Orifice Regulator Sizing for Gas Purging

Hello Everyone ....!!

Its been a long gap, since i've written presented you with some technical stuff,

Hope everyone is safe and fine.... Belated Ugadi wishes to all of our readers.

Being busy with job & other activities, not able to contribute much here and feeling bad about it.

Today, i'm going to write a simple post on estimating the seat orifice diameter required for purging a gas into a system for a specific purpose at a given rate.

This calculation can be used for estimating the nozzle / orifice size required to purge gasses like H2, N2, HCl, NH3 etc.

Here, in the subject case i've considered a requirement of purging dry HCl gas into reactor containing reactants and the reaction is a semi-batch, where there is no thermal accumulation.

As a part of preliminary assessment, i've generated a pressure RC1 study to evaluate the heat of reaction and after extrapolating it to the commercial batch size, below are identified:

1. As per the energy balance which is performed using the available utility, the addition time is 4 hours

Learn how to estimate the addition time from RC1 data.

2. In - line to the addition time of 4 hours, the mass flowrate is derived as 200 Kg/hr.

(Uniform flow of gas is recommended, hence the mass flowrate is derived as total quantity / time)

Now the problem statement is defined and the solution to be identified i.e., estimation of orifice regulator sizing.

Step - 1: Estimate the HCl volumetric flowrate & Corresponding air flowrate

Density of HCl gas = Mol. Wt. of HCl / 22.414 = 36.46 / 22.414 = 1.626 Kg/m3

(Considering HCl as ideal gas; At STP 1 mole of gas occupies 22.414 L of volume).

Volumetric flowrate = Mass flowrate/density = 200 (Kg/hr) / 1.626 (Kg/m3) = 123 m3/hr.

Corresponding Air flowrate = HCl flowrate x (HCl SG)^0.5

( HCl SG = HCl density / Air density; Air density = Air mol. wt. / 22.414 = 28.84/22.414 = 1.29)

= 123 x (1.626/1.29)^0.5 = 138 m3/hr.

Step - 2: Estimation of Air-flow in NM3/hr

For estimating the air flowrate in NM3/hr we need the cylinder pressure and temperature;

Cylinder pressure is 80 bar.g and temperature is 70 C,

Air flowrate = Air flowrate x (273.15 x Cylinder pressure) / ((Temperature+273.15)*1.001325)

= 123 x 273.15 x 80 / ((70 + 273.15) x 1.001325) = 8805 NM3/hr.

Step - 3: Estimation of orifice sizing

Seat orifice area = Air flowrate (in NM3/hr) / (0.33 x inlet pressure (a)).

= 8805 / (0.33 x (80 + 1)) = 329 mm2 = 0.5 inch2.

Orifice diameter = (4 x 0.5 / 3.141)^0.5 = 0.81 inch.

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About The Author

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Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.
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