Emerson Process Experts

My colleague, Deb Franke, pointed me to a great article in her RSS feeds. The ChemicalProcessing.com article, Innovative Fixes for Saving Energy in Plants, describes some ideas to help reduce plant energy costs. Although energy costs have come down in recent weeks, they are still one of the largest controllable costs as I have mentioned in an earlier post.

The article points out innovative solutions including dual drive pumps, variable speed motors, water/glycol systems, automated blowdown systems, low BTU sweep gas and wireless sonic leak detectors. Give the article a read if you think some of these might apply in your plant processes.

I forwarded the article to Emerson's Lou Heavner, whom you may recall from earlier advanced process control application posts. I asked what new and innovative, energy saving ideas he might have to share.

Lou had a couple of ideas. But, being the modest sort, he added a caveat that they may not qualify as new or innovative. To me, if you're looking for ways to reduce your energy costs and you didn't consider one of these, it's definitely new.

Lou's first thought was on distillation processes. He writes:

In distillation, relative volatility and hence difficulty of separation tends to improve at lower pressure. When cooling water and/or air are used to condense the overheads, the pressure is often tightly controlled for stability in the face of changing ambient conditions and the extra cooling capacity available during nights or colder weather is not fully utilized. If pressure is allowed to "float" and as much condensing occurs as is possible, pressure will fall in the column and separation will normally improve. This means less heat is needed in the reboiler and hence energy savings when using steam or some other "costly" utility stream to provide reboil.

His second thought was around combustion processes burning fuel gases with changing compositions. Lou notes:

In heaters or boilers where the gaseous fuel consists of a hydrocarbon mixture of varying composition (like refinery fuel gas), a change in fuel can have an effect on the heat generated by combustion and on the excess air level in the flue gas for a given fuel flow rate. Sometimes, if variability of the flue gas justifies, companies will install fuel quality analyzers that measure composition or heating value. In many cases, the same thing can be achieved and better flow control at the same time, by using a Coriolis mass flow meter. It turns out that the mass flow of a hydrocarbon and the "btu" flow are directly related since both are related directly to MW.

You can't do this with PT compensated flow, because it knows nothing of MW. But Coriolis measures mass directly and can be used to reduce variability of "btu" feed to the burner. This can be dramatic where the fuel gas varies significantly. It is not a good solution if the "btu" content changes due to the presence of inerts (like N₂ or CO₂) or non-hydrocarbons (like H₂ or CO), since they do not exhibit a linear relationship between mass flow and "btu" flow. But if they are present in small quantities and don't vary much, the concept can still work.

On processes that degrade the "quality" of energy, Lou shares:

Saving energy can be as simple as minimizing thermodynamically irreversible operations. Mixing, heat transfer, and throttling of process flows are common examples of irreversible processes. In general, industry should avoid over-purifying/heating/cooling followed by mixing or blending to achieve the target composition/temperature. Process design should attempt to get as much work as possible out of utilities and recover as much heat as possible. Pinch technology is one approach to heat integration design used by process engineers. Of course, there are practical limitations like capital cost considerations, dynamic response and controllability, and availability/reliability of utilities, especially ambient cooling.

Also, control valves should be selected to minimize throttling losses and allocation and valve position should be used to minimize overall pressure drop in systems like utilities where resources are shared by different units or equipment. For example, if multiple reactors are cooled with a shared refrigeration unit, the coolant temperature setpoint can be raised (reducing the refrigeration required) until one of the user's demand exceeds the capability of its corresponding control valve to deliver.

Let's hope that something between the ChemicalProcessing.com article and Lou's thoughts provides you at least one idea that can help reduce your plant's energy bills.

Tags: advanced process control | APC | distillation column | fuel gas | mass flow meter | control valve | energy costs | plant energy |

August 12, 2008 in Boilers, in Distillation Column, in Energy Management, in Final Control Element, in Measurement, in Process Optimization | Comments (0)

Two very knowledgeable people in safety instrumented systems (SIS), Mike Boudreaux and Riyaz Ali, shared with me the story behind the recent news about the DVC6000 SIS digital valve controller (operated by 4-20mA) being certified to be compliant with IEC 61508 for use up to SIL 3 safety instrumented functions (SIF).

With this certification, DeltaV SIS logic solver's HART two-state, 4-20mA output and the Fisher DVC6000 SIS without any additional solenoids or other auxiliary devices can be used for SIL 3 applications. This configuration provides capturing trip events during safety demand, which provides crucial data for reliability and analysis by safety engineers of event. It's also helpful information for regulatory audits.

Now, I used my trusty friend Google to learn more about the HART two-state channel and found this page in DeltaV Books On-Line on the function block in the logic solver that helps make this happen. Basically:

…DeltaV SIS Logic Solver Digital Valve Controller (LSDVC) function block provides an interface to the DVC6000 SIS for safety shutdown and for partial stroke testing. The HART Two-state Output Channel provides the control signal and the HART communications path to the digital valve controller. You can configure the output channel to have an OFF_CURRENT of 0 mA or 4 mA. The control signal can command the valve controller to the tripped state regardless of the configured OFF_CURRENT value. Using an OFF_CURRENT value of 4 mA allows HART communication between the Logic Solver and the valve controller whether the valve controller is in the normal or the trip state. When the OFF_CURRENT is 0 mA, the power is removed entirely when the LSDVC function block drives the channel Off.

Mike noted that continuous diagnostics is possible because the valve closes when delivered a 4 mA signal. The DVC6000 SIS records the results of a demand event by logging all the results of travel and pressure data points in the microprocessor memory. This event log is critical for plant personnel, reliability engineers, and auditing authority to understand the final element status before and after the trip or demand event. Before the new certification was obtained, diagnostics would be lost on shutdown because the signal to the DVC would be 0 mA.

These on-line diagnostics coupled with partial stroke testing can be automatically initiated from the DeltaV SIS logic solver. This means that the final control element is periodically checked to help protect against spurious trips and to test for demand availability. The operator can also manually initiate these partial stroke tests from operator faceplates. The DVC6000 provides pass/fail status back via HART digital communications for alarming and historical event recording.

Riyaz pointed out that Type B devices (generally microprocessor-based) the IEC 61508 international safety standard (part 2, table 3) mandates redundancy in SIL 3 applications. This means the DVC6000 SIS connected to the DeltaV SIS HART two-state channel is suitable for SIL 1 and SIL 2 applications without redundancy, but for SIL 3 SIFs, IEC61508 mandates a full redundancy or hardware fault tolerance of one.

Achieving this certification helps reduce the components in these SIFs and increase the diagnostic coverage and capture of historical SIS information on demand.

Tags: IEC 61508 | IEC 61511 | logic solver | safety instrumented system | SIS | safety integrity level | SIL |

August 8, 2008 in Abnormal Situation Prevention, in Final Control Element, in Safety | Comments (0)

I've seen a number of stories about applications for wireless transmitters, but not for wireless valve monitoring. That all changed earlier this week when I received a Twitter direct message "tweet" from a colleague. For those not yet on Twitter, it's an option to send direct communications, unseen by others, when you have a reciprocal follow relationship with one another. It's like instant messaging but comes with the stream of others' short notes in your follow list. I have it set up where these direct messages come as text messages to my phone as well. I mention all this because it's another way communications are rapidly evolving from the world of email in which we've lived over the past many years.

The Valve magazine article, The Reliability and Security of Wireless Valve Monitors, is written by Emerson's Kurtis Jensen, an instruments product manager for Fisher and Valve Automation products.

One of Kurtis' closing paragraphs provides the primary reasons process manufacturers may consider wireless monitoring on some of their valves:

Most operations have a large number of "blind valves" that are either manual or semi-automatic but provide no valve position feedback, normally because of cost or location. As such valves age, their performance can degrade to sluggish, slow operation. The true position of the valve may be questionable, and operators have to start visiting certain trouble-prone valves to verify their position. Where valve position monitoring does not currently exist, wireless monitoring is a great way to start using this technology with minimum risk."

If you've ever come across the ModelingandControl.com blog, you'll know that sluggish valve performance is a contributor of deadtime that impacts overall control performance and plant efficiency.

As with any newly introduced technology, its ease of use is critical in its adoption. Kurtis notes that an upcoming release of a wireless position monitor product is non-contact and does linkage-less position sensing. After attaching and calibrating the device, it sends valve position information wirelessly across the self-organizing network to the automation system or asset management software.

He discusses some of the reliability and security aspects that I've described in earlier posts. The reliability aspects are largely to do with the self-organizing nature of the WirelessHART field networks. Alternative communications paths are taken from the devices to the wireless gateway when permanent or temporary obstacles happen.

Security is addressed in the WirelessHART standard and described by Kurtis through its changing encryption, message authentication, data verification and frequency hopping.

An important point made is that, "…wireless should not be viewed as a direct replacement for wired instrumentation." It's well suited for:

…hard-to-reach locations, in areas hazardous to plant personnel, where power does not exist and where running wires is not allowed or prohibitively expensive, to name a few.

This certainly opens up opportunities in many facilities to reduce the number of blind spots the operations staff face that must be covered by periodic manual inspection. The opportunities for wireless monitoring may be with the valves were early notification of performance degradation can help avoid overall poor control performance.

Tags: valve monitoring | valve position | WirelessHART | deadtime | self organizing network |

July 30, 2008 in Final Control Element, in Technologies, in Wireless | Comments (0)

Recently, Emerson's Fisher Control Valve and Regulators division announced that several lines of control valves received SIL 3 certification for on/off operation per the IEC 61508 international safety standard. Safety valves with digital valve controllers have been certified for many years, but these are the first control valves to achieve this independent third-party certification. Up to this point, the prior use methodology has been required to demonstrate the control valves are "proven in use" for safety applications.

I caught up with Andy Evans, a product manager in Fisher's European operations. Andy shared with me the motives behind pursuing this certification:

…the architectural constraints in IEC 61508 state that a final element needs a Safe Failure Fraction of greater than 60% to be used in a SIL 2 loop as a single device. The generic data, which was being used prior to having specific FMEDA (Failure Modes, Effects, and Diagnostic Analysis), was less than 60%.

Andy also noted that process manufacturers were increasingly requesting the certification given the efforts required with the "prior use" approach. The team decided to pursue certification for the Fisher GX, Vee-ball, easy-e and HP valve families.

The valve technology organization worked with the third-party safety professionals, Exida. They followed the basic process outlined in the IEC 61508 standard. The team went through an initial documentation plan including verification and validation (V&V) followed by the detailed writing of the safety requirement specifications (SRS). These activities completed the analysis phase of the safety lifecycle.

They went through the FMEDA for the mechanical portions of the actuators and valve bodies based on their physical properties and field experience. This analysis looks at the effect of each component in the valve failing in its worst possible way and then categorizing that failure.

Exida has a database of frequency of failure for each type of component. These failures are categorized into safe & dangerous (dangerous meaning stopping the valve moving to its safe state) and detected & undetected.

After the FMEDA analysis was performed, functional tests (integral), conceptual design, and detailed design assessments were done.

The final steps on the path to certification were a thorough evaluation of the engineering development process and documentation assessment for design modifications, change request processes and impact analyses.

Having these control valves certified for up to SIL 3 safety instrumented functions provide process manufacturers great flexibility in the selection of final control elements for their IEC 61511 safety compliance efforts.

Tags: safety integrity level | SIL | IEC 61508 | IEC 61511 | safety requirement specification | SRS | safety lifecycle | FMEDA | safety instrumented functions |

June 25, 2008 in Final Control Element, in Safety | Comments (0)

I read Siemens' Charles Fialkowski's latest post, Introducing a non-redundant, redundant SIL 3 solution? about their SIL 3 HART I/O card. He discusses how technology has changed where newer SIL-3 rated safety instrumented systems (SIS):

...don't require redundancy to achieve high levels of safety. In the past, safety systems required dual, triple or even quadruple redundancy just to achieve high levels of safety.

He points out that advances in technology have allowed diagnostic coverage not possible in earlier SIS designs. He closes his post:

Another common misunderstanding is how these systems address field redundancy (sensors and final control elements). While I can't speak for the Emerson or Yokogawa system, I do know for a fact that the new Siemens HART analog input module handles redundant field devices just like any dual, triple or quadruple redundant system would.

I thought I'd give the Emerson perspective so I caught up with DeltaV SIS product manager Mike Boudreaux. He first pointed out that DeltaV SIS has HART I/O and the DeltaV SIS logic solvers are SIL3 certified in simplex (non-redundant) mode and have been since DeltaV SIS began shipping in 2005. Other safety instrumented systems also accept HART I/O, but only to pass-through the HART data to asset management systems. DeltaV SIS makes this HART status information available in the logic solver.

Mike noted that only the analog, 4-20mA process variable (PV) is used for the safety instrumented function (SIF). The digital HART PV's are not accessible for use in SIFs, but the device status provided by the HART digital communications protocol is passed along with an analog input in DeltaV SIS. If a HART transmitter detects a problem, the status for an analog input will become "Bad." Conditions for a Bad status include earth leakage detection, loss of HART communications, device malfunction and device fixed-loop current to name a few.

This Bad status can be used in the logic solver. For example, in a multi-transmitter SIF, a voter block can be configured to ignore an input value if it is Bad. In accordance with the international safety standard IEC 61511, this capability can be used to provide continued safe operation of the process while the faulty part is repaired. DeltaV SIS will alert operations of this problem so that the device can be maintained in the specified mean time to repair (MTTR). Alternatively, the voter block can be configured to treat a detected failure as a vote to trip, which provides increased safety.

When a HART device detects a problem, an alert is displayed on the DeltaV operator station. SIS faceplates and detail displays for HART devices help operators view and manage HART device alarms.

DeltaV SIS also uses the HART communications protocol to enhance partial stroke testing. It validates the operation of the final control element—the most critical and most likely to fail in a safety instrumented function. The logic solver can generate HART commands to initiate a partial stroke test in a digital valve controller. The operators can initiate partial stroke tests manually from their operator workstations or they can be scheduled to occur automatically based on the specified test interval. The results from these tests are captured and integrated with the system event history. An alarm can be generated if a partial stroke test fails, alerting maintenance that there is a potential problem with a valve.

This diagnostic coverage and information feedback to operations provide process manufacturers better tools for compliance with the IEC 61511 safety lifecycle compliance efforts.

Update: Welcome readers of Gary Mintchell's Feed Forward blog. Thanks for the shout out, Gary!

Tags: HART communications | IEC 61511 | safety instrumented system | safety instrumented function | mean time to repair | safety lifecycle |

June 9, 2008 in Abnormal Situation Prevention, in Final Control Element, in Measurement, in Safety | Comments (0)

In several parts of the world including North America, Emerson Process Management sells some of its products and services through local business partners. I came across a great Pulp & Paper magazine article, Control Valve Management Can Pay Off Big, written by Jeff Klatt. Jeff is with one of these local business partners, R.E. Mason.

Jeff recounted his experiences as a large paper mill's asset manager. What struck me about the article were not the technologies they ultimately applied, but rather his systematic approach to process improvement. I'll highlight some of the steps he recounts in the article to see if they might spur some ideas for improvement in your operations.

Jeff cited a study conducted by Emerson's Fisher Valve business that found that 80% of the control valves used by process manufacturers were not operating within their optimum parameters. Getting process improvements by addressing these was a large part of last week's post, Start with the Basics to Reduce Process Variability.

He described his initial step:

It seemed logical to first get acquainted with the valves in the mill and understand their roles in the papermaking process. One-by-one, I visited valves throughout the three main sections of the mill -utilities, fibers and product (papermaking) - documenting every one and building a personal database. Identifying, locating, and visually inspecting nearly 1,600 control valves in the mill turned out to be a monumental task that took months to complete.

Through this tedious process, he also engaged operations, which:

…explained which control loops had the greatest effect on product quality, productivity, and safety/environmental considerations. This knowledge was essential in establishing the most important valves, and in the end about 25% of all the valves were prioritized as critical to the mill's mission. These became the valves on which the majority of maintenance attention was focused.

As is often the case, this tedious work lays the foundation for future savings. He also had all the storerooms spare parts identified, tagged and catalogued. This effort allowed greater use of existing stock and fewer purchases of new parts, which improved the mill's working capital. In one year alone, 20 good control valves taken out of service and put into one of the storerooms were returned into service saving $55,000 (USD) in cost.

The prioritization of the critical control valves also provided focus on where to apply the technologies to improve the performance of the process. Jeff and team used the Flowscanner tool to find out more about the condition of the highest priority valves to direct the maintenance efforts. Also, digital valve controllers were added to these critical control valves over time to provide real-time diagnostics with the AMS software to begin a program of predictive maintenance. A valve's signature can be compared with its baseline performance to identify problems. These can be addressed before actual failures or variability-creating conditions occur. Jeff's team documented $50,000 a year in maintenance cost savings.

Jeff highlighted other savings such as a valve variability problem on a CIO2 flow valve being identified and addressed resulting in an annual savings of a $140,000. Another was documenting the useful lifecycle extension of 162 tested valves by an average of two years. Calculated cost savings were $86,000.

While the savings are impressive because they reoccur over time, the approach is what I found instructional. It started with a commitment to focus time and energy on these control valves because of their critical role in the process. Next was the discipline to analyze the current state and work with operations to identify the most critical control valves. This process laid the groundwork for the application of some of the technologies described to achieve lower costs and greater efficiency. From Jeff's quantified results, it appears this focus paid dividends.

Tags: pulp & paper | digital valve controller | DVC | process variability | control valve | valve maintenance |

May 23, 2008 in Asset Optimization, in Final Control Element, in Plant Equipment, in Pulp & Paper | Comments (0)

I received an email with a great question to an earlier post, Improving Local Control around Safety Shutdown Valves. The question was:

Can you provide more information on your Local Control panel with Safety Shutdown Valve that haves a quick exhaust systems; can the partial stoke test not close the valve do to differential pressure on the quick exhaust system. Also if a shutdown signal is given during a test will it close the valve?

I spoke to Riyaz Ali, who shared his expertise in the earlier post. Here's his great answer in its entirety with picture and hyperlink added by me:

It is true that use of quick exhaust valve (QEV) on large valve with DVC6000 SIS for partial stroke test may dump large air during test. Generally, QEV operates on water column pressure differential and are sensitive. However, we recommend using volume booster on those applications where stroking speed is concern. One may argue that Volume Booster is for "Fill" time and not for "Exhaust". However, we have done test in the lab and established that volume booster will be much better pneumatic accessories, specifically when used with DVC6000 SIS for partial stroke test without causing instability in the operation during partial stroke test and as well meeting stroking speed requirements.

The picture illustrates a schematic of a large spring-return piston actuator with a DVC6000 and a volume booster to achieve a stroking speed requirement of less than two seconds.

During PST test, if demand arises DVC6000 SIS will take valve to safe state.

Here is more information about the LCP100 (Local Control Panel) for your perusal.

I hope that pulling this process safety-related question out of the realm of email into the open might help someone else with similar questions.

Update: I'd like to thank commenter JM for pointing out my LCP100 hyperlink going to the wrong spot. I've fixed. Thanks, JM!

Tags: safety instrumented system | SIS | process safety | safety shutdown | quick exhaust valve | QEV | piston actuator | volume booster |

April 29, 2008 in Final Control Element | Comments (1)