Energy & Fuels 1989, 3, 154-160
154
Effects of Coal Concentration on Coprocessing Performance+ S. A. Fouda,* J. F. Kelly, and P. M. Rahimi Energy Research Laboratories, Canada Centre for Mineral and Energy Technology (CANMET), Energy, Mines and Resources Canada, 555 Booth Street, Ottawa, Ontario K I A OG1,Canada Received August 24, 1988. Revised Manuscript Received November 22, 1988
In an effort to assess coprocessing as a primary upgrading technology, a study was carried out on the effects of coal concentration on the overall process performance. Slurries containing 0-39.5 wt 70 maf subbituminous coal in Cold Lake vacuum bottoms were processed in a continuous-flow bench-scale unit under the same operating conditions. The tests were carried out in a single-stage CSTR unit with once-through operation using a dispersed slurry-phase disposable additive. Marked improvement in the process operability was observed with the addition of coal. Increased distillate yields were obtained at low coal concentration. In the range of 10-30 wt % maf coal concentration, the distillate yield was constant and was equal to that for the no coal case. The gross distillate quality changed only marginally with coal Concentration. The sulfur removal did not change, but the oxygen removal increased with coal concentration. The extent of anisotropic solids formation was markedly decreased by adding coal, and the extent of vanadium and nickel removal increased with increasing coal concentration. The results show that no significant penalties were observed in terms of process yields or product qualities by including coal in the feed to operate in the coprocessing mode. Moreover, beneficial effects such as the inhibition of coke formation and the enhancement of metals removal were observed.
Introduction
The simultaneous upgrading of mixtures of coal and residua from heavy oils, bitumens, or conventional crudes offers an attractive route for synthetic fuels production.' From a coal liquefaction standpoint, the replacement of recycle carrier oil with upgradable residue reduces plant capital costs and results in more efficient utilization of the reactor volume. From a residue conversion standpoint, the added coal improves the operability of the process by acting as an adsorbent for coke that might form during the reaction. It also enhances the removal of heavy metals. It was reported that the presence of coal in the feedstock results in a synergistic effect in terms of distillate yield.2 Using blends of short contact time coal extracts and heavy residues resulted in increased distillate yields and the enhancement of heteroatom removal during coal/oil copro~essing.~Coal has a lower hydrogen/carbon atomic ratio than oil. The improved operability and the catalytic effects of coal are therefore likely to be offset by the lower quality of coal relative to heavy oil. Increasing the coal concentration in the feedstock may therefore have adverse effects on the process. Studying the effects of coal concentration on process performance will help determine an optimum coal concentration range where the beneficial effects are dominant. This paper describes the effects of coal concentration on the coprocessing of an Alberta subbituminous coal and Cold Lake vacuum bottoms. Experimental Section Forestburg subbituminous C coal was obtained from Luscar Ltd. (Diplomat mine). Fresh samples of run-of-mine coal were 'Presented at the Symposium on Coal-Derived FuelsCoprocessing, 195th National Meeting of the American Chemical Society and 3rd Chemical Congress of North America, Toronto, Ontario, Canada, June 5-10, 1988.
shipped in sealed plastic bags contained in 45-gal drums. The nut-sized coal was dry ground in the presence of dry ice to -200 mesh (75 pm). The ground coal was placed in plastic bags and blanketed with argon to minimize oxidation during storage. An additive was prepared from a portion of the coal by impregnation with iron sulfate heptahydrate in a water slurry. After mixing, the slurry was dried under vacuum a t e 7 0 "C to 8-10 wt % moisture content to obtain a coal-based additive. The Cold Lake vacuum bottoms, nominally the +450 "C fraction, were obtained from the Strathcona refinery of Imperial Oil Ltd. The coal and oil feedstock characteristics are given in Tables I and 11, respectively. Slurry feeds with coal concentrations up to 39.5 wt % on a moisture- and ash-free basis were prepared by mixing the appropriate amounts of ground coal, coal-based additive, and oil such that the iron (Fe) concentration in the slurry feed was maintained a t 0.52 f 0.16 wt % for all the coal concentrations used. The slurries were proceased in a nominal 1kg/h continuous-flow stirred tank reactor unit.4 A schematic diagram of the unit is shown in Figure 1. Coprocessing was carried out in a single-stage once-through mode of operation by using the prepared dispersed slurry-phase disposable additive. All experiments were carried out at 450 OC, 13.9 MPa pressure, 1f 0.05 kg/(h.L) nominal space velocity and 71.4 g/kg of slurry feed (4500 SCFB) hydrogen flow rate. These conditions are not optimum for high conversion operation but were chosen a priori to avoid the effects of possible retrogressive reactions. Under the conditions chosen, the coke
(1) Speight,J. G.; Moschopedis, S. E. Fuel Process.Technol. 1986,13, 215-230. ( 2 ) Duddy, J. E.; MacArthur, J. B.; Mclean, J. B. Proceedings of the DOE Direct Liquefaction Contractors' Reuiew Meeting; PETC: Pittsburgh, PA, 1986; pp 304-320. (3) Greene, M.; Gupta, A.; Moon, W. Presented at the EPRI 11th Annual Conference on Clean Liquid and Solid Fuels, Palo Alto, CA, May 1986. (4) Kelly, J. F.; Fouda, S. A.; Rahimi, P. M.; Ikura, M. In Proceedings of the Coal Conuersion Contractors' Reuiew Meeting, Calgary, Alberta, 1984; Kelly, J. F., Ed.; Report SP85-4; CANMET, Energy, Mines and Resources Canada: Ottawa, 1985; pp 397-423.
0887-0624/89/2503-Ol54$01.50/0 Published 1989 by t h e American Chemical Society
Energy & Fuels, Vol. 3, No. 2, 1989 155
Effects of Coal Concentration o n Coprocessing
F i g u r e 1. Schematic diagram of the continuous-flow bench-sale coprocessing unit. Table I. Characteristics of Forestburg Subbituminous C Coal Proximate Analysis (wt % As Received) 19.17 volatile matter 34.00 moisture ash 7.68 fixed carbon 39.15 carbon hydrogen sulfur Fe Ni cal/g
Ultimate Analysis (wt % Dry Basis) 64.04 nitrogen 3.87 ash 0.53 oxygen (by difference) Metal Content (ppm) 2379 V 18
4933
Calorific Value btu/lb
1.65 9.50 20.41
trace
8879
Petrographic Analysis (vol % As Received) 92.2 inertinite 3.1 vitrinite liptinite 2.6 mean reflectance 0.42 Table 11. Characteristics of Cold Lake Vacuum Bottoms General Characteristics specific gravity, 15/15 OC 1.038 aromaticity ('H NMR) 34.5 Conradson carbon 17.1 viscosity, P residue, w t % at 80 "C 249.12 pentane insolubles, w t % 23.48 at 110 "C 21.59 benzene insolubles, wt % 0.2 Distillation (Spinning Band Method) 420 residue (+525 "C), wt % 83.2 IBP, OC distillate (-525 "C), w t % 16.8 carbon hydrogen sulfur Fe Ni
Elemental Analysis (wt % ) 78.6 nitrogen 9.3 ash 5.5 oxygen (by difference) Metal Content (ppm) 18 V 93
0.6 0.0
5.9
235
formation as identified by petrographic analysis of the residue product was only 0.28 wt % based on maf slurry feed. The coprocessing slurry product was subjected to spinning band distillation to obtain a distillate product (-525 "C fraction), a residue product (+525 OC fraction) and product water. The gross characterization of the distillate product included determination of specific gravity by PARR densitometer, boiling range by simulated distillation (ASTM D227), hydrogen, carbon, and nitrogen content by using a Model CHN 240 Perkin-Elmer analyzer, sulfur content by using a X-ray fluorescence analyzer (Princeton Gamma Tech Model loo), and PONA analysis by using a GC/MS instrument (Finnigan 4000 instrument with INCOS data system). Aromaticity was determined from 'H NMR spectroscopy by using
a Varian CFT-20 pulse Fourier transform instrument and the Brown-Ladner equation! The residue product was characterized by elemental analysis and solvent extraction using pentane, toluene, and tetrahydrofuran for estimating the oils, asphaltenes, and preasphaltenes contents, respectively. Ash and metal contents were determined by following ASTM D-402 on a Jane1 Ash Model 850AA spectrometer.
Results and Discussion When the vacuum bottoms were processed by using ferrous sulfate heptahydrate powder to provide an iron concentration of 0.52 f 0.16 wt % based on slurry feed, in the absence of coal, plugging occurred in the reactor outlet line due to enhanced coke formation. Long duration operation was not possible. However, an 80-min test at steady state allowed collection of enough product sample to report yield data. Using 2-3 wt % maf coal impregnated with ferrous sulfate (i.e. the coal-based additive) significantly improved the operability and markedly increased the distillate yield and the pitch conversion. The largest improvement in performance was observed for coal concentrations of less than 5 wt 70.As the coal concentration was further increased, no operational problems were encountered up to approximately 40 wt % maf coal. However, in the 10-30 wt 70 range of coal concentration, the distillate yields and pitch conversions were similar to those for the no coal case. Slurry Feed Characteristics. The addition of Forestburg subbituminous coal to Cold Lake vacuum bottoms results in both positive and negative effects on the quality of the slurry feed. Figure 2 illustrates the changes in feed quality as the concentration of coal in the slurry feed is increased. Figure 2 shows that the addition of coal results in a lower H/C atomic ratio and higher oxygen, lower sulfur, and slightly higher nitrogen contents. Both the vanadium and nickel contents decrease when the coal concentration is increased. Although not shown in Figure 2, the viscosity and the specific gravity of the slurry feed were increased b y the addition of coal. This increase, however, did not cause handling or pumping problems over the coal concentration range investigated. Distillate Yield. The overall distillate yield (C5-525 "C) is shown as a function of coal concentration in Figure 3. For the no coal case, the overall distillate yield was 62.6 wt % based on maf slurry feed. The addition of 2-3 wt ( 5 ) Brown, J. K. Ladner, W.
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