Power control joins process control to aid energy efficiency

Better energy efficiency is possible in many process settings, devices and facilities. Here's how experts target applications, coordinate personnel, and use advanced process control (APC) for the most benefits.

By Jim Montague

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There's more than one way to skin a cat, but there are thousands of ways for process applications to get more efficient and save energy. Because gains are possible in so many production stages, settings and components, they require thoroughly investigating individual applications, focusing on requirements needed to implement potential savings, and coordinating staff to maintain them.

Of course, the search for efficiency unfolds against a backdrop of rising and falling energy prices, logistics and availability issues, as well as standards and regulations mandating increased energy conservation, such as ISO 50001 on site energy management and the European Union's 2020 energy strategy for reducing greenhouse emissions. However, even though fuel and power have been less expensive lately, most users now seem to have it permanently on their do-more-with-less radar. Rules aside, this is likely because they have the right software and other tools to make managing energy a true contributor to their bottom lines.

"Most energy efficiency efforts were historically driven by price shocks, but it's different now because we've reached a point where metering is part of the whole manufacturing process. There are more—and more accurate—meters, not only on pump controls and flowmeters, but also on more electrical equipment," says Bruce Billedeaux, senior consultant at system integrator Maverick Technologies, a Rockwell Automation company. "Previously, there was just an electric meter when power came into the building, but now the whole energy stream is metered.

For more, take a look at Control's list of energy efficiency tools from The U.S. Dept of Energy, EPA, among many others.

"For example, there used to be many unmetered valves, but now every variable-speed drive (VSD) has a meter that can show energy consumption. Onsite and close-to-real-time process controls have advanced enough that they can be used for energy monitoring and management, too. Previously, orifice plate flowmeters with DP sensors were only ±5% or ±10% accurate, and they weren't accurate enough for energy metering. But now we have magnetic and transit-time ultrasonic flowmeters with better than 1% accuracy, and they can be used to measure energy, too."

Billedeaux adds, with the belief that natural gas prices will remain historical low for a decade or more even if demand grows, there's increasing interest in using it instead of electricity. "This is obvious for thermal applications, but there's also interest in using natural gas for prime movers and onsite generation," he explains. "With low cost gas, and coincident thermal demand, co-generation has great prospects."

Michael Robinson, national marketing manager for projects, solutions and services, Endress+Hauser, adds that, "Implementing energy efficiency in process automation can be a difficult business decision to champion because new and added measurement devices are often needed, and that means increased technology migration and installation costs, which is why many projects don't get funded during customers' budget processes. This is unfortunate because in energy-efficiency projects with advanced process control (APC), for example in product dehumidification, these types of projects yield double benefits, such as consumption of less BTUs of heat and providing users more direct control of the moisture content in the produced product. For instance, if the customer contract states that a specified product will have no more than 20% moisture, we can now help them get to 19.9% instead of the 17% they are currently operating at. As a result of often prohibitive installed costs, we typically assist with a lot of micro projects to prove out the assumptions of energy efficiency programs, but often these projects fail to produce the necessary internal rate of return on the capital invested versus what other capital investments can yield, and these projects find no internal champion in the organization and get shelved."

Renovation windows

No doubt one of the most popular times to seek and add energy-saving solutions is during periodic renovation and migration projects. As part of its own ongoing savings program, MOL Group recently improved energy efficiency and process stability at its up to 12-million-m3/d gas distillation plant in Algyõ, Hungary, by upgrading its distributed controls to Emerson Automation Solution's DeltaV process automation system (Figure 1). MOL also implemented DeltaV's embedded APC by adding its SmartProcess Distillation Optimizer software that enabled model-predictive control for the plant's distillation columns, simplified installation, and eased operator adoption. This improved control and performance of Algyõ's gas fractionation section, and reduced MOL's energy costs by €1.2 million annually.

"Our experience shows distillation columns are highly interactive, multivariable processes that are difficult to control, and so DeltaV was customized for us," says Attila Bodócs, production chief at MOL. "DeltaV, its embedded APC tools, and its engineering/consulting services were instrumental in helping MOL achieve such a significant efficiency improvement.”

Bodócs reports that SmartProcess automatically adjusts key flows on the plant's column, which enables MOL to make product more reliably and safely. In fact, as soon as APC was commissioned on the first column, MOL began generating benefits, including ensuring that product quality more closely matched customer specifications without using excess energy. So far, Emerson’s distillation solution was applied to five of the plant’s six gas distillation columns. Hot oil consumption was reduced 40%, and operational stability improved as the process automatically corrects variations. Also, operator workloads were reduced because there's is no longer a need to make small manual adjustments, which were previously necessary to keep the column operating at product quality limits.

Bob Sabin, consulting engineer with Emerson's Industrial Energy Solutions Group, adds that, "Many energy efficiency tools have existed for a long time, but lately their costs have been coming down, which means energy doesn't have to be looked at in a vacuum anymore, but can be just another key performance indicator (KPI) in a good manufacturing operation. More of our customers are considering energy along with their other KPIs, and it's one that can be easily affected by local operating decisions, more so than items like raw material costs. If your site has good reliability, availability and energy control, then it's more likely you're going to outperform your industry peers."

Sabin adds that most energy-intensive applications like boilers, fired heaters and distillation columns operate with single-loop input controls and computers, which keep them running fully automatic for optimal throughput, stability, quality and safety. "What's changed is that control blocks and functions are now more straightforward to use, so engineers need to know their controls can benefit from standardized hardware, PCs, networking buses and more mature software, and that their closed loops can talk fast enough to incorporate energy, too," he says.

Likewise, Robin Moulder, senior engineer at NRG Energy, and Ewa Michalowski, senior project manager at Schneider Electric just began replacing the oil igniter controls on the coal-fired Unit 1 at NRG's Big Cajun II power plant in New Roads, La. This igniter routinely starts Unit 1 in response to local electricity demand. The 35-year-old power plant has three units and is rated at 1,708 megawatts (MW).

2016 State of Technology: Latest trends in power systems

All three units were designed to burn Powder River Basin (PRB) sub-bituminous coal. Unit 1 and Unit 3 presently burn PRB coal, but Unit 2 was converted burn all natural gas and is no longer coal-capable. The igniter on Unit 3 had been upgraded to using natural gas a year earlier. Replacing the igniter's controls requires custom cabinets and I/O, new logic for controllers, factory acceptance tests (FAT), installation, testing and commissioning.

"We had to convert Unit 1's igniter so it could burn natural gas," says Moulder. "It used to burn only diesel fuel oil, and it was controlled by Foxboro I/A and some PLCs for local functions, such as outputs to valves and lights. We needed to go to natural gas as the start fuel, and control it with Foxboro I/A with remote I/O, so we wouldn't have to wire as many field devices and I/O points back to the relay room. Because our plant is 35 years old, this room is under the control room, and all devices were originally wired to it. Now we only need wires going to our valve-control racks, which is a more efficient use of our factory-assembled skids and racks. We also typically use fiberoptic cabling to reach more remote systems like our burner management system (BMS) and distributed control information system (DCIS)."

Dr. Peter Martin, vice president of business value consulting and Edison master at Schneider Electric, explains, "When you go back 15 years, the price of power was consistent over six months to a year. However, deregulated grids and competition varied supply and demand over those connections, and this created a relationship between price of electricity and consumption. This created a need for combining process and power control, and adding them to energy pricing models."

Martin adds that Schneider Electric's combined control solution is its year-old Integrated Power and Process Management (IPPM) program, which manages energy consumption by balancing the three critical variables of energy, raw materials and production value, which is the actual value of an end product at the time it was produced. “All three variables are closely related, which means there can be great variation in production value based on when products are made," says Martin. "The right discussion becomes what are we doing in real time to be effective, and what can still be transactional? Monthly data isn't good enough anymore, so we're also moving to real-time accounting and data analysis."

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