Honeywell Process Solutions has enhanced its UniSim design and simulation software designed to help improve safety and reduce capital expenditures for both new and existing installations.
The new UniSim Design Blowdown Utility, designed specifically for oil and gas, petrochemical, and chemical industry applications assists in designing systems to allow for safe depressurisation of process equipment. It also helps companies manage capital costs by more accurately selecting the right construction materials and blowdown system sizes needed for the site.
Understanding depressurising behaviour in a blowdown system is critical to the function of the system and ultimately the safety of the facility and employees. Rapid depressurising and gas expansion can result in very low temperatures, potentially putting equipment at risk of brittle fracture if the construction material goes below its ductile-brittle transition temperature.
In addition, the entire pressure relief system, including safety valves, relief orifices, flare piping and knockout drums, must be sufficiently sized to handle the flowrates that occur during blowdown, in addition to the piping and capacity of the flare system.
For new constructions, an accurate prediction of the minimum vessel wall temperature during blowdown is important for the selection of the appropriate construction material, for the elimination of overdesign and with the additional benefit of lowering project costs.
Similarly, having an accurate prediction of the maximum flow rate during blowdown is important for the reduction of overdesign associated with the relief valve/network sizing, without compromising on safety. For existing facilities, blowdown studies can prompt for changes in operating procedures, process equipment material or capacity in order to avoid brittle fracture during blowdown.
UniSim Design achieves improved fidelity by using a modeling approach consistent with the new recommended practices and analytical fire method set forth in the Sixth Edition (Jan 2014) of the API Standard 521 Pressure-relieving and Depressuring Systems. Validation tests show that the UniSim Design Blowdown Utility matches experimental data from publically available and proprietary sources, with the desired accuracy for blowdown prediction.