Pre-heat loco water to cut coal bills?

[melmerby]

Why not do away with the coal and just use electricity?

[melmerby]

The Brienz Rothorn steam (rack) locos have electric pre-heaters.

[Dave John]

Sums. (feel free to check them} 

 

Let us assume a small locomotive with a boiler containing 1 tonne of water. 

 

Let us assume an initial temperature of 20  C and a final temperature of 100 C . 

 

Let us assume the efficiency of a boiler when lagged in free air is 80 % . 

 

I estimate that would require about 120 kWh of electricity.  To preheat that quantity of water in an hour would need a 120 kW immersion taking about 480 A at normal mains voltage. I feel it is unlikely that such a current would be available at most preservation locations. 

 

A search tells me that the average cost of electricity in the UK is 34 p/kWh, so 120 kWH would be about 40 ukpounds. 

 

Note that this is a preheating calculation. To actually turn water at 100C into boiler pressure steam requres considerable further energy, presumably from burning coal. 

 

 

 

 

[rogerzilla]

14 hours ago, Dave John said:

Sums. (feel free to check them} 

 

Let us assume a small locomotive with a boiler containing 1 tonne of water. 

 

Let us assume an initial temperature of 20  C and a final temperature of 100 C . 

 

Let us assume the efficiency of a boiler when lagged in free air is 80 % . 

 

I estimate that would require about 120 kWh of electricity.  To preheat that quantity of water in an hour would need a 120 kW immersion taking about 480 A at normal mains voltage. I feel it is unlikely that such a current would be available at most preservation locations. 

 

A search tells me that the average cost of electricity in the UK is 34 p/kWh, so 120 kWH would be about 40 ukpounds. 

 

Note that this is a preheating calculation. To actually turn water at 100C into boiler pressure steam requres considerable further energy, presumably from burning coal. 

 

 

 

 

If you used an immersion heater, boiler efficiency would be closer to 100%.  It can approach 80% when using coal (when, of course, a load of heat, and some small pieces of fuel, are lost up the chimney).

[Nearholmer]

You’d need a very well-lagged vessel to get close to 100%, and I’m sceptical of 80% on a locomotive-type boiler fed on lump coal, although that can be bettered with a stationary boiler fed with pulverised fuel, but ….. 

 

The cheapest way of warming water is often by gas, so maybe we connect our locomotive boiler in a circulatory  system, so as to permit gradual build-up of temperature with no thermal shocks, to a ‘best modern practice’ gas boiler, as a way of achieving pre-heating. There must be off-the -shelf gas boilers for use in industrial processes that have the capacity needed.

 

The loco should be kept indoors, and wrapped in a nice big duvet while this goes on.

 

I don’t know how practical it would be, or whether the costs would work out favourable to coal, but maybe even use a distributed-flame gas burner inserted through the fire hole door to take the temperature up from pre-heat to just short of steam-raising.

 

 

Edited April 26, 2023 by Nearholmer

[MPR]

This website is no longer updated, but provides lots of useful links to "modern steam" - discussing many of the issues in this thread.

I found the DLM website particularly interesting (they built the rack locomotives mentioned earlier in the thread)

https://www.martynbane.co.uk/index-old.htm

 

[Blandford1969]

On 25/04/2023 at 18:17, Jeremy C said:

Coal for railway locomotives is extremely expensive at the moment (I've heard talk of £500 per ton), but so is electricity (£0.35/kWh is the cost I use at work). 

A long time ago the price of gas was tied to the price of coal and followed it. Now it is the opposite way round. Prices have fallen a but from their height but are still very expensive and a serious concern to many. 

[tomparryharry]

The Western had a hot water flushing plant at sheds like Old Oak, Bristol, Ebbw Jct, etc.  Its principal aim was to keep the boiler reasonably warm when being washed out. My electrics isn't too hot, but depending on the usage, something similar such as a battery charger for a milk float would be technically feasible. 

 

Hot water vis-a-vis  injector is a bit of a no-no. The temperature difference  between cold water & pressurised steam is the 'working envelope' to enable kinetic energy to be created. The hotter the feed water, the less efficient the injector becomes.

[adb968008]

Is converting to oil burning instead of coal not a better proposition ?

 

Also resolves the burning ash problem in hot / dry seasons.

Edited May 6, 2023 by adb968008

[rogerzilla]

Oil burning coats the tubes with a nasty tar which has to periodically be removed by the fireman, using sand.  The pollution thus caused is quite horrendous (and visible as an enormous black cloud).

[pete_mcfarlane]

4 hours ago, rogerzilla said:

 The pollution thus caused is quite horrendous (and visible as an enormous black cloud).

I'm thinking of the Russian aircraft carrier (on the rare occasions it actually works).

[jonhall]

When I visited Cheyenne to see the UP heritage workshops, the UP Challenger was attached to a pre-heat system to bring the boiler up to temperature over the few days before they need to steam it - I'm not sure if the Big Boy does, but it seems likely.

 

Jon

[Wickham Green too]

On 26/04/2023 at 14:35, Nearholmer said:

You’d need a very well-lagged vessel to get close to 100%, and I’m sceptical of 80% on a locomotive-type boiler fed on lump coal, although that can be bettered with a stationary boiler fed with pulverised fuel, but ….. 

...... but I don't think anybody's yet mentioned fireless locomotives on this thread ! 🙄

[Reorte]

19 hours ago, jonhall said:

When I visited Cheyenne to see the UP heritage workshops, the UP Challenger was attached to a pre-heat system to bring the boiler up to temperature over the few days before they need to steam it - I'm not sure if the Big Boy does, but it seems likely.

Is that to reduce fuel costs when running or just to carefully manage thermal stress?

Edited May 9, 2023 by Reorte

[009 micro modeller]

12 hours ago, Wickham Green too said:

...... but I don't think anybody's yet mentioned fireless locomotives on this thread ! 🙄

Still used in Germany until recently (and still?): 

 

 

I think they had a fireless at Quainton Road at one point and fed it from a static steam locomotive.

[Wickham Green too]

Or if you prefer your locos a little more 'workaday' : - 

 

Henschel & Baldwin machines : Brasil Mill, Cuba ; 24/2/09

[jonhall]

2 hours ago, Reorte said:

Is that to reduce fuel costs when running or just to carefully manage thermal stress?

I suspect its a thermal stress thing, but IIRC its an oil burner, so it might also make lighting up easier as well?

 

Jon

[rogerzilla]

You couldn't get an heavy oil burner going from cold at all - you had to have steam to heat the fuel and make it fluid.  Some locos used coal to get things going but a static steam supply would work too.

[Pete the Elaner]

Pre-heating water for a steam boiler was exactly the principle of the Franco-Crosti boiler.

Nice idea but the drawbacks outweighed the benefits.

[rogerzilla]

The Italians seemed to make it work better.  There's a fine example in "Von Ryan's Express", used by the SS troops chasing Frank Sinatra and his fellow escapees.

 

Edit: an FS Class 743, apparently.

Edited May 10, 2023 by rogerzilla

[LMS2968]

It tended to improve loco, especially boiler, efficiency but if you had an engine which was already pretty efficient, as measured as a steam engine, it lost much of its effect. The standard 9Fs were already pretty good so the effect of the Crosti boiler were not very significant.

[Peterem]

Wasn't a by-product of fitting condensing gear to locomotives a significant water temperature rise in the tanks?  So much so that the condenser-fitted Midland 2441 0-6-0t locos needed a double tank wall and air gap to stop the paint on the sides blistering. To my knowledge no-one ever claimed this offered any sort of performance advantage, and it was rarely fitted or used unless regulations required it.

[LMS2968]

Condensers were usually fitted to engines regularly and frequently working through extended tunnels, e.g. the underground. The rise in water temperature in the tanks from their use was sufficient to demand the application of a feed pump in addition to the injectors which were used outside the tunnels.

[Jeremy Cumberland]

27 minutes ago, Peterem said:

Wasn't a by-product of fitting condensing gear to locomotives a significant water temperature rise in the tanks?  So much so that the condenser-fitted Midland 2441 0-6-0t locos needed a double tank wall and air gap to stop the paint on the sides blistering. To my knowledge no-one ever claimed this offered any sort of performance advantage, and it was rarely fitted or used unless regulations required it.

That's right. As far as I am aware, all locomotives fitted with condensers had a feed pump to cope with the higher feed water temperature.

 

Both condensing and pre-heating of feed water were common in water pumping and marine applications, and are universal in power generation, but they are separate processes. Condensing was done to increase efficiency (or get more power out, if you prefer), and created a vacuum of about 10 psi on the exhaust side of the piston or turbine. This requires a supply of cold water, something that railway locomotives don't have, which is why it was never adopted.

 

Condensing on locomotives was done so that the uneven exhaust from the cylinders wouldn't draw smoke (=unburnt coal) from the firebox and send it out of the chimney, and the necessary draught through the fire was created by using the blower instead. However, there wasn't enough cold water in the tanks for condensing to work for the entire journey, and it was only turned on for short periods. Presumably this was just after adding coal to the fire, but I don't recall ever reading an account of how exactly condensing was used on steam locomotives on underground railways. Sometimes it seems it was not used at all.

[rogerzilla]

Condensing was also used on desert railways, for the same reason as on steamships (no fresh water supply). There was usually some kind of radiator in a tender to cool the exhaust steam sufficiently.  They would need to get the oil out of it too, or the boiler would prime horribly.