Purpose
To formalize and compare the performance of different grate shaking modes and grate hole sizes to better understand char/ash fines purging and prevention of reduction bell packing.
Methods
Grate
The standard grate (3/16" perf) was replaced with expanded metal with diamond hole openings of 3/8x3/4".
Expanded metal
Grate Shaker and Control
A double eccentric shaker was used with silicone tubing seal attached to grate via 1/2" rod, yielding largely vertical forces on grate with eccentric RPM in the 100s.
Grate shaking was triggered at a pressure ratio (P_comb/P_reactor) of 0.3, shaking for 1 second. Triggering pressure ratio was not smoothed.
Double eccentric shaker. Seal using high temp silicone tubing, which limited horizontal play.
Reactor Regulation
Reactor pressure regulation was held at ~constant 6 inH2O during main run using a pulsed on/off solenoid valve and 5 gallon buffer tank. This system is being explored as a component of the research kit.
Fuel
Fuel was air dry cedar chips (Acapulco) and coarse cypress chips 1/4-1" mesh (GWRY), cedar chips first, transitioning to cypress.
Coarse cyrpess chips (left) and cedar chips (right)
Results
Compared with previous testing (Grate Shake Test Run 20100621) of grate shaking, shaking duty cycle was significantly reduced.
In a previous run using a different shaker ("KA" - single eccentric close to rod in complete enclosure through compression fitting) and using standard 3/16" hole perf, the shaking duty cycle reached 80-100% during the end of the run (GEK run of 1.3 hours).
The grate shaking duty cycle during the GEK run of 1.1 hours was ~0.5%.
The effectiveness of shaking did decrease over this period, with shaking becoming more frequent toward the end of the run:
x-axis: Grate Shaking Events (1 second each)
y-axis: time of event (deciseconds)
Note that four shaking events are consecutive (#14-17), considering this one event would make the slope more linear.
Interpreting the graph: It can be expected that after a fresh start, materials will reach an equilibrium state, after this point, the ideal plot would be a linear curve (constant shaking).
Bypass Char/Ash
During the run, roughly 2 liters of char bypassed the grate, material was obviously coarser than the fines passed through the 3/16 grate (example of char from Maker Fair run, below). During a day of running at Maker Fair, roughly 3-4L liters of char/ash passed through the grate, over a total run of 5-7 hours.
Samples of char from the run (20100922, left) and char from Maker Fair (right).
Grate shaking is very rare, compare with grate shaking during 20100813 run (GEK running from 60-150 mins, 60-70 minutes can be ignored [P_comb reading atmosphere]):
Cycling of the PID output (duty cycle) may be caused by variation of compressed air supply pressure as compressor turns on and off with ~constant air consumption. Variation from 20-32 minutes likely from premix air valve adjustment, left fixed afterward.
Fuel consumption rate/augering is constant w/ duty cycle of ~35-40%