Authors: Michael Mwembeshi and Pietro Martinelli
Designing and deploying process analyzers capable of providing real-time rheological characterization of non-Newtonian processes continues to be a challenge in general, but even more so with processes that exhibit time-varying non-Newtonian rheological characteristics. Traditionally, grab sampling is used to facilitate rheological characterization where such information is crucial to process management and plant operations of the facility. Grab sampling allows for periodic snapshots of process conditions; however, this approach has many downsides, chiefly that laboratory analysis can be time consuming, which can impact the facility’s throughput and production goals. On the other hand, even though there exist various commercially-available, process-viscosity monitoring technologies, it is recognized that measurements of dynamic or apparent viscosity provided by such monitors, particularly monitors that operate at fixed shear rates, do not constitute adequate rheological characterization of non-Newtonian processes.
This paper presents and compares two design solutions for implementing process analyzers intended for generalized, real-time rheological monitoring. It shows that even for designs that build on the same core technology, technical and commercial considerations could either aid or hinder the justification for integrating rheological analyzers into the design of a facility that would otherwise use grab sampling.
This paper supports the approach of integrating well-established COTS technologies, such as torsional oscillation viscometers (TOVs), with programmable logic controllers (PLCs) for providing cost-effective, rheological-analyzer solutions that can be delivered within the timeframe of a demanding project schedule. In addition, based on simulation results discussed herein, this paper demonstrates the viability of implementing the rheological-analysis function on a PLC. To aid the assessment of the analyzer’s functional-logic capabilities, a process model was developed to simulate time-varying rheological characteristics. The model sequentially transitioned from Shear-Thickening, to Newtonian, to Shear-Thinning, to Bingham-Plastic rheology and repeated the cycle. Both the process model and the analyzer logic were developed using Do-more Designer™ PLC programming software.
The PLC code was run using the PLC software (“PLC Simulator”), which comes with the Do-more Designer™ software. PLCs remain the de facto platform for implementing real-time monitoring and control across a wide range of industries. PLC simulation results showed that the rheological-analyzer logic was capable of real-time tracking of the “true” values of the parameters that define the rheological characteristics of the simulated process.
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