AU2006202251A1 - Process for reducing contaminants in condensate resulting from the conversion of bauxite to alumina - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

TO BE COMPLETED BY APPLICANT Name of Applicant: Actual Inventor: Address for Service: Invention Title: ASHLAND LICENSING AND INTELLECTUAL PROPERTY LLC Lynn N. Hildebrand CALLINAN LAWRIE, 711 High Street, Kew, Victoria 3101, Australia PROCESS FOR REDUCING CONTAMINANTS IN CONDENSATE RESULTING FROM THE CONVERSION OF BAUXITE TO ALUMINA The following statement is a full description of this invention, including the best method of performing it known to us:- 25/05/06,15734 Cover gp,1 PROCESS FOR1 REDUCING CONTAMINANTS iN CONDENSATE RESULTING FROM THE' CONVERSION:OF BAUXITE TO AlUMNA (00,001] Tet h~ica Flild'of the Invendon (00002], This invention relates to a process for'it-ducing fiti contanants in con densate resut from. the conversion -of bauxite'to iilumns (000033 bnd ind of tre Invt1on (000043 There arm mayly industrial. procets that use prioicess water in carrying out reactions, as an em Iluent for removing uhwsmted by-poducts,usaduntadfom yohrfcin.

Examples of industrial poe8s which .u A- p robes watei, inolude, fdr dxanlpla, the refining of petoleum;, the production of olefins, polymers, and organic acdds; the production of metals, e.g. aluminum, iron, steel, and copper the benefaction of Coal.

[00005] The process water often comes ifito contact with a variety of contamninants when the industrial process is, carried out. These contaxnitants remain in the prodeuc water.

Although there may be many containants, in the process water and they vary depending upon the type of industrial process car ied out, the more deleterious coritambinnis include suspended solids, oil and grease, metals, and silicate compoundl.

[00006] The process water is often subject to elevated temperatures. It may be converted to steam, which often, undergoes condensation. The oondensate may also contain the conitainants thit are present in the process -water.

(00007] Although there are many methods kno .w n for remo'ving contaminants from aqueous systems, these methods cannot be sucessfully used to remove contaminants from process water and condensates,* particularly without reducing thi heat capacity of the pro Icess w ater and/or condensate., The teiipraure of the condensate typically ranges from about $0 0 C to I100 0 C, most typicalfly fom 950C to I 00"C. What makes. it difficult to purify the condensate is the presence of suspended solids, which can be 1000 times is high as, that found ih other confaminatei aqueott systemns. Because the temnperftt is elevaed it is diftdilt t6 purlly codensiftM, paftW&A9~ withbut rediicing the heat (71 capacity of the contdesAte. Additionally, the difficulty is compounded because the condensate may have- high alkcalinity, vwhiich inaefte the stabili .ty of the emul.1si on of oil found in the process water and/or oftdenbate.

(00008] The e6ev-ted tempentiture and high lkaINty of the condensite a1o, irnpaifs the INDusefulnesg of chelbia typicaiyf used to break t emulsion, anid/or coi4uate suspitded solids. Thus, maby procftfts that culd be Uled to puffy~ 1 coiideb~ae at iot dbompatible with the hi gh 1t ahd: alkality.

[0009] The temperature of condeftsate tdally rathIgs between S'0C And 1004t. If the purificatioti doi be camedd out Without -afy redilctioti in the heat -capacity of the condensate, a kreat deMl of cergy can bte aateved. The waTr does not have'to, be reheatted for use in the pt~s ras bailer feeca4r.

(00010] One example of process water and/or condensate, whiich has the pofential for reuse, is that generated by the production of aluknina fiom bauxkite *ore. The majority of aluminum produced today is inhnufactdred .fr-6m biauxite ore. One of the piimay means for converting bauxite ore to alumina is by the Dayer proces as shown in Figure 1. The aluftiiia is then cOhVesle to timifinin, which is prodiced coinhieftiaily by the electrolytic smeltittg of alumi&a [00011] The Bayer proces ffir pfca66611 of biokite dTb iMo aluminfa iivdlVes the high remoetature 'digesdoni of the babkitt ore in a soldtion 6f sddii~h hydtdkide (cdiitic).

The dige~ton typically thkesplace at 100 to 300 psi. The effluent from the digestion is flashed, i.e. reduced in prtsur, in eleven stages to atmosphdric pressure. Eacth step produces steam as the pressure drops. This -steasnh is fed into a heatter cOil in the next immediate downsafra veasel to condense the steam inito process Water and/or (71 condensate. This condenswe is often waste because contains small amounts of aluiminum, iron, silica causti, and oiganics. The conltamilnation ii caused by caryover of effltritn liquor into the flashed dtm. The co0ntazhkiatidh- c~nrin bdffi soluble and (71 ~~~insoluble mat"ra. The inhodu1Wl ateil is Y'efred tov as ted mud".

(00012) Both the red mud and the dissolved material are present in thie process water and/or condensate at varying amoiunts dependig olpon various operating conditions. Often an C1 antifoam is used to keep high froth levels fr-om increasing carryover. The antifoazn may contri bute to the orgSnc coabii'idn in the oon~dftsate. The typical aluninta plant will produtce thousands df gdlona per mhinute of Nhs condensate. It is often Wasted, but could be used for boiler mnake up Wifer if the'purity *ert iniproved. This could tegult in millions of dollars sived each year at eiaph t site.

[60013] For purpses of descibig this inventon, condensate is condensate that results frm the condensation of steam generated'from any stage 'of the process whereby bauxite is converted to alumnina, particularly the Biyier process. There are three major sources of condensate in an alumina facility. There is the digestion condensate that is the most contamrintated, the evaporator condensate which is sohiewbat contaminated, and the clean condensate from surface condensers and the like (cloted systems with no process contact). The condensate carries imipurities such as mineral oil, silica, iron oxide, aluminum and other suspended solids from the ore. Because condensate usually contains some of the caustic from the digestion process, the oil can be Wtongly emulsified and the alutnium dissolvdd. The pH of the condensate can vary over Wide ranges, but it highly alkaline. The pH is tyically 10.0 to 11.0, [000 14] Because the temperature of the condeh~ae is typically from about 95*-100*C, it has the potential to be used as a boiler feedwater if the impurities could be removed. However, if utilized without treatment, the boilers would exhibit frequentfailures, which would result because of the precipitation of iinjuiifes. Because there is no effective and economical way of removing, the inpU'rities from the condieasate, the condehi~tit is frequently wasted.

100015] Al citations referred to in this application are expressly incotedti byrefermce.

[000163 Description of the Drawings [00017] Figure 1 is a diagram, which illustrates how the Bayer process is typically carried out.

The Bayer process is used to convert bauxite ore to alumina and i4entifies condensate streams used in the. pro-css. The proceks generates condensate cointaning contaminats.

[00018] Brief Summnary of the Inventiob [00019] This invention relates to a process for redlucing contaminants in contanoinated condensate resulting from the conversion of bauxite to alumina, wherein said process comprises the steps of.

adding an inorganic coagulant in whouit to sUftciernt to partially or completely coagulate the solids in said condefishte; and filtering said condensate in amount.

[00020] Preferably, the condensate is fur-ther purified so that it can be used as boiler feed water.

Methods used to fu"er purify the process water include dernineralibation with ion exchange, reverse osmosis, evaporation, p~il defnineralizabon, de~assifiation, and mixed bed demineralization.

[00021] Addition of the inorganic coagulant causies contaminants in the condensate to coagulate. The coagulated conatait are then removed in the filtering step.

[00022] In some cases, particularly When the condensate is contkminated With latge amounts of suspended solids, it may be useful to clari the condensate after coagulation and before filtering. Clarifyng the condensate before filtering enabl es one to dami out the process ci more effectively when the condensate ontains higheir concentrations of solids. Thus, the process can be used mhore effectively in different industrial settings.

[00023] The prociess is particularly useful for removing inpurities from condensate, which is generated by the productio'n of alumina from bauite ore. Aftcr the cobdensate has been purified, it can: then be recycled throu gh the process used to convert bauxite to alumina, or if clean enough, it can be used as boiler feedwater.

(00024) The process is particularly useful, because impurities can be removed from the condensate without any substantial reduction in the heat capacity of the process water and/or condensate. The heat capacity in some cases excceids one million BTU's per 1,000 gallons of process water and/or condensate.

[00025] The process can be carried out on-line with negligible heat loSs. The time it takes for the contaminated water to enter the treatment and leave the treatment process is approximately 30 to 90 seconds. It is because of this rapid treatment time that the temperature of the condensate can be maintained before it is re-used.

[00026] Detailed Description of the invennon [00027] The detailed description and examples will illustrate specific embodiments of the invention will enable one skilled in the art to practice the invention, including the best mode. It is contemplated that many equivalent embodiments of the invention will be operable besides these specifically disclosed.' O [00028] The function of the inorganic coagulant is to coagulate the contaminants in the INO condensate, so that the contaminants can then be removed by subsequent filtering.

Examples of useful inorganic coagulants include, for example, polychlorinated aluminum, polyaluminum silicate sulfate, lime, alum, ferric chloride, ferrous sulfate, ferric sulfate, aluminum sulfate, aluminum chloride, polyaluminum chloride, aluminum chlorohydrate, and sodium aluminate, and alkali metal silicates.

[00029] The amount of the inorganic coagulant typically used is from about I ppm to about 1000 ppm, preferably from about 5 ppm to about 200 ppm, most preferably from about ppm to about 100 ppm.

[00030] As was mentioned previously, it may be useful to clarify the condensate after coagulation and before filtering when the solids content is high. Although any means know in the art can be used to clarify the condensate, one method that has been shown to be particularly effective, is to pass the condensate through settling device, preferably a separator, e.g. a Lamella® gravity settler/thickener, which is sold by Parkson Corporation. The separator reduces the suspended solids in a liquid stream. Typically, the separator is used if the incoming suspended solids is higher than the filter, e.g. the Dyna-Sand filter, can handle effectively, e.g. typically if the turbidity is greater than 120 NTU.

0 S(00031] Settling may be accomplished by a variety means. Traditionally, settling was accomplished by placing the liquid containing the suspended solids in a quiescent pond such as a sedimentary basin that may be several acres, where the solids were allowed to settle. A more modem approach is to pass the liquid through a clarifier where the particle size is increased by using a polymer to increase the settling rate. The material (7 settles faster in a clarifier thap it does in a pond, because of the increased size of the 0 suspended solids and increased density of the particulate material suspended in the fluid.

Nc [00032] The conventional clarifier is usually a large tank so the fluid velocity may be reduced to less than one or two feet per minute. The configuration may vary from a long rectangular basin that is fed from one end to a circular design fed in the middle. All use the same principal of settling the solids through the clear fluid to the bottom of the vessel. Because the depth is several feet, this may take a long time. This is why the vessels are so large.' [00033] Recent technology involves mechanical separation augmented by the use of a polymer to change the physical character of the suspended particles to be separated. This process uses a series of parallel plates set at an angle from horizontal 45 to degrees) that collect the particles from the fluid that passes through them in parallel.

The plates span the entire unit of the clarifier. The solids then settle only several inches onto each of the plates. The clear water passes upwards and overflows where it is channeled for end use, while the solids accumulate on the plates. Large systems may use twenty or so parallel plates, while smaller system may require only eight or ten plates.

[00034] Although a variety of filters are useful for carrying out the filtration step of the process, the preferred filter is a fluidized bed filter, particularly an upflow sand filter. This filter Sutilizes a fluidized bed where the media in the fluidized bed develops a negative charge. This allows the cationic coagulants to pre-coat the filter, which causes the contaminants to stick to the media. This enables one to use less coagulant and the coagulant is removed from the stream, preventing it from becoming an impurity in the filtered fluid.

N (00035] Particularly useful, as the filter, is the DynaSand® filter supplied by Parkson Corporation. This filter is a continuous-backwash, upflow, deep-bed, granular-media filter. Recycling the sand internally through an airlift pipe and sand washer continuously cleans the filter media. The cleansed sand is redistributed on top of the sand bed, allowing for continuous flow of filtration and rejected water. Other features of the filter include a continuously cleaned sand bed, no moving parts, low pressure drop, high solids capability, and a top-feed design.

[00036) Preferably, after coagulation, and possibly clarification, and filtering, the turbidity of the condensate is 1.0 NTU or less. After the suspended solids are removed from the condensate, there still may still dissolved materials such as sodium hydroxide, aluminum, and smaller amounts of iron, calcium, silica, organics, etc. remaining in the condensate. Preferably, these materials need to be removed from the process water and/or condensate, so the condensate can be used as boiler feed water. Any number of processes may be added downstream from the filter to complete this purification process, e.g. demineralization with ion exchange (cation or anion), reverse osmosis, evaporation, partial demineralization, decarbonation, degassification, and/or mixed bed demineralization. Any proven technique for removing ionic contaminants from water streams should be effective as a second stage in this condensate recovery process.

[00037] The treatment time from entering the filter to exiting the ion exchange unit varies depending upon the degree of contamination and flow rate, but typically takes less than minutes, more typically from about 5 to about 15 minutes.

[00038] As was pointed out previously, the subject process is particularly useful for treating process condensate generated by the Bayer process used to produce alumina from bauxite. In the Bayer process, condensate is generated as follows: The flash steam that is produced from pressure reduction of the digester effluent is used to beat the feed to the digester. The flash steam is ultimately condensed and is the largest source of condensate that is produced.

Further downstream in the process, solids are removed for disposal and the clear supernate (containing caustic and dissolved alumina) is precipitated in a series of multiple effect evaporators. These evaporators produce the second largest stream of condensate.

(00039] Note that both these streams are generated by the process rather than from condensed steam from the powerhouse. This is why they are so contaminated.

[00040] Other sources of condensate are the condensed steam from the surface condensers and steam heated process vessels.

[00041] After the contaminated condensate is treated, it can be piped (the motive pressure of the steam may be sufficient to transport it) or pumped, if necessary, to the boiler feedwater unit, recycled in the process, or sent to a holding tank where is stored until it is ready to be used.

[00042] Abbreviations and/or Definitions [00043] ALK 10004] ALK total alkalinity as calcium carbonate.

[00044] AL aluminum.

[00045] FILTER a fluidized bed sand filter supplied by Parkson Corporation under the trademark DynaSandO sand filter.

[00046] NA soluble sodium.

[00047] TOC total organic carbon.

[00048] Examples [00049] While the invention has been described with reference to a preferred embodiment, those skilled in th art will understand that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the paricular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims, it this application all units are in the metric systemn and all amounts and percentages are by weight, unless otherwise expressly indicated.

[00050] Example [00051] Clarification of condensate generated by the Bayer process [00052] for producing alumina [00053] This example illustrates how the process is used to remove contaminants from the regenerative condensate The source of RC is digester water from the surface condensers used in the Bayer process for producing alumina. The alumina is produced from bauxite by the Bayer process as shown Figure 1. The temperature of the RC is from about 80 0 °C to about 100°C. The sample is piped from the process and the purification took place on-line.

[00054] From about 10 ppm to about 50 ppm of polyaluminum chloride are added to RC. The condensate was then filtered using FILTER to remove the coagulated solids.

[00055] After the filtration process, the resulting condensate is passed through a strong acid cation and then a decarbonator. If the resulting condensate purity meets ASME feedwater guidelines, pH is adjusted to 8.3 10.0 and sent to the deaerator. If quality does not meet ASME feedwater guidelines, the condensate is sent to a strong based anion before going to the deacrator. Treatment time is typically from 5 to 15 minutes depending on the degree of treatment and the flow rate.

[00056] The contaminants (CNT) in the condensate and their amounts before treatment (BT), after filtration and after decarbonation and demineralization (ADD) are measured for the RC stream. The most important contaminants in this process are total suspended solids (TSS), alkalinity (ALK), aluminum sulfate (SO 4 and soluble sodium (NA).

(00057] There is no significant loss of heat from the contaminated process water during the treatment process, and the time it takes for the contaminated water to enter the N treatment and leave the treatment process is less than several minutes.

[00058] The amounts of several different contaminants are reduced or removed when the C< process condensate was treated according to the process. A decrease in turbidity indicates the effectiveness of the process in removing suspended solids. If the condensate is treated with an inorganic coagulant, filtered, and then subject to decarbonation and/or demineralization, it is possible that the purified water can be used N" as boiler feedwater or recycled as process water.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form or suggestion that the prior art forms part of the common general knowledge in Australia.

Claims (13)

1. A process for reducing contaminants in contaminated condensate resulting from the refining of aluminum, wherein said process comprises the steps of: adding an inorganic coagulant to the condensate in an amount sufficient to partially or completely coagulate the solids in said condensate; and filtering said condensate.

2. The process of claim I wherein the temperature of the condensate is from 80° C to I0ooC.

3. The process of claim 2 wherein pH of the condensate is adjusted to from about 7.0 to about

4. The process of claim 3 wherein the acid is sulfuric acid.

The process of claim 4 wherein the filter used for filtering is an upflow sand filter.

6. The process of claim 5 wherein the condensate is generated from the production of alumina from bauxite ore.

7. The process of claim 6 wherein the process used to prepare the alumina from bauxite ore is the Bayer process.

8. The process of claim 7 wherein the condensate is selected from the group consisting of digestion condensate, evaporator condensate, and clean condensate from surface condensers.

9. The process of claim 8 wherein the condensate is clean condensate from surface condensers. The process of claim 9 wherein the purified condensate is recycled in the Bayer process for converting bauxite ore to alumina.

The process of claim 9 wherein the wherein the condensate is further purified by demineralization with ion exchange, reverse osmosis, evaporation, partial demineralization, degassification, decarbonation, and/or mixed bed demineralization.

11. The process of claim 10 wherein the purified process condensate is used as boiler feedwater.

12. The process of claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11 wherein the inorganic coagulant is selected from the group consisting of polychlorinated aluminum, polyaluminum silicate sulfate, lime, alum, ferric chloride, ferrous sulfate, ferric sulfate, aluminum sulfate, aluminum chloride, polyaluminum chloride, aluminum chlorohydrate, and sodium aluminate, and alkali metal silicates, and mixtures thereof.

13. A process as defined in claim I and substantially as hereinbefore described with reference to the example. DATED this 25th day of May 2006 ASHLAND LICENSING AND INTELLECTUAL PROPERTY LLC By their Patent Attorneys Callinan Lawrie 0