OA20590A

OA20590A - Oxyfuel clinker production with special oxygen addition

Info

Publication number: OA20590A
Application number: OA1202000403
Authority: OA
Inventors: Jost Lemke; Eike Willms
Original assignee: Thyssenkrupp Industrial Solutions Ag
Priority date: 2018-04-30
Filing date: 2019-04-26
Publication date: 2022-11-29

Abstract

Methods and systems for the production of cement clinker, wherein an oxygen-containing gas, which has a proportion of 15 vol.% or less of nitrogen and a proportion of 50 vol.% or more of oxygen, is guided from a first section of the cooler directly adjoining the kiln head to the rotating kiln and optionally also guided to the calciner and wherein more than 50 vol.% (preferably more than 85 vol.%) of the gas flows supplied to the combustion processes in total consist of oxygen.

Description

Oxyfuel clinker production with spécial oxygen addition

The présent invention relates to processes and plants for producing cernent clinker, in which an oxygen-containing gas having a proportion of 15% by volume or less of nitrogen and a proportion of 50% by volume or more of oxygen is conveyed from a first section of the cooler directly adjoining the top of the furnace into the rotary furnace and is optionally additionally conveyed to the calciner.

Processes and plants in which air is introduced into the clinker cooler and preheated, with part of this air being able to flow into the furnace, are known from the prior art. Furthermore, it is known that mixtures of CO₂ and O₂ instead of air can be supplied to the cooler.

Examples of prior art are EP 1 037 005 B1, JP 2007-126328 A or DE 100 13 929 C2. Further examples are WO 99/06778 A1 and US 3 162 431 A.

Owing to steadily increasing requirements in terms of économies and ecology, there is still a need for improved plants and processes for producing cernent clinker.

It was accordingly an object of the présent invention to provide, inter alla, improved plants and processes for producing cernent clinker, which do not hâve the disadvantages ofthe prior art and are improved in respect of économies and ecology compared to the plants and processes of the prior art.

The object is achîeved according to the présent invention by the subject matter of the appended daims, with the dépendent daims indicating preferred embodiments.

Further embodiments of the invention are derived from the following description.

The présent invention provides, in one embodiment, a rotary furnace plant for producing cernent clinker, which plant comprises an apparatus configured for feeding oxygen-containing gas which has a proportion of 15% by volume or less of nitrogen and a proportion of 50% by volume or more of oxygen from a first section of the cooler directly adjoining the top of the furnace into the rotary furnace and optionally additionally into the calciner, and where the plant is configured for feeding gas i

streams which in total consist to an extent of more than 50% by volume, preferably of more than 85% by volume, of oxygen into the combustion processes.

In a further embodiment, the présent invention correspondingly provides a process for producing cernent clinker, wherein an oxygen-containing gas having a proportion of 15% by volume or less of nitrogen and a proportion of 50% by volume or more of oxygen from a first section of the cooler directly adjoining the top of the furnace is conveyed into the rotary furnace and optionally additionally the calciner, where the total gas streams fed to the combustion processes consist to an extent of more than 50% by volume, preferably more than 85% by volume, of oxygen.

The plant of the invention or the process of the invention can thus be compared to a type of oxyfuel process.

Compared to concepts known hitherto, the plant of the present invention is also distinguished by the fact that, inter alia, no conventional O2/CO2 mixture is supplied as secondary gas at the top of the furnace, but instead a very pure oxygen gas is used. This would hitherto not hâve been explored in detail because of anticipated problems due to higher combustion températures in the rotary tube furnace and reduced gas volume flows (i.e. lower carrying capacîty of the gas or gases for solid in the calciner and preheater région). However, these problems hâve been able to be overcome by a number of targeted modifications of the process and consequently lead to a significantîy reduced construction height and a reduced space requirement of the plant combined with a higher CO₂ concentration in the exhaust gas.

In preferred embodiments of the present invention, the rotary furnace plant consists of a cyclone preheater, an in-line calciner without tertiary air conduit, a rotary furnace and a cooler. A conduit for intermediate air runs from the cooler to a middle cyclone stage in the preheater and subsequently to the raw mill.

In preferred embodiments of the present invention, the cyclone preheater consists of a multistage cyclone cascade which is operated using a significantîy smaller amount of gas. The exhaust gas volume flow downstream of the preheater is from about 0.50 to 0.70 standard m³/kg of clinker. The ratio of amount applied to exhaust gas can accordîngiy be higher than hitherto possible and is, in one variant, from 1 to 2 kg/kg of solid to gas, preferably from 1.3 to 1.9 kg/kg of solid to gas. Parallel to the cyclone cascade, there is an additional cyclone stage which is supplied with hot air from the cooler. Based on the flow of meal, this additional stage is, in a preferred embodiment, located centrally within the cyclone cascade.

If the exhaust air fronri the cooler is to be utilized for purposes other than meal preheating, it is also possible for preheating to be effected only by means of exhaust gases from the calciner.

In further embodiments of the présent invention, the preheater can be configured as fluidized-bed reactor, in particular in the form of a so-called bubble-forming fluidized bed.

Accordingly, in some embodiments ofthe présent invention, the ratio of solid fed in to exhaust gas in the preheating step is set to greater than 1.0 kg, preferably greater than 1.3 kg, of solid per 1 kg of gas, preferably from 1 to 2 kg/kg of solid to gas, particularly preferably from 1.3 to 1.9 kg/kg of solid to gas, or the plant is appropriately configured for setting such a ratio (amount fed in to exhaust gas stream) in the preheater.

In various embodiments, the calciner corresponds substantially to the classical design, with the solid/gas ratio being significantly higher; there are local solids loadings of more than 2 kg per kg of gas, for example from 2 to 8 kg per kg of gas. The major part (more than 60%, for example about 80%, of the heat of the fuel is converted in the calciner. Despite an initial oxygen concentration of about 75%, the meal présent provides a sufficient heat sink to prevent overheating. If coarse substitute fuel (having edge lengths of >100 mm) is to be burnt, an inclined région having a relativeîy high résidence time for the fuel may hâve to be provided. Examples of such inclined régions are stair-type steps, push gratings, back-pushing gratings, etc.

Accordingly, in some embodiments ofthe présent invention, the ratio of solid fed in to exhaust gas in the calcination step is set to greater than 1.0 kg, preferably greater than 1.3 kg, of solid per 1 kg of gas, preferably from 1 to 2 kg/kg of solid to gas, particularly preferably from 1.3 to 1.9 kg/kg of solid to gas, or the plant is configured appropriately for setting such a ratio in the calciner.

Since the plant is, for the purposes of the présent invention, preferably operated without “tertiary air or “tertiary gas” (i.e. a gas stream which bypasses the furnace and is connected to the calciner), it is possible to use, for example, a separate combustion chamber which is supplied with “tertiary air” or “tertiary gas” in a construction different from the conventional construction.

Possible alternatives in the context of the présent invention are preferably flow of the furnace exhaust gas over the fuel in the inclined région of the calciner as variant integrated into their calciner or a shortened design which is attached to the one calciner without inclined surfaces.

According to the présent invention, the rotary furnace is supplied with hot gas from the section of the cooler nearest the front. This is an oxygen-containing gas having a proportion of 15% by volume or less of nitrogen and a proportion of 50% by volume or more of oxygen.

In one variant of the présent invention, the gas is very pure oxygen (more than 90%).

The rotary furnace burner conveys the fuel into the sintering zone, for which purpose recirculated CO₂ or a mixture of CO₂ and oxygen is used as transport gas for the fuel.

For the purposes of the présent invention, the amount of fuel is selected so that the required nature of the sintering zone is achieved. For the production of cernent clinker, a hot, first région of the furnace having a length of about 1/3 of the total length of the furnace is provided by the combustion, the function of which région is the formation of C3S (tricalcium silicate or alite) and at the hottest point of which material températures of more than 1450°C are achieved. In order to ensure a sufficient extension of this hot région to the about first third of the furnace, the use of relatively coarse fuels compared to the prior art is conceivable in some embodiments, since very fast burning occurs in the hot oxygen atmosphère. At the same time or as an alternative, it is conceivable to reduce the primary gas amount and/or the blower side pressure which is usually necessary in rotary furnace burners to form the flame. Both resuit in savings in electric energy consumption and smalier flow machines for încreasing the pressure and accelerating the primary gas. The amount of fuel converted in the sintering zone is 20% or more of the total heat provided by the fuel. Since the entire amount of oxygen necessary for the combustion process is fed in to the rotary furnace, the oxygen excess in the sintering zone is about λ = 5 (i.e. excess relative to the amount of oxygen necessary for the combustion).

However, it is equally possible in the context of the présent invention to fire clinker having high C₃S contents and low C₂S (dicalcium silicate) contents. The clinker mineralogy is usually set via the raw meal mixture. Usual values for cernent clinker containing 65% of C₃S, 13% of C₂S, etc., are a lime standard of 95, TM=2.3 (alumina modulus), SM=2.5 (silicate modulus). If a higher température is set in the sintering zone at the same résidence time, it is possible to increase the lime standard. In this case, a higher C₃S content is achieved in the product at the same free lime contents. C₃S-rich clinkers achieve better strength propertîes in the cernent compared to clinkers which are lower in C₃S. Since the C₂S component is more difficult to mill than the C₃S comportent, the higher C₃S content also results in a réduction in the electric energy consumption necessary for cernent milling.

As an alternative, there is also the possibility of reducing the résidence time of the material in the furnace. In variants, it is possible to shorten the furnace in respect of the résidence time when cernent clinker having the above-mentioned standard values” is to be produced at relatively high températures. One preferred embodiment could be turning the furnace more quickly (e.g. at more than 5 rpm) and/or setting a smalier furnace inclination.

Owing to the greatly increased amount of oxygen available in the sintering zone, fast burning of even less well worked up fuels can be expected. These can be fuels which are coarser, moister or hâve a lower calorific value. If, for example, a solid fuel such as coal is used for the process of the invention, the fuel has to be milled less finely. This saves electric energy which otherwise has to be provided for milling of the fuel. However, the fuel can likewise hâve been dried to a lesser extent. This saves thermal energy which can be utilized elsewhere. The process of the invention and the plant of the invention are thus particularly advantageous for use of waste fractions, known as substitute fuels.

For the purposes of the présent invention, the flame in the firing furnace can be cooled by, for example, the three following methods A), B) and C) or a combination thereof. This is particularly advantageous when the amount of fuel necessary for the combustion or the combustion conditions, in particular the highly enriched oxygen atmosphère, lead(s) to high flame températures.

A) Recirculation of part of the furnace exhaust gas to the furnace inlet, combined with targeted cooling of this gas. Cooling ofthe gas preferably occurs indirectly by means of a heat exchanger which can be preceded by a dust removal device, for example a séparation cyclone. The quantity of heat removed by the indirect heat exchange can be integrated into a concept for waste heat utilization.

B) Recirculation of part of the furnace exhaust gas by means of a separate calcination train which is followed by a cyclone separator, combined with targeted cooling of this gas. Cooling of the gas preferably occurs directly in the separate calciner with séparation cyclone, by part of the raw meal which has not been deacidified being able to be introduced into the gas stream and the gas température thereof being able to be set.

C) Introduction of clinker dust into the hot air fed in to the furnace. This in practical terms extends the flame, so that the hot régions of the furnace are moved in the direction of the middle of the furnace, and the furnace inlet région is also operated at a higher température. This leads overall to a réduction in the heat demand in the calciner région.

The cooler, or clinker cooler, can for the purposes of the présent invention be divided in process engineering terms into at least three functionally different parts:

A first part into which the oxygen-containing gas is fed and in which the oxygen is preheated and fed to the rotary furnace. This part differs from the conventional cernent production process and known oxyfuel processes in that, unlike the conventional cernent production processes, no ambient air is introduced and, in contrast to the known oxyfuel processes, no premixing of recirculated preheater exhaust gas with oxygen occurs and as a resuit a smaller amount of gas is fed to the furnace. At the same time, however, heat is recovered from the hot furnace product and recircuiated to the rotary furnace, with the gas stream being able to be significantly hotter compared to the other processes because of its smaller amount. In one variant of the présent invention, an amount of oxygen sufficient for the combustion in the furnace and calciner is in particular fed in to this part.

A second part in which a séparation between the hot gas stream fed to the rotary furnace and the gas stream conveyed past the furnace occurs. The séparation can, for example,

a) occur mechanically, e.g. via a crusher, optionally with preceding column of material, or a dividing wall which is positioned above the clinker bed and séparâtes the gas spaces, or

b) occur by means of a System consisting of two or more spatial séparation devices, with an intermediate gas, which either acts as inert gas (in particular CO₂, Ar, H₂O) for the combustion process or acts as combustion gas (O₂), or a mixture of these gases, being supplied to the resulting intermediate space.

A thîrd part in which the final cooling of the clinker is carried out using any desired medium. This can conventionally be air or an internally recircuiated gas stream which is fed to the cooler with the objective of further heating, e.g. for downstream utilization in a System for utilization of waste heat.

In the présent invention, a considérable excess of heat can arise due to the small amount of gas taken off from the cooler as combustion air, for example when using a cross-flow cooler. The clinker exiting from the région whose heat content is not utilized for the combustion can hâve températures of about 1000°C. The excess of heat can be produced by cooling of the clinker from about 1000’C to about 100°C. This heat can be used for supplying heat to an intermediate preheating stage in the preheater and feeding the remaining heat to the raw mill. As an alternative, this heat can be used, at least partly, for génération of electric power.

In a classical steam circuit, it is possible to achieve significantly higher hot steam pressures compared to conventionally operated cernent plants because the gas température level in the last superheater stage is up to 900°C, or in some variants even above this. Comparée! to the températures of about 350°C - 400°C normally présent downstream of preheater, this is signîficantly higher. This steam turbine can thus also achieve a higher efficiency. In addition, smaller heat losses occur in the génération of electric power because the heat exchangers utilized for offtake of heat can be arranged close to one another.

In order to predry the raw meal in the raw mill in such a way that only a comparatively low heating power has to be expended for drying in the preheater, the heat supply and to a lesser extent the température available are usually of interest. For this purpose, it is possible to utilize the cooler exhaust gas not used in waste heat utilization or else the gas stream exiting from waste heat utilization. This generally has a sufficiently high température and heat content in order to realize drying of the raw meal.

Ideally, and thus preferred, is positioning of the raw mill in the vicinity of the cooler in order to keep the gas paths for the gas network short. In the case of intermediate waste heat utilization, for example for génération of electric power, the mill is arranged downstream of the cooler.

In the oxyfuel process, pollutant circuits arise in a manner similar to the conventional process for the production of cernent clinker. If there is an internai pollutant circuit between furnace and preheater, as similarly occurs for sulfur and chlorîne in clinker production, a System which removes pollutants from the circuit at the interface between furnace and preheater or furnace and calciner is also necessary here. If a solid is taken off and subsequently treated further externally in order to reduce the pollutant level, there are no changes from the conventional clinker production process. If a gas stream is taken off because the chlorîne circuit is high, this also contains a high proportion of oxygen. In conventional rotary furnaces, bypass gas amounts of 15%, based on the gas stream présent in the furnace inlet, are taken off at présent. Since the oxygen of the oxygen-containing gas in the case of the présent invention has prevîously been produced, for example, by fractionation of air, i.e. a process having a high energy consumption, it is useful to feed this stream back into the calciner as combustion gas.

For this reason, the following flow régime is used for the bypass plant in embodiments of the présent invention. The bypass stream is taken off from the furnace inlet, mixed with a cold return gas, subsequently cooled further to about 140°C by means of a gas-gas heat exchanger and an evaporative cooling tower and subsequently subjected to dust removal, with the pollutants, predominantly alkalis, sulfur and chlorine, condensing on the filter dust and being precipitated with the latter. The remaining gas stream is divided and fed to a further cooler which is preferably indirect and optionally also cools to below the dew point, so that moisture présent in the gas condenses out. This part is used to cool the hot bypass gas. The other part is, before it can be recirculated to the calciner, advantageously at least partially freed of moisture and subsequently heated in the gas-gas heat exchanger by means of the exhaust gas which has been cooled in the bypass cooler. The water used in the evaporative cooling tower is, after having been taken from the water store, preheated by means of an indirect heat exchanger in order to cool the water exiting from the injection cooler. The water exiting from the injection cooler is cooled further in an air cooler and subsequently partly fed to the water réservoir or recirculated to the injection cooler.

One embodiment of the présent invention relates to a process for producing a hydraulic binder, preferably cernent clinker, from at least one starting material, consisting of at least the steps of preheating of the starting material, calcination of the preheated starting material, firing of the calcined starting material with the objective of producing hydraulically active minerai phases, cooling of the hydraulic binder, characterized in that the total gas streams fed to the combustion processes consist to an extent of more than 50% by volume, preferably more than 85% by volume, of oxygen.

One embodiment of the présent invention relates to a process for producing cernent clinker and/or hydraulic clinker, which can be, for example, Portland clinker, consisting of a preheater, an (entrained flow) calciner, a rotary furnace and a cooler, characterized in that the gas fed from the cooler to the furnace plant (rotary furnace and calciner) consists to an extent of more than 50% by volume, preferably more than 85% by volume, of oxygen.

One embodiment of the présent invention relates to a process for producing a hydraulic binder from at least one starting material, consisting of at least the steps of preheating of the starting material to calcination température, calcination of the preheated starting material, firing of the calcined starting material with the objective of producing hydraulically active minerai phases, cooling of the hydraulic binder, characterized in that the gas streams fed to the combustion processes comprise more than 50% by volume of oxygen and consist to an extent of less than 50% by volume of recirculated exhaust gas from a combustion process which is characterized by a nitrogen content of less than 8% by volume in the moist reference State.

One embodiment of the présent invention relates to a process for producing hydraulic cernent clinker from at least one starting material, consisting of at least the steps of preheating of the starting material, calcination of the preheated starting material, firing of the calcined starting material with the objective of producing hydraulically active minerai phases, cooling of the hydraulic binder, characterized in that the preheating occurs in a cyclone preheater in which the ratio of solid fed in to exhaust gas is from greater than 1 to 2 kg of solid per 1 kg of gas, preferably from 1.3 to 1.9 kg of solid per kg of gas.

One embodiment of the présent invention relates to a plant for producing hydraulic cernent clinker, consisting of at least one cyclone preheater, an entrained flow calciner, a rotary furnace and a clinker cooler, characterized in that the entrained flow calciner has a nonvertical section into which coarse fuels having an edge length of more than 100 mm (i.e. non-entrainable size) are introduced and hot gases flow over them in the calciner.

One embodiment of the présent invention relates to a process for producing hydraulic cernent clinker from at least one starting material, consisting of at least the steps of preheating of the starting material, calcination of the preheated starting material, firing of the calcined starting material with the objective of producing hydraulically active minerai phases, cooling of the hydraulic binder, characterized in that a gas substream from plant components located upstream in the flow direction of material (e.g. from the furnace inlet or downstream of the calciner) is recirculated to the top of the furnace/the combustion, i.e. the main burner.

One embodiment ofthe présent invention relates to a process for producing hydraulic cernent clinker from at least one starting material, consisting of at least the steps of preheating of the starting material, calcination of the preheated starting material, fîring of the calcined starting material with the objective of producing hydraulically active minerai phases, cooling of the hydraulic binder, characterized in that a gas having a content of 85% by volume of oxygen is fed to a first section of the cooler.

One embodiment of the présent invention relates to a process for producing hydraulic cernent clinker from at least one starting material, consisting of at least the steps of drying and milling of the raw material, preheating of the starting material, calcination of the preheated starting material, fîring of the calcined starting material with the objective of producing hydraulically active minerai phases, cooling of the hydraulic binder, characterized in that hot air from the clinker cooler is at least partly fed to preheating and subsequently drying and milling, with mixing with the exhaust gas from the calcination and firing process being avoided.

One embodiment of the présent invention relates to a process for producing hydraulic cernent clinker from at least one starting material, consisting of at least the steps of drying and milling of the raw material, preheating of the starting material, calcination of the preheated starting material, firing of the calcined starting material with the objective of producing hydraulically active minerai phases, cooling of the hydraulic binder, characterized in that the oxygen-rich gas taken from the furnace inlet région is, after being depleted in sulfur, chlorine and similar components, recirculated to the furnace System. In this embodiment, the oxygen which is usually produced in an expensive process is firstly collected and can be utilized further and, secondly, précipitation ofthe waste products chlorine and sulfuron dust is achieved.

In one embodiment of the présent invention, the oxygen-containing gas is N₂depleted air, in particular very greatly N₂-depleted air.

In one embodiment ofthe présent invention, the oxygen-containing gas is air which is highly enriched in O₂.

ln one embodiment of the présent invention, the oxygen-containing gas is pure (technical-grade) oxygen.

In one embodiment of the présent invention, the oxygen-containing gas is not an O2/CO2 mixture.

In one embodiment of the present invention, the gas stream fed in is not a recirculated gas.

In one embodiment of the present invention, the gas stream fed in does not contain any recirculated gas.

In one embodiment ofthe present invention, the oxygen-containing gas is not air or any treated or worked-up air. This is a preferred embodiment.

It has been taken into account that a small amount of air may possibly be sucked in from outside during operation ofthe plant under reduced pressure. A small amount in this case means less than 10% by volume, in particular from 1 to 5% by volume. This air which may hâve been sucked in from outside is not taken into account in the définition of the oxygen-containing gas.

In one embodiment of the present invention, only small proportions, preferably none, of the oxygen-containing gas leave the cooler as exhaust air.

In some embodiments of the present invention, the fuel energy introduced into the rotary furnace (secondary apparatus for binder sintering) amounts to less than 33% (1/3) of the fuel energy necessary for the process.

In some embodiments of the present invention, the quantity of heat introduced into the rotary furnace is less than 30% of the total quantity of heat introduced into the process, with the total heat energy corresponding to the sum of the heat energy introduced into the rotary furnace, the calciner, the exhaust gas path and the rotary furnace gases.

In some embodiments of the present invention, the total amount of exhaust gas produced by combustion and calcination for the binder (cernent clinker) is less than <1 standard m³/kg of clinker. One standard m³ of gas corresponds to 1 m³ of gas at a pressure of 101.325 kPa at a température of 273.15 K.

ίη some embodiments of the présent invention, the CO₂ concentration in the exhaust gas is above 85% or more.

In some embodiments of the présent invention, the recirculation of exhaust gas is limited to less than 15%.

In the context of the présent invention, it is possible to obtain CO₂ having a greatly increased purity downstream ofthe preheater, so that the further work-up is easier or is more advantageously possible compared to the previous prior art.

In the context of the présent invention, it is possible to match the amounts of gas and fuel to one another so that, contrary to the expectations of the prior art, there are significantly fewer or even no problems caused by higher combustion températures and reduced gas volume flows.

The présent invention also provides, inter alia, the following embodiments designated by Roman numerals:

I. Process for producing cernent clinker, comprising the steps

a) preheating ofthe starting material to calcination température,

b) calcination ofthe preheated starting material, c) firing of the calcined starting material in a furnace, d) cooling of the cernent clinker, characterized by the step

e) feeding of an oxygen-containing gas having a proportion of 15% by volume or less of nitrogen and a proportion of 50% by volume or more of oxygen from a first section of the cooler directly adjoining the top of the furnace into

i) the rotary furnace and ii) optionally additionally the calciner.

la. Process for producing cernent clinker, comprising the steps

a) preheating ofthe starting material to calcination température,

b) calcination ofthe preheated starting material, c) firing of the calcined starting material in a furnace, d) cooling of the cernent clinker,

i) the rotary furnace and ii) optionally additionally the calciner, characterized in that the total gas streams fed to the combustion processes consist to an extent of more than 50% by volume, preferably more than 85% by volume, of oxygen.

II. Process according to embodiment I or la, characterized in that the ratio of solid fed in to exhaust gas in step a) is set to greater than 1.0 kg, preferably greater than 1.3 kg, of solid per 1 kg of gas, preferably from 1 to 2 kg/kg of solid to gas, particularly preferably from 1.3 to 1.9 kg/kg of solid to gas, where the preheater is preferably a cyclone preheater.

III. Process according to embodiment I, la or II, characterized in that the ratio of solid fed in to exhaust gas in step b) is set to greater than 1.0 kg, preferably greater than 1.3 kg, of solid per 1 kg of gas, preferably from 1 to 2 kg/kg of solid to gas, particularly preferably from 1.3 to 1.9 kg/kg of solid to gas, where the calciner is preferably an entrained flow calciner.

IV. Process according to any of embodiments I to III, characterized in that coarse fuels having an edge length of 70 mm or more, preferably 100 mm or more, are introduced into the calciner, which is preferably an entrained flow calciner having a nonvertical section, so that the hot gases flow over them in the calciner.

V. Process according to any of embodiments I to IV, characterized in that a gas substream from plant components located upstream in the flow direction of material, preferably from the furnace inlet or downstream of the calciner, is recirculated to the top of the furnace for combustion.

VI. Process according to any of embodiments I to V, characterized in that hot exhaust air from the clinker cooler is fed

a) at least partly to preheating, or

b) at least partly to drying and milling, or

c) at least partly to preheating and subsequently to drying and milling, with mixing with the exhaust gas from the calcination and firing process being avoided.

VII. Process according to any of embodiments I to VII, characterized in that the oxygen-rich gas taken off from the furnace inlet région is, after having been depleted 10 in at least sulfur and chlorine, recirculated to the furnace system.

VIII. Process according to any of embodiments I to VII, characterized in that the gas

i) contains 75% by volume or more of oxygen, preferably 85% by volume or 15 more, 90% by volume or more, 95% by volume or more, 98% by volume or more or

99% by volume or more, or il) contains 10% by volume or less of nitrogen, preferably 8% by volume or less, 6% by volume or less, 4% by volume or less, or has a nitrogen content below the 20 détection limit, or iii) contains 75% by volume or more of oxygen, preferably 85% by volume or more, 90% by volume or more, 95% by volume or more, 98% by volume or more or 99% by volume or more, and contains 10% by volume or less of nitrogen, preferably 25 8% by volume or less, 6% by volume or less, 4% by volume or less, or has a nitrogen content below the détection limit.

IX. Process according to any of embodiments I to VIII, characterized in that the amounts of gas and fuel fed in are regulated as a function of combustion température 30 and gas volume flows.

According to the invention, the process is characterized in that the introduction of the oxygen-containing gas is set such that there is an excess of oxygen at the main burner and residual amounts of the oxygen go to the calciner for combustion there.

XI. Process according to any of embodiments I to X, characterized in that the introduction of the oxygen-containing gas is carried out exclusively on the side of a gas séparation device which is arranged in the cooler and directly adjoins the top of the furnace, where the gas séparation device is i) a mechanical gas séparation device, ii) a System based on supply of a barrîer gas, or iii) a combined system.

XII. Plant for producing cernent clinker, comprising a preheater, a calciner, a rotary furnace and a clinker cooler, characterized in that the plant has, at the section of the cooler directly adjoining the top of the furnace, a device for feeding gas from the cooler to i) the rotary furnace and ii) optionally additionally to the calciner, where the gas fed in has a proportion of 15% by volume or less of nitrogen and a proportion of 50% by volume or more.

XIla. Plant for producing cernent clinker, comprising a preheater, a calciner, a rotary furnace and a clinker cooler, wherein the plant has, at the section of the cooler directly adjoining the top of the furnace, a device for feeding gas from the cooler to i) the rotary furnace and ii) optionally additionally the calciner, which device is configured for feeding in a gas having a proportion of 15% by volume or less of nitrogen and a proportion of 50% by volume or more of oxygen, and wherein the plant is configured for feeding gas streams which in total consist to an extent of more than 50% by volume, preferably more than 85% by volume, of oxygen to the combustion processes.

The advantages of the present invention a ri se, inter alia, from the following aspects: since furnace and preheater are always designed according to the amount of gas, the advantage of the omission of nitrogen from the mixture is that new plants can be made significantîy smaller and are therefore considerably cheaper, or existing plants can be operated with a significantîy higher capacity after conversion.

The various configurations, embodiments and variants of the present invention, for example, but not restricted thereto, of the various daims, can be combined with one another in any desired way, as long as such combinations are not contradictory.

The present invention can also be combined with the spécifie subject matter of the parallel invention “Oxyfuel clinker production without recirculation of the preheater exhaust gases, in particular the following embodiments designated by the Roman numerals Cl to CXII, where these combinations are expressly also subject matter of the present invention:

Embodiment Cl. Process for producing cernent clinker, comprising the steps a) preheating of the starting material to calcination température, b) calcination ofthe preheated starting material, c) firing ofthe calcined starting material in a rotary furnace, d) cooling of the cernent clinker, e) introduction of an oxygen-containing gas having a proportion of 15% by volume or less of nitrogen and a proportion of 50% by volume or more of oxygen, into i) the calciner, characterized in that no gases from the rotary furnace are fed to the calcination, one-train or multitrain cyclone preheaters whose indivîdual cyclones are connected to one another in a cascade-like manner are used for preheating, material transfer and/or gas transfer is possible between the individual cyclone preheaters and no recirculation ofthe preheater exhaust gases occurs.

Embodiment Cia. Process for producing cernent clinker, comprising the steps a) preheating of the starting material to calcination température, b) calcination ofthe preheated starting material, c) firing of the calcined starting material in a rotary furnace, d) cooling of the cernent clinker,

e) introduction of an oxygen-containing gas having a proportion of 15% by volume or less of nitrogen and a proportion of 50% by volume or more of oxygen, into i ) the calciner, characterized in that no gases from the rotary furnace are fed to the calcination, one-train or multitrain cyclone preheaters whose individual cyclones are connected to one another in a cascade-like manner are used for preheating, material transfer and/or gas transfer is possible between the individual cyclone preheaters and no recirculation ofthe preheater exhaust gases occurs, and characterized in that the ratio of solid fed in to exhaust gas in step a) is set to greater than 1.0 kg of solid to gas.

Embodiment CH. Process according to embodiment Cl or Cia, characterized in that multistage one-train or multitrain cyclone preheaters are used.

Embodiment Clll. Process according to any of embodiments Cl, Cia or Cil, characterized in that two-train cyclone preheaters having from two to six stages, preferably five stages are used.

Embodiment CIV. Process according to any of embodiments Cl to Clll, characterized in that Crossing of meal streams but no Crossing of the gas streams occurs after each stage between the preheaters of a multitrain cyclone preheater.

Embodiment CV. Process according to any of embodiments Cl to CIV, characterized in that preheating occurs with involvement of at least one carbonator.

Embodiment CVI. Process according to any of embodiments Cl to CV, characterized in that a preheater having a carbonator of a second preheater train is supplied with exhaust gases coming from the rotary furnace, where the exhaust gases hâve a smail proportion of CO2 of less than 35% in the dry reference state.

Embodiment CVIL Process according to any of embodiments CV to CVI, characterized in that the carbonatization température is set by means of a carbonator with cooler,

Embodiment CVIII. Process according to any of embodiments Cl to CV11, characterized in that the température in the calciner or the amount of gas in the calciner or the température and the amount of gas in the calciner is regulated by means of partial recirculation of gases, where the recirculated gases are exhaust gases from one of the preheater stages following the calciner, preferably the first preheater stage following the calciner.

Embodiment CIX. Process according to embodiment CVIII, characterized in that the feeding of the recirculated gases occurs afterthe first séparation cyclone or between the first and penultimate séparation cyclones or after a plurality of séparation cyclones.

Embodiment CX. Process according to any of embodiments Cl to CVII, characterized in that the amounts of oxygen-containing gas and fuel fed in to the calciner are regulated as a function of calcination température and température in the preheater.

Embodiment CXI. Process according to any of embodiments Cl to CX, characterized in that recirculation of the calciner exhaust gases additionally occurs.

Embodiment CXIL Plant for producing cernent clinker, comprising a preheater, a calciner, a rotary furnace and a clinker cooler, where the plant has a device for feeding gas to i) the calciner, where the gas fed in has a proportion of 15% by volume or less of nitrogen and a proportion of 50% by volume or more of oxygen, characterized in that no air from the rotary furnace is fed in to the calciner, cyclone preheaters whose individual cyclones are connected to one another in a cascade-like manner are used as preheaters and material transfer and/or gas transfer is possible between the individual cyclone preheaters and there is no recirculation device for the preheater exhaust gases.

Embodiment CXIIa. Plant for producing cernent clinker comprising a preheater, a calciner, a rotary furnace and a clinker cooler, where the plant has a device for feeding gas to i) the calciner, where the gas fed in has a proportion of 15% by volume or less of nitrogen and a proportion of 50% by volume or more of oxygen, characterized in that no air from the rotary furnace is fed in to the calciner, cyclone p_reh_eaters whose individual cyclones are connected to one another in a cascade-like manner are used as preheaters and material transfer and/or gas transfer is possible between the individual cyclone preheaters and there is no recirculation device for the preheater exhaust gases, and characterized in that the plant is configured for setting the ratio of solid fed in to exhaust gas in the preheater to greater than 1.0 kg of solid to gas.

The présent invention will be illustrated in more detail below with reference to the drawings. The drawings are not to be interpreted as being limited and are not true to scale. Furthermore, the drawings do not contain ail features which are présent in conventional plants but hâve been reduced to the features necessary for the présent invention and an understanding thereof.

Description of figures:

In figures 4 and 5, transitions of solid are depicted as solid arrows and transitions of gaseous materials are depicted as dotted arrows.

Figure 1 illustratively depicts a cooler (clinker cooler) K which is divided into five different cooling zones K1 to K5. Here, gas is fed in appropriately via the various blowers G. Cooling air for the clinker but no combustion air to the furnace is fed in via the blowers G assigned to the zones K3 to K5. The oxygen-containing gas A, which is conveyed as combustion air into the furnace, is fed in via the blower assigned to the zone K1. Barrier gas B is fed in via the blower assigned to the zone K2. This barrier gas can, for example, consist to an extent of 85% by volume or more of carbon dioxide, with the balance being inert gas, or, for example, consist to an extent of 85% by volume or more of oxygen with the balance being in inert gas. For the présent purposes, the term inert gas preferably refers to components such as water vapor, argon, etc. In both cases, the gas B serves as barrier gas for sealing the oxygen région from the air région ofthe cooler. Furthermore, a CO₂ divider Ta which functions as a resuit of supply of the barrier gas is depicted in figure 1.

Figure 2 illustratively depicts a cooler (clinker cooler) K mostly as shown in figure 1. The only différence from figure 1 is that the CO₂ divider Tb is configured as mechanical divider at which the séparation of oxygen-containing gas is effected by means of supply of barrier gas and mechanical means, for example pendulum-like dividing walls resting movably on the bed. Although not shown in figure 2, the zone K2 can optionally be omitted when the mechanical CO₂ divider is sufficiently effective.

Figure 3 shows two flow diagrams which illustrât© two possible variants of the présent invention, in which hot clinker from the furnace enters cooler part 1 and at the same time oxygen-containing gas is conveyed from the cooler part 1 into the furnace (récupération of combustion gas to the furnace). A gas séparation device is arranged adjoining the cooler part 1, and this device in turn adjoins cooler part 2. At the cooler part 2, the clinker then leaves the plant and is brought to the silo. In the upper part of the figure, a mechanical gas séparation device 2b between cooler part 1 (corresponding to cooling zone K1) and cooler part 2 (corresponding to cooling zones K3 to K5) is depicted, while a gas séparation device 2a based on barrier gas is shown in the lower part. In connection with cooler part 2, heat recovery for purposes other than use for combustion occurs in both variants, with heat carriers being combustion air, CO₂, etc. The cooler part 2 in both cases firstly adjoins a heat exchanger System which can be based on direct heat exchange or on indirect heat exchange. Subsequently, a waste gas treatment, which can encompass dust removal and/or a stack, is depicted for both variants.

Figure 4 shows a plant for clinker production, in which the involvement of the cooler exhaust air in preheating is depicted. The cooler is, in comparison with figures 1 and 2, depicted in simplified form in that only one blower is depicted to the left for the introduction of oxygen-containing gas according to the présent invention, and the 5 other four blowers are shown for the introduction of air. In the embodiment depicted in this figure, the cooler exhaust air is conveyed via a cyclone separator for removing solid particles into the preheater.

Figure 5 describes a similar embodiment to that in figure 4, but the waste heat is utilized differently from what is shown in figure 4. Here too, the cooler exhaust air is 10 conveyed through a cyclone separator but then not into the preheater stage but instead is conveyed through a heat exchanger and then into the raw milling plant for drying the raw meal.

List of reference symbols:

K Cooler (clinker cooler)

Ta Gas séparation device with barrier gas (CO₂ divider (barrier gas))

Tb Mechanical gas séparation device or mechanical gas séparation device in combination with barrier gas (CO₂ divider (mechanical or mechanical/barrier gas combination))

G B lower

Kl Cooling zone 1 (first cooling zone)

K2 Cooling zone 2 (second cooling zone)

K3 Cooling zone 3 (third cooling zone)

K4 Cooling zone 3 (fourth cooling zone)

K5 Cooling zone 5 (fifth cooling zone)

A Oxygen-containing gas

B Barrier gas hV Hot combustion air

Al Exhaust air

O Furnace

KT1 Cooler, part 1

KT2 Cooler, part 2

AB Exhaust gas treatment

W Heat exchanger System

S Silo

Preheater

1a Preheater (upper section) b Preheater (lower section)

1c Preheating cyclone supplied with cooler exhaust air

Calciner

Rotary furnace

4a Cooler using oxygen as cooling medium

4b Cooler using air as cooling medium

Air-air heat exchanger

100 Raw material

100a,b Hot meal

101 Hot meal to calciner

102 Hot meal to rotary furnace

103 Hot clinker

104 Hot clinker (about 1000°C)

105 Cold clinker

200 Oxygen (> 85%)

201 Secondary gas

202 Furnace exhaust gas

203 Calciner exhaust gas

203a Exhaust gas from lower preheater section

204 Preheater exhaust gas

300 Cooler feed air

301 Cooler exhaust air

302 Cooler exhaust air to raw mill

400 Air to heat exchanger

401 Heated airto raw mil

500 Fuel for main firing

501 Fuel for calciner

Claims

1. A process for producing cernent clinker, comprising the steps

a) preheating of the starting material to calcination température,

b) calcination ofthe preheated starting material,

c) fi ring of the calcined starting material in a rotary furnace,

d) cooling ofthe cernent clinker,

i) the rotary furnace, characterized in that the total gas streams fed to the combustion processes co nsi si to an extent of more than 50% by volume of oxygen, characterized in that the introduction of the oxygen-containing gas is set so that there is an excess of oxygen at the main burner and residual amounts of the oxygen go into the calciner for combustion there.

2. The process as claimed in claim 1, characterized in that step e) additionally comprises ii) feeding ofthe oxygen-containing gas into the calciner.

3. The process as claimed in claim 1 or 2, characterized in that the ratio of solid fed in to exhaust gas in step a) is set to greater than 1.0 kg of solid to gas, wherein at least one cyclone preheater is used for preheating.

4. The process as claimed in any of claims 1 to 3, characterized in that the ratio of solid fed in to exhaust gas in step b) is set to greater than 1.0 kg of solid per 1 kg of gas, wherein the calciner is an entrained flow calciner.

5. The process as claimed in any of claims 1 to 4, characterized in that coarse fuels having an edge length of 70 mm or more are introduced into the calciner, which is an entrained flow calciner having a nonvertical section, so that the hot gases flow over the coarse fuels in the calciner.

6. The process as claimed in any of ciaims 1 to 5, characterized in that a gas substream from plant components located upstream in the flow direction of material, from the furnace inlet or downstream of the calciner, is recirculated to the top of the furnace for combustion.

7. The process as claimed in any of ciaims 1 to 6, characterized in that hot exhaust air from the clinker cooler is fed

a) at least partly to preheating, or

b) at least partly to drying and milling, or

8. The process as claimed in any of ciaims 1 to 7, characterized in that the oxygen-rich gas taken off from the furnace inlet région is, after having been depleted in at least sulfur and chlorîne, recirculated to the furnace System.

9. The process as claimed in any of ciaims 1 to 8, characterized in that the gas i) contains 75% by volume or more of oxygen, or ii) contains 10% by volume or less of nitrogen, or has a nitrogen content below the détection limit, or iii) contains 75% by volume or more of oxygen, and contains 10% by volume or less of nitrogen, or has a nitrogen content below the détection limit.

10. The process as claimed in any of ciaims 1 to 9, characterized in that the amounts of gas and fuel fed in are regulated as a function of combustion température and gas volume flows.

11. The process as claimed in any of daims 1 to 10, characterized in that the introduction of the oxygen-containing gas is set so that the oxygen fed in is sufficient for complété combustion at the main burner and in the calciner.

12. The process as claimed in any of daims 1 to 11, characterized in that the introduction of the oxygen-containing gas is carried out exclusively on the side of a gas séparation device which is arranged in the cooler and directly adjoins the top of the furnace, wherein the gas séparation device is i) a mechanical gas séparation device, ii) a System based on supply of a barrier gas, or iii) a combined System.

13. A plant for producing cernent clinker, comprising a preheater, a calciner, a rotary furnace and a dinker cooler, wherein the plant has, at the section of the cooler directly adjoining the top of the furnace, a device for feeding gas from the cooler to i) the rotary furnace, which device is configured for feeding in a gas having a proportion of 15% by volume or less of nitrogen and a proportion of 50% by volume or more of oxygen, and wherein the plant is configured for feeding gas streams which in total consist to an extent of more than 50% by volume of oxygen to the combustion processes, characterized in that the introduction of the oxygen-containing gas is set so that there is an excess of oxygen at the main burner and residual amounts of the oxygen go into the calciner for combustion there.

14. The plant as claimed in daim 13, characterized in that it additionally has ii) a device for feeding the oxygen-containing gas into the calciner.