METHOD AND DEVICE FOR REDUCING NOX EMISSIONS FROM A ROTARY TUBULAR FURNACE

Abstract

In a method for reducing NOx emissions in a rotary kiln of a clinker production plant, fuel delivered by a burner of the rotary kiln is burnt along with primary air delivered by the burner, the primary air having a lower oxygen content and a higher temperature than the ambient air and being obtained by mixing ambient air with waste gas from the rotary kiln or from a heat exchanger that is connected to the rotary kiln and is used for preheating raw meal. The primary air is furthermore obtained by admixing hot air, in particular waste air from a clinker cooler.

Description

Method and device for reducing the NOx emissions of a rotary kiln The invention relates to a method for reducing the NOx emissions of a rotary kiln. Clinker production plant in which fuel supplied by a burner of the rotary kiln is burned with primary air supplied by the burner, and the primary air has a lower density than the ambient air. oxygen content and a temperature higher than that of the ambient air, wherein the primary air is obtained by mixing ambient air with exhaust gas from the rotary kiln or from a heat exchanger connected to the rotary kiln for preheating raw meal. The invention further relates to a device for Conducting such a procedure. A procedure of the type mentioned above is in the DE 3530683 AI described. Cement clinker is predominantly produced in a rotary kiln with a pre-connected cyclone preheater and a downstream clinker cooler. The raw meal is heated and pre-calcined in a heat exchanger and then baked in an oven at temperatures between approximately 900 °C and 100 °C. The material enters the furnace and is converted to clinker at approximately 1,450°C in the sintering zone. The temperature of the area responsible for the formation of the The combustion gases required for clinker minerals reach temperatures of up to 2,200°C. This process inevitably produces nitrogen oxides, which can be reduced through primary or secondary measures. Primary measures aim to reduce the formation of nitrogen oxides. Secondary measures The measures aim to remove the nitrogen oxides produced through catalytic and non-catalytic processes. For reasons of reducing environmental pollution, various legal regulations prescribe emission limits for nitrogen oxides. Currently, the prescribed emission limits between 200 and 800mg NOx / Nm3. Secondary measures for NOx reduction include selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) of the exhaust gas. The chemical reaction is selective, so that the Nitrogen oxides (NO, NO2) are reduced, while undesirable side reactions such as the oxidation of sulfur dioxide to sulfur trioxide are largely suppressed. The reaction requires an ammonia component (e.g., ammonia (NH3), urea (CH4N2O), or others), which is added to the exhaust gas. The products of the reaction are water (H2O) and nitrogen (N2). However, these secondary measures increase operating costs and can result in the exhaust gas containing ammonia. The method for primary NOx reduction proposed in DE 3530683 AI is based on the reduction of the The oxygen content of the primary gas supplied to the burner is reduced. This decreases the thermal formation of NOx. To compensate for the lower oxygen content, the primary gas is also supplied at a higher temperature. The primary gas used here is exhaust gas from the rotary kiln or the heat exchanger, which may be mixed with ambient air. One difficulty with this method is... Setting the optimal temperature level and the This represents the oxygen content of the primary gas. The temperature and oxygen content are crucial for the combustion process and thus for the quality of the resulting clinker. of crucial importance, whereby it is particularly important to ensure conditions that remain as consistent as possible. If the primary gas temperature is too high, the The NOx reduction effect is no longer sufficiently present. In turn, an excessively low temperature leads to acid condensation of the recirculated exhaust gas. The sulfur content leads to corrosion problems. Regarding the oxygen content, optimization is necessary to find a compromise between too low a content, where the combustion process is inefficient, and too high a content, where the extent of NOx reduction is insufficient. In addition, predefined values ​​of the The total volume flow rate of the primary gas must be maintained in order to optimize the combustion process. It is therefore desirable that, within the framework of exhaust gas recirculation for the purpose of NOx reduction, specified temperature, Oxygen content and volume flow values ​​must be regulated and maintained as precisely and consistently as possible. This is not satisfactorily possible with the method according to DE 3530683 AI, because the oxygen content and the temperature of the primary air cannot be set independently of each other. 4. An increase in the proportion of recirculated exhaust gas in the primary gas, for example, leads, depending on the The mixing ratio does lead to a reduction of the Oxygen content can be adjusted to a desired level, but this also leads to a change in temperature by a value that cannot be freely chosen. Furthermore, natural factors also contribute to this. Fluctuations in the temperature of the ambient air and the exhaust gas lead to an uncontrollable change in the temperature of the primary gas. The present invention therefore aims to… To improve exhaust gas recirculation processes in such a way that the temperature and oxygen content of the The primary gas and, if applicable, the volume flow rate can be adjusted as independently as possible from each other to ensure sufficient NOx reduction while simultaneously optimizing the to achieve combustion conditions. To solve this problem, the invention essentially provides, in a process of the type mentioned at the outset, that the primary air is further obtained by mixing it with warm air, in particular exhaust air from a clinker cooler. By adding a third air stream, namely warm air, to the ambient air and exhaust gas as needed, a suitable Mixing ratio, temperature and oxygen content of the primary gas are largely independent of each other. be hired. Because a third one is now involved. If control parameters are available, the desired primary gas properties can also be set when fluctuating environmental conditions within further Areas are simplified compared to the state of the art. Here, warm air is understood to mean air that has a has a higher temperature than ambient air, with the use of exhaust air from a clinker cooler being preferred. The warm air preferably has a temperature between or above the temperature of the exhaust gas and that of the ambient air. A preferred procedure stipulates that the The mixing ratio of ambient air, exhaust gas, and warm air is regulated so that the primary gas is supplied to the burner at a temperature of 50–250°C, particularly 100–150°C, and with an oxygen content of 8–18 vol.%, particularly 13–16 vol.%. The volume flows of ambient air, exhaust gas, and warm air are thus selected and coordinated to achieve the desired primary gas properties. For this purpose, the temperature and oxygen content of the primary gas are measured continuously or at regular intervals by sensors, ideally directly before it enters the burner. This data is then fed into a control system that calculates suitable values ​​for the volume flows and generates control commands for corresponding actuators in the supply lines. This takes into account the temperature and the Oxygen content of the available ambient air, exhaust gas, and warm air. On the other hand, Characteristics of the control loop between the point of mixing of the individual volume flows and the point of measurement at the inlet of the primary gas before the Brenner takes into account, for example, a pressure and thus temperature increase caused by a component arranged here. Main blower. It was found that adhering to the above-mentioned values ​​for temperature and oxygen content of the primary gas represents an ideal compromise between the respective requirements. This represents the conflicting requirements of a sufficient reduction of NOx values ​​on the one hand and ensuring an efficient combustion process in the rotary kiln, the economic viability of kiln operation and the maintenance of good clinker quality on the other. Another control variable that can be advantageously used is the The total volume flow rate of the primary gas is used. In this context, the method is preferably performed as follows: It was carried out that the mixing of ambient air, exhaust gas and warm air is regulated to obtain a volume flow of the primary gas adapted to the process. Regarding the temperature of the individual primary gas streams, the following values ​​are preferred. The warm air can be used at a temperature of 80–150°C, a temperature level that can be easily achieved by using the exhaust air from the clinker cooler. The recirculated exhaust gas is preferably used at a temperature of 100–200°C. It is further preferred that exhaust gas with an oxygen content of 6-10 vol.% is used. In the context of the invention, primary air is defined as the sum of all conveyance flows supplied to the combustion chamber by the burner of the rotary kiln. The burner in this context is, in particular, the burner for the Main firing system of the rotary kiln. Such burners typically have a plurality of channels for primary gas, in particular at least one channel for supplying the swirl component of the primary gas and at least one for supplying the axial component of the Primary gas. The primary air is further supplemented by the... The amount of air supplied for fuel delivery is measured. Secondary air refers to the air supplied to the combustion chamber from outside the burner, e.g., from the side of the burner. The majority of the combustion air is supplied via the secondary air supply. Preferably, according to the invention, 5-20 vol% of the combustion air is supplied to the rotary kiln as primary gas and 80-95 vol% as secondary air. Secondary air is supplied. According to another aspect, the invention relates to a device for carrying out the above-described Method comprising a rotary kiln with a burner, an exhaust gas-side connection to the rotary kiln Heat exchangers with or without calciner, and one Clinker cooler, wherein a primary gas supply for the burner with a main blower is provided, wherein upstream of the main blower a mixing device with a ambient air supply, an exhaust gas supply fed by the exhaust gas of the heat exchanger, and one supplied by the exhaust air of the The warm air supply is arranged for the clinker cooler. Preferably, the ambient air supply, the exhaust gas supply, and the warm air supply are each connected to a The control elements are equipped for regulating the volume flow, wherein the control elements are connected to a control device to which measured values ​​from a temperature sensor and oxygen content sensor arranged downstream of the main blower are supplied, wherein the control device is configured for adjusting the control elements so that a predetermined temperature of preferably 50-250°C, in particular 100-150°C, and a predetermined oxygen content of preferably 8-18 vol.%, in particular 13-16 vol.%, of the fuel supplied to the burner is maintained. The supplied primary gas is adhered to. Furthermore, it is preferably intended that the The control device for adjusting the control elements is set up so that a predetermined volume flow rate of the primary gas supplied to the burner is maintained. The invention is described below with reference to a [something] in the The schematically illustrated embodiment is explained in more detail in the drawing. In Fig. 1, a chimney 1 is shown. The diagram shows the extraction of exhaust gas from a heat exchanger of a raw meal preheater. Exhaust gas is diverted from the chimney 1 via a pipe 2, the diverted volume flow being adjustable via a control element 3. The blower for extracting the exhaust gas is designated 4. The exhaust gas is preferably passed through a condenser 5, in which water is extracted from the exhaust gas. It can then be recycled. The oxygen content, temperature, and, if applicable, the pressure of the exhaust gas are measured by means of sensors 6, with a further control element for adjusting the volume flow designated 7. The exhaust gas is then fed into a mixing chamber 8. Exhaust air from the chimney 9, specifically from the clinker cooler, is also fed into the mixing chamber 8. The exhaust air is routed via a duct 10 and a The blower 12 is guided. Sensors 11 measure the temperature and, if applicable, the pressure of the exhaust air. The volume flow of the exhaust air can be adjusted with a control element 13. Furthermore, ambient air 14 is supplied to the mixing chamber 8 via a line 15. The mixture of ambient air, exhaust gas, and exhaust air is supplied as primary gas to the burner 19 of the rotary kiln via a blower 17 and a line 18. Part of the Primary gas can also be supplied as transport gas to corresponding metering devices for fuels via line 21 and blower 22. For adjusting the The volume flow rate of the primary gas is controlled by a regulating device 16. planned. At measuring point 20, the temperature, oxygen content, pressure and volume flow rate of the primary gas measured and in a not shown The control device compares the setpoint values. In case of a deviation from the setpoint values, the control device works together with the control elements 3, 7, 13 and a control element (not shown) for adjusting the ambient air volume to effect a correction.

Claims

Patent claims:

1. Method for reducing the NOx emissions of a rotary kiln of a clinker production plant, in which the NOx supplied by a burner of the rotary kiln is Fuel is burned with primary air supplied by the burner, and the primary air has a higher density than the Ambient air has a lower oxygen content and a has a higher temperature than the ambient air, with the primary air being produced by mixing ambient air with exhaust gas from the rotary kiln or from a connected unit. The heat exchanger connected to the rotary kiln, which serves to preheat raw meal, is thereby obtained characterized in that the primary air is further supplied by Mixing with warm air, especially exhaust air from a clinker cooler, is preserved.

2. Method according to claim 1, characterized in that the mixing ratio of ambient air, exhaust gas and warm air is regulated such that the primary gas is supplied to the burner at a temperature of 50-250°C, in particular 100-150°C and an oxygen content of 8-18 vol.%, in particular 13-16 vol.%.

3. Method according to claim 1 or 2, wherein characterized by the fact that the mixing of ambient air, exhaust gas and warm air is used to obtain a mixture suitable for the process. The volume flow of the primary gas is regulated by an adjusted flow rate.

4. Method according to claim 1, 2 or 3, wherein characterized by the use of warm air with a temperature of 80-150°C, preferably 90-100°C.

5. Method according to one of claims 1 to 4, characterized in that exhaust gas with a temperature of 100-200°C, preferably 145-185°C, is used.

6. Method according to one of claims 1 to 5, characterized in that exhaust gas with an oxygen content of 6-10 vol.%, preferably 6-8 vol.%, is used.

7. Method according to one of claims 1 to 6, characterized in that 5-20 vol% primary gas and 80-95 vol% secondary gas are supplied to the rotary kiln.

8. Method according to any one of claims 1 to 7, characterized in that a portion of the primary gas is used as Transport gas is used for fuels.

9. Device for carrying out the method according to one of claims 1 to 8, comprising a rotary kiln with a burner, a heat exchanger connected to the rotary kiln on the exhaust gas side, and a clinker cooler, wherein a primary gas supply for the burner is provided with a A main blower is provided, with the upstream position of the main blower a mixing device with a ambient air supply, an exhaust gas supply fed by the exhaust gas of the heat exchanger, and one supplied by the exhaust air of the The warm air supply is arranged for the clinker cooler.

10. Device according to claim 9, characterized in that the ambient air supply, the exhaust gas supply and the Each warm air supply is equipped with a control element for regulating the volume flow, the control elements being connected to a control device that receives measured values ​​from a sensor arranged downstream of the main blower. are supplied to temperature sensors and oxygen content sensors, with the control unit for adjusting the Regulatory bodies are established so that a predetermined Temperature of preferably 50-250°C, particularly 100-150°C, and a predetermined oxygen content of preferably 8-18 vol.%, particularly 13-16 vol.%, of the burner The supplied primary gas is adhered to.

11. Device according to claim 9 or 10, wherein characterized in that the control device is set up to adjust the control elements so that a predetermined volume flow of the primary gas supplied to the burner is maintained.