What type of oil requires preheating and with what equipment?

#6 oil, which is often a heavy fuel oil, requires preheating to reduce its viscosity before it can be effectively pumped and burned in combustion equipment. This type of oil is more viscous at lower temperatures, making it challenging to handle and ignite in its thicker state.

An oil heater is used for the preheating process, typically raising the temperature of the #6 oil to a level where its flow properties improve, allowing it to be efficiently utilized in boilers, engines, or turbines. The heating ensures that the oil can be atomized properly for combustion, leading to more efficient operation and reduced emissions.

In contrast, the other oils listed in the other choices have different characteristics and handling requirements. While they may require some form of management or heating, they do not necessitate the same level of preheating as #6 oil, making it essential to know the specific requirements for each type of fuel oil in boiler operations.