Person using touch screen

Engineers can use the CompresXpress touch screen function to access compressor functions and operations.

Increasingly, natural gas pipeline operators are looking for new technologies that can help improve efficiency and increase throughput. At the same time, they are scrambling to meet new regulations while maintaining profitability.

To help gas unit control operators meet these goals, two companies have combined two cutting-edge technologies that optimize compressor efficiency at far less cost and effort than other options. The new software package includes eRCM, a model-based technology developed by ACI Services, Inc., that allows compressors to run up to their full load capacity, safely; and the CompresXpress unit control panel (UCP) developed by Control Systems International, Inc. (CSI).

The goal here is to describe how operators can use the new combination of technologies to keep their compressors running safely, longer, and with more total throughput.

Reviewing your options
Some gas compressor operators have stopped trying to maximize compressor performance and are reaping significant benefits. Their compressors are running longer, with less downtime, greater throughput, and higher efficiency. It may sound counterintuitive, but it works.

Most large gas transmission companies use custom-programmed PLCs to control their units along thousands of miles of pipelines. The giant engines that power the compressors along these pipelines are usually fueled by the product in the pipeline, whether it is natural gas, natural gas liquids, or liquefied petroleum gas. So, it makes sense that if the compressors and engines powering them are operating efficiently, there’s more to sell and more profit to be had.

The problem is that many operators attempt to gain that increased throughput and efficiency in any of several counterproductive ways:

• Push each compressor to its maximum operating level until the piston rods and crosshead pin bushings fail; repair or replace the unit; do it all over again.
• Run compressors below full load. It keeps everything running, but it only increases throughput and efficiency by avoiding downtime.
• Painstakingly calculate by hand the optimum operating characteristics of each compressor so that they run safely. Then keep recalculating those characteristics as the operating conditions change.
• Develop specialized, custom programs for PLCs that perform all those calculations continuously, which, while doable, has limits because the math necessary to do this job most effectively is too advanced to run on a PLC.

The first option is costly. The second option is less costly, but it misses opportunities to push the throughput envelope. The third option is time consuming and costly. The fourth option just doesn’t go far enough, and it’s also expensive.

There’s no question as to the benefit of improving system performance at the unit control level while maintaining safe, reliable operations. An unscheduled shutdown or failure could cost an operator as much as $10,000 a day.

Option 2 doesn’t do much to prevent that from happening, yet many major gas gathering and producing companies commonly operate compressors below full load. Their goal, of course, is to reduce the risks of exceeding rated engine power and compressor rod load when conditions change unexpectedly. Some turn to Option 1 and push their compressors to run over maximum load specs in an effort to get more throughput; but this increases the risk of damage to the compressor and creates safety hazards. Both compressor overload and underload can lead to maintenance headaches, increased down time, greater inefficiency and lower throughput. These problems, in turn, cut into profits while increasing fuel operating costs.

Options 3 and 4 have the potential to achieve increased throughput and greater efficiency. But Option 3 depends on operators or technicians doing the job, which can be time consuming and costly. And Option 4 is constrained by the lack of math capabilities in the PLC.

Moreover, in order to implement Options 3 or 4, you need to keep detailed data on each compressor while continuously adjusting the parameters that control the compressors. It takes a great deal of complicated math and programming algorithms to correctly tune six engines and six compressors to achieve peak efficiency. Multiply that by the number of stations on the line and you have an enormous amount of calculations to create, apply, maintain, and re-adjust as operating conditions change.

Developing a solution

CompXpress Screenshot

Operators can now deploy the combined CompresXpress/eRCM software package to improve compressor efficiency.

It was in this context that ACI and CSI decided to create an industry solution that would optimize compressor efficiency at a lower cost. The key here was a focus on “optimizing” and not “maximizing.” Over the long run, pushing a compressor to the max leads to higher costs and more headaches. Optimizing compressor operations keeps the compressors running safely, longer, and with more total throughput.

As part of this effort, ACI developed a model-based technology called eRCM that allows compressors to safely run up to their full load capacity. It eliminates manual calculations; the need to program constraint equations; and the need to operate below maximum safe load step. eRCM automatically calculates the maximum safe load step for each compressor and continually adjusts based on changing process conditions – even if a compressor no longer matches its original specs.

No PLC exists with the ability to perform eRCM’s complex math functions. So, CSI added eRCM to its CompresXpress unit control panel (UCP). CompresXpress is a highly configurable UCP that can handle all the basics – or the basics plus advanced complex control, including the complex calculations required by eRCM.

While CompresXpress is a standard product that includes all the standard and advanced applications that one expects from a UCP, it is unique in that those advanced applications can be customized to suit user needs primarily through configuration, not programming. CompresXpress with eRCM can deliver a significant increase in compressor efficiency that can reduce fuel costs, extend compressor life, and reduce downtime and overhaul costs.

Norm Shade, ACI Services, Inc., president, says the improved efficiency offered by CompresXpress with eRCM can pay for itself very quickly. “Some companies have found that the technology investment can pay for itself in a matter of days – days, not years, days and that’s a significant cost savings and bottom line profit generator.”

CSI’s manager of new business development, Jim Bowman adds: “CompresXpress is different from your run-of-the-mill compressor controller. CompresXpress is purpose-built to automate large and complex units requiring load step controls. But it’s scaleable, too, down to any smaller size unit. When you add the eRCM model-based technology to the CompresXpress technology, which has been out there since the mid-1990s, you’ve got the best technology out there for determining the optimum load step for any given process condition. And it comes in a package that costs significantly less than your typical PLC/HMI systems. You can easily see an instant 5 to 15% increase in throughput – and in many cases more.”