Energy & Fuels 2003, 17, 1437-1444
1437
Improvement of Product Quality and Yield on the NEDOL Coal Liquefaction Process Sadao Wasaka* New Energy and Industrial Technology Development Organization (NEDO), Higashi-Ikebukuro, Toshima-Ku, Tokyo 170-6028, Japan
Kouji Sakawaki Japan Planning Organization, Inc., 3-20 Kioicho, Chiyoda-ku, Tokyo 102-0094, Japan
Yoshinobu Nogami and Kenji Inokuchi SRC Technologies Co., Ltd., 3-4-12, Ootsuka, Bunkyou-ku, Tokyo 112-0012, Japan
Michiharu Mochizuki and Masumi Itonaga Nippon Steel Corporation, Futtsu-Shi, Chiba 293-8511, Japan
Hirokazu Oda and Toshimitsu Suzuki Faculty of Engineering, Kansai University, Suita-Shi, Osaka 564-8680, Japan Received January 9, 2003. Revised Manuscript Received July 18, 2003
To improve the product quality in the NEDOL coal liquefaction process (which was developed by the New Energy and Industrial Technology Development Organization, NEDO), improvement of the NEDOL process was proposed and tested by a continuous plant, which can process 1 ton of coal per day. In the improved process, the products and recycle solvent are simultaneously hydrogenated in the solvent hydrogenation section. Although the recycle solvent of the improved process became lighter and degradation of the recycle solvent quality was supposed, via moresevere hydrogenation conditions in the solvent hydrogenation section, the hydrogen-donating capability of the recycle solvent was maintained and degradation was not recognized. On the other hand, the hydrodynamics of the coal liquefaction reactors was studied and mean residence time of the liquid phase (MRT) in the coal liquefaction reactors was measured using neutrons. An increase in the MRT was observed, and this increase seemed to be caused by vaporization of the increased lighter fraction in the recycle solvent. As a result, the product oil yield was increased by 2-3 wt %, compared to the original NEDOL process, and remarkable reduction of the heteroatoms in the product oils was confirmed. The nitrogen content in the products was reduced from several thousands parts per million (ppm) in the original NEDOL process to 50 days in the improved process, which adopts simultaneous hydrogenation of the products and recycle solvent, was achieved, and the reliability of this process was verified.
Introduction The New Energy and Industrial Technology Development Organization (NEDO) has conducted research and development of coal liquefaction technology since the second oil crisis. NEDO has developed the so-called NEDOL process through research work that spanned from basic research to pilot-plant operation. The principal feature of the NEDOL process is the ability to obtain higher oil yield, even under relatively mild coal liquefaction conditions, using a recycle solvent that has higher hydrogen-donating capability.1-4 For this pur* Author to whom correspondence should be addressed. E-mail:
[email protected].
pose, the NEDOL process has a solvent hydrogenation section that enhances the hydrogen-donating capability of the recycle solvent, and the distillate separated in the distillation section is hydrogenated before being recycled to the coal liquefaction reactors as the recycle solvent. (1) Wasaka, S.; Kobayashi, M.; Imada, K. Proceedings of the 9th Japan/Australia Joint Technical Meeting on Coal, Melbourne, Australia, June 1-2, 1999. (2) Wasaka, S.; Ibaragi, S. Proceedings of the 17th Pittsburgh Coal Conference, Pittsburgh, PA, September 11-14, 2000. (3) Wasaka, S.; Ibaragi, S.; Hashimoto, T.; Tsukui, Y.; Katsuyama, T.; Shidong, S. Proceedings of the 7th Japan-China Symposium on Coal and C1 Chemistry; Haikou, China, 2001; pp 245-248. (4) Wasaka, S.; Ibaragi, S.; Hashimoto, T.; Tsukui, Y.; Katsuyama, T.; Shidong, S. Fuel, 2002, 81, 1551.
10.1021/ef030009x CCC: $25.00 © 2003 American Chemical Society Published on Web 08/29/2003
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Figure 1. NEDOL process flow in the continuous plant with a processing capacity of 1 ton of coal per day.
The quality of coal-derived oils produced in the NEDOL process is not equivalent to that of gasoline and diesel fuel in the current petroleum market.5 To increase the quality to an equivalent level, further refining is required in a refining plant that is equipped in a coal liquefaction plant or an external petroleum refining plant. In addition, coal-derived crude oil produced in a coal liquefaction plant contains heteroatoms (such as sulfur and nitrogen) and olefins. These are unstable during storage and heteroatoms, especially, decrease catalyst life in the refining process. Therefore, a reduction in the amount of heteroatoms and olefins before processing in the refining plant is required. Moreover, improvement of the oil quality of the coal liquefaction crude oil inside the coal liquefaction plant before it is sent to the refining plant leads to a reduced load for processing it in the refining plant. Economical and efficient methods for improving the quality of the coal-derived crude oil must be studied. More-effective use of the solvent hydrogenation section, which is used to improve the hydrogen-donating capability of the recycle solvent, was considered for improving the product quality. In this paper, results of the study regarding a method that hydrogenates the entire distillate, including the recycle solvent and product oils, and results of the demonstration in a continuous plant, which can process 1 ton of coal per day, will be described. Experimental Section Apparatus. Figure 1 shows the NEDOL process flow. The NEDOL coal liquefaction process consists of four sections: a coal preparation section, a liquefaction section, a distillation section, and a solvent hydrogenation section. In the coal (5) Omori, K.; Sato, H.; Miyata, Y. Proceedings of the Annual Meeting of the Japan Institute of Energy, Tokyo, 2002; p 60.
preparation section, coal is dried and pulverized. The pulverized coal is mixed with a 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 to improve solvent quality and is then recycled to the coal preparation section as a hydrogenated recycle solvent. The NEDOL process was modified to improve the quality of the product oils, and the modified NEDOL process was demonstrated in a continuous plant that can process 1 ton of coal per day. Figure 2 shows the modification outline of the NEDOL process to the modified NEDOL process. Although the NEDOL process hydrogenates only the heavy distillate in the reactor effluent to be recycled, the modified NEDOL process hydrogenates the entire distillate, including the light fraction and the heavy fraction supplied from the distillation section in the solvent hydrogenation section. The hydrogenated distillate is separated into product oils and a recycle solvent to be recycled to the coal preparation section. The principal feature of the modified NEDOL process is the improvement of the product oil quality and the hydrogen-donating capability of the recycle solvent simultaneously, via hydrogenation of the entire distillate. The continuous plant exactly simulates the NEDOL process, and the data from the plant correlate with those from a pilot plant that has been constructed and operated for the purpose of acquiring the data for design and construction of commercial- or demonstration-scale plants.6 The modified NEDOL process shown in Figure 2 consists of the same process units and equipment as the NEDOL process and is different only in the process sequence of hydrogenation and distillation of the reactor effluent. Because the NEDOL process has already been demonstrated in the pilot plant, the scale-up risks of the units and equipment that comprise the modified NEDOL process seem to be small. (6) Onozaki, M.; Ishibashi, H.; Aramaki, T.; Sakai, N.; Kobayashi, M.; Chiba, T.; Morooka, S.; Mochida, I. J. Jpn. Inst. Energy 2000, 79, (12), 1159.
Improvement on the NEDOL Coal Liquefaction Process
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Figure 2. Process modification in the continuous plant with a processing capacity of 1 ton of coal per day. Table 1. Operation Conditions of Coal Liquefaction and Solvent Hydrogenation operation mode
run 1
run 2
run 33
property
NEDOL
modified NEDOL
modified NEDOL
coal proximate analysis ash volatile matter fixed carbon elemental analysis carbon hydrogen nitrogen sulfur oxygen H/C atomic ratio O/C atomic ratio
Coal Liquefactiona catalyst (wt %) 3.0 3.0 temperature (K) 738 738 pressure (MPa) 17 17 b 3 G/L (N m /kg) 0.7 0.7 coal, concentrated (wt %) 40 40 slurry feed rate (t/day) 2.5 2.5
3.0 738 17 0.7 40 2.5
Solvent Hydrogenation 598 618 10 10 0.5 0.5 1.0 0.6
618 14 0.5 0.6
temperature (K) pressure (MPa) G/Lb (N m3/kg) LHSV (h-1)
Table 2. Properties of Coal Tested in Continuous Plant with a Processing Capacity of 1 Ton of Coal per Day
a
value Tanito-Harum 4.3 wt % dry coal 47.0 wt % dry coal 48.7 wt % dry coal 76.9 wt % dafa coal 5.9 wt % dafa coal 1.6 wt % dafa coal 0.3 wt % dafa coal 15.6 wt % dafa coal 0.91 0.15
The abbreviation daf denotes dry ash free.
a
Tanito-Harum coal was used for each coal liquefaction run. bG/L is the ratio of feed gas to feed slurry.
Operating Conditions. Operation of the modified NEDOL process was conducted under the conditions shown in Table 1, and operation of the NEDOL process was conducted to compare differences in respective process performances. Coal liquefaction conditions for the modified NEDOL process were identical to those of the NEDOL process. The reaction temperature was 738 K, the reaction pressure was 17 MPa, and the ratio of feed gas to feed slurry (G/L) was 0.7 N m3/kg. The reaction temperature of the solvent hydrogenation reaction in the modified NEDOL process was increased by 20° and the liquid hourly space velocity (LHSV) was decreased from 1.0 h-1 to 0.6 h-1. Moreover, in run 3 of the modified NEDOL process, the total pressure in the solvent hydrogenation was increased to 14 MPa. To increase solvent quality, the solvent
hydrogenation conditions used in the modified NEDOL process were more severe than those of the NEDOL process. Coal and Catalyst Properties. Table 2 shows the properties of the Tanito-Harum coal that was used in the examination. Tables 3 and 4 indicate the properties of the coal liquefaction catalyst and solvent hydrogenation catalyst, respectively. Natural pyrite was used as the coal liquefaction catalyst, and a Ni-Mo supported alumina catalyst was used in the solvent hydrogenation. Hydrodynamics Measurement. NEDO has been developing a method for analyzing the hydrodynamics in coal liquefaction reactors using neutrons.7-11 In the continuous plant, an apparatus that was comprised of a neutron source and a (7) Clark, N. K.; Foster, N. R.; Weiss, R. G.; Newman, G. R. Ind. Eng. Chem. Fund. 1983, 22, 502.
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Table 3. Properties of the Coal Liquefaction Catalyst property
value
catalyst metal content iron magnesium calcium elemental analysis carbon hydrogen nitrogen sulfur particle size, D50
natural pyrite 46.72 wt % 0.05 wt % 0.32 wt % 0.11 wt %
