Force Flow Scales

Measurement methods for chemical storage tank inventory calculation

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radar-sensor-mounted-above-polypropylene-tank
A radar sensor mounted above the polypropylene tank, eliminating the need for an additional process connection.

By Greg Tischler

The compositions of chemicals in use today are as diverse as the manufacturers and the distributers who ensure there is a steady supply for consumers and industry alike. Likewise, the technology these companies use to measure and manage their chemical inventories can be just as diverse.

These facilities have an array of options for measuring the amount of chemicals inside their tanks. One large chemical manufacturer and distributor had previously been using weigh scales installed beneath every tank and vessel. However, they recently switched to high frequency through-air radar sensors.

Weigh scales: the classic measurement

Weigh scales, sometimes referred to as load cells, are widely used for measuring inventory in large tanks. These scales are installed under a chemical tank to make a weight measurement. Using this measurement and a known density, the sensor electronics can output a volume to help facilities better manage their inventory.

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Weigh scale technology is easy to understand, and it works. A weight measurement is made mechanically, which can easily be calculated into an accurate volume measurement using a known density and a simple formula. Since weigh scales have no contact with the medium being measured, these sensors can measure any liquid chemical despite corrosive or harmful properties.

Straightforward measurement, however, is where the simplicity ends. Installation alone can be costly, time-consuming, and labour-intensive. Installing a single system means lifting the entire vessel and placing the weigh scale underneath. Shutting down a process or taking a vessel out of use, if necessary, only increases costs further.

Weigh scales can also be expensive to maintain. These instruments make a mechanical measurement, so they need to be regularly cleaned, recalibrated, and repaired.

All of this takes valuable time for maintenance crews, yet for many facilities, this process has become routine. Every few months, vessels are taken out of service, so maintenance crews can inspect and recalibrate the instrumentation.

High frequency radar measurement

Through-air radar works by emitting radio microwaves from the radar antenna system to the measured product, where it is reflected by the product surface and back to the antenna system. The radar sensor uses time of flight to measure the level of the product. Radar sensor electronics can use the level measurement and the vessel geometry to calculate product volume inside the tank.

The real-world benefits of high frequency 80 GHz radar can be seen in an array of applications, including chemical tanks. Radar sensors with 80 GHz frequency have enhanced focusing, the ability to make measurements through plastic vessels, and special software to generate an accurate and reliable echo curve to interpret the level inside the vessel.

A radar beam’s focus is dependent on two factors: the size of the radar transmitter’s antenna and its transmission frequency. A smaller antenna or a lower frequency results in a wider, less focused beam. Conversely, a larger antenna or a higher frequency results in a narrower, more focused signal.

Therefore, a radar sensor using a high 80 GHz frequency can accurately measure in small or narrow vessels, with little to no interference.

Radar signals can also penetrate non-conductive products like plastic and fibreglass. Since many chemicals are stored in tanks made of polyethylene, commonly referred to as poly tanks, an 80 GHz radar sensor can simply be installed above these tanks, without the need for an additional process connection. This simplifies and decreases the costs associated with installation.

The intelligent electronics within today’s 80 GHz radar sensors multitask to meet individual user’s needs. In their most basic function, the electronics output a level measurement, but they can also calculate a volume measurement using known vessel geometries. Those same electronics can even filter out signal interference from condensation, or dust and dirt built up on the antenna, so there is no need for regular maintenance, cleaning, or recalibrations.

Upgrading to new measurement technology

The chemical manufacturer and distributor had grown tired of constantly calibrating their weigh scales. Tanks at this facility ranged in size from small portable tanks to large vessels capable of holding thousands of litres.

Over time, measurements would drift, which resulted in slight measurement errors at best, and dangerous, costly spills at worst. Plus, whenever the facility needed to move a tank, the weigh scale sensors would have to be recalibrated and recertified. The cost of maintaining all the weigh scales was growing.

After exploring the available measurement options, operators at the facility chose the VEGAPULS C 11. This 80 GHz radar sensor has a fixed cable connection attached to a chemical-resistant PVDF housing. Installation was inexpensive and straightforward.
Maintenance staff simply installed some of the radars in existing process connections on top of the tanks, or hung the radar above the poly tank and measured through the top of the vessel.

Better results with better technology

Installing the new VEGAPULS C 11 radar sensors resulted in accurate measurements, which eliminated inventory errors, overfilling, and safety concerns related to incorrect measurements. The new radar sensors provided accurate volumetric measurement outputs without the need for ongoing maintenance.

A simple swap of measurement instrumentation improved operational efficiency and safety records. Now, the company is moving forward with plans to standardize the measurement instrumentation at their other facilities.

Greg Tischler is with Vega Americas. For more information contact VEGA Instruments Canada. Email: canadaquotes@vega.com

Read the full article in ES&E Magazine’s June 2021 issue:

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