How to use a batch-core in prolonged heating?

[rava]

I'm in the process of building a batch-core rocket stove with plancha, white oven and warm-water-heater.

I've build rocketstoves before but am new to the batch box. I've kept al the dimensions quite strict so it should work well.


My question at the moment is; is this type of batch stove suitable to keep running trough out the day for extended cooking times?

I'm looking for this stove to have a high daily output. We're cooking for 10, sometimes 30 people, 3 times a day. And its warming up our 1500 litre water-buffer via an heat-exchanger.


It has an octagonal riser out of insulation bricks 15,5 cm in diameter.

Is it good practice to regularly add more wood? or better stick to the batch use and have pauses between batches. And how long?
Right now I can still do some design changes if needed.


Thank you all for such an informative forum. It has been of great help.

[peterberg]

Yes, it can be done. Start with a regular batch to bring the whole of the core up to working temperature and add bigger pieces a couple at the time. I tested it in 2012 and it works as long there're long yellow flames going on.
Wish you succes!

[rava]

Ah, exactly what I hoped to hear. And from the master himself
Many thanks to you Peter. Your work has been the inspiration and guideline to this build.
I will soon make some time to put some progress pictures on-line.

[pinhead]

To expand on Peter's explanation, I have done similar - and have burned for upwards of 12 to 14 hours at a time during the peak of winter.

After the firebox is good and hot - and I mean scorching hot - I can load a huge hardwood log that will barely fit through the door and put a few small splits in the top two corners. At that firebox temp the splits will spontaneously light off, providing flame on all four corners of the log which will burn cleanly for a number of hours by itself.

This presupposes an extremely hot firebox - to the point that often-times the bark on the log will be lit before I even lower it into place on top of the coals. The ends of splits will likewise start off before I get them fully loaded.

[jmacro]

I have a similar question and different feed back. I build a batch rocket following the 6" measurements to boil sap, with the intent to burn all day. The biggest issue that I ran in to is an excess of charcoal. The pan was only at a boil when the yellow flames of fresh wood was loaded. To get around this, we did smaller and more frequent loads. At first we did ~ 3/4 loads every 1hr-1.5 hr and lost a lot of boil time letting the stove burn off the charcoal, and settled into a 1/4 load every 30 min, to keep the yellow flame, rocket noises and boil more continuous

All that said, I have come to 2 conclusions. In the context of this thread, I am considering sloping the floor of the burn chamber to allow charcoal to roll / settle to front of chamber, so that primary air can speed up the. Second, I think that converting to a DSR style will allow more heat to be contained and directed to the boiling pans.

Would love any thoughts / suggestions on this. Thanks

[martyn]

You could try an 8” J tube, the main issue would be the height of the riser but you must already have dealt with that on your present batch box?

[fiedia]

May be you are not using the bell thermal mass. 

You did not show your set up. Where do you put your boiling sap? 

There is a solution. In my BBR, temperatures stay above 100°C for more than 7 hours after one burn. Just need more details. Some pictures please.

[jmacro]

Hi Fiedia,
No Bell thermal mass. We call it Franken-stove, because we have been throwing stuff together to experiment and it looks ugly...but works.

Please see the pictures in link below.
drive.google.com/drive/folders/1yfrBuVlnZhPwBVKAZ_F0N8CFkBVvSZwm?usp=drive_link

[martyn]

Wow that is some stove but I dont see anything that looks like a batch rocket in those pictures?

[fiedia]

Well, I guess you plan to build a second prototype to improve your sap process.

May be DSR2 is a good solution as it does not require a long riser. It would be more convenient in case you put your sap on top of the stove.

The most important is the bell around the burning core. You will get much longer boiling embedding the whole core in a bell with rather thick walls, 10cm / 4 " at least. 

Leave a gap of at least 5cm / 2" between core and bell walls in order to bring the core side heat to the top through convection. The bell length and width can be adjusted to the size of your sap trays, may be 2 side by side or more.

Put a 5 cm / 2" thick heavy high temp brick or concrete ceiling on top of your bell. Leave a minimum gap of at least 10 cm / 4" between core top and ceiling bottom, double would be better. It is important to get thermal stratification (hot gases staying at the top).

The flue opening should be put at the bottom of the bell, absolutely not the top. This will improve the heat transfer between hot gazes and bell surface. 

You will get better results if you build an oven around your trays. It will improve the sap temperature and keep it boiling longer. Leave some small openings for the steam.

You should get your sap boiling for hours with one single burn. 

[jmacro]

Martyn, the Batch rocked is the lower section. Build to the 6" specs. The riser is made of 8" stove pipe lined with 1" ceramic blanket. The riser was bent to allow a workable height. The chopped up barrel currently is our " cook" surface, more of a pan holder.

Fiedia, we defiantly do plan on improving. This was more of a proof of concept / familiarization build. If I understand correctly, you are saying that if we enclose the core in a bell and cook / boil off the top, I wont have to worry about continuous loading? Thank you for your response.

If the above if correct and I just didn't build correct/ all the way, I still would like to discuss the continuous burning and charcoal build up. If the plans for the sap collection continue, I still see the volume of sap needing to be evaporated out growing the ability of the stove at some point. So how would one go about conducting a continuous burn of fresh fuel?

[andrewb]

Apr 1, 2024 12:09:57 GMT -8 jmacro said:

Martyn, the Batch rocked is the lower section. Build to the 6" specs. The riser is made of 8" stove pipe lined with 1" ceramic blanket. The riser was bent to allow a workable height. The chopped up barrel currently is our " cook" surface, more of a pan holder.

Fiedia, we defiantly do plan on improving. This was more of a proof of concept / familiarization build. If I understand correctly, you are saying that if we enclose the core in a bell and cook / boil off the top, I wont have to worry about continuous loading? Thank you for your response.

If the above if correct and I just didn't build correct/ all the way, I still would like to discuss the continuous burning and charcoal build up. If the plans for the sap collection continue, I still see the volume of sap needing to be evaporated out growing the ability of the stove at some point. So how would one go about conducting a continuous burn of fresh fuel?

 Hello imacro

 I suggest a grate could be used to get enough oxygen to the charcoal.

 It is difficult without forced air of sufficient pressure to blow ashes out of the grate inlets, to keep any metal grate cool enough not to oxidize. 

A brick grate without forced air will just plug. If the grate can be accessed hot to remove ashes while burning it could be workable.

It may be that pulling the charcoal to the front where the air gets to it will work. I anticipate you having over-fueling issues though due to excess heat on the fresh wood.

Maybe a J rocket with a longish fuel tube slanted at 22 Degrees from vertical will work better for this task.

or a shorty batch port and after burner with a sloped at 30 degree angle from vertical box bed with inlet at top of box parallel to fuel.