Week 8 Challenge

In this week it is required to find out various sizing details of a pressure safety valve using Aspen HYSYS. it is done using the safety analysis feature of HYSYS.

1. In this question it is required to find out the relieving temperature, orifice area, orifice designation for the given pressure relieving scenario. To accomplish this in each scenario we have to perform safety analysis using PSV for each case with the correct over pressure scenario.

The first scenario is a fire case scenario for a vessel (separator).

The conditions and composition of the initial stream are as follows:

The vessel dimensions and vessel properties are shown as below:

After performing Safety analysis with the current stream with Fire case as the sizing scenario, the sizing and designation of the PSV is completed. The details are shwon in the below images:

Operating and design conditions for the PSV:

The Orifice calculation is shown below:

All the required values rearding the question are shwon in the above two images.

Line sizing calculation is shown below:

2. In this question it is required to find out the maximum possible saturated steam flow across the control valve for sizing the downstream PSV

Firstly, the streams need to be converged with the given input conditions. HYSYS will calculate CV value of the control valve with the respective conditions and composition. It is then required to to go to the size valve tab and converge the Control valve with the rated CV with trial and error of the mass flow rate.

The initial conditions and composition of the streams Upstream and downstream of the valve:

As it is seen from the image the valve opening is 50 percent and valve CV is 37.06.

The final conditions of the streams after adjusting the control valve to the rated CV:

As it is seen from the image it taken as 100 percent valve opening which is a worst case scenario for control valve failure. The fow rate adjusted for the rated CV is 540 kg/hr. In this question failure of automatic controls is taken as a sizing scenario.

The orifice calculations and the operating conditions for the PSV is shown below:

The line sizing calculation is shown below:

3. In this question it is required to find out the inlet & outlet line sizing, orifice area, orifice designation for the given pressure relieving scenario. The scenario is pump discharge blocked outlet scenario.

The composition of the streams and the conditions are shown as follows:

The pump NPSH is shown below:

The orifice calculations for the PSV is shown below along with the operating & design conditions for the PSV:

The Line sizing calculations are shown below:

NOTE: Apart from the above details the save files for each cases are attached alongwith these answers for better evaluation.