If you want to describe something as black, really black, you might say it’s black as coal. It’s a poetic metaphor, but consider it in more practical terms. Say you’re trying to figure out how much coal is in a coal bunker that’s bigger than a house. You open the hatch, shine in a flashlight and see a lot of, well, black. Not exactly conducive to developing an accurate estimation of the contents.
Dave Wombacher, who works at the Luminant Baldwin Power Station, deals with this issue every day as the facility works to optimize coal distribution among its complex of bunkers. He told his own story, relating the problem and solution, in a presentation at Emerson Exchange 2018, and created an article from the presentation which is now published in Power Engineering February 2019, Measuring the Level in Coal Bunkers at Illinois Power Plant. He describes the problem:
An operator following the long-standing manual measurement procedure lifts up a roof section and peers into the bunker with the aid of a flashlight. This presents a host of problems including difficulties seeing through coal dust, accurately determining the actual level and avoiding slip-and-fall hazards. These issues are exacerbated because the operator typically works alone. An automated means of continuously and accurately measuring level was needed, but this would require an innovative solution capable of reading the characteristic peaks and valleys that form in coal bunkers.
Dave and Luminant had run headlong into the great challenge of measuring level with solids: they don’t settle like liquids. Peaks and valleys get in the way and make accurate level measurement difficult if not impossible. When you can hardly see what’s in the bunker, it’s even worse. Determining level in this situation is a critical measurement because of the complex system of coal handling necessary to keep the pulverizing systems fed evenly. The two bunker systems are both huge at 186 feet long, 35 feet wide and 48 feet tall. Here’s how it used to work:
An operator must be working in the bunker room and in communication via radio with the coal yard and the control room. He or she determines the bunker level by peeling back the dust belt/mat to look inside the bunker with a flashlight, in effect acting as the level instrument. The operator determines which bunker needs coal and at what point the tripper car can be moved to the next bunker. The operator must also tell the control room personnel how long they need to keep supplying coal to the belt. Since the operator can reliably only see only about 15 feet into the bunker, he or she always fills the bunker to within a foot or so of the roof to provide a safety margin, which is often not the desired level.
Fortunately, a technology emerged to solve the problem. Working with Experitec, one of Emerson’s Impact Partners, Dave learned about the Rosemount 5708 3D Solids Scanner with its Acoustic Phased Array transducer. It’s able to create an accurate 3D model of the surface of the pile and analyze the topography to calculate an accurate volumetric reading of the bunker contents. Usually one scanner can cover a large interior, but in this case given the sheer size and another critical constraint, Emerson had to think outside the box and create a custom solution.
In most applications, a survey is taken of the storage vessel or container to determine optimal placement of each transmitter. But in this case, the 13 existing openings in the bunker roof had to be used to mount the transmitters because it was too expensive to drill new holes in the thick concrete roof. This limitation forced Emerson to produce a custom design, using the output from each of the 13 transmitters as inputs to a software program hosted on a PC, referred to as the bunker scanner controller (BSC). Although the software program is a standard Emerson platform designed for use in conjunction with the 5708, it had to be customized for this particular application to produce the required 3D view of the coal levels in the bunker.
The article goes into more detail about how data from the scanners helps guide the distribution mechanism, but suffice it to say, the system works. Operator trips up to the bunker area are far less frequent and the whole operation is more highly automated.
You can find more information like this and meet with other people like Dave Wombacher 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.