By Scott Broadley, Broadley-James
A flexible manufacturing environment has become an important element in nearly every manufacturing sector. It's no different for the bioprocess industry.
We can create greater manufacturing flexibility through the use of portable, skid-mounted process equipment interconnected and controlled with digital fieldbus technologies.
In some applications in the bioprocess industries, the introduction of single-use vessel and separation technology provides further flexibility in process design and operation. However, the fixed-wiring practices of a traditional installation limit many of the potential benefits of a portable environment.
We can show how fieldbus technologies used on a skid will reduce wiring complexity. But physical connection points into the control system inherently restrict equipment movement and create their own maintenance issues.
Our application of WirelessHART technology provides our customers a new flexibility in manufacturing that addresses both monitoring and control applications. A major benefit of WirelessHART is the user may move the equipment with no impact on control system configuration.
However, when applying any new technology, it is important that we consider whether the technology is appropriate for the application. We've applied WirelessHART to a portable, skid-mounted, single-use bioreactor.
Skids Know Their Place
Skid-mounted equipment is commonly used to speed on-site construction of a new manufacturing facility. At Broadley-James, we manufacture small, portable, bio-reactor skids with instrumentation and automation system attached. We also make some of the components—sensors, for instance—that make up the parts of the skid. Emerson provides most of the instrumentation and automation system.
Oftentimes, the equipment on the skid is customized to customer preferences for materials of construction, field devices, interconnecting piping and process design and equipment and support structures. Skid-mounted packaged equipment can include a broad range of designs for process and utility applications such as refrigeration units, vacuum pumps, heat exchangers, chemical-injection systems, reactors and filter packages.
In an industrial plant, skid-mounted equipment normally represents a small portion of the process and must be integrated into the plant distributed control system (DCS) to enable coordinated plant operation. To provide consistency in maintenance, the field devices may be directly integrated into the plant DCS. In older installations, this integration required that wiring from each field device be brought into a termination panel on the skid and wiring run for each field device from the termination box to the DCS. With the adoption of Foundation fieldbus by major DCS suppliers, the wiring between the termination panel and the DCS can be greatly simplified.
However, when a skid is portable and routinely moved within the plant, even a few pluggable connections to the DCS can become a maintenance issue. Also, when a piece of equipment is used in multiple locations, the design of the DCS software often doesn't allow movable connections without added configuration complexity.
WirelessHART field devices solve many of these issues since the connection to the DCS is independent of its physical location. Through the use of WirelessHART field devices, a physical connection to the DCS is no longer required (Figure 1).
As when applying any new technology, it is good to understand the devices that are available for WirelessHART and how they can be integrated into the control system.
The HART Communication Foundation, its member companies and industry leaders developed WirelessHART technology to meet the unique requirements of wireless networks operating in process plants. The integration of WirelessHART field devices into a DCS is done through a WirelessHART gateway. The gateway provides access to the WirelessHART network through one or more access points. In most cases, the gateway also will contain the network manager that handles communication bandwidth and routing. This network manager is responsible for the creation of routes that can be used to perform communications with the network devices.
The network manager continually collects data from devices and uses this information to adjust routing and scheduling. It establishes the communication schedule to transfer process data, alerts, diagnostics and other traffic to the gateway for access by the plant automation host. For network devices such as actuators, interlocks or any device that affects the process, the network manager establishes scheduled communication that the plant automation host can use to send setpoints and outputs to the field devices.
As field devices are installed in the field, they form a mesh network with the gateway. Alternate paths for communications are established automatically to avoid a single point of failure. When only HART transmitters are available for a measurement, a WirelessHART adapter can be used to make information in the HART transmitter or positioner available over the network.
Wireless handheld devices support direct communication to field devices. For security, one-hop-only communication is supported with the handheld device.
Dedicated manufacturing sites that produce a single product are quite common in the life science industry. To achieve quality targets, this fixed equipment is often highly automated in order to maintain repeatable operating conditions and desired production rate. However, a significant portion of time available for production is lost to the need to sterilize in place (SIP) and clean in place (CIP) this equipment. The number of field devices and control system logic associated with SIP and CIP often exceeds those required for normal production. As a result, there are significant economic benefits in a skid-mounted, single-use process design that eliminates or minimizes the need for SIP and CIP. This is in line with a life science industry trend toward a more flexible design that supports the production of multiple products. The cost of manufacturing can be spread over several products using this approach. A manufacturer also can justify smaller batches more easily in such a flexible manufacturing environment.
Major manufacturers in the life science industry have installed skid-mounted, single-use equipment in both upstream processes, such as cell culture, and downstream processes, such as tangential flow filtration (TFF). In most cases the deployment of skid-mounted, single-use technology has been limited to in-development or early-phase, clinical-trial situations. However, as manufacturers gain more experience with larger-scale units based on this design, we think the reduced initial costs and flexibility will drive this technology into large-scale manufacturing.
Prove the Benefits
Another improvement in small batch process involves the vessel itself. The stainless steel tank typically used for bioreactors can be replaced by a skid-mounted, single-use bioreactor (SUB) bag. The flexibility of a modern DCS allows construction of modular, exchangeable components that can accommodate a number of different-sized SUB bags and a variety of sensor types.
Rapid turnaround between bioreactor runs is the one of the more appealing features of a SUB system. A new disposable bioreactor bag can be installed in an hour or two depending on the size. Alternatively, a new vessel holder, ready to go, can be wheeled over to the control system and hooked up to cables and coolant lines in even less time. Cart-mounted control system designs allow the user to connect to bag sizes from 50 to 500 l by just rolling up a bag-holder cart of the desired size. Sterile sensors can be inserted into the bag via Kleenpak connectors embedded in the bag wall. In some bag designs, optical sensors are embedded into the bags themselves. Features like these and more have led to an industry migration to SUBs at the product-development level and increasingly in production.
To demonstrate the benefits of using WirelessHART transmitters with a single-use bioreactor, Broadley-James instrumented a 100 l SUB with WirelessHART pH, temperature and pressure transmitters (Figure 2).
The bioreactor pH and temperature were controlled over a series of batch runs using the WirelessHART measurements. The pH measurement was communicated on a 1-second, exception-reporting basis. The temperature was reported on a 2-second basis. A mammalian cell culture was used for each batch run. For purposes of comparison, wired pH and temperature measurements also were available during each batch run. The screen capture showed the setpoint response of temperature control based on the WirelessHART input.
We enjoyed similarly good performance for pH control using the WirelessHART input, monitoring response to 0.05 changes in pH setpoint. An unexpected outcome of the test was the WirelessHART input showed immunity to noise spikes that had an impact on the wired measurement. The screen capture compared the WirelessHART pH and wired pH measurement during a time when the wired pH measurement exhibited a noise spike.
The observed pH and temperature control using wireless measurements was equivalent to that achieved with wired transmitters. In summary, while disposable bioreactor systems bring on new concerns and risks that need to be vetted and managed, such systems have fully arrived and are changing the industry with notable cost saving features and benefits.
The application of WirelessHART field devices in portable skid equipment can enable simpler engineering and construction, flexible startup, faster deployment and project completion and meet changing automation needs. Thousands of WirelessHART installations are successfully operating globally in demanding environments industry-wide. WirelessHART has proven to be a reliable robust wireless technology. Some of the reasons for this wide acceptance in the process industry are addressed here.
The remote link can be mounted in Class I, Div. 1, Zone 0 and links the wireless field network into the gateway. Each device has intelligence to discover neighbors and dynamically establish/reconfigure paths to form a self-organizing mesh network with the gateway.
WirelessHART includes several features to provide built-in 99.9% end-to-end reliability in all industrial environments. The WirelessHART network is built on standards such as IEEE 802.15.4 Frequency-Hopping Spread-Spectrum. Also, major manufacturers have introduced gateway redundancy, which protects the wireless network from any single point of failure to ensure that data is delivered even if there is a malfunction. Thus, WirelessHART can be applied in critical monitoring and control applications.
WirelessHART employs robust security measures to protect the network and secure the data at all times. These measures include the latest security techniques to provide the highest levels of protection available. All messages are secured through AES-128 bit encryption. Also, the network operates at 2.4 GHz. Frequency hopping between 16 channels avoids interference and obstacles. Devices joining the network must have the same join key and network ID as the network manager.
The design of WirelessHART is compatible with HART-enabled control systems. In most cases the same tools that are used to work with HART devices are used to diagnose and set up WirelessHART devices. Using the WirelessHART handheld device, setup and calibration can be done locally at the device.
WirelessHART for Control
Devices that conform to the WirelessHART specification can sense measurements at update rates of up to once per second. WirelessHART also allows exception reporting for network efficiency and to optimize battery life. Devices only communicate a measurement value if it changed significantly since the previous communication. Also, a value will be communicated if the time since the last communication has exceeded a required reporting time.
Availability of WirelessHART Transmitters
A wide range of WirelessHART transmitters and analyzers are currently available from major manufacturers. For example, within the past year manufacturers have announced commercial transmitters for measurements such as pressure, flow, level, temperature, conductivity, pH and vibration.
In the event a wireless transmitter is not offered for a measurement, an adapter can be used to convert a HART device to WirelessHART. For example, adapters are available for interfacing to HART valve positioners. In addition, WirelessHART devices for position monitoring, and machinery health management devices for predictive maintenance are offered by some manufactures.
Scott Broadley is principal at Broadley-James (www.broadleyjames.com), builders of bioprocess solutions in Irvine, Calif.