Application of dynamic models to distillation column relief analysis in solving flare capacity issues

Major oil companies have pledged to achieve net zero in emissions by 2050. The over-design of flare and relief systems capacity, whilst necessary as a safety requirement directly increases leakage rates and consequently purging flows and stack emissions. Often available capacity and current peak load is unknown and hard to qualify. Conventional approaches use empirical or steady state methods for determining column relief capacity. These often over-estimate peak flows and cannot predict the timing of overpressure, changes to the rate over time or the duration of the relief event, all of which are necessary to adequately size safety systems.

In petrochemical plants, overpressure in distillation columns can occur because of a trip or shutdown of equipment causing an imbalance in heat input or flowrate to the column. Global failure scenarios such as power or cooling water failure are the most common cause of governing flare loads affecting multiple columns. Power failure & loss of condensing duty, with residual heat input from reboilers or fired heaters, leads to vaporization of the liquid inventory in the column. However, not all columns will reach overpressure if the residual heating is insufficient, and the pressurization time of each will be different.

Dynamic column models provide the transient relief flowrates over the event duration and can reduce relief loads by 10% (narrow boiling mixture) to 80% (wide boiling mixture). When these models are coupled to the flare network, the realistic peak header flowrates are reduced with lower resultant backpressures.

This webinar will showcase PSE’s dynamic modelling capabilities for distillation column relief loads and flare capacity analysis.

A recent case study for a refinery flare will illustrate how the current flare capacity was quantified for the global power failure scenario and sufficient excess capacity was confirmed for connection of significant additional column loads. The topics covered include:

1. Dynamic assessment of individual relief loads
   1. The key phenomenon that determine the relief loads and the important modelling features to consider.
   2. Effect of column internals including tray performance and weeping
   3. Project case examples demonstrating the reduction achievable in individual relief loads through dynamic assessment
   4. The use and confirmation of HIPPS in reducing flare loads.
2. Time dependency between different columns
   1. Factors influencing the rate of vaporization of liquid inventory
3. Integrated flare system analysis
   1. The influence of packing in reducing flare flowrates.
   2. Backpressure and line sizing assessment – confirming selection of relief valve type

Presenter(s)

Sathish Natarajan, Principal Consultant Engineer, PSE

Sathish Natarajan is a Principal Consultant Engineer, within PSE’s Process Safety group based in Houston. He is a chemical engineer with an M.S. from University of Illinois. Sathish has over seven years of experience with PSE, using PSE’s proprietary gFLARE^® technology. He has led and executed a large variety of safety projects across upstream and downstream sectors and is an experienced technical resource for PSE model development activities.

Hugo Rodrigues, Senior Consultant Engineer, PSE

Hugo Rodrigues is a Senior Consultant Engineer, within PSE’s Process Safety group in London. He is a chemical engineer with an M.Eng from Instituto Superior Técnico, Portugal. Hugo has eight years of experience with PSE, working on and leading safety projects, using PSE’s proprietary gFLARE technology. Hugo has experience in flare and relief verification studies and applying column modelling and flare dynamics.