Plant for the thermal treatment of raw meal using an electric heating device

Abstract

Plant (100) for the thermal treatment of raw meal (10) for the production of quicklime (11) or for the activation of clays, comprising a cyclone heat exchanger (200) in which more than one heat exchanger cyclone (110, 210, 310, 410) is connected in series, within which an electrically heated heating contact surface (115, 215, 315, 415) is arranged, which is designed such that the raw meal (10) slides in the heat exchanger cyclones (110, 210, 310, 410) over the electrically heated heating contact surface (115, 215, 315, 415), wherein the individual heat exchanger cyclones (110, 210, 310, 410) are connected to each other via a gas riser (111, 211, 311). are connected, in which gas flows from a heat exchanger cyclone (210, 310, 410) located upstream in the direction of gas flow into a next heat exchanger cyclone (110, 210, 310) located downstream in the direction of gas flow, wherein a line (205, 305,405) for raw meal (10) from the heat exchanger cyclone (110, 210, 310) located downstream in the direction of gas flow into a gas riser (111, 211, 311) which leads to the heat exchanger cyclone (210, 310, 410) located upstream in the direction of gas flow, wherein the connection between the line (205, 305, 405) for raw meal (10) and the gas riser (111, 211, 311) has a raw meal box (206, 306, 406) within which an electrically heated raw meal chute (207, 307, 407) is provided as a further heating contact surface.

Description

The invention relates to a process for the thermal treatment of raw meal for the production of quicklime or for the activation of clays and to a plant corresponding thereto.For the production of quicklime (CaO), it is known to finely grind lime (CaCO 3) from natural deposits to form what is known as raw meal and to dry it suspended in a gas stream and to feed it to a thermal treatment. Burnt lime (CaO) is, in addition to further substances, a starting material for the production of cement clinker, but also for the production of soda. Quicklime is also used as base in various chemical processes and is used in inorganic binders. Ground quicklime is stated differently depending on the industry. In the cement industry, a flour of a mixture of quicklime and silicate-containing rock is called "raw flour". In other sectors, the pure lime is also referred to as "raw meal" before it is burnt. Before the lime is burnt, i.e. thermally treated (CaCO 3) the raw meal is dried and brought to a temperature just before its temperature of hemolysis. For this purpose, it is customary to pass hot combustion gases from a downstream combustion and, if appropriate, sintering process as waste heat through successive heat exchanger cyclones, where the still moist raw meal flows against the hot exhaust gases. In the individual and successive heat exchanger cyclones, the raw meal is brought into intimate contact with the hot combustion gases and immediately separated again from the hot combustion gas. During this repeated suspension of the lime (CaCO 3) in hot combustion exhaust gases and re-separation, the heat contained in the hot combustion exhaust gases is transferred to the still cold and moist raw meal. As a result, the hot combustion air cools and the raw meal heats up, dries and is brought to just before the temperature of the hemolysis, i.e., the temperature at which lime (CaCO 3) decomposes into carbon dioxide (CO 2) and burnt lime (CaO). The endothermic calcination using fossil fuels takes place only in a further reactor which follows the heat exchanger. Combustion exhaust gases which comprise carbon dioxide (CO 2) nitrogen oxides (NOx) and volatile organic constituents (ICl) are formed during calcination. Volatile Organic Compounds, VOC).In the course of the conversion of the process for producing cement clinker from raw meal or for firing lime to processes which still produce only water vapor (H 2 O) and carbon dioxide (CO 2) as waste gases, on the one hand only little waste heat or too little is produced which is to be easily recovered at this point of drying and preheating. Furthermore, when producing unavoidable carbon dioxide (CO 2) as gas, the aim is to keep this gas as free as possible from other gases, such as, for example, atmospheric nitrogen (N 2), nitrous gases (NOx) from combustion processes and volatile organic constituents (VOC), in order to be able to capture the carbon dioxide (CO 2) as far as possible without necessary purification for later sequestration or utilization.In German laid-open specification DE 10 2011 014 498 A1, a method and a plant for producing a clinker substitute are disclosed. This is based on calcined clay, which is preheated in cyclones for calcination. The cyclones are optionally also electrically heated.It is an object of the invention to provide a plant for the thermal treatment of lime in which exhaust gas purification before the separation or compression of the carbon dioxide (CO 2) is unnecessary.The object according to the invention is achieved by a plant having the features according to claim 1.According to the concept of the invention, a thermal treatment of the raw meal or the clay at electrically heated heating contact surfaces is provided in a heat exchanger cyclone. The thermal treatment may comprise drying and preheating to just before the temperature of the hemolysis. However, the thermal treatment can also proceed further and comprise the further endothermic calcination.For the purpose of implementation, a plant is provided which has a cyclone heat exchanger. More than one heat exchanger cyclone is connected in series in the cyclone heat exchanger. Within the cyclone heat exchangers, electrically heated heating contact surfaces are arranged in each case, which are designed such that the raw meal in the heat exchanger cyclones slides over the electrically heated contact surfaces. The raw meal thus flows through the cyclone heat exchanger and is dried in an electric furnace, preheated and also calcined depending on the power of the electric heating. This heat exchanger cyclone furnace can also activate clay by thermal treatment instead of lime.For the most intensive possible contact of the raw meal with the electric heating contact, it can be provided that the electrically heated heating contact surface in the individual heat exchanger cyclones is integrated as a conical insert into the conical outlet of the cyclone. The conical insert fits exactly into the lower cone of a heat exchanger cyclone, wherein the dimensions can comprise a heat exchanger cyclone up to 5 m diameter and up to 10 m height.In the plant, it is provided that the individual heat exchanger cyclones are connected to each other via a gas riser line in which gas flows from a heat exchanger cyclone upstream in the gas flow direction into a next heat exchanger cyclone ion downstream in the gas flow direction, wherein a line for raw meal leads from the heat exchanger cyclone downstream in the gas flow direction into a gas riser line which leads to the heat exchanger cyclone ion upstream in the gas flow direction, wherein the connection between the line for raw meal and the gas riser line has a raw meal box, within which an electrically heated heating contact surface is likewise provided, via which the meal slips and is suspended in the gas flow of the gas riser line. In addition, the line itself, in which the flour flows, can also be equipped with electrically heated heating contact surfaces. The raw meal or clay is thus heated not only in the heat exchanger cyclones but also in the conduits between the heat exchanger cyclones and during the entry from the conduits into the cyclones.The cyclone heat exchanger has individual stages through each individual heat exchanger cyclone. If raw meal is thermally treated or clay is activated, the specific heat absorption is coupled with the state of the raw meal or clay. Moist raw meal or moist clay can absorb heat which leads to evaporation of the moisture. Dry raw meal or dry clay can absorb a predetermined amount of heat per unit mass of raw meal / clay according to its specific heat capacity, which leads to an increase in the temperature of the raw meal or clay. When the temperature of the hemolysis is reached, an additional heat requirement for carrying out the strongly endothermic hemolysis arises. In order to complete the desired change of state in each stage of the cyclone heat exchanger, it can be provided that a regulating device regulates the heating power of each heating contact surface according to a temperature difference, wherein temperature probes measure the temperature at a point before the relevant heating contact surface and at a point after the relevant heating contact surface, both points with respect to the raw meal flow direction, and the temperature difference is generated from subtraction of both measured temperatures.The invention is explained in more detail with reference to the following figures. It shows: FIG. 1 shows an inventive plant for illustrating the inventive method, FIG. 2 shows detail A from FIG. 1 with a conical insert as heating contact surface in a heat exchanger cyclone, FIG. 3 shows detail B from FIG. 1 with a flour chute as a heating contact surface in a flour box.FIG. 1 shows a plant 100 according to the invention. The plant 100 comprises a cyclone heat exchanger 200 outlined by the brackets. The cyclone heat exchanger 200 is flown through from bottom to top with process heat-carrying exhaust gas of a downstream sintering process. In this case, the hot exhaust gas from the downstream process passes into the lower gas riser 101. The exhaust gas in the gas riser 101 then enters the lowermost heat exchanger cyclone 110 in which it is directed tangentially into the upper, cylindrical part of the heat exchanger cyclone 110. As a result of the tangential introduction, a strong vortex forms in the heat exchanger cyclone 110, therefore the name "cyclone", in which dust contained in the gas collects on the inner sides of the outer wall due to centrifugal force. The gas can leave the heat exchanger cyclone 110 only through a dip tube (comparative dip tube 420) projecting centrally from above into the heat exchanger cyclone 110, wherein the dip tube, which is not visible here, extends as far as close to the tip of the lower cone of the heat exchanger cyclone 110, so that the vortex of gas necessarily increases its angular velocity at the radius which is constantly decreasing. In this case, the centrifugal force which acts on the dust suspended in the gas and conducts it to the outer wall becomes greater with a smaller radius, so that the dust slips down on the inner side of the outer wall and exits from the heat exchanger cyclone 110 at the bottom as product 11. When the raw meal 10 is in intensive contact with the outer wall of the heat exchanger cyclone 110, the raw meal 10 is heated at a heating contact surface 115 in the form of a conical insert. Raw meal from the heat exchanger cyclone 210 is injected into the exhaust gas by means of a meal box 206 which is connected to the next heat exchanger cyclone 210 located downstream in the gas flow direction via a raw meal line 205. In this case, the raw meal originating from the heat exchanger cyclone 210 is additionally heated on the meal chute 207 by an electrically heated heating contact surface on the heated meal chute 207. The gas from the heat exchanger 110 leaves the heat exchanger 110 via the gas riser 111. The above-described process is repeated using the heat exchanger cyclone 210 and the flour box 306 with the flour chute 307 designed as an electrically heated contact surface. This repeats in the next stage with heat exchange cyclone 310 and flour box 406 until finally the last heat exchange cyclone 410 is reached. There, the gas is fed from the heat exchanger cyclone 410 via a gas riser 411 into the dust separator 600. The dust separated in the dust separator 600 is introduced with the raw meal feed into the meal box 506, where the still moist raw meal 10 is fed. The cyclone heat exchanger 200 acts like an electric furnace in which the raw meal 10 is dehumidified, preheated and even calcined depending on the electrical power of the heating contact surfaces.In this embodiment of the plant 100, a control device 150 controls the electrical power of the individual heating surfaces, namely the heating surfaces 115, 215, 315 and 415 and the electrically heated flour chutes 207, 307, 407 and 507. The electrical power consumption of the heating surfaces is adjusted individually by the control device by the temperature difference determined by temperature probes. These temperature probes are present in the raw meal lines 205, 305 and 405 and in the gas riser lines 101, 111, 211 and 311, wherein the placement of the temperature probes can be individually adapted depending on the requirement.In a special embodiment of the plant according to the invention, provision can be made for a gas recirculation line to lead from the gas outlet of the cyclone heat exchanger to the gas inlet in the form of the gas riser line, wherein a compressor conveys the gas recirculated in the gas recirculation line to the gas inlet and a slide valve in the gas recirculation line controls the amount of recirculated gas. This gas recirculation line recirculates exhaust gas, consisting essentially of carbon dioxide (CO 2) and water (H 2 O), back into the loop of the plant to re-generate heat from the cyclone heat exchanger.FIG. 2 shows the detail A from FIG. 1 with a conical insert 412 as heating surface element 415 in a heat exchanger cyclone 410. The heat exchanger cyclone 410 can have diameters of up to 5 m and a height of up to 10 m. According to the idea of the invention, it is planned to insert into each heat exchanger cyclone 110, 210, 310 and 410 a conical insert 412 equipped with an electrical resistance heater 413. The electric resistance heater 413 is supplied with electric power.FIG. 3 shows the detail B from FIG. 1 with an electrically heated flour chute 407 as heating surface. Raw meal 10 enters the meal box 406 from above, is deflected by the electrically heated meal chute 407 and leaves the meal box 406 again into the gas riser line 211 arranged there. The path of the raw meal 10 is shown by the arrow drawn in.LIST OF REFERENCE CHARACTERS10 Raw meal 11 product 100 plant 200 cyclone heat exchanger 101 gas riser 105 line 110 heat exchanger cyclone 111 gas riser 115 heating contact surface 150 regulating device 205 line 206 raw meal box 207 heated raw meal chute 208 heating contact surface 209 temperature probe 210 heat exchanger cyclone 211 gas riser 215 heating contact surface 305 line 306 raw meal box 308 heating contact surface 307 heated raw meal chute 309 temperature probe 310 heat exchanger cyclone 311 gas riser 315 heating contact surface 405 line 406 raw meal box 407 heated raw meal chute 408 heating contact surface 410 heat exchanger cyclone 411 gas riser 412 conical insert 413 resistance heater 415 heating contact surface 420 immersion pipe 506 raw meal branch 507 heated raw meal chute 600 dust separator 610 recirculation line 620 compressor 630 slide A detail B detail

Claims

Plant (100) for the thermal treatment of raw meal (10) for the production of quicklime (11) or for the activation of clays, having a cyclone heat exchanger (200), in which more than one heat exchanger cyclone (110, 210, 310, 410) is connected in series, within which in each case an electrically heated heating contact surface (115, 215, 315, 415) is arranged, which is designed such that the raw meal (10) slides in the heat exchanger cyclones (110, 210, 310, 410) over the electrically heated heating contact surface (115, 215, 315, 415), wherein the individual heat exchanger cyclones (110, 210, 310, 410) are connected to one another via in each case a gas riser line (111, 211, 311), in which gas from a heat exchanger cyclone (210, 310, 410) located upstream in the gas flow direction into a next heat exchanger cyclone (110, 210, 310, 410) located downstream in the gas flow direction, 310), wherein a line (205, 305, 405) for raw meal (10) leads from the heat exchanger cyclone (110, 210, 310) located downstream in the gas flow direction into a gas riser line (111, 211, 311) which leads to the heat exchanger cyclone (210, 310, 410) located upstream in the gas flow direction, wherein the connection between the line (205, 305, 405) for raw meal (10) and the gas riser line (111, 211, 311) has a raw meal box (206, 306, 406), within which an electrically heated raw meal chute (207, 307, 407) is present as a further heating contact surface.Installation according to Claim 1, characterized in that the electrically heated heating contact surface (115, 215, 315, 415) in the individual heat exchanger cyclones (110, 210, 310, 410) is present as a conical insert (412) as a heating contact surface which is electrically heated.Plant according to claim 1, characterised in that an additionally electrically heated heating contact surface (208, 308, 408) is present in the line (205, 305, 405) for raw meal (10).Plant according to one of Claims 1 to 3, characterized in that a regulating device (150) regulates the heating power of a heating contact surface (107, 115, 207, 208, 215, 307, 308, 315, 407, 408, 415) in each case according to a temperature difference, wherein temperature probes (209, 309, 409) measure the temperature at a point upstream of the relevant heating contact surface (107, 115, 207, 208, 215, 307, 308, 315, 407, 408, 415) and at a point downstream of the relevant heating contact surface (107, 115, 207, 208, 215, 307, 308, 315, 407, 408, 415), both points with respect to the raw meal flow direction.Plant according to one of Claims 1 to 4, characterized in that a gas recirculation line (610) leads from the gas outlet of the cyclone heat exchanger (200) to the gas inlet in the form of the gas riser line (101), wherein a compressor (620) conveys the gas recirculated in the gas recirculation line (610) to the gas inlet and a slide (630) in the gas recirculation line (610) controls the amount of recirculated gas.

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