Operations Management, 5th Edition Chapter 21 -- Buffalo Alkali and Plastics

Chapter 21: 17. Maintenance and Reliability
Buffalo Alkali and Plastics

Buffalo Alkali and Plastics

Buffalo Alkali and Plastics, a prominent producer of soda ash, began operations in the United States in 1880 using the Solvay Process. Buffalo, New York, was selected as the site for the soda ash operation because of the close proximity of both brine wells and limestone deposits, both necessary to the Solvay Process. The initial complex was later expanded for the production of chlorine, caustic soda, chlorinated solvents, industrial detergents, and polyvinyl chloride. With considerable success in this initial operation, Buffalo Alkali and Plastics built eight additional plants in the central and southern regions of the United States during the first half of the twentieth century.

Even with this diversification and expansion, Buffalo Alkali and Plastics' principal product continues to be soda ash. Until the 1960s, soda ash was almost exclusively produced by the Solvay Process. However, huge deposits of bona, or natural soda ash, have been discovered in Wyoming. (Trona ore is mined directly and is purified by dissolution, evaporation, and recrystallization. Production costs for natural soda ash are much lower than those for synthetic soda ash produced by the Solvay Process.) Buffalo Alkali and Plastics' plants remain competitive only because of their close proximity to markets. Freight charges incurred in shipping soda ash from Wyoming to markets served by the synthetic plants tend to offset the lower production costs of mining/purification operations. (Principally, soda ash is used in the manufacture of glass by combining certain ratios of sand and soda ash and fusing the mixture under high temperature.)

Even when freight charges are considered, synthetic soda ash producers remain competitive with bona producers only if their plants maintain high-volume operations. Synthetic plants have large investments in fixed costs and must sustain high production rates to remain above the breakeven point. Area markets support these high rates. Glass manufacturers and other users of soda ash consume the entire output of local synthetic plants and supplement this source of supply by purchasing higher priced bona ash.

Production rates for the synthetic plants usually depend on the number of calciners (pronounced cal-a-ners) available for operations. A calciner is comprised of a steel pipe, 60 feet in length and six feet in diameter. The Buffalo, New York, complex has 32 calciners, each with a daily capacity of 100 tons of soda ash. The plant capacity is 3,000 tons per day. Therefore, hence, 30 of the 32 calciners must be available for service to maintain maximum output.

Because of the intense heat in the fire zone, the one-inch- thick steel shell of the calciner is eventually oxidized and cracks. When this occurs, the shell is pulled out. The burned-cracked section (approximately 15 feet) is cut out, and a new section is welded into place. The repaired shell is reinstalled in the brick housing; drive mechanisms are attached; and the calciner is returned to service. (Heat-resistant alloys are impractical for this operation because of the enormous cost and prolonged delivery dates for such alloy shells.)

The central problem for this operation is to determine the appropriate maintenance for calciner repairs. A large number of recent shell failures has reduced the number of calciners available for service to 25. A check of maintenance logs for the past ten years revealed 180 shell failures. On further examination of these logs, monthly failure probabilities were developed. These appear in Table 1. Repair procedures involve laying 100 feet of railroad track at the end of a failed calciner on which a crane rides to remove the cracked shell. The repair procedure averages three weeks (15 working days) with a standard deviation of three days. A schedule of repair time versus cumulative probability is in Table 2. (The dispersion is usually a result of working overtime.) The crane track cannot be permanently installed at each calciner because it would obstruct other equipment repairs.

TABLE 1 Monthly shell failure probabilities
	Failures	Probability
	0	0.22
	1 or less	0.55
	2 or less	0.80
	3 or less	0.92
	4 or less	0.96
	5 or less	0.97
	6 or less	0.98

TABLE 2 Repair time probabilities using normal repair procedures (crane truck)
	Time	Probability
	6 days or less	0.001
	9 days or less	0.02
	12 days or less	0.16
	15 days or less	0.50
	18 days or less	0.84
	21 days or less	0.98
	24 days or less	0.999

Repairs may be expedited, however, by renting a large mobile crane. The rental cost of this crane is $1,500 per day with a minimum charge of $12,000 per rental. With the rented crane, two calciners may be repaired simultaneously. Moreover, the average time for repairs using the rented crane is reduced from three weeks to two weeks (ten working days) with a standard deviation of two days. A schedule of repair times versus cumulative probability appears in Table 3. Other maintenance material and labor costs for these two repair approaches (rented crane and installed crane) are estimated to be equal. Profit and overhead contribution from a ton of soda ash is estimated to be $12.00.

TABLE 3 Repair time probabilities using accelerated procedures (rental crane)
	Time	Probability
	4 days or less			0.001
	6 days or less		0.02
	8 days or less		0.16
	10 days or less		0.50
	12 days or less		0.84
	14 days or less		0.98
	16 days or less		0.999