Making the Mint green

They may have a licence to print money, but that didn’t stop the Royal Mint from taking steps to minimise its impact on the environment. Here we learn how pH monitoring was key to cleaning up its processes

BASED in Llantrisant near Cardiff, the Royal Mint’s main business consists of the production of UK circulating coins, the manufacture, marketing and distribution of UK and overseas collector coins and medals, the manufacture of official medals, and the sale of coin based jewellery and collectables. The Royal Mint is a UK governmental organisation, its primary responsibility lies with the provision of UK coinage; however it also has an international reputation for the manufacture of high quality coins and blanks for over 100 countries worldwide.

The Royal Mint is committed to 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 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. The company recently worked with Integrated Effluent Solutions to improve its pH control by installing the Analytical Technology. (ATi) Q45/72 pH/ORP monitor.

Effluents originating from metals finishing plants in the UK are strictly controlled by The Pollution Prevention and Control (PPC) regulations. PPC is a system that has been put in place by the Environment Agency to ensure that manufacturers adopt an integrated approach to pollution control. Companies in the UK discharging effluents to a public sewer require a current and valid consent to discharge under the PPC regulations. The sewerage operator, which is often the company supplying water to the site, awards this discharge consent to the organisation.

By issuing the discharge consent, regulatory bodies aim to eliminate potentially hazardous substances, including heavy metals, acidic and alkaline materials found in trade effluents. As these substances can contain qualities that make their treatment difficult or complex, it is essential that 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. However, due to the nature of the metals being manufactured, the effluent in the pH sensor tank is extremely glutinous, meaning 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. pH control can also be very 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 and to better comply with Environment Agency regulations. 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.

They worked with Integrated Effluent Solutions (IES), a company with a proven background in effluent treatment, to review its existing pH systems and to improve the pH control and efficiency of the effluent plants. IES is an independent company supplying a wide range of products for effluent and wastewater treatment including treatment chemicals, effluent treatment plants, pH monitoring and control, online analysers and flow and level monitors.

Conventional pH/ORP sensors have an open reference system, meaning that 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 and the sensors fail much more frequently, resulting in decreased efficiency as well as increased costs.

To overcome these problems caused by conventional pH monitoring systems, IES provided a solution using proportional hydroxide dosing and the implementation of auto-clean pH controllers from Analytical Technology. ATi is a US- and UK-based supplier of gas and water monitors for use in a wide range of applications.

Since installing the ATi Q45/72 monitor, the Royal Mint has experienced significant benefits in terms of increased productivity, reduced costs and regulatory compliance. By using the auto-clean Q45/72 monitor, the Royal Mint 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 has led to greatly reduced operator intervention as well as a marked improvement in the pH control of the plant. The application of this technology has also enabled the Royal Mint to eliminate costly replacement pH electrodes.

Graham Hartry, Environmental Manager (Blank Processing) at the Royal Mint, comments: “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 stand-alone solution to pH control challenges, enabling us to reduce operator intervention at the same time as improving effluent control.”

To meet the specific requirements of the Royal Mint, IES selected ATi’s Q45/72 pH/ORP monitor. The system is designed for use in industrial and municipal applications and contains sensors specifically engineered to function normally in applications where conventional sensors typically fail.

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, which can destroy conventional pH sensors. 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 contains a unique auto-clean option, which 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. This auto-clean option prolongs the life of the pH electrode and ensures that the sensor measures the pH of the effluent rather than a crust built up on the electrode.

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, so that the volume of hydroxide added is proportional to the pH signal from the pH controller.
 

By Garry Tabor, sales manager europe, Analytical Technology Inc, Andy Dargue, technical director, Integrated Effluent Solutions Ltd and Graham Hartry, environment manager, Blank Processing Department, Royal Mint