US3151974A

US3151974A - Process for the operation of blast furnaces

Info

Publication number: US3151974A
Application number: US189698A
Authority: US
Inventors: Rheinlander Paul
Original assignee: Huttenwerk Salzgitter AG
Current assignee: Huttenwerk Salzgitter AG
Priority date: 1961-04-26
Filing date: 1962-04-24
Publication date: 1964-10-06
Anticipated expiration: 1981-10-06
Also published as: GB985577A; BE616918A

Description

United States Patent 3,151,974 RUCESS FGR THE GTERATTGN @F ELAT FURNACES Paul Rheinliinder, Wolfenhuttel, Germany, assignor to Huttenwerk Salzgitter Ahtiengeselischaft, Saizgitter- Drutte, Germany, a German company No Drawing. Filed Apr. 24, 1962, Ser. No. 189,63 Claims priority, application Germany, Apr. 26, i nl,

H 42,414; Apr. 9, 1962, H 45,415

8 Claims. (Cl. 754-2) Attempts have repeatedly been made to supply some of the carbon necessary for reduction and heat economy in blast furnaces by the injection of solid, liquid and gaseous fuels into the furnace hearth, thus not only saving coke but also replacing it by a fuel which does not occupy furnace space, is simple to convey and, in some cases, is cheaper than coke. These attempts have been completely or partially unsuccessful so that the idea has not been adopted in practice. Solid, liquid or gaseous fuels introduced into a blast furnace hearth through the tuyeres have a cooling effect on the hearth coke, where it is at a maximum temperature, and this is so even if such fuels are introduced with a blast of a higher temperature than otherwise conventional. Furthermore, the combustion zone situated in front of the blast furnace tuyeres does not have the oxygen required for the complete combustion of such fuels.

When solid coal dust is injected together with the blast air, the heat required to convert the coal dust ash into slag is taken from the temperature-sensitive hearth of the blast furnace, while when liquid or gaseous hydrocarbons are injected, for example petroleum, petroleum products, natural gas, or the like, the heat required for the endothermic cracking process has to be supplied at the blast furnace hearth. These functions additionally constitute a load on the furnace hearth because the supply of fuels is not always uniform, but is frequently possible only with fluctuations per unit of time, as a result of the furnace operation.

The object of the invention is to replace some of the cok charged at the blast furnace throat, by liquid or gaseous hydrocarbons, in the form of petroleum, petro leum products or natural gas. To solve this ditficult problem, according to the invention, the petroleum products or natural gas are not introduced as such together with the blast air into the blast-furnace hearth, as was previously the case, but instead they are cracked and the cracked products comprising soot, hydrogen, carbon dioxide and nitrogen are then introduced into the furnace. It is preferable to inject into the blast furnace hearth together with the hot blast air the soot originating from the cracking and to use only a small fraction of the cracked gases as a carrier gas. The major part of the cracked gas consisting substantially of hydrogen, carbon monoxide and nitrogen, is then introduced into the furnace boshes or shaft, Where it has a reducing or heating action. The introduction may take place in the zone of the shaft in which heat is additionally required due to the expulsion of carbon dioxide from the ores. The soot blown into the furnace hearth together with the blast air through the tuyeres is readily combustible at a low ignition temperature. No ash has to be converted into slag as is the case with coal dust.

Surplus cracked gas consisting mainly of hydrogen and carbon monoxide and nitrogen may also be used as longdistance gas or town gas. In that case, it is previously brought to long-distmce gas or town gas density and calorific value by mixing it with a supplementary gas, for example, natural gas. The cracked gas has a density of about 0.329 (referred to air l) and a top calorific value of 2460 kilogram calories per cubic meter. By the addition of 0.08 cu. meter of blast-furnace gas (density 1.02,

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calorific value 900 kilogram calories per cubic meter) and 0.38 cubic meter of natural gas (density 0.67, calorific value 11,100), to each cubic meter of cracked gas a long-distance or town gas is obtained with a density of 0.455 and a top calorific value of 4620 kilogram calories per cubic meter.

The cracking process which precedes the introduction into the blast furnace can be performed particularly advantageously in regenerative chambers equipped with a ceramic lattice. Two pairs of chambers, i.e., four regenerative chambers, are required for a continuous cracking operation. While heating up takes place in two of these chambers, the chambers heated by blast-furnace throat gas or by fuel oil to about 1400 C., the cracking process takes place in the second pair of chambers which have previously been heated to 1400 C. To bring about the cracking air is heated to about 1300 to 1400 C. in the first of the pair of chambers, and oil is injected into the hot air leaving the chamber, the amount of oil being approximately 2.5 metric tons per 1,000 cubic meters. The quantity of air in relation to the quantity of oil injected is so small that the oil is only extremely incompletely burned in the second of the pair of chambers and is cracked there into soot and a gas consisting mainly of hydrogen, carbon monoxide and nitrogen. One metric ton of oil gives about 800 kg. of soot and 1700 cubic meters of cracked gas containing 71% H 10% Co and 19% N The heat stored in the cracking chamber lattice during the heating-up period furnishes the energy required for the cracking process, so that the cracked products retain the temperature to which the hot air required for cracking was previously heated. When the cracked product temperature has dropped to about 1200 C., the regenerative chambers are switched over. The first pair of chambers which were hitherto undergoing heating-up only, now serve for air heating and cracking, while the second pair of chambers is heated with blast furnace throat gas or fuel oil again to a temperature of about 1400" C.

After leaving the regenerative chambers the cracked products enter a cyclone in which the soot and the cracked gas are separated from one another. The cracked gas can all be used in the blast furnaces, namely in the boshes or shaft as a reducing or heating agent, or alternatively, part of the gas after appropriate preparation, can be used as long-distance or town gas. A small proportion of the cracked gas accumulating in the cyclone is utilized for the conveyance of the soot from the cyclone to the blast furnace tuyeres.

It is advantageous not to introduce the soot from the cyclone directly into the blast-furnace hearth, but to conduct it into a reservoir container from which it is then injected into the hot air by some of the cracked gas and blown together with the blast air into the blast-furnace hearth. The storage of soot in the reservoir renders the cracking operation independent of the blast furnace operation, so that no interruptions are necessary, for example, in the event of blast-furnace disturbances.

Instead of performing the cracking process in regenerative chambers followed by a cyclone, it may also be performed entirely in a cyclone. In this case hot air is injected into the cyclone through the inlet which leads tangentially into the cyclone, the hot air preferably being tapped from the blast-furnace blast pipe, and oil is injected into the hot stream of air. The ratio of hot air to oil is again so adjusted that the oil undergoes only extremely incomplete combustion in the cyclone and is cracked into soot and cracked gas. The hot air serving for cracking may also be oxygen-enriched. The soot accumulating in the cyclone emerges from the bottom end of the cyclone together with a small proportion of cracked gas. It is preferably again fed to a storage container fol lowing the cyclone, and is introduced from the container with a little of the cracked gas serving as carrier gas, together with the blast-furnace blast air, into the furnace hearth. The major portion of the cracked gas leaves the cyclone at the top end. It is blown into the blast-furnace boshes or shaft or part of it is used as long-distance or town gas after being enriched, for example, by means of natural gas.

Instead of performing the cracking process in a single cyclone, it may be performed in a number of individual cyclones which are then so connected to the blast-furnace tuyeres that the soot emerging from the bottom end of the cyclone passes directly into the nozzles and blast-air of the furnace. Such individual cyclones may also be replaced by oil burners preceding the blast-furnace tuyeres, particularly tangential burners.

The cracking process can be conveniently controlled in hot cyclones of the kind described, for example by producing varying amounts of soot by varying the ratio of hot air and oil, and thus adapting the supply of fuel to the blast-furnace hearth to the furnace operation.

Finally, some of the petroleum products may be cracked in the top part of the blast-furnace shaft. The heatconsuming cracking process then takes place at the expense of the perceptible heat of the blast-furnace gas ascending in the furnace shaft. The throat gas temperature is diminished in these conditions and reduction takes place. The cracked gas calorific value can then be used together with the throat gas.

The introduction of the cracked gases resulting from the cracking of liquid or gaseous hydrocarbons, into the blast furnace, lowers the partial pressure of the hydrogen contained in the blast furnace gas and increases that of the reducing gas constituents, for example, the carbon monoxide and hydrogen. This results in an increase in the amount of indirect reduction and a lowering of the coke consumption.

I claim:

1. In a process for the operation of a blast furnace wherein part of the coke charged at the throat of the furnace is replaced by hydrocarbon materials selected from the group consisting of petroleum and natural gas which are cracked outside the furnace and then introduced therein in the form of soot and a gaseous product comprising hydrogen, carbon monoxide and nitrogen, the steps which comprise cracking said materials by an incomplete combustion with hot air to obtain a maximum amount of soot, the ratio being approximately 2.5

the group consisting of petroleum and natural gas which are cracked outside the furnace and then introduced therein in the form of soot and a gaseous product comprising hydrogen, carbon monoxide and nitrogen, the steps which comprise cracking said materials by an incomplete combustion with hot air to obtain a maximum amount of soot, tapping said air from the supply of blast air to the furnace, the ratio being approximately 2.5 metric tons hydrocarbons to 1,000 in. air; separating said soot from the gaseous products obtained by said cracking; separating said gaseous products into a small fraction and a relatively larger, major, fraction; entraining said soot in said small fraction; injecting said small fraction .and its entrained soot into the furnace hearth; and introducing said larger fraction into said blast furnace above the hearth thereof.

3. In a process for the operation of. a blastfurnace wherein part of the coke charged at the throat of the furnace is replaced by hydrocarbon materials selected from the group consisting of petroleum and natural gas which are cracked outside the furnace and then introduced therein in the form of soot and a gaseous product comprising hydrogen, carbon monoxide and nitrogen, the steps which comprise cracking said materials by an incomplete combustion with hot air in a central cyclone preceding the blast furnace to obtain a maximum amount of soot, the ratio being approximately 2.5 metric tons hydrocarbons to 1,000 in. air; separating said soot from the gaseous products obtained by said cracking; separating said gaseous products into a small fraction and a relatively larger, major, fraction; entraining said soot in said small fraction; injecting said small fraction and its entrained soot into the furnace hearth; and introducing said larger fraction into the blast furnace above the hearth thereof.

4. In a process for the operation of a blast furnace wherein pant of the coke charged at the throat of the furnace is replaced by hydrocarbon materials selected from the group consisting of petroleum and natural gas which are cracked outside the furnace and then introduced therein in the form of soot and a gaseous product comprising hydrogen, carbon monoxide and nitrogen, the steps which comprise cracking said materials by an incomplete combustion with hot air in individual cyclones preceding the blast furnace tuyeres to obtain a maximum amount of soot, the ratio being approximately 2.5 metric tons hydrocarbons to 1,000 m. air; separating said soot from the gaseous products obtained by said cracking; separating said gaseous products into a small fraction and a relatively larger, major, fraction; entraining said soot in said small fraction; injecting said small fraction and its entrained soot into the furnace hearth; and introducing said larger fraction into the blast furnace above the hearth thereof.

5. In a process for the operation of a blast furnace wherein part of the coke charged at the throat of the furnace is replaced by hydrocarbon materials selected from the group consisting of petroleum and natural gas which are cracked outside the furnace and then introduced therein in the form of soot and a gaseous product comrising hydrogen, carbon monoxide and nitrogen, the steps which comprise cracking said materials, to obtain a maximum amount of soot, in two series-connected regenerative chambers heated to approximately 1,400 C.; heating air to 1,3001,400 C. in the first of said two heated chambers; passing said heated air into the second heated chamber; injecting said hydrocarbons into said heated air in the second chamber, the ratio being approximately 2.5 metric tons hydrocarbons to 1,000 m. air; cracking said hydrocarbons by said hot air in said second chamber; separating in a cyclone said soot from the gaseons products obtained by crack-ing; separating said gaseous products into a small fraction and a relatively larger, major, fraction; entraining said soot in said small fraction; injecting said small fraction and its entrained soot into the furnace hearth; and introducing said larger fraction into the furnace above the hearth thereof.

6. In a process for the operation of a blast furnace wherein part of the coke charged at the throat of the furnace is replaced by hydrocarbon materials selected from the group consisting of petroleum and natural gas which are cracked outside the furnace and then introduced therein in the form of soot and a gaseous product comprising hydrogen, carbon monoxide and nitrogen, the steps which comprise cracking said materials by an incomplete combustion with hot air to obtain a maximum amount of soot, the ratio being approximately 2.5 metric tons hydrocarbons to 1,000 m. air; separating said soot from the gaseous products obtained by cracking in a cyclone; storing the soot in a container following said cyclone; separating said gaseous products into a small fraction and a relatively larger, major, fraction; entraining l :59 said soot in said small fraction; injecting said small fraction and its entrained soot into the furnace hearth; and introducing said larger fraction into the furnace above the hearth thereof.

7. In a process for the operation of a blast furnace wherein part of the coke charged at the throat of the furnace is replaced by hydrocarbon materials selected from the group consisting of petroleum and natural gas Which are cracked outside the furnace and then introduced therein in the form of soot and a gaseous product comprising hydrogen, carbon monoxide and nitrogen, the steps Which comprise cracking said materials by an incomplete combustion to obtain a maximum amount of soot, the ratio being approximately 2.5 metric tons hydrocarbons to 1,000 m. air; separating said soot from the gaseous products obtained by said cracking; separating said gaseous products into a small fraction and a relatively larger, major, fraction; entraining said soot in said small fraction; injecting said small fraction and its entrained soot into the furnace hearth; and introducing said larger fraction, While hot, into said blast furnace above the hearth thereof.

8. In a process for the operation of a blast furnace wherein part of the coke charged at the throat of the furnace is replaced by hydrocarbon materials selected from the group consisting of petroleum and natural gas which are cracked outside the furnace and then introduced therein in the form of soot and a gaseous product comprising hydrogen, carbon monoxide and nitrogen, the steps which comprise cracking said materials by an incomplete combustion With hot air to obtain a maximum amount of soot, the ratio being approximately 2.5 metric tons hydrocarbons to 1,000 m. air; separating said soot from the gaseous products obtained by said cracking; separating said gaseous products into a small fraction and a relatively larger, major, fraction; entraining said soot in said small fraction; injecting said small fraction and its entrained soot into the furnace hearth; introducing part of said larger fraction into said blast furnace above the hearth thereof; adding to the remainder of said larger fraction blast furnace gas and natural gas to obtain desired density and calorific value; and burning the resulting mixture to meet external fuel requirements.

References ited in the file of this patent UNITED STATES PATENTS 1,349,598 Basset Aug. 17, 1920 1,872,900 Crocker Aug. 23, 1932 2,420,398 Kinney May 13, 1947 2,719,083 Pomykala Sept. 27, 1955 2,833,643 Newman May 6, 1958 2,952,533 Cuscoleca Sept. 13, 1960

Claims

1. IN A PROCESS FOR THE OPERATION OF A BLASTD FURNACE WHEREIN PART OF THE COKE CHARGED AT THE THROAT OF THE FURNACE IS REPLACED BY HYDROCARBON MATERIALS SELECTED FROM THE GROUP CONSISTING OF PETROLEUM AND NATURAL GAS WHICH ARE CRACKED OUTSIDE THE FURNACE NAND THEN INTRODUCED THEREIN IN FORM OF SOOT AND A GASEOUS PRODUCT COMPRISING HYDROGEN, CARBON MONOXIDE AND NITROGEN, THE STEPS WHICH COMPRISE CRACKING SAID MATERIALS BY AN INCOMPLETE COMBUSTION WITH HOT AIR TO OBTAIN A MAXIMUM AMOUNT OF SOOT, THE RATIO BEING APPROXIMATELY 2.5 METRIC TONS HYDROCARBONS TO 1,000 M.3 AIR; SEPARATING SAID SOOT FROM THE GASEOUS PRODUCTS OBTAINED BY SAID CRACKING; SEPARATING SAID GASEOUS PRODUCTS INTO A SMALL FRACTION AND A RELATIVELY LARGER, MAJOR, FRACTION; ENTRAINING SAID SOOT IN SAID SMALL FRACTION; INJECTING SAID SMALL FRACTION AND ITS ENTRAINED SOOT INTO THE FURNACE HEARTH; AND INTRODUCING SAID LARGER FRACTION INTO SAID BLAST FURNACE ABOVE THE HEARTH THEREOF.