R Parian wrote:Thank you for such a detailed account with quality pictures! Where did you purchase the CFB and the CF riser materials? I'm trying to find alternate sources for my own custom build.
thomas rubino wrote:Solomon;
Turn that warped cfb around and fire it again. It will go straight.
Ryan Adobe wrote:I wonder if you were able to overfuel it by scaling it up.
Ryan Adobe wrote:Also, I wonder if having a cold outside air temperature on either end of an open system like that would "supercharge" the system, and increase the temperature to an unsafe degree? I bet that the same core installed into a full system, in a house that is above outside temperature, with a large thermal mass on the back end would behave differently. Pretty cool post, nice work!
Ryan Adobe wrote:I'm surprised you didn't burn your eyebrows off when taking the photo down the riser..
Scots John wrote:That riser looks super cool, did you see any steam rising as that can cause hairline fractures.
Yes, this is quite possible, and I have thought about that. Having a full feed tube would reduce the draft a little also, and the barrel over the top of the riser would definitely reduce the draft, and also, I don't need four feet of riser either. That would reduce the draft. Definitely some areas that can be experimented with. And I have enough board to replace the burnt parts so I can certainly try again. And if the risers completely fail, I can just do CFB riser as well.
Michael Fundaro wrote:I am definitely not an expert in rocket mass heaters but with your entire set up exposed to air I believe you did not have an adequate heat sink around your material. Perhaps, if it was completely surrounded by the cob media the heat would have been absorbed into the cob and your material might have faired better, or survived unscathed.
R Parian wrote:I contacted Zartech but haven't heard back yet. How much was the CFB and was it 36"x48"? Do they have CFB that has a higher temp rating than the 2300 F board?
Nick Williams wrote:Used to be responsible for the mechanical integrity of some big industrial furnaces...
Not saying it's what happened here, but drying refractory materials is more than just getting above the boiling point of water. As the materials used to form the refractory heat up, they actually release moisture at temperatures well above the boiling point of water. Gibbsite to boehmite at about 300 F, boehmite to alumina at about 500 F (don't quote me on those compounds or temperatures, it's been a while since I cared enough to look them up, and I'm sure there are other dehydration reactions in other refractory materials). As a consequence, the first time you fire up a furnace with fresh refractory in it, you heat it relatively slowly (depending on the thickness, I've had dryouts as slow as 25 F/hr for a dual-density transfer line in a steam methane reformer), and hold for extended periods of time (like 12 hours in some cases) at those dehydration temperatures so you don't generate a bunch of steam and spall everything off all at once. Once all the water has been generated and driven off, you bring it up to full operating temperature. It's not nearly as big a deal after the first firing, or if the refractory was fired prior to installation, but for that first burn, it can be a big deal.