Marine environment protection
The problem of marine environment protection is one of the most important today. At least 6 million tons of oil and oil products are discharged into the oceans annually.
35% of the oil pollution is generated by ships. The remaining 65% is caused by natural seepage, atmospheric fallout, off-shore production, coastal facilities and land run-off.
Pollution is a serious threat to the life of people and other living creatures including vegetation.
That's why the International Convention for the Prevention of Pollution from ships is considered to be a very important document. Special organizations in almost all countries to control the effective execution of the rules. The duty of the staff of these organizations is to investigate the cause of pollution and inspect the equipment aboard vessels. Only 3% of oil discharged into the oceans annually is caused by accidents. Most of the marine pollution from ships is the result of routine operating practices: cleaning cargo tanks, discharging sea-water ballast, engine-room bilges and so on. For tankers, the use of crude oil washing during unloading and the proper use of on-board equipment greatly reduce the pollution from the engine-rooms, ballasted fuel tanks, ballasted cargo-tanks and the like. Ship's equipment for the prevention of marine pollution may include an oil filtering system, tanks for oil residues, slop tanks, an oil discharge monitoring and control system, an oil-water separator, a bilge water separator, a sewage treatment plant, an incinerator. Special equipment prevents any discharge of oily water into the sea.
Steam turbines
The turbine is a heat engine consisting of a rotor carrying moving blades, a casing in which the rotor revolves,
and stationary nozzles through which the steam is expanded or directed. Glands, bearings, throttle valve, governor and other devices are necessary for operation of the unit. In the steam turbine, two steps are required to convert the potential energy of the steam into useful work. First step, the pressure energy is converted into kinetic energy as the steam expands through the nozzles and the pressure drops. Second step, the kinetic energy of the jet is converted into useful work.
There are two types of turbines: impulse and reaction turbines. In impulse turbine the steam expands only through stationary nozzles with a decrease in pressure and an increase in velocity. In this process the potentional energy of the steam is converted into kinetic energy. In reaction turbines the steam drop in pressure and at the same time expands as it passes across both the moving blades and stationary blades.
There may be high, intermediate and low pressure turbines. There may be single-cylinder turbines and compound. Compound turbines are tandem-compound and cross-compound.
As to the direction of steam flow the turbines are axial-flow and radial-flow. There may be condensing and non-condensing.