Simplification of the process of capturing carbon dioxide from exhaust gases of a cement system

Abstract

The invention relates to a device for thermally treating a mineral material. The device has a heat consumer, in particular a comminuting device (10), and a treatment device (20), wherein the treatment device has a gas outlet, and the heat consumer, in particular the comminuting device (10), has a gas inlet. The invention is characterized in that the device has a gas-gas heat exchanger (30), said gas-gas heat exchanger (30) having a first side with a first inlet and a first outlet and a second side with a second inlet and a second outlet. The gas outlet is connected to the first inlet, and the second outlet is connected to the gas inlet. The gas-gas heat exchanger (30) is a rotary heat exchanger.

Description

[0001] Simplifying carbon dioxide capture from exhaust gases of a cement plant

[0002] The invention relates to a plant for the thermal treatment of a mineral material, for example for the production of clinker, in which the resulting carbon dioxide can be separated in a particularly efficient manner.

[0003] The cement industry, in particular, is comparatively heavily involved in carbon dioxide emissions, as in addition to the carbon dioxide produced from the fuel, further carbon dioxide also escapes from the treated limestone, for example. Therefore, there are many approaches to capturing the carbon dioxide produced in this way to prevent emissions.

[0004] WO 2011 / 029 690 A1 discloses a process for producing cement with CO2 separation.

[0005] The higher the initial carbon dioxide content, the easier the separation of carbon dioxide is. Therefore, processes are known that use the purest oxygen possible during thermal treatment, thus minimizing contamination of the resulting carbon dioxide, particularly with nitrogen. Such processes are known, for example, from DE 10 2018 206 673 A1 or DE 10 2018 206 674 A1. However, this only makes sense if the subsequent nitrogen input is also minimized as much as possible.

[0006] To efficiently utilize heat in a thermal treatment plant, the exhaust gas from the preheater can be used, for example, to utilize the heat during mill-drying of the incoming material stream. The disadvantage of this approach is that air is likely to be entrained, thus reducing the carbon dioxide concentration, which in turn increases the effort required for separation.

[0007] DE 340 49 43 A1 discloses a process and a plant for firing sinterable material such as cement clinker from limestone, dolomite, or similar minerals containing raw materials. WO 2011 / 029 690 A1 discloses a process for producing cement with CO2 separation.

[0008] An exhaust gas purification system with heat recovery is known from US 2011 / 0073023 A1.

[0009] DE 10 2008 053 ​​135 B3 discloses a process and a plant for producing cement clinker.

[0010] The object of the invention is to make optimal use of the heat and to minimize the entry of secondary air into the main gas flow.

[0011] This object is achieved by a device having the features specified in claim 1. Advantageous further developments emerge from the subclaims, the following description, and the drawing.

[0012] The device according to the invention is used for the thermal treatment of a mineral material, for example for producing clinker from limestone. The device has a heat consumer, in particular a comminution device, and a treatment device. The treatment device has a gas outlet. The gas outlet is the point at which the gas stream leaves the thermal treatment device, usually at the point in a preheater where the mineral material is also applied. The material flow and gas flow are usually in opposite directions across the entire device, although they often run parallel in sections. The heat consumer, in particular the comminution device, has a gas inlet. Warm gas is supplied through the gas inlet, which in turn is capable of removing moisture from the material, for example.Such systems are known to those skilled in the art in a wide variety of designs and are used, for example, for clinker production from limestone or the production of artificial pozzolans from clay. The precise design of the thermal treatment device or the heat consumer, in particular the comminution device, is not essential to the invention and can be implemented according to the state of the art.

[0013] According to the invention, the device comprises a gas-gas heat exchanger. The gas-gas heat exchanger has a first side with a first inlet and a first outlet, and a second side with a second inlet and a second outlet. The gas outlet is connected to the first inlet. The warm exhaust gas from the thermal treatment device is thus fed into the first side of the gas-gas heat exchanger, where it releases its heat. The second outlet is connected to the gas inlet; the gas heated in the second side of the gas-gas heat exchanger is thus fed to the heat consumer, in particular the comminution device. The gas-gas heat exchanger is a regenerator, or more precisely a rotary heat exchanger. In a rotary heat exchanger, a usually disc-shaped body provided with gas passages is rotated. One part of the rotating body is located in the first side, the other part in the second side.Here, the flow through the rotating body is in one direction on the first side and in the opposite direction on the second side. This effectively creates a counterflow heat exchanger, which enables the most complete heat transfer possible. Such rotary heat exchangers are now often used, for example, in building air conditioning technology. The advantage of a rotary heat exchanger is its relatively compact design. In return, it is accepted that when the rotating body rotates, there is always a certain, but comparatively small, exchange of gas between the first side and the second side through the gas channels of the rotating body. However, this is within an acceptably small range compared to the total volume flow. This means that the waste heat can be used efficiently, without high equipment costs and without contamination of the carbon dioxide-containing gas.Typically, recuperators, such as shell-and-tube or plate heat exchangers, are used as heat exchangers in the thermal treatment of mineral materials. The advantage of this is that the two gases are spatially separated, preventing mixing between them. This is particularly useful in exhaust gases, as pollutants, suspended matter, or carbon dioxide cannot pass from the exhaust gas into the other gas. However, the invention does not use a recuperator, but rather a regenerator, or more precisely, a rotary heat exchanger.

[0014] In a further embodiment of the invention, the first outlet is connected to a carbon dioxide separation device. Preferably, the first outlet is connected to a carbon dioxide separation device via a dust removal device. Thus, the carbon dioxide can be separated with only very minimal contamination by foreign gases, which minimizes the separation effort.

[0015] In a further embodiment of the invention, the treatment device comprises a preheater and a calciner. Additionally, the treatment device may also comprise a rotary kiln. The gas outlet is located at the gas flow end of the preheater.

[0016] In a further embodiment of the invention, the heat consumer is a comminution device. In the comminution device, the mineral raw material, for example, limestone, is typically first comminuted, in particular crushed and / or ground. Simultaneously or subsequently, drying usually also takes place to remove the water, thus eliminating the energy required for this later in the thermal treatment device.

[0017] In a further embodiment of the invention, the comminution device is a mill. For example, the mill is a vertical roller mill.

[0018] In a further embodiment of the invention, the first outlet is connected to a dust removal device. By using the gas-to-gas heat exchanger, the gas stream can be sufficiently cooled, eliminating the need for an additional cooling device, such as an evaporative cooler.

[0019] In a further aspect, the invention relates to a method for operating a device according to the invention. The ratio of gas supplied to the first inlet to the second inlet is selected such that the gas stream exiting the first outlet requires no further cooling for further processing, in particular dust separation. If ambient air (e.g., 20°C) is used as the gas for the second side, the cooling of the gas stream in the first side can be easily and specifically adjusted by adjusting the ratio of the gas flows.

[0020] In a further embodiment of the invention, the gas on the first side is not cooled below 100°C, preferably not below 120°C. This prevents water condensation in the rotating body. This has several advantages. Firstly, condensation on the first side and evaporation on the second side would require large amounts of heat. Secondly, the gas stream on the second side would be humidified, which would subsequently also serve for drying in the comminution device.

[0021] The device according to the invention is explained in more detail below using an embodiment shown in the drawing.

[0022] Fig. 1 schematic representation of the device

[0023] In Fig. 1, the device according to the invention is shown highly schematically and not to scale.

[0024] The mineral material, such as limestone, is fed to the comminution device 10, such as a vertical roller mill, where it is crushed and simultaneously dried by the gas stream. The material stream is then fed to the treatment device 20, more precisely to the preheater 21. The preheated material enters the calciner 22 and the rotary kiln 23, and then into the material cooler 24, where it can be removed as a product, such as clinker.

[0025] The gas stream passes through the material cooler 24, preheated, into the rotary kiln 23 and from there into the calciner 22. Combustion reactions typically take place in the rotary kiln 23 and in the calciner 22 to generate the energy required for the thermal treatment. In the preheater 21, the gas stream then transfers a large portion of its heat to the material stream. The gas stream leaves the preheater at, for example, 300°C. This gas stream is fed into the first side of the gas-gas heat exchanger 30 and passed through the rotating body 31. In the example shown, the rotating body 31 rotates about an axis of rotation arranged vertically in the plane of the image. In the rotating body 31, the gas stream transfers the heat to the rotating body 31, which, due to the flow direction, is warmer on the top side than on the bottom (in this illustration).The cooled gas stream is fed, for example, at 120°C into a dust removal device 40 and then into a carbon dioxide separation device 50.

[0026] For example, ambient air at 20°C is supplied to the second side of the gas-to-gas heat exchanger 30. This gas flow is selected to be slightly smaller than the gas flow from the treatment device 20, so that the gas is supplied to the second side of the gas-to-gas heat exchanger 30 of the comminution device 10 at 275°C, for example.

[0027] Reference symbol

[0028] 10 Shredding device

[0029] 20 Treatment device

[0030] 21 preheaters

[0031] 22 Calciner

[0032] 23 rotary kilns

[0033] 24 material coolers

[0034] 30 gas-gas heat exchangers

[0035] 31 rotating body

[0036] 40 Dust extraction device

[0037] 50 carbon dioxide capture device

Claims

Patent claims 1 . Device for the thermal treatment of a mineral material, the device comprising a heat consumer and a treatment device (20), the treatment device having a gas outlet, the heat consumer having a gas inlet, characterized in that the device comprises a gas-gas heat exchanger (30), the gas-gas heat exchanger (30) having a first side with a first inlet and a first outlet and a second side with a second inlet and a second outlet, the gas outlet being connected to the first inlet and the second outlet being connected to the gas inlet, the gas-gas heat exchanger (30) being a regenerator, more precisely a rotary heat exchanger.

2. Device according to claim 1, characterized in that the first outlet is connected to a carbon dioxide separation device (50).

3. Device according to one of the preceding claims, characterized in that the treatment device (20) comprises a preheater (21) and a calciner (22), wherein the gas outlet is arranged at the gas flow end of the preheater.

4. Device according to one of the preceding claims, characterized in that the heat consumer is a comminution device (10).

5. Device according to claim 4, characterized in that the comminution device (10) is a mill.

6. Device according to one of the preceding claims, characterized in that the first outlet is connected to a dust removal device (40).

7. A method for operating a device according to any one of the preceding claims, characterized in that the ratio of gas supplied into the first inlet to gas supplied into the second inlet is selected such that the The gas stream exiting the first outlet does not require any further cooling for further processing.

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