We discussed the problem with Lubrizol engineers; a few days later when Joe was meeting Metso factory personnel he raised the idea of using a Metso kajaaniMCA Consistency Analyzer (Figure 1). This device uses patented microwave “time of flight” technology. Flight time of the microwave sent across the pipe depends on the dielectric constant of the material in the medium. Because solids typically have a lower dielectric constant than water, the microwave signal travels faster through solids than water. This travel time across the pipe bears a linear relationship with % solids. The technology has served for years to measure stock consistency at paper mills and solids in process streams at municipal sewage plants.
The analyzer never had been used on CPVC slurries; so, Lubrizol suggested trial runs to prove its validity for that service; Metso agreed and FCX Performance arranged for the trials. Metso personnel assisted with the initial instrument installation and set up. Lubrizol staff then tested the device from June to September 2007. Slurries of various resin grades were sampled and laboratory measurements for % solids were compared to the kajaaniMCA Consistency Analyzer’s readings.
The analyzer gave steady, repeatable results over a sustained time period that corresponded closely with lab data. Readings fluctuated with feed tank level.
The plant historically had observed that % solids varied with tank level. One contributing factor had to do with tank agitation. The tank agitator has dual blades. When tank level is near or slightly above the top agitator blade, mixing is more uniform. Another contributing factor is that when tank level is low, water in the slurry is more likely to pump out first, leaving more CPVC in the tank and raising the % solids. Measurements from the analyzer proved this theory.
The kajaaniMCA readings allowed calculation of mass flow rate and, thus, much tighter regulation of additive dosing. The process stayed in control as the slurry’s flow rate and % solids shifted.
Due to the dynamics of the dryer, there typically tends to be a three-to-four-hour delay from when a change is made in additive dosing to when a change is seen in the end product. Using the kajaaniMCA Analyzer, the change appears only two hours after switching from ratio control to mass flow control. This indicates the accuracy of CPVC measurement and the improvement using measured-mass instead of ratio control.
Historically, 5% of all material treated with the additive was produced out of spec. The first two runs in which the kajaaniMCA Consistency Analyzer was used for process control yielded no out-of-spec material. Lubrizol Advanced Materials targets an off-spec limit of less than 1% for additive-treated resins.
Collaboration among Lubrizol, FCX Performance and Metso Automation has truly created a win-win-win situation. The plant now has achieved accurate measurement of slurry % solids while FCX, which sells Metso products, and Metso itself have opened up a new market for the analyzer.
Kerry Haight is a process engineer for Lubrizol Advanced Materials, Inc., Louisville, Ky., a subsidiary of The Lubrizol Corporation. Joe LaPoint is a chemical engineer and account manager for FCX Performance, Indianapolis, IN. E-mail them at Kerry.Haight@Lubrizol.com and jlapoint@FCxPerformance.com.