What is the purpose of the deaerator heating steam inlet balance pipe?

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There are generally two sources of steam for heating the deaerator: one comes from the fourth-stage extraction steam of the turbine and is used for normal operation (steam pressure of about 1.4 MPa), while the other comes from external auxiliary steam, serving as a backup and starting source (steam pressure of about 0.8 MPa). On these two steam supply pipelines, we can also see pipes equipped with check valves, which connect the steam inlet pipe to the deaerator; these are the deaerator steam inlet balance pipes. Why is this pipe needed? Let’s first take a look at the newly taken interior photos of the deaerator. As we can see, in order to ensure full contact with the condensed water in the deaerator and achieve a better deoxygenation effect, both heating steam supply pipelines are designed to extend deep into the bottom of the deaerator, from where the steam is sprayed out through nozzles. Let’s imagine a situation where the turbine unit is operating normally and the four-stage extraction systems are in use as intended. When the unit loses load and the main steam valve and control valves suddenly close, the extraction flow is interrupted, causing the pressure in the fourth extraction stage to drop sharply. The deaerator, however, has a large capacity to store heat, so its pressure drops more slowly. As a result, the pressure in the deaerator ends up being higher than that in the fourth extraction stage. The water inside the deaerator then flows into the fourth extraction pipeline through the nozzles. If, unfortunately, the check valve in the fourth extraction stage does not close properly, water will enter the turbine, leading to a serious accident known as water hammer in the turbine. At this point, our balance pipe comes into play: if the above situation occurs, the pressure in the deaerator will be higher than that in the fourth extraction stage; the check valve in the balance pipe is then pushed open, allowing the pressure in the fourth extraction stage to equalize with that in the deaerator, and as a result, water cannot flow back. A simple and practical design that ensures the safe operation of the steam turbine unit.