Hi Buddy,
I probably should apologize for the last post, it glosses over various issues but it was late at night and there is just so much Rankine cycle technology that you can cover at one time from a standing start.
(Note to the fanboys, there is NO Schoell Cycle, what they have built is a Rankine cycle engine and even their claimed improvements are all well known and accepted.)
The point is that Harry is claiming that supercritical operation is some kind of universal panacea for all the issues plaguing steam generator design. For subcritical boilers these mostly related to tube burnout, this is typically caused by DNB although the build up of scale on the tube wall is also problematic, it also acts as an insulator and disrupts the ability of the water flow to carry away dangerous amounts of heat. Most burners in power boilers are meant to produce heat sufficient to destroy the boiler; the flowing water and production of steam is meant to prevent temperatures rising to destructive levels.
Supercritical pressure DOES eliminate DNB but, as mentioned, that is not the only source of potential damage. ANYTHING that all raises temperature too high destroys the tube. In fact, we could argue that eliminating steam bubbles is not a clear win, but instead a tradeoff. When water evaporates into steam it has to absorb the Latent Heat of Vaporization. This has two beneficial effects:
1. temperature doesn't rise as water is evaporated into steam (it's 212 on the kitchen stove, turn up the flame and it just boils faster rather than hotter).
2. latent heat is a considerable amount of energy, it takes a lot of heat energy to boil water.
These two effects combine to give us a zone where the temperature does NOT rise in a linear fashion with heat input. We have to avoid putting in so much heat that we don't get DNB but we also have a stretch of tube where the temperature is fixed even if we don't tweak the ratio of fuel to water precisely. Call it a margin of error.
Schoell apparently has a different coil for each of 6 cylinders, essentially 6 boilers working in parallel. These are fed by a pump with 6 cylinders, each supplying the same amount of water to each boiler coil. Presumably this means that by having a single fire they can maintan the same temperature in each coil. Well, it sounded good.... First, I have NEVER seen an utterly uniform fire. If you read the original Lamont patents you realize that he was having problems with the flame bouncing around and heating things unevenly. It appears some of this might be due to the cooling action of the tubes themselves disrupting the state of the gasses in the combustion zone. Secondly, I have never seen two piston pumps that deliver exactly the same amount of fluid. They might be close but there is always some difference either due to construction variances or simply differences in wear. I would also be less-than-amazed to find that each engine cylinder uses a slightly different amount of steam depending on manufacturing tolerances and wear.
Even if these differences are very small, over a period of time they are going to result in different temperatures in each tube. None of the Cyclone patents disclose any control systems of note and their design is far more sensitive than a steam generator with a single pathway, or parallel paths that merge and separate occasionally. Given that they have one fire, the only feasible control methodology would be to vary the feed water rates into each coil separately. Since there is only one fire, however, maintaining identical pressure in each coil is going to be almost impossible....you can accurately control temperature or pressure in a coil with a single input such as feed water, but you need to also control the firing rate to do both. I see no way to adjust a single flame spread across six boilers and regulate each identically.
Well, this could go on for a long time, so might as well cut it short. Buddy put his finger on what some experts (mechanical engineers, even) consider one of the weakest points of the whole Cyclone system.
Regards,
Tom
Harry schoell
Re: Hi presure
April 10, 2003 06:41PM
Andy,
what I am trying to do ,as in my original thread (searching), the higher the pressure the smaller the machine. At SC their is no control problems as you are dealing with a super heated fluid only. Multitubes present no problems. Tube burnout is no problem, no dry spots. I haven't heard a good reason why not . Please enlighiten me. I am designing and building test engines. They are very unusual and are a complete package. Should have been done by now, other enginering projects have taken up my time. Frustrating to look at half finished engines. thank y
