Part of the system is comprised of vacuum units which are in place for hogging and holding tasks. In order to evacuate air once accumulated in the air cooled condenser (in power plants) and steam ducts, the process of hogging and holding will be necessary. Accumulated air, once evacuated in the air cooled condenser (ACC) of the power plant and steam ducts will sit idle in the hogging cycle. This enables the air to be returned through a series of ducts and turbines to operational use. First, the evacuated heated air must reach a certain preset level of vacuum pressure. The vacuum pressured needed must be sufficient for the task, neither too high to present a high pressure nor so low that it is unable to achieve the state of proper steam condensate.
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