12 March 2013
RWE Gas Storage is an underground gas storage operator in the Czech Republic, operating six facilities with a total capacity of almost three billion cubic metres. Gas is stored in porous underground facilities during low-off take periods and supplied to users when demand peaks. The facility has active operating reserves of 900 million cubic meters with a current maximum daily output of 15 million cubic meters and is supplied by 47 production wells via an underground pipeline. Incoming gas is filtered and metered, then compressor units generate the necessary injection pressure. After the gas cooling process, the gas is pumped through high-pressure pipes into wells connecting to the storage caverns. The company is continually looking to improve the overall effectiveness of its underground gas storage facilities as measured by the maximum daily input and output. To improve the total amounts required better control, which required higher visibility into the process. However, manually reading over 100 pressure and temperature measurements took around two hours every shift. Having so many manually read gauges was a particular problem when the gas injection rate was higher. This required manual supervision along the entire pipeline, which utilised most of the operations resources. Automating these measurements would give operators greater visibility into the process and increase their efficiency, which would enable them to perform other, more important activities. As well as gaining access to diagnostic data from existing control valves new online pressure, temperature and level measurements were required. Improved visibility to the process would enable operators to run the facility closer to capacity minimising downtime by detecting problems that would, otherwise, lead to unplanned maintenance. This would help to increase overall input and output at the facility. Time limitsThe difficulty was completing the necessary work in the limited time available. The upgrade needed to be performed in a short space of time as any planned maintenance or upgrade projects at the facility can only be performed during two short periods – about two weeks in the autumn and again in the spring – when neither injection nor withdrawal takes place. Such tasks need to be carefully planned, and even then there are limitations in terms of the size of project that can be completed within the tight timeframe. The scale of the project, including upgrades to existing valves and installation of over 100 new measurement points, would be difficult to complete in the time available. To add to the difficulty of the task, there was no available existing cabling infrastructure to support the new digital measurement devices, and a lack of available I/O cards in the control host. RWE investigated the possibility of installing new cabling throughout the facility to connect the new and upgraded devices, but installation could not be accomplished in the two-week window. Even if the upgrade were divided into smaller projects it was still not possible to complete within the timeframe. There was also no possibility of increasing the shutdown period. Every day the facility was not available to withdraw gas would cost RWE an estimated $250,000 in lost income. A wired solution was therefore not an option.The use of wireless technology would remove the need to install new cabling, significantly reducing the overall upgrade project time, making the project more manageable and ensuring it could be completed without additional plant downtime. RWE estimated that upgrade projects using wireless take only a quarter of the time required to install wired devices. Gaining diagnostics capabilitiesThe company selected Smart Wireless technology from Emerson Process Management which is based on IEC 62591 (WirelessHART) communications. The availability of HART data, including diagnostics from new and existing devices, was a significant reason for selecting this technology. Having the opportunity to diagnose potential device problems quickly and easily without having to go out into the field could further improve operator efficiency at the facility. Another advantage of Smart Wireless technology was the ability for RWE to continue to operate injection/withdrawal even when wireless transmitters were being installed. Unlike a wired solution, Smart Wireless did not require new I/O cards in the control host. Smart Wireless gateways were merely added to the existing Modbus network and all data from the wireless transmitters was then available within the existing control system. This also meant that the instrumentation upgrade did not have to be completed within the allotted two-week downtime. Tasks could be split into manageable sections and implemented ‘live’, with no concern about overrunning and affecting normal operations. Five separate wireless networks were installed using five gateways to deliver data from across the entire 50,000-m2 facility back into the control system. Over 100 new Smart Wireless devices were installed. Predominantly these were wireless pressure and temperature transmitters, but a number of Guided Wave Radar level transmitters and control valves were also connected using Emerson’s THUM adapters.The pressure and temperature transmitters now provide continuous measurement of gas at different sections of the pipeline to calculate volume of gas. Other applications include measuring boiler oil level using the THUM adapters to connect to Rosemount 5300 Guided Wave Radars, and monitoring pipeline microfilters using wireless pressure transmitters to detect changes caused by blocked filters. Within the gas cooling section of the facility, existing Fisher control valves now have THUM adapters installed to provide additional diagnostic information. By implementing wireless, rather than a wired solution, the company saved around 20% on the cost of installation and commissioning. The total saving is much higher considering the potential lost income from the plant being unavailable during the required extended shutdown period. Having installed the wireless networks, the company is also saving 10% per year on maintenance costs. Remote online access to diagnostic information has enabled potential problems with instruments to be identified and corrected earlier, before poor measurements affect the process. Access to online data also reduces the number of trips into the field as problems can be spotted and often solved without leaving the control room. The wireless network is able to work without failure or lost transmissions despite the distance between devices being up to 200m with an environment that includes masonry/steel construction. Emerson’s AMS Suite predictive maintenance software is used to monitor network performance. During the project phase, this was also used to help calibrate instruments. AMS Suite is now used to provide ongoing device and wireless network diagnostics. The next planned step for the company is to export this data into its own management reporting system.
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