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Energy & Fuels 2003, 17, 412-418
The Influence of Hydrodynamics on the NEDOL Coal Liquefaction Reaction Sadao Wasaka* and Masumi Itonaga New Energy and Industrial Technology Development Organization (NEDO), Higashi-Ikebukuro, Toshima-Ku, Tokyo 170-6028, Japan
Kouji Sakawaki and Kenji Inokuchi Mitsui SRC Development Co., Ltd., Chiyoda-Ku, Tokyo 101-0063, Japan
Michiharu Mochizuki Nippon Steel Corporation, Futtsu-Shi, Chiba 293-8511, Japan
Keith Clark CSIRO Division of Energy Technology, Sydney, Australia
Hirokazu Oda and Toshimitsu Suzuki Faculty of Engineering, Kansai University, Suita-Shi, Osaka 564-8680, Japan Received September 4, 2002
In NEDOL’s 1-ton-per-day process supporting unit, a plant designed to provide support data for the NEDOL coal liquefaction process which has been developed up to the 150-tons-per-day scale, the hydrodynamic behavior of coal slurry in the coal liquefaction reactors was observed using neutron absorption tracer equipment. The results clarified that the three reactors installed in series in the plant performed in a complete mixing mode providing sufficient contact between the liquid and hydrogen gas. It was also found that the increase of the gas feed rate resulted in the increase of liquid-phase mean residence time (MRT). This increase of MRT resulted in a decrease in the coal liquefaction residue yield and an increase in the coal liquefaction oil yield. However, the increase of the MRT did not improve the naphtha (C4-493 K fraction) yield because of vaporization of the light oil (493-623 K fraction) in the coal liquefaction reactors.
Introduction It has been reported that the hydrodynamic behavior in a coal liquefaction reactor affects the coal liquefaction reaction.1-6 It is particularly important to understand the relationship between the reaction behavior and the hydrodynamics in a liquefaction reactor for the scaleup of a coal liquefaction reactor. However, it is difficult to observe the hydrodynamics in a liquefaction reactor * To whom correspondence should be addressed. Energy and Environment Technology Development Department, New Energy and Industrial Technology Development Organization, SUNSHINE 60, 30F, 1-1, 3-Chome Higashi-Ikebukuro, Toshima-ku, Tokyo, 170-6028, Japan. E-mail:
[email protected]. Telephone: +81-3-3987-9441. Fax: +81-3-5992-3206. (1) Onozaki, M.; Namiki, Y.; Ishibashi, H.; Takagi, T; Kobayashi, M.; Morooka, S. Energy Fuels 2000, 14, 355-363. (2) Onozaki, M.; Namiki, Y.; Ishibashi, H.; Takagi, T.; Kobayashi, M.; Morooka, S. Ind. Eng. Chem. Res. 2000, 39, 2866-2875. (3) Onozaki, M.; Namiki, Y.; Sakai, N.; Kobayashi, M.; Nakayama, Y.; Yamada, T.; Morooka, S. Chem. Eng. Sc. 2000, 55, 5099-5113. (4) Onozaki, M.; Namiki, Y.; Ishibashi, H.; Kobayashi, M.; Itoh, H.; Hiraide, M.; Morooka, S. Fuel Process. Technol. 2000, 64, 253-269. (5) Itoh, H.; Hiraide, M.; Kidoguchi, A.; Onozaki, M.; Namiki, Y.; Ishibashi, H.; Ikeda, K.; Inokuchi, K.; Morooka, S. Ind. Eng. Chem. Res. 2001, 40, 210-217. (6) Ikeda, K.; Sakawaki, K.; Nogami, Y.; Inokuchi, K.; Imada, K. 2000, 79, 373-378.
operated under conditions of high temperature and high pressure, and there have been few reports that quantitatively analyze the relationship between the hydrodynamics in coal liquefaction reactors and coal liquefaction reaction behavior. Through the development of the NEDOL process, the hydrodynamics in coal liquefaction reactors have been observed quantitatively in continuous coal liquefaction plants. Clark et al. developed a neutron absorption technique (NAT) for studying the liquid-phase residence time in small-scale coal liquefaction reactors in 1983.7 The NAT was applied to a process development plant for the direct coal liquefaction process with a capacity of 2.4 tons of coal per day, constructed at Kawasaki,8 Japan, and a brown coal liquefaction plant with a capacity of 50 tons per day, at Victoria, Australia.9 After these (7) Clark, K.; Foster, N. R.; Weiss, R. G.; Newman, G. R. Ind. Eng. Chem. Fundam. 1983, 22, 502. (8) Ogawa, T.; Miyazawa, K.; Sakai, N.; Yoshida, F.; Moriguchi, S. In Proceedings of International Conference of Coal Science, Amsterdam, 1987; p 319. (9) Tanaka, Y.; Tamura, M.; Kageyama, H.; Clark, K. N. In Proceedings of the 2nd Japan/Australia Joint Technical Meeting on Coal, Tokyo, 1992; p 198.
10.1021/ef0201937 CCC: $25.00 © 2003 American Chemical Society Published on Web 01/28/2003
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Figure 1. Simplified process flow sheet of NEDOL process employed in the 1 t/d PSU for the liquefaction tests.
Figure 2. Hydrodynamics measurement apparatus using neutron installed in the 1 t/d PSU.
projects, NEDO (New Energy and Industrial Technology Development Organization) installed a NAT facility at a process supporting unit with a capacity of 1 ton of coal per day (1 t/d PSU), constructed at Kimitsu, Japan, and acquired the data of hydrodynamics in the NEDOL coal liquefaction reactors.10 On the bases of these data, a NAT facility for a pilot plant with a capacity of 150 tons of coal per day (150 t/d PP), constructed at Kashima, Japan, was designed and installed. The scale-up data for the coal liquefaction reactors of the NEDOL process (10) Mochizuki, M.; Imada, K.; Ikeda, K.; Inokuchi, K.; Nokami, Y.; Takeda, T.; Sakawaki, K. In Proceedings of 4th Japan/German Symposium on Bubble Columns, Kyoto; 1997; p 393.
were acquired through the comparison of the operation data of the 1t/d PSU11,12 and 150 t/d PP by the NAT facility.13 In the 1 t/d PSU, supplemental data for the 150 t/d PP were acquired because the 150 t/d PP was limited in its ability to alter certain operation conditions such as feed gas and feed slurry ratio (G/L). This paper (11) Sakawaki, K.; Nokami, Y.; Inokuchi, K.; Kawabata, M.; Imada, K.; Tachikawa, N.; Mogi, T.; Ishikawa, I. In Proceedings of 34th Sekitan Kagaku Kaigi in Japan, Sendai, 1997; pp 119-122. (12) Sakawaki, K.; Nokami, Y.; Inokuchi, K.; Kawabata, M.; Imada, K.; Tachikawa, N.; Mogi, T.; Ishikawa, I. In Proceedings of 34th Sekitan Kagaku Kaigi in Japan, Sendai, 1996; pp 89-92. (13) Sakai, N.; Saegusa, H.; Kobayashi, M.; Tachikawa, N.; Ishikawa, I.; Morooka, S. Fuel Process. Technol. 2001. In press.
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Figure 3. Residence time distribution of coal liquefaction conditions and water-hydrogen system in first coal liquefaction reactor. Table 1. Specifications and Injection Conditions of Tracer Tracer chemical formula particle size specific gravity
Gd2O3 2.0 (D50) 7.41
(µm) (-)
Tracer Slurry tracer particle concentration (wt %) slurry specific gravity (-) slurry temperature (K) injection rate injection time
Injection Conditions (L/min) (min)
50 1.76 423 2.7 0.37
Table 2. Specifications of Neutron Source source half-life period amount of source strength of source amount of neutron irradiation
(year) (µg) (mCi) (n/s)
252Cf 2.65 (at time of shipping) 2 1.07 (at 40MBq) 4.6 × 106
describes the influence of the hydrodynamics on the coal liquefaction reaction behavior based on the experiments conducted under various coal liquefaction conditions in the 1 t/d PSU. Experimental Section Coal Liquefaction Apparatus. Figure 1 shows a simplified process flow of the NEDOL process employed in the 1t/d PSU. The 1 t/d PSU precisely represents the NEDOL process
and the data from the unit correlate with those from the 150 t/d pilot plant constructed and operated for acquiring data for design and construction of commercial, or demonstration, scale plants. Experimental data and samples employed in this study were acquired from the 1 t/d PSU. The NEDOL coal liquefaction process consists of four sections: coal preparation section, liquefaction section, distillation section, and solvent hydrogenation section. In the coal preparation section, coal is dried and pulverized. The pulverized coal is mixed with hydrogenated solvent and catalyst. The mixture is fed to the liquefaction reactors and coal is liquefied in the reactors. Products from the reactors are separated into product oils and recycle solvent. The recycle solvent is hydrogenated in a solvent hydrogenation reactor for improving solvent quality and recycled to the coal preparation section as hydrogenated solvent. Hydrodynamics Measurement Apparatus. The NAT technique was applied for observing the hydrodynamics in the coal liquefaction reactors. The technique utilizes the interaction of very low energy neutrons (thermal neutrons) with an element which has a very strong tendency to absorb that neutron into its nucleus (Gd). Clark et al.7 describe the technique in detail, but it involved reducing the energy of neutrons being emitted from a Californium-252 source in a paraffin filled “howitzer”. This “howitzer” provided a flux of low energy neutrons that passed through the vessel carrying the hydrogenation products and was detected by a neutron detector located on the other side. The Gd carried in the hydrogenation fluid absorbed some of the flux of neutrons as it passed between the neutron detector and howitzer. The
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Table 3. Coal Liquefaction Conditions Employed in the 1 t/d PSUa
run no.
coal
catalyst
temp (K)
1 2 3 4 5 6 7 8 9 10 11 12
Tanito-Harum Tanito-Harum Tanito-Harum Tanito-Harum Tanito-Harum Tanito-Harum Tanito-Harum Tanito-Harum Tanito-Harum Tanito-Harum Tanito-Harum Tanito-Harum
SIS SIS NP NP NP NP NP SIS NP NP NP NP
738 738 738 738 738 738 738 723 723 723 738 738
a
liquefaction reaction conditions pressure catalyst G/L PDQI (MPa) added (wt%) (NL/kg) (mg/L) 17 19 17 17 17 17 17 17 17 17 17 17
3.0 4.0 3.0 3.0 3.0 3.0 3.0 2.0 2.0 2.0 3.0 3.0
700 900 700 500 1100 700 700 700 700 700 700 700
10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 12.0
slurry feed (t/d)
H2 concn (vol %)
coal concn (wt %)
2.50 2.50 2.50 2.50 2.50 2.75 2.50 2.50 2.50 2.50 2.50 2.50
85.0 85.0 85.0 85.0 85.0 85.0 85.0 85.0 85.0 85.0 90.0 85.0
40 40 40 40 40 45 45 40 40 40 45 50
NP: Natural pyrite. SIS: synthetic iron sulfide. PDQI: proton donor quality index.
concentration of Gd tracer in the hydrogenation fluid was then related to the reduction in the flux of neutrons reaching the detector. To observe the hydrodynamics in the coal liquefaction reactors of the 1t/d PSU, apparatus, comprising a howitzer containing a neutron source and a neutron detector, were installed at the first coal liquefaction reactor exit and the third coal liquefaction reactor exit. The tracer was injected in the first liquefaction reactor entrance as shown in Figure 2. Finely dispersed gadolinium oxide, an inert and low-toxicity compound that is one of the strongest naturally occurring absorbers of neutrons, was used as the tracer. The specifications and injection conditions of the tracer are indicated in Table 1. Gadolinium oxide was distributed through the liquid phase in the coal liquefaction reactors and closely followed the movement of the liquid phase. The specifications of the neutron source installed at the first and third liquefaction reactors are shown in Table 2. After the tracer is injected into the first coal liquefaction reactor entrance, it passes the first and the third coal liquefaction reactor exits. The tracer absorbs neutrons passing between the neutron source and detector at these points, and the quantity of neutrons reaching the detector decreases in proportion to the quantity of the tracer passing through the reactors. The amount of neutrons detected is counted from the time the tracer is injected and the amount of absorbed neutrons is calculated. Changes of tracer concentration passing the reactor exit are calculated by the amount of neutrons absorbed, and the liquid phase mean residence time (MRT) and residence time distribution of liquid phase (RTD) are numerically calculated using eqs 1 and 2, respectively.
∫0∞ tC(t)dt/∫0∞C(t) dt )∑tC(t)∆t/∑C(t)∆t
τ)
(1)
where τ is mean residence time (min); t, elapsed time from injection (min); C(t), tracer concentration at time t (Gd2+ mol/ L); and ∆t, measurement interval of tracer concentration (min).
E(θ) ) τE(t) E(t) ) C(t)/
(2)
∫0∞C(t) dt
where τ is mean residence time (min); t, elapsed time from injection (min); C(t), tracer concentration at time t (Gd2+ mol/ L); and θ, dimensionless time ()t/τ). Before the experiments in the coal liquefaction conditions, blank tests were conducted. Apparatus comprising same materials and geometry as the measurement part of liquefaction reactors was used for the blank tests. In the blank tests, the relationship between the amount of passed neutrons and void volume in the reactor was measured, and in the volume
Table 4. Properties of Coal Liquefaction Catalysts Natural Pyrite metal (wt %) Fe Mg Ca
elemental analysis (wt %) particle size C H N S other 50 (µm)
46.40 0.07 0.15 0.10
