Chaff Launch

Sunday, March 29, 2009

Sunday Ship History: Ship Propulsion - Steam Turbines

A few weeks ago, Sunday Ship History took a look at early steam powered ships that used the walking beam engine. Now it's time to look into the basic steam cycle as it developed in ships using high pressure and low pressure steam turbines.

Mostly, this is about steam turbine. As set out here, steam turbines are a logical progression from the waterwheels that have long been used by mankind:

The waterwheel is an ancient device that uses flowing or falling water to create power by means of a set of paddles mounted around a wheel. The force of the water moved the paddles, and the consequent rotation of the wheel is transmitted to machinery via the shaft of the wheel.
Improvements to the waterwheel included refinement of the paddles into curved blades, apparently an Arab innovation:
A primitive water turbine, which had water wheels with curved blades onto which water flow was directed axially, for use in a watermill, was first described in an Arabic text written in the 9th century, during the Arab Agricultural Revolution.
Modern hydroelectric dams use variations on this ancient concept to produce electricity by using the water stored by the dams to flow through water turbines, which are connected to generators (see here). See also here.

The steam turbine is a logical follow on to water turbine technology, though it has a long history:
The first turbine of which there is any record was made by Hero of Alexandria, 2,000 years ago, and it is probably obvious to most persons that some power can be obtained from a jet of steam either by the reaction of the jet itself, like a rocket or by its impact on some kind of paddle wheel
While there were early versions of steam turbines, it was in the 1880's that the modern steam turbines were developed by, among others, Sir Charles Parsons:
. . . Dr de Laval of Stockholm undertook the problem with a considerable measure of success. He caused the steam to issue from a trumpet-shaped jet, so that the energy of expansion might be utilized in giving velocity to the steam. Recent experiments have shown that in such jets about 80 per cent of the whole of the available energy in the steam is converted into kinetic energy of velocity in a straight line, the velocity attained into a vacuum being about 4,000 feet per second. Dr de Laval caused the steam to impinge on a paddle wheel made of the strongest steel, which revolved at the highest speed consistent with safety, or about half the velocity of the modern rifle bullet, for the centrifugal forces are enormous. Unfortunately, materials are not strong enough for the purpose, and the permissible speed of the wheel can only reach about two-thirds of that necessary for good economy, as I shall presently explain. Dr de Laval also introduced spiral helical gearing for reducing the enormous speed of rotation of his wheel (which needed to be kept of small diameter because of skin fraction losses) to the ordinary speeds of things to be driven, and I shall allude to this gear later as a mechanism likely to play a very important part generally in future turbine developments.

In 1884 or four years previously, I dealt with the turbine problem in a different way. It seemed to me that moderate surface velocities and speeds of rotation were essential if the turbine motor was to receive general acceptance as a prime mover. I therefore decided to split up the fall in pressure of the steam into small fractional expansions over a large number of turbines in series, so that the velocity of the steam nowhere should be great. Consequently, as we shall see later, a moderate speed of turbine suffices for the highest economy. This principle of compounding turbines in series is now universally used in all except very small engines, where economy in steam is of secondary importance. The arrangement of small falls in pressure at each turbine also appeared to me to be surer to give a high efficiency, because the steam flowed practically in a non-expansive manner through each individual turbine, and consequently in an analogous way to water in hydraulic turbines whose high efficiency at that date had been proved by accurate tests.
Photo caption:
Until the invention of the steam turbine by Charles Parsons (1854-1931) in 1884, steam engines could not turn fast enough to produce electricity efficiently on a large scale. Used at the Cambridge Electric Light Station, this radial flow turbine-generator was the first to prove that turbines could be run as economically as the best steam engines. It used the energy of high-pressure steam at 200 degrees centigrade to run the turbine. Turning at 4,800 revolutions per minute, it had a power output of 100 kilowatts a second and operated for 30 years. Steam turbines still drive most generators today.(photo credit Science Museum/Science & Society Picture Library)
In addition to being used for the generation of electricity, steam turbines began to be used for ship propulsion:
As Parsons saw it, his invention of the steam turbine had direct application to marine propulsion and electrical generation. Both of these require high efficiency and have steady loads. Marine propulsion had the added benefit of requiring smooth operation and a high power density engine.
***
By 1892 the power of his turbines had increased from the very first prototype of 4 kW in 1885 to a respectable 100kW. But there were still no buyers and no market. By now his engines were powerful enough to power small boats. He decided to build a boat that would demonstrate the potential of his machine. In 1894 Parsons took out patent No. 394 for 'Propelling a vessel by means of a steam turbine, which turbine actuates the propeller or paddle shaft directly or through gearing'. The steam turbine blasted jets of high-pressure steam against blades inside a wheel, producing a continuous rotational motion instead of the push-pull action of previous steam engines.
***
In pursuance of this objective, after experiments with model boats, the company constructed Turbinia. Built of steel, She was 100ft long, 9ft broad and with a draught of 3ft had a displacement of 44.5 tons. She was fitted with a double-ended water tube boiler working at 210 psi. The first set of machinery consisted of a single radial flow turbine driving a single shaft, which at 2400 rpm developed 960 horse-power. The speed of the boat proved to be much less than hoped for. The highest speed recorded was less than 20 knots. The complication was due to the high rotational speeds of the propellers which caused the phenomenon of cavitation to occur. Like the Wright brothers developing the aeroplane a few years later, the turbine design was pushing many technological limitations simultaneously. Parsons had to remedy this problem also. Cavitation was a phenomenon recognised and named by William Froude. The propellers were spinning at 18,000 rpm, so fast that the water pressure decreased, forming bubbles, a cavity. The power was going into making bubbles instead of pushing the boat.

The remedy was to operate at lower rpm with more turbines and propellers. The radial flow turbine was replaced by 3 parallel flow turbines, one high, one intermediate and one low pressure, to reuse the same steam in succession, each driving a separate shaft having 3 triple bladed screws, there being 9 propellers in all. With steam at 157 psi the speed of the central shaft was 2000 rpm and 2230 on the wing shafts. On trial with this new configuration a speed of 34.5 knots was obtained, or about 4 knots more than the fastest destroyers afloat. The results were spectacular, but still nobody was listening.
***

The Royal Navy authorities immediately realised the great advantages of steam turbines and after negotiations an order was obtained from the admiralty for a turbine driven destroyer in 1898 - HMS Viper. Parsons's investment of 24,000 pounds to get to this point had paid off. On a massive scale, turbines were adopted for Navy ships and the large ocean liners. By 1904, 26 ships had been engineer by parsons direct drive turbines. Famous ships like the Mauretania, Titanic and H.M.S. Dreadnought were all powered by Parsons turbines. Electric power generation on land also almost exclusively adopted steam driven turbine generators. In 1909 it was shown that geared turbines, that is reducing the high turbine speed to a more usable shaft speed by means of gears, gave a significant saving in coal consumption of about 15%. In 1912 Parsons wrote to Lord Fisher stating 'I have come to the conclusion that gearing between engines and screw shafting will be essential.' As a result the destroyers HMSs Badger and Beaver with partial gearing (1911) and HMSs Leonidas and Lucifer with fully single reduction gearing (1913) were produced.
Information on HMS Viper here - this "torpedo boat destroyer" was capable of speeds in excess of 34 knots, though suffering from excessive low speed fuel consumption. Turbine powered ships could go faster because they were not constrained by thephysical limitations of the steam pistons in reciprocating steam engines ships.

The first major U.S. Navy ships with steam turbine propulsion were Florida-class battleships. In an odd footnote to history, USS Texas (BB-35) and USS New York (BB-34)though built after the completion of three U.S. turbine powered battleships were built with reciprocating steam engines as the result of a dispute with turbine manufacturers.

In 1917, midshipmen at the Naval Academy were provided with this book largely about steam turbines.

It is safe to say that from the early 1900's through WWII, the marine steam turbine propulsion dominated fleet applications. Even later nuclear powered ships use their power plants to generate steam for steam turbines. However, in more recent days the steam turbines have been giving way to gas turbines (jet engines) and diesel power plant or some combination thereof.

With the retirement of USS Kitty Hawk, steam powered ships may have seen their final days in the U.S. fleet, replace by more efficient power plants:
As the USS Kitty Hawk sails its final course, it marks the close of an era for steam power in the U.S. Navy.

The aircraft carrier, which is scheduled for decommissioning in 2009, relies on its 1,200-pound-per-square-inch steam boilers to launch aircraft, propel the ship and provide hot water for showers and washing dishes, the Navy said in a news release.

The boiler system was first introduced in 1948 on experimental Mitscher-class destroyers. Although it was temperamental and complicated, it replaced the less powerful 600-psi boilers of the day, according to the Navy.

Sixty years later, the Kitty Hawk and its steam technology soon will be replaced by the nuclear-powered USS George Washington.

The old carrier’s boiler technicians might be the last sailors to operate the conventional — and challenging — steam power system, the Navy said.

"This is the last time you’re going to see eight conventional boilers for a steam plant," Master Chief Petty Officer Michael Gwinn of the Kitty Hawk engineering department was quoted as saying in the release.
While the steam era lasted, however, tens of thousands of young men and women were trained in the operation of modern marine boilers and in the application of the steam from those boiler to the steam turbines that propelled thousands of Navy ships. Part of the training was material like this:
The function of a boiler in the steam cycle is to convert water into steam. Reliability in operating naval boilers and associated equipment is important for the power plant to operate at maximum efficiency.
And there was a time when all surface officers had to memorize the basic steam cycle (see also here to understand what was happening down in the vital heart of the ship (click to enlarge).

But the basic function of the boilers on any steam powered ship was to generate steam for use in the engine - whether that engine was reciprocating or turbine.

And in the boiler spaces and the engine rooms (the U.S. Navy generally kept the spaces with the turbines separated from the boiler spaces), the work was hot, dirty, noisy and, to top it off, dangerous. But without the dedication of the Boiler Technicians and the Machinists Mates there would be no high speed torpedo runs or racing to engage the enemy or to launch aircraft or sprinting for recovery of downed pilots.

The world of the "snipe" on a steam ships was almost like working in an underground mine - with no windows on the world and all to often the only words from the command level were complaints. Boiler Technicians (BT's) and Machinist Mates (MM's) loved the bridge watch officers who could and would brief them about what was anticipated up above and when to expect the need for more steam and more burners to be cut in. This is one of the many reasons it was vital for the bridge officers to understand the basic steam cycle and the flow of steam to the turbines.

They are a dying breed, so render up a salute to the old steam snipes!

Notes: Turbina photo source.

Turbina drawing source.

3 comments:

  1. Anonymous6:03 PM

    As a old BT myself, after reading the last two paragraphs brought a tear filled with pride to my eyes. Yes the job was not forgiving, always hot and noisey. But I wouldn't trade a single day for anything. Very nice article.

    ReplyDelete
  2. Prasanth3:32 AM

    I echo your views. Nothing ever compares to Good old steam

    ReplyDelete
  3. Anonymous8:48 PM

    Steam is not gone from carriers although the time of the conventional boiler system has past.
    Todays nuclear carrier fleet uses steam produced from nuclear reactors.
    Modern nuclear carriers have two nuclear reactors.
    The ships still use engine rooms with turbines and reduction gears just like the old boiler steam systems.
    So the only thing that changed is the way the steam is produced.
    Nuclear power is awesome.

    ReplyDelete