Process for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate
11130689 · 2021-09-28
Assignee
Inventors
- Nicholas Charles Nelson (Zürich, CH)
- Herbert Riepl (Gödersdorf, AT)
- Wolfgang Kreuger (Feistritz/Rosental, AT)
Cpc classification
B01D2311/25
PERFORMING OPERATIONS; TRANSPORTING
B01D2311/04
PERFORMING OPERATIONS; TRANSPORTING
C02F1/68
CHEMISTRY; METALLURGY
B01D2311/243
PERFORMING OPERATIONS; TRANSPORTING
B01D2311/04
PERFORMING OPERATIONS; TRANSPORTING
B01D65/02
PERFORMING OPERATIONS; TRANSPORTING
B01D61/14
PERFORMING OPERATIONS; TRANSPORTING
B01D2311/08
PERFORMING OPERATIONS; TRANSPORTING
B01D2311/2642
PERFORMING OPERATIONS; TRANSPORTING
B01D2311/06
PERFORMING OPERATIONS; TRANSPORTING
B01D2311/06
PERFORMING OPERATIONS; TRANSPORTING
International classification
B01D61/14
PERFORMING OPERATIONS; TRANSPORTING
Abstract
The present invention relates to a process for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate, a process for the mineralization and/or stabilization of water as well as the use of the aqueous solution comprising at least one earth alkali hydrogen carbonate obtained by the process for the mineralization and/or stabilization of water.
Claims
1. A process for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate, comprising the steps of: a) providing water; b) providing at least one earth alkali carbonate-comprising material; c) providing CO.sub.2 or an acid having a pK.sub.a-value <5; d) combining the water of step a) with the at least one earth alkali carbonate-comprising material of step b) and the CO.sub.2 or acid of step c) in any order such as to obtain an aqueous suspension S1 comprising at least one earth alkali hydrogen carbonate; e) filtering at least a part of the aqueous suspension S1 obtained in step d) by passing the aqueous suspension S1 through at least one submerged membrane module in order to obtain an aqueous solution S2 comprising at least one earth alkali hydrogen carbonate, wherein the at least one submerged membrane module is located in a container; and wherein process steps d) and e) are carried out in the same container and air or process fluid is recirculated across at least a part of the surface of the at least one submerged membrane module.
2. The process according to claim 1, wherein step d) comprises the steps of i1) combining the water of step a) with the CO.sub.2 or acid of step c), and i2) combining the mixture of i1) with the at least one earth alkali carbonate-comprising material of step b); or ii1) combining the water of step a) with the at least one earth alkali carbonate-comprising material of step b), and ii2) combining the mixture of ii1) with the CO.sub.2 or acid of step c).
3. The process according to claim 1, wherein process steps d) and e) are carried out in a reactor tank.
4. The process according to claim 1, wherein the at least one submerged membrane module has a pore size of <1 μm.
5. The process according to claim 1, wherein air or process fluid is recirculated from the bottom to top direction of the at least one submerged membrane module and/or container.
6. The process according to claim 1, wherein the container is sealed and air at the top of the container is used as the feed and reintroduced at the bottom of the container.
7. The process according to claim 1, wherein the process comprises a further step f) of backwashing the at least one submerged membrane module with water, optionally CO.sub.2 or an acid having a pK.sub.a-value <5 is added to the water.
8. The process according to claim 1, wherein the at least one earth alkali carbonate-comprising material of step b) is selected from the group consisting of precipitated calcium carbonate, modified calcium carbonate, ground calcium carbonate and mixtures thereof.
9. The process according to claim 1, wherein the at least one earth alkali carbonate-comprising material of step b) is ground calcium carbonate being selected from the group consisting of marble, limestone, chalk and mixtures thereof.
10. The process according to claim 1, wherein the at least one earth alkali carbonate-comprising material of step b) is provided in dry form or in form of an aqueous suspension; and/or the at least one earth alkali hydrogen carbonate obtained in step d) comprises calcium hydrogen carbonate.
11. The process according to claim 1, wherein the acid provided in step c) has a pK.sub.a-value <4 and/or the acid is selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid or citric acid and/or mixtures thereof.
12. The process according to claim 1, wherein the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate obtained in step e) has an earth alkali concentration as earth alkali hydrogen carbonate in the range from 20 to 1 000 mg/l; and/or has a pH-value in the range from 6.1 to 8.9.
13. A process for the mineralization and/or stabilization of water, the process comprises the steps of (i) providing water to be mineralised, (ii) providing an aqueous solution comprising at least one earth alkali hydrogen carbonate obtained by the process as defined in claim 1, (iii) combining the water to be mineralised of step (i) and the aqueous solution comprising at least one earth alkali hydrogen carbonate of step (ii) in order to obtain mineralised water.
14. The process according to claim 13, comprising a further step (iv) of adding a base to the mineralised water of step (iii).
15. Use of an aqueous solution comprising at least one earth alkali hydrogen carbonate obtained by the process according to claim 1 for the mineralization and/or stabilization of water or as mineralized water.
16. The use according to claim 15, wherein the water is desalinated or naturally soft water.
17. The process of claim 4, wherein the pore size is <0.1 μm.
18. The process of claim 5, wherein CO.sub.2 or acid of step c) is added to the air or process fluid.
19. The process of claim 8, wherein the at least one earth alkali carbonate comprising material in step b) is ground calcium carbonate.
20. The process of claim 10, wherein the at least one earth alkali hydrogen carbonate obtained in step d) consists of calcium hydrogen carbonate.
Description
BRIEF DESCRIPTION OF THE FIGURES
List of Reference Signs
(1) (1): reactor tank (2): submerged membranes (module) (3): product storage tank (4): carbon dioxide injection (5): recirculation air (6): pressure measurement of recirculation air (7): pressure measurement in reactor tank (8): pressure measurement in aqueous solution (9): aqueous solution S2 (10): flow measurement of aqueous solution (11): level measurement in reactor tank (12): turbidity measurement in aqueous solution (13): calcium carbonate storage silo with dosing screw feeder (14): vessel for preparing a suspension of calcium carbonate (15): side stream water supply to process (16): suspension of micronized calcium carbonate (17): main process flow (17a): main branch of the main process flow (17b): side branch of the main process flow (18): measurement of pH of blended water stream (19): measurement of electrical conductivity of blended water stream (20): storage tank for Ca(OH).sub.2 (21): Ca(OH).sub.2 dosing process stream (22): pH measurement of final water stream (23): conductivity measurement of final water stream (24): final treated water stream (25): calcium carbonate dosing screw feeder
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(16) The scope and interest of the invention will be better understood based on the following examples which are intended to illustrate certain embodiments of the invention and are non-limitative.
EXAMPLES
1 Measurement Methods
(17) In the following the measurement methods implemented in the examples are described.
(18) pH of an Aqueous Suspension or Solution
(19) The pH of a suspension or solution was measured using a WTW Multi 3420 pH meter with integrated temperature compensation and a WTWWTW SenTix 940 pH probe. The calibration of the pH electrode was performed using standards of pH values 4.01, 7.00 and 9.21. The reported pH values are the endpoint values detected by the instrument (the endpoint is when the measured signal differs by less than 0.1 mV from the average over the previous 6 seconds).
(20) Solids Content of an Aqueous Suspension
(21) Moisture Analyser
(22) The solids content (also known as “dry weight”) was determined using a Moisture Analyser HR73 from the company Mettler-Toledo, Switzerland, with the following settings: temperature of 120° C., automatic switch off 3, standard drying, 5 to 20 g of product.
(23) Particle Size Distribution (Mass % Particles with a Diameter <X) and Weight Median Diameter (d.sub.50) of a Particulate Material
(24) Weight grain diameter and grain diameter mass distribution of a particulate material were determined via the sedimentation method, i.e. an analysis of sedimentation behaviour in a gravitational field. The measurement was made with a Sedigraph™ 5120 or a Sedigraph™ 5100 of Micromeritics Instrument Corporation.
(25) The method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurement is carried out in an aqueous solution of 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples are dispersed using a high speed stirrer and supersonics.
(26) Turbidity of an Aqueous Suspension of Solution
(27) The turbidity was measured with a Hach Lange 2100AN IS Laboratory Turbidimeter and the calibration was performed using StabCal turbidity standards (formazine standards) of <0.1, 20, 200, 1 000, 4 000 and 7 500 NTU.
(28) Hardness of the Aqueous Solution
(29) The ions involved in water hardness, i.e. Ca.sup.2+(aq) and Mg.sup.2+(aq), have been determined by titration with a chelating agent, ethylenediaminetetraacetic acid (EDTA—disodium salt 0.01 M). For buffering pH constant at 10, NH.sub.3—NH.sub.4Cl buffer was used. Titration using Eriochrome Black T as indicator determines total hardness due to Ca.sup.2+ (aq) and Mg.sup.2+ (aq) ions until the solution turns from wine red to sky blue. The amount of total hardness has been calculated by the following equation:
Hardness=Volume of EDTA (ml)×0.01×100.08×1000/(Volume of sample (ml))
(30) The magnesium hardness was calculated by determining the total concentration of calcium and magnesium ions as well as the concentration of calcium ions. The concentration of calcium ions was determined by first completely precipitating the magnesium ions as Mg(OH).sub.2(s) by adding a 50% w/v NaOH solution, swirling the solution and waiting until complete precipitation. Subsequently, hydroxynaphthol blue was added and the sample was titrated with 0.01 M EDTA until the solution changes to sky blue.
(31) Conductivity
(32) The conductivity was measured at 25° C. using Mettler Toledo Seven
(33) Multi instrumentation equipped with the corresponding Mettler Toledo conductivity expansion unit and a Mettler Toledo InLab® 741 conductivity probe.
(34) The instrument was first calibrated in the relevant conductivity range using commercially available conductivity calibration solutions from Mettler Toledo. The influence of temperature on conductivity is automatically corrected by the linear correction mode. Measured conductivities were reported for the reference temperature of 20° C. The reported conductivity values were the endpoint values detected by the instrument (the endpoint is when the measured conductivity differs by less than 0.4% from the average over the last 6 seconds).
(35) Temperature
(36) The temperature was measured with a handheld WTW probe of Xylem Analytics.
(37) Alkalinity of the Aqueous Solution
(38) The alkalinity of the aqueous solution has been determined by titration of a sample with a 0.1 M solution of hydrochloric acid. The end point of the titration is reached at a constant pH of 4.3. The amount of the alkalinity has been calculated by the following equation:
Alkalinity=Volume of acid (ml)×0.1×100.08×1000/(2×Volume of sample (ml))
Acidity of Aqueous Solution
(39) The acidity of the aqueous solution has been determined by titration of the free CO.sub.2 with a 0.01 M solution of sodium hydroxide. The end point of the titration is reached at a constant pH of 8.3. The amount of free CO.sub.2 has been calculated by the following equation:
Free CO.sub.2=Volume of NaOH (ml)×0.01×44.01×1000/Volume of sample (ml)
Langelier Saturation Index (LSI)
(40) The Langelier Saturation Index (LSI) describes the tendency of an aqueous liquid to be scale-forming or corrosive, with a positive LSI indicating scale-forming tendencies and a negative LSI indicating a corrosive character. A balanced Langelier
(41) Saturation Index, i.e. LSI=0, therefore means that the aqueous liquid is in chemical balance. The LSI is calculated as follows:
LSI=pH−pH.sub.s,
wherein pH is the actual pH value of the aqueous liquid and pH.sub.s is the pH value of the aqueous liquid at CaCO.sub.3 saturation. The pH.sub.s can be estimated as follows:
pH.sub.s=(9.3+A+B)−(C+D),
wherein A is the numerical value indicator of total dissolved solids (TDS) present in the aqueous liquid, B is the numerical value indicator of temperature of the aqueous liquid in K, C is the numerical value indicator of the calcium concentration of the aqueous liquid in mg/l of CaCO.sub.3, and D is the numerical value indicator of alkalinity of the aqueous liquid in mg/l of CaCO.sub.3. The parameters A to D are determined using the following equations:
A=(log.sub.10(TDS)−1)/10,
B=−13.12×log.sub.10(T+273)+34.55,
C=log.sub.10[Ca.sup.2+]−0.4,
D=log.sub.10(TAC),
wherein TDS are the total dissolved solids in mg/l, T is the temperature in ° C., [Ca.sup.2+] is the calcium concentration of the aqueous liquid in mg/l of CaCO.sub.3, and TAC is the alkalinity of the aqueous liquid in mg/l of CaCO.sub.3.
2 Examples
(42) Inventive Installation—Preparation of an Aqueous Solution of Calcium Bi-Carbonate
(43) A general process flow sheet of one installation according to the present invention is shown in
(44) A calcium hydrogen carbonate solution (9) is produced in permeate stream and this could be used to increase the mineral content and alkalinity of another flow.
(45) The feed water was obtained from reverse osmosis system, producing water of the following water specification: Sodium: <1 mg/l Chloride: <2 mg/l Calcium: 8 mg/l Magnesium: <1 mg/l Alkalinity: 12 mg/l (as CaCO.sub.3) ° dH: 1.12 pH: 6.9 Conductivity: 24 μS/cm
(46) A calcium hydrogen carbonate solution can be produced using the above mentioned equipment in the following manner: Reactor tank (1) is originally filled with a calcium carbonate suspension of 5.0 wt.-% to a defined volume that covers the submerged membrane's surface determined by level measurement in the reactor tank (11). A blower starts recirculating air volume (5) from the top of the reactor tank (1) to diffusers located at the bottom of the submerged membranes (2) to ensure a homogenous suspension is maintained within the reactor tank (1) and to provide some cleaning effect for the submerged membranes (2). The air volume (5) is recirculated at a rate of around 200 times per h. A controlled quantity of carbon dioxide is added at (4) in the air stream. Carbon dioxide loaded recirculation air passes over the submerged membranes (2) from the bottom to the top of the reactor tank (1) creating turbulence, and carbon dioxide passes from the air stream to the calcium carbonate suspension increasing the amount of dissolved carbon dioxide within the suspension. The reaction between the calcium carbonate and the dissolved carbon dioxide allows the formation of an alkaline calcium hydrogen carbonate solution within the reactor tank (1). At the same time, calcium carbonate is added to the vessel (14) from the storage silo (13) for the preparation of a calcium carbonate suspension within the vessel (14). A loss-in-weight screw feeder is used to accurately measure the quantity of calcium carbonate added. Water is also added to the tank and a mixer used to create a homogenous suspension of a known solids content. The suspension (16) of micronized calcium carbonate is then transferred to the reactor tank (1) at a rate equal to the amount of calcium carbonate that is dissolved through reaction with the carbon dioxide, so that the total amount of undissolved calcium carbonate within the reactor tank (1) remains constant. An aqueous solution S2 (9) of filtrated permeate is extracted from the reactor tank (1) through the submerged membranes (2).
(47) Start-Up Pilot Unit
(48) Natural calcium carbonate powder (Millicarb® from Omya International AG, Orgon France, d.sub.50=3 μm) was used as starting material in a pilot plant according to the inventive installation. Reactor (1) was filled with 900 l of prepared 5 wt.-% calcium carbonate powder suspension, executed by level control (11). Recirculation air stream (5) fan started with 10 m.sup.3/h for regeneration of membranes via turbulence. Overpressure of airflow was measured by (6).
Example 1
(49) To produce high loaded concentrate (˜250 mg/l alkalinity) 99 g of carbon dioxide (4) was dosed to recirculating air stream within 1 h. Continuous production was started at the end of the first hour recirculation time. During continuous production a suspension of 250 mg/l calcium carbonate (16) was added to the reactor (1) to account for the continuous dissolution of calcium carbonate within the reactor tank (1). At the same time a clear aqueous solution S2 (9) was extracted through the submerged membranes (2) with a concentration of 250 mg/l calcium bi-carbonate (measured as calcium carbonate) using a bi-directional dosing pump. Both ratios—suspension of micronized calcium carbonate (16) and aqueous solution (9)—were controlled by level measurement (11) in reactor tank (1) and flowmeter measurement (10) of the aqueous solution S2 (9). Primary settings of ratios depend from achievable membrane flux rates and were measured as trans-membrane-pressure (8). Quality of aqueous solution S2 (9) was controlled by turbidity measurement (12) and titrations.
(50) The operating conditions and water quality results are given in Table 1 and Table 2 below.
(51) TABLE-US-00001 TABLE 1 Process streams of Example 1. Process stream (16) (9) (5) Description Calcium Calcium bi- Recirculation air carbonate carbonate suspension solution S2 Flow rate (l/h) 1 250 1 250 20 000 Solids content 0.025 0 0 (wt.-%) Concentration 0 220 110.sup.a (mg/l) .sup.aEquivalent dosage of carbon dioxide into reactor based on flow rate of water through reactor.
(52) TABLE-US-00002 TABLE 2 Water Quality of Example 1. Process stream (9) Description Calcium bi-carbonate solution S2 Alkalinity (mg/l as CaCO.sub.3) 220 Hardness (mg/l as CaCO.sub.3) 214 pH 7.4 Temperature [° C.] 21.5 Turbidity [NTU] 0.1
(53) In comparison to patent application EP 2 623 467 A1, the above process using the installation according to the present invention has a much better energy efficiency. According to Table 4 of EP 2 623 467 A1, 35 l/h of permeate was produced in 4 different trials from a tubular membrane module (Microdyne-Module MD 063 TP 2N). The suspension in these trials was circulated through the tubular module at a rate of 3 2001/h with 1.5 bar pressure to produce this permeate stream. The hydraulic energy required to produce this permeate was therefore:
Hydraulic energy(W)=V×ρ×p
where:
V=flow rate of fluid (m.sup.3/s)
ρ=density of fluid (kg/m.sup.3)
p=outlet static pressure of pump (kPa)
(54) For the example from patent application EP 2 623 467 A1, with the following inputs:
(55) V=3 200 l/h=8.8e-04 m.sup.3/s
(56) ρ=1 000 kg/m.sup.3 (for water without any other details)
(57) p=1.5 bar=150 kPaW=8.888e-04×1 000×150=133 W
(58) This produced an average of 54 l/h permeate, and therefore the power consumption per cubic metre of permeate produced can be calculated as:
Power/cubic meter=0.133 kW±0.035 m.sup.3/h=3.8 kW.Math.h/m.sup.3
(59) Using an installation according to the present invention and as shown in
(60) The hydraulic energy is therefore calculated as:
Hyrdaulic energy(W)=V×ρ×p=3.47e-04×1000×50=17.4 W
(61) This produced an average of 1 250 l/h permeate, and therefore the power consumption per cubic metre of permeate produced can be calculated as:
Power/cubic meter=0.0174 kW±1.25 m.sup.3/h=0.014 kW.Math.h/m.sup.3
(62) Therefore the specific power consumption (power per cubic meter of permeate produced) is over 270 times less with the present invention than that of the patent application EP 2 623 467 A1.
(63) The CO.sub.2 efficiency according to tests with the inventive installation shown in
(Free CO.sub.2 in water+CO.sub.2 dosed)/molecular weight of CO.sub.2:(Final Alkalinity−Initial Alkalinity)/molecular weight of CaCO.sub.3=(2+110)/44.01 g/mol:(220−12)/100.08 g/mol=2.54:2.08=1.22:1
(64) The CO.sub.2 efficiency according to tests performed with an installation according to patent application EP 2 623 467 A1 was shown to be: 110/44.01 g/mol:170/100.08 g/mol=2.5:1.7=1.47:1
(65) Inventive Installation—Preparation and Dosing of Aqueous Solution of Calcium Bi-Carbonate to Increase the Mineral and Alkalinity Content of a Desalinated Water
(66) A general process flow sheet of one installation according to the present invention is shown in
(67) A calcium hydrogen carbonate solution is produced in an aqueous solution S2 (9) and dosed into the main process flow (17) to increase the mineral content and alkalinity of the main process flow.
(68) The feed water was obtained from reverse osmosis system, producing water of the following water specification: Sodium: <1 mg/l Chloride: <2 mg/l Calcium: 8 mg/l Magnesium: <1 mg/l Alkalinity: 12 mg/l (as CaCO.sub.3) ° dH: 1.12 pH: 6.9 Conductivity: 24 μS/cm
(69) A calcium hydrogen carbonate solution can be produced in a side stream using the above mentioned equipment in the following manner: Reactor tank (1) is originally filled with a calcium carbonate suspension of 5.0 wt.-% to a defined volume that covers the submerged membrane's (2) surface measured by level measurement (11) in the reactor tank (1). A blower starts recirculating air volume (5) from the top of the reactor tank (1) to diffusers located at the bottom of the submerged membranes (2) to ensure a homogenous suspension is maintained within the reactor (1) and to provide some cleaning effect for the membranes. The air volume (5) is recirculated at a rate of around 200 times per h. A controlled quantity of carbon dioxide is added in the air stream at e.g. position (4). Carbon dioxide loaded recirculation air passes over the submerged membranes (2) from the bottom to the top of the reactor creating turbulence, and carbon dioxide passes from the air stream to the calcium carbonate suspension increasing the amount of dissolved carbon dioxide within the suspension. The reaction between the calcium carbonate and the dissolved carbon dioxide allows the formation of a calcium hydrogen carbonate solution within the reactor tank. At the same time, calcium carbonate is added to the vessel (14) from the storage silo (13) for the preparation of a calcium carbonate suspension within the vessel (14). A loss-in-weight screw feeder is used to accurately measure the quantity of calcium carbonate added. Water is also added to the vessel (14) and a mixer used to create a homogenous suspension of known solids content. The suspension of micronized calcium carbonate (16) is then transferred to the reactor tank (1) at a rate equal to the amount of calcium carbonate that is dissolved through reaction with the carbon dioxide, so that the total amount of undissolved calcium carbonate within the reactor tank (1) remains constant. An aqueous solution S2 (9) of filtrated permeate as clear concentrated calcium hydrogen carbonate solution is used to add the calcium and bicarbonate to the main process flow (17) via a bi-directional dosing pump. A product storage tank (3) was used as a buffer also for backwashing sequence every 10 min.
(70) Start-Up Pilot Unit
(71) Natural calcium carbonate powder (Millicarb® from Omya International, Orgon France, d.sub.50=3 μm) was used as the starting material in the pilot plant. Reactor tank (1) was filled with 900 l of prepared 5 wt.-% calcium carbonate powder suspension, executed by level measurement (11) in reactor tank (1). Recirculation air stream (5) fan started with 10 m.sup.3/h for regeneration of membranes via turbulence. Overpressure of airflow was measured by (6).
Example 2
(72) To produce high loaded concentrate (˜250 mg/l alkalinity) 99 g of carbon dioxide (4) was dosed to the recirculating air stream within 1 h. Continuous production was started at the end of the first hour recirculation time. During continuous production a suspension of 250 mg/l calcium carbonate (16) was added to reactor (1) to account for the continuous dissolution of calcium carbonate within the reactor tank (1). At the same time a clear aqueous solution S2 (9) was extracted through the submerged membranes with a concentration of 250 mg/l calcium bi-carbonate (measured as calcium carbonate) and discharged via bi-directional dosing pump through the product storage tank (3) in main stream (17). Both ratios—suspension of micronized calcium carbonate (16) and aqueous solution S2 (9)—were controlled by level measurement (11) in reactor tank (1) and flow measurement (10). Primary settings of ratios depend from achievable membrane flux rates and were measured as trans-membrane-pressure (8). Quality of aqueous solution S2 (9) was controlled by turbidity measurement (12) in the aqueous solution (9) and titrations. Quality of first blend was measured via pH (18), electrical conductivity (19) and titrations of the blended water stream.
(73) The operating conditions and quality results are given in Table 3 and Table 4 below.
(74) TABLE-US-00003 TABLE 3 Process streams of Example 2. Process stream (15) (16) (9) (5) (17) Description Raw water Calcium carbonate Calcium bi-carbonate Recirculation Main process side stream suspension solution S2 air flow Flow rate (l/h) 1 250 1 250 1 250 20 000 3 750 Solids content (wt.-%) 0 0.025 0 0 0 Concentration (mg/l) 0 0 .sup. 220 110.sup.a 20 .sup.aEquivalent dosage of carbon dioxide into reactor based on flow rate of water through reactor.
(75) TABLE-US-00004 TABLE 4 Water Quality Results of Example 2. Process stream (9) (24) Description: Calcium bi-carbonate Final solution S2 water Alkalinity (mg/l as CaCO.sub.3) 220 81 Hardness (mg/l as CaCO.sub.3) 214 85 pH 7.4 7.25 Temperature [° C.] 21.5 21 Turbidity [NTU] 0.1 0
Inventive Installation—Preparation and Dosing of Aqueous Solution of Calcium Bi-Carbonate Followed by pH Adjustment, to Increase the Mineral and Alkalinity Content of a Desalinated Water and Stable it with Respect to its Saturation Index
(76) A general process flow sheet of one installation according to the present invention is shown in
(77) A calcium hydrogen carbonate solution is produced in an aqueous solution S2 (9) and dosed into the main process flow (17) to increase the mineral content and alkalinity of the main process flow (17). A calcium hydroxide suspension at 5.0 wt.-% and of high purity is dosed (21) in the main process flow (17) after the dosing of the calcium hydrogen carbonate solution to create the desired final water quality of the final treated water stream (24).
(78) Feed water is provided in all process flows, the feed water was obtained from reverse osmosis system, producing water of the following water specification: Sodium: <1 mg/l Chloride: <2 mg/l Calcium: 8 mg/l Magnesium: <1 mg/l Alkalinity: 12 mg/l (as CaCO.sub.3) ° dH: 1.12 pH: 6.9 Conductivity 24 μS/cm
(79) A calcium hydrogen carbonate solution can be produced in a side stream using the above mentioned equipment in the following manner: Reactor tank (1) is originally filled with a calcium carbonate suspension of 5.0 wt.-% at to a defined volume to that covers the submerged membrane's (2) surface measured by level measurement (11) in reactor tank (1). A blower starts recirculating air volume (5) from the top of reactor tank (1) to diffusers located at the bottom of the submerged membranes (2) to ensure a homogenous suspension is maintained within the reactor tank (1) and provide some cleaning effect for the submerged membranes (2). Volume is recirculated at a rate of around 200 times per h. A controlled quantity of carbon dioxide (4) is added in the air stream. Carbon dioxide loaded recirculation air passes over the submerged membranes (2) from the bottom to the top of the reactor tank (1) creating turbulence, and carbon dioxide passes from the air stream to the calcium carbonate suspension increasing the amount of dissolved carbon dioxide within the suspension. The reaction between the calcium carbonate and the dissolved carbon dioxide allows the formation of calcium hydrogen carbonate solution within the reactor tank (1). At the same time, calcium carbonate is added to the vessel (14) from the storage silo (13) for the preparation of a calcium carbonate suspension within the vessel (14). A loss-in-weight screw feeder is used to accurately measure the quantity of calcium carbonate added. Water is also added to the tank and a mixer used to create a homogenous suspension of known solids content. The suspension of micronized calcium carbonate (16) is then transferred to the reactor tank (1) at a rate equal to the amount of calcium carbonate that is dissolved through reaction with the carbon dioxide, so that the total amount of undissolved calcium carbonate within the reactor tank (1) remains constant. An aqueous solution S2 (9) of filtrated permeate as clear concentrated calcium hydrogen carbonate solution is used to add the calcium and bicarbonate to the main process flow (17) via a bi-directional dosing pump. A product storage tank (3) was used as a buffer also for the backwashing sequence every 10 minutes. A second dosing pump was used to add the calcium hydroxide suspension at e.g. position (21) stored in a storage tank (20) to the main process flow (17).
(80) Start-Up Pilot Unit
(81) Natural calcium carbonate powder (Millicarb® from Omya International, Orgon France, d.sub.50=3 μm) and a calcium hydroxide suspension (Schäferkalk, Precal 72, 20 wt.-% concentration in water) have been used as starting materials in a pilot plant. The Schäferkalk product (Precal 72) is a highly reactive 20 wt.-% calcium hydroxide suspension, for effective pumping it has been diluted to 5 wt.-% (21) and directly dosed into the final treated water stream (24). Reactor tank (1) was filled with 900 l of prepared 5 wt.-% calcium carbonate powder suspension, executed by level measurement (11) in reactor tank 1. Recirculation air stream (5) fan started with 10 m.sup.3/h for regeneration of membranes via turbulence. Overpressure of airflow was measured by (6).
Example 3
(82) To produce high loaded concentrate (˜250 mg/l alkalinity) 99 g of carbon dioxide (4) was dosed to recirculating air stream within 1 h. Continuous production was started at the end of the 1 h recirculation time. During continuous production a suspension of 250 mg/l micronized calcium carbonate (16) was added to reactor tank (1) to account for the continuous dissolution of calcium carbonate within the reactor tank (1). At the same time a clear aqueous solution (9) was extracted through the submerged membranes (2) with a concentration of 250 mg/l calcium bi-carbonate (measured as calcium carbonate) and discharged via bi-directional dosing pump through the product storage tank (3) in main process flow (17). Both ratios—suspension of micronized calcium carbonate (16) and aqueous solution S2 (9)—were controlled by level measurement (11) in reactor tank (1) and flow measurement (10) of the aqueous solution S2 (9). Primary settings of ratios depend from achievable membrane flux rates and were measured as trans-membrane-pressure (8). Quality of aqueous solution (9) was controlled by turbidity measurement (12) and titrations. Quality of first blend was measured via pH (18), electrical conductivity (19) and titrations. To reach the desired final water quality with a Langelier Saturation Index of 0 for the final treated stream (24), the calcium hydroxide suspension (21) from tank (20) was dosed into the final treated water stream (24) also.
(83) The operating conditions and water quality results are given in Table 5 and Table 6 below.
(84) TABLE-US-00005 TABLE 5 Process streams of Example 3. Process stream (15) (16) (9) (21) (5) (17) Description Raw water Calcium carbonate Calcium bi-carbonate Calcium hydroxide Recirculation Main process side stream suspension solution S2 suspension air flow Flow rate (l/h) 1 250 1 250 1 250 0.42 20 000 3 750 Solids content (%) 0 0.025 0 5 0 0 Concentration (mg/l) 0 0 220 50 000 110 20 .sup.a Equivalent dosage of carbon dioxide into reactor based on flow rate of water through reactor
(85) TABLE-US-00006 TABLE 6 Water Quality Results of Example 3: Process stream (9) (24) Description: Calcium bi-carbonate Final solution S2 water Alkalinity (mg/l as CaCO.sub.3) 220 88.5 Hardness (mg/l as CaCO.sub.3) 214 92.5 pH 7.4 7.95 Temperature [° C.] 21.5 21 Turbidity [NTU] 0.1 0
Inventive Example 4: Dissolution of Magnesium Hydroxide by Using the Process Set Out in FIG. 1
(86) 4.1 Equipment
(87) The following equipment was used for the tests: 2150 litre “Membrane Calcite Reactor” (MCR) consisting of: Cylindrical stainless steel reactor of volume 2150 l with required connections, Microdyn Bio-cel BC-50 submerged membrane unit installed inside reactor, Lid to seal reactor, Instrumentation for level control and pressure monitoring, Blower system configured such that it forms a blower recirculation loop, consisting of: Blower operated by variable speed drive, Feed pipework to blower connected from top of reactor (connected to lid) Discharge pipework connected to diffuser manifold at bottom of submerged membrane unit, Permeate pump to extract concentrate solution through membrane, with flow meter to measure flow rate Carbon dioxide dosing system, consisting of: Carbon dioxide bottle Pressure regulator to decrease pressure from bottle at 50 bar to 5 bar Mass flow meter and control valve to regulate and measure the dosing of carbon dioxide Dosing connection to blower discharge pipework Slurry Make-Down (SMD) system, consisting of: Slurry make-down (SMD) tank with electric mixer and tank level instrumentation, Feed water supply to tank, controlled to maintain level within tank Loss-in-weight dosing feed system to accurately add required amount of micronized calcium carbonate to the SMD tank, Hopper supplying micronized calcium carbonate to the loss-in-weight feeder, Slurry feed pump to dose calcium carbonate suspension produced in SMD tank to the 2150 l reactor, Dosing hose connecting slurry feed pump and 2150 l reactor Magnesium hydroxide dosing system, consisting of: Storage tank containing a suspension of 25% magnesium hydroxide Prominent Gamma L dosing pump Discharge hose from dosing pump connected to dosing hose between slurry feed pump and 2150 l reactor (part of SMD system) Magnesium dosing system is configured such that the magnesium hydroxide is dosed into the suspension of micronized calcium carbonate (16).
4.2 Procedure:
(88) The following procedure was used to run the trials: 1. The SMD tank was filled with water and calcium carbonate dosed into the tank to produce a suspension S1 as per the settings provided in Section 4.3. 2. The SMD control was placed into automatic mode so that water would be continually replenished in the SMD tank when suspension was withdrawn from the tank, and calcium carbonate would be continuously dosed to ensure a consistent suspension was generated of concentration provided in Section 4.3. 3. The 2 150 l reactor was filled with a suspension containing 5% of micronized calcium carbonate S1. The technical details of the micronized calcium carbonate are provided in Section 4.3. 4. The lid of the reactor was closed and a tight seal was ensured. 5. The blower was energized to run, keeping the micronized calcium carbonate in suspension S1. 6. Carbon dioxide was dosed into the blower recirculation loop, as per the settings provided in Section 4.3. 7. The permeate pump was operated at a set speed to provide the required flow rate and extract a clear solution S2 from the reactor tank, as per the settings provided in Section 4.3. 8. The slurry feed pump was operated at a set speed to ensure that the level within the reactor tank remains constant. 9. The magnesium hydroxide dosing pump was set to varying speeds to dose the required quantity of magnesium hydroxide into the process as per the test settings provided in Section 4.3. 10. Samples of the concentrated solution S2 extracted by the permeate pump were analysed for the following water qualities by the methods described above: a. Alkalinity (in mg/l) b. Total hardness (in mg/l) c. Magnesium hardness (in mg/l) d. Acidity (as mg/l CO.sub.2) e. pH, conductivity, temperature & turbidity
4.3 Test Settings
(89) The following test settings were used during the trials:
(90) TABLE-US-00007 TABLE 7 Test setting Mg(OH).sub.2 Suspension Blower SMD Permeate CO.sub.2 CO.sub.2 Mg(OH).sub.2 dose (ml/hr) Trial volume speed CaCO.sub.3 conc. flow rate dose rate dose rate dose rate as 25% No. (l) (Nm.sup.3/hr) (mg/l) (l/hr) (mg/l) (g/min) (mg/l) suspension 1 1800 7.5 250 3000 154 7.7 0 0 2 1800 7.5 250 3000 154 7.7 30 308 3 1800 7.5 250 3000 154 7.7 60 615
4.4 Measured Results
(91) TABLE-US-00008 TABLE 8 The results measured for Trial 1: Total Mg Acidity pH Conductivity Turbidity Temperature Alkalinity Hardness Hardness [mg/L [—] [μS/cm] [NTU] (° C.) [mg/L] [mg/L] [mg/L] CO.sub.2] 7.3 483.0 0.01 17.8 260.2 260.2 −0.49 37.0 7.2 496.0 0.01 18.2 260.2 263.2 −0.24 37.8 7.2 486.0 0.01 17.7 261.2 272.2 1.46 40.5 7.3 483.0 0.01 17.5 260.7 263.2 −0.24 39.6 7.2 487.0 0.01 16.4 263.2 258.2 −1.46 44.0 7.3 476.0 0.01 15.3 259.2 273.2 1.22 42.7 7.3 479.0 0.01 15.4 260.2 264.2 0.00 41.8
(92) TABLE-US-00009 TABLE 9 The results measured for Trial 2: Total Mg Acidity pH Conductivity Turbidity Temperature Alkalinity Hardness Hardness [mg/L [—] [μS/cm] [NTU] (° C.) [mg/L] [mg/L] [mg/L] CO.sub.2] 7.3 445.0 0.01 15.4 245.7 270.2 9.72 35.2 7.3 446.0 0.01 15.3 248.7 271.2 14.83 30.4 7.2 466.0 0.01 15.0 260.2 265.2 13.37 39.6
(93) TABLE-US-00010 TABLE 10 The results measured for Trial 3: Total Mg Acidity pH Conductivity Turbidity Temperature Alkalinity Hardness Hardness [mg/L [—] [μS/cm] [NTU] (° C.) [mg/L] [mg/L] [mg/L] CO.sub.2] 7.1 439.0 0.01 16.1 241.7 279.2 25.53 27.7 7.2 415.0 0.01 15.2 225.2 253.2 26.01 28.6 7.2 424.0 0.01 15.1 230.7 255.2 24.55 27.7 7.3 418.0 0.01 15.3 229.7 267.2 26.98 27.3 7.2 420.0 0.01 14.9 229.2 267.2 26.98 27.7 7.2 415.0 0.01 14.4 229.7 257.2 23.58 28.2 7.3 420.0 0.01 17.8 229.2 258.2 27.23 26.4
(94) The results provided for Trial 1 (Table 8) show that very stable values can be generated for the alkalinity of the concentrated solution S2 without magnesium hydroxide dosing. Stable values are also generated for the total hardness and magnesium concentrations.
(95) The results provided for Trial 2 (Table 9) show that the dosing of 30 mg/l of magnesium hydroxide provide between about 10-14 mg/l of magnesium. This is as expected as magnesium hydroxide has a molecular weight of 58.3 g/mol, of which magnesium is 24.3 g/mol, or 41.7% of this amount.
(96) The results provided for Trial 3 (Table 10) show that over the course of the experiment, very stable results were achieved for all values, in particular alkalinity and magnesium concentrations. For this trial, 60 mg/l of magnesium hydroxide were dosed. This should ideally add a 25 mg/l of Mg.sup.2+ ions. This is in line with the results which demonstrate an average of 25.8 mg/l magnesium in the concentrated stream extracted from the reactor, with of range of between 23.6-27.2 mg/l magnesium. The results are also outlined in
(97) In all cases, the turbidity of the concentrated stream was measured to be 0.01 NTU.
CONCLUSION
(98) From these trials, it can be gathered that the inventive process, that has been developed for the dissolution of micronized calcium carbonate, can be used to effectively dissolve magnesium also—in the form of magnesium hydroxide. The results were very stable demonstrating that the process can also be accurately controlled. This method has the advantage that it produces a concentrated stream void of turbidity in the absence of unwanted anions.
(99) In summary, it has been shown that this process provides a cost effective alternative to current processes. Furthermore, the process can be effectively controlled to dose the desired amount of calcium and, if desired, magnesium.