LNG

I discovered Nick Denbow's Industrial Automation Insider blog this weekend and added it to my list of automation and process industries-related blogs. He had a post about university students studying the feasibility of using liquefied natural gas (LNG) as a fuel source in short sea shipping.

I mention this since I had just gotten my hands on an LNG-related presentation that Emerson's Mark Coughran is giving at the upcoming Emerson Exchange technical conference. You may recall Mark from some of our past process optimization-related posts. Mark's presentation is titled, Solving Loop Interactions in a New LNG Train Using Combined Emerson Tools.

This LNG producer had several key level loops operating in manual mode, which consumed a portion of the operators' attention to maintain process stability, quality of propane and butane, and overall throughput. Many of the flows had large variability and the pressure loops were slow or oscillatory.

These loops included a drum level controller on a heat recovery steam generator, a De-Aerator level controller in the utilities plant, and all the controllers on the Cryogenics units. Mark notes that it's typical when starting a new plant based on a new design that the interactions between loops have not been fully considered and that controllers may be initialized with default values.

The De-Aerator control is critical to boiler production and reliability. The operators were operating this level loop in manual and were constantly fighting interactions between pressures and flows. The controls involve a pressure loop on the low-pressure steam and cascaded flow and level controller on the polished condensate line into the drum surge tank. Mark and the team optimized the performance by tuning the pressure loop first and making its response the fastest. Using the Entech Toolkit to measure process dynamics and to help identify controller PID parameter settings, they were able to tune the loops to avoid oscillatory loop response and separate the dynamics and interactions between loops. After testing the performance, the loops were returned to automatic and cascade modes of control.

In the presentation, Mark will share how they tuned fuel-gas supply pressures and user pressures to hold their setpoints better and not to interact by applying Lambda tuning and slowing down the response of the upstream supply pressure loop. Other process optimization improvements were done to an incinerator airflow loop on a sulfur recovery unit, inlet surge drum level on a fractionator unit, and liquefaction unit inlet flow and pressure controllers.

In each case, Mark presents the simplified piping and instrumentation diagram (P&ID) and the original trends of the loops operating in automatic mode before optimized loop tuning applied. He then describes how the operators expect the process to perform. Next, he shares what process dynamics were measured, and the trends after the new PID parameters were placed in service. He concludes with the results of these changes and the suggested educational course of learning for the engineers and operating staff to maintain optimized loop performance.

The result of this optimization effort was to move all of the controllers into automatic mode and give the operators the confidence to change setpoints and maintain automatic mode even during startup and shutdown sequences. With daily revenues over a million U.S. dollars, these improvements in throughput, quality, and overall process stability quickly paid for the work performed.

If you're coming to the Emerson Exchange and are responsible for the performance of the loops in your plant, this is a presentation you'll not want to miss.

MP3 | iTunes

Emerson South Korea general manager, Patrick Deruytter was in Austin recently. You may recall Patrick from earlier posts about large FPSO projects being performed there. He has an upcoming presentation at FLNG Project Advancement on accelerating FLNG (floating liquefied natural gas) project delivery using a main automation contractor approach.

For those unfamiliar with FLNG, it borrows the idea of floating production, storage and offloading by building a liquefied natural gas facility on a tank ship. From Wikipedia:

LNG is principally used for transporting natural gas to markets, where it is regasified and distributed as pipeline natural gas.

According to a World FLNG Market Report:

The IEA [International Energy Agency] forecasts annual growth in natural gas supply will average 1.6% from 2006 to 2030. By 2030, natural gas will account for 23% of total worldwide primary energy supply. The difficulties in progressing onshore projects in LNG has driven the adoption of FLNG which now offers an increasingly important method of bringing gas from stranded reserves to the market.

I saw an advanced copy of Patrick's presentation. In it, he notes that process automation touches every element of an FLNG vessel including production units, hull, ballast, power generation and distribution, fire and safety systems, and information management systems (IMS).

Automation typically accounts for only 3% of the capital costs for an FLNG project, but is critical to its successful operation. The automation technology and project execution methodology play a large role in determining how successful ongoing operations will be.

The Construction Industry Institute (CII) described a PEpC (Procurement, Engineering, procurement and Construction) process that can produce:

...savings in time between 10 and 15 percent and savings in total project labor cost between 4 and 8 percent were possible.

CII describes how the PEpC process does this:

...utilize supplier expertise in all phases of the project life cycle by developing an advance procurement strategy and reaching agreement with suppliers on strategic procurement items and/or systems prior to the associated project engineering activities.

Patrick described how this process works on FLNG processes. Working as a main automation contractor (MAC), his team helps develop the execution plan and schedule, procurement specifications, design and execution specifications, device communication protocols, power/heat/loading estimations, measurement technologies, and role/responsibility matrices--all in the front end engineering design (FEED) phase of the project.

Post-FEED, the team develops cost estimates, clarifies scope of MAC supply for the engineering and procurement construction (EPC) contractors, and develops control system detailed design and integrated tests for long lead-time equipment such as compressors and tank storage.

He describes the role automation technology can play. A distributed modular approach for the automation reduces control room footprint, reduces cable size and weight, and facilitates modular design, pre-assembly and test which helps reduce the project timeline. Wireless instrumentation can reduce the project tasks required by eliminating power and grounding efforts, I/O and cabinet design, installation, and commissioning.

Also, electronic marshalling reduces design, engineering, drawings, cabinets and the associated incremental installation and commissioning effort required.

These technologies combined with a structured project execution methodology help to reduce the overall project risk and cost. It also provides the vessel's staff with the control, safety, and information required for efficient, ongoing operations.

The key in accelerating project execution for FLNG is in deploying recent technologies such as wireless and electronic marshalling combined with an advanced project execution model such as MAC.

MP3 | iTunes

I saw in my Sound Off blog RSS feed that Dan Hackett, part of Emerson's Daniel Measurement and Control business, did a podcast interview with Walt Boyes. The 25-minute podcast is on some new Daniel Ultrasonic flow measurement technology being introduced at the upcoming Emerson Exchange.

Dan starts by describing how these critical ultrasonic flow measurements work. I thought Dan's explanation was more understandable than my Guadalupe River rafting analogy in an earlier post. If there's no flow, the time it takes the ultrasonic pulse to travel across the pipe from one side upstream to the other side downstream and back is the same. As the flow increases, the time difference between the travel across the pipe each way increases--since one way the pulse goes with the flow and the other way it goes against the flow.

Dan described how some of the Daniel liquid and gas ultrasonic flow meters have 4 measurement paths to get different measurements at different points to integrate an average flow. The average axial velocity multiplied by the area of the pipe gives the uncorrected volume flow rate through the ultrasonic flow meter.

He described how these critical meters are used primarily in custody transfer applications. For those not familiar with the term, custody transfer is like the cash register where the possession of feedstocks, intermediates, and finished products changes hands between companies, governments, or countries. The measurements must be highly accurate and agreed to by both parties.

As Walt pointed out in one of his questions, ultrasonic flow measurement, because of low-pressure drop and high turndown capability, can handle a wide range of applications from very high temperatures to very high pressures. Dan described an application in gas measurement where this technology was being applied. Offshore and onshore gas production measure high-pressure natural gas--usually at the custody transfer point with the gas distribution pipelines. High volume consumers of natural gas, such as power plants and aluminum producers will meter the incoming natural gas. Also, many municipal districts measure the incoming natural gas before it goes into their distribution systems for the area businesses and residences.

For liquid custody transfer, crude oil production and processing are typical applications for ultrasonic flow measurement. Dan mentioned that right now it's mainly used in the feedstock and finished products areas of refineries, and less so in the process itself, where other flow measurement technologies are typically applied. In a refinery, the custody transfer surrounding the incoming crude and the refined products such as gasoline, diesel fuel, and kerosene are good applications for ultrasonic flow measurement. A final application Dan notes was liquefied natural gas (LNG) facilities where the incoming natural gas is measured and also in regasifiers where the liquid is converted back to high pressure gas for final distribution.

The new ultrasonic flow meter transducer being shown at the Emerson Exchange extends the temperature and viscosity range to address more applications like the heavy crudes found in the oil sands and oil shales. Typically, conditioning processes were required to reduce viscosity and or temperature, which add operational costs to the custody transfer measurement process.

One of the big enhancements Dan mentioned was on the software side, where diagnostics now embedded expert knowledge to identify conditions such liquid fractions in gas and pipeline deposit layer buildup. In oil & gas applications, the first case helps spot expensive liquid condensate giveaway. Accumulated buildup inside of pipes impacts the integrity of the custody transfer measurements. When these diagnostics are connected to the Daniel CUI 5 or AMS Device Manager software, operators and maintenance personnel are notified of a problem immediately and offered suggestions for corrective action. The CUI 5 baseline viewer provides a consolidated view for monitoring performance within pre-set ranges.

I found the podcast to be 25 minutes well spent as well as the recent email newsletter in getting up to speed on the latest developments in ultrasonic flow measurement and good application fits.

MP3 | iTunes

A 2004 study by the U.S. Department of Energy shows continued global growth for the like Liquefied Natural Gas (LNG) industry as one of the sources to meet global energy demand. Our Micro Motion division recently announced that Coriolis technology is ideal in cryogenic mass flow metering applications like LNG (-153.1 degC). LNG can be stored and transported much more efficiently in a liquid state than in a gaseous state.

I came across a Chemical Engineering magazine article entitled, Flow Measurement in Bitter Cold: How to Use Coriolis Meters in Cryogenic Service which better describes why Coriolis technology works well in the bitter cold of more than -100 degC.

The authors, Emerson's Tim Patten and Keven Dunphy describe how harsh temperatures pose problems for many flow measurement technologies. These problems are related to mechanical parts, wetted seals, and materials of construction with poor impact strength. And from a measurement standpoint, it's expensive to keep the cryogenic fluids cold, so they are kept slightly below their boiling points. As the fluid flows past an obstacle such as a valve, flashing can occur. Pockets of gas form in the liquid making flow measurement difficult at best.

Tim and Keven point out that Coriolis technology is well suited since it has no moving wetted parts, nor temperature sensitive materials, and it has the accuracy required to satisfy custody transfer regulations. They recommend careful attention be paid to the pressure drop across the meter to avoid flashing by increasing the meter size. Their rule of thumb:

...the difference between the discharge pressure and liquid vapor pressure at the fluid temperature should be maintained at a factor of at least three times the pressure drop across the meter.

The article also provides tips on density measurement limitations, insulation best practices, and non-linear compensation. These tips apply not only to LNG but other cryogenic applications like liquid helium.