Fuelling a Boiler using Electricity

Instead of going all-out electric which would, let's face it, be the most efficient - How about running a 12V compressor and use the boiler as a compressed air tank?

Edited By Jon Gibbs on 20/03/2018 09:57:47

Nice to see figures quoted but they have me thinking heresy! Converting electricity into heat to make steam to drive an engine isn't an efficient way to turn chemical energy into motion. It combines the inefficiency of a steam engine with the inefficiencies of battery power. Yuk. As Duncan's figures show, it could be made to work, but only at a hefty disadvantage. You would need a special reason for doing it that way.

My heretical alternative is to use the batteries in a fake electrically powered tender. Electric motors are massively more efficient than small reciprocating steam engines which would offset the shortcomings of the battery. My 'steam engine', also a fake, would be fitted with a small coal fire and low-pressure boiler used only to produce the authentic look, sound, and smell of steam. Actually, in this configuration, the boiler could be a mere kettle, not pressured at all. On the track the 'engine' is pushed by the electric tender which provides all the motive power. In doing so modified motion work would pump good looking wet-steam out of the boiler and up the chimney.

An electric "steam engine" of this type might be useful on a club track giving rides to the public because steam is far sexier than IC and electric. Safer and less technically demanding because the boiler isn't a pressure vessel; quick and easy because the engine doesn't have to be fired and controlled by a trained driver, nor does steam have to be raised before the engine starts work. Also reliable and low maintenance. Sustained running of the 'steam engine' could be managed with a back-up stock of pre-charged batteries or a fleet of electric tenders.

I expect it's already been done!

Dave

Superheating the steam would be a bit of a problem but if the engine is not using superheaters then you won't have a problem.

Mike

You did! Thought I'd read all the postings - obviously not! Great minds think alike...

Built 1935, converted early 50's, ran through the war, so can't have been that bad. According to OSNock and Wikipedia it showed a slight advantage in coal consumption, but as Jon says it was best at it's design speed, but for an express passenger loco that's what you want. For further reading see**LINK**

Swedes had some successful, ones, and USA built one with 6300 hp capable of over 100 mph (well they would wouldn't they!)

You can have electrically heated superheaters, Bill Hall used a coil of pipe round a radiant fire element. You could just pass a current through the stainless pipe, but might need some power electronics to get high current low voltage. Making a boiler sounds best to me.

This is turning into a very good thread and pulling some neat ideas out of the woodwork.

Just as a reminder, the original idea of an electrically heated boiler was to quickly get my DYAK running under her own steam. She needs so much work doing to the current boiler, that a new one would be required. The electrically heated option was to make a new boiler design simpler.

The current boiler does have a superheater.

The idea of storing steam using a mains electricity supply doesn't really work. The amount of energy needed to raise water to the temperature appropriate to the working pressure is much smaller than the energy needed to convert the water to steam at the same temperature. So as soon as the engine moves and steam is used a significant amount of energy is needed to replace the steam. So, as mentioned, you either need a large storage capacity or you need to run at higher pressure. I'm not sure how'd you'd convert the high pressure steam to lower pressure suitable for the engine. I suppose you could use isentropic expansion through a nozzle to drop the pressure at constant entropy. But in doing some of the enthalpy is converted to kinetic energy. That probably wouldn't be much use in a conventional steam loco. On the hand it'd be perfect for a steam turbine. That's how steam turbines work in practice. The high pressure steam is converted to low pressure high velocity jets through nozzles which then drive the turbine blades.

So, as well as redesigning the boiler a quick conversion of the engine to a steam turbine might be on the cards.

Andrew

Hmm a kettle produces steam at a similar rate/volume to a loco boiler.

A kettle is 3kW, my 0-4-0 shunter is 80W.

Even for 1kW you would need 83 amps @12V which is a lot....

Maybe a 48v circuit with small batteries on board to even out the supply from the rails provided by a generator. Might need an inverter on the train to boost the voltage after the drop due to resistance of iron rails.

Those numbers give an idea of just how inefficient a steam locomotive is.

Assuming Neil's electric shunter to be of roughly similar power to a steamer of the same gauge, 3000W to get about 80W at the wheels suggests steam has a running efficiency of less than 3%. In comparison, a small electric motor will be about 70% efficient and a big one (>100kW) might nudge 95%. Steam has the advantage of being a prime mover, whereas power has to be generated and somehow made available to electric trains.

Neil - out of interest, have you ever measured your shunter's drawbar pull and acceleration whilst pulling a load, or raced it against steam? (I'd guess Southam out-performs steam locos until the battery goes flat!)

Dave

I think a steam loco has the advantage with starting torque. Stalled an electric motor will just get warmer, a piston can build up pressure behind it until the safety valves blow off., and effects like wire-drawing are irrelevant at starting speeds.

It seems an average kettle is nearer 1800W but it's not a huge issue here.

Steam is about 3% efficient but many of the inefficiencies are getting heat into the water from the coal.

Some numbers I crunched, based ons 26 lb model. 1/6 m/s is 3.6mph or a scale speed of 43mph, bear in mind an almost identical prototype had a top speed of 16mph... :

Given the actual results I've achieved these are in the ballpark, I suspect efficiency is bit lower due to losses in my chunky home-cut gear train with plain bushes.

Starting a heavy load the wheels will spin.

Notionally its comparable to a Tich but I think Tich's ability to start with a heavy load is greater.

Two comments

1) Induction heaters for cold starting diesel engines come in two types.

The ones, often described as Thermostarts, or Flamestarts, electrically heat a rod, so that it expands, unseats a ball, allowing fuel onto the element, where it catches fire.

You do not want one of this type.

The other type, more recently used in cars, is purely a heating element. Each "glow plug" draws about 45 Amps on 12 Volts, so you might need a BIG battery to power each one for 15 minutes, even if it only looks like 10 Amp Hours!

2) The fireless steam loco seen in Runcorn was probably one of the last Sentinel "fireless cookers". They were were used in areas of chemical works where no flames were allowed. The last ones were built in the early 1960s, and painted Brunswick green, with lining. think that they went to ICI.

The loco was charged from a superheated steam main. The charging steam melted lead, to act as a thermal reservoir, and regenerator. It was similar to a vehicle powered by rechargeable batteries . When pressure fell to a certain level, they returned to the charging point for a top up.

Howard

Neil Wyatt said:

"Steam is about 3% efficient but many of the inefficiencies are getting heat into the water from the coal."

Actually, not so. A model boiler is a bit less efficient than full size, but still up in the 60% range. The real fly in the ointment is the small difference in steam enthalpy between inlet and exhaust of the engine unit. That is where the second law really kicks in. In short, you are throwing away most of the energy in the steam you are creating.

Martin

The Swiss had some electric steam shunting locos. There was a good reason for this: shortage of coal during WW2 and plenty of hydroelectric power and a need to shunt unelectrified sidings. They were converted back after the war.

Howard mentioned fireless locos using lead, there was also a type that used potash. The heat from the charging boiler dried out the potash to make it anhydrous, and when running a bit of the exhaust steam was directed into the potash, where it combined and released the latent heat of chrystalisation. This would allow the storage of more energy than just a boiler full of water. They would still only be a short range affair.

John