Development of a compact core, provisional title "Shorty".

[peterberg]

Dec 5, 2023 6:21:04 GMT -8 independentenergy said:

Hi Peter, I was looking for a core with these characteristics, when you have a good enough version I could build it.
I have a construction with a cooking plate and a small bell, connected to a 10 meter chimney in 150mm insulated stainless steel.
I opened a post ( donkey32.proboards.com/thread/4055/replace-tube-batch-box ) for some advice on which core to install since I demolished the jtube that powered the system, this design is compact enough and not too much else for a cooking plate.
but I can only build with hard refractory bricks, no insulation except on the outside.

I answered the earlier post, so further communication is through there.

[independentenergy]

Thank you peter

[peterberg]

On December 5 and 6 I did one testrun each day, both with a different idea in mind.
Let's start with the first, that one was to find out how compact the fuel could be loaded specifically. And as much as reasonably could be crammed in without blocking the air stream passing over the fuel.



This did go very well, the oxygen went down to 4.5% being close to the critical level of 4%, CO stayed down the 500 ppm mark for 40 minutes, while the burn itself lasted for 64 minutes. It also generated excellent average numbers, O² 10,75%, eff 89.03%, CO 265.5 ppm, TR 151.03 ºC. Much better than the minimum requirements of the EU norm. Maybe the fuel at the bottom of the firebox could have been somewhat bigger in order to extend the burn somewhat.



The second burn, in a cold heater, was done to find out what would happen with an open core. To be honest, I was using a spark screen that blocked the air stream to some extend. Probably to about 40%, so more than half of the front was completely open. In order to avoid smoke in my workshop i started the thing with a small fire in front of the port.



The Testo was running at the time, the situation above was about the point that I loaded some more fuel. Later in the burn, at 13 minutes, I added three more pieces.



As can be seen, there's lots of space between the different pieces so air is able to run through. The CO reacted to this by a slight bump in the level and corrected itself again rather quickly. At 23 minutes the fuel pile collapsed, visable in the O² and efficiency lines. And also ever so slightly in the CO line.



Not bad at all, given the fuel wasn't particular large and very, very dry, 9% moist to be precise. The fuel raced through, making a lot of noise and a short burn time, just 42 minutes. The numbers are obviously not as good as the former testrun. O² 13.08%, eff 81.74%, CO 359 ppm, TR 194.5 ºC. The higher levels of O² and TR both had a knock-on effect on overall efficiency but that's to be expected.

Next plan: test how the open system would behave with larger fuel and top lit.

[independentenergy]

thanks Peter for your tests, they are exactly what I was hoping for without a door, it seems like it can be done

[fruitbat]

I'll add my thanks for sharing your findings, really exciting stuff. The only slight disadvantage of this design is the lack of visual aspects in the riser, but a small price to pay for such a low height, simple build.

[andrewb]

Nov 24, 2023 9:50:14 GMT -8 peterberg said:

Here's the liner inside the riser box, done in 25 mm superwool. It shows a bit higher than the port, I took the surplus off later. There wasn't a difference that the Testo could measure so I am confident upto the port's top will be enough. Of course it could be done in any refractory material, the wool was the easiest since the hired wet saw was returned at the time.

Hello Peter
First post here. I have been playing with fire 5 years now using your information as a jump off point, to build a wood chip burner for my farmer brother. Thanks a lot for investing work of sharing your testing. I will post some photos soon on a new thread.
I suggest trying to modify the liner inside the riser. Remove the two sides and the pieces beside the port, that are not back of the burn riser, and put another layer or two of the superwool against the backside. this would then hopefully make the port stream split into two smaller vortex. I would put the top exit to the back at 100% system size so that the gas stream has to hit the top and move backward to exit.

[independentenergy]

Dec 9, 2023 13:39:20 GMT -8 andrewb said:

Nov 24, 2023 9:50:14 GMT -8 peterberg said:

Hello Peter
First post here. I have been playing with fire 5 years now using your information as a jump off point, to build a wood chip burner for my farmer brother. Thanks a lot for investing work of sharing your testing. I will post some photos soon on a new thread.
I suggest trying to modify the liner inside the riser. Remove the two sides and the pieces beside the port, that are not back of the burn riser, and put another layer or two of the superwool against the backside. this would then hopefully make the port stream split into two smaller vortex. I would put the top exit to the back at 100% system size so that the gas stream has to hit the top and move backward to exit.

personally I think not to put that part of superwool because I use a 6 cm wide brick for the throat so I think it is already deep enough, even if I noticed in my batch box that has been in operation for 8 years that that part of the upright wears a lot, a material which can be easily replaced even if less durable I find it useful.

[peterberg]

Hmmm... I could (sort of) do what you guys suggested.
First iteration: taking out the pieces beside the port and adding another layer at the back. I don't want to compromise on the volume in this stage too much, so the floor shape of the riser box is still a square this way.
Second iteration: both the pieces left and right out as well. So now the floor plan is a rectangle but wider than before, so it's larger, csa-wise.
Third iteration: Adding a third layer at the back. So the riser box' floor will be a more pronounced rectangle then but maintaining more or less the same cross section area as compared to the first iteration. Just guessing here, we'll see how it'll turn out.

Assuming one test a day and two tests for each iteration this will keep me busy for a week. The remaining day is for reports, pictures and diagrams.

[peterberg]

As andrewb and independentenergy suggested, I took out the superwool left and right from the port. And added another layer at the back, looking like this:



After closing it up I loaded the firebox with softwood, about 3.2 kg in total.



It started up quickly, the burn commenced in short order and went totally wrong. The O² kept coming down, all the way to about 3.5%. At the cross-over of 4.5% O², the CO went sky-high, way beyond the scale of the diagram. Regrettably, I am unable to produce a diagram because the software of the Testo crashed, close to the end of the burn and I wasn't able to retrieve the data. Someday, I have to figure out how to do that, provided it is possible, of course.

The next run, cold again in about 8 hours, I tried again using a wider port. To 70% this time, just to make sure the combination of 60% port and new internal layout of the riser box wasn't the culprit. I loaded up again and started with a slightly more modest load, without the pallet bobbins at the bottom.



It turned out I was right, the above mentioned combination wasn't why it went wrong. In other words, the burn commenced as quick as before and the O² got even lower this time, to 2.7%. As one may believe, I wasn't pleased, at all. The only change was the layout of the liner in the riser box, combined with the wider port in the second run.



Oh, forgot to mention there was black smoke from the chimney during the CO double peak. In order to show how high above the acceptable level the CO came, I changed the scale for that line from 5000 ppm to 12000 ppm. Maximum acceptable level is 1200 ppm on average, without peaks. This turned out to be 1713 ppm on average with a double peak up to 11264 ppm.



Tomorrow, wheather permitting, I'll run another test using a slightly different layout. The plan is to cut the sides of the liner out so that only the double layer at the back remains. Frankly, I think the pattern will repeat itself.

[andrewb]

Thanks Peter for the experiment, I was curious what would happen and now we see.
One reason I suggested what I did is because I am trying to understand why the version 3 with a ceiling port and horizontal swirl works and this one with the slot down to the bottom does as well. When I watch my chip burner run with a secondary at the port I can see that the volatile gasses are heavier than the hot secondary air. The flame ram horns start at the boundary between the hot air and the heavier fuel gas. Seems to me that you still had that with the swirl in the middle but with swirl at the port side the gasses do not seem to mix before they cool to much to combust. I had expected a rear wall slot to the floor level to belch smoke since it doesn't have secondary air between the fuel and the swirl.
I am excited by your work, I don't have a testo!

FAILURE is SUCCESS in progress

[independentenergy]

it might be interesting to reverse course and add two more pieces to the right and left of the door and by doing so further lengthen the groove and remove the piece of superwool from the bottom.

[fruitbat]

So many variables as always! I've been wondering whether there would be benefits to making the exit port round- obviously the diameter and the position would both have an effect. Back to the old concept of orifice plate flow restrictors which have been discussed here in the past.

Could a round port give a more stable and reliable restriction to flow rate to create the right amount of back pressure to prevent overfueling?

[peterberg]

Dec 13, 2023 3:23:33 GMT -8 independentenergy said:

it might be interesting to reverse course and add two more pieces to the right and left of the door and by doing so further lengthen the groove and remove the piece of superwool from the bottom.

I understand what you say about adding the two pieces left and right of the port. But I am in the dark what you mean by "further lengthen the groove and remove the piece of superwool from the bottom." What do you mean by groove? And there isn't superwool at the bottom of the riser box but refractory brick instead.

[peterberg]

Dec 13, 2023 3:39:25 GMT -8 fruitbat said:

So many variables as always! I've been wondering whether there would be benefits to making the exit port round- obviously the diameter and the position would both have an effect. Back to the old concept of orifice plate flow restrictors which have been discussed here in the past.

Could a round port give a more stable and reliable restriction to flow rate to create the right amount of back pressure to prevent overfueling?

In order to make the exit port round I would need a watercooled diamond drill so a hole could be made in the kiln shelf. Also, when this isn't working satisfactory, another drill? How many drills would I need to find out which is the best one?
I won't go that route, my goal is to make it possible for a novice to build a core against reasonable cost. Making the core more complicated to build is right opposite of what I am aiming for.

[independentenergy]

Dec 13, 2023 3:58:35 GMT -8 peterberg said:

Dec 13, 2023 3:23:33 GMT -8 independentenergy said:

it might be interesting to reverse course and add two more pieces to the right and left of the door and by doing so further lengthen the groove and remove the piece of superwool from the bottom.

I understand what you say about adding the two pieces left and right of the port. But I am in the dark what you mean by "further lengthen the groove and remove the piece of superwool from the bottom." What do you mean by groove? And there isn't superwool at the bottom of the riser box but refractory brick instead.

I wrote it wrong.
My idea is to add two pieces of superwool to the sides of the door, two on the right and two on the left, and leave only one piece of wool on the back.
extend the depth of the door so that if it was previously 3 cm by adding two 2.5 pieces of wool it will become 8 cm