Green, Whole Tree Chip Boiler - Feasibility

[jebatty]

I just started doing some background research on green, whole tree chip boilers. The concept would be to use one for multi-building district heating in a fairly large institutional setting. Pluses immediately are on-site forest land that will supply the chips and therefore minimal transportation cost.

First, does anyone have experience with these, particularly in a cold climate like northern Minnesota? Second, these are some of the issues I have identified, and how are these dealt with, do they cause problems? Third, are there other issues that need to be examined?

1) The chips consist of fines, bark, needles/leaves, twigs, and branches, as well as solid and decayed wood from the bole of the tree, and on-site dirt and debris, and as such they contain a much higher percentage of incombustible material. What is the impact on ash production, what effect on need and frequency to clean the boiler, do they produce clinkers that cause operational problems?

2) The chips are wet (45-65% moisture). Does this cause more labor, operational, and maintenance costs for the boiler than dry chip boilers?

3) Do wet chips in storage have spontaneous combustion issues?

4) How susceptible are wet chips to freezing into clumps and blocks, or solid masses, resulting in operational problems or failure of the loading mechanism to fuel the boiler? The area climate typically not only is well below freezing, but frequently well below 0F for substantial periods of time.

5) Do wet chips result in higher emissions than dry chips?

6) Can any green chip boilers also burn green chunk wood or stove wood material, such as rounds and splits? Can they burn seasoned chunk or stove wood material (20% MC +/-)?

7) Are any green chip boilers classified as gasification boilers?

Thanks for the input.

 

[tom in maine]

The University of Maine did a lot on this in the late '70's and '80's. Norm Smith was an agricultural engineer who
installed many units. Dick Hill showed me one that the university used for many years to heat a large utility building.
They were fairly simple and were gasifiers.
I think quality of chips was critical for proper feeding. I am not sure if there is anything online.

 

[Karl_northwind]

You have Abionova/woodmaster in your neighborhood. I can't comment on their chip boilers though.

I can only answer a couple of these:

wood gun makes a chip/pellet feeder option for the E-500 and E-1000. This might be useful if you didn't know.

we will be dealing with the Heizomat chip boilers when they're available here. small to really large. I'm not sure which sizes will be available here. they have 2 different ash removal systems. their website will give you more information than I can. they also manufacture wood handling and chipping equipment.

they recommend de-rating the boiler 30% if you're burning green chips to account for the latent heat lost up the stack. I'm planning a trip to the factory this fall, and will report back.

cheers,
Karl

 

[peakbagger]

If you go to this link and read the publications, all questions will be answered

http://www.biomasscenter.org/resources/publications.html

BERC supported numerous school heating systems. The reality is that these systems no longer meet emissions requirements in most areas and a baghouse or electrostatic precipitator is most likely required to meet PM limits.

If you stick with residential solid fuel things are fairly easy, but once you go with district type system, all sorts of government regulations kick in that will make such a project unfeasible for most. Basically you have to comply with federal EPA regs called area source Boiler MACT.

By the way if you are serious after reading the info, drop me a PM

 

[BoilerBob]

http://www.finkmachine.com/

These guys have installed district heating, with wood chip gasification boilers. Very smart and dedicated owner, importing Austrian boilers.

 

[PassionForFire&Water]

What BTU output are you looking at?

Not many appliances that can handle over 45% MC
50% MC being the upper limit

 

[heaterman]

Moisture content that high will present a number of issues. There will be more ash and "clinkers" to deal with along with a substantial loss of efficiency.
The chip burning co-gen plant near me has their fuel pile spontaneously combust/smolder about once every summer after a warm spell but you're talking about a very large pile of chips there. When it gets very cold (less than zero for a few days) the pile will freeze in spots and cause feeding problems also.

I would think that using fuel with that level of MC would mean a moving grate type burner.

Emissions standards may be more difficult to reach using fuel like that also. Establishing a high enough temperature for good gasifcation is the same no matter what type of fuel is being used. High moisture content lowers combustion temperatures regardless.

Can it be done? Yes. Will it present more maintenance issues than burning fuel <35-40%? Yes again.
A boiler setup with an O2 controlled burner will be just about mandatory with that type of fuel.

 

[jebatty]

Primary issues have been identified and the feasibility study is progressing.

 

[PassionForFire&Water]

Primary issues have been identified and the feasibility study is progressing.

What BTU output are you looking at?

 

[jebatty]

Two boilers, one 2 million btuh and the other 5 million btuh. Possibilities would include 2 x 1 million and 2 x 2.5 million to provide operational flexibility and redundancy. Maximum continuous output would only occur during the coldest winter periods. Substantial thermal storage is contemplated.

 

[heaterman]

Two boilers, one 2 million btuh and the other 5 million btuh. Possibilities would include 2 x 1 million and 2 x 2.5 million to provide operational flexibility and redundancy. Maximum continuous output would only occur during the coldest winter periods. Substantial thermal storage is contemplated.

There are boilers that will modulate down to near zero output so large storage volume may not be required.

 

[PassionForFire&Water]

Two boilers, one 2 million btuh and the other 5 million btuh. Possibilities would include 2 x 1 million and 2 x 2.5 million to provide operational flexibility and redundancy. Maximum continuous output would only occur during the coldest winter periods. Substantial thermal storage is contemplated.

Viessmann/KOB; pyrot & pyrotek up to 1,250 kW
Viessmann/Mawera up to 13,000 kW
Heizomat up to 990 kW or 3,375,000 BTU
Ebner Vynke up to?
ACT up to 3.5 mmBTU

I would stage this with 2 or even 3 units per setup.
This gives you much more flexibility.
This becomes very economical now a days with smaller output units being very reasonably priced.

You will need to plan substantial chip handling capabilities and find a good engineering solution so the chips don't freeze up in winter

 

[Rory]

I don't have any technical knowledge to offer, but there's a bit of a revolution going on around here with school districts and colleges using large chip fueled boilers. I don't know exactly what types of chips they use, but there's a lot of enthusiasm for using a locally produced fuel, and that's a good thing.

 

[jebatty]

I'm aware of the modulating design of chip boilers. But staging with two or more boilers does not adversely affect the ability to modulate, instead I think it both enhances the modulation ability and it also provides redundancy to better insure that a "down" boiler would not put the user in a no-heat situation. Of course, since the chip boilers would supplant existing fossil fuel boilers, the design also contemplates retaining fossil fuel backup. Nevertheless, both for energy security and independence as sell as economy in operational cost, it likely would be better to have staged chip boilers. I haven't priced the capital and operational costs of staged chip boilers vs one large boiler, and that also will need to be evaluated.

 

[heaterman]

Many of the better and more experienced makers of chip burners have control packages that will allow multiple boiler installations to not only modulate each boiler but also step fire them in sequence in response to load. They will also rotate the lead/lag configuration to keep run time fairly equal on all units. I know that one of the manufacturers control is also internet connectable to allow off site monitoring of operating parameters. They are as fully sophisticated as any gas or oil fired equipment.

 

[jebatty]

Just a thought. Are there any large boilers, 2-5 mmbtu range, that have automated handling of round wood splits, perhaps 24-48" length, 6-8" diameter? If so, do they operate/modulate much like a chip boiler?

 

[Rory]

A fresh example of the spread of large scale biomass, from this morning's Bangor Daily News -
http://tinyurl.com/mg7ubhp
University of Maine at Fort Kent, SAD 27 break ground on $4 million biomass project


Wilson G. Hess, president of UMFK, said on Thursday that the groundbreaking marked the conversion of the entire campus from foreign oil to local biomass alternative fuel sources for heat and hot water needs.
“The project will spur northern Maine’s growing wood pellet and biomass fuel markets by consuming nearly 1,000 tons of wood biomass annually,” he explained. “It will serve as a working environmental education example of local renewable fuel replacing imported non-renewable oil, dramatically reducing the university’s annual energy costs and carbon footprint.”

The full article is at http://tinyurl.com/mg7ubhp

 

[slowzuki]

Local university district heats with green chips. They buy loads from woodland contractors chipping for pulp. I think in the winter they burn about 20-30 tonnes a week? Fair amount of ash generated, they have a complete cell at the landfill.

 

[SmokeEater]

I haven't given your numbers too much thought yet but have developed and built a chip fired boiler that utilizes the same MC chips that you are proposing. We had problems of chips freezing in truck trailers left overnight, but found that the chips did not freeze when in larger piles that were worked by a loader or dozer. The chips had to be magnetically inspected, overs had to be reground in a hog, different chip MCs were blended, and were stored under cover year round after all of the above. We burned 30 tons per hour and used an ESP to remove most particulates as required by the NYSDEC and EPA. The boiler had a moving grate, but I did consider a fluidized bed boiler and didn't investigate thoroughly that option.