Lighting The Way for UV Disinfection
Pharmaceuticals manufacturing involves the handling of powders and volatile, flammable solvents such as iso-propanol. Consequently, there is every opportunity for explosive atmospheres to form.
Where this is the case, the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) require that new equipment and protective systems must be selected on the basis of the requirements set out in the EU ATEX Directive (Directive 94/9/EC) and enshrined in the Equipment and Protective Systems for Use in Potentially Explosive Atmospheres Regulations 1996 (as amended) (EPS) unless the risk assessment finds otherwise.
An ageing process water ultraviolet disinfection unit at AstraZeneca’s Avonmouth facility near Bristol fell into this category and was classified as a Zone 2 hazardous area, meaning a place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only. The original UV system was costing a lot to maintain and was an outdated design using a large and complex nitrogen purged enclosure to protect the system. It was the job of project manager Daniel Arthur to replace it and he turned to atg Evoqua for guidance.
atg UV has some 30 years’ experience in UV disinfection for pharmaceutical manufacturing, where the technology was a standard approach long before it was accepted into sectors such as water supply. Process water, these days often produced by reverse osmosis, has very high UV transmittance (typically >95%) and is normally continuously recirculated from a storage tank via a UV disinfection unit to points of use with unused process water being returned to the tank. AstraZeneca’s requirement was for a flow of 25m3/h – a large system by pharmaceutical industry standards – with a 4-log (99.99%) reduction in the number of viable bacteria in the water and, of course, compliance with ATEX. An additional constraint was that the unit would have to be retrofitted to the process water pipework during a planned shutdown.
Hazardous areas are nothing new to atg UV. The company’s systems incorporate not only Ex d (flame proof) UV reaction chambers and control panels, but Ex e (enhanced safety) amalgam UV lamps and Ex ia (intrinsically safe) instrumentation. Ex d enclosures are designed to withstand an internal explosion by using specially engineered joints which permit and control the expansion of gases whilst preventing the explosion from being transmitted to the external atmosphere.
atg UV says that by comparison with nitrogen purged designs – which use positive gas pressure to create a safe area within the panel – Ex d equipment is safer, smaller, lighter and requires less installation and maintenance activity. In addition, due to the complex nature of purged designs and the requirement for a safe gas supply, Ex d solutions are often more cost effective to both purchase and install.
Slightly more of a challenge to atg UV’s engineers was how to retrofit the new UV chamber within the confines of the planned shutdown. UV technology has moved on since the original plant was installed at Avonmouth and atg’s UVLA-2200-6 was smaller than the original lamp with different connections.
To ensure an easy installation in the restricted space of the plant room, atg UV’s engineers re-designed the inlet and outlet connection and fabricated off-site a special unit that would directly replace the existing one. The installation was completed without difficulty and was commissioned in time for the scheduled system re-start. The new Ex d control panel (pictured) was only a third of the size of the original.
The pharmaceutical grade UVLA-2200-6 reaction chamber is a hygienic design to the Pressure Equipment Directive and is fabricated in 316L stainless steel electro-polished to a 0.4 Ra internal finish. It uses two high efficiency amalgam lamps to deliver a minimum UV dose of 40 mJ/cm2 (based on a single pass) in accordance with NSF/ANSI Standard 55: Ultraviolet Microbiological Water Treatment Systems, the established requirement for a point-of-use (POU) Class A system.
To ensure that the required dose is delivered to all parts of the reaction chamber, the chamber is fitted with an intrinsically safe UV intensity monitor. The Ex d Spectra IP66 control and power panel is fabricated in copper-free aluminium alloy with an epoxy coating.
Daniel Arthur comments: “Moving to current best practice with the atg UV system is much simpler than the old one, it’s safer and performs better. It also needs less maintenance and has reduced our operating costs”.