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Escaping Steam

Discussion in 'Engine Room Engines & Propulsion Systems' started by Jemma Hyder, Dec 15, 2001.

  1. Ken Marschall

    Ken Marschall Member

    Burning the late night oil here and just happened across this thread. Interesting.

    In my three-plus decades of painting Titanic I have often wondered how the venting steam appeared over the ship. Not far from where I live there are several refineries which vent steam constantly. The colder the air, the more evident the steam is, and the higher it goes, often eventually making its own cloud thousands of feet in the air. On the frigid night Titanic went down, no doubt the steam rose similarly.

    Steam hanging in a cloud or fog around the funnels? No way. That steam is hot. The air is icy. Heat rises. And rises....

    Whether or not the steam eventually dissipated (dried up) depended on the humidity level. What was the humidity at that location on the night of April 14-15?

    Ken
     
  2. >>What was the humidity at that location on the night of April 14-15?<<

    Interesting question. I'm not aware of any such records still extant unless somebody can find the information in a logbook. Nobody on Titanic ever mentioned making such observations that I recall.
     
  3. Ken's description of refinery steam is exactly so. I've verified it here in Ohio at similar temperatures to Titanic that night. The plume does go straight up to some great height, although I have no way to measure it.

    Letting my imagination run wild...I've noticed that a storm on the horizon will often be illuminated like a roadside sign by internal lightning. The bolts will cause an entire cloud to appear distinctly in the night sky. This leads me to wonder...if...Boxhall had launched his rockets earlier and into the steam cloud...would the result have been more noticeable to other ships?

    No answer to that question, of course. Just a curious thought.

    -- David G. Brown
     
  4. I have seen the sketch made by James Hyland that Allan referred to, and it does suggest that steam was blowing off from vents on the first 3 funnels. But Hyland's sketch, however, shows only the vents on the rear of these funnels blowing off steam, nothing from the front ends. But that could easily have been a detail that he overlooked. He also shows a rocket going off, a masthead light at the top of the main mast, as well as a masthead light on the foremast. But we know the Titanic only had the one masthead light, that on the foremast. I believe he drew this sketch on the Carpathia which had two masthead lights, and thus filled in those details on his sketch accordingly. So I am not sure how accurate his sketch really is regarding the blowing off of steam.

    But we have two descriptions, one from Lawrence Beesley, the other from Norman Chambers, that suggest the escaping steam came from one pipe only.

    Lawrence Beesley: "one was the roar and hiss of escaping steam from the boilers, issuing out of a large steam pipe reaching high up one of the funnels..."

    Norman Chambers: "...[steam] coming through one single steam pipe on the starboard side of the forward funnel, made a terrific loud noise; so loud, indeed, that persons on the boat deck could only communicate by getting as close as possible and speaking loudly."

    Regarding the blowing off of steam using silent blowoffs, we know BR 6 was flooding, and according to Beauchamp, they were ordered to draw the fires shortly after the collision. He estimated that job took about 15 minutes after they shut the dampers, but he also said that someone, who I assume was junior 2nd assistant engineer Shepherd, said "that will do" and they all ran up the escape as water was coming up over the stokehold plates (2 feet above the tank top). It is not clear they actually finished the rakedown job completely. But once they left that boiler room they never returned. (Barrett and Shepherd were sent back but noticed the flooding there and return to BR 5.) So maybe they had no way to use any silent blowoff arrangement from this room after it was abandoned. And maybe this is why the safety valves popped venting the steam on the forward funnel.

    By the way, the ship was designed to carry steam at a working pressure of 215 psi at the input to the reciprocating engines, and that we have reports (Cavell) that they may have carried 225 psi in the boilers at the time of the accident. The boilers were tested to withstand 430 psi. I will let others guess as to what the safeties were set to.
     
  5. The Silent Blow off can only be controlled from the engine room usually the starting platform, not from individual boiler rooms!
     
  6. Allan, this assumes of course that the Titanic had such a silent blow off capability in the first. I assume from what you describe, the way they would divert steam to go directly to the condensers would be to take it from the main engine supply lines via bypass valves to lines that went directly to the condensers. I have not seen this described anywhere for these ships. Do you have any information?
     
  7. Noel F. Jones

    Noel F. Jones Active Member

    Notwithstanding the very credible anecdotal evidence coming forward here, I find myself in extreme difficulty with this concept of a bypass line ('silent blow-off') from the boiler range direct to the condensers.

    To subject the condensers to steam at the top of the system thermodynamic gradient when they were designed to handle the reciprocating LP exhaust at the most (as when running astern), seems hard on the hardware if not actually bloody dangerous.

    Having regard to the severe increase in latent heat and pressure, the seawater throughput must be accelerated exponentially to cope. I doubt if there was sufficient pumping capacity, either seawater or wet-air.

    A glance at a representative textbook elicits a potential gradient of the order of 150 to 20 lbs/psi with a concomitant temperature drop from 358 to 142 degrees F. whereas the normal load would be 20 to 3 lbs/psi and 228 to 142 degrees F.

    And no mention of a bypass line!

    Without running the equations I would think that if such a bypass line existed the system would soon back up and relieve itself via the primary escape pipes to the atmosphere; thus rendering any 'silent blow-off' an abject redundancy at best.

    Feel free to educate me otherwise. Any certificated steam chiefs out there?

    Noel
     
  8. Having worked on and sailed on steamships all of which had silent blow offs believe me it works but Chiefs don't like using it as it can damage the condenser tubes. Most vessels built from around 1890 were so equipped.
     
  9. Dave Brown had asked me to calculate the amount of time it would take to blow off the boilers in BRs 5 and 6. I will not attempt to do that since it depends on so many unknowns. But what I have done was to calculate the steam supply rate to the engines from the boilers for running at full speed ahead just prior to the collision.

    Here it is:

    High Pressure (HP) cylinder diameter = 57 inches (HP radius R = 57/2 = 27 inches)

    Stroke L = 75 inches

    Total HP cylinder volume = p R[sup]2[/sup] L = 171,757 cu inches

    Assuming 75% cutoff at full speed,* we get an intake volume V = 0.75 x 171,757 = 128,823 cu inches per stroke on one side of the cylinder.

    Since the engines were double acting we get an input flow rate of 2 x 128,823 = 257,646 cu inches per engine revolution.

    At a rotational rate of 76 rpm at full speed we have an intake rate from the boilers of 76 x 257,646 = 19,581,096 cu inches per minute per engine.

    With two engines, we get a total of 19,581,096 x 2 = 39,162,192 cu inches per minute of steam being supplied by the boilers.

    Since there are 1728 cubic inches per cubic foot, we get a total intake rate of 39,162,800/ 1728 = 22,663 cu ft per minute.

    The specific volume of saturated steam with 215 psig (230 psia) at the HP cylinder input is 2.02 cu ft per lbs.**
    Therefore, in terms of boiler supply, we get 22,664/2.02 = 11,219 lbs/minute, or expressed in tons (2240 lbs/long ton) per minute, we get 11,220/2240 = 5 tons per minute being supplied from the boilers.

    With 24 double acting boilers on line, that is a supply rate of 467 lbs of steam per minute per boiler to the engines.

    * USS Texas ran at almost 80% cutoff at full speed ahead (21 knots)
    ** D.A.Mooney, "Mechanical Engineering Thermodynamics," Prentice-Hall, 1953.

    Cheers,
     
  10. Erik Wood

    Erik Wood Member

    Thanks Sam for the math they indeed represent what I suspected and somewhat what I came up with on my own. If I can I would like to change the direction of conversation regarding the steam dump.

    If it was done automatically without consent from the engineers (as I have seen done before)it is fairly remarkable that it stopped when it did. But the fact that it was released whether by yanking on the chain or automatically the fact remains that it was released. I have seen an emergency steam dump twice in my career. Once was because someone in the engine room noticed or somehow figured out that the gauge was not reading correctly. I was the Officer of the Watch and when the Chief Engineer informed me of the nature of the problem, without consulting the Captain I gave him permission to do what he needed to do. The second was just after a maneuver in which the "old man" decided we needed to stop to figure a couple of things out after traveling at ALL AHEAD FULL. Don't know why it wasn't pushed but it was dumped.

    This means that something occured requiring to happen, which is obviously to much steam. If it dumped on it's own automatically that would mean that some error in the rest of the system may have occured. If it was done manually it would mean that someone of authority decided it was a real bad idea to have all this steam still running in some form in the system.

    I remind all that I am a "throttle jockey" by trade and not a "snipe" so my experience is with using them, not maintaining them or physically operating them so my recollections may be distorted somewhat.
     
  11. I decided to see if could identify the silent blow-off valve and piping in the Olympic engine room plans printed in "Engineering". First, I read what my copy of "Machinery and Pipe Arrangement on Shipboard" had to say regarding the topic of the silent blow-off. This book, published in 1922, was written by C.C. Pounder, a marine engineer at H&W in those days and, later, the head of department there. In all cases illustrated, the silent blow-off Pounder shows is of somewhat surprisingly smaller bore than I anticipated, and is introduced between the main stop valve and the bulk head emergency stop valve, most often right in the main range or at one end of the main steam cross connection right on the engine room bulkhead. Here, shadowed in gray, is what I believe to be the silent blow-off valve on the Olympic and Titanic. Note the long stem leading down to the handwheel just above the release clutch for the watertight door:

    93639.jpg

    Here is the plan view of the same valve:

    93640.jpg

    Normally, the line from this valve would be lead to the main condenser (or, one of the main condensers) which, in normal marine reciprocating engine practice, would have been located right along side the LP cylinder of the engine. In this case, it seems that rather than run a long line aft through and through the after bulkhead, they simply took advantage of a large conduit which was already a direct passage to the condenser -- the eduction pipe from the LP cylinders. This would seem to have a decided advantage over the usual arrangement in that the large size and length of this pipe would have allowed the steam to expand quite a bit before it entered the condenser rather than allowing steam at high pressure to impinge on the tubes and tube plates within the condenser.

    Regards,

    Scott Andrews
     
  12. Hi Scott: That is obviously for the starboard side engine that you show. Is there one on the port side also?

    For those that may not recognize what are in the diagrams, the first one Scott showed was looking forward toward the watertight door between the reciprocating engine room and boiler room No. 1, on the starboard side of centerline. The second diagram is looking down from above, and the forward LP cylinder of the starboard engine is visible on the right.
     
  13. As a check on my steam flow rate calculations above I noticed in the 1911 Shipbuilder issue that the feedwater system was designed to handle 700,000 lbs of feedwater per hour through both heaters. That comes out to 5.2 long tons per minute, which must compensate for the same amount of steam being produced per minute in the boilers.

    Conservation of mass wins again.
     
  14. Hi Sam,

    No, there is no similar connection mirrored on the port side, and this is consistent with what is illustrated and diagrammed in C.C. Pounder's book. This connection certainly looks very small when compared to either the main steam lines or the waste pipes of the safety valves, but then the silent blow-off was only intended to prevent popping off when the dampers were closed and the fires banked. The normal situation where the silent blow-off would have been used followed well-announced changes in speed. Examples of such cases would be the Titanic's stops at Cherbourg and Queenstown, where the process of slowing the combustion and evaporation rates would have begun in response to the bridge's orders for a reduction in revolutions during the ship's approach into the harbor, well before the engines were stopped and the engine room put on stand-by. No silent blow-off connection would be capable of dealing with the oversupply of steam resulting from a sudden stoppage from running at full speed.

    Regards,

    Scott
     
  15. Noel F. Jones

    Noel F. Jones Active Member

    And furthermore, on the matter of the condenser air pumps the Shipbuilder reprint states: "The pumps are capable of performing their duty with a steam pressure of 120 lb per sq.in. but the steam cylinders can withstand the full boiler pressure of 215 lb." (page 61).

    So presumably this extreme was anticipated under some mode of operation.

    However: "No silent blow-off connection would be capable of dealing with the oversupply of steam resulting from a sudden stoppage from running at full speed."

    My misgivings exactly. It's not often I get educated on web sites (says he, with characteristic churlishness') but on this occasion, while still retaining some incredulity, I have to concede that 'silent blowoffs' were indeed installed on marine steam plant.

    ---------------------------------------

    I have printed out Sam Halpern's exposition re boiler output for future general reference.

    "The specific volume of saturated steam with 215 psig (230 psia) at the HP cylinder input is 2.02 cu ft per lbs.**"

    I note the process falls back on tabulated data. Is there any facile formula by which this data can be arrived at?

    Noel
     
  16. Noel: The steam tables in D.A.Mooney, "Mechanical Engineering Thermodynamics," Prentice-Hall, 1953, were taken from another reference: J. H. Keenan, F. G. Keyes, "Thermodynamic Properties of Steam," Wiley, 1936. I have not seen that reference which may explain how these tables were derived. The number I gave was extrapolated from two values for dry saturated steam:

    200 psia -> 2.288 cu ft/lb, and 250 psia -> 1.8438 cu ft/lb.
     
  17. Noel F. Jones

    Noel F. Jones Active Member

    Sam:

    "200 psia -> 2.288 cu ft/lb, and 250 psia -> 1.8438 cu ft/lb."

    Quite. Ripper (Heat Engines, Longmans, 1921) gives 2.26 and 1.83 for the same range.

    The same work tells us that "...it takes ten times the amount of cooling water (assumed 55 degrees) to cool one pound of steam at 212 degrees as it takes to cool the same weight of water at 212 degrees to the same final temperature of 105 degrees."

    Hence my unabated incredulity. I would agree with Scott Andrews that this 'silent blow-off' facility was not primarily intended to divert any sudden excess of pressure from the safety valves (or, concomitantly, to save anyone's hearing!), rather it was intended to perform at some more moderate condition of operation.

    In the case of Olympic/Titanic the modest ducting to only the port side condenser seems to confirm this. Surely, if some extreme were anticipated, both condensers would be brought into play.

    All this fits in with Allan Condie's reference to chief engineers' reservations about risk to condenser tubes.

    Noel
     
  18. A few random questions for the "steam heads" among us...

    If the entire system was designed to operate at +215 pounds of pressure, and if the dampers were closed when the ship stopped, and if all of the auxiliaries were kept operating, and if additional pumps were brought on for dewatering...would there really have been all that much "excess" steam to get rid of?

    Something else, we've debated why the ship steamed for a sort time after the accident. Could it be that Chief Engineer Bell requested this as a way of working off excess steam in the system until the "silent blowoff" could handle the situation?

    Where did the steam go that was in the boilers of boiler room #6? The furnaces there were drawn down immediately following the accident. What would they have done with the steam in view of the fact that there was expectation this compartment would be flooded with cold water which...in 1912...was a concern for explosions. Where did that steam go?

    Emergency overpressure steam valves obviously are set to "pop off" at some safe number of pounds. But, what causes them to close back down? Do they close at a specific number of pounds pressure, or is it random?

    Any thoughts?
     
  19. Hi David,

    "...if the dampers were closed when the ship stopped, and if all of the auxiliaries were kept operating, and if additional pumps were brought on for dewatering...would there really have been all that much "excess" steam to get rid of?

    The short answer is "yes". One only needs to look at the difference in size between the main condensers and the auxiliary condenser, which was intended to deal with the exhaust of all four main generating sets as well as all of the auxiliaries in use while in port. The main condensers had a combined surface area of 50,000 sq. ft. - almost 14 times the 3,600 sq. ft. of the auxiliary condenser. Granted that at sea, there are numerous auxiliaries running that are idle in port - main circulating pumps, fewer feed pumps, forced lubrication pumps for the turbine and shaft bearings, etc. - but even without calculating an approximate for the exhaust steam from these sources, this still leaves a huge gap between what the auxiliaries would consume versus the 6 to 700,000 lbs. per hour that would be consumed while under way.

    Regards,
    Scott Andrews
     
  20. The question is simply how long it takes for a boiler to cease generating steam at full output. When you realise the top of the funnels was around 150 feet from the firebars the draught created to drawn the heat through the furnaces would be considerable. The first job was to shut the dampers and close off some of the fan intakes into the boiler room. If you have a slow burning grate at home and shut the damper it is amazing how quickly the fire stops burning - well imagine this scenario applied to 100+ furnaces on Titanic. But there would be a time delay and thus boiler pressure would go up and the safety valves would pop - only seating when boiler pressure fell down to around 200 psi and it would continue to fall once the fires had been either drawn or air to them cut off. Another factor not documented is a common method of shutting up boilers from venting excess steam is to increase the feed to them. By bringing in the additional feed pumps it would be possible to lower the boiler pressure by increasing the water level - in emergency this can be done by bypassing the feed heaters so that cold feed is introduced.
    It may of course be a fact that due to the flooding of boiler rooms 5 and 6 that access to all valves was not possible and this is why the steam vented to atmosphere for a prolonged period.
     
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