System for contacting gases and liquids

Abstract

A system for contacting gases and liquids includes a vessel containing inert particles, wherein the total volume of the inert particles is from 1 to 20% of the total working volume of the vessel.

Claims

1. A system for contacting gases and liquids, comprising: a vessel containing inert particles; a single orifice located at the base of the vessel configured to allow gas to pass into the vessel; a gas outlet located above the surface of the working volume while in use, configured to allow gas to pass out of the vessel; a liquid inlet configured to allow liquid to pass into the vessel; and a liquid outlet configured to allow liquid to leave the vessel; wherein: the total volume of the inert particles is from 1 to 20% of the total working volume of the vessel; the liquid inlet, the liquid outlet, the gas inlet and the gas outlet are arranged such that the liquid passes the gas in counter-current flow through at least a portion of the vessel while in use; the liquid outlet comprises an effluent passage extending into the vessel; the inlet of the effluent passage is located below the liquid inlet; and the liquid leaves the vessel via the effluent passage due to the hydrostatic pressure of the liquid in the vessel while in use.

2. A system according to claim 1, wherein the total volume of the inert particles is from 3 to 15% of the total working volume of the vessel.

3. A system according to claim 1, wherein the single orifice is located centrally at the base of the vessel such that gas can be introduced centrally into the vessel.

4. A system according to claim 1, further comprising a liquid provided in the vessel, wherein the density of the inert particles is 15% or less above or below the density of the liquid.

5. A system according to claim 1, where the inert particles have a particle size of from 1 mm to 25 mm.

6. A system according to claim 1, wherein the base of the vessel has a conical shape.

7. A system according to claim 1, wherein the introduction of a gas into the vessel causes the inert particles to follow a circular or elliptical path within the vessel, to produce mixing between the gas and the liquid.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention will now be described, by way of example only, with reference to the accompanying figures, in which:

(2) FIG. 1 shows a schematic view of a system for contacting gases and liquids in accordance with the invention;

(3) FIG. 2 shows a graph illustrating CO.sub.2 capture for different gas flow rates using the system of the present invention;

(4) FIG. 3 shows a graph illustrating ion removal for different gas flow rates using the system of the present invention; and

(5) FIG. 4 shows a graph illustrating pH variation with time for different gas flow rates using the system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) The present invention identifies that the use of inert particles can enhance mixing within a gas-liquid contactor/reactor system and provide a high gas-liquid interfacial area for effective mass transfer.

(7) FIG. 1 depicts an example of a system for contacting gases and liquids in accordance with the invention. The system comprises a vessel 100 having a cylindrical body 101. The vessel 100 has a base 102, which is attached to one end of the cylindrical body 101. The other end of the cylindrical body 101 is closed, but may be open to the atmosphere, depending on the specific use of the system. A temperature control jacket for controlling the temperature of the vessel 100 optionally surrounds the vessel 100.

(8) In the arrangement shown in FIG. 1, the vessel is orientated vertically when in use, with the base 102 located at the bottom of the vessel 100 when viewing the vessel 100 from the front.

(9) Liquid is fed into the vessel through a liquid inlet 103. The liquid inlet 103 is depicted toward the top of the vessel in FIG. 1; however, its location is not limited, but is preferably above the maximum working level of the liquid when the vessel 100 is in use.

(10) Gas is fed into the vessel though a gas inlet 104. The gas inlet 104 is provided as a single orifice located at the bottom of the base 102 in FIG. 1 but in other embodiments, multiple orifices may be used. The size of the orifice(s), the gas velocity, as well as the gas to liquid ratio depend on the type of gas contact or the reaction system. The gas may be injected into the vessel as a jet using a nozzle (not shown in FIG. 1).

(11) Liquid leaves the vessel 100 via a liquid outlet 105. The outlet can comprise an effluent passage 107 extending into the vessel from vessel exit point 110. The vessel exit point 110 (the point at which the liquid crosses the outer boundary of the vessel 100) is preferably located at approximately the same height as the liquid inlet 103. If the liquid leaves the vessel due to hydrostatic pressure, then the exit point 110 is located below the working level of the liquid. If the liquid leaves the vessel with the use of a pump, then the exit point 110 can be located at any position on the vessel 100.

(12) Gas leaves the vessel 100 via a gas outlet 106. The gas outlet 106 is depicted on the top surface of the vessel 100 in FIG. 1; however, its location is not limited, but is preferably located above the working level of the liquid when the vessel 100 is in use.

(13) The liquid inlet 103, the liquid outlet 105, the gas inlet 104 and the gas outlet 106 are preferably arranged such that the liquid passes the gas in counter-current flow through at least a portion of the vessel 100 while in use, for improved gas-liquid contact. For example, if the gas inlet 104 and the gas outlet 106 are arranged such that the gas is introduced at the bottom of the vessel and leaves at the top, then the liquid inlet 103 and liquid outlet 105 are preferably arranged such that the liquid flows in a downward direction past the gas through at least a portion of the vessel 100 while in use.

(14) The above-described counter-current flow between the gas and liquid is preferably achieved with the provision of an effluent passage 107 extending from the exit point 110 into the vessel 100, as shown in FIG. 1. The effluent passage 107 directs the flow of liquid from a point inside the vessel 100 to the exit point 110 and could take the form of a tube or pipe, for example.

(15) The inlet 108 to the effluent passage 107 is preferably located at a level below the liquid inlet 103 and is preferably located within the bottom 30% of the vessel (i.e. the bottom 30% of the distance between the top of the base 102 and the working level of the liquid), more preferably within the bottom 20% of the vessel and even more preferably within the bottom 10% of the vessel. This arrangement creates counter-current flow, as the gas flows upwards through the vessel 100 while the liquid flows downwards in order to exit the vessel via the inlet 108 to the effluent passage 107. Preferably, once the liquid effluent enters the effluent passage 107, the hydrostatic pressure of the liquid in the vessel 100 while in use causes the liquid effluent to flow through the effluent passage 107.

(16) The provision and arrangement of the effluent passage 107 also reduces the entrainment of gas bubbles in the liquid effluent. This is because the resistance that gas bubbles face at the effluent passage inlet 108 are much higher than the resistance throughout the rest of the interior of the vessel 100.

(17) The effluent passage inlet 108 is preferably provided with a filter for blocking solid particles from entering the liquid effluent passage 107.

(18) The system further comprises inert particles 109, which are provided inside the vessel 100 when in use. The total volume of the inert particles 109 is from 1 to 20% of the total working volume of the vessel 100 (i.e. the volume of liquid in the vessel during operation), preferably from 3 to 15% of the total working volume of the vessel 100 and more preferably from 5 to 10% of the total working volume of the vessel 100.

(19) The inert particles 109 are preferably inert with respect to the gas-liquid system and should not react when contacting any of the liquids or gases within the vessel 100. Furthermore, the inert particles 109 preferably do not act as a catalyst for the reaction system. The material of the inert particles 109 will thus depend on the liquid and gas used in the system but could be plastic, for example. The inert particles 109 are preferably spherical and preferably have a diameter of from 1 to 25 mm, more preferably of from 3 to 20 mm and even more preferably of from 5 to 15 mm. For non-spherical particles, each of the particles preferably has a volume corresponding to an equivalent spherical diameter d.sub.v

(20) $\left(i.e.d_v=2\sqrt[3]{\frac{3V}{4}},\mathrm{where}V\mathrm{is}\mathrm{the}\mathrm{volume}\mathrm{of}\mathrm{the}\mathrm{non}\text{-}\mathrm{spherical}\mathrm{particle}\right).$

(21) When the vessel 100 is in use, the inert particles 109 are dispersed and move within the vessel to promote mixing between the gas and the liquid and to provide a higher gas-liquid interfacial area for effective mass transfer between the two phases. The movement of the inert particles 109 within the vessel is caused by the gas entering the vessel 100 through the gas inlet 104. The gas is preferably introduced centrally at the base 102 of the vessel 100 to cause the inert particles 109 to move along a circular or elliptical path up and down the vessel 100 while in use.

(22) To assist with the movement of the inert particles 109, the base 102 of the vessel 100 preferably has a conical shape tapering down to the gas inlet 104. This allows the inert particles 109 to slide into the gas feed region at the bottom of the vessel 100 without the formation of dead zones at the bottom of the vessel 100.

(23) The density of the inert particles 109 is preferably similar to that of the liquid so that the inert particles 109 can move more easily throughout the vessel 100 while in use. A density similar to that of the liquid preferably means 15% or less above or below the density of the liquid at the operating temperature of the vessel 100, more preferably 10% or less and even more preferably 5% or less.

Examples

(24) The contactor system described in this invention was evaluated for the capture of CO.sub.2 through reactions with ammonium hydroxide. The reaction was carried out through contacting a gas mixture containing 10% CO.sub.2 and 90% air with ammonium hydroxide (25% NH.sub.3) mixture with saline wastewater, namely desalination reject brine. The water had 7% salinity, which included different ions including sodium, magnesium, and calcium. The reactions were carried out in a jacketed, stainless steel cylindrical vessel with an internal diameter of 78 mm, a height of 700 mm, and a total working volume of 3000 ml. The gas was injected at the bottom of the reactor through a one-hole orifice with a diameter of 3. The liquid was fed via the liquid inlet near the top of the vessel and exited via the effluent passage described above. The inert particles were made from transparent thermoplastic (poly(methyl 2-methylpropenoate)), with an average particle size of 13 mm and a density of 1020 kg/m.sup.3.

(25) The CO.sub.2 capture and ions (Na, Mg, Ca) removal percentages were optimized by RSM (Response surface methodology) using the Minitab 17.0 application. As a fitting statistical tool, Minitab 17.0 offers multilevel factorial screening designs, and numerical optimization can be followed by analyzing the critical factors and their interactions. The design of runs was in accordance with central composite design (CCD). The three major factors, which affect both CO.sub.2 capture and ions removal are gas flow rate, temperature and ammonia to NaCl molar ratio; these factors were operated in the range of 0.6 to 2.3 l/min, 13.2 to 46.8 C., and 1.7 to 3.3 NH.sub.3:1NaCl for gas flow rate, temperature, and molar ratio, respectively. The other two factors, which only affect CO.sub.2 capture, were studied in another CCD. These factors were volume of the inert particles and gauge pressure in the reactor; they were operated in the range of 3 to 17 vol % and 0 to 2.9 bar (0 to 0.29 MPa), respectively. Water samples were withdrawn from the reactor every hour and tested for ions removal using an inductively coupled plasma (ICP) spectrometer. Meanwhile, the effluent gas was continuously passed through a moisture trap then sent to a CO.sub.2 gas analyser to detect the CO.sub.2 percentage. Variation of the water pH with time was also recorded.

(26) Based on the response surface methodology modelling, the optimum operating conditions were found to be a temperature of 19.30.5 C.; a gas flow rate of 1 5432 ml/min; a NH.sub.3/NaCl molar ratio of 3.30.1; a pressure of 20.2 bar gauge (0.20.02 MPa gauge); and a total inert particles volume of 6.60.1 vol. %. Experiments were carried out at these optimum conditions for two gas flow rates 1 542 ml/min and 4 000 ml/min, at a fixed liquid flow rate of 12.5 ml/min. Both experimental runs were carried out at atmospheric pressure. The experimental results are summarised in Table 1 and plotted in FIGS. 2, 3 and 4 for CO.sub.2 capture, ions removal and pH, respectively.

(27) For the low gas flow rate (1 542 ml/min), the experiment was run for 11 hours, whereas for the other flow rate (4 000 ml/min), the reactor was operated for 5 hours. The experimental results clearly indicate that the reactor system was very stable and reached steady state. The CO.sub.2 removal reached steady state after 3 hours for the low gas flow rate and about 4 hours for the high gas flow rate. Similarly, ions removal reached steady state after 3 hours and 6 hours for low and high gas flow rate, respectively. The attainment of steady state seemed to be more evident for the pH level in the reactor as shown in FIG. 4. As expected, the gas residence time inside the reactor seemed to have significant effect on the CO.sub.2 capture, but the effect was not as important on the ions removal as shown Table 1. As more gas passes through the reactor system, less CO.sub.2 gets captured (about 90%). Nevertheless, the difference between the two cases in CO.sub.2 capture efficiency is not substantial given the large difference in gas-to-liquid ratio (G/L). For the low gas flow rate, the gas to liquid ratio (G/L) was 123, and the capture efficiency was 97%, whereas for the higher gas flow rate, the G/L was 320 and the capture efficiency was 90%. These experiments show that the contactor/reactor system of the present invention is very effective in gas-liquid contact/reaction and can achieve a very stable steady state operation.

(28) TABLE-US-00001 TABLE 1 Gas flow rate Gas flow rate Conditions 1 542 ml/min 4 l/min Temperature 19.3 C. 19.3 C. Liquid flow rate 12.5 ml/min 12.5 ml/min Inert particles vol % 6.6 6.6 Molar ratio 3.3 NH.sub.3:1NaCl 3.3 NH.sub.3:1NaCl Gas/liquid flow ratio 123 320 CO.sub.2 capture 97.7% 90.1% efficiency Na removal 32.5% 30.0% Mg removal 97.2% 98.4% K removal 49.1% 37.0% Ca removal 87.3% 85.1% Run time 660 min 360 min

(29) Those skilled in the art will recognize that the foregoing description and examples have been presented for the purpose of illustration and example only. Modifications and variations of the present invention are possible in light of the above teaching without departing from the spirit and scope of the invention as defined in the appended claims.