For all the challenges faced by engineers trying to solve difficult level applications, they have one thing in their favor: liquids level out. Even viscous products eventually settle more-or-less evenly in a vessel. Such is not necessarily the case with solids. Some may behave nicely, largely like liquids, while others are more like solids, forming vertical displacements to rival the Himalayas.
Trying to get a meaningful level measurement in such a situation is indeed a challenge, as Lydia Miller points out in her article, The Right Stuff, in the autumn 2018 issue of Dry Bulk quarterly. These characteristics do not make the task any easier, as she reminds us.
When determining liquid level, there is only the need to measure a single point on the surface, because the level will be identical at any point within the vessel. With solids, however, the material surface consists of a multitude of peaks and troughs that constantly shift as the vessel is filled and emptied. Depending on how much material piles up before sliding, along with the vessel’s width, the difference between the level of a peak and a trough can be up to 100%.
This problem makes continuous automated level measurement problematic. Mechanical methods to plumb the depths of a vessel from the top are still in use in many facilities.
Often, manual measurement methods continue to be used because that is the way it has always been done or because there are concerns with using or implementing an automated system. However, significant progress has been made with automated systems for solids measurement, and many operators of modern production plants have upgraded to continuous automated measurement technology. Today, integrating automation into solids measurement can improve safety, reliability, and repeatability, and enable accurate continuous measurements to be accessed from remote locations such as a control room.
The ability to get a meaningful reading from the comfort of the control room without the need for a tape measure and flashlight is the ultimate goal, especially for plant personnel who have to climb a ladder, open a hatch and peer inside a vessel. Some have tried guided-wave radar (GWR) which works very well for providing a very accurate point reading. In some applications, this is sufficient and far better than any manual or mechanical approach, but it does not compensate for the hills and ravines often found when storing solids in vessels. Non-contacting radar can cover a slightly larger area, but is still a point reading for all practical purposes. Compensating for terrain requires a much different approach: a 3D solids scanner.
Acoustic phased array antennas, often used in 3D solids scanners, generate a mixture of three audible or acoustic signals, including one dust-penetrating, low-frequency acoustic signal, and receive multiple echo signals from the contents of a storage vessel. Digital analysis of these echoed signals produces accurate level and volume measurements by mapping all the signals across the entire surface within the beam angle of the device. Matching the received data with known vessel dimensions allows 3D solids scanners to calculate product volume, enabling the immediate and accurate listing of inventory value for accounting and financial reports.
The scanner she’s talking about is the Rosemount 5708 3D Solids Scanner, which uses acoustic phased-array technology to measure the high and low points and compensate for the formations to deliver an accurate and continuous picture of the vessel contents. When it comes to inventory value, you can’t ever be too accurate.
You can find more information like this and meet with other people looking at the same kinds of situations in the Emerson Exchange365 community. It’s a place where you can communicate and exchange information with experts and peers in all sorts of industries around the world. Look for the Level Group and other specialty areas for suggestions and answers.