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

Abstract

The invention relates to a plant (200, 300) for the thermal treatment of raw meal for the production of burnt lime, comprising a reactor (205, 305) within which the electrically heated heating contact is arranged, which is designed such that the raw meal (10) slides over the electrically heated heating contact, According to the invention, the electrically heated heating contact consists of a plurality of electrically heated sliding surfaces (210, 310) arranged in pairs offset from one another and vertically one above the other, so that the raw meal (10) slides from above as if via cascades between the sliding surfaces (210, 310) arranged in pairs, wherein the sliding surfaces (210, 310) are arranged in the reactor (105) and wherein the sliding surfaces (210, 310) have openings through which gas generated during the thermal treatment flows and additionally heats the raw meal (10) sliding over the sliding surfaces (210, 310).

Description

[0001] The invention relates to a plant for the thermal treatment of raw meal for the production of burnt lime.

[0002] To produce burnt lime (CaO), it is known that lime (CaCO3) from natural deposits is finely ground into so-called raw meal, suspended in a gas stream, dried, and then subjected to thermal treatment. Burnt lime (CaO), along with other substances, is a raw 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 is called differently 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 burnt lime is also referred to as 'raw meal'.For the calcination, i.e. the thermal treatment of lime (CaCO3) in the form of raw meal, it is usually placed in an entrained-flow reactor into which a flame extends or, depending on the further process, hot exhaust gases from a downstream rotary kiln are fed. During this thermal treatment, not only is carbon dioxide (CO2) formally driven out of the natural lime (CaCO3), which is an endothermic process, but due to the high activation energy, a comparatively high temperature of approximately 800°C is necessary to trigger the thermolysis of the lime (CaCO3). To generate the high temperature, fuel must be burned, and the flame enters the entrained-flow reactor. The exhaust gases from the calcination process contain carbon dioxide (CO2) from the burnt lime (CaCO3) and also carbon dioxide (CO2) from the combustion of fossil fuels. In addition to carbon dioxide (CO2), the exhaust gas also contains nitrous gases (NO). x) and other exhaust gas components, such as volatile organic compounds (VOCs). In order to sequester carbon dioxide (CO2), which is recognized as harmful to the climate, the exhaust gas must be subjected to a purification process to separate atmospheric nitrogen (N2), the nitrous gases, and the VOCs from the exhaust gas before sequestration.

[0003] The online publication http: / / web.archive.org / web / 20230810231918 / https: / / www.ibu-tec.de / anlagen / drehrohrofen / (archived on August 10, 2023) reports on rotary kilns for calcining lime. In one example, the required heat is generated electrically.

[0004] German patent application DE 10 2023 202 994 A1 discloses a device and method for burning limestone. In the device, lime is burned in a rotary kiln, with the heat for this being generated electrically.

[0005] German patent application DE 44 31 508 A1 discloses a lime burning process and a corresponding device. The lime is burned in a vacuum furnace, which in one embodiment can also be electrically heated.

[0006] It would be desirable to conduct the process for the thermal treatment of lime in such a way that the complex exhaust gas purification before sequestration is not necessary.

[0007] The object of the invention is therefore to provide a plant for the thermal treatment of lime in which exhaust gas purification before sequestration of carbon dioxide (CO2) is unnecessary.

[0008] The object of the invention is achieved by a system having the features of claim 1. Further advantageous embodiments of the system are specified in the subclaims to claim 2.

[0009] According to the concept of the invention, it is therefore provided that the raw meal, regardless of whether it is mixed with silicate-containing rock, as is common in the cement industry, or whether the raw meal is present as pure ground lime, is heated at an electrically heated heating contact. In order to transfer the necessary amount of heat to the raw meal, it can be advantageous in a design of the plant according to the invention for the speed at which the raw meal is guided past the electrically heated heating contact to be slowed down by a structural arrangement of sliding surfaces as an electrically heated heating contact. For this purpose, it is provided that the electrically heated heating contact consists of several electrically heated sliding surfaces arranged in pairs offset from one another and vertically one above the other, so that the raw meal slides from top to bottom between the paired sliding surfaces as if in cascades, whereby the sliding surfaces are arranged in the reactor.The several electrically heated sliding surfaces, arranged in pairs offset from one another and vertically one above the other, act like baffles that slow down the flow of raw meal as the raw meal trickles from top to bottom over the sliding surfaces.

[0010] Furthermore, the sliding surfaces are designed to have openings through which gas produced during the thermal treatment flows and additionally heats the raw meal sliding over the sliding surfaces. The openings are open to the side and towards the sliding raw meal so that the raw meal does not fall through the openings. The gas coming from below, however, flows through the openings and thus also flows through the sliding raw meal. During this mixing, the heat present in the gas is transferred to the raw meal, heating it additionally. The flow of the hot exhaust gases from the thermal treatment at lower levels of the electrically heated heating contact thus means recuperation of the heat electrically introduced into the raw meal.

[0011] All reactor types presented here feature a vapor outlet. The vapors, which consist primarily of carbon dioxide (CO2) and water (H2O), still contain suspended raw meal. The suspended raw meal can be separated in a cyclone separator. The exhaust gas exiting the cyclone separator can also be passed through a heat exchanger to extract the heat from the vapors as process heat. Since this heat is not very high, the heat recovered from the vapors is suitable for drying other materials.

[0012] The invention presented here, the electrical firing of raw meal, whether with silicate-containing rock or as pure lime flour, initially appears very costly and therefore unattractive. However, if electrical energy can be generated from process heat elsewhere or from renewable energies, then electrical firing, combined with the necessary sequestration of the carbon dioxide (CO2) produced during firing, is a highly attractive option, both from an economic and climate-balance perspective.

[0013] The invention is explained in more detail with reference to the following figures. It shows: Fig. 1 a plant for the thermal treatment of raw meal using an electric heating device, Fig. 2 a plant for the thermal treatment of raw meal using an electric heating device in a further embodiment.

[0014] In Fig. 1 shows a system 200 for the thermal treatment of raw meal 10 using an electric heating device. The system 200 is characterized in that the sliding surfaces 210 have openings through which vapors 215 and carbon dioxide (CO2), both generated on the lower sliding surfaces 210, can flow through the upper sliding surfaces 210. The exhaust gas, namely the hot vapors 215 and the hot carbon dioxide (CO2), flows through the raw meal 10 on the upper sliding surfaces 210, thereby additionally heating the raw meal trickling there. This additional heating of the raw meal 10 means a recuperation of the waste heat generated at the temperature necessary for the thermolysis of the lime (CaCO3) to burnt lime (CaO). To prevent the raw meal from falling through the openings, the openings are provided with a partial compartment surface D in the sliding direction. This partial roof surface D is shown more clearly in the enlarged view of detail A.Here, the reactor 205 shown is equipped with a gas vent at the top 204 of the reactor 205. This gas vent arrangement results in a countercurrent gas flow within the reactor 205, which is represented by vertical arrows drawn in the reactor 205. The gas flows upward into the gas vent in the top 204 of the reactor 205, while the finished burnt or calcined product falls into the base 206 of the reactor 205. There, the finished burnt or calcined lime is discharged through a rotary valve 213. The burnt or calcined lime 11 separated in the dust separator 207 is combined with the product from the rotary valve 213. The exhaust gas, on the other hand, flows through a flow regulator 214 and compressor 216 for further sequestration.

[0015] In Fig. 2 shows a plant 300 for the thermal treatment of raw meal 10 using an electric heating device in a third embodiment. Unlike the cascade-like sliding surfaces 210 in the previously mentioned embodiments, in this embodiment the sliding surfaces 310 are electrically heated heating contacts, closely spaced and wave-shaped sliding surfaces 310, which form a meandering or undulating gap between them, running essentially from top to bottom. Within the gap between two sliding surfaces 310, a mixing movement is formed by a trickling of the raw meal 10 and a gas countercurrent, in which the raw meal 10, which is present with the already partially burned or calcined lime 11, is swirled up, similar to a countercurrent reactor. The gas countercurrent has a heat-recovering effect, which already applies to the embodiment of the plant in Fig.2. It is important here that the distance between the two sliding surfaces 310 is not too wide, so that a separation cannot occur between the trickling of the raw meal and the upward flow of the exhaust gas. On the other hand, the distance must not be so small that the raw meal 10 falls as if through a pipe and rolls towards the upward flowing gas, so that the gas and the freely trickling raw meal 10 mutually block each other's path. The sliding surfaces 310 are connected on one side to resistance heaters 311. The gas flows upward into the gas outlet in the head 304 of the reactor 305, while the finished burnt or calcined product falls into the base 306 of the reactor 305. There, the finished burnt or calcined lime is discharged through a rotary valve 313. The burnt or calcined lime 11 separated in the dust separator 307 is combined with the product coming from the rotary valve 313.The exhaust gas, on the other hand, flows through a flow regulator 314 and compressor 316 for further sequestration. LIST OF REFERENCE SYMBOLS 10 Raw flour, unburned 11 Raw flour, roasted 12 Raw flour, roasted 200 system 201 Rotary valve 204 Head (Reactor) 205 reactor 206 feet (reactor) 207 cyclone separators 208 Coarse material discharge 209 Fines / Gas outlet 210 sliding surface 211 resistance heating 213 Rotary valve 214 flow regulator 215 brothers 216 compressors 300 system 301 Rotary valve 304 Head (Reactor) 305 reactor 306 feet (reactor) 310 sliding surface 311 resistance heating 313 Rotary valve 314 Flow regulator 315 brothers 316 compressors A Detail D Partial roof area

Claims

[1] Plant (200, 300) for the thermal treatment of raw meal for the production of burnt lime, comprising a reactor (205, 305) within which the electrically heated heating contact is arranged, which is designed such that the raw meal (10) slides over the electrically heated heating contact, characterized by , that the electrically heated heating contact consists of several electrically heated sliding surfaces (210, 310) arranged in pairs offset from one another and vertically one above the other, so that the raw meal (10) slides from top to bottom as if via cascades between the sliding surfaces (210, 310) arranged in pairs, wherein the sliding surfaces (210, 310) are arranged in the reactor (105) and wherein the sliding surfaces (210, 310) have openings through which gas generated during the thermal treatment flows and additionally heats the raw meal (10) sliding over the sliding surfaces (210, 310). [2] Plant according to claim 1, characterized by that the electrically heated heating contact consists of several vertically arranged and wave-shaped sliding surfaces (310) which are arranged parallel to one another and form an undulating gap between them in pairs. [3] Plant according to one of claims 1 or 2, characterized by that the reactor (205, 305) has at least one discharge opening for the vapors produced during the thermal treatment, which is connected to a dust separator (212, 312) which separates raw meal (10) from the vapors. [4] Plant according to claim 3, characterized by that a heat exchanger is arranged in the gas path, which dissipates heat from the escaping vapors.

Images