Saturday, November 27, 2010

What are Pumps?

A pump is a device used to move fluids, such as liquids, gases or slurries.

A pump displaces a volume by physical or mechanical action. Pumps fall into five major groups: direct lift, displacement, velocity, buoyancy and gravity pumps.Their names describe the method for moving a fluid. Pumps which are commonly seen in the engine room are Centrifugal pumps, Gear Pumps, Reciprocating Pumps, Eductors.

Centrifugal pump

A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the pressure and flow rate of a fluid. Centrifugal pumps are the most common type of pump used to move liquids through a piping system. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward or axially into a diffuser or volute chamber, from where it exits into the downstream piping system. Centrifugal pumps are typically used for large discharge through smaller heads. These type of pumps are used are used in the marine industry for Ballasting, Fire pumps, General Service Pumps, Sea water Service pumps, Sea Water cooling pumps, Distallate pumps, Fresh Water Jacket Cooling Pumps and etc usually it is use with tranferring water only and not oil.

Gear pump

This uses two meshed gears rotating in a closely fitted casing. Fluid is pumped around the outer periphery by being trapped in the tooth spaces. It does not travel back on the meshed part, since the teeth mesh closely in the centre. it is also used in various hydraulic power packs.Since this is a very strong pumps which can withstand high pressures and can carry heavy liquids it is mainly used to transfer oils onboard ships. Such as Fuel Oil Transfer Pumps, Fuel Oil Supply Pumps, Pumps for feeding the FO Purifier, Pumps for circulating lube oil and etc.

Reciprocating-type pumps
Reciprocating pumps are those which cause the fluid to move using one or more oscillating pistons, plungers or membranes (diaphragms).
Reciprocating-type pumps require a system of suction and discharge valves to ensure that the fluid moves in a positive direction. Pumps in this category range from having "simplex" one cylinder, to in some cases "quad" four cylinders or more. Most reciprocating-type pumps are "duplex" (two) or "triplex" (three) cylinder. Reciprocating pumps are now typically used for pumping highly viscous fluids including concrete and heavy oils, and special applications demanding low flow rates against high resistance like pumping Bilge using a Bilge Separating Oil Tank to the sea. It requires the liquid to flow slowly so that it can be check by a PPM alarm if it still has unacceptable quantity of oil in it thus returning it back to the bilge tank for further filtration.

Eductor-jet pump

This uses a jet, often of steam, to create a low pressure. This low pressure sucks in fluid and propels it into a higher pressure region. Mainly used for stripping water in Ballast tanks. This is because if you use other pumps to strip the ballast tanks, the pumps might be air-bound when ballast tank is already empty thus the packing gets burned due to no water cooling. Making Eductors the practical way to Strip Water from Tanks.

Friday, November 26, 2010

What is a Marine Boiler?

A boiler is defined as "a closed vessel in which water or other liquid is heated, steam or vapor is generated, steam is superheated, or any combination thereof, under pressure or vacuum, for use external to itself, by the direct application of energy from the combustion of fuels, from electricity or nuclear energy."

Also included are fired units for heating or vaporizing liquids other than water where these units are separate from processing systems and are complete within themselves. This definition includes water heaters that exceed 200,000 Btu/hr heat input, 200 degrees Fahrenheit at the outlet, or 120 gallons nominal water containing capacity.

Boilers are one of the essensial equipments onboard ships. It's purpose is to provide heating to the the main deisel propulsion engine, to the bunker F.O. tanks(to make it less viscous for transfer purposes as well as easy ignition). The steam generated by the boiler can also be use for cleaning, and heating of the seawater in the freshwater generator thus evaporating it to make it potable water.

There are two types of boiler mainly use in the Marine Industry, The water-tube boilers and the fire-tube boilers. The most common of which is the water-tube. In the water-tube type, water passes though lines of tube where it is heated by the used of a burner and a furnace.

What is a Marine Fresh Water Generator?

"Water, water everywhere, and nary a drop to drink." Old cargo ships from years back were required to carry large supplies of fresh water to sustain the crew on a long voyage. A ship that had run out of drinking water would be carrying a sad crew indeed. Today, most commercial ships are equipped with a freshwater generator, a type of evaporator that converts sea water into drinkable, fresh water.

The concept of a freshwater generator is simple; sea water is evaporated using a heat source,either by stream from the boiler, main engine jacket cooling water, or by electric coil separating pure water from salt, sediment and other elements. When the ship is underway, the heat from the cooling water of the engine is used. To minimize fuel consumption and maximize the heat generated by the main propulsion engine.
There are two main elements in a freshwater generator, one heat exchanger evaporates the sea water, and another condenses the fresh water vapor into drinking water. In the condenser element, the vapor is condensed through cooling, often simply using cold seawater to cool the outside of the unit.

The freshwater generator should include a feature to monitor the salinity of the processed water. If the salinity exceeds a specified level, usually between one and ten parts per million (ppm), the freshwater generator will automatically return the water to the feed line and put it through the cycle again.

What is Marine Engineering?

From Wikipedia, the free encyclopedia

Marine engineering involves the design, construction, installation, operation and support of the systems and equipment which propel and control marine vehicles, and of the systems which make a vehicle or structure habitable for crew, passengers and cargo.

Marine engineering is allied to mechanical engineering, although the old marine engineer requires knowledge (and hands-on experience) with electrical, electronic, pneumatic, hydraulic, chemistry, control engineering, naval architecture or ship design, process engineering, steam generation, gas turbines and even nuclear technology on certain military vessels.

Marine engineering on board a ship refers to the operation and maintenance of the propulsion and other systems such as:electrical power generation plant; lighting; fuel oil; lubrication; water distillation and separation; air conditioning; refrigeration; and water systems on board the vessel. This work is carried out by Marine Engineering Officers, who usually train via cadet ships sponsored by a variety of maritime organizations. There are also training centers at post-secondary institutions that offer marine engineering programs, such as Autonomous Underwater Vehicle research; marine renewable energy research; and careers related to the offshore oil and gas extraction and cable laying industries.

History of marine engineering

One of the most notable figures in marine engineering in antiquity was Archimedes, who experimented with buoyancy, developed the water screw, and pre-industrial naval weapon systems. Pioneers in marine engineering in Britain include William Froude and Isambard Kingdom Brunel, who illustrated the effectiveness of the screw propeller, amongst other notable achievements. The oldest surviving marine engine was designed by William Symington in 1788. The ship 'Turbinia' first demonstrated the superiority of the steam-turbine engine, which is still used for marine propulsion today in some niche applications. In America, the University of Michigan's Department of Naval Architecture and Marine Engineering can be tracked to an 1879 act of Congress, which authorized the U.S. Navy to assign a few officers to engineering training establishments around the country. Mortimer E. Cooley was the first lecturer in the department.[2]

Marine engines

Marine engineering emerged as a discipline with the arrival of marine engines for propulsion, largely during the latter half of the 19th century. Early marine engineers were known as "stokers" as they 'stoked' the coal fires of steam engined ships more or less from the middle of the 19th to the middle of the 20th centuries; the term is still used affectionately by modern ship's engineering staff to describe their role.