Wartsila ?31DF Series Product Manual page 148

9. Cooling Water System
The structure and arrangement of cooling water expansion tank may need to be approved by
Classification Society project-specifically.
The balance pipe down from the expansion tank must be dimensioned for a flow velocity not
exceeding 1.0...1.5 m/s in order to ensure the required pressure at the pump inlet with engines
running. The flow through the pipe depends on the number of vent pipes to the tank and the
size of the orifices in the vent pipes. The table below can be used for guidance.
Table 9-1
Nominal pipe size
9.2.12 Drain tank (4T04)
It is recommended to collect the cooling water with additives in a drain tank, when the system
has to be drained for maintenance work. A pump should be provided so that the cooling water
can be pumped back into the system and reused.
Concerning the water volume in the engine, see chapter Technical data. The water volume in
the LT circuit of the engine is small.
9.2.13 HT preheating
The cooling water circulating through the cylinders must be preheated to at least 60 ºC,
preferably 70 ºC. This is an absolute requirement for installations that are designed to operate
on heavy fuel, but strongly recommended also for engines that operate exclusively on marine
diesel fuel.
The energy required for preheating of the HT cooling water can be supplied by a separate
source or by a running engine, often a combination of both. In all cases a separate circulating
pump must be used. It is common to use the heat from running auxiliary engines for preheating
of main engines. In installations with several main engines the capacity of the separate heat
source can be dimensioned for preheating of two engines, provided that this is acceptable
for the operation of the ship. If the cooling water circuits are separated from each other, the
energy is transferred over a heat exchanger.
9.2.13.1 HT heater (4E05)
The energy source of the heater can be electric power, steam or thermal oil.
It is recommended to heat the HT water to a temperature near the normal operating
temperature. The heating power determines the required time to heat up the engine from cold
condition.
The minimum required heating power is 5 kW/cyl, which makes it possible to warm up the
engine from 20 ºC to 60...70 ºC in 10-15 hours. The required heating power for shorter heating
time can be estimated with the formula below. About 2 kW/cyl is required to keep a hot engine
warm.
Design data:
Preheating temperature
Required heating power
Heating power to keep hot engine warm
9-10
Minimum diameter of balance pipe
Max. flow velocity (m/s)
DN 32 1.1
DN 40 1.2
DN 50 1.3
DN 65 1.4
Max. number of vent pipes
with ø 5 mm orifice
3
6
10
17
min. 60°C for starts at LFO or gas; Min 70°C for startings at HFO
5 kW/cyl
2 kW/cyl
Wärtsilä 31DF Product Guide
DBAE248994