first test burn with garn controlled by lambda o2 sensor, and flue gas temp, no hard data yet , the parameters start by pressing a button to open the motorized combustion air damper and enable the fan to run at 60hz for 5 minutes to get the fire up to temp, 7% 02 request modulates fan speed from 50 to 80hz, a cutoff on 02 controll at 12% at this point i have2 choices, one to reload press button and repeat program or run rest of burn at 50hz untill flue temp declines to 200degf at witch point blower shuts down and flue closes 80% 2 hrs later, end of program. i also have a low water indicator , a program or manual toggle ,a indicator light that i can see from the house that blinks at the 12% let run or reload , and a system shut down. what seems to happen is that after the initial 5 minute startup 02% is about 4% at witch point the fan ramps up to 80hz for 30+/- minutes and then gradually ramps down to maintain7«out 15 minutes passing 7% the fan decreases speed to 50hz, when o2 threshold of 12% reached fan runs at 50 hz to end. it will take some time to see how it responds with varied mc content wood. i have to get the trending software from rockwell to graph burn . any thoughts welcome
02 controlled timer free garn
- Thread starter TCaldwell
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Educate me a bit - I'm not familiar enough with the Garn to understand what the effect is of varying the fan speed. I'd assume that you're aiming for enough extra air to ensure complete combustion, but no more than that... but maybe I don't know exactly what your goal is.
In the downdraft gasifier world, we're concerned with the ratio of primary to secondary air, and especially with getting just the right amount of secondary air. I don't know how that translates to the Garn world.
In the downdraft gasifier world, we're concerned with the ratio of primary to secondary air, and especially with getting just the right amount of secondary air. I don't know how that translates to the Garn world.
in the garn the p/s air is pre calibrated and not adjustable only the combined cfm is adjustable with a 3 phase motor and inverter/vsd. the p/s air independant control would require extensive internal mods, so moderate control can be had by modulating the one draft inducer fan using the ammt of unburned o2 in the flue gas as the parameter, stoichiometeric complete combustion with a little excess o2 works out to approx 7% unburned o2 in the flue gas, through monitoring feedback of the o2 % the fan increases or decreases to maintain the desired o2%. it is a little rudementary with the garn design but should take care of the initial puffing from lack of combustion air,and too much air at end of burn when there are only coals. in a boiler like yours you could use stack temp to control primary air, low stack temp more primary air than secondary air and secondary air would be controlled by o2 in fluegas, the primary air to make the gas and the secondary air to burn it
heaterman
Minister of Fire
TC. I've wondered if a person could get the same throttling effect by using a motorized flue damper to restrict air flow on the outlet side of the blower vs the expense of a 3PH motor+VFD setup like you have. Just a random thought from a random mind................
Jim K in PA
Minister of Fire
Very interesting Tom. As Steve mentioned, it would be great to have a way to achieve a little more control without the high cost of the 3P VFD motor. I want to add a small controller that would shut the fan down when flue outlet temps get down to storage temp+20, and then shut a motorized intake damper when outlet temps get to storage temp+5. That should be cheaper and easier, but certainly not as efficient as what you are working toward.
BTW - just from an operational standpoint, I notice that 80% of my heat input happens in the time period of Start+10min through STart+40min. I am still amazed at the rapid heat transfer into the tank you get with the GARN.
BTW #2 - I also have been experimenting lately with fuel load position and size within the primary chamber. I have learned how to get gassification going within 4-5 minutes at times by not shrouding the SRC with wood that is too close to the rear, and not too high in the chamber. Using a reasonable amount of dry, light wood (pine is great) at the center of the fuel stack also enhances quick transition to gassification and high temp burn.
I like how simple my GARN is, and how well it works right "out of the box". But that does not keep my mind from wandering. . . :lol:
BTW - just from an operational standpoint, I notice that 80% of my heat input happens in the time period of Start+10min through STart+40min. I am still amazed at the rapid heat transfer into the tank you get with the GARN.
BTW #2 - I also have been experimenting lately with fuel load position and size within the primary chamber. I have learned how to get gassification going within 4-5 minutes at times by not shrouding the SRC with wood that is too close to the rear, and not too high in the chamber. Using a reasonable amount of dry, light wood (pine is great) at the center of the fuel stack also enhances quick transition to gassification and high temp burn.
I like how simple my GARN is, and how well it works right "out of the box". But that does not keep my mind from wandering. . . :lol:
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