Apparatus for measuring disentrainment rate of air

The apparatus for measuring disentrainment rate of air includes a Confined Plunging Liquid Jet Reactor (CPLJR) having a downcomer column surrounding a liquid jet. The end of the downcomer column is partially immersed in a receiving liquid pool contained in a reservoir. A conical ring is placed in the downcomer column below the liquid jet, the ring bearing against the wall of the downcomer column and forming a seal to define a headspace in the column. A gas supply and first bubble meter are connected to the column above the conical ring to supply gas and measure total entrainment. A second bubble meter connected to the headspace between the ring and the receiving pool measures disentrainment, and a third bubble meter connected to headspace above the receiving pool outside the column measures net entrainment.

BACKGROUND

The disclosure of the present patent application relates to fluid mechanics, and particularly to an apparatus for measuring the disentrainment of air in a confined plunging liquid jet reactor.

2. Description of the Related Art

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. Although such jet reactors have been known and used for decades and many devices and theoretical models have been proposed for measuring and predicting the gas entrainment and disentrainment rates obtained or obtainable using the devices, none have been entirely satisfactory.

Thus, an apparatus for measuring disentrainment rate of air solving the aforementioned problems is desired.

SUMMARY

The apparatus for measuring disentrainment rate of air includes a Confined Plunging Liquid Jet Reactor (CPLJR) having a downcomer column surrounding a liquid jet. The end of the downcomer column is partially immersed in a receiving liquid pool contained in a reservoir. The apparatus may include a pump connected by conduit to the bottom of the reservoir and connected by conduit to a nozzle at the top of the downcomer column that forms the liquid jet to recycle the liquid. A conical ring is placed in the downcomer column below the liquid jet, the ring bearing against the wall of the downcomer column and forming a seal to define a headspace in the column. A gas supply and first bubble meter are connected to the column above the conical ring to supply gas and measure total entrainment. A second bubble meter connected to the headspace between the ring and the receiving pool measures disentrainment, and a third bubble meter connected to headspace above the receiving pool outside the column measures net entrainment. Since gases, in general, are sparingly soluble in liquid, the collected gases through the second and third bubble meters (that measure the disentrainment and net entrainment rates, respectively) can partially or entirely be recirculated through the first bubble meter. This could be very beneficial when dealing with expensive gases.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIGS. 1A and 1B, the apparatus101for measuring disentrainment rate of air includes a Confined Plunging Liquid Jet Reactor (CPLJR) having a downcomer column111surrounding a liquid jet129. The end of the downcomer column111is partially immersed in a receiving liquid pool107contained in a reservoir105. The apparatus101may include a pump123connected by conduit to the bottom of the reservoir105and connected by conduit122to a nozzle125at the top of the downcomer column111that discharges the liquid jet129to recycle the liquid. A conical ring127is placed in the downcomer column111below the liquid jet129, the ring127bearing and abutting against the wall of the downcomer column111and forming a seal to define a headspace in the column111below the ring127. A gas supply and first bubble meter151are connected to the column above the conical ring127to supply gas and measure total entrainment. A second bubble meter152connected to the headspace between the ring127and the receiving pool107measures disentrainment, and a third bubble meter153connected to headspace above the receiving pool107outside the column111measures net entrainment. Recirculation loops154and155, connected through valves156and157, are connected to the three bubbles meters151,152and153.

In an alternative, the liquid jet125may be supplied with liquid from an external source through conduit137controlled by a suitable valve.

In an aeration operation, liquid, which is typically recycled from reservoir105, is injected into downcomer111through injection nozzle125. Gas, which may be air, entering the downcomer column111from a gas source through the first bubble meter151and its associated conduit, is entrained into the flow of liquid129exiting the nozzle125under pressure from the pump123in a jet of liquid, traverses the opening in the conical ring and plunges into the receiving pool107in the reservoir. The majority of the gas is entrained in the liquid jet129as a fine dispersion of bubbles131, carried to a greater depth than an unconfined system by the downcomer column, and exit the column111into the reservoir105entrained in the receiving pool107. However, a portion of the bubbles131is disentrained in the column111and enters the headspace between the conical ring127and the receiving pool107, and another portion of the bubbles131coalesce to form an upflow of larger bubble133entering the headspace outside the column111and above the receiving pool107beneath a ceiling of the reservoir105.

The downcomer column111is formed as a vertical tube that is partially immersed in a receiving liquid pool107contained in the reservoir105. The top end of the tube is connected to the injection nozzle125, the distance between the nozzle125and the top surface of the receiving pool defining the length of the liquid jet129. The other end (bottom) of the downcomer column111is left open to the receiving liquid pool107in the reservoir105. In this configuration, the downcomer column111functions as a confining tube.

The CPLJR reactor is utilized to improve gas mass rate transfer into liquid. This is achieved by increasing the liquid jet129penetration depth and the contact time between the gas and liquid. The CPLJR reactor also improves transfer by increasing the gas-liquid contact surface through hindering or reducing the tendency of descending primary bubbles131to coalescence into secondary ascending secondary bubbles133. The primary bubbles131, being smaller, provide a better mass transfer rate. The increase in primary bubble contact with the liquid and the reduction of the tendency of the descending primary bubbles131to coalescence into secondary ascending secondary bubbles133may, in turn, enhance the plunging jet reactor efficiency with regards to mass transfer rate. In order to improve efficiency of the transfer rate, adjustments may be made in the pressure and velocity of the liquid discharged through the nozzle125and the depth of the downcomer column111in the reservoir105, typically at a depth below the top surface of the liquid pool107in the reservoir105.

In order to determine how much of the gas is being retained in the liquid, measurements are taken of the gas as it is supplied to the downcomer column111above the conical ring127, disentrained inside the downcomer column111below the conical ring127, and entrained above the pool107outside the column111.

The disclosed technology provides a method for measuring the total air entrainment (QTA, measured at gas flow meter151), the disentrainment rate (QDS, measured at gas flow meter152) caused by bubbles rising up inside the downcomer column111, and the measured/net air entrainment (QN, measured at gas flow meter153). The determination of the disentrainment rate is significant because it (the rate of disentrainment) can be correlated with different properties of the fluid and of the system. The determination of entrainment may be used to adjust the depth of the downcomer column111below the top surface of the liquid107in the reservoir105. The disclosed technology also provides a method of recirculating the undissolved and disentrained air through loops154and155, connected through valves156and157.

The use of the disclosed technique may lead to more results and new developments regarding the mechanisms and new correlation, which may reveal which of the two systems, i.e., unconfined or confined systems, render an increase in their air entrainment rate. This presents a method which may also help to develop a model that relates total entrainment rate (QTA) to disentrainment rate (QDS) and net entrainment rate (QN) as shown as:
QTA=QNf(Vj,Lj,DC&dn)+QDSf(Vj,Lj,DC&dn)  (1)
where Vj=Liquid jet flow rate from the nozzle; Lj=Liquid jet length; dn=Nozzle diameter; DC=Downcomer diameter; QN=Net/measured entrainment rate; QDS=Disentrainment rate; QTA=Total entrainment rate.

Once this is done an optimization model can be applied by increasing the net entrainment rate through minimizing the dis-entrainment rate.