Deaerator height
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Placing the thermal deaerator at a high elevation is intended to prevent cavitation in the feed water pump; the deaerator should be arranged to provide the feed water pump with sufficient head, which must be no less than the sum of the following values. 1. The difference between the vaporization pressure of the water at the inlet of the feed pump and the operating pressure of the deaerator. 2 NPSH of the feed water pump. 3. Pressure drop in the inlet pipe of the feed water pump. 4. Margin for the safe operation of the feed water pump, generally set at 3–5 kPa. Based on the performance of boiler feed pumps commonly used in our country, the installation height of atmospheric deaerators is generally greater than 7 m, while that of medium-pressure deaerators is not less than 11–13 m. How are these 7-meter and 11-meter figures calculated roughly?
This height of 7 to 11 meters was likely established many years ago, when technology was still quite underdeveloped. For our previous project, we initially planned to install 4 tanks with a capacity of 200 cubic meters on an 8-meter-high steel structure, but that idea was later modified. The following solutions can be adopted to reduce the installation height of the deaerator: 1. Use a VS6 pump, which is a commonly used approach ； 2. Last time I heard from their designers that they planned to introduce nitrogen gas. I have left that project and didn’t ask in detail. You can ask the personnel in charge of refinery design for advice ； 3. Add one more feed water pump. In short, as long as the results of the calculations or simulations show that the operating conditions meet the relevant requirements for NPSH, that is sufficient.