A shocking way to compress CO2

Compressing carbon dioxide captured from power plants to 1,500–2,200 psia for pipeline transmission or underground injection is a challenge that requires eight stages or more, using conventional compressors. A compressor that promises to do the job in two stages, for 50–60% of the installed cost, is being developed by Ramgen Power Systems, Inc. (Bellevue, Wash.; www.ramgen.com).

Ramgen has been working on the compressor for some time, supported by the U.S. Dept. of Energy (DOE, Washington D.C.; see CE, June 2006, p. 16), but the project has received a boost from Dresser-Rand Group Inc. (Houston, Tex.). Dresser-Rand has committed to a staged investment in the company, says Ramgen president Peter Baldwin, who spoke at the recent Spring National Meeting of the AIChE in Tampa, Fla.

Baldwin notes that the inlet flow in conventional compressors is typically limited to a Mach number of below 0.90 at the inducer blade tip, to avoid generating shock waves in the blade passages. In contrast, Ramgen’s "Supersonic Shock Wave Compressor" borrows from supersonic aircraft engine inlet technology, using a combination of rotor rpm and inlet vane design to operate at a relative Mach 2. Instead of conventional blades the machine uses rotating disks whose rims are contoured to form inlet compression ramps that mimic the inlet design of supersonic aircraft engines (diagram). The goal is to achieve a pressure ratio of 100:1 in two stages, each with its own separate drive.

In association with Dresser-Rand, Ramgen is working on a 13,000-hp (10-MW) second stage that could handle the CO 2 generated by a 250-MWe power plant. "The second stage is the high-pressure stage, so it’s the critical one," says Baldwin. "We expect to have it running sometime in 2011." He adds that, besides CO2, the compressor could be used for other heavy molecular weight gases and low-temperature applications.

Batch Processing: Staying Alive

Repeatability, flexibility and visibility via automated control systems can help batch processors make it through the recession

As it is with all chemical processors, the current economic climate is forcing batch processors to produce more saleable product at a better profit margin from the same assets. Increasing flexibility, reliability and visibility while decreasing batch cycle times via integrated automation systems can help increase throughput and the chance of survival.

Staying afloat

Undoubtedly it’s difficult to get more product from a process, especially in the wake of staff reductions and facility shutdowns. However it is possible to improve batches in an effort to ensure longevity even during an economic crisis. To do so, experts recommend the following:

Increase reliability. Since the product from many batch processes is immensely valuable and any loss of a batch due to failure will result in a large financial setback, ensuring reliability is especially important during the current economic downturn

Reduce batch cycle time. Like other chemical processors, batch processors need to get more from less. Getting a batch cycle down from 12 h to 11 h and 45 min translates into additional revenue from the same assets, so it is prudent to find ways to reduce batch cycle times

Increase flexibility. Flexibility, too, is crucial at this time as processors are being asked to produce a wider range of products from the same equipment with very little setup-related downtime between batches

Track and trace. In this sagging economy, many batch processors are cutting back on documentation and quality procedures. Experts warn that this is only laying a trap for the future as regulations regarding record keeping are becoming more stringent. Historical batch information can also be used to improve a process. For these reasons, batch processors must begin to step up their game in this area

True batch control

While taking these actions may seem difficult, automation vendors do provide solutions that can help. Increasing reliability, they say, lies in moving sophisticated and intelligent batch automation down the automation hierarchy and into the controller. "In the past there were hierarchical systems where recipe management and other aspects of batch processing and unit control were run in a server and the actual phases and individual building blocks were done in the controller," says Maurice Wilkins, vice president of the Global Strategic Marketing Center with Yokogawa (Newnan, Ga.; www.yokogawa.com) and chairman of the World Batch Forum (Research Triangle Park, N.C.; www.wbf.org). "But now unit supervision can be done in the controller as well."

This means that the unit can stand alone inside the controller, where before a server was needed to manage the operation. "Controllers are becoming more powerful, which lets you run more inside the controllers themselves. This is where batch processing is headed because you can do more with less equipment," says Wilkins.

Chris Morse, product marketing manager for batch with Honeywell (Morris Township, N.J.; www.honeywell.com), agrees that this is the ticket to more successful batch operations. "Moving the procedural levels of batch control into the controller provides a robust environment and reliability," says Morse. "We call it ‘bumpless redundancy,’ meaning that if one controller fails, the system automatically moves to the back up with no single point of hardware or software failure that will cause the batch to hold, which could be dangerous or involve economic loss."

In addition, this recent move helps with cycle time reduction. In previous generations of batch automation, there was a server involved, which left dead time in communication between that server and the controller. "We have customers who have calculated that by reducing dead time, they can increase their annual throughput by up to 3%," notes Morse. "They can sell that additional product, which means they have successfully reduced cycle time and improved productivity."

Using advanced process control as part of the batch process can also help improve yield by allowing users to make more informed decisions about equipment and processes, says Todd Stauffer, PCS 7 marketing manager with Siemens Energy & Automation (Alpharetta, Ga.; www.siemens.com). "Advanced process control is a way to understand how you’re currently running so you can make fine adjustments to the process with ease," he says. "With the distributed control systems of the past, it was difficult and costly to make small changes unless you were knowledgeable in the vendor’s programming."

Integrating information

Providing integration at a variety of levels can also help processors boost their batch. At the operator level, it’s important to provide a common user interface and concept across all the systems, not just the batch or automation system. Further up the automation pyramid, integration with ERP (enterprise resource planning) systems allows processors to seamlessly move from order to order input, to planning and inventory management and then into kicking off the batch process.

Vendors are tackling this in a variety of ways. Honeywell is more deeply integrating the batch automation functions into the system, so "it does batch right out of the box rather than being an installed application on top of the automation system," says Morse. "This provides the user consistency in look and feel, which reduces the training requirements for maintaining and operating a system."

One of the newest developments in the area of integration is with Honeywell’s Experion Process Knowledge System (PKS), which offers new integrated batch functionality through the new Experion Batch Manager. "Every item of batch automation can be changed online with this system," explains Morse. "We’re taking measures to be able to manage large numbers of recipes and integrate with ERP systems. A batch can be kicked off by an external system, usually an ERP, without paper or manual handling between the ERP and automation system." He says this provides flexibility and ease of change between orders and batches.

Siemens is handling the integration challenge through its Simatic IT product, which bridges the gap between its PCS 7 control system and Simatic Batch. While Simatic Batch is a graphical tool that allows users to make recipe changes in a drag-and-drop environment, there was still difficulty in getting the information for those changes from the IT people to the process control folks. "We are providing Simatic IT to make those two worlds talk in an effort to increase flexibility," says Robert Purvy, PCS 7 technical consultant with Siemens.

"Typically there are IT guys and process control guys, but batch processors need to make that line blur if they want to increase productivity via flexibility," he says. "The information and data regarding scheduling, warehousing and material management that is normally in the scope of IT has got to make it to the process control people so they have information on the quality of the raw materials if it differs from the information in the ERP system."

"Having integration between these normally disparate entities will also enable batch processors to quickly change from one product to another if something comes up," says Purvy. "Quite simply, integration provides batch processors with information in real time, which enables them to produce more products with the same equipment, make changes on the fly, optimize production runs and keep track of it all."

Track and trace

And keeping track of it all is especially important as regulations regarding documentation and record keeping grow tougher every day. Not only does tracking and tracing keep batch processors in compliance, it also helps them understand the process, enabling process improvements.

Most suppliers of automation solutions provide some sort of track-and-trace, documentation and historical analysis functionality in their offerings. Rockwell Automation (Milwaukee, Wis.; www.rockwellautomation.com), for example, offers its Plant PAx Process System and, within that, a batch management and control function focused on batch and sequence management, which leverages Integrated Architecture and Factory Talk. Factory-Talk Batch software provides modules for batch management, manual work instructions, materials management and material usage tracking, forward/backward track and trace, regulatory compliance, validation and other tracking activities.

"Not only does this help with regulatory compliance and product recalls, it also turns data into usable information, which helps batch processors truly understand and optimize the process," says Andy Stump, segment manager for Rockwell Automation’s Process Systems Team.

He says the Factory-Talk Batch product provides web-based reporting, which offers a range of standard out-of-the-box reports for track and trace, material usage, electronic batch reporting and exception reporting. "The system takes all that data, collects it and gives the user a report that can be used to fine tune the process," he says. What it boils down to is that batch processors are using modern and reliable batch control systems to gather and study the information collected by track and trace functions. This enables the user to make informed decisions to achieve the levels of flexibility and increased productivity necessary to stay alive during the economic downturn.