Ship power plants - Brief Overview

All systems and mechanisms of ship power plants (SPP) can for convenience be divided as follows:

main plant used for ship propulsion;
auxiliary plant used for energy supply at moorage and for start-up of the main plant;
electrical used for electric energy supply;
general purpose systems and mechanisms.

Standard SPP transform heat energy into mechanical work or electric energy.

Main SPP consists of the main engine, main gear, shafting and propulsive agent. All these elements as a whole are machine-propulsive complex. Continuous work of the main SPP is provided by feeding systems of fuel, oil for mechanisms oiling, cooling systems, air-gas system, process air supply system.

Main SPP are group by various features:

by type of the main engines of SPP:
- installations with internal combustion engine, in general, diesels ones;
- steam engines;
- gas and steam turbines;
- nuclear power plants (NPP);
- and mixed plants, i.e. comprised of several plants of various types;
by type of propulsion shafts – one, two or multi-shaft (most often are installed at large war ships);
by number of engines: one, two and multi-engine (two-engine are used at large vessels, and multi-engine – at vessels with electrical main gears);
by type of the main gear – with direct, mechanical, electrical, combined and complex gear;
by type of the propulsion device – propellers, hydraulic jets, airscrews, and vane propellers.

There are other classification features.

Auxiliary SPP consists of ship electric power plant (SEPP) and auxiliary boiler plant (ABP) producing low pressure steam. As a SEPP, internal combustion engines, steam or gas turbines can be used.

Ship Diesel Plants

Today, about 90% of the world civil fleet is equipped with diesel SPP (56% in Russia). The first diesel SPP ship was built in Russia, only few years after invention of this engine. Time tells that owing comparatively small dimensions and high productivity, such plants meet all daily wants of the fleet in full.

And it is necessary to make a special emphasis on diesel-electrical power plants (DEPP). Though they are less saving comparing to diesel ones, they are exemplar when frequent change of propeller rotation mode is necessary. These SPP feature in torque moment equal for fore and back run, and at small speed it is bigger comparing to diesel SPP with mechanical gear.

Stirling Engine

Today Stirling engines are being enhanced which are more saving and ecology-friendly comparing to diesel engines. These engines use external heat supply (of every type – starting from heat of end product of fuel combustion and ending with solar energy). Fluids and gases can be used as a working medium. The main limitation of such engine is need to keep up ultra-high pressure as to maintain parameters comparable with characteristics of internal combustion engine, and big square of heat-exchange elements. The power plant of such type is noiseless, provides low vibrations, has long life due to simple construction and works at minimum temperature gradient.

At the moment, the submarine fleet of Sweden is equipped with such engines. The Russian submarine fleet also performs research in this direction.

Gas Turbine

Gas turbine (GT) consists of a compressor, combustor and a turbine itself. GT comprises advantages of the diesel engine and steam turbine. As a diesel, GT does not need boilers to produce steam, as a steam turbine, it has no reciprocal elements. With its small weight, GT produces more energy than diesel PP, has short setting-up procedures and high acceleration.

Its main disadvantage is diseconomy which can be mastered by means of raising temperature of exhaust gases and usage of exhaust heat in electric energy production. For example, effective thermoelectric semiconductor transducer can help with it. Its operating principle is based on generation of electromotive force while samaric sulphide (SmS) semiconductor is being uniformly heated without external temperature gradients. Coefficient of efficiency of the working sample is over 40%, so commercial production is possible.

Steam Turbine

Steam turbine is an engine where the supplied steam heat is converted into kinetic energy used for mechanical work. Today, steam-turbine plants as main SPP are used only at large war ships and high speed and large container ships with main engine over 40 000 hp. As part of complex PP, ST are used at nuclear ships.

Nuclear Power Plants

Ship nuclear power plant (SNPP) consists of a nuclear reactor, steam-generator and steam turbine. Controlled fission reaction aimed at production of enormous amount of heat is led in the reactor. Via the cooling circle, the heat is supplied to the steam-generator; the produced steam is supplied to the turbine where gained kinetic energy is converted into mechanical work. Undoubtedly, SNPP differs in high capacity and possibility of long autonomous work. Its disadvantages are high cost of construction and servicing.

The first civil ship with SNPP (Lenin icebreaker) was built in the USSR. Being the leader in the field of nuclear ship building, Russia continues enhancement of SNPP. Thus, nuclear icebreaker ЛК-60Я which is in construction at the moment will be equipped with new Ritm 200 reactor plant which differs in gravity circulation raised up to 60% requiring application of less power pumps. The capacity factor of this plant is 0.75, safety factor is also elevated. Core refueling is going to be held once per 7 years, while modern icebreakers this period equals to 2.5-3 years.

Development Prospects

Modern nuclear plants with water cooling are futureless comparing to plants with liquid metal cooled reactors. Such scheme was at first used at Sea Wolf submarine of the US navy; as a primary circuit cooler they used a mix of fusible metals potassium and sodium. In our country lead-bismuth alloy is used as a cooler. This scheme can be used with paraffin-like organic materials (diphenyl and triphenyl), but there are problems of corrosion or resinous material formation.

Another problem being solved by Russian engineers is direct conversion of heat energy into electric by means of thermoelectrical (TEG), magnetohydrodynamic (MUDG) or thermoemissive (TEG) generators.

Environmental degradation encourages usage of low-waste, ecology-friendly SPP. At the Far East accumulator or, at least, mixed diesel-accumulator plants are proposed for usage at coastal vessels (i.e. passenger). In addition, accumulators can be charged at night via port power supply networks which will help to solve the problem of energy redistribution.