Work at Northern Arizona University (NAU) -2008

The NAU Engr, Dept. had an ongoing project to extract pine-oil from Ponderosa Pine wood-chips. They had already recovered some pine-oil, but the process was far from practical for commercial use.

I got involved to try and make a more commercially viable process for pine-oil recovery. As a retired Chemical Engineer, I volunteered my time, and built much of the test equipment in my garage and kitchen. After some abortive efforts with co-current rotary drying we decided to concentrate on fluidized beds after finding a patent that indicated that it was possible. This is a technology I was familiar with.  It is routinely used oil-refinery Fluidized Catalytic Crackers (FCCs).

We made at least a half-dozen test units and fairly quickly found that fluidizing the wood-chips required some fairly intense air-jets to eliminate “rat-holing”.  We found that the intense air-jet made by releasing a spring loaded bellows worked reasonably well. This created pulsed-fluidization which is well studied in the literature, but mainly for round or nearly round particles.

We found that the conventional means of creating the pulses did not work. However, the more energetic pulses from the spring loaded bellows worked quite well.

We instrumented the unit to allow a time-slice heat-and-material balance to be made during a batch run of the unit. We tested both the pine-oil and moisture content of the wood  at several times during the run.  We discovered a strange phenomenon (at the time) where the water was removed while the pine-oil stayed behind. These runs were made without heating the gas significantly, and the evaporation of the moisture made the fluid bed quite cold (about 50 F).

This was a desirable characteristic in collecting pine oil because there is only about 0.6% pine-oil and nearly 100% water (on a dry wood basis). If the water and pine=-oil all came off together there was going to be a problem separating the small amount of oil from a large amount of water.

We built yet another test unit to better investigate the phenomenon.  It used controllable pulses of compressed air, and the air could be heated. Tests showed that at very low temperatures (below about 50 F) the moisture could be removed without removing much pine-oil, but the advantage went away when the temperature increased. These tests and results were published in a peer-reviewed paper.

The process was not commercially useful at such low temperatures because the amount of dryer gas would be huge.  The maximum amount of water that can be carried away by the dryer gas is when the gas is saturated or at 100% RH.  At low temperatures the dryer gas can’t hold much water. We had run out of money and ideas for pine-oil recovery and we shut the project down.

Work at Forest Energy – 2009

Lar took a job at Forest Energy Inc as a process engineer.  He was asked to use his experience to build a commercial wood-chip dryer.  A version of the pulse-fluidization process was attempted using fast-acting butterfly valves to create the pulses, but it became clear that there was more testing and development than the owners could afford, and the pulsing gas was going to create problems with a commercial unit.  The effort was abandoned.

Development Back in Flagstaff – 2010

Lar had returned to NAU as an instructor.  He and I decided to carry on with a dryer development effort on a small scale to see if there were ways to improve the process.  We built a small unit in my kitchen (a 3′ x 4′ bench with a 6″ deep x 12″ wide fluid-bed).  We tried dozens of variations and got quite adept at making changes and performing quick tests.

We discovered that with a sloped bed with a jet of gas across the entire bed could blow the chips upward without rat-holing. Although our batch unit just recirculated the chips, we could see that the chips could be thrown up and forward to the next bed in a continuous design.

We made a rough plan to further test the design so it could be  commercialized.  We applied for Associate status with our local business incubator NACET (Northern Arizona Center for Entrepreneurship and Technology) and were accepted.

NACET suggested that we contact NAU about our findings and get clearance so there would be no problems in case we needed investors.  We disclosed our basic findings to NAU.