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The Final Control Element’s Role in the Safety Loop

by Jim Cahill

I used to be one of those who thought of the logic solver piece of a safety loop as being the "safety system." In reality it’s the sensors, logic solvers, and final control elements which make up the safety loop, or safety instrumented function (SIF) in safety-speak.

Tom Jeansonne, a regional sales manager in Emerson’s Valve Automation division, presents a paper at next week’s Emerson Exchange entitled Safety Instrumented Systems, The Role Of The Final Control Element. Tom sets the tone for the importance of the final control element in the safety loop. It exists for the purpose of taking the process to a "safe" state when predetermined conditions are violated.

The final control element or actuated valve typically remains energized for long periods of time in a fixed position. According to Offshore Reliability Data (OREDA), when failures do occur in the safety loop, it happens in the final control element 50-60% of the time. The key is to reduce the Probability of Failure on Demand (PFD) to meet the appropriate safety integrity level (SIL). The standards IEC 61511 and ANSI/ISA S84 defined this risk-based approach to safety.

Tom describes a way to reduce PFD for final control elements through partial stroke testing. As the name implies, the actuator and valve are periodically operated a partial amount to help ensure the valve will perform on demand. This testing process also increases the diagnostic coverage on the final control element while allowing the normal process operations to continue. In turn this can extend the time between scheduled plant shutdowns reducing operating costs and increasing efficiency while maintaining SIL ratings.

With digital controllers like the Fisher Fieldvue DVC6000 and smart logic solvers like the DeltaV SIS system, these partial stroke tests can be automatically performed and data compared and retained. These tests can identify issues like broken valve stems, torque degradation, stick slip, friction degradation, and pneumatic path leakages. Any anomalies can be sent to the operations and maintenance staff as valve stuck alerts, travel/pressure/deviation alerts, and supply pressure alerts. These diagnostics help identify any issues before the final control element is requested by the logic solver to take the process to a safe state.

Tom sums up his presentation with how the Valve Automation group has packaged the DVC6000 with several different types of Bettis, FieldQ, Hytork, and El-O-Matic actuators, and solenoids into a SIL-PAC TÜV and Exida-certified final control element solution.

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September 27, 2006 in Safety | Comments (0) | Trackback (1)

Better Beer Quality by Measuring Dissolved Oxygen

by Jim Cahill

One of the workshops that caught my eye at next week’s Emerson Exchange meeting is Dave Anderson’s Dissolved Oxygen Measurements Improve Beer Quality and Lower Operating Costs. Dave is from Emerson’s Rosemount Analytical division. This probably caught my eye because I’m a fan of quality beer.

Dave helps us novices with the basics like what dissolved oxygen actually is. It’s the concentration of Oxygen (O2) in liquid phase remaining after exposure of gaseous oxygen to an aqueous solution. The process of brewing is aerobic where the yeast requires oxygen to convert the sugars to ethanol in the fermentation process. The dissolved oxygen measurement is important since too much oxygen can create unwanted side effects, including excess Dimethyl sulfide. This compound negatively impacts the beer’s taste.

The Rosemount Analytical Dissolved Oxygen sensors are designed to handle high pressure surges and not be as sensitive to flow rates. Most oxygen sensor can handle a few clean-in-place (CIP) operations which clean and sterilize the process vessels and piping. This sensor was designed to handle more than twenty of these CIP cycles.

Dave mentions the key process areas where brewers should measure dissolved oxygen. These areas include: brewhouse wort kettle, fermentation/aging tank, de-aerator vessels in the packaging area, and the utilities. Also, it is important to develop best maintenance practices to maintain highly accurate measurements over time.

Better control of the dissolved oxygen levels throughout the brewing process has great impact on the quality of the beer produced. And that makes us global beer consumers happy indeed. I hope to see a few of you next week in Nashville!

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September 26, 2006 in Analyzers | Comments (0) | Trackback (0)

Welcome ModelingAndControl.com!

by Jim Cahill

The overall IQ of the blogosphere just went up a few notches. It's great to see Terry Blevins and Greg McMillan collaborating on the ModelingAndControl.com blog.

They are off to flying start to help us better understand process control. As I've mentioned in several recent posts on education, this is one of the most pressing issues facing process manufacturers as automation and control professionals retire.

Terry starts with a post about Control Basics and Terminology. He shares a class he put together around process control complete with tests.

Greg starts with a post, Unification of PID Controller Tuning Rules. Greg offers his top ten reasons to devise your own tuning rule and simulation test.

If these first two posts are any indication of what's to come, then you want to subscribe to their RSS feed. If you're unfamiliar with RSS, give our RSS Start Kit a two-minute peek.

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September 25, 2006 in Education | Comments (0) | Trackback (0)

Managing Your Project Data Flow Requirements

by Jim Cahill

Anyone who has been a project engineer knows that there are some areas of a project with more inherent risk to schedule and cost more than others. Areas like data integration between hardware, software and systems need early attention so that they can be resolved before the pressures of the critical path are felt.

One of the Emerson Exchange papers being presented in the Project Work Processes track is Data Flow Requirements for Main Automation Contractor (MAC) projects. Emerson’s Mike Simpson and Jim Davis from our West Coast Business Partner, Caltrol, convey processes, procedures, and tools for the information formats, milestones, sequences, and timing for smoother project execution.

Mike notes that many of the decisions for standards and responsibilities are made during Front End Engineering Design (FEED) phase. These have major impact on the data exchange processes during project execution. Their recommendation is to set the communications rules during this phase of the project and confirm all the data sources and predecessors.

The key is to designate a single coordinator for all data exchange. This person establishes the data exchange standards including: data types, formats, media, due date, supplied by, supplied to, risks. A database application with milestone alerts can help to issue project controls for completion and near term due exchange alerts and all long term milestones.

When on a project with a new process or process technologies, Mike and Jim recommend testing to avoid surprises. Split this work into two phases with the first phase, a thin slice phase and the latter, the main phase. The thin slice phase lets you test new hardware, control strategies, and/or communications to discover surprises. This testing helps avoid committing your entire project to the new technology and avoid assumed methods of engineering and implementation without assessing how it will work.

Mike and Jim show examples of how this applies in integrating process units and process skids using serial and digital bus-based communications and taking advantage of software tools like Intergraph’s SmartPlant Instrumentation to manage this project data flow.

Mike notes that it really boils down to early involvement in the FEED phase of these MAC projects where it is critical to plan these well-executed data hand-offs.

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September 25, 2006 in Data Management, in Project Services | Comments (0) | Trackback (0)

Distillation Column Energy Savings

by Jim Cahill

I had the chance to catch up with James Beall while he was here in Austin for meetings. You may remember James from an earlier post of a refiner in dire need of process stabilization assistance.

James will be presenting a paper at the rapidly approaching Emerson Exchange meeting in Nashville. He’ll be presenting a short course and two workshops, including one entitled, Coordinated Loop Tuning Saves Energy on Distillation Column. He is co-presenting this with two engineers from the Monsanto Corporation.

The project they profile is on one of their distillation columns. The team started by diagnosing the current performance of the column. They discovered by looking at uncompressed history data that there were problems with several key valves which had excessive deadbands. This caused limit cycling on the level and manipulated flow into the column. This was fixed by installing Fieldvue DVCs (digital valve controllers.)

Distillation Column Loop InteractionAfter getting better performance from the valves from the digital valve controllers, the team attacked the issue of the interactions between the loops on the distillation column. The approach taken was to set a loop tuning sequence and began manual output step tests to detect problems and measure process dynamics.

James used Emerson's Entech Toolkit which performed high-speed, uncompressed data collection and provides an analysis of non-linearities. It also analyzed the process dynamics, calculated tuning, and performed simulations of loop response. Prior to this work each loop had been tuned independently and therefore the process dynamics were not coordinated between these loops.

By manipulating the closed loop time constant, the team was able to coordinate the speed of the loops and determine the critical tuning sequence to account for the process dynamics and loop interactions. The results from this optimized tuning were a 27% reduction in reflux and 5% energy savings from lower steam usage.

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September 20, 2006 in Distillation Column, in Process Optimization | Comments (0) | Trackback (0)

ISA Marketing and Sales Summit—Meeting You Half Way

by Jim Cahill

The ISA put together a marketing and sales summit held for the suppliers of process automation to process manufacturers around the world. Now, if you’re a process manufacturer, you’re probably asking yourself whether or not it’s a good thing for us to discuss how we communicate better with you.

Jane Lansing, the vice president of marketing for the whole Emerson Process Management group, kicked off the morning with a keynote address on how we communicate and perhaps should communicate with you. I hope this post stimulates some of your ideas with comments about how we could do this better.

A key idea Jane raises is how we as automation suppliers in our communications don’t do a good job of thinking about engineers beyond their narrow role as engineers. All of us have multiple roles as business professionals, parents, family members, sports enthusiasts, community volunteers, etc. which shapes who we are. This narrow focus leads to thinking of communications in terms of specs, features, and benefits. Also there's a trend from specialist to generalist among manufacturers with fewer and more time-pressed automation professionals through retirement and reorganization. Much of this expertise has moved to automation suppliers and integrators. Jane describes these trends as creating a situation where suppliers seemingly are marketing to themselves. The language of specs, features and benefits are more meaningful to the experts within the suppliers’ organization than the engineers within the manufacturing organizations.

Jane’s point is that automation suppliers need to try to meet you half way--where we better understand what you are trying to accomplish and the role our automation technologies and expertise can play. This is opposed to throwing a bunch of specs, features and benefits your way and asking you to figure it out (in your spare time of course!)

Looking at automation suppliers collectively, what do you think?

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September 14, 2006 | Comments (2) | Trackback (0)

Optimized Blending Through Better Flow Measurement

by Jim Cahill

In an earlier blending applications post, I mentioned some of the advantages of online/inline blending over traditional, batch-based blending. It’s a process which crosses many industries including refining, pulp and paper, chemicals/specialty chemicals and food and beverage to name a few.

I came across an article, Optimizing blending operations by Julie Valentine, a refining specialist in Emerson’s Micro Motion division. Julie notes that for refiners, the motivation for changes to the blend process are in improved control, improved measurement, improved analyzers and improved optimization techniques. One of the keys is high performance flow measurements of the raw materials to precisely control their flow rate as they are blended together. The Micro Motion Coriolis flow meters are extensively used for both the raw material and final blending product flow measurement. Their 0.1% accuracy couple embedded advanced control in control systems like the DeltaV system, enable blend optimization to be done within the control system.

In the article, Julie describes a U.K. lube blending plant which switched from a sequential measurement system to a flow measurement based system. This switch enabled the raw materials to simultaneously flow into the mixing tanks, increasing the throughput of the operation. The accurate measurement of the raw materials meant that the blend would be on-spec as it was filling in the mix tank, and shortened the overall mix cycle, again increasing throughput.

The Coriolis meters also provide high accuracy density measurements, which was important since blend component pipe headers are cross connected and this density measurement can quickly spot and notify operators of cross contamination which can affect the quality of the blend.

One other example Julie cites is where the blending optimization for the blend of gasoline allows refineries to make use of the blend components available from production and choose the blend which will produce the required specification at the lowest cost, while also managing inventory levels.

The accuracy of the flow measurement is critical to the blend optimizer. Julie cites a study where poor flow measurement with 0.3% accuracy translates into lost profitability of up to $200,000 per year for a 100,000BPD facility. This is caused by the blend optimizer making the wrong optimization decisions based upon the inaccurate data it receives.

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September 13, 2006 in Blending, in Measurement, in Refining | Comments (0) | Trackback (0)

Achieving IEC 61511 Safety Compliance with a Little Help

by Jim Cahill

As the international safety standard IEC 61511 (ISA S84.02 in the U.S.) has provided process manufacturers a risk-based approach to safety in their plants.

Many organizations including Emerson are providing training and project execution services to assist these manufacturers in better understanding and complying with this standard. I’ve mentioned some of the training courses in an earlier safety engineering training post.

Obviously it takes people experienced in process safety to develop this training and execute safety projects. I had the opportunity to catch up with Bob Gale, a certified SIS Consultant and SIS lead in our Refining and Chemical industry organization. He has over 30 years of process automation experience, 20 of these in process safety, and is nationally recognized for his work in the development of the American Institute of Chemical Engineer’s (AIChE) chemical process safety practice guidelines.

Bob was also instrumental in helping the Refining and Chemical become part of Emerson’s global effort to achieve TÜV-certification in Functional Safety Management Systems in accordance with IEC 61511 for management and control of safety instrumented systems (SIS) applications.

Bob recently served as an SIS Consultant for a DeltaV SIS system used in an ultra low sulfur diesel plant application. In this capacity, he and the Emerson SIS project experts work with the manufacturer to verify the appropriate SIL levels and risk mitigation strategies of the safety instrumented system along with assisting the client with the conceptual design of the various Safety Instrumented Functions. Bob also works with manufacturers on all the earlier phases of the safety life cycle, from the Process Hazard Analysis through to Layer of Protection Analysis and SIL Determination.

For those working to achieve IEC 61511 compliance, Bob believes the place to start is with the education on the standard to understand the scope of the safety lifecycle. Of course he also believes you should assemble an experienced project team to help from the up front analysis, through the engineering, installation, commissioning, and ongoing support phases.

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September 7, 2006 in Education, in Safety | Comments (0) | Trackback (0)

Understanding Process Control and Process Dynamics

by Jim Cahill

The need to educate newer process automation engineers has been a continuing conversation among the process automation blogs (examples here, here, and here.)

I caught up with Norm Ito, a variability management specialist who helps process manufacturers optimize the performance of regulatory control and instrumentation using the EnTech process.

Norm feels that the tremendous advancements in automation technology have caused the focus of education to be on the software, displays, and information integration. What has been missing is the focus on the basics of control, including effective loop turning methods and evaluation techniques required to optimize the process.

Through Emerson Educational Services, Norm has been trying to address this shortcoming by teaching a Modern Loop Tuning course. The course is designed for engineers, operations, and maintenance folks involved from design, evaluation, implementation, or tuning of the controls within the process. It begins with a basis for understanding the complexity and interaction of a process, its dynamics, and how to tune the controls to remove process variability. This variability can impact the quality of what’s being produced as well as the stability of the running process.

Norm believes the learning best happens by taking a very practical, hands on approach. His students use dynamic simulators to demonstrate and practice various loop tuning rules and see their impact on the simulated process. Through this process, a better understanding of the process dynamics and loop interactions is developed which is the first step towards selection of a suitable control strategy and tuning parameters.

With this basis of understanding of process control and process dynamics, the ultimate goal is to optimize the performance of the process. Norm and the team of variability management specialists take a holistic view to performance optimization by helping process manufacturers remove constraints and sources of instability though proper process design, control strategy application, effective instrumentation, in addition to this robust loop tuning technique.

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September 5, 2006 in Education, in Variability Management | Comments (0)

The Longest Continuously Operated Refinery in the U.S.

by Jim Cahill

As blogs have brought self-publishing to individuals and their growth has skyrocketed, the next wave--self-published videos--have arrived and even come to our conservative world of process automation.

YouTube and Google Video are two examples of sites where you can upload your videos to share with the world.

I bring this up because I received an email this morning of a video done by Pennsylvania Cable Network with their PCN Tours series. The 52:35 video features a tour of American Refining Group in Bradford, Pennsylvania in the U.S. They are celebrating 125 years as the United States longest continuously operated refinery.

Take a look at 17:45 and 20:15 and you'll see Emerson's DeltaV system in their crude unit control room and reformer control room. It's great that PlantWeb technology could play a role in their success.

As we continue to move forward in this new age of communications, please let me know if your process automation work is highlighted in one of these newer self-publishing mediums like blogs, podcasts, or videos.

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September 1, 2006 in Miscellaneous, in Refining | Comments (0) | Trackback (0)