<<

Mass from solutions

GEA Messo PT Range of Products

Individual plants for the Crystallization and evaporation Plants for environmental chemical, pharmaceutical and technologies for the chemical, protection food processing industries pharmaceutical and food processing industries

(Unit operation, evaporation, (Entire technology concepts, based (Based on precipitation, evaporation, crystallization, thermocompression) on precipitation, evaporation, crystallization) ◊ Crystallization plants crystallization) ◊ Pickling bath liquor recycling ◊ Evaporation plants (all ◊ Common salt production plants plants concentration under significant ◊ Reaction crystallization plants for ◊ Landfill concentration scaling conditions) several base/acid reactions plants ◊ Industrial waste water ZLD plants ◊ Treatment plants for slags from the secondary aluminum industries

2 Content

Messo in the field of crystallization 4

Crystallization in history and presence 5

Crystallization in theory and practice 6

Types of crystallizers 10 Forced circulation crystallizer Turbulence (DTB) crystallizer OSLO crystallizer Peripheral components

Application examples 13 Surface cooling crystallization Vacuum cooling crystallization Evaporative crystallization

Modern applications 16 Flue gas desulfurization (FGD) Recovery of caffeine Salt from secondary aluminum slag Ammonium sulfate from the caprolactam process

Research and development services 18

Product experience 19

3 Messo, synonym for crystallization

IN THE FIELD OF MASS supersaturation, and other physical CRYSTALLIZATION FROM properties of the subject process SOLUTIONS, MESSO’S liquors. Not only the design of EXPERTISE encompasses all crystallizers but the development of basic types of crystallizers for the optimized separation processes for our crystallization from solutions, such clients’ needs is in the focus of MESSO as the forced circulation or draft-tube chemists and engineers. (MSMPR) crystallizer, the turbulence In order that its know-how is (DTB) crystallizer, and the fluidized continually enriched with new bed (OSLO) crystallizer. MESSO is developments in the field of Crystals of citric acid in polarized light thus in a unique position to address crystallization, MESSO has established the special needs of each of its the close cooperation of several leading clients, depending on the required European Universities’ Research Centers product crystal quality and size. for information exchange. MESSO In addition to the center piece of a engineers share their wealth of practical crystallization system, the crystallizer, experience with the international GEA Messo PT is well established as MESSO offers its clients the supply community globally recognized technology supplier of optimized peripheral equipment, through presentations during scientific and plant constructor in the field of in several levels of involvement. symposia, publications of pertinent solution – and melt crystallization and MESSO routinely supplies upstream articles and the arrangement of national related concentration technologies with and downstream components, and international crystallization focus on business activities to a selected such as the preconcentration (in seminars. MESSO contributions have range of industrial applications. multiple effect, mechanical vapour been included in several technical recompression, flash, and other handbooks and the well-known GEA Messo PT has been established as a evaporator configurations), the Ullmanns’ Technical Encyclopedia. merge of the German based GEA Messo dewatering (thickening, This state of experience, broad technical GmbH and the Netherlands based GEA or ), , solids background, updated skills and in-depth Niro PT B.V. into one operational entity. handling and packaging. MESSO also research are brought to bear on each The newly formed company combines supplies piping and instrumentation and every project MESSO handles. the two technology centers for solution and process control systems for its The results are tailor-made solutions crystallization (MESSO) and melt plants, installations in prefabricated that combine optimal investment with crystallization/freeze concentration and modularized sections, and turnkey plant functionality, reliability, modern (NIRO PT) allowing to use all cross- installations, as required by the client. technology, safety, and respect for fertilizing synergies between solution MESSO is a leader in its field through the environment. MESSO engineers and melt crystallization. At the same in-depth reviews of its operating always look for the most feasible plant time, our customers profit from installations and research and configuration which – at the end – is a better support out of larger and development. The Research and also the cheapest investment. consolidated departments in sales, Development Department of MESSO A large part of MESSO’s business comes project management, services and is housed in a three-hundred-square from repeat clients; this is the best administration. Experience counts meter facility, equipped with test units testimony for the quality of our work, for a lot in the implementation of that simulate batch and continuous the commitment of our engineers, and crystallization systems and our operation of all basic types and the performance of our equipment. combined track record makes GEA configurations of crystallizers. It has Messo PT the supplier of choice for in-house analytical capabilities for many of our customers. direct determination of concentration,

4 Crystallization in history and presence

the compounds that make it impure. importance. The possible crystal size Further, there are cases where of a given compound is dependent on crystallization is used to concentrate a its chemical and physical properties, solution, by crystallizing and removing and those of the solution in which it the solvent (freeze concentration). is dissolved. In parallel, the crystal One quality that is present in all size is dependent on the equipment crystallization systems, regardless of the used to crystallize it, and the method final use of the solvent or the crystal, by which the equipment is operated. is the ability to separate the crystals The crystallizer used can contribute In antiquity, settlements developed from the mother liquor. This ability to improving the crystal size, within around, and exploited sites where salt is a function of the crystal size, physical and energy boundaries, by was easily available, whether as and, by extension, a function of the controlling the nucleation, the attrition, rock, brine, or derived from solar separation equipment that can be and the growth rate of crystals, and evaporation. For example, salt was used. Centrifugation is by far the most by destroying a fraction of the smaller produced in the Pharaonic Egypt at efficient separation method, if the crystals present in the crystallizer the Nile Delta; similarly, the Romans average crystal size is large enough. itself. Inattention of these parameters, recovered salt at Ostia seacoast (near It is therefore logical to expect that on the other hand, can contribute to a Rome) and the same happened all over of the characteristics of a crystallizer, degradation of the crystal size. the world (e.g. in China). These and the crystal size it produces is of great many other production sites prove that crystallization from solution is one of the oldest unit operations practiced by humankind. While crystallization in solar ponds is still in regions with plentiful sunshine, its low production rate and mediocre product purity prevents this technology to be used generally. As the world developed through industrial age, the demand for crystalline chemicals increased in variety, quantity, and quality. This led to the birth of crystallization technology that aimed at improving the methods and equipment used in crystallization operations. Modern crystallizers can boast specific production rates that are several orders of magnitude higher than solar ponds, have low manpower requirements, and low production costs. The specific requirements of a crystallizer can vary widely, depending on the nature of the product, and its intended use: pharmaceutical and food products require higher purity, for example, while fertilizers need larger crystal size; the crystal size and final moisture are not as important in crystallization systems which produce an intermediate compound. There are cases where the real product of the crystallizer is the solvent: crystallization is used to separate from the solvent A 16th century salt works 5 Crystallization in theory and practice

A key parameter for crystallization is the supersaturation. Supersaturation is the temporary increase of concentration of the solute in the solvent above its equilibrium, and is produced by evaporation, cooling, , salting out, etc. The area over the normal solubility, in which a system can be supersaturated, is also called the 1. Crystallization processes, shown in equilibrium (solubility) diagrams ”metastable” region. Supersaturation is the driving force of crystallization. Proper control of supersaturation is of critical importance in achieving acceptable results. The most common crystallization operations today are those of evaporative crystallization and of indirect and direct (vacuum) cooling: In the former, crystallization occurs after some amount of solvent is removed, and this is due to the relatively ”flat” solubility of the system at hand (Fig. 1a). In the latter case, the solubility is rather steep (Fig. 1b), and supersaturation can be achieved by cooling easily. 2. Kinetics of crystallization

The crystal growth rate, a parameter region, and secondary nucleation, that measures how fast a crystal grows, which is caused by contacts is, for most systems, exponentially between a crystal and another surface, dependent on the supersaturation (Fig. and occurs within the metastable 2). However, the end result of the crystal region (Fig. 2). Crystal-to crystal and size obtained in a crystallizer is not a crystal-to impeller contacts are the matter only of the growth rate, but most common sources of secondary also of the nucleation rate (how many nucleation. Secondary nucleation is crystals take part in crystal growth), and therefore affected by the mixing energy the attrition rate (how easily input to the crystallizer. crystals break, and how small are the broken fragments). The nucleation rate Combining these characteristics of is also a function of the supersaturation, crystallization, it can be said that and is affected by supersaturation to a large singular crystals are formed far greater degree than the growth rate at low nucleation rates. Fig. 3 is (Fig. 2). a simplification (exaggerated for As a result of these very complex purposes of illustration) of this premise, relationships, the supersaturation at and concerns two crystallizers that have which a crystallizer will operate the same amount of supersaturation, 10 must be chosen with great care. g, from which crystals will grow. This is to demonstrate the strong influence of There are two common types of the nucleation rate on the mean crystal nucleation mechanisms. size. Due to the two different nucleation Primary (homogeneous) nucleation rates (5 nuclei and 40 nuclei) the result occurs at the onset of crystallization, are two different crystal sizes; either 5 when the concentration of crystals of 2 g each or 40 crystals of 250 the solvent exceeds the metastable mg each. 6 Most crystallizers need to produce large singular crystals, because this improves crystal purity and handling characteristics, and very often the crystalline product’s marketability. To achieve a larger crystal size, it is therefore important to: ◊ Control the supersaturation in the crystallizer so that it does not exceed the metastable region; ◊ Choose an operating point of such supersaturation that growth rate is maximized; ◊ Optimize the mixing energy input so that supersaturation is controlled, while secondary nucleation is minimized.

3. Influence of nucleation on crystal size

As can be seen from the above, the method and intensity of mixing in a crystallizer is very critical, as it is what most influences the supersaturation and secondary nucleation of the system. Mixing, therefore, is a basic design feature in a crystallizer unit. The instantaneous operation cycle of a typical vacuum cooling FC crystallizer, with respect to the solubility of a system, is illustrated in Fig. 4. The fresh feed at temperature and concentration represented by point (1) enters the crystallizer and is mixed with the crystallizer contents that are 4. Control of tip supersaturation (vacuum cooling crystallization) at concentration and temperature (3). The resultant mixture is at point (2), passes through the pump, and reaches the boiling surface of the slurry in the crystallizer. Upon boiling, the solution reaches point (4), which is well into the metastable zone. The supersaturation generated in this way is consumed by crystal growth of crystals present in the crystallizer vessel, as the supersaturated liquid is cooled adiabatically to point (3), and the cycle is completed.

7 Since it is important to maintain the These ideas are embodied in the two peak supersaturation (point 4) within kinetic equations below. The mass the metastable zone, the location deposition rate (dm/dt) resp. the con- of point (2), and more importantly, that sumed supersaturation per cycle time is of point (4), can be adjusted, by design- dependent on the surface of suspended ing the recirculation rate in crystals (A) and on the level of super- the crystallizer. saturation (ΔC). Secondary nucleation

B0 depends on dissipated mixing energy If the supersaturation generated in one (ε, suspension density (m) and level of cycle is not completely consumed by the supersaturation (ΔC): end of the cycle, the starting point for the next cycle will be somewhat further from the saturation curve. After some time, the whole cycle will migrate so far into or even above the metastable Crystal size is influenced by the time zone, that it will adversely affect crystal that the crystal stays in the crystallizer growth and nucleation. It is therefore (retention time), where, under proper important to provide sufficient opportu- operating conditions, it may grow. There nity (efficient mixing) and suitable sites is, however, a competing quality in this (sufficient crystal surface) for the super- arrangement that affects the crystal size saturation to be consumed. Otherwise, adversely. Mechanical attrition (Ga) is the crystal size will suffer, and the crys- the rate of removal of material from tallizerwill be subject to incrustations. a crystal (as opposed to Gk, the linear, kinetic crystal growth rate), and it is dependent on the crystal retention time, the magma density, the mixing energy and the hydrodynamic design of the sys- tem. It is therefore to be expected that under certain conditions, crystal size will peak at a certain retention time, and

will thereafter become smaller, as Ga

overpowers Gk and the effective crystal growth rate is minimized.

8 MESSO-type crystallizers; FC, DTB, OSLO

9 Types of crystallizers

All this is considered in modern types Forced circulation crystallizer of continuous crystallizers. Crystallizers with longer retention times are The forced circulation (“FC”) crystallizer vessel is circulated, in plug flow operated with less specific energy (Fig. 1) is the most common type of fashion, through the , input, resulting in lower nucleation crystallizer in the industry. and returned to the crystallizer vessel rates. The impacts between crystals The average FC crystallizer evaporates again, where its supersaturation is and the impeller pump blades are the solvent, thus increasing the relieved by deposition of material on most effective source for the nuclei supersaturation in the process liquor, the crystals present in the slurry. The production. These impacts are at least and causing crystallization to occur. supersaturation is controlled so as 100fold more effective than crystal/wall Most conventional FC units operate to avoid spontaneous nucleation, by and crystal/crystal impacts. Therefore, under vacuum, or at slight super sufficient circulation capacity. types of crystallizers differ mainly in atmospheric pressure. The evaporated solvent is conducted design and the position of the impeller The FC consists of four basic to the vacuum system, where it is pump. components: the crystallizer vessel, condensed and removed. which provides most of the volume The FC crystallizer is used for general, dictated by the residence time simple crystallization operations, where requirements, the circulating pump, large crystal size is not a requirement. which provides the mixing energy, The FC design aims to protect the the heat exchanger, which supplies crystal size from reduction from the energy to the crystallizer (in a typical crystallizer environment, evaporative crystallization operation), but has no features to aggressively and the vacuum equipment, which increase the crystal size. handles the vapours generated in the crystallizer. Slurry from the crystallizer

1. Forced circulation (FC) crystallizer 2. Turbulence (DTB) cystallizer 3. OSLO crystallizer

10 Turbulence (DTB crystallizer)

The MESSO turbulence with draft tube and baffle (DTB) crystallizer (Fig. 2) is the typical modern type of crystallizer in the industry. This crystallizer has been named so because it provides for two discharge streams, one of slurry that contains the product crystals, and another, that is mother liquor (saturated solvent) with a small amount of fines. The configuration of the crystallizer is such that it promotes crystal growth, and can generate crystals of a larger average size than could be achieved in an FC. Most conventional turbulence crystallizers operate under vacuum, or at slight super atmospheric pressure. 4. Simplified flow sheet The turbulence (DTB) crystallizer has been studied widely in crystallization theory, and can be modelled with accuracy. Its distinct zones of growth and clarified mother liquor make it possible to define in terms of kinetic parameters, and thus growth and nucleation rates can be determined. These features make the turbulence crystallizer very suitable to mathematical description, and thus subject to good operating control. 5. Spin bath regeneration plant

OSLO crystallizer)

This crystallizer type (Fig. 3) originally The primary advantage of the OSLO represented the first major step in crystallizer until today is the ability modern crystallization technology and to grow crystals in a fluidized bed, equipment design. It was invented which is not subject to mechanical by F. Jeremiassen of Krystal A/S, circulation methods. A crystal in an Oslo, Norway, in 1924, and it took the OSLO unit will grow unhindered, to name of the city in which the design the size that its residence time in the originated. It is also referred to as fluid bed will allow. The result is that “growth-“, “fluid-bed-”, and “Krystal-” an OSLO crystallizer will grow the type. largest crystals, as compared to other As the successor of Davy Powergas’ crystallizer types. The slurry is removed and A. W. Bamforth’s crystallization from the crystallizer’s fluidized bed and technology, MESSO owns all sent to typical centrifugation sections. documentation of OSLO installations Clear liquor may also be purged from built by these two companies. This the crystallizer’s clarification zone, if background, added to MESSO’s own necessary. From each of these basic extensive experience makes MESSO the types of crystallizers a number of premier designer of OSLO crystallizers different applications are designed from 6. Planning model of an evaporative in the world. MESSO engineers to fulfil the special crystallization plant (Abu Dhabi) needs of the customers. 11 Peripheral components

The crystallizer is the heart of a 25%wt. in the crystallizer, while crystallization system, but there are a centrifuge operates best at 50 to several components, in the periphery, 60%wt. suspension, the suspension that need to be considered before the is preconcentrated in thickeners or final product can be collected. The hydrocyclones. The underflow of the suspension from the crystallizer has thickener or hydrocyclone is sent to the to be separated, the crystals have to be centrifuge for separation. Depending dried and packed. The vapours have to on the product CSD (and to a lesser be condensed and the noncondensables degree on the physical properties of the to be extracted by vacuum pumps. suspension) there is a choice between Fig. 4 shows a simplified flow sheet of a types of centrifuges: generally, the complete crystallization plant operated decanter and peeler are used for smaller on the principle of evaporative particles, and the screen bowl and the crystallization under vacuum. pusher for larger particles. In some Details from a picking bath liquor Depending on process considerations cases of very small particle sizes or very regeneration unit (crystal size, evaporative duty, etc.) one fragile crystals, filters are used, instead of several types of crystallizer can be of centrifuges. Filters, however, are installed instead of the FC crystallizer usually not as efficient as centrifuges in shown, including multiple-effect units. separating the solvent from the crystals. Instead of using steam for heating (as The small amount of residual solvent shown), one could utilize mechanical or left on the crystals after the separation thermal vapour recompression. step, is removed in a dryer. In the illustration, the vapours from There are several types of dryers that the (last) crystallizer are condensed in are used, depending on crystal size, a surface condenser; however, a mixing crystal chemistry (reactive nature, condenser could be chosen, instead. tendency to decompose, oxidize, etc.), The suspension in the crystallizer can crystal fragility, and initial solvent be withdrawn by overflow, as shown, or content. The most common types of pumped out, using pumps with special dryers used are fluid bed (stationary or specifications. Because suspension vibrating), and the flash dryer. densities are usually between 15 to

Details from a picking bath liquor regeneration unit 12 Application examples

Melt crystallization of Vacuum cooling crystallization bisphenol A adduct

Beside a number of applications for Vacuum cooling crystallization is inorganic products (e.g. Glauber’s salt, usually chosen if the solubility of the carnallite) modern surface cooling substance to be crystallized is strongly suspension crystallizers are used also dependent on temperature, and if the for melt crystallization, e.g. to crystallize vapour pressure of the solvent is high bisphenol-A (BPA) phenoladduct, enough for this application to allow the prepurification step for the melt the use of conventional vacuum from synthesis. The eutectic point equipment. Vacuum cooling of the melt is about 39°C, and the crystallization is the preferred cooling crystallizer is operated at 45–50°C. The crystallization method for continuous BPA, which is used in the production operation conditions, due to the fact of polycarbonate, is crystallized in a that the supersaturation is generated Loop crystallizer for bisphenol A adduct surface cooled crystallizer from the by adiabatic cooling of the solvent at melt, which consists of BPA, phenol the liquor level. This means that the The selection of equipment and the and some impurities. The pure crystals energy is removed from the crystallizer design of a crystallization operation is are separated in centrifuges and at a location that is far less prone to dependent on, and influenced by washed with phenol. The design should encrustations, and with a method that several process-specific factors. The recognize the tendency of the product requires far less mixing energy input to following examples illustrate how to form incrustations on the heat the crystallizer slurry. these factors influence the choice of exchange surfaces, there being the place crystallizer type: of the highest supersaturation in the entire system. Polished surfaces and Surface cooling crystallization small temperature differences are some of the techniques used in modern Surface cooling crystallization will designs to control the effects of this be selected if the solubility of the problem. The surface-cooled crystallizer substance to be crystallized is strongly is a simple FC unit, in which the dependent on temperature, and if process slurry is cooled in the tube-and vacuum cooling crystallization cannot shell heat exchanger in the circulating be chosen, e.g. the vapour pressure loop (loop crystallizer). Growth type required to achieve the endpoint crystallizers are not commonly chosen, temperature is too low for the plant due to the low settling rate of the utilities, or too expensive. crystals, which makes fines separation at the crystallizer very difficult.

Spin bath regeneration plant 13 Potassium chloride refinery for industrial grade quality, triple-effect vacuum cooling crystallization

Vacuum cooling crystallization Recovery of pickling bath of potassium chloride effluent liquors

This example shows the recrystalli- Vacuum cooling crystallization can zation of potassium chloride in also be used to purify solutions, by industrial grade from fertilizer quality. crystallization of the solute. The The crude KCl is dissolved at elevated pickling of mild steel sheets with temperatures in a recycled stream of sulfuric acid produces an aqueous waste mother liquor. The resulting solution, stream containing ferrous sulfate and now saturated with potassium sulfuric acid. Cooling of that solution chloride, is fed to a multiple-stage, forces ferrous sulfate to crystallize as vacuum cooling crystallizer train. FeSO4.7H2O. From the viewpoint of the In order to fulfil the requirement of mother liquor composition, this is a Vacuum evaporators for brine concentration coarser crystals, the type selected is way to purify the solution. At the same the DTB crystallizer. Fines dissolving time, the seven molecules of water that is possible, by adding water to each is removed with the crystallized ferrous crystallizer’s clear liquor overflow. The sulfate causes the reconcentration of number of stages is optimized on the the sulfuric acid. The solution basis of maximum heat recovery (the thus treated can be recycled to the recycled mother liquor is reheated in pickling bath. The vacuum cooling is condensers using the vapours leaving achieved in a single-effect draft-tube the hotter crystallizers). Barometric crystallizer which is operated together (direct-contact) condensers are usually with a high-vacuum generator (a employed, so that the water content steam ejector or chilled water surface of the mother liquor is increased, condenser). This modern process may and thus its dissolving capacity is be operated for a couple of months improved. Steam is used (in separate without interruptions for washouts. heat exchangers) to heat the recycled, and diluted, mother liquor to the temperature required by the dissolver step, and the loop is closed by returning the mother liquor to the dissolver. The crystals are separated in pusher centrifuges, washed and dried. The typical crystal sizes averages are 0.8 to 1.0 mm.

14 Evaporative crystallization Crystallization of sodium chloride

Evaporative crystallization is usually This example shows a crystallization crystals are dried and packed. In order a process that is conducted under plant for table salt, operated with to maintain the level of impurities vacuum, just like the vacuum cooling concentrated brine from a solar pond. in the system to an acceptable level, crystallization. This process is chosen In addition to three FC crystallizers, some mother liquor is removed as when solubility of the solute is nearly there is an OSLO crystallizer, used by hydrocyclone overflow, and purged. independent of temperature. As the plant to produce a fraction of its Some plants of this type have been in vacuum cooling crystallization, output as coarse crystals. The plant is supplied for the production of up to special scaling problems are not a operated as a quadruple-effect unit. 2.5 t/h coarse (mean size greater than serious problem as long as boiling on The coarse crystals from the OSLO 2 mm) salt and additionally 10 t/h of the heater surface is avoided, and are separated on a pusher centrifuge, normal salt. the special case of inverse solubility whereas the salt produced in the FC (solubility decreases with temperature) crystallizers is separated on screen is recognized and taken into bowl centrifuges, after being counter- consideration. currently washed with fresh feed liquor in a washing thickener. The product

Salt recovery from solar brine with OSLO crystallization

15 Modern applications in environmental protection

Flue gas desulfurization (FGD): crystallizers supplied to recover calcium to minimize caffeine decomposition. scrubber effluent chloride dihydrate salt. The first stage is The process encompasses active carbon a gypsum seeded preconcentrator, and treatment used to remove impurities Concentration of scrubber effluent the second stage is the calcium chloride that influence the product colour, from FGD systems in thermal power crystallizer. The crystal product is followed by a two-stage falling film plants has been practiced for about separated on a screen bowl centrifuge, evaporator driven by process vapours two decades. Plants for concentration dried, packed and reused in another compressed to a higher pressure by of these waste waters to dryness are industrial application. a single mechanical compressor. In in fact evaporative crystallization order to minimize residence time in units, and should not be designed as the evaporators, the final concentrate simple evaporation units. Usually, FGD Recovery of caffeine is produced in a separate, smaller concentration units are combined with unit. This concentrate is finally cooled pretreatment facilities, such as heavy When caffeine is extracted from to ambient temperature in a surface metals precipitation, in order that it coffee by the supercritical carbon cooled loop crystallizer, to crystallize may be possible to recover a brine or a dioxide method, a caffeine containing caffeine monohydrate. The crystals are product salt pure enough to be recycled waste water is produced. Evaporation, calcined to remove the water of in the process. This example shows an combined with a surface cooling hydration, and packed. This caffeine installation for the concentration- crystallization separates this waste product is used in the manufacture to-dryness of the liquid effluent from a water into a caffeine of food grade of soft drinks. flue gas cleaning system in an industrial quality, and pure distillate which can be waste incineration facility. This plant reused for the decaffeination process. consists of a heavy metals precipitation Short residence times at the higher and a double-effect evaporative temperatures is important in the crystallization unit, with two FC evaporative step of this process, in order

Triple-effect four stage evaporation crystallization of ammonium sulphate in DTB (caprolactam process) with after-crystallization (FC) 16 Salt from secondary aluminum slag

When aluminum scrap is molten centrifuge, dried and compacted into down, the liquefied aluminum must pellets which can be reused in the be protected from exposure to the generation of the molten salt layer (in atmosphere to avoid its oxidation and the beginning of this process). to absorb the impurities of the scrap. This protection is provided by a layer This crystallization method can be used of molten salts, preferably a mixture for the recovery of a single salt, as well of potassium and sodium chloride as salt mixtures. that floats over the aluminum. This salt remains after the recovery of the aluminum, and is cast into ingots. Because of the impurities in this solid mass, left over from the scrap Vacuum cooling crystallizer for copperas aluminum residue, exposure of the ingots to humidity causes evolution of Vacuum filter for citrate extractrion various gases. The gases evolved are poisonous and Ammonium sulfate from the centrifuges, where the crystals are explosive, and the generated caprolactam process washed and separated from the mother from dissolution of the ingot liquor. The centrifuged crystals are is saturated with salts. Consequently, Ammonium sulfate is a by-product of dried and screened, and the undersize landfill-disposal of this waste was the synthesis of caprolactam. Multiple fraction is recycled for recrystallization. severely restricted in Europe during effect evaporative crystallization The centrate is taken over by an the eighties, and processes had to be is the well-established process to after crystallizer (FC) to improve developed to solve this problem in an recover crystalline ammonium sulfate yield. These fine and impure crystals environmentally sound way. and market it as fertilizer. In the last are concentrated by means of an few years, the fertilizer marketplace has hydrocyclone and the concentrated The slag is treated mechanically to seen an increased demand for larger suspension is redissolved in the feed recover most of the metallic aluminum crystals, and for a narrower size liquor. A part of the hydrocyclone for direct recycling, and is then fed to distribution. The example shows a overflow is taken as the liquid process a cascade process at elevated triple effect evaporative crystallization purge. temperatures to achieve fast degassing plant using DTB crystallizers for the under controlled process conditions production of ammonium sulfate of an and to dissolve the salts. The degassing average crystal size of about 2 mm. The is made in the absence of atmospheric solution is fed counter-currently (with air, thus ensuring that the whole system respect to the steam flow sequence) operates above the gas mixture’s upper in order to improve crystal growth explosion limit. The gases evolved conditions by combining the are purified and fed to an incinerator highest process temperature and that allows the plant to recover the highest impurity concentration. The combustion energy. After degassing, the MESSO turbulence (DTB) crystallizers remaining residue is separated from the use bottom-entry, custom-designed salt solution by filtration on a . axial flow internal recirculation The filter cake containing aluminum pumps, which provide superior mixing oxide is usually sent to a landfill. characteristics at a lower power The solution is fed to a single-effect requirement than common agitators. mechanical vapour recompression The product crystal size is evaporative FC crystallizer, operated enhanced by fines destruction systems. at about atmospheric pressure. The Each DTB crystallizer discharges slurry resulting crystallized mixed salt to a common slurry collection Salt crystallizer; modified FC-type product is separated on a pusher tank. The slurry is then fed to pusher 17 Research and development services

Chemical laboratory and pilot plant facilities

the chemical compositions of solutions and minerals. Our research and development facility has equipment that accurately represents most types of crystallizers, and this is used as necessary to simulate the specific design envisioned for our clients. These process designs can be tested in small pilot plants brought together according to the specific process requirements, and samples can be produced for further (market) tests. In case of products The MESSO chemical laboratory that are too sensitive to be shipped and pilot plant facility is available to to our facility, or that require special develop the basic information necessary handling (due to safety or health for the design of crystallization plants concerns) our team may perform the as well as the most appropriate overall necessary tests or investigations in processes for our clients. The chemical our clients’ facilities. We are proud laboratory is able to define physical to have developed and optimized properties to the crystallizer designer, production processes for the chemical, such as the metastable zone width pharmaceutical and food industry (supersaturation), desupersaturation jointly with our customers and tailor- rates, viscosity, density of a range of made for the individual project. compositions, the system solubility, We continue to improve – for the formation of mixed crystals, as well as benefit of our customers.

18 Our product experience

Acetylsalicylic acid & salts Magnesium ammonium sulfate Sodium salicylate Adipic acid Magnesium chloride Sodium sulfate Ammonium bromide Magnesium hexafluorosilicate Sodium tartrate Ammonium dimolybdate Magnesium sulfate Sodium thiocyanate Ammonium hydrogenfluoride Malic acid & salts Sorbic acid & salts Ammonium sulfate (also by reaction) Methionine Sulfanilic acid & salts Ammonium thiosulfate Ascorbic acid & salts Nickel acetate Tartaric acid & salts Nickel nitrate TMP Benzoic acid & salts Trimellitic acid Bisphenol A Pentaerythritol Potash from various sources Urea Caffeine Potassium bromide Vinasse evaporation Calcium chloride Potassium carbonate Calcium formate Potassium chlorate Yeast effluent processing Calcium tartrate Potassium chloride Carnallite Potassium dichromate Zinc sulfate 6-hydrate Citric acid & salts Potassium hydrogencarbonate Zinc sulfate 7-hydrate Cooling Tower Blowdown Potassium permanganate Copper chloride Potassium phosphate (Industrial) Copper sulfate Potassium sulfate Potassium sulfate from Dextrose (Glucose) Na2SO4 & KCl (conversion) Dichlorobenzene Dicyandiamide Salicylic acid & salts Dipentarythritol Salt (based on sea salt respectively brines) Epichloro hydrine process Silver nitrate effluent ZLD Sodium acetate Sodium ascorbate Ferrous sulfate from process effluents Sodium carbonate Ferrous sulfate from TiO2 Sodium chlorate Fumaric acid & salts Sodium chloride from sea salt Glutamic acid & salts Sodium chromate (& Na2SO4) Guanidine nitrate Sodium cyanide Sodium dichromate Hexachlorocyclohexane Sodium disulfite Sodium dithionite Isomaltulose Sodium fluoride salts Ketogulonic acid & salts Sodium formate Sodium glutamate Lactic salts Sodium ketogulonate Lactose Sodium nitrite (waste) Landfill Leachate Sodium perborate Concentration & ZLD Sodium perchlorate Lauryllactam Sodium phosphates (industrial)

19 Contact us at: www.gea-messo-pt.com

Competence centers in crystallization

Process Engineering GEA Messo PT

Germany: The Netherlands: Friedrich-Ebert-Strasse 134 De Beverspijken 7b 47229 Duisburg 5221 EE ‘s-Hertogenbosch Tel. + 49 2065-903 0, Fax + 49 2065-903 199 Tel. + 31 73 6390 390, Fax + 31 73 6312 349 info.geamesso.de @ geagroup.com sales.niropt.nl @ geagroup.com 03/2010 All rights reserved. Printed in the Netherlands All rights reserved. 03/2010