Field of the invention

The invention relates to the supply of heat energy from the kiln system of a clinker burning department in a plant for manufacture of cement clinker to separate use applications.

A kiln system often comprises a preheater, a calciner, a rotary kiln and a clinker cooler. Waste heat from the cement kiln system is typically used for the drying of raw materials or fuels but increasingly also as a source of power generation.

Background of the Invention

The manufacture of cement clinker in a clinker burning department requires a high input of heat energy with a considerable amount of heat loss, commonly utilized for raw material and fuel drying, and for power generation in a waste heat recovery power plant (WHR) if remaining heat from the clinker burning department is available. A clinker burning department operating with present technology requires a heat input of approximately 3,2 MJ/kg clinker, where 1,7 MJ/kg clinker or about 55% are bound in the chemical changes of the clinker product and some inherent heat losses.

The design of the kiln system and the characteristics of the fuel to a large extent define the specific relationships between gas flow and material flow and thereby set the conditions for the potential heat recovery in the preheater and the clinker cooler.

In a historical context, the emergence and development of the preheater and clinker cooler were designed to recover heat back to the clinker burning process and has achieved a very successful reduction of approximately 50% of the specific heat consumption compared to the early rotary kiln systems.

The main reactions in the clinker burning department occur at 800-900°C for the calcination of limestone and at 1400-1500°C for the clinker mineral formation, where the high temperatures create the challenges in reducing the associated heat loss. It is the hot exhaust gases from the preheater and the hot excess cooling air from the clinker cooler that make up the conventionally accessible waste heat, which is generally available in the range of 300-350 °C and may account for 1,2 MJ/kg clinker (37%).

The accessible waste heat resource is primarily used to provide heat for drying of raw materials and fuels, and residual heat may also be used to generate power with a WHR power plant. The heat available for WHR depends on the moisture content of the raw materials and fuels. The available temperature of the hot exhaust gas and excess cooling air limit the possibilities of making effective use of the waste heat for separate use applications. It would be advantageous to be able to apply a system for extraction of heat in the form of hot combustion gas and/or preheated meal to supply heat for separate uses, wherein the temperature of the extracted heat is higher than conventionally available as accessible waste heat, to enable separate use applications with a more efficient use and transfer of heat.

It would be further advantageous to be able to apply a system to supply hot gas and/ or boost the extracted hot combustion gas to increase the temperature and/or the quantity to meet the needs of a separate use application wherein a heat input as fuel is combusted with hot air recovered from the clinker cooler while mixing hot extracted gas and/or recycled exhaust gas.

Object of the invention

It is an object of the present invention to overcome or at least alleviate one or more of the above problems of the prior art and/or provide the consumer with a useful or commercial choice.

It is a second object of the present invention to provide a system and method to extract heat from the kiln system of a clinker burning department in a plant for manufacture of cement clinker for separate uses, where a part of the hot combustion gas is extracted from the preheater before the exhaust gas outlet stage, while a supplementary heat input as fuel is added in the kiln system, resulting in a transfer of heat, which reduces the temperature and quantity of the preheater exhaust gas and obtains a high temperature of the extracted combustion gas, transforming a part of the conventional waste heat into a high temperature heat supply for separate use applications, resulting in a reduced specific heat loss and carbon dioxide emission of the combined kiln system and separate use applications.

It is a third object of the present invention to provide a system and method to extract heat from the kiln system of a clinker burning department in a plant for manufacture of cement clinker for separate use, where a part of the preheated meal is extracted from a preheater stage, while a supplementary heat input as fuel is added in the kiln system and regulating the kiln feed to maintain same net feed to the rotary kiln, resulting in a transfer of heat, which reduces the temperature of the preheater exhaust gas and obtains a high temperature preheated meal, transforming a part of the conventional waste heat into a heat supply as preheated meal, for separate use applications, resulting in a reduced specific heat loss and carbon dioxide emission of the combined kiln system and separate use applications.

It is a fourth object of the present invention to provide a system and method to boost the heat extracted from the kiln system to a temperature and/or heat quantity in a combustion chamber, to meet the needs of the separate use application, where an additional heat input as fuel and hot air, recovered from the clinker cooler of a clinker burning department in a plant for manufacture of cement clinker, are combusted while mixing extracted combustion gas and recycled exhaust gas into the combustion chamber to control the temperature and/or heat quantity to the required levels, intending to reduce specific heat loss and carbon dioxide emission from the combined use of kiln system and separate use application.

It is a fifth object of the present invention to provide an alternative to the prior art. Summary of the invention

An existing clinker burning plant is configured to optimize heat energy use within the plant process and even with good conditions only 55% of the heat input are chemically bound in the product. About 10% of the heat waste is so dispersed that it cannot be utilized. The remaining third of the waste heat is found in the preheater exhaust gas and the clinker cooler excess air. These hot gases leave the plant at low temperatures generally in the range 300-380°C and are mostly used for drying raw materials and fuels. If they were used to generate power, the conversion efficiency would likely be about 18%.

The conventional use of the preheater as a heat exchanger for hot combustion gas and raw meal, operates the preheater in a conventional balanced mode, maintaining a fixed relation of material to gas throughout the preheater to achieve maximum heat recuperation back to the clinker burning process.

The present invention reconfigures the conventional preheater by taking out hot gas or hot material from within the preheater for one or more separate uses while activating an unrecognized feature of the preheater when operating in an unbalanced mode where the removal of heat by Law of Conservation results in a lower exhaust gas temperature and a proportionally lower temperature of the preheated raw meal. Calculations show that the extraction of heat in the form of hot gas from the outlet at an intermediate stage cyclone in the preheater, derives most of its heat content above 80% from the reduction of exit gas temperature and a smaller part from the temperature reduction of preheated meal. The lower temperature of the preheated meal is here compensated by the addition of a small quantity of supplementary fuel to the kiln system, which is further supported by using preheated combustion air recuperated from the clinker cooler.

The overall function of the conventional preheater can in this way be reconfigured into a multi-purpose heat exchanger, that supplies hot gas and/or hot meal at high temperatures like 400-800°C for one or more separate purposes, while achieving lower exhaust gas temperature from the preheater gas exit. This use of the preheater in this mode takes on a resemblance to the heat pump function, where a small investment of energy results in a heat stream which accounts for 2-3 times the invested heat value of the energy. In the reconfigured preheater the investment is the supplementary heat compensation from fuel and the extracted heat is the combination of the reduced heat loss from the preheater exit and supplemental heat input, which may also reach 2-3 times the supplemental heat input, until the available waste heat is depleted.

The possibility also to extract heat as a preheated meal provides new ways to achieve product drying causing less heat loss from large amounts of vapor and heated air or maintaining a low oxygen atmosphere while condensing the vapors. His is possible by diverting preheated meal and feeding the preheater with additional meal to maintain same constant net meal input for the process.

The limit for this unbalanced operation removing heat from the preheater, is when the exit temperature is reduced to a level where condensations may cause corrosion issues. In order to exceed this point heat boosting can be used to increase heat production from waste heat by burning further supplementary fuel in recovered waste heat as hot excess air used to reheat recycled separately used hot air. The ability to supply 700°C hot gas for the separate use of producing power can increase the conversion efficiency to 38% or more and thereby more than double the potential power yield per unit heat.

The invention enables the transfer of heat from a kiln system of a clinker burning department to separate use applications, wherein heat is extracted from the preheater while a supplementary heat input as fuel is added in the kiln system, resulting in a transfer of heat, which reduces the temperature and quantity of the preheater exhaust gas and obtains a high temperature of extracted heat as gas or meal, transforming a part of the conventional waste heat into a high temperature heat supply for separate use applications, resulting in a reduced specific heat loss and carbon dioxide emission of the combined kiln system and separate use application.

The separate use application is a heat consuming process or plant which becomes accountable for the heat input and sharing the carbon dioxide emission related to the combined heat input.

The extracted heat may be applied in several separate uses including, but not limited to, power generation, preparation of Supplementary Cementitious Materials (SCM), fuel drying and gasification, alumina calcination, lime production, raw materials drying.

In a first aspect, the invention relates to a system for extraction of hot combustion gas to supply heat for separate use, said hot combustion gas extracted from a preheater of a clinker burning department in a plant for manufacture of cement clinker, said plant comprising a preheater, a rotary kiln, a clinker cooler, said preheater preferably comprises two or more cyclone stages, where the hot combustion gas is preferably extracted from one or more locations between a rotary kiln gas outlet and an exhaust gas outlet stage cyclone of the preheater, said plant being connected to a separate use application which is a heat consuming process or plant which can receive a heat input as hot combustion gas from said clinker burning department, wherein a part of the hot combustion gas is extracted from the preheater, while a supplementary heat input as a fuel is added in the kiln system, resulting in a transfer of heat, which reduces the temperature and quantity of the preheater exhaust gas and obtains a high temperature of the extracted combustion gas, transforming a part of the conventional waste heat into a high temperature heat supply for separate use applications, resulting in a reduced specific heat loss and carbon dioxide emission of the combined kiln system and separate use applications.

The system extracts hot gas incorporating a heat fraction from the exhaust gas, which would otherwise leave the system, and a supplement of fuel input in the rotary kiln enabling extraction of a more potent heat source for separate use.

The system may further comprise a calciner, wherein a supplementary heat input as fuel to the calciner can also occur. Kiln systems with a calciner accepts a wider range of fuels expanding the supplementary heat sources. The hot gas may be extracted from the gas outlet duct of a cyclone before the gas is mixed with material from a cyclone stage above and/or extracted through a parallel cyclone to provide partially dedusted hot combustion gas. The object is to remove a minimal amount of kiln dust with the extracted hot gas and to reduce effects on separate use application.

The extracted hot combustion gas for separate use may be based on a supplementary heat input as sustainable fuel supplying a competitive and/or sustainable heat input for the separate use application. Benefitting the reduction in use of fossil fuel types to generate heat.

The extracted heat may be transferred and used in a separate application for generation of electrical power in an electric power plant. The extracted hot gas will have a high temperature enabling a higher efficiency in the conversion to power.

The extracted heat is preferably transferred and used for preparation of materials such as calcined clay and/or similar activation of ferro/alumina silicates and/or pozzolanic materials to be used as a Supplementary Cementitious Material in a partial replacement of cement clinker in cement manufacture. Producing a material for partial replacement of cement clinker with heat extracted from the cement production doubles the benefit.

The extracted heat may be transferred and used for heat treatment of alumina in an alumina calcination plant or lime manufacture in a lime kiln system. Extracted hot gas can also benefit related industry which shares the need for high temperature manufacture.

The extracted heat may be transferred and used in a separate application while any residual heat in the subsequent gas may be used for drying of raw materials either for clinker manufacture or for the separate use application. Low grade heat can in many cases be used for drying.

The extracted hot combustion gas with a low oxygen content is preferably used for heat treatment of fuels to prepare the fuels for combustion, such as by drying, pyrolyzing or gasifying the fuel while either returning the resulting gas to a combustion in the kiln system or supplying the resulting gas to a separate use while either returning fuel residuals to either the kiln system or collection for carbon separation and storage. Low oxygen avoids the hazard of premature combustion.

The extracted hot combustion gas with a high carbon dioxide content is preferably cooled substantially by a separate use application such as with a boiler for electrical power generation and then be conditioned and prepared for capture as a gas or liquid for separation and subsequent use or storage of the carbon dioxide by another process. Being able to extract hot gas with a high content of carbon dioxide provides an excellent opportunity to collect the carbon dioxide for capture. The extracted hot combustion gas with a high carbon dioxide content which has preferably been cooled substantially by a separate use application, such as with a boiler for power generation, is partially recirculated as cooling gas in the recovery part of the clinker cooler while injecting a proportional quantity of oxygen into the recirculated cooling gas and/or the kiln burner, while increasing the carbon dioxide content in the combustion gases to benefit utilization of kiln system and/or reduce nitrogen oxide emissions and/or benefit a carbon capture application. Recirculating carbon dioxide with oxygen injection increases the carbon dioxide concentration in the extracted gases further improving the conditions for carbon dioxide capture.

The extracted hot gas may be transferred and used in a separate use application resulting in a reduced load on the exhaust gas handling system of clinker burning department thereby enabling a proportional increase of the production capacity of the kiln system to utilize the available capacity of the kiln and/or gas handling system. The extracting of hot gas from the kiln system may enable a rebalancing or optimizing of the kiln system with an increased production.

The extracted hot gas may to be transferred to a separate use application, that requires a higher temperature or heat input than available from the kiln system, which is then boosted in a combustion chamber, where additional fuel and additional hot combustion air, recovered from the clinker cooler, are combusted to the required heat/temperature level, while partially mixing recycled exhaust gas to control temperature and/or heat content. The extracted hot gas may require an additional boost to suit the heat requirement.

In a second aspect, the invention relates to a system for extraction of preheated meal to supply heat for separate use, extracted from the preheater of a clinker burning department in a plant for manufacture of cement clinker, said plant preferably comprising a preheater, a rotary kiln, a clinker cooler, said preheater comprising two or more cyclone stages, where the preheated meal is extracted from one or more cyclones located between the hot meal inlet of the rotary kiln and the kiln feed meal entry of the preheater. said plant being connected to a separate use application which is a heat consuming process or plant which can receive a heat input as preheated meal from said clinker burning department, wherein a part of the preheated meal is extracted from the preheater, while regulating the meal feed to maintain same net feed to the rotary kiln combined with a supplementary heat input as fuel to the kiln system, resulting in a transfer of heat, which reduces the temperature of preheater exhaust gas and obtains a high temperature extraction of preheated meal, transforming a part of the conventional waste heat into a high temperature heat supply for separate use applications, resulting in a reduced specific heat loss and carbon dioxide emission of the combined kiln system and separate use applications. The system extracts preheated meal incorporating a heat fraction from the exhaust gas, which would otherwise leave the system, and a supplement of fuel input in the rotary kiln enabling extraction of a more potent heat source for separate use.

The system may further comprise a calciner, wherein the supplementary heat input as fuel can also occur in the calciner. Kiln systems with a calciner accepts a wider range of fuels expanding the supplementary heat sources.

The extracted preheated meal may be used as a heat source for drying raw material by mixing preheated meal into the raw grinding process to subsequently become a part of the raw meal product. Conveying heat to the drying of raw material with a meal enables a reduction of heat loss from gases leaving the drying process.

The extracted preheated meal may be used as a heat source in a separate cyclone heat exchanger comprising one or more cyclone stages to heat ambient air and/or recirculated exhaust gas with residual heat and oxygen to provide preheated combustion air while the cooled meal is returned to a suitable location in the kiln or raw material grinding system. The preheated meal conveys heat to support a combustion process to reduce fuel requirement.

The extracted preheated meal may be used as an oxygen free heat source of incombustible material for drying and/or gasification and/or pyrolysis in the preparation of a fuel in a reactor, such as but not limited to, a rotary drum to produce a gaseous fuel for a separate use application such as but not limited to hot gas boosting and subsequently returning the used preheated hot meal with any fuel residues to the kiln system or to separate recovery of fuel residues. The preheated meal serves as an oxygen free heat source of incombustible material well suited for transferring heat to treat the fuel.

In a third aspect, the invention relates to a method for extraction of hot combustion gas to supply heat for separate use applications, said hot combustion gas extracted from a kiln system of a clinker burning department in a plant for manufacture of cement clinker, said method preferably comprising the steps of: extracting heat in the form of hot combustion gas from one or more locations within the preheater below the exhaust (top) cyclone(s), at temperatures corresponding to the cyclone stage temperatures, while reducing the heat content of the exhaust gas both in quantity and temperature, while adding a supplementary heat input as fuel, wherein a part of the hot combustion gas is extracted from the preheater, while a supplementary heat input as a fuel is added in the kiln system, resulting in a transfer of heat, which reduces the temperature and quantity of the preheater exhaust gas and obtains a high temperature of the extracted combustion gas, transforming a part of the conventional waste heat into a high temperature heat supply for separate use applications, resulting in a reduced specific heat loss and carbon dioxide emission of the combined kiln system and the separate use application. The extraction of hot combustion gas at high temperatures for separate applications makes up a way to convert waste heat into a valuable heat resource for separate applications and reduce the heat loss and carbon footprint of the shared heat use.

In a fourth aspect, the invention relates to a method for extraction of preheated meal to supply heat for separate use, extracted from the kiln system of a clinker burning department in a plant for manufacture of cement clinker, said method preferably comprising the steps of: extracting heat in the form of preheated meal from one or more locations within the preheater representing cyclone stage temperatures of the preheater between inlet and outlet of either combustion gas or kiln meal and adding a supplementary heat input, wherein a part of the preheated meal is extracted from the preheater, while regulating the meal feed to maintain same net feed to the rotary kiln combined with a supplementary heat input as fuel to the kiln system, resulting in a transfer of heat, which reduces the temperature of preheater exhaust gas and obtains a high temperature extraction of preheated meal, transforming a part of the conventional waste heat into a high temperature heat supply for separate use applications, resulting in a reduced specific heat loss and carbon dioxide emission of the combined kiln system and the separate use application.

The extraction of preheated meal at high temperatures for separate applications enables a conversion of waste heat into a valuable heat resource for separate applications and reduce the heat loss and carbon footprint of the shared heat use.

The first, second, third and fourth aspects of the present invention may be combined.

BRIEF DESCRIPTION OF THE FIGURES

The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

Embodiments of the invention, by way of example only, will be described with reference to the accompanying figures listed here:

Figure 1 schematically illustrates a cement clinker burning system showing hot gas extraction according to the present invention.

Figure 2 schematically illustrates a cement clinker burning system with a calciner showing hot gas extraction according to the present invention. Figure 3 schematically illustrates heat extraction from preheater cyclones according to the present invention.

Figure 4 schematically illustrates a boosting of extracted hot combustion gas from preheater according to the present invention.

Figure 5 schematically illustrates heat extraction for WHR coupled to recirculation with oxygen addition as combustion air for heat recovery in cooler.

Figure 6 schematically illustrates the relationship between the hot gas temperature and the extraction percentage.

Figure 7 schematically illustrates the relationship between the heat extraction and the extraction percentage.

Detailed description of the invention

The invention goes beyond the conventional practice of heat energy management in a clinker burning department, which is focused on low heat consumption of the clinker manufacture through internal process improvements with the understanding that extraction of heat from within the kiln system boundary of the clinker burning process will only affect heat economy negatively.

With this invention heat is extracted from within the boundaries of the preheater in the kiln system of a clinker burning department considering the preheater boundaries to comprise the hot combustion gas outlet(12), the preheater meal inlet(13), the rotary kiln meal inlet(33) and the kiln gas outlet(32). The extraction of heat causes a reduction of heat contained in the gas outlet(12) and material outlet temperature from bottom of cyclone(ld) in the preheater. The reduction of heat leaving the preheater with exhaust gas(12) is a benefit reducing the heat loss while the reduced temperature of the preheated material from cyclone(ld) requires a supplementary heat input of fuel to the kiln system to compensate for lower meal temperature. The extracted heat incorporates the reduced exhaust gas(12) heat and the supplementary heat input as fuel.

The extraction of hot combustion gas(71) is intended for use as a heat input to a separate use in a process that can utilizes the extracted heat, such as by replacing a heat input or substituting a corresponding fuel input. The separate use can take over or share the accountability of the heat and hot gas constituents and/or the used extracted gas can be returned in a colder state to the kiln system for further treatment according to regulations.

The heat accounting can be made with heat balances for the kiln system and separate uses as individual systems and/or as a combined system. The heat extracted from the kiln system should not be considered a heat loss unless it has become inaccessible for other processes. Any heat extracted from the kiln system for separate use shall be accounted for in the associated heat balance ensuring that all heat is managed and used optimally for the benefit of heat efficiency and reduced specific heat loss and carbon dioxide emission. The invention is based on the characteristics of the preheater(l) as a heat exchanger with a direct contact surface for heat transfer and a ratio between gas and material contributing to the heat exchange ratio. When an extraction point is added in the preheater(l), the conditions above the extraction point are changed leaving less gas in the upper part towards the exhaust gas outlet(12) and a lower gas/material ratio which enhances the heat capture of the material resulting in a lower exhaust gas(12) temperature.

The extraction of heat as hot combustion gas from within the preheater(l) may be taken from any location with a temperature higher than the exhaust gas(12) temperature stage, which is already at the preheater boundary, including the kiln riser(33) which is connected to the rotary kiln gas outlet.

Kiln system with calciner

Heat extraction as hot combustion gas is also possible from a kiln system with calciner(2) where the supplementary heat is added in the calciner(2). The kiln system with calciner(2) has more flexibility having two combustion zones and access to recuperate hot combustion air(21) from the clinker cooler(4). This is beneficial for the extended use of sustainable fuel types.

Gas extraction system

The preferred location for extraction is at the cyclone gas outlet, as a branch duct or from a parallel cyclone added to the stage and sized to handle the extracted gas quantity. The gas is extracted before feed material from a cyclone stage above is added. This is to benefit a low dust content in the extracted hot combustion gas. The hot gas extraction can also be done simultaneous from 2 or more points and provide hot extracted gas for separate uses at different temperature levels.

Application of separate heat use from sustainable fuel source

While the transfer of heat from the kiln system can improve heat efficiency and total carbon dioxide emission, the use of sustainable fuels in the kiln system can through the transfer to the separate use, supply a sustainable advantage to substitute other fuels and/or heat sources, with sustainable heat transferred from the kiln system.

The combustion process in a cement kiln is designed to produce very high temperatures for the burning/ sintering of the cement minerals. The burning process can to a high extent be supported with alternative fuels of sustainable type like biomass and some waste material fuels according to regulations. These fuels may also be used for supplementary heat in combination with heat extraction. The benefit is the possibility to provide heat from a sustainable fuel source for the separate use.

Separate use applications

The invention enables transfer of hot combustion gas from the preheater to several uses such as, but not limited to, electrical power generation, clay calcination, lime and alumina calcination, gasification of fuels and drying of fuels and raw materials.

Power generation

The use of the extracted heat at a higher temperature potential can enable a higher efficiency of the power generation with a competitive heat source which may be based on fuels with a high ratio of sustainability and providing a significant improvement in power generation in combination with manufacture of cement clinker. Benefiting a higher conversion efficiency of heat to power enables better use of heat and energy at the plant while becoming more self- sufficient and improving the supply of power for future initiatives necessary for improvements of sustainability.

Preparation of Supplementary Cementitious Materials (SCMs)

The use of extracted heat at temperature levels suitable for the preparation of SCM additives to reduce the cement clinker content in cement is a separate use that can benefit from higher heat efficiency in a separate use serving a coupled reduction of greenhouse gases by reducing clinker use in cement and reducing waste heat in the manufacture of SCM.

Alumina calcination or lime burning

The use of the extracted heat to benefit the separate uses of preparing alumina by drying and calcination or the production of burnt lime. The combined use of heat benefits a reduced heat loss and carbon dioxide emission.

Drying raw materials

As the availability of conventional waste heat may be reduced by the benefits of separate use applications, the approach to drying of raw materials will be adapted with a careful heat management that also optimizes the actual heat requirement by selecting a raw material handling designed to minimize the drying requirement and cost as the waste heat should no longer to be considered a free resource. Benefitting a focus to manage all heat sources and uses. Therefore any residual heat from a separate use should also be returned for drying of raw materials and/or fuels for kiln system and/or separate use.

Gasification

The use of extracted hot combustion gas with a low oxygen can be used for preparation of alternative non mineral and sustainable fuels for combustion in a reactor for drying and/or gasifying the fuel for separate use where the unvolatized fuel may be partly separated to improve the quality of the combustion and reduce the emission of carbon dioxide, while returning the fuel residuals to either the kiln system or the separate recovery of fuel residuals. Low oxygen heat is a key benefit for the gasification of fuels.

Carbon dioxide cooling

The extracted hot combustion gas with a significant content of carbon dioxide is cooled substantially by a separate use application such as, but not limited to, a boiler for electrical power generation and then further conditioned and prepared for capture as a gas or liquid before use or storage of the carbon dioxide by other processes. Preparing the process exhaust gas for capture of carbon dioxide makes most use of the heat content benefit before subsequent carbon capture.

Recirculation of extracted hot combustion air

The extracted hot combustion gas with a low oxygen content and a high carbon dioxide content is cooled substantially in a separate use application such as with a boiler for electrical power generation, and then partially recirculated as cooling gas in the recovery part of the clinker cooler(4) while injecting a proportional quantity of oxygen into the recirculated cooling gas and/or the burner to support the combustion in the kiln system while achieving a higher carbon dioxide content in the combustion gases both to benefit utilization of kiln system and/or reduce nitrogen oxides emissions and/or concentrate the carbon dioxide content for efficient carbon capture. Increase kiln system capacity

The extracted hot combustion gas used for separate use applications may result in a reduced load on the exhaust gas handling system of the clinker burning department and can enable an increased production capacity of the kiln system while utilizing the available capacity of the exhaust gas handling system to increase the kiln efficiency and reduce the specific heat consumption of the kiln system.

Boosting of extracted hot combustion gas

In case the separate use application requires more heat than can be extracted from the kiln system, the extracted hot combustion gas(71) can be boosted with heat from a combustion chamber(70), burning a suitable fuel in a mix of recovered heat from the clinker cooler(4) and recycled exhaust gas(12). The heat boosting can enhance the heat supply and application of separate uses.

Extraction of preheated meal

The extraction of heat as preheated meal from the preheater(l) of a kiln system combined with a supplementary heat input as a fuel to the kiln system is a alternative way to make heat available for separate uses. Some preheated meal from any cyclone in the preheater(l) may be diverted to supply heat to a separate use while the removed preheated meal is replaced with a more fresh feed to maintain same net meal input to the kiln process. The extracted preheated meal is collected after having transferred the heat to the separate use and returned to the kiln system at a suitable location. The transfer of heat from the preheated raw meal reduces the temperature of the preheater exhaust gas and results in a reduced heat loss and carbon dioxide emission of the combined kiln system and separate use application.

Kiln system with calciner

The extraction of preheated meal from a preheater(l) is also possible from a kiln system with calciner(2) where the supplementary heat is added in the calciner(2). The kiln system with calciner(2) has more flexibility having two combustion zones and access to redirect hot combustion air(21) from the clinker cooler(4). This is beneficial for the extended use of sustainable fuel types.

Preheated meal for drying raw materials

The extraction of preheated meal from a preheater(l) can be used as a heat source for drying raw materials by adding the preheated meal into the grinding process and subsequently either to become a part of the raw meal product or to be removed after having transferred the heat and returned to a suitable location in the kiln system.

Heating of ambient air or process gas

The extraction of preheated meal from a preheater(l) can be used as a heat source for heating ambient air and/or process gas with residual oxygen to provide preheated combustion air while the cooled meal is returned to a suitable location in the kiln system.

Gasification of fuel

The extraction of preheated meal from a preheater(l) can be used to as an oxygen free heat source of incombustible material for drying and/or gasification of fuel without input of combustion air in a reactor, such as but not limited to, a rotary drum(51) to produce a gaseous fuel for a separate use application or for heat extraction boosting, to enhance temperature and quantity of extracted heat while returning the used preheated hot meal with any fuel residues to the kiln system or to separate recovery of fuel residues. Method of extracting heat as hot combustion gas

The heat is extracted as hot gas from within the preheater(l) for use in a separate application. The hot combustion gas is extracted from the outlet of one or more cyclones except from within the preheater boundaries while a supplementary heat input as a fuel is added to the kiln system resulting in a substantial heat transfer at higher temperature that available from the conventional exhaust gas waste heat. The method reduces the preheater(l) exhaust gas heat loss by reducing amount and temperature of the exhaust gas effectively transfering the heat loss into a potent heat supply for a separate use application. Enabling a better use of the heat and contributing to a high heat efficiency and reduced specific heat consumption and carbon dioxide emission of the combined kiln system and separate use application.

Method of extracting preheated meal

The heat is extracted as preheated meal from the preheater(l) for use in a separate application. The preheated meal is extracted by diverting meal from one or more cyclones or by inserting parallel cyclones at the relevant stages designed to divert preheated meal for extraction while regulating the meal feed to maintain same net meal feed to the rotary kiln. The extraction is combined with a supplementary heat input as fuel to the kiln system resulting in a transfer of heat which reduces the temperature of the preheater exhaust gas transforms a part of the conventional waste heat into a high temperature heat supply for separate use, resulting in a high heat efficiency and reduced specific heat consumption and carbon dioxide emission of the combined kiln system and separate use application.

Figure 6 schematically illustrates the relationship between the hot gas temperature and the extraction percentage.

Figure 7 schematically illustrates the relationship between the heat extraction and the extraction percentage.

In a calculation using a five-stage preheater and extracting hot gas from the outlet of the third stage cyclone the temperature of the hot gas and preheater exit gas is expressed in proportion to the fraction of gas being extracted show in figure 6. With no extraction the temperature at the extraction point is 724°C and the preheater exit temperature is 361°C. With increasing extraction, the hot gas temperature reduces along with the preheater exit temperature. At 30% extraction the hot gas would be 645°C and the preheater exit 230°C. The corresponding heat extraction is shown in figure 7 where increasing gas extraction provides increasing heat for separate use, requiring a compensating input while reducing the preheater heat loss. At 25% extraction half of the preheater heat loss has been transferred to heat recovered for a separate application, at a significantly higher temperature and usefulness requiring a smaller supplementary fuel compensation

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. It should also be understood that the form of this invention as shown is merely a preferred embodiment. Various changes may be made in the function and arrangement of parts; equivalent means may be substituted for those illustrated and described; and certain features may be used independently from others without departing from the spirit and scope of the invention as defined in the following claims. List of references:

(1) Preheater (preheats the kiln feed through heat exchange with hot combustion gas') shown with 5 stages comprising a. Preheater exhaust gas outlet cyclone b. Second cyclone from exhaust gas outlet c. Third cyclone from exhaust gas outlet d. Fourth cyclone from exhaust gas outlet e. Bottom cyclone with material feeding the rotary kiln

(12) Preheater exit gas from top cyclone stage

(13) Kiln feed inlet to preheater

(2) Calciner (further preheats and calcinates the kiln meal by burning fuel with recuperated combustion air from the clinker cooler)

(21) Tertiary air duct

(22) Calciner fuel input

(3) Rotary kiln

(31) Main burner fuel input

(32) Rotary kiln hot gas outlet/kiln riser

(33) Rotary kiln hot meal inlet

(4) Clinker cooler (recuperating heat from the clinker as hot air)

(42) Excess cooling air outlet (cold end)

(43) Clinker output

(44) Excess cooling air outlet (hot end)

(51) Rotary drum reactor

(52) Fuel input for drum reactor

(53) Used meal with fuel residues returned to kiln system

(70) Booster vessel to further heat extracted hot combustion gas

(71) Hot gas extraction from cyclone stage(lc)

(72) Preheated meal extracted from cyclone stage(lc)

(73) Boosted extracted hot combustion gas

(74) Gasified fuel gas for separate use heat boosting

(75) Parallel extraction cyclone

(81) WHR (heat use)

(82) Raw material drying (heat use)

(83) Oxygen addition