Calculation of control valve diameter
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The selected size for the control valve per the specification is DN150; flow restriction is not taken into account, and the calculation is based on the pipeline dimensions. Using the formula Q=A*V*ρ, the flow rate is calculated to be 49914 kg/h (with an average flow speed of 1 m/s). This value was taken from the standard HGT 20570.6-1995; could the pipe diameter be too small? Is this correct?
How are the pressure before and after the valve determined? Are there any software for simulation calculations?
This is a flash valve; in the two-phase gas-liquid condition downstream of the valve, it is not possible to use the pVA formula to estimate the flow rate. As a rough estimate, the flow velocity in an 8-inch pipe is 1.2 M/S, while the inlet flow velocity at a 6-inch valve is 2 M/S, which is below the minimum requirement of 3 M/S for flash vaporization conditions; therefore, a 6-inch valve is appropriate.