Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G OR C10K; LIQUIFIED PETROLEUM GAS; USE OF ADDITIVES TO FUELS OR FIRES; FIRE-LIGHTERS
  • C10L9/00—Treating solid fuels to improve their combustion
  • C10L9/02—Treating solid fuels to improve their combustion by chemical means

Definitions

• the present invention relates to reducing the reactivity of coke and in particular its carboxy reactivity and air reactivity which are important during carbon electrode use.
• coke formed from petroleum refinery streams is classified as No. 1 or premium coke, and No. 2 or regular coke.
• Premium coke differs from regular coke by its predominant metallic, crystalline appearance and a low linear coefficient of thermal expansion (CTE).
• the refinery petroleum coke Prior to the formation of electrodes, the refinery petroleum coke must first be calcined. Calcination usually occurs with temperatures in excess of 2200°F, (1204°C), preferably above 2500°F (1371°C). The calcination densifies the coke and removes volatile matter while changing the carbon to hydrogen ratio.
• the coke which leaves the calciner at these high temperatures must then be cooled. This is typically accomplished in a cooler wherein water is sprayed onto the coke. The water by evaporation cools the coke to a suitable temperature. This calcined, cooled coke is then formed into electrodes.
• aluminium is formed by the electrolysis of alumina wherein the oxygen from the alumina combines with the carbon of the electrode to form carbon dioxide. A second and unwanted reaction occurs when the carbon dioxide again reacts with the carbon to form carbon monoxide. While 0.45 lbs. per lb. of aluminium is utilized for the electrolysis, 0.05 lbs. of carbon per lb. of aluminium is lost in forming carbon monoxide.
• the ability of a carbon electrode to react with C0 2 to form carbon monoxide is known as the carboxy reactivity.
• electrodes are used in arc furnaces for melting of steel.
• a similar unwanted reaction occurs with air reacting with the carbon to form carbon oxides.
• 15-25% of the carbon is lost to this air reactivity reaction.
• U.S. Patent No. 3,320,150 notes that high reactivity can sometimes be due to the type of binder material or binder coke that is used and thus suggests a decrease in reactivity by utilizing a fine coke with a reactivity lower than the binder coke.
• U.S. Patent No. 3,454,363 discloses the removal of metal contaminants from coke to lower reactivity. It is noted that the presence of cations is detrimental to some of the potential applications of coke, and thus the coke is contacted with a cation exchange resin to remove cations and thus lower reactivity.
• the invention therefore provides a process for reducing the reactivity of calcined coke by the steps of:
• the calcining of coke is known to those in the art and is typically accomplished in a rotary calciner. Calcining temperatures are usually in excess of 2200°F (1204°C), with coke exiting the calcining at temperatures as high as 2700°C (1482°C).
• the coke is then cooled in a cooler as described previously, by directly contacting the coke with water. It is desired to cool the coke to a temperature of around 300°F (149°C), and thus air cooling is uneconomical. Typically, it takes approximately 1 lb. of water per lb. of coke during this cooling process. Normally well water has been utilized as a source for this cooling stage.
• water normally contains a variety of dissolved compounds, with each compound breaking into its respective charged part or "ion" when dissolved.
• Positively charged ions are called cations while the negatively charged ions are called anions.
• phosphates Some species of phosphates have been used in water treatment systems to prevent corrosion and deposits in distribution lines. These have included polyphosphates such as sodium hexametaphosphate or sodium tripolyphosphate in less than stochiometric amounts. The addition of polyphosphates inhibits calcium carbonate deposition by sequestration. However, due to the fact that evaporation occurs when utilizing water as a cooling agent to calcined coke, the use of these polyphosphates would not be expected to have any effect on the reactivity of the coke.
• the amount of acid to be added to the water used for cooling depends upon the type of water being utilized and the degree of reduction in reactivity preferred. For most waters, including well water, it has been found that amounts between 5-1,000 ppm are sufficient. While reactivity does decrease in the use of amounts and the 20-80 ppm range, a preferred range may be stated between 100-600 ppm.
• the orthophosphoric acid may be injected into the water stream at any point prior to the water contacting the hot calcined coke.
• Injection systems for addition of small amounts of additives into aqueous mediums is well known in the art and need not be described in detail.
• orthophosphoric acid was first diluted with water prior to injection.
• a metering pump was
• Examples 1 and 2 show the effects of the addition of low quantities of phosphoric acid to the CO 2 reactivity values.
• Table II below shows the effect of higher rates of addition of phosphoric acid to the cooling water.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Combustion & Propulsion (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Organic Chemistry (AREA)
• Electrolytic Production Of Metals (AREA)
• Coke Industry (AREA)
• Carbon And Carbon Compounds (AREA)
• Catalysts (AREA)

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• 1981
  • 1981-09-07 JP JP14081681A patent/JPS57117585A/ja active Pending
  • 1981-10-13 EP EP81304759A patent/EP0055508A3/de not_active Withdrawn

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