AU594365B2 - High purity coke - Google Patents

Description

594365 Form

AUSTRALIA

PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Short Title: mnt. Cl: Application Number: Lodged: (,L4qq1ct Complete Specification-Lodged: Accepted: Ths ~~umnt ontafln the an c'v. Lic ent made under Seci~f 49andis orrct for printsng Lapsed, Published: 0 o '~1Thprity: 0 0009 0 *09 09 9 Art: *1 0 0499 COMPLETE-AFTER-PROVIS TONAL PH 2396 BY APPLICANT .'Npme of Applicant: 0 0 Address of Applicant:, Actual iniventor: COMALCO ALUMINIUM LIMITED, 55 Collins Street, Melbourne, Victoria 3000 John Cranimond NIXON John Alan EADY Christopher Geoffrey GOODES Address for Service:, CLEMENT HACK CO.,, 601 St. Kilda Road, Melbourne, Victoria 3004, Australia.

Complete Specification for the ,-ventlon entitled: "HIGH PURITY COKE" The following statement is a full dr~scriptlon of this Invention, including the best method of performing It known to me:- PF/CPlF/2/80 1 3 2 S 4*t *9 S( .5 a HIGH PURITY COKE Field of the Invention fi This invention relates to a new type of high purity coke and a process for making the same. The new type of coke has many applications, such as a blast or electric furnace reductant, but is especially suited to the production of anodes for aluminium smelting. In this application it has significant advantages over conventional materials presently used.

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3 Current Status of Technology Aluminium is produced commercially by electrolysis of alumina dissolved in molten cryolite, using carbon electrodes. Carbon dioxide is released at the anode as a result of the oxygen liberated on the decomposition of alumina. That is, the liberated oxygen reacts with and consumes the carbon anode. In theory, 0.33 kg of carbon is consumed per kilogram of aluminium produced, while in practice carbon consumptions closer to 0.45 kg are experienced. The carbon consumpticon in excess of theoretical is a result of various side reactions known to occur in the cell, such as dusting and airburn. Anodes used in the electrolytic production of aluminium are normally fabricated from petroleum coke and coal tar binder pitch. Petroleum coke is a #0.05 by-product of the petroleum industry while binder pitch is derived from high temperature coke oven tars.

*9* o 44 Specific coke properties desired for anode S. manufacture include low electrical resistivity, low reactivity, high density, low porosity, high resistance to thermal shock and most importantly, high purity. It is also desirable that the coke and pitch form a strong, coherent bond during anode manufacture. The fact that petroleum coke is a by-product of the petroleum industry introduces several distinct disadvantages in these respects. The petroleum cokes currently used in the fabrication of anodes vary markedly in nature, particularly in terms of porosity, and often contain significant levels of impurities. The major impurities include S, Si, V, Ti, Fe and Ni. Whilst S is troublesome due to environmental concerns, the heavy metals, and particularly vanadium, cause both a reduction in the current efficiency of the electrolytic cell and adversely affect the quality of the metal produced. When high purity metal is required, in electrical applications, therefore, expensive refining steps may be necessary.

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A further disadvantage of petroleum coke is that its production is mainly confined to the United States.

Transportation costs to other countries can become significant.

Clearly, it would be advantageous to find alternative sources of anode materials which retain the desirable properties of petroleum coke, but avoid the specific disadvantages, viz., high impurity and variable porosity levels. An added incentive in finding an alternative carbon j 10 source is the resulting independence of the aluminium industry Ji relative to the unrelated petroleum industry. In this manner the consistency and supply of high quality coke to the aluminium industry could be ensured.

,Ii Many other workers have also recognised the desirability and in some cases necessity, of developing V alternatives to-petroleum coke. For example, anodes have been produced from low ash coal and used in aluminium smelters.

The properties of these anodes were, however, inferior and high carbon consumptions resulted. More recent attempts to 20 produce anodes from the briquetting of low ash coal have also proven to be unsuccessful.

Further attempts to produce an alternative to petroleum coke have included coke from shale oil, from solvent refined coal and from pitch derived from high temperature coke oven tar. While these processes have been found to produce coke with some desirable properties, for example low impurity levels, are generally uneconomic. A relatively qmall quantity of coke is derived from coke oven tar in Japan, although this coke is limited in supply and, consequently, demands a premium price. No commercial plants exist for the production of coke from either shale oil or solvent refined coal.

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i "~i q- 3 -r 5 General Description of the Invention A technique for producing a high quality coke according to the invention, hereafter named "FPDC (Flash Pyrolysis Delayed Coking) Coke", is largely based upon a novel combination or integration of two processes, namely flash pyrolysis and delayed coking. Individually, both processes are intended for markedly different purposes.

Therefore, in addition to combining the processes in a novel manner, it is also necessary to modify the conventional operating philosophies of the two processes in order to produce the desired FPDC coke.

4 4* S 4$ "Flash pyrolysis" is a process whereby a carbonaceous feedstock is rapidly heated in a fluidized bed, in the absence of oxygen, to produce a relatively high tar yield. In its conventional intended application, tars produced by this p'rocess (FPT) are used as an intermediary in the production of liquid fuels. This requires substantial hydrogenation, in contrast to the de-hydrogenation required for the production of FPDC coke.

?0 "Delayed coking" is the process used commercially to produce petroleum coke from refining residues. In conventional refinery practices with petroleum feedstocks, the sobjective is to maximize the recovery of liquid components at the expense of coke yield. Petroleum coke is, therefore, a by-product of the refinery. Feedstocks to the coker are al'o S I quite variable, resulting in regular shifts in coke quality.

Delayed coking as applied to FPT according to this invention differs significantly from the process normally applied to refinery residues. In this application maximizing the coke yield, consistency and quality are the primary concerns. The coker must, therefore, be operated in a significantly different manner to conventional refinery residues.

i I 6 In addition to product consistency and low levels of trace metals, we have found that FPDC coke has other and unexpected advantages over petroleum coke. These include low porosity, high density,low resistivity, low reactivity and good compatibility with binder pitch. There is also the potential to produce low sulphur coke, provided a coal feedstock containing suitably low levels of sulphur is used.

For example, Australian coals fall clearly into this category.

FPDC coke is not, therefore, merely a substitute for petroleum coke but offers advantages for anode manufacturers.

A flowsheet for the new coke making process is shown in Figure 1. Broadly, a starting feedstock of coal is subjected to flash pyrolysis to produce tar, gas and residual char. The tar produced by flash pyrolysis is subsequently filtered to remove unseparated char, and then used as a feedstock to the delayed coking unit. A high yield of FPDC coke is obtained in comparison w th petroleum coke feedstocks t and, therefore, the delayed coking unit must be operated in a significantly different manner to that of the prior, art. As 20 an optional step, the FPT may be neutralized prior to coking, using process derived ammonia gas. This neutralization stage can most likely be avoided, however, if suitable materials of constrvution are used in the plant.

Detailed Description A preferred embodiment of the process will now be described in greater detail with reference to the flowsheet shown in Figure 1.

A major advantage of the new process is that it is applicable to a wide range of carbonaceous starting materials.

For the best yields of tar (and therefore FPDC coke), the carbon precursor should contain c significant proportion of volatile material and have a low caking tendency. A large il I 7 ij i number of coals, both black and brown, satisfy these criteria and are relatively inexpensive in comparison to premium coking coals. In addition to coals, other materials such as oil shales and tar sands could also be used. Although the nature of the feedstock will not affect the quality of the coke, it will determine the properties of the other process streams.

The as-mined feedstock must be physically treated prior to pyrolysis. In the case of black coal, the following preferred procedure may be adopted; Beneficiation, to reduce the ash content to around 20% or less.

Air drying of the washed coal to <10% moisture.

t*4 I Crushing of the coal to<0.18mm particle size.

I 4 It should be noted that ash reduction through beneficiation is a widely used procedure in the coal industry, although with a different intention in mind. Although this step is not essential in the process, and in no way affects the properties of the FPDC coke, ash reduction is desirable to ensure the quality of the char product. For materials other than coal, oil shale for example, it may not be feasible nor S desirable to reduce the ash level to any extent. The char S produced would be, consequently, of lower fuel value.

i The followingflash pyrolysis stage is central to the S new process and involves the rapid heating of the feedstock to high temperatures in an inert atmosphere. A number of different flash pyrolysis technologies have been developed, with the aim of producing an intermediate coal liquid suitable for upgrading to a crude oil equivalent, while also producing a combustible char. A flash pyrolysis process developed by the CSIRO has been found suitable for the process of this 4

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8invention, because of its high yield of tar and suitability of the latter for delayed coking. Other flash pyrolysis technologies could also be applied to the process of the invention, although lower yields of coke may result.

IN the CSX1RO process crushed and dried coal is injected~ into a fluidized bed reactor at temperatures between 400 and 800 0 c and the coal is rapidly heated at rates approaching 10~ C S 1 The process is conducted in an inert atmosphere, at atmospheric o near atmospheric pressure. The coal decomposes into tar vapour, char and gas components. The vapours are rapidly removed from the reaction zone and cooled to condense the tar fraction. The combination of a high t f L I II I I (I lIlt

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I I I II heating rate and rapid quenching of the tar vapours results in high liquid yields being obtained.

t*~jJ~ 1 "1A critical factor affecting the yield and properties of the tar is the pyrolysi8 Lemperature selected. Within a range of 400 arid 800 0 C, an optimum tar yield was obtained at 600 Q.

Some comments onr the characteristics of the products of flash pyrolysis are given below:- Flash pyrolysis tar is a complex combination of the atoms C, H, N, 0 and S, varying in ratios according to the production conditions and nature of feedstocks, In order to produce the highest yield on coking, it is desirable for the tar to have a low H/C ratio and, most importantly, a high conradson Carbon coking value. This value is an irdicator used widely inf the petroleum industry to predict tha coke yield' of potential coker feedstocks. Flash pyrolysis tar has a Ccradson Carbon coking value around twice that of conventional petroleum feedstocks. Consequently, different del.ayed coking procedures are required. It should be noted that the properties of FPT vary significantly from those of r -u1 9 high temperature coke oven tar, specifically in terms of aromaticity and oxygen content. Because of the particular characteristics of high temperature coke oven tar, light components must first be distilled prior to delayed coking.

Such a stage is not required with FPT, however.

The char produced from the flash pyrolysis of coal is in a pulverized form, is dry and has a high surface area.

These properties make it very suitable as a pulverized fuel for power station use. Char produced from coal is, therefore, a very useful by-product of the FPDC coke process. Char Q a t O produced from higher ash materials, such as oil shale, may not

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o e be suitable for power generation, however, because the ash present in the starting material reports almost totally in the eo a char.

0 o o Pyrolysis gas consists of a range of hyd:-ocarbon gases, in addition to CO, C02 and hydrogen. Analyses indicate that this gas will have a medium energy value and hence will be suitable as an in-process fuel, however it also has specific characteristics which permit its ready conversion to 0 o0U hydrogen gas. This is very convenient as hydrogen may be used for the upgrading of coal liquids produced from the delayed coking of flash pyrolysis tar.

6 04 During flash pyrolysis, complete separation of char from tar vapours, prior to condensation, is not always achieved. For this reason a tar filtration stage may be required in the invention. The nature of the solids material carried over into the tar during flash pyrolysis indicates that a number of commercial filtration processes will be suitable and, most importantly, that filtration can be achieved efficiently at a moderately low cost. Ease of filtration of FPT has been successfully demonstrated, with almost complete removal of solid material being achieved. The addition of in-process oils derived from the delayed coking

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4 10 unit has been shown to have a beneficial effect on filtration rates and critical filtration parameters. Preferred pressure filtration methods include rotary drum filters and candle filters.

As an additional step, it may also be necessary to neutralize the acidic components of the FPT prior to coking to avoid corrosion and contamination of the coke with iron. The neutralization step could be achieved by passing process derived ammonia gas through molten FPT, although other alternatives are available. Neutralization, combined with tar ,o filtration, ensures that the FPDC coke is at least of equal 0 Spurity compared with petroleum coke, and far superior in respect of certain elements. It should be recognized, however, that the neutralization and filtration stages may not ,X5 be necessary in a commercial plant. This will depend on the Schar/tar vapour separation efficiency achieved and the selection of corrosion resistant materials for plant construction, Flash pyrolysis tar plus in-process oils from the neutralization and filtration units are sent to the delayed coking module for coke production. In commercial practice, the operation of the delayed coker is varied according to the characteristics of the coker feedstock, although the objective Sis always to maximize the yield of the liquid products. As petroleum coke is considered only as a by-product of the petroleum refinery no attention is paid to either quality or consistency. Coke yield is a complex function of coking conditions and the nature of the feedstock. One advantage of coking flash pyrolysis tar is that a very high coke yield can be obtained in comparison with petroleum feedstocks, although to acnieve this the coker must be operated under a different set of conditions. Specifically, a higher feedrate is required, this being critical in order to achieve the desired rate of volatile evolution and hence to produce FPDC coke with r h ;i r 1 i i i iJ I 11 acceptable density and porosity characteristics. Because the properties of the FPT Leed to the delayed coker can be carefully maintained and controlled, FPDC coke of consistent quality may be ptoduced. Other important coking parameters include recycle, ratio of desired coker oils, drum pressure and temperature, each of which must be tailored to suit the specific properties of the feedstock and the product distribution required.

In the process of the invention, flash pyrolysis tar and in-process oils are sent to the bottom of a fractionator S where material with a boiling point lower than the desired end e' point is flashed off. The desired end point for FPT is around 250 C. The remainder is combined with recycle heavy oils derived from the coker (at around 15-20% recycle) and pumped 15 to a preheater and then on to the coking drum. The coke drum is filled over an extended period, usually 24 hours, after which time the top of the coke drum is taken off and the coke removed, usually by hydraulic cutting. The appearance £ad bulk form of the new coke are identical to petroleum coke and well suited for conventional coke handling procedures and current anode fabrication techniques. This is extremely desirable as FPDC coke could be directly substituted for petroleum coke in a commercial smelting process plant, without ,the need for expensive equipment modifications or replacement.

In addition to coke, both oils and gas are also produced during delayed coking of FPT. The coker oils riay be divided into two fractions, namely the 'light oils' which have a boiling point less than 300 C and heavy oils which boil above 300 0 C. The heavy oils are recycled to the coker in order to improve coke yield. Another desirable feature of the process is that the light oils could be a suitable feedscock to an oil refinery for further upgrading to liquid fuel status. The oils would first require some upgrading to increase the hydrogen content and reduce the aromaticity of r i ,f' i r i i_ _Ill i 12 the liquid, however. This upgrading can be performed by hydrogenation, according to conventional and proven technologies. The gases produced both from flash pyrolysis and delayed coking of FPT are suitable for conversion to pure hydrogen, using established oil refinery technology.

Alternatively, 'the gases are of medium to high energy content and could be used to generate power via combustion, Flash pyrolysis tar coke removed from the coker typically contains a volatile content ranging between 4 and 15%. As with petroleum coke, this level can be controlled accurately by varying the coking temperature. In order to be suitable for electrode production the volatile content must be reduced to less than This reduction is achieved by 0 calcination. Accompanying the reduction in volatile (and hydrogen) content of the coke is a general shrinkage in the coke matrix and a corresponding rise in bulk density.

S,~Q Calcination of the FPDC coke is performed in the exact manner of the calcination of petroleum coke, typically in a rotating drum calcination furnace at temperatures ranging 20 between 1100 and 1300°C, Below 1100 0 C insufficient volatiles removal occurs while calcination above 13000 can lead to excessive decrepitation and hence high coke porosity.

4 i 4 Properties of the calcined ?PDC coke are excellent in comparison with petroleum coke, exhibiting extremely low impurity levels and excellent consistency. The low inpurity levels will allow a premium grade high purity metal to be made, FPDC coke also displays a number of unexpected properties which are highly desirable. These include: High density and low porosity articul arly in the 1-30 m range. This resu:t in a low requirement for binder pitch and, r" 1 13 with low impurty levels, will render the coke relatively un-reactive towards airburn and CO 2 attack.

Low resistivity, which will result in anodes with significantly lower resistance, and hence energy consumption.

(ii) (iii) High coherence and strength.

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Low sulphur levels, when a suitable starting feedstock is used. This is highly desirable for environmental reasons.

In audition to anodes for the aluminium industry, many of these particular characteristics of FPDC coke are desirable in a blast or electric furnace reductant.

Calcined FPDC coke can be fabricated into anodes suitable for aluminium production using a similar piocedure to petroleum (soke. In the case of pre-baked anodes, taiis involves crashing and screening the rmaterial to the desired granulometry or particl.e size range, the addition of binder pitc' at levels ranging between 10 and 20%, followed by mixing at temperatures between 120 and 200 0 C. Binder pitch is generally derived from by-product tars taken from high temperature carbonization oven. The new coke and pitch mixture is then formed into blocks and baked at temperatures approaching 1200 0 C. Fabrication of Soderberg type anodes 25 differs from pre-baked anodes in that the coke and pitch mixture is baked in-situ in the electrolytic cell.

Consequently, a lower baking temperature is achieved.

The coke of the invention differs from petroleum coke in terms both of the optimum coke granulometry to give the best anode properties, and the level of binder pitch S11 -14 required. In particular, FPDC toke requires less fines than petroleum coke which could reduce crushing costs. In addition the optimum pitch level is typically 1-2% less than for petroleum cokes. This reduction would result in very significant cost savings, as pitch is a relatively expensive component of the anode. A further advantage in anode manufacture is that, unlike petroleum coke, FPDC coke is a mainstream product not subject to fluctuations in coke properties and overall quality. As a result, with FPDC coke it is not necessary to change anode fabrication conditions in S response to changes in coke properties, such as occurs with S petroleum coke, Consequently, anodes can always be fabricated from FPDC coke at the optimum conditions.

SC,. After fabrication of anodes from FPDC coke, they 1,,15 must then be baked under similar, but not necessarily identical, conditions to those employed with conventional petroleum coke anodes.

The properties of the carbon anodes derived from the Snew material are similar to, and in some cases superior, to iJ 20 those prepared from petroleum coke. Superior properties include high purity, low resistivity and high Strength. A further advantage has also be noted. The microstructure of FPDC coke is very similar to that of binderes., allowing excellent bonding between the two to occur. This similarity will also reduce their differential reactivity, resulting in a lower propensity for dusting.

Production of the new FPDC coke is demonstrated in the following example.

15 Flash Pyrolysis A sample of high volatile steaming coal, washed to around 20% ash, was crushed and screened to less than 180 microns. The composition of the coal was as follows: Analysis 15 (Air Dried Basis) Moisture Ash Volatile Matter Fixed Carbon Specific Energy (MJ/kg) Carbon Hydrogen Nitrogen Sulphur Oxygen wt% 19.8 42.5 34.7 25.8 60.6 Ii. 2 0.9 10.0 It X i i

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The coal was fed to a fluidized bed flash pyrolysis reactor, at a rate of 20 kilograms per hour. The pyrolysis temperature was maintained at 6000C by means of natural gas injection. The following product yields were obtained, expressed on a dry, ash-free bases: t t t I t t t 4 t Tar Gas Char These products had the following properties: Char Air Dried Basis Moisture Ash Volatile Matter Fixed Carbon wt% 2.2 36.0 13.9 47.5 j.

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16 Specific Energy CMJ/kg) 20.0 Gas Me than e Ethane Ethylene N-Bu tarie Hydrogen Rema in de r Vol 40. 11.5 trace 28.0 10. Tar Dry Ash Free Basis 4440 o o, 4~ 4 :~s 9 4444 44 4 4 44 44 41 44 9 4149 81.4 7. 6 1. 1 9. 9

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S by difference 0 atomic H/c 1. 12 Tar Filtration I 41 4 4 *91

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4 4 44 4 Tar fezzm tahe qr~-:izeus ccample, containing 1.2$ ash, was filtered to less than 0.05% ash in a pressure filtration unit, Optimum filtration conditions were found to occur in the following ranges: ii '1 51 lemperature r-Lessu re Recycle oil* 140-160 0

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350-450 KPa 40-50% cok~ing of Refers to 'light oils' derived Afrom the delayed fpt.

4- I. 17 Delayed Coking A laboratory coker having an internal diameter of was used. Filtered FPT was introduced into the coke drum at a rate of 250gm/hr. The delayed coking unit was operated at a temperature of 480 C and a pressure of 400 KPa, with 15% heavy oil recycle. Following 38 hours of operation, coke was removed from the drum and a mass balance calculated. The following yields were obtained; Input Output mass (kg) 9.48 1.67 Filtered FPT Heavy Oil 4,44 4 44 4":4 4I 4 4441 (t 4 4 I 4*e 44 4444 4 44 44 4 4 44 4e 4 FPT Coke Heavy Oil (BP>300 0

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Light Oil (BP<3000C) Gas (by difference) mass (kg) 4.71 2.47 0.99 2.98 Yield,% of Fresh Tar 49.7 8.4 10.4 31.4 11.15 11.15 100.0 It is likely that a coke yield of 60% will be achieved when heavy oils are recycled to extinction.

The properties of the gas and light oil are shown below.

lip i r 18 FPT COKER

GAS

Gas Atialyscs (Vol Commercial [let.

Feedstock Coker Gas Carbon Monoxidec Carbon Dioxide Methane Ethan e Ethylene Propane Propylene N-Butane 5.2 4.8 47.8 14.1 3.1 4.2 3's 0,4 5.8 1.4 48.0 11.5 9.3 4.7 3.2 0094 0 40 04 0 00 4 0040 0 0 0 0400 0 0444 *04 0 0 00 0 00 0 0 0 0440 4 40 04 1 0000 0 01 0 0 0 0t 0040 0 40 00 0 0 4 0 0 4000 00 Oil Analyses FPT Light Crude Oil Coker Oil (Gippsland,Vic) Approx. B oilng Range 66-453 40-590+ Na'ptha (<180 0 C) vol 8 34 Kerosene (180-230 0 C) Vol 21 9 Diesel (230-350 0 C) vol 4925 Dl (350 0 C EP) vol 22 32 Specific Gravity (20 0 C. g/cc) 0.98 0.80 It Aromatic C by C" 3 NMR 59 g OH/9 56.0 Wt% C 81.6 8 r) wt% if 9.6 A4 wt% N 0.4 0.01 wt%. S 0.2 0.1 Wt% 0 8.2 ata~mic H/C 1.4 1.9 The FPDC coke produced in the laboratory delayed coking facility was found to contain 10% volatile matter, typical of un-calcined petroleum coke. The coke was subsequently calcined at 1300 0 C for one hour, and was found to have the following properties F19/9 k6-mr

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p *^1 19 Physical Properces FPDC Coke -3 Real Density (gem 1.99 Resistivity (fmnm) 0.89 Bulk Density(1.40-2.36mm fraction) 0.88 Porosity (1-30pm, mm 3 25 Typical Range Pet. Coke 2.00-2.08 1.0-1.25 0.73-0.85 60-90 Typical Range Pet. Coke Chemical Properties (wt%) FPDC Coke 0 I, r tot Ash Nickel Vanadium Sodium Calcium Silicon Iron Sulphur Volatiles Water 0,31 .0012 <.002 <.0045 <.0023 .026 0.097 0.15-.50 .015-.05 .035-.05 .015-,05 .005-.01 .01-.05 .01-.05 1,5-3.5 .46 0.1 0.3 41-i~ II I V k I t The high levels of iron and silicon observed in the FPDC coke most likely arise from corrosion of laboratory equipment. This problem appears to be exacerbated by the high surface to volume ratio encountered, as corrosion also occurred to a lesser extent when using petroleum feedstocks in the same equipment. Although a neutralization stage could be included in a full-scale plant, it is likely that the problem may be avoided by the use of more appropriate materials of construction.

A feature of the FPDC coke is the low levels of trace metals, such as Ni, V, Na and Ca which will enable very pure aluminium metal to be produced. The current efficiency of an aluminium cell using anodes fabricated from FPDC coke will also be improved, because of the high coke purity.

The sulphur content of the coke is also low, although this is F19/9 r iff~i;" 20 related to the sulphur content of the coal feedstock.

As demonstrated in the example, FPDC coke displays a number of unexpected benefits in addition to purity. These include high density, low porosity in the 1-30 micron range and low electrolytic resistivity.

Anode Fabrication In order to demonstrate the benefit of FPDC coke for anode manufacture, a number of prebaked laboratory anodes were fabricated and tested. The coke was first crushed and screened to the desired granulometry, mixed with binder pitch and baked at 1150 0 C. The properties of such anodes are shown in the following, in comparison with anodes fabricated from petroleum coke on a similar scale.

Anode Properties gog Ps9 a s 0,4 Property FPDC Coke Anode 500gm Scale FPDC Coke Anode 5kg Scale Typical Range Pet.Coke Binder Pitch Content (wt%) Green Density (g/cc) Baked Density (g/cc) Porosity Resistivity (pQm) Compressive Strength (MPa) Carbon Consumption V Theoretical) 1.69 1.70 16.7 42.1 110 1,68 1.59 18.9 56.0 34.1 118 14.4 1.70 1.57 19.2 51.2 33.2 15-17 1.54-1.65 1.52-1.60 17-25 50-70 30-55 119 110-130 a 4 I *It should be noted that pitch demand for anodes fabricated on the 500gm scale is artificially high, related to the relatively fine granulometry.

The perceived advantages of FPDC coke in pre-baked anode manufacture were confirmed in the laboratory anodes. These advantages included, in comparison with petroleum coke, low pitch requirement high F19/9 4 j -I I I i -21 purity, low resistivity, high strength, high density and low porosity. Good bonding was observed between the binder and FPDC coke. Similar advantages Co Chose obtained in pre-bake anodes may also b expecC,2d in Soderbei.g, Type anodes.

It will clearly be understood ChaC Che invention in its general aspects is noC limited to Che specific details referred to hereinabove.

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Claims (7)

1. 2. Process according to claim 1 in which the carbunaceous startinig material is coal, oil shale or tar sand.
2. 3. Process according to claim 1 further comprising the following step:- calcining coke produced in step to produce a high purity coke of volatile content less than
3. 4. High purity coke produAced by the process of any one of claims 1 to 3. 23 Process for the production of high purity coke from black coal, which comprises the following steps:- beneficiating the coal to an ash content not exceeding air drying the product of step to less than 10% moisture crushing the product of step to a particle size less than 0,18mm injecting the prodluct of step into a 10 fluidised bed reactor in whirn it is rapidly heated in an inert atmosphere to a temperature in the range 400 S to 800°C at atmospheric or near atmospheric pressure, whereby it decomposes into tar vapour, char, and gas components rapidly quenching the product of step to condense liquid tar, and, if necessary, filtering the liquid tar to remove char therefrom subjecting the liquid tar to delayed coking to produce coke and coker oils 0 dividing the coker oils from step into light oils boiling below 300 0 C and heavy oils boiling Sabove 300°C, and recycling heavy oils to step (f) calcining coke from step to produce a high purity coke of volatile content less than
4. 6. Process according to claim 5 in which the tar produced in step is filtered and acidic components of the said tar are neutralised prior to step S1^
5. 7. Process according to claim 6 in which the noutralisation is effected using ammonia produced in the flash pyrolysis step (d) SALi
6. 8. Proce~ f from s t filtration) 24 3s according to claim 6, in which light oils e p are recycled~ t o the tar 'neutralisation step.
7. 9. High purity coke produced by the process of any one of claims b to 8. 09010010 #4 9 0009 O 04 #1 0 0040 I 0009 *0 0 0 0 *0 0 00 0 0. 0010 DATED THIS 13TH DAY OF NOVEMBER 1989 COMALCO ALUMINIUM LIMITED ALCOA OF AUSTRALIA LIMITED ALCAN AUSTRALIA LIMITED By their Patent Attorneys; GRIFFITH HACI( CO.- Fellows Enstitt.te of Patent Att~krneys of: Nustralia. #0410 o 4. 0 00 0 0 00 009020 A 0