An ‘entitlement’ approach to continuous process control improvement
Greg: During our process control improvement (PCI) initiative at Monsanto and Solutia, we developed a methodology that went from opportunity sizing to opportunity assessment, ending up with a list of opportunities prioritized based on cost and benefits. The ones involving just tuning or configuration were at the top. The ones with good benefits and capable of being done in a week were classified as “quick hits.” I had the pleasure of working with Bart Propst who was a very astute and enthusiastic supporter of the PCI effort at the Chocolate Bayou Plant in Texas. Bart is presently the process control leader of this plant for Ascend Performance Materials. It is reassuring to see how Bart has developed a practical and sustainable approach to PCI at a time when it seems industry is getting distracted from essential opportunities.
Stan: What is the upper level view?
Bart: Ascend has a great legacy of continuous automation improvement. The last seven years have brought new continuous improvement tools to Ascend. We use an “entitlement” view of improvement. Consequently, we document the theoretical maximum and the value of each incremental improvement. We use the all the continuous improvement tools, such as Six Sigma, Lean, operational equipment effectiveness (OEE), and statistical process control (SPC) to define where we are and what we are working to improve. Mostly, it’s reducing the variability and changing the mean to be closer to the optimum. Operators are encouraged to push the process, but tend to end up in a comfortable place for a variety of reasons.
Greg: We find key temperature loops directly or indirectly related to composition are using a setpoint based on an operator concern from a once having a problem with being closer to the optimum stemming from a process equipment or design constraint. Simulation, better involvement and training of the operators, and better knowledge and metrics of the process enable us to all be on a common objective basis. Medium fidelity models help us ascertain and develop the optimums and the online metrics of key performance indicators (KPIs) as detailed in the May 2015 “Control talk” column, “Getting innovation back into process control.” The January 2011 “Control talk” blog, “Extending Process Control Analysis Benefits Tips” provides insight into the neglected opportunity that is the margin imposed by the operator because of an incident and/or a lack of process knowledge. The operator is going to take the most conservative approach, particularly if there are no metrics or knowledge of the associated loss in profitability.
Stan: How did you get the resources needed?
Bart: Since the site automation team was formed in 2009, we have grown from six to 11 members. We initially worked on the maintenance, reliability and projects for the site automation infrastructure. We staffed up due to site growth and to work through our interlock assessments for Safety Instrumented Systems (SIS) ISA84 compliance. As we came off the peak of the ISA84 work, we started looking for automation productivity projects. We started with an opportunity assessment of 36 projects—everything from instrumentation health, regulatory control and alarm management to batch analysis, advanced process control (e.g., model predictive control) and site-wide energy optimization. Scoring the projects in terms of benefit, timing and resources, we sorted a list of 36 projects with ratings of high-value, low-effort at the top. Initially, our emphasis is on low- or no-capital, engineering-only projects; we continually review and refine the list.
Greg: How do you attain sustainability of benefits?
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Bart: We recognize the need to assign resources to maintain the improvements. The person who led the SIS effort is now leading the Six Sigma approach (define, measure, analyze, improve and control). We get the right people involved who understand the process and the operation. The production unit people have the right KPI metrics, and we have mutual accountability and involvement. We are biased toward chemical engineers, because of the need to understand process objectives and relationships.
We have had to go back and rework projects to realize the benefits of $200K to $400K. We had some difficulty getting the operators to run the systems as intended because we didn’t do our homework. We are working on three new projects with planned benefits of $1 million or more per year.
Greg: I agree. Most of the knowledge I needed came from my elective courses in mechanical engineering and chemical engineering for my B.S. in Engineering Physics and M.S. in Control Theory. Even more so, my understanding of cause and effects and what was really important was gained from the development and use of dynamic, first-principle process models for key unit operations throughout my career. I had to develop and program the ordinary differential equations (ODE) for material and energy balances. I recently showed how the ODE reveal simple expressions for the process gain and primary time constant, providing considerable insight as to how these key dynamic parameters change with design and operating conditions as seen in the online Control Global paper, “First Principle Relationships for Process Dynamics.” I also developed charge balances recently expanded as described in the Chemical Processing March 2016 article, and momentum balances as documented in my 2010 Momentum Press book, “Centrifugal and Axial Compressor Control."
Stan: Tell us more about the documentation of opportunities?
Bart: The opportunity assessment (OA) sheet has evolved. More than half of the list involves specific process improvements. The rest focuses on using the tools more effectively, such as the one for multivariate statistical process control (MSPC) for batch processes. We are looking at a tool that would allow us to overlay batch profiles to determine if a batch is different, how and why. For example, after completion of the feeds to the reactor and setting of fixed coolant flow, we look at the free rise of the batch profile. Whether the trajectory is faster or slower and whether the peak is higher or lower should tell us something about the difference in the chemistry.
Greg: I found that MSPC (e.g., data analytics) has potentially more value in batch processes because there is no need of the dynamic compensation required in continuous processes for synchronization of upstream inputs and downstream process outputs. Also, while MSPC does not deal directly with nonlinearities of continuous processes, the piecewise linear fit of batch profiles addresses the nonlinearities of batch processes. I like the fact that principal component analysis (PCA) removes cross-correlations in inputs, and you can drill down to see the relative contribution of each measurement.
Stan: What takes up the biggest chunk of your time?
Bart: The biggest part of our time is spent defining and developing the project scope, benefits and key performance indicators (KPIs). We spend time developing key process indicators that everyone agrees on. Loop performance monitoring using KPIs is an example of quick indicators of instrumentation or control valve performance issues. We are leveraging the engineering tools available to us to execute these projects, such as taking advantage of the ability of DeltaV Predict Pro embedded in the distributed control system to rapidly implement small multivariable process control (MPC) projects and standalone advanced process control (APC) solutions where it makes sense.
Greg: What about migration projects?
Bart: Automation improvement projects are a large part of our effort. We do a failure mode effects analysis (FMEA) to document the risks of obsolete control systems. We are finding it valuable to put productivity improvement on top of migration to get the project funded and deliver improved yield, throughput and reduced energy from the new capabilities of modern control systems. In addition to the lower maintenance and the greater on-stream steam from improved reliability, the new systems have less physical limitations than communications between controllers and the network. Plus there is new functional capability courtesy of embedded APC tools and improved communication.
I like to use the term “automation” rather than APC for all improvements so everyone is involved and gets credit. We are using the whole automation tool kit.
Greg: I love the idea of not doing a copy job. I think it is such a discredit to not take advantage of the incredible power and flexibility of modern systems. I like the use of the term “automation” because it also provides better recognition of automation as a profession and the value of the International Society of Automation (ISA). It also avoids the negativity toward APC projects that occurred due to unnecessary complexity; deficient definition, testing and training; and poor support and maintenance.
Stan: How do you get true credit for automation?
Bart: This gets tricky, as we saw in a recent application of MPC for thermal oxidizer temperature control that had a compound response complicating the PID control scheme. There was a $700K per year benefit clearly seen in reduced natural gas usage. However, the improvement also reduced steam make to a turbo-generator, reducing electricity generated by $300K per year. We reached a compromise of about $400K per year in net benefit because of lost electrical power generation from less steam to the turbo-generators. We spent many hours to align the benefit with measureable accounting for the natural gas reduction and the electrical purchases. Sometimes the loss of benefits is greater than expected. You need to be upfront and make sure you don’t just shift costs to a different cost area.
Greg: How do you decide what to contract out?
Bart: We recently completed a decision analysis on whether we should use existing or hire new group members versus contracting out the services needed. We tried to hire an APC resource but couldn’t find a good fit. We decided to develop the ability to support MPC and contract out parts of the implementation where more experience was important. We went from a goal of $1 million to $2 million a year in benefits by way of automation.
The automation improvement leader is an experienced Ascend engineer, so we retain complete responsibility for all aspects of projects. We own it all. We use specialty engineering contractors for specific applications or tools we are not familiar with. These projects could involve deploying a DeltaV APC application or designing, modeling and commissioning a larger MPC application. Contractors are used remotely to review test results, tune and monitor MPC performance. We see this as a good way to leverage contractor expertise. We learned a lot of the practical aspects of a successful MPC installation many years ago from Mike Brown, Soundar Ramchandran, Russ Rhinehart and Greg.
Greg: I had the great fortune of working with Mike Brown on innovative solutions at Solutia. I was impressed by how he could become an excellent friend and confident of the operators, besides using extensive practical knowledge to ensure a successful MPC. I share some of this in my series of “Control talk” columns with Mike Brown, July-Sept 2010; “Process Performance Improvement - Part 1,” “Process Performance Improvement - Part 2," and “Process Performance Improvement - Part 3."
Stan: How do you determine the scope?
Bart: We do what makes sense. We give the manufacturing units a tool they can use. If they don’t call you when it’s off, it indicates the solution is more hassle than it is worth.
Greg: Are there changes in management?
Bart: As we started down the automation improvement development, each of us in the group completed task assessments of everything we did for month to assure it aligned with our site goals. The outcome was that we were spending 5-10% of our time doing other people’s work. We then developed written plans to turn the work over the responsible groups. We think this was an excellent exercise. We freed up about 10% of the group’s time. I also gained a much better understanding of and appreciation for what our group is doing.
Greg: If you want to know about my take on process control improvement, see the June and July 2014 “Control talk” blogs, “Process Control Improvement Perspective” and “Process Control Improvement Recommendations.” If you want to get into how important personal relationships and a benefit-driven approach is, check out the June 2012 “Control talk” column, “The Human Factor.”
Top 10 requests you don’t want to hear
- (10) For operators to monitor tuning, display all process variables with six digits
- (9) To reduce changes in process inputs, tune the controller so that the controller output and process variable don’t move
- (8) To get to a higher setpoint faster, tune the controllers so the valve that stops the rise of the process variable doesn’t open till the process variable reaches setpoint
- (7) To avoid the cost of separate isolation valves, use on-off valves as throttling valves
- (6) To save the cost of larger actuators, use piston instead of a diaphragm actuators
- (5) Just in case we expand, choose vortex meter capacity greater than twice max flow
- (4) Just in case we expand, choose control valve capacity greater than twice max flow
- (3) To save energy, allocate less than 10% of the system drop for valve at max flow
- (2) Use advanced process control to eliminate the need to upgrade the instrumentation
- (1) Use Internet of Things (IoT) instead of first principles to solve all control problems
