BECOMING A GOOD CHEMICAL ENGINEER

HOW TO BECOME A GOOD CHEMICAL ENGINEER PART 2

A few years ago, I published an article titled HOW TO BECOME A GOOD CHEMICAL ENGINEER. While the article was generally very well received, there were some constructive comments that I received. The main criticism was it was more of a general engineering coverage. This comment challenged me to expand things and cover some key areas of chemical engineering. Chemical engineering is a very broad discipline and getting broader. Chemical engineers have had successful careers in areas such as research (industrial, environmental, pharmaceutical, biological), plant operations, process design, process control, project development, project management, marketing, supply chain, and general management to name a few. My experience has been primarily in the areas of process design, plant operations and project development. So, my comments and examples are probably more relative to these areas.

It is my experience that there are 5 major technical areas that a chemical engineer working in these 3 areas (process design, plant operations and project development) need to master. These areas do not include the calculation (manual or computer) aspects of chemical engineering. In my case these were well covered in academic courses and I assume the same is currently true.

The 5 major areas are as follows:

? Learn what is happening inside process equipment

? Be fundamental in all approaches

? Learn how to evaluate the required technical depth

? Be always vigilant to the safety aspects of any technical recommendations.

? Learn a disciplined problem-solving approach

After I compiled this list of 5 major areas, I realized that they were split by the action verbs “Be” and “Learn”. I think this emphasizes the need for an engineer to continue learning regardless of his/her experience level. Now looking at these areas in more detail with examples, here is what we see.

Learn what is happening inside process equipment

While there are computer simulation programs to cover a large number of process operations, they do not allow one to visualize what is actually happening inside the equipment. While a simulation program or hand calculations may indicate how high a liquid level should be to provide sufficient Net Positive Suction Head (NPSH) for a pump, it does not provide any visualization for what happens if the liquid level is too low. However, understanding what is happening at the inlet to the pump makes it is easy to understand. The rotation of the impeller of the centrifugal pump creates a lower pressure at the eye of the impeller and draws fluid into the pump. If this lower pressure is too low vaporization of some of the incoming fluid will occur. This vaporization will cause the pump to operate at less than design, possibly to be very noisy, and the operator to say the pump is “gassing up”. This learning can occur by observing the pump in operation or by studying the details of the pump. In the process design phase, this problem is eliminated by a high enough elevation of fluid so that the NPSH available exceeds the NPSH required. Another example is a distillation column. What does flooding, downcomer filling or tray weeping look like inside the distillation column? Other examples where understanding is as important as manual calculations or computer simulation include (but not limited to) sonic velocity, reciprocating compressor ribbon valves, or choice of VLE model.

Be fundamental in all approaches

While time pressures often create a temptation to diagnose situations quickly and develop an action plan, this diagnosis should always be tested against a more fundamental approach. While even the most fundamental approach to engineering requires one to make assumptions, these assumptions should always be tested against fundamental concepts along with the necessary calculations.

A very simple example of this would be diagnosing that the failure to achieve the target temperature of a stream was due to a fouled heat exchanger. A more fundamental approach of estimating the heat transfer coefficient of the suspect heat exchanger and comparing it to design or previous values might reveal that the problem was associated with non-design flow rates, inaccurate temperature measurements or changes in utility conditions.

Assumptions associated with devolatilizing polymers often ignore the simple kinetic relationship shown below:

R = k*(C-Ce).

Where:

R = The rate of the volatile removal.

K = The kinetic constant or the mass transfer coefficient.

C = The actual concentration of the volatile in the polymer phase.

Ce = The equilibrium concentration of the volatile in the polymer that depends on the concentration of the volatile in the gas.

Unfortunately, there have been occasions where it was assumed that if the polymer temperature was above the boiling point of the volatile that there would not be any volatile in the polymer. This can result in fires in the shipping vehicles.

A centrifugal pump supplier will provide a head curve (head vs flow rate) based on tests with water at a standard fixed temperature. To convert this head curve to a differential pressure vs flow rate curve, the design density of the fluid being pumped must be used as opposed to the density of water at a standard temperature.

In the process design world, make sure that you have good understanding of the fundamentals of even what might be considered mundane things such as sizing process piping. Some of the areas that require more than a rough guess at piping sizing include the following:

? Number of fittings (elbows, tees, valves) – While the number of fittings is not known until a final layout is determined, it is often that these fittings increase the effective pipe length my 100%.

? Pneumatic conveying piping design – Conveying solids with air or nitrogen requires that the number of elbows needs to be minimized and also the use of long sweep elbows. This avoids pressure drop associated with solids settling to the outside of the elbow and being resuspended in the gas.

? Piping that contains both liquid and vapor phases – The design of this type of pipe requires careful consideration of flow regime as well as pressure drop.

? High velocity gas flow – This type of flow might be encountered in safety valve headers and requires that the velocity along the line does not exceed sonic velocity.

Learn how to evaluate the required technical depth

While this is an important area, it is also very difficult to quantify. It also depends on the environment. For example, during a startup or emergency environment, there is little time for technical depth. However, this is also an environment where decisions need to be correct and can best be made by experienced personnel. The process industry history is filled with examples of poor decisions made quickly by inexperienced people. The technical depth discussed here is the depth that is required to solve an engineering problem whether it is operational, project development or a design problem. Here are some questions that might be of value in assessing the amount of technical depth that is required.

1. Is there a real need for a quick answer or just confirmation that the problem is being considered?

2. Are time pressures causing hidden problems that are uncovered by an engineer’s natural curiosity being ignored? An unusual noise when walking through the plant might uncover an incipient equipment failure. The question of what color to paint a new distillation tower might uncover that sunlight reflectivity was important to avoid a slightly elevated temperature.

3. Is the necessary expertise available to solve problem or is a consultant required?

4. Does the time allocated to complete the project fit a reasonable time line?

Be always vigilant to the safety aspects of any technical recommendations.

Too often, an engineer will provide a technical recommendation without thinking about the safety ramifications of the proposal. His/her logic will be that safety is the job of the protocol setup to review the safety of new changes – an operations supervisor, a safe operating committee or management of change. This attitude leads to the individual proposing the operating or facilities change making bold statements to get the project approved by the safety protocol. It would not be unusual for the individual selling the safety aspects of the project to proclaim – “I am staking my professional reputation on this”. When it is put into practice, the operator maybe staking his life on it being safe.

Learn a disciplined problem solving approach

While there are a whole host of problem-solving techniques, the steps below are critical to any approach:

Step 1: Verify that the problem actually occurred.

Step 2: Write out an accurate statement of what problem you are trying to solve.

Step 3: Develop a theoretically sound working hypothesis that explains as many specifications of the problem as possible.

Step 4: Provide a mechanism to test the hypothesis.

Step 5: Recommend remedial action to eliminate the problem without creating another problem.

These steps are described in more detail in my book:

PROCESS ENGINEERING PROBLEM SOLVING

Avoiding the Problem Went Away But It Came Back Syndrome

Published by John Wiley