Patent Description:
In particular, the present invention refers to a method for the cooling and heat recovery of materials at very high temperature, such as the clinker of the cement production cycle or slags resulting from industrial processes like the steel production cycle or like the slags and ashes resulting from the coal combustion, waste and other heavy fuels.

In several types of industrial processes, materials at very high temperature are produced which must be cooled to allow their subsequent use, storage or management. Traditionally, in the cement production cycle, clinker is produced at high temperature (typically about <NUM>) inside rotary drum furnaces. The clinker is then unloaded from the furnace and must be cooled. The clinker's cooler is part of the cement production line and affects the efficiency and cost-effectiveness of the plant, with the dual purpose of recovering heat from the cooling of the clinker in order to return it to the rest of the cement cooking plant and to allow to reduce the clinker's temperature to an adequate level for the transport and subsequent use equipment located downstream of the furnace. In particular, in the known art, the cooler generally uses moving grates for the moving of the material and the heat is recovered by blowing air into the cooler through the moving grates and directly inside the hot material, thus obtaining hot air which is then used for combustion processes and/or for the preheating of the materials entering the cement production cycle.

The cooling of the clinker must be quick to improve the mineralogical and grindability characteristics and for a better reactivity of the cement produced. However, the high temperatures involved, the extreme abrasiveness of the clinker, the variety of grain size with which it is produced in the furnace, the possibility that in some steps the clinker exits the furnace in liquid phase instead of solid phase, make the clinker's cooler a very expensive component subject to frequent onerous maintenance services.

The possible presence of liquid clinker may damage mechanical apparatuses and block the passage channels of the cooling air.

Moreover, problems of insufficient air availability and, therefore, insufficient cooling of the clinker and overheating and damage of the mechanical parts of the cooler, which are in contact with the material, can occur. The cooling system, therefore, has room for improvement from the point of view of achieving a quicker and more reliable cooling, in addition to being less economically onerous, and also obtaining an energy recovery which is thermodynamically more favourable than the simple hot air production.

On the contrary, referring to the case of the steel production cycle, a step is traditionally provided in which the liquid steel is formed or transformed inside furnaces and containers in which a molten slag containing various types of materials (e.g. silicon oxides), which must be separated from the liquid steel, is separated. For this purpose, the slag is traditionally allowed to cool outdoors. This method allows only the recovery of the slag as an inert material.

In fact, the solid slag, suitably ground, can be usefully used as filling material in civil works, such as road sub-bases.

However, the open-air cooling of the slag is by no means an optimal method, neither from an energy nor environmental point of view.

In fact, when it is unloaded, the liquid slag comprises a large amount of thermal energy, reaching temperatures higher than <NUM>. In this regard, it is estimated that the slag contains therein as much as <NUM>% of the thermal energy fed altogether into the steel production cycle. Moreover, while it cools in the open air, the slag releases fumes and vapours into the environment which, as well as dissipating in turn the thermal energy, are also polluting.

The treatment of the slag is therefore another of the problems that the steel industry must solve, in particular to improve the energy efficiency of the steel mills.

At the same time, as in many other industrial sectors, the aim is to limit the emission of pollutants as much as possible in order to favour the environmental issues. Overall, reliable and effective solutions for the management of cooling and heat recovery from the hot slag have not yet been implemented in the implementation practice.

It should still be noted that problems of cost, maintenance charges and improvability of the heat recovery qualitatively analogous to those in the case of clinker for the production of cement or slags for the production of steel, can also be found in other sectors of application, such as the case of the ashes from the combustion of coal, waste or other heavy fuels.

Document <CIT> discloses a system for the production of cement clinker from powdery and fine-grained raw materials using a cyclone preheater, a pre-calcification device, a kiln and a cooler. In order that the fine powders filtered from the exhaust gases of the preheater can be reliably preheated and pre-calcified and then burnt in a kiln as cement clinker, after the first stage of the preheater a smaller part of the material is branched off and fed together with the total fine powder from the filter at the upper end of the pre-calcification device. This mixture passes through the pre-calcification device from top to bottom, is guided in co-current with the air for combustion and, with the fuel supply, is pre-calcified and then fed into the kiln inlet.

<CIT> illustrates a method for manufacturing a cementitious product involving the steps of:.

Document <CIT> describes a process for the production of cement clinker in a plant equipped with a cyclone preheater, a pre-calcification reactor, a rotary kiln and a clinker cooler. The combustion gases produced by the rotary kiln are separated from the gases of the preheater so that they do not mix, the preheater reactor is fed with an oxygen-rich gas, and a portion of the gases leaving the cyclone preheater is recycled into the preheater reactor, or even into the preheater, so that a suitable flow is obtained to suspend the material in the preheater. The other, non-recycled portion of the gas, which is rich in carbon dioxide, is adapted to limit the amount of CO2 discharged, by means such as carbon sequestration.

Document <CIT> illustrates an apparatus for recovering heat from hot slag comprising a heat exchanger with at least two concentric cylinders that can rotate around their concentric axis. The first cylinder comprises an inlet for slag and another comprises an outlet for slag. A slag transmission path is derived between the inlet and outlet and passes through the first cylinder in a first direction and through another cylinder in the opposite direction. A method is also described for recovering heat from hot slag by passing the hot slag from an inlet to an outlet of a heat exchanger in a first direction along a first tubular part of the heat exchanger and then in an opposite direction along a second concentric tubular part of the heat exchanger. As the slag moves through the heat exchanger, air passes from the outlet to the inlet.

<CIT> illustrates a system for increasing the yield of cement clinker recovered from a kiln, which yield is improved by feeding a particulate material comprising silica and an oxide of at least one of calcium and aluminium, e.g., fly ash, into contact with the hot cement clinker; the fly ash melts into a partially molten material that chemically reacts with the hot clinker to produce a pyroformed cement clinker of crystalline hydraulic silicates. There is an extruder for the hot cement clinker downstream of the cement clinker formation, which is added to the hot cement clinker at the upstream end of the kiln unit cooler, or inside the kiln, downstream of the combustion zone, and more specifically in the initial cooling zone at the discharge end of the kiln.

Object of the present invention is to solve the above-mentioned technical problems by means of a method for the cooling and heat recovery from materials at very high temperature, which increases the overall energy efficiency of the industrial process in which such materials are produced.

Another object of the invention is to provide a method for the cooling and heat recovery from materials at very high temperature which allows a fast and quick cooling of the material entering, in order to improve its characteristics and to reduce its dimensions, the costs and wear and tear problems of the mechanical parts in contact with the hotter material.

Another object of the invention is to provide a method for the cooling and heat recovery from materials at very high temperature which is environmentally friendly. A further object of the invention is to provide a practical and cheap solution to the above-mentioned problems.

These purposes are achieved by a method for the cooling and heat recovery from materials at very high temperature, where the aforesaid method comprises at least the following steps of:.

The advantages of this implementation include the fact that it is able to bring some material at very high temperature very quickly from a temperature between <NUM>,<NUM> and <NUM>,<NUM> (typical temperature range of the clinker production in the cement production cycle or slag production in the steel production cycle) to a much lower temperature between <NUM> and <NUM>, by mixing it with colder material, thus resulting in the quick solidification of any liquid part present when entering. Additionally, it is able to achieve a subsequent cooling to a temperature low enough to allow an easy moving and management of the material exiting, between <NUM> and <NUM>. Furthermore, by simultaneously using the enthalpy of the material to recover energy with production of useful heat through a cooling process that can be a closed circuit one, and by using any heat-transfer fluid (e.g. by using water and generating medium or high pressure steam that is suitable for subsequent energy uses), this increases overall energy efficiency.

Further characteristics of the invention can be deduced from the dependent claims.

Further characteristics and advantages of the invention will become clear from reading the following description provided by way of non-limiting example, with the aid of the figure depicted in the accompanying drawing, wherein:.

The present invention will now be described with particular reference to the accompanying figure.

In particular, <FIG> depicts a schematic view of a plant, generally denoted by the reference numeral <NUM> and configured to implement the method according to an implementation of the invention.

First of all, the plant <NUM> comprises a mixing system <NUM> which is configured to receive both a material A at a very high temperature and a recirculated material B that is solid and at a low temperature, i.e. at a temperature between <NUM> and <NUM>.

In particular, the material A at very high temperature considered by way of example can be steel mill slag at a temperature between <NUM>,<NUM> and <NUM>,<NUM> (temperature at which this type of slag is melted and, therefore, in liquid phase), whereas the recirculated material B is solid slag.

In a preferred embodiment, the mixing system <NUM> can comprise a rotary and/or vibrating drum, with a horizontal or inclined axis, within which an optimal mixing of the material A at very high temperature with the recirculated material B takes place once they have flowed into such rotary drum.

Moreover, the mixing system <NUM>, in addition to or in place of the above-mentioned rotary drums, can further comprise chutes, cyclone or funnel chambers, tubs or combinations thereof.

Although, by way of example, a mixing system <NUM> in which only one inflow point of the material A at very high temperature and only one inflow point of the recirculated material B is visible within the mixing system <NUM>, has been disclosed herein, there may of course be more than one inflow point of the material A at very high temperature and/or more than one inflow point of the recirculated material B within such mixing system <NUM>.

From the mixing system <NUM>, a mixed material C exits at an intermediate temperature, e.g. between <NUM> and <NUM>.

The mixed material C may be in the liquid, solid state or in liquid and solid mixture, depending on the characteristics of the entering material A.

The plant <NUM> further comprises a continuous-flow channel <NUM> for transporting the material at intermediate temperature exiting the mixing system <NUM>.

The continuous-flow channel <NUM> can be selected from a cooled-tube device, of the fixed or rotary type, a pneumatic-flow device, a vibrating-table device or a drag-chain device. Other types of continuous-flow transport of the material at intermediate temperature, known in the art, may equally be provided.

The mixing system <NUM> depicted herein by way of example, as consisting of a single point for feeding the mixed material C into the continuous-flow channel <NUM>, may alternatively have multiple points for feeding the mixed material C onto said continuous-flow channel <NUM> or other equivalent continuous-flow transport means.

A step of heat recovery is also carried out inside the continuous-flow channel <NUM>. The step of heat recovery from the material transported in the continuous-flow channel <NUM> can be carried out by means of a closed-circuit exchanger <NUM> or by means of an open-circuit blown-air exchanger or a mixed exchanger.

A flow of material D at low temperature therefore exits the continuous-flow channel <NUM> and is fed to a flow dividing system <NUM>.

The flow dividing system <NUM> can comprise mechanical diverters, chutes, sieves, distribution chambers or combinations thereof.

Two flows of material at low temperature exit the flow dividing system <NUM>.

In particular, a first part of material E at low temperature and which has therefore completed the described cooling process, and a second part of material F which is instead recovered by means of a moving and recirculating system <NUM>, exit the flow dividing system <NUM>.

Finally, the material at low temperature, recovered when exiting the flow dividing system <NUM>, is returned by the moving and recirculating system <NUM> toward the inlet of the mixing system <NUM> (see also the arrow B in <FIG>) for the mixing thereof with the material at very high temperature.

Specifically, the moving and recirculating system <NUM> for moving and recirculating the solid material at low temperature can comprise a system selected from a pneumatic, auger or drag chain conveying system.

An example of thermal and energy balance is now presented for the case of a material entering with characteristics similar to the steel mill slag, with liquid inflow and solid outflow.

The material A at very high temperature entering, in the liquid state, the mixing system <NUM> has a mass flow rate m equal to m = <NUM> t/h, a temperature T equal to T = <NUM>,<NUM> and a specific enthalpy h equal to h = <NUM> kJ/kg.

The recirculated material B entering the mixing system <NUM> has a mass flow rate m equal to m = <NUM> t/h, a temperature T equal to T = <NUM> and a specific enthalpy h equal to h = <NUM> kJ/kg.

The mixed material C exiting the mixing system <NUM> has a mass flow rate m equal to m = <NUM> t/h, a temperature T equal to T = <NUM> and a specific enthalpy h equal to h = <NUM> kJ/kg.

The power P recoverable from the step of heat recovery from the material transported inside the continuous-flow channel <NUM> is equal to about <NUM> MW.

The material at low temperature exiting the continuous-flow channel <NUM> obviously still has a mass flow rate m equal to m = <NUM> t/h, a temperature T equal to T = <NUM> and a specific enthalpy h equal to h = <NUM> kJ/kg.

This material is divided by the flow dividing system <NUM> into a first part of material E at low temperature and which has therefore completed the described cooling process, i.e. a flow of material equal to m = <NUM> t/h and that has a temperature T equal to T = <NUM> and a specific enthalpy h equal to h = <NUM> kJ/kg, and into a second part of material F which is instead recovered by means of a moving and recirculating system <NUM>, i.e. a flow of material equal to m = <NUM> t/h and that has a temperature T equal to T = <NUM> and a specific enthalpy h equal to h = <NUM> kJ/kg.

The total steady-state effect of the described system is therefore to bring the material A, having a hourly flow equal to M = <NUM> t/h, from a temperature equal to T = <NUM>,<NUM> to a temperature equal to T = <NUM> and from a specific enthalpy h equal to h = <NUM> kJ/kg to a specific enthalpy h equal to h = <NUM> kJ/kg.

Claim 1:
Method for the cooling and heat recovery from materials at very high temperature, where the aforesaid method comprises at least the following steps of:
- conveying material at very high temperature into a mixing system (<NUM>);
- transporting the aforesaid material exiting the mixing system (<NUM>) inside a continuous flow channel (<NUM>);
- carrying out a step of heat recovery from the transported material;
- wherein said method is characterized in that of comprising the further following phases:
feeding a flow of material exiting at low temperature from the aforesaid continuous flow channel (<NUM>) to a flow dividing system (<NUM>);
- recovering a part of the low-temperature material exiting the aforesaid flow dividing system (<NUM>);
- moving the part of recovered material at low temperature by means of a moving and recirculating system (<NUM>); and
- conveying the recovered material at low temperature for mixing it with the material at very high temperature in the mixing system (<NUM>).