DD227689A1 - PROCESS FOR REMOVING SULFATIVE OVERRIDING OF SALT SOLUTIONS - Google Patents

Abstract

The invention relates to a process for the degradation of sulphate Uebersaettigungen in the evaporation of solutions of Kalirohsalzverarbeitung. The invention has the object and the object to develop a method for the degradation of sulfate oversubsidia in the evaporation of saline solutions by Impfkristallzugabe. The technical task has been solved by a selective Impfkristallrueckfuehrung made to the evaporation process.

Description

Title of the invention

Process for breaking down sulphate supersaturations of salt solutions

Field of application of the invention

The invention relates to a process for the degradation of sulphatic supersaturations in the evaporation of solutions of Kalirohsalzverarbeitung. The process can be used in the preparation of potassium salts from hard salts, the processing of which is not possible by the undesired formation of sulphatic double salts with the hitherto practiced hot-dissolving process, and in the preparation of concentrated magnesium chloride solutions from mixed salts (hard salt and carnallitite).

Characteristic of the Known Technical Solutions For the desulphation of salt solutions, a number of processes are known which are carried out according to the principle of precipitation, deep cooling and evaporation.

To avoid unwanted double sulphate formation in hard salt processing, there are proposals for reducing the MgSO ₄ content of the circulating operating solutions by desulphating a partial stream or the entire circulation solution. It is known to deep-freeze with crystallization of Epsom salt (MgSO ₄ .7H ₂ O), kainite (KGl MgSO ₄ 2.75 H ₂ O) and schoenite (K ₂ SO ₄ .MgSO ₄ .6H ₂ O) and evaporation to higher MgCl ₂ contents with crystallization

of ieserite (MgSO ₄ .E ₂ O), 5/4 hydrate (MgSO _4, 1.25H ₂ O) and langbeinite (EpSO ₄ .2MgSO ₄ ) followed by separation of the crystals.

During the evaporation of salt solutions, the sulphate content is lowered according to the requirements before, during or after the evaporation process.

Desulphurization prior to evaporation is necessary if sulphurised salts (negative temperature coefficient of solubility) and impurities of the products are unavoidable. This is "the case with saline evaporation for NaCl production" where a chemical cleaning of the Eohsols by means of soda and lime (or caustic soda) is carried out with the aim of precipitating the CaSO ₄ as far as possible. Prior to the evaporation of MgOl ₂ -LOSUiIgen can be reduced by known methods, the MgSO ₄ content by adding OaCl ₂ , but CaS0 ₄ supersaturations of the solutions Frequently, desulphation of the solution is carried out after the evaporation process. Lifting Precipitation methods is the so-called thermal desulphation, in which the solution is kept at high temperatures for several hours and turbulence is added, so that degradation of sulphate can occur Saturations by the interaction of residence time, turbulence and temperature occurs. There are also proposals to reduce the residence time by adding seed crystals, where possible, the salts used in the "supersaturation degradation crystallizing in fine-grained form (large specific surface area) should be used.

Since the Entsulfatisierung before or after the evaporation process with additional energy and equipment expenses and often with a use more expensive. Chemicals have been developed, methods have been developed for the reduction of sulphate supersaturations immediately during evaporation, which also reduces the heating surface

The so-called gypsum sludge process is used in the saline industry, which prevents surface encrustations and ecoduct impurities through the use of GaSON seed crystal recirculation · This process has also been transferred to other processes, such as the production of drinking water and evaporated salt from preconcentrated seawater of sulphide waste liquor in the pulp industry and of zinc sulphate solution and on the production of GaClp from waste products of soda industxia ·

There are also proposals to reduce over-saturation in the process automation of the building industry and in the production of concentrated MgCl ₂ solutions

In the second Pail a process was realized (DD WP 200 2728) in which during the evaporation process only MgSO.sub.2 and NaCl were crystallized out, the crystals were separated by hot clarification and partly as seed material for evaporation.

Due to the high NaCl content (60 percent) of the Eristallisates the effectiveness is limited, and the evaporators are subject by the high solids loading (up to 300 g / l) in TSawälzkreislauf a high wear.

Another method (DE AS 251 3947) provides for the addition of Langbeinit seed crystals in the preparation of concentrated MgClp solutions by Eindanipfung mother solutions of Kalidüngesalzherstellung · In the evaporation process Langbeinit is crystallized, separated and partially converted to Ealiumsulfat fertilizer, and a part of Langbeinits is recycled as inoculant · It is also a method known by the processing of hard salts unwanted Doppelsulfatbildungen by lowering the MgSO ₂ ^ content of the circulating operating solutions by evaporation of a partial stream of the hot saturated solution from the EohsalzverlÖsung under

Langbeinit-Impfkristallückführung and addition of fine-grained EJl are to be avoided. The seed which is separated from the evaporated solution is contaminated by MaGI, resulting in disadvantages with respect to the rate of crystallization and the content of the circulating solution in the evaporation plant.

Object of the invention

The aim of the invention is to avoid the disadvantages of the known processes for the reduction of sulphate supersaturations in the evaporation of salt solutions by seed crystal recycling and thus to improve the economics of the preparation of Kalidüngesalzen from hard salts, in the processing of the double sulphate must be prevented, and the production of concentrated MgCl 2 solutions to contribute from mixed salts.

DISCLOSURE OF THE INVENTION The object of the invention is to develop a process for breaking down sulphate supersaturations in the evaporation of salt solutions by seed crystal addition, which increases the effectiveness of the seed crystals and high cloud densities (rapid wear of the apparatuses and pipelines) in the evaporation stages be avoided.

It has been found that the degradation of sulphate supersaturations in addition to the known factors such as residence time, turbulence, amount and grain size of the seed crystals is also influenced by contamination of the seed material such as HaOl. The use of contaminated inoculum reduces the rate of crystallization, which can not be compensated by increasing the amount of added pail. In the case of stronger impurities, the increase in the concentration of the pesticides is also limited by the maximum possible cloud densities in the evaporation stages.

Surprisingly, it has been found that the seed crystals of

Magnesium sulphate (for example MgSO.sub.2. 1,25 H ₂ O) or Langbeinite (E ₂ SO 2 .HgSO.sub.2) usually has a substantially smaller particle size than the undesired constituents, so that separation by wet classification is possible ·

According to the invention, the object is achieved in that a selective Impfkristalllückführung is made for evaporation process Aus.der hot evaporated solution, the unwanted crystal components are largely removed by wet classification and then separated the sulfate-rich solid by hot clarification of the solution. In certain cases, the Eristallisat can be almost completely separated from the evaporated solution and recovered from the resulting suspension optionally using additional Anstellösungen by Haßklassierung the solids fraction for Impfkristallverwendung · In order to prevent crystallization of other salts, the wet classification and hot clarification must be carried out at temperatures , which are not substantially below the discharge temperature of the suspension from the binder · The purified seed is added in the formulated amount to the evaporation plant in the required amount, the excess Eristallisat can be halved or further processed after further liquid separation · The supply of Impfkristallisates to the evaporation process must be in multi-stage Plants are carried out in the stage in which the solution is already almost saturated with sulphate salts, whereby dissolution is prevented · When commissioning the On steam system, the seed crystals v-or the achievement of sulphate supersaturations in the solution from a heated Eührbehälter, which must be filled before the shutdown of the system, are supplied. For longer interruptions of the evaporation process, the seed crystals can also be separated from the solution by centrifugation and intermediately stacked. In this case, the recrystallizate is when restarting the plant in

Add saturated saturated solution and at the required time in a suspended form.

The invention will be explained in more detail with reference to two exemplary embodiments.

Embodiment 1

100 nr / h of a solution having the composition 216 g / l KCl, 171 g / l HaGl, 58 g / l MgCl ₂ , 50 g / l MgSO ₄ and 787 g / l

• JQ HpO, which is obtained in a processing process for the production of potash fertilizers, are fed with a temperature of 95 ⁰ C an evaporation process. With the addition of seed crystals containing, in addition to other salt fractions, 4 t / h of a crystallizate consisting of 90 percent langbeinite and 10 percent sodium chloride, 6.5 t / h of water are removed from the solution during this evaporation process. Is formed 96 nryh solution with the composition 243 g / l KCl, 167 g / l UaCl, 66 g / l MgCl ₂ * 25 g / l MgSO ₄ and 768 g / l H ₂ O at a temperature of 110 ⁰ C.

₂ q and 8 t / h of crystallizate, which consists of 80 percent langbeinite and 20 percent sodium chloride. According to the invention, this suspension is subjected to a hate-classifying process in which 0.8 t / h of sodium chloride are separated off in a thickened salt slurry which is present in the

₂ c processing process is returned so that the pesticide enters the Yerarbeitungsrückstand. The remaining suspension is then clarified in a thickener, wherein the pesticide is largely recovered in a salt slurry on the underflow. From this salt mash are suitably 4 t / h of pesticide, which consists of 90 percent Langbeinit and 10 percent of sodium chloride, recycled in the evaporation process, 3 »2 t / h of pesticide of the same composition are led out as an intermediate from the process and further processing to potash fertilizers. The solution resulting from the thickener overflow is likewise

re-fed processing process.

Embodiment 2

100 m-yh oarnallitol of the composition 326 g / l MgCl ₂ 23 g / l MgSO ₄ , 42 g / l KDl, 26 g / l NaCl and 864 g / l H ₂ O are obtained by removal of 25.5 vb water in a two-stage countercurrent evaporation plant to a concentration of 430 g / l MgCl ₂ , 13 »5 g / l MgSO ₄ , 56 g / l EDl, 24 g / l ITaCl and 8O5 g / 1 H ₂ O evaporated, wherein 75, 8 m ^ / h solution incurred. The evaporation takes place at temperatures of 80 ⁰ C in the Brüdenbeheizten stage 1 and 120 ⁰ C in the steam-heated stage 2 using saturated steam at 350 kPa

 In stage 2 are 9 1 / h salt mash, the substantially

each consisting of 5800 kg / h solid magnesium sulfate - 5/4 hydrate and kg / h sodium chloride and an adhesive solution with 430 g / l MgCl ₂ and the other components in the specified ratios, fed as inoculum. 1528 kg / h of MgSO _4. 1> 25 H ₂ O and 780 kg / h of NaCl crystallize out of the solution in this stage.

The withdrawn from the evaporation stage 2 120 ⁰ C hot suspension consisting of 82.2 m-yh solution with 430 g / l MgCl ₂ , 7328 kg / h MgSO ₄ . 1.25 H ₂ O and 1460 kg / h ITaCl, is charged to a Eundkläparparat sediment in the 692 kg / h coarse sodium chloride and 810 kg / h MgSO ₄ · 1.25 H ₂ O with a much smaller particle size and from removed from the process. The overflow of the Bundkläparparates passing turbidity is practically completely clarified in a downstream thickener.

From the underflow of the thickener 9 m-yh salt mash with 5800 kg / h MgSO ₄ .1.25 H ₂ O and 680 kg / h HaCl are branched off and recycled to the evaporation stage 2, while 710 kg / h MgSO ₄ . 1.25 H ₂ O and 83 kg / h HaCl also out. be removed from the process. 8 kg / h MgSO ₂ ,. 1.25 HO and 4.5

T ¹ Cm.

oc kg / h HaCl pass through the thickener upper reaches and enter the cooling stages with the hot solution

Evaporation are downstream. After cooling to 26 ⁰ C, the magnesium chloride brine of the composition thus obtained is 461 g / l IiIgCl J ₂ 18.8 g / l MgSO ^, 2 g / l is Cl, 4.5 g / l Nagl and 856. g / l H ₂ O separated from the crystallized in the cooling stages 15 »3 t / h carnallite by clarifying in a further thickener ·

Claims (5)

invention claim 1. A process for the degradation of sulphate supersaturations of salt solutions in the evaporation by Impfkristallzugabe characterized in that a selective Eristallrückführung takes place, the unwanted PB components from the evaporated solution by wet classification largely removed, the sulfate-rich crystals separated by hot clarification of the solution and partially in a suspended form is attributed to the Sindampfprozeß as inoculant. 2.. Method according to item 1, characterized in that the dimension classification and the hot clarification are carried out at temperatures which do not differ significantly from the boiling point of the solution in the last steam stage. 3 · Method according to item 1 and 2, characterized in that the supply of the seed crystals takes place in that evaporation stage, in which the solution is already saturated in sulphate salts. 4. The method according to item 1 to 3, characterized in that the seed crystals at the beginning of the evaporation aas a stack container, which is heated and provided with a stirrer, are fed at a time in a suspended form, at which the saturation of the solution of sulfate salts almost is reached. · 5. Process according to items 1 to 4, characterized in that prior to the completion of the evaporation process, the amount of seed crystal is collected in a heated and stirrer-equipped stacking container and interposed in suspended form, which is at the beginning of the evaporation process according to point 4 'is.