PROCESS FOR THE PREPARATION OF HIGH ALUMINA CEMENT

Abstract

High alumina cement is produced in a submerged combustion melter, cooled and ground.

Claims

1. Process for the preparation of high alumina cement comprising: introducing a solid batch material for preparation of high alumina cement into a melter; melting the solid batch material in the melter by submerged combustion to form a liquid melt; withdrawing at least a portion of the liquid melt from the melter; cooling said discharged liquid melt to obtain solidified melt; and grinding the solidified melt to appropriate grain size.

2. The process of claim 1, wherein the melting chamber walls are cooled, for example comprising double steel walls separated by circulating cooling liquid, preferably water, and are not covered by a refractory lining.

3. The process of claim 1, wherein heat is recovered from the hot fumes and/or from the cooling liquid.

4. The process of claim 1 wherein heat is recovered from the hot fumes to preheat the raw materials.

5. The process of claim 1 wherein part at least of the melt is withdrawn continuously or batchwise from the melter.

6. The process of claim 1 wherein the submerged burners of the melter are controlled such that the melt volume is increased by at least 8%, preferably at least 10%, more preferably at least 15% or 20%, compared to the volume the melt would have with no burners firing.

7. The process claim 1 wherein the submerged combustion is performed such that a substantially toroidal melt flow pattern is generated in the melt, having a substantially vertical central axis of revolution, comprising major centrally inwardly convergent flows at the melt surface; the melt moves downwardly at proximity of the vertical central axis of revolution and is recirculated in an ascending movement back to the melt surface, thus defining an substantially toroidal flow pattern.

8. The process of claim 1 wherein the melting step comprises melting the solid batch material, in a submerged combustion melter by subjecting the melt to a flow pattern which when simulated by computational fluid dynamic analysis shows a substantially toroidal melt flow pattern in the melt, comprising major centrally inwardly convergent flow vectors at the melt surface, with the central axis of revolution of the toroid being substantially vertical.

9. The process of claim 8 wherein towards the melter bottom, the flow vectors change orientation showing outward and then upward components.

10. Production equipment for the preparation of high alumina cement comprising (i) a submerged combustion melter (1) comprising melting chamber (3) walls (19) and a melting chamber bottom, submerged burners (21,22,23,24,25,26), and equipped with a raw material discharge (10) or feeder and melt outlet (9), (ii) a melt cooling station and (iii) a grinding station.

11. The production equipment of claim 10 wherein the melting chamber walls (19) are cooled, for example comprising double steel walls separated by circulating cooling liquid, preferably water, and are not covered by refractory lining.

12. The production equipment of claim 10 wherein submerged combustion burners (21,22,23,24,25,26) are arranged at the melter bottom in a substantially annular burner zone, preferably on a burner circle (27).

13. The production equipment of claim 10 wherein the burners (21,22,23,24,25,26) are arranged with a distance between adjacent burners of about 250-1250 mm, advantageously 500-900 mm, preferably about 600-800, even more preferably about 650-750 mm.

14. The production equipment of claim 10 wherein each burner axis and/or a speed vector of the melt moving upwards over or adjacent to the submerged burners (21,22,23,24,25,26) is slightly inclined from the vertical, for example by an angle which is ≧1°, ≧2′, ≧3° or ≧5 and/or which is ≦30°, preferably ≦5′, more preferably ≦10°, notably towards the center of the melter.

15. The production equipment of claim 10 wherein each central burner axis is inclined by a swirl angle with respect to a vertical plane passing through a central vertical axis of the melter and the burner center, the swirl angle being ≧1°, ≧2°, ≧3°, ≧5° and/or ≦30°, ≦20°, ≦15° or ≦10°.

Description

[0039] An embodiment of a melter suitable for use in accordance with the present invention is described below, with reference to the appended drawings of which:

[0040] FIGS. 1a and 1b are schematic representations of a toroidal flow pattern in a submerged combustion melter;

[0041] FIG. 2 shows a vertical section through a submerged combustion melter;

[0042] FIG. 3 is a schematic representation of a burner layout for a melter of FIG. 2; and

[0043] FIG. 4 schematically shows a production line according to the invention.

[0044] With reference to the figures, a toroidal flow pattern is preferably established in which melt follows an ascending direction close to submerged burners 21, 22, 23, 24, 25, 26 which are arranged on a circular burner line 27, flows inwardly towards the center of the circular burner line at the melt surface, and flows downwards in the proximity of the said center. The toroidal flow generates agitation in the melt, ensures good stirring of the melt, and absorption of raw material into the melt. Furthermore, it has been determined that the flow as generated also reduces foam generation at the top of the melt; the gas or foam bubbles being entrained back into the melt, thus reducing its density.

[0045] The illustrated melter 1 comprises: a cylindrical melting chamber 3 having an internal diameter of about 2.0 m which contains the melt; an upper chamber 5; and a chimney for evacuation of the fumes. The upper chamber 5 is equipped with baffles 7 that prevent any melt projections thrown from the surface 18 of the melt being entrained into the fumes. A raw material feeder 10 is arranged at the upper chamber 5 and is designed to load fresh raw material into the melter 1 at a point 11 located above the melt surface 18 and close to the side wall of the melter. The feeder 10 comprises a horizontal feeding means, for example a feed screw, which transports the raw material mix to a hopper fastened to the melter, the bottom of which may be opened and closed by a vertical piston. The bottom of the melting chamber comprises six submerged burners 21, 22, 23, 24, 25, 26 arranged on a circular burner line 27 concentric with the melter axis and having a diameter of about 1.4 m. The melt may be withdrawn from the melting chamber 3 through a controllable outlet opening 9 located in the melting chamber side wall, close to the melter bottom, substantially opposite the feeding device 10. The melt withdrawn from the melter may then be allowed to cool and subsequently ground as required.

[0046] The temperature within the melt may be between 1400° C. and 1600° C., preferably 1450° C. and 1550° C., depending on the composition of the melt, desired viscosity and other parameters. Preferably, the melter wall is a double steel wall cooled by a cooling liquid, preferably water. Cooling water connections provided at the external melter wall allow a flow sufficient to withdraw energy from the inside wall such that melt can solidify on the internal wall and the cooling liquid, here water, does not boil. The internal melter wall is not lined with any refractory material.

[0047] The submerged burners 21,22,23,24,25,26 comprise concentric tube burners operated at gas flows of 100 to 200 m/s, preferably 110 to 160 m/s and generate combustion of fuel gas and oxygen containing gas within the melt. The combustion and combustion gases generate agitation within the melt before they escape into the upper chamber and then through the chimney. These hot gases may be used to preheat the raw material and/or the fuel gas and/or oxidant gas (eg oxygen, industrial oxygen have an oxygen content 95% by weight or oxygen enriched air) used in the burners. The fumes are preferably filtered prior to release to the environment, optionally using dilution with ambient air to reduce their temperature prior to filtering.

[0048] With reference to FIG. 4, raw material from a raw material storage 30 is charged into the furnace 1 as described above, and withdrawn thereof for cooling 32 and further downstream treatments known per se. The discharged melt is allowed to cool at a temperature suitable for further downstream operation, including grinding 34 to appropriate grain size and/or storing 36,38. The grinding is advantageously effected in several stages, including a first stage 39 that reduces the particle size of the solidified melt to a size suitable for downstream fine grinding 40 which in turn may be carried out in a manner known per se, in several stages, in order to reach a particle size as is common in the cement manufacturing industry. Mostly the final grain size is a powdery grain size. For example, it is such that 100% of the particles pass a 90 μm screen in a dry circuit. The production line further comprises dryers as appropriate and as is known per se; these devices have not been shown in the figures.

[0049] With respect to the exemplified melter, it has been found that the turbulent aerated melt showed almost no foam floating at the top of the melt, and it has been determined that the turbulent aerated melt showed a volume (averaged over a 1 minute time period) of 30-50% higher than that calculated on the basis of the raw material fed into the melter and maintained at the same temperature. The volume was.

[0050] The high alumina cement obtained is of high quality. The above described production process is less energy demanding then known processes, because of the choice of submerged combustion melters that allow for improved energy transfer to the melt, shorter residence times and thus less heat loss, and because the high stirring leads to a more homogenous melt at reduced melt viscosity, which in turn may allow for operation at reduced temperatures. Furthermore, submerged combustion may advantageously be performed in water-cooled melters which are easier and less costly to maintain and repair and which further allow for recycling of the energy withdrawn from the cooling fluid.