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Inert Gas Purging Requirement Calculation

Purging is an activity used to remove oxygen in piping or vessels to certain concentration, for example 2%-mole. It uses inert gas, usually nitrogen, to do that.

In this post, I want to share you how to calculate inert gas for purging activity. There are three different calculation methods used.

Dilution Purging

In dilution purging method, the inert gas simply flows through the vessel and reduces the concentration of unwanted component. It is used for tanks, reactors, and other vessels. Figure below is used to determine requirement of inert gas. Read More

Sizing of Compressor and Instrument Air Capacity

I want to share you how to size or select minimum capacity of air compressor and instrument air dryer. Air compressor is usually used as feed air for:

  • Instrument air (for instrumentation or feed air for nitrogen generator)
  • Utility air (for utility station)

Instrument Air Requirement for Instrumentation

Instrument air is required in operation of control valve and shut down valve. The rules below is used to calculated instrument air requirement for instrumentation:

  • Control valve (CV) – steady state condition: 1 scfm/valve
  • Control valve (CV) – transient condition: 6.25 scfm/valve
  • Shut down valve (SDV) – steady state condition: 0
  • Shut down valve (SDV) – transient condition: 4.8 scfm/valve

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Condensate Load Calculation

I just read some pages on Handbook of Chemical Engineering Calculations 2nd edition, written by Nicholas P. Chopey and got interested in calculation of condensate load in order to determine the capacity of steam trap. I will take one example, where the steam indirectly heats a liquid through metallic surface, as in heat exchanger and kettles.

Case I

For example, we have 1892.5 L of water heated in 30 min from 22.2 to 100 oC with 50-psig (344.7-kPa) steam in the jacket of kettle. How much condensate formed?

For normal warm up load, the quantity of condensate can be calculated by the following equation: Read More