BR112014021588B1 - high temperature etching process for etching a bayer process liquor - Google Patents

Abstract

HIGH TEMPERATURE CAUSTICATION PROCESS FOR CAUSTICATION OF A BAYER PROCESS ALCOHOLIC DRINK A high temperature causticization process for the causticization of a Bayer process alcoholic beverage is disclosed. The process comprises the steps of: a) adding a quantity of a causticizing agent to the Bayer process alcoholic beverage in a reactor vessel operating at a target reaction pressure for a given target reaction temperature, b) allowing the causticizing agent to reacting with the Bayer process alcoholic beverage for a sufficient residence time to produce a reaction sludge comprising an amount of reaction solids in an etched Bayer alcoholic beverage; and, c) subjecting the reaction sludge to the solid / liquid separation at a target separation temperature to produce a separate stream of reaction solids and a stream of clarified etched Bayer alcoholic beverage product. The process is characterized by the fact that the target reaction temperature is not less than 115 ° C and the target separation temperature is not less than 115 ° C.

Description

FIELD OF THE INVENTION

[001] The present invention relates to a process and system for the etching of a Bayer liquor.

BACKGROUND OF THE INVENTION

[002] In the Bayer process for the production of alumina, a concentrated sodium aluminate solution is produced by grinding and digesting bauxite in a caustic soda solution, usually under conditions of elevated temperature and pressure. After mud clarification, the concentrated sodium aluminate solution is cooled and seeded with gibsite crystals, causing gibsite to crystallize from the solution. Gibsite is calcined to produce alumina, while depleted (or "spent") liquor is recycled to digest more bauxite.

[003] During digestion, part of the caustic is consumed in undesirable reactions with impurities inside the bauxite, reducing the productivity of the liquor. One of the most significant of these reactions results in the formation of sodium carbonate, resulting from the dissolution of inorganic carbonates within the present mineral phases, or from the thermal and oxidative degradation reactions of organic compounds. If not controlled, with each cycle of the liquor through the process the concentration of sodium carbonate would continue to rise, with a corresponding reduction in the liquor's ability to digest gibsite or bauxite boehmite. Carbonation also occurs due to the CO2 atmosphere reacting with diluted liquor in the bauxite residue disposal area that is returned to the alumina refinery circuit.

[004] The most common technique for controlling the concentration of soda ash in Bayer process liqueurs is etched using quicklime or lime. This process can be carried out within the digestion circuit itself (by introducing lime with bauxite in a process referred to in the art as 'internal caustication'), or, more commonly, as a side flow process in a referred process in the technique as 'outside caustication'. The addition of Cal directly with bauxite is not common, except where Cal is needed to control other impurities (such as titanium or phosphorus), because too concentrated liquors contribute to poor efficiency. Unless the temperature is very high during caustication, most lime suffers side effects with the aluminate in solution to produce species of calcium aluminate, particularly tricalcium aluminate (TCA, often also referred to as C3A in the cement industry). In the most prevalent side stream or 'external caustication', a diluted flow of liquor (usually taken from one of the sludge washing stages) is reacted with a lime suspension, usually at a temperature that is close to, but below, the boiling point atmospheric combination liquor. Alternatively, lime sludge is sometimes added directly to the sludge washer. The amount of sodium carbonate converted and the efficiency of using lime are dependent on many variables, but in most refineries, the efficiency of lime is in the vicinity of 50 to 70%.

[005] The caustication reaction of pure mixed solutions of sodium carbonate and sodium hydroxide with Lime is quite simple. The final concentration of hydroxide and carbonate ions is a function of the activities of the various ionic species present, in equilibrium with the solid phases of calcium hydroxide and calcium carbonate. The reaction can be described by the following equation:

[006] When the reaction in equation (1) takes place in a Bayer process liquor, it is advantageous if the sodium carbonate that is present as an impurity in the Bayer process liquor reacts with calcium hydroxide, the calcium carbonate form (usually in the form of calcite). The liquor from the Bayer process is said to be 'causticada' because the reaction of (1) above results in the generation of sodium hydroxide (also known in the art as 'caustic'). Real reaction occurs when lime is added to a Bayer process liqueur is complicated by competing side effects. More specifically, International Patent Publication number W00018684 (PCT / AU1999 / 00757) co-owned by Rosenberg, disclosed for the first time, that when calcium hydroxide (Ca (OH) 2) is added to a Bayer process liquor , reacting to form an unstable intermediate compound, known as 'hydrocalumite' (nominally of the formula [Ca2AI (OH) 6] 2. 14CO3.Oh.514H2O) before forming either (i) calcium carbonate (CaCO3) or (ii) tricalcium aluminate ('TCA'). These two reaction pathways available, the formation of TCA is undesirable, because it consumes alumina and lime without removing carbonate.

[007] In the alumina industry it is common to refer to the level of carbonate impurities in a Bayer liquor in terms of the proportion of caustic, or C / s'. Typically, the C / S ratio of the concentrated liquor stream in many alumina refineries is in the range of 0.8 to 0.85. Higher C / S ratios are difficult to achieve, because caustication processes currently in use are unable to fully remove all the sodium carbonate in the liquor fed to them economically. For example, liquor with an S concentration of 135 g / L will normally only etch at a C / S ratio of about 0.890. This limitation arises because the traditional implementation of the lime caustication reaction is controlled by a number of complex equilibria, including a concurrent reaction involving the aluminate ion in which TCA is formed.

[008] Australian Patent Application number 2004224944 (Roach et al.) Discloses a process for etching alkaline solutions at 140 ° C, using lime. The process results in a rapid increase in the proportion TC / TA liquor following with proportion TC / TA decreases with the increase of the residence time. The TC / TA ratio referred to by Roach is equivalent to the C / S ratio terminology used in this patent specification. The rate of decrease in the C / S ratio from the point of maximum gain increases with increasing lime load and increasing temperature. The etched Bayer process solution is cooled before being directed to a dedicated solid separation stage to remove lime from solid waste and returned to the Bayer circuit. However, while Roach et al advocate a residence time of less than 15 minutes at 140 ° C, Roach et al give no information as to how to avoid degradation of the C / S ratio during the cooling process before separation.

[009] It is an objective of the present invention to at least partially overcome the above problems associated with the state of the art, or by providing an alternative to the same.

SUMMARY OF THE INVENTION

[0010] In accordance with a first aspect of the present invention, a high temperature etching process is provided for the etching of a Bayer process liquor, the process comprising the steps of: a) adding an amount of etching agent to the liquor of Bayer process in a reactor vessel operating at a target reaction pressure for a given target reaction temperature; b) allowing the etching agent to react with the Bayer process liquor for a sufficient residence time to produce a reaction sludge comprising an amount of reaction solids in an etched Bayer liquor; and, c) subjecting the reaction sludge to the solid / liquid separation at a target separation temperature to produce a separate stream of reaction solids and a stream of clarified etched Bayer liquor;

[0011] the process characterized by the fact that the target reaction temperature is not less than 115 ° C and the target separation temperature is not less than 115 ° C.

[0012] In one form, said target separation temperature is at or above the target reaction temperature. In one form, said target separation temperature is no more than 5 ° C or no less than 10 ° C or no less than 15 ° C or no less than 20 ° C below the target reaction temperature. In one form, the target reaction temperature is between 115 ° C and 300 ° C or between 115 ° C and 180 ° C or between 120 ° C and 155 ° C. In one form, the sufficient residence time of step b) is less than 1 minute, less than 3 minutes, less than 5 minutes, less than 10 minutes, less than 15 minutes or less than 20 minutes. In one form, step c) is conducted in a solid / liquid separator and the process additionally comprises retaining the reaction sludge in the solid / liquid separator for a period of time not exceeding one hour, not exceeding 45 minutes, or not exceeding 30 minutes. In one form, the solid / liquid separator is a pressure decanter, a pressure filter, a cyclone, or a centrifuge.

[0013] In one form, the ratio of total caustic concentration to total alkali concentration of the Bayer process liquor, when expressed in grams of sodium carbonate per liter of solution, exceeds 0.9, exceeds 0.92, exceeds 0.94 or exceeds 0.95 after adding the amount of etching agent. In one form, the causticizing agent is one or both of the lime or hydrocalumite. In one way, the caustic agent is lime extinguished. Slaked lime can be formed by adding lime to the water or adding lime to a Bayer process liqueur. In one form, the Bayer process liquor has an initial total alkali concentration of between 40 and 250 grams or between 80 and 160 grams per liter or between 130 and 170 grams per liter expresses the grams of sodium carbonate per liter of solution. In one form, the Bayer process liquor has an A / C ratio of between 0.2 and 0.95, or between 0.3 and 0.8, or preferably greater than 0.55.

[0014] In one form, the process liquor Bayer is preheated before step a). In one form, the Bayer process liquor is preheated to the target reaction temperature in a heating circuit, the heating circuit comprising one or more heating stages. The heating stage can comprise direct or indirect steam injection. In one form, the clarified etched liquor is cooled after step c) by countercurrent heat exchange with the Bayer process liquor. In one form, the Bayer process liquor is either an exhausted Bayer liquor or a diluted Bayer liquor. The Bayer process liquor can be an overflow washer liquor.

[0015] In one form, step a) is performed in the presence of a TCA inhibitor. In one form, the TCA inhibitor is an anionic organic surfactant. In one form, the anionic organic surfactant is selected from the group comprising: an anionic homopolymer, an anionic copolymer, a polyacrylic acid, a polymer bearing hydroxamate functional group, a hydroxamic acid, a humic acid, a tannic acid, a lignosulfonate, a fatty acid, a sulfonated carboxylic acid, a carboxylic acid, and a polyhydroxy carboxylic acid.

[0016] In accordance with a second aspect of the present invention, a high temperature etching process is provided for the etching of a Bayer process liquor, the process comprising the steps of: a) adding an amount of etching agent to the liquor of Bayer process in a reactor vessel operating at a target reaction pressure for a given target reaction temperature; b) allowing the etching agent to react with the Bayer process liquor for a sufficient residence time to produce a reaction sludge comprising an amount of reaction solids in an etched Bayer liquor; and, c) subjecting the reaction sludge to the solid / liquid separation at a target separation temperature to produce a separate stream of reaction solids and a stream of clarified etched Bayer liquor;

[0017] the process characterized by the fact that the target separation temperature is at or above the target reaction temperature and the target reaction temperature is greater than the atmospheric boiling point of the Bayer process liquor.

[0018] In one form, the target reaction temperature is between 115 ° C and 300 ° C or between 115 ° C and 180 ° C or between 120 ° C and 155 ° C.

[0019] In a form, the sufficient residence time of step b) is less than 1 minute, less than 3 minutes, less than 5 minutes, less than 10 minutes, less than 15 minutes or less than 20 minutes. In one form, step c) is conducted in a solid / liquid separator and the process additionally comprises retaining the reaction sludge in the solid / liquid separator for a period of time not exceeding one hour, not exceeding 45 minutes, or not exceeding 30 minutes. In one form, the solid / liquid separator is a pressure decanter, a pressure filter, a cyclone, or a centrifuge.

[0020] In one form, the ratio of total caustic concentration to total alkali concentration of the Bayer process liquor, when expressed in grams of sodium carbonate per liter of solution, exceeds 0.9, exceeds 0.92, exceeds 0.94 or exceeds 0.95 after adding the amount of etching agent. In one form, the causticizing agent is one or both of the lime or hydrocalumite. In one way, the caustic agent is lime extinguished. Slaked lime can be formed by adding lime to the water or adding lime to a Bayer process liqueur. In one form, the Bayer process liquor has an initial total alkali concentration of between 40 and 250 grams or between 80 and 160 grams per liter or between 130 and 170 grams per liter expresses the grams of sodium carbonate per liter of solution. In one form, the Bayer process liquor has an A / C ratio of between 0.2 and 0.95, or between 0.3 and 0.8, or preferably greater than 0.55.

[0021] In one form, the Bayer process liquor is preheated before step a). In one form, the Bayer process liquor is preheated to the target reaction temperature in a heating circuit, the heating circuit comprising one or more heating stages. The heating stage can comprise direct or indirect steam injection. In one form, the clarified etched liquor is cooled after step c) by countercurrent heat exchange with the Bayer process liquor. In one form, the Bayer process liquor is either an exhausted Bayer liquor or a diluted Bayer liquor. The Bayer process liquor can be an overflow washer liquor.

[0022] In one form, step a) is performed in the presence of a TCA inhibitor. In one form, the TCA inhibitor is an anionic organic surfactant. In one form, the anionic organic surfactant is selected from the group comprising: an anionic homopolymer, an anionic copolymer, a polyacrylic acid, a polymer bearing hydroxamate functional group, a hydroxamic acid, a humic acid, a tannic acid, a lignosulfonate, a fatty acid, a sulfonated carboxylic acid, a carboxylic acid, and a polyhydroxy carboxylic acid.

[0023] According to a third aspect of the present invention, a high temperature etching process is provided for the etching of a Bayer process liquor, the process comprising the steps of: a) adding an amount of etching agent to the liquor of Bayer process in a reactor vessel operating at a target reaction pressure for a given target reaction temperature, said target reaction temperature is greater than the atmospheric boiling point of the Bayer process liquor; b) allowing the etching agent to react with the Bayer process liquor for a sufficient residence time to produce a reaction sludge comprising an amount of reaction solids in an etched Bayer liquor; and, c) subjecting the reaction sludge to the solid / liquid separation at a target separation temperature to produce a separate stream of reaction solids and a stream of clarified etched Bayer liquor;

[0024] the process characterized by the fact that the target separation temperature is not more than 5 ° C or not less than 10 ° C or not less than 15 ° C or not less than 20 ° C below temperature target reaction.

[0025] In one form, the target reaction temperature is between 115 ° C and 300 ° C or between 115 ° C and 180 ° C or between 120 ° C and 155 ° C.

[0026] In a form, the sufficient residence time of step b) is less than 1 minute, less than 3 minutes, less than 5 minutes, less than 10 minutes, less than 15 minutes or less than 20 minutes. In one form, step c) is conducted in a solid / liquid separator and the process additionally comprises retaining the reaction sludge in the solid / liquid separator for a period of time not exceeding one hour, not exceeding 45 minutes, or not exceeding 30 minutes. In one form, the solid / liquid separator is a pressure decanter, a pressure filter, a cyclone, or a centrifuge.

[0027] In one form, the ratio of total caustic concentration to total alkali concentration of the Bayer process liquor, when expressed in grams of sodium carbonate per liter of solution, exceeds 0.9, exceeds 0.92, exceeds 0.94 or exceeds 0.95 after adding the amount of etching agent. In one form, the causticizing agent is one or both of the lime or hydrocalumite. In one way, the caustic agent is lime extinguished. Slaked lime can be formed by adding lime to the water or adding lime to a Bayer process liqueur. In one form, the Bayer process liquor has an initial total alkali concentration of between 40 and 250 grams or between 80 and 160 grams per liter or between 130 and 170 grams per liter expresses the grams of sodium carbonate per liter of solution. In one form, the Bayer process liquor has an A / C ratio of between 0.2 and 0.95, or between 0.3 and 0.8, or preferably greater than 0.55.

[0028] In one form, the Bayer process liquor is preheated before step a). In one form, the Bayer process liquor is preheated to the target reaction temperature in a heating circuit, the heating circuit comprising one or more heating stages. The heating stage can comprise direct or indirect steam injection. In one form, the clarified etched liquor is cooled after step c) by countercurrent heat exchange with the Bayer process liquor. In one form, the Bayer process liquor is either an exhausted Bayer liquor or a diluted Bayer liquor. The Bayer process liquor can be an overflow washer liquor.

[0029] In one form, step a) is performed in the presence of a TCA inhibitor. In one form, the TCA inhibitor is an anionic organic surfactant. In one form, the anionic organic surfactant is selected from the group comprising: an anionic homopolymer, an anionic copolymer, a polyacrylic acid, a polymer bearing hydroxamate functional group, a hydroxamic acid, a humic acid, a tannic acid, a lignosulfonate, a fatty acid, a sulfonated carboxylic acid, a carboxylic acid, and a polyhydroxy carboxylic acid.

[0030] According to a fourth aspect of the present invention, a causticization process is provided substantially as described in this document with reference to and as illustrated in the accompanying figures.

BRIEF DESCRIPTION OF THE FIGURES

[0031] To facilitate a more detailed understanding of the nature of the invention, various modalities of the causticisation and system improvement process will now be described in detail, by way of example only, with reference to the attached figures, in which:

[0032] Figure 1 is a conceptual flow diagram of a first embodiment of the present invention showing a basic implementation;

[0033] Figure 2 is a schematic illustration of a modality of a reactor vessel for use with the process of the present invention.

[0034] Figure 3 is a schematic illustration of an embodiment of a solid / liquid separator for use with the process of the present invention;

[0035] Figure 4 is a conceptual flow diagram of a second embodiment of the present invention including a countercurrent heating / cooling circuit;

[0036] Figure 5 is a conceptual diagram of a third embodiment of the present invention in which the causticizing agent is a hydrocalumite slurry; and,

[0037] Figure 6 is a conceptual flow diagram of a third embodiment of the present invention in which the causticizing agent is a mixture of a re-impregnated hydrocalumite sludge and a stream of lime supplement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] To facilitate a more detailed understanding of the nature of the invention, several modalities of the caustication and system improvement process will now be described in detail, by way of example only, with reference to the attached figures, in which:

[0039] Figure 1 is a conceptual flow diagram of a first embodiment of the present invention showing a basic implementation;

[0040] Figure 2 is a schematic illustration of an embodiment of a reactor vessel for use with the process of the present invention.

[0041] Figure 3 is a schematic illustration of an embodiment of a solid / liquid separator for use with the process of the present invention;

[0042] Figure 4 is a conceptual flow diagram of a second embodiment of the present invention including a countercurrent heating / cooling circuit;

[0043] Figure 5 is a conceptual diagram of a third embodiment of the present invention in which the causticizing agent is a hydrocalumite slurry; and,

[0044] Figure 6 is a conceptual flow diagram of a third embodiment of the present invention in which the causticizing agent is a mixture of a re-impregnated hydrocalumite slurry and a stream of lime supplement.

DETAILED DESCRIPTION OF PREFERENTIAL MODALITIES

[0045] Throughout this specification the various terms commonly used in the alumina industry are used. In the interests of clarity, such terms are now defined.

[0046] The term 'Bayer process alcoholic beverage' refers to a caustic sodium aluminate liquor generated by digestion of bauxite (dissolution) in a caustic soda solution at elevated temperatures and pressures. In Bayer alcoholic beverages, the main constituents are sodium aluminate and sodium hydroxide. Other impurities in the alcoholic beverage chain are present as soluble sodium salts.

[0047] The term 'A' refers to the concentration of alumina in the liquor and more specifically to the concentration of sodium aluminate in the liquor, expressed in g / L equivalent of alumina (AI2O3).

[0048] The term 'C refers to the concentration of liquor, this being the sum of the sodium hydroxide and sodium aluminate content of the liquor expressed in g / L equivalent to the concentration of sodium carbonate in caustic soda.

[0049] The term 'A / c' is, therefore, the ratio of the concentration of alumina, the concentration of caustic soda.

[0050] The term "S" refers to the concentration of sodium or, more specifically, to the sum of "C" and the actual concentration of sodium carbonate, this amount, again being expressed as the equivalent concentration g / L of sodium carbonate. Thus, the S-C (sodium concentration minus caustic soda concentration) gives the actual concentration of sodium carbonate (Na2∞3) in the liquor, in g / L.

[0051] Level of impurity of the process liquor Bayer process carbonate is expressed in terms of the caustic to soda ratio, or C / s'. A fully etched Bayer process liquor (carbonate free) will have a C / S ratio of 1.00.

[0052] The term 'exhausted Bayer process alcoholic drink' refers to a stream of liquor, after the gibsite precipitation stage and before digestion. An exhausted liquor usually has a low A / C ratio. The term 'diluted Bayer process alcoholic beverage' refers to a stream of liquor with a low S, typically less than 220g / L.

[0053] The term 'TCA' is used to refer to tricalcium aluminate, having the chemical formula of Ca3 [AI (OH) 6] 2, which is also commonly written using the formula 3CaO. AI2O3.6h2O (TCA6) or C3AH6 in the cement industry notation.

[0054] The term 'lime', used throughout this specification is a generic term used to refer to calcium oxide (CaO or "Cal") in dry form, or calcium hydroxide (5o2) in the form of a suspension of lime or the dry form of Ca (OH2 also known as 'hydrated lime'). Thus, a 'lime sludge' is produced when the lime is mixed with an erasing solution that can be any aqueous solution, usually water. In an alumina refinery, a diluted Bayer liquor can be used as a solution to extinguish due to the presence of water in such diluted Bayer alcoholic beverages.

[0055] 'Caustication' is the term used by people skilled in the art of the Bayer process to describe the carbonate process that is removed from a Bayer liquor and replaced with hydroxide through the addition of lime and precipitation of insoluble calcium carbonate.

[0056] The term 'hydrocalumite' is used throughout this specification to refer to aluminum-based double hydroxide of the form [Ca2AI (OH) 6] 2 X2 nH2O, where 'X' represents a charge-balancing anion or anions. For example, when X is carbonate, hydrocalumite may have the formula of [C «2 ^ / (C> z /) 6] 2- (ü3 or Ca2AI (OH) 6] 2. 1 / 2CO3.Oh.51 / 2H2O, depending on several factors that govern the preferential interleaving of the species, the interlayer regions are filled with a balanced load of ions and water molecules.

[0057] The term 'Lime efficiency' is defined as the percentage of available Lime that is converted to calcium carbonate during caustication. Various processes were used to calculate the efficiency of lime, including Total inorganic carbon analysis (TIC), X-ray fluorescence analysis (XRF), gravimetric thermal analysis (TGA), liquor or mass balance.

[0058] Throughout the specification, unless otherwise stated, the word "include" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a quoted integer or group of whole numbers, but not the exclusion of any other whole number or group of whole numbers.

[0059] A first embodiment of the process of the present invention will now be described with reference to the process flow chart illustrated in FIG. 1 where the process is generally designated by the reference numeral (10). A quantity of a causticizing agent (12) and a preheated Bayer process liquor (14) are mixed in a reactor vessel (16) operating at a target reaction pressure for a reaction temperature of a given destination. The causticizing agent is allowed to react with the Bayer alcoholic beverage for a sufficient residence time to produce a reaction sludge, consisting of a quantity of reaction solids in a caustic Bayer liquor. The reaction sludge subjected to solid / liquid separation to produce a separate flow from the reaction solids and a stream of clarified etched Bayer liquor product. With reference to figure 1, a solid / liquid separator (20) is prepared to receive the reaction sludge (18) and produce an overflow stream of the clarified causticized Bayer liquor (22) and a subflow stream of thickened reaction solids ( 24). The reaction solids present in the reaction sludge removed from the reactor vessel will include calcium carbonate, hydrocalumite and TCA in varying proportions, depending on the operating conditions of the reactor vessel.

[0060] The process of the present invention is characterized in that the best results are obtained when both the target separation temperature and the target reaction temperature are not less than 115 ° C. The target separation temperature can be equal to or higher at the target reaction temperature. Alternatively, the target separation temperature is less than the target separation temperature may be lower than that target reaction temperature, as long as the target separation temperature is not less than 115 ° C. Alternatively, the target separation temperature is lower that the target separation temperature provided that the temperature differential between the target separator temperature and the target reaction temperature is not greater than 5 ° C, not more than 10 ° C, or not more than 20 ° C.

[0061] Because the limit set for the target reaction temperature is greater than the atmospheric boiling point of the Bayer process liquor (typically 105 to 108 ° C), the target reaction pressure is greater than the atmospheric pressure. The reactor vessel (16) is a pressure vessel which is capable of operating at the target reaction temperature. The target reaction temperature can be in the range of 115 ° C and 300 ° C, more preferably in the range of 115 ° C and 170 ° C or more, preferably in the range of 120 ° C and 155 ° C. Using the process and the system of the present invention, reaction products are removed from the reaction slurry under pressure and temperature conditions by means of which flashing of the reaction sludge is avoided. Flashing would result in a sharp drop in temperature and an increase in S that encourages the undesirable formation of TCA. Solid / liquid separation can be performed using a pressurized decanter, a pressurized decanter, a pressurized thickener, a filter or any other suitable solid / liquid separator that is capable of operating under pressure at an elevated temperature. In this way, the reaction sludge is kept at or above the target reaction temperature after separation.

[0062] As defined above in 'foundation of the invention', International Patent Publication number W00018684 (PCT / AU1999 / 00757) co-owned by Rosenberg described the two competitor reaction pathways that can be followed to calcium hydroxide (Ca (OH) 2) is added to a Bayer process liquor. The first reaction pathway, which is desirable, leads to the formation of calcium carbonate. The second reaction route, which is undesirable because it consumes alumina, is the formation of TCA. For both the first and the second reaction path, the first compound that forms very quickly is the unstable intermediate compound, known as 'hydrocalumite'. Because there are two competing reactions taking place, there are also two pseudo competing equilibria - the first being the pseudo balance between calcite and hydrocalumite and the second being the pseudo-balance between TCA and hydrocalumite. The present invention is based in part, the realization that, for the given 'concentration, the reaction path favors the formation of calcite over TCA is favored at higher target reaction temperatures, but, in order to capitalize on this, reaction solids should be separated as quickly as possible from the reaction sludge without any significant drop in temperature to avoid reversing calcite to hydrocalumite. Without wishing to be bound by theory, the inventors found that if the reaction sludge is allowed to cool while the reaction solids are still in contact with the etched Bayer alcoholic drink, the calcite present in the reaction solids reverts to unstable hydrocalumite. This unstable hydrocalumite can then follow the second reaction pathway that results in the formation of stable, but undesirable TCA at low temperatures. Using the process and system of the present invention, the reaction products are separated out of the reaction slurry as quickly as possible and without any significant drop in temperature.

[0063] The Bayer process liquor (14) which is fed to the reactor vessel (16) is heated to a temperature that is equal to or above the target reaction temperature just before being introduced into the reactor vessel (16). For best results, there is no mixture of the preheated Bayer process liquor (14) and the etching agent (12) outside the reactor vessel (16). The causticizing agent can be heated in a similar way, before being loaded into the reactor vessel. The ratio of the Bayer process liquor to the amount of causticizing agent added will depend on the concentration of carbonate present in the Bayer process liquor. As an example, the ratio can be greater than or equal to 10: 1, 15: 1 or 20: 1, with higher percentages required for caustication dilute Bayer process alcoholic beverages and Lower proportions required if the Bayer process liquor has a high carbonate concentration. Thus, preheating the causticizing agent is less critical than preheating the Bayer process liquor and can be compensated with the Bayer process liquor at a temperature above the target reaction temperature of heating so that the target reaction temperature achieved after mixing the caustic agent with the liquor from the Bayer process.

[0064] The Bayer process liquor will have a 'S' concentration of between 40 and 250 g / L (preferably between 130 and 170 g / L or between 80 to 160g / L) and an A / C ratio of between 0.2 and 0.95, between 0.3 and 0.8 and preferably greater than 0.55. An example of a suitable causticizing agent is Cal, while an example of a suitable Bayer process liquor is a diluted Bayer liquor as a first washer overflow or a second washer overflow from a Bayer process circuit, the lime can be lime live, hydrated lime or, for best results, extinguished lime. When calcium oxide is used as a causticizing agent, an exothermic blackout reaction will occur very quickly when Cal comes in contact with the water present in the Bayer process liquor, resulting in the formation of calcium hydroxide.

[0065] The present invention is additionally based in part on the realization that, for the given concentration 'S', increasing the reaction temperature of the target increases the proportion of equilibrium C / S that can be achieved. As an example, for a 150 g / L S, the equilibrium C / S ratio when operating at a temperature of 140c is ~ 0.94 considering that at 103 ° C, the equilibrium C / S ratio it's just 0.90. The additional advantage of operating at higher reaction temperatures is the residence time to achieve this C / S rate. Using the process and system of the present invention, the formation of TCA is minimized to achieve high caustic efficiency. The side reaction to TCA can be further suppressed using an additive, as discussed in more detail below.

[0066] A personification of a suitable reactor vessel (16) for high temperature causticization is illustrated schematically in Figure 2, in the form of a vertical pressure vessel. A pipeline reactor can be used as an alternative. The reactor vessel is one of a plurality of reactor vessels arranged in parallel. Referring to Figure 2, the reactor vessel (16) generally means vertical and includes an elongated cylindrical pressure vessel wall (36) of sufficient strength and thickness to withstand the pressures, temperatures and corrosivity of the reaction slurry. The reactor vessel is provided with a plate-shaped upper end (38) and a gas inlet (42) for introducing a gas into the closed upper end (38) of the reactor vessel (16). Closed upper end of the additional reactor vessel is provided with an internal distributor (44), in the form of an internal distributor plate or an internal distributor cone, to promote rapid mixing of the causticising agent and Bayer process liquor.

[0067] In the embodiment illustrated in Figure 2, the amount of caustic agent (12) is introduced to the reactor vessel (16) through a caustic agent inlet (48), while the preheated Bayer process liquor (14 ) is introduced into the reactor vessel via a separate Bayer process beverage inlet (46). Using the process and system of the present invention, the causticizing agent and Bayer process liquor are not allowed to mix with each other until after both have been introduced into the reactor vessel. When an amount of lime is added to a preheated Bayer process liquor under the reactor vessel's operating conditions, hydrocalumite forms so quickly at the target reaction pressure and target reaction temperature that reaction solids can deposit as a scale at the place where mixing occurs first.

[0068] In the modality illustrated in Figure 2, the reactor vessel was developed specifically to overcome this scale problem. In the present embodiment, the caustic agent inlet (48) and the liquor inlet from the Bayer process (46) are provided at the closed upper end (38) of the reactor container (16). Inlet of the causticising agent (48) has a first end (50) ending outside the reactor container (16) of a second end (52) ending inside the reactor container (16) at a height that is displaced vertically a predefined distance a from the maximum height of the dispenser (44). Liquor inlet of the Bayer process (46) has a first end (56) terminating outside the reactor vessel and a second end (58) terminating within the reactor vessel. The second caustic agent inlet end (52) is coaxially aligned with the second liquor inlet end (58) of the Bayer process (46) and organized in such a way that the second inlet end (58) of Bayer process liquor (46) ends at a height within the reactor vessel that is above the height of the second caustic agent inlet end (52). In this way, the preheated Bayer process liquor discharged from the second end of the Bayer process liquor inlet forms a curtain around the amount of caustic agent being charged into the reactor container through the second end of the caustic agent inlet. This arrangement is used to minimize the scale that might otherwise occur when the etching agent first comes into contact with the liquor from the Bayer process.

[0069] In use, a non-reactive gas stream (23) is fed through the gas inlet (42) at the closed top end (38) of the reactor vessel (16) to create a gas plug (60) above the level reaction sludge bed (62). The flow rate of the nonreactive gas (23) introduced into the closed upper end (38) of the reactor vessel (16) is controlled using a first control valve (68). The second end (52) of the caustic agent inlet (50) and the second end (58) of the Bayer process liquor inlet (48) both terminating inside the gas plug (60) to minimize sizing of the caustic inlet agent (48) and the entry of Bayer process drinks (46). The gas plug (60) is used to avoid direct contact between the etching agent and the pre-heated Bayer process liquor within their respective inlets. Any suitable non-reactive gas, such as nitrogen or air, can be used to supply the reactor container buffer. Suitable non-reactive gases include air or nitrogen. The gas plug is maintained by increasing or decreasing the pressure of the non-reactive gas using the first control valve (82) to ensure that the level of the reaction sludge bed (62) does not rise above the maximum height of the internal distributor (44) which would result in a poor mix of causticizing agent and alkaline liquor.

[0070] While the modality illustrated in Figure 2 shows a special arrangement that reduces sizing, other arrangements that encourage the mixing of the causticizing agent and pre-heated Bayer process liquor inside the reactor container lids would be suitable, provided the second end of the caustic agent inlet is never immersed in the preheated Bayer process liquor to ensure that no mixing of the caustic agent and Bayer process liquor can occur within the second end of the caustic agent inlet.

[0071] The reactor vessel (16) is additionally provided with a closed lower end (64) for accumulation of the reaction sludge. The lower end may be flat, hemispherical or conical, although hemispherical is preferred as the most efficient design in terms of strength against the thickness of the material for a pressure vessel. The lower end (64) includes reaction sludge outlet (66) to remove the reaction sludge stream (18) from the reactor vessel (16). A duct (70) leads from the reaction sludge outlet (66) of the reactor vessel (16) to the reaction sludge inlet (72) of the downstream solid / liquid separator (20). The flow rate of the reaction sludge outside the reactor vessel can be controlled using the first control valve (68) which controls the flow of non-reactive gas (23) at the closed top end (38) of the reactor vessel (16) to increase or decrease the pressure in the reactor vessel (16). Alternatively, a variable speed drive pump (not shown) can be used instead of or in combination with a control valve (not shown) positioned in the duct (70) in the event that there is a pressure drop between the reactor vessel (16) and the solid / liquid separator (20).

[0072] As an example, when the causticizing agent is Cal, the process liquor Bayer is an overflow washer liquor and the target reaction temperature is 140 ° C, the first control valve (68) can be regulated to ensure that the slurry residence time in the reaction vessel (16) is between 30 seconds and 5 minutes, preferably 2 to 4 minutes. If the causticizing agent is hydrocalumite and the Bayer process liquor is a diluted Bayer process liquor, a residence time of at least 10 minutes and preferably 15 minutes in the reactor vessel should be used for best results. When the causticizing agent is hydrocalumite, the hydrocalumite can be added alone or mixed with an amount of lime. Residence times in the reactor vessel are required at low target reaction temperatures. Advantageously, using the process and system of the present invention, shorter residence times are used for higher target reaction temperatures in order to minimize the formation of TCA and decrease capital costs.

[0073] Using the process of the present invention, the pressurized reaction sludge from the reactor vessel (16) is directed through the duct (70) to the solid / liquid separator (20) downstream with no significant reduction in temperature. For best results, the target separation temperature is equal to or higher than the target reaction temperature. A pressure drop between the reactor container (16) and the solid / liquid separator (20) can be tolerated, as long as the pressurized sludge does not flash, since this would result in an unacceptably high temperature drop. The use of non-reactive gas to form the gas plug at the closed end of the reactor vessel is used to control this pressure drop. The solid / liquid separator (20) can be any device that is capable of separating the reaction solids from the pressurized reaction slurry at the target separation temperature and target separation pressure to produce the clarified causticate flow (22) . For example, the solid / liquid separator can be a pressurized filter, a pressurized decanter, a pressurized thickener, a centrifuge or a pressure decanter. The separator is one of a plurality of separators.

[0074] An embodiment of an appropriate solid / liquid separator (20) in the form of a pressure wine bottle is illustrated schematically in Figure 3. In this embodiment, the reactor vessel (16) generally means vertical and includes a wall of elongated cylindrical pressure vessel (36) of sufficient strength and thickness to withstand the pressures, temperatures and corrosivity of the reaction sludge. The separator is provided with a closed plate-shaped upper end (74) and a vent (75), which can be opened if necessary to allow the release of gases that can accumulate in the container during operation. An overflow outlet (77) is provided at the upper end (74) of the separator to facilitate removal of the clarified etched liquor overflow stream (22). The plus separator is provided with a lower section (76) for accumulation and subsequent removal of the underflow stream of thickened reaction solids (24). The lower section (76) of the separator (20) is provided with an underflow outlet (80) through which the thickened reaction solids underflow stream (24) is removed from the separator (20). The bottom section can be hemispherical or tapered, although tapered is preferred to encourage the overflow of thickened reaction solids from the separator. Preferably, the lower section (76) has sloping sides (78), as indicated in FIG. 1 and these sloping sides should be at an angle (labeled 'α' in Figure 3) between 30 and 60 degrees from the horizontal. An angle of about 45 degrees to the horizontal is preferred, because such a conical shape is easier to manufacture and represents an acceptable height sanction, providing a good flow of solids out of the container.

[0075] A portion of the current underflow of thickened reaction solids (24) can be recirculated through a recirculation port (82) disposed in the bottom section (76) of the separator (20), if desired to help control viscosity of the bed of thickened solids (92). A second control valve (84) is provided in a duct (86) away from the subflow outlet (80) to regulate the flow of the thickened reaction solids flow (24) negative overflow without loss of pressure in the separator (20 ). A variable speed drive pump (not shown) can be used instead of, or in combination with, the second control valve (84). As an example, when the causticizing agent is lime and process liquor Bayer is a spent or diluted process liquor Bayer, the thickened reaction solids bed (92) is maintained to ensure a residence time of less than one time in the separator (20). When the Bayer process liquor is an exhausted or diluted Bayer process liquor and the causticizing agent is hydrocalumite (alone or in combination with lime), residence times plus the sludge reaction in the separator can promote undesirable chemical reactions that result in the formation of ACT. However, longer residence times allow the accumulation of a larger bed of thickened solids (92), resulting in an increase in an increase in the thickness of the thickened solids underflow stream (24) o the improved recovery of the causticized liquor overflow clarified (22) of the overflow outlet (77).

[0076] The separator (20) is provided with a sludge inlet (72) through which the pressurized solid-liquid sludge from the reactor container (16) is fed into a feed well (90) located inside the upper section ( 74) of the separator (20). The feed well is used to reduce the speed and kinetic energy of the pressurized reaction slurry such that it collides with the bed (92) of thickened reaction solids already accumulated in the separator (20) in use. The outlet end (94) of the feed pit is positioned at a predetermined distance at the mud bed level (96).

[0077] To help sediment the reaction solids and encourage solid / liquid separation, a flocculant is added to the pressurized reaction sludge through one or more flocculant injector (s) (88). The flocculant is injected into the duct (70) upstream of, or adjacent to the mud inlet (72) at a point of maximum turbulence. Alternatively or additionally, flocculant can be added via a spray line (98) directly to the feed well (90). The flocculant can be diluted with a diluted Bayer process liquor like process water, prior to addition. The flocculant dose is determined as a function of the mass flow rate of solids present in the reaction sludge entering the separator (which in turn is a function of the Bayer process liquor flow rate (14) and the amount of agent caustication (12) within the reactor vessel (16) and clarity of the causticated liquor subflow stream clarified (22). Suitable flocculants include, but are not limited to, anionic sodium polyacrylate or similar flocculant, such as available ALCAR 600 Allied Colloids, Limited, diluted to a concentration of less than 1.0% by weight.

[0078] The lower section (76) of the separator (20) is additionally provided with an agitator (100) extending from a drive shaft (102). The agitator (100) is provided with one or more arms (104) correspondingly positioned to follow the inner profile of the lower section (76) to leave as little area as swept as possible. In use, the pressurized reaction sludge (18) of the reactor vessel (16) is directed through a duct (70) at the sludge inlet (72) of the separator (20) in which it receives an injection of flocculant via the flocculant of one or more injector (s) (88). The pressurized reaction sludge enters the supply well (90) and flows downwards to the outlet end (94) of the supply well (90). The reaction solids form 'flakes' that deposit on the top of the thickened solid bed (92). Over time, the caustic liquor rises to the top of the separator (20), where it is removed through the overflow outlet (77) as the caustic liquor burst stream clarified (22). The agitator (100) is used to eliminate dead spots in the bed (92) that could otherwise lead to scale deposition. The agitator (100) encourages the flow of thickened reaction solids to the subflow outlet (80) and provides assistance in further thickening the reaction sludge to increase the separation rate.

[0079] In one embodiment the present invention, the target reaction pressure can be set higher than the target separation pressure to avoid the need to pump the reaction sludge from the reactor vessel (16) to the separator (20). As an example, when the target reactor pressure is around 540 kPag (as measured at the upper end of the reactor vessel), the target separation pressure can be around 510 kPag (as measured at the end of the separator). The pressure within the separator is maintained at the target separation pressure, controlling the rate of removal of overflowing current from the clarified caustic liquor or the rate of removal of thickened reaction solids current, or both, from the separator. The target separator pressure and temperature are kept high enough at all times during the operation to avoid flashing the causticized liquor or depressurizing the reaction sludge.

[0080] The primary variables in the invention process of the present are the feed rate of Bayer process liquor to the reactor vessel, the rate of addition of the causticizing agent to the reactor vessel, the target reaction temperature, the separation temperature of the target and residence time in the reactor vessel. In the case when the caustic agent is Cal, the amount of Cal charged to the reactor container is the most important control parameter in the process. Excessive lime loading to the reactor vessel can result in TCA formation and a drop in C / S and A / S of the clarified causticized stream, produced by the separator. Insufficient lime loading can also result in a C / S deficit of the clarified causticized liquor produced by the separator. Accurate measurement of the initial C / S and S rate and flow of the preheated Bayer process liquor added to the reactor vessel is used to calculate the required Cal loading rate required to achieve a target C / S to minimize the risk of formation undesirable TCA. In any case, using the process and system of the present invention, the total time span between the point at which the amount of causticizing agent (12) is first mixed with the Bayer process liquor (14), the reactor container (16) and the point at which the clarified causticized liquor overflow (22) and the negative burst flow of thickened reaction solids (24) is removed from the separator is greater than 15 minutes.

[0081] A second embodiment of the present invention is now described with reference to the schematic diagram of Figure 4, to which reference numerals refer to the parts. In the present embodiment, the reactor container (16) and separator (20) operate in the manner described above with respect to the first embodiment. Downstream of the separator (20), the current underflow of thickened reaction solids (24) is cooled before being discharged to one or more atmospheric tank (s) (200) to avoid flashing. As an example, cooling of the thickened solids overflow stream can be achieved by mixing with an exhausted Bayer liquor stream (202), such as a second overflow washer to avoid flashing after overflow from atmospheric tanks. Cooling can also be achieved using any other liquid, such as water or process water. Alternatively, a depressurization chamber (not shown), operating at a lower pressure than the separator can be used. Alternatively, if direct mixing of the thickened reaction solids with another undesired current, the thickened reaction solids underflow current stream can be cooled using an appropriate heat exchanger such as an enclosure and tube heat exchanger.

[0082] Upstream of the reactor vessel (16), a feed stream of a Bayer process liquor (201) is heated to form the preheated Bayer process liquor (14) a heating circuit (202). The heating circuit (202) consists of one or more heating stages (204). An example of a suitable heating phase is a heat exchanger, a shell and tube heat exchanger, or direct steam injection. The heating stages (204) are shown in the heating circuit (202) of Figure 4. Downstream of the separator (20) the clarified caustic overflow flow stream (22) is cooled, using a cooling circuit ( 206) composed of one or more refrigeration stages (208) to form a causticada liquor refrigeration flow clarified (210). An example of a suitable cooling stage is a heat exchanger. The causticized clarified liquor can be directed to one or more product liquor tank (s) (212) to store or cool clarified causticized liquor (210) and can be returned directly to a Bayer process circuit.

[0083] In the mode illustrated in Figure 4, the heating circuit (202) and the cooling circuit (206) are countercurrent for heat recovery with three heating / cooling phases (204 and 208, respectively). Using the countercurrent arrangement of Figures 4, at least some of the heat from the causticated liquor overflow stream clarified (22) is used to preheat the liquor feed stream from the Bayer process (201).

[0084] In the first stage (214) of the heating circuit (202), the Bayer process liquor feed stream (201) is heated by heat exchange with the clarified caustic overflow stream (22) to form cooled clarified etched liquor (210) and a first partially heated stream of Bayer process liquor (216). In the second stage (218) of the heating circuit (202), the first partially heated stream of Bayer process liquor (216) is additionally heated by exchanging heat with a warm condensed current (220) discharged from the third stage (222) of the heating circuit (202) to form a second partially heated stream of the Bayer process liquor (224) and a cold condensed stream (226). In the third stage (222) of the heating circuit (202), the second partially heated stream of the Bayer process liquor (224) is heated to the target reaction temperature by exchanging heat with a sufficient amount of steam (228) to form the preheated Bayer process liquor (14) and the warm condensed stream (220). As an example, sufficient steam at a pressure of 1300kPag can be added next to the housing of a housing and tube heat exchanger to produce a Bayer process liquor preheated to a target reaction temperature of 140 ° C. The cooled clarified caustic liquor stream (210) is discharged from the heating circuit (202) at a temperature below the atmospheric boiling point of the Bayer process liquor. Alternatively, the Bayer process liquor feed stream (201) can bypass the first and second stages of the heating circuit and be heated to the target reaction temperature in the third stage of the heating circuit using only steam. However, this requires the use of an alternative cooling current to decrease the temperature of the clarified causticized liquor to below boiling point at atmospheric pressure.

[0085] It must be clearly understood that the heating and cooling circuit of the circuit can remain separate and independent of another and any number of heating / cooling stages can be used depending on relevant factors such as the level of heating and cooling to be achieved and the size and efficiency of heating / cooling used. It should be more understood that the use of the heating circuit (202) and the cooling circuit (206) is entirely optional for the operation of the present invention. The clarified etched liquor (210) can alternatively be flash-cooled prior to its introduction into a Bayer process circuit.

[0086] A third embodiment of the present invention is now described with reference to the flowchart of Figure 5, to which reference numerals refer to the parts. In this modality the causticating agent is a hydrocalumite sludge (300). A suitable way of producing a hydrocalumite slurry is by adding an amount of lime (302) to a Bayer process liquor bypass stream (304) in a mixing tank (306). the process liquor from Bayer's bypass flow is cooled to between 60 and 80 ° C above the mixing tank (306) to ensure that the hydrocalumite present in the hydrocalumite slurry (300) is stable. The residence time in the mixing tank can vary between 2 hours and 20 minutes with the best results obtained with a residence time of about 60 minutes. The caustication reaction that occurs when the hydrocalumite paste (300) is mixed with the preheated Bayer process liquor (14) in the reactor container (16) to form calcite is endothermic. To compensate for this, the liquor from the Bayer process (14) must be preheated to a temperature above the target reaction temperature before being introduced into the reactor vessel (16). The mixing tank (306) is provided with a low shear stirrer (308) to minimize the reaction of unwanted side effects that produces TCA. Best results for this third embodiment of the present invention are obtained when an amount of TCA inhibitor (described in more detail below) is added to the mixing tank (306).

[0087] Cal is added to the mixing tank (306) is preferably Cal with an S concentration of 15-20 gpL to achieve high conversion rates to hydrocalumite and high conversion of hydrocalumite to calcite in the reactor vessel. Vigorous mixing or by direct injection of lime into the liquor stream entering the tank or a short residence pre-mix tank (not shown) is necessary to ensure good conversion of lime to hydrocalumite. Conversion rates for hydrocalumite when lime is extinguished at ~ 10 gpL are only 50-70%. This increases to 90% when Cal is cleared at an S concentration of 15-20 gpL. There is some residual lime (UN reacted) in the hydrocalumite sludge (300). This residual lime is available to react with calcium carbonate when the hydrocalumite sludge (300) is added later to the reactor vessel (16). Calcite and other impurities that may be present in the calcium oxide used to produce Cal may also be present. When the hydrocalumite sludge produced in the mixing tank is used as a causticizing agent (12) which is mixed with the preheated Bayer process liquor (14) in the reactor vessel (16), the residence time in the reactor vessel is as range of 5 to 30 minutes, preferably around 10 to 15 minutes.

[0088] A fourth embodiment of the present invention is now described with reference to the flowchart of Figure 6, to which reference numerals refer to the parts. In this embodiment, the caustic agent is a mixture of a hydrocalumite re-impregnated with mud (400) and a supplementary lime mud (402) to provide an increase in C / S achieved. The re-impregnated hydrocalumite sludge (400) is generated by directing the hydrocalumite sludge (300) from the mixing tank (306) to a filter (308) to produce a highly causticized liquor stream (310) and a hydrocalumite filter cake ( 312) which is retained by the filter (308). The hydrocalumite filter cake is mixed with a re-impregnated liquor (314) in a mud tank (316) to produce the re-impregnated hydrocalumite sludge (400). An example of this embodiment, a chilled clarified caustic liquor portion (210) is used as the bypass stream of the Bayer process liquor (304) fed to the mixing tank (306). Since the reaction that occurs to form hydrocalumite, when Lime is mixed with a Bayer process liquor is exothermic, the process liquor from the bypass Bayer flow can be subcooled, using a cooling phase (316) to ensure that the final mixture (including the reaction heat) is at the desired reaction temperature in the mixing tank (306).

[0089] A fifth embodiment of the present invention is now described in which an amount of TCA inhibitor, such as sucrose or sodium gluconate, is added to the process at one or more TCA inhibitor dosage points (150) to suppress the kinetics of TCA reaction. Dosing with the TCA inhibitor allows a higher C / S to be achieved with greater efficiency of Cal, higher concentration of alumina in the causticated liquor. The TCA inhibitor also provides greater process control. The TCA inhibitor stabilizes the hydrocalumite as soon as it forms, preventing the usual simultaneous side reaction that leads to the formation of TCA.

[0090] TCA inhibitor can be added in any flow upstream of the reactor container or within the reactor of the container itself to any of the modalities described previously of the present invention and to any of the schematic flowcharts of figures 1,4, 5 or 6 For example, the TCA inhibitor can be added before, during or after preheating the Bayer process liquor (14). The TCA inhibitor can be added with the amount of causticizing agent (12) being added to the reactor vessel (16) or dosed directly into the reactor vessel (16) itself. It is also possible to dose the TCA inhibitor in other locations within a Bayer process circuit, since a significant proportion of the TCA inhibitor is present in the reactor vessel (16). Best results with minimal inhibitor consumption are achieved when the TCA additive dosing point is the reactor vessel or added to the Bayer process liquor immediately upstream of the reactor vessel.

[0091] Appropriate TCA inhibitors described in co-ownership International Patent Publication Number W00018684 (PCT / AU1999 / 00757) reduces the undesirable reaction of hydrocalumite to form TCA, without appreciably influencing the hydrocalumite reaction with carbonate in the form of calcium carbonate. Virtually any class of surfactant can be used as a TCA inhibitor, providing it adsorbs the hydrocalumite structure. For example, sugars like sucrose and glucose and polysaccharides like starch can be used. However, organic anionic surfactants are more effective. A non-exclusive list of examples of TCA inhibitors includes the following materials, their salts and derivatives: any anionic homopolymers or copolymers (for example, polyacrylic acid and its copolymers with acrylamide, or polymers with hydroxamate functional groups), hydroxamic acids, humic acids and tannic, lignosulfonates, fatty acids, sulfonated carboxylic acids, carboxylic acids and polyhydroxy carboxylic acids.

[0092] Point of amount of TCA inhibitor to be added is dependent on a number of relevant factors, including the type of TCA inhibitor selected and the location of the TCA addition point. Thus, the dose rate for a specific inhibitor must be determined by the experiment.

[0093] Advantages of various aspects of the present invention are further described and illustrated by the following examples and experimental test results. These examples and experimental results are illustrative of a variety of possible implementations and should not be construed as limited to the invention in any way. It can be seen from the experimental data presented below that the etching process of the present invention has demonstrated the ability to consistently reach a C / S of 0.940 at 140 ° C with a lime efficiency of more than 90% or greater than 95% on a concentration of S in the range of 125-170 g / L, as measured in the overflow current removed from the separator when the caustic agent is Cal. Larger S operation is possible, but at a higher C / S penalty that can be achieved. The minimum residence time in the reactor container is somewhere between 40 seconds and 3-4 minutes when using live slaked lime as the caustic agent and 15 minutes when using recycled hydrocalumite as the caustic agent.

Example 1: Lime as caustic agent in the presence of TCA inhibitor

[0094] In this example, the caustic agent is lime hydrated in deionized water and the liquor from the Bayer process is the first washer overflow. The TCA inhibitor used was sodium gluconate, added to the first washing machine liquor before adding Cal, such that the final concentration after adding Cal mud was 0.075 g / L. The initial A, C and S of the first washer overflow is shown in 10 minutes in Table 1 below.

[0095] The first overflow liquor was collected from the refinery and filtered to remove suspended solids, the filtered liquor (1,999 liters), then was added to 3.75 liters stirred along the Parr reactor with the TCA inhibitor. The reactor was sealed and the liquor was heated to 140 ° C.

[0096] Industrial grade hydrated lime sludge (available Ca (OH) 2 84.7%) was prepared by weighing 31.65 g of hydrated lime in a polypropylene flask and added 150ml of deionized hot water (80 ° C ). This load of hydrated lime was calculated to increase the C / S of the first washer overflow by 0.945 assuming lime efficiency at 90%.

[0097] The hydrated lime was quantitatively transferred with the aid of a small volume of deionized washing water to a 300ml stainless steel injection container attached to the 3.75 liter reactor through a series of valves. The injection container was sealed, pressurized with nitrogen gas, and the hydrated lime slurry injected into the reactor.

[0098] The reactor was maintained at 140 ° C for a total time of 120 minutes. Reaction sludge samples were taken at reaction times (representative of residence times) shown in Table 1 below. Each reaction sludge sample was filtered through a 0.45 pm Supor filter membrane.

[0099) The filtrate was analyzed for A, C and S and the solids were washed with deionized water and wet cake analyzed by X-ray diffraction.

[00100] Table 1: Liquor analyzes for Example 1

[00101] The liquor analysis shown in Table 1 above demonstrates that the C / S ratio rises rapidly in less than 5 minutes and remains stable for the full 120 minutes over which the reaction sludge was kept in the reactor vessel. XRD analysis of the reaction solids sampled at the end of 120 minutes shows that the reaction solids are predominantly calcite with very little TCA present and very little residual hydrocalumite remains.

[00102] It is evident from table 1 that the TCA inhibitor allowed improvement in C / S through the addition of Lime, as a causticizing agent for a Bayer liquor preheated to 140 ° C to be retained for up to two hours, allowing sufficient time to transfer the reaction sludge from the reactor vessel to a solid / liquid separator for removal of reaction solids.

Example 2: Lime as causticizing agent - no separation from the reaction sludge

[00103] This example demonstrates the effect on the C / S ratio when Lime is used as a causticizing agent (without the addition of a TCA inhibitor) and rapid separation of reaction solids is not conducted. In this example, a first overflow liquor was collected from the refinery and filtered to remove suspended solids, the filtered liquor (2.630 liters) Then it was added to a stirred 3.75 liter Parr reactor, the sealed reactor, and then the liquor heated to 144 ° C. The initial, C and S of the first washer overflow is shown in 10 minutes in table 2 below.

[00104] A sample of lime sludge was taken from the refinery and analyzed for solids in% (23.0%) and the filtered and washed solids were dried and analyzed by XRF to give a dry Ca (OH) 2 content (62, 64% as CaO). The lime sludge load was calculated to increase the C / S of the first washer overflow by 0.945 assuming lime efficiency at 90%.

[00105] The slaked lime sludge (172.6) was transferred quantitatively with the aid of a small volume of deionized washing water to a 300ml stainless steel injection container attached to the 3.75 liter reactor through a series of valves. The injection vessel was then sealed, pressurized with nitrogen gas, and the hydrated lime slurry injected into the reactor.

[00106] The reactor was maintained at 140 ° C for 30 minutes. Reaction sludge samples were taken at reaction times (representative of residence times) shown in Table 2 below. Each reaction sludge sample was filtered through a 0.45 pm Supor filter membrane. The filtrate was analyzed for A, C and S and the solids were washed with deionized water and wet cake analyzed by X-ray diffraction.

[00107] Table 2: Liquor analyzes for Example 2

[00108] From the analysis of liquor defined in Table 2 above, it is evident that the C / S did not reach the same value reached in Example 1, and that there is a rapid degradation of the C / S ratio over time, with a drop begins to occur after five minutes. XRD analysis of the solids after 5 minutes shows that substantial TCA has already formed in this system, indicating an unstable system. From the behavior of C / S liquor after 5 minutes, it is clear that additional TCA continues to form until a C / S equilibrium of liquor (without inhibitor) has been reached at ~ 23 minutes (~ 0.890).

Example 3: Lime as Caustication Agent - Cooling effect before separation of reaction solids from reaction sludge

[00109] In this example, the caustic agent is lime hydrated in deionized water and the liquor from the Bayer process is the first washer overflow. The TCA inhibitor used was sodium gluconate, added to the first washing machine liquor before adding Cal, such that the final concentration after adding Cal mud was 0.075 g / L. The initial A, C and S of the first washer overflow is shown in 10 minutes in Table 3 below.

[00110] The first overflow liquor was collected from the refinery and filtered to remove suspended solids, the filtered liquor (2,000 liters), then it was added to 3.75 liters stirred along the Parr reactor with the inhibitor, the sealed reactor and then the liquor heated to 14140 ° C.

[00111] The hydrated lime sludge in industrial grade (available Ca (0H) 2 84.8%) was prepared by weighing 34.72 g of hydrated lime in a polypropylene bottle and added 180 ml of deionized hot water (80 ° C ). The hydrated lime load was calculated to increase the C / S of the first washer overflow from 0.945 to 90% lime efficiency. The hydrated lime was transferred quantitatively with the aid of a small volume of deionized washing water to a 500ml stainless steel injection container attached to the 3.75 liter reactor through a series of valves. The injection vessel was then sealed, pressurized with nitrogen gas, and the hydrated lime slurry injected into the reactor.

[00112] The reactor was maintained at 140 ° C for 40 minutes. In 40 minutes, an internal cooling coil was then used to cool the reactor contents to 90 ° C during the subsequent 30 minute period of time (with a total reaction time of 70 minutes). Reaction sludge samples were taken at reaction times (representative of residence times) shown in Table 3 below. Each reaction sludge sample was filtered through a 0.45 pm Supor filter membrane. The filtrate was analyzed for A, C and S and the solids were washed with deionized water and wet cake analyzed by X-ray diffraction.

[00113] Table 3: Liquor analyzes for Example 3

[00114] Table 3 shows that the C / S is stable during the first 40 minutes at 140 ° C and that the C / S proportion decreased substantially when the reactor sludge was cooled to 90 ° C. This result shows that, when the reaction sludge is allowed to cool without first separating the etched liquor from the reaction solids it results in a decrease in the C / S of the liquor. This effect was seen in shorter reaction times as well.

[00115] Laboratory results confirmed that this drop in C / S liquor, which occurs when the reaction sludge is cooled (without first separating the etched liquor from the solids present in the reaction sludge) is even worse when the reaction occurs without the addition of a TCA inhibitor.

[00116] XRD exams confirmed a change in the proportion of TCA in the solids after 40 minutes and 70 minutes. Only one trace of TCA was present in 40 minutes, when the system is stable. Substantial TCA was present after 70 minutes after C / S dropped from 0.914 by cooling the reaction sludge without first separating the reaction solids from the causticized liquor.

Example 4: Hydrocalumite sludge as a causticizing agent in the presence of a TCA inhibitor

[00117] In this example, the causticizing agent is hydrocalumite impregnated in the first washer overflow.

[00118] The first overflow liquor was collected from the refinery and filtered to remove suspended solids, the filtered liquor (1.2 liters) was then added to a stirred 2.0 liter Parr reactor with the inhibitor, the sealed reactor, and then the liquor heated to 145 ° C. A hydrated lime suspension of industrial grade (available CA (OH) 2 85.0%) was prepared by weighing 26.46 g of the hydrated lime in a polypropylene bottle and adding 124ml of adding deionized water hot to (80 ° C). The hydrated lime slurry was added, with stirring, to 537 ml_ of first overflow of caustic washer (C / S ~ 0.940) preheated to 80 ° C, to form a hydrocalumite slurry. This hydrocalumite slurry was reacted in a polypropylene flask for 30 minutes at 80 ° C in a running water bath. Through the light caustication reaction of Ca (OH) 2 for hydrocalumite the C / S of this liquor reached 0.984, producing a highly causticized flow of liquor, designated as (310) in the modality illustrated in Figure 7.

[00119] The hydrocalumite slurry was then filtered under vacuum to produce a de -colored hydrocalumite cake (the solids are not washed). The hydrocalumite cake was then re-impregnated in 92 ml_ of washer overflow at 80 ° C and returned to the running water bath for an additional 15 minutes at 80 ° C to completely disperse the cake. This is the re-impregnated hydrocalumite slurry is then used as the causticising agent in the modality illustrated in Figure 7.

[00120] In this example, the Bayer process liquor is the first washer overflow. The TCA inhibitor used was sodium gluconate, added to the first washing machine liquor before adding the re-impregnated hydrocalumite slurry. The initial A, C and S of the first washer overflow is shown at 0 minutes in Table 4 below.

[00121] The first overflow liquor was collected from the refinery and filtered to remove suspended solids. The filtered liquor (2,000 liters) was then added to a 3.75 stirred Parr reactor with the inhibitor, the sealed reactor, and then the liquor heated to 140 ° C. The re-impregnated hydrocalumite sludge was transferred quantitatively with the aid of a small volume of deionized water to a 300ml stainless steel injection container attached to the 2.0 liter reactor, through a series of valves. The injection vessel was then sealed, pressurized with nitrogen gas, and the hydrocalumite slurry injected into the reactor.

[00122] The reactor was maintained at 140 ° C for 120 minutes. The reactor contents were sampled over time, with the mud samples filtered through a 0.45 pm Supor filter membrane. The filtrate was analyzed for A, C and S and the solids were washed with deionized water and wet cake analyzed by X-ray diffraction.

[00123] Table 4: Liquor analyzes for Example 4

[00124] Beverage analysis shows that C / S is stable during the 120 minutes of reaction, with little or no change in the composition of the drink. This is directly comparable to Example 1, and shows that in the presence of TCA inhibitor it is equally effective when the causticizing agent is hydrocalumite as well as with lime.

[00125] The effect shown in Table 3, whereby C / S drops substantially when the reactor sludge is cooled before removal of the reaction solids from the causticized liquor has also been observed when hydrocalumite sludge is used instead of lime as the causticizing agent.

[00126] Now that several modalities of the invention have been described in detail, it will be evident to people skilled in the art in chemical engineering that countless variations and modifications can be made without departing from the basic concepts of inventives. For example, the overflow rate of the reactor vessel (16) can be controlling the rate of removal of the overflow stream from the clarified etched Bayer liquor (22) from the overflow outlet (77). All such modifications and variations are considered to be within the scope of the present invention, the nature of which must be determined from the above description and the appended claims. In addition, the previous examples are provided to illustrate specific embodiments of the invention and are not intended to limit the scope of the process of the invention.

Claims (29)

1. High temperature etching process for etching a Bayer process alcoholic beverage (14), characterized by the fact that the process comprises the steps of: a) adding a quantity of causticizing agent (12) to the alcoholic beverage of Bayer process (14) in a reactor vessel (16) operating at a target reaction pressure for a given target reaction temperature; b) allowing the causticizing agent (12) to react with the Bayer process alcoholic drink (14) for a sufficient residence time to produce a reaction sludge (18) comprising an amount of reaction solids in a Bayer alcoholic drink etched at a reaction temperature of at least 115 ° C; and c) subjecting the reaction sludge (18) to the solid / liquid separation while maintaining the reaction temperature of at least 115 ° C to produce a separate stream of reaction solids (24) and a stream of caustic Bayer alcohol product clarified (210). 2. Searing process, according to claim 1, characterized by the fact that the temperature at which the solid / liquid separation occurs is greater than the atmospheric boiling point of the Bayer process alcoholic beverage. 3. The caustication process, according to claim 1, characterized by the fact that the temperature at which the solid / liquid separation occurs is greater than the atmospheric boiling point of the Bayer process alcoholic beverage. 4. Etching process according to claim 1 or 2, characterized by the fact that the target reaction temperature is between 115 ° C and 300 ° C. 5. Etching process according to claim 1 or 2, characterized by the fact that the target reaction temperature is between 115 ° C and 180 ° C. 6. Etching process according to claim 1, characterized by the fact that the sufficient residence time of step b) is less than 1 minute. 7. Searing process according to claim 1, characterized by the fact that the sufficient residence time of step b) is less than 10 minutes. 8. Searing process according to claim 1, characterized by the fact that the sufficient residence time of step b) is less than 20 minutes. 9. Searing process according to claim 1, characterized by the fact that step c) is carried out in a solid / liquid separator (20) and the process additionally comprises retaining the reaction sludge (18) in the water separator solid / liquid (20) for a period of time not exceeding one hour. 10. Searing process according to claim 1, characterized by the fact that step c) is carried out in a solid / liquid separator (20) and the process additionally comprises retaining the reaction sludge (18) in the water separator solid / liquid (20) for a period of time not exceeding 30 minutes. 11. Searing process according to claim 1, characterized by the fact that the solid / liquid separator (20) is a pressure decanter, a pressure filter, a cyclone, or a centrifuge. 12. Etching process, according to claim 1, characterized by the fact that the ratio of total caustic concentration to total alkali concentration of the Bayer process alcoholic beverage (14), when expressed in grams of sodium carbonate per liter of solution , exceeds 0.9, after adding the amount of causticizing agent (12). 13. Etching process, according to claim 1, characterized by the fact that the ratio of total caustic concentration to total alkali concentration of the Bayer process alcoholic beverage (14), when expressed in grams of sodium carbonate per liter of solution , exceeds 0.95, after adding the amount of causticizing agent (12). 14. The etching process according to claim 1, characterized by the fact that the etching agent is one or both of the lime or hydrocalumite. 15. Etching process according to claim 1, characterized by the fact that the etching agent is extinguished lime. 16. The caustication process according to claim 1, characterized by the fact that the extinguished lime is formed by adding quicklime to the water or by adding quicklime to a Bayer process alcoholic beverage (14). 17. The caustication process according to claim 1, characterized by the fact that the Bayer process alcoholic beverage has an initial total alkali concentration of between 40 and 250 grams per liter expresses the grams of sodium carbonate per liter of solution. 18. Searing process according to claim 1, characterized by the fact that the Bayer process alcoholic beverage has an initial total alkali concentration of between 80 and 60 grams per liter expresses the grams of sodium carbonate per liter of solution. 19. Searing process according to claim 1, characterized by the fact that the Bayer process alcoholic beverage (14) has an A / C ratio of between 0.2 and 0.95. 20. The caustication process according to claim 1, characterized by the fact that the Bayer process alcoholic beverage (14) has an A / C ratio greater than 0.55. 21. The etching process according to claim 1, characterized by the fact that the Bayer process alcoholic beverage (14) is preheated before step a). 22. The caustication process according to claim 21, characterized by the fact that the Bayer process alcoholic beverage (14) is preheated to the target reaction temperature in a heating circuit (202), the heating circuit ( 202) comprising one or more heating stages (204). 23. The etching process according to claim 22, characterized by the fact that a heating stage (204) comprises direct or indirect steam injection. 24. The caustication process, according to claim 1, characterized by the fact that the clarified etched alcoholic beverage is cooled after step c) by countercurrent heat exchange with the Bayer process alcoholic beverage (14). 25. The etching process according to claim 1, characterized by the fact that the Bayer process alcoholic drink is an exhausted Bayer alcoholic drink (202) or a diluted Bayer alcoholic drink. 26. The etching process according to claim 1, characterized by the fact that the Bayer process alcoholic beverage is a washer overflowing alcoholic beverage. 27. The etching process according to claim 1, characterized by the fact that step a) is carried out in the presence of a TCA inhibitor. 28. The etching process according to claim 27, characterized by the fact that the TCA inhibitor is an anionic organic surfactant. 29. The caustication process according to claim 28, characterized by the fact that the anionic organic surfactant is selected from the group comprising: an anionic homopolymer, an anionic copolymer, a polyacrylic acid, a hydroxamate functional group of polymer, hydroxamic acid, humic acid, tannic acid, lignosulfonate, fatty acid, sulfonated carboxylic acid, carboxylic acid, and polyhydroxy carboxylic acid.

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