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, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L9/00—Treating solid fuels to improve their combustion
  • C10L9/08—Treating solid fuels to improve their combustion by heat treatments, e.g. calcining

Definitions

• the invention relates to a process for calcining green coke containing combustible volatile matter in at least two stages, whereby in a first stage the green coke is heated in a furnace to a temperature of between 750 °C and 1000 °C and in a second stage in a second furnace to a temperature of between 1200 °C and 1600 °C.
• green coke made from a suitable hydrocarbon feedstock may be converted to high quality needle coke for use in high performance graphite electrodes which are applied in electric ore furnaces, or other purposes, like in baked carbon anodes in aluminium cells.
• the green coke after the water being removed at relatively low temperatures, is heated (precalcinated) in a furnace to a temperature which necessary to release_at least. a part of the combustible volatile matter, generally around 800 °C.
• the coke is calcined in a second furnace to a temperature in the range between 1200 °C and 1600 °C.
• a shaft kiln In principle in each of the stages either a shaft kiln, a rotary kiln or a rotary hearth furnace may be used, depending on the specific circumstances. After the precalcination cooling of the product may optionally take place, before the second stage calcination is carried out.
• the patent literature describes a number of processes for calcining coke, for example UK patent specification 1,603,924, UK patent applications 2,093,061 and 2,016,512, German patent specification 2,931,475 and US patent specification 4,291,008.
• the invention relates to a process for calcining green coke containing combustible volatile matter in at least two stages, whereby in a first stage the green coke is heated in a furnace to a temperature of between 750 °C and 1000 °C and in a second stage in a second furnace to a temperature of between 1200 °C and 1600 °C, characterized in that the heating in the first stage is carried out with a controlled heat-up rate of less than 60 °C/min in the temperature range of between 600 °C and 800 °C, whereby said heating up is achieved by hot combusted volatile matter, which is obtained by withdrawing the released volatile matter from the first stage, burning said volatile matter outside the first stage and recycling the burnt volatile matter to the first stage.
• Part of the hot combusted gases may be obtained by burning an additional combustible gas outside the first stage and introducing the burnt gas into the first stage.
• a major advantage of the process according to the invention is that the calcined coke contains sufficient coarse material, which makes it especially suitable for the manufacture of ultra high power electrodes.
• the first stage namely the precalcination in a non-oxidizing atmosphere
• the atmosphere in the precalcination stage could also be described as reducing.
• any type of furnace is suitable, a rotary kiln is preferred.
• any type of kiln may be suitable. Preference is given to the combination of a rotary kiln with a rotary hearth furnace. in the first and second stage respectively.
• the heat-up rate control in the first stage is regulated by the temperature and the amount of combusted gases, which preferably flow countercurrently with the direction in which the green coke flows.
• the direction in which the green coke flows has a small angle with the horizontal surface.
• the inclination of said rotary kiln is generally below 5°.
• the retention time of the coke in the first kiln may be so chosen that the heat-up rate does not exceed 60 °C per minute, preferably the heat-up rate is less than 40 °C per minute.
• the green coke is introduced and due to the rotation of the kiln and the gravity the green coke moves to the lower end of the kiln.
• the combustible volatile matter released from the green coke in the first stage leaves the upper end and is recycled via a burner to the first stage furnace. Additional combustible gas if necessary, and air are added, so that combustion takes place in the burner.
• the combusted gases entering the lower part of the kiln have a temperature of between 900 °C and 1300 °C. A part of the combustible volatile matter is withdrawn from the recycling system before entering the burner.
• the right temperature and the amount of burnt gas necessary to achieve the controlled release of the combustible gases from the green coke is in this way secured.
• the amount of oxygen in the air introduced into the burner is generally completely used for combustion of the gases, before these are recycled to the furnace in the first stage.
• the precalcined coke leaving the lower part of the kiln is transported to a rotary hearth furnace or other kiln.
• the kilns of the first and the second stage may be so arranged that the transport takes place by gravity.
• the inlet of the calciner may be positioned immediately below the outlet of the precalciner and the precalcined coke is directly dropped into the coke feeding device of the calciner. Transportation may also take place by means of a conveyor.
• the obtained product may preferably be cooled to a temperature below 100 °C, or even to room temperature.
• the second stage (calcination) may take place in any kind of furnace, in which the presence of free oxygen may be tolerated. Preference is given to a rotary hearth furnace, which is well known in industry.
• process according to the invention may be carried out in such a way that only one furnace is used with two different stages: the precalcination and the calcination, wherein the temperatures and gas compositions are controlled.
• Green coke with a water content of 9X weight was introduced at the upper end into a rotary kiln (with a length of 12 metres and an internal diameter of 0.5 metre) and precalcined to a temperature of 826 °C.
• the green coke was introduced at a rate of 250 kg/h, while the kiln was operated at 2 rpm (rotations per minute), the inclination being 2.5 degrees.
• the green coke was obtained as residue in the steam cracking process of naphtha and gas oil.
• the green coke was heated-up with a flue gas which had a temperature of 950 °C and which gas flowed in the direction countercurrently with the direction in which the coke was moving.
• the outlet temperature of the flue gas was 480 °C.
• the flue gas which contained no free oxygen was produced by external stoichiometric combustion in a burner chamber of 16 kg/h natural gas with. 206 kg/h air of ambient temperature and quenching the adiabatic flame temperature with a recycle of 730 kg/h of the total amount of 1081 kg/h of kiln-off gas. 357 kg/h of the kiln-off gas is withdrawn from the recycle stream. 218 kg/h of precalcined coke was obtained at the lower end of the rotary kiln.
• the heat-up rate of the coke in the temperature range of from 600 °C to 800 °C was 24 °C/min.
• precalcined coke was introduced at a rate of 100 kg/h at the upper end into a second rotary kiln with a final temperature of 1380 °C.
• This rotary kiln was operated at 3.6 rpm and had the same length and diameter as the first kiln.
• the inclination was 2.5 degrees.
• the coke was heated up by once through countercurrent heat exchange in an oxidizing atmosphere with a flue gas which.had an inlet temperature of 1480 °C.
• the flue gas was obtained by combustion of natural gas with air and additional air was added to maintain an oxidizing atmosphere in the kiln.
• Starting from 100 kg/h of precalcined coke 94 kg/h of calcined coke was obtained. Real density was 2.13 g/ml.
• the green coke was heated-up with a flue gas which had a temperature of 950 °C and which gas flowed in the same direction as the coke was moving in the kiln.
• the flue gas. was obtained by burning 17 kg of natural gas with 221 kg/h air of ambient temperature and was quenched with 312 kg/h additional air of ambient temperature. Burning of the released combustible gases took place in the rotary kiln. No recycle of the flue gas took place. 214 kg/h of precalcined coke was obtained.
• the heat-up rate of the coke in the temperature range of from 600 ° to 800 °C could not be controlled, when additional air was used.
• the precalcined coke was calcined in the second rotary kiln under exactly the same conditions as described in the example. Starting from 100 kg/h of precalcined coke 94 kg/h of calcined coke was obtained. Real density was 2.13 g/ml.

Landscapes

• Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Engineering & Computer Science (AREA)
• Combustion & Propulsion (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Organic Chemistry (AREA)
• Coke Industry (AREA)
• Compositions Of Oxide Ceramics (AREA)
• Inorganic Insulating Materials (AREA)
• Carbon And Carbon Compounds (AREA)
• Processing Of Solid Wastes (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Control And Other Processes For Unpacking Of Materials (AREA)
• Fertilizers (AREA)
• Mold Materials And Core Materials (AREA)
• Solid Fuels And Fuel-Associated Substances (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (3)

Family

ID=10559530

Family Applications (1)

Country Status (8)

Cited By (4)

Families Citing this family (1)

Citations (5)

Family Cites Families (2)

• 1985
  • 1985-03-12 CA CA000476282A patent/CA1260868A/en not_active Expired
  • 1985-03-18 AT AT85200407T patent/ATE49017T1/de not_active IP Right Cessation
  • 1985-03-18 DE DE8585200407T patent/DE3574988D1/de not_active Expired - Fee Related
  • 1985-03-18 EP EP85200407A patent/EP0158387B1/de not_active Expired
  • 1985-04-10 BR BR8501688A patent/BR8501688A/pt unknown
  • 1985-04-10 ES ES542105A patent/ES542105A0/es active Granted
  • 1985-04-10 JP JP60074560A patent/JPH064857B2/ja not_active Expired - Lifetime
  • 1985-04-10 NO NO851426A patent/NO167301C/no unknown

Patent Citations (5)

Also Published As

Similar Documents

Legal Events