I don't need another project right now but this has been in the background for several months and I figure it's time to post about it. I'm trying to clean up and get rid of stuff I will never use. This project is based on a heater that I don't want to scrap.

I bought it 30+ years ago for a project and it sadly has spent the last 20 or so outside under cover. There is some surface rust. Today I dragged it out from under the deck and put it on a cart.

It is a 75000 btu navy engine coolant heater. It runs on diesel and 24 volts and I did run it way back then to test it.









I ve spent some time over the last few days looking for the manual which I do have somewhere. I did find the box of spare parts. It's a metal box about 15" x 15" x 25" filled to the top with spares all in sealed packages. This thing is mil spec and it was/is quite fancy. It even had a pyrometer to monitor the flame. (gotta find that manual)

The plan is to replace the oil burner with a modern style pellet burner. It will take about 10 lbs of pellets per hour to replace the oil.

If you take out the oil burner the rest of it is a 1/8" thick walled stainless steel flash boiler and a 24 volt recirc pump and a 24v blower.

I've looked at a lot of pellet stoves and the nice ones have self ignition and are self extinguishing (you turn off the pellet supply), automatic pellet feed etc and an oxygen sensor so you can control the combustion. All fun little mechanisms to build.

What prompted thinking about this now it that last month an electronics magazine published an article on building an interface for a Bosch Lambda sensor (oxygen sensor). If I waited a few years that would be obsolete and I would have to design my own so I ordered all the parts for the sensor system. I got the Bosch sensor itself on ebay on the weekend. It has been shipped and the bulk of the electronic components arrived here this morning.

It will take a while to design it and collect the parts at reasonable prices. I need to make or buy one or more small augers. 2 1/2"-3" to move the pellets. Probably drive them with stepping motors. What seems to be the best ignitor for the pellets is a jet of very hot air. Then you don't have a heating element buried in the fire.

In operation a microcontroller will run the thing based on measuring the oxygen in the exhaust gases (and temperature) and adjusting the fan speed to provide the correct air mixture. It will also look at water temperature and flow so nothing overheats etc.

First step will be to get some penetrating oil on all the fasteners.

Chris

Now that is a project!
Mechanical and electronics.

But I wonder about the original purpose
“A coolant heater?”

It was originally designed to preheat the diesel engines in a ship before starting them.

The term "coolant heater " does sound a little funny.

It was built by: Fluid Heat Division, Anchor Post Products Inc, Baltimore, MD

The tag says the boiler is tested to 60 psi for a working pressure of 30 psi. Therefore it could remain connected in a pressurized cooling system. It was model #B75-17 and serial number #0741 so maybe they didn't make a lot of them.

It is a pretty fascinating device, being mil spec. All the external wiring is in cooper braid sheathing.

Chris

I found the manual. What a big help it will be. Large fold out scaled drawings for everything (60 pages of manual plus 10 four page fold out drawings). Theory of operation. It's great. Drawings are dated 1953. The boiler is spec'd at 70% efficiency. Single pass shell boiler, the combustion chamber is inside. Material is stainless steel welded at the seams. Fittings are cast brass, silver soldered to the main tank.

I've been reading about burning wood pellets for a while. As they burn, 20% of the heat comes from the embers and 80% from the gas released in combustion. You add more air to the hot gas to burn it (the gas). The target for the oxygen sensor is about 1.2 which means a small amount of un reacted oxygen in the exhaust. The jet of flame from the pellets will look very similar to that from the original oil burner.

Chris

Cjmac,

Could you post a link for those pellet stove heat source numbers?
Is that what they call ”secondary” combustion?
Do you know if anyone has tried to pull off that gas as “wood gas” for use in an engine?

I went through a lot of sites. I will try to select a few good links. Yes I believe it is refered to as secondary combustion. I'm still learning this too. There are some good sites relating to wood gas generators. I keep getting them too as they are closely related. With "wood gas" the gas with the 80% of the heat enegry is harvested and fed into an internal combustion engine. They were able to run cars that way during WW2. I will post a link to that too.

Something I found on a wood gas site was the use of a diesel engine glow plug to light the fire. They only last a few years but it seems to me to be a lot easier than the hot air ignitor I was thinking about.

Chris

Chris, could the designation " coolant heater " suggest something like a "block heater" for some big diesel equipment in cold climes?

The manufacturer describes it as a device to preheat engines, domestic hot water or heat interior spaces. I bought it way back when to heat my sailboat but never used it.

Chris

Hi Kbs

Here are some links. Not in any particular order.

youtube of pellet burner

Home gasifier

Controller similar to what I want to build

good combustion info

Look around page 32-34 of this one (above link)

Chris

Thanks for the links.
I do on occasion check in on the wood gas guys.
They seem to have a lot of problems with getting their fuel the right size and dryness.

When I read your explanation, I wondered if anyone had tried pellets as a wood gas fuel

It looks like it has been done in Europe.

I just read that one of the biggest, if not the biggest North American exports is wood chips and wood pellets to Europe. They come from eastern Canada and the US southeast.

I don’t know about any net energy savings. Making pellets is a bit of a job.

The wood gas guys are trying to get energy at little cost from easily available fuel. Pellets would be premium fuel for wood gas but an unnecessary expense or extra step. You can make gas with lots of types of biomass because you have a large amount of fuel involved at any time and lots of heat to drive off moisture. The pellets have low moisture low ash and are consistant in fuel quality. Better suited to an automated process like I want to do. Stuff I've read suggests that pellets would be about half the cost of oil. The numbers are probably for the US where oil is less expensive than here (go figure!). I looked at a couple of small scale pellet making machines and I can't see it being economical. A big plant certainly could be. For what I want to do, I'm pretty sure I can get quite carried away with building this and still come out ahead financially in the long term. I have a hot tub which is rarely used because it has become too expensive to leave running all the time for the amount we use it. (electricity). It would take 12h to heat it from cold with the 5500w heater in it so to use it you pretty much leave it on all the time. This heater would be able to heat it from cold in maybe 2 hours for 2-3 dollars in wood pellets. Use the hot tub 5-6 times a month for less than $20 instead of $60+. Wood pellets are carbon neutral so there negligible greenhouse gas emissions. I live on Vancouver Island which still has some forestry so softwood pellets are obtainable. (still cost more than in the US)

So, this project means I keep the hot tub and potentially get some use out of it and I found a use for the engine preheater. I wanted to get this project started now so I can collect parts for it, and so I can plan for a location for it and dig any underground trenches etc while I'm digging this place up to reno the house.(tracked backhoe)

I appreciate your interest in this.

Chris

The key is to always keep the big picture in view.
Look at all the inputs and their costs.
Somewhere along the line our ‘Leaders’ have lost that ability.

Apparently they send large ships full of pellets from Vancouver to Europe too. A couple of people have been killed as a result of gases generated by such large quanties of pellets together in the holds of the ships.

I don't think it would be practical to make them in a small plant. A big plant attached to a sawmill would have economy of scale.

Anyway....

I have an evolving spreadsheet of calculations for this project. It looks like I need to burn about half a cup pf pellets per minute to get 75000 BTU out of the boiler. I need to know that sort of thing to come up with an auger and firebox arrangement.

The Lambda oxygen sensor arrived today.




I need to find a mating plug for this connector (hopefully without going to an autowrecker). I found a part number for it but nobody seems to sell it online.





Chris

Surprise... Replacement Ox sensor connector

Gotta love my subconscious at times when it says stuff like: "I've seen that somewhere... was it J.C. Whitney?"

Doc

Neat project. Alternative fuel sources and self reliance are things that I'm very interested in. My old house has a fuel oil funace, I got a stand alone pellet stove 3 years ago and haven't fired the oil funace since. Heating costs cut in half.
One thing that I've been researching lately is steam power. I wondered if it wouldn't be possible to use a single heat source to heat water for radiant heating/domestic needs and to generate steam to power a generator. Seeing that you're planning this boiler project and the back up generator, maybe you could combine the two. That's one less project

Thanks, I saw the pile of pellets in the back corner of your shop. I'm glad to hear it is working well for you. The plan is that my renovated house will have in floor radiant heating. Then you can get heat from anything that can make hot water. My ultimate goal is to use a heat pump for primary heating. Both pellets and diesel have to get here in a small boat or using an expensive barge. For backup power diesel is ideal (as oppposed to my neighbors with year old gas in their portable Hondas) and it can heat the house in a pinch. The heat recovery part takes some of the cost out of test running it for an hour or so a month and it gives the option of heating the house up faster than the heat pump would be able to do. (although I probably have to have an electric boiler as backup anyway)



I do plan to connect the two and a lot of the research I've been doing applies to both projects (mainly heat transfer and heat exchangers). There are still a lot of details to work out. Physically, right now they are destined to be far apart. The genset has to be 20' from the house and will be out back. The pellet boiler should be as close as is reasonable to the hot tub which is out front. I would love to put them together in a building out back but the heat loss for the long run of pipe to the hot tub would be too high.

The target is a level of self reliance but in terms of energy costs, I can't come close to generating power cheaper than the electric company. The generator will be about $.70 per Kwh and with capturing the heat I can get to an equivalent of about $.30 per Kwh. Still about 3 times what I pay for power..

If there was no electricity available it would be a whole different ball game.



My guess is that you can't do it efficiently on a small scale. It would be fun to do.

Chris

Hi Jesse, and anyone else with a pellet stove, I'm trying to figure out how big the fire bowl needs to be. The target is 75,000 btu which is 10 pounds of pellets per hour which I roughly calculate to be about half a cup a minute. That means half a cup per minute has to burn out of the pile of burning pellets. This requires some sort of critical size of fire. I haven't found any documentation on this. Too big and I run out of space and too small and I won't get enough heat.

So, how big is the pile of burning pellets in your stove and how many BTUs is the output?

No rush for the answer (I've got lots of other stuff to work on), but any input I can get from you guys would be great.

I'm thinking that the fire bowl will be made from stainless (3/16" or 1/4") moulded into the end of a piece of stainless pipe with the auger in it. Holes for air in and ash out and maybe coat it with a high temp ceramic to reduce sticking and erosion/corrosion. Thinking about ITC 213.


Thanks

Chris

i saw a post saying no electric.. i saw one with backup 12 volt battery for both auger and the fan.. not sure how long if would last though.. wonder if you have solar pannels to recharge the battery.. during the day..
i know that those 12 volt backup sump pump.. dont last more then 24 hrs..unless you have a deep cycle battery that is 3 foot long

Chris,

My stove is a Breckwell Big-E, 55,000 max btu, which I figured based on my usage to be about 7.7 lbs per hour. The fire "basket" or "bowl" or whatever you'd like to call it is about 3 1/4" x 3 1/4" x 2 1/2 deep. and it's got aprox. 1/8"-3/16" slotted holes in the bottom that take up probably half of the bottom's surface area. It must be kept fairly clean underneath, otherwise ash builds up, blocks airflow, the pellets don't burn up enough before more are fed, and the basket overflows. Other than that the fire basket's size seems fine.

If you're planning 10 lbs/hr (23% more than my max) I'd say about a 4" x 4" x 3"-3 1/4" deep basket would be a good size.

Don't know if this will help you or not, but looking through the stove's manual I found the circut board timing rates. Total cycle time is 14.5 seconds and at the highest setting the auger is running 12 of those 14.5 seconds. The auger is aprox. 2" outside diameter with aprox. 2" between blades. I've got no idea how many rpm.

Thanks Jesse, that is a big help. I was thinking of around 2.5" for the auger. Based on the piece of stainless pipe I have. I did find the formula (guideline) for augers and the pitch is equal to the diameter unless you want to push up more than 30 degrees slope. I think my fire pot will have to be rectangular due to the space constraints in the boiler, I will go with a volume of 25% larger than yours. I won't go deep because the flame has to go off horizontally to get into the boiler. I will try to come up with some drawings soon. I'm still playing with ideas for dealing with the ash.

Chris