Dumper upgrades boost reliability
Coal handling equipment reliability improved at two power plants after refurbishment
By Randall Johnson, Tennessee Valley Authority
Rotary railroad car dumpers first gained widespread adoption for bulk materials transportation no more than 50 years ago. At that time, the concept of rotating a loaded railcar 180 degrees to dump its entire load was considered revolutionary.
Today, such equipment, often called roll dumpers, seems so commonplace that the current state-of-the-art dumper designs may go unrecognized because of their external similarities to the earliest developments. Current rotary car dumper systems are more efficient, accurate and productive. Because they have been more or less dependable, many dumper installations in use today date from the very early years. However, wear, weathering and new demands on such aging equipment naturally take their toll.
Reduced reliability of dumpers were the circumstances facing the Tennessee Valley Authority (TVA) at the end of the 1980s. Coal handling installations at the Kingston, Shawnee, Gallatin, Widows Creek and John Sevier sites were all approximately 40 years old and had an original design life of 25 years. Further, each had been operating beyond its original design capacity almost since the date that they began operating.
In the pre-World War II era, the standard railroad hopper car carried 70 tons. The dumpers had just been built and readied to operate when the standard was raised to 100-ton cars. Quick evaluations of their specifications allowed the builders and TVA to adapt them to the new, higher tonnage demands.
However, stress and heavy work took its toll and, by 1989, each installation began showing its age. Several dumpers were out-of-doors and fully exposed to a range of weather conditions. All featured clamping systems that had long since been superseded by simpler, more reliable engineering and manufacturing designs. Each dumper also needed new, more sophisticated, more effective car positioning and safety devices.
By this time, TVA engineers had became more watchful for signs of catastrophic failures at the unsheltered dumpers and closely monitored the frequency of breakdowns and downtime at all power plants. It appeared that the future economics of fossil fuel usage would increase each power plant?s need for dependable, productive coal handling and car dumping systems.
The fossil fuel procurement department routinely reviews cost data to identify and track the components that make up procurement and fuel handling costs. During the winter of 1987-88, the work identified railcar dumpers at both the Kingston and Shawnee plants as major contributors to increasing costs. Weathering was not the major problem here because both installations were under cover. However, the real needs involved improved reliability and greater efficiency.
The decision making process
Decisions on major equipment upgrades normally are reached in several steps at TVA. These are finding reasons for improvement, defining the problem, analyzing related data, identifying potential solutions, reviewing the results of applying the solution of choice and, if successful, using that choice in similar situations throughout the system. Facts are the guiding factor in all phases ranging from the analysis phase through the solution (which includes funding justification and procurement) and study phases.
There was plenty of data to guide engineers to dumper problem areas and needs at Kingston and Shawnee, hence the process took only several weeks to reach the solution phase. For example, operating records showed frequent mechanical breakdowns, which, of course, resulted in idled unloaded coal cars, thereby resulting in the loss of system capacity. The analysis quickly focused on increased handling costs traceable to the dumpers.
The original equipment had been built and installed by Heyl & Patterson, Pittsburgh, Pa., and that company was selected to perform the refurbishment of these two plants? rotary car dumpers. One advantage to selecting this original contractor for the equipment upgrade was that it still had the original plans and knew the scope of the projects in question.
A major area in the upgrading project involved replacing the mechanical car clamping systems. The original technology had never been replaced or even upgraded on the dumpers and it tended to be complex and bulky. Car clamps were replaced by a new system that is expected to operate for another 20 years.
It is important to mention that TVA was not trying to increase throughput in these upgrades. Both plants have takeaway capacities that are matched to their fuel consumption requirements so there was and is no need to expand unloading capacities. At Kingston, materials handling capacities are 1,000 tons per hour. The old and new dumpers easily exceed that. Our concerns from beginning to end were those of improved reliability and greater efficiency at the dumper stage of fuel handling.
Because the Kingston and Shawnee dumpers were always under roof, they were not structurally deteriorated. Almost from the earliest planning, the staff focused largely on the refurbishing procedure that was adopted rather than replacing them. The job included installing entirely new electrical control systems?electro-mechanical brakes, photo-electrically controlled position equipment, new kinds of limit switches and controls, and improved lighting.
Also replaced were all major mechanical components, including drive gearing, trunnion wheels, in-rails and the clamping systems. Although electronic scales were added in replacement projects at the John Sevier, Widows Creek and Gallatin power plants, they were not needed at Kingston and Shawnee. Retrofits are still being evaluated.
These dumper refurbishments and replacements met TVA goals very well and are an accepted part of the long-term planning for fossil-fuel utilization. In 1993, fossil fuels accounted for 76.1 percent of all TVA power generation, which is 25,000 MW. On that scale of operation the ability to dump coal railcars carrying 100 tons or more efficiently, reliably and completely is an economic asset that increases the number of available suppliers and the geographic range of resources. These same advantages also give TVA greater ability to meet and adapt to future environmental needs. END
Randall E. Johnson is a manager fuel measurement and handling for Tennessee Valley Authority (TVA). He earned a bachelor?s degree in civil engineering from West Virginia University. Johnson is a registered professional engineer. Prior to joining TVA, Johnson worked at Lively Manufacturing and Equipment Co., G.T. Lilly Engineering as project engineer.
TVA?s rotary coal dumpers have undergone extensive refurbishment including a major refit of the car clamping mechanism.