In this Issue:
- Project Spotlights:
- PROCESS NOW OFFERING COMPUTATIONAL FLUID DYNAMICS MODELING
- POLYMER PILOT PLANT DETAIL DESIGN
- Technical Discussion: BEWARE API vs ASME – RELIEF VALVE ORIFICE SIZE
- Safety Pause: Routine Operations – It Could Happen to You!
PROCESS NOW OFFERING COMPUTATIONAL FLUID DYNAMICS MODELING
CFD modeling provides time-accurate, three-dimensional insights into fluid motion, reaction chemistry, particle trajectories, heat transfer, and free surface dynamics. The development of new fluid modeling algorithms, combined with modern computational architectures, now enable engineers to simulate the performance of fluid handling equipment with a fidelity that rivals what can be measured experimentally. Just a few examples of where we can use CFD:
- Multi-Phase Newtonian and Non-Newtonian Fluids
- Mixed Tanks (Agitator Performance, Reactant or Impurity Concentrations, Impact of Internals)
- Piping (flow profile, flashing liquids, slurries)
- Heat transfer
- Chemical Reactions
- and much much more
POLYMER PILOT PLANT DETAIL DESIGN
Process Engineering Associates, LLC (PROCESS) was contracted by the client, a specialty polymers manufacturer, to provide continued project engineering support during the detail design / build phases of their polymer pilot-plant project. The purpose of PROCESS’ effort was to provide value-added consultation and process engineering support to both the client and the engineering company that is providing detail design, procurement, and construction management of the polymer plant. PROCESS’involvement spanned the detail design phase of the project up to and including the final Pre-Startup Process Hazards Analysis (PHA).
PROCESS’ initial effort was to update the previously developed design basis addendum to document key changes that had been made to the process design prior to initiating the detail design effort. PROCESS also initiated and guided the team through a change in heat transfer fluid to mitigate the incidence of multiple fire scenarios.
Technical Discussion – BEWARE API vs ASME – RELIEF VALVE ORIFICE SIZE
Many are not aware of the major differences between the orifice sizes and discharge coefficients suggested by the API and the actual, ASME values used by the relief valve vendors. According to API-520, Part 1, the API orifice sizes and discharge coefficients are assumed values and are to be used only for the initial selection of the relief valve. They were developed to facilitate choosing a relief valve size early in a project and to ensure that the relief valve finally purchased will have a certified capacity that meets or exceeds the required relief capacity.
However, the differences in capacity between the initial choice of API orifice and the actual ASME orifice can be significant. For most projects, the actual ASME orifice can provide a much greater flowrate. When one also considers the following:
- Conservatisms in estimating the required relief loads;
- Calculated orifice sizes are usually between the standard, letter designated API sizes. When this occurs, the next larger orifice size is chosen resulting in the valve being oversized with just an API orifice;
- The certified ASME discharge coefficient is derated by a factor of 0.9 resulting in another potential source of over design; the final, purchased, relief valve can be greatly oversized.
Routine Operations: It Could Happen to You
Routine operations are sometimes the most dangerous because we become complacent about them. Don’t believe it? This story involves an old wastewater treatment system that utilized 98% sulfuric acid which was pumped from a storage tank directly into the process.
During a routine shutdown, the engineer happened to be down on the floor when the time came to shut down the sulfuric system. The shutdown sequence involved cutting off the pump then closing an automatic shutoff valve on the pump discharge. Since the engineer was in the vicinity, the control room operator called over the speaker to just cut off the pump using the local switch. The area around the sulfuric system required the use of chemical goggles. So the engineer took the time to go grab some from a bin located on the floor and put them on. As the engineer approached the pump switch, a pipe gasket suddenly blew and 98% sulfuric was sprayed on him. Fortunately it was not much, and other than suffering the loss of a favorite tee shirt due to death by acid holes, he was unhurt.
It turned out that a control room operator had closed the pump discharge valve before the engineer had a chance to shut down the pump. In theory, the piping components should have held even under the deadhead pressure of the pump, but components have a way of wearing out and weakening. The incident resulted in a review of procedures and a much-needed automation of some operations (including the addition of interlocks, such as not allowing the pump discharge valve to be closed until the pump had been shut down). But the real lesson was this – even though routine operations may have been safely performed without incident hundreds or even thousands of times, there will eventually be that one time when something goes wrong. It would have been easy to not bother with taking the extra 15 steps to go get the chemical goggles before entering the acid area – but thankfully he did.
Still not convinced? Then try this story that has nothing to do with a chemical plant. A farmer hopped off his tractor one day several years ago to do some small task such as picking up something in his way. He left the tractor running presumably with the Brake On but it started moving and he was caught up in a hay baler and killed. Now you have to know that this guy had done exactly the same thing hundreds of times in his life before and had never given it a second thought. But this one in a million (or really, 1 in 10,000th time), with the engine running, the tractor somehow engaged and it cost this fellow his life.
So ALWAYS follow safety protocols. Even when performing routine operations. Even if you don’t work in a chemical plant, one of these days – and you can count on it – you will be very glad you did follow safety protocol.
In both of the stories above (firsthand from PROCESS employees), the people involved were in Skill Based Mode, having done the task so many times they no longer paid attention to the potential dangers involved with it. Skill Based Mode is part of the Human Performance model and is used in an array of industries from Nuclear to Medical to Aviation. Numerous tools are available for in depth training, but as an introduction, human actions are grouped into three performance modes including 1) Knowledge Based 2) Rule Based and 3) Skill Based. Let’s build these from the ground up just like the diagram at the top of the article.
Skill Based performance is something you can do on “auto pilot”. Liken this to driving from home to work every morning. You could do it with your eyes closed or even arrive at work and not remember stopping at a red light or making a turn. You are in skill based mode where your attention is low and mistakes can be caused due to this lack of attention. Mistakes happen in this mode at the rate of 1:10,000. But remember, you are doing this task a lot!
Rule Based performance is something where you must engage the ole brain a bit more for a non-routine task. Using a car scenario again, this would be like driving to work and a road is closed. You know how to drive a car and follow road signs, but are having to plan a different route, plan your turns, pay attention to landmarks or new signage, etc. Mistakes happen in this mode due to misinterpretation and failure to recognize changes at the rate of 1:1,000.
Knowledge Based performance is a time when you are operating on your skills and judgement. This would be like driving in a foreign county. You know how to drive your car, but maybe you now have to drive on the opposite side of the road or road signs are in a different language. Mistakes happen in this mode when you don’t have all of the information you need and are relying on assumptions. These mistakes happen at the rate of 1:10, but you aren’t in this mode very often.
You should be just as diligent about your safety protocol on task number 10,001 as you were on task 1. Recognizing what mode you are operating in and what errors can occur during that task is an important step in keeping you and those around you safe!
PROCESS extends our, prayers, thoughts, and best wishes to those affected by Hurricane Florence and the catastrophic events that have followed. We express our sincere appreciation to the emergency workers and volunteers who are working to maintain the safety of those in the communities. PROCESS supports our many clients, colleagues, and friends along the East Coast as they journey to a safe restart of their respective facilities and put the pieces of their lives back together.
PROCESS offers a full range of Process Design and Process Safety Services to clients around the globe. Our services include conceptual process design; simulation and modeling feasibility studies; FEL-0,1,2, and 3 (Schedule-A process design packages); front-end-engineering design (FEED); debottlenecking; process optimization; on-site operations support; process safety training; safety program development; on-site process safety auditing, performance of hazard assessments; and other services designed to meet the needs of our clients.
Process Engineering Associates, LLC
700 South Illinois Ave Suite A-202
Oak Ridge, TN 37830
Call Us: (865) 220-8722