P fired boilers

We have talked about this in several topics. I think first brought the subect.

I am wondering what eaxtly kind of an air souse was used on these boiler. Radial fans are designed to move air and turbo chargers are designed to produce pressure. Is there some type of plade configuration in between to do both? Would a turbo do the job.

Andy

Andy,

Considering a 1200 lbs/ hr car steam generator, then figure on an air supply around 600 cu/ft/min.
If you are talking about a Velox steam generator, then the generator is in the combustion chamber of a full scale gas turbine. Definitely not usable in any steam car.
A turbocharger blower section is high pressure, modest cfm and definitely noisy. Remember it is an axial flow blower, depending on the wheel design and can deliver 40 psi plus today. Requires very high speed and quite a high horsepower to drive it, far beyond any reasonable electric motor.
A squirrel cage blower wheel with backwards curved vanes, is ideal. Good output and easily delivers 20-30 inches Hg.
Lots of good design data on Wikipedia.

Jim.

The navy used Foster-Wheeler P-fired boilers on the Garcia class frigates. The boiler room had 2 boilers running 1200 PSI at 1000 F.

Combustion air was supplied by an 11 stage axial flow compressor which was connected to 3 prime movers:

1. Electric Motor
2. Steam Turbine
3. Gas Turbine


The gas turbine was driven by flue exhaust gasses. These three power sources could be used singly or in combination as needed . As I understand the operation, it typically went something like this. The electric motor powered the axial compressor when starting the boiler from cold iron, drawing power from either shore connection or the ships diesel generators. During cruise the driving force was supplied by the boiler exhaust gases. The steam turbine was used to supply added oomph when rapid acceleration or high sustained speeds were necessary.

Assuming most axial flow compressors of that era raise pressure about 1 atmosphere per stage; we can figure the combustion air was supplied at something near, or perhaps even a bit above, 150 psi.

Probably the only more - or - less credible design for a small P-fired boiler that I know of is that patented by Nathan C Price. Interesting guy, worked for Doble, worked on Besler's steam airplane, designed all kinds of steam waste heat and propulsion systems for a few different aviation companies and eventually designed an axial flow afterburning jet engine while working for Lockheed in the late 30s...including bleed air for boundry layer control....about 15 years ahead of the curve. Too bad the government didn't fund Lockheed.

Anyhow, see his patent # 2,223,856 at: [docs.google.com]

Ken

Ken.

Can't tell much from the drawing of the turbo compressor.

A car turbo makes pressure. But obviously if there were no restriction you would have no pressure. But there has to be a CFM. You have to have the air to burn the fuel. I would think that the air flow in lb/sec could be figured from the hourse power. Given the efficiency, BTU/lb of fuel and the air fuel ratio one could figure lb/sec of air. Some of the turbos I have looked are getting a 33% increase in lb/sec. Can't say how much of that came from increased RPM and what part came from increased torque.torque.

Ken how was the stack restricted on thoes boilers. There has to be some restriction to get pressure. Aer the tubes spaced closer to do that?

Electric turbos are starting to appear on production vehicals. Audi has one. The advantage of an electric turbo is reduced lag and better performance at low RPM. They have seperated the exhaust turbin from the turbo. The turbine runs a generator. So driving a turbo at high RPM with an electric moter can be done. There is an aftermarket electric turbo kit available useing an AIRESEARCH turbo.compressor.

Andy



Edited 1 time(s). Last edit at 06/28/2014 03:10AM by steamerandy.

Hi Andy,

I don't think the Foster Wheeler had that much in the way of intentional restriction in the flow, but I'm not an expert on that particular unit, just had a few briefings. Jet engines can have diesel like compression ratios (over 20:1) without significant addition of restriction. Steam turbines can take quite a number of stages for the steam pressure to diminish, but most of them have little in the way of intentional restriction. It is simply that turbines, in and of themselves, comprise a significant resistance. When you contemplate how much potential energy they are converting to mechanical energy, you realize that the conversion that their mere action must be quite resistive.

Ken

I'm considering a 50 mm diameter axial flow fan with a spinning cup burner on the output end for a model size burner. It should be very throttleable with modern radio equipment that would allow a variable needle valve to be mixed electronically with the fan speed. The fan speed could be linked to the intake valve that controls engine admission. The fuel flow could also be linked to steam pressure.

The shaft protruding from the motor would drive the spinning cup. Since the fan spins around 38,000 rpm, the cup can be very small. It would take some custom ducting to split the air flow between the cup and the main burner air. See the pictures below as well as a more complete description at [www.hobbyking.com]

Lohring Miller

Hello Andy,

Andy, what is the boiler to be used for? An "on the road car' has different requirements than a LSR car. (My favorite topic.)

An LSR car should require a pressurized combustion boiler for compactness. I haven't had time to run the numbers myself but some smart friends of mine have looked at it. Maybe you could try some back of the envelope math on it and see what this looks like to you. I will when I get the time.

Here's how it works: The Lamont tank pressure is at 1,300 psi. Saturated steam is run through a throttle which is controlled by combustion pressure. The steam is then run through 316 SS tubing, which is directly in the fire. The tubing is almost white heat. This goes to an ejector which pressureizes the air to 49 psi and heats it to about 1,400 deg. After that fuel (kerosine) is injected and ignits rather quickly.

The steam in the combustion products helps to radiate heat.

The useful lifetime of this boiler is about four hours.

Best Regards

Bill G.

Bill,

From my understanding the idea of a P-fired boiler is to have the combustion gasses passing thrugh the boiler pressurized. The idea is that the compressed gasses would have a higher heat content by volume as it would be denser. The higher density would increase convection heat transfer to the tube. So a p-fired boiler could be smaller then a non P-fired boiler of the same capacity. This would also mean that less surface are would be needed for the p-fired boiler. So one could use a high temperature stainless through out, maybe, for about the same cost of a mixed meterials non-P-fired boiler.

I have done experments with a donut shaped combustion chamber. The outside fired boiler design I have posted on that Harry is using on his engines. I have been able to gat a very high density combustion firing with propain and compressed air. I set it up the burner as a venture mix initially. But on hard firing could not get enough air. So used an air gun and just kept cranking up the propain. Centrifugal force holds the fire in the circuler combustion chamber. This was with chamber od of only 11 inchs.

Not planning on using propain. These were tests I ran on fire box meterials and designs..

I am geting ready to go to the next stage. The donut fire box needs a somewhat high flow rate to generate the centrifugal force. An automotive turbo obviously can produce a mass flow rate for considerable hourse power. Ones I am looking at move enough air to make 400+ HP. That is more air mass then any squrial cage fan of compariable size.

Anyway one of the things we need do is to get the power plant into a smaller space. Jim how much power could be packed into the space available on a Cobra.

Anyway I think a P-fired boiler needs checking out more.

Andy



Edited 1 time(s). Last edit at 06/28/2014 05:35PM by steamerandy.

Andy,
Ask yourself first what is the engine configuration you would use? Where do you want to put it?
My scribbling was good for about 250 hp and 2,500 ft/lbs with a draft boosted Lamont.

Actually quite a bit of space, since both good 427SC Cobra kit cars have more than enough room to install the big block Chevy. Best bet is to go to the Factory Five and ERA kit cobra sites and look at everything they post on that car, probably the best kit Cobras out there, Factory five especially.
Both web sites take you all through the design of their cars in detail and both have a big list of nice options.

You might also take a good look at the last years Chevy C-4 Corvette 95-96, the last one with the transmission on the engine and a really great handling car. Tons of aftermarket body parts if you want to change the looks. Extremely tough rear end with lots of ratios available, huge disk brakes too Open the hood and the whole front end out to the tires opens up. They were down on power so right now the C-4 is the cheapest Corvette you can buy, nobody wants them. Lots of good reference books and manuals on Amazon.
A super cream puff 96 convertible in mint condition was $12K.
Jim



Edited 2 time(s). Last edit at 06/29/2014 12:20PM by Jim Crank.

Hi Andy,

That centrifugal combustion chamber, as you describe is interesting. In an SES boiler the combustion starts from a ,If memory serves, flat plate burner with lots of holes in it, like a propane burner. It seems like a good burner, but I would wonder how well it would lend it'self to pressureized combustion?

If, perhaps then, using a centrifugal pressueized combustion chamber in the center of two SES type coil stacks, then the more intense heat produced could be more easily absorbed. Just a picture that came to mind.

Best,----

Bill G.

Hi all:

Personally, I'm not inclined to get into some sort of engineering furball here--but WTH here goes:

My contention is, the power consumption required to operate a pressurized combustion system (in particular at the relatively miniscule scales we are interested in) simply doesn't make any sense when we can achieve higher efficiencies on the "inside" of the boiler with much smaller energy expenditures.

Of, course--I'm talking forced recirculation yet again. OTOH it would be valuable to do an engineered comparison of the augmentations each of these represent.

I'm not presenting myself as any expert here, just something with potential to consider.

As always FWIW,

Bill H.

Bill
My steam-atomized burner used no outside power and no steam from the boiler. It does not require a fuel pump and burns very hot. For me its drawback is the noise. My design only burned three gal per hour but they can be built in any size and for any type of fuel. The nozzle design would lift fuel from three feet.


Rolly's steam atomizing burner
[www.youtube.com]

Hi. Bill Gatlin

I know the S.E.S boiler design.



The donut shaped combustion I was talking about is a vary different design:





It uses a circuit like the S.E.S. boiler having the superheater coiles behind the generating coils. Water enters the iner most coil, flow up and down layered coils outword. Then over the superheating section to coils cloesest to the fire and then back to the superheater section. It could be a simple once through, A spill over or a LaMont fairly easily. The fire box is aroound the coils. The basic concept came from another old steamer at a SACA meet in Danvill. My reasions are completely different. This design gives the highest ratio of radiant area. An anology would be a fixed hight cylander. The larger the diameter the greater the surface area.

My experments so far were just testing methods and meterials for fabracating the fire box. Thats why I was trying to fire it so hard. Stress testing.

It is tangentiall fired and the fire stays in the fire box. Firing as hard as I could. The centerfugal fource came from the firing rate.

Andy

From US Navy Publication, "Principles of Naval Engineering":

The Foster-Wheeler P-fired boiler was quite a bit different than previous naval boilers. It ran up to 150 psi combustion air pressure versus a peak of maybe 15 for earlier units. For the same output it had about half the footprint and even less volume.

Most earlier boilers resembled the Doble, or SES, in that the tubing in the burner area was mostly to protect the boiler housing and any steam generated was more incidental....the heat transfer was by convection by way of a number of tubes in the gas flow path. By observation, the radiant tubing is the primary source of heat collection in the P-fired boiler, the circular layout maximizes the radiant tube surface whereas other boilers tended to minimize it.

Convection is still relevant and takes place in the tubing directly outside the radiant tubes, the gas flow is radially outward with the space along the outer wall of the "can" directing the gas to the supercharger. The boiler naturally recirculates in both the radiant and convection tubing by way of a steam drum/water separator and downcomers.

This design lends itself to forced recirculation, it would be simple to add a pump to the downcomer to force the flow.

In an automotive unit I could see replacing all the radiant tubes with one reasonably larger diameter radiant coil fed by a recirculation pump from the drum. The outer convection coils could be parallel flow with some mixing headers to prevent overheating of a single pathway. These could also be fed from the recirc pump but also take in boiler feed water at the pump inlet. Some finned tubing in the exhaust stack might make for a good economizer and the superheater could be a combined radiant/convective affair with the radiant part on the top or bottom of the can and the convective just outside the radiant coil.

Ken, That sounds interesting.

I think my outside fired boiler might have an advantage.

As the combustion gases are cooled (heat transfered to tubes) and getting denser.
The inward flow is into a smaller and smaller cross sectional area.
The gas flow speed would be greater then an outword flow. Hopefully staying turblant.
The iner tubes are more close spaced. The spacing by design could varied from layer to layer.
More coil layers need for an equilivant surface area would have a longer flow path. The heat transfer is cross counterflow.

I plan to use variable firing with electronic combustion air/fule ratio controle. Multi fuel capable. I think the on/off firing control created some of the problems with historical mono tube boilers. Maybe part of the reason the White having variable firing worked so well. A micro computer can swith between on/off and variable as needed. At some pont a forced air burner, on the low output side, will not function. It can only be tuned down to a limit. And on/off firing would be neccessary.

Maybe the better approach would be a rotary compresser and an air atomizing burner.

Andy

On the one hand, this seems rather silly, what with all this turbomachinery to make a pressurized boiler. If you are able to use a gas turbine, then it would be much more efficient and maybe power dense too, to have the gas turbine *before* the boiler.

You know, they reach nT = 0.6 that way.

On the other hand, there might be the odd application for a PF boiler.
If the fuel is well mixed in, it could be advantageous for Nox emissions.

Quote

The effect of pressure on NOx emission during char particle combustion was examined in chemical-reaction control and diffusion control regimes. A fixed bed was used for batch testing under 0.1−1.6 MPa. It was found that with increasing pressure, NOx emission decreased extremely, when char combustion rate was controlled by reactant gas diffusion into the char particle at high temperature. The extent to which NOx was reduced in char particles strongly influenced the NOx emission from char pressurized combustion. Pressure increased residence time for diffusion of NOx throughout the char particle and consequently further increased the reduction of NOx in the char particle. Both pressure and temperature strongly influenced the conversion of fuel-N in char to NOx. When pressure was raised from 0.1 to 1.1 MPa, the conversion of fuel-N to NOx fell from 0.18 to 0.06 at 973 K, and from 0.68 to 0.13 at 1173 K. NOx emissions were lower when large char particles were combusted than when small ones were combusted. It was also observed that practically no N2O was formed in to any extent in the char particle.

URL

Quote

Abstract
The effect of fuel–air unmixedness on NOx emissions from industrial lean premixed gas turbine burners fueled
with natural gas is analyzed in the pressure range from 1 to 30 bar. The analysis is based on a model where
NOx production is split, according to a Damköhler number criterion, into a “prompt” (fast) contribution generated
within the very narrow instantaneous heat release region (flamelet) and a “postflame” (slow) one, generated in
the combustion products. Using GRI3.0 chemical kinetics, it is found that (a) the prompt NOx contribution is
approximately a factor of 3 less sensitive to adiabatic flame temperature variations than postflame NOx and (b)
prompt and postflame NOx change with pressure respectively according to an exponent αPR −0.45 and αPF 
0.67. It is shown that total NOx emissions change from being mostly of prompt type at 1 bar to being mostly
of postflame type at 30 bar, so that the effect of fuel–air unmixedness on NOx emissions significantly increases
with increasing pressure. The combination of these findings yields a negative NOx pressure exponent under fully
premixed conditions across a rather large range of equivalence ratios but a positive one for levels of fuel–air
unmixedness typical of industrial burners. This result is confirmed by the application of the NOx model in the
large eddy simulation of the ALSTOM EV double cone burner, which gives, in line with experimental data, an
NOx pressure exponent growing, with equivalence ratio, from 0.1 to 0.67.
© 2007 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

URL

Personally, I am partial to the didjeridoo boilers I found near when I first joined here. They had the side benefit of making a horrendous howling wail.

steamerandy Wrote:
-------------------------------------------------------
> Ken.
>
> Can't tell much from the drawing of the turbo
> compressor.
>
> A car turbo makes pressure. But obviously if there
> were no restriction you would have no pressure.
> But there has to be a CFM. You have to have the
> air to burn the fuel. I would think that the air
> flow in lb/sec could be figured from the hourse
> power. Given the efficiency, BTU/lb of fuel and
> the air fuel ratio one could figure lb/sec of air.
> Some of the turbos I have looked are getting a 33%
> increase in lb/sec. Can't say how much of that
> came from increased RPM and what part came from
> increased torque.torque.
>
> Ken how was the stack restricted on thoes boilers.
> There has to be some restriction to get pressure.
> Aer the tubes spaced closer to do that?
>
> Electric turbos are starting to appear on
> production vehicals. Audi has one. The advantage
> of an electric turbo is reduced lag and better
> performance at low RPM. They have seperated the
> exhaust turbin from the turbo. The turbine runs a
> generator. So driving a turbo at high RPM with an
> electric moter can be done. There is an
> aftermarket electric turbo kit available useing an
> AIRESEARCH turbo.compressor.
>
> Andy

A turbo makes pressure, but it has to keep up with the engine too. A 5.6 liter v8 sucks something like 300 cu ft per minute at 3000 rpm. The turbo may indeed blow enough air.

Dan

frustrated Wrote:
-------------------------------------------------------
> From US Navy Publication, "Principles of Naval
> Engineering":


What is the name of that boiler in the picture?

Dan

Dan,
That is a Foster-Wheeler Velox steam generator. There is a lot of information about the Velox combustion concept you can look up. Just remember, they were not designed for wide range flexible operation, but at fixed output and they are big and noisy. Considering the gas turbine they use, the frequent starting and stopping in a steam car would be more than just frustrating. The time lag constantly starting one up all the time would be more than just annoying.
If you read the history of the practicality and use of the Velox as developed by Brown-Bovari, it was rapid starts and high output in smaller sizes compared to the usual huge four story high powerhouse boilers and as load peaking units in power house generator installations they were after.
I would forget any idea of using a Velox steam generator and consider one with a draft booster using an exhaust steam turbine in a car. Not in a LSR car either, we considered that for our car and dropped the idea like a hot potato, just not needed.

Pressurized combustion is a good thing; but let's keep it reasonable, 150 psi combustion or anything like that is just not realistic in any car system. 20"-30" draft will easily double the evaporation rate, So how much power do you really need anyhow in a vehicle??
There is an experience one gets by driving a lot of real steam cars on the road vs. imagining them on some computer program. In probably 75% of the time you are in town just piddling along and some intense firing rate is the last thing you need. Now on the road drag racing some kid in his souped up Corvette, you want all the power you can lay your hands on. This is exactly what a draft booster gives. Think about that for a moment. Achievable practicality vs. an overheated imagination.
Jim



Edited 1 time(s). Last edit at 01/25/2015 01:57PM by Jim Crank.

Jim:

I agree about achievable practicality. I think my main concern is for the boiler to be reasonably sized. I think the SES boiler was a step in the right direction, but still pretty bulky. If modest pressure doubles steam rate, then you may not need turbo.

My initial thought was using an automotive turbo connected to a motor-generator, so the turbo would be generating electricity all the time. But I do realize that would be a whole R&D effort all by itself.

Dan

Probably worth mentioning about the Combustion Engineering P-fired boiler is that it went into a few US Navy frigates, unlike a stationary power plant these systems may provide enough power to just make steerage way one minute and be sprinting at flank speed the next; for a larger steam plant that is a lot of variability. The boiler could achieve this because the turbocharger unit also had an electrical element; the system could be easily cold iron started with the motor driving the fan and the motor could supply the immediate draft needed when you wanted to beat feet in a hurry. Actually, the system is faster responding than the Doble as that is dependent on the passing steam mass; the Combustion Engineering system responds almost instantly. I think something vaguely similar would be beneficial on an automotive system.

Regards,

Ken

You got it pretty much right on turbines ,even add vanes and all matter of thing to reduce restriction from turbolences.
Look at turboshafts they even balloon out the exhaust pipe to reduce restriction....That stack would make one heck of a balloon exhaust pipe on a ship....
You also had about 3 or 4 different burners used on Naval ship depending on time period.Can't remember where but somebody on Utube actually loaded the training videoes for the 1950's navy boilerman school.

You look at some of the burners used by steamers like Doble in automobiles and you will see that they were building jet
engines before there were jets...sort of like happened with the 32 cams the steamers used before there was even a internal combustion engine.

frustrated Wrote:
-------------------------------------------------------
> Probably worth mentioning about the Combustion
> Engineering P-fired boiler is that it went into a
> few US Navy frigates,
>

I'm not familiar with the combustion engineering unit. Got any links?

I'm also looking into moderate pressure, porous ceramic combustion. Maybe even embed the tubing in the porous ceramic. I was reading about am experimental boiler (surface combustion boiler) that used porous fire plugs for the combustion. It's flameless, and apparently the heat per cubic foot of combustion space was almost as good as the Velox.

Dan

Dan,
Look for industrial space heaters. Porous ceramic, gas fired. Used frequently for heating outside areas because of the amount of IR they pour out.
Jim

Jim:

Further thoughts on a turbo. If you design the boiler correctly, theoretically the exhaust air coming out of the combustion chamber would hardly have any energy left, so there wouldn't be any energy to run an inflow turbine anyhow. And besides, I see you don't need that much boost.

I do like the concept of having a turbine run a centrifugal compressor and a motor-generator all on one shaft though. But now I'm thinking the turbine should be an impulse turbine running on exhaust steam, or bypass steam when the car isn't moving. The motor-generator runs the blower when cold, and then generates electricity when hot. Plus you could spin up the blower when you need higher output instantly, without lag from waiting for steam at the turbo. You'd have a lot of control over blower speed. All your accessories could be electric.

There's some switched reluctance motors now that can run above 100k rpm, and can also generate as well as being a motor. It's all done in the drive electronics.

Dan

P.S.: what rpm would Doble's steam turbine have tipically run at?



Edited 1 time(s). Last edit at 01/27/2015 12:17PM by dullfig.

Dan,
The exhaust from a 1200 lb/hr Doble steam generator does not have enough energy left to power anything and remember this supply of hot gas is cyclic, not continuous.
Unless you want to put impossible backpressure on it, if you don't see why there is the high firebox pressure in a Velox concept, then the whole discussion of using one in a car is moot. Frankly I seriously doubt one even could and don't see the need to contemplate scaling a Velox down to car size anyhow.
In E-14 which was well instrumented, the exhaust temperature runs about 375-450°F when on the road.

In this small size an impulse turbine is infinitely worse than a radial inflow. Take a look at the Barber-Nichols chart attached and remember the impulse turbine has to obey the 1/2-V ratio to get any efficiency. A car exhaust doesn't begin to provide enough velocity or energy to do this.
Go lift the hood of a C-4 Corvette, a good host car, and see where you would cram all this duct work and machinery. My opinion for what it is worth is to forget the Velox concept for any passenger car use.

The hotel loads are way too big to contemplate using this supposed gas turbine to run anything. AND, don't forget this is a collection of cyclic loads, not continuous ones and each is used at separate times.
When you are stopped there is no exhaust or bypass steam, the plant is simply completely shut down.

In Doble E-14, the draft booster ran about 9,500 rm when full out.
Jim

Jim, I'm probably not explaining clearly, wouldn't be the first time

No, I'm not thinking Velox anymore. I'm just calling the draft fan "blower".

About back pressure at the turbine: there's back pressure between the LP and HP cylinders anyhow. Wouldn't a turbine at the exhaust act as a third compound? Kinda like the Titanic setup. Any power robbed from the engine would be recovered by the turbine (sorta). You need an auxiliary engine anyways, right?

Or would idling your main expander to run auxiliaries be a better solution?

Dan

Dan,
What many found decades ago was it was a very smart idea to have the feed pump independent and not depending on the main engine running. You can get into very embarrassing situations in heavy traffic and some hills with a monotube. Starting up from a stop in long cutoff uses a lot of steam and thus water. A couple of these and the coils are dry and there you sit, overheated, the fire shut down and no water going in, blocking traffic. Had this happen with that miserable Doble several times in San Francisco thanks to only the main engine driving the water pumps.
With the White, I just pull over, kick it into neutral and idle the engine until everyone is happy again. This is where your idling the main engine idea works superbly well.

You don't necessarily need an auxiliary engine. Those usually consume about 10-15% of the steam generator output, take up space, burn more fuel, cost money to build and add more machinery, when there is a beautiful way around this. This is exactly what that Waterman system can accomplish so easily and no added unreliable electronics messing things up. Combine the Waterman pump with the Lamont and you have a super system.

Now you are talking about a compound with a third turbine stage tacked on? Don't need this at all. Forget the piston compound and consider that if the blades on the power recovery turbine are designed correctly, it does the work of compounding better than any piston second stage. Ken and I address this in our paper.
Jim

All files from this thread

File Name	File Size		Posted by	Date
rotary-cup-burner1.jpg	49.7 KB	open | download	lohring	06/28/2014	Read message
31823-sub1.jpg	137.4 KB	open | download	lohring	06/28/2014	Read message
boiler.jpg	56.7 KB	open | download	steamerandy	06/29/2014	Read message
boiler1.jpg	48.6 KB	open | download	steamerandy	06/29/2014	Read message
sesboiler.jpg	81.3 KB	open | download	steamerandy	06/30/2014	Read message
scan10001.jpg	95 KB	open | download	frustrated	07/01/2014	Read message
nsds_turbine_chart.pdf	676.4 KB	open | download	Jim Crank	01/27/2015	Read message