What occurs during shrinkage in a boiler system?

During shrinkage in a boiler system, the phenomenon describes a situation where there is a decrease in boiler water levels due to the steam generation process. This typically occurs when steam is produced faster than it can be replaced with feedwater. In this scenario, the firing rate of the boiler is often reduced to prevent a further drop in water level, and as a result, the overall heating effect diminishes, leading to increased drum pressure. When the steam demand decreases, the generated steam in the drum decreases, allowing pressure to build due to reduced output.

This explanation elucidates why the correct answer pertains to a decrease in the firing rate correlating with increased drum pressure during shrinkage. Understanding this relationship helps in managing boiler operations effectively, ensuring safety, and maintaining system efficiency.