APPARATUS AND PROCESS FOR PRODUCTION OF BURNT LIME OR DOLOMITE

Abstract

An apparatus for production of burnt lime or dolomite has: a shaft furnace having a preheating zone, a reaction zone, a separation zone and a cooling zone; a first feed apparatus for CO.sub.2 at the boundary of the separation zone to the reaction zone; a first removal apparatus at the boundary of the cooling zone to the separation zone; a second removal apparatus for CO.sub.2 at the start of the preheating zone; and at least one heating apparatus.

The shaft furnace also has a third removal apparatus for CO.sub.2 above the reaction zone; the third removal apparatus opens into the second removal apparatus outside the shaft furnace and upstream of the at least one heating apparatus; the second removal apparatus opens into the at least one heating apparatus; and the first feed apparatus is formed by the at least one heating apparatus for the shaft furnace.

Claims

1. Apparatus for production of burnt lime or dolomite, having: a shaft furnace having a preheating zone, a reaction zone, a separation zone and a cooling zone; a first feed apparatus for CO.sub.2 at a boundary of the separation zone to the reaction zone; a first removal apparatus at a boundary of the cooling zone to the separation zone; a second removal apparatus for CO.sub.2 at a start of the preheating zone; and at least one heating apparatus; wherein the shaft furnace also has a third removal apparatus for CO.sub.2 above the reaction zone; the third removal apparatus outside the shaft furnace opens into the second removal apparatus upstream of the at least one heating apparatus; the second removal apparatus opens into the at least one heating apparatus; and the first feed apparatus is formed by the at least one heating apparatus for the shaft furnace.

2. Apparatus according to claim 1, wherein the at least one heating apparatus is a regenerator system, an electrical heating system or a combination thereof.

3. Apparatus according to claim 1, wherein the at least one heating apparatus has a regenerator system, and the latter has at least two regenerators, a first preheater, a feed for fresh air, and a feed for a fuel.

4. Apparatus according to claim 3, wherein the first removal apparatus is connected to the regenerator system.

5. Apparatus according to claim 1, wherein the apparatus has exactly one heating apparatus.

6. Apparatus according to claim 1, wherein there is no heat exchanger in the third removal apparatus.

7. Apparatus according to claim 1, wherein the first removal apparatus is in contact with the second removal apparatus in a form of a second preheater.

8. Apparatus according to claim 1, wherein the second removal apparatus is connected directly to the first feed apparatus via a shortcut conduit upstream of a point at which the third removal apparatus opens into it.

9. Process for producing burnt lime or dolomite in an apparatus having: a shaft furnace having a preheating zone, a reaction zone, a separation zone and a cooling zone; a first feed apparatus for CO.sub.2 at a boundary of the separation zone to the reaction zone; a first removal apparatus at a boundary of the cooling zone to the separation zone; a second removal apparatus for CO.sub.2 at a start of the preheating zone; at least one heating apparatus; and a third removal apparatus for CO.sub.2 above the reaction zone; wherein the third removal apparatus opens into the second removal apparatus outside the shaft furnace and upstream of the at least one heating apparatus; the second removal apparatus opens into the at least one heating apparatus; and the first feed apparatus is formed by the at least one heating apparatus for the shaft furnace; wherein a) limestone or dolomite rock is introduced into the preheating zone of the shaft furnace; b) preheated CO.sub.2 at a temperature T.sub.1 and with a mass flow rate m.sub.1 is introduced into the shaft furnace via the first feed apparatus between separation zone and reaction zone; c) a portion A of the CO.sub.2 with mass flow rate m.sub.3 and temperature T.sub.3 is removed from the shaft furnace via the third removal apparatus above the reaction zone; d) remaining CO.sub.2 with temperature T.sub.2 is removed from the shaft furnace via the second removal apparatus at the start of the preheating zone, a portion B of the CO.sub.2 removed is passed onward with mass flow rate m.sub.B, and a portion C is sent to other uses or suitable deposits with mass flow rate mc; e) portion A of the CO.sub.2 is combined with portion B of the CO.sub.2 to give a mixed gas with temperature T.sub.8, and the mixed gas with temperature T.sub.8 is heated to temperature T.sub.W in the at least one heating apparatus, and the CO.sub.2 with temperature T.sub.W forms at least a portion of the preheated CO.sub.2 which is fed to the shaft furnace in process step b) via the first feed apparatus; f) the burnt lime or dolomite is cooled in the cooling zone by cooling air supplied, and the cooling air with temperature T.sub.8 and mass flow rate m.sub.5 is removed again from the shaft furnace via the first removal apparatus between the cooling zone and the separation zone; and g) the cooled burnt lime or dolomite is discharged from the shaft furnace with temperature T.sub.out and mass flow rate m.sub.out.

10. Process according to claim 9, wherein the process further comprises: h) a portion D of the CO.sub.2 removed in process step d) is fed into the CO.sub.2 preheated to temperature T.sub.W via a shortcut conduit before it is introduced into the shaft furnace.

11. Process according to claim 9, wherein, prior to process step e), portion B of the CO.sub.2 removed in process step d) is heated to temperature T.sub.2V in a preheater by a portion of the cooling air removed in process step f).

12. Process according to claim 9, wherein, in process step e), the at least one heating apparatus comprises at least one regenerator, a preheater, a fresh air feed and a fuel feed, and fresh air is heated to a temperature T.sub.FV in the preheater; the fresh air heated to temperature T.sub.FV for combustion with a fuel selected from carbonaceous fuels and/or hydrogen; and combustion gases formed in the combustion are guided through the at least one regenerator at a temperature T.sub.7 and heat the at least one regenerator to temperature T.sub.RK at a top of the at least one regenerator and T.sub.RF at a bottom of the at least one regenerator.

13. Process according to claim 12, wherein the fresh air heated to temperature T.sub.FV in the preheater is additionally supplied with a portion of the cooling air removed in process step f), and the mixed gas serves for combustion with the fuel selected from carbonaceous fuels and/or hydrogen; and the combustion gases formed in the combustion are directed through the at least one regenerator at the temperature T.sub.7 and heat the at least one regenerator to temperature T.sub.RK at the top of the at least one regenerator and T.sub.RF at the bottom of the at least one regenerator.

14. Process according to claim 9, wherein a combustion temperature in the shaft furnace is controlled by controlling the temperature T.sub.1 while the mass flow rate m.sub.1 is constant, or by controlling the mass flow rate m.sub.1 while the temperature T.sub.1 is constant.

15. Process according to claim 9, wherein reactivity of the burnt lime or dolomite is controlled by controlling the mass flow rate m.sub.out.

Description

[0167] The present invention is elucidated in detail hereinafter by 11 figures with one comparative example and 2 working examples.

[0168] FIG. 1 shows a shaft furnace for burning of lime from the prior art;

[0169] FIG. 2 shows one embodiment of the present invention;

[0170] FIG. 3 shows a further embodiment of the present invention;

[0171] FIG. 4 shows a further embodiment of the present invention;

[0172] FIG. 5 shows a further embodiment of the present invention;

[0173] FIG. 6 shows a further embodiment of the present invention;

[0174] FIG. 7 (A) shows a regenerator system which is operated by a process from the prior art; (B) shows a regenerator system which is operated by the present process; (C) shows a regenerator of a regenerator system;

[0175] FIG. 8 (A) shows the temperature progression in a regenerator system on charging and discharging which is operated by a process from the prior art; (B) shows the temperature progression in a regenerator system on charging and discharging which is operated by the process according to the invention;

[0176] FIG. 9 shows a comparative example according to the prior art;

[0177] FIG. 10 shows a working example 1 of the present invention;

[0178] FIG. 11 shows a working example 2 of the present invention.

[0179] FIG. 1 shows a shaft furnace 280 for burning of lime from the prior art. In the shaft furnace 280, lime is added via the feed 290. The shaft furnace 280 has a preheating zone 300, a reaction zone 310 and a cooling zone 320. Between cooling zone 320 and reaction zone 310, air and fuel are introduced into the shaft furnace 280 via a fuel and air feed 250. The combustion reaction in the shaft furnace 280 generates sufficient energy to deacidify the lime. At the bottom end of the cooling zone 320, cooling air is introduced via the feed 260 in order to cool the burnt lime before the lime discharge 270. These processes from the prior art do not offer any technical means of generating highly concentrated CO.sub.2 within the process that can be sent directly to further utilization and/or compressed and stored in suitable deposits. Alternatively, it is possible to use solely downstream CO.sub.2 separation methods that entail considerable energy expenditure and financial investment.

[0180] FIG. 2 shows one embodiment of the present invention. The shaft furnace 20 has a preheating zone 21, a reaction zone 22, a separation zone 23 and a cooling zone 24. The limestone is introduced into the shaft furnace at the start of the preheating zone via the limestone feed 10. The lime is at a temperature T.sub.KS and is introduced into the shaft furnace 20 at a mass flow rate mics. CO.sub.2 at temperature T.sub.1 with a mass flow rate m.sub.1 is introduced into the shaft furnace 20 via the first feed apparatus 40 at the boundary of the separation zone 23 to the reaction zone 22. The temperature T 1 and mass flow rate m.sub.1 of the CO.sub.2 are chosen such that sufficient energy is introduced into the shaft furnace 20 to deacidify the limestone in the reaction zone 22. Above the reaction zone 22, a portion A of the CO.sub.2 is removed from the shaft furnace 20 via the third removal apparatus 80 at a temperature T 3 and a mass flow rate m.sub.3. At the start of the preheating zone 21, at the top of the shaft furnace 20, the remaining CO.sub.2 is drawn off from the shaft furnace 20 via the second removal apparatus 70. The remaining CO.sub.2 is at a temperature T.sub.2 and is drawn off at a mass flow rate m.sub.2. The removal apparatus 70 has a filter 200 for dedusting of CO.sub.2 and a fan 210 for conducting the CO.sub.2 onward in the removal apparatus. A portion m.sub.C of the CO.sub.2 is removed from the process. This portion can be provided for further utilization in other processes and/or compressed and stored in suitable deposits.

[0181] A portion m.sub.B of the CO.sub.2 in the second removal apparatus 70 is passed onward. The third removal apparatus 80 opens into the second removal apparatus 70, and the CO.sub.2 gas streams passed onward in the two removal apparatuses are mixed with one another. The CO.sub.2 which is subsequently passed onward in the second removal apparatus 70 then has a temperature T.sub.8 and a mass flow rate m.sub.8. Before the CO.sub.2 is directed into the heating apparatus 140 at temperature T.sub.8, it is dedusted again in a hot gas filter or hot gas cyclone 201 and passes through a hot gas fan 211. The CO.sub.2 is heated to a temperature T.sub.W in the heating apparatus 140. According to the invention, the heating apparatus may be a regenerator system 90, an electrical heating system 100 or a combination of these. After leaving the heating apparatus, the CO.sub.2 arrives back in the shaft furnace 20 via the first feed apparatus. In this embodiment, the temperature T.sub.W corresponds to the temperature T.sub.1. A portion of the CO.sub.2 thus flows in a circuit and introduces the energy required for the deacidification reaction inter alia into the shaft furnace 20.

[0182] There is therefore a virtually pure CO.sub.2 atmosphere in the shaft furnace 20 within the preheating zone 21 and the reaction zone 22. At the end of the cooling zone 24, cooling air is introduced into the shaft furnace 20 at a mass flow rate m.sub.air via the second feed device 50. The cooling air is at a temperature T.sub.air and cools the burnt lime in the cooling zone 24. At the boundary of the cooling zone 24 to separation zone 23, the cooling air heated to temperature T.sub.5 is drawn off again from the shaft furnace 20 at a mass flow rate m.sub.5. Since the separation zone 23 is between the cooling zone 24 and the reaction zone 22, a separation of the CO.sub.2 atmosphere in the preheating zone 21 and reaction zone 22 from the air atmosphere in the cooling zone 24 is enabled. The cooling air removed at temperature T.sub.5 can be utilized further within the process in accordance with the invention in the apparatus or in the process, or else not be utilized further within the process.

[0183] The burnt lime is discharged from the shaft furnace by an apparatus for discharge 30 with temperature T.sub.out and mass flow rate m.sub.out.

[0184] The inventive apparatus 1000 thus makes it possible to use CO.sub.2 as an energy carrier in order to introduce the energy demand for the deacidification reaction into the shaft, where the CO.sub.2 is circulated, or excess CO.sub.2 is sent to a further use and/or compressed and stored intermediately in suitable deposits. Furthermore, no combustion reaction takes place within the shaft furnace 20, which means that no fuels or ashes thereof are introduced into the shaft furnace 20.

[0185] The removal of portion A of the CO.sub.2 via the third removal apparatus 80 reduces the exit temperature T.sub.2 of the remaining CO.sub.2 on removal from the furnace via the second removal apparatus 70. Because of the reduced temperature at the top of the furnace, the loss of energy that occurs as a result of the removal of the CO.sub.2 stream m.sub.C from the overall process is significantly reduced compared to prior art processes. The heat capacity flow ratio of CO.sub.2 to limestone in the present invention is advantageously in the range from 1 to 2.0, preferably in the range from 1 to 1.6, more preferably in the range from 1 to 1.2. The CO.sub.2 filters and fans in the second removal apparatus 70 may also advantageously be designed for correspondingly lower temperatures.

[0186] FIG. 3 shows a further embodiment of the present invention. The construction is the same as is described in FIG. 2. The heating apparatus 140 in this embodiment is a regenerator system 90. The regenerator system 90 has two regenerators 91, 92 that can be charged and discharged in alternation. The CO.sub.2 flows through the second removal apparatus 70 with mass flow rate m.sub.8 and temperature T.sub.8 at the bottom of the charged regenerator, where it is heated to temperature T.sub.W, and it is fed back to the shaft furnace 20 from the top of the regenerator via the first feed apparatus 40. In this embodiment, temperature T.sub.W corresponds to temperature T.sub.1 with which the CO.sub.2 is introduced into the shaft furnace 20. The regenerators 91, 92 of the regenerator system 90 are charged with a combustion gas. The regenerator system 90 also has a first preheater 93. A feed of fresh air 94 directs fresh air at temperature T.sub.F into the preheater with a mass flow rate m.sub.F, where it is heated to temperature T.sub.FV. In this embodiment, the cooling air removed from the shaft furnace 20 at the boundary of the cooling zone 24 to the separation zone 23 via the first removal apparatus 60 is mixed with the heated fresh air at temperature T.sub.FV, and the mixed gas serves as combustion air for the combustion. Before the fresh air is mixed with the cooling air, the cooling air at temperature T.sub.5 is dedusted beforehand in a suitable hot gas filter or hot gas cyclone 202 in order to keep the introduction of dust into the regenerator system 90 as small as possible.

[0187] The combustion gas is created by feeding in a fuel via a feed of fuel 95. The combustion air used here is the heated fresh air and the heated cooling air. The combustion gas at a temperature T.sub.7 which is generated in the combustion of the fuel is directed through the regenerators 91, 92, in order to charge these. The combustion gas is introduced at the top of the regenerator, heats it to a temperature T.sub.RK, and is led off again at the bottom of the regenerator. This heats the bottom of the regenerator to a temperature T.sub.RF. The combustion gas led off at the bottom of the regenerator is advantageously directed through the first preheater 93, which means that the residual heat in the combustion gas can be utilized for heating of the fresh air. In order to remove the cooling air from the shaft furnace, to suck in the fresh air and then to direct the combustion gas through the regenerator, it is possible to use a fan 212.

[0188] FIG. 4 shows a further embodiment of the present invention, wherein the construction is similar in principle to that in FIG. 2. This embodiment has a connection via a shortcut conduit 71 from the second removal apparatus 70 to the first feed apparatus 40. The shortcut conduit allows a portion D of the CO.sub.2 removed by suction via the second removal apparatus 70 at the top of the furnace with a temperature T.sub.2 and a mass flow rate m.sub.D to be introduced into the first feed apparatus 40. This makes it possible to control the temperature T.sub.1 of the CO.sub.2 which is introduced into the shaft furnace 20. The introduction of the CO.sub.2 with temperature T.sub.2 via the mixing conduit 71 allows fluctuations in the temperature T.sub.W with which the CO.sub.2 comes from the heating apparatus 140 to be balanced out. The mixing conduit 71 may have a fan 214.

[0189] If the heating apparatus 140 comprises a regenerator system 90, particularly the discharge operation of the regenerator 91, 92 in the regenerator system 90 can lead to periodic fluctuations in the temperature T.sub.W with which the CO.sub.2 exits from the regenerator 91, 92. Without further control, temperature T.sub.W will correspond to the temperature T.sub.1 with which the CO.sub.2 is introduced into the shaft furnace 20. In that case, the shaft furnace 20 will then be charged with CO.sub.2 having a periodically fluctuating temperature. This also means an energy input into the shaft furnace 20 that fluctuates over time. These fluctuations will affect the temperatures in the shaft furnace, which will correspondingly likewise be subject to fluctuations. Fluctuating temperatures in the shaft furnace are a barrier to uniform lime quality. The apparatus according to the invention and the process according to the invention can avoid the fluctuations in energy input and hence in combustion temperature. In particular, the controlling of temperature T.sub.1 via the supply of CO.sub.2 at temperature T.sub.2 via the shortcut conduit 71 to the CO.sub.2 at temperature T.sub.W from the heating apparatus enables the desired control of temperature. Depending on the mixing ratio of CO.sub.2 at temperature T.sub.W and CO.sub.2 at temperature T.sub.2, the temperature T.sub.1 can be adjusted and hence controlled.

[0190] In addition, FIG. 4 shows an apparatus 1000 in which a portion X of the cooling air removed via the first removal apparatus 60 is directed into the second preheater 120. The heated cooling air is removed from the shaft furnace with temperature T.sub.5 and mass flow rate m.sub.5. The cooling air is dedusted by means of a suitable hot gas filter or hot gas cyclone 202. A portion X is fed to the second preheater 120 and hence utilized to heat the mass flow m.sub.B to a temperature T.sub.2V. The cooling air is led off downstream of the second preheater. For this purpose, it is possible to use suitable fans 213. The portion X of the cooling air may be all the cooling air removed from the shaft furnace 20 or else only a portion thereof. If the heating apparatus 140 comprises a regenerator system, it is possible to direct a portion Y of the cooling air removed into the regenerator system 90, where it can be used as combustion gas as already described. The proportions X and Y may if required be divided between 0% and 100%, where X+Y=100%.

[0191] FIG. 5 shows a further embodiment of the present invention, wherein the construction is similar in principle to that in FIG. 4. The heating apparatus 140 used is an electrical heating system 100. The CO.sub.2 is directed into the electrical heating system via the second removal apparatus 70, where it is heated to temperature T.sub.W. It is directed from the electrical heating system via the first feed apparatus 40 into the shaft furnace 20.

[0192] FIG. 6 shows an embodiment of the present invention that has all the features of the invention already described. The heating apparatus 140 in this embodiment is designed as a combination of a regenerator system 90 with an electrical heating system 100. The apparatus 1000 has both a shortcut conduit 71 and a second preheater 120. The cooling air drawn off via the first removal apparatus 60 is partly directed into the second preheater 120 and partly into the regenerator system 90.

[0193] FIG. 7(A) shows a regenerator system 400 which is operated by a process from the prior art. For charging, combustion gas flows through the regenerator 401. For combustion, lean gas is directed through the preheater 420 via the feed 420 and heated. The heated lean gas is utilized as fuel. The combustion air fed in is cooling air 410 which is removed from the shaft furnace. The combustion gas formed in the combustion is directed into the regenerator 401, which results in charging thereof. The residual heat in the offgas flowing out at the bottom of the regenerator is directed through the preheater 403 and hence utilized for heating of the lean gas. The lean gas used is, for example, blast furnace gas or steel gas. These regenerator systems 400 are used according to the prior art in the steel industry, where the gases mentioned are available.

[0194] FIG. 7 (B), with respect to FIG. 7 (A), once again shows a regenerator system 90 which is operated by the present process. This regenerator system 90 enables the flexible utilization of fossil or renewable fuels. In particular, the regenerator system 90 can advantageously be used in the lime industry, in which lean gases, for example blast furnace gas, are unavailable. High-energy fuels are used in the lime industry, for example natural gas. However, these cannot be used in regenerator systems 400 from the prior art, since the high-energy fuels cannot be heated in a preheater. The regenerator system 90 according to the present invention remedies this disadvantage and hence enables uncomplicated use of the invention in the lime industry. A detailed description of the mode of function of the regenerator system 90 can be found in the description of FIG. 3.

[0195] FIG. 7 (C) shows a regenerator 91 of the regenerator system 90. At the top of the regenerator 96, the combustion gas is introduced 98 and flows through the regenerator 91 on charging, and leaves it again at the bottom of the regenerator 97 via the outlet 99. The regenerator 91 is heated to temperature T.sub.RK at the top of the regenerator 96, and to temperature T.sub.RF at the bottom of the regenerator 97.

[0196] On discharge, the CO.sub.2 flows into the regenerator via the second removal apparatus 70 at temperature T.sub.8 at the bottom of the regenerator 97, flows through it and leaves the regenerator 91 at the top of the regenerator 96 with temperature T.sub.W via the first feed apparatus 40.

[0197] FIG. 8 (A) shows the temperature progression in a regenerator system 400 from the prior art, as shown in FIG. 7 (A), on charging and discharging. In the diagram i), the regenerator 401 is charged by the feeding 410 of a combustion gas. The combustion gas forms as a result of the combustion of cooling air (feed via cooling air feed 410) which is removed from a shaft furnace with a fuel (feed via fuel feed 420). The mass flow of the combustion gas is therefore determined to a crucial degree by the mass flow of the cooling air. The combustion gas is typically at a high temperature above 2000 C. At the top of the regenerator 96, the storage medium of the regenerator 401 is therefore charged to a temperature above 2000 C. Over the entire length x of the regenerator, the combustion gas releases thermal energy to the storage medium, and leaves the regenerator 401 at the bottom of regenerator 97 typically at a temperature of about 700 C. The diagram ii) shows the discharging of the regenerator 401. CO.sub.2 is typically introduced into the bottom of the regenerator 97 at a temperature of about 700 C. via the CO.sub.2 feed 440 and directed through the entire length x of the regenerator. At the top of the regenerator 96, the CO.sub.2 leaves the regenerator 401 via the outlet 450 at a temperature T.sub.1. At the changeover from charging to discharging, the top of the regenerator 96 is therefore supplied firstly with combustion gases at a temperature of above 2000 C. and, straight after the changeover to discharging, with CO.sub.2 at a temperature T.sub.1. The heat capacity flow ratio between combustion gas that flows through the regenerator system on charging and CO.sub.2 that flows through the regenerator system on discharging is well above 1.5, typically in the range from 2 to 2.5 (Yang et al.). At the top of the regenerator 96, the temperature level fluctuates significantly, such that great thermal stresses arise in the storage material. This leads to the numerous disadvantages already described.

[0198] FIG. 8 (B), by contrast, shows the temperature progression in a regenerator system 90 according to the present invention, as shown in FIG. 7 (B), on charging and discharging. In the diagram i), the regenerator 9 is charged by the supply of a combustion gas 98. The combustion gas forms as a result of the combustion of fresh air (supply via fresh air feed 94) and optionally cooling air (supply via first removal apparatus 60), which is drawn off from the shaft furnace, with a fuel (supply via fuel feed 95). The mass flow rate of the combustion gas is determined to a crucial degree by the mass flow rate of the fresh air and is therefore flexibly adjustable. This makes it possible to adjust the heat capacity flow ratio between combustion gas that flows through the regenerator system on charging and CO.sub.2 that flows through the regenerator system on discharging in such a way that it is in the range from 0.9 to 1.1. At the top of the regenerator 96, a significantly smaller thermal stress thus acts on the regenerator material. This has a positive effect on the service life of the storage material of the regenerator and hence on the maintenance intensity thereof. The economic viability of the overall process is thus significantly increased.

[0199] The combustion gas may, for example, have a temperature of about 1450 C. At the top of the regenerator 96, the storage medium in the regenerator 91 is therefore charged to a temperature of about 1450 C. Over the entire length x of the regenerator, the combustion gas releases thermal energy to the storage medium, and at the bottom of the regenerator 97 leaves the regenerator 401 typically at a temperature of about 800 C. Diagram ii) shows the discharging of the regenerator 91. CO.sub.2 is typically introduced into the bottom of the regenerator 97 at a temperature of about 700 C. via the second removal apparatus 70 and directed through the entire length x of the regenerator. At the top of the regenerator 96, the CO.sub.2 leaves the regenerator 91 via the first feed apparatus 40 at a temperature of, for example, 1350 C. At the changeover from charging to discharging, the top of the regenerator 96 is therefore supplied firstly with combustion gases at a temperature of about 1450 C. and, straight after the changeover to discharging, with CO.sub.2 at a temperature of about 1350 C. The difference in temperature at the top of the regenerator 96 is thus significantly reduced, which means that the thermal stresses that occur are also significantly decreased.

[0200] FIGS. 9 to 11 show a comparative example according to the prior art and two working examples of the invention. For these examples, it was assumed that complete physical separation of the gas atmospheres (CO.sub.2 in the reaction zone and cooling air in the cooling zone) is assured. All process parameters such as temperatures and mass flow rates are specified in examples. In addition, the energy flows that are introduced or removed are specified. These were identified in each case by the symbol E and the addition already used for the corresponding temperature and the corresponding mass flow rate. All energy flows reported in the examples are based on a reference temperature of 0 C.

Comparative Example 1

[0201] FIG. 9 shows a process example according to the prior art. All the CO.sub.2 which is fed to the shaft furnace 20 via the feed apparatus 40 and exits from the limestone during the deacidification flows in the direction of the top of the furnace and is removed via the removal apparatus 70. The heating apparatus 140 is supplied with the flow of energy required for the process. For comparability, it was assumed by way of simplification that this flow of energy can be utilized entirely for heating of the CO.sub.2 (mass flow rate m.sub.8), and that no heat losses occur, for example, as a result of a combustion process. The heating apparatus here is otherwise unspecified. The heated cooling air which is removed from the shaft furnace 20 via the removal apparatus 60 is not utilized further within the process.

Working Example 1

[0202] FIG. 10 shows an embodiment of the present invention that increases the energy efficiency of the process example shown in FIG. 9 according to the prior art. Proceeding from the process example in FIG. 9, according to the invention, the third removal apparatus 80 is used for this purpose, by means of which a portion of the CO.sub.2 flowing upward within the shaft furnace 20 is removed and then mixed with the remaining CO.sub.2 from the top of the furnace, heated, and supplied again to the shaft furnace 20 via the feed apparatus 40. Thus, not all the CO.sub.2 flows in the direction of the top of the furnace, and the mass flow rate m.sub.2 and temperature T.sub.2 are lowered by comparison. As a result, the CO.sub.2 flow rate m.sub.C leaves the process at a lower temperature, which reduces the loss of heat by comparison. This likewise becomes clear by virtue of the lower energy demand for heating of the circulating CO.sub.2 (mass flow rate m.sub.8) through the heating apparatus 140.

Working Example 2

[0203] FIG. 11 shows an embodiment of the present invention having all the features of the invention that have already been described. The process according to the invention was conducted by the embodiment of the invention shown. All the cooling air sucked out by the first removal apparatus 60 was fed here to the second preheater 120. The heating apparatus used was a regenerator system 90. The combustion gas for the loading of the regenerator system 90 was created by the supply of natural gas L as fuel and heated fresh air at temperature T.sub.FV.

LITERATURE

[0204] [Maerz Ofenbau A G] Maerz Ofenbau A G, Sustainable lime burning technology with shaft kilns, ZKG 6/2021 [0205] [Yang et al.] Yang et al., Novel Lime Calcination Systems for CO.sub.2 Capture and its Thermal-Mass Balance Analysis, ACS Omega, 5 (42), 27413-27424, 2020 [0206] [Schiele/Berens] E. Schiele/L. W. Berens, Kalk [Lime], Verlag Stahleisen M. B. H. Dusseldorf, 1972, page 190, section 4.3.4.4

LIST OF REFERENCE NUMERALS

[0207] 10 limestone input [0208] 20 shaft furnace [0209] 21 preheating zone [0210] 22 reaction zone [0211] 23 separation zone [0212] 24 cooling zone [0213] 30 apparatus for discharging burnt lime [0214] 40 first feed apparatus [0215] 50 second feed apparatus [0216] 60 first removal apparatus [0217] 70 second removal apparatus [0218] 71 shortcut conduit [0219] 80 third removal apparatus [0220] 90 regenerator system [0221] 91, 92 regenerator [0222] 93 first preheater [0223] 94 feed for fresh air [0224] 95 feed for fuel [0225] 96 top of regenerator [0226] 97 bottom of regenerator [0227] 98 combustion gas feed [0228] 99 offgas outlet [0229] 100 electrical heating system [0230] 120 second preheater [0231] 140 heating apparatus [0232] 200 filter [0233] 201 filter [0234] 202 filter [0235] 210 fan [0236] 211 fan [0237] 212 fan [0238] 213 fan [0239] 214 fan [0240] 250 fuel supply and air supply [0241] 260 cooling air supply [0242] 270 lime discharge [0243] 280 shaft furnace [0244] 290 limestone feed [0245] 300 preheating zone [0246] 310 reaction zone [0247] 320 cooling zone [0248] 400 regenerator system [0249] 401 regenerator [0250] 402 regenerator [0251] 403 preheater [0252] 410 cooling air feed [0253] 420 fuel feed [0254] 430 offgas outlet [0255] 440 CO.sub.2 feed [0256] 450 CO.sub.2 outlet [0257] 1000 apparatus