Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
  • C10B57/00—Other carbonising or coking processes; Features of destructive distillation processes in general
  • C10B57/04—Other carbonising or coking processes; Features of destructive distillation processes in general using charges of special composition
  • C10B57/06—Other carbonising or coking processes; Features of destructive distillation processes in general using charges of special composition containing additives
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
  • C10B55/00—Coking mineral oils, bitumen, tar, and the like or mixtures thereof with solid carbonaceous material

Definitions

• Electrode grade graphite is manufactured from a commercial grade of coke having an acicular, anisotropic microstructure called needle coke, see U.S . 2 , 775, 549 to Shea, Dec . 25 , 1956 , Cl. 201-42 , made by delayed coking of certain petroleum residues under specific conditions of heat and pressure. To produce graphite from such coke, it is necessary to heat it to a temperature in the range of 2000-3000oC, which has the dual function of supplying energy for the conversion of the carbon in the coke to the graphitic crystalline form and of volatilizing impurities .
• puffing When carbon bodies made from such cokes are heated at temperatures in the vicinity of 1000-2000oC, various sulfur-containing compounds decompose, attended by a rapid and irreversible expansion of the carbon body. This phenomenon is termed "puffing". During the production of graphite articles, particularly high performance graphite electrodes, puffing is extremely undesirable as it may destroy the structural integrity of the piece and render it marginal or useless for its intended purpose.
• Puffing of a carbon article made from high sulfur cokes generally starts at about 1500oC, and may result in a volumetric expansion of as much as 25%. It is not simply an elastic expansion but should be characterized as an inelastic, irrevers ible expansion.
• puffing phenomenon in acicular needle cokes with a relatively large amount of sulfur, sulfur atoms are bonded to carbon atoms by covalent bonds, either in carbon ring structures or linking rings . These bonds are less stable at high temperatures than the carbon-to- carbon bonds. On heating, the carbon-sulfur bonds rupture, the sulfur is freed, then reacts with hydrogen to form hydrogen sulfide. The simultaneous rupture of these bonds and evolution of hydrogen sulfide and other sulfur containing materials causes the physical expansion called puffing.
• additives have usually been added during the mixing stage when various sizes and grades of coke particles are mixed, before being wetted with pitch, formed into the desired shape, baked at an intermediate temperature and graphitized at high temperatures.
• Additives have included primarily metal salts and oxides, as disclosed in British 733,073, Greenhalgh, July 6, 1955, Cl. 90 b; French 1,491,497, Gillot et al., Aug. 11, 1967, Cl. C 01 b; French 2,035,273, Continental Oil, Dec. 18, 1970, Cl. C 10 b 57; U.S. 3,642,962, Wallouch, Feb. 15, 1972, Cl.
• French 1,491,497 discloses the use of chromium oxide at 0.2-5% in a mixture with coke and a binder as a catalyst, enabling graphitization to occur at temperatures in the range of 1200°-2000°C.
• French 2,035,273 discloses a low sulfur coke produced by the addition of 0.3-5% of sodium carbonate to the coking stream mixture and subsequent hydrogenation of the coke at high temperature.
• British 733,073 discloses the use of oxides of chromium, iron, copper, or nickel incorporated in the grinding stage of coke, mixed with pitch, shaped, baked at 1200oC, and graphitized at 2500°-2800°C.
• U.S. 3,563,705 discloses the use of mixtures of iron or calcium compounds with small amounts of titanium or zirconium compounds as puffing inhibitors incorporated into the coke-binder mixture.
• U.S. 3,338,993 discloses the use of calcium, magnesium, strontium, and barium fluorides as puffing inhibitors with raw or calcined coke and binder, mixed, shaped, baked and graphitized.
• U.S. 3,642,962 discloses the use of 1-3% calcium cyanamid or calcium carbide as desulfurizing agents and puffing inhibitors, mixed with raw coke prior to calcining.
• CTE is also of vital importance in the production of graphite for certain applications. Electrodes for electric furnace melting of steel must have a low CTE to avoid excessive differential expansion at operating temperatures and the resultant spalling, which in turn causes excessive consumption of the electrode and cost in operation. Other applications requiring dimensional stability at high temperatures are well-known although of somewhat less economic importance. In general, the addition of any foreign material to a graphitizing carbonaceous mix will have, in addition to its desired effect, such as puffing inhibition, the effect of increasing the CTE of the graphite body.
• a needle coke is distinguished by its physical structure when microscopically examined, showing long needle-like acicular particles.
• Such cokes to be suitable for manufacture of graphite electrodes to be used in ultra-high powered electric steel furnaces, should have a graphite CTE characteristic of less than 5 ⁇ 10 -7 /oC measured over the range of 0o-50oC.
• Needle cokes for lower powered electric steel furnaces may have a graphite CTE characteristic of as much as 7 ⁇ 10 -7 /oC over the 0o-50oC range.
• the blends of cokes must be thoroughly mixed to avoid the difficulties present in making uniform homogeneous blends and in thoroughly coating the particles, which are often as much as 7mm. in diameter, with the puffing inhibitor. Both of these difficulties can lead to non-uniform dispersion of the inhibitor and to puffing, even though there is sufficient inhibitor present in the total mix to prevent puffing.
• a large amount of the inhibitor is at relatively greater distance from the centers of the coke particles in the larger coke particle mixes as opposed to the smaller particle mixes used in smaller electrodes. Migration of the inhibitor into the centers of the large particles becomes progressively more difficult and less effective as the coke particles increase in size.
• the puffing problem is further increased with the rate of graphitization of the carbon bodies.
• Optimum distribution of the inhibitor throughout the structure of the carbon body to be graphitized is essential as the degree of puffing for any coke particle blend is highly rate sensitive, being directly related to the rate of temperature increase during the graphitization cycle.
• the figures in certain of the examples given will show a much higher dynamic puffing at a 14oC/min. temperature rise than for a 5oC/min. rise.
• ⁇ T rate of temperature
• DP dynamic puffing increase
• l amount of inhibitor
• k proportionality factor
• a petroleum coker feedstock which would normally produce a puffing coke due to its high sulfur content is rendered nonpuffing by the addition of a small quantity of puffing inhibitor to the feedstock as a fine particle size powder.
• Puffing inhibitors such as iron oxide and/or calcium fluoride may be pre-dispersed in a high concentration in a small quantity of the feedstock (fresh feed or furnace feed), or in compatible material miscible with the feedstock, or dispersed in the total coker stream and added either batchwise to a batch type coker, or continuously to the main stream in a delayed coker.
• a current of inert gas or steam bubbled through the batch type coker during the run aids in keeping the puffing inhibitor in suspension without significantly increasing the CTE of the finished product during batchwise coking.
• this is not essential.
• the present invention involves the use of this type of coking operation.
• Iron oxide is formed when any of numerous iron bearing materials is calcined, including organometallic compounds and salts.
• Minerals such as magnetite (Fe 2 O 3 ), limonite (2Fe 2 O 3 ⁇ 3H 2 O) ; and pyrites (FeS 2 ) and salts such as ferric sulfate and nitrate when roasted in air are converted to ferric oxide, and may be used to form the oxide.
• the reactive species may be elemental iron, produced by reduction of the Fe 2 O 3 by coke during graphitization.
• Calcium fluoride is also highly effective as an inhibitor with slightly superior performance as compared to iron oxide. Mixtures of the two inhibitors have shown a synergistic result, being more effective than either of the two when used alone.
• inhibitor in this manner produces a coke which is lower puffing and produces a graphite which has a lower CTE than from a coke conventionally inhibited by a dry mix.
• CTE of the graphitized coke was determined by preparing small 5/8" ⁇ 5" (1.6 ⁇ 12.7 cm.) electrodes by the procedure disclosed in U.S. patent 2,775,549, (except for calcination of the coke to 1250°C), and measuring their elongation over the temperature range of 0o to 50°C.
• a decant oil the fractionater tower bottoms from a catalytically cracked gas oil fraction, also termed slurry oil, or other equivalent hydrocarbon residue, is conveyed from the fractionater 33 through line 10 and meter 14 to diversion valve 17, where a portion of the feedstock is diverted through valve 13, and meter 15 to disperser 18. Simultaneously a portion of inhibitor 12 is weighed in scale 16 and conveyed to disperser 18 where it is dispersed in the feedstock to a specific concentration by weight. Alternately a compatible liquid and additives from supply 19 are metered through valve 11 to valve 13 and meter 15 to disperser 18.
• a compatible liquid and additives from supply 19 are metered through valve 11 to valve 13 and meter 15 to disperser 18.
• the inhibitor is dispersed and discharged through line 22 and meter 23 to mixer 24 where it is mixed with the main portion of the feedstock coming through line 20 and meter 25, to the exact proportion desired.
• the concentrate mixed with the feedstock is pumped by pump 27 through line 26 to furnace 29, then through line 31 to coker drums 28 and 28a, where it is conventially delay coked.
• the overheads are taken off through line 32 and sent to the fractionater 33.
• the disperser which may be any of several types of equipment well known in the art, preferably a high shear or colloid mill. Alternately, a roller or ball mill could be used.
• the puffing inhibitor dispersion and feedstock are metered into the mixer 24 where they are mixed in the correct proportions to give a concentration of approximately 0.05-0.5 wt. % puffing inhibitor in the feedstock which is then pumped into the coker 28.
• the viscosity of the feedstock is extremely low and some means is necessary to minimize settling and a concentration of the puffing inhibitor in the lower portion of the coker during batchwise coker operation.
• EXAMPLE 1 The micronized puffing inhibitors, calcium fluoride and iron oxide (having approximately the same particle size distribution) were individually mixed with samples of a fresh feed decant oil coker feedstock, at 0.1 wt. % level in a high speed blender for about 5 minutes. The mixtures were coked under identical conditions in 4 liter resin flasks.
• Puffing was measured by taking representative samples by the method of ASTM D346-35, crushing, mixing 100 g coke and 25 g pitch, and molding plugs at 12,500 psi (879 kg./cm. ). The plugs were measured by micrometer and. placed in a dilatometer. The temperature was raised to 1200oC over a period of 50 ⁇ 10 min., then the test was run at a temperature increase of 5o or 12-16oC/min. over the 1200 -2900oC range, with measurements taken every five minutes. The reported DP is the maximum degree of elongation (or shrinkage) measured. All of the DP's below were at 14oC/min. rise except as noted.
• a CTE of the graphite body of as much as 7 ⁇ 10 -7 /oC may be acceptable, but for ultra high power electrodes for electric steel furnaces the upper limit is generally 5 ⁇ 10 -7 /oC.
• feedstocks may well need and be beneficially treated with inhibitor additions of as much as 0.5%, resulting in a 2% ash level in the final coke.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Carbon And Carbon Compounds (AREA)
• Coke Industry (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)

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• 1980
  • 1980-01-23 DE DE8080900363T patent/DE3065647D1/de not_active Expired
  • 1980-01-23 WO PCT/US1980/000135 patent/WO1980001569A1/en not_active Ceased
  • 1980-01-23 JP JP50049480A patent/JPS55501183A/ja active Pending
  • 1980-01-30 CA CA344,658A patent/CA1132930A/en not_active Expired
  • 1980-08-15 EP EP19800900363 patent/EP0022855B1/en not_active Expired

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