Gassifier Questions?

[Graham]

I'm going to replace my central boiler next summer with another stove looking into the gassifiction types. I have a forced air propane furnace with a heat exchanger in the plenum of the furnace, for the boiler. Are most of these furnaces pressurized units or are they open to atmosphere? The water storage topic, is it the same idea as the 140 gallons of water that my central boiler holds? These storage units, some have copper tubing is there water in the unit itself? I plan on building a wood shed next summer and a building for the furnace, does the furnace shed have to be insulated? I keep hereing they need dry wood, will they burn green wood at all or does it just smolder? I don't know of any one with a gassifing furnace, is there anything unusual to running them or loading them? I'm just wondering if it will be much different then running my central boiler. I'm looking to get a setup that I can fill once or twice a day, and will reduce the amount of wood that I need to burn. Currently in january and febuary when the tempature dips to -30Celcius or -22 fahrenheit I need to fill the furnace 2-3 times a day and usually need to relight it once when I get home from work. How would I size a furnace for my house, It is 2800sq/ft dhw about 25 years old with original windows, well insulated. Last winter I burnt 8-10 cords I'm guessing, of Popular (85%) and ash (15%).

Great forum, and lots of info.

Thanks for the help.

 

[Eric Johnson]

Welcome to the Boiler Room, Graham. It's always nice to have another Canadian member.

I'm sure others will jump in with suggestions, questions and observations, but I think you came to the right place. Since you already have the infrastructure in place, I think your switch to a new boiler will be a lot easier than trying to do it from scratch. And we're starting to see some promising new gasifiers coming on the market, designed to replace conventional OWBs like yours, with gasification models that pretty similar in both appearance and ease of use, but much more efficient and clean burning.

I think you should have dry wood to get the most out of a gasifier, but some brands claim that you can burn green wood, and from what I hear, it's true--although as I said, I think dry is always better.

It's late now so I can't address all your questions in detail right now, but I would suggest that you read some of the threads to pick up some basic information on gasification, and I'm sure that all of your questions will be addressed in short order. I would also suggest that you click on the Cozy Heat banner above, and check out the Blue Forge. Its design seems to be similar to the OWB gasifiers I was talking about earlier, so that ought to get you headed in the right direction. As you get into it, we can start to narrow your options down to fit your situation. This is a great group--I think you'll find that we like to answer questions and discuss new ideas.

 

[Seyiwmz]

Graham, I have the EKO 40 Gasifier, ran it for 3 yrs now. I have no problem with getting 24 hrs out of 3 loadings. Once before bed, once in the morning, and once after work. I just got done running 21 days straight without re-lighting the fire. I didn't have my water storage hooked up yet, so I just ran continiously. Re-loading is very quick. I turn off my control unit, turn on my overhead smoke vacuum that I home built, open door, load wood, turn on control unit, shut off vacuum, walk away in confidence. The on-board computer does the dirty work. Pretty easy, I think you could train a monkey to do it.

Our Fire Departments use water to put out fires, so trying to burn wet wood amounts to the same logic. They say that you have to basically waste 20% of the heat value (btu's) to dry the wood before it will burn. Why waste heat value just drying the wood? Just cut your wood in advance. After work yesterday I buzzed up 2 facecord for next year. Great exercise for free. No club membership fees. Good luck. Seyiwmz

 

[Nofossil]

Additional comment on green wood:

If you're running a boiler that's 25% efficient in the first place, losing 20% is of your potential heat only takes it down to 20% - hardly noticeable. If the boiler is 85% efficient, losing 20% of that is a much bigger hit and much more noticeable. I think that's part of the story.

The second part is that wood with higher moisture content makes it harder to start and/or sustain the secondary combustion. I've had real difficulty when trying to start a fire with wood that isn't completely dry. Once it's going, a few greener pieces won't hurt anything.

Some folks don't like to start fires, and a major attraction of large boilers is that you can fill them with huge chunks of green wood and you'll still have coals six days later.

Gasification boilers are at their best when they're running flat out, although most brands idle pretty well. If you get a really large boiler, it will be idling almost all the time - not gasifying.

Storage helps with this. Storage typically means 500 gallons or more - ideally, enough to carry you for a day or so. That allows you to build a fire in the evening to heat both the house and the storage. The fire can burn flat out, going out sometime in the night. The tank can then keep you warm until the next evening. In warmer weather or with a bigger tank, you can skip days while staying comfortable.

Storage adds complexity, but everyone who has it seems to love it. I ran a year without, and I'm on my second year with. I've documented my system on my site - link is in my signature below.

 

[Eric Johnson]

Thinking about the discussion in another thread about modulating the fan speed more aggressively through modifications to the controller--with the goal of increasing efficiency and reducing idle time--has got me thinking. First, I think that if it was that effective, they would program that feature into the controller. They already do at the top end of the temp range, so obviously it's possible.

But all that aside, I had another idea that I thought I'd bounce off nofossil, or anyone else who might have some expertise where heat exchangers are concerned.

Would it make sense to change the flow rate through an intank heat exchanger as the tank heats up, to increase the heat transfer efficiency? I know that nofossil observed that as the tank heats, the hx's ability to transfer heat from the boiler diminishes as the Delta T gets smaller. If you could manipulate the rate of flow, say through some kind of variable speed pump, could you goose up the heat transfer at higher temps?

 

[Nofossil]

I think this needs to be another thread.....

Thinking about the discussion in another thread about modulating the fan speed more aggressively through modifications to the controller--with the goal of increasing efficiency and reducing idle time--has got me thinking. First, I think that if it was that effective, they would program that feature into the controller. They already do at the top end of the temp range, so obviously it's possible.

I think if you're the boiler controller, you have a hard time predicting the heat load. There's a lot of 'throttle lag', so attempting to modulate effectively under the range of installations and operating conditions that might be encountered would be a challenge. I don't get the impression that boiler controllers represent the pinnacle of software sophistication.

But all that aside, I had another idea that I thought I'd bounce off nofossil, or anyone else who might have some expertise where heat exchangers are concerned.

Would it make sense to change the flow rate through an intank heat exchanger as the tank heats up, to increase the heat transfer efficiency? I know that nofossil observed that as the tank heats, the hx's ability to transfer heat from the boiler diminishes as the Delta T gets smaller. If you could manipulate the rate of flow, say through some kind of variable speed pump, could you goose up the heat transfer at higher temps?

I just bought a Grundfos three speed pump (an item with negative WAF, as it turns out). My goal is to modulate the wood circulator speed as a method of controlling the inlet and outlet temps.

For in-tank HX, I expect that water velocity is well above the point where more speed will result in significantly more heat transfer. Simple qualitative test: If the outlet temp is within a few degrees of the tank temp, then higher speed would give you more heat transfer. If there's a more significant difference, then the water is already going through fast enough that it doesn't have the dwell time to get as much temperature rise as it could. If that's the case, increasing the flow rate even more will mostly have the effect of lowering the outlet temp.

 

[Eric Johnson]

Actually, what I had in mind was lowering the flow rate for greater dwell time in the hx. That may be at odds with the need to get the heat away from the boiler, but if it results in more heat getting into the tank, it might be a net positive. But that's just idle drive-time speculation on my part. I have several different pumps, including two Grundfos 3-speeders (WAF neutral, for some reason, probably because she doesn' know they exist, and wouldn't know what to make of them if she did), so maybe sometime I'll swap them out when everything is hooked up and see what happens. I think putting a Taco 007 in place of the Grundfos 26-96 would affect the flow rate (not sure exactly how), but it might not be good for the pump. Just enough knowledge to be dangerous, as they say.

There is an impressive amount of lag time with my system on a cold start. I liken it to waiting for a wave. You're standing in ankle deep water facing land, waiting for the water level to rise. Next thing you know, you've got this huge wall of water crashing down on your head. Or, like flooring a big engine at a slow speed in a high gear--it takes awhile to overcome the forces working against it, but once it does, look out. I have a big heat load, so I've learned how much wood to put in the firebox for the desired effect (usually).

On the controller issue, do you think hooking an outdoor thermostat to the controller would help compensate for the lag-time?

 

[ISeeDeadBTUs]

Just cut your wood in advance. After work yesterday I buzzed up 2 facecord for next year. Great exercise for free. No club membership fees.

But. . . .but. . . .but. . . .What about the cute pony-tailed chicks with dampness in the right places?? Last time I was at the gym for a workout, they were nicely displayed around about the place.

 

[Graham]

nofossil what is the average temp in the winter where you are and what would a really cold day be? here the average temp is probably -20C or -4F and a cold day would be -40C or -40F, I'm just wondering if I would have to keep a fire on all the time or every second day. I would just hate to put the money out and find out it is more work and babysitting then the furnace I currently have. Does anybody have a blue forge, or know much about them? The storage tank is it copper tubing full of heated water from the boiler sitting in a insulated tank?