MEASUREMENT PROCEDURES - Emerson

1 ASAEL SHARABI, Emerson AUTOMATION SOLUTIONS, USA, EXPLAINS HOW THE LATEST 3D LEVEL SCANNER TECHNOLOGY ENABLES ACCURATE VOLUME MEASUREMENT OF UREA TO IMPROVE INVENTORY MANAGEMENT. SOLID MEASUREMENT PROCEDURES Inventory is one of the most important facets of a production and storage process, and its effective management is increasingly recognised as a key component of an organisation s financial health and profitability. Accurate and reliable MEASUREMENT of bulk solids, such as urea, is critical for inventory control and maintaining efficient operations.

2 However, many types of level instrumentation used successfully in other process industries cannot withstand the special challenges of the fertilizer industry, such as dusty conditions that can obstruct MEASUREMENT readings or the need for volume measurements to support bulk solid inventory fertilizer production, raw materials and final products are stored in large silos or warehouses. Unlike liquids that have a relatively easy to measure level surface, the surface of solid materials is rarely flat, with peaks and troughs that change as the storage unit is filled and emptied.

3 Performing manual measurements is time-consuming, inaccurate and fails to provide the data needed to support best practice in inventory management. It also creates safety concerns, as | WORLD FERTILIZER | REPRINTED FROM MAY / JUNE 2017workers can be required to perform duties in hazardous locations. This is especially the case when materials such as urea are traditional approach to monitoring inventory in this industry has been to use load cells to monitor incoming and outgoing movements, with mechanical devices known as yo-yos deployed to measure levels in vessels.

4 However, both technologies have limitations in terms of accuracy, reliability and repeatability of MEASUREMENT . Yo-yos feature a weight attached to a wire being lowered onto the surface of the solids at scheduled times. The device calculates the level of the product based on the length of wire required before the weight touches the surface. However, as the spool mechanism is in contact with the product, these systems require regular maintenance exposing operators to hazardous products and trips up to the top of tall silos.

5 Also, losing the weight due to a broken wire can cause serious problems further down the production , accuracy with this MEASUREMENT technique is no better than 10 15%. In a warehouse, capable of storing thousands of tonnes, that adds up to a large invisible inventory, which is a problem. Such unreliable measurements leave process operators with insufficient information for effective day-to-day decision-making and inventory solutions can help with some of these issues. Technologies such as radar and ultrasonic enable continuous measurements in silos.

6 These technologies, when correctly applied and installed, help to improve safety and enable process levels to be monitored remotely from the comfort of a control room. However, devices that measure the level at a single point within a vessel do not account for variations caused by peaks and troughs, making any MEASUREMENT of volume extremely inaccurate and unreliable. At large storage facilities, installing multiple devices to obtain additional level data helps to provide a more accurate calculation of the total volume of materials in the vessel.

7 However, the calculation may still be inaccurate if the surface of the media does not follow the expected dramatic undulations and varying surface of solids makes measuring the level in a vessel less than useful when trying to determine the amount of product being stored. For example, the level at one point in the vessel might be at a height that suggests the vessel is 50% full, directly beneath a filling point it could be 100% or above the emptying point it could be 0% full. These huge variations make it impossible to calculate how much material is actually being stored.

8 Instead of a level at one location (or even several), and maximum or minimum levels, the metric required is the total volume of the solids. Technologies for measuring solids level and volumeNew acoustic frequency scanner technologies can now replace traditional single point level measurements with continuous online volume MEASUREMENT , and also offer visualisation of peaks and valleys within devices called acoustic scanners are based on sonic (acoustic) technology and are similar to ultrasonic, but operate at lower frequencies.

9 This is useful in a typical dusty solids application because low-frequency sound waves are absorbed less as they travel through dust than high-frequency sound waves. Acoustic-based scanners are unaffected by environmental conditions, such as dust, filling noise, humidity or temperature. In addition, acoustic devices are inherently self-cleaning, with any dust particles that coat the horns being driven out by the vibrating membranes. Although solids being measured must have a bulk density above short t/m3, there is no need to perform any special calibration for different 1.

10 Solids level MEASUREMENT technologies. Figure 2. Rosemount 5708 series 3D FROM MAY / JUNE 2017 | WORLD FERTILIZER | A further benefit of lower frequency devices is that they use a wider beam angle. In solids applications, where the objective is to map as much of the surface as possible, a wide beam angle is preferred as it allows more of the surface to be mapped with fewer mapping technologies provide accurate and reliable resultsRecognising the need for accurate volume measurements of bulk solids and powders in large storage vessels, Emerson has developed a range of 3D solids scanners that use a combination of acoustic MEASUREMENT and 3D mapping technologies.