arrangement via an outlet on the tank . The customer specified that the outlet was via a 3 ” flanged connection and the location of this agreed during the design phase of the project . To ensure compatibility with the customer ' s process , the system was also supplied with the counter to the flange for simple on-site installation .
From a practical perspective , in the future , the pH neutralisation system might need to be relocated , cleaned or inspected . For this reason , they included a foot mounted drain valve allowing the customer to empty the tank when required .
Control Panel
The control panel is mounted into the front enclosure , behind a removable transparent covering . This pH neutralisation system uses a number of inputs to fully automate the treatment of pH correction of the waste water with very little human involvement required .
The waste water is transferred to the treatment tanks using the air operated double diaphragm pumps . As the volume of waste water generated can vary depending on the processes occurring in the customer ’ s factory , two air operated double diaphragm pumps have been fitted ; one acting as a duty transfer pump and the second acting as an assist . The duty and assist pumps mean that during normal operation , the duty pump has the flow rate to transfer enough volume of waste water to the treatment tank to ensure it can be corrected .
As the processes used by the customer vary , the amount of waste-water generated can also vary . To cope with increased volumes , a second air operated double diaphragm pump has been fitted as an assist . This potentially doubles the amount of waste water that can be transferred to the treatment
tank , preventing the sump from flooding in times of increased production .
The duty transfer pump and assist transfer pump are controlled based on the level in the sump . By using low level float switches located in the sump , at a high level , the duty pump is called to transfer the waste water . If the level continues to rise to the second high level ( high-high-level ), then the assist pump is engaged to reduce the volume of waste water in the sump and transfer it for treatment .
Each air operated double diaphragm pump uses an air feed line which passes through a solenoid valve . The solenoid valve is controlled from a level controller within the control panel which in turn takes it ' s signal from the level electrodes .
In addition to the level control circuits for the air operated diaphragm transfer pumps , the control panel also houses : -
Neutralising pH Controller
In a pH neutralisation system , having an accurate pH controller designed for industrial usage is crucial . The P7687 combines accurate pH measurement with precision control functionality .
The P7687 is part of AWE Ltd ’ s new generation of process control instruments with this specific model featuring PID control of pH . As the P7687 is a PID ( Proportional , Integral and Derivative ) pH controller it provides a signal to the dosing pumps enabling them to automatically adjust the speed or frequency that the dosing pumps operate at , meaning that the pH can be very precisely controlled to the desired set-points .
The PID control allows the customer to accommodate wide fluctuations in the measured pH value , as well as ensuring that only as much chemical as is required to neutralise the pH between the set-points is dosed into the wastewater treatment tank .
Discharge pH Controller
The discharge pH controller is another P7687 pH controller taking a signal from a PS90s located in the waste-water or effluent outfall sump . The discharge pH controller constantly monitors the treated wastewater to ensure that it is compliant with the customers consent to discharge agreement .
In this particular installation , it ’ s imperative that the final pH level is logged so the P7687 is continually providing the discharged pH value to the data logger .
Data Logger
The control panel also includes a digital data logger in the form of the new AWE-99 colour touchscreen data logger .
The AWE-99 along with the larger AWE-141 digital data loggers are capable of data logging inputs from 4-20mA signal , High Speed Counter or a Modbus value amongst many , many , other input signals . In this instance the value from the discharge pH controller is being logged to create a trend graph showing the change in pH over time .
All this data is being logged directly to the onboard memory of the AWE-99 , the customer also has the option of backing this log up to an external USB drive which can be connected to the front of the AWE-99 . In addition - with a built in web-server the AWE-99 can be connected to the customers local intranet , allowing them to view the discharge pH from any device connected to the local network .
The AWE-99 digital data-logger allows the customer to log the pH of their final effluent discharge which can then be examined by an external regulatory body so that they remain compliant with their consent to discharge agreement .
The AWE-99 data logger fitted to the customer ' s pH neutralisation system was supplied complete with 2 additional inputs , meaning that the customer can also log the final effluent discharge flow from a V-Notch tank and the final temperature if required . As a fully expandable instrument , the AWE-99 can be fitted with many further inputs even if the data-logger is already installed and in-situ .
CONTINUED ON PAGE 48 twitter : @ surfaceworldmag APRIL 2021
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