Marine Link
Monday, July 16, 2018

Locomotive Superheather Company


HIGHLY SUPERHEATED STEAM The Greatest Single Means of Reducing Fuel Consumption


IN undertaking the construction of a merchant marine, the United States has placed itself in competition with the rest of the world in ocean transportation.

In some respects American ships are the equal and possibly the superior of similar foreign vessels. They are handicapped, however, by the effect on operating costs of higher wages to be paid the crews, as well as other conditions which affect these costs adversely. One of the major operating costs is that of fuel, and while in many respects the boiler and engine equipment of American ships is of the best, little has been done in the adoption of practices which reduce the amount of fuel required for power production. Probably the most effective means of accomplishing this is to use superheaters and highly superheated steam.

Superheated steam is steam which has been heated after it is removed from contact with the water from which it is being generated. While it is in contact with the water it is known as saturated steam, and superheating it increases its volume and prevents condensation in the engine cylinders. With superheat of 200 to 250 degrees, the resulting fuel economy ranges from 12 to 20 per cent, a most important saving in operating costs,

particularly under present-day fuel costs.

The importance of such an economy will be borne home when it is considered that Great Brit-ain, France, Germany, Holland, Japan, and in fact almost all nations which have an extensive merchant marine are operating superheater ships in large numbers and are turning them out from their yards as rapidly as possible. The United States, in spite of this fact and the additional evidence of the value of superheat arising from its almost universal use in locomotive and modern stationary engineering practice, has done little in the use of superheaters in its merchant vessels. This statement does not overlook the American vessels which are fitted with so-called low-degree superheaters, as these were tried out years ago by European vessel owners and have proved, wherever tried, to be of little value.

It will thus be readily seen that in order to effectively compete with the many foreign ships, which now have the advantage of this great econ-omy, highly superheated steam must be adopted for American vessels. The very considerable increase in the steaming radius 011 a given bunker capacity of a high superheat ship over a corresponding vessel with no superheat, or with low superheat, means a marked reduction in operating cost, and in building new vessels an added advantage is that smaller boilers are ample to produce the specified power.

The most satisfactory method and that in general use of producing highly superheated steam is to pass the steam through tubes of relatively small diameter which are placed in the path of the gases of combustion. When employed in connection with the Scotch marine boiler, which is used most extensively because of its good steaming qualities, freedom from trouble and the ease with which it may be repaired when necessary, the superheater equipment consists of one or more pairs of steam headers or collectors, connected by several units or elements clamped to the header. The apparatus is located in the uptake and in a portion of the boiler tubes. Steam passing from the boiler to the engine or turbine flows through the superheater and thus is brought into close contact with the gases of combustion. A portion of the heat of these gases is transferred to the steam, with the result that the steam becomes superheated.

Headers are located at the front of the boiler and usually are placed in a vertical position opposite the blank spaces between the groups of tubes or at the sides of the boiler. They are supported from the boiler head by brackets and at the top are provided with flanges for the connection of the saturated steam pipe leading from the boiler and the superheated steam pipe leading to the engine. The units that convey the steam from the saturated to the superheated headers are arranged with from two to seven loops, which are located in the boiler tubes. The tubing used in the fabrication of the units is cold-drawn seamless steel, and each loop is composed of two pieces of tubing which are bonded at the rear (combustion chamber) end by return bends forged integrally with the tubing. These loops are supported on the centre line of the boiler tubes, which permits the gases of combustion to touch all of the exterior surface and at the same time presents the least obstruction to the passage of soot and cinders. Units are attached to the headers by means of clamps and studs. Each clamp accommodates two unit ends and is attached to the header by means of a single stud and nut located at the centre of the clamp. Gaskets are used between the unit ends and the headers. These are fabricated from materials developed especially for this pur-pose and capable of resisting high steam tempera-tures. The unit seats on face of the headers are recessed in order to provide a secure connection between units and headers and also to prevent the uptake gases from coming into contact with the gaskets.

By the use of highly superheated steam, fuel economies of from 12 to 20 per cent may be ob-tained, when compared with saturated steam per-formance, and at the same time an equal amount of work may be done. In addition to the fuel economies obtained, at all times, when new vessels are designed boilers may be made of smaller size and the capacity of fuel bunkers (either coal or oil) may be reduced. The incorporation of these features provides a greater capacity for revenue cargo, which alone is an item of sufficient impor-tance to add considerably to a vessel's earnings.

In general, the higher the degree of superheat the greater will be the economy and the greater the net return on the investment. The use of highly superheated steam offers a means of permanently reducing the operating charges and of increasing the cargo-carrying capacity, steaming radius and speed of a vessel by improving the mechanical and thermal efficiency of the machinery, thus in a measure offsetting the excessive cost of all other items irrespective of their source, and, therefore, increasing the net earnings of the vessel. The use of highly superheated steam in marine service is not new, and has been adopted as a standard by practically all of the leading steamship companies of foreign countries. If the shipping of the United States is to expand full advantage must be taken of the best and most efficient methods, among which highly superheated steam occupies a prominent position.

The superheater equipment described above is manufactured by the Locomotive Superheater Company, 30 Church Street, New York, designers and builders of superheaters for all classes of service.

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