U.S. petroleum coke production expected to increase

Edward J. Swain
Consultant Houston

Production of petroleum coke in the U.S. is expected to continue to increase in the coming years. In the U.S., refiners are processing lower quality crudes than in the past.

Lower gravity and higher sulfur content crudes prompt more coke production. In the U.S. and other countries, the increased demand for transportation fuels will result in additional refining coking facilities.

Any additional petroleum coke produced should be fuel-grade coke (also called green coke) since the markets for calcined grade and premium grade cokes are limited. Fuel-grade coke comes directly from the coking drums. It is a low-cost energy source for some utilities and industries. Calcined coke is low sulfur fuel- grade coke that has been through calciners. It is used to produce anodes.

This article updates an earlier one and includes data for 1996 crude runs (OGJ, Jan. 13, 1997, p. 46).

U.S. petroleum coke capacity

The Energy Information Administration (EIA) reports that as of Jan. 1, 1997, there were 152 operating refineries and 5 idle refineries with 16.3 million b/sd crude oil distillation capacity. The 54 operating refineries with coking units have some 9.6 million b/sd crude oil capacity. These 54 refineries are mostly medium or large complex facilities. They represent 59% of the total crude oil distillation capacity.

Table 1 [69,928 bytes] shows the U.S. crude oil and coking capacity grouped by Petroleum Administration for Defense District (PADD). (For a map of PADDs, see OGJ, Jan. 13, 1997, p. 46). PADD 3 (Texas, New Mexico, Arkansas, Louisiana, Mississippi, and Alabama) contains the largest coking capacity and includes 20 operating refineries. PADD 5 (the U.S. west coast plus Nevada, Arizona, Alaska, and Hawaii) has the second largest coking capacity and includes 14 operating refineries.

Table 2 [99,925 bytes] lists the 10 leading U.S. refining companies with regard to coker feed capacity. Mobil Oil Corp. leads in coker capacity. Mobil has delayed coking facilities in all five of its refineries.

Technology

U.S. refineries use three types of coke processing technologies: delayed coking, Fluid Coking, and Flexicoking. The majority of the U.S. coking facilities are of the delayed coking type (48 out of 54 coking units).

Delayed coking technology is open art technology. Although the process is offered by several licensors, no fundamental differences exist between the technologies. Most of the differences are related to the licensor's design and commercial experience. One exception is Conoco's technology, which involves a specific scheme for increasing liquid yield relative to the other open art technologies. The Conoco scheme can result in making less coke.

The Fluid Coking and Flexicoking technologies are offered by Exxon Research & Engineering Co. Refineries use a licensing fee for these two technologies. There are four Fluid Cokers and two Flexicokers in the U.S.

U.S. production

Petroleum coke produced by U.S. refineries has increased about 43% during the past 10 years, even though crude oil runs have increased only about 10% (a crude oil increase of 1.34 million b/sd). The 10-year history of the production of fuel-grade petroleum coke is illustrated in Fig. 1 [55,018 bytes].

Petroleum coke production rate, expressed as short tons of coke per 1,000 b/cd of crude oil input (st/1,000 b/cd), has increased about 29% over the past 10 years ( Table 3 [44,298 bytes]). Limited growth in coke production occurred between 1987 and 1990, but major growth occurred from 1990 to 1996. New coking units came on stream between 1990 and 1993.

Table 4 [33,936 bytes] shows petroleum coke production from refineries grouped by PADDs for 1992-1996. PADD 3 refineries represent about 44% of the U.S. coke capacity. Because the heavy fuel oil market is very limited in PADD 3 and because the refineries are processing lower-quality crude oils, PADD 3 refineries have installed coking units to aid in reducing the production of heavy fuel oil.

The 86,805 short tons per calendar day (st/cd) of coke produced in 1996 U.S. refining operations represents 94.8% of coke production capacity.

Lower gravities, higher sulfur

The driving force for increased petroleum coke production in the coming years will be lower-quality crude oils, which have lower gravities and higher sulfur content than previously used crudes.

The decreasing gravity trend of crude oils processed during the 1987-1996 period is illustrated in Fig. 2 [58,776 bytes]. A 10-year regression shows the gravities of crude oils processed by U.S. refiners decreasing at a moderate rate of 0.12? API/year. However, over the past 5 years, the decreasing moderate rate is 0.04? API/year. If the decreasing gravity trend continues, U.S. coke production of 90,000 st/cd will easily be reached by the year 2000.

The increasing sulfur content in petroleum coke is directly related to the increase in sulfur content of the crude oils processed by U.S. refiners. The increasing trend for the 1987-1996 period is shown in Fig. 3 [57,492 bytes].

A 10-year regression shows the sulfur content of crude oils processed by U.S. refiners increasing at a moderate rate of 0.016 wt %/year. However, over the past 5 years, the trend is decreasing at a moderate rate of 0.004 wt %/year. This rate of change suggests that today's imported crude oils have slightly less sulfur than those imported during the 1987-1992 period.

The sulfur level of the fuel-grade coke determines the end market of the coke. Coke with a sulfur content of 2 wt % or less is usually used for the production of anodes. Some coke with a sulfur content of 2.01-3.00 wt % is blended with low-sulfur coke and also used for anode production. In general, coke with a sulfur content of 2.01-5.00 wt % stays as fuel grade coke.

Exports

A major portion of petroleum coke produced by U.S. refineries, 65.7%, was exported in 1996. This fraction is slightly higher than the 5-year average of about 64.6%. Although U.S. industries are learning that petroleum coke is a low-cost energy source for power generation, coke production is increasing faster than the number of new projects that use coke.

Table 5 [33,185 bytes] presents a 5 year (1992-1996) pattern of coke exports from the five PADDs. Export cokes include fuel-grade coke, calcined coke, and premium coke. Estimated amounts of export cokes in 1996 consist of 47,500 st/cd of fuel-grade coke, 8,610 st/cd of calcined grade coke, and 915 st/cd of premium grade coke.

Seven countries received about 68% of the 1996 exported petroleum coke. Table 6 [56,245 bytes] presents a 5-year (1992-1996) pattern of those countries that imported U.S. petroleum coke. Japan is the major importing country of U.S. petroleum coke. The grade of coke that Japan imports is almost 100% fuel-grade coke with a trace of premium coke. The Japanese combine the fuel-grade coke with coal to make fuel in processing industries.

Although Canada ranks sixth in importing petroleum coke from the U.S., it ranks first in importing calcined coke. Of the U.S. petroleum coke that Canada imports, 60% is fuel grade, 35% is calcined grade, and 5% is premium grade.

As the demand for transportation fuels increases and as the quality of processed crude oils decreases, foreign refineries will install new cokers (mainly delayed). Already, several major crude oil producing countries are installing delayed cokers to upgrade their extra-heavy crude oils into marketable crude oils. The increased supply of coke capacity will reduce the demand for U.S. exported petroleum coke.

Imports

A limited quantity of fuel-grade coke is imported into the U.S. to meet specific product quality demands of calcined coke. The fuel- grade coke has desirable properties and is usually routed directly to calciner sites near the ports of entry. The past 5-year history of imported fuel-grade coke, reported by the EIA, is shown in Table 7 [21,794 bytes].

Power plant fuel

Public utility companies have been increasing their interest in using petroleum coke as a supplemental fuel with coal. The past 5-year history of public utility companies using fuel-grade coke, reported by the EIA, is shown in Table 8 [12,903 bytes]. Four of the 18 public utility companies that used fuel-grade coke in 1996 consumed 56% of the total coke. The four were Pennsylvania Power & Light Co., Tampa Electric Co., Northern States Power Co., and Northern Indiana Public Service Co.

The relationship between the prices of petroleum coke and various grades of coal is presented in Fig. 4 [56,237 bytes] and Fig. 5 [56,394 bytes]. For power plants, the use of fuel-grade coke as a fuel requires investment of a dual solid fuel handling and crushing system. The economic return is not easily seen when looking at delivery costs of solid fuel at dollars per short ton ($/st) (Fig. 4). However, when looking at dollars per million BTUs, Fig. 5 shows that the price of petroleum coke is at least 43% lower than the price of bituminous coal.

Because petroleum coke has a low price, a high heating value, and a low ash content, it is advantageous to use petroleum coke blended with coal as fuel. The disadvantages of petroleum coke as a fuel are the expense of a dual solid fuel handling and crushing system, the high sulfur content, and the high nickel and vanadium content.

Cogeneration

Some refineries that produce petroleum coke consume a portion or all of the coke they produce as a solid fuel to generate steam, and, more recently, as fuel for cogeneration facilities. In 1996, the EIA reported an average of 1,767 st/cd of petroleum coke used within U.S. refineries. In recent years, several cogeneration facilities have been installed next to refineries for over-the-fence sales of petroleum coke.

Texaco's cogeneration facilities at El Dorado, Kan., produces 40,000 kw of electric power and 180,000 lb/hr of high-pressure steam. Syngas produced in Texaco's gasifier and natural gas are fed to the cogeneration facilities. The majority of feed to the gasifier is 120 tons/day of petroleum coke produced at the refinery. The gasifier and cogeneration facilities came on-line in mid-June 1995.

Koch Refining Co. in St. Paul, Minn., is considering erecting a 250,000 kw cogeneration facility that will use petroleum coke as the primary fuel.