Moving bottom and fly ash can create massive maintenance and budget problems for coal burning utility plants. The abrasive ash quickly erodes most pipeline. Replacing blown pipe eats into the budget and means downtime.
Tampa Electric Company (TEC), Tampa, Florida, is no stranger to ash line maintenance. Its Big Bend Station, located 15 miles south of Tampa in Apollo Beach and its Gannon Station, located just 10 miles north of Big Bend on Tampa Bay, are both coal-fired power plants. Thousands of feet of pipe snake through the plants, conveying the abrasive bottom and fly ash created by the burning of the coal. Big Bend Station with a 1755 MW capacity is TEC's newest and largest power plant. It provides more than half of the company's total generating capability. The Station burns approximately 14,000 tons of bituminous Kentucky coal every day.
Big Bend Units One, Two and Three with a combined capacity of 1285 MW, burn low sulfur coal. Big Bend Four with a 470 MW capacity burns standard sulfur coal and is equipped with a flue gas desulfurization system (FGD) or "scrubber" to remove the sulfur, one of the first to be designed and installed in the United States to produce commercial grade gypsum as a by-product.
Built between 1957 and 1967, Gannon Station has six service units and a capacity of 1230 MW. It burns low sulfur coal. At both plants, the company had experienced problems with hardened steel and cast iron slag sluice lines. The hardened steel lines lasted an average of eight to 18 months; the cast iron sections often had to be changed or rotated every four to six months.
In the late 1970s, plans to build Big Bend Four and conversion plans at Gannon Station provided TEC with an opportunity to solve its persistent pipeline abrasion problems. TEC engineering set up an on-site test to determine what type of pipe could withstand the abrasive ash. Several pipe manufacturers were invited to submit samples for testing.
Eight manufacturers of PVC pipe, unlined fiberglass pipe, fiberglass pipe lined with ceramic tile, carbon steel, cast iron, basalt lined pipe and ceramic component pipe submitted samples. To ensure fairness, the test pipe was installed in similar locations and in areas where wear was usually most severe.
Some of the test pipe failed in minutes, some in hours. Others lasted months and longer. A basalt-lined pipe manufactured by Kalenborn Abresist Corporation, Urbana, Indiana, was among the pipes that lasted the longest and was still in service where it was tested until it was replaced in 1990. Commenting on the results, Rex Morgado, Tampa Electric Engineering Technician, said, "The amount of wear was significant in all the others, but not ABRESIST®."
TEC officials reviewed the results and talked with another utility that used the basalt lined pipe. After factoring in cost evaluations and a ten-year warranty from Kalenborn Abresist, they chose to install the basalt lined pipe.
The ten-year warranty was twice the normal usually given. Kalenborn Abresist asked only that they be allowed to inspect the pipe at five and ten year intervals.
Two, mile long, ten-inch basalt pipelines were installed at Big Bend. One pipeline conveys bottom ash; the other line conveys fly ash. Jetpulsion™ power drives the ash and water through the pipe at a velocity of eight to 12' per second. Big Bend is a closed loop system so the water from the slurry is run through weirs to retention ponds for reuse.
At the same time TEC was building Big Bend Four, they were converting some of the units at Gannon Station to coal-fired units. Initially, all six units burned coal. During the 1970s, four of the units had been converted to oil-fired to meet environmental requirements. The other two units had continued to burn low-sulfur coal.
In the early 1980s as oil prices began to rise, TEC reconverted the oil burning units to coal burning units that used low-sulfur coal.
During the conversion, TEC installed approximately 1200' of 8" ABRESIST basalt lined pipe to convey bottom ash slurry from Gannon One, Two, Three and Four to dewatering bins. Over ten million gallons of saltwater and bottom ash slurry are moved through the pipe at 110 psi by high pressure saltwater pumps.
Over the long haul, how did the basalt lined pipe withstand the abrasion?
In 1989, at the five-year warranty inspection at Big Bend and Gannon, the straight pipe showed little to no wear. At elbows and turns, where the flow direction changes and wear is usually most severe, there was only an 3.18mm (1/8") of wear or less. ABRESIST elbow lining is 30mm (1.18") thick while standard straight pipe is 22.3mm (7/8"). In some places, the swirl pattern from the original manufacturing process was still evident.
At the ten-year inspection in July 1994 at Big Bend Four, the basalt pipe once again showed little wear, even in the elbows. Some of the original glazing was even still visible.
During the ten-year inspection at Gannon Units One, Two and Four showed some wear, about 4mm (.158") was observed near the pipe ends. The rest of the pipe showed little wear.
At Gannon Unit Three, one 90 degree elbow exhibited more wear, about 8-10mm (.316" to .394"). This same elbow was inspected at the five-year mark.
Morgado was on hand at both the five- and ten-year warranty inspection. He said, "Even though the wear was atypical, there was not much difference between the five- and ten-year inspections with this elbow."
Due to the excellent performance of the basalt lined pipe, TEC subsequently installed ABRESIST pipe in Gannon Five and Six and Big Bend One, Two and Three. Morgado said, "Based on previous experience with the basalt pipe, we installed ABRESIST to convey all of the bottom ash at Gannon."
In business for almost a century, Tampa Electric is an investor owned utility. The company serves 480,000 customers in a retail service territory covering nearly 2,000 square miles in west central Florida. Its parent company, TECO Energy, owns several energy related companies which are involved in mining, transportation, wholesale power and other diversified interests.