CH631691A5 - PLANT FOR THE TRANSFORMATION INTO CLINKER PORTLAND OF WET MELME OF RAW MATERIALS FROM CEMENT. - Google Patents

Description

The present invention has the purpose of realizing a plant capable of offering an economic solution to the problems mentioned above and, in particular, to that of the transformation of existing conventional ovens by humid way into others with high thermal economy, which will later be called briefly "semi-wet".

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This object is achieved according to the invention with a plant for the transformation into wetland clinker of wet sludge of raw materials from cement having a water content of 28% - 45%, comprising an apparatus for partial dehumidification of aqueous sludge , from which the partially dehumidified sludge is fed to a dryer run in co-current by gases coming from a multistage preheater, a de-dusting device connected to the outlet 35 of said dryer, from which the powdery material is fed to the first preheating stage, a rotating kiln to which the preheated material in the last preheating stage is fed and which is connected to the entrance of this last preheating stage, as well as a clinker cooler connected to the exit of the rotating kiln, characterized by the fact that the apparatus for partial dehumidification of aqueous sludge consists of al minus a horizontal centrifugal separator directly connected to the entrance of the dryer.

In the plant, the aqueous slime of a mixture of raw materials, preferably ground and homogenized according to a conventional process by humid way (and therefore containing from 28% to 45% of water), can first of all be 50 thickened up to a residual humidity of 18% - 22% of water by centrifugation in continuous machines, of simplicity and economy of operation much higher than the filter presses used so far in the cement industry (thickening process).

55 The thickened paste thus obtained (18% -22% of water) is fed to a thermal appliance which can carry out the further processes of:

- drying by evaporation with mechanical and electrostatic dedusting 60 of the exhausted gases;

- preheating of the dried powder in two cyclones, the second of which also acts as a dust collector for the next stage;

- partial decarbonation of the pre-65 dry powder heated by treatment in a reactor equipped with a cyclone dust collector-preheater (second cyclone of the previous stage);

- completion of decarbonation and clinkeriz-

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631691

zation of the partially decarbonated mixture coming from the above reactor in a rotating oven;

- cooling of the clinker obtained in a cooler.

The reactor can be placed along a duct that feeds the combustion gases coming from the rotating oven to the preheating stages and the same reactor can also reach the hot gases produced in a special combustion chamber through any type of fuel and hot air coming from the clinker cooler. .

The function of this reactor is to determine the partial decarbonation of the preheated mixture and, at the same time, to give the combustion gases leaving, by flow rate and temperature, the appropriate thermal content to dry the thickened slime.

If a component of the raw material mixture is available with a low natural moisture content, it can be ground alone by dry means and,

as dry powder, dosed in a suitable measure and fed or together with the mixture dried in the first preheating stage, or together with the thickened slime in the drying stage.

A possible embodiment of the system according to the present invention will be described below with reference to the attached drawing, in which:

fig. 1 shows the scheme of the entire system,

fig. 2 shows a detail of the plant itself, and fig. 3 is a horizontal section along the line III-III of fig. 2.

The aqueous slime containing from 28% to 45% of water is dosed to a horizontal centrifugal separator 1, here dehumidified to 18% + 22% of water and then transferred at constant flow (possibly with one or more components of the raw raw material prepared for dry way and dosed by a pond-doser 5) in a dryer 2 run, in co-current, by gas coming from a first stage of preheating 7. The solid matter, dried and powdery, is taken in suspension from the gases and then separated from the same in dust collectors with cyclones 3 and in an electrofilter 4. This powder is then fed (possibly with one or more components of the raw raw material prepared dry and separately dosed by the weigher-doser 5) in the flue gas flow that pass through a conduit 6 connecting a second preheating stage 12 and the first preheating stage 7.

The material captured in the first stage 7 reaches the base of a reactor 8 in which it is taken in suspension by the combustion gases coming from a rotating furnace 13 and by the combustion gases produced in a chamber 9 which uses any type of fuel with hot combustion air coming from a clinker cooler 10 after any dedusting in a gravity or centrifugal type separator 11.

The flue gases produced in the chamber 9 are made to flow tangentially into the reactor 8, as illustrated in particular in Figures 2 and 3.

From the reactor 8 the preheated matter passes, in suspension, into a cyclone 12: here it is separated and fed to the rotating oven 13 where decarbonation is completed and clinkerization is carried out.

The clinker produced in the oven 13 is cooled in the cooler 10.

If required by special circumstances, the drying process in the dryer 2 is partly carried out by also using a portion, more or less important, of. hot air from the clinker cooler 10 (see in duct 1 the duct 14 indicated by dashed lines).

The main advantages of the integrated process plant, according to the described embodiment of the present invention, are the following:

The centrifugal separators 1 operate according to a continuous process and can be inserted as a whole in the dryer, performing the triple function of thickeners, feeders and air exclusions (function

15 the latter indispensable for the high depression existing inside the dryer).

The dosing of the sludge with 28% + 45% of water at the inlet of the centrifugal separators is thus made possible.

By using, according to the prior art, pressure filters, as thickeners, to obtain slurry, a discontinuous production is obtained, that is, by batches; the panels obtained require to be reduced in size, accumulated, weighted and fed to the drying system by means of air exclusion valves. The operation of the air exclusions 25 is always problematic with sticky material as thickened slime often occurs; their imperfect operation invariably penalizes the thermal efficiency of the drying process through the entry of false air.

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The possibility of introducing one or more components of the raw material in the form of dry powder into the dryer 2 or into the duct 6 which leads to the first preheating stage 7 is allowed, which for the limited natural humidity 35 or if used for correction purposes modest it is convenient to grind dry.

Uses are made possible:

- the sensitive heat of the oven gases for drying the thickened slime, after their use in the

40 pre-calcination and preheating of the dried mixture;

- part of the hot air made redundant by the cooling of the clinker as a comburent in the precalcination reactor;

45 - other part of said hot air - possibly - as additional drying gas, in dryer 2.

The operation of the precalcination reactor allows to decrease the fuel supplied in the oven

50 rotating with reduction of the thermal load on the refractories and of the temperatures in the clinkerization zone. Therefore, the evaporation of the volatile compounds from the material being cooked and the extent of their enrichment cycle in the entire cooking system are also reduced. The same reactor allows - by varying the quantity of fuel burned there - to obtain the most convenient volumes of gas, and at the appropriate temperature, at the entrance of the drying stage.

The transformation of existing wet ovens into 60 semi-wet ovens is extremely simple and adequately economical, reducing their thermal consumption from the conventional values of 1250 + 1600 kCal / kg clinker to no more than 950 kCal / kg clinker.

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1 sheet of drawings

Claims (2)

631691 CLAIMS 1. Plant for the transformation into wetland clinker of wet sludge of raw materials from cement having a water content of 28% -45%, including a partial dehumidification equipment (1) of the aqueous sludge, from which the partially dehumidified sludge is fed to a dryer (2) run in co-current by gases coming from a multistage preheater, a dedusting device (3, 4) connected to the output of said dryer, from which the powdery material is fed to the first stage (7) of preheating, a rotating oven (13) to which the preheated material in the last preheating stage (12) is fed and which is connected to the entrance of this last preheating stage, as well as a clinker cooler (10) connected to the exit of the rotary kiln, characterized in that the partial dehumidification apparatus of the aqueous sludge consists of at least one centrifugal separator oriz zontale (1) directly connected to the inlet of the dryer (2). System according to claim 1, characterized in that a weighing device (5) is connected to the inlet of the dryer (2) for the addition of at least one corrective component in the form of dry powder. System according to claim 2, characterized in that the weighing device (5) can be connected alternatively to the preheater. Plant according to claim 1, characterized by a reactor (8) of partial decarbonation of the preheated powdery material coming from the first preheating stage (7), said reactor (8) being placed along the connection duct between the rotating oven (13) and the last stage of preheating (12). 5. Plant according to claim 4, characterized in that hot gases produced in a combustion chamber (9) are used in the reactor (8) with the use, as oxidiser, of hot air coming from the clinker cooler (10). Numerous plants for preheating and cooking the dry mix of raw materials from cement are known in the Portland cement technology, as well as their recognized advantages of thermal economy and simplicity of installation. Moreover, they are not economically usable when the natural humidity of the raw materials requires their treatment (grinding and homogenization) by the so-called wet process, which involves cooking an aqueous slime, of the ground mixture of the raw materials, containing from 28% to 45% of water (depending on the nature of the same) and, therefore, an expensive consumption of thermal energy, between 1250 and 1600 kCal / kg of clinker. There are still numerous systems - modern and large - which operate according to this process and with such high consumption, would require an adequate transformation to make their operation economical. There are known proposals and attempts to spray aqueous sludge (containing 28% - 45% of water) of a mixture of raw materials from Portland, obtained with the process by wet process, into the exhaust gas of a rotating kiln to cause its rapid transformation into a powder dry to preheat, then, in suspension and cook, then, in a rotating oven. 2 However, it appears that practical difficulties and not brilliant results have hitherto prevented a large industrial development of this principle. There are also known systems for dehumidifying the aqueous melts in question by filtration both under vacuum and under pressure. Filter presses are the most frequently used devices for this purpose. However, they have the drawback of operating in a discontinuous or semi-continuous way, and the complication of requiring - downstream from them - further treatment, storage and dosing devices so that the material can be fed to any drying system. and cooking. It should also be noted that the financial costs related to the investment for the plant, as well as the 15 operating and maintenance costs, of the filtration of the slime under pressure sometimes exceed the cost of the thermal energy required by the evaporation of the separated water by filtration, so that the process is not economic.