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Fuel Consumption of Steam Vessels Balanced Design for Best Results—Overall Efficiency Real Test—Care in Operation an Important Factor—Rapid Improvement in Recent Years overall engineering efficiency. It is the resultant of a combination of elements which go to make up a complete power plant. Having a composite background fuel consump- tion then is not indicative in detail of the merits or demerits of individual items which make up the whole. Marine steam power plants can be designed to obtain fuel rates as low as 0.55 pounds of oil per shaft horse- power hour for all purposes’ by proper engineering co-ordination. How far it actually pays to design a ship’s power plant for low unit fuel consumption evolves upon a study of the laws of diminishing returns. The deciding factor is one of economics; in other words, one of evaluating fuel savings against increased capi- tal charges. The point of maximum returns dif- fers on various types and classes of vessels. In ships of small power rating many economic measures are not applicable because the unit cost of the equipments do not drop pro- portionately with the power. Eco- nomic evaluations must also take into account the trade route of the vessel, percentage of time underway and in port, and fuel prices at ports of call. Low fuel consumption then should be considered as an_ engineering achievement, rather than as an eco- nomic achievement. The shipowner is interested in maximum returns, which means striking a proper bal- ance of values. Steam Engineering Takes Stock When steam machinery first began its defense against the inroads of the diesel engine it had to begin by making a thorough study of itself. Sleepless nights were spent over “Mollier diagrams’ and ‘‘heat bal- ance calculations.” The Rankine and Carnot cycles began to take on concrete meanings. Investigations were made of auxiliary arrange- ments and feed water heating sys- tems. Elimination of heat losses and the conservation of low head heat be- came the slogans of the application engineering departments. Out of all this was evolved a new technique and a better understanding of funda- mentals. When some of the established en- gineering methods came under the eye of the analyst many of the find- Fieve: consumption is an index of The author, Frank V. Smith, is a member of the staff of the Federal and Marine Department of the General Electric Co. This article was prepared at the request of the editor. By Frank V. Smith ings were startling. Excess auxiliary exhaust steam was being piped di- rectly to the main condensers and extra power was being applied to the circulating pumps to get rid of the excess heat—amounting to some 952 B.t.u.’s per pound of steam. Boiler efficiencies were but from 70 per cent to 75 per cent efficient because of lack of knowledge regarding the theories of combustion. Steam aux- ilaries were found to consume from 30 to 50 per cent of the total steam generated. Available energy and throttling losses were found to be excessive. The first studies were made to eliminate waste by means of properly co-ordinating the engineering appa- ratus abroad the ship. These first studies showed that in many cases savings in fuel of from 5 per cent to 15 per cent could readily be attained with little or no additional capital expenditure. In other words, ships that were burning from 1.1 to 1.2 pound of fuel oil per shaft horse- power hour were thrown together rather than designed. There are a lot of ships today in this class that need a doctor. They need a little superheat here and a little feed heater there. The second phase of the economy engineering program was to devise. means of attaining still higher over- all efficiencies. Several avenues pre- sented themselves, as shown by the following groups: Group I: Raising the greatest pos- sible amount of steam for the amount of fuel burned. (a) Through better boiler design. (b) Through better combustion efficiency. Group II: Getting the greatest amount of useful energy out of the steam so raised. (a) Through in- creased prime mover efficiency. (b) Through more efficient means of pow- er generation for auxiliary purposes. (c) Through more efficient auxili- aries. (d)By reduction of throt- tling and available energy losses to a minimum. - Group III: Heat conservation. (a) through improved methods of heating the feed water. (b) Through salvage of part of the heat in the stack gases. Material progress has been made in group 1. Modern boilers are now de- signed (without air preheaters or economizers) to give efficiencies of from 81.5 per cent to 82.5 per cent, or a gain of from 7.5 per cent to 11.5 per cent over the average values which were normally being attained but a decade ago. Part of this gain has been due to modifications in the MARINE REVieEw—January, 1931 boiler design itself, and part to a better combustion efficiency. In the latter, proper atomization of the fuel oil and proper air regulation have played a prominent part. Boilers, fuel oil burning apparatus, and air regu- lation arrangements, which give less than 81.5 per cent efficiency, are now out of date and belong to a past era of engineering. Permanent progress has been made under group II. The mechanical efficiencies of tur- bines have been increased. Ten years ago marine turbine efficiencies ranged from 65 per cent to 75 per cent whereas today they are normally de- signed for efficiencies ranging from 75 per cent to 80 per cent, depending upon the power rating and steam conditions.. The more economical use of steam has also been accomplished through an increase in the initial pressure and temperature and the improvement in vacuum apparatus. The combined gains due to both the increased tur- bine efficiencies and the improved steam conditions amount from 10 per cent to 20 per cent over what was. considered normal but ten years ago. Looking Into the Auxiliaries The auxiliaries which heretofore were practically all steam. driven were responsible for very large losses, not only because they were large steam consumers themselves, but also because they were responsible for what is known as pyramidal losses. On turbine ships it was practically impossible to secure a. proper heat balance with an all-steam auxiliary layout because the limit of auxiliary exhaust that could be utilized in the feed water heaters was but 12% per cent of the total steam raised. In- creasing turbine’ efficiencies and adopting steam conditions which would further reduce the quantity of steam used by the main power plant, further. aggravated the _ problem. Auxiliary electrification became the answer to this vexing problem. The method of generating electric power for the auxiliaries then be- came a subject for analysis. The pos- sible solutions in the case were as follows: (a) Use of condensing turbine- driven generators. (b) Use of diesel engine-driven generators. (c) On electrically driven ships: 1. Power from the main pro- pelling units by the transform- er method. 2. Power from the main pro- 31