Installation for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate
11230481 · 2022-01-25
Assignee
Inventors
- Nicholas Charles Nelson (Zürich, CH)
- Herbert Riepl (Gödersdorf, AT)
- Wolfgang Kreuger (Feistritz/Rosental, AT)
Cpc classification
Y02A20/131
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
C02F1/68
CHEMISTRY; METALLURGY
International classification
C02F1/68
CHEMISTRY; METALLURGY
Abstract
The present invention relates to an installation for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate, the use of the installation for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate as well as the use of the installation for the mineralization and/or stabilization of water.
Claims
1. An installation for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate, the installation comprising a) a process flow line providing water, b) at least one dosing unit being suitable for dosing at least one earth alkali carbonate-comprising material into at least a part of the water provided in the process flow line for obtaining an aqueous suspension comprising at least one earth alkali carbonate-comprising material, c) at least one means being suitable for dosing CO.sub.2 or an acid having a pK.sub.a-value<5 into at least a part of the water provided in the process flow line or the aqueous suspension comprising at least one earth alkali carbonate-comprising material for obtaining an aqueous suspension S1 comprising at least one earth alkali hydrogen carbonate, and d) a container being connected to the at least one process flow line by an inlet, wherein the container i) is configured such that at least one submerged membrane module is located in the container for filtering at least a part of the aqueous suspension S1 by passing the aqueous suspension S1 through the at least one submerged membrane module in order to obtain an aqueous solution S2 comprising at least one earth alkali hydrogen carbonate, and ii) comprises at least one outlet for releasing the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate from the container; wherein the container comprises recirculating means which are configured such that air or process fluid is withdrawn from the container via a retentate side of the at least one submerged membrane module and recirculated across at least a part of the surface of the at least one submerged membrane module from the bottom to top direction of the at least one submerged membrane module and/or container; and wherein the at least one outlet is connected to a permeate side of the at least one submerged membrane module.
2. The installation according to claim 1, wherein the at least one dosing unit is i) connected to a storage container for solid material, and/or ii) configured such that the at least one earth alkali carbonate-comprising material is directly dosed into the water provided in the process flow line, or iii) connected to a vessel suitable for preparing an aqueous suspension comprising at least one earth alkali carbonate-comprising material, wherein the vessel is connected to the process flow line by an inlet for introducing the water provided in the process flow line and an outlet for releasing the aqueous suspension comprising at least one earth alkali carbonate-comprising material, or iv) connected to the container.
3. The installation according to claim 1, wherein the container is a reactor tank.
4. The installation according to claim 1, wherein the at least one means c) is i) configured such that the CO.sub.2 or acid having a pK.sub.a-value<5 is directly dosed into the water provided in the process flow line, or ii) connected to a vessel suitable for preparing an aqueous suspension S1 comprising at least one earth alkali hydrogen carbonate, wherein the vessel is connected to the process flow line by an inlet for introducing the water provided in the process flow line and an outlet for releasing the aqueous suspension S1 comprising at least one earth alkali hydrogen carbonate, or iii) connected to the container.
5. The installation according to claim 1, wherein the at least one submerged membrane module a) has a pore size of <1 μm, and/or b) has a flux of ≥10 l/(m.sup.2h), and/or c) is of a ceramic, polymer, or other synthetic material.
6. The installation according to claim 1, wherein the at least one process flow line comprises one or more main process flow line(s).
7. The installation according to claim 6, wherein the at least one process flow line comprises two main process flow lines.
8. The installation according to claim 7, wherein the at least one dosing unit is located in the side branch of the main process flow line.
9. The installation according to claim 7, wherein the main branch of the main process flow line and the side branch of the main process flow line are configured such that they are merged together upstream of the container.
10. The installation according to claim 1, wherein the at least one process flow line comprises one main process flow line and one or more side process flow line(s).
11. The installation according to claim 10, wherein the at least one process flow line comprises one main process flow line and two side process flow lines.
12. The installation according to claim 10, wherein the at least one dosing unit is located in the side process flow line or, if present, in the side branch of the side process flow line.
13. The installation according to claim 10, wherein the main branch of the side process flow line and the side branch of the side process flow line are configured such that they are merged together upstream of the container.
14. The installation according to claim 10, wherein the main process flow line and the side process flow line are configured such that they are merged together downstream of the container.
15. The installation according to claim 1, wherein the installation further comprises base dosing means downstream of the container for introducing a base to the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate.
16. The installation according to claim 6, wherein the installation further comprises base dosing means for introducing a base to the main process flow line downstream of where the side process flow line and main process flow line are merged together.
17. The installation according to claim 3, wherein the reactor tank is a sealed reactor tank.
18. The installation according to claim 1, wherein the at least one submerged membrane module has a pore size of <0.1 μm.
19. An installation for the preparation of an aqueous solution comprising at least one earth alkali hydrogen carbonate, the installation comprising a) a process flow line providing water, b) at least one dosing unit being suitable for dosing at least one earth alkali carbonate-comprising material into at least a part of the water provided in the process flow line for obtaining an aqueous suspension comprising at least one earth alkali carbonate-comprising material, c) at least one means being suitable for dosing CO.sub.2 or an acid having a pK.sub.a-value<5 into at least a part of the water provided in the process flow line or the aqueous suspension comprising at least one earth alkali carbonate-comprising material for obtaining an aqueous suspension S1 comprising at least one earth alkali hydrogen carbonate, and d) a container being connected to the at least one process flow line by an inlet, wherein the container i) is configured such that at least one submerged membrane module is located in the container for filtering at least a part of the aqueous suspension S1 by passing the aqueous suspension S1 through the at least one submerged membrane module in order to obtain an aqueous solution S2 comprising at least one earth alkali hydrogen carbonate, and ii) comprises at least one outlet for releasing the aqueous solution S2 comprising at least one earth alkali hydrogen carbonate from the container; wherein the container comprises recirculating means which are configured such that air or process fluid is withdrawn from the container via a retentate side of the at least one submerged membrane module and recirculated across at least a part of the at least one submerged membrane module from the bottom to the top direction of the at least one submerged membrane module and/or the container; wherein the recirculating means are configured to recirculate the air or process fluid directly from an upper recirculation outlet of the container to a location within the container at or below the at least one submerged membrane module or a lower recirculation inlet of the container.
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): storage container for calcium carbonate (14): vessel for preparing a suspension of calcium carbonate (15): side process flow line water supply to process (16): suspension of micronized calcium carbonate (17): main process flow line (17a): main branch of the main process flow line (17b): side branch of the main process flow line (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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(15) 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
(16) In the following the measurement methods implemented in the examples are described.
(17) pH of an Aqueous Suspension or Solution
(18) 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).
(19) Solids Content of an Aqueous Suspension
(20) Moisture Analyser
(21) 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.
(22) Particle Size Distribution (Mass % Particles with a Diameter<X) and Weight Median Diameter (d.sub.50) of a Particulate Material
(23) 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.
(24) 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.
(25) Turbidity of an Aqueous Suspension of Solution
(26) 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.
(27) Conductivity
(28) The conductivity was measured at 25° C. using Mettler Toledo Seven
(29) Multi instrumentation equipped with the corresponding Mettler Toledo conductivity expansion unit and a Mettler Toledo InLab® 741 conductivity probe.
(30) 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).
(31) Temperature
(32) The temperature was measured with a handheld WTW probe of Xylem Analytics.
(33) Hardness of the Aqueous Solution
(34) 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)×0.01×100.08×1 000/(Volume of sample (ml))
Alkalinity of the Aqueous Solution
(35) 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)×0.1×100.08×1 000/(2×Volume of sample (ml))
Acidity of Aqueous Solution
(36) 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)×0.01×44.01×1 000/Volume of sample (ml)
Langelier Saturation Index (LSI)
(37) 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 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
(38) Inventive Installation—Preparation of an Aqueous Solution of Calcium Bi-Carbonate
(39) A general process flow sheet of one installation according to the present invention is shown in
(40) 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.
(41) 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
(42) A calcium hydrogen carbonate solution can be produced using the above mentioned installation 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).
(43) Start-Up Pilot Unit
(44) 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
(45) 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.
(46) The operating conditions and water quality results are given in Table 1 and Table 2 below.
(47) 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 .sup. 110.sup.a (mg/l) .sup.aEquivalent dosage of carbon dioxide into reactor based on flow rate of water through reactor.
(48) TABLE-US-00002 TABLE 2 Water Quality of Example 1. Process stream (9) Description Calcium bi-carbonate solution S2 Alkalinity (mg/l as 220 CaCO.sub.3) Hardness (mg/l as 214 CaCO.sub.3) pH 7.4 Temperature [° C.] 21.5 Turbidity [NTU] 0.1
(49) 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 3 200 l/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)
(50) For the example from patent application EP 2 623 467 A1, with the following inputs:
(51) V=3 200 l/h=8.8e-04 m.sup.3/s
(52) p=1 000 kg/m.sup.3 (for water without any other details)
(53) p=1.5 bar=150 kPa
(54) W=8.888e-04×1 000×150=133 W
(55) 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
(56) Using an installation according to the present invention and as shown in
(57) The hydraulic energy is therefore calculated as:
Hydraulic energy (W)=V×ρ×p=3.47e-04×1 000×50=17.4 W
(58) 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
(59) 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.
(60) 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
(61) 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:
(62) 110/44.01 g/mol:170/100.08 g/mol=2.5:1.7=1.47:1
(63) Inventive Installation—Preparation and Dosing of Aqueous Solution of Calcium Bi-Carbonate to Increase the Mineral and Alkalinity Content of a Desalinated Water
(64) A general process flow sheet of one installation according to the present invention is shown in
(65) 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.
(66) 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
(67) A calcium hydrogen carbonate solution can be produced in a side process flow line using the above mentioned installation 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.
(68) Start-Up Pilot Unit
(69) 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
(70) 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.
(71) The operating conditions and quality results are given in Table 3 and Table 4 below.
(72) TABLE-US-00003 TABLE 3 Process streams of Example 2. Process stream (15) (16) (9) (5) (17) Descrip- Raw Calcium Calcium Recircu- Main tion water carbonate bi- lation process side suspension carbonate air flow process solution flow S2 Flow rate 1 250 1 250 1 250 20 000 3 750 (l/h) Solids 0 0.025 0 0 0 content (wt.-%) Concen- 0 0 220 .sup. 110.sup.a 20 tration (mg/l) .sup.aEquivalent dosage of carbon dioxide into reactor based on flow rate of water through reactor.
(73) TABLE-US-00004 TABLE 4 Water Quality Results of Example 2. Process stream (9) (24) Description: Calcium bi- Final water carbonate solution S2 Alkalinity (mg/l as 220 81 CaCO.sub.3) Hardness (mg/l as 214 85 CaCO.sub.3) 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
(74) A general process flow sheet of one installation according to the present invention is shown in
(75) 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).
(76) 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
(77) A calcium hydrogen carbonate solution can be produced in a side process flow line using the above mentioned installation 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).
(78) Start-Up Pilot Unit
(79) 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
(80) 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 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.
(81) The operating conditions and water quality results are given in Table 5 and Table 6 below.
(82) TABLE-US-00005 TABLE 5 Process streams of Example 3. Process stream (15) (16) (9) (21) (5) (17) Description Raw water Calcium Calcium bi- Calcium Recirculation Main side process carbonate carbonate hydroxide air process flow suspension solution S2 suspension 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.sup.a 20 .sup.aEquivalent dosage of carbon dioxide into reactor based on flow rate of water through reactor
(83) TABLE-US-00006 TABLE 6 Water Quality Results of Example 3: Process stream (9) (24) Description: Calcium bi- Final water carbonate solution S2 Alkalinity (mg/l as 220 88.5 CaCO.sub.3) Hardness (mg/l as 214 92.5 CaCO.sub.3) pH 7.4 7.95 Temperature [° C.] 21.5 21 Turbidity [NTU] 0.1 0
Example 4: Use of Ceramic Membrane within Membrane Calcite Reactor (MCR) in Accordance with FIG. 1
(84) 4.1 Equipment
(85) The following equipment was used for the tests: “Membrane Calcite Reactor” (MCR) consisting of: Rectangular PVC reactor with maximum volume of 75 l and required connections, Cembrane SiCFM-0828 Silicon carbide submerged membrane module with 0.828 m.sup.2 of membrane area installed inside reactor. Cembrane SiCFM-0828 Silicon carbide is a ceramic membrane. A method for producing ceramic membranes suitable for the invention are described e.g. in EP 3 009 182 A1. The content of the patent application EP 3 009 182 A1 is thus hereby incorporated by reference. Lid to seal reactor, Instrumentation for level control Instrumentation for pressure monitoring—in particular Trans-Membrane Pressure (TMP), 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, consisting of the following: Pump operated by variable speed drive, 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 75 l reactor, Dosing hose connecting slurry feed pump and 1800 l reactor Control system that performs the following functions: Controls the permeate pump to achieve the requested flow rate Controls the slurry feed pump to ensure the reactor level remains constant Runs the blower at the requested speed.
4.2 Procedure:
(86) 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 below. 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. 50 l of the suspension containing 1% of micronized calcium carbonate S1 were supplied into the 75 l reactor (Membrane Calcite Reactor). During the process, the reactor was replenished with a suspension of micronized calcium carbonate S1 to ensure a continuous process. 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. The pump speeds was varied to achieve a range of flow rates 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 tanks remains constant. 9. 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. Acidity (as mg/l CO.sub.2) d. pH, conductivity, temperature & turbidity
(87) The operational settings for each trial were recorded, including flow rate, TMP, temperature.
(88) 4.3 Test Settings
(89) The following test settings were used during the trials:
(90) TABLE-US-00007 TABLE 7 Test settings SMD CO.sub.2 CO.sub.2 Suspension Blower CaCO.sub.3 Permeate dose dose Trial volume speed conc. flow rate rate rate No. MCR (l) (Nm.sup.3/hr) (mg/l) (l/hr) (mg/l) (g/min) 1a 50 7.5 160 325 76 0.40 1b 50 7.5 160 325 84 0.45 2a 50 7.5 160 420 64 0.45 2b 50 7.5 160 420 78 0.55 3a 50 7.5 160 500 90 0.75 3b 50 7.5 160 500 85 0.70 4a 50 7.5 160 600 85 0.85 4b 50 7.5 160 600 80 0.80 4c 50 7.5 160 600 75 0.75 5a 50 7.5 160 700 82 0.95
4.4 Measured Results
(91) TABLE-US-00008 TABLE 8 Measured results Suspen- CO.sub.2 Concen- Alka- sion conc CO.sub.2 trate S2 Perme- Alka- Hard- Acid- linity Volume to dose flow Filter Contact ability Cond. linity ness ity Est. Test MCR dose [g/ rate flux time TMP [LMH/ pH [μS/ Turb T [mg/L [mg/L [mg/L [mg/L # [l] [mg/L] min] [L/hr] [lmh] [min] [mbar] bar] [—] cm] [NTU] [° C.] CaCO.sub.3] CaCO.sub.3] CO.sub.2] CaCO.sub.3] 1a 50 76 0.4 325 393 9 275 1339 7.2 295 0.0 17.2 151.6 153.0 17.6 144.9 1a 50 76 0.4 325 393 9 288 1266 7.2 304 0.0 16.8 156.1 155.0 22.9 149.7 1b 50 84 0.45 325 393 9 297 1205 7.1 314 0.0 16.0 161.1 158.0 25.1 155.1 1b 50 84 0.45 325 393 9 294 1200 7.2 314 0.0 15.4 160.1 156.0 24.2 155.1 1b 50 84 0.45 325 393 9 305 1157 7.1 313 0.0 15.4 158.6 160.0 22.0 154.6 1b 50 84 0.45 325 393 9 308 1145 7.1 310 0.0 15.4 157.6 154.0 22.9 153.0 2a 50 64 0.45 420 507 7 339 1364 7.1 273 0.0 16.0 141.6 155.0 18.5 127.0 2a 50 64 0.45 420 507 7 338 1352 7.1 257 0.0 15.5 133.6 145.0 16.3 118.4 2b 50 78 0.55 420 507 7 362 1242 7.0 278 0.0 14.8 139.1 148.0 22.0 129.7 2b 50 78 0.55 420 507 7 385 1167 7.0 282 0.0 14.8 145.1 148.0 22.9 131.9 2b 50 78 0.55 420 507 7 392 1139 7.0 265 0.0 14.5 138.6 154.0 21.1 122.7 2b 50 78 0.55 420 507 7 407 1094 7.0 265 0.0 14.4 139.6 153.0 22.0 122.7 2b 50 78 0.55 420 507 7 409 1091 7.0 271 0.0 14.5 140.1 143.0 22.9 125.9 3a 50 90 0.75 500 604 6 312 1786 7.0 367 0.0 16.5 151.1 165.0 24.2 149.7 3a 50 90 0.75 500 604 6 330 1649 7.0 312 0.0 15.5 158.6 163.0 26.0 147.6 3a 50 90 0.75 500 604 6 341 1577 7.0 320 0.0 15.0 161.1 165.0 26.0 151.9 3a 50 90 0.75 500 604 6 355 1514 7.0 317 0.0 15.0 161.6 165.0 26.0 150.3 3b 50 85 0.70 500 604 6 361 1482 7.0 309 0.0 14.8 156.6 158.0 24.2 145.9 3b 50 85 0.70 500 604 6 423 1265 7.1 325 0.0 14.8 163.6 170.0 24.6 154.6 3b 50 85 0.70 500 604 6 415 1292 7.0 328 0.0 14.9 164.1 167.0 24.2 156.2 3b 50 85 0.70 500 604 6 435 1227 7.1 344 0.0 14.7 169.6 174.0 22.0 164.9 4a 50 85 0.85 600 725 5 372 1759 6.9 277 0.0 15.6 138.1 152.0 25.1 130.8 4a 50 85 0.85 600 725 5 376 1720 6.9 291 0.0 15.1 145.1 158.0 25.1 138.4 4a 50 85 0.85 600 725 5 474 1358 6.9 286 0.0 14.9 143.6 147.0 26.4 135.7 4b 50 80 0.80 600 725 5 488 1313 6.9 273 0.0 14.7 136.6 151.0 29.9 128.6 4b 50 80 0.80 600 725 5 459 1389 6.9 280 0.0 14.5 140.1 147.0 26.4 132.4 4b 50 80 0.80 600 725 5 483 1320 6.8 250 0.0 14.5 134.1 125.0 27.7 116.2 4b 50 80 0.80 600 725 5 461 1383 6.9 267 0.0 14.5 131.6 138.0 25.1 125.4 4b 50 80 0.80 600 725 5 494 1312 6.8 312 0.0 15.2 137.6 140.0 29.5 139.5 4c 50 75 0.75 600 725 5 482 1307 6.8 267 0.0 14.0 132.1 135.0 26.4 115.1 4c 50 75 0.75 600 725 5 432 1472 6.9 268 0.0 14.4 135.1 136.0 26.0 115.7 4c 50 75 0.75 600 725 5 500 1272 6.9 264 0.0 14.4 135.1 137.0 23.8 113.5 4c 50 75 0.75 600 725 5 507 1255 7.0 260 0.0 14.4 135.1 135.0 24.2 111.4 4c 50 80 0.80 600 725 5 526 1209 7.0 270 0.0 14.4 137.6 135.0 23.8 116.8 4c 50 80 0.80 600 725 5 500 1269 7.0 271 0.0 14.3 136.6 138.0 23.8 117.3 4c 50 80 0.80 600 725 5 413 1540 7.0 291 0.0 14.4 147.6 147.0 25.5 128.1 4c 50 80 0.80 600 725 5 426 1486 6.9 270 0.0 14.2 136.6 138.0 26.4 116.8 5a 50 82 0.95 700 845 4 429 1759 6.9 272 0.0 15.1 137.1 139.0 23.8 123.8 5a 50 82 0.95 700 845 4 536 1388 6.9 275 0.0 14.5 136.1 154.0 26.4 125.4 5a 50 82 0.95 700 845 4 475 1540 6.9 275 0.0 13.8 137.1 149.0 26.8 125.4 5a 50 82 0.95 700 845 4 531 1371 6.9 266 0.0 13.6 134.1 138.0 26.4 120.5
(92) The results provided in Table 8 demonstrate that high flux rates can be achieved by using the ceramic membranes as the at least one submerged membrane module (up to 845 lmh) and, moreover, these high flux rates were achieved by stable and almost constant Trans-Membrane Pressure (TMP) values. The flux rates are normalized over the TMP (together with the temperature) to generate a permeability value for the membranes. The permeability value for the ceramic membranes as the at least one submerged membrane module are fairly constant over the whole range of flux rates. As can be seen from Table 8, the permeability of the ceramic membranes as the at least one submerged membrane module in this process are in the range of 1100-1790 lmh/bar.
(93) Furthermore, the use of the submerged membrane module results in a lower specific energy consumption for the operation of the blower.
(94) A ceramic membrane tower of 79 m.sup.2 membrane area, has a maximum blower air flow rate of 150 Nm.sup.3/hr. Using the results of the tests that show that a stable flux rate of 800 lmh is achievable, then such a tower can produce a flow rate of 800 lmh×79 m.sup.2=63.2 m.sup.3/hr. Normalising this flow rate over the maximum blower air flow rate, then it can be shown that the specific flow rate (flow rate per Nm.sup.3/hr of blower air) is 0.421 m.sup.3/hr of permeate per Nm.sup.3/hr of blower air.
(95) In addition to the above benefits, the trials demonstrated that very low contact times can be achieved by using the at least one submerged membrane module—as low as 4 minutes.
CONCLUSION
(96) Trials with ceramic membranes as the at least one submerged membrane module within a remineralization process have demonstrated that much higher flux rates can be achieved during stable operation. Higher flux rates result in reduced specific energy consumption from the blower and reduced contact times for the process which reduces the overall footprint of the process, which is of major importance for large scale desalination processes. Furthermore, the increased permeability of the membrane module can provide a reduced pressure drop across the membrane module and hence reduced energy consumption for applications where energy costs are of major importance.