Emerson’s Todd Fortman and an engineer with a distributor shared an application story around truck loading and unloading. Their abstract:
A Wisconsin based chemical distributor required an accurate and efficient truck loading and unloading solution. With over fifty chemicals needing to be loaded into twenty to thirty multi-compartment trucks daily, they required a flexible and robust solution. The plant desired a system that would minimize operator error and provide a safe solution in a Class I / Division I environment. The solution would need to be able to handle air in the system, as a blow down process was required.
They opened their presentation describing some of the challenges with truck loading. Entrained air is a common issue in this application. The distributor recently opened a new truck loading facility of chemicals where the source chemicals come in via rail.
Key project requirements for bulk loading and unloading were accuracy, reliability, temperature correction, ease of use for operators, and improved integration with the site PLCs. Positive Displacement (PD) meters with air eliminators had historically been used for load/unload measurement. The measurement devices are located in Class 1 Division 1 areas.
The distributor became aware of Coriolis flow and density measurement technology. They performed extensive testing with fluids with entrained air rand from 5-20% void fraction. These tests were much tougher than the application would require. The Micro Motion meter technology performed best with an average error across this range of entrained air of 0.5% versus 5% with other devices tested. This amounts to 5 pounds per thousand pounds instead of 50 pounds.
Meters were preferable to truck scales since the bays were dual-use between trucks and rail cars.
Coriolis technology is fundamentally a mass flow measurement technology. Density is measured by the frequency of vibration of the tubes in the meter. The Micro Motion web site has an excellent theory of operation section if you are unfamiliar with how this technology works.
24 2-inch Elite Micro Motion meters with enhanced core processors and 1700 transmitters were used in the solution. There is a pump at the tank which pumps through the meter to the loading arm. A three-way valve sets where the flow is inbound to the tank, or outbound to the railcar or truck. The application was optimized for entrained air which includes a vertical flow installation, and elbow and control valve after the meter to add back pressure as required and operating the 2″ meter in its upper range.