Flicking the switch on hazardous spills

Hazardous spillage often conjures up images of caustic ammonia liquid and fumes spewing out uncontrolled from huge tanks. This is definitely dangerous but often, the dangers associated with spillage exist in the most innocuous and unlikely places like processing plants and dairies.

According to John Immelman, managing director of Endress+Hauser Australia, most spillages are caused by overfilling tanks and vessels.

"Spillage can be prevented by turning off the filling pumps or closing the inlet valve. The turn off 'trigger' is normally a high level switch mounted at the top of the tank. When the liquid rises to the switch level, the pump is turned off preventing further filling and consequent spill," he says.

Food and beverage plants periodically undergo cleaning-in-place (CIP) and sterilisation-in-place (SIP). This requires strong cleaning chemicals that need to be closely monitored and carefully managed.

Accidental discharge of these chemicals into the surrounding environment can cause serious damage. In a dairy, for example, even the accidental spillage of cream can be cause for concern as it will need to be carefully disposed of after being suitably treated.

"It is critical that plant managers and engineers choose the right level detection switches as they can prevent the accidental discharge of toxic products into the environment," says Immelman.

"A well selected, correctly installed level switch will save companies the expense associated with treating and disposing of spilt material. Moreover, it will safeguard companies against punitive fines in the event of an unavoidable accident."

"Endress+Hauser offers spillage detectors such as high level switches, commonly known as Liquiphant, but there are a number of other technologies that can be used. Most other types of switches can have their reliability influenced negatively by the properties of the liquid ie, viscosity, conductivity, density etc. In many cases, a simple $500 level detection switch is all that is needed to protect a company's assets from the problems associated with spillage," says Immelman.

Endress+Hauser believes that process application is unique and temperature, pressure, corrosion, abrasion and atmospheric conditions must be taken into account in selecting the appropriate level switch.

"Also to be factored in are process connections, housing types, power supply type, outputs (relay or transistor) and chemical compatibility. Safety ratings are becoming increasingly critical and a host of new standards such as IEC 61 508 must be considered in selecting a level switch," says Immelman.

"We have a guide called the Selection and Engineering Guide for Level Measurement, which assists the user in making more informed decisions. The guide also offers vital information on different measuring principles for level limit detection and its application and installation in liquids as well as in bulk solids."

Immelman says that all process industries need anti-spillage switches such as mining, chemical, petrochemical, wastewater treatment, dairies, breweries and pulp mills.

"Managers of plants, both small and large, must first assess the risks associated with the equipment being controlled and then determine the necessary risk reduction needed."

"It is imperative to determine the safety integrity level (SIL) rating of a plant prior to ordering the process instrumentation," he says, adding that SIL ratings 1, 2, 3 and 4 offer probability of a dangerous failure over time and can be used to measure the range of risk reduction afforded by a piece of equipment.

Endress+Hauser has also developed radiometric detection switching gamma instrumentation for use where conventional methods for level detection switching in chemical, petrochemical, oil and gas, mining, paper and pulp, and energy applications are inappropriate.

"In some anti-spillage switching applications, it is not possible to attach the detection equipment to the vessel in any way. It could be that the temperature is too high, pressure is too high or it's too dangerous to penetrate the vessel," says Immelman.

"In these cases, a very small (pinhead-size) radioactive source beam (gamma ray) is directed at the vessel and a detector on the other side measures the strength of the gamma ray. When the liquid rises to the level of the beam, the beam strength is attenuated and the detector switches."

"Whether unloading an oil tanker or manufacturing cream cheese, spills can be hazardous to people, property and the environment, and to a company's bottom line. Fortunately, this is often an easy problem to fix and basically requires an understanding of SIL ratings and the installation of relatively low-cost level switches," says Immelman.