Formula for biomass vs BTU output for compost

[Madscientist267]

Didn't know where exactly to put this; a few categories potentially applied. I settled on water since that's the target use for the energy.

I toyed with this idea a while back, but couldn't figure out how exactly I would come up with the source for the compost, and now, after digging around in the back 'yard', it became clear. Now I know many are skeptical, and more or less have shot this down in the past, but...

I have this annoying tree that grows in the form of several (many several?) saplings called a "black locust". This thing has a few annoying traits, the least of which is the sapling stage's one inch (ish) thorns that grow out of the thing every few inches.

The other is the one I intend to exploit; I figured I had killed a few of them by removing all of the foliage from the main 'trunk' (about 3/4" diameters currently), but the damn things just sprouted more, as if I had pruned it, and of a substantial amount in just a few weeks.

At the time, I was only concerned with regaining access to my bug zapper which the foliage had obscured. Being lazy, I only had a pair of dikes with me and hacked up what I could, with a willy-nilly attitude. BUT - I figure with optimum pruning, these things can really put out, and I'd just have to wear chain mail or something to harvest them.

The pile of 'branches' that I pulled off of the main trunks were all left in a pile, and they are composting into a fine powder rather readily. I think I'm on to something here.

So what I need to know is, how do I (roughly) calculate how much heat I can get out of a given amount of this stuff, and what might the critical mass be?

I realize there are several variables to this, but I'm thinking it will be useful as a preheat for DHW at the very least. I'm thinking something like a 6 or 8 foot diameter 'bin' made out of brick(?) and then insulated, to contain the compost. Maybe 8 feet tall? Run some tubing through it running to a heat exchanger in a closed loop under the house.

I wouldn't necessarily be all that worried about overall efficiency, but just use common sense efficiency (insulation, etc). I'd use it on a "get what it can" approach, maybe having a recirc pump that only runs when triggered by a pressure switch that senses the change in pressure or something when a hot valve is opened. That part is still grinding amongst the gears at this point...

Whatcha think?

Steve

[wdyasq]

Some time ago I read reports on a house so heated. I remember the compost pile was a bit larger.

The nice thing is the compost for the garden after heat in the winter.

Ron

[Madscientist267]

Yup. We have 2 good sized flower beds that could really use it too.

I really think this is plausible - I gave up a while back without a decent source, but this stuff grows like wildfire. I'll take some pics tomorrow of the area where they are growing when I have some light; we can go more from there...

[PeterAVT]

Way I see it, the compost will give off as much energy as the plants took in while it was growing. It just spreads it out slower over a long time. When you burn wood it gives off a lot of heat in a short time, but when you compost it, its the other way around. I have a cubic yard of grass clippings got up over 100 F for almost 2 weeks. I imagine you could concentrate the heat into a small box with real good foil insulation.

[wdyasq]

A pile of manure:

http://mb-soft.com/public3/globalzc.html

Enjoy,

Ron

[dnix71]

Black locust is Robinia pseudoacacia, and all parts of that tree are considered poisonous. It is also excellent hardwood. Before you go composting this tree, can you get a local garden shop/ag extension agent to properly identify your tree?

If you need to warm your house in the winter, you could put plastic against an exposed exterior wall and then build a compost pile against that.

[Madscientist267]

I dont think the toxicity will be a problem, it is used extensively for firewood for the same reasons I want to use it as compost. I've been hit with the thorns a few times in the process of removing what I already have; there were no side effects, other than the pain associated with the prick itself.

Any poison that is there must be minimal, and since I won't be allowing them to mature, they won't be podding. Apparently this is where the most significant levels of poison are found. After I found them, I went looking for the source, and found the adult trees all over the place around where I live. They are almost 'viral' in the sense that they grow and reproduce at a very successful rate, to the point of being a nuisance.

I've identified them properly (I'm about 99% sure) as black locust; being able to compare all of the traits of both the saplings and adults. Everything matches.

These things are ideal in every way, unless someone is worried about toxins leaching from the compost; but this would be a problem naturally anyway when the leaves fall from the tree during fall.

I'm still going to get a botanist (or someone resembling one) to look at them so they can tell me the best method for pruning them to keep them from growing out of control, while taking as much yield from them as possible at the same time.

Pics to come of the area where I'm going to source from...

Steve

[dnix71]

I grew up in Tampa. There is a public park/beach area on the Courtney Campbell Causeway that someone planted Oleander because they have pretty flowers and are salt tolerant.

The locals know that Oleander is poisonous, but some tourist didn't and used twigs for kindling on their barbeque on the beach.

Black locust spread all too well, as you have noted. It's considered an invasive nuisance in some places, so you might be doing a favor by removing it from neighbors land (with their permission of course). That way you would have lots to work with, without having to grow all your own.

[Madscientist267]

Very nice - This is the kind of info I was looking for... It's going to take some trial and error runs, but this is an excellent guide to get me started...

Steve

[Madscientist267]

Here are the pics:

This is the "crop" that I will be able to harvest:

This is what this entire area looked like at the beginning of spring before they took over:

This is the new growth in just 4 weeks at the top of one of the 'trunks':

And a closer shot of just how far these things have come up since the beginning of the season (the bug zapper is about 6 feet off the ground, and is about 1 foot or so tall):

...and has almost become completely obscured again in just 4 weeks!!

DEFINITELY a worthy crop for this purpose!

Steve

[Stonebrain]

Madscientist,

You have to choose.Producing biomass(wood in this case) or getting rid of the stuff.

You can't do both at the same time.

If you want to get rid of it you have to pull out the roots with a tractor and some kind of teeth that go through the ground or/and mow extremely frequently.If it is regrowth from preveously cut trees (from the pics I've the impression that's the case)you will have to destroy the stump or cut the regrowth very frequently(few times a year) to exhaust the stumps.

I know the stuff it's very agressive and spread out with roots near the surface that make new growth allover.However frequently mowing should prevent the stuff from taking over where you want to keep grass.

But it's a very good source of firewood,excellent,very lonng lasting fenceposts and good timber too.Fast growing as bonus.

If you want to make use of any of it's qualities,as firewood or fenceposts cut it every 4-10 years.This will give  a very good yield of btu's,and one of the best quality posts there is.

But if you cut it a few times a year you will exhaust the roots and yield will drop very soon,even with this tree that seems indistructible.

Anyway,cutting and burning firewood is much easier,more efficient,then winning heat from composting and prooven to work.

Drawback is that you won't have compost.But if you put the woodash back under the trees you won't exhaust the soil.

cheers,

stonebrain

[Stonebrain]

I forgot,

you can allways collect the leaves in winter for composting and crazy experiments

[Madscientist267]

Well, the original intent was to eliminate them, particularly after I found the thorns. Those things are evil. But after seeing the rate at which they grow, and looking at the pile that I set aside when I originally cut them (just never dragged them away), they are going to be perfect for compost. I need to cut them back in such a way that they never become adults, and also get as much yield out of them as I can. It can be done, I just need to know how big the compost pile needs to be to make useful heat for preheating DHW.

Burning them will be a waste, there's not enough there to get but one fire out of, and most of the heat would just escape. Composting them will let me extract the energy slowly, giving me useful heat to work with, without wasting as much.

Steve

[Stonebrain]

Those young sprouts are mostly water(that's why they compost so fast),not much btu's in there.

It's a pity to see how much energie people spend to make their land improductive

cheers,

stonebrain

[Madscientist267]

I dont think you understand... there's so much of it, and it's easy to get.

[Stonebrain]

Yeah,

Not sure we're on the same planet.

Good luck anyhow.

cheers,

stonebrain

[SteveCH]

Do some Internet searching about heating with compost and/or heating greenhouses with it. [I know this doesn't answer your original question, just more info']. A couple yr. ago, I was searching for alternative ways to heat water [dhw] and came across some reprinted articles from the 19th century about greenhouses in England. One of the methods of heating them in order to produce crops of citrus was to have a large bin at one end of the house, dug into the ground, and at the bottom was a set of pipes which were covered with compostables [old straw,  hay, manure, etc.] which heated the water that was in those pipes. Don't know how they circulated the water back then, but you have plenty of options today. Pretty interesting stuff, drawings and old photos though unfortunately I have no records of the web sites and etc. where I found them.

[Madscientist267]

I think actually I've seen the site you're talking about... his system was much larger than the one I am intending, but he also used it to not only heat DHW, but his house as well, and I believe he was producing methane and using it for cooking fuel and such. Something about innertubes as bladders comes to mind.

This kind of thing may not be the most ideal way to get RE, but when you've got it, you've got it. I live in an area where these things have taken over, and people are also putting out bag after bag of leaves in the fall - I'm sure they wont mind if I take them away as opposed to the trash guy. I have a decent size yard as well (as you can see from the pics) that if I bothered to collect the clippings, I could significantly add to the project as well.

My thing is, I am looking for ways to save some money in the long run, and many aspects of RE don't lend readily to that. Composting however may very well be one of the better ones in this area once the containment and collection costs are recovered. I don't look to see them all that high, with the exception of the coil and heat exchanger parts. I can get building materials for next to nothing around here, it's just a matter of being at the right place at the right time.

I wanted to do more in the solar arena, but after doing some research, my costs are prohibitive (at least for the moment). I figure a couple hundred bucks and I could have a compost system up and running, as opposed to a several thousand for everything I intend to do with solar. Wind is out of the question too, since it's a rare occasion that it blows hard enough here to get any useful juice out of it.

There's going to be some hard work involved in keeping the energy flowing, but the amount I can save on hot water alone will make it worthwhile for me. With 5 of us in the house, water heating is a significant part of the bills...

Steve

[Bruce S]

MadS267;

I did something similar this a long time ago, when I had nearly an acre of land.

Here's what I did and how it worked out.

1St how far your water run to and from pile will of course make a big difference.

I took no real measurements, just that I had a garage 20 feet away and NO heat in it. Plus my pile was fed from landscape trucks with shreaded stuff just so you know.

I had a bunch of big diameter copper pipes left over from still building big meaning 2 inch inside diameter. Using my pipe bender I made three full turns of the longest piece, put rubber standoffs between each coil so they did not touch. The rubber wasn't anything more than old rubber snubbers from old engine motors mounts for the 350CID Impala.

I then dug to trenches going from the back of the garage out to the pile area and laid down old galvanized pipe out close to it and wrapped both pipes with the Frost King brand pipe wrap just like the stuff in basements or crawl spaces.

To connect the two I used old unions and soldered the coil to a couple reducers to get down to the 3/4 inch galv pipes.

For the pile, I set the coil on a couple clay bricks to keep them off the ground and piled the landscape stuff under it, wasn't more then 2 inches deep.

I had the trucks dump the piles on top of this.

The pile measurements were 15 feet diameter and started off at being 2 feet tall, then got as the trucks kept dumping the stuff up to 4 feet high.

I had to put an old canvas tent side on it as the neighbors didn't like the smell of decaying wood "stuff" :-D.

Thinking back it was probably the canvas that helped it by keeping heat in and rain in enough to feed the needed moisture.

Even in the winter it would steam, however , winter I didn't keep a lot of water in it since the pipes were only covered by 3 inches of ground dirt.

I only did this because the garage was cold the the pile kept steaming, and RE wasn't on my mind, only finding warmth while working in garage.

I do know that the water when I turned on a little self priming pump would send the water out to the pile, and come back into an old school bus under seat heater core and was really nice and warm. Kept coffee cup warm too. a little 12V fan blew air out into area.

It seems like it took a full month before it started steaming at first when the trucks keep dumping but it kept it up all through winter.

I'll dig through my old 35mm and 110 pics and see if I have ANY pics of it. More than likely it'll be party pics with pile in back ground though.

SO it does work.

Hope any of this helps.

Bruce S

PS. Black Locust is NASTY stuff! thorns hurt for days!! still cutting it down at in-laws home, but it sure does look nice burning in fireplace :-) we let it grow all year then cut the biggest ones down in October about 3 inches diameter 16 inch long pieces.

He lets it grow to keep stray dogs out of yard, deer don't seem to mind it though.