THERMAL TREATMENT OF MINERAL MATERIALS IN A REDUCING ATMOSPHERE USING ALTERNATIVE FUELS

Abstract

An apparatus for thermal treatment of mineral materials may include a first combustion chamber, a second combustion chamber, and a reactor for the thermal treatment of mineral materials. The first combustion chamber is configured for burning a first fuel fed by a first fuel feed device, and the first combustion chamber and the second combustion chamber are connected via a first conduit for transferring hot gases from the first combustion chamber into the second combustion chamber. The second combustion chamber is configured for burning a second fuel that is different than the first fuel and is fed by a second fuel feed device. The second combustion chamber and the reactor are connected via a second conduit for transferring hot gases from the second combustion chamber into the reactor. The reactor has a third feed conduit for introducing a third fuel.

Claims

1.-10. (canceled)

11. An apparatus for thermal treatment of mineral materials, the apparatus comprising: a first combustion chamber configured to burn a first fuel, with the first combustion chamber comprising a first fuel feed device for introducing the first fuel; a second combustion chamber configured to burn a second fuel that is different than the first fuel, the second combustion chamber being connected to the first combustion chamber via a first conduit for transferring hot gasses from the first combustion chamber into the second combustion chamber, wherein the second combustion chamber comprises a second fuel feed device for introducing the second fuel; and a reactor for thermal treatment of mineral materials, wherein the second combustion chamber and the reactor are connected via a second conduit for transferring hot gases from the second combustion chamber into the reactor, wherein the reactor has a third fuel feed conduit for introducing a third fuel.

12. The apparatus of claim 11 wherein the first fuel is coal, coal dust, oil, natural gas, biogas, methane, ethane, propane, butane, or hydrogen, wherein the second fuel is a substitute fuel.

13. The apparatus of claim 11 wherein the first combustion chamber includes a first oxygen feed device, wherein the second combustion chamber includes a second oxygen feed device, wherein at least one of the second combustion chamber, the second conduit, or the reactor includes a sensor for measuring oxygen content.

14. The apparatus of claim 11 wherein the second combustion chamber is configured to burn the second fuel on a grate.

15. The apparatus of claim 11 wherein the reactor is a calciner.

16. The apparatus of claim 11 wherein the reactor is an entrained-flow calciner.

17. The apparatus of claim 11 wherein the reactor is a rotary tube furnace.

18. A process for thermally treating mineral materials, the process comprising: combusting a first fuel in a first combustion chamber; transferring hot gasses from the first combustion chamber into a second combustion chamber; combusting a second fuel in the second combustion chamber; transferring hot gasses from the second combustion chamber into a reactor; and substoichiometrically combusting a third fuel in the reactor and thermally treating mineral materials.

19. The process of claim 18 comprising regulating introduction of the third fuel for substoichiometric combustion based on a color of the thermally treated mineral materials after removal from the reactor.

20. The process of claim 18 comprising regulating introduction of the third fuel for substoichiometric combustion based on a measured parameter, wherein the measured parameter is oxygen content in the second combustion chamber, oxygen content in a connection between the second combustion chamber and the reactor, oxygen content in the reactor, or a property of a product of the thermally treated mineral materials after removal from the reactor.

21. The process of claim 18 wherein thermally treating the mineral materials is performed at an oxygen partial pressure pO.sub.2 of less than 10.sup.−8 bar.

22. The process of claim 18 wherein thermally treating the mineral materials is performed at an oxygen partial pressure pO.sub.2 of less than 10.sup.−11 bar.

23. The process of claim 18 wherein thermally treating the mineral materials is performed at a volume ratio of CO.sub.2/CO of less than 1000.

24. The process of claim 18 wherein thermally treating the mineral materials is performed at a volume ratio of CO.sub.2/CO of less than 50.

25. The process of claim 18 wherein thermally treating the mineral materials is performed at an air index of less than 1.

26. The process of claim 18 wherein thermally treating the mineral materials is performed at an air index of between 0.70 and 0.99.

27. The process of claim 18 wherein thermally treating the mineral materials is performed at an air index of between 0.85 and 0.98.

Description

[0065] FIG. 1 shows a schematic view of the apparatus of the invention. The apparatus comprises at least the following elements. An entrained flow calciner 4 comprises a product inlet opening 4a, a product outlet opening 4d for discharge of the calcined mixture 1b produced and a fuel gas opening 4c. The product inlet opening 4a is preferably arranged above the fuel gas opening 4c in the flow direction of the fuel gas. As a result of this arrangement, a suspendable mineral mixture 1a (e.g. clay minerals) which can be entrained in the fuel gas stream can be conveyed, after preheating in preheating stages, e.g. cyclone preheaters 9, by the fuel gas stream or calcination stream 2 through the entrained-flow calciner 4 and is calcined within the entrained-flow calciner 4. A combustion chamber 16 is connected to the fuel gas opening 12a and a combustion gas feed conduit 12b (for example for air or air mixtures having a varying oxygen content) and a fuel feed conduit 13. Valves 6 make it possible to regulate the combustion gas feed conduit 12b. The combustion chamber 16 further comprises a combustion on a grate 3. The combustion on a grate 3 makes it possible for solid, liquid or highly viscous fuels or combustible waste materials to be burnt and utilized. A residue opening 4b makes it possible to remove the fuel residues which do not burn. The fuel present in the combustion chamber 16 is ignited by an ignition burner 14 with fuel introduction conduit 15. Furthermore, a product feed conduit 8 is connected to the product inlet opening 4a. In addition, an air feed conduit 7 for an additional gas stream 5 is provided, with the air feed conduit 7 being connected via at least one valve 6 to the entrained-flow calciner 4 and/or the combustion on a grate. The proportion of oxygen in the entrained flow calciner 4 can be regulated and controlled via the valve 6 and the air feed conduit 7 and optionally connected blowers 17. An oxygen probe 10 and a device for data processing 11 (not shown) are optionally also present.

[0066] Two further apparatuses according to the invention are depicted in FIG. 2 and FIG. 3. FIG. 2 shows an embodiment with an entrained-flow calciner 109a and FIG. 3 shows an embodiment with a rotary tube furnace 109b.

[0067] In both embodiments, a first fuel, for example coal dust fluidized in air, is initially introduced via a first fuel feed device 101 into the first combustion chamber 102 and burnt there. The hot gases which arise are conveyed via a first connection into the second combustion chamber 105. There, the substitute fuel is fed via a second fuel feed device 104, for example a screw, to the second combustion chamber 105 and burnt on a grate, which here has a step-like configuration. In this way, the ash from the second fuel is conveyed to the ash discharge 106 and discharged. In order to improve the combustion of the second fuel in the second combustion chamber 105, the second combustion chamber 105 has a second oxygen feed device 103. The hot gases from the second combustion chamber 105 are conveyed via a second connection into the reactor 109a, 109b.

[0068] In the first embodiment of FIG. 2, the reactor is an entrained-flow calciner 109a. The entrained-flow calciner 109a has a third fuel feed device 107 and a starting material feed conduit 108. The process is regulated so that the third fuel is converted in a substoichiometric combustion in the entrained-flow calciner 109a and a reducing atmosphere is thus generated. Downstream of the entrained-flow calciner 109, the product is separated off in a cyclone 110 and taken off through the product discharge conduit 111, while the hot gases are fed through the offgas conduit 112 to, for example, a preheater. In this embodiment, starting material and hot gases are conveyed in cocurrent.

[0069] In the second embodiment shown in FIG. 3, the reactor is a rotary tube furnace 109b. In this embodiment, starting material and hot gases are conveyed in countercurrent, which constitutes a significant difference from the first embodiment of FIG. 2. The starting material feed conduit 108 is arranged at the end of the rotary tube furnace 109b opposite the second connection. At this end, there is also the offgas conduit 112 through which the hot gases can be conveyed into a calciner and/or a preheater. The third fuel feed device 107 is arranged next to the third connection and thus at the same end of the rotary tube furnace 109b as the product discharge conduit 111.

LIST OF REFERENCE NUMERALS

[0070] 1a Mineral mixture [0071] 1b Calcined mixture [0072] 2 Calcination stream [0073] 3 Combustion on a grate [0074] 4 Entrained-flow calciner [0075] 4a Product inlet opening [0076] 4b Residue opening [0077] 4c Fuel gas opening [0078] 4d Product outlet opening [0079] 5 Additional gas stream [0080] 6 Valve [0081] 7 Air introduction conduit [0082] 8 Product feed conduit [0083] 9 Preheating stages [0084] 10 Oxygen probe [0085] 11 Device for data processing [0086] 12a Fuel gas opening [0087] 12b Combustion gas feed conduit [0088] 13 Fuel feed conduit [0089] 14 Ignition burner [0090] 15 Fuel introduction conduit [0091] 16 Combustion chamber [0092] 17 Blower [0093] 101 First fuel feed device [0094] 102 First combustion chamber [0095] 103 Second oxygen feed device [0096] 104 Second fuel feed device [0097] 105 Second combustion chamber [0098] 106 Ash discharge [0099] 107 Third fuel feed device [0100] 108 Starting material feed conduit [0101] 109a Entrained-flow calciner [0102] 109b Rotary tube furnace [0103] 110 Cyclone [0104] 111 Product discharge conduit [0105] 112 Offgas conduit