Process Engineering Project /AN

You have three hours to start up the C2-C4 fractionation train. A P&ID for the plant is appended in Figure 1. The plant has undergone scheduled maintenance, and has been pressure tested to 40 bar with nitrogen by the commissioning team. The plant has been subsequently depressurised, and signed over to your shift team to begin production. Your feedstock is a two-phase mixture with the following composition:

Component Mole fraction
N2 0.046
CO2 0.008
methane 0.155
ethane 0.169
propane 0.260
i-butane 0.047
n-butane 0.107
i-pentane 0.031
n-pentane 0.034
heavies 0.143

Once the plant is running the four products should be at the following specification:

C2 – Minimum 75% Methane and Ethane
C3 – Minimum 85% Propane
C4 – Minimum 70% i-butane and n-butane
Heavies – Maximum 5% i-butane and n-butane

Your target feed processing rate is 210 m3/hr. Off-spec product should not be produced under any circumstances. There should be minimal flaring of product, and you should be aware that liquid sent to drain incurs a significant cost to the company. Running the plant significantly above the target specification will incur a penalty.

If the target specification is met and you can demonstrate that the plant has been at steady state for a period of 15 minutes then you can proceed to attempt the extended targets to produce 85% Methane and Ethane, 91% propane, 78% i- and n-butane and achieve less than 2.5% i- and n-butane in the heavies stream. If you can achieve steady-state under these conditions then you should switch to meet this new specification at a feed flowrate of 130 m3/hr.

Steady-state should be judged by monitoring temperature and product flow trends from your process. When oscillating flows are present you can assume a steady-state will be reached if there is clear evidence of controlled damping and no operator inputs are made during the period