Safe, Reliable and Accurate Loading and Unloading Operations

Loading and unloading operations for chemical producers must be performed safely, reliably, and accurately. I caught up with Emerson’s Martin McDonough on ways to mitigate risks and improve operational performance.

These operations can be some of the highest-risk operations within a facility and account for as much as 80% of transport-related incidents. In addition to mitigating risks to personnel and the environment, loading and unloading operations must have accurate product quantity and quality accountability, high throughput and utilization management, and compliance with standards and regulations.

Accurate accountability of product quantity and quality for both unloading and loading operations is critical as it serves as the basis for the chemical plant’s beginning and end of the mass balance calculations. There are many reasons why accurate measurements are essential, the most obvious being that it is the basis of trust between buyer and seller for custody transfer of the product. This measurement functions as the cash register and is used for billing customers. Chemical plants obviously do not want to give product away and often need to meet and maintain a regulatory compliance standard in these applications.

Maximizing throughput, particularly in a plant’s loading operations, can provide a competitive advantage and increase profitability in direct relation to increasing the capacity to load and unload trucks and railcars. Poor system design that increases the risk of human errors can have significant consequences that can result in spillage, emissions, and increased risks to safety for both workers and the public. And while accurate flow rate and total flow measurement are critically important, it is of no value if the quality of the shipment is not within specifications.

For many chemicals, density, specific gravity or percent concentration are quality parameters that are measured by analyzing a small sample of the product. This provides a snapshot of the quality, but it may not be representative of the full load if there is stratification or if solids settle in the supply tank. A continuous quality measurement not only ensures product quality for the entire load but also makes throughput more eliminating wait times for manual sampling.

For accurate and repeatable custody transfer, flow measurement is essential. Micro Motion Coriolis meters measure three independent variables—mass flow, density, and temperature. These three measurements calculate volume by dividing mass by density and using temperature and live density for concentration and specific gravity-related units. Unlike traditional flowmeters, Coriolis meter performance is unaffected by changes in fluid properties like density and viscosity. Coriolis meters can accurately measure flow in both directions and indicate the flow direction. For this reason, it is common for one meter to be used in loading, unloading, or transloading applications where any number of products are transferred to and from tanks and transport vehicles.

Level measurement is another essential technology in loading and unloading applications. Point-level solutions such as Rosemount 2160 vibrating fork level indicators enable high and low-level alarms and prevent pump dry run conditions or tank overfills. Rosemount guided wave radar and non-contacting radar provide continuous level measurement to perform level control, interface detection, and pump control.

Flame and gas detection solutions should be applied, given the hazardous nature of materials transferred in loading and unloading operations. For loading and unloading of gaseous fuels or liquid fuels with high amounts of combustible vapor, there are several gas detection options:

  • If there are multiple bays, with all the main points of vulnerability in one clear line of sight, an open-path gas detector can be used to detect large-scale gas leaks that might occur anywhere along the line of sight of the detector. Depending on the installation, this can be a distance of 7-200 meters.
  • Point gas detection can be deployed for smaller loading applications, or applications requiring more specific location detection and accuracy—wired, using the Rosemount 925FGD, or wireless, using the Rosemount 928 to monitor for toxic gases.
  • For specific applications that involve the loading/unloading of highly pressurized gases, an ultrasonic gas leak detector can be used. This uses acoustic technologies to listen for exact ultrasonic frequencies created by the leak of pressurized gases (regardless of chemical composition) that can be leaking from a small hole or rupture. While an ultrasonic cannot confirm a gas leak’s exact location, amount, and combustibility, it can offer the fastest possible response time for early detection.

Should there be a fuel leak, the risk of fire at these sites is naturally high, with various machinery and ignition sources nearby. The use of flame detectors, especially the Rosemount 975MR multi-spectrum infrared detectors, should be used. This model offers the best possible combination of detection speed performance and false alarm immunity. These detectors can be returned to specialized fire alarm panels to activate suppression systems or tied back to the local DCS or ESD to shut down machinery.

Finally, from a reliability perspective, continuous pump monitoring can identify issues before they lead to downtime. Wireless sensors combined with operational built-for-purpose analytics help identify problems early and provide notification to schedule maintenance.

Visit the Solutions to Optimize Your Chemical Plant Performance page on for more on this and other solutions to drive improved operational performance and to contact Martin and other chemical industry experts to discuss your application.

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