WO2015044403A1

WO2015044403A1 - Use of waste heat

Info

Publication number: WO2015044403A1
Application number: PCT/EP2014/070735
Authority: WO
Inventors: Bernd Wacker
Original assignee: Siemens Aktiengesellschaft
Priority date: 2013-09-30
Filing date: 2014-09-29
Publication date: 2015-04-02

Abstract

The invention relates to the use of waste heat, especially during the production of aluminium oxide, for supporting at least one first high-temperature process (HTP, HTP1, HTP2) and at least one low-temperature process (NTP, NTP1, NTP2), wherein the low-temperature process permits a support using a heat transfer medium (WTM) having a lower temperature (T2, T3, T4) than the temperature (T1, T1', T2) of a heat transfer medium (WTM) intended for the support of a high-temperature process (HTP, HPT1, HTP2). The waste heat is transferred from at least one source (Q, Q1, Q2) to the high-temperature processes (HTP, HPT1, HTP2) and/or the low-temperature processes (NTP, NTP1, NTP2), using a heat transfer medium (WTM). Steam is advantageously used as the heat transfer medium (WTM). Especially when producing aluminium oxide from bauxite, the process steps of the Bayer process as low-temperature processes (NTP, NTP1, NTP2) are advantageously supported. A control device 100 and at least one control valve (S1) support the distribution of the heat transfer medium (WTM) among the processes (HTP, HTP1, HTP2, NTP, NTP1, NTP2). Distribution is based on temperatures (T1, T2, T3, T4) and/or pressure values (p1, p2, p3, p4) and/or flow speeds of the heat transfer medium (WTM). Support for the processes (HTP, HTP1, HTP2, NTP, NTP1, NTP2) also takes into consideration the (current) need for heat of the individual processes (HTP, HTP1, HTP2, NTP, NTP1, NTP2).

Description

description

The invention relates to a method for using waste heat, in particular in the production of aluminum, and to an apparatus for carrying out such a method. Furthermore, the invention relates to a control device and a system.

The production of aluminum from bauxite is a very energy intensive process. The production of alumina from bauxite by the Bayer process and aluminum from alumina by fused-salt electrolysis requires a great deal of electrical energy and heat energy. In particular, much heat energy is required in the hydrochemical treatment of the bauxite by the Bayer process. In particular, the last step of the Bayer process, the calcination of the aluminum hydroxide obtained to alumina, requires a lot of heat energy, with a portion of the heat energy through

Emission is lost. Efforts to protect the climate and avoid costs are making an effort to save energy, especially in the production of aluminum. The Bayer process is used to produce aluminum oxide from the mineral bauxite. The bauxite is ground and mixed with an alkali, in particular sodium hydroxide, and reacted at an elevated temperature and elevated pressure. In the reaction, the insoluble constituents (red mud) are separated from the reaction mixture by filtering. From the remaining solution aluminum hydroxide Al (OH) _{3 is} crystallized out. The liquor is reused after increasing the concentration. CN 201803598 U describes the use of waste heat from hot combustion exhaust gases in the production of aluminum. It is an object of the invention to save energy through an improved use of waste heat, especially in the production of aluminum or aluminum oxide. The object is achieved by a method for utilizing waste heat, in particular in the production of aluminum oxide, wherein the waste heat from at least one source is provided, wherein the waste heat to support at least one high-temperature process and / or at least one low-temperature process is used in which, after the support of a high-temperature process, the support of at least one further high-temperature process and / or the support of at least one further low-temperature process, and wherein the respective further high-temperature process and / or the respective further low-temperature process with the remaining waste heat of the preceding High-temperature process or low-temperature process is supported.

The object is further achieved by a device for utilizing waste heat, in particular in the production of aluminum oxide, wherein a source is provided to provide the waste heat, wherein the waste heat to support at least one high-temperature process and / or provided at least one low-temperature process is, after supporting a high-temperature process, the support of at least one further high-temperature process and / or at least one further low-temperature process is provided, and wherein the respective further high-temperature process and / or the respective further low-temperature process with the remaining waste heat of each preceding high-temperature process or low-temperature process is provided for assistance.

The object is further achieved by a control device, wherein the control device is provided for controlling and / or regulating and / or monitoring a device according to one of claims 8 to 11. The object is further achieved with a system according to claim 13.

Under a plant is understood in this context, a plant for the production of at least one base material. Basic substances are, for example, aluminum oxide, aluminum hydroxide, and / or aluminum. Such a plant, as well as a device described above, can also be used for the production of other basic materials such as non-ferrous metals, metal oxides or mineral products.

A control device advantageously serves to control processes and method steps, in particular the temperatures of individual processes or individual process steps, and can be integrated in a control system of a system. However, such a control device, possibly together with sensors and control valves for retrofitting an existing system and / or for extending the control of the system, is advantageous.

The further dependent claims represent advantageous embodiments of the method or the device.

Waste heat occurs in the form of hot exhaust gases, hot pipes that release heat in and / or outside, and cooling processes. The process of calcination is advantageous as a rich source of waste heat. The combustion gases which are produced during the production of steam are advantageously used as another source, whereby heat is withdrawn from the combustion exhaust gases and this again serves as waste heat to support further processes described below (high-temperature processes and low-temperature processes). Another advantageous source is the waste heat in the fused-salt electrolysis of the aluminum oxide. In fused-salt electrolysis, a large amount of heat energy is lost by emission to the environment. The waste heat is advantageously received by means of a heat exchanger. Advantageously, a heat transport medium is passed through the heat exchanger, wherein the heat transport medium absorbs the waste heat via the heat exchanger.

The heat transfer medium is transferred through pipelines to a high temperature process or a low temperature process. As a heat transport medium is water or water vapor and possibly a liquid metal or a mineral oil product. Water vapor, especially under high pressure, is particularly advantageous because the water vapor can be used directly for the high-temperature processes and low-temperature processes. Advantageously, the pipes are thermally insulated, so that emission of waste heat through the walls of the pipes during transport of the heat transfer medium is reduced. Hereinafter, the term process is used instead of high temperature process or low temperature process, especially if both a low temperature process and a high temperature process are meant equally. Process steps are in particular process steps of the Bayer process for recovering aluminum from bauxite. The treatment of the red mud extends through the filtration until the removal of the remaining liquor, so that the red mud requires less landfill space in subsequent landfill. Caustic soda is used in particular as the lye. However, potassium hydroxide or another caustic solution is also to be subsumed under the term caustic.

A high temperature process, particularly in the production of aluminum, is power generation with a turbine and / or use of the steam to assist in a process step, where the steam is also the heat transport medium. In the generation of steam and the heat transport medium by means of another heat exchanger Give off the waste heat to the steam water or serve to further heating of water vapor. High-temperature processes are processes in a temperature range between about 400 ° C and 2,000 ° C. Low temperature processes are processes and / or process steps that take place at temperatures below about 500 ° C. Low-temperature processes are, for example, the heating of liquor and / or the heating of a lye / bauxite mixture. The filtration of red mud, which is obtained in the production of alumina and must be separated from the liquor and the covering of the liquor (the evaporation of water to increase the concentration of the liquor) are also low-temperature processes. As stated above, the waste heat is first fed to a process, thereby partially consumed and subsequently the remaining waste heat, in particular in the form of the cooled heat transfer medium, fed to at least one further process.

For example, as a first high-temperature process, an electric energy is generated by means of a turbine. The incoming into the turbine heat transport medium, in particular water vapor, has a temperature of at least 1,000 ° C and a pressure of several bar. The steam is called saturated steam. After the turbine, the heat transport medium still has a temperature of at least 450 ° C and is occasionally referred to as wet steam due to the possibly existing water droplets / moisture. There are specially designed turbines for receiving wet steam. Following the generation of electrical energy by the turbines, the water vapor still has one, for the generation of electrical energy too low temperature or too low pressure.

After passing through both turbines and / or after passing through the first turbine, the heat transport medium can be supplied to a further process, in particular a low-temperature process. In a particularly advantageous embodiment, a low-temperature process serves as a process Step of the Bayer process for the production of aluminum oxide. Another beneficial process after a high temperature process is the support in the production of water vapor.

In a low-temperature process, a heat transfer medium of a low pressure and with a temperature below 400 ° C can be used. Additional advantages are provided by the successive supply of the heat transfer medium to a high-temperature process and a low-temperature process, in particular if the subsequent low-temperature process can be assisted by means of a heat transfer medium of a lower temperature / lower pressure.

In an advantageous embodiment, the waste heat is used to support the high-temperature process, the remaining waste heat is split to support another high-temperature process and another low-temperature process, and wherein the remaining waste heat of the further high-temperature process is used to support a further low-temperature process.

The generation of electrical energy from water vapor advantageously takes place with two turbines connected in series. The heat transport medium, in particular the steam, passes through the first turbine. In the first turbine kinetic and potential energy is removed from the heat transport medium. As a result, the heat transport medium cools and then passes with a lower temperature and possibly a lower pressure in another turbine. The second turbine also removes thermal and potential energy from the heat transfer medium and converts the thermal and potential energy into kinetic energy, whereby the kinetic energy is converted into electrical energy by means of a generator. The first and the second turbine are advantageously operated with steam, wherein the steam has a temperature of about 1,000 ° C in the first turbine and above 500 ° C in the second turbine. Here both processes of energy production from water vapor are referred to as high-temperature processes. Between the two turbines, the heat transport medium can also be partially fed to another process, in particular a low-temperature process.

It is possible that at least one low-temperature process is supported with a heat transfer medium of a temperature of> 500 ° C. An example of such a low-temperature process between the two high-temperature processes is the generation of water vapor, wherein either the heat transport medium is provided as water vapor for a process or by means of a heat exchanger, the thermal energy of the heat transport medium is used to generate water vapor. Specifically, with a heat transfer medium of a low temperature, in particular below a temperature of 300 ° C, the heat transport medium can serve to preheat water, wherein the preheated water is used to generate water vapor. The Vor¬

Heating of the water, in particular by means of a tube-in-tube heat exchanger, is also referred to as feedwater pre-heating. The water vapor after the passage of the second turbine regularly has a temperature of just about 300 ° C. Water vapor of such a low temperature is not suitable for the effective generation of electrical energy. However, steam at a temperature of about 300 ° C is well-suited for supporting steps of the Bayer process and / or for treating red mud and / or heating purposes of buildings.

In principle, it is possible to support a low-temperature process by means of a heat transfer medium, which is suitable for supporting a high-temperature process. The arrangement of high-temperature processes before low-temperature processes in the tiered supply of the Heat transport medium, however, serves to save energy, since processes that take place at high temperatures can not be supported with a heat transport medium of a lower temperature.

In a further advantageous embodiment of the method, the waste heat is used to support a high-temperature process, wherein the remaining waste heat of the high-temperature process supports at least one low-temperature process.

Advantageously, after the support of a high temperature process, the heat transport medium is made available to a low temperature process. Regularly, the temperature and / or the pressure of the heat transfer medium after the support of a high-temperature process is no longer sufficient for another high-temperature process. For a higher energy efficiency, especially when using waste heat, it is therefore advantageous to use the heat transport medium also to support low-temperature processes. Thus, after generation or assisting in the production of steam, the steam serving to treat red mud, may be fed to further low temperature processes. A treatment of red mud with a heat transport medium relates in particular to the support of the filtering of the red mud or the removal of the remaining water / the residual liquor from the red mud with the aid of the heat transport medium. Further, the heating of the liquor and / or the lye-bauxite mixture can be supported with the aid of the heat transport medium. In the heating of liquor and or in the heating of a reaction mixture in the production of aluminum hydroxide, the essential steps of the Bayer process are carried out at temperatures below 100 ° C to 200 ° C. Thus, the steps of the Bayer process in principle by means of the heat transfer medium at a temperature of <300 ° C can be supported. By supplying the heat transport medium, in particular water vapor, to a step of the Bayer process, it is also advantageously possible to assist with a heat transport medium which has already been used to generate steam and / or electrical energy. In this way, the greatest possible energy savings can be realized.

In a further advantageous embodiment of the method, the high-temperature process and / or a further high-temperature process is a generation of steam or a generation of electricity.

High temperature processes are processes that take place at temperatures above 400 ° C. Such processes are either the production of water vapor, the generation of electrical energy by means of a turbine connected to a generator and / or heating of a reaction mixture or raw material in the production of aluminum. The generation of water vapor is advantageously carried out either by the direct use of the heat transport medium, if the heat transport medium is water vapor, or indirectly by the heating of water and / or water vapor by means of another heat exchanger, through which the heat transport medium is passed.

In a further advantageous refinement of the method, the low-temperature process and / or a further low-temperature process are a process step of the Bayer process and / or support steam generation.

Fields of application for the waste heat in the Bayer process are the heating of the reaction mixture, consisting of the lye, the bauxite, the heating of the liquor to increase the concentration of the liquor and to support the filtering of the reaction mixture for the separation of the red mud. The reaction steps of the Bayer process are regularly found at Tempe- temperatures below 300 ° C and are therefore well suited for the use of waste heat.

To assist steam generation, water is preheated by the heat transfer medium in another heat exchanger. For example, the water can be heated from a temperature T equal to 15 ° C to a temperature T equal to 60 ° C and the 60 ° C warm water in a further step to the required temperature of the water vapor.

By using waste heat of a temperature up to 300 ° C can advantageously be used to support the processes of the Bayer process, the heat transport medium, which is no longer suitable for power generation. This saves energy by 4%.

In a further advantageous embodiment of the method, the process step of the Bayer process is the filtering of red mud and / or the heating of a mixture of liquor and bauxite and / or to support a filtering and / or treatment of red mud and / or the heating of a liquor ,

When filtering red mud, steam is used regularly to separate off the remaining water / to separate off the existing liquor. Furthermore, the steam can be used to dry the red mud. Advantageously, this reduces the volume of the red mud, removes sodium hydroxide or another base material from the red mud and thereby saves landfill space. By means of a further heat exchanger, the heating of the reaction mixture, in particular the lye or the lye / bauxite mixture by the waste heat is advantageous, in particular in an autoclave, advantageous.

By using waste heat, especially waste heat

Temperature below 300 ° C, can through the use The use of waste heat saves considerable amounts of energy.

In a further advantageous embodiment of the method, the unwanted waste heat is stored in a heat storage.

The storage of the waste heat which is not required is possible in an insulated collecting container, the insulated collecting container being provided for receiving heated heat transport medium and / or for storing water vapor. The stored waste heat can be used at a later time to support individual processes of the Bayer process or to generate electricity and / or to heat premises.

In an advantageous embodiment of the device, a step of the Bayer process is provided for utilizing the waste heat.

The Bayer process is used, as stated above, for the production of aluminum oxide from bauxite with the aid of lye, in particular of sodium hydroxide solution. In the claimed device, the waste heat is conducted from the source by means of pipelines to the reaction steps or reaction vessels, which require heat energy.

By such a device, in particular waste heat of a temperature of below 500 ° C can be used advantageously and thus reduces the use of conventional heat sources, such as a combustion furnace or an electric heater. Thus, energy is advantageously saved and the manufacturing costs are reduced. In a further advantageous embodiment of the device are provided as high-temperature processes, generation of electric current by means of a turbine and / or the generation of water vapor, as a low-temperature process a step in the Bayer process or support for the production of steam is provided.

Power is generated regularly by a generator driven by a turbine. The turbine is by means of the heat transfer medium, wherein the heat transport medium in particular steam at a temperature of up to 1,600 ° C and a pressure of up to 100 bar and possibly even more. In the production of water vapor, the heat transport medium can be used either directly as water vapor for further processes, if the heat transport medium medium water or water vapor. If the transport medium consists, for example, of a petroleum product, the heat transport medium can be used for heating or for evaporating water and thus for generating steam.

In a further advantageous embodiment, the device has a control device and optionally further control and regulating devices and control valves and optional sensors, wherein the control valves control the flow of a heat transfer medium, the sensors determine temperatures and / or pressure values, wherein a division of the heat transport medium WTM basis the temperatures and / or pressure values of the heat transfer medium to the high-temperature processes and / or the low-temperature processes is provided, and wherein a control and / or regulation of the distribution of the heat transfer medium WTM using the control device and / or the at least one optional control and Control device is provided.

To distribute the waste heat by means of the heat transport medium, the heat transport medium is routed regularly through pipelines from the source or the sources to the at least one high-temperature process and / or to the at least one low-temperature process. Advantageously located in the piping sensors. The sensors are used to determine the temperature, the pressure values, and / or the flow velocity. the heat transfer medium within certain areas of the piping. The determined temperatures, pressure values or flow velocities of the heat transport medium at the at least one point are transmitted by the sensors to a control device. On the basis of the temperatures, the pressure values and / or the flow velocity of the heat transfer medium, the control device controls the control valves which serve to distribute the heat transfer medium to the high-temperature processes or low-temperature processes.

Advantageously, the control device also serves to log the use of waste heat and can thus advantageously determine the saving of energy.

The invention will be described and explained in more detail below with reference to FIGS. Show it

1 shows a simple scheme of using waste heat,

2 shows another simple scheme,

3 shows a scheme with two sources,

4 shows the use of waste heat with a return of the heat transport medium,

5 shows an embodiment of the use of waste heat, and FIG 6 shows a further embodiment of the use of waste heat.

1 shows a simple scheme of the use of waste heat. In this scheme, the waste heat in a source Ql is transferred to a first high temperature process HTP. A heat transfer medium WTM serves to transport the waste heat. The heat transfer medium WTM has a temperature Tl and a pressure value pl after the output of the source Ql. The waste heat remaining from the high-temperature process HTP is transferred to a first low-temperature process NTP1 and transferred to a second low-temperature process NTP2. After the high temperature process, the heat transport medium WTM has a temperature T2 and a pressure value p2. Between the high temperature process HTP and the second low temperature process NTP2 is a control valve Sl. The control valve Sl is used to divide the remaining waste heat of the high-temperature process HTP on the first low-temperature process NTP1 and the second low-temperature process NTP2. The control valve Sl is advantageously operated by means of a control device 100, or manually. Advantageously, the distribution based on the temperature T2, the pressure value p2 and / or the flow rate of the heat transport medium WTM and based on the heat demand of the low-temperature processes NTP1, NTP2 distributed to the low-temperature processes NTP1, NTP2.

The source Q 1 is advantageously the calcination or the waste heat of the fused-salt electrolysis in the production of aluminum or aluminum oxide. The high-temperature process HTP is, for example, the generation of electrical energy with at least one turbine and one generator. The kinetic energy that has been provided by means of a turbine can also be used for comminution of the bauxite by means of a turbine-driven mill. The turbine can be designed as a so-called back pressure extraction turbine or as a removal condensation turbine. Advantageously, at an outlet of the turbine steam is taken off via a valve Sl and fed to a low-temperature process NTP1, NTP2. FIG 2 shows another scheme of the use of waste heat. Here, a high-temperature process HTP and a second low-temperature process NTP2 supplied with waste heat from a source Ql. The remaining waste heat of the HTP high-temperature process is used to support the first low-temperature NTP2 process. The heat transport medium WTM, which for

High-temperature process HPT is passed, has a temperature Tl and a pressure value of pl. The portion of the heat transport medium WTM, which supports the second low-temperature process NTP2, has a temperature Tl ¹ and a pressure value pl ^λ .

After the high-temperature process HTP, the heat transfer medium WTM still has a temperature T2 and a pressure value p2 on. The heat transport medium WTM is fed to a first low-temperature process NTP1 after the support of the high-temperature process HTP. After the high-temperature process HTP, the heat transport medium has a temperature T2 and a pressure value of p2.

The second low-temperature process NTP2 is, for example, a treatment, in particular a filtering, of red mud. Another option for the use of waste heat is the use of waste heat in a second low-temperature NTP2 process. The second low-temperature process NTP2 is assisted by means of a heat transfer medium WTM of a high temperature, so that rapid heat transfer to another substance, for example the bauxite and / or a bauxite-liquor mixture, advantageously with a further heat exchanger 3 'is made possible , Thus, a fast and effective heating of a reaction mixture in the Bayer process and thus an increased yield of the respective product and an increased efficiency can be realized.

In general, the heat transport medium WTM can be condensed again after passing through the low-temperature processes NTP1, NTP2 and reheated in the source. 3 shows a schematic with two sources Q1, Q2. The first source Ql serves to support the high-temperature process HTP and a low-temperature process NTP. The second source Q2, together with the first source Ql, serves to support the low temperature process NTP.

The heat transport medium WTM for supporting the high-temperature process HTP has a temperature Tl and a pressure value pl. The waste heat of the first source Ql and the second source Q2 is through a heat transport medium WTM from the sources through, preferably separate, pipelines to the

Processes HTP, NTP transfer. The heat transfer medium WTM, which transfers the waste heat from the first source Ql in support of the high-temperature process HTP, has a temperature Tl and a pressure pl. The heat transport medium WTM, which transmits the waste heat from the first source Ql to support the low-temperature process NTP, has a temperature Tl ¹ and a pressure value pl ^λ . The heat transfer medium WTM, which transmits the waste heat from the second source Q2 in support of the low-temperature process NTP, has a temperature ΤΓ ¹ and a pressure value pl ^λ .

The remaining waste heat of the high-temperature process HTP serves to support another process HTP, NTPl, either a high-temperature process HTP or a low-temperature process NTPl. The remaining waste heat of the low temperature process NTP serves to support at least one further low temperature process NTP2. After the high-temperature process HTP, the heat transport medium WTM still has a temperature T2 and a pressure value p2, wherein the temperature T2 is regularly smaller than T1. After the low-temperature process NTP, the heat transport medium has a temperature T3 and a pressure value p3.

Optionally, waste heat, which is released in the context of the high-temperature process HTP, also serve to support at least one low-temperature process NTP. This is symbolized by the dashed arrow between the high temperature process HTP and the low temperature process NTP. Thus, the high temperature process HTP acts as a source for at least one low temperature process. For example, the waste heat in the power generation by a generator G can be used to heat rooms.

4 shows a use of waste heat with a return of the heat transfer medium WTM. The waste heat is transferred from a first source Ql to a heat transport medium WTM and sent to a first high-temperature process HTP1. The remaining waste heat of the first high-temperature process HTPl is transferred to a first low-temperature process NTP1 and supports the first low-temperature process NTPl. The remaining after the first low-temperature process NTPl Waste heat is supplied in the form of the heat transfer medium WTM a second source Q2. The second source Q2 heats the heat transport medium WTM again to a sufficient temperature Tl ^λ and densifies the heat transport medium if necessary. again to a sufficient pressure value pl ^λ , so that the heated and possibly. compressed heat transfer medium WTM is again suitable for supporting high-temperature processes HTP1, HTP2 and / or the low-temperature NTP2 process. The heated and possibly compressed heat transport medium WTM is then passed either to support the first high-temperature process HTP1 and / or to support a second high-temperature process HTP2 and / or to the second low-temperature process NTP2. The heat transport medium WTM has after the first source Ql a temperature Tl and a pressure value pl. After the support of the first high temperature process HTP1, the heat transport medium WTM has a temperature of T2 and a pressure value p2. The temperature value Tl or the pressure value pl is regularly lower than the temperature value T2 and / or the pressure value p2. After the support of the first low temperature process NTP1, the heat transport medium WTM has a temperature T3 and a pressure value p3. The temperature T3 is regularly lower than the temperature Tl and the temperature T2. After a second source Q2, the heat transport medium has a temperature Tl ^λ and a pressure value pl ^λ . The temperature T and optionally the pressure value p increase in the second source Q2. The second source Q2 may be a conventional source of Q2, in which the heat transport medium WTM is heated for example by means of a combustion furnace from the temperature T3 to the temperature Tl. ¹ However, particularly advantageous is the waste heat from another process, such as the melt electrolysis, as a source Q2 for heating the heat transfer medium from the temperature T3 to a temperature Tl ^λ used. If necessary, compression of the heat metransportmediums WTM between the individual processes HTPl, NTP1, HTP2, NTP2 instead.

A control device 100 controls the distribution of the heat transport medium WTM to the high-temperature processes HTPl, HTP2 and / or the low-temperature processes NTP1, NTP2 by means of control valves S1. The allocation is based on the (Ab) - heat demand of the individual processes NTP1, HTPL, NTP2, NTP2 and the temperature Tl, Tl ¹ and / or the pressure value pl, pl ^{λ of} the heat transport medium WTM instead. Furthermore, the control device 100 advantageously serves to monitor the processes NTP1, HTPL, NTP2, NTP2, so that the heat transport medium WTM is used as efficiently as possible. This monitoring is indicated by the hatched double arrows.

FIG. 5 shows an embodiment of the device for utilizing waste heat in the production of aluminum oxide A1 ₂ 0 ₃ . The first source Q1 is a calcining furnace, the calcining furnace for converting aluminum hydroxide

Al (OH) ₃ to alumina A1 ₂ 0 ₃ is used. The conversion of aluminum hydroxide Al (OH) ₃ to alumina A1 ₂ 0 ₃ is carried out by heating the aluminum hydroxide Al (OH) _3rd The aluminum hydroxide Al (OH) ₃ is the product of the preceding steps of the Bayer process, with individual steps of the Bayer process involving waste heat, in particular as low-temperature processes NTP1,

NTP2 can be supported. The heating of the aluminum hydroxide Al (OH) ₃ is carried out by means of a combustion furnace 5, which is arranged in the calcination furnace. In one area, the unused heat of the calcination, ie the waste heat, is transferred to the heat transfer medium WTM with a first heat exchanger 3.

As heat transfer medium WTM advantageously serves water or water vapor. The calcination furnace serves as the source Ql of the waste heat. Optionally, the heat transport medium WTM is preheated in another source Q2, by means of combustion exhaust gases. After passing through the heat exchanger 3 in the calcining furnace, the heat transport medium WTM has a temperature of temperature Tl and a pressure value pl. Through a pipeline, the heated heat transport medium WTM is passed to a first turbine Rl. The drive of the first turbine Rl by means of the heat transport medium WTM is the first high-temperature process HTP1. Advantageously, the heat transport medium WTM on entering the turbine Rl has a temperature Tl = 1.200 ° C to Tl = 1.600 ° C and a pressure pl of, for example, 20 bar. The heat transport medium WTM, usually water vapor or water, is referred to as saturated steam in front of the entrance to the turbine Rl. In the turbine Rl serves the

Saturated steam for moving the turbine Rl, wherein kinetic energy is transmitted to a generator G and wherein the generator G generates electrical energy from the kinetic energy. The remaining waste heat from the first turbine Rl, manifested by the heat transport medium WTM, has a temperature T2 of at least 500 ° C and a pressure p2 of several bar.

After the first turbine R 1, the heat transport medium is partially transferred to a second turbine R 2 or a first low-temperature process NTP 1. The proportion of the heat transport medium WTM that is transmitted to the first low-temperature process NTP1 is determined by the control valve S1 based on the temperature T2 and / or the pressure value T2 of the control device 100 and / or by a control and regulating device 10. A sensor 9 serves to determine the temperature T2 of the heat transport medium WTM. The sensor 9 is advantageously provided close to the outlet of the first turbine R1 for determining the temperature T2 and / or the pressure value p2 and / or the flow speed of the outgoing heat transfer medium WTM. The sensor 9 and the control valve Sl are connected to the control device 100 and / or a control and regulating device 10. The control device 100 determines the advantageous fraction of the heat transport medium WTM in support of the low-temperature process NTP1, which contributes to the further heat exchange process. shear 3 'is transferred to the low temperature process NTP1.

After passing through the further heat exchanger 3 ', the heat transport medium has a temperature T3 and a pressure value p3. The temperature T3, pressure value p3 and / or the flow velocity of the heat transport medium WTM is also determined with a sensor 9. Advantageously, the outgoing heat transport medium WTM is used after the first low-temperature process NTP1, if appropriate, for the provision of water vapor and possibly heated once again and / or compressed.

The part of the heat transport medium WTM from the first turbine Rl, which does not support the low-temperature process NTP1, is directed into a second turbine R2. The second turbine R2 is advantageously a turbine R2, which is suitable for a wet steam. Wet steam, ie steam at a temperature of 400 ° C to 1,000 ° C and a pressure of several bar usually requires a different type of turbine R2 than the first turbine Rl for conversion into kinetic energy. The kinetic energy generated at the turbine R2 is transmitted to a generator G and serves in conjunction with the generator G for generating electrical energy. The power generation by the wet steam is classified as the second high-temperature process HTP2.

The remaining waste heat, that is to say the heat transport medium WTM which leaves the second turbine R2, advantageously serves to support a second low-temperature process NTP2. The heat transport medium WTM has, after the second turbine R2, a temperature T4 and a pressure value p4. The remaining waste heat is discharged through the further heat exchanger 3 ^λ to be supported second low-temperature process NTP2 by the heat transfer medium WTM flows through the other heat exchanger 3 '. Instead of the further heat exchanger 3 'or after the passage of the heat transfer medium WTM through the further heat exchanger 3', the heat Transport medium itself be used to support the Bayer process or a treatment of red mud. After supporting the second low-temperature process NTP2, the heat transport medium still has a temperature of T5 and a pressure value of p5.

On the basis of the temperatures T1, T2, T3, T4, T5 and / or on the basis of the pressure values I, P2, P3, P4, P5 and, if appropriate, based on flow velocities of the heat transport medium WTM, the heat transport medium WTM is transferred to the high-temperature processes HTP1 , HTP2 and / or the low-temperature processes NTP1, NTP2 distributed. The distribution also depends advantageously on the needs of the process steps to be supported and / or on the (temporal) demand for electrical and / or kinetic energy. The distribution is thereby by a

Control device 100 and control devices 10 instructed. The sensors 9 and the control valve Sl are connected to the control and regulating device 10 and / or the control device 100.

The heat transport medium WTM, in particular in the case of water vapor, is advantageously fed to a condenser and / or compressor (not shown). After condensation / compression, the heat transport medium WTM is again in liquid form and can be reheated in the source. This closes a cycle of the heat transfer medium WTM.

The turbines R1, R2 can be different turbines. Advantageously, the heat transport medium WTM first passes through a high-pressure turbine which is suitable for saturated steam. Following the first turbine is a medium-pressure turbine R2, which is suitable for wet steam, a further use of the heat transfer medium WTM, which is present after passing through the first turbine Rl usually as wet steam. Some turbines have an outlet opening from which heat transfer medium WTM different temperature T and pressure p can be removed. The removed heat transport medium WTM can then serve to support further processes HTP, NTP, in particular low-temperature processes NTP, NTP1, NTP2. 6 shows a further embodiment of the use of waste heat. A first source Ql is used to absorb the waste heat of exhaust gases, wherein the exhaust gases are generated in the calcination furnace. The waste heat is transferred by means of a heat exchanger 3 to the heat transfer medium WTM. The heat transport medium is then brought to a temperature Tl and a pressure value pl in a heat exchanger 3 of the second source Q2. As the second source Ql is the calcination furnace, wherein unused heat is transferred from a heat exchanger 3 to a heat transfer medium WTM. The first source Q1 is advantageously a tube-in-tube heat exchanger 3. Through the tube-in-tube heat exchanger 3, some of the waste heat is removed from the exhaust gases of the incinerator of the calcination furnace. The cooled exhaust gases are then released through a chimney to the environment. The heat transport medium WTM is conducted through pipelines to the high-temperature process HTP and to a first low-temperature process NTP1 and to a second low-temperature process NTP2. The distribution of the heat transport medium WTM to the processes NTP1, HTP1, HTP2 is carried out by control valves Sl.

The distribution of the heat transport medium WTM is based on the temperature of the heat transport medium Tl, T2, the pressure values pl, p2 and possibly the flow velocities of the heat transport medium WTM, wherein the temperatures Tl, T2, the pressure values pl, p2, and possibly the flow rates by sensors be determined. Further, the waste heat can also be stored in the form of the heated heat transport medium WTM the temperature Tl and the pressure value pl in a heat storage WS.

Occasionally there is a surplus of waste heat, ie, there is an excess of heat transfer medium WTP a temperature Tl available. With such a Überangebot becomes the Heat transfer medium WTM stored in a heat storage WS. In the case of a lack of waste heat, for example in the event of a failure of a source Q1, Q2 of the waste heat, the high-temperature processes HTP1, HTP2 and / or the low-temperature processes NTP1, NTP2 with waste heat from the heat storage WS, ie with heat transport medium WTM, become Heat storage supplies. The allocation is carried out by means of the control valves Sl.

The control valves Sl are controlled by a control device 100, wherein the control means control and

Control devices 10 has. The control and regulating devices 10 are advantageously used as interfaces between the control device 100 and the control valves Sl and / or the sensors 9. The sensors 9 are also connected to the control valves S1 and / or to the control and regulating device 10.

The control device 100 and / or the control and regulating devices 10 advantageously receive process data from the high-temperature processes HTP1, HTP2, the low-temperature processes NTP 1, NTP2 and / or the heat storage WS. This should be symbolized by the dashed connecting lines. The control unit can also serve to control and / or regulate further processes of the plant, in particular procedural steps of the Bayer process.

Low-temperature processes NTP1, NTP2 are understood to mean reaction steps, in particular of the Bayer process, which can be assisted with a heat transfer medium at a temperature below 500 ° C. In particular, process steps of the Bayer process and / or the treatment of red mud are advantageously supported with a heat transport medium WTM a temperature of up to 300 ° C. As high-temperature processes HTP1, HTP2 is the generation of kinetic energy, for example, to drive a Umwälzmechanismus or for the treatment of bauxite and for converting the kinetic energy into electrical energy with a generator G understood. Furthermore, the heat transfer medium WTM can be used to generate steam or, if the heat transfer medium is water or water vapor, the heat transfer medium can itself also serve to support the processes that require water vapor.

The invention relates to the use of waste heat, in particular in the production of aluminum oxide, for supporting at least one first high-temperature process HTP, HTP1, HTP2 and at least one low-temperature process NTP, NTP1,

NTP2, wherein the low-temperature process NTP, NTP1, NTP2 allows a support with a heat transport medium WTM, which has a lower temperature than that of the temperature of a heat transfer medium WTM, which is provided to support a high-temperature process HTP. The waste heat is thereby transferred from at least one source Q, Q1, Q2 with the aid of a heat transport medium WTM to the high-temperature processes HTP, HTP1, HTP2 and / or the low-temperature processes NTP, NTP1, NTP2. As heat transfer medium WTM advantageously serves water vapor.

In particular in the production of aluminum oxide from bauxite, the process steps of the Bayer process are advantageously supported as low-temperature processes NTP, NTP1, NTP2. A control device 100 and at least one control valve S1 supports the distribution of the heat transport medium WTM to the processes HTP, HTP1, HTP2, NTP, NTP1, NTP2 on the basis of temperatures T1, T2, T3, T4 and / or pressure values pl, p2, p3, p and / or flow velocities of the heat transfer medium WTM and based on the needs of the individual processes HTP, HTP1, HTP2, NTP, NTP1, NTP2. Low-temperature processes HTP, HTP1, HTP2, NTP, NTP1, NTP2 are in particular the provision and / or support in the provision of steam and / or the heating of a substance such as the red mud and / or a reaction mixture.

High-temperature processes HTP, HTP1, HTP2 are in particular the drive of a turbine Rl, R2 and / or the generation and / or provision of steam. The invention relates to the use of waste heat, in particular in the production of aluminum oxide, to support at least a first high-temperature process HTP, HTP1, HTP2 and at least one low-temperature process NTP, NTP1, NTP2, wherein the low-temperature process support with a heat transport medium WTM allowed, which has a lower temperature T2, T3, T4, than the temperature Tl, ΤΓ, T2 of a heat transfer medium WTM, which is provided to support a high-temperature process HTP, HTP1, HTP2. The waste heat is thereby transferred from at least one source Q, Q1, Q2 with the aid of a heat transport medium WTM to the high-temperature processes HTP, HTP1, HTP2 and / or the low-temperature processes NTP, NTP1, NTP2. As heat transfer medium WTM advantageously serves water vapor. Particularly in the production of alumina from bauxite, the process steps of the Bayer process are advantageously supported as low-temperature processes NTP, NTP1, NTP2. A control device 100 and at least one control valve S1 supports the distribution of the heat transport medium WTM to the processes HTP, HTP1, HTP2, NTP, NTP1, NTP2. The distribution takes place on the basis of temperatures T 1, T 2, T 3, T 4 and / or pressure values p 1, p 2, p 3, p 4 and / or flow velocities of the heat transport medium WTM. The support of the processes HTP, HTP1, HTP2, NTP, NTP1, NTP2 also depends on the current need for heat of the individual processes HTP, HTP1, HTP2, NTP, NTP1, NTP2.

Claims

claims

1. A method for utilizing waste heat, in particular in the production of alumina, wherein the waste heat from at least one source (Q, Ql, Q2) is provided, wherein the waste heat to support at least one high-temperature process (HTP, HTP1, HTP2 ) and / or at least one low-temperature process (NTP, NTP1, NTP2) is used, wherein after the support of a high-temperature process (HTP, HTP1, HTP2), the support of at least one further high-temperature process (HTP, HTP1, HTP2) and / or Support of at least one further low-temperature process (NTP, NTP1, NTP2) takes place, and wherein the respective further high-temperature process (HTP, HTP1, HTP2) and / or the respectively further low-temperature process (NTP, NTP1, NTP2) the remaining waste heat of the respective preceding high temperature process (HTP, HTP1, HTP2) or low temperature process (NTP, NTP1, NTP2) is supported.

2. The method of claim 1, wherein the waste heat to support the high-temperature process (HTP, HTP1, HTP2) is used, the remaining waste heat to support another high-temperature process (HTP, HTP1, HTP2) and another low-temperature process (NTP, NTP1, NTP2), and where the remaining waste heat is further

High-temperature process (HTP, HTP1, HTP2) to support another low-temperature process (NTP, NTP1, NTP2) is used.

3. The method of claim 1, wherein the waste heat to support a high-temperature process (HTP, HTP1, HTP2) and the remaining waste heat of the high-temperature process (HTP, HTP1, HTP2) at least one low-temperature process (NTP, NTP1, NTP2 ) supported.

4. The method according to any one of the preceding claims, wherein the high-temperature process (HTP, HTP1, HTP2) and / or a Another high temperature process (HTP, HTP1, HTP2) is a generation of steam or a generation of electricity.

5. The method according to any one of the preceding claims, wherein the low-temperature process and / or another low-temperature process is a process step of the Bayer process and / or a steam generation is supported.

6. The method of claim 5, wherein the process step of the Bayer process comprises filtering red mud and / or heating a mixture of liquor and bauxite and / or to aid in filtering and / or treating red mud and / or heating a liquor is.

7. The method according to any one of the preceding claims, wherein unneeded waste heat in a heat storage (WS) is stored.

8. Apparatus for utilizing waste heat, in particular in the production of aluminum oxide, wherein a source (Q, Q1, Q2) is provided for providing one of the waste heat, the waste heat being used to support at least one high-temperature process (NTP, NTP1, NTP2) and / or at least one low-temperature process (NTP, NTP1, NTP2) is provided, whereby after the support of a high-temperature process (HTP,

HTP1, HTP2) the support of at least one further high-temperature process (HTP, HTP1, HTP2) and / or at least one further low-temperature process (NTP, NTP1, NTP2) is provided, and wherein the respectively further high-temperature process and / or the respective further low-temperature process Process (NTP, NTP1, NTP2) with the remaining waste heat of the respective preceding high-temperature process (HTP, HTP1, HTP2) or low-temperature process (NTP, NTP1, NTP2) is provided for support.

9. Device according to claim 8, wherein a step of the Bayer process is provided for utilizing the waste heat.

10. Apparatus according to claim 8 or 9, wherein as high-temperature processes (HTP, HTP1, HTP2) a generation of electric current by means of a turbine (Rl, R2) and / or the generation of water vapor are provided, wherein as low temperature Processes (NTP, NTP1, NTP2) a step of the Bayer process and / or support the generation of steam are provided.

11. Device according to one of claims 8 to 10, wherein the device comprises a control device (100), optionally further

Control and regulating devices (10) and control valves (Sl) and optional sensors (9), wherein the control valves (Sl) control the flow of a heat transfer medium (WTM), the sensors (9) temperatures (Tl, T2, T3, T4 ) and / or pressure values (pl, p2, P3, p4), wherein a division of the heat transport medium (WTM) based on the temperatures (Tl, T2, T3, T4) and / or pressure values (pl, p2, p3, p4) of Heat transport medium (WTM) on the high-temperature processes (HTP, HTP1, HTP2) and / or the low-temperature processes (NTP, NTP1, NTP2) is provided, and wherein a control and / or regulation of the distribution of the heat transfer medium (WTM) using the control device (100) and / or the at least one optional control and regulating device (10) is provided.

12. Control device (100), wherein the control device (100) for controlling and / or regulating and / or monitoring a device according to one of claims 8 to 11 is provided.

13. Plant, in particular for the production of aluminum and / or alumina, comprising a device according to one of claims 8 to 11 and / or a control device (100) according to claim 12.