Laimet Screw Auger Chipper
preparation for commercial gasification projects, especially those of
large size, has been a major problem for those seeking to change over
to renewable biomass available from forestry activity. With only
smaller fine chips from conventional plate or drum chipping technology,
it is difficult to obtain a fuel chip specification to meet the needs
of charcoal size in the packed bed of gasifiers.
I first saw the screw auger chipper sold as the Sasmo brand back in 1985, and have always believed this method could replace the traditional wood block fuel, and eventually in 2000, tested chips cut with a Sasmo in Northern Ireland. The chips were clean cut, critical to unrestricted flow movement, but very uneven in size due to the wood coming from storm damaged trees, mainly decaying. This created a lot of fines and dirt like material, causing unusual gasification problems. This was resolved by screening.
With fuel preparation the critical fuel supply issue, a recommendation was made to purchase the latest version of the Sasmo chipper, now redesigned and marketed as Laimet HP-25, www.laimet.com for our Californian project with CalForests. This development project will be reported separately. Tractor driven for these tests, the chipper is now being set up with it's own engine.
Given the rare opportunity to actually test out some of the lesser know facts of gasification fuel chip behaviour in a gasifier of know performance, provided positive experience for those attending, that I am sure will percolate down into other uses and needs for specification sized chip.
Chips are not easy to photograph in a way that truthfully convey size, but you can see the changes as explained in the text.
These tests were conducted in August 2008.
This is the HP 25 Laimet screw auger chipper located in California that was purchased to evaluate this method of fuel preparation specifically for gasification application.
|Because we were testing four different species of conifer available from the collection region, The chips were blown into recycled fertilizer bags for separate gasification trials.|
|Having waited since 1985 to get to use one of these machines, the first log had to be signed off by all involved.|
|We tested three sizes of screw auger blades, and this is from the smallest blade.|
|Having the first log stick and stall due to our over cautious low RPM speed level, provided this photo of how the chip cuts develop using a screw motion.|
|Instead of lifting full length logs, we cut them into 5ft (1.5m) lengths for easier handling by hand. The finish site will incorporate equipment for full log handling. Each 5ft length took three seconds to chip.|
|These are the medium chip, and take note of the average size, compared to the following differing species.|
|Medium chip, but smaller size range.|
|Medium chip, again with differing size range.|
|This is the business end of the Laimet Chipper, showing the small screw auger being changed. This took 1.5 hrs with quite a struggle until we learnt the tricks not covered in the instruction manual. We changed the blades four times in ten days, but this is not normally done once in use.|
|The screw augers are shipped like this, in a cage that is used to return the augers back to the factory for total rebuilding. The blade edges are like razors, and very hard. The big screw is on the right, and medium on the left.|
|This is the biggest chip size, and as you can see, it has a good chunky structure.|
|The same big chip/chunk side on, showing none of the linear fracturing commonly seen in small chips.|
|Changing species, the big chip/chunk changes it's size ratios, and shattering produces more fines. Wood moisture also play a big part in how the chip cuts.|
|From previous experience of fines in chip, we screened out the fine bark and whatever else fell through the screen. These fines always gravitate to the bottom of piles, and get picked up as a slug, causing a complete change to the staged char evolution in a packed carbon bed common to many gasifiers.|
|Note the oversized end chunks from the log. These too need separating out as their char evolves at a differing rate to the average small chip|