Patent Application
20200330934
The disclosure of the present patent application relates to gas-liquid reactors, and particularly to a confined plunging liquid jet reactor with a modified downcomer designed to reduce bubble disentrainment.
There are many industrial processes where it is necessary to mix a gas, such as air, with a liquid. Although sometimes a simple sparged system with a tube or air stone releasing bubbles directly below the surface of the water will suffice, for some processes, e.g., aerobic wastewater treatment, air pollution abatement, froth flotation and fermentation, an improved gas absorption rate is desirable. In such circumstances, a plunging jet reactor may be used to achieve a high mass transfer rate at low capital and operating cost.
Plunging jet devices improve gas absorption rates by creating a fine dispersion of bubbles and by increasing the contact time between the gas bubbles and the liquid at relatively low power inputs. A plunging jet may be operated as an unconfined device or as a confined device. In an unconfined plunging jet reactor system, a liquid jet plunges into an open liquid pool, creating a conical downflow dispersion of fine bubbles and a surrounding upflow of larger, coalesced bubbles. The penetration depth of the bubbles is small due to the spreading of the submerged jet, and hence the bubble contact time with the liquid is short.
In a confined system, a Confined Plunging Liquid Jet Reactor (CPLJR) uses a vertical tube or downcomer column that surrounds the liquid jet and that is partially immersed in the receiving liquid pool contained in a reservoir. Hence, the entrained bubbles may be carried to large depths by the liquid downflow. The top end of the tube is connected to a nozzle, while the other end (bottom) is left open to the receiving liquid pool.
Improvements in the gas mass rate transfer into liquid can be achieved by increasing the liquid jet penetration depth and the contact time between the gas and liquid, as well as increasing the gas-liquid contact surface through hindering or reducing descending primary bubble coalescence into secondary ascending bubbles. With regard to the latter, smaller bubbles tend to give better mass transfer rates. However, despite the various parameters that may be varied in order to improve the mass transfer rate, conventional CPLJ reactors, such as reactor 100, still suffer the drawback of gas rising from the receiving tank 116 back into the open lower end 114 of the downcomer 108. This factor is referred to as the “disentrainment rate”, and depends upon the process operating conditions, such as the jet velocity, nozzle diameter, downcomer diameter, and jet length. It would obviously be desirable to be able to minimize or remove disentrainment of the bubbles from the CPLJR process, resulting in improvement of gas entrainment into the liquid, as well as reducing the size of the gas bubbles to improve mass transfer. Thus, a confined plunging liquid jet reactor with a modified downcomer solving the aforementioned problems is desired.
The confined plunging liquid jet reactor with a modified downcomer includes a downcomer having an upper end, an open lower end, and a gas inlet for receiving gas from an external source. A plurality of longitudinally-extending baffles are mounted on an inner surface of the downcomer adjacent the open lower end thereof. A nozzle is mounted on the upper end of the downcomer for receiving a pressurized liquid from an external source to generate a liquid jet. The liquid jet impinges on a mixture of the liquid and the gas contained within the downcomer. The open lower end of the downcomer is positioned within a receiving tank such that a portion of the mixture of the liquid and the gas exits the open lower end of the downcomer to flow into the receiving tank. In use, the longitudinally-extending baffles interfere with toroidal and swirling fluid motions that occur inside the downcomer. This reduces the disentrainment of gas bubbles, thus increasing the net entrainment rate.
In an alternative embodiment, the longitudinally-extending baffles may be removed from the downcomer and replaced by a sieve or porous screen, which is mounted transversely within the downcomer. The porous screen hinders bubble coalescence by breaking the air bubbles into smaller/primary bubbles, increasing the bubble penetration depth, and thus increasing mass transfer. In another embodiment, the downcomer column may be modified to include both longitudinal baffles and at least one sieve.
These and other features of the present disclosure will become readily apparent upon further review of the following specification.
Similar reference characters denote corresponding features consistently throughout the attached drawings.
As shown in
The nozzle 12 is vertically oriented and creates a high velocity jet of liquid 14 that impinges into a body of liquid 16 located beneath the nozzle 12. Gas G is drawn into the process near the point of impingement through gas inlet 26, or the gas may be air from the headspace in the downcomer above the liquid 16. The plunging jet 14 impinges into the body of liquid 16, which is confined by the downcomer 18. The downward force of the plunging jet 14 fights buoyancy forces of the entrained gas G within a mixing zone 20. The gas-liquid mixture (G+L) flows down through a pipe flow zone 22, such that the liquid and excess gas both flow downward to exit the downcomer 18 at its open lower end 28 into a receiving tank 30. Although not clearly shown in the schematic diagrams of
As noted above, and as shown in
The alternative embodiment shown in
In order to test the confined plunging liquid jet reactor with modified downcomer 10 of
It is to be understood that the confined plunging liquid jet reactor with modified downcomer is not limited to the specific embodiments described above, but encompasses any and all embodiments within the scope of the generic language of the following claims enabled by the embodiments described herein, or otherwise shown in the drawings or described above in terms sufficient to enable one of ordinary skill in the art to make and use the claimed subject matter.
