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 Preheated combustion air my thoughts

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Gary B.



Posts : 47
Join date : 2014-03-18

PostSubject: Preheated combustion air my thoughts   Sun Nov 22, 2015 9:13 am

Gary B here from Minnesota. I have been working on a preheater for combustion air for my large batch box rocket stove I built last year. I know some of you are thinking where is the cast riser batch rocket heater stove you were building. Well my health has been poor for a few months now so I have had to put that project on hold for a while. I was so looking forward to this new stove design and I can't tell you how it bothered me to be so close to done and all of the sudden I am just to weak to work on it. Well my new stove was sort of like PPotty's cast riser but my design was going to have a combustion air preheater like no other. Well as I am putting in my time trying to recover I decide I can probably work an hour or so a day if nothing is to heavy so ok I decide I am going to try and build a combustion air preheater for my original stove. Also this will give me a chance to test my design out before I weld up my cast riser stove with this same preheater.  So I have been corresponding  back and forth with Dale (trying2hard). Our goal was to have the combustion air as hot as we could get prior to entering the batch box. PPotty and a few others will back me up that preheated combustion air is the best thing you can do to raise the efficiency. So many good things happen when you have preheated combustion air: first thing you can do is slow down the air speed coming in and going out of your stove. I think this is one of the things that is over looked. With my new preheater it is amazing how much more I can slow down this air movement. So now the stove gets even hotter as it is not getting cooled off by room temp air flying through burn chamber, your wood consumption goes down as you don't have roaring fire ( my fire color is purple with orange tips). So now you have time to scrub off a lot more heat with a good heat exchanger. So any how I have sent Dale pictures of this preheater and since I can not get pictures to post I have asked him to post here for me. Once Dale posts these I will explain system as it will make a lot more sense. I can tell you I have been burning this combustion air preheater for some  time now and I am very impressed. I spent around $100.00 on this and I would do it again with out a doubt.
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gadily
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Join date : 2013-12-08

PostSubject: Re: Preheated combustion air my thoughts   Sun Nov 22, 2015 9:46 pm

hi gary as a plumber i see plenty of benefits to the system using preheated air

1, air rises its giving a push upwards
2, more heat within firebox
3, cleans glass
4, pushes the gas towards the riser
5, slow down the air input to firebox

i see 2 benefits to this system one is at primary air the other is at secondary air

many are striving towards heated primary air and using quick heat for the secondary air im also considering pushing higher heat at the secondary air with the new build

there is draw backs to this effort the heat within the riser can be very hot indeed and any metal that is used is going to take the brunt of very high heat

my idea is to use a firebrick at top of riser mainly to displace some of the vortex tube heat by deflecting some of the heat away from the top
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ppotty1 Admin
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Join date : 2013-09-30

PostSubject: Re: Preheated combustion air my thoughts   Wed Dec 09, 2015 11:39 am

Hi Gary, i look forward to seeing what you have come up with, your dead right about slowing down the air flow and getting more heat I realised this when i fired up the stove last year and it dawned on me what was going on. When I built the latest stove I was working towards gassification in the firebox and being able to decrease the air flow to burn less fuel. I said in the video not only do you burn less fuel but the temp really ramps up but not just due to the gassing. as air moves slower more is released from the exchanger and alot of that is due to the cast riser. There are also other things going on and all of them start to act together in a magical way.
I couldn't have known all the facts until it was built and working and the bugger of it is...that then gave me new ideas to further increase heat output but it would mean a new build.
I will be building another stove but will have the luxury of working in a warm workshop this time and no deadline, the stove can be much smaller now due to what is going on with all the elements working together, ive been working through ideas and coming up with solutions thanks to the last stove pre heating is essential to output.
I like the fairly heavy cast riser because of the benefits it gives later on in the burn cycle and have been working on ideas to improve it which I know I can achieve.
But like before when it is built I know I will see room for further improving output...which is the bug bear of stove building for me.
Hope your on the road to recovery.
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gadily
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PostSubject: Re: Preheated combustion air my thoughts   Wed Dec 09, 2015 9:01 pm

I would agree but i also think super heating the secondary air could improve your system much better ppotty
instead of your normal quick run for it as i believe it would make a lot of difference in doing so

they way id possible do it is by tapping into the front heated air area and a run over to it

something which i think that you could do easily from your stove
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ppotty1 Admin
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PostSubject: Re: Preheated combustion air my thoughts   Thu Dec 10, 2015 10:00 am

I disagree somewhat on the need to heat the secondary air to higher temps, what the firebox is producing is a gas and the gas wont burn anymore efficient on super heated air it will most likely burn just as well on cold air, the sec air on mine goes into the riser around 250C which i think is sufficient for the job its doing. More benefits are to be gained on the primary.
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