Wood-fired Steam Heating

WoodSteam_life

Jamie Hall said:

The output the check valve will reduce the pressure of the steam and cause a good bit of it to condense, although some will likely get by into the bulk tank.

I might have to remove that valve going to buffer tank to make sure steam flashes freely, good point. In which case I might have to raise it so that hot water doesn't rush into the buffer?

Should I also remove the three-way mixing valve on the boiler return? I am thinking mixing the less hot buffer water with the hottest water from the boiler to avoid thermal shock.

WoodSteam_life

I found this industrial steam schematic, now wondering if my small-commercial set up would have to have a feedpump too like Jamie suggested... but still, I won't have such a dedicated boiler that can put out satisfactory amount of steam. I might have to fabricate it after all, probably copy gas-powered boiler design.

ChrisJ

@WoodSteam_life

I run 0.50 to 1" WC and there's nothing going 60mph in my steam mains or runouts I assure you. 

I suppose it's possible but I'm my situation not even close.  Maybe  10 mph and that's after the radiation starts pulling.


Believe me overall we're both on the same page (low pressure is where it's at) I just don't agree with the numbers.

leonz

ChrisJ said:

I've never understood comments like "Steam travels faster at 2 psi than it does at 30 psi."

It seems like it's an incomplete statement.

To me, the pressure differential between the condenser and the boiler is what determines the speed of the steam. 30 PSI at the boiler and 0 PSI at the condenser makes for some fast steam.

If I remember my reading correctly:

There are fewer molecules traveling down the steam pipe highway at two PSIG allowing them to reach drag strip speeds where at thirty PSIG they are acting like big bumper cars in a very tiny tube.

Jamie Hall

Basic thermodynamics. If you want to make steam, you need to have a heat source which is at a temperature high enough for the water to evaporate. For 2 psi steam, that is around 215 F, Anything less than that, and steam will not be created -- in fact, as it cools, it will condense.

In your buffer tank you have a large reservoir of water which will be at less -- probably considerably less -- than that temperature. Therefore, any steam which you feed into that tank will promptly condense, Now it will heat the water -- but it cannot heat it beyond its condensing temperature. You will, eventually, reach an equilibrium point where the relative humidity above the water is at 100 -- saturated water vapour (which could be regarded as steam) and the water below will also be at steam temperature -- let's say around 215 if you can run the thing at 17 psia (2 psig if you are at sea level).

You cannot extract heat from this system without condensing some of the steam -- which, of course, is your ultimate objective. The problem is that without heat input, you will rapidly run out of steam in the bulk tank. You will still have hot water -- but without a heat input, it will not evaporate and make more steam.

Now if your boiler can run at a high enough temperature, and a pressure to keep the water in the boiler from boiling, you can allow that water to pipe to the tank and enter through an orifice, where it will be at a lower pressure and, thus, will flash into steam. But -- it must be at a higher temperature than the steam already in the tank. Perhaps not as much as 15 psig, but a good bit more than 2 psig. That will work -- you don't need the check valve in the hot water line to the bulk tank, and without pumps the cross connection to the return will not do anything at all, so that can go away. You will need a check valve in the return line from the tank to the boiler, however.

Your storage tank will act -- briefly -- as a buffer, but as I noted above there will be very little energy actually stored in the tank in the form of steam. There will be energy in the hot water, but that isn't useful. To put some hard numbers on that, let use suppose that you have a 500 gallon storage tank, half full of steam. That would be around 2 pounds of steam. That will release only 2000 BTU when it condenses -- and that is the end of your usable energy storage in that tank.

Now there is a twist to this which would allow you to extract some of the heat in the hot water, and there is a fair amount of it -- if you allow the water temperature to drop while the boiler is off to around 112 F, to pick a round number, 200,000 BTU as a matter of fact. If your system were well sealed against a vacuum, the whole thing would drop into a deep vacuum as the "steam" was condensed in your radiation in the greenhouse and the house. This, however, would presume that your system was, in fact, sealed against a vacuum sufficiently tightly to evaporate the water at that temperature -- and that the radiation in your house and greenhouse was large enough to produce usable heat at that temperature. I don't recall seeing an estimate of heat loss for those structures, but if I assume 50,000 BTUh, which is probably low, that would suffice for four hours of usable heat with the boiler off -- assuming, as I said, that the radiation is large enough to deliver that heat.

leonz

WoodSteam_life said:

Jamie Hall said:

As drawn, at least as I interpret the drawing it won't.

Yes Jamie, I am talking about steam, not hot water! I am not interested in radiant heat, I need to put steam radiators in the greenhouse as well as the house and without steam traps if it's a one-pipe system.

Why do you need a pump if I want steam to build up in the buffer tank? That tank is my battery, thermal deep cycle battery so that the boiler doesn't have to run around the clock wearing itself out. The idea is to generate enough steam to sustain the system. Yes the big tank would also hold hot water, but that water would be the condensate that returns from the main, not from the boiler. What is the point of pumping hot water into buffer tank if I need it to flash into steam? I cannot have my main run directly from a boiler riser, these boilers aren't designed for that, these are hot water boilers for radiant heat, but I do need to generate steam, and I need your help make it happen guys.

ChrisJ, the fast traveling dry steam has enough space in a 2-3" diam pipe to whistle around and yes it travels at 60 miles an hour at 0 psi, the higher the pressure, the slower it goes and the condensate gravitates towards the tank so long as vents are present and no micro bubbles are impeding every turn of the steam seeking the lowest pressure point.

leonz, I am not interested in coal, this is a firewood thread, a steam heating problem in need of a solution. I either modify an existing wood-fired system to flash into steam or I fabricate an actual steam boiler from scratch and hope I don't cause an explosion later.

=================================================================

I am going to save you some time and work if you have no real interest in a coal fired steam boiler that can do what you want with low pressure steam with little work.

================================================================

If you want a wood fired gasification steam boiler for a one pipe system you should look
at the Alternate heating systems E250 wood boiler.

The E250 is an induced draft boiler that can be used to make low pressure steam, it is not a flash steam boiler, it has been tested to 250,000 BTU per hour for low pressure steam making and can heat 9,000 square feet.

It has a 2 pass gas burning system with a refractory brick lined combustion chamber.

The firebox is 48 inches long so you could load it with pulp wood lengths of firewood.

www.alternateheatingsystems.com/product/commercial-wood-boilers/

WoodSteam_life

Jamie Hall said:

E250 wood boiler

This is encouraging, thank you!

leonz

Please keep in mind that you want and need DRY Steam to obtain the most benefit for heating.

Mr. Holohan has said in his past writing's if I remember them correctly about steam heat that the more tapping's you have in the steam chest the faster steam will travel to the radiators.

Having four tapping's in the steam chest feeding a double drop header is all the better to allow steam to travel faster to the radiators.

You need adequate ceiling height for the risers to create the double drop header to allow you to pipe it together- if you did this in a tall woodshed/lean to you would not have to worry about ceiling height as the steam header could just pass through the wall of the woodshed to the greenhouse and the same three inch header would travel to the home to the attic for dry top fed steam, it would just need heavy insulation and a perhaps a grape lined trellis to support the pipe and hide it.

If your steam chest has 4 two inch tapping's you would use more tees, nipples, and unions and then connect to the next larger size piping-for example 3 inch to create the larger header pipe that would transition to a 4 inch header with 4 unions and have the 4 inch header pipe to the radiators and a street Ell at the opposite end reduced to the same size as the side tapping in the boiler that would allow the condensate to fall back to the boiler water level.

The dry steam will travel very fast to the radiation because it is not carrying water vapor along with it.

There is nothing to say you could not pipe dry steam from a woodshed to the greenhouse using top fed steam and then the same elevated header would travel to the attic to feed a header pipe in the attic that would top feed the dry steam to the radiators in the home.

You should be able to buy all the steam boiler controls from AHS if you decide to purchase the boiler from them and asking for a change order to add 2 extra tappings in the steam chest will cost a bit more but I am sure they would do this for you.

Just so you know they make wood pellet and wood chip feeding systems for this boiler too so the work needed to tend it would be next to none as a wood chip storage shed would be right next to the boiler on the other side of a wall.

I hope I have not missed anything OR MADE ANY MISTAKES-Erin, please correct any mistakes I have made in error.