I got the idea of a monorator hopper from the old gasifier designs for cars in the WW2 era. I had moisture problems in my first gasifiers and found this in my reading.
The heated moist air (from the burning fuel on the bottom of the pile) rises up in the hopper and flows back down the (cooler) sides of the hopper and condenses and is collected in a moat (so it doesn’t flow back onto the wood). Then you would have to waste energy to vaporize the water again in an endless cycle diluting (with steam) what gas you may have produced. This same steam will foul a spark plug immediately. Even when I used to get a burnable gas, there would still be moisture sizzling in the test flame nozzle. Then I found this pic (above). This is my version. The moat has a double valve drain system to the outside. The hopper gets heat from the steam, hot air rising, etc. The outside of my hopper is hot, but always cool enough to condense the steam in side. It works great. View through cleanout and bolting access port. 3 ports equally spaced.
Here is my moat and drain hole. Note the steepness of my grate compared to the picture above. I need to insure the fuel flow so an external vibrator is also employed. As you can see from my video, it collects all the moisture that is in the feed stock. Below this at the nozzle level there is (or should be) complete combustion of the now dry feedstock. This complete combustion produces CO2 and H2O which is then broken into C, H, and O atoms as it passes through the restriction into the char bed. These atoms are then immediately recombined into the burnable gases, carbon monoxide (CO), methane (CH4) and hydrogen (H2). If the design is correct no H2O should be produced or present at this point. A drop out tee before the carb would capture the errant drop of H2O.
Forgetting the work involved, this is without a doubt one of the most significant improvements I’ve made in my gasifier quest. This should solve your water problem, it did for me. One should be able to bolt this on to an existing burner with a little adaption. You can see my mounting bolts coming up through the hopper base. It bolts onto my burner unit.
It is a bit of a pain bolting it down this way. I’ll figure something different for my next one. Just about the only reason to remove it would be gasket failure. The grate does move to straight up and down making access a little better.
You’re right, the fire tube is longer than it has to be. I used what I had figuring it would give me a longer run and save me the hassle of more building. It works fine, even if I need a step ladder to fill it. Ha, Ha.
PS: if you want to see my complete build, Go to; Small engines, scroll to “My first small engine run”. Then look at comments 140 thru 190.