Lesson 5 Central Cooling Water System 第 5 课 中央冷却水系统

Design features and working principle 设计特点和工作原理 The central cooling system is an alternative( 替代物, 替代形式 ) to the conventional seawater cooling system,

based on the same design principles with regard to cooler locations, flow control and preheating, but with a central cooler and one additional set of pumps.

Maintenance( 维修保养 ) work is minimized by the use of a central cooler, as this is the only component that is in contact with seawater. All other parts of the system use inhibited( 防腐蚀 ) freshwater in accordance with( 按 照 ) MAN B&W’s specifications ( 说明书 ).

The low and high temperature systems are directly connected to gain the advantage of preheating the main and auxiliary engines during standstill( 停车 ).

As all fresh cooling water is inhibited and common for the central cooling system, only one common expansion tank( 膨胀水 箱 ) is necessary for deaeration ( 除气 ) of both the low and high temperature cooling systems.

This tank accommodates( 调节, 适应 ) the difference in the water volume caused by changes in the temperature.

To prevent the accumulation ( 聚集 ) of air in the cooling water system, a deaerating tank is located below the expansion tank.

An alarm device is inserted( 插入 ) between the deaerating tank and the expansion tank so that the operating crew can be notified if excess air or gas is released, as this signals a malfunction( 故障 ) of engine components.

Operation at sea The seawater cooling pumps pump seawater from the sea chests( 海底 门 ) through the central cooler, and overboard. Alternatively, some shipyards( 船厂 ) use a pumpless scoop( 收集器, 吸入口 ) system.

On the freshwater side, the central cooling water pumps circulate the low-temperature freshwater, in a cooling circuit, directly through the lubricating oil coolers of the main engine, the auxiliary engines and the scavenge air coolers.

The jacket water cooling system for the auxiliary engines is equipped with engine-driven pumps and a by-pass system integrated in the low- temperature system,

Whereas( 而 ) the main engine jacket system has an independent pump circuit with jacket water pumps, circulating the cooling water through the main engine to the freshwater generator( 造水机 ) and the jacket water cooler.

A thermostatically( 恒温地 ) controlled 3-way valve at the jacket cooler outlet mixes cooled and uncooled water to maintain an outlet water temperature of ℃ from the engine (Fig. 5-1 ).

Operation in port During operation in port, when the main engine is stopped, but one or more auxiliary engines are running, valves A are closed and valves B are open.

A small central water pump will circulate the necessary flow of water for the air cooler, the lubricating oil cooler, and the jacket water cooler of the auxiliary engines.

The auxiliary engine-driven pumps and the above-mentioned integrated loop ensure a satisfactory jacket cooling water temperature at the auxiliary engine outlet.

The main engine and the stopped auxiliary engines are preheated by the operating auxiliary engine(s).