Having read through this entire thread, I see that there are a couple of questions that have not been answered about the nuclear power source for the steam engine. I would like to add my two cents on that.
First, my background, 6 year Navy
Nuc Electrician Qualified Submarines, and 30 years in the Nuclear Electrical
Generation business as an operator. Currently a Licensed Senior Reactor Operator.
Second the question about how to drive a submarine, there were a few odd subs that had different designs:
The Sea Wolf SSN 575 originally had superheated steam, thanks to a liquid sodium cooled reactor.USS Seawolf (SSN-575) - Wikipedia, the free encyclopedia
This did not work well due to problems with the super heater and the entire Nuclear Steam Supply System was replaced with a conventional PWR reactor and Steam Generators.
The Triton USS Triton (SSRN-586) - Wikipedia, the free encyclopedia
which had two reactors and two engine rooms etc. Expense and unneeded complexity ended this boats life early.
The Narwhal had a PWR for steam supply, but used natural circulation instead of noisy Reactor Coolant
Pumps, she also had NO reduction gears between the turbine and the prop. USS Narwhal (SSN-671) - Wikipedia, the free encyclopedia
There may have been a submarine with turbine to electric generator
to electric motor
to the shaft to the prop, but I am not aware of any specific boat. In virtually all other cases, the NSSS on a submarine uses two or more turbines to spin a set of reduction gears to spin a shaft (which usually has an electric motor
on it as well that is used when the reactor is unavailable) that spins a propellor.
The Swedish submarines are the ones that use the stirling engine. Gotland class submarine - Wikipedia, the free encyclopedia
Third there was a question about steam generators and moving parts
. A steam generator
can be almost anything that makes steam, Steam generator - Wikipedia, the free encyclopedia
but in the context of this discussion, it was for a nuclear power plant Steam generator (nuclear power) - Wikipedia, the free encyclopedia
In this case, there are NO moving parts to the steam generator, there are many moving parts to make it all work, but the steam generator itself is just a very large specialized heat exchanger
that takes pressurized hot water and makes SATURATED Steam (not super heated) Superheated steam - Wikipedia, the free encyclopedia
Disadvantages to use of Saturated steam include entrained water which impacts the turbine and steam piping. These components must be engineered to withstand this impingement.
Advantage of the saturated steam over the superheated steam is that you don't have to burn something else, or come up with some more complicated method to use the reactor. Babcox and Wilcox commercial
power plants use a once through steam generator which gives them a small amount of superheat. Another way to get superheated steam with a reactor plant was used at Indian Point unit 1 (long since removed from service) that used a PWR to make steam in the Steam Generators, then fed that steam to a coal fired super heater.
Back to the original posters suggestion that coal could be used on a small boat to make steam, thereby getting cheaper propulsion
than by use of Diesel or Gas. Having worked with steam in both in the Navy
and at a commercial
nuclear power plant, I can't imagine tolerating that kind of hazard on board a small personal boat. Steam is dangerous, in my opinion when combined with the fuel
source it is much more risky than a diesel engine and fuel.
First of all you have the issue of the heat, and the risk of a burn. Either from the hot metal of the steam plant, or a steam leak and a steam burn.
Then you have the risk of a leak in the generator. Where I work we use very clean water for the feed to our steam generators (theoretically pure water has a conductivity of 0.055 micro S/cm Introduction to Conductivity
the water we use is ~0.056 micro S/cm. When we cleaned our steam generators, we still wound up removing several hundred pounds of metal. You will not have access to this quality of water for your steam plant, nor will you even get close. In the article I mentioned here they state that power plant boilers use 1.0 micro S/cm water, you will have some difficulty in getting even that quality of water.
Whether you have a nuclear reactor heating
your steam generator or you burn coal, you will still have the same issue on the steam side of your generator. The problem with all the metal in the steam generator is that it reduces heat transfer, and more importantly provides a place for chemicals like sodium chloride (salt) to hide out and cause corrosion
of your steam generator. When you develop a leak (not if, but when) the steam generator will be out of service
until it gets fixed. If the leak is through the heat transfer surface area you will be putting steam/water on your coal. This can result in a Steam Explosion similar to what happened in the Chernobyl nuclear plant, this can be very destructive even if it is only interacting with burning coal. If the steam leak is out of a pipe it will cut through almost anything it is pointed at for example that nice thick fiberglass hull
of your boat, and now you have another leak to worry about.
So that is the added risk of steam in your boat, now what about the coal itself, consider the affects of wet coal The Myth Of Storing Wet Charcoal and Spontaneous Combustion
note that this page is about how wet CHARcoal will not self ignite, but it is clear that it also points out that it is a problem with COAL getting wet. (How will you avoid that on a boat?)
Now compare the storage
area required for the coal compared to the diesel fuel. (I am assuming diesel vs gas due to the risks associated with the use of gas on a boat).
Energy in diesel between 34MJ/litre and 38MJ/litre What is the energy content of diesel
Energy in coal 6.5 kJ per 250 g of coal What is the energy content of coal
This shows that you will need way more space for the coal than the diesel (just in case you had not already figured that out). Then there is the delivery
system how are you going to get the coal into the boiler?
None of these points make it an unworkable solution, just point out why it is not a common practice anymore. There are better, safer and more efficient methods of moving your boat, and yes they may cost a bit more in the long run. (Just how much do you really think it will cost to build a one of a kind coal fired steam piston engine driven boat?)
Sorry for the very long post, I have never been accused of being short or concise. However, I believe I have given some accurate complete answers to the questions that were asked.
If I have made a mistake here somewhere, please let me know, as I love to learn, and I am always studying.