Comments by "Keit Hammleter" (@keithammleter3824) on "How to Annoy the Steam Engine Community" video.
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I'm sorry, Mike, but you still have this in quite a mess, and added errors that were not in your engines video.
1. You have omitted the presence and important role of the feedwater heaters. They result in considerable coal saving. I have explained feedwater heating in another post to this video. Refer that post or the Shipbuilder Olympic class Special Edition June 1911 page 63.
2. You have re-stated that the steam pressure into the turbine as 9 Lb/in^2 absolute. I showed in another post to this video that a pressure that low could not be employed - it would result in too low a turbine exhaust temperature and thus cause condensation to water in the later blades of the turbine. This would result in loss of power and rapid turbine blade failure and thus would never have been allowed. Refer that post or the US DoE Steam Turbine Calculator.
3. At 5:51 you said that the "[double bottom] ... stood about 5 feet above the keel." This will mislead many if not most people, as the bottom of the double bottom is in contact with the sea - there is no projecting keel as there is in a sailboat.
4. (Minor error) At 6:23 you said feedwater needs to be topped up from the distilling plant due to evaporation and contamination from grease etc. Evaporation is basically what a boiler does - evaporation loss should not occur as nowhere in the system is water in contact with the atmosphere. The main causes of loss of feedwater are:- a) the need to blow down each boiler and clean the fire tubes periodically, b) leaks via imperfect seals; c) operator error in turning valves etc. The need to shut down each boiler in turn to clean it is why more boilers were provided than necessary for the steam consumption of the various engines and auxiliaries.
Many ships continually drained off a small amount of feed water and dumped it into the sea to prevent contaminant buildup, instead of doing boiler blow-downs as frequently, but I don't specifically know if the Olympic class did this.
5. At 9:15 thereabouts you stated that condensation in the steam pipes meant a need for steam separators. Separators were required anyway, because the steam from a continuous-flow boiler such as the Scotch boiler used in Titanic can only be wet steam, as there has to be liquid water in the boiler. To get dry steam, you would have to heat the water above the boiling point at the working pressure - that would mean no liquid water could be in the boiler to boil. Steam pipes were lagged (insulated) and condensation in the steam pipes should be minimal. This is why superheating has to be done after the boiler and not within it.
6. At 9:16 you stated that superheating heated the steam "high above the condensation temperature". That's true, in steamships generally, but it is a misleading statement. It misses the point. Superheating is not about adding lots of heat, it is about heating a liquid above the CRITICAL POINT TEMPERATURE (for H2O, 374 C or 705 F). This may or may not be well above the boiler temperature. For a boiler pressure at almost the critical point pressure (3200 Lb/in^2 for H2O) the temperature would be raised only slightly.
The critical point of a substance is the the combination of temperature and pressure that determines whther the substance can only exist as a pure gas or not. Raise it above the critical point temperature and it can only be a gas, regardless of how low the pressure is, so long as the pressure is below the critical point pressure. Superheated steam obeys the kinetic gas laws and thereby increases steam engine efficiency. Superheated steam can only be dry steam, as you have realised.
7. In the indicator diagram you showed at 13:24, you shaded the area below 14.7 Lb/in^2 absolute, and it looks like covering 1/3 the graph. You claimed that it means you get 1/3rd the power in the steam by operating below atmospheric pressure. THIS IS NOT SO. That would mean the top of the graph is at 2 atmospheres pressure. It appears from the hard to read numbers that the vertical scale is logarithmic, not linear. So the top of the graph is not 2 atmospheres, it is 10 atmospheres. In any case, Titanic's steam pressure was 14.6 atmospheres.
The turbine was able to contribute 1/3 of the total shaft output power not because there was 1/3 the energy still left in the steam, it was because turbines are about 4 times more thermodynamically efficient that reciprocating engines.
8. You claimed at 13:32 that the turbine "would actually assist the main engines by drawing steam through them. Clearly that is ridiculous. If the reciprocating engine exhaust steam went straight to the high vacuum of the condensers, a greater expansion could be designed for in the reciprocating engines and they would both be more efficient AND produce more power. The turbine is an impedance to the recip engines, not an aid. The recip engines without a turbine could produce not as much efficiency and power as the whole hybrid system, but more than they did in Titanic never the less.
9. At 13:50 you state that the condenser vacuum is created by the cooling of the steam. Clearly that is nonsense. A condenser is in essence a pipe through which the steam goes through, with cold water on the outside on the pipe to carry away the heat. In Titanic, the condensers were a very great number of pipes receiving the steam in parallel, but the principle is the same. Whatever is the pressure at one end of the pipe must be pretty much the same as at the other end. What creates the vacuum is the feedwater pumps drawing the condensed water out. Sure, a volume of steam condenses to a much small volume of water, but that isn't what creates the vacuum. If it wasn't for the pumps, the water wouldn't get sucked out and you would have no vacuum.
10. At 14:34 you stated that James Watt's engine ran purely at a vacuum. This is not so. Only the condenser was operated at a vacuum (about 0.1 atmosphere) by spray cooling. Steam pushed the working piston up. (Later Boulton and Watt used double action). Steam pressure in Watt's engines was about 7 to 10 Lbs/in^2 above atmospheric.
Possibly you were thinking of Newcomen's engine, in which steam at minimal pressure was admitted to the cylinder, than a jet of cold water condensed the steam within the cylinder, allowing atmospheric pressure on the top of the piston to push the piston down.
Newcomen engines were absolutely dreadfully inefficient, partly due to minimal steam pressure and partly because a lot of steam was wasted warming the cylinder up again at every stroke. When I was at university, the technicians had built a Newcomen engine about 1.5 metres high - it had so little power it couldn't overcome it's own friction.
11. At around 16:35 you compare Titanic's coal consumption (600 tones per day) with the roughly similar size Lucitania (1000 tonnes per day), stating that it showed Titanic's power plant was ver efficient. That is not a valid conclusion. Titanic cruised at 21 knots, Lucitania cruised at 24 knots. The power required to overcome drag rises as to the cube of speed, so with all other things equal, we should expect Lucitania to need 600 x (24/21)^3 i.e., 895 tonnes. But all other things might not be equal. It would take a lot of research to get a definitive answer.
12. At 17:23 you stated that Titanic's powerplant was "engineering genius". Hardly. Harland & Wolf tried the hybrid reciprocating/low pressure turbine configuration only once before (in 1909), and never went back to it. No other ship builder tried it. The fact is, a pure turbine installation is FAR more efficient. The reasons why the Olympic class got the hybrid system is that Harland & Wolf had a large skilled and semi-skilled workforce that made reciprocating engines in house and all relevant patents had expired. To use turbines they would have had to purchase them, so using reciprocating engines saved White Star capital expense, and delayed the point at which H&W had to start laying people with obsolete skills off.
Titanic's plant was competently designed but very much a compromise imposed by business constraints. The turbine was not used in an optimal way and could only be used when proceeding ahead at full cruising speed or close to it.
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A turbine input of 9 Lb/in^2 absolute cannot be correct. It is not the absolute bit that’s wrong, it’s the amount. It is likely a reporter’s error in the reference Mike cited. I show why below.
An engineer would get an accurate picture by consulting standard steam tables and a lot of math too complex to show in a YouTube post. However there are some online steam plant calculators based on accurate math that we can use.
The best and easiest to use is the US Department of Energy’s Steam System Modular Tool Steam Turbine Calculator. To use this calculator we need to enter:-
# the steam mass flow rate,
# turbine input steam pressure and temperature, and
# the outlet pressure.
# the turbine thermodynamic (isentropic ie assume no heat or mass loss) efficiency.
The DoE calculator calculates the power output and the temperature of the steam at the turbine outlet.
The DoE calculator also electrical generator efficiency as in input, because these days the main application of steam turbines is power stations. Since we only want shaft power, set this to 100%.
Harland & Wolf never disclosed the mass flow. However www.titanicology.com shows how it can be calculated from the published reciprocating input pressure, HP cylinder volume and RPM – 6200 Lb/min, i.e., 372 kLb/hr. [Note, Titanic’s boiler capacity, 260 Lb/min per boiler, exceeded this by about 17% – due to the need to clean boilers while underway and to feed electricity generators and auxiliaries. So Titanicology’s estimate is reasonable.
A reasonable value for a large low pressure turbine thermodynamic efficiency is 80%.
The outlet pressure is no problem, it is 1 Lb/in^2 absolute i.e., -13.7 PSIG , an entirely typical condenser operating point at that time. We are told by The Shipbuilder special edition that the input pressure is 9 PSIA i.e., -5.7 PSIG but it gave no temperature. This doesn't matter, we can just try progressively higher temperatures until no condensation occurs in the turbine.
Steam condensing within a turbine would cause serious problems – blade erosion, loss of efficiency, vibration due to unsteady flow conditions. It cannot be allowed.
The DoE calculator shows that 385 F just avoids condensation with 9 Lb/in^2 absolute input, producing a shaft output of 14 megawatts i.e., 18,800 HP. It can’t of course be as high as 385 F as that is close to boiler temperature. We need to change another parameter. There is little scope for changing the output pressure, increasing it to 2 Lb/in^2 absolute only drops the required input temperature to 319 F – still way too high.
Let’s try an input of +9 PSIG, with all other values unchanged. This time we get a warning that there must be water in the inlet, for all temperatures up to 238 F. We can’t accept that, as it would hydraulic lock the reciprocating engines and wreck them. So +9 PSIG cannot be right. And 238 F is still too high to allow the reciprocating engines to work at proper reduction.
Trying a turbine input of -2.8 PSIG (11.9 PSIA) in the DoE calculator, with 202 F, we don’t get condensation in the turbine or reciprocating engines. The calculator then gives us 12.0 MW i.e., 16,100 HP. Say 16,000 HP allowing for friction etc.
Conclusion: -
# A turbine input of 9 Lb/in^2 absolute is possible but not in Titanic as it requires a steam temperature almost as high as the boiler output.
# Neither can 9 Lb/in^2 gauge be right, as that would mean heavy condensation in the reciprocating engines, causing rapid catastrophic damage.
# A turbine input of 11.9 Lb/in^2 at 202 F is compatible with Titanic’s plant, does not give condensation in either the turbine or the reciprocating engines, and produces a turbine shaft output of 16,000 HP, which is correct. In practice, we would want a safety margin against condensation, operate the turbine with an input of 204 F.
Perhaps the reporter for The Shipbuilder magazine wrote down 9 when he should have wrote 11.9.
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