Some time ago, a client had a heat and material balance that they wanted recreated and scaled, but the only documentation the client had in regards to process chemistry was a set of PFDs with stream tables. Based on the flow rates and compositions on the page (what was appearing and disappearing), I had to reverse engineer the reaction sets and conversions. This was complicated by the fact that multiple components were used in several different simultaneous reactions.
After submitting the final product to the client, they had a question about the amount of water in the reactor outlet as the new reactor design would not incorporate an old quench line. When I explained how I came up with the reaction set, their response was: “Huh, I didn’t even know that reaction was happening!” I have also been on site visits where I asked about the process chemistry and an engineer told me, “I don’t really know the exact chemistry, we just mix the chemicals in this order and it makes this one.” The site had Safety Data Sheets (SDS) for the raw materials and the products, but there was no documentation or data on any of the intermediates or their properties.
These stories are slightly paraphrased, but I tell them because as a process engineer in the field, it is crucial to know your process chemistry and what materials you have running through your pipes. While this may seem like common sense, documentation gaps in process chemistry are more common than you might realize. Perhaps ironically, two significant elements of the required Process Safety Information (PSI) portion of the Process Safety Management standard (CFR 1910.119) are process chemistry and reactivity data. The importance of this information cannot be overstated as it feeds into many other portions of the PSM standard. For instance, process chemistry and reactivity data inform the following facility design, risk, and maintenance programs:
- Relief System Design Basis: Relief system calculations require physical and thermodynamic property information about the materials of the process in order to ensure proper sizing and selection of relief devices. This is especially true when it comes to runaway reaction scenarios, and not just for the obvious reactions. For instance, facilities that handle chemicals prone to self-accelerated decomposition should have reactivity data for process reactions and decomposition reactions to ensure the relief devices on storage vessels are adequately sized to prevent overpressure in the event of a runaway reaction.
- Process Hazard Analysis (PHAs): Knowing the chemical hazards of the process – for raw materials, products, and intermediates – is important to informing the consequence for PHA scenarios where the materials end up outside of the pipe. Knowledge of the chemical hazards of the process (such as pyrophoric tendencies, auto-ignition temperatures, or toxicity) is important to developing an accurate representation of the risk posed to personnel.
- Mechanical Integrity Program: Process chemistry is also essential to providing a high quality Damage Mechanism Review (DMR). Corrosion engineers must know their damage mechanisms, but it is not their responsibility to be intimately familiar with the process being reviewed. DMRs involve the process engineer for the unit, which is another reason why it is important to know what materials you are working with and your process parameters. The information that comes out of a DMR is vital to developing Integrity Programs, as well as informing the frequency and type of inspections required to prevent premature failures.
These are just a few examples, but there are other aspects of PSM that are impacted by process chemistry, such as Electrical Area Classifications, Facility Siting, Emergency Response Plans, Dispersion Models, and Fire Hazard Analyses (to name a few). The unit engineer should be the keeper of process information, which includes the process chemistry. They should take ownership of this piece of process safety information and do the homework to understand their process. Even when there is no existing documentation, most facilities usually have someone (typically in Operations) who has been around long enough to know the process well. Search out these people and learn from them. In short, do the homework and take ownership. If you have any questions about how to get started, Cognascents welcomes the opportunity to serve your process safety, process engineering, and mechanical integrity needs.
