Which of the following is NOT one of the four systems required to operate steam boilers?

The answer identifies cooling as the system that is not one of the four essential systems needed to operate steam boilers. In the context of steam boiler operations, the primary systems include steam generation, feedwater supply, fuel supply, and often a safety system.

The steam system is responsible for delivering steam to the desired location for heating or process demands. The feedwater system is critical as it provides the boiler with the water necessary for generating steam, ensuring that the boiler does not run dry. The fuel system is equally important as it introduces the energy source, whether it be natural gas, oil, or solid fuels, required for the combustion process that produces steam.

Cooling, while it can be related to some aspects of plant operation, such as in heat exchangers, is not a fundamental component of the steam boiler's core operational systems. Each of the other three systems plays a direct role in the conversion of water to steam and the management of that steam for effective energy transfer and use. Understanding these distinctions is vital for anyone working with high pressure boilers, as it underscores the critical systems needed for their safe and effective operation.