A Hycontrol low power microwave system has replaced a gamma radiation blocked chute detector at Singleton Birch’s lime kiln. Reasons why include the original system’s cost, safety, operator training needs and licensing requirements
Independent lime supplier Singleton Birch produces quicklime, hydrated lime, natural hydraulic lime, graded chalk, aggregates and other products and services from its site in Batts Coombe Quarry in Somerset.
The company’s blocked chute detection system plays a key role in ensuring a steady, uninterrupted supply of crushed limestone to the lime kiln, determining when the feed hopper is empty and needs to be refilled. Until recently, nucleonic devices were considered to be the only reliable form of instrumentation for level measurement in such harsh applications.
However, although nucleonics provides a technically competent technology, this measurement technique requires a radiation source from a radioactive isotope, such as Caesium Cs137 or Cobalt 60 in order to detect the presence of material in the hopper. The radiation source then has to be shielded so that the radiation is only directed through the hopper wall towards the product. Levels of radiation detected on the opposite side of the hopper are then used to determine whether there is a blockage or not.
The potential dangers, cost and licensing requirements associated with the use of nuclear sources in industrial environments led to Singleton Birch to examine other measurement techniques, eventually choosing a low power microwave system from Hycontrol.
A key advantage of the microwave technology is its ability to ‘see through’ low dielectric materials... This means that low cost replaceable windows can easily be fitted into the sides of a chute, vessel or container, keeping the process closed with no disruption to material flow
According to Hycontrol, straightforward cost comparisons alone give microwave technology a favourable advantage, but additional costs of ownership for the nucleonics system include the added mandatory site security, operator training, provisions for checks from the authorities plus annual licensing fees. In addition, the nuclear sources have a high cost of disposal.
Microwave level switches from Hycontrol provide a simple, non-contact, non-intrusive option suitable for applications on both liquids and solids. Batts Combe is a typical installation consisting of a microwave transmitter and receiver, mounted facing one another across the bottom of the hopper. During operation the transmitter emits a continuous, low power, 24 Ghz microwave beam to the receiver and an output relay is energised or de-energised when this beam is obstructed by the material being monitored. The switch trigger point is determined by the amount of microwave energy received and can therefore be adjusted to cater for specific products and applications.
An advantage of the microwave technology is its ability to ‘see through’ low dielectric materials such as refractory bricks, ceramics, plastics and polymers. This means that low cost replaceable windows can easily be fitted into the sides of a chute, vessel or container, keeping the process closed with no disruption to material flow and the microwave transmitters/receivers at arms length away from the harsh environment. The system is easy to set up and calibrate and the microwave signals are unaffected by high dust levels or material build up on the sides of the chute. In the Batts Combe application, low friction, temperature resistant PTFE windows are utilized.
Microwave power levels are well below any required industry standards and therefore this device requires no special procedures for its operation and use. Depending on the application, the addition of a flow switch module means the same detector set can provide flow and no-flow detection together with blocked chute alarms.
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