What are the two classes of forced circulation boilers?

Forced circulation boilers are designed to enhance the efficiency of water circulation within the system, and they can be categorized into two main classes based on their operational characteristics. Controlled circulation boilers use pumps to ensure that water is consistently circulated through the boiler, maintaining a specific flow rate and pressure. This type is engineered to prevent boiling in certain areas, allowing for improved heat transfer and efficiency. Conversely, once-through boilers operate with a single pass of water, where water is continuously fed, heated, and evaporated as it moves through the system. This design minimizes the amount of water required and can achieve very high steam qualities.

Saturated and superheated refer to the state of the steam produced rather than the circulation method in the boiler. Integrated and separate does not accurately describe the operation of forced circulation systems, while batch and continuous pertain more to processes rather than the flow characteristics of boiler systems. Therefore, the classification of controlled circulation and once-through is the most accurate representation of the two classes of forced circulation boilers.