How do we obtain reliable estimates of relief load in a distillation column?Jan-2022
Maria Guerra, KBC (A Yokogawa Company), Maria.Guerra@kbc.global
Relief loads are typically obtained by steady state simulation and normally bring a significant overdesign due to the approximative nature of the assumptions. When this approach is not valid and a more accurate estimate is required, building a detailed dynamic simulation model (for example, using Petro-SIM dynamics) is the alternative choice. The dynamic simulation model can be run in order to reproduce the behaviour of the column during many contingency scenarios such as power failure, cooling water failure, pump failure, and external fire. The dynamic calculation will provide the transient of the mass and heat transfer processes coupled with the thermodynamic equilibrium that will take place in the involved pieces of equipment: the vapour and liquid contact in each column tray or packing section, the dynamic calculation of residual energy supplied for the column material boiling, the residual column overhead cooling combined with the flow rate changes as pumping equipment shuts down. Published experiences report significant savings in flare network modifications as well as in relief valves and their installation replacement.