jet and filter looked like after two hours or running.  Clean metal!  No tar!  Even with 15-20% moisture content wood in tropical humid air!  I was very happy to open the filter and find things in this condition on my first run in Costa Rica.

These runs had a thermocouple installed at the constriction point in the hearth to measure temp.  The TC is pushed into a SS tube welded into the hearth at the constriction, protruding about 3/8" into the bed..  The other end of the TC is wound around the wall of the vessel and out through the instrument port at the top of the reactor.