Engine cooling systems optimization

By Keith Henderson at June 20, 2010 13:17
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One of the many areas of interest as part of the Danish Greenship Project is reducing the energy consumption of the engine cooling systems. For the investigation, a MAN B&W engine in a 35,000 dwt bulk carrier is used to study both sea water and lubrication oil cooling systems. Project studies indicate that there is an unnecessarily high pressure drop and therefore flow resistance in the sea water cooling circuit resulting in wasteful energy consumption. By specifying a larger capacity heat exchanger the flow resistance would decrease permitting the use of smaller pumps with an energy saving that could be as much as 90 per cent and save 160 tons of CO2 per pump per year! Using a different type of oil pump and / or optimizing the flow through the lubricating oil recirculation system, around five per cent of energy can be saved, equivalent to more than 110 tons of CO2 per annum.
One of the many areas of interest as part of the Danish Greenship Project is the cooling system of the engine. It is one of the most energy consuming items and if the systems can be optimized would lead to beneficial savings.
For the investigation, a MAN B&W engine in a 35,000 dwt bulk carrier is used to study the main sea water cooling system and lubrication oil cooling system. These two systems consume the majority of the energy used for cooling.
The study found that it is usual practice for the sea water cooling system to be designed according to preliminary requirements stated in the ship’s building specifications but too early to include important items such as the flow resistance of the heat exchangers, filters and placement of these items.
Project studies indicate that there is an unnecessarily high pressure drop and therefore flow resistance in the sea water cooling circuit resulting in wasteful energy consumption. The conclusion is that by specifying a larger capacity heat exchanger the flow resistance would decrease permitting the use of smaller pumps resulting in an energy saving that could be as much as 90 per cent. This is approximately ten per cent of the total electrical power generated by the ship – a saving of 160 tons of CO2 per pump per year!
The lubricating oil recirculation system pumps oil from the lower tank or sump, passing through a heat exchanger to cool the oil, then via a thermostatic control valve, a back flush filter and into the engine. Using a different type of oil pump and / or optimizing the flow through the system, it is estimated that around five per cent of energy can be saved, equivalent to more than 110 tons of CO2 per annum.

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