Process and installation for treating oil-containing mill scale and similar materials.

0001The invention relates to a method and a plant for processing oil-containing, wet mill scale and similar substances according to the preamble of claim 1 and claim 7.

0002Mill scale and mill scale sludge occur in rolling mills when the scale layer has to be removed before the rolling process. Tinder is iron oxide, which can be added to the raw material again in a sintering plant, for example. In the rolling mill, scale mixes with water, which is used as cooling water or as pressurized water for spraying off the scale layer, and with oil or grease, which was used, for example, to lubricate bearings. Larger scale particles can be separated in a wastewater treatment plant for the rolling water of the rolling mill, however, complete deoiling is not possible. Finer scale particles can only be separated from the circulating water to a limited extent by settling, but otherwise by filter. They form the mill scale sludge, which still has a high water content of up to 30% and an oil content of up to more than 6%. If the roller scale sludge is used for sintering, not only does the water evaporate, but at least some of the oil escapes unburned. In some cases, oily components condense in today's electrostatic precipitators, which have the task of cleaning the flue gases of the sintering plant from dust to a legally specified minimum level. If organic material in the flue gas is exposed to high loads, fires or, in the limit case, explosions can also occur in the filter, which is easily caused by electrical flashovers between the spray and precipitation electrodes of the electrostatic filter. Condensed oil components make it more difficult to clean the precipitation electrodes, and oil that is not separated increases the cloudiness of the emitted flue gas indirectly (by impairing the function of the electrostatic filter) and immediately (as a condensed oil mist).

0003Killmann and Schellberg reported on options for the treatment of the roller scale at the 1988 Duisburg Recycling Days. One solution is two-layer sintering, in which a further layer of oil-containing roller scale sludge is placed on a first, lower sinter mixture without mill scale sludge, which is ignited first, which is to be ignited separately at a suitable time. The oil escapes from the upper layer and is burned as it passes through the lower layer. However, this process can only be carried out if the exact process conditions are adhered to and would require considerable modifications to existing sintering plants. Attempts have also been made to attempt to free oil from mill scale sludge at temperatures above 100 ° C in a coke gas-air mixture oven, and it has been determined that the original oil content of 7% above 280 ° C oven temperature is less than 0 , 1% could be reduced.

0004In the area of ​​industrial plants, such as a blast furnace and a steelworks, oil-containing substances such as sands often occur, from which the oil is difficult to remove and which must therefore be brought to a special landfill. An extraction of these irregularly occurring oil-containing substances can be very complex under certain circumstances. Removal of oil from these substances by simple means would therefore be desirable, even if the substances themselves cannot be fed into the blast furnace.

0005It is the object of the invention to largely remove oil from oil-containing solids, such as mill scale and in particular mill scale sludge, and to develop a method and a system with which mill scale can be processed in an energy-saving manner and without risk of fire in modern dust filter systems. Another object of the invention is to use the energy content of the oil contained in the mill scale or similar solid.

0006This object is achieved with the characterizing features of claim 1 and claim 7. Further refinements of the invention result from claims 2 to 6 and 8 to 14. Thereafter, a largely dewatered solid, as usual freed from foreign bodies, such as mill scale, which may also be in the form of mill scale sludge, possibly sintered pieces being broken beforehand, in a continuous furnace at temperatures at which the moisture and volatile oils escape and the rest Burn oils, possibly by cracking, treated.

0007The treatment takes place directly in connection with the operation of an iron ore sintering plant.

0008It is state of the art to recover hot exhaust air, especially from the first part, from the cooler of the sintering plant and to use it. It is often used as preheated combustion air in the ignition furnace of the same sintering plant. There are also other operationally realized uses, such as extracting steam for the steam network of a hut or preheating combustion media for consumers outside the sintering plant.

0009According to the invention, the hot exhaust air from the cooler of a sintering system is fed to a continuous furnace in which the hot exhaust air and the oil-containing solid are guided in countercurrent, such as mill scale. The evaporated, partly also burned oil exhaust air leaves the continuous furnace, has cooled due to the evaporation of moisture from the mill scale and due to the heating of the mill scale by an amount corresponding to the heat capacity flow conditions and is due to its still large heat content as preheated combustion air Ignition furnace fed to the sintering plant. At temperatures above 1,000 ° C, the part of the oil that has not yet burned, which comes from the continuous furnace with the combustion air and where it was thermally released from the mill scale or other solid, also burns there. The high combustion temperatures and the - albeit small - excess of oxygen in the ignition furnace of a sintering plant ensure the complete combustion of the oil. A load on the smoke filter of the sintering plant by oil is thus avoided. The calorific value of the oil is fully used in the continuous furnace, there by partial combustion, and in the ignition furnace, there by residual combustion.

0010In the preferred treatment of mill scale, the dry, hot and thermally oil-free mill scale coming from the continuous furnace is fed directly to the return material of the sintering plant, for. B. the hot return material, and in this way reaches the iron ore mixture to be sintered. The mill scale can also be fed directly to the iron ore mixture, bypassing the return material flow, which makes it easier to control the sintering system with regard to balancing the amount of return material and the use of return material. The heat content of the hot mill scale is - apart from the inevitable losses during transport - introduced into the iron ore mixture. It is therefore preheated in accordance with the heat and quantity ratios of mill scale / iron ore mixture and thus passes under the ignition furnace of the sintering plant. A large part of the heat coming from the continuous furnace with the hot mill scale is therefore used.

0011Are other oily substances, such as. B. sands to treat, the oil can also be removed from them with the help of the hot exhaust air of a sinter cooler and their introduction into the ignition furnace of the sintering plant. However, the oil-free, dried sands are generally not fed to the sintering plant, but are discharged oil-free from the material flow of the sintering plant. In general, they do not meet the requirements of the ore mixtures to be processed in the sintering plant in terms of material and timing.

0012In an embodiment of the invention, it is proposed to use a rotary tube furnace as a continuous furnace. An alternative to this is the use of a deck oven, as was previously often used for roasting sulfidic ores. Both furnaces allow the countercurrent principle to be used for the hot sinter cooler exhaust air and the wet, oily mill scale.

0013Because of the heterogeneous properties of mill scale - strongly changing wetness, different feed grain, fluctuating oil contents - the addition quantity of the mill scale to the continuous furnace is preferably controlled according to the temperature of the exiting exhaust air fed to the ignition furnace. In this way, constant operation of the ignition furnace is made possible. The feed material should preferably remain in the continuous furnace for a maximum of about 30 minutes. amount, since this test time is sufficient after tests have been carried out.

0014It is preferably provided that at a cooler exhaust air temperature that is less than a predetermined limit, z. B. above 350 ° C, the supply of wet, oil-rich mill scale is interrupted. It is also preferred for controlling the cleaning function of the continuous furnace, the temperature of the hot mill scale emerging from the continuous furnace z. B. to be measured infrared-optically and to interrupt the inflow of wet mill scale to the continuous furnace if this temperature falls below a limit value. In order to enable maintenance work on the continuous furnace also during the operation of the sintering plant, it is expedient in this case to be able to feed the hot cooler exhaust air directly to the ignition furnace by means of a slide and a feed line past the continuous furnace. A cyclone for dust separation is preferably connected upstream of the ignition furnace. The hood for extracting the hot radiator exhaust air is equipped in a known manner with safety devices for blowing off hot radiator exhaust air.

0015The figure shows the system parts of a preferred example in a highly simplified and only schematic manner.

0016The sintering machine 1, a traveling grate, is supplied with pretreated mix via a feed device 2, and in the ignition furnace 3 the coke contained in the mix is ​​ignited by ignition gas. The sinter cake is crushed through a sting crusher 4 into the sinter cooler 5, to which cooling air is fed via a blower 6. After calibration and screening (not shown), the finished sinter is forwarded from the cooler 5 via the conveying path 7 to the blast furnace. The flue gas from the sintering machine 1 is drawn off via an electrostatic filter 8 by a blower 9 and blown off via a chimney 10. The hot cooler exhaust air is drawn off from the hot part of the sinter cooler 5 via a hood 11 and passed via a line 23 into a continuous furnace 12 through which the mill scale to be treated flows in countercurrent. The cooler exhaust air now passes from the continuous furnace 12 into a dust separator 13 and is introduced into the ignition furnace 3 as warm combustion air by a fan 14. This combustion air contains the flue gas from the oil burned in the continuous furnace and volatile and low-boiling components of this oil, which burn in the ignition furnace 3 at a temperature above 1000 ° C.

0017The mill scale is fed to the continuous furnace 12 by a suitable conveyor 15 with an adjustable delivery rate. The hot scale, freed from oil, is z. B. via discharge channels 16 or another suitable transport device to the mixing device 17, in which ore, aggregates and coke breeze are mixed and into which sintered waste can be introduced via a conveyor device 18 after separation from the finished sinter behind the cooler 5. The oil-free mill scale can also be added directly to the sintered waste. The mix passes through mixing and rolling drums, not shown, and then arrives at the feed device 2.

0018The hot, dry mill scale brings heat into the mix. The hot radiator exhaust air cools down when the wet mill scale dries, but is also reheated by partial combustion of oil in the continuous furnace and feeds residual volatile oil to the ignition furnace 3 as a further fuel.

0019From the dependencies of heat requirements for drying, for thermal cleaning of oil and heating of the mill scale, also taking into account the oil calorific value on the one hand, and the air requirement of the ignition furnace of the sintering system, on the other hand, the maximum quantities of mill scale that can be processed in a sintering system result. As described, the maximum amounts are not constant because of the heterogeneous properties. The following example gives an example.<tables id="tabl0001" num="0001"><img file="EP0446779A2_D0001.tif" /></tables>

0020By lowering the pilot air temperature from 300 ° C to lower temperatures, the maximum possible throughput increases: At 200 ° C pilot air temperature, the roll count quantities that can be processed are otherwise 54 t / day.

0021Blast gas from a line 18 is usually used as the ignition gas in the ignition furnace 3, and the combustion air is preheated depending on the blast furnace gas available. In the system according to the invention, separate preheating of the combustion air is not necessary, since there is still sufficient warm cooler exhaust air available. The above examples show the relationship between the pilot air temperature and the possible throughput of mill scale through the continuous furnace.

0022Because of the different composition of the mill scale, it is advantageous to monitor the temperatures and intervene to control them. A temperature meter 19 determines the temperature of the cooler exhaust air supplied as combustion air and throttles or stops the supply of mill scale into the continuous furnace 12 via control devices (not shown) or allows the cooler exhaust air to flow through a bypass 20. A temperature meter 21 determines the temperature of the hot radiator exhaust air and intervenes in a similar manner if this z. B. temporarily drops below a predetermined value. Furthermore, the temperature of the mill scale behind the continuous furnace 12 can also be monitored via a temperature meter 22 in order to ensure that sufficient thermal cleaning has taken place. The specified temperature meters and other control devices of the sintering plant can work together via a computer to produce optimal process conditions.