MXPA96003786A - Method and plant for the manufacturing of scrap decland portland mineraliz - Google Patents

Abstract

The present invention relates to a method for the preparation of a mineralized Portland cement clinker or slag in a calcination furnace system, where the raw mix feed material is subsequently subject to preheating, calcination, burning and finally cooling, characterized in that the mineralizer is added to the feed material stream after the feed material has been fed to the process and before the feed material has passed through the clinker or scorcher formation zone.

Description

METHOD AND PLANT FOR THE MANUFACTURE OF MINERALIZED PORTLAND CEMENT SCUGE The present invention relates to a method and a plant for the preparation of slag or clinker of mineralized Portland cement, in a system of calcination furnace for dry or semi-dry process, where the feed material of raw material mixture is being subjected to preheating, calcination, burning and finally, cooling. The principal oxide components of Portland cement clinker (CaO, SiO, AlaO * and Fe "0") normally represent 96-97% of the chemical analysis. The relative levels of these four oxides control the proportions of the four main minerals of the slag, C ^ S, C «S, CgA and C.AF, and these proportions have a fundamental influence on the properties of the cement. However, the minor components that can constitute the remaining 3-4% can have a very significant influence on the slag processing process and on the properties of the cement. In the system of four pure components, the C "S does not form below 1250 ° C. The presence of minor components can decrease this temperature, thus facilitating the formation of C3S. The term "mineralizer" is used for components that increase the formation of C "S and facilitate the sintering reactions in the rotary calcination furnace.

A method for the manufacture of mineralized slag is known from British Patent No. 1,498,057. According to this method, fluorine and sulfur are added during the preparation of the raw material mixture, usually in the form of fluorite (CaF ") and gypsum (CaSO, • 2H2O), the main goal being to obtain a slag with a fluorine content of about 0.25% by weight and an SO- content of about 2.5% by weight. The method of said patent is focused on the use in a rotary calcination furnace of the wet process type, which was used extensively at the date of publication in 1975, but considered today as non-economic due to the substantial quantities of energy needed for drying, and it has been proven that it is extremely difficult to transfer the method to newer systems of kiln for calcination for dry or semi-dry process, more energy efficient, which incorporate a preheater and a calciner. Thus, despite the very substantial improvements in cement quality that can be achieved (see, for example, Moir, Phil Trans Roy Soc Lond., 1983, A310, 127-138) by this method according to British Patent No. 1,498,057, it is well known that the field of application of this method has been very limited. This is probably attributable to the operational difficulties associated with the implementation of the method, both in terms of control of the production of the slag, and with respect to the occurrence of blockages in the cyclones and in the ascending ducts. Therefore, an object of the present invention is to provide a method and a plant for manufacturing mineralized cement slag or clinker, where the plant is constructed so that the preheating and at least part of the calcination process takes place outside the furnace , in a manner such that problems associated with the known art are avoided. A first operational difficulty is to determine how to control the entrance of the mineralizer and how, at the same time, to ensure the necessary degree of homogeneity in the feed material of the raw material mix. From British Patent No. 1,498,057 it appears that the mineralizer is mixed with the raw material mixture feed material before it is burned (page 5, line 89 - page 6, line 43).

The addition of the mineralizer in this way will undoubtedly result in a high degree of homogeneity, but it will not be possible to quickly regulate the entry of the mineralizer in relation to the raw materials, so that the operation of the furnace and the properties of the finished cement slag can be controlled in this way, since the mineralizer constitutes a fixed percentage of the total amount of the raw material. Particularly in conjunction with the construction of mineralized slag with a high sulphate content, it is important to control the temperature variations in the formation zone of the clinker or slag. This is due to the tendency of the sulphate to decompose in S0 ~ in the formation zone of the clinker or slag, and to condense in the colder regions of the furnace. When the temperature of the clinker formation zone is increased, the evaporation of the S0"will increase, which will result in higher sulfate concentrations in the colder regions of the furnace. The situation can become so critical that the continuous operation of the furnace becomes impossible due to the annular formations in the furnace or the formation of blockages or blockages in the preheater system, unless the entry of the sulphate into the feed material of The raw mix is temporarily reduced or eliminated altogether, Conversely, if the temperature of the clinker or slag formation zone has decreased, severe dust circulation can result between the furnace and the cooler, and the operation The continuous operation of the furnace will become impossible, unless the entry of the sulfate is reduced or eliminated.With the use of the method according to the invention, as indicated in claim 1, these problems are avoided since it is possible to use the input amount of the mineralizer as a controlled parameter for the manufacture of clinker or mineralized slag during off-limit operating conditions s, 15 of the oven. If appropriate, some of the mineralizer can be added to the raw mix feed material before grinding and homogenization, while the remaining mineralizer inlet needed is used for process control. In some cases, the raw mix feed material will have a natural content of the mineralizer, but, provided the content is not excessively high, it will still be possible to control the entire process 25 by the subsequent addition of the mineralizer. It is also possible to add two or more different mineralizers to different points in the process line, independent of each other, in order to control the process and the product. A second operational difficulty that is well known when ordinary slag or clinker of Portland cement with a high content of mineralizer, particularly SO, and F, is burned in the raw mix feed material, refers to the precipitation of solids and the occurrence of blockages when the material passes through a temperature range of approximately 700 to 900 ° C. It has been found that in the presence of significant concentrations of these mineralizers in the preheating zone, the condensation of chlorides on the feed material particles of the preheater, results in the formation of a minor but significant amount of a melting phase. at temperatures as low as 680 ° C which, upon reaction with the oxide components in the feed material at high partial pressures of C0 ~, prevailing in the preheating suspension cyclones, solidifies through the formation of the mineral spurrite (2C2S-CaCO). The formation of an excess of 5% by weight of spurrite in the feedstock can result in impaired flow properties of the feedstock, leading to severe blockages and in the end to production standstill. In the North American Patent N? 5,183,506 The method chosen to solve this problem involves the use of a special mixture of plaster. In order to reduce or eradicate the problems associated with the blockages in the precursor cyclones and the ascending pipelines between the cyclones, the mineralizer can be advantageously added in a stage where calcination has begun to take place, for example, where the feed material has been preheated to more than 700-750 ° C, preferably to more than 800 ° C. Such an action will further improve production by ensuring a smooth flow of the feed material through the preheater, since substantial deterioration of the flow properties of the feed material may occur when the mineralizer is added, depending on the type of mineralizer that is used. select In a pre-calcination plant with a separate cooler, such as a grate cooler, it may be further advantageous to add the mineralizer to the tertiary air duct, through which hot air is directed from the cooler to the calciner. The air in the tertiary air duct, in connection with this solution, will ensure that the mineralizer is transported to the calciner. If appropriate, the mineralizer may be subject to prior drying in excess of air from the cooler, before it is added to the tertiary air duct. The mineralizer may be a sulphurous product, and in conjunction with this product another mineralization component or an auxiliary substance containing fluorine or zinc oxide or copper may be used, but preferably, the addition of such a component or substance will no longer be necessary. that this is already present in raw materials. It has been recognized that through the combined presence of the fluorine and sulfur components in the clinker or slag, at concentrations of at least 0.15% by weight of F and 1.5% by weight of SO-, the combination is achieved. early in the calcination process and the development of increased resistance in the finished product. Through the reduction in the content of the mineralizing components in the raw mix feed material, and through the introduction of said components into the feed material stream at a temperature higher than 800 ° C, the content of mineralizer in the feed material in the preheating zone, is reduced, which effectively eliminates or at least significantly reduces the risk of blockages in the preheating zone, which is important when the mineralizer is a component that contains sulfur. The exact degree of reduction in the content of mineralizer in the feed material in the preheating zone will obviously depend on the degree of recirculation characteristic of the oven system in question, although it is clear that said content can never be less than the corresponding content in the raw mix feed material. However, research has indicated that if the risk of blockages is to be eliminated or subsequently reduced, contents of at most 1.2% by weight of SO- in an ignition-free base should be observed, or 0.14% in weight of F in an ignition loss free base, or both in the feed material in the preheating zone, and the same limits should therefore apply to the composition of the raw mix feed material. The sulfur-containing component may among other things be natural gypsum (CaSO, • 2H20), hemihydrate (CaSO, • 1 / 2H-0) (basaite), anhydrite (CaSO,), calcium or magnesium langbeinite, barite or other minerals that contain sulfur and that also contain calcium or magnesium. The sulfur-containing component could also be a waste product, for example, gypsum FGD (Desul-furization of Combustion Gas), desul-furization products containing sulphite or sulfur, sulphate-containing industrial by-products such as ammonium sulfates or iron-based sulfates, cement kiln kiln dust, sulfur-containing fuel such as coal or coal or oil with high sulfur content. Desulfurization products are formed when the combustion gases, for example from power plants, are cleaned from S0-. The desul-furization of semi-dry combustion gas produces a byproduct of calcium sulfite and calcium sulfate, which may also contain inclusions of finely divided products and otconstituents. Modern methods of desulfurization in wet process are able to produce a very clean plaster, which initially arises, however, in the form of wet waste or sediment or a filter cake. After being subjected to drying, the aforementioned product can, for example, find application in the manufacture of pressed gypsum fiber or this can replace the natural gypsum in the manufacture of cement, w it is jointly ground with the clinker or slag in the cement mill. In turn, at this point, the range of applications for the desulfurization product, derived from semi-dry desulphurisation, is very limited, and it is also a complicated factor that the elimination of the product is difficult due to the Theological properties not favorable of the product. Anotinteresting by-product is the anhydrite contaminated with CaF- and H-SO ,, formed during the manufacture of hydrofluoric acid from fluorspar and sulfuric acid. In the future, anotbyproduct may arise which involves the destruction of asbestos: a proposed method involves the dissolution of asbestos in hydrofluoric acid (HF), followed by neutralization with calcined limestone, resulting in a product consisting of MgO, SiO-, CaF- and a certain amount of CaSO, * 2H-0. Finally, anotoption to be considered is the use of phospho-gypsum (for example, gypsum which is the by-product derived from the manufacture of phosphoric acid based on crude phosphate and sulfuric acid). By means of the method according to the invention it is now possible to employ these waste products in the cement manufacturing process, in an appropriate manner, since experience has shown that the operational difficulties discussed above can be avoided when the products of waste are not processed togetwith the raw material, but ratare added separately to the process. Examples of suitable fluorine-containing components are fluorite, fluorine apatite, cryolite or fluorine-containing industrial by-products such as hexafluorosilicic acid or silicon tetrafluoride, preferably fluorite. The invention will now be explained in furtdetail, with reference to the drawing, which shows one embodiment of the invention. The drawing shows a cement calcination furnace plant of the generally known type, which comprises a preheater 1, which in the figure consists of three cyclones, a calciner 2 with a separation cyclone 3 and a rotary kiln 4 with cooler 5 of clinker or slag. In a plant of the aforementioned type, the manufacture of cement is carried out according to a method w the raw material of cement is introduced into the inlet 13 in the upper part of the preheater 1, passing through the pre-heater in counter-current 1 with the exhaust gases from the furnace 4 and the calciner 2. The exhaust gases are extracted through the preheater 1 and discharged in 14 by means of an exhaust gas fan, not shown. The raw material 5 is transported from the preheater 1 via a duct 7 down to the calciner 2, w it is calcined and passed in suspension to the separation cyclone 3. , the calcined raw material separated from the exhaust gases and transported through of a duct 6 towards the rotary kiln 4 where, by means of the heat coming from the burner 9, the raw material is burned to become clinker or slag. The clinker or slag then falls into the cooler 5 where it is cooled with air. A part of hot air ^ 5 produced in this way passes to the rotary kiln, another part of it directed through the tertiary air duct towards the calciner. The rest of the cooling air directed to the cooler is diverted to 10. 2o A mineralizer that does not have any harmful effect on the flow properties of the raw material, can, in principle, be added anywhere after the raw material it has left the warehouse where the raw material may have been subject to homogenization, and then the raw material has been added to the process through a dosing apparatus. A mineralizer, such as a sulfur-containing component, which arises for example as a by-product of the combustion gas desulfurization, can be advantageously fed to the calciner either directly by means of the pipeline 12 or by adding the mineralizer to the pipeline. tertiary air 8, by means of duct 11 so that the mineralizer is carried by the hot air from the cooler to the calciner. In this way, when the mineralizer is directed towards the calciner and towards the subsequent separation cyclone, the calciner and the cyclone will operate as a homogenizer, facilitating the perfect mixing of the SO- in the raw material stream. If the by-product contains sulfur in a lower oxidation state, for example sulfite or sulfide, it can be advantageously added in 11 or 12, so that these sulfur compounds can be oxidized in sulphate in the calciner. If it is added at 13, this will result in the formation of a small amount of SO- which is entrained in the exhaust gases. If drying of the mineralizer is required before use, it will be possible to extract excess hot air from the cooler at 10, for use in the conventional drying apparatus. In a preferred embodiment of the method where sulfur and fluorine may be present, the composition of the raw mix feed material is such that the sulfur content Xp is at most 1.0% by weight, calculated as SO- in a free base of LOI (Loss to Ignition) or fluorine content Xp is at most 0.12% by weight calculated on an LOI-free basis, or these two conditions are met, in particular that X? is :: at most 0.8% by weight, or Xp is at most 0.10% by weight, or both, specifically, that X? is at most 0.6% by weight, or Xp, is at most 0.08% by weight, or both, such that Xg is at most 0.4% by weight or Xp is at most 0.06% by weight, or both.

Claims (15)

1. A method for the preparation of a mineralized Portland cement clinker or slag in a calcination furnace system, wherein the raw mix feed material is subsequently subject to preheating, calcination, burning and finally cooling, characterized in that the mineralizer is it adds to the feed material stream after the feed material has been fed to the process and before the feed material has passed < through the clinker training zone

2. A method according to claim 1, characterized in that the mineralizer is added to the stream of the feedstock after the feedstock has been heated to more than 800 ° C.

3. A method according to claim 1, characterized in that the addition of the mineralizer is carried out in the area where the raw mix feed material is being preheated.

4. A method according to claim 1, characterized in that the system is one that has a special calcination zone, and because the mineralizer is added to this zone.

5. A method according to claim 1, characterized in that the furnace system is one that has a special calcination zone, and because the mineralizer is added to a tertiary air duct connecting the cooler to the calcination zone.

6. A method according to claims 1 to 9, characterized in that the mineralizer is a product containing sulfur, for example, natural gypsum, hemihydrate (basaite), anhydrite, langbeinite, barite or other sulfur minerals containing calcium or magnesium, or because the mineralizer is a waste product with sulfur, selected from sulphates such as gypsum FGD (Compound Gas Desulfurization) desulphurization products containing sulphite or sulfur, sulphate-containing industrial byproducts such as ammonium sulfates or iron-based sulfates , cement kiln dust, fuel containing sulfur such as coal or coal or oil with high sulfur content.

7. A method according to claims 1 to 9, characterized in that the mineralizer is a fluorine-containing product, for example fluorite, fluorine apatite, cryolite or fluorine-containing industrial by-products such as hexafluorosilicic acid or silicon tetrafluoride, preferably fluorite. .

8. A method for the preparation of clinker or Portland cement clinker, mineralized, said clinker having a sulfur content of at least 1.5% by weight, calculated as SO- and a fluorine content of at least 0.15% by weight, calculated as F , in a kiln system where the raw mixture is subsequently subjected to preheating, calcination, burning and, finally, cooling, wherein the composition of the raw mixture material is such that one or both of the following conditions are met : 1) the content of sulfur X? is at most 1.2% by weight, calculated as SO- in an ignition-free base, 2) the fluorine content X "is at most 0.14% by weight, calculated on a loss-free basis at ignition, and wherein a component containing sulfur or a component containing fluorine, or both, is introduced to the feed material stream at a point in the process where the temperature of the feed material stream is above 800 ° C, either the amount of the sulfur-containing component or the fluorine-containing component, or both, sufficient to ensure that the final Portland cement clinker or slag has the required sulfur and fluorine content.

9. A method according to claim 8, characterized in that X is at most 0.8% by weight, or Xp is at most 0.10% by weight, or both.

10. A method according to claim 8, characterized in that X? is at most 0.4% by weight, or X "is at most 0.06% by weight, or both.

11. A method according to claims 8 to 10, characterized in that the addition of the sulfur-containing component and / or the fluorine-containing component, or both, is carried out in the area where the feed material of the crude mixture It is being preheated.

12. A method according to claims 8 to 10, characterized in that the furnace system is one having a special calcination zone, and because the sulfur-containing component and / or the fluorine-containing component is added to this. calcination zone.

13. A plant for the manufacture of clinker or mineralized slag, which comprises an inlet for the processed raw mixture, a preheater, a calcination zone, a furnace, and a cooler, characterized the plant because it has an entrance for a mineralizer, located after the position in which the raw mixture is being fed.

14. A plant according to claim 13, characterized in that the inlet for the mineralizer is located after the preheater.

15. A plant according to claim 13, characterized in that the inlet for the mineralizer is located at a point along the tertiary air duct. ABSTRACT The invention relates to a method and a plant for the manufacture of mineralized Portland cement clinker or slag. The mineralizer can be for example gypsum, fluorine, or a waste product containing these or other mineralizers. By means of the method according to the invention it will be possible to avoid some of the problems associated with the known technique, since it is possible to use the entrance of the mineralizer as a controllable parameter during the manufacture of the clinker or mineralized slag. In order to reduce or eradicate the problems in terms of clogging and blocking in the preheater cyclones and in the ascending ducts between the cyclones, the mineralizer can be advantageously added after the cyclone, which handles the feed to the calciner, for example, the last cyclone in the preheater, or the preheater stage further down in a plant which does not incorporate a calciner. This involves that there will be no problems in ensuring a smooth flow of raw material through the preheater, since substantial deterioration of the flow properties of the raw material can occur when the mineralogiser is added ahead of the preheater, depending on the type of material. mineralizer that is selected.