Odor treatment in the clinker cooler

Abstract

Method for manufacturing cement clinker comprising providing a moist secondary fuel and drying the fuel with a hot gas thereby generating an off-gas containing pollutants, providing a raw meal, preheating and optionally precalcining the raw meal, sintering it to provide hot cement clinker, passing the hot cement clinker into a cooler, and passing cooling gas into the cooler to cool the hot cement clinker, wherein the off-gas is used as cooling gas and / or mixed with cooling gas having been heated by cooling the clinker, so that the pollutants are oxidized or decomposed providing a clinker cooler exhaust gas containing less or no pollutants, and cement clinker cooler for deodorizing off-gas from secondary fuel drying, wherein a duct with openings for passing the off-gas into the cooler is arranged above the clinker and at least one hood comprising a top and two side plates is rotatably supported by the duct.

Description

Odor treatment in the clinker cooler

[0001] The present invention relates to a method for reducing malodor from secondary fuels in cement clinker production and to a method for manufacturing cement clinker with moist secondary fuels as well as to a clinker cooler for deodorizing off-gas from secondary fuel drying.

[0002] Cement clinker manufacturing is nowadays mostly achieved by sintering a raw meal in a rotary kiln. The raw meal is usually provided by mining raw materials and grinding them to an appropriate fineness. Energy is typically provided by burning fuels. The current processes and devices are adapted to save energy by a sophisticated use of residual energy in material and gas streams.Thus, raw meal is preheated by kiln exhaust gas, using a preheater, mostly a cyclone preheater. Normally, preheated raw meal is fed to a calciner to convert at least a part of the calcium carbonate into calcium oxide, since that is generally more efficient than calcination in the kiln. Combustion gas for the kiln is at least partly provided by hot gas from the clinker cooler and the remaining hot gas is used for various purposes like raw material drying, fuel drying, recovering heat in one or more heat exchanger(s), and combustion gas for the calciner.

[0003] To save natural raw materials and fossil fuels it is long known to use byproducts and waste as raw materials and fuels, replacing at least a part of the classical ones. Using secondary fuels allows the saving of natural resources and also presents a beneficial use of the calorific values in waste. Secondary fuels are for example, but not limited to high calorific waste materials, like used tires, waste oil and solvents, industrial and domestic waste commonly in pre-treated form, and plastic, textile, and paper waste. Some of these fuels may cause problems due to odorous compounds contained in them or formed during their storage or during their drying. Those are especially fuels with a moisture content of more than 10 wt.-%, often of at least 15 wt.-% like:- fuels obtained from processing solid municipal or industrial waste, in the form ofsolid recovered fuel (SRF) and refuse derived fuel (RDF) both with a typical moisture content in the range from 10 or 15 to 25 wt.-%- municipal sewage sludge with a typical moisture content ranging from 70 to 85 wt.-%- paper fiber sludge with a typical moisture content ranging from 40 to 55 wt.-%.

[0004] SRF and RDF are made from dry, non-hazardous waste that cannot be recycled or composted. They contain various waste materials, including paper, cardboard, wood, textiles, and plastics. Their production involves several stages of processing the materials, normally including crushing, mechanical sorting (e.g., by airflow or by size using e.g., a trommel screen), and separation of ferrous metals. The material is subsequently ground to the required size depending on the endusers’ requirements. The difference between SRF and RDF is the degree of processing. RDF runs through less processing steps. It is screened for recyclable materials and subsequently crushed. SRF is often tailor-made for the end-user, which typically involves grinding and mixing different input streams to create a homogeneous quality with a higher calorific content and lower moisture.

[0005] Municipal sewage sludge is the residual material produced as a waste of municipal wastewater purification. It is a complex mixture that includes organic matter from human waste, food particles, microorganisms, trace chemicals, and inorganic solids. Essentially, it is what remains after treating wastewater in municipal treatment plants. While it poses challenges due to harmful substances, it also contains valuable nutrients like phosphorus, nitrogen, and potassium.

[0006] Paper sludge consists mainly of wet short cellulose fibers in water.During the paper making and paper recycling process, fibers which are physically too short to bind with the longer fibers constituting the sheet end up falling through the press section, together with the excess water. The water is carried to a wastewater system, where the main goal is to separate, process and return clean water into the environment, or recirculate it back into the paper mill. Once themajor amount of water has been separated, the cellulose fibers which are still left in the water are called paper sludge.

[0007] All these secondary fuels have in common that they contain organic materials. The content and type of organic materials varies, depending on the fuel source. Over time, organic matter decomposes, releasing volatile compounds of which many create unpleasant smells. Also, bacteria and other microorganisms break down organic material, producing volatile compounds. Further, these secondary fuels mostly contain significant amounts of water that are removed for efficient use as fuel. During drying of secondary fuels, volatile compounds are released from the solid material, since heating up leads to an increased volatilization. Additionally, the decomposition of organic compounds and biological activity in the material increase with rising temperature, thereby releasing further volatile compounds. Especially for municipal sewage sludge drying, the volatile compounds causing malodor, designated pollutants herein, are well-known. They fall into several major groups:- sulfur compounds, such as hydrogen sulfide (H2S), mercaptans like methane thiol (CH3SH), organic sulfides like dimethyl sulfide (CH3-S-CH3) and dimethyl disulfide (CH3-S-S-CH3);- nitrogen compounds, such as ammonia (NH3), amines like methylamine (CH3NH2) and dimethylamine (CH3-NH-CH3);- organic compounds, such as organic acids like acetic acid and propanoic acid, aldehydes like acetaldehyde and propionaldehyde, ketones like acetone and 2-butanone.Pollutants arising from paper sludge or SRF / RDF drying are of the same type with a focus on organic compounds.

[0008] Innumerable proposals have been made to remove the malodor from exhaust gas. Established methods are absorption, adsorption, condensation, thermal treatment, contacting with ions, and biological treatment. All thesemethods have advantages and disadvantages so that there is not one best method for all kinds of exhaust gas. Instead, an individual solution must be found for each specific process. There are already proposals with regard to using secondary fuels in cement manufacturing. According to WO 2010 / 124702 A1 the off-gas from drying secondary fuels shall be used as cooling gas in the clinker cooler. To ensure complete destruction of the odorous substances, the gas is passed into the recuperation zone of the clinker cooler and becomes part of the secondary air passed from the cooler into the kiln. In US 2005 / 0274067 A1 , the hot gas from the clinker cooler is used to directly or indirectly dry the fuel and the off-gas from the drying is passed into the kiln or calciner after condensing contained water. Both proposals emphasize that it is the high temperature in the kiln which ensures complete removal of malodor. However, the amount of secondary air that can be introduced into a kiln is limited and it may not be possible to pass all off-gas into the kiln. Furthermore, it is a disadvantage of these proposals that not only the pollutants are passed into the kiln, but any other substance volatilized during drying also enters the kiln, which could affect the clinker production. To avoid these problems, US 2012 / 0247371 A1 describes treating the off-gas from drying the secondary fuel by mixing it with calciner exhaust gas directed at a selective catalytic reduction (SCR) unit. This proposal is problematic since it necessitates a SCR unit and careful control of the mixing ratio to maintain a suitable temperature for the SCR. Furthermore, in oxyfuel processes this is not possible, as the exhaust gases usually contain significant amounts of air, which shall not enter the kiln system.

[0009] Surprisingly, it has now been found that it is not necessary to introduce the off-gas into the recuperation zone of the cooler, not even to pass it through the clinker bed. Gas introduced into the cooler downstream of the recuperation zone is still heated to temperatures that are fully sufficient to oxidize and / or decompose pollutants. Passing the off-gas from fuel drying into the clinker cooler downstreamof the recuperation zone safely destroys the malodor without having the gas entering the kiln as has been shown during trials at a drying facility.

[0010] The problem of malodor in drying secondary fuel for cement manufacturing is thus solved by a method for manufacturing cement clinker with integrated fuel drying comprising:- providing a secondary fuel having a moisture content of > 10 wt.-%,- drying the secondary fuel with a hot gas thereby generating an off-gas containing malodorous pollutants and a fuel with a moisture content of < 10 wt.-%,- providing a raw meal,- preheating and optionally precalcining the raw meal in a preheater or in a preheater and calciner providing preheated or preheated and precalcined raw meal,- passing the preheated or the preheated and precalcined raw meal into a kiln and sintering it to provide hot cement clinker,- passing the hot cement clinker into a cooler,- passing a cooling gas into a recuperation zone of the cooler to cool the hot cement clinker and provide the cement clinker,wherein the off-gas is passed into the cooler after the recuperation zone and into the aftercooling zone as additional cooling gas and / or for mixing with the cooling gas above the clinker, wherein the off-gas enters the cooler at a position in the aftercooling zone, where the temperature of the off-gas after mixing with the gas in the cooler and / or after contact with the clinker is at least 300 °C to provide a clinker cooler exhaust gas containing no or less pollutants. The object is also achieved with a method for cleaning off-gas from secondary fuel drying in cement manufacturing in a cement plant, wherein secondary fuel with a moisture content of > 10 wt.-% is provided and dried with a hot gas to a moisture content< 10 wt.-%, thereby generating an off-gas comprising malodorous pollutants, passing the off-gas into a clinker cooler of the cement plant after a recuperation zone and into an aftercooling zone as additional cooling gas and / or for mixing withthe cooling gas above the clinker, wherein the off-gas enters the cooler at a position in the aftercooling zone, where the temperature of the gas after mixing with the gas in the cooler and / or after contact with the clinker is at least 300 °C to provide a clinker cooler exhaust gas containing less or no pollutants. Finally, the problem is solved by a clinker cooler adapted to receive an off-gas from fuel drying for removing malodorous pollutants contained in the off-gas.

[0011] In a clinker cooler of a cement plant, the hot clinker is normally cooled down with a cooling gas, most often ambient air. The cooling gas is blown through a moving bed of hot clinker whereby the clinker cools down while the gas is heated up. The exhaust gas from the hot part of the clinker cooler, called secondary air, is used as combustion gas in the clinker kiln. The part of the cooler from which the heated gas is passed into the kiln is called recuperation zone. The adjacent colder part of the clinker cooler, downstream of the recuperation zone, is called aftercooling zone. The exhaust gas from the aftercooling zone of the clinker cooler, herein designated clinker cooler exhaust gas, passes from the cooler into an exhaust gas duct and has various uses. It can be used for drying raw materials or fuels. It can be used as combustion gas in the cement raw meal precalcination, i.e., as tertiary air (which can be considered gas from the recuperation zone but is herein defined as part of the clinker cooler exhaust gas). It can be taken out of the system and cooled externally via heat exchangers to exploit the contained heat energy. The amount and temperature of the clinker cooler exhaust gas is fluctuating, as the amount of exhaust gas used as secondary air is used to control the pressure in the kiln. Air is the most common cooling gas, but apart from a minimum amount of oxygen for the gas passed into the recuperation zone there is no need to use air. Oxygen in pure or diluted form can also be fed to the kiln separately from or in addition to the secondary air. Thus, the cooling gas passed into the recuperation zone of the cooler and then into the kiln as secondary air can contain no or not enough oxygen for burning the fuel in the kiln. In cement kilns operating in the oxyfuel mode, oxygen diluted in circulating kiln exhaust gas, i.e.,carbon dioxide, is typically used for cooling in the recuperation zone. To limit the amount of circulating gas, air is normally used in the aftercooling zone of the cooler even when the kiln operates in the oxyfuel mode. In principle, any gas can be used for cooling the clinker as long as the gas has an appropriate temperature, does not react with the clinker or at least not with a substantial amount of the clinker, and causes no processing problems like a danger of explosion or corrosion of the equipment.

[0012] The hot clinker is gradually cooled down from 1400 °C to temperatures of < 160 °C or < 100 °C in the clinker cooler. At the transition from recuperation zone to aftercooling zone the clinker has a temperature from 800 °C to 1000 °C.Depending on the part where the cooling gas passes through the clinker bed, the cooling gas has a residence time inside the hot clinker bed of approximately 0.2 to 0.5 seconds. The residence time above the clinker surface in the clinker cooler ranges from 1 to 3 seconds. The colder the clinker, the longer the residence time is. The residence time in the exhaust gas duct(s) of the aftercooling zone is typically several seconds, i.e., from 1 to 10 seconds, more often from 2 to 5 seconds, depending on the kiln layout.

[0013] Gas introduced into the gas space inside the cooler and above the clinker mixes with the heated cooling gas, wherein the resulting temperature depends on the amounts and temperatures of the mixed gases. The residence time of the gas mixed into the heated cooling gas above the clinker depends on how the gas is mixed in. According to the invention, means are preferably provided in the clinker cooler that ensure a thorough mixing of the heated cooling gas with the off-gas from the fuel drying when the off-gas is not used as additional cooling gas and introduced into the clinker cooler above the clinker. Suitable are for example a plurality of hoods rotatably mounted on a duct with openings for introducing the off-gas. The hoods have a top and two opposing side plates withthe other two sides being open. Thereby, the off-gas is thoroughly mixed with the heated cooling gas inside the hood(s) before it flows into the cooler exhaust duct.

[0014] Thus, the present invention also relates to a cement clinker cooler comprising a hot clinker inlet, a cooled clinker outlet, means for transporting the clinker from the hot clinker inlet to the cooled clinker outlet, means for passing cooling gas into the clinker from below, an outlet for secondary air connected to the kiln, and an outlet for clinker cooler exhaust gas connected to a clinker cooler exhaust gas duct, wherein a duct with openings for passing an off-gas from secondary fuel drying into the cooler for deodorizing the off-gas is arranged in the cooler above the clinker and at least one hood comprising a top and two side plates is rotatably supported on the duct by the top. One useful and preferred shape of the hoods is a U-shape with the radius of the top corresponding to the radius of the duct. The hoods are rotatably supported by the top of the duct with the openings in the duct directed towards the clinker, i.e. downwards. In a preferred embodiment, the hoods are laid on top of the duct, so that they can rotate about it. A screw is preferably foreseen to fix the distance between the two side plates of the hood. The length of the side plates is adapted to the distance between the duct and the clinker surface with the side plates ending approximately directly above the usual surface level of the clinker. Preferably, the hoods are from metal. Metal withstands the high temperatures and has a high heat conductivity. Thereby, the hoods not only promote rapid mixing of the gases but also serve as hot surface passing sensitive heat into the gas mixture. Furthermore, the hot metal surface enhances chemical reactions, i.e., the desired oxidation / pyrolysis of the pollutants. The introduced off-gas is forced downwards towards the clinker surface by the hoods, where the mixed gas is dissipated into the surrounding heated cooling gas on the clinker surface level. The side plates of the hoods can become smaller either at a selected height or continuously along their height forming slits that to allow some gas dissipating already above the clinker surface. The width and location of the slits ensure a high differential pressure that creates turbulencesin the injected off-gas, which leads to a proper mixture of the off-gas with the hot clinker cooling gas.

[0015] The gas from the recuperation zone has temperatures of > 1000 °C. The gas from the aftercooling zone has combined temperatures in the range of 200 °C to 500 °C. This gas can be split into different streams. Thereby, a hot stream called mid-air with temperatures around 700 °C and a colder stream with 150 °C to 400 °C can be obtained. Adding the off-gas to the cooling gas or above the clinker at a point close to the recuperation zone is advantageous when the pollutants require comparably high temperatures for oxidation / pyrolysis. That can be due to either their nature or their amount or both. Often, mixing with the colder stream and / or using the off-gas as cooling gas at a position where the heated cooling gas becomes such a colder stream suffices.

[0016] According to one embodiment of the present invention, the off-gas from secondary fuel drying is used as cooling gas in the aftercooling zone of the clinker cooler where it is heated up to temperatures sufficient for oxidizing or decomposing malodorous compounds, i.e., the pollutants. According to another embodiment of the present invention, the off-gas is added to the heated cooling gas above the surface of the clinker in the cooler in the aftercooling zone. This embodiment advantageously avoids contact between off-gas and clinker almost completely, i.e., the clinker and the off-gas have substantially no contact. Thereby, any possible adverse influence by the off-gas on the clinker quality is avoided. For example, the off-gas could contain substances able to deposit on the clinker or when the off-gas contains a very high amount of water this might react with the clinker and diminish clinker yield. Both embodiments can also be combined, so that the off-gas can be used as cooling gas and is concurrently or alternatively mixed into the heated cooling gas above the clinker.

[0017] The secondary fuels having a moisture content of > 10 wt.-%, often of > 11 wt.-% or > 12 wt.-% or > 15 wt.-% are dried as known per se by contactingthem with hot gas in a drying unit. Thereby, fuel with a moisture content of< 10 wt.-%, preferably < 5 wt.-%, is obtained. During drying, volatile compounds that are frequently malodorous can be emitted by the fuel and form the malodorous pollutants contained in the off-gas. These pollutants must be removed or at least their amount sufficiently reduced. To achieve this, the off-gas is passed into the aftercooling zone of the clinker cooler. When the off-gas is used as cooling gas, it is heated up to the temperature of the clinker at the particular position, which typically ranges from 1000 to 300 °C, forming at least a part of the clinker cooler exhaust gas in the aftercooling zone. When the off-gas is mixed with the heated cooling gas, it is heated to a temperature resulting from the amounts and temperatures of the off-gas and the heated cooling gas, e.g. inside the cooler or inside the hood into which the off-gas is introduced. A suitable temperature of the off-gas after contact with the clinker and / or mixing with the heated cooling gas is at least 300 °C, preferably at least 400 °C, most preferred at least 500 °C. The clinker cooler exhaust gas flows into the exhaust air duct of the clinker cooler. An average temperature, typically ranging from 200 to 500 °C, arises in the clinker cooler exhaust air duct. The residence time in the duct suffices to complete oxidation and decomposition of the pollutants to the desired extent. In the method according to the present invention the amount of pollutants is generally reduced to 10 % or 5 % or 1 % or 0.1 % or less of the amount of pollutants originally contained in the off-gas. While the perception of malodor is somewhat subjective, the compounds considered herein as malodorous pollutants are those perceived as having a perceptible bad or unpleasant odor by all persons with an intact sense of smell. While there may be rare individuals perceiving the odor of a specific compound like acetone as pleasant, herein the average and predominant perception is determining, thus, such compounds fall within the term malodorous pollutants. Even good smelling compounds are perceived as malodor when they arise in too high concentration. Consequently, the term malodorous pollutants refers to compounds causing a strong smell rather than only to compounds perceived as bad smelling by every person.

[0018] The position where the off-gas is passed into the cooler can be adjusted in several ways. First, a cement clinker cooler usually has several inlets for cooling gas along the length of the means for transporting the clinker from the hot clinker inlet to the cooled clinker outlet. When the off-gas is used as cooling gas, the position is most easily adjusted by selecting the appropriate cooling gas inlet for passing the off-gas into the clinker cooler. Naturally, it is also possible to provide additional inlets for the off-gas. When the off-gas is mixed with the heated cooling gas above the clinker surface inside the cooler, it is likewise possible to provide several inlets for the off-gas along the length of the means for transporting the clinker from the hot clinker inlet to the cooled clinker outlet, only those are at the top of the cooler and not at the bottom. In the cement clinker cooler according to the invention, the position of the means for introducing can be designed adjustable and / or several means can be foreseen. In one variant, the hoods can be configured adjustable in position, e.g., by an adjustable mounting of the duct. More than one set of hoods can be foreseen in the cooler and the off-gas passed into the duct of the set able to achieve the desired temperature of the mixed gas formed by passing the off-gas through the duct openings into the heated cooling gas. Using more than one set of hoods also allows cooling a higher amount of offgas. Further, using several sets of hoods allows to partially return some cooler exhaust gas into the cooler.

[0019] Typically, the volatile compounds causing malodor, i.e., the pollutants, are decomposed, i.e., pyrolyzed, or oxidized in a temperature range from 200 °C to 500 °C. Table 1 below shows the auto-ignition points of the main pollutants:

[0020] Table 1

[0021] These self-ignition points are mainly below the temperature to which the compounds are exposed after passing into the clinker cooler. Even if no complete oxidation in the hot clinker bed and exhaust ducts occurs, e.g., due to a too short residence time, the malodorous substances are cracked into intermediates which do not have the same smell. Very odorous off-gas streams from e.g., municipal sewage sludge drying or paper sludge drying are preferably passed to parts in the clinker cooler adjacent to the recuperation zone. Less odorous off-gas from e.g., SRF-dryers can be passed to the rearward parts of the clinker cooler. Thus, by selecting the point where the off-gas enters the clinker cooler, the temperature of the off-gas after contact with the clinker and / or mixing with the heated cooling gas is adjusted to the needed temperature for oxidizing and decomposing the malodorous pollutants. Insertion adjacent to the recuperation zone usually results in temperatures of the off-gas / exhaust gas of at least 600 °C or at least 800 °C. Introduction in the rearward parts of the clinker cooler provides temperatures of the off-gas / exhaust gas of at least 300 °C often at least 400 °C or at least 500 °C.As a result, the pollutants contained in the off-gas are oxidized and / or pyrolyzed due to the temperature increase either completely or at least to the desired extent. The point of introduction is adapted to the necessary temperature governed by the kind of pollutants, that is either known or easily determined, and the amount of offgas that shall be deodorized.

[0022] It is an advantage of the methods according to the invention that the clinker promotes odor reduction when the off-gas is used a cooling gas. Interaction of the off-gas with the clinker enhances the effect of the thermal treatment. In both variants of the methods, i.e., when using the off-gas for cooling and when mixing it with the heated cooling gas, the exhaust gas passes a fabric filter for dedusting, inside which odorous substances need to pass a layer of very fine alkaline raw meal with low velocity, which leads to a further decrease of odor. The exhaust gas can also pass one or more other common exhaust gas treatment units of the cement plant like devices removing acidic substances like SOx (with x = 2 or 3), removing NOx (with x = 0 or 2), and / or conditioning the gas before it is vented to the atmosphere. Carbon capture units also become more and more common in cement plants and the cooler exhaust gas can be treated in them, too. As a result, the methods according to the invention ensure that the off-gas is suitably cleaned before being vented without necessitating the installation of costly and / or complex gas treatment devices for the fuel drying unit.

[0023] The moisture contained in the off-gas from the secondary fuel drying can be condensed before passing the off-gas into the cooler. However, this is neither necessary nor preferred. It was found that a moisture content of up to 95 VoL-% has no negative effects on the clinker quality. The moisture content in the off-gas depends on the moisture content of the secondary fuel and the type of dryer.Typically, the off-gas contains from 3 VoL-% up to 20 VoL-% moisture for evaporative type dryers, or from 60 VoL-% up to 95 VoL-% moisture for contact type dryers.

[0024] The preferred embodiments of the methods according to the present invention are defined in the following.Embodiment 1 : Method for manufacturing cement clinker comprising:- providing a secondary fuel with a moisture content of > 10 wt.-% or > 15 wt.-% and drying the fuel with a hot gas, thereby generating an off-gas comprising malodorous pollutants and a fuel with a moisture content < 10 wt.-%, especially < 10 wt.-%,- providing a raw meal, preheating and optionally precalcining the raw meal in a preheater or in a preheater and calciner providing preheated or preheated and precalcined raw meal, passing the preheated or the preheated and precalcined raw meal into a kiln and sintering it to provide hot cement clinker, passing the hot cement clinker into a cooler, passing cooling gas into the cooler to cool the hot cement clinker and provide the cement clinker,- passing the off-gas into the aftercooling zone of the cooler as cooling gas and / or above the clinker for mixing it with cooling gas having been heated by cooling the clinker, wherein the off-gas is passed into the cooler at a position, where the temperature of the gas after mixing with the heated cooling gas is at least 300 °C to provide a clinker cooler exhaust gas containing less or no pollutants.Embodiment 2: Method for cleaning off-gas from secondary fuel drying in cement manufacturing in a cement plant, wherein secondary fuel with a moisture content of > 10 wt.-% or > 15 wt.-% is provided and dried with a hot gas to a moisture content < 10 wt.-% especially < 10 wt.-%, thereby generating an off-gas comprising malodorous pollutants, passing the off-gas into an aftercooling zone of a clinker cooler of the cement plant as cooling gas and / or above the clinker for mixing it with cooling gas having been heated by cooling the clinker, wherein the off-gas is passed into the cooler at a position, where the temperature of the gas after mixing with cooling gas having been heated by cooling the clinker is at least 300 °C to provide a clinker cooler exhaust gas containing less or no pollutants. Embodiment 3: Method according to embodiment 1 or 2, wherein the secondary fuel has a moisture content in the range from 11 or 12 or 15 to 85 wt.-% and / or issolid recovered fuel obtained from processing solid municipal or industrial waste, refuse derived fuel obtained from processing solid municipal or industrial waste, municipal sewage sludge, paper fiber sludge, or a mixture of two or more thereof. Embodiment 4: Method according to embodiment 3, wherein the solid recovered fuel has a moisture content ranging from 11 or 12 or 15 to 25 wt.-% and / or the refuse derived fuel has a moisture content ranging from 11 or 12 or 15 to 25 wt.-% and / or the municipal sewage sludge has a moisture content ranging from 70 to 85 wt.-% and / or the paper sludge has a moisture content ranging from 40 to 55 wt.-%.Embodiment 5: Method according to any one of embodiments 1 to 4, wherein the malodorous pollutants are sulfur compounds, such as hydrogen sulfide, mercaptans like methane thiol, organic sulfides like dimethyl sulfide and dimethyl disulfide; and / or nitrogen compounds, such as ammonia, amines like methylamine and dimethylamine; and / or odorous organic compounds, such as organic acids like acetic acid and propanoic acid, aldehydes like acetaldehyde and propionaldehyde, ketones like acetone and 2-butanone.Embodiment 6: Method according to any one of embodiments 1 to 5, wherein the amount of the malodorous pollutants contained in the off-gas is reduced to 10 % or less of the originally contained amount, preferably to 5 % or less of the originally contained amount, more preferred to 1 % or less of the originally contained amount, most preferred to 0.1 % or less of the originally contained amount.Embodiment 7: Method according to any one of embodiments 1 to 6, wherein the off-gas is passed into the aftercooling zone of the cooler at a position, where the temperature of the gas after contact with the clinker and / or after mixing with the cooling gas having been heated by cooling the clinker is at least 400 °C, preferably at least 500 °C, or where the temperature is at least 600 °C or at least 800 °C. Embodiment 8: Method according to any one of embodiments 1 to 7, wherein the secondary fuel is dried to a moisture content of < 5 wt.-%.Embodiment 9: Method according to any one of embodiments 1 to 8, wherein the off-gas has a moisture content of 3 VoL-% or more up to 20 VoL-% or from60 VoL-% or more up to 95 VoL-%.Embodiment 10: Method according to any one of embodiments 1 to 9, wherein the clinker cooler exhaust gas is used as tertiary air, bypass gas, and / or is passed into an exhaust gas treatment unit of the cement plant.Embodiment 11 : Method according to embodiment 10, wherein the exhaust gas treatment unit is adapted for retaining dust and / or for removing acidic substances like SOx (with x = 2 or 3) and / or for removing NOx (with x = 0 or 2) and / or for conditioning the gas, preferably is a dedusting unit, most preferred a fabric filter. Embodiment 12: Cement clinker cooler comprising a hot clinker inlet, a cooled clinker outlet, means for transporting the clinker from the hot clinker inlet to the cooled clinker outlet, means for passing cooling gas into the clinker from below, an outlet for secondary air connected to the kiln, and an outlet for clinker cooler exhaust gas connected to a clinker cooler exhaust gas duct, wherein a duct with openings for passing an off-gas from secondary fuel drying into the cooler for deodorizing the off-gas is arranged in the cooler above the clinker and at least one hood comprising a top and two side plates is rotatably supported on the duct by the top.Embodiment 13: Cement clinker cooler according to embodiment 12, wherein the side plates have a length adapted to the distance between the duct and a surface of the clinker on the means for transporting so that the side plates end directly above the clinker surface.Embodiment 14: Cement clinker cooler according to embodiment 12 or 13, wherein the hoods are U-shaped and / or from metal.

[0025] The invention will be illustrated further with reference to the appended figures, without restricting the scope to the specific embodiments described. The invention includes all combinations of described and especially of preferred features that do not exclude each other. If not otherwise specified any amount in % or parts is by weight and in the case of doubt referring to the total weight of the composition / mixture concerned. A characterization as "approximately", "around"and similar expression in relation to a numerical value means that up to 10 % higher and lower values are included, preferably up to 5 % higher and lower values, and in any case at least up to 1 % higher and lower values, the exact value being the most preferred value or limit. The term "substantially free" means that a particular material is not purposefully added to a composition and is only present in trace amounts or as an impurity. As used herein, unless indicated otherwise, the term "free from" means that a composition does not comprise a particular material, i.e., the composition comprises 0 weight percent of such material.

[0026] In the figures:figure 1 schematically depicts a cement manufacturing plant using the methods according to the invention with using the off-gas as cooling gas,figures 2 to 5 illustrate a clinker cooler with means for mixing the off-gas with the heated cooling gas according to the invention, andfigure 6 schematically depicts a cement manufacturing plant using the methods according to the invention with mixing the off-gas with the heated cooling gas.

[0027] Figure 1 schematically shows a plant for manufacturing cement clinker according to the invention, implementing the method for cleaning off-gas according to the invention. In figure 1 , solid material passageways are depicted as solid lines, flow pathways of gases are depicted as broken lines.

[0028] The plant mainly comprises a preheater 1 , calciner 2, kiln 3, and cooler 4. The cooler 4 has a recuperation zone 4a and an aftercooling zone 4b. The localization of the boundary between the zones is variable and depends on parameters like temperature of the clinker entering the cooler, gas flow rates, and velocity of the clinker inside the cooler.

[0029] The clinker production proceeds as known per se. Thus, a raw meal rm is fed to the preheater 1 , where it is preheated in countercurrent with kiln exhaust gas. Next, the preheated raw meal passes into the calciner 2, where usuallyadditional heat is introduced, e.g., by a calciner burner, so that the preheated raw meal is precalcined. The preheated and precalcined raw meal is then transferred into the kiln 3. At the kiln inlet and within the adjacent part of the kiln 3, the calcination is completed, i.e., calcium carbonate is calcined to calcium oxide, as far as calcination was incomplete in the calciner 2. Moving forward in the kiln 3, the temperature increases and finally the raw meal is sintered to provide the hot cement clinker he. The kiln burner (not shown) is located towards the end of the kiln 3 adjacent to the cooler 4, where fuel, combustion gas and secondary air are introduced into the kiln 3. Gases move in countercurrent to the raw meal / clinker inside the kiln 3. The hot clinker he passes, usually falls, from the kiln 3 into the cooler 4, and specifically, into the recuperation zone 4a of the cooler 4. Cooling begins there and is caused by a cooling gas eg being blown through the clinker bed. The clinker bed is moving from the cooler inlet to the cooler outlet. Due to the cooling gas eg, the temperature of the clinker decreases.

[0030] Somewhere along the cooler length the temperature of the clinker has decreased to a value in the range from 1000 to 800 °C which indicates the boundary between the recuperation zone 4a and the aftercooling zone 4b. The gas introduced into the clinker bed in the aftercooling zone 4b is off-gas og from the fuel drying 5 receiving secondary fuel sf and hot gas hg. The off-gas og is heated while it cools the clinker. Due to the position of addition in the cooler 4, the temperature of the off-gas og reaches at least 300 °C by contact with the clinker and during subsequent passage in the exhaust gas duct, i.e., a temperature high enough to oxidize and / or decompose the pollutants contained in the off-gas og. Additional gas can be and often is introduced into the aftercooling zone 4b, depending on the amount of off-gas og generated. Thereby, a sufficient amount of gas for cooling the clinker is provided, independently of the amount of off-gas og arising in secondary fuel drying 5. At times when the secondary fuel drying 5 is not working at all, other gas can be used as the only gas introduced into the aftercooling zone 4b. The point of feeding this additional gas depends on wherethe off-gas og is introduced, i.e., the additional gas can be introduced at points before or after the off-gas introduction or admixed with the off-gas og, and also any combination thereof can be applied. Usually and preferably, the additional gas is air.

[0031] The heated and deodorized exhaust gas eg can be used in the same way as cooler exhaust gas arising in plants using fossil fuels or secondary fuels not showing malodor problems. For example, it can be passed into heat exchange units to exploit the contained energy and / or used to dry raw materials or fuels and / or serve as combustion gas for precalcining the raw meal rm. The cooled clinker cc leaves the cooler 4 and is further processed as usual (typically stored or ground and stored).

[0032] In figures 2 to 5, a cooler 4 equipped with means for thorough mixing of the off-gas og with the heated cooling gas eg is shown. Gas flow directions are indicated with solid arrows in figures 2 to 5. Figure 2 shows a section through the cooler 4 perpendicular to the movement direction of the hot clinker he, figure 3 shows a section along line A-A in figure 2, figure 4 shows a section along line B-B in figure 2, and figure 5 shows a section along line C-C in figure 2.

[0033] The hot clinker he, by and by becoming the cooled clinker cc while travelling through the cooler 4, is moving in a direction perpendicular to the plane in figure 2. Above the clinker surface cs an exemplary set of five metallic hoods 10 is shown. Other materials for the hoods are possible, but metal is preferred due to heat stability, heat conductivity and possible enhancing of oxidation / pyrolysis reactions. The hoods 10 are arranged in a line above the clinker surface cs and supported near the top of the cooler 4 by a duct 11 shown in broken lines. The duct 11 has openings 12, not depicted in figure 2, through which the off-gas og is passed into the heated cooling gas eg above the clinker surface cs of the hot clinker he inside the hoods 10. Thereby, the heated cooling gas eg and the off-gas og are thoroughly mixed, because the heated cooling gas flows upwards throughthe hot clinker he and the off-gas og flows downwards from the duct 11. Then, the stream of off-gas og introduced into the hoods 10 forces the mixed gas out of the hoods 10 both above the surface of the hot clinker he and through the slits 13 formed along the side of the side plates 14 of adjacent hoods 10. As seen in figure 3, the hoods 10 are U-shaped, with their top 15 supported by the duct 11 and the side plates 14 fixed at a selected distance with a screw 16. As best seen in figure 4 and 5, the hoods 10 on the duct 11 extend from one side of the cooler 4 to the other, so the hot clinker he entering on the left in figures 4 and 5 passes below the hoods and move forward towards the end of the cooler on the right of figures 4 and 5. Rotatably supporting the hoods 10 on the duct 11 allows them to turn when the clinker surface cs is momentarily higher than on the average due to a big clinker lump or an uneven distribution of the hot clinker he in the moving clinker bed.

[0034] There are several options for adjusting the position of mixing the off-gas og with the heated cooling gas eg. In one variant, the hoods 10 can be configured adjustable in position, e.g., by an adjustable mounting of the duct 11. More than one set of hoods 10 can be foreseen in the cooler 4 so that the off-gas is passed into the duct 11 of the set able to achieve the desired temperature of the mixed gas formed by passing the off-gas og through the duct 11 into the heated cooling gas eg. Using more than one set of hoods 10 also allows cooling a higher amount of off-gas. Further, using several sets of hoods 10 allows to partially return some cooler exhaust gas eg into the cooler.

[0035] Figure 6 shows a plant analogous to that in figure 1 , except that in figure 6 the off-gas og is not used as cooling gas eg but mixed with the heated cooling gas eg above the clinker surface cs, preferably in a means as illustrated in figures 2 to 5. Thus, off-gas og from drying secondary fuel sf in drying unit 5 is passed to the aftercooling zone 4b of the cooler 4 above the clinker bed. There, it is mixed with the heated cooling gas eg above the surface cs of the moving bed of hotclinker he and not introduced into the bed from below as in figure 1. Cooling gas eg is used for cooling the hot clinker he in the recuperation zone 4a and in the aftercooling zone 4b of the cooler 4. Everything else is as in figure 1.List of reference numbers1 preheater2 calciner3 kiln4 cooler with 4a recuperation zone and 4b aftercooling zone5 fuel drying10 hood11 duct12 opening13 slit14 side of hood15 top of hood16 screwrm raw mealhe hot clinkercs clinker surfaceeg cooling gasog off-gas from fuel dryingsf secondary fuelhg hot gaseg cooler exhaust gascc cooled clinker

Claims

Claims1. Method for manufacturing cement clinker comprising:- providing a secondary fuel with a moisture content of > 10 wt.-% and drying the fuel with a hot gas, thereby generating an off-gas comprising malodorous pollutants and a fuel with a moisture content < 10 wt.-%, - providing a raw meal, preheating and optionally precalcining the raw meal in a preheater or in a preheater and calciner providing preheated or preheated and precalcined raw meal, passing the preheated or the preheated and precalcined raw meal into a kiln and sintering it to provide hot cement clinker, passing the hot cement clinker into a cooler, passing cooling gas into the cooler to cool the hot cement clinker and provide the cement clinker,- passing the off-gas into the cooler after the recuperation zone and into the aftercooling zone as cooling gas and / or above the clinker and mixing it with cooling gas having been heated by cooling the clinker, wherein the off-gas is passed into the cooler at a position, where the temperature of the gas after contact with the clinker and / or after mixing with the heated cooling gas is at least 300 °C to provide a clinker cooler exhaust gas containing less or no pollutants.

2. Method for cleaning off-gas from secondary fuel drying in cement manufacturing in a cement plant, wherein secondary fuel with a moisture content of > 10 wt.-% is provided and dried with a hot gas to a moisture content < 10 wt.-%, thereby generating an off-gas comprising malodorous pollutants, passing the off-gas into an aftercooling zone of a clinker cooler of the cement plant as cooling gas and / or above the clinker for mixing it with cooling gas having been heated by cooling the clinker at a position, where the temperature of the gas after contact with the clinker and / or after mixing with the cooling gas having been heated by cooling the clinker is at least300 °C to provide a clinker cooler exhaust gas containing less or no pollutants.

3. Method according to claim 1 or 2, wherein the secondary fuel has a moisture content in the range from 11 or 12 or 15 to 85 wt.-% and / or is solid recovered fuel obtained from processing solid municipal or industrial waste, refuse derived fuel obtained from processing solid municipal or industrial waste, municipal sewage sludge, paper fiber sludge, or a mixture of two or more thereof.

4. Method according to claim 3, wherein the solid recovered fuel has a moisture content ranging from 11 or 12 or 15 to 25 wt.-% and / or the refuse derived fuel has a moisture content ranging from 11 or 12 or 15 to 25 wt.-% and / or the municipal sewage sludge has a moisture content ranging from 70 to 85 wt.-% and / or the paper sludge has a moisture content ranging from 40 to 55 wt.-%.

5. Method according to any one of claims 1 to 4, wherein the malodorous pollutants are sulfur compounds, such as hydrogen sulfide, mercaptans like methane thiol, organic sulfides like dimethyl sulfide and dimethyl disulfide; and / or nitrogen compounds, such as ammonia, amines like methylamine and dimethylamine; and / or odorous organic compounds, such as organic acids like acetic acid and propanoic acid, aldehydes like acetaldehyde and propionaldehyde, ketones like acetone and 2-butanone.

6. Method according to any one of claims 1 to 5, wherein the amount of the malodorous pollutants contained in the off-gas is reduced to 10 % or less of the originally contained amount, preferably to 5 % or less of the originally contained amount, more preferred to 1 % or less of the originally contained amount, most preferred to 0.1 % or less of the originally contained amount.

7. Method according to any one of claims 1 to 6, wherein the off-gas is passed into the aftercooling zone of the cooler at a position, where the temperature of the gas after contact with the clinker and / or after mixing with the cooling gas having been heated by cooling the clinker is at least 400 °C, preferably at least 500 °C, or where the temperature is at least 600 °C or at least 800 °C.

8. Method according to any one of claims 1 to 7, wherein the secondary fuel is dried to a moisture content of < 5 wt.-%.

9. Method according to any one of claims 1 to 8, wherein the off-gas has a moisture content of 3 VoL-% or more up to 20 VoL-% or from 60 VoL-% or more up to 95 VoL-%.

10. Method according to any one of claims 1 to 9, wherein the clinker cooler exhaust gas is used as tertiary air, bypass gas, and / or is passed into an exhaust gas treatment unit of the cement plant.

11. Method according to claim 10, wherein the exhaust gas treatment unit is adapted for retaining dust and / or for removing acidic substances like SOx (with x = 2 or 3) and / or for removing NOx (with x = 0 or 2) and / or for conditioning the gas, preferably is a dedusting unit, most preferred a fabric filter.

12. Cement clinker cooler comprising a hot clinker inlet, a cooled clinker outlet, means for transporting the clinker from the hot clinker inlet to the cooled clinker outlet, means for passing cooling gas into the clinker from below, an outlet for secondary air connected to the kiln, and an outlet for clinker cooler exhaust gas connected to a clinker cooler exhaust gas duct, wherein a duct with openings for passing an off-gas from secondary fuel drying into the cooler for deodorizing the off-gas is arranged in the cooler above the clinker and at least one hood comprising a top and two side plates is rotatably supported on the duct by the top.

13. Cement clinker cooler according to claim 12, wherein the side plates have a length adapted to the distance between the duct and a surface of the clinker on the means for transporting so that the side plates end directly above the clinker surface.

14. Cement clinker cooler according to claim 12 or 13, wherein the hoods are U-shaped and / or from metal.

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