The technological peculiarities of brines by desalination of mineralizated waters

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The technological peculiarities of brines by desalination of mineralizated waters

Hasanov A.A.

Mamedova F.M.

Abstract

desalination process brine

The technological scheme of discharge brines utilization of desalination plants is proposed, which is based on a change of the complex stage of NaCl - Na2SO4 system separation on comparatively simple and sifficiently studied stage of NaCl - CaCl2 system separation. It is based on the deep desulphatization of brines by calcium - containing solutions, produced in their own technological cycle of processing and includes the stages of gypsum crystallization, precipitation of magnesium hydroxide, thermal separation of the NaCl - CaCl2 system.

Key words: discharge brines, desulphatization, crystallization, precipitation.

Main part

The refining industry is one of the branch, consuming a huge amount of water. At the all stages of technological processes the waste waters are formed. Depend on source of its formation, the waste waters are subdivided on neutral, oil-containing, salt - containing (discharges of electro-desalination plant-EDP), sul - phur-alkiline, acid, hydrogensulphide-containing. The total mineralization of saltcontaining discharges of EDP is within 30-40 g/l [1]. These waste water are related to waters of sulphate-choride type. By aim use of electro-desalination plant waste waters a possibility of their desalination have been studied after removal from its composition of oil products, [2]. The results of given research shown that the discharge brines of desalination plants contain the components of initial water, but in more concentrated form. The consentration degree of these brines depend on ion composition of initial water and method of its processing.

By ion-exchange purification-by Na, Mg-Na. Cation - exchange process, and Cl, NaCl - anion - exchange process the discharge brines are formed on stages of regeneration and washing of ionites, are characterized by supersaturation by gypsum and by more high salt content - from 90 up to go g/l depending on method washig of ionite [3]. The existing technologies utilization of minirelizated waters brines are complicate and no ever ensure the formation of homogenous salt products.

Since the waste waters from electro-desalination plant of refining factories are related to waters of sulphate-chloride type, then a majority of known decisions by utilization of the brines include the sufficiently complicate stage of NaCl - Na2SO4 - H2O system separation [4]. A complexity of this stage and a problem receive of homogen products in significant degree connect with nearness of solubility of this system components.

The aim of research was study of technological peculiarities of the scheme utilization of discharge brines of of minirelizated waters desalination plants.

The essential difference in solubility of component of the last simplify and make cheaper the processing. The proposed technology, shown on the picture 1, include: the deep desulhatization of brine by processing of it by CaCl2 in crystallizer - settler 2 with precipitation and filtration of gypsum; lime pretreatment of mother solution in settler 3 with precipitation and filtration of Mg(OH) 2; acidification; evaporation of mother brine (NaCl - CaCl2 - H2O) in evaporation plant 5 up to total concentration of salts equal 400 g/l with crystallization of NaCl and separation of it in centrifuge 8. The residual brine CaCl2 with small admixture of NaCl (~1.8%) is partly recycled in initial brine for desulphatization and the rest amount of CaCl2 is taken from system as markeable product corresponding to state standard 450 - 58. Part of secondary steam condensate is used for washing of chemical products, the remaining amount is mixed with base flow of desalinated water.

1 - Crystallizer - settler of gypsum; 2 - settler for precipitation of Mg(OH) 2;

3 - Tank for lime milk; 4,5 - evaporation plant; 6 - filtrating equipment; 7 - centrifuge for separation of NaCl; I - discharge brine; II - CaO; III - acid; IV - secondary steam; V - initial steam; VI - condensate; VII - CaSO4 - 2H2O; VIII - Mg(OH) 2; IX - CaCl2; X - NaCl

Picture 1. Technological scheme utilization of discharge brines of desalination plants

The main peculiarity of given technology from ecological and economical point of view is recirculation of the CaCl2 part in utilized brine.

Taking into consideration the technological - economic indices it is necessary to reduce to a minimum the consumption of CaCl2, but by that with aim prevention of magnesium hydroxide pollution by gypsum and creation of conditions for scale - free regime work of evaporation plant the technological limitations on de - sulphatization depth must be taken into consideration. Residual content of sulphate-ions in brines, processed by CaCl2, may be calculated by empirical equation of plural regression:

[SO4]^res =461 e^{(-a0026 CaCl2} > (0,987 +0,001 NaCl)

(0,013 Na2SO4 - 1,3) (1)

The received equation is correct in following field of concentration change (mg-eqv/l): CaCl2=800-2000; NaCl=450-1650; Na2SO4=150-450 and temperatures 20-40⁰C. Calculation by equation (1) shown that a deep

1-Concentration degree of initial water m=5; 2 - m=6; 3-m=7

The residual content of sulphate-ions by processing of mineralizated waters concentrates makes up 7-10 mg - eqv/l. This sulphates content is enough for exclusion of gypsum separation on lime pretreatment stage, but it is not enough for effective of scale - less work of evaporators. According to [6] a scale formation is eliminated also by introduction of nanoparticles on base of anhydrite. By evaporation of solution a scale is not formed, the relatively big crystals of sodium salt are formed and the anhydrites crystals grow extremely slowly.

Picture 2. Concentration of residual sulphate - ions depending on specific consumption of calcium containing solution

Considered technology conclude the stages of sedimentation and filtration of gypsum and magnesium sediments. Gypsum sediment may be separated from brine in radial, multishelf settlers.

By experimental research on settler model it have been determined, that dependence of sedimentation effect P (relation of clarified zone height to the total height) from time sedimentation (t) in the field concentration of sediment equal C=20-40g/l is good approximated by empirical formula:

p = - c-igt 0,102-0,005C (2)

The relative error of this equation don't exceed 8%. According to calculation by C=40g/l and initial height of sediment layer 2,5 m - a time necessary for clarification of solution on 2/3 height, makes up 60 desulhatization (97-98%) is achieved in field values of specific consumption CaCl2, equal 0,3-0,4 m³/m³ (pnc.2).

For simplification of the stage separation of gypsum particularly by big consumption of utilizated brine, instead of gravitational settlers the vortex reactor with weighted layer of sediment are recommended.

In research [7] by precipitation of magnesium hydroxide from used regenerative solutions of Na-cation filters in schemes of the complex processing of mine water it is shown that a known equation for aggregating substances tp/te = (hp/h:)ⁿ [8] may be used for calculation of settlers and the experimental value of degree index being n=0,8is determined. But these research are conducted in concentrated solutions of sodium chloride and magnesium concentration up to 250 mg-eqv/l. For brines of more high mineraliztion the high concentrations of magnesium and the comparatively low concentrations of sodium chloride are characteristic. Therefore on the columns with different height of layer the sedi - mentative properties of magnesium hydroxide sediment with concentration 7-14 g/l characteristic for considered conditions are investigated. It have been determined, that in given conditions also the value of n may be accepted equal 0,8.

Proceeding from possibility calculation of technological parametrs of settlers by data, received in laboratory cylinders with small height of water column (by h=40sm), the dependence of precipitation duration of Mg (OH) 2 with clarification of 2/3 height of layer from total concentration of sediment (C), temperature (t) in field 20 - 50°C and concentration of NaCl (CNaci) in field 4-10% is investigated. The following regression equation is received:

^T2/3⁼0,8C+1,2 CNaCl+0,13T - 0.08C CNaCl -

0.02C_№Crt + 0.0016C CNaCl - 0.013CT - 7.4 (3)

The average error of equation - is 4,4%.

The calculation shown that in industrial conditions by initial height being equal 2,5 m, the rate of coprecipitation of magnesium hydroxide forming on stage of lime pretreatment of desulphatizatizated concentrates of mineralizated waters (C=10,2 g/l, CNaCl=4,9%, t=40⁰C), make up 32 sm/hour. That kinetic of magnesium hydroxide precipitation is considered will do quite well for periodically conducted process [7]. For intensification of the process separation of Mg(OH) 2 the membrane modulus on base of tubular filtrating elements may be used. According to [8] by specific capacity of memberane -10^-6 m³/(m² ¦ sec) and by working pressure 0,2 MPa the selectivity made up 95%.

From essence of the proposed technology utilization of desalination plants brines it is follow, that it may be recommended for processing of mineralizated waters concentrates.

By given technology both brine of thermal and membrane desalination plants may be utilizated.

Conclusions

0. The technological scheme utilization of desalination plants discharge brines is proposed

1. The plant is based on change of complicate stage separation of NaCl-Na2SO4 system on comparatively single stage separation of NaCl-CaCl2 system

2. The empirical formules for calculation of residual concentration of sulphate-ions, effect of gypsum sediment precipitation, duration of magnesium hydroxide precipitation are proposed.

Literary references

1. Shitskova A.P., Novikov Y.V. Environment protection in refining industry-M. Chemistry 1980-175 ^p

2. Development of wasteless technology processing of waste waters with high content of salts /Mamedova F.M., Huseynova M.A. /Science, technology and education №5 v. 1, 2017 p. 32-35

3. Feyziyev Q.K. Higheffective methods of softening and desalination of water-M. Energyatom issue, 1988-192 p.

4. Complex processing of mineralizated waters / A.T. Pilipenko, I.Q. Vakhnin. Kiyev: Nauk Dumka, 1984. - 284

5. Author certificate USSSR MKICO2F 1/04. Method processing of waste waters of Na - cationite filters / Y.N. Reznikov, I.Q. Rugulenko. was published 30.08.81. Bulletine N32

6. Furman A.A., Beldy M.P., Sokolov I.D. Sodium salt. Production and use in chemical industry - M. Chemistry 1989-272 p.

7. Softening of regenerativ solutions of Na - cationite filters by sodium hydroxide / A.B. Zabralo, Q.K. Shablovskaya. // Chemistry and technology of water - 1995. - 7, №1. - p. 12-16

8. Ditnersky Y.I. Khojainov Y.M, Titov A.A. Perspectives development of complex technology separation of mineral raw material and production of sweet water from world ocean / Chemical Industry - 1991. - №8. - с. 34-38.

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