2 replies to this topic

I have a low-pressure boiler, essentially a stovetop autoclave to which I have attached a threaded nozzle. Attached to the nozzle is a stainless steel pipe that connects to a three-way splitter. Each branch has an inline ball valve and terminates at the bottom of a tank containing a water solution. The idea is simple, use the steam to separately maintain or increase the temperature of the each water solution. The problem is that due to the low quality of the steam, I get water hammer in the pipe and the water solutions cannot be brought to a boil. My solution is to superheat the steam by sending the pipe thru the gas fire heating the boiler (perhaps in a coil) before it goes on to my water tanks.

My concerns are:
The superheated steam will expand back into the autoclave where it will superheat the steam in the vessel which will cause more water to vaporize and become superheated until I get spill over or a rupture.
I cannot close all three valves without creating a high pressure system leading to a rupture.

My thoughts are:
Place a steam injector between the autoclave and the superheating site so that steam can be injected into the hot pipe without it expanding back into the autoclave. (where do I get one of those?)
Place a pressure relief valve on the main pipe before the branching.

Comments? Criticisms? Alternatives?

jw

[DRS]

For heat transfer applications, steam at saturated conditions is the best solution. Note that the specific heat of superheated steam (at 1 bar a) is just half that of water. I don't see any need to superheat the steam for water heating application. I would either go for a new and efficient boiler or take a direct(fired or electric) water heater.

For heat transfer applications, steam at saturated conditions is the best solution. Note that the specific heat of superheated steam (at 1 bar a) is just half that of water. I don't see any need to superheat the steam for water heating application. I would either go for a new and efficient boiler or take a direct(fired or electric) water heater.

I think that the specific enthalpy has more bearing on the heat transfer than specific heat. One (1) kilogram of superheated steam at one (1) atmosphere and 150C has a total heat of 419kJ sensible, 2257kJ latent and 105kJ superheat.

The purpose of the superheat is twofold:
It prevents the steam from condensing back to water before it reaches its destination. This is done in most steam boilers. See the fire tube and water tube boiler diagrams at wikipedia.

The dry steam carries more heat and thus has more heat to give up. As the steam moves through the (liquid) water, it will lose heat and the water will gain heat. Saturated steam is 2% liquid water suspended mechanically and contains much less energy than dry steam.