Efficient engine temperature control

01 Jan 2003

Improved automation will this year enhance performance of key system for
controlling seawater cooling pumps.

Central engine cooling systems can be a source of wasted energy. The pumps must be designed to pump high volumes of water when water and air temperatures are high to remove the heat generated in the entire engine room under full load. However, vessels tend to spend very little time in waters with the highest seawater temperature and the engine is not always at full load.
One effective mechanism for dealing with this challenge is Engard system from Alfa Laval. During the first quarter of this year the company will be releasing a new electronic control system, to further automate Engard by using a version of the EPC 50 controllers used on other Alfa Laval separating and fuel conditioning units, so there will be a common operator interface for all systems. Promised are improved fault monitoring and information display, as well as easier operation. Hence it is interesting to look at the development of Engard, a process which relied heavily on help from Swedish ship operator Wallenius Lines.
Alfa Laval says that data developed with the help of Wallenius Lines shows that a typical deep sea vessel spends only about 5% of its operating time in waters with temperatures over 30oC and that 85% of the time is spent in waters of 25oC or lower.
This means that the seawater pumps are pumping far too much water for most of the time, consuming far more power than is really needed. Alfa Laval and Wallenius concluded that considerable savings could be made if the flow of seawater could be adjusted to match the seawater temperature and engine load. The two companies subsequently developed Engard, which is designed to control the seawater pumps to provide the minimum flow to remove the heat generated in the engine room.
Alfa Laval says: "Unlike other systems, Engard does not need special pumps or frequency controlled systems but operates with simple standard pumps equipped with two-speed motors and using standard starters."
When installed with the company?s central cooling plate heat exchangers, Engard can reduce seawater pumping energy costs by as much as 80% when compared with a simple system based on 100% flow pumps only, claims the company. This is because for most of the time a single pump running at 900 rev/min is sufficient and this uses only 15% of the energy required at full load and maximum seawater temperature.
Alfa Laval says: "If we take a typical medium sized vessel with an 18,750kW main engine and two 1,500kW auxiliary engines operating 300 days of the year then this programme shows that when using two 100% flow pumps without control, the energy consumption will be almost 1.2 million kW. The same vessel using Engard and three 50% flow pumps with two speed motors would only consume about 200,000 kW." If onboard energy costs $0.1/kW then the money saving is $100,000 per annum.
The Engard system has the ability to alter pumping capacity based on specific conditions within the system, which Alfa Laval says is unique and calls a "self adaptive parameter value" function. This provides "start and forget" security for the cooling requirements of the engine room.
In all systems designed for operation with Engard, a bypass line and a three-way mixing valve control the amount of low temperature fresh water that passes though the coolers. A temperature transmitter placed in the line after the mixing valve compares the water temperature with the set point (usually 36oC) and adjusts the degree of bypass accordingly. If the water temperature is too high then the three-way valve will close down forcing more water through the coolers. Conversely, if the water temperature is too low then the three-way valve will open reducing the amount of water flowing through the coolers.
The valve itself does not control the system, all it does is trim the temperature of the water in the circuit. However the position of the valve relative to the water temperature is used to generate trigger values indicating that a change in pumping capacity is required.
"Engard is a very reliable system and it saves us a lot of money in the form of reduced energy usage," says Göran Sondefors, senior fleet manager for Wallenius, which has used the system since 1990.

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