WO2009095121A1

WO2009095121A1 - Plant for manufacturing cement

Info

Publication number: WO2009095121A1
Application number: PCT/EP2008/066005
Authority: WO
Inventors: Peter Rosholm; Kim Clausen
Original assignee: FLSmidth AS
Current assignee: FLSmidth AS
Priority date: 2008-02-01
Filing date: 2008-11-21
Publication date: 2009-08-06
Anticipated expiration: 2010-08-01
Also published as: DK200800141A

Abstract

Described is a plant for manufacturing cement, which plant comprises a cyclone preheater (1) for preheating cement raw materials, a calciner (3) for calcination of preheated cement raw materials, a kiln (5) for burning cement clinker, as well as means (12) for removing volatile components, such as chloride, alkali and sulphur, from the cement manufacturing plant. The plant is peculiar in that at least some of the means (12) for removing volatile components from the plant are located after the calciner (3) viewed in the direction of movement of the gases. It is hereby obtained, that significant amounts of volatile components, such as chloride, particularly KCI, may be removed from the plant since the removal is effected at the location of the plant where the highest concentration of these components occur, thereby avoiding coatings and clogging further upstream in the preheater. Also, the energy loss will be reduced since the gases after the calciner have a temperature which is lower than that occurring immediately after the kiln, and, therefore, there the volatile components need not to be cooled to the same extent in order to achieve condensation. Another advantage of the plant according to the invention is that the draught conditions and the mixing ratio of the gases which are drawn through the calciner and the preheater will be far less disrupted.

Description

PLANT FOR MANUFACTURING CEMENT

The present invention relates to a plant for manufacturing cement, which plant comprises a cyclone preheater for preheating cement raw materials, a calciner for calcination of preheated cement raw materials, a kiln for burning cement clinker, as well as means for removing volatile components, such as chloride, alkali and sulphur, from the cement manufacturing plant.

Cement manufacturing plants of the aforementioned kind are well known. During manufacturing of cement different types and compositions of volatile components, such as chloride, alkali and sulphur, will often be introduced together with the cement raw materials and the fuel. These volatile components will circulate in the kiln system of the plant between the burning zone in which they undergo evaporation and the preheater zone in which they undergo condensation, and may cause clogging and unsteady kiln operation. One of the most common chloride compounds circulating in the kiln system is KCI .

The known plants use a bypass which is located in immediate proximity of the exhaust gas outlet of the kiln in order to divert a portion of the exhaust gases from the kiln, typically between 2 and 10 per cent of the kiln exhaust gases, thereby ensuring continuous extraction of volatile components from the cement manufacturing plant. In a traditional kiln bypass, the extracted kiln exhaust gases are cooled in a separate chamber by the application of air and/or water to a temperature which is lower than the condensation temperature of the volatile components, thereby allowing the volatile components to be separated in solid form from the exhaust gases, for subsequent disposal or application in the finished cement or for other purposes.

Measurements performed by the applicant of the present patent application at plants of the aforementioned type have, however, indicated that substantial amounts of KCI may be present in the exhaust gases which are discharged from the calciner. This is ascribable to the fact that the phase balance between KCI in liquid phase and in steam phase entails that a substantial amount of KCI will be present in the steam phase in the exhaust gases being discharged from the calciner. The KCI carried along from the calciner will undergo condensation on the cement raw materials further upstream in the preheater, typically in the second and third lowermost cyclone stage, giving rise to coatings and clogging. This problem has proved to be particularly pronounced at plants where the calciner comprises a zone which is operated at a high temperature which may for example be in excess of 900° C. The traditional plants have proved to be ineffective in addressing this problem.

It is a further disadvantage of the traditional plants that the exhaust gases which are extracted via the bypass system have a relatively high temperature ranging between 1000 and 1200 ⁰C, and that the energy loss occurring in connection with the subsequent cooling of the extracted exhaust gases hereby is relatively high. It is a further disadvantage that the draught conditions and the mixing ratio of the gases which are drawn through the calciner and the preheater, and which is a combination mixture of combustion air to the calciner, typically air from a subsequent clinker cooler, and kiln exhaust gases, will often be disruptively affected by variations in the quantity of exhaust gases being extracted via the bypass system. Also, the bypass system in a traditional plant may be adversely affected by fall-through, unburned material from the calciner.

It is the object of the present invention to provide a plant for manufacturing cement by means of which the aforementioned disadvantages are eliminated or significantly reduced.

According to the invention this is achieved by a plant of the kind mentioned in the introduction, and being characterized in that at least some of the means for removing volatile components from the plant are located after the calciner viewed in the direction of movement of the gases. It is hereby obtained, that significant amounts of volatile components, such as chloride, particularly KCI, may be removed from the plant since the removal is effected at the location of the plant where the highest concentration of these components occur, thereby avoiding coatings and clogging further upstream in the preheater. Also, the energy loss will be reduced since the gases after the calciner have a temperature which is lower than that occurring immediately after the kiln, and, therefore, there the volatile components need not to be cooled to the same extent in order to achieve condensation. Another advantage of the plant according to the invention is that the draught conditions and the mixing ratio of the gases which are drawn through the calciner and the preheater will be far less disrupted.

The means which are located after the calciner viewed in the direction of movement of the gases for removing volatile components from the plant, and which in principle may comprise any appropriate means for this purpose, should preferably be located ahead of the location where preheated raw material from the preheater is introduced into the gases. This is due to the fact that the preheated material will lower the temperature of the gases, causing volatile components to undergo condensation on the preheated material and thereby reducing the amount of volatile components which can effectively be removed from the plant.

In one embodiment the means may comprise a condensation body which at a temperature which is lower than the condensation temperature of the volatile components is configured for being led into and away from the gases, so that volatile components when brought into contact with the condensation body will undergo condensation and be deposited on the body. The condensation body may for example comprise one or several discs protruding partially into the gases and partially positioned outside the gases, and being configured for rotation about their centreline. Also, the means may advantageously comprise means for active cooling of the condensation body, said means may comprise means for cooling the surface of the condensation body by the application of air, water or another cooling medium, and/or cooling channels provided in the condensation body for circulation of cooling medium.

In another embodiment the means may comprise a bypass for extracting a portion of the gases being discharged from the calciner, a cooling device for cooling the extracted gases and a separation unit for separating the condensed volatile components and dust from the gases. In this embodiment the plant comprises preferably a separation unit, such as a cyclone, which is located between the calciner and the mentioned bypass in order to minimize the amount of calcined raw material entrained in the extracted gas stream. The separation unit may appropriately be constituted by the cyclone which at all cement manufacturing plants of the kind mentioned in the introduction is located after the calciner.

The invention will now be explained in further details with reference to the drawing, being diagrammatical, and where

Fig. 1 shows a first embodiment of a cement manufacturing plant according to the invention, and

Fig. 2 shows a sectional view of a second embodiment of a cement manufacturing plant according to the invention.

In Fig. 1 is seen a plant for manufacturing cement clinker, which plant comprises a cyclone preheater 1 , a calciner 3 with separation cyclone 11 , a rotary kiln 5 and a clinker cooler 7. Cement raw materials are introduced via an inlet F in the inlet duct to the uppermost cyclone stage of the cyclone preheater 1 , being preheated, calcined and burned into clinker by being transported first through the preheater 1 , the calciner 3, and then through the rotary kiln 5 in counter flow to hot exhaust gases which are formed at, respectively, a burner 8 in the rotary kiln 5 and a burner 9 in the calciner 3, and combustion air which is introduced to the calciner 3 via a duct 10, and being drawn through the preheater string 1 by the application of a not shown fan. The burned clinker is subsequently cooled in the clinker cooler 7 by the application of cooling air. The shown plant also comprises means 12 for removing volatile components, such as chloride, alkali and sulphur, from the cement manufacturing plant.

According to the invention at least some of the means 12 for removing volatile components from the plant are located after the calciner 3 viewed in the direction of movement of the gases so that the relatively substantial amounts of volatile components which circulate in this part of the plant can thus be removed from the plant in a manner which is advantageous from the viewpoint of energy and operational efficiency, and thus coatings and clogging further upstream in the preheater can be avoid. The means 12 are located ahead of the location 19 where preheated raw material from the preheater is introduced to the gases.

In the embodiment shown in Fig. 1 , the means 12 comprise a bypass and they are located after the separation cyclone 11 of the calciner 3 in order to minimize the amount of calcined raw material entrained in the extracted gas stream. The shown bypass comprises a mixing chamber 13 for extracting and cooling a portion of the gases from the calciner 3, a separation cyclone 14 for separating coarse solid particles from the cooled gases being diverted from the mixing chamber 13, said solid particles possibly being returned to the kiln 5, a conditioning tower 15 for additional cooling of the gases, a filter 16 for separating dust with a high content of chloride, alkali and/or sulphur, as well as a fan 17 for drawing the gases through the mentioned bypass. The mixing chamber 13 comprises in the embodiment shown a tubular housing which is provided at one end with an inlet for gases from the calciner 3 and provided at its other end with an outlet for cooled gases. The gases from the calciner 3 are cooled in the mixing chamber 13 using cooling gas which is introduced via a tangential inlet 18.

In the embodiment shown in Fig. 2 the means 12 are located ahead of the separation cyclone 11 of the calciner 3 and comprise a condensation body in the form of a disc 21 , which is fitted on a shaft 22, being capable of rotation through the use of appropriate means. In Fig. 2 the disc 21 is located immediately after the calciner 3 in such a way that approximately one-third of the disc 21 projects into the gases in the discharge duct from the calciner 3 and so that approximately two-thirds of the disc 21 are located outside. By using one or possibly several rotating discs 21 which are introduced into and removed from the gas stream during their rotation, it will be possible to continuously remove volatile components from the cement manufacturing plant.

During the operation of the plant shown in Fig. 2 the disc 21 rotates in such a way that its coldest part is constantly introduced into the gases in the discharge duct from the calciner 3. Hence volatile components present in steam phase in the gases, will, when brought into contact with the disc 21 , be cooled to a level below their condensation temperature so that they are condensed and deposited on the disc 21. The hottest parts of the disc 21 are simultaneously moved out of the discharge duct and can subsequently be cleaned of deposited condensation products through the use of for example appropriate scraping elements.

The plant may further comprise means, not shown, for injecting water onto that part of the disc 21 which is located outside the discharge duct in order to obtain an enhanced cooling.

Claims

1. A plant for manufacturing cement, which plant comprises a cyclone preheater (1 ) for preheating cement raw materials, a calciner (3) for calcination of preheated cement raw materials, a kiln (5) for burning cement clinker, as well as means (12) for removing volatile components, such as chloride, alkali and sulphur, from the cement manufacturing plant, characterized in that at least some of the means (12) for removing volatile components from the plant are located after the calciner (3) viewed in the direction of movement of the gases.

2. A plant according to claim 1 , characterized in that the means (12) are located ahead of the location (19) where preheated raw material from the preheater is introduced into the gases.

3. A plant according to claim 1 or 2, characterized in that the means (12) comprise a condensation body (21 ) which at a temperature which is lower than the condensation temperature of the volatile components is configured for being led into and away from the gases.

4. A plant according to claim 3, characterized in that the condensation body (21 ) comprises one or several discs (21 ) protruding partially into the gases and partially positioned outside the gases, and being configured for rotation about their centreline (22).

5. A plant according to claim 3, characterized in that the means (12) comprise means for active cooling of the condensation body (21 ).

6. A plant according to claim 5, characterized in that the means for active cooling of the condensation body (21 ) comprise means for cooling the surface of the condensation body by the application of air, water or another cooling medium, and/or cooling channels provided in the condensation body (21 ) for circulation of cooling medium.

7. A plant according to claim 1 or 2, characterized in that the means (12) comprise a bypass comprising a mixing chamber (13) for extracting and cooling a portion of the gases from the calciner (3), a separation cyclone (14) for separating coarse solid particles from the cooled gases being diverted from the mixing chamber (13), a conditioning tower (15) for additional cooling of the gases, a filter (16) for separating dust with a high content of chloride, alkali and/or sulphur, as well as a fan (17) for drawing the gases through the mentioned bypass.

8. A plant according to claim 7, characterized in that the mixing chamber (13) comprises a tubular housing which is provided at one end with an inlet for gases from the calciner (3) and provided at its other end with an outlet for cooled gases, as well as a tangential inlet (18) for introducing cooling gas into the mixing chamber (13).

9. A plant according to claim 7, characterized in that comprising a cyclone (11 ), which is located between the calciner (3) and the said means (12).