Heat capture from compost using radiator in pile of woodchips

initrade

The title says it all.

Composting woodchips get up to 140F and stay there for a few months. Some systems have been made to remove the heat from the wood chips, but I would propose palletized radiators, stacked and connected in serial, with water circulated through copper tubing.

Is this the right place to ask that question?

initrade@gmail.com

EBEBRATT-Ed

Don't know. Seems to me the rads would transfer heat from the wood chips initially and then heat transfer would stop with the rads surrounded by ashes.

Jamie Hall

Don't know if there is a right place to ask that question -- but I have two concerns about the idea. First, to get composting to work and keep working, it is necessary to turn the pile or heap or windrow or what have you from time to time. Radiators in the middle of it are going to interfere with that...

Second, and perhaps much less obvious is that if you are withdrawing heat via the radiators, you will have a problem with the composting itself. Composting is absurdly sensitive to temperature, and you are effectively cooling the pile with the radiators and the water going through them. With very careful control, you could probably keep it going, but...

That said, the concept -- in somewhat different form -- is not new: it's found in some types of wastewater treatment plants, where the sludge from anaerobic primary settling is taken to anaerobic digesters, where -- under rather carefully controlled conditions -- it composts and the off gas from composting, which is mostly methane (but with a nice compliment of assorted sulphur and nitrogen acids -- wonderful on the machinery) is either flared or is used to heat the sludge (there's that temperature control...) and sometimes to power engines for the facility. The same principle is used on larger animal farming operations with the manure., and again results in enough off gas to maintain the proper temperature in the manure and, often, to power machinery on the farm.

Wood chips alone need additional material to compost well -- the nutrient balance is way off.

On the whole, it's going to be a lot easier to burn the woodchips for heat or power, and control the emissions (which is a headache, but quite manageable and uses well known processes).

Hot_water_fan

I wonder if a hydro air unit would be easier? Take some heat off the top while staying out of the pile itself. If you’re using a water source heat pump, you could use lower temps from the compost, not just the 140.

hot_rod

I put some hydronic  coils in a compost once, what I found us the coils cooled down the compost fairly quickly

I don’t know how you could calculate the BTU output of the pile to pull the amount it can generate without dropping to the point where the heat stops?

EdTheHeaterMan

Contemplating Complicated Concepts Continues to Confound Compost Converter

Woodchip, woodchuck would chip away at energy usage. So how much wood would a wood chip chip, if a wood chip could chip wood in order to reclaim any energy?

Film at eleven!

initrade

HAHA! Thanks everyone.
Static piles give heat for long periods without turning.
Not sure how to respond to each person.

initrade

@Jamie Hall no. not necessary to turn. aeration is helpful for process control (cooling or feeding the aerobic bacteria, want to keep it from going anaerobic and stinky).

And correct, it is not new. https://www.permaculturenews.org/2011/12/15/the-jean-pain-way/

But has been improved on and continued in different directions.
https://www.amazon.com/Compost-Powered-Water-Heater-greenhouse-buildings/dp/1581571941/ref=sr_1_1?keywords=9781581571943&linkCode=qs&qid=1689014612&s=books&sr=1-1

I'm surprised no one has pointed out that the process could be corrosive to the copper tubing! however I have thought of that a little.

Fittings are on the outside of the pile. That takes care of seams. But also looking for ideas of what to coat the copper with (?).

hot_rod

What size pile do you have? That would give you some idea on what to expect, energy wise

A few wheelbarrows of compost may not heat much. A six yard dump truck load may do some good 

id stick a thermometer in the pile  and regulate flow to what the pile can keep up with If you cool it too much the breakdown if chips stops

Id consider the coated stainless CSST
Better heat transfer with corrugations, although a bit more pressure drop to pump through, and the coating would protect the tube from ph issues

initrade

@hot_rod 15' x 15' x 1' pallets. stacked 4-5 high. with the woodchips dumped directly into the frame, with hay bales to around to frame it and hold in the woodchips.



I'll look into the coated stainless CSST because you are right, more surface area. I just wonder if the coating will cut down on conductivity. But thanks for that.

I just need to find a welder, make one, and I know exactly where to get the ground up woodchips.

hot_rod

You have a lot more to work with. Mine was just one of those green barrel type composter with a crank to stir it occasionally.

I think the coating would be worth the small penalty to keep that thin tube from getting pin holes from aggressive chips or ???

You can find it un-coated, it was used for solar tubing. We use to stock 1/2, 3,4 and 1"

Dormont is a Watts company that makes it down south somewhere. We got ours from Germany, although the factory was in Turkey.

I also discovered you can anneal and soften it and wind it very tightly. This HX I built to fit into a 2" connection on a tank.

Seems like the frame could be the heat exchanger if you built it from tube?
Build it like a ladder, headers at both ends to keep the length of the pumped circuit shorter, instead of the serpentine you show. Flow into one leg, out the opposite for reverse return balancing.

Dave Carpentier

All kinds of organics get hot as they rot. Maybe the question is, how many btu/hr can you extract without cooling the pile to the point of non-composting temperatures.
Absolutely, there is energy that can be captured, but is it enough energy to justify the costs of setting the process up ? A research dept of a college etc would not care about justifying the cost/benefit, but you might.
I like the idea of capturing the gases and burning those, but of course that comes with it's own issues too.

tim smith

what about copper nickel tubing. Holds up better to corrosives. Good conductor too.
they use it in sea water applications mostly. Also used for chlorine pool heat exchangers. Not awful price either.

tim smith

from W&O catalog.
Overview class 200 pipe .065 wall thickness equivalent to type K copper
70/30 Copper Nickel is uniquely qualified as an ideal candidate for piping systems in the ship-building industry due to its alloy properties, including low general corrosion rates in seawater, resistance to stress corrosion cracking due to ammonia in seawater, high resistance to crevice corrosion and stress corrosion due to chlorides, good pitting resistance, ready weldability, ease of fabrication and inherent resistance to biofouling.

kcopp

If we are talking about temps in the 140F range why not just use a good quality PEX tubing and go w/ that?

hot_rod

The rule of thumb that Tom (Solartechnics) discovered is 3 times the amount of pex, compared to copper to transfer the same amount of BTUs per hour.

This was for large solar tanks with coils submerged inside.

psb75

Haven't they done much of this research using the "Jean Pain" compost mounds with black poly pipe?