Integrated process for the production of clinker with treatment of bypass dusts produced by the kiln

Abstract

It is described an integrated process for the production of clinker by dry process, with treatment in continuous of by-pass dusts produced by the kiln, wherein the solid matter to treat consists of bypass dusts of a clinker production process, containing compounds of chloride, sodium, potassium and sulphur, such a process comprising the following steps: a) extraction of the bypass dusts directly from the phase of quench, without intermediate storage, at a temperature comprised between 150 and 200 C., with a moisture content varying from 0.1 to 3% by weight, preferably from 0.1 to 0.5% by weight, and with a quantity of calcium carbonate lower than 55% by weight; b) mixing of said dusts coming from step a), within a maximum time comprised between 2 and 10 minutes, preferably lower than about 5 minutes, with water up to a water/dusts ratio varying from 2:1 to 4:1, preferably from 2.5:1 to 3.5:1, in a way to obtain a mixture with a moisture content comprised between 45 and 75% by weight, preferably between 50% and 55% by weight, even more preferably equal to about 50% by weight; c) mechanical stirring of the mixture diluted up to complete dissolution of the soluble salts; d) mechanical separation of the mixture so diluted in a liquid fraction containing water and soluble salts and in a solid fraction in form of cake or crust.

Claims

1. An integrated process for the production of clinker by dry process, with treatment in continuous of bypass dusts produced by the kiln, wherein the solid matter to treat consists of bypass dusts of a clinker production process, containing compounds of chloride, sodium, potassium and sulphur, such a process comprising the following steps: a) extraction of the bypass dusts directly from the phase of quench, without intermediate storage, at a temperature comprised between 150 and 200 C., with a moisture content varying from 0.1 to 3% by weight, and with a quantity of calcium carbonate lower than 55% by weight; b) mixing of said dusts coming from phase a), within a maximum time comprised between 2 and 10 minutes, with water up to a water/dusts ratio varying from 2:1 to 4:1, in a way to obtain a mixture with a moisture content comprised between 45 and 75% by weight; c) mechanical stirring of the mixture diluted up to complete dissolution of the soluble salts; and d) mechanical separation of the mixture so diluted in a liquid fraction containing water and soluble salts and in a solid fraction in form of cake or crust.

2. The integrated process according to claim 1, wherein the sum of steps a)-b) is carried out in a period of time varying from 2 to 10 minutes.

3. The integrated process according to claim 1, wherein the reintroduction of the treated solid fraction is provided upstream of the grinding of the raw mixture.

4. The integrated process according to claim 2, wherein the reintroduction of the treated solid fraction is provided upstream of the grinding of the raw mixture.

5. The integrated process according to claim 1, wherein the sum of steps a)-b) is carried out in a period of time lower than about 5 minutes.

6. The integrated process according to claim 1, wherein the moisture content of step a) varies from 0.1 to 0.5% by weight.

7. The integrated process according to claim 1, wherein the water/dusts ratio of step b) varies from 2.5:1 to 3.5:1.

8. The integrated process according to claim 1, wherein the moisture content of step b) varies between 50% and 55% by weight.

Description

(1) The integrated process and the apparatus according to the present invention are illustrated in FIG. 1.

(2) With reference to FIG. 1, bypass dusts are extracted from the clinker kiln 1, by means of a probe for sampling gases 2 and are fed to a cooling system 3 of the extracted gases for dilution with air from which they are fed to a nebulized water cooling tower 4 and to a depulverization device 5.

(3) The bypass dusts collected by the depulverization device 5 are thus fed through line 6 to a feeding system 7 to the bath of dissolution and mixing 8. To this bath is also fed, through line 9, the required quantity of water. The suspension of dusts in water, suitably mixed, is then fed through line 10 to the washing apparatus 11.

(4) The phase of washing of the dusts can be achieved according to any of the methods known to the state of the art and with whichever apparatus already known to and applied by the state of the art in this respect.

(5) In particular, step d) of mechanical separation of the mixture so diluted can be achieved through suitable means of separation such as rotary drum filters, belt filters, pressure filters, per se known, and allows to obtain a liquid fraction containing water and soluble salts exiting through line 12 and a solid fraction in form of cake or crust exiting through line 13.

(6) The solid fraction in form of cake or crust, coming from such a mechanical separation phase can be subjected to one or more further washings with water or with proper washing fluid.

(7) These further phases of washing of the dusts can be achieved by feeding the water or the washing fluid in counter-current with respect to the fluid direction of the solid fraction.

(8) The washing apparatus can also be provided at the exit with a device for drying the solid fraction.

(9) Such a drying device or removal of the water or of the suitable washing fluid from the solid fraction can provide the removal of the water by use of a gaseous flow, preferably air, possibly by applying also a pressure lowering, obtained through suction pumps.

(10) With the objective to better illustrate the invention is now provided the following example which shall be considered as illustrative and not limitative of the same.

EXAMPLE 1

(11) The present example has been carried out on a sample of about 6 tons of by-pass dusts, coming from the cement factory of Tourah, belonging to the Egyptian branch Suez Cement of Italcementi Group, having an average composition as reported in the table below:

(12) TABLE-US-00001 DUST Chemical Analysis Loss on Ignition % 11.61 (LOI) Cl % 9.66 Spectrometric RX Analysis SiO2 % 15.03 Al2O3 % 3.54 Fe2O3 % 2.28 CaO % 39.78 MgO % 1.68 SO3 % 4.42 Na2O % 4.27 K2O % 6.23 SrO % 0.11 Mn2O3 % 0.03 P2O5 % 0.11 TiO2 % 0.26

(13) Said dust therefore contains about 48% by weight of CaCO.sub.3, as derivable from the percentage of loss on ignition.

(14) The dusts have been extracted in continuous in proper fractions of 1.5 tons from the zone of quench and fed in continuous to a mixing and dissolution bath having a volume of about 1 m.sup.3, in which the dusts have been gradually mixed with about 750 liters of water (for a total of 3000 liters) and sent, always in continuous, to the drying phase.

(15) The phase of preparation of the suspension and sending to the washing and dehydration system has been effected in a period of time of about 5 minutes. In the case of the present example, the material to be subjected to drying has been arranged on a water-resistant carpet and, during the moving forward of such a carpet from the loading zone to the unloading zone, the wet material has been dehydrated. At the end of the dehydration phase, corresponding to the end of the passage of the material on the water-resistant carpet and carried out under standard conditions, the recovered material resulted in a crust apparently dry, having a residual content of moisture of 18% by weight.

(16) The recovered material had on average scale the following chemical composition on the dry matter:

(17) TABLE-US-00002 SLUDGE Chemical Analysis Loss on Ignition % 28.09 (LOI) Cl % 0.99 Spectrometric RX Analysis SiO2 % 13.91 Al2O3 % 3.42 Fe2O3 % 2.33 CaO % 44.26 MgO % 1.62 SO3 % 3.09 Na2O % 0.73 K2O % 0.91 SrO % 0.11 Mn2O3 % 0.02 P2O5 % 0.09 TiO2 % 0.20

(18) It has been further observed that, extending the periods of permanence of the material in the dispersed phase in water, the dehydration of the dust/water suspension got increasingly difficult.

(19) The process according to the present invention is moreover particularly efficient in order to diminish the content of chloride of the bypass dusts: it started indeed from an initial content equal to 9.66% by weight to arrive at a residual content in the treated material equal to 0.99% by weight.