Volumetrics with Velocity
Brill was not joyriding at the Brilliant, Ohio, electric generating plant, but was using AEP’s mobile mapping system to map the surface of coal stored at the plant. As he rode, small dots appeared on an onboard computer screen, showing where he was mapping. Those dots were later used to construct a finished topographic drawing detailing the surface of the coal. The Civil Laboratory of the Civil & Mining Engineering Division at AEP’s Dolan Labs located in Groveport, Ohio, worked with GeoLogic Computer Systems (Waterford, Mich.) to develop the mapping system to inventory coal storage piles. AEP has broadened the use of the system for gathering topography and site-specific feature locations for preliminary site surveys of new construction and to carry out annual as-built mapping of power plant landfills. The process is similar for each use:
- A robotic total station (RTS) is set up near the site. The RTS is oriented and aimed so its infrared beam locks onto a light-emitting diode (LED)-equipped, 360-degree prism mounted on the ATV.
- A remote positioning unit (RPU), directly connected to a computer mounted on the ATV, receives raw data output via radio transmissions from the RTS.
- The computer constantly downloads raw data from the RPU, processes it and stores x, y and z coordinates in an ASCII file, simultaneously plotting them on an onboard LCD monitor. These plotted points correlate to the ATV’s current location.
In coal pile inventories, core drilling using the CAST (Continuous Auger Sample Tube) method is also done at various locations on a coal pile. Samples are taken every 2.5' down to the pile’s base and accurately weighed to determine the density of the coal pile.
Preliminary data gathered from drilling samples and mobile mapping is E-mailed from the plant to Mark Flynn, survey specialist and system coal pile inventory coordinator at the Civil Lab. Using CAD computers and software, Flynn generates volumes and densities, prepares maps and cross sections, and issues a final report to the plant. With this report, the plant calculates its tonnage of current stored coal.
A Unique Mapping System for Utilities“We know surveying firms that use this method, but as far as we know, no other utility uses it, so we’re pretty unique,” Flynn says. “It makes coal inventory accounting as paper-free and seamless as possible.”
AEP first used the process in its fall 1995 inventories. In winter 1996, AEP purchased a mobile mapping system. In spring 1997, the inventories were performed completely by AEP employees and equipment, and they have been done this way exclusively since.
“We know we have something we’re doing well. It adds value to the company, and with onset of competition in the electric utility industry, we will need to know these figures more rapidly, more accurately and possibly more often,” says Charles Cassell, manager of the Civil Lab.
State public utility commissions require electric utilities to inventory their coal supplies annually, but it is also good business practice. Each fall or spring, AEP surveys coal yards of its own 16 plants and two others owned by consortiums, all located mainly along the Ohio River. Only plants where inventory variances are out of acceptable range are re-surveyed.
“It’s an accounting issue,” Flynn says. “We take a physical inventory, just like items on a shelf, only you can’t count coal like items on a shelf. Coal must be measured with a process that takes into account three dimensions. This is a way of measuring and testing to determine an accurate volume.”
For many years, independent contractors conducted aerial surveys for AEP, augmented on-site with drilling and nuclear densometers to determine coal pile volumes. Density drilling and aerial photography were seldom done at the same time. It was a less efficient process, and it took a month or more to receive results.
“The new system is more accurate, and we can keep better track of the base maps,” Flynn says. “It’s also quicker. The crew goes out to a plant on Monday, and I mail a report back to the plant by Friday.”
Cost savings can be directly linked to using the mobile mapping system over the aerial mapping method. The new system saves considerable time and expense that was required to properly prepare and mark coal piles before aerial surveys. This process had to be repeated by plant employees if weather on a scheduled flyover day was cloudy. Now, the plant needs only to send its baseline report to the Civil Lab prior to the survey.
A Flexible and Safe PracticeThe system is capable of using the Global Positioning System (GPS) and also ties into a pulsed laser measuring device, which can measure the angle and distance to an object 200' to 300' away without using a reflector. The Criterion laser device (Laser Technology Inc., Englewood, Colo.) can be either hand-held or mounted on a tripod.
A disk drive is mounted on the ATV, a 4x4 Polaris Xplorer 500, as well as a 486 computer that runs GeoSite programs (GeoLogic) on Windows 95. Programs include GeoTopo for conducting coal pile and topographic surveys, GeoPoint for determining stakeout coordinates, GeoField for roadway grade checking and GeoPipe for determining excavation depth for laying pipe.
"The combination of these pieces of equipment allows the measuring team to rapidly and accurately collect the x, y and z locations of many points on a coal pile," Flynn says. "We estimate that 10 to 15 hours is required to survey an average AEP coal pile, and in this time, as many as 10,000 points can be collected - with as little as 1' between points. This creates an extremely dense and detail-rich map - nearly a thumbprint of the site."
In comparison, an on-foot survey of the average coal pile, about 30 to 40 acres in size, could be done in about the same time, but with only about 400 to 500 points recorded, resulting in a much less detailed and accurate map.
The mobile mapper results in a more dense, precise, accurate map, with far more capability for the surveyor and those who use the maps for accounting purposes. In the field, the software allows the surveyor to zoom in to control data points and see views from different directions on the monitor. It also allows the creation of many other details, such as overlaying existing maps over new survey data for comparison.
AEP uses the overlay feature to comply with its "no travel zone" safety practices. At most coal stockpile facilities, feeders are used to distribute material. Feeder areas are prone to "rat holing" or bridging - stockpiled coal can give way without warning, burying the equipment and employee. This is why AEP determines the highest elevation of compacted coal around those feeders and then loads a predetermined background drawing showing the corresponding "no travel zone" perimeter. Perimeters are derived using the draw down angle for feeders at particular facilities. Any mapping features needed within these zones are gathered from well outside the perimeter by using the pulsed laser.
An entire file of data from a typical site survey using the system can be stored in a single 3.5-inch floppy disk because the system is based on ASCII linear files.
State regulations mandate surveys of AEP's power plant landfills, which are used to dispose of ash, a by-product of burning coal to produce electricity.
"State environmental protection agencies require that any change in a plant's landfill be recorded annually. They-and we-want to make sure the landfill looks like it is supposed to, that it's built the way it's designed," Flynn says. "Depending in which state the landfill is located, a survey must be done annually to ensure that the facility remains in compliance with environmental regulations."
The new systems growth prospects are good. "The mobile mapper has more capabilities than we use it for," Flynn says. "The options exist to market this service outside our company. There is interest from industries that need to map landfills on an annual basis."
In addition to mapping coal piles and landfills, the system has also helped AEP map a preliminary site plan for a new training facility, re-route two roads at two different power plants and provide a preliminary site map of a new transmission station.
Sidebar: Measuring a Coal Storage Pile
- Two known control points are needed, as well as a file with background information (i.e., perimeters, drains, coal feeders).
- Set instrument over one control point; backsight target set over second control point. This establishes coordinates and bearings for the ATV program.
- Point the instrument at the target on the ATV and start driving.
- The program automatically records the shots as the ATV moves along.