Thermocouple + Pyrometer = entertainment

[ohbie1]

I replaced the sight glass with a ceramic disk that has a 12" K thermocouple that sticks into the gasification chamber. This is connected to a pyrometer (set for K) that I mounted on the front of the boiler. The BOSS wants to know why it's taking me so long to start the fires.
I sit and watch the meter and change one of the many variables to see how it affects Temp. This is like a video game for peak efficiency fanatics; you get hooked pretty quickly.......thinking of another variable that might raise temp. The pri and sec air controls make this game fully interactive.
So far I have seen a high of 2200 deg. on the meter.
The type of wood burned makes a diff. My junk wood(Tulip Poplar & Sassafrass) runs at 1800, the Ash, Oak, Maple at 2000-2200.
Most interesting so far is, I found that the air settings recommended by Tarm in the manual do NOT produce the highest temps in my chamber.

 

[flyingcow]

I've got my innova set at 50% primary(top adj) and 75%(bottom).I burn beech/rockmaple. I'm burning soft ample/white birch etc for a few weeks. Didn't seem to make much diff on settings. Talked to tarm, they thought it was ok. My stack runs at 400, when it starts creeping up, time to clean. I like the idea of a pyro. Nice toy.

 

[flyingcow]

Alos when I start a fire, if its starting slow, i open the secondary up while I'm gathering wood. Opens up and starts quicker. Fill stove, close back to 75%.

 

[TCaldwell]

high secondary burn temps are only part of the picture, basically you will get gasification over 1200degf , the key is two fold, you want to run the most primary ,co2 wood gas production coupled with the least secondary , o2 control. this will represent its self in damper positions that are not always opposite in position. often during high burn both dampers will be 80% closed, in theory you have the concept start and end of burn high primary, low secondary , and middle of burn a little towards the opposite. of course different wood combinations will vary the damper positions to try to maintain a preset o2 level in the fluegas, the stoichiometeric or optimum values for wood combustion are 7.5% o2 and 13% co2, this represents a burn with a lower secondary burn temp, but lasts much longer with a low flue temp, thus actually producing the most btus per lb of wood. when you attain very high secondary burn temps the primary is too high a volume for the secondary to burn off, thus a rich or very low o2 % in the fluegas and higher flue temps. what we been discussing is combustion effiency, the second part of this is boiler combuster and hx design, each of witch manufacturers differ.as far as temps go you want to know what the highest average differential over the course of a burn between the secondary type k and a type k in the flue representing the ability based on design for your specific boiler to absorb the btus produced. in the long run this will not be indicated by the highest secondary temps observed. the formula is temp differential x cfm x 1.08= btus absorbed by boiler. omega engineering has a inexpensive type k differential display. for example with the garn at a stoichoimeteric ratio a average 2 load burn will take 4 hrs and yield a 60/80 deg temp rise, a average secondary temp below 1500degf, if i change the o2/co2 ratio to run richer the same 2 load burn will take less than 3 hrs, a little less temp rise coupled with a higher secondary and flue temp.

 

[ohbie1]

for example with the garn at a stoichoimeteric ratio a average 2 load burn will take 4 hrs and yield a 60/80 deg temp rise, a average secondary temp below 1500degf, if i change the o2/co2 ratio to run richer the same 2 load burn will take less than 3 hrs, a little less temp rise coupled with a higher secondary and flue temp.

So can I conclude from this that I should aim for a secondary temp of 12-1500 degrees rather than trying for the highest secondary possible. This would be easy since I have the K couple in the secondary?

 

[TCaldwell]

that would be a conservative approach, however some of the combustor and hx designs will accept a lower o2/co2 ratio and still be efficient. the idea is to run as much primary as the secondary will burn off in a way that manifests itself as to have the highest type k differential for the average of the burn. this takes a portable flue gas analyser, type k reader and lots of boiler face time and patience. you might enquire with the boiler manufacturer about test results and optimum ratios that they try to achieve. if their control of 02 is not directly from a o2 sensor, they probably have a direct correlation through dataloging results of 02/flue temp, and use a type k as their means of control, with a good enough end result . manipulation on your part of the air ratios will help you get a handle on how your boiler reacts, with a batch burn boiler the wood load and needed parameters are always changing to maintain a desired o2, this becomes easier with a auto feed system.

 

[ohbie1]

I lowered my secondary air today. The sec. temp is about 1500. I see a big difference in wood consumption. Before, a full load never gave me more than a 2hr. burn. Today it's already burning 2 1/2 hrs, and it looks like I'll get 3 to 3 1/2. That's a lot more heating time. I always burn full out full time(no idling), so I'm going to have to take readings on the storage tank delta T I'm getting with this new(to me) method.

Thanks.

 

[heaterman]

high secondary burn temps are only part of the picture, basically you will get gasification over 1200degf , the key is two fold, you want to run the most primary ,co2 wood gas production coupled with the least secondary , o2 control. this will represent its self in damper positions that are not always opposite in position. often during high burn both dampers will be 80% closed, in theory you have the concept start and end of burn high primary, low secondary , and middle of burn a little towards the opposite. of course different wood combinations will vary the damper positions to try to maintain a preset o2 level in the fluegas, the stoichiometeric or optimum values for wood combustion are 7.5% o2 and 13% co2, this represents a burn with a lower secondary burn temp, but lasts much longer with a low flue temp, thus actually producing the most btus per lb of wood. when you attain very high secondary burn temps the primary is too high a volume for the secondary to burn off, thus a rich or very low o2 % in the fluegas and higher flue temps. what we been discussing is combustion effiency, the second part of this is boiler combuster and hx design, each of witch manufacturers differ.as far as temps go you want to know what the highest average differential over the course of a burn between the secondary type k and a type k in the flue representing the ability based on design for your specific boiler to absorb the btus produced. in the long run this will not be indicated by the highest secondary temps observed. the formula is temp differential x cfm x 1.08= btus absorbed by boiler. omega engineering has a inexpensive type k differential display. for example with the garn at a stoichoimeteric ratio a average 2 load burn will take 4 hrs and yield a 60/80 deg temp rise, a average secondary temp below 1500degf, if i change the o2/co2 ratio to run richer the same 2 load burn will take less than 3 hrs, a little less temp rise coupled with a higher secondary and flue temp.

Heaterman likes this!

 

[TCaldwell]

Ohbie, at least this is a starting point, and you can adjust p/s for higher and lower secondary and flue temps. my testo 327 combustion analyser results indicate a average effiency across the burn cycle between 84.5% and 86.5% based on a starting water temp of 150 degf , the normally aspirated garn will hit these numbers but for a much shorter time frame thus lowering the averaged effiency over the burn. aside from the testo for spot or reference checks, i have a insitu o2 analyser that dsplays real time the o2% and a calculated co2 % and outputs these as 4-20mA signals that are input to a control box that i had made witch will independantly send the desired scaled o2 and co2 percents to modulating control dampers. this box is capable of adjusting the percents to run rich or lean, not unlike a engine tuners device in principle. i suspect the boiler manufacturers contact a controls company like rku, who provides with a adjustable % controler, the mfgr tests and datalogs to find the corresponding flue temps for damper or motor setpoints that are most efficient over the burn cycle, then rku programs a controler with non adustable setpoints for that particular boiler. as you see some manufacturers use a oxygen sensor with a thermocouple for control,
Heaterman, where is dectra's control system?

 

[flyingcow]

I lowered my secondary air today. The sec. temp is about 1500. I see a big difference in wood consumption. Before, a full load never gave me more than a 2hr. burn. Today it's already burning 2 1/2 hrs, and it looks like I'll get 3 to 3 1/2. That's a lot more heating time. I always burn full out full time(no idling), so I'm going to have to take readings on the storage tank delta T I'm getting with this new(to me) method.

Thanks.

Since I've run my Innova I've had a minimum of 3 to 3 1/2 hour burns. Seems to work well. Fairly consistant with others and the same sized unit. Seems like you've had something out of wack.

 

[ohbie1]

FLYING COW
Since I've run my Innova I've had a minimum of 3 to 3 1/2 hour burns. Seems to work well. Fairly consistant with others and the same sized unit. Seems like you've had something out of wack.[/quote]

Only thing that's been out of wack is me. I've been striving for higher and higher sec. chamber temps., burning up the wood like crazy. Thanks to TCaldwell's posts, I now realize there is more to the efficient burn than just high sec. temps. Better late than never..........The things you learn from this forum are amazing AND important.

 

[Rick Stanley]

You guys remind me of a couple friends of mine that are "hyper-milers". I'd never heard of the term before I'd met these guys. For those who don't know, "hyper-mileing" is making extreme efforts toward attaining higher mpg with your car.

To begin with, they both own hybrids, then they go further and tinker with them to get better gas mileage same as you guys do with your boilers.
But, much of what they do is technique. They coast down hills. They completely shut down the engine and coast down hills. For miles, at times, because they have pet routes to and from destinations and rarely come and go the same way because they plan their routes by the lay of the land so they can coast more going both ways. They keep logbooks filled with data like what approach speeds work best for cresting a certain hill to result in the longest coast distance.
Anyway, beyond that, throttling technique is huge, an art form really, according to them. Nice even smooth acceleration on upgrades is critical. Rounding curves close to the inside to save ground, but not so much as to lose momentum, while at the same time keeping the perfect throttle position.
On flat ground, they're always seeking the sweet spot on the throttle. Enough gas to keep things moving, but just enough. So as to get a real feel for the gas pedal, these throttling techniques are mastered by driving barefoot.

So, the next time you build a fire take your shoes off.

 

[ohbie1]

Rick

That hyper mileing sounds great; I've got to get into that. It occurs to me that if you are driving barefoot you WILL improve MPG since you leave your shoes home..........less weight=more MPG.