Titanic's Prime Mover - An Examination of Propulsion and Power

A Closed Loop System

The purpose of Titanic’s plant was to extract stored energy from coal and convert that energy into useful work used to move the ship, power equipment, heat and light living spaces, and refrigerate perishable food stores. For propelling the ship, the heat energy released from the burning of coal in the ship’s boilers was transferred into steam which was then sent to the ship’s engines where it was converted into mechanical work turning the ship’s propellers. As with other steam vessels of the time, Titanic’s power plant was a closed-loop thermodynamic system that took exhaust steam from the engines and condensed it back into fresh water, reheated it, and then feed it back to the boilers. A schematic of the entire power plant arrangement is shown below.

High pressure saturated steam (red) from the boilers at 215 pounds-per-square-inch gauge pressure (psig) at 394° F is fed to the high-pressure (HP) cylinder on each reciprocating engine. Here the steam is expanded down to 78 psig at 322° F (yellow) and then fed to the intermediate-pressure (IP) cylinder where it is expanded down to 24 psig at 266° F (green). The steam at the output of the IP cylinder is then  fed to a pair of low-pressure (LP) cylinders which further expanded the steam. The exhaust steam from the output of the LP cylinders from both reciprocating engines, now at 9 pounds-per-square-inch absolute (psia) pressure and 188° F (light blue), is then directed to changeover valves where it is led to the input of the Parsons’ reaction turbine.

In the turbine the steam is further expanded down to 1 psia at 102° F (blue) where it is then delivered to a pair of surface condensers where the exhaust steam is condensed back into feedwater at a temperature of about 70° F (very dark blue). The two condensers had a combined cooling surface of 50,550 square-feet, and were designed to work under a vacuum of 28 inches with cooling water at 60° F. Four gunmetal centrifugal pumps (not shown in the schematic) were fitted for circulating sea water through these condensers. Each pump had suction and discharge pipes of 29 inches in diameter, and each pump was driven by a compound steam engine.

On the Titanic and Olympic, the turbine engine was cut in only when the reciprocating engines were running ahead at half speed (50 revolutions per minute) or higher. During maneuvering operations or when going astern, the turbine would be bypassed as steam from the reciprocating engines would be redirected by the changeover valves to exhaust directly into the two main condensers.

A pair of dual-type Weir's air pumps drew off the feedwater from each condenser as well as venting air and non-condensable gases to the atmosphere, exiting with the condenser circulating water discharge. The feed water was discharged from the air pumps through separate feed lines to two 2,790 gallon feed tanks, one placed on each side of the ship just abaft the bulkhead dividing the engine rooms.

From the feed tanks, the water drained into two 48 cubic-foot hotwell tanks, one located on each side of the reciprocating engine room. From these tanks the feedwater was drawn off by two pairs of Weir hotwell pumps, one pair working each tank. From the hotwell pumps, the feed water was forced through two pairs of feedwater filters, which removed grease, lubricating oil and other contaminants. From the feed filters, the water flowed to a Weir "Uniflux" horizontal-surface feedwater heater located on the forward transverse bulkhead on the starboard side of the reciprocating engine room. Here the feedwater, still under the pressure from the hotwell pumps, flowed through the tubes of the heater. Meanwhile, exhaust steam at 5 psia from the four steam engines that ran the ship’s electric dynamos was passed through the shell and around the tubes of this surface heater where it was condensed by the cooler feedwater flowing inside the tubes. This heat exchange process raised the feedwater temperature from about 70° F to 140° F. A Weir's mono-type air pump handled the condensed steam from the dynamo engines that came out of the heater, adding this water to the feed supply.

Still under the pressure from the hotwell pumps, the feedwater leaving the surface heater flowed upward to a Weir's direct contact heater located high up at the level of D deck at the ship’s centerline on the forward bulkhead of the reciprocating engine room. Here the feed water passed through a spring-loaded valve and entered the interior of this heater where it dropped through a conical dispersion plate causing it to fall in droplets through a cloud of exhaust steam that was admitted from the ship's many auxiliary engines that ran various pumps and the refrigeration equipment.⁸ This simultaneously raised the temperature of the feed water from 140° F to 230° F  while condensing the incoming exhaust steam from the auxiliary engines and adding it to the feed supply. The direct contact heater also acted as the main controller for the return feed pumps by way of an internal float control that automatically regulated the steam supply to the feed pumps and the hotwell pumps, thereby causing these to work in unison.

From the direct contact heater, the feedwater flowed down by gravity to four pairs of Weir's main feed pumps, two pairs being located at floor level on both sides of the forward end of the reciprocating engine room. The feed pumps supplied boiler feedwater through a set of feed mains to the various boiler rooms at a pressure greater than the working pressure of the boilers. These pumps were connected to the feed mains through valve chests which allowed any pump to feed any feedwater main. From there, the water was manually admitted to the boilers, the level being carefully maintained to keep the boiler tubes and furnaces submerged while maintaining the correct volume of space above the surface of the water for the production of steam.

This entire process worked continuously as long as the main plant was in operation. There was a much smaller auxiliary condensing plant located on the starboard side of the reciprocating engine room which was used to handle the auxiliaries while the ship was in port.

The ship was also equipped with a silent blow-off from the main steam pipeline for use as a "bleed line" to regulate the rise in steam pressure that would otherwise occur when the plant was put on stand-by and the fires banked. This was to prevent the safety valves from popping off which might otherwise occur. The silent blow-off connection was never used to "dump" a load of steam into the condensers. On the Titanic they led a silent blow-off line from near the starboard side stop valve to the main LP outlet pipe of the starboard reciprocating engine. From there the steam was sent to the main starboard side condenser when the change-over valves were set as they would be with either the turbine or all main engines stopped. By first expanding the high-pressure, high-temperature steam in this massive outlet pipe, potential damage to the connections between the tubes and plates in the condenser that might otherwise occur was avoided. 

Despite being a close loop system, there were always some loss of feedwater supply. Additional fresh water for the boilers was carried in fresh-water tanks in the ship’s double bottom. These were located under the reciprocating and turbine engine rooms and had a total capacity of just over 1000 tons. Distilled fresh water could also be re-supplied from three evaporators located near the aft watertight bulkhead on the starboard side of the turbine engine room. If needed, each evaporator could produce 60 tons of fresh water every 24 hours.