Ind. Eng. Chem. Prod. Res. Dev. 1986, 25, 198-201
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Carbonization in a Tube Bomb. 1. Carbonization of Petroleum Residue into a Lump of Needle Coke Isao Mochlda,*+ Yozo Koral,+ Yasuhlro Nesuml,' and Takashl Oyama' Research Institute of Industrial Science, Kyushu University, Kasuga 8 16, Fukuoka, Japan, and Marifu Refinery, Koa Oil Company, Ltd., Kuga-Gun 740, Yamaguchi, Japan
The carbonization of a petroleum residue was studied by using a tube bomb, with which the pressurized carbonization of rapM heating was operable under conditions similar to those employed in a commercial delayed-coking process. Such a carbonization provided a small lump of needle coke (ca. 8 g), which was evaluated to be comparable to a commercial one prepared from the same feedstock in terms of appearance, optical texture, coefficient thermal expansion value, and bulk density. The pressure and heating rate were found to be influential factors in the production of such a needlelike lump coke in the tube bomb. Carbonization properties of fractions of a petroleum residue were also examined by the same apparatus to evaluate them as the feedstock for the needle coke.
Introduction Needle coke, which is an essential precursor for the graphite electrode for an electric arc furnace, has been produced by a delayed coker of large scale (Kurami, 1973; Mantell, 1976). Ita low coefficient of thermal expansion, high density, high electric conductivity, and low puffing are critically required (Letzia, 1977a,b, 1981). Such qualifying characteristics have been recognized to be strongly influenced by the nature of feedstocks and operational carbonization conditions. However, the scientific relation between them was far from established. The laboratory preparation of the real needle coke similar to the commercial one has been most desired for such a study, although the optical anisotropy of the coke and its development have been extensively studied to elucidate the detail mechanism (Marsh an Walker, 1979; Mochida et al., 1980; Mochida and Korai, 1983). We studied pressurized carbonization of a petroleum residue and its fractions in a tube bomb, which was heated in a sand bath at a high heating rate (Davies et al., 1977; Mochida et al., 1984a). Griffin et al. (1983) studied the carbonization of a coal liquid with a similar bomb. Controlling the heating rate as well as the carbonization pressure was found to enable the preparation of a lump coke that appears to be very similar to the commercial coke in appearance and structure. The lump cokes thus prepared from a small amount of feed (less than 40 g) allow the measurement of some characteristic properties of the needle coke described above. Procedures for the preparation of a lump of needle coke in a tube are described in the present paper. Such a procedure is very useful to evaluate the influences of the feedstocks and carbonization conditions on the coke properties in the laboratory, assisting the mechanistic study of commercial delayed coking. Experimental Methods Some analytical data of the samples and a petroleum residue (a vaccum residue of low sulfur crude (LSVR))and ita fractions (maltene and asphaltme separated by propane extraction) are summarized in Table I. Kyushu University. 1 Marifu
Refinery. 0196-4321/86/1225-0198$01.50/0
A sample (20-40 g) was weighed in a glass tube (diameter 15 mm, height 200 mm), which was put in the tube bomb (diameter 20 mm, height 200 mm). The bomb, equipped with two locks, was flushed with nitrogen flow several times before sealing. The pressure of nitrogen in the bomb was adjusted at room temperature before the carbonization. The sealed tube was immersed into the sand bath, which was kept at a prescribed temperature. The sample in the tube was heated to a prescribed temperature within 2 min. When the heating was started in the bath from room temperature, the rate was 250 'C/min. Along with the carbonization, evolving gas was purged through the control valve to adjust the pressure to the prescribed level until the end of carbonization, which took usually ca. 3 h. The produced coke was recovered in a lump form from the bomb for examination of the qualities as a needle coke. The coke was further calcined in an electric furnace at lo00
"C. The coke was examined with a reflected polarized microscope (Leitz, Orthplanpol) and a scanning electron microscope (JEOL JSM-25s). The optical anisotropic units were classified by their size as follows: flow domain >60 pm, flow 20-60 pm, coarse mosaic 5-20 pm, and fine mosaic
