Keeping chemicals safe

To get the right sensor specification means it needs to be made of the right materials, sometimes needing expensive alloys and elastomer seals in the construction. During fitting or removal, both sensor and process will also require containment, isolation and decontamination, as well as comprehensive personal protection equipment ( i.e. COSSH regulations). This often results in mandatory closing off an area of the plant while any equipment installation or removal is taking place on the vessel. These necessary health and safety procedures incur extra safety risks and cost.

When storing chemicals, especially those that are highly acid or alkali, they are generally highly toxic, corrosive substances that can leave residues and readily give off vapours and fumes. Any contact with, or release into the atmosphere can quickly create  a very hazardous environment for personnel. At Cory, these chemical products require careful monitoring and accurate level measurement to remove any risk of overfill, and ensure the process has ample supply.

“We wanted a new level system that would avoid any repeat of the issues with the original sensors, ideally eliminating process contact and any risks experienced with the previous technology.” Said the Cory instrument engineer.  VEGA proposed to use contactless radar sensors mounted above and outside the vessels looking through the vessel top  to measure the liquid level inside.

When it comes to liquid level measurement of chemicals a sensor generally requires a process connection into the vessel to get its ‘sensing part’ to connect into the process - even when using a top mounted ‘non contact’ device - it could be a rod, cable or diaphragm. So, to be able to measure any process variable completely without contact provides many benefits; from longevity of operation, protection from  chemicals and the process, along with the increased safety through reduction or complete elimination of exposure to harmful substances. Radar has quite a unique ability to measure the level of a liquid down right through an opaque plastic vessel top or window on a nozzle, completely from the outside.

With new materials and manufacturing techniques, more and more companies are utilising plastic vessels and tanks for chemical and bulk liquid storage. These are quicker to make, are generally more cost effective and have good chemical resistance, as well as being lighter to manoeuvre during installation. They can also offer a longer lifespan and lower maintenance than equivalent steel painted, lined or coated vessels, for example.  Many even come with ‘integrated bunds’ for overflow or overspill protection. We also see plastic IBC’s as one of the most common vessels for bulk transport of intermediate quantities of liquid. Radar technology can be used to measure liquid level through the top of all these vessel types.

Radar uses microwave technology. Just as you see every day in a microwave oven using plastic glass and other non metallic, non-conductive containers that allow the microwaves to pass through and only interact and heat the conductive, water-based foods inside. (that's why you cannot heat dry powders in a microwave oven). A level radar has the same capability, it can transmit signals through plastic and other non conductive materials (like glass and ceramic) and reflect back off a liquid level inside.  And, with a good dynamic range (sensitivity) it can also deal with any condensate or sublimation on the inside of the vessel roof.

Using 80 GHz radar offers several benefits; firstly the higher focusing means it achieves good penetration through the plastic vessel roof, it also offers more mounting position options (i.e. closer proximity to vessel wall or nozzles) and less likely to pick up any unwanted false signals.  They also have a wide measuring range capability from very small to very tall vessels, up to 30m high.  Lastly, high dynamic sensitivity to handle condensation and build up inside the roof caused by fumes or sublimation from the products inside. It can even measure low reflectivity, oil-based hydrocarbons in some applications of this type.