COMPARISON OF FZTEL PROPERTIES OF PETROLEUM COKES 

AND COALS USED IN POWER GENERATION 

James J. Baker, Jefiey G. Rolle, Robert Llerena, 

k J. Edmond Co. 

1530 West 16th Street, Long Beach, CA 90813 

Keywords: 

INTRODUCTION 

petroleum coke, coal, fuel properties 

U.S. petroleum coke production is projected to continue to increase, reaching 90,000 dcd (short 

tons per calendar day) by the year 2002, primarily due to refining heavier and higher sulfur 

content crudes [I]. In 1996 the coke production was 86,805 dcd and 65.7% of the annual 

I 

production was exports. Green (raw) petroleum cokes are mostly used as utility fuels (about 73% 

for fuel grade) combining with coal to make fuel in processing industries. Petroleum cokes are 

produced at refineries using three different types of coking processes: delayed, fluid, and 

flexicoking. The delayed coker is mostly used at forty-eight refineries. The other fluid coker (4 

units) and fledcoker (2 units) are less utilized. Coke products fiom a delayed coker are classilied 

as shot, sponge or needle coke depending on their chemical and physical characteristics. 

Utility companies used 3,852 dcd of petroleum coke (less than 5% of annual production) as a 

power plant supplemental fuel blending with coal in 1996, because petroleum coke has advantages 

of low price (36% lower at Wst or 46% lower at %/MMBtu), high heating value, and low ash 

content [I]. The disadvantages of petroleum coke as a fuel are expense of a dual solid bel 

handling and crushing system, high sulfur, high nickel and vanadium content. Normally cokes are 

blended with coals at 10-20% before burning in boilers because of their low volatile matter and 

high sulfur content. Average quality of coke bumed is: on as-received basis, 13,930-14,820 

Btdlb, 5.5% sulfur, and 0.5-3.8% ash. 

Some refineries 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. An average of 1,767 st/cd of 

petroleum coke was used within reheries in 1996. Texaco cogeneration power pht at El 

Dorado refinery, Kansas gasifies a delayed coke to produce syn-gas for a combustion turbine fuel 

[2]. Typical composition of the delayed coke is: on dry basis, 90% carbon, 4% hydrogen, 4% 

sulfur, 1.5% nitrogen, 0.5% oxygen, and 0.5% ash. Other coke-fueled cogeneration plants bum 

100% delayed coke [3] or 100% fluid coke [l] in a circulating fluidized bed (CFB) steam 

generator. Delayed coke fines sized to 0.25 in. (6 mm) is fed to the CFB hace along with 

crushed limestone. Typical composition of the delayed coke feed is: on dry basis, 89.2% carbon, 

3.7% hydrogen, 5% sulfur, 1.8% nitrogen, 0.3% ash, and 15,050 Btu/lb of high heating value 

(HHV). The coke contains approximately 10.6% moisture. 

Cement industry consumes a large portion of fuel-grade petroleum coke (35.5% of world 

demand) to combust in kilns [l]. The addition of cokes can constitute up to 50% of the fuel 

mixture and is carellly controlled conducting test bum due to detrimental effects of high sulfur 

and vanadium content to concrete quality. Sulfur contamination can cause cement cracking and 

preheater plugging-fouling due to combination with alkalies, and high vanadium content above 

500 ppm can cause cement to lose strength. The cement kilns operate as scrubbers, absorbing 

sulfur and other contaminants into hished cement. 

U.S. utility companies consume about 80% of annual coal production (approximately 1,000 

million short tons in 1995) burning in boilers to generate electricity [4]. The coal production 

consists of 60% bituminous, 30% subbituminous, 8% lignite and small percentage of anthracite. 

U.S. exports annually about 90-1 10 millions tons (9-1 1% oftotal production). 

Coal gasification process technologies have been extensively tested in conjunction with integrated 

gasification combmed cycle (IGCC) systems to improve efficiency, environmental performance, 

and overall cost effectiveness in electric power generation [5]. Several successll demonstration 

projects are: British GaslLurgi gasifier, Texaco Cool Water gasification plant, Shell Coal 

Gasification Process, Dow Coal Gasification Process (Destec), etc. Full-scale projects are now 

proceeding in The Netherlands, Germany, Spain and Italy on a commercial basis. Utah (SUFCO) 

coal, an export western bituminous coal, was the predominate coal gasified at the Texaco Cool 

Water plant [6] and also tested in the Shell demo-plant [5]. Typical coal properties are: 0.4% 

sulfur, 8.8% ash, 12,360 Btu/lb (HHV), and 2,200 deg F of ash fusion temperature. The SUFCO 

Utah coal has low sulfur, low iron and high sodium content. Shell demo-plant tested a delayed 

coke which has low ash, high sulfur, low oxygen, low calcium, high vanadium, and high nickel 

1 

I 

I 

80 
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Content. Feed properties of the delayed coke are: on dry basis, 10.6% volatile matter, 0.5% ash, 

5.2% sulfur, 89.3% carbon, 3.6% hydrogen, 1.35% nitrogen, 0.03% chlorine, 0.1% oxygen, 

15,350 Bru/m (HHV), and 61 hardgrove grindability index (HGI). The coke contains 9.3% 

moisture and ash mineral analysis shows 0.8% lime, 1.2% sodium oxide, 71.8% vanadium 

pentoxide, and 7.4% nickel oxide. Texaco and Kellogg (KRW) gasification processes also 

extensively tested petroleum cokes as raw material to gasifier [7,8]. 

Coal ash is classified into two categories: lignitic ash is defined as having more (CaDtMgO) than 

ferric oxide; and bituminous ash is defined as having more femc oxide than the sum of CaO and 

MgO. The Utah coal is classified a western high volatile bituminous coaL but has lignitic ash. 

Ash characterization methods such as slagging and fouling indices are different in calculation 

depending upon bituminous or lignitic ash [9]. Chemical composition of coal ash affects dag 

viscosity, which is an important criterion for determining the suitabC7 of a coal ash for use in a 

&%-tap cyclone fumace. Slag flow readily at or below a viscosity of 250 poise. The temperature 

at which this viscosity of ash occurs is called T,,, temperature. The preferred maximum TzJo for 

wet-bottom applications is 2,450 deg F. 

The alkali metals, sob and potassium, have long been associated with the fouling tendencies of 

coal ash. Correlations in fouling index have been developed using various parameters such as 

strength of sintered tly ash and total alkali content for bituminous ash, and sodium content done 

for lignitic ash. AU bauminous coals contain enough sulfur and alkali metals to produce corrosive 

ash deposits on superheaters and reheaters, and those containing more than 3.5% sulfur and 

0.25% chlorine may be particularly troublesome. The elements in coal ash corrosion are sodium, 

potassium, aluminum, sulfur and iron, which are derived ffom the mineral matter in cod Fouling 

observed in a CFBC boiler firing coal and petroleum coke was attriiuted to agglomeration of 

sulfate and carbonate, not due to high concentration of nickel and vanadium present in petroleum 

coke (306 and 870 ppm, respectively) [lo]. 

The objective of this study is to evaluate and compare various fuel properties of petroleum cokes 

and bituminous coals used in power generation, comparing different cokes produced ffom several 

refineries in U.S. and export western coals sampled at the Los Angeles Export Terminal (LAXT). 

Four fluid cokes, fourteen delayed cokes and &e export coals are included for evaluation based 

on recent analysis data accumulated for the past two years (1997-1998). 

SAMPLING, PREPARATION AND ANALYTICAL METHODS 

Representative samples of petroleum cokes and coals have been obtained 60m various refineries 

located in California, Texas, Louisiana, Kansas, Illinois and other states, and storage facilities at 

numerous national ports. Laboratory samples are prepared for fuel properties analysis following 

the procedures and principles in handling listed in the ASTM Methods D 346, D 2013 and D 

2234. Laboratoly test methods using various advanced analytical instruments are described in the 

Quality Assurance Manual of k J. Edmond Company [l I]. 

RESULTS AND DISCUSSION 

Important fuel properties of three significantly different types, delayed coke, fluid coke and export 

western coal are presented for comparison in Tables 1-3. Petroleum cokes evaluated for this 

study are produced in various U.S. refineries located in west coast (WC), Gulf coast (GC), mid 

west (MW), and south east (SE), which are phady consumed in export to foreign countries 

(65.7%) and in der extent (less than 10%) used m domestic power generation and cement kiln 

fuel mix. Export western coals sampled at the LAXT are high volatile bituminous coals with low 

sulfur and iron content. They are primarily produced in Utah and Colorado for power generation. 

The throughput capacity of LAXT is 10 million metric tons per year, which is correspondent to 

about 10% of current coal export to foreign countries. 

Based on data presented m Tables 1-3, five different arbitrary groups of concentration or value 

of several primary - fuel properties are used as indicators of different levels of properties as follows: 

ywLQWr-Q= MediumHigh xa-mh 

sulfur, wt% 1-2 2-4 4-6 

Asb, wt% 0.5 1-2 9-10 

Volatile Matter, wt% 2.5-6.1 9.5-13 40.2-4 1.1 

Btu/lb 12600-13400 14200-14600 15200-15600 

Nitrogen, wt% 1.2-2.2 2.8-3.2 

Vanadium, PPm 270-400 500-800 900- 1400 2300-2900 

Nickel, ppm 25-200 400-500 700+ 

81 
-fuel properties of petroleum cokes used in power 

generation. Three fluid cokes (WC-1, WC-2 and WC3), one bed coke (WC-4) and six delayed 

cokes (WC-5, SW/MW-1, SWiMW-2, SE, SUGC, E/MW) are mcluded for comparison. Fluid 

and bed cokes (WC-I to WC-4) have been extensively used m circulating fluidized bed 

combustors at cogeneration power plants. WC-2 and WC-3 fluid cokes also represent export 

quality to foreign countries. 

Fluid coke generated fiom a fluidized bed reactor is a solid, spherical particulate normalty smaller 

than 8 me& (98% for WC-2 and WC-3, and 74% for WC-4, as shown in Table 1). The coke is 

very hard and abrasive, suitable for direct use m a circulating fluidiz,ed bed combustor, and 

generally have lower HGI than delayed coke and cod Typical moisture content is very low in the 

rangt of 0.3 to 1.2% except for export cokes having 7-11.5% which increased to control dus! 

during transportation. Sulfur content for fluid cokes, WC-1, WC-3 and WC-4, is low m the range 

of 1.0 to 2.1%; and WC-2 coke has medium sulfur with 3.3%, somewhat lower than other 

delayed cokes listed in Table 1 (4-6%). A& content of WC-1 and WC-2 cokes is very low m the 

range of 0.35 to 0.46%, and WC-I and WC-2 cokes have a little higher ash fiom 1.1 to 1.5%. 

These ash values are significantly lower compared to coals (9.2-lo%), which is normally claimed 

as an advantage as heL 

Calorific value for all fluid cokes studied is medium m the range of 14,200-14,400 Btuilb (dry 

basis), relatively high compared to coals (12,600-13,400 BWlb dry basis). Volatile matter 

content is low in the range of 2.5 to 6.1% for all fluid cokes, compared to delayed cokes (9.5- 

13%) and coals (40.2-41.1%). Power plant startup is easier with fuels having higher volatile 

matter. However, serious operational problems m burning petroleum cokes as 100% or 10-20% 

blend mix have not been reported. Fluid cokes, WC-2, WC-3 and WC-4, have relatively low 

nitrogen content m the range of 1.4 to 2.2%, while WC-1 has a higher nitrogen of 3%, similarly 

,observed with some delayed cokes (2.8-3.2%). Coals evaluated for this study have a low 

nitrogen of 1.2 to 1.5%. 

Vanadium content for WC-1 and WC-2 is medium m the range of 650 to 850 ppm, near 

concentration used m the cement kiln fuel mix (530-760 ppm for SW/MW-1 and SW/MW-2), but 

higher than that for good anode-grade cokes (270-400 ppm). WC-3 and WC-4 cokes show the 

highest V content in the range of 2300 to 2900 ppm among petroleum cokes and coals evaluated 

for this study. Detrimental affects with this high V content (as much as 10,000 ppm) have not 

been reported m the operation of steam generating combustors [12]. Sodium content for WC-I 

and WC-2 cokes is low m the range of 80 to 180 ppm, which is similarly observed m good anodegrade sponge cokes (25-200 ppm). WC-3 and WC-4 cokes have a higher Na content of 480 to 

500 pprn compared to WC-1 and WC-2. Most of delayed cokes studied have a low Na content 

(50-160 ppm) except for WC-5 and WC-E4 (380-450 ppm). 

Six delayed cokes m Table 1 (WC-5, SWm-I, SW/MW-2, SE, SUGC, E/MW) have been 

used as fuel blend mix m pulverized coal combustors for steam generation and cement kilns. 

These cokes are &el grade, green (raw) cokes with high ash, high sulfur and high metal content 

ranging sponge to shot coke. Typical ash content is m the range of 0.25 to 0.65%; sulfur content 

in the range of 3.1 to 6%; vanadium fiom 530 to 1700 ppm; nickel ftom 190 to 600 ppm; and 

sodium ftom 80 to 380 ppm Calorific value is high m the range of 15,000 to 15,580 Btu/Ib 

(m, dry basis), producing more heat during combustion than fluid cokes and coals. Size 

distribution covers wide range of particle size fiom -6 mm to +40 mm depending on fines, lump or 

ROC (run of coker) delivered &om refineries. Typical HGI is in the range of 35 to 60, mostly 

higher than coal HGI (49, with shot content varying fiom 0 to 80%. Typical moisture content is 

in the range of 5 to 9%, and volatile matter varies fiom 9.5 to 13%. 

Two delayed cokes, SW/Mw-1 and SW/MW-2 have been fiequentiy used in cement kiln 

operation, as fuel mix (up to 50%). Typical sulfur and vanadium content (controlled quality 

parameters for cement application) ofthese cokes vary m the range of 3.1 to 3.8% and 530 to 760 

ppm, respectively. Sulfur and vanadium content are higher than those required for good anodegrade sponge coke (3% and 400 ppm, respectively). 

Table 2 presents analysis results ftom eight export delayed cokes. These cokes have been mostly 

used as utilay hels cornbig with coal to make fuel m processing industries. Fuel property data 

in the table update export quality analysis of petroleum cokes previously reported [I I]. Export 

qualdy criteria of green (raw), fuel-grade cokes are dependent upon buyer's requirements of coke 

specifications. As shown m the following for west coast cokes, ptimary criteria hquently used 

82 
L 

\ 

i 

1 

t 

\ 

are: Size distribution, moisture, sulfur, a&, volatile matter, fixed carbon content and calorific 

value; and secondary are: nitrogen, vanadium and sodium content. In addition, complete 

ash mineral analysis is sometimes required to report. 

Ox6,OxlO 01 -2 & +25 

Moisture, wt% 8-12,9-12 or 9 max 

sulfur, wt% 1 max, 2 max or 3 max 

Ash, wt% 0.5 max, 1 max or 1.5 max 

VolatileMatter,wt% 9-13, 11-12.5 or 14 max 

Fixed Carbon, wt% 88-90 or 87 min 

HGI 45-50 or 50 min 

Bdlb 15,000 min 

Nitrogen, wt% 

Vanadium, ppm 

Soh PPm 

b=wmx 

size, mm 

(dry basis) 

2,253.5 or 2.9 max 

500-800 or 700 max 

200-300 or 700 max 

Eight delayed cokes in Table 2 (WC-E1 to WC-E8) are produced in relineries located in west 

coast. These cokes are good quality, fuel-grade green (raw) cokes, which generally have lower 

ash, sulfur and metal content than six delayed cokes in Table 1 used in domestic power 

generation. Typical ash content is in the range of 0.18 to 0.45%; sulfur content m the range of 

0.8 to 4%; vanadium 6om 270 to 1150 ppm; nickel fiom 180 to 550 ppm; and sodium 6om 50 to 

450 ppm Calorific value is high in the range of 15,300 to 15,520 Btuilb (HHV, dry basis), as 

ely observed with delayed cokes m Table 1. Size distribution covers wide range of particle 

size fiom -6 mm (30-99%) with hes, to +40 mm (3-47%) with lump or ROC (run of coker) 

depending on delivery 60m reheries. Typical HGI is in the range of 35 to 80, mostly higher than 

coal HGI (49, with shot content varying fiom 0 to 60%. Typical moisture content is in the range 

,of 7 to 12%, and volatile matter varies fiom 10 to 12.5%. 

Table 3 summarizes analysis results &om five export westem coals (type I to V). These coals 

sampled at the LAXT are high volatile bituminous coals with low sulfur and iron content. They 

are primady produced in Utah and Colorado and used as utdity fuels for power generation. Coal 

quality specifications for export were previously reported [ 1 I]. primary fuel propehes of coal 

are: proximate, ultimate, calorific value, HGI, size distribution, ash mineral analysis and ash fusion 

temperatures. 

Typical ash content of export western coals is high in the range of 9.2 to 10%; sulfur content is 

very low in the range of 0.45 to 0.6%. These coals are classified as western high volatile 

bituminous coal, but have lignitic ash having more (CaWMgO) than ferric oxide [9]. F?imary 

constituentsof coal ash are silica (52.3-58.6%), alumina (11.6-21%) and lime (5-13.1%). Ferric 

oxide content m ash is low 6om 4.4 to 5.9% compared to eastern bituminous coal (20-30%); 

sodium oxide content is high fiom 1.8 to 4.2%. Calorific value is low in the range of 12,640 to 

13,360 Btdb (HHV, dry basis), compared to fluid cokes and delayed cokes in Tables 1 and 2. 

Size distribution shows top Size of 2 inches having 92-100% 50 mm x 0 mm and 11.6-33% 2 mm 

x 0 mm Typical HGI is in the range of 43 to 46. Typical moisture content is in the range of 7.7 

to 10.3%, andvolatilemattervaries~om40.2 to41.1%. 

Data for coal ash characteristics used for selection of feed coal and boiler design criteria are also 

presented in Table 3. Ash and slag Viscosity plot parameters are: silica ratio, base-to-acid (B/A) 

ratio, Tzm and slagging mdex Fouling plot parameters are: alkalies as sodium oxide and fouling 

index 191. Typical silica ratio ism the range of 0.712 to 0.828; BIA ratio fiom 0.2 to 0.386; T,, 

6om 2,420 to 2,760 deg F; and slagghg index is medium to high m the range of 2,114 to 2,263. 

Typical alkalies as sodium oxide is high in the range of 2.5 to 4.5; and fouling mdex is high 6om 

1.8 to 4.2. Very low sulfur content with theses coals may lower corrosive ash deposits caused by 

reacting with sodium, potassium, aluminum and iron, but addition of high sulfur petroleum cokes 

as fuel mix may maease corrosion reactions with alkali metals. Coal type El and V with high 

B/A ratio of 0.386 and 0.372 have low T,,, (2,420 and 2,450 deg F, respectively) meeting 

requirement for operation of slag-tap cyclone fiunace. 

SUMMARY 

Various &el properties of four fluid cokes, fourteen delayed cokes and five export western coals 

were an+d and are compared for use in power generation. Important fuel quality parameters 

(typical and range) are tabulated for comparison, using recent analysis data accumulated for the 

, 

83 
past two years (1997-1998). Primary properties evaluated are: heating value, sulfur, nitrogen, 

ash, moisture, volatile matter content, hardgrove grindability index, Size disaibufon, and mineral 

analysis. In addition, coal ash characteristics such as silica ratio, base-to-acid ratio, ash fusiility, 

alkalies, TZJoI slagging index, fouling index, etc. are discussed. 

Petroleum cokes as 100% fuel or 10-20% fuel mix with coal have been used in power generation 

without serious operational problems reported, even burning with some cokes of high vanadium 

content (1,000-3,200 ppm). Some cokes have high sulfur content up to 7%. high nitrogen 

content up to 3.5%, and low HGI down to 25 (for delayed coke). Typical sulfur content of most 

cokes studied varies in the range of 0.8 to 4.1%; nitrogen varies in the range of 1.3 to 3.2%; and 

HGI vanes from 40 to 80 (for delayed coke), mostly higher than coal HGI (45). 

Petroleum cokes as fuel mix (up to 50%) have been used in cement kiln operation. Typical sulfur 

and vanadium content (controlled quality parameters for cement application) of delayed cokes 

mixed m kiln vary m the range of 3.1 to 3.8% and 530 to 760 ppm, respectively. 

Export delayed cokes are good quality, fuel-grade green (raw) cokes, which generally have lower 

ash, sulfur and metal content than delayed cokes used m domestic power generation. Typical ash 

content is in the range of 0.18 to 0.45%; sulfur content fiom 0.8 to 4%; vanadium fiom 270 to 

1,150 ppm; nickel fiom 180 to 550 pprn; and sodium fiom 50 to 450 ppm Calorific value is high 

in the range of 15,300 to 15,520 Btdb (HHV, dry basis). 

Price of fuel grade petroleum coke is normally below 5 $/ton at refinery, however, transportation 

cost si&cantly increases the price at power plant (21 $/ton, 1996 annual average delivered). 

Demand and supply of petro(eum coke are dictated by three important factors such as refinery 

cost, coke quality and transportation cost. Location of refinery and power plant seems an 

important factor to be considered. 

Export westem coals are high volatile bituminous coals with low sulfur and iron content, and are 

used as utility hels for power generation. Typical ash content is high in the range of 9.2 to 10%; 

sulfur content is very low in the range of 0.45 to 0.6%. Ash fiom these coals are defined as 

lignitic ash having more (CaDtMgO) than femc oxide. Ferric oxide content in ash is low fiom 

4.4 to 5.9% compared to eastern bituminous coal (20-30%); sodium oxide content is high fiom 

1.8 to 4.2%. Calorific value is low in the range of 12,640 to 13,360 BMb (HHV, dry basis), 

compared to petroleum cokes. Coal ash characteristics used for selection of feed coal and boiler 

design criteria are discussed relating to slag viscosity, fouling, and corrosion. Coal fype JII and V 

have low TZ5@ meeting requirement for operation of slag-tap cyclone furnace. 

The SUFCO Utah coal, one of he export westem bituminous coals evaluated for this study, was 

extensively tested at several gasification demonstration plants for IGCC systems m addition to 

variety of petroleum cokes as feed material to gasifiers. 

REFERENCES 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

E. J. Swain, Oil & Gas Journal, Nov. 10, 1997,79-82; May 20, 1991,49-52. 

A. K Rhodes, Oil & Gas Journal, Aug. 5, 1996,3 1-35. 

K W. Richardson and F. D. Taibi, Oil & Gas Journal, Apr. 5, 1993,38-42. 

R Graham, ASTM Standardization News, Mar. 1998,3643. 

Kerk-othmer Encyclopedia of Chemical Technology, Volume 6,4th Ed., Gadicatioo, 

541-568 (1993). 

D. H. Watts, Sixth Annual International Pittsburgh Coal Conference, Sep. 25-29,1989, 

A. M. Robin, et. al, Si Annual International Pittsburgh Coal Conference, Sep. 25-29, 

1989,244-254. 

F. M. Floyd and R K Agrawal, Sixth Annual International Pittsburgh Coal Conference, 

Sep. 25-29, 1989, 559-568. 

Babcock & Wilcox Company, "Steam - Its Generation and Use: Steam 40", Chap. 20, 

Fuel Ash Effects on Boiler Design and Operation (1992). 

E. J. Anthony, et. aL, 215th ACS National Meeting, Dallas, Preprints of Symposia, 

Division of Fuel Chemistry, Vol. 43, No. 1, 163- 166 (1998). 

J. M. Lee, J. J. Baker, R Llerena, J. G. Roue, 214th ACS National Meeting, Las Vegas, 

Reprints of Symposia, Division of Fuel Chemistry, Vol. 42, No. 3,844-853 (1997). 

R W. B~yers, ACS National Meeting, Preprints of Symposia, Division ofFuel Chemistry, 

569-581. 

VOL 38, NO. 4, 1237-1244 (1993). 

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Table 3. FUEL PROPERTIES OF EXPORT WESTERN COALS USED IN POWER GENERATION 

a9