Method for thermally treating raw meal using an electric heating device, and system corresponding thereto

Abstract

The invention relates to a method for thermally treating raw meal (10) in order to produce burnt lime (11) or for activating clays. According to the invention, the raw meal (10) is thermally treated on an electrically heated heating contact surface (107, 115, 207, 208, 215, 307, 308 315, 407, 408, 415) in a heat exchanger cyclone (110, 210, 310, 410). Correspondingly, the invention relates to a system (100) for carrying out the method according to claim 1, comprising a cyclone heat exchanger (200) in which there is more than one heat exchanger cyclone (110, 210, 310, 410) connected one behind the other, within each of which an electrically heated heating contact (115, 215, 315, 415) is arranged which is provided such that the raw meal (10) in the heat exchanger cyclones (110, 210, 310, 410) slides over the electrically heated heating contact surface (107, 115, 207, 208, 215, 307, 308, 315, 407, 408, 415).

Description

[0001] Process for the thermal treatment of raw meal using an electric heating device and corresponding plant

[0002] The invention relates to a process for the thermal treatment of raw meal for the production of burnt lime or for the activation of clays and a corresponding plant.

[0003] To produce burnt lime (CaO), it is known to finely grind lime (CaCO3) from natural deposits into so-called raw meal, suspend it in a gas stream, dry it, and then subject it to thermal treatment. Burnt lime (CaO), along with other substances, is a starting material for the production of cement clinker, but also for the production of soda. Burnt lime is also used as a base in various chemical processes and in inorganic binders. Ground, burnt lime has different names depending on the industry. In the cement industry, a flour made from a mixture of burnt lime and silicate-containing rock is called 'raw meal'. In other industries, pure lime is also referred to as 'raw meal' before it is burned. Before burning, i.e., the thermal treatment of the lime (CaCO3), the raw meal is dried and brought to a temperature just below its thermolysis temperature.For this purpose, it is common practice to pass hot combustion gases from a downstream firing and, if applicable, sintering process as waste heat through successive heat exchanger cyclones, where the still-moist raw meal flows counter to the hot exhaust gases. In the individual and successive heat exchanger cyclones, the raw meal comes into intimate contact with the hot combustion gases and is immediately separated from the hot combustion gas. During this repeated suspension of the lime (CaCO3) in hot combustion exhaust gases and subsequent 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 in the process and is brought to just below the thermolysis temperature, i.e. the temperature at which lime (CaCO3) decomposes into carbon dioxide (CO2) and burnt lime (CaO).Endothermic calcination takes place in a separate reactor following the heat exchanger, using fossil fuels. Calcination produces combustion gases containing carbon dioxide (CO2), nitrogen oxides (NOx), and volatile organic compounds (VOCs).

[0004] In the course of converting the process for producing cement clinker from raw meal or for burning lime to processes that only generate steam (H2O) and carbon dioxide (CO2) as exhaust gases, little or no waste heat is generated, which can be easily recovered at this point in the drying and preheating process. Furthermore, when generating unavoidable carbon dioxide (CO2) as a gas, efforts are being made to keep this gas as free as possible from other gases, such as atmospheric nitrogen (N2), nitrous gases (NOx) from combustion processes, and volatile organic compounds (VOCs), in order to capture the carbon dioxide (CO2) for later sequestration or use, if possible without the need for purification.

[0005] The object of the invention is therefore to provide a process for the thermal treatment of lime in which exhaust gas purification before the separation or compression of carbon dioxide (CO2) is unnecessary.

[0006] The object of the invention is achieved in that the raw meal is heated on heating contact surfaces in a heat exchanger cyclone, which are heated to the required temperatures via an electrical resistance heater.

[0007] The corresponding system comprises a cyclone heat exchanger, within which electrically heated heating contact surfaces are arranged in the individual heat exchanger cyclones. The cyclone heat exchanger is designed such that the raw meal slides over the electrically heated heating contact surfaces in the heat exchanger cyclones. Further advantageous embodiments of the system are specified in the subclaims to claim 2.

[0008] According to the concept of the invention, thermal treatment of the raw meal or clay is provided on electrically heated contact surfaces in a heat exchanger cyclone. The thermal treatment may include drying and preheating to just below the thermolysis temperature. However, the thermal treatment may also go further and include further, endothermic calcination.

[0009] To carry out the process, a system is provided that features a cyclone heat exchanger. Several heat exchanger cyclones are connected in series within the cyclone heat exchanger. Electrically heated contact surfaces are arranged within each cyclone heat exchanger, designed so that the raw meal slides over the electrically heated contact surfaces in the heat exchanger cyclones. The raw meal flows through the cyclone heat exchanger and is dried, preheated, and, depending on the power of the electric heater, calcined, just like in an electric kiln. This heat exchanger cyclone kiln can also activate clay through thermal treatment instead of burning lime.

[0010] To ensure the most intensive contact between the raw meal and the electrical heating contact, the electrically heated heating contact surface in the individual heat exchanger cyclones can be integrated as a conical insert into the conical outlet of the cyclone. The conical insert fits precisely into the lower cone of a heat exchanger cyclone, and the dimensions of a heat exchanger cyclone can range up to 5 m in diameter and 10 m in height.

[0011] The system can be designed so that the individual heat exchanger cyclones are each connected to one another via a gas riser, in which gas flows from a heat exchanger cyclone located upstream in the gas flow direction into the next heat exchanger cyclone located downstream in the gas flow direction. A line for raw meal leads from the heat exchanger cyclone located downstream in the gas flow direction into a gas riser, which leads to the heat exchanger cyclone located upstream in the gas flow direction. The connection between the line for raw meal and the gas riser has a raw meal box, within which an electrically heated heating contact surface is also provided, over which the meal slides and is suspended in the gas stream of the gas riser. 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 therefore not only heated in the heat exchanger cyclones, but also in the pipes between the heat exchanger cyclones and as it enters the cyclones from the pipes.

[0012] The cyclone heat exchanger has individual stages, each with its own heat exchanger cyclone. When raw meal is thermally treated or clay is activated, the specific heat absorption is linked to the condition of the raw meal or clay. Moist raw meal or moist clay can absorb heat, which leads to the evaporation of the moisture. Dry raw meal or dry clay can absorb a predetermined amount of heat per unit mass of raw meal / clay, depending on its specific heat capacity, which leads to an increase in the temperature of the raw meal or clay. When the thermolysis temperature is reached, additional heat is required to carry out the highly endothermic thermolysis.In order to complete the desired change of state in each stage of the cyclone heat exchanger, it can be provided that a control 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 respective heating contact surface and at a point after the respective heating contact surface, both points in relation to the raw meal flow direction, and the temperature difference is generated by subtracting both measured temperatures.

[0013] The invention is explained in more detail with reference to the following figures. They show:

[0014] Fig. 1 shows a system according to the invention to illustrate the method according to the invention,

[0015] Fig. 2 Detail A from Figure 1 with a conical insert as heating contact surface in a heat exchanger cyclone,

[0016] Fig. 3 Detail B from Figure 1 with a flour chute as heating contact surface in a flour box.

[0017] Figure 1 shows a system 100 according to the invention to illustrate the method according to the invention. The system 100 has a cyclone heat exchanger 200, outlined by the square brackets. Exhaust gas carrying process heat from a downstream sintering process flows through the cyclone heat exchanger 200 from bottom to top. The hot exhaust gas from the downstream process enters the lower gas riser 101. The exhaust gas in the gas riser 101 then enters the lowest heat exchanger cyclone 110, where it is guided tangentially into the upper, cylindrical part of the heat exchanger cyclone 110. Due to the tangential introduction, a strong vortex forms in the heat exchanger cyclone 110, hence 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 only leave the heat exchanger cyclone 110 through an immersion tube (compare immersion tube 420) extending centrally from above into the heat exchanger cyclone 110. The immersion tube, not visible here, extends almost to the tip of the lower cone of the heat exchanger cyclone 110, so that the gas vortex inevitably increases its angular velocity with the ever-decreasing radius. The centrifugal force acting on the dust suspended in the gas and directing it to the outer wall increases with decreasing radius, so that the dust slides down the inner side of the outer wall and out of the heat exchanger cyclone at the bottom.

[0018] 110 exits as product 11. Upon intensive contact of the raw meal 10 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 hot exhaust gas via 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. 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 previously described process is repeated with the heat exchanger cyclone 210 and the flour box 306 with the flour chute 307 designed as an electrically heated contact surface.This is repeated in the next stage with heat exchanger cyclone 310 and flour box 406, until the final heat exchanger cyclone 410 is finally reached. There, the gas from heat exchanger cyclone 410 is fed into dust separator 600 via a gas riser 411. The dust separated in dust separator 600 is fed with the raw meal feed into flour box 506, where the still-moist raw meal 10 is added. The cyclone heat exchanger 200 acts like an electric furnace in which the raw meal 10 is dehumidified, preheated, and, depending on the electrical power of the heating contact surfaces, even calcined.

[0019] In this embodiment of the system 100, a control device 150 regulates the electrical power of the individual heating surfaces, namely the heating surfaces 115, 215, 315, and 415, as well as the electrically heated flour chutes 207, 307, 407, and 507. The electrical power consumption of the heating surfaces is individually adjusted by the control device based on the temperature difference determined by temperature probes. These temperature probes are located in the raw meal lines 205, 305, and 405, as well as in the gas risers 101, 111, 211, and 311, whereby the placement of the temperature probes can be individually adjusted depending on requirements.

[0020] In a particular embodiment of the system according to the invention, a gas recirculation line can be provided, running from the gas outlet of the cyclone heat exchanger to the gas inlet in the form of a gas riser. A compressor conveys the gas recirculated in the gas recirculation line to the gas inlet, and a valve in the gas recirculation line controls the quantity of the recirculated gas. This gas recirculation line recirculates exhaust gas, which consists essentially of carbon dioxide (CO2) and water (H2O), back into the system's circuit to recover heat from the cyclone heat exchanger.

[0021] Figure 2 shows detail A from Figure 1 with a conical insert 412 as a heating surface element 415 in a heat exchanger cyclone 410. The heat exchanger cyclone 410 can have a diameter of up to 5 m and a height of up to 10 m. According to the concept of the invention, it is planned to insert a conical insert 412 equipped with an electrical resistance heater 413 into each of the heat exchanger cyclones 110, 210, 310, and 410. The electrical resistance heater 413 is supplied with electrical current.

[0022] Figure 3 shows detail B from Figure 1 with an electrically heated flour chute 407 as the heating surface. Raw flour 10 enters the flour box 406 from above, is deflected by the electrically heated flour chute 407, and exits the flour box 406 again into the gas riser 211 located there. The path of the raw flour 10 is indicated by the arrow.

[0023] LIST OF REFERENCE SYMBOLS

[0024] Raw meal 310 heat exchanger cyclone

[0025] Product 311 Gas riser

[0026] Appendix 315 Heating contact surface

[0027] Cyclone heat exchanger 405 line

[0028] Gas riser 406 raw meal box

[0029] Line 407 heated raw meal chute

[0030] Heat exchanger cyclone 408 heating contact surface

[0031] Gas riser 410 heat exchanger cyclone

[0032] Heating contact surface 411 gas riser

[0033] Control device 412 conical insert

[0034] Line 413 resistance heating

[0035] Raw meal box 415 Heating contact surface heated raw meal chute 420 Immersion tube

[0036] Heating contact area 506 raw meal loads

[0037] Temperature probe 507 heated raw meal chute

[0038] Heat exchanger cyclone 600 dust separator

[0039] Gas riser 610 recirculation line

[0040] Heating contact surface 620 compressor

[0041] Line 630 valve

[0042] Raw flour box A Detail

[0043] Heating contact surface B Detail heated raw meal chute

[0044] Temperature probe

Claims

PATENT CLAIMS 1. A process for the thermal treatment of raw meal (10) for the production of burnt lime (11) or for the activation of clays, characterized by - thermally treating the raw meal (10) or the clay on an electrically heated heating contact surface (115, 215, 315, 415) in a heat exchanger cyclone (110, 210, 310, 410).

2. Plant (100) for carrying out the method according to claim 1, comprising a cyclone heat exchanger (200) in which more than one heat exchanger cyclone (110, 210, 310, 410) is connected in series, within each of which an electrically heated heating contact surface (115, 215, 315, 415) is arranged, which is designed such that the raw meal (10) in the heat exchanger cyclones (110, 210, 310, 410) slides over the electrically heated heating contact surface (115, 215, 315, 415).

3. Plant according to claim 2, 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.

4. Plant according to one of claims 2 or 3, characterized in that the individual heat exchanger cyclones (110, 210, 310, 410) are each connected to one another via a gas riser (111, 211, 311), in which gas flows from a heat exchanger cyclone (210, 310, 410) located upstream in the gas flow direction into a next heat exchanger cyclone (110, 210, 310) located downstream in the gas flow direction, 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 (111, 211, 311), which leads to the heat exchanger cyclone (210, 310, 410) located downstream in the gas flow direction upstream heat exchanger cyclone (210, 310, 410), 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.

5. Plant according to claim 4, characterized in that an additional electrically heated heating contact surface (208, 308, 408) is present in the line (205, 305, 405) for raw meal (10).

6. Installation according to one of claims 2 to 5, characterized in that a control device (150) controls the heating power of each heating contact surface (107, 115, 207, 208, 215, 307, 308, 315, 407, 408, 415) according to a temperature difference, wherein temperature probes (209, 309, 409) measure the temperature at a point in front of the respective heating contact surface (107, 115, 207, 208, 215, 307, 308, 315, 407, 408, 415) and at a point after the respective heating contact surface (107, 115, 207, 208, 215, 307, 308, 315, 407, 408, 415), both points in relation to the raw meal flow direction.

7. Plant according to one of claims 2 to 6, 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 (101), wherein a compressor (620) conveys the gas recirculated in the gas recirculation line (610) to the gas inlet and a slide valve (630) in the gas recirculation line (610) controls the quantity of the recirculated gas.

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