A Quarterly Newsletter of Parr Instrument Company | December 2016 | Vol. 3 No. 4
Features and Benefits
Parr has recently introduced a new agitator available for use in stirred reactors: a machined spiral stirrer. Available for reactors with volumes between 300 mL and 7.5 L and compatible with both standard and footless mag drives, these new agitators provide excellent mixing for highly viscous substances like heavy oils and polymers, or slurries with significant solids content. These agitators are more robust than previous generations of spiral stirrers as they are machined from a solid bar of stainless steel or any other material of construction in which Parr reactors are offered.
We have recently provided these stirrers for use with reactors with both flat bottom and tapered bottom geometries, with upflow and downflow versions available. Note the presence of a bottom scraper designed to lift material off the cylinder bottom.
The blades of the machined spiral stirrers are quite strong, so unlike the previous generation of sheet metal spirals, a second set of blades is not required. This often makes it possible to provide internal reactor parts (thermowell, dip tube, etc.) which reach nearly to the bottom of the reactor.
Because these agitators are designed for use with viscous materials which may require higher torque delivery than standard impeller stirrers, and are often used at lower stirring speeds, please consult Parr Technical Service for suitable motor, belt and pulley, or gearbox configurations, or with any other questions.
See examples of these stirrers in action in the videos below:
|200 – 300 RPMs in 300 mL Mini Reactor||Bottom view in custom cylinder||Side view in same custom cylinder|
For further information about stirrer options, please contact Parr Customer Service.
Rupture Disc Replacement
Rupture discs supplied on Parr reactors will need to be changed out from time to time. This may be due to a bursting of the disc or as part of a routine maintenance schedule. Parr offers rupture discs in two different diameters, ¼” and ½”. Regardless of the diameter it is important that the rupture disc assembly is installed correctly to prevent damage to the rupture disc holder or the reactor head itself.
There are three styles of holders for the rupture discs. The A888HC2, A707HC2 and the A1417HC. In this edition we are going to focus on the most widely used holder, the A888HC2. This style holder can be found on almost all reactors sized two liter and smaller. When changing this disc it is best to detach the vent line and then remove the 366VBAA ¼” NPT coupling. This allows free access to the 5/8” hex on the A888HC2 assembly. Once the A888HC2 assembly has been removed from the reactor head, the 49HC2 orifice cone will most likely have to be removed to gain access to the rupture disc. The worn or burst disc and the 527HC orifice ring may now be removed. We recommend cleaning any residual 424HC2 anti-seize lubricant and inspecting the parts for wear. This includes the mating cone seat in the reactor head. More Teflon tape can also be applied to the ¼” NPT thread on the 433HC4 at this time.
Now the rupture disc is ready to be re-installed. Always make sure you apply a little 424HC2 anti-seize to all of the metal to metal contact surfaces. Start with the 433HC4 placed upside down in your hand. Next, set the 527HC orifice ring in place followed by the rupture disc and finally the 49HC2 orifice cone. If it is at all possible, have someone help you hold the reactor head upside down as you thread the assembly back in. This will keep the individual components of the assembly from shifting during installation. If holding the head upside down is not an option, the anti-seize is generally a sufficient “glue” to hold everything together. After the assembly is finger tight in the reactor head finish tightening it with a 5/8” socket and a torque wrench set to 33ft.-lbs. The last step is to re-install the 366VBAA coupling and the vent line.
Please refer to operating instructions 231M Safety Rupture Disc Assemblies for further information on Parr rupture discs.
Accuracy in the Pressure Display Module
The Pressure Display Module is an excellent way to get a digital read out of the pressure on a 4848 Controller. It can be used as a means to shut off the heater in case of an overpressure, and when coupled with a PC communication cable and software, it allows a digital measurement that can be logged on a PC.
The PDM’s usefulness is limited by its accuracy. The standard transducer used with a PDM (Ashcroft model G2) has an accuracy of 1% of its full scale. As an example, a 0-1000 psi transducer will be accurate to ±10 psi, where a 0-5000 psi transducer will be accurate to ±50 psi.
The transducer accuracy is also affected by temperature. The transducer carries a 1% accuracy at temperatures from -20°C to 85°C. Between 85°C and its maximum temperature of 125°C, the accuracy increases to 1.5% of full scale. A cooling sleeve, for cooling water, is common when the transducer is mounted near the hot zone of the system.
The allowable error is larger than one might expect. Our most common transducer range of 0-3000 psi has an allowable error of ±30 psi! Fortunately, few applications require a very accurate pressure reading in absolute terms; in the majority of Parr reactor applications (such as a Hydrogenation) it is the pressure drop that is most important.
The easiest way to improve accuracy is to shrink the range of the transducer. A 0-500 psi transducer will only carry an allowable error of ±5 psi. But this also means that the transducer must be replaced with a higher pressure one if the working pressure is above 500 psi. It’s also not uncommon to put two transducers on a pressure vessel, and isolate the lower pressure one when operating above its maximum allowable working pressure.
For applications requiring the combination of greater accuracy and higher pressure, higher accuracy transducers are available. They carry more cost and require custom power supply hardware in the controller, but can usually be installed in the 4848, 4838, and 4871 Controllers with some modification.
Parr stirred reactors are widely used in hydrometallurgical applications where acid leaching of ores is the preferred method to extract metal ions. A widespread example of this technology is the acid leaching of nickel ions from laterite ores, a first step in the path to the production of stainless steel. To avoid vessel corrosion by the aggressive sulfuric and hydrochloric acids used in this process, vessels are most commonly constructed of titanium. Not all extractions are done with acids. Aluminum, for example, is extracted from Bauxite ores with the use of caustic solutions where the preferred material of construction for the vessel is Inconel or Monel. This will be a topic of a future discussion. To learn more about the use of titanium for acid leaching, please see Parr’s Technical Note No. 204 – Hydrometallurgical Applications, R.W. Schutz and L.C. Covington’s Hydrometallurgical Applications of Titanium available for purchase from ASTM International, or by contacting Parr Technical Service.
Parr Team Member Focus
Justin Gilroy, Assembly Manager
Justin Gilroy has been with Parr for four years and serves as our Assembly Manager, overseeing the Special Assembly, Electrical Assembly, Calorimeter Assembly, Repair, and Imprint/Hydro departments. Justin received his B.S. degree in Industrial Engineering from Iowa State University in Ames, Iowa and went on to earn his M.B.A. from Saint Ambrose University in Davenport, Iowa.
In addition to enjoying working with so many talented people on a day in, day out basis throughout the entire company, Justin said he loves “working in a place where there are so many creative and unique challenges that we have the opportunity to help solve in order to support our customers. When you come from a place making over 1,000,000 toothbrushes a day to seeing and knowing nearly every custom order that goes out it really makes coming to work fun. It also really shows this organization’s adaptability, creativity, and capability.”
Outside of his time at Parr, Justin says he is blessed to have a wonderful family at home. He and his wife, Melissa, just celebrated their 10th Anniversary in November and he “couldn’t imagine doing life without her.” Justin has three little ones – Caleb (5), Grace (3) and Ethan (1) that keep him busy and are so much fun for him to come home to every night.
Justin is just one of the many examples of our very dedicated and talented team members here at Parr that we are very grateful to have on board!
We are currently compiling our 2017 Trade Show Schedule. Please send us a list of any shows where you will be representing Parr in 2017 and we will be happy to further your exposure by adding them on our Trade Shows page.
Email your trade show schedule to firstname.lastname@example.org.