In 1969 and 1970, a 273-mile, 18-inch pipeline was constructed from Kayenta, Arizona, to the 1500 megawatt Mohave power plant near Bullhead City, Arizona, for handling of up to 5,000,000 tons of coal per year in slurry form. Black Mesa Pipeline was a subsidiary of Southern Pacific Pipe Lines, Inc. and acted as a subcontractor to the Peabody Coal Company in providing transportation from mine to power plant under a 35-year contract. It was, at the time, the world’s largest and longest coal carrying pipeline with a total gross investment as of January 1, 1976 of $38,865,636 ($195,392,713 in 2023).
In a liquids pipeline, pressure moves the product rather easily and from a static line startup can be resumed without difficulty. In a solids carrying pipeline, the material to be transported must be finely ground in precise proportions before suspending in water to achieve liquid flow patterns. To reduce the friction and wear with the pipe, the velocity of flow must be kept to within narrow limits. This mixture of half water and half solids is called slurry.
The operation of a coal slurry pipeline had been carried on successfully only once before and that was in a smaller 10-inch pipeline and over a short distance on relatively flat terrain in Ohio. Because of the rugged terrain, four pumping stations were required. With the exception of one location having 1,750 horsepower positive displacement units, all were equipped with 1,500 horsepower pumps to deliver the pressure required to lift the slurry over peaks higher than 6,500 feet. The most precipitous and difficult pressure requirement was to push the slurry up 1,600 feet in less than 25 miles. To accomplish that, four large duplex-piston pumps were required, and at the time, they were the largest positive-displacement pumps in the world. They were specially developed for Black Mesa Pipeline.
Another unique feature of the pipeline was the concern of a 3,000 feet precipitous drop from the top of the Black Mountains to the Colorado River. In order to control the rate of flow during the abrupt descent, the diameter of the pipe was reduced from 18 inches to 12 inches.
An independent agency sampled and weighed the coal in order to determine the royalties that were paid to the Indian tribes, the transportation and sales volume, and the revenue paid by the power company to the mine and pipeline company. Approximately 3,800,000 tones of coal were transported in 1975 as the generating units continued to improve their performance.
The pipelines responsibility did not begin until the coal reached the Black Mesa slurry preparation plant. At that point, the raw coal was crushed to ¼-inch and smaller particles. The rough ground coal was then mixed with water was fed into one of three rod mills in order to grind the coal into a very fine size producing the finished slurry. The slurry was retained in storage tanks and held in suspension by a large propeller before entry into the pipeline. Each storage tank held 600,000 gallons, enough to supply the pipeline for a two-hour period of maximum operation pumping at 660 tons of coal per hour.
At the end of the 273-mile journey, the pipeline company’s responsibility ended as slurry was delivered to one of many storage vessels designed for the slurry operation and the supply source required at the Mohave generating plant. This plant was the first in the world designed to use coal delivered in slurry form. Before the coal could be burned in the station’s furnaces, the water was removed. That was accomplished by running the slurry through large containers. Most of the recovered water was used by the station in the cooling processes. The slurry came out in a damp-cake form, and then it went into a series of pulverizers, where a grinding action plus high temperature air reduced the coal to a dry powder. The hot air then carried the powdered coal into furnaces, producing steam with a temperature of 1,000 degrees Fahrenheit, which drove large turbines to produce electricity. The power generated served that needs of consumers in Arizona, Nevada, and California.
The remote area of the Black Mesa where the source of coal was prepared for transportation, provided stability and economic growth to a once forgotten section of the Navajo-Hopi Reservation. As a result, it was stated that better schools, hospitals, new homes, and new jobs were provided. Thirty-eight of the 53 total employees work for Black Mesa Pipeline were located on the Black Mesa. Of those 38, 29 were either Navajo or Hopi origin.