Mint solution right on money

The Royal Mint manufactures coins and blanks for both domestic and global markets. Based in Llantrisant, near Cardiff, its main business is producing UK circulating coins.

The Royal Mint was looking at ways of improving its manufacturing processes to ensure minimum impact on the environment. Like all manufacturing plants, water effluents from the Royal Mint are strictly regulated by the Environment Agency (EA), and by local authorities through consent to discharge. In order to comply with these regulations, the Royal Mint operates effluent monitoring systems that can cope with the large amount of fouling that can occur within sensing tanks.

Effluents originating from metals finishing plants in the UK are strictly controlled by the EA’s Pollution Prevention and Control (PPC) regulations. Companies in the UK discharging effluents to a public sewer require a current and valid consent to discharge under PPC regulations.

Discharge consent

The sewerage operator, which is often the company supplying water to the site, awards this discharge consent to the organisation. By issuing the consent, regulatory bodies aim to eliminate potentially hazardous substances. These include heavy metals, acidic and alkaline materials found in trade effluents. Because these substances can contain qualities that make their treatment difficult or complex, it is essential their discharge into public sewers be regulated.

The consent to discharge specifies various parameters, including the maximum daily discharge volume, metal loading, chemical oxygen demand, pH, temperature, and suspended solid concentration. In order to comply with these regulations, the Royal Mint has traditionally used precipitation plants with hydroxide dosing to adjust the pH value of its effluents. But, due to the nature of the metals being manufactured, the effluent in the pH sensor tank is extremely glutinous. This means that pH probes and electrodes require cleaning a minimum of once per shift. As a result of this sensor fouling, the pH readings can be less reliable, which is exacerbated by the poor response time of the electrodes. Control of pH can also be poor, and often requires operator input to ensure regulatory compliance.

The Royal Mint recently began to seek an alternative pH system in order to improve the quality of its effluents. The organisation also required a system that would eliminate the need for everyday cleaning and operator maintenance, and improve efficiency in a cost-effective way.

Integrated Effluent Solutions (IES) worked with the Royal Mint to review its existing pH systems. Conventional pH/ORP sensors have an open reference system, meaning the reference element and electrolyte are in contract with the process.

This allows chemicals to diffuse into the reference chamber and alter the reference system. As the reference junction becomes contaminated, the reference potential shifts. The chemicals can then attack the reference wire, meaning that the sensor cannot function.

When these problems occur, cleaning and calibration cycles increase. The sensors fail much more frequently, resulting in decreased efficiency. To overcome these problems, IES provided a solution using proportional hydroxide dosing, and the implementation of Auto-Clean pH controllers from ATi.

To meet the specific requirements of the Royal Mint, IES selected ATi’s Q45/72 pH/ORP monitor. The Q45/72 system is designed for use in industrial and municipal applications.

The differential pH/ORP sensors in ATi’s Q45/72 monitor consist of a sealed reference system with a second glass pH electrode as the reference element in the sensors. The glass reference system protects the sensor from chemical poisons such as sulphide, cyanide, chlorine and bisuphite.

Sensor electrodes can be user-specified to ensure measurement reliability and maximum sensor lifetime. The type of glass used in the pH electrodes can be selected for optimal performance, and the metal electrode for ORP measurement can be platinum or gold, depending on the chemical makeup of the process solution.

The monitor selected for the Royal Mint application is designed to extend cleaning intervals on pH and ORP sensors in applications with high levels of solids contamination. The ATi Auto-Clean Q45/72 system uses an integral high-pressure air supply to automatically remove contaminants from the face of the sensor.

Featuring a time controller that the operator can increase or decrease depending on water quality, the monitor automatically places outputs in a hold condition during cleaning to prevent false readings or alarms.

In order to accurately monitor pH levels in effluents, the pH monitor installed at the Royal Mint is directly linked to the digital dosing pump, This is so that the volume of hydroxide added is proportional to the pH signal from the pH controller.

Regulatory compliance

Since installing the new monitor, the Royal Mint says it has experienced significant benefits in terms of increased productivity, reduced costs and regulatory compliance. It says it can ensure that it achieves compliance with consent to discharge regulations, while eliminating the need for regular and costly sensor cleaning.

To meet the particular circumstances of the Royal Mint, the pH controller’s Auto Clean air wash function operates every two hours. As a result, the monitors can operate for six months or more without any maintenance.

This, according to the Royal Mint, has led to greatly reduced operator intervention, as well as a marked improvement in the pH control of the plant.

Graham Hartry, environmental manager at the Royal Mint, says: “Ensuring compliance with environmental regulations is extremely important to the Royal Mint, and we take our commitment to controlling our effluents seriously. When looking into improving our pH systems, we found that most sensors required cleaning, either manually or by installing a separate cleaning system.

“By supplying the ATi Q45/72 Auto-Clean monitor, IES has provided us with a standalone solution to pH control challenges.”

WWEM stand 54/55