Patent GB-785863-A (GB)
Title: Improvements in or relating to carbonization of carbonaceous materials
IPC: C10B49/10
Filed: 1956-02-07
Abstract: 785,863. Coking-apparatus. KELLOGG CO., M. W. Feb. 7, 1956 [Feb. 14, 1955; June 23, 1955], No. 3780/56. Class 55 (1). Solid fluidized carbonaceous material, e.g. coal, shale, lignite, oil sands, is carbonized by preheating and drying the feed material in a zone superimposed upon the carbonizing zone, passing the preheated and dried material downwardly as a confined stream into a pre-treating zone immediately below the carbonizing zone, in which pre-treating zone combustion with a limited amount of oxygen raises the temperature sufficiently to remove some volatiles and prevent agglomeration of the material in the carbonizing zone, and passing the pre-treated material upwardly into the carbonizing zone; in which it forms a dense bed superimposed by a dilute phase of low solid concentration, the volatiles being removed from the dilute phase and the devolatilized solids from the dense bed. Pulverulent coal is fed into a standpipe 4 in which it is fluidized, and with additional fluidizing gas, e.g. steam, is conveyed by pipe 8 to a drying and preheating vessel 10 in which the coal bed 12 is kept at about 270‹ F. A conduit 14 within the bed 12 receives, through the pipe 34, coal which is withdrawn at 22 from the bottom of the drying zone and is heated to about 480‹ F. in an exchanger 28 heated by a cat cracker decanted oil at a temperature of about 680‹ F., which enters at 30 and leaves at 32. Some of the preheated coal flows over the top of the pipe 14 into the drying zone, and some flows through a pipe 44 to the bottom of a pre-treatment zone 42, the proportions being adjusted by a valve 58. The zone 42 is divided from the carbonizing zone 40 by a vertical baffle 66 and has a bottom grid 60, for distributing the fluidizing gases, and a top grid 54 leading to the carbonizing zone. The pre-treatment is at a temperature of about 725‹ F., the heat being derived from combustion with oxygen, or air admitted at 64. Steam or flue gas also is admitted for fluidization purposes. About four per cent of the fuel is combusted, the tendency to cohere being eliminated from the remainder. The fuel passes upwardly through the grid 54 to the carbonizing zone where a temperature of 950‹ F. is attained, combustion air for this being supplied at 70. The residence times in the zones 42, 40 are 25 and 60 minutes respectively. The char is discharged at 62 from the space defined by the baffle 66. Hot char may be passed in regulable quantity to the pre-treatment zone 42, by injecting superheated steam at 68 into a stand pipe 48 leading to a cyclone and down pipe 50. The gaseous products, i.e. tar vapours, steam and combustion gases, are withdrawn through a cyclone 46 and pipe 52. The char is passed by pipe 72 to a cooler 74, the heat exchange being with cat cracker decanted oil which enters at 32 at 400‹ F., leaves at 30 at 600‹ F., is further heated to 680‹ F. for admission at 30 to the heat exchanger 28. The char passes through a char pot 98 and pipe 80 to a hopper 84, water being injected at 82 for cooling the char. The water is flashed to steam, which with the fluidizing gases, is removed through the cyclone and pipe 108 to a scrubber, having a water spray 104. Slurry from the scrubber passes, with additional water supplied at 94, to the char discharged at 92 from the hopper 84. Steam is withdrawn at 102. Some relatively cool char may be returned from the char pot 98 to the lower end of the cooler 74. The tar vapours from the carbonizing zone 40 are passed by pipe 52 to the tower 112 to be cooled and scrubbed with liquid tar admitted at 142. The vapours subsequently pass through perforated trays 116 and a mist eliminator 118 to remove entrained droplets. The tar is removed by a pump 136 and passed through a cooler 140 to the pipe 142, some being recycled and some discharged at 138. The gases, mainly steam and combustoin products, leave through a pipe 120, a cooler 122, an accumulator 124 where a further separation of gas and liquid occurs, and a precipitator 128 to atmosphere at 130. The liquids from the accumulator 124 and from the precipitator 128 are added to the product tar being discharged at 138. In a modification, the levels of the bed 12 of wet coal and of the preheated coal in the conduit 14 are kept below the top of the conduit so that there is no direct mixing. Coal is withdrawn from the bed 12, is heated by heatexchange, a part of the heated coal is returned to the bed whilst the remainder is further heated in another exchanger and supplied to the conduit 14. The throughput of solids in the second exchanger is augmented by solids withdrawn from the conduit 14 and returned to the conduit. The conduit 44 is downwardly extended to supply the pre-treatment zone as in Fig. 1. In another modification, unfluidized wet coal is fed to a hopper in which it is fluidized for passage, through a vertical standpipe, into the drying bed 12. The pre-heating bed 14 is at the side of the bed 12 and is separated therefrom by a vertical partition having an opening through which solids pass from bed 12 to bed 14. The beds 12, 14 are independently heated by extracting solids and returning the same through a heat-exchanger. Alternatively, wet coal is fed to and remains unfluidized in a hopper from which it gravitates through a vertical pipe to the bed 12, becoming fluidized on the way. The mixing of the fresh feed and the drying coal is facilitated by continuously withdrawing, by means of a fluidizing gas, coal from the bed 12 and delivering it to the vertical pipe from the hopper to the bed 12.