METHOD OF PRODUCING CEMENT CLINKER AND A SECOND CALCINED MATERIAL

Abstract

A method of producing cement clinker and a second calcined material, wherein the cement clinker is produced in a first production line and the second calcined material is produced from a raw material in a second production line by carrying out the following procedures e) optionally drying the raw material in a dryer, g) calcining the optionally dried raw material in a rotary kiln to obtain the second calcined material, wherein the sensible heat of a hot gas in the first production line is used as a heat source in the calcining step g) for calcining the raw material, and wherein the rotary kiln exhaust gas coming from the calcining step g) is introduced into the first production line for the secondary combustion of the rotary kiln exhaust gas.

Claims

1. A method of producing a first calcined material, which is cement clinker, and a second calcined material, wherein the cement clinker is produced in a first production line by carrying out the following steps: a) preheating raw meal in a preheater in counter current flow to hot exhaust gases coming from a clinker furnace, b) optionally pre-calcining the preheated raw meal in a pre-calciner, c) calcining the preheated and optionally pre-calcined raw meal in the clinker furnace in counter current flow to combustion gases of a clinker furnace burner to obtain cement clinker, d) cooling the cement clinker in a clinker cooler, wherein the second calcined material is produced from a raw material in a second production line by carrying out the following steps: e) optionally drying a raw material in a dryer, f) optionally crushing the optionally dried raw material in a crusher, g) calcining the optionally dried and optionally crushed raw material in a rotary kiln to obtain the second calcined material, h) optionally cooling the second calcined material in a cooler, wherein a sensible heat of a hot gas in the first production line is used as a heat source in the calcining step g) for calcining the raw material, and wherein the rotary kiln exhaust gas coming from the calcining step g) is introduced into the first production line for the secondary combustion of the rotary kiln exhaust gas.

2. The method according to claim 1, wherein a clinker cooler off-gas from the clinker cooler is used as said heat source in the calcining step g).

3. The method according to claim 1, wherein the rotary kiln exhaust gas is introduced into the pre-calciner or the preheater of the first production line.

4. The method according to claim 1, wherein the raw material is selected from sludges resulting from washing of sand or aggregates, asphalt, (waste) gypsum, contaminated earth, wet fly ash, other waste or demolition materials, road cleaning sludges, filter cakes from treatment processes of soil and waste washing, and combinations thereof.

5. The method according to claim 1, wherein the raw material is dried in said drying step e) for reducing the amount of free water to <20 wt-%.

6. The method according to claim 1, wherein the sensible heat of a hot gas in the first production line is used as a heat source in the drying step e) for drying the raw material.

7. The method according to claim 1, wherein the dryer and the cooler of the second production line are operated in a heat exchanging relationship so that the sensible heat drawn from the second calcined material during the cooling step h) is used as a heat source for drying the raw material in the drying step e).

8. The method according to claim 1, wherein the dryer and the cooler of the second production line are operated in a heat exchanging relationship so that the a loss of sensible heat to the raw material during the drying step e) is used as a cooling source for cooling the second calcined material in the cooling step h).

9. The method according to claim 1, wherein a drying screw is used for drying the raw material in the drying step e).

10. The method according to claim 1, wherein fuel is burnt in a burner of the rotary kiln for calcining the raw material in step g).

11. A system comprising a first production line for producing a first calcined material, which is clinker, and a second production line for producing a second calcined material, wherein the first production line comprises: a) a preheater for preheating raw meal in counter current flow to hot exhaust gases coming from a clinker furnace, b) optionally a pre-calciner for pre-calcining the preheated raw meal, c) a clinker furnace for calcining the preheated and optionally pre-calcined raw meal in counter current flow to combustion gases of a clinker furnace burner to obtain cement clinker, d) a clinker cooler for cooling the cement clinker, wherein the second production line comprises: e) optionally a dryer for drying a raw material, f) optionally a crusher for crushing the optionally dried raw material, g) a rotary kiln for calcining the optionally dried and optionally crushed raw material to obtain the second calcined material, h) optionally a cooler for cooling the second calcined material, wherein the first production line and the second production line are connected by a first heat exchanging pipe for feeding a sensible heat of a hot gas from the first production line to the rotary kiln as a heat source for calcining the raw material, and wherein the first production line and the second production line are connected by a second pipe for introducing a rotary kiln exhaust gas coming from the rotary kiln into the first production line for the secondary combustion of the rotary kiln exhaust gas.

12. The system according to claim 11, wherein the first heat exchanging pipe is in fluid communication with a clinker cooler of the first production line to feed a clinker cooler off-gas from the clinker cooler as said heat source into the rotary kiln of the second production line.

13. The system according to claim 11, wherein the second pipe is in fluid communication with the pre-calciner or the preheater of the first production line for introducing the rotary kiln exhaust gas into the pre-calciner or the preheater, respectively.

14. The system according to claim 11, wherein the first production line and the second production line are connected by a third heat exchanging pipe for feeding the sensible heat of a hot gas from the first production line to the dryer as a heat source for drying the raw material.

15. The system according to claim 11, wherein the dryer and the cooler of the second production line are connected with each other in a heat exchanging manner so that the sensible heat drawn from the second calcined material in the cooler is used as a heat source for drying the raw material in the dryer.

16. The system according to claim 11, wherein the dryer and the cooler of the second production line are connected with each other in a heat exchanging manner so that a loss of sensible heat to the raw material in the dryer is used as a cooling source for cooling the second calcined material in the cooler.

17. The system according to claim 11, wherein the dryer is designed as a drying screw, comprising a screw conveyor for conveying the raw material and a heat exchanger surface for transferring heat from a heat exchanger fluid to the raw material while being conveyed.

18. The system according to claim 11, wherein the rotary kiln comprises a burner.

19. The system according to claim 11, wherein the cooler is designed as a cooling screw, comprising a screw conveyor for conveying the second calcined material and a heat exchanger surface for transferring heat from the second calcined material to a heat exchanger fluid.

20. The method according to claim 1, wherein the second calcined material is a material having pozzolanic and/or latent hydraulic properties.

Description

[0058] The invention will now be described in more detail with reference to an illustrative embodiment shown in FIG. 1. FIG. 1 schematically illustrates a first production line 1 and a second production line 2. The first production line 1 is a clinker production line and comprises a preheater 3, to which a raw meal 4 is fed in order to preheat the raw meal 4 in counter current flow to hot exhaust gases coming from a clinker furnace 6. The hot exhaust gases are discharged through the stack 20. After passing through the preheater 3, the raw meal is fed into a pre-calciner 5, in which the preheated raw meal is pre-calcined. The pre-calcined raw meal is fed into the clinker furnace 6, where the raw meal is calcined in counter current flow to combustion gases of a clinker furnace burner 7 to obtain cement clinker. The cement clinker withdrawn at the downstream end of the clinker furnace 6 is introduced into a clinker cooler 8 and the final clinker product is stored in a silo 9. A first partial amount of the off-gas from the clinker cooler 8 is used as combustion gas in the clinker furnace 6 and a second partial amount of said off-gas is used as tertiary air, which is fed to the pre-calciner 5 via a tertiary air duct 10.

[0059] The second production line 2 comprises a dryer 11, in particular a drying screw, to which raw material 12, such as sludges resulting from the washing of sand or aggregates, is fed, in order to remove water from said raw material. The dried raw material is fed into a rotary kiln 13, where it is calcined at a temperature of 400-1.000° C. The calcined material, such as calcined clay is withdrawn at the downstream end of the rotary kiln 13 and is introduced into a cooler 14 and the final calcined material is stored in a silo 15.

[0060] In order to provide the thermal energy to the rotary kiln 13 that is required for the calcination process, a partial amount of the off-gas from the clinker cooler 8 or from other suitable heat sources from the first production line is fed to the rotary kiln 13 via a pipe 16.

[0061] Further, the exhaust gas from the rotary kiln 13 is introduced into the pre-calciner 5 of the first production line 1 via a pipe 17 for the secondary combustion of the rotary kiln exhaust gas.

[0062] Further, the cooler 14 and the dryer 11 are connected with each other by tubings 18 and 19, in order to establish a closed loop for exchanging heat between said components via a heat exchanging fluid that circulates in said tubings 18 and 19.

[0063] To sum up, the invention results in the following advantages. [0064] Increasing the energy efficiency in the thermal treatment of raw materials to obtain a material having pozzolanic and/or latent hydraulic properties. [0065] Replacement of scarce materials required for the production of composite cement (i.e. limestone, fly ash, granulated blast furnace slags). [0066] The thermal treatment of raw materials for the production of a material having pozzolanic and/or latent hydraulic properties can be performed with 100% alternative or renewable fuels. [0067] Ecologically friendly recycling of contaminated wastes. [0068] Production of a material having pozzolanic and/or latent hydraulic properties suitable for the utilization in composite cements with a maximum feed of contaminated material streams. [0069] Replacement of energy intense clinker resulting in ecological and economic benefits. [0070] Lower CO.sub.2 footprint compared to conventional methods (e.g. flash calcination). [0071] Reduced investment and operating costs compared to a flash calciner.