CN116601115A - Method for reducing carbon - Google Patents
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- CN116601115A CN116601115A CN202180057685.1A CN202180057685A CN116601115A CN 116601115 A CN116601115 A CN 116601115A CN 202180057685 A CN202180057685 A CN 202180057685A CN 116601115 A CN116601115 A CN 116601115A
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Abstract
A method for controlling carbon output of an alumina refinery, the method comprising the steps of: capturing water vapor from a flash train in the refinery, compressing the captured water vapor, and utilizing at least a portion of the energy in the captured water vapor to heat a process stream within the alumina refinery.
Description
Technical Field
The present application relates to a method of controlling carbon output of an alumina refinery.
Background
The bayer process is a cyclic process in which bauxite is leached in a hot caustic solution to dissolve alumina-containing minerals. Undissolved solids are separated and the liquid is cooled to precipitate aluminum hydroxide. The precipitated material was removed and calcined at about 1000 ℃ to form alumina. The cooled bayer liquor is reheated and recycled to the digestion stage. As much as possible, energy is captured and reused in the process to encourage energy efficient alumina production.
Alumina refining is energy intensive, requiring an average energy of about 10.7GJ for the production of 1 ton of alumina worldwide. About 70% of this energy is consumed in the dissolution and precipitation portions of the process, the remaining 30% being consumed in calcination. Thus, energy is used as efficiently as possible to reduce costs and carbon dioxide emissions. Typically, alumina refineries are powered by steam generated in a boiler, which steam may also be used to power the refinery. Steam is produced by the combustion of fossil fuels, typically coal, but also including natural gas and less common petroleum, resulting in carbon dioxide emissions.
Alumina refineries are known to use flash vessels to reduce the temperature of liquid streams within the refinery. The liquid stream enters the flash vessel and the pressure is reduced, producing a cooled liquid stream and pressurized water vapor. Typically, the flash vessels are arranged in series in a row group (bank) or column group (train). In fluid communication with the flash vessel row group is typically a corresponding heater row group. The steam flashed from the flash vessel is sent to a corresponding heater as known in the art to re-use the energy present in the pressurized steam.
It is known to use flash vessels and banks thereof in many locations in alumina refineries, including:
a. cooling the dissolved liquid prior to clarification;
b. cooling the clarified liquid prior to precipitation;
c. cooling the liquid from the evaporation loop; and
d. cooled in the precipitation circuit.
Common to these systems is that the liquid cools as it travels along the flash train. The flash steam exiting the last flash vessel in the series is typically too cold to heat any heater and is therefore considered unusable.
Because of this energy loss and the reliance on fossil fuel generated steam to provide energy, fossil fuels represent a significant portion of the total cost of alumina production and produce significant greenhouse gas emissions. Alumina production using natural gas typically produces about 0.55 tons of carbon dioxide per ton of alumina, while an equivalent refinery producing alumina using coal typically produces about twice the mass of carbon dioxide per ton of alumina. Global alumina production in 2019 was about 1.32 million tons.
The foregoing discussion of the background to the application is intended to facilitate an understanding of the present application. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge as at the priority date of the application.
Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
Throughout the specification, unless the context requires otherwise, the term "solution" or variations such as "solution(s)" will be understood to include slurries, suspensions and other mixtures containing undissolved and/or dissolved solids.
It will be appreciated by those skilled in the art that variations and modifications of the application described herein may be made based on those specific descriptions. It is to be understood that the application includes all such variations and modifications. The application also includes all of the steps, features, compositions and compounds referred to or indicated in the specification, individually or collectively, and any and all combinations of any two or more of said steps or features.
The scope of the application is not to be limited by the specific embodiments described herein, which are for illustrative purposes only. Functionally equivalent products, compositions, and methods are clearly within the scope of the application as described herein. The entire disclosure of all publications (including patents, patent applications, journal articles, laboratory manuals, books, or other documents) cited herein are hereby incorporated by reference.
Disclosure of Invention
According to the present application there is provided a method for controlling carbon output of an alumina refinery, the method comprising the steps of:
capturing water vapor from at least one location in the refinery;
compressing the captured water vapor; and
the energy in the captured water vapor is utilized to heat a process stream within the alumina refinery,
wherein the captured water vapor is compressed in an electric compressor, wherein the electric energy has less than 0.5t CO 2e Carbon strength of/MWhr.
According to the present application there is provided a process for preparing low carbon alumina from an alumina refinery, the process comprising the steps of:
capturing water vapor from at least one location in the refinery;
compressing the captured water vapor; and
the energy in the captured water vapor is used to heat a process stream within the alumina refinery,
wherein the captured water vapor is compressed in an electric compressor, wherein the electric energy has less than 0.5t CO 2e Carbon strength of/MWhr.
According to the present application there is provided a method of utilizing low grade heat in an alumina refinery, the method comprising the steps of:
capturing water vapor from at least one location in the refinery;
compressing the captured water vapor; and
the energy in the captured water vapor is utilized to heat a process stream within the alumina refinery.
The method of utilizing low grade heat in an alumina refinery may include the additional steps of: compressing captured water vapor in an electric compressor, wherein the electric energy has less than 0.5tCO 2e Carbon strength of/MWhr.
According to the present application there is provided a method for controlling carbon output of an alumina refinery, the method comprising the steps of:
capturing water vapor from a flash train in a refinery;
compressing the captured water vapor; and
the energy in the captured water vapor is utilized to heat a process stream within the alumina refinery.
In the context of this specification, the term control is understood to include reducing the carbon output of an alumina refinery. The term reduction is understood to include reduction of carbon output compared to an equivalent alumina refinery using fossil fuel fired boiler steam as known in the art. The term "reducing" is also understood to include retrofitting an existing alumina refinery with the present application and building a new alumina refinery with the present application.
In the context of this specification, the term carbon export shall be taken to mean the tonnage of carbon dioxide produced per ton of alumina produced by a refinery.
In one form of the application, the method of the application reduces the carbon output of an alumina refinery by 10%. In an alternative form of the application, the process of the application reduces the carbon output of an alumina refinery by 20%. In an alternative form of the application, the process of the application reduces the carbon output of an alumina refinery by 30%. In an alternative form of the application, the process of the application reduces the carbon output of an alumina refinery by 40%. In an alternative form of the application, the process of the application reduces the carbon output of an alumina refinery by 50%. In an alternative form of the application, the process of the application reduces the carbon output of an alumina refinery by 60%. In an alternative form of the application, the process of the application reduces the carbon output of an alumina refinery by 70%. In an alternative form of the application, the process of the application reduces the carbon output of an alumina refinery by 80%. In an alternative form of the application, the process of the application reduces the carbon output of an alumina refinery by 90%. In an alternative form of the application, the process of the application reduces the carbon output of an alumina refinery by 95%.
In one form of the application, the electrical energy is generated from a renewable energy source. Renewable energy sources may include wind, sun, water, tides, geothermal, and biomass. In an alternative form of the application, the electrical energy is generated from a zero carbon source (e.g., hydrogen or nuclear energy). The electrical energy may be stored in the battery after production and before use.
It will be appreciated that the step of compressing the water vapour will increase both its temperature and its pressure.
In one form of the application, the captured water vapor is a source of water vapor that would not otherwise be used as an energy source in an alumina refinery.
Some water vapor streams are close to ambient conditions and do not have a temperature differential to perform useful work within the refinery. Some water vapor streams are typically vented to the atmosphere due to local energy imbalances. Such a water vapor stream is particularly suitable for the present application.
The present application enables energy previously considered to be in the waste stream to be collected.
Alumina refineries contain a large number of potentially low energy water vapor streams or wastewater vapor streams. Attractive water vapor streams are water vapor streams from flash trains, particularly from the last flash vessel in the flash trains, such as those found in digestion, heat exchange and evaporation circuits.
In one form of the application, water vapor is captured from flash vessels in a flash train.
In one form of the application, the flash train includes a plurality of flash vessels.
If the water vapor is from a flash vessel in a flash train, it is preferably from the last or penultimate flash vessel in the train.
In one form of the application, the process stream is a heater in a flash train. The flash train set may be the same flash train set from which the water vapor is sourced.
In one form of the application, the process includes the additional step of feeding the heated process stream to a flash train. Preferably, the step of feeding the heated process stream to the flash train comprises feeding at least a portion of the heated process stream to the flash train.
In one form of the application, the heater train precedes the flash train.
In one form of the application, the flash train is a heat recovery flash train.
In one form of the application, the flash train includes at least two flash vessels.
In one form of the application, the water vapor is from the last and/or penultimate flash vessel in the flash train.
In one form of the application, the process stream is the last and/or penultimate heater in the array.
In one form of the application, the heater array comprises one or more heaters.
The water vapor may come from a liquid flash system or a water flash system. The liquid flash system may include digestion, heat exchange, evaporation, and precipitation. The water flash system may include external cooling of the precipitate and calcination of the flue gas.
The flash train set may form part of a digestion loop, a heat exchange loop, an evaporation loop, a precipitation loop, or a calcination heat recovery system in an alumina refinery.
In one form of the application, the method includes the further step of outputting excess compressed water vapor from the flash train.
In one form of the application, there are at least two heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery. In an alternative form of the application, there are at least three heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery. In an alternative form of the application, there are at least four heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery. In an alternative form of the application, there are at least five heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery. In an alternative form of the application, there are at least six heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery. In an alternative form of the application, there are at least seven heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery. In an alternative form of the application, there are at least eight heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery. In an alternative form of the application, there are at least nine heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery. In an alternative form of the application, there are at least ten heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery. In an alternative form of the application, there are at least eleven heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery. In an alternative form of the application, there are at least twelve heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery. In an alternative form of the application, there are at least thirteen heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery. In an alternative form of the application, there are at least fourteen heat recovery liquid flash and heating stages between the source of water vapor in the refinery and the process stream. In an alternative form of the application, there are at least fifteen heat recovery liquid flash and heating stages between the source of water vapor in the refinery and the process stream. In an alternative form of the application, there are at least sixteen heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery. In an alternative form of the application, there are at least seventeen heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery. In an alternative form of the application, there are at least eighteen heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery. In an alternative form of the application, there are at least nineteen heat recovery liquid flash and heating stages between the source of water vapor in the refinery and the process stream. In an alternative form of the application, there are at least twenty heat recovery liquid flash and heating stages between the water vapor source and the process stream in the refinery.
In one form of the application, there are two heat recovery liquid flash and heating stages between the water vapor source and the process stream of the refinery. In an alternative form of the application, there are three heat recovery liquid flash and heating stages between the refinery water vapor source and the process stream. In an alternative form of the application, there are four heat recovery liquid flash and heating stages between the refinery water vapor source and the process stream. In an alternative form of the application, there are five heat recovery liquid flash and heating stages between the refinery's water vapor source and the process stream. In an alternative form of the application, there are six heat recovery liquid flash and heating stages between the refinery's water vapor source and the process stream. In an alternative form of the application, there are seven heat recovery liquid flash and heating stages between the refinery's water vapor source and the process stream. In an alternative form of the application, there are eight heat recovery liquid flash and heating stages between the refinery's water vapor source and the process stream. In an alternative form of the application, there are nine heat recovery liquid flash and heating stages between the refinery water vapor source and the process stream. In an alternative form of the application, there are ten heat recovery liquid flash and heating stages between the refinery's water vapor source and the process stream. In an alternative form of the application, there are eleven heat recovery liquid flash and heating stages between the refinery's water vapor source and the process stream. In an alternative form of the application, there are twelve heat recovery liquid flash and heating stages between the refinery water vapor source and the process stream. In an alternative form of the application there are thirteen heat recovery liquid flash and heating stages between the refinery water vapor source and the process stream. In an alternative form of the application, there are fourteen heat recovery liquid flash and heating stages between the refinery water vapor source and the process stream. In an alternative form of the application, there are fifteen heat recovery liquid flash and heating stages between the refinery water vapor source and the process stream. In an alternative form of the application, there are sixteen heat recovery liquid flash and heating stages between the refinery's water vapor source and the process stream. In an alternative form of the application, there are seventeen heat recovery liquid flash and heating stages between the refinery's water vapor source and the process stream. In an alternative form of the application, there are eighteen heat recovery liquid flash and heating stages between the refinery's water vapor source and the process stream. In an alternative form of the application, there are nineteen heat recovery liquid flash and heating stages between the refinery's water vapor source and the process stream. In an alternative form of the application, there are twenty heat recovery liquid flash and heating stages between the refinery water vapor source and the process stream.
The production of alumina by the bayer process requires calcining precipitated aluminum hydroxide to alumina, as follows:
2Al(OH) 3 +heat → Al 2 O 3 +3H 2 O
Different types of calciner designs are commercially used with different fuel types (e.g., oil, gas, coal) and operating conditions (e.g., excess air). Thus, a variety of calciner flue gas temperatures and compositions may occur; it is estimated that about 35% to 45% by mass of the gas leaving the calcination ("calciner flue gas") is water, other components including carbon dioxide and volatile organic carbon compounds. In addition, the calciner flue gas may contain entrained particulate alumina.
The bayer process loses a significant amount of heat through the calciner flue gas. It is estimated that most of the available heat is low grade sensible or latent heat released upon condensation of water vapor in the flue gas. However, since the dew point is below 100 ℃ (typically 80 to 83 ℃), the latter can only be recovered as low grade heat under atmospheric conditions. However, low grade heat, although large in number, is generally considered to be of limited use in the bayer process.
According to the present application there is provided a method of utilizing low grade heat in an alumina refinery, the method comprising the steps of:
heating the fluid stream with calciner flue gas to provide a heated fluid stream;
passing the heated fluid stream through a flash train;
capturing water vapor from the flash train;
compressing the captured water vapor; and
at least a portion of the energy in the captured water vapor is utilized to heat a process stream within the alumina refinery.
In one form of the application, water vapor is captured from flash vessels in a flash train.
In one form of the application, the flash train includes a plurality of flash vessels.
In one form of the application, the flash train includes a flash vessel.
In one form of the application, the step of heating the process stream includes passing the process stream through at least one heater in the array of heaters.
In one form of the application, the water vapor is from the last and/or penultimate flash vessel in the flash train.
In one form of the application, the process stream is the last and/or penultimate heater in the array.
In one form of the application, the heater array comprises one or more heaters.
Advantageously, the present application also reduces the water consumption of an alumina refinery.
The step of compressing the captured water vapor may be repeated. There may be multiple compression steps to achieve the desired water vapor condensation temperature.
In a low temperature alumina refinery, where it is desired to compress water vapor from about 50 ℃ to a condensing temperature of about 170 ℃, it may be necessary to connect about 13 low speed centrifugal compressors in series. In a high temperature alumina refinery, where it is desired to compress water vapor from about 50 ℃ to a condensing temperature of about 300 ℃, about 20 low speed centrifugal compressors may be required. In a high temperature alumina refinery where waste vent vapors are compressed at about 100 to 300 ℃, about 15 low pressure compressors are required.
In one form of the application, the water vapor from the flash train is less than 80 ℃.
In one form of the application, the step of compressing the captured water vapor is repeated to obtain the desired water vapor condensation temperature.
In one form of the application, the step of compressing the captured water vapor is performed by mechanical vapor recompression. Advantageously, mechanical vapor recompression reduces reliance on fossil fuel generated heat sources to provide high condensing temperature vapor.
Mechanical vapor compression may be performed by a centrifugal compressor, an axial compressor, or a turbo compressor. Centrifugal compressors can be classified as either high-speed or low-speed compressors. Low speed centrifugal compressors are typically around 3300 rpm. High speed centrifugal compressors typically operate at 6000rpm or higher. High speed compressors generally provide a higher compression ratio.
In one form of the application, a plurality of mechanical vapor compressors in series is provided wherein compressed vapor from a first compressor in series is passed through a second compressor for further compression. This process may be repeated until the vapor is at the desired condensing temperature.
In one form of the application, the captured water vapor is compressed in an electric compressor, wherein the electrical energy has less than 0.5t CO 2e Carbon strength of/MWhr.
In one form of the application, the electrical energy has less than 0.4t CO 2e Carbon strength of/MWhr. In an alternative form of the application, the electrical energy has less than 0.3t CO 2e Carbon strength of/MWhr. In an alternative form of the application, the electrical energy has less than 0.2tCO 2e Carbon strength of/MWhr. In an alternative form of the application, the electrical energy has less than 0.1t CO 2e Carbon strength of/MWhr.
In one form of the application, the electrical energy is generated from a renewable energy source.
In one form of the application, the electrical energy is generated from a zero carbon source (e.g., hydrogen or nuclear energy).
In one form of the application, the electrical energy is stored in the battery after generation and prior to use.
The method of the present application may comprise the step of removing particulate matter from the captured water vapour prior to the step of compressing the captured water vapour.
Particulate matter may wear the impeller of the high-speed vapor compressor. This can be addressed by using steam cleaning methods, such as demisters, scrubbers, and/or cyclones, optionally installed in an in-line cleaning system, utilizing caustic solution to dissolve gibbsite scale. Such an in-line cleaning system may be continuous or intermittent.
The water vapor may contain corrosive droplets, water droplets, and mist, which may include small solid matter adhering to the droplets.
It should be appreciated that different sources of water vapor may contain different particulate matter. For example, the water vapor from leaching may comprise, inter alia, bauxite residue, unreleased bauxite; the water vapor from precipitation may contain hydrates and the like; the water vapor from the spent liquor may comprise fine alumina, scale products, etc., while the water vapor from the calcination may comprise alumina, etc.
Advantageously, the present application can eliminate the need for alumina refineries to rely on fossil fuel generated heat sources.
Drawings
Other features of the application are more fully described in the following description of several non-limiting embodiments of the application. The description is included for the purpose of illustrating the application only. And should not be construed as limiting the broad inventive disclosure, disclosure or description of the application as set forth above. The description is made with reference to the accompanying drawings, in which:
FIG. 1 is a schematic flow diagram showing how a method according to an embodiment of the application may be used;
FIG. 2 is a schematic flow diagram showing how a method according to an embodiment of the application may be used;
FIG. 3 is a schematic flow chart diagram showing how a method according to an embodiment of the application may be used;
FIG. 4 is a schematic flow chart showing how a method according to an embodiment of the application may be used;
FIG. 5 is a schematic flow chart diagram showing how a method according to an embodiment of the application may be used;
FIG. 6 is a schematic flow chart diagram showing how a method according to an embodiment of the application may be used;
FIG. 7 is a schematic flow chart diagram showing how a method according to an embodiment of the application may be used;
FIG. 8 is a schematic flow chart diagram showing how a method according to an embodiment of the application may be used; and
fig. 9 is a schematic flow chart diagram showing how a method according to an embodiment of the application may be used.
Detailed Description
Those skilled in the art will recognize that the application described herein may be varied and modified from those specifically described. It is to be understood that the application includes all such variations and modifications. The application also includes all of the steps, features, compositions and compounds referred to or indicated in the specification, individually or collectively, and any and all combinations or any two or more of said steps or features.
FIG. 1 shows a flow diagram of an alumina refinery employing low digestion temperatures in the range of 145 ℃ to 190 ℃. A high temperature digestion refinery in the range of 191 ℃ to 290 ℃ is the same as a low temperature digestion refinery but with more flash stages to achieve the same export liquid temperature. Some refineries heat bauxite slurry and liquid in a heat exchanger, while some refineries heat bauxite slurry and liquid separately. The type of dissolution does not change the application of the application; however, higher compressor outlet pressures are required to achieve higher digestion temperatures.
The ground bauxite 12 is fed with a caustic solution to a digester 14 and digested in a known manner at 145 to 190 ℃. A green liquid (16) is fed to a series of flash vessels (18) to gradually reduce the temperature and pressure. Four flash vessels in series are depicted in fig. 1. It will be appreciated that in practice the number of flash stages required will depend on the dissolution temperature. The raw liquid 20 leaving the final flash vessel 24 (discharge vessel) is near atmospheric pressure and at a temperature of about 110 ℃. Flash steam 26 from each flash vessel is used to heat a corresponding heater (see below). Excess steam 28 from the discharge vessel 24 cannot be utilized due to insufficient condensing capacity in its associated heater.
The flashed green liquor 20 is sent to a clarification stage 30 during which it is cooled to below boiling point, and then it enters a heat exchange stage 32 to further reduce the temperature. The liquid enters the 34 heat exchange stage at about 103 c and exits 36 at about 80 c. The heat exchange stage 32 also includes a series of flash vessels 38. Four flash vessels in series are depicted in fig. 1. It should be understood that in practice, fewer or more flash vessels may be used.
The liquid leaving 36 the heat exchange stage 32 has a temperature of about 80 c and enters the precipitation stage 40 to precipitate aluminum hydroxide. The liquid passes through a series of precipitators in which the temperature of the liquid gradually decreases. This may be achieved by liquid/liquid heat exchangers, e.g. plate heat exchangers 42, 44, two shown in fig. 1, but in practice more or fewer may be used. The cooling water 46 is used to cool the final heat exchanger 34.
Aluminum hydroxide is precipitated from the cooled liquor in precipitation loop 40 and solids (not shown) are removed to provide a reject 48. The temperature of the spent liquor 48 is about 60 deg.c, which is recycled to dissolve additional bauxite. The temperature of the waste liquid 48 must be raised to the desired digestion temperature by a number of heating stages prior to recycling. It should be appreciated that different alumina refineries may operate different numbers or different types of heating stages. However, all alumina refineries recycle the spent liquor and must raise its temperature. The first stage shown in fig. 1 is a heat exchange stage 32. Flash steam 50 from flash vessel 38 in heat exchange stage 32 is used to heat a corresponding heater 52. The temperature of the effluent 48 entering the heat exchange stage 32 is about 62 c and exits 54 at about 83 c. Importantly, there is a temperature difference of about 20 ℃ between the raw liquor 34 entering the heat exchange stage and the waste liquor 54 exiting the heat exchange stage 32. There is also a temperature difference of about 20 c between the raw liquor 36 leaving the heat exchange stage and the waste liquor 48 entering the heat exchange stage.
The effluent 54 exiting the heat exchange stage is sent to an evaporation stage 60 to increase its caustic content prior to recycling to the digestion 14, as is known in the art. The evaporation stage 60 also includes a series of heaters 62 and flash vessels 64. Their interrelationships are the same as described above for the digestion vent stage 18 and the heat exchange stage 32. That is, the flash steam 66 from the flash vessel 64 is used to heat the corresponding heater 62. The last heater 68 in the evaporation stage uses a new steam source 70 to reach the desired temperature. This is the only way to heat the liquid, since the flash vapor without any flash vessel can heat the liquid to the desired condensing temperature (condensing temperature). New steam 70 is produced from fossil fuels and contributes to the carbon footprint of the refinery.
The temperature of the concentrated liquid exiting 72 the evaporation stage 60 is approximately equal to the temperature of the liquid entering the evaporation loop 60 and enters the final heater 80 to reach the temperature required to dissolve additional bauxite. The final heater 80 heats the liquid as described above. Flash steam 28 from flash vessel 24 is used to heat a corresponding heater 82.
The flash vapor 84 from the first flash vessel 86 can only heat the liquid to a temperature about 25 c below the digestion temperature. The new vapor 88 must be relied upon to heat the liquid in the final heater 90 and reach the desired dissolution temperature. The use of fossil fuels to generate new steam 88 consumes energy and contributes to the carbon footprint of the refinery. The final liquid 92 is at a temperature of about 160 ℃ (for low temperature refineries) and enters the digester 14. It should be appreciated that for high temperature refineries, a large number of heaters and corresponding flash vessels are required.
In some refineries, the reject 48 is sent directly to the evaporation stage 60 rather than the heat exchange stage 32, and the evaporator feed 54 enters the coldest heater 94 and exits the final flash vessel 48.
The present application can be used in both existing refineries and new refineries as described above. It should be appreciated that the use of the present application in a new refinery may provide greater flexibility than retrofitting the present application in an existing refinery. In the former case, the introduction of the present application may present chemical and thermodynamic even spatial limitations.
FIG. 2 shows a flow chart illustrating how the present application may be used in the design of a new refinery. A set of mechanical vapor recompressors 100 are installed to compress vapor from flash vessel discharge 28. Although only one compressor is depicted in fig. 2, a series of compressors will actually be used. The compressors compress water vapor and, for a typical low speed centrifugal compressor, each provides a temperature rise of about 8-15 ℃. The vapor 102 exiting the last compressor may be sent to a live heater 90 or a penultimate heater 91. During some digestion, the vapor 102 exiting the last compressor may be directed to a digester.
Alternatively, the steam may be compressed to a lower condensing temperature and directed to the heater prior to the heater 90 to save compressor capital and operating costs.
The eluted liquid 20 is sent for clarification as described above. The clarified liquid 34 at about 103 ℃ is sent to a heat exchange stage, in which case the heat exchange stage uses a liquid/liquid heat exchanger 104 to cool the liquid instead of liquid flash evaporation. The cooled liquid 36 is sent to precipitation as described above. In fig. 2, the precipitation stage comprises a series of precipitators. There are one or more cooling stages in the precipitate in which waste heat is generated. In this example, one or more flash vessels 106 (only one shown in fig. 2) in series flash the liquid, releasing cooled water vapor. The water vapor 108 (which would not otherwise be utilized) passes through a series of mechanical vapor compressors 110 to raise its condensing temperature. The water vapor 112 leaving the last compressor is sent to the last heating stage 90 directed to the effluent of digestion. In this way, the ability to heat the waste stream to the digestion temperature is facilitated by recovering the energy available in the process and reducing or eliminating the need to provide additional boiler generated steam.
Fig. 3 depicts how the present application may be used in an evaporation loop 60 of an existing alumina refinery. A series of ten heaters 62 and ten flash vessels 64 are depicted, but it should be understood that a greater or lesser number may be used depending on the requirements of the refinery. Alumina refinery flash systems typically consist of 5 to 12 heating stages followed by the same number of flash stages. The final heating stage 68 typically uses fresh steam 70 in a low temperature digestion refinery and low pressure steam from the digestion flash vessel in a high temperature digestion refinery. The final heating stage typically provides a temperature increase of 18 ℃ to 25 ℃. The final flash stage 67 is typically a barometric flash stage in which the vapor is condensed with cooling water 69 (see fig. 1). The temperature drop is typically, but not always, about the same as in the last heating stage. The condensing temperature in the final flash stage 67 is typically about 50 ℃ and is controlled by the cooling water circuit.
The vapor stream 120 from the final flash vessel 67 is sent to a series of mechanical vapor compressors 122. The condensing temperature of the steam 124 from the last compressor is about 170 deg.c for heating the last heater 68, thereby reducing or eliminating the need to provide additional boiler generated steam 70 at this portion of the refinery.
In contrast to fig. 1, a cooling tower 69 is not necessary. The water vapor 120 leaving the final flash vessel 67 is typically not used and treated by the cooling tower 69, but is sent to a set of mechanical vapor recompressors 120 (only one shown). The water vapor leaving the last compressor is at the new vapor pressure and may actually exceed the requirements for heating the last heater. It is expected that about 90% of the water vapor 126 will be used to heat the final heater 68, with the remaining 10% being recycled elsewhere in the refinery 128. The recycled vapor may need to be further compressed.
The application is equally applicable to other locations in the bayer circuit where steam from a boiler is used, said locations being characterized by having a heat input at 130 ℃ or higher and a waste heat rejection at 70 ℃ or lower. The application is also applicable to evaporators by which waste heat vapor can be recovered from the cold end, compressed and used at the hot end.
Fig. 4 depicts how the present application may be used in the vaporization circuit 60 of an existing alumina refinery, with some optimization relative to the embodiment shown in fig. 3.
By inputting and outputting vapor to each stage within the compressor train, the compressor train can be optimized to minimize capital and operating costs. For example, compressed water vapor may be output from an intermediate stage of the compressor train for heating tasks requiring only a lower final temperature, such as caustic washing tasks, caustic alkalization tasks, and oxalate seed heating.
As shown in fig. 4, the present application allows for the use of at least one additional heating stage 130 prior to the last heater 68, further minimizing capital and operating costs.
The present application also allows for the use of at least one additional flash vessel 132 prior to the last flash vessel 67, thereby further minimizing capital and operating costs.
By taking vapor from the penultimate flash stage 132, the vapor flow required to be compressed 120 in the final stage is reduced, thereby saving power and ultimately reducing carbon emissions while maintaining the same final stage compressor output conditions.
The evaporator loop may produce plant steam that is over-required. Plant steam may be exported or imported to balance the steam requirements. The evaporators typically used in refineries feed at the coldest heater and exit from the last flash vessel, however, many evaporators feed partway up the heater train and exit partway up the heater train, just prior to the inlet.
Fig. 5 depicts how the present application may be retrofitted into an existing alumina refinery at precipitation stage 40. Precipitation systems typically require cooling, wherein energy is wasted before the precipitator or en route down the precipitator. The temperature drop is typically about 20 ℃. There are typically one or more cooling stages within the bank of settler rows. Cooling is typically performed by liquid slurry/liquid heat exchange as shown in fig. 1.
In this embodiment, the final heat exchanger 44 and cooling tower 46 (see FIG. 1) are replaced by at least one flash vessel 106 in series, as previously described. The water vapor 108 from the at least one flash vessel 106 is compressed in a set of mechanical vapor compressors 110 and used elsewhere in the refinery.
FIG. 6 depicts other ways in which the application may be implemented. As an alternative to fig. 5, the cooling water 142 loop may be flashed in multiple flash vessels to recover waste heat, which is then compressed 144.
Cooling by liquid-liquid heat exchange 150 between digestion and precipitation is known to increase precipitation yield, but the approach temperature of the heat exchanger is typically limited to greater than 18 ℃ to avoid excessive vapor emissions. An extension of the present application is to use liquid-liquid heat exchange at a smaller approach temperature to increase the amount of vapor vented, as shown in fig. 7. This may also be enhanced by including heat recovery from the condensate and/or calcined alumina cooler to achieve lower approach temperatures and thereby obtain additional exhaust vapors.
If sufficient heat is recovered before the digestion vent heater, the digestion vent heater may no longer be needed.
With a multi-stage vapor compressor, the steam can be extracted for use in various facilities of the refinery without altering the energy balance within the flash train set, as shown in FIG. 8. It is now possible to extract vapor from the flash train, but this can disrupt the temperature distribution down the flash train, reducing efficiency. Extracting vapor at a pressure that best matches downstream facility requirements reduces the capital investment and compression operating costs of the compressor. As described in the vaporization optimization, one or more additional heaters may be used immediately before the last heater 90 (utilizing plant steam), with steam supplied from the intermediate compressor 160, to reduce the capital investment and compression operating costs of the compressor.
As described above, the digestion vent heater 162 may no longer be needed. The reconfiguration of the heater array may use additional heaters 164 before the last heater 90 heater.
As shown in FIG. 9, the present application may use an upstream component of the heat recovery of the calciner 170 to produce hot water. This heat recovery process is described in australian patent 2009225953, the contents of which are incorporated herein by reference. Water 172 from scrubber 174 is flashed down in one or more flash tanks 176 to produce water vapor 178, and water vapor 178 is then compressed 180 to produce plant steam 182, as shown in fig. 9. As previously mentioned, water may be flashed in one or more stages to minimize MVR capital and operating costs. The warm water 184 is also recovered.
The sum of all vapor sources in a refinery may exceed the amount of vapor that needs to be compressed to provide sufficient plant vapor for the refinery. If excess, cooling water may be applied to the final stage flash vessel (typically the in-vapor pressure flash vessel) to remove excess waste heat vapor. Alternatively, the refinery may be configured to not capture all of the waste heat vapors and achieve refinery equilibrium by an alternative heat source (most likely a boiler).
The power load modulation capability is important for managing the cost of power, especially in high renewable energy grids. The compressor consumes a high load and if the load is properly modulated, a significant cost savings can be realized. Load modulation type:
a. each time the load is reduced (partially or fully shut down) for 5 minutes to 4 hours to avoid peak load costs. Peak load fees are typically charged when the grid approaches peak power consumption.
b. Auxiliary service "spin reserve" by drastically reducing load based on grid low frequency signals "
Participate in.
The high inertia of the mvr compressor will allow "boost emergency services" to participate in short term events of up to around 15 seconds. For these events, the electrical load increases or at most 15 seconds to help maintain grid stability.
An outline of the calculations that demonstrate the advantages of the present application is given below.
a. As a basic scenario, a standard alumina refinery operating with natural gas to produce steam under the conditions of fig. 1 produces 0.55 tons of CO 2e Per ton of alumina.
b. At the current 0.7 ton CO 2e The embodiment of FIG. 2 operating on the power grid of/MWhr will produce 0.50 ton CO 2e Per ton of alumina.
c. The embodiment of fig. 2 operating on a zero-carbon grid will produce 0.15 tons of CO 2e /
Ton of alumina.
Claims (24)
1. A method for controlling carbon output of an alumina refinery, the method comprising the steps of:
capturing water vapor from a flash train in a refinery;
compressing the captured water vapor; and
at least a portion of the energy in the captured water vapor is utilized to heat a process stream within the alumina refinery.
2. The method for controlling carbon output of an alumina refinery of claim 1, wherein the water vapor is captured from flash vessels in the flash train set.
3. The method for controlling carbon output of an alumina refinery of claim 1, wherein the flash train set comprises a plurality of flash vessels.
4. The method for controlling carbon output of an alumina refinery according to any one of the preceding claims, comprising the additional step of feeding a heated process stream to the flash train set.
5. The method for controlling carbon output of an alumina refinery of claim 4, wherein the step of feeding a heated process stream to a flash train set comprises feeding at least a portion of the heated process stream to the flash train set.
6. The method for controlling carbon output of an alumina refinery according to any one of the preceding claims, wherein the step of heating the process stream comprises passing the process stream through at least one heater in a bank of heaters.
7. The method for controlling carbon output of an alumina refinery of claim 6, wherein the heater train set precedes the flash train set.
8. The method for controlling carbon output of an alumina refinery of any one of the preceding claims, wherein the flash train set is a heat recovery flash train set.
9. The method for controlling carbon output of an alumina refinery of any one of the preceding claims, wherein the flash train set comprises at least two flash vessels.
10. The method for controlling carbon output of an alumina refinery according to any one of the preceding claims, wherein the water vapor is from the last and/or penultimate flash vessel in the flash train set.
11. The method for controlling carbon output of an alumina refinery according to any one of the preceding claims, wherein the process stream is from the last and/or penultimate heater in the train set.
12. The method for controlling carbon output of an alumina refinery according to any one of claims 6-11, wherein the heater train group comprises one or more heaters.
13. The method for controlling carbon output of an alumina refinery according to any one of the preceding claims, wherein the flash train group forms part of a digestion loop, a heat exchange loop, an evaporation loop, a precipitation loop, or a calcination heat recovery system in an alumina refinery.
14. The method of controlling carbon output of an alumina refinery according to any one of the preceding claims, wherein said method comprises the further steps of:
heating the fluid stream with calciner flue gas to provide a heated fluid stream;
passing the heated fluid stream through a flash train and forming water vapor;
15. the method for controlling carbon export of an alumina refinery according to any of the preceding claims, comprising the further step of exporting excess compressed water vapor from the flash train.
16. The method of controlling carbon output of an alumina refinery of any one of the preceding claims, wherein the water vapor from the flash train group is below 80 ℃.
17. The method for controlling carbon output of an alumina refinery according to any one of the preceding claims, wherein said step of compressing captured water vapor is repeated to obtain a desired water vapor condensation temperature.
18. The method for controlling carbon output of an alumina refinery according to any one of the preceding claims, wherein said step of compressing captured water vapor is performed by mechanical vapor recompression.
19. The method for controlling carbon output of an alumina refinery according to any of the preceding claims, wherein a plurality of mechanical vapor compressors are provided in series, wherein compressed vapor from a first compressor in series is passed through a second compressor for further compression.
20. The method for controlling carbon output of an alumina refinery according to any of the preceding claims, wherein the captured water vapor is compressed in an electric compressor, wherein the electric energy has less than 0.5t CO 2e Carbon strength of/MWhr.
21. The method for controlling carbon output of an alumina refinery of claim 20, wherein said electrical energy is produced from a renewable energy source.
22. The method for controlling carbon output of an alumina refinery of claim 20, wherein said electrical energy is produced from zero carbon energy sources such as hydrogen or nuclear energy.
23. The method for controlling carbon output of an alumina refinery of any one of claims 20-22, wherein the electrical energy is stored in a battery after production and before use.
24. The method for controlling carbon output of an alumina refinery according to any one of the preceding claims, comprising an additional step of removing particulate matter from the captured water vapor prior to the step of compressing the captured water vapor.
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU2020902780 | 2020-08-06 | ||
| AU2021900240 | 2021-02-03 | ||
| AU2021901201A AU2021901201A0 (en) | 2021-04-22 | Method For Carbon Reduction | |
| AU2021901201 | 2021-04-22 | ||
| PCT/AU2021/050855 WO2022027100A1 (en) | 2020-08-06 | 2021-08-05 | Method for carbon reduction |
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| CN116601115A true CN116601115A (en) | 2023-08-15 |
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