Many Ethanol plants running today are using a combination style pH electrode with a non-flowing reference to measure pH in the Mash Slurry transfer line from the Mash slurry mix tank to cook. The Mash is being pumped out of the Mash Slurry tank is at approximately 180 °F and 40 to 60 psig. The original pH electrode systems that were installed during plant construction are online retractable assemblies and are mounted in orientations from completely horizontal to completely vertical and everywhere in between.
The combination probe that is being used will typically drift out of calibration very quickly. Also, the probe is damaged sometimes from excessive removal from the process. The reason this probe drifts out of calibration is due to the fact that the non-flowing reference system plugs and becomes fouled by the mash passing by it. pH measurements are only as good as the reference required to make this measurement. If the reference is not doing its job, the measurement electrode will drift.
Yokogawa manufactures a multi-probe holder called the FF20 – flow through fitting or the FS20, which is pH chamber assembly with 1⁄2" NPT process connections. With these holders we use a combination electrode, part number: SC21C-AGC55 for measurement and reference and a separate temperature sensor part number: SM60-T1. The Yokogawa electrode system works due to the fact that the SC21C-AGC55 combination probe uses a pressurized reference system. By using plant air regulated to a KCl reservoir, the SC21C-AGC55 utilizes a positive flowing reference that does not foul.
Plants using this system typically check the pH measurement against a grab sample and only make adjustments if the sample and the online measured values are more than 0.2 pH difference from one another. Typically, the system will not need daily or weekly calibrations. Most plants will pull the electrodes once a month for cleaning and calibration in a standard 4 and 7 buffer solutions.
The Yokogawa pH system is not retractable from the process. It is usually best to put the Yokogawa pH electrodes in a by-pass or recirculation line that you can add isolation valves for isolating the probes from the process for maintenance and calibration. The probe assembly should be mounted downstream of the Slurry Tank transfer pump. Ideally it will be in a recirculation line going back into the tank or into the suction side of the slurry pump.
The picture below shows an installation that is actually flowing from left to right. The arrows indicate the direction of the mash flow through the recirculation line and back into the suction side of the pump. You will get an idea of the installation of the Yokogawa probes and the pressurized reference KCl reservoir from this picture. The reservoir pressure is typically set 1 to 2 psig above the slurry line pressure. The KCl reservoir will require refilling every 2-3 months for most applications.
The FLEXA™ series analyzers are used for continuous on-line measurements in industrial installations. With an option for single or dual sensor measurement, they are the most flexible two-wire analyzer available.
The PH450 pH and ORP analyzer is a multivariable analyzer that combines pH with temperature and ORP (Redox) measurement, which can be utilized through different output functions: two mA current outputs, four independent SPDT contact outputs and HART.
The FU20 and FU24, all-in-one pH and ORP, sensors show how Yokogawa applies the motto "Simple is best" to sensor technology.
- FF20/FS20 Fittings for pH and ORP
- Full range of fittings
- Emphasis on designs that reduce installation and maintenance time
- Save operation costs
The heart of a pH measuring loop is the electrode system. Yokogawa has designed a wide range of electrodes to ensure this heart keeps beating under the most severe conditions.
pH and ORP meters, analyzers and transmitters are used for continuous process monitoring of pH and ORP to ensure water/product quality, monitor effluent discharge, batch neutralization, pulp stock, scrubbers, cooling towers, chemical, water/wastewater treatment and many other applications.
- pH and ORP sensors
- Proper pH electrode/sensor selection critical for optimal measurement results
- Installation options include retractable, flow thru, immersion, and direct insertion
Contact a Yokogawa Expert to learn how we can help you solve your challenges.