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Analyses of Illinois No. 6 Coal Liquefaction Results Generated in the Wilsonville, Alabama Unit A. M. Valente and D. C. Cronauer* BP Products North America, Incorporated, Warrenville, Illinois 60555 Received June 21, 2004. Revised Manuscript Received November 8, 2004
A database was set up to correlate the coal liquefaction results generated at the Department of Energy (DOE) Advanced Two-Stage Coal Liquefaction Facility in Wilsonville, AL. Published information available in the public domain was used, centering on runs made with Illinois No. 6 seam bituminous coal with two reactors in a close-coupled mode. A linear regression analysis was performed to determine the effects of process variables on conversions and product yields. Bimodal catalysts were more effective than a unimodal catalyst, as indicated by 10 wt % higher resid + unconverted coal conversion, 1 wt % greater hydrogen consumption, 19 wt % greater C4-1000 °F liquid production, and 14 wt % lower resid yield. Another significant result was a lower coal conversion, hydrogen consumption, C1-C3 yield, light (IBP-350 °F) distillate yield, and C1-C3 selectivity, when using half-volume reactors rather than full-volume reactors under similar conditions, including space velocities. This was apparently due to flatter reactor temperature profiles and lower catalyst-to-thermal volume ratios. Overall preferred processing conditions for converting coal to distillate liquids included the use of EXP-AO-60 catalyst, high reactor temperatures (>810 °F, 432 °C) and a high process solvent resid concentration (>50 wt %, if mechanically possible). The space rate of coal in the reactors is best set at a point where resid production is minimized, if justifiable by process economics.
Introduction and Background The Department of Energy Advanced Two-Stage Coal Liquefaction Facility was located in Wilsonville, AL; it was operated between 1970 and 1992 with funding by the U.S. Department of Energy (DOE), the Electric Power Research Institute (EPRI), and Amoco Corporation. It had a nominal capacity of 6 tons of coal per day. Many process descriptions have been published; selected references that summarize the operating modes are sited.1-3 The pilot plant was operated in close-coupled, integrated two-stage liquefaction (CC-ITSL) mode with and without interstage separation using “ashy recycle”. All the data presented herein were generated with the reactors in one of these configurations. In summary, the unit consisted of a feed system, two ebullated-bed reactors designed by HRI, Inc., and a product recovery system. The reactors were close-coupled, in that the solid/liquid separation (SLS) unit (ROSE-SRSM, Residuum Oil Supercritical Extraction-Solids Rejection of Kerr-McGee, Incorporated) was placed after the second reactor. Significant improvements were achieved in liquid yield by close-coupling the reactors.2 The * Author to whom correspondence should be addressed. Current address: Argonne National Laboratory, 9700 South Cass Ave., Argonne, IL 60439. E-mail address:
[email protected]. (1) Lamb, C. W.; Nalithan, R. V.; Johnson, T. W. Prepr. Symp.s Am. Chem. Soc., Div. Fuel Chem. 1986, 24, 1091. (2) Nalitham, R. V.; Lee, J. M.; Lamb, C. W.; Johnson, T. W. Fuel Proc. Technol. 1987, 17, 13-27. (3) Catalytic, Inc., Topical Report, DOE Contract No. DE-AC2280PC50041, EPRI Contract No. RP1234-1-2, Document No. DOE/PC/ 50041-82, 1990.
aforementioned aspect of “ashy recycle” refers to the recycle of mineral matter and unconverted coal from the product stream of the second reactor back to the feed stream of the first reactor. The addition of a supported catalyst in either the first stage, second stage, or both stages was also studied at the Wilsonville facility. All the runs using Illinois No. 6 coal in the close-coupled mode were made with a supported catalyst, in either the second stage only (designated as thermal/catalytic, T/C) or both stages (C/ C). The experimental run in the T/C mode (Run 250) was not included in this regression analysis, because it was too limited and skewed the final results. The results of Run 250 have been reported4 and they are discussed by Nalitham et al.2 The operations and results of the subsequent runs used in this study are available in the open litereature.5-9 A summary of these runs has also been reported and evaluated by Lee and Cantrell.10 Evaluations of the Wilsonville liquefaction runs made with sub-bituminous coal have been reported.11,12 Em(4) Catalytic, Inc., Technical Progress Report Run 250 with Illinois No. 6 Coal, No. DOE/PC/50041, 1986. (5) Catalytic, Inc., Technical Progress Report Run 251 Part I with Illinois No. 6 Coal, No. DOE/PC/50041, 1987. (6) Catalytic, Inc., Technical Progress Report Run 252 with Illinois No. 6 Coal, No. DOE/PC/50041-98, 1988. (7) Catalytic, Inc., Technical Progress Report Run 253 with Illinois No. 6 Coal, No. DOE/PC/50041-99, 1991. (8) Southern Electric International, Inc., Technical Progress Report Run 257 with Illinois No. 6 Coal, No. DOE/PC/50041-121, 1989. (9) Southern Electric International, Inc., Technical Progress Report Run 261 with Illinois No. 6, Burning Star Mine, No. DOE/PC/50041, 1991. (10) Lee, J. M.; Cantrell, C. E. Fuel Proc. Technol. 1991, 29, 171197.
10.1021/ef0400565 CCC: $30.25 © 2005 American Chemical Society Published on Web 01/28/2005
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Valente and Cronauer Table 1. Catalyst Properties
AMOCAT 1C diameter (in.) pore structure surface area (m2/g) pore volume (cm3/g) metals content (wt %) nickel molybdenum cobalt
1/
1/
12, 16 bimodal 188 0.86
2.3 10.5
AMOCAT 1A 1/
16
bimodal 218 0.80 8.8 2.5
phasis was directed toward the evaluation of dispersed and supported catalyst use. Munkvold et al.11 concluded that (i) the first stage should be catalytic, but the differences between soluble and supported catalysts were not sizable; (ii) the second stage should use a supported catalyst in an ebullated-bed configuration; and (iii) operation using a soluble precursor in the first stage is more hydrogen efficient, but generates a nominally heavier product. Lee et al.12 included the conclusions that (i) a hybrid system combining a dispersed molybdenum slurry and a supported catalyst was more effective than using the dispersed slurry and supported catalysts separately; (ii) the use of a dispersed catalyst improved coal and resid conversions, allowing for lower thermal severity in the first stage and higher severity in the second stage; (iii) the use of a supported catalyst in the second reactor increased hydrogenation and heteroatom removal, and (iv) the addition of a dispersed molybdenum catalyst precursor improved process operability. Formation of the Database The format in which the Wilsonville pilot plant data was reported has changed over the years. A database design for runs in CC-ITSL mode was developed to standardize the data. All runs at the Wilsonville pilot plant since the start of Run 250 in 1985 have been made in close-coupled mode. Illinois No. 6 seam coal has been used in more of these recent runs than any other single coal. Therefore, this study centered upon the conversion of Illinois No. 6 coal in the CC-ITSL mode. Sixteen process variables were used in the linear regression analysis of unit conversions and yields. These independent parameters and their corresponding variable names are listed below. Table 1 lists the range and mean value for each of the independent quantitative variables. Because of the recycle of high boiling liquids to form the coal slurry to the first stage, the two stages are interrelated. The products of the first stage influence the products of the second stage and vice versa. For this reason, the focus of this paper is on the two stages as a single unit. Unit Feed Variables. Process Solvent Resid. The process solvent resid (PSR) is defined as the weight percentage, on a moisture-ash-free (MAF) basis, of the recycle solvent that boils at >1000 °F. Process Solvent Cresol Insolubles. The term process solvent cresol insoluble (CI) is designated as the weight percentage, on an MAF basis, of the recycle solvent that (11) Munkvold, G.; Valente, A. M.; Cronauer, D. C. Prepr. Symp.s Am. Chem. Soc., Div. Fuel Chem. 1994, 39 (1), 92-97. (12) Lee, J. M.; Vimalchand, P.; Davies, O. L.; Cantrell, C. E. Prepr. Symp.sAm. Chem. Soc., Div. Fuel Chem. 1994, 37 (4), 1886-1894.
EXP-AO-60 1/
16
Shell 317 1/
20
Shell 324 1/
16
bimodal 241 0.78
bimodal 235 0.75
unimodal 165 0.48
2.5 10.7
2.6 11.6
2.7 13.2
is insoluble in cresol. This is primarily mineral matter and unconverted coal. Coal Concentration in Feed Slurry. The coal concentration (abbreviated as CoalConc) in the slurry is defined as the concentration of coal, on an MF(moisturefree) basis, after it is mixed with recycled solvent, in the slurry that is fed to the first reactor. Stage One Reactor Variables. Reactor Temperature. The reactor temperature (denoted as Temp1) is designated as the average temperature, in Kelvin, over the length of the reactor. For full-volume reactors, the temperature is a mathematical average of 13 points; for half-volume reactors, eight points are used.4 Average Catalyst Age. The average catalyst age (denoted as CatAge1) is defined as the amount of resid and cresol insoluble (CI) matter that was fed to the reactor per amount of catalyst initially charged and subsequently added. (The units for this variable are written as (lb resid + CI)/lb catalyst.) In the first stage, the CI matter consists of both fresh feed coal and CIs in the recycle solvent. Fresh Catalyst Addition Rate. Fresh catalyst addition rate (denoted as CatAdd1) is designated as the pounds of fresh presulfided catalyst added to each stage per ton of MF coal fed to the first stage of the entire two-stage unit. (The units for this variable are written as lb/ton MF coal.) An equal amount of deactivated catalyst is withdrawn from the reactor, to maintain a constant catalyst charge. Space Rate. The space rate (denoted as SpRate) is defined as the feed rate of MF coal per cubic foot of single reactor volume. (The units for this variable are written as lb MF coal/(h ft3 reactor volume).) A full reactor volume is designated as Vr. For all the runs used in this analysis, the first stage reactor volume was equal to the second, with both reactors at either full volume or half volume. Thus, the space rate for the first reactor is equal to that of the second, and, subsequently, only one was included in the modeling. Stage Two Reactor Variables. Reactor Temperature, Temp2. Same definition as Temp1, given previously. Average Catalyst Age, CatAge2. Same definition as CatAge1, given previously. Fresh Catalyst Addition Rate, CatAdd2. Same definition as CatAdd1, given previously. Other Variables (Qualitative, Set Variable Value to “1” If True or “0” If False). Both Reactors at Half Volume. The abbreviation “HalfVol” refers to the use of half-volume reactors. To increase the throughput per unit volume in the two-stage system effectively, reactors were modified for use at approximately half volume. This change actually resulted in the use of only 47% the total volume and only 38% of the catalyst charge
Illinois No. 6 Coal Liquefaction in Wilsonville, AL
(because of reactor internals).4 Although the space rate for a feed rate of coal through a full-volume reactor was approximately the same as that of half the flow rate through a half reactor, the ratio of coal to catalyst volume was significantly decreased. Interstage Vent Separator Used. The notation “Vent” is designated as the qualitative variable (0 or 1) indicating the use of an interstage separator to vent gases and low-boiling liquids from the bulk stream between the first and second reactors. If the separator was not operated, all products from the first stage were fed directly into the second stage. Catalyst Specification. The following catalysts were used: Shell 317, Shell 324, Amoco EXP-AO-60, and a combination of AMOCAT 1A catalyst in the first stage and AMOCAT 1C in the second (designated as Amocat1a). The properties of each of the catalysts are presented in Table 1.
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Figure 1. Effect of the first reactor temperature (Temp1) on yields.
Model Descriptions and Discussion The overall goal of this pilot-scale experimentation was to establish conditions to obtain a maximum yield of distillate liquids by high coal conversion and selective hydrogen incorporation; no statistical design was used in the choice of operating variables. Often, more than one process variable was changed between run periods. In deriving the regression equations, major noninteractive variable effects were first identified. Interaction and curvature terms were then created, and statistically insignificant terms were eliminated. These models may be considered as predictive equations within the range of variations of the independent variables. They also serve as a means to understand key operating variable trends for a given set of conditions. Because no commercial facility exists, these trends help to form a conceptual understanding of commercial coal liquefaction. All models are linear regressions (sometimes including quadratic or interaction terms) having the following form:
Figure 2. Effect of the second reactor temperature (Temp2) on yields.
Figure 3. Effect of the first reactor catalyst age (CatAge1) on yields.
Y ) A + Bx1 + Cx2 + ... Effects of Operating Variables on Overall Yields The overall yields of C1-C3, C4-C6, IBP-350 °F, 350-450 °F, 450-1000 °F, and resid products, as a function of each of the process variables, are presented in Figures 1-6. These graphs are derived from the regression equations presented herein. A detailed analysis of the model and the corresponding process variable effects is addressed in the following section. (Note that the distillate cuts are defined in terms of typical refinery distillate ranges (in degrees Fahrenheit, °F) and IBP denotes the initial boiling point of the recovered distillate.) Figures 1 and 2 show the effects of the first- and second-stage reactor temperatures (Temp1 and Temp2, respectively) on the overall yields of hydrocarbon products. The yields most influenced by reactor temperature are C1-C3, IBP-350 °F, and resid production. The yield of 450-1000 °F liquids is not a function of either Temp1 or Temp2, according to the regression equations. However, the overall yields of 1000 °F products increases
Figure 4. Effect of the second reactor catalyst age (CatAge2) on Yields.
as Temp1 or Temp2 increases; therefore, the rate of heavy fractions being cracked to intermediate boiling products matches that of their cracking to form lower boiling products. Figures 3 and 4 demonstrate how catalyst aging affects the overall yields. Catalyst aging of either stage results in less resid conversion (an increase in resid yield) with a decrease in the yield of 450-1000 °F liquids. The IBP-350 °F yield decreases as the secondstage catalyst ages. The yields of hydrocarbon gases and 350-450 °F liquids do not change significantly as the
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The variations in the independent variables are shown as absolute percentage deviations from the mean values (the “base points”). The model results are only plotted over the range of each independent value used in this analysis. Coal Conversion. The predicting equation for the conversion of coal to a cresol-soluble product (in terms of wt % MAF coal) is
Figure 5. Effect of the process solvent resid (PSR) concentration on yields.
Figure 6. Effect of the inverse space rate (1/SpRate) on yields.
catalyst age increases. This observation implies that the formation of hydrocarbon gases is primarily thermal. Figure 5 shows how the concentration of resid in the feed process solvent correlates with the shift in the yield of hydrocarbon products. The overall yield of resid decreases and the yields of both the IBP-350 °F and 450-1000 °F products increase as the concentration of resid in the recycle process solvent increases. Figure 6 presents the effect of inverse space rate (1/ SpRate) changes on yield structure. All the hydrocarbon yields are somewhat dependent on the space rate (SpRate). Within the range of SpRate values studied, the yields of all of the 1000 °F products increase as 1/SpRate increases (increasing nominal residence time). Of course, the resid yield decreases as 1/SpRate increases. Regression Analysis and Predictive Equations The resulting regression models for the major conversions and yields are presented below. The range and mean values of the independent variables are given in Table 2, whereas the confidence levels and t-statistics are presented in Table 3. The effects of changes in the independent variables over the range demonstrated at the Wilsonville facility are presented for each model.
coal conversion ) -1845 + 0.0964(PSR) + 794.2(1/SpRate) + 2.723(Temp1) + 2.724(Temp2) 0.00384(Temp1)(Temp2) - 1.150(HalfVol) + 0.938(Shell317) - 1.074(Shell324) Figure 7 shows the effect of changes in PSR, 1/SpRate, Temp1, and Temp2 on coal conversion, according to the model. Coal conversion is dependent upon the reactor temperatures of each stage. The temperature coefficients of each stage are virtually the same; therefore, each is of equal importance. The interaction of the two stage temperatures is negative, which dampens the temperature effect of a single stage. According to the model, an increase in Temp1 and Temp2 from the lowest of the ranges (762 °F/679 °F) to the highest (834 °F/824 °F) would cause only a 4 wt % MAF increase in coal conversion. However, these specific combinations of reactor temperature have not been demonstrated at the pilot plant. In Figure 7, the first-stage temperature seems to be more significant. This is due to the interaction term with Temp2 and the fact that the average second stage temperature is higher that the first. The effect of 1/SpRate (nominal residence time) on coal conversion is small but significant. Much of the dissolution of Illinois No. 6 seam coal occurs in the initial time period. Thereafter, the conversion increase with longer residence time is only incremental, as observed in Figure 7. An increase in the process solvent resid (PSR) level causes only a minor increase in coal conversion, as shown in Figure 7. Over the entire range of PSR values (24-50 wt % MAF), the change in coal conversion is only ∼2 wt %. The hydrogen-donating properties of the residuum may help to prevent some retrogressive reactions and, thus, increase conversion of coal to cresolsolubles. Because of operability and pump ability problems, the PSR could not be increased beyond 50 wt %. The substitution of half-volume reactors for fullvolume reactors (but maintaining the same space rate) results in a 1.15 wt % decrease in coal conversion. The most probable reason for this is that, when the reactors are at half volume, the internal liquid recirculating rate
Table 2. Range and Mean Values of Independent Variables PSR) PSCI CoalConc Temp1 CatAgel CatAdd1 1/SpRate SpRate Temp2 CatAge2 CatAdd2
low value
high value
mean value
24 wt % MAF 4.0 wt % MAF 28.8 wt % MAF 679 K (762 °F) 248 (lb resid + CI)/lb cat 0 lb/ton coal 0.0018 lb coal/(h ft3) × Vr 548 (h ft3/1b coal)/Vr 633 K (679 °F) 179 (lb resid + CI)/lb catalyst 0 lb/ton coal
50 wt % MAF 12.2 wt % MAF 40.0 wt % MAF 719 K (834 °F) 3665 (lb resid + CI)/lb cat 3.0 lb/ton coal 0.0033 lb coal/(h ft3) × Vr 300 (h ft3/1b coal)/Vr 713 K (824 °F) 3213 (lb resid + CI)/lb catalyst 3 lb/ton coal
41 wt % MAF 11.6 wt % MAF 33.1 wt % MAF 700 K (801 °F) 1703 (lb resid + CI)/lb cat 1.3 lb/ton coal 0.0024 lb coal/(h ft3) × Vr 415 (h ft3/1b coal)/Vr 682 K (768 °F) 1716 (lb resid + CI)/lb catalyst 0.8 lb/ton coal
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Table 3. Confidence Levels and t-Statistics variable Shell 317 Shell 324 HalfVol PSR Temp1 Temp2 (Temp1)(Temp2) 1/SpRate Shell 324 HalfVol PSR Temp1 CatAgel Temp2 CatAge2 1/SpRate Shell324 PSR Temp1 CatAgel Temp2 CatAge2 1/SpRate (CatAge2)2 Shell324 HalfVol Vent PSR Temp1 Temp2 CatAge2 1/SpRate (PSR)(Temp2) Shell324 PSR CatAgel CatAge2 1/SpRate
confidence level Coal Conversion 99.9 94.8 99.6 99.9 99.8 99.8 99.7 98.5 Hydrogen Consumption 99.9 98.7 99.2 99.9 99.5 99.3 99.9 99.9 C4-1000 °F Yield 99.9 99.9 99.9 99.9 99.9 86.8 99.9 99.4 IBP-350 °F Yield 99.9 99.9 96.1 99.7 99.9 97.5 97.0 99.9 99.8 450-1000 °F Yield 99.2 96.6 96.0 96.7 99.6
Hydrogen Efficiency 99.3 95.7 99.2 99.9 99.6 CO + CO2 + NH3 + H2S Yield Shell317 99.9 Shell324 99.9 EXPCat 99.9 HalfVol 99.9 CoalConc 99.9 CatAgel 99.9 CatAge2 99.9 (Shell317)(CoalConc) 99.9 NH3 Yield Shell324 98.8 PSR 93.4 CatAgel 99.8 CatAge2 99.9
Shell324 PSR CatAdd1 Temp2 CatAge2
t-statistic 3.65 -2.02 -3.12 4.34 3.39 3.34 -3.29 2.60 5.12 2.66 -2.86 -5.91 3.03 -2.92 3.90 -7.8
variable
confidence level
Resid + Unconverted Coal Conversion She11324 99.9 Vent 99.5 CoalConc 99.9 Temp1 99.9 CatAgel 99.8 Temp2 99.9 CatAge2 99.9 1/SpRate 99.9 C1-C3 Yield Amocatla 98.1 HalfVol 92.4 Temp1 99.9 Temp2 99.9 1/Space Rate 99.9 (Temp1)(Temp2) 99.9 C4-C6 Yield 99.7 99.9 99.9 99.9 99.8
-6.40 4.65 5.53 -4.26 5.61 1.55 7.55 -2.98
Amocatla Shell324 EXPCat Temp1 1/Space Rate
-7.30 -5.57 -2.17 -3.27 4.54 -2.38 -2.29 5.74 3.34
Shell317 Vent Temp1 Temp2 1/SpRate (Temp1)(Temp2)
-2.81 2.22 -2.15 -2.23 3.07
Shell324 PSR Temp 1 CatAgel Temp2 CatAge2 1/SpRate (CatAgel)(CatAge2)
-2.89 2.11 2.83 3.97 -3.15
Amocatla Shell317 PSR Temp2
Resid Yield 99.9 99.9 99.9 32.9 99.9 37.1 99.9 94.8 Water Yield 99.3 99.9 99.9 99.9
4.08 3.74 6.81 4.64 3.76 4.33 -5.03 -3.85
Shell324 EXPCat PSR Temp1 CatAgel Temp2 1/SpRate
CO + CO2 Yield 99.9 99.9 87.8 92.2 99.1 90.6 99.7
-2.87 1.99 3.73 -4.27
EXPCat CoalConc CatAdd1
is set at a high rate. This produces more mixing and, thus, a flatter temperature profile. When the reactors are operated at full volume, the coal slurry may be exposed to an average temperature of 800 °F; however, the actual temperature range over the reactor is ∼775825 °F. This higher temperature is likely the factor that increases the overall coal conversion.
t-statistic
350-450 °F Yield 96.6 98.5 98.2 98.1 99.5 97.9
H2S Yield 99.7 98.9 98.2
-6.37 3.07 11.00 5.49 -3.51 7.59 -5.93 10.61 2.49 -1.84 3.94 3.78 4.76 -3.71
3.17 4.78 5.94 7.24 3.34
2.21 2.58 2.50 2.48 3.02 -2.44
5.41 -3.87 -4.67 -0.43 -4.35 0.49 -5.86 2.03 2.89 3.67 3.50 -4.11
5.97 4.46 -1.69 1.97 -3.22 -1.85 3.22 3.53 2.64 2.66
Coal conversion was nominally higher with the Shell 317 catalyst than with the other catalysts (AMOCAT 1C, EXP-AO-60, and Shell 324). The Shell 317 and the first two catalysts were bimodal, whereas the Shell 324 catalyst had a unimodal pore structure. There seems to be little reason for the Shell 317 being more effective, other than the fact that it was nominally smaller and
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Figure 7. Effect of the percentage change in operating variables on coal conversion.
Valente and Cronauer
Figure 9. Effect of the percentage change in operating variables on hydrogen consumption.
sion. Specifically, as SpRate is decreased, the residence time is increased, giving the products more time to convert. Hydrogen Consumption. The equation for the overall consumption of hydrogen, expressed in terms of wt % MAF coal, in the two-stage unit is
Figure 8. Effect of the percentage change in operating variables on the resin + uncovered coal (R + UC) conversion.
had more external catalyst area. Catalyst age was not a significant factor; therefore, catalyst deactivation is apparently not critical to coal conversion. Conversion of Resid + Unconverted Coal (R + UC). The regression model for conversion of resid plus unconverted coal (fresh feed coal and any unreacted coal in the recycled solvent: R + UC) to 1000 °F product is
R + UC conversion ) -423.8 + 2.07(CoalConc) + 0.307(Temp1) - 0.00158(CatAge1) + 0.242(Temp2) - 0.00309(CatAge2) + 9648(1/SpRate) + 2.70(Vent) - 9.52(Shell324) The effects of changes in CoalConc, Temp1, Temp2, CatAge1, CatAge2, and 1/SpRate on R + UC conversion are shown in Figure 8. Of course, coal concentration in the slurry (CoalConc) has a large effect on the R + UC conversion. Because higher temperatures promote thermal breakdown of the coal and coal resid, increases in temperature have a positive effect on R + UC conversion. The temperatures Temp1 and Temp2 have approximately equal effects on R + UC conversion, as depicted by their equivalent slopes. The Shell 324 catalyst shows 9.52 wt % less R + UC conversion than does the base AMOCAT 1C. This Shell 324 catalyst is the only one with an unimodal pore structure, and it has the lowest pore volume (0.48 cm3/g vs 0.75-0.86 cm3/g). These properties should account for its reduced activity toward conversion of resid to 1000 °F product. Aging of the catalysts in both stage catalysts is also significant, as shown in Figure 8. As the catalyst ages, it has less activity toward hydrogenation, because of coking and plugging of the pores. As also shown in Figure 8, the relatively steep slope of the 1/SpRate line indicates that relatively small changes in SpRate significantly affect R + UC conver-
H2 consumption ) -32.2 + 0.0260(PSR) + 0.0381(Temp1) - 0.000168(CatAge1) + 0.0130(Temp2) - 0.000235(CatAge2) + 1044.5(1/SpRate) - 0.365(HalfVol) - 1.16(Shell324) The effect of these variables on hydrogen consumption is shown in Figure 9. An increase in the concentration in the recycled process solvent has a positive effect on the consumption of hydrogen for two obvious reasons. First, resid consumes hydrogen as it breaks down to distillates. Second, resid has hydrogen-donating properties, and a higher resid concentration likely improves hydrogen transfer to the liquids and the dissolving coal. The temperatures of both stages are important, and their corresponding lines (in Figure 9) have the highest slopes. Greater cracking of coal and heavy liquids occurs at higher temperatures. Increasing the 1/SpRate value also causes increased hydrogen consumption. As SpRate decreases, hydrogenation of the coal liquid occurs, and, thus, more hydrogen is consumed. Catalyst aging in both stages also affects the hydrogen consumption. As the catalyst ages and loses hydrogenation activity, the hydrogen consumption consequently decreases. Figure 9 shows the moderate decrease in hydrogen consumption as the catalysts age in each stage. The use of reactors at half volume versus full volume results in a moderate decrease in hydrogen consumption. This is possibly due to the flatter temperature profile over the reactor length, as discussed previously. The higher range of liquid temperatures in the case of full-volume reactors causes an extensive breakdown of the coal liquid, resulting in greater hydrogen consumption. The lower catalytic/thermal volume may also be contributing to lower hydrogen consumption. Liquefaction runs made using the unimodal Shell 324 catalyst show 1.16 wt % MAF less hydrogen consumption than the average of all similar runs with the other catalysts. This lower hydrogen usage is attributed to the unimodal distribution of pores and its low pore volume and surface area.
Illinois No. 6 Coal Liquefaction in Wilsonville, AL
Figure 10. Effect of the percentage change in operating variables on C1-C3 yield.
Figure 11. Effect of the percentage change of operating variables on C4-1000 °F yield.
C1-C3 Yield. The equation for estimating the yield of C1-C3 gases (in wt % MAF coal) is
C1-C3 gas yield ) -1696.2 + 2.383(Temp1) + 2.326(Temp2) - 0.003258(Temp1)(Temp2) + 1100.5(1/SpRate) - 0.5324(Amocat1a) 0.5628(HalfVol) As shown in Figure 10, C1-C3 gas yield is primarily dependent on the temperatures of both reactors, the coefficients of which are practically equal. As temperature is increased, the yield of C1-C3 gas also increases. This effect is dampened marginally by the negative interaction of Temp1 and Temp2. The effect of SpRate is also significant but relatively small (i.e., a change of
