Californian Biochar Maker and Shasta GasifierShasta 2 Gasifier (Update)
Since the Shasta 2 Gasifier at CalForest Nurseries in California was put work in February 2014 for the Winter heating, it's operation completed just on 1,000 hours without failure of the gasifier itself. Failures of fuel lock seals into their actuating motors was the main problem causing automated shut down, so will be now replaced with separated actuators. The system was able to demonstrate a push button start from cold (after checks to all the fuel feeding conveyors) and walk away operating reliability for the day/night operation.
The boiler pipelines have now been extended into a second greenhouse for the 2015 Winter heating, and indications are that there is still plenty of additional heat in reserve. The first start of this year did bring surprise however, in that the wood chip being gasified had a moisture content of 40%. The Shasta 2 still made a combustible gas, but initial ignition of the burner nozzle was difficult on the standard air setting, so less air and it ignited immediately. Wet wood isn't an option but the log pile was left open without its covers, and a lesson was had by all concerned.
New Char Making Project.
It's been almost two years since my last visit to CalForest, and my visit in the last week of January 2015 was of special significance to commission a new concept of continuous charcoal manufacture. The conceptual process was first proposed in 2007, but put on the backburner as the focus was on gasifier development for heating and engine power generation. While biochars have a role to play within the Nurseries of CalForest, as a commercial product, it's production costs are an inhibiting factor for those consumers who need large quantities. With forest fires a problem in many countries, fuel reduction programmes within forests sees large amounts of green forest chip becoming available, with a potential for char making.
As stated, the target fuel is green forest chip which at best does not make good quality char for barbecue or cooking applications. The cost in time for retort type charring to capture the pyrolysis gas cannot be justified if the end result is only a char that then needs briquetting before it can be used. As a tonnage production, it's application as biochar is of course dependent on price to the end user, and our project is designed to explore the potential to reduce costs of the production cycle.
Starting in November 2014, the original char maker design concept was reviewed and a few changes made as to how the char extraction was accomplished, but to first prove these changes, a wooden model was built. Char collected from the Shasta 2 waste clean outs were used to obtain the fluid flows expected from forest chip fine char providing a visual demonstration that the extraction process was very stable across the length of the bed. As a base line specification, we were looking for 5-7 m3/hr, or roughly 1ton/hr from about 5 ton green chip. Availability depends of course where the system is located,but an expected 1,900hrs/year, could see a healthy 9,500 ton reduction of these raw chip piles. With fuel flows of that order, we had to use the main fuel feeder conveyor of the Shasta 2 gasifier, combined with a lot of observation to run it all manually. For this reason, it is envisaged that a twin charmaking installation would better utilize the cost of fuel feeding infrastructures. The prototype was completed in the last week of January 2015.
Based on previous knowledge regarding the chars ability to retain uncracked pyrolysis oils and tars (creating a strong acetic or acrid smell), the need for a char of consistent quality and evenness of carbonisation, created a design need to even out all these variables. Linked with a dwell time between the refuelling cycles, we soon discovered that anything less than complete carbonised char created operational problems to the extraction system, but once we learnt to start the system correctly, these issues were resolved
Built as a test of concept, the charmaker was proven to function within our pre-set design parameters, which now justifies the next phase of development. This includes a internal fuel pile leveller/refuel sensor,heat resistant air nozzles, and change to the extraction auger design to prevent jambing. Flare stack closures will facilitate the shut down procedure, as will fuel feeder locks on the fuel input end to exclude all free air entry. Like a gasifier, the charmaker must never be allowed to run out the fuel completely to facilitate an easy start-upThe start-up from ignition to gas burning at the flare stack was fasterthan anticipated once we found the ideal air flow settings, and 5-10 minutes gave us time to be closely watching all the visible phenomena,especially the oxidation colour through the air nozzles and temperatures well over the 1,000C. The pyrolysis gas was burnt to waste cleanly demonstration that it could become a reliable source of close coupled heating as required.
Although we have designed a charmaker for chips, it's performance factors should also apply to any nut shell or fruit stone/pip, which in time will be tested with results shown on the Fluidyne Archive files. Also to be tested, is tar free gas extraction to run an auxiliary engine generator for stand alone operation of the system. This is done by drawing the gas from the char extraction chamber reducing the amount of pyrolysis gas being burnt to waste at this stage of demonstration.
These commissioning charmaking tests were independently monitored onsite by Tom Miles www.trmiles.com
|Charmaker layout R-L. (A) Temporary vertical plastic tube chip feed from main conveyor.(B) Inclined input feed auger fills centrally into charmaker hopper.(C) Water cooled char extraction auger being connected.(D) Char discharge transfer box with two inclined auger positions for filling directly into standard cube char bag.|
|Ready for first test, charmaker from motors end shows air fan feeding into tee connection to twin air manifolds, and char auger extraction motor. Char extraction control motor just visible on right side of air tee. Hoses connect water cooled char chamber walls and extraction auger. The size of the actual charmaker is quite small compared to the size of it's fuel feeding system|
|Shasta 2 gasifier clean-out char used to pre-load charmaker before filling with chips. This char is residue that discharges with the gas on completion of the gas making cycle at around 900C. The char was damp from storage bag reducing all dust hazard, and making it easy for me to shovel.|
|First pyrolysis gas from this new process. We found that at lower output, only one flare stack was required.|
|First test oxidation zone colour indicates lower than 1,200C, due to raw wood chip mixed with char.|
|Oxidation zone whiter colour of second test confirms that bed temperatures were well over 1,200C with char extraction temperatures dropping to under 500C before entering the water cooled extraction auger.|
|Big trouble on first start-up, as raw chip was accidentally dropped under the oxidation zone without carbonisation jambing the extraction auger.|
|First run char with raw chip removed from jambed auger.|
|Bent handle of fuel rod probe which sits on the top of the
hopper chip pile, was used to manually establish the full/empty refuel
Each refuel cycle will required about 7 cubic feet at the designed output, but this can be varied depending of the fuel quality increasing if the fuel is lower in moisture rather than green.
|Pyrolysis flare from the second test had a greater radiation factor indicating hotter oxidation zone temperatures. This can be felt as a stinging to bare skin.|
|Char chunk from the second test shows that fuel size variation has not affected the carbonising process.|
|Char chunk broken open exhibits a dry crispy texture without any acrid or acetic odour.|