Wireless monitoring, asset protection

PEMEX Tula Refinery increased efficiency with wireless connectivity by protecting critical assets related to cooling towers with process sensor and vibration monitoring, data collection, and analysis. Wirelessly transmitted information will help predictive maintenance; 20 hours per week of manual data collection can be used more productively.


Due to the number of structures and obstacles between the point-to-point wireless links, in some places, masts with higher elevation were needed. This is an example of a transmission tower installed to overcome the line-of-sight problem inside productiveThe PEMEX Tula Refinery increased efficiency and is protecting critical cooling towers assets with wireless monitoring and analysis of process and vibration sensor data. Wirelessly transmitted information will help predictive maintenance efforts, and 20 hours per week of manual data collection time can be used more productively.

The Tula Refinery, in the state of Hidalgo, Mexico, is responsible for the throughput of approximately 300,000 barrels a day of crude oil. The refinery, owned by PEMEX Refinación (PEMEX Refining), serves Mexico City and Central Mexico. Safe, economical, and reliable production of petroleum-based products is crucial.

PEMEX Refining is an arm of state-owned Petroleos Mexicanos (PEMEX), one of the largest oil and gas companies in Latin America. Several years ago, the refinery management chose to upgrade the facility to protect and enhance this $9 billion investment. In particular, engineers there chose to upgrade the monitoring and protection for its cooling towers, which are critical to the oil refining process.

A refinery uses water to heat fluids and cool equipment during the refining process; cooling towers allow the water to be cooled and stored for reuse.

Asset management

Large cooling fans regulate the temperature of the water within the tower. Under certain conditions, such as mechanical wear, axis misalignment, and oil leaks, the motors can vibrate at an extraordinarily high rate. This vibration can lead to a shorter useful life for the fan engine and reduction gearbox, causing an unexpected and dangerous shutdown of the fan and less uniform water temperature control.

PEMEX Refining, working with Representaciones y Montajes S.A. de C.V. (RYMSA), a system integrator located in Mexico City, developed a solution by creating a monitoring system to reduce wear and tear on mission-critical equipment and reduce monitoring expenses.

Figure 1. Block diagram of vibration monitoring and process control of cells within cooling towers. Courtesy: RYMSA






















Figure 1 shows the diagram of the monitoring system that was developed and deployed by RYMSA. It consists of vibration measurement devices connected to a mechanism that shuts off the cooling fan engines when abnormal vibration is detected. The monitoring system is designed to transmit information on the status of the fans and the water cells continuously using a wireless radio in a satellite electrical room. From the satellite room, the data is sent wirelessly to an operations center.

By using 5.8 GHz backbone communication on the Hirschmann radio and 2.4 GHz in the Emerson Smart Gateway, both wireless systems work together, without frequency interference. Both Wi-Fi systems are visible in the same mast installation. Courtesy: PEMEX, BAutomated monitoring provides continuous data while saving personnel time and effort, reducing risk. It collects and integrates all important information into one data stream. In the past, technicians had to climb each cooling tower hourly to read and register the measurements manually. This methodology could result in motors being subjected to unnecessary stress between the time vibrations began and the next time manual measurements are collected and analyzed.

Resolving terrain challenges

Oil refineries, like some other industrial facilities, are a difficult terrain for establishing wireless connectivity. Plant structures such as pipe racks, towers, heaters, the cooling towers themselves, and the fin fans are typically arranged in a way that makes it difficult to get acceptable line-of-sight for effective signal transmission. In addition, PEMEX required Class I Division 2 rated equipment, which is designed to guard against sparks—a dangerous manifestation in the potentially volatile atmosphere of an oil refinery.

The monitoring system depends upon a communication network that works effectively and reliably in this difficult environment. RYMSA worked with wireless vendor field engineers to develop a solution that would provide for strong, clear signals despite physical challenges.

To provide the solution, signals from monitoring devices within the cooling towers are transmitted through wireless devices deployed in a star topology into a wireless gateway located in the satellite room. The gateway is connected into a bridge access point via a Power over Ethernet (PoE) layer 2 switch. Signals pass through an industrial Ethernet point-to-point 5.8 GHz wireless link to another access point near the operations center located 500 to 600 meters away.

Figure 2. Line-of-sight is critical to transmission of strong, clear signals; deployment must ensure that there is no disruption of the Fresnel Zone. Courtesy: RYMSAUsing a series of calculations, and by routing antennas carefully throughout the site, the installation team ensured that robust and reliable wireless connections could be made. To guarantee the Fresnel zone (the area in which radio waves spread after they leave the antenna) is undisturbed, higher masts were needed for the wireless radios in certain areas, such as the hydrosulfurization area. In other areas, a repeater station had to be used to overcome the null or difficult line-of-sight location of the radios and antennas.

Other access points are installed in various locations around the refinery to provide a communication backbone that supports point-to-point and point-to-multipoint wireless Ethernet connections. Rapid spanning tree protocol (RSTP) redundancy ensures network availability.

Figure 3. To ensure line-of-sight for wireless transmissions, precise measurements were made. Various types of antennas were used to achieve optimum results. Courtesy: RYMSADual-radio design allows the access point to act as a repeater or bridge as necessary (Figure 3). In the future, all access points will be linked in a redundant (RSTP-based) ring network when the current edge points are linked to provide network redundancy.

RYMSA used network management software with managed Ethernet switches to evaluate signal quality and strength measurements during the process of positioning and aligning the antennas. The graphical interface and easy-to-use software helped ensure that each antenna was optimized for maximum signal strength and bandwidth.

A second benefit of the dual-radio design was the ability to avoid frequency interference. While one radio operates at 2.4 GHz frequency to communicate with smart gateways and wireless sensors, the other radio operates at 5.8 GHz to support the wireless LAN backbone between the satellite room and the operations center. The higher frequency serves well in situations where complicated radio line-of-sight geometries make it difficult to establish high-quality, reliable communication links. Using a variety of IP65-rated antennas (omnidirectional, directional, and sector antennas) covers the performance and bandwidth needs of the facility.

Figure 4. A screen shot depicting the discovery of network devices located within the refinery. Courtesy: RYMSAWith the network management and monitoring software (see Figure 4), RYMSA installers and PEMEX operators easily discovered and configured network components, reducing overall project costs. RYMSA estimated that use of the tool reduced the amount of programming time required to develop and configure the network by 30%, when compared to traditional command-line interface (CLI) configuration through a serial console.

Process sensor data

The first link became operational on Feb. 15, 2010, and Phase 1 of the project was completed in December 2010. Today, PEMEX can monitor all general process variables such as water level; pressure, temperature, and flow; water PH; conductivity; and turbidity. PEMEX uses chemical analysis to calculate and regulate cooling tower efficiency.

View of the PEMEX plant area in which the line-of sight conditions made a great challenge to achieve communication. The combination of omnidirectional and directional antennas made this wireless solution possible. Courtesy: PEMEX, BeldenWith regular readings of the performance of the fans, PEMEX expects that machine life will be extended. Vibration monitoring of the motors, reduction mechanisms, and pumps allows plant personnel to create predictive maintenance schedules for the machinery.

Finally, a centralized human machine interface (HMI) concentrates and logs all the variables and graphics related to refinery operation, saving more than 20 hours per week, or more than 960 hours per year that can be dedicated to other productive activities.

The successful deployment of an automated monitoring system at the PEMEX refining facility has provided PEMEX with a roadmap for increasing automation in other facilities. Attention to detail and the possibilities of significant savings in both extended equipment life and reduced manual monitoring and reporting are strong incentives for continued deployment.

- Ricardo Velázquez Espinosa is Industrial Networking Solutions Manager, Mexico & CA, at Belden Inc., and Rafael Montandon Spinoso is project manager at RYMSA. Velázquez can be reached at ricardo.velazquez@belden.com. Montandon can be reached at rafael.montandon@rymsa.org. Edited by Mark T. Hoske, content manager CFE Media, Control Engineering, Plant Engineering, and Consulting-Specifying Engineer. Hoske can be reached at mhoske@cfemedia.com.




Wireless technologies used at PEMEX Tula Refinery - see article linked at bottom.

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