The independent type Ⅰ central cooling water system consists of three separate circuits, namely the seawater circuit, the high-temperature freshwater circuit, and the low-temperature freshwater circuit.
⑴ seawater circuit
The seawater circuit is quite simple. Two seawater pumps inhaled seawater from the seawater mains sending into the central cooler. Cool low-temperature freshwater directly discharged to the outboard.
⑵ high-temperature freshwater circuit
A high-temperature freshwater circuit (the host cylinder water cooling system) is a closed-loop system. Two high-temperature freshwater pumps will send high-temperature freshwater into the host of the cylinder, piston and injector cooling, and then discharged from the highest point of the main engine, after the three-way thermostat valve, high-temperature freshwater cooler or bypass pipe, and gas cabinet back to the high-temperature freshwater pump suction port.
In the host freshwater discharge pipeline, installed parallel a water machine or a light system, using high-temperature freshwater waste heat to make freshwater, as added fresh water on board to use. It is an energy-saving device.
Installed in the high-temperature freshwater cooler inlet and outlet bypass line The three-way thermostat valve is used to control the host freshwater outlet temperature. The general requirements of the host freshwater outlet temperature are controlled at 80 ℃ or so. The adjustment of the freshwater temperature of the main machine can be achieved in three different ways. ① adjust the amount of freshwater entering the cooler. ② adjust the amount of fresh water in the main engine. ③ adjust the amount of low-temperature freshwater or seawater entering the high-temperature freshwater cooler. Although these three methods can adjust the freshwater temperature, the latter two methods will cause the host into and out of the water temperature to be too large or too slow, which are rarely used in the ship. Moreover, a three-way thermostat valve can be installed in the more excellent inlet pipe and located in the outlet pipe. The system also features a high-temperature water expansion tank, which can:
1) Allows freshwater flowing in closed circulation lines to cause swelling when the volume changes due to temperature changes
2) Expel the vaporized gas in the pipeline due to local heat out of the system. Thus, the highest point of freshwater exports is generally connected to a ventilation pipe and an expansion tank.
3) Can use the static pressure head in the expansion of the water tank so that the suction pipe is always maintained at a high water pressure, to avoid the low-pressure vaporization in the pipe, to maintain pressure stability
4) Can use the expansion tank to add freshwater loss
5) Treatment water quality in the dosing sites
⑶ low-temperature freshwater circuit
The cryogenic freshwater circuit is also a closed-loop system. The whole loop is the same as the conventional seawater cooling system but must also be cooled by seawater. In the actual ship, low-temperature water is also divided into several ways: diesel generators, air coolers, air compressors, air conditioning, refrigeration, atmospheric condensers and other cooling. The system is much more complex.
The three-way thermostatic valve in this circuit is installed in the central cooler outlet. The outlet temperature of the cryogenic freshwater cooler is generally controlled at 36 ° C. It also established a special low-temperature water expansion tank.
Where the system is located in two pumps, one of the pumps is spare and required to start automatically and make a conversion.
The difference between independent type Ⅱ central cooling water system and type Ⅰ is that the main cooler, called low-temperature freshwater cooler, is cooled by the seawater the same as high-temperature freshwater cooler, whose working principle and system are the same. In addition, the position of the cooling pump and the cooler in the closed circulatory system can be varied in two different ways. The main difference between the two arrangements is whether the freshwater pump is directly connected to the freshwater inlet line or the outlet line. The freshwater from the cooling pump first enters the main engine inlet, which can keep the cooling water in the host to maintain high pressure, so the cooling water in the cylinder cooling chamber is not easy to vaporize, which can guarantee the good cooling effect of the diesel engine. The disadvantage of this arrangement is that the cooling water pressure from the host entering the cooler has been reduced, and the seawater may leak into the freshwater at the cooler tube sheet. Freshwater through the cooling pump out, first into the freshwater cooler, then to the host of the components to cool, and finally return to the cooling pump suction port. The advantages and disadvantages of this arrangement are just the opposite.