One of my goals for my postcard series is to show a rebuilding society that prioritizes reducing waste and externalities, and examining what weird technologies might appeal to them because of those goals/limitations. So I've been wanting to do a scene of a caustic soda locomotive ever since I first heard about them.
Soda locomotives were a type of fireless steam locomotive that barely made it out of the prototype phase, where the boiler is surrounded by a tank of ‘caustic soda’ (usually one of several possible chemicals), which generates heat when mixed with water. The heat produces steam in the boiler, which is used to drive the pistons, but instead of being released, its condensed and added to the soda to create more heat. This goes on until the soda gets too dilute to produce more heat, but it can be 'recharged' by drying it out again.
These never really took off because it took more coal to dry the soda at the station than to just run a conventional steam locomotive, and electric trains quickly came into their own and filled the niche of quiet, low-pollution trains for inside cities and tunnels.
But I feel like these could pair well with solar steam generators (another late-1800’s design) stationed along the tracks, to create analogue, solar-powered trains. These could run on existing unpowered tracks, without requiring any new electrical infrastructure, just the isolated drying stations.
The train crew would just exchange wet soda for dry and start again (looks like that took about 45 minutes). The cool thing is that this arrangement could be asyncronous - the station can dry out the caustic soda, then store it for when the train shows up. The train can run on cloudy days or at night, as long as they get enough sunny days to dry out big batches of soda at the stops along the way. And the solar concentrators can be huge and optimized for their location because they don’t have to move.
The focus of these postcards isn’t on technological utopias so much as on societies that are reexamining how to do things as they rebuild, anachronistically combining all kinds of tech. So trains and solar concentrators built with 1800’s technology seem like an easier starting place.
The concentrators require fairly simple materials (mirrors or polished metal) and math to make (plus some simple mechanical timing or basic motors/electronics to get them to follow the sun without a human turning a crank).
Most of the descriptions I've seen of drying the caustic soda mention pumping superheated steam through the dilute mix from another (coal) boiler, so it seems like you could use almost any design from the earliest solar steam generators to something like these modern ones depending on the society’s manufacturing capabilities. The solar concentrator/boiler I referenced for the art is a design from 1901.
(The most common modern design for solar steam generation I've seen is that sort of mirrored-trough-and-vaccum-lined-tube system. I mostly went with the big round reflector because I was worried the trough design wouldn't read as distinct from photovoltaic panels in this art style.)
The trains could run with minimal pollution using these simple technologies, and even if their range is lower, or they're not as fast, that might be a trade off this society would accept.
Ideally they would use existing tracks and passenger or freight cars, and only need new infrastructure around whatever station fueled them up on their route (or at a destination). I think this applies to the compressed air locomotives just as well as the caustic soda ones.
(If you don’t like the idea of caustic soda locomotives, but you still want this idea to work, another option with a shorter range is compressed air locomotives. Instead of drying the soda, the station would be using a solar steam engine or windmill or water wheel to run an air compressor, steadily filling a tank which would be used to top up locomotives on their route. This would still allow for isolated infrastructure to power a train along unpowered rails. IRL these mostly saw use in mines.)
The locomotive in the scene is based on a real-life fireless locomotive. They’re similar, but filled with super-hot steam by external sources. They seemed like a good reference for what a caustic soda locomotive might have looked like had the concept reached a more polished, production format. But they don’t really fit my goal for tolerating intermittency as they’d need the heat source to be going when they stopped for a refill.
Glad you liked it :)
You're hired!
I was thinking something that looks a bit like a steel-framed ISO tank, but smaller and with more connectors. At a minimum you would need:
Installing and removing the steam pipe flanges would not be elegant, requiring a rattle gun (like tire shops use to change your wheels). Maybe there are some more elegant solutions? Especially since it's so easy to accidentally pressurise a system after only tightening some of the bolts (woops).
They wouldn't look like the nice, uniform, dry powdered stuff you're used to, instead they'd be unevenly coloured slime :)
I might be wrong specifically about the copper carbonate product, but the others are probably right. No brass, no bronze and no copper allowed (sadly).
Here's a quick shot at a side view of what I'm thinking of. It doesn't show as many gauges etc as I'd have liked, but feel free to point out any modifications you think it needs!
Hey Jacob,
Lovely subtle background with soft edges and technical side profile :) This is way beyond what I was expecting. My only artistic complaints would be the odd reflection on the round tank.
Where is the water stored? The engine will need a tank of its own to hold this. The modular units would only hold water temporarily, you would probably want to drain them before lifting them off. Water would also be consumed during the trip from leaks and from adding it to the caustic soda.
How do you imagine your tank being lifted? It looks like it's currently setup for a shipping-container style ISO twistlock lift (where you hook onto the top 4 corners with some sort of frame hanging from the crane). I was instead imagining a central lifting point and a traditional single-cable crane. Your idea is probably better -- the frame is already strongest at the corners and you can potentially couple/uncouple without needing to climb on top.
A really important question would be whether or not we're using relatively low pressure steam like classical engines (a few atmospheres) or high pressure steam (a few hundred atmospheres). From my vague uneducated understanding of the rankine cycle that steam engines approximately use: higher pressures and temps might allow better efficiency. Your size of tank might only be feasible for lower pressures, at higher pressures you would use multiple tanks with smaller radius (this makes them much stronger, assuming the same wall thickness in both).
I'll state again that I'm not a train person nor have proper in-depth knowledge of a lot of areas required to properly design such a train, this is all mostly guesswork.
Some random thoughts of my own, much more rushed and poorly drawn than yours:
EDIT: Woops, should have made the tanks black rather than shiny silver. They'll need to be craned onto the solar collectors and then dried, so a darker black body would be better.
This is really cool, thank you for taking the time to model your design, it really helps me picture it, and it seems like there's some good advantages there in smaller modular units being easier to lift off, and capable of higher pressure.
I copied an original soda locomotive design, where the water boiler is inside the larger tank of caustic soda:
The soda heats the water, releasing steam, which is run in pipes back and forth through the boiling tank and soda tank to further heat it, then driven through the pistons, before being condensed and released into the outer vessel to produce more heat.
I like the idea of pushing the design choices further, mixing in electric motors etc.
The good news is the canisters of soda don't need to be lifted into the focal point of the solar concentrator. Historically at least it sounds like they often connected them to an external (coal) boiler and pipes superheated steam through to dry them. It seems to me these could use a similar setup with a hookup leading to something like this: https://inhabitat.com/old-fashioned-steam-engines-could-solve-solar-energy-storage-problem/concentrated_solar/
That should lower the labor amount a bit, and make for safer work.
Somethings from further afield to consider: maybe hoisting tanks up onto the circular solar concentrators is a bad idea.
(1) Store and use the NaOH in long, skinny pipes (instead of big tank modules). Then mount them on linear solar concentrators.
(2) Keep the modules, but crane them onto the ground near the solar concentrators and use superheated steam from the concentrators to dry the modules. Less hoisting. The modules already have a piping system in them (isolated from the NaOH) for generating steam, just use it in reverse and open the NaOH chamber so water can escape to the atmosphere as it dries.
I love this design, and this writeup is awesome! If I do a story featuring these trains this will be a huge help.
I'm definitely doing a scene of these weird cyberpunk-looking steam locomotives. I love the framed tank design, I think they could look a bit like a bigger, clunkier version of these things when they're closed up:
(Or, I suppose, a modern diesel with the cab in front, though that might make lifting the boiler more finicky.)
I'm not sure about the process of lifting them and attaching them, but this is a great start. Maybe they'd use one of those cranes that hangs from the ceiling on rails.
I'll sketch what I think you've described in a bit, to make sure I've got the layout right. (I'm gonna have to look up some train designs to make sure the connectors are pointed in sensible directions.) Plus sometimes sharing schematics attracts additional input/corrections which would be cool.
Good catch. Having the boiler in front would make some lifting logistics easier, because you could swing it off in a circular arc rather than needing a crane that can move linearly.
That simple difference might allow smaller, simpler cranes at the various outposts (reserving a full gantry ceiling crane for the workshops or more major stops).