Korsnäs Gävle is the second largest producer of liquid-packaging board in the world and is also a major manufacturer of white top kraftliners, sack paper and kraft paper. At its paper and board production unit at Gävlebukten (Gävle Bay), 150 km north of Stockholm on the east coast of Sweden, protecting the local environment is an important concern.
For example, water from heat exchangers is carefully monitored for contamination prior to its return to the sea. This monitoring is necessary because small internal leaks in the heat exchanger may result in the discharge of hazardous chemicals into the local environment.
Fortunately, any leak of acids, bases, or salts will raise the electrical conductivity of the water and is easily detected using a conductivity sensor. Monitoring the conductivity levels therefore enables us to verify compliance with environmental monitoring legislation, which is required for continued production at the plant.
Recently, however, a renovation project within the utilities section of the Gävlebukten plant meant that remote I/O for instrumentation performing the conductivity measurement would be removed. Therefore, the mill needed an alternative way to transmit conductivity readings back to the control room.
"Initially, we considered installing new cable runs, but the process would have taken too long and would have delayed the renovation project. The application presented a great opportunity for us to install and evaluate Emerson's Smart Wireless technology," Hallenberg explains.
Great for communications
Wireless also presented itself as an ideal communication technology for a second application. To comply with evolving environmental legislation and avoid potential fines, there was an impending need to establish new continuous monitoring of emissions from aerated basins and ponds. For this application, 22 sensors measuring pH, dissolved oxygen (DO), and temperature of the water had to be installed, and they all needed to be connected back to the central monitoring system.
As with the heat-exchanger application, there were no available cable runs to quickly establish connections to the new devices. The closest available wired connection point was more than 500 m. Installing new cabling would present a considerable challenge and cost. Trenching would be required, and the total cost of installation would amount to Euro 200 per meter.
"We evaluated the available wireless options, and Emerson's Smart Wireless technology based on the IEC62591 (WirelessHART) standard was selected for this second application as well," Hallenberg adds. "We immediately undertook a field trial, which proved that Smart Wireless would not have any problems coping with the distance and placement challenges. In addition we discovered that bad weather does not interfere with the wireless system at all."
Up on the roof
The Smart Wireless technology was installed by Korsnäs Gävle engineers, with Emerson providing very minor assistance during startup. A Smart Wireless Gateway was mounted on the recovery boiler roof and receives the signals from the wireless transmitters. Data is then integrated seamlessly into the existing control and data acquisition systems at the plant. Once operational, the wireless network has performed without any problems or lost signals.
For the conductivity measurements of water from the heat exchangers, the mill used Emerson's Rosemount® 6081-C transmitter, which is a self-powered Smart Wireless transmitter that can be connected to any contacting conductivity probe to transmit the measurement data over the wireless network. There is no need for an additional adapter product to be used, and as with all Smart Wireless transmitters the 6081C forms part of the wireless network, transmitting data almost immediately after installation.
To monitor the aerated basins and ponds, a further six Rosemount wireless transmitters, each with four available inputs, were installed to transmit 4-20mA signals from 22 analytical sensors. These provide the necessary data to enable the company to meet its environmental requirements.
Less than two months after ordering the Smart Wireless devices the whole system was fully operational. That is very fast for implementing 30 new measurement points.
Also, once the network is in place, the mill have found that adding additional devices becomes very simple. New devices can be simply installed where and when they are required and almost instantly they connect to the existing network and start transmitting data back to the control room.
"For example, with the Smart Wireless network established, we were able to install new measurement points to monitor temperature in the wastewater pits before the water is released into the aerated basins/ponds," Hallenberg says. "This information helps to ensure that a good environment is maintained in the ponds for the organisms to break down the micro pollutants. Previously there were no measurements at all in place and the cost of implementing new points was prohibitive."
Smart Wireless technology has helped the Gävle mill with various processes
For this application, seven Rosemount temperature transmitters have been installed, providing the company with a better understanding of water temperatures without operators having to make regular trips to perform manual measurements. The addition of extra wireless devices places no strain on the network; in fact it actually strengthens it by adding more routes for data to be sent from each transmitter to the gateway.
The success of these water monitoring applications has led to a fourth use of Emerson's Smart Wireless technology. Korsnäs Gävle has three 30-m wood chip digesters within the main processing part of the plant. Differential pressure transmitters monitor filters within the digesters to ensure they do not plug and reduce the performance of the continuous cooking process. Previously a wired monitoring solution was installed on one of the digesters, but this had been a difficult and time consuming task. The digesters are completely covered with insulation that has to be removed to fit the cabling and then returned afterwards. It therefore took almost two weeks just to install the wiring.
Because the Smart Wireless network has already been established at the plant, wireless transmitters will be applied to the remaining two digesters. Eight Rosemount 3051S wireless differential pressure transmitters will be installed. Because the insulation will not need to be removed for new cabling, the installation of the wireless solution is expected to take just a day to complete. The wireless devices will form part of a semi-control application. The pressure measurements across the filter will not only enable the mill to identify plugged filters and to schedule their cleaning, but they will also enable adjustments to be made to the process between maintenance periods.
WirelessHART conductivity transmitter
|Industrial conductivity measurement is valuable for control in applications where measuring and controlling the conductivity of chemical concentration allows effective scrubber performance, where detecting leakage of cooling water from jackets or heat exchangers into processes helps avoid contamination, or where detecting leakage of the process into the cooling water enables fouling or corrosion to be avoided. It is valuable for equipment protection as well, such as its use for monitoring boiler feedwater and permeate to ensure pure mineral-free water, which is important for protecting condensers, heaters, pumps, piping, boilers, and turbines that produce power.
With more than half of end-user liquid analytical applications requiring conductivity measurement, Emerson Process Management launched the Rosemount® Analytical Model 6081-C, an IEC 62591 (WirelessHART)-compliant contacting conductivity transmitter.
Wireless technology is ideal for conductivity applications that are too difficult to reach, too dangerous to access, or too costly to perform with a wired transmitter. Because the Model 6081-C complies with the IEC 62591 wireless communications standard, it is fully compatible with a host of other wireless devices. All Emerson Smart Wireless devices, including the 6081-C, function in a self-organizing network in which every wireless device in the network acts as a router for nearby devices. This ensures very high data transmission reliability and network availability; all devices work together to identify the most efficient communication path, regardless of radio interference sources or barriers that may inhibit wireless communication.
In addition to its wireless capability, the Model 6081-C transmitter is compatible with both 2-electrode and new 4-electrode sensors. It is also compatible with Emerson’s AMS Suite predictive maintenance software for fully integrated access to predictive diagnostics in a comprehensive asset management application. The Model 6081-C offers a measurement span from 0 to 600,000 μS/cm.
Advanced diagnostics allow real-time monitoring of sensor condition for efficient maintenance scheduling. Local device keypad access permits set up, configuration and trouble-shooting in situ. Quick Start menus enable in-process deployment within one minute. Intelligent power management extends power module life and reduces replacement frequency. User menus and prompts are available in six languages.