I don't understand the pros and cons of wet, dry, saturated, and superheated steam, and why one would want one versus the other. Do you know?"
Yes. Lets leave those terms out of it and talk about superheated water.
Superheated water is water heated above its normal boiling point (212F) but kept as water by applying pressure to keep it from converting to steam. If we keep the water under about 10 PSI of pressure, we can heat it to 240F without it boiling.
So at 240F and 10 PSI, I will have a boiler full of water. There won't be any steam. The reason I want this is because water is very dense compared to steam and thus I can have my boiler hold a lot of energy.
Now, when I open the valve on my boiler, the pressure drops. And when the pressure drops, that superheated water starts to boil. In effect, the liquid water under pressure releases energy as steam. It will go from 240F down to 212F as the pressure goes from 10PSI down to 0 PSI. It will reach equilibrium at 212F and 0 PSI. The energy lost between going from 240F to 212F is the amount of steam energy it will release.
The difference between storing superheated water and generating steam by boiling water is that superheated water stores energy that can be used to heat the mash quickly. When I open the valve on my boiler, all the energy in the water from 240F down to 212F will be released as steam, plus the energy of the element if it is on.
When one boils water in a pot without any backpressure, there is no superheated water and there is no pressure change. Very little energy is stored. The energy you get is that of the heating element and that's it.
Superheated steam is steam heated above its boiling point. Steam will absorb more energy than it does at its boiling point. So we could superheat steam at 0 PSI to 240F. (Normal boiling point is 212F, so we get 28F of superheating. The problem with superheating the steam is that steam is very light compared to water and it would take a very large vessel to store enough steam to absorb the same amount of energy as superheated water. In fact, steam takes 1600x the volume that water does for the same weight. (Steam stores more energy per pound though... but it still takes tons more volume to store energy as steam than as superheated water.)
I like your corny steam vessel idea, but I just wonder if it will be safe enough... and there are a lot of commercially produced items that might be as effective and possibly safer since they were designed to make steam rather than to serve beverages.
A corny keg is a pressure vessel. 240F is way below the temp at which stainless steel or brass or copper or even plain steel starts to weaken. The nice thing about using an electric heating element is that there are no electric or flame burners heating parts of the keg up to 5 or 600F or 1000F or higher, because those sorts of temps can change materials over time and make them subject to failure.
Standard testing procedure for steam pressure vessels is to pressurize them with water to 2 or 3x their working pressure and watch for leaks. Once everything holds that kind of pressure, the vessel is considered sound and rated for the working pressure. Model railroaders test their steam boilers this way.
The relief valve and shutting the element off when the water reaches a maximum safe temp (240F) will ensure the vessel never gets over pressured. The maximum pressure vaporized water can make at 240F is 10 PSI.
Liquid water is another matter ! If the corny was filled entirely to the brim with no air space and then heated to 240F, it could generate enormous pressures because water is incompressible. Luckily we have a pressure relief valve to limit the pressure is these sorts of circumstances. However, with a void space above the water, the liquid water can expand and the vaporized water (steam) will only generate 10PSI of pressure.
There are 2 sorts of things that could go wrong with my steam vessel.
1) leakage or failure at rated pressure, 10PSI. Corny kegs are rated to 130PSI. I'll be pressure testing mine to 30PSI. People carbonate beer at 15 PSI all the time. When was the last time you heard of a corny failing doing this ?
2) failure because of over pressure. My kegs setup will have 3 things to prevent this. 1. A pressure relief valve. 2. A temperature sensor 3. A mechanical pressure gage. Multiple things have to fail and the temperature would really have to rise before my corny would get to an over pressure situation.
I think my steam boiler will be a lot safer than working under an HLT suspended 6 feet in the air.
For example, check out the JR/AR 1.5 to 8KW steamers on the Reimers Inc site. Like I wonder if the little 1.5KW version of this one would do the trick. Of course, unless found used and for a steal, it is likely to be a lot more expensive than your solution.
There is nothing wrong with using a premade steam generator. A pressure cooker heated by a 1.5KW stove element will provide 1.5KW of energy to the mash, less the heat lost from the burner and tubing and steam leakage loses.
My corny will have a 4.5KW element in it. So even if I didn't store any superheated water, I'll be heating my mash with 4.5KW of power, less any losses. That is nothing to sneeze at !
Storing the superheated water is icing on the cake. I'll dough in and do a protein rest while the heating element in my boiler is getting the water up to temp. Then, when its time to do a mash step, I open the valve and release heat at the rate of 10 to 15KW into the mash. I'll be able to raise the temp of my mash very quickly, all without exposing it to temps any higher than 240F ! That is a very gentle heat compared to a RIM system.
I dislike 3 things about using a flame to make steam. 1) It is possible to generate very hot super heated steam. In my system the steam will be at 240F maximum. As soon as it touches the cooler mash bed, its temp will be lower. Its a gentle heat, good for the wort and mash bed. 2) flames and electric burners generate high temperatures which weaken the boiler and tubing materials over time. The 240F water in my system doesn't get hot enough weaken anything. A flame easily does and without proper materials engineering, vessel or tubing failure can occur. 3) the flame chemistry comes into play. Using a flame with excess oxygen to heat metal things can really affect the metal things over time.