Sparger reactor

Some industrial operations involving bubble and drop formation are extraction, direct contact heat exchange, distillation, absorption, sparger reactors, spray drying and atomization, fluidization, nucleate boiling, air lifts, and flotation. 

Both air oxidation of hquid cyclohexane in a sparger reactor and HNO3 oxidation in a liquid-liquid reactor are two-phase reactors, which wiU be discussed in Chapter 12. 

Example 12-3 An aqueous solution contains 10 ppm by weight of an organic contaminant of molecular weight 120, which must be removed by air oxidation in a sparger reactor at 25°C. The liquid is admitted at 1 liter/sec. The air at 1 atm is admitted at 0.5 liter/sec. An impeller disperses the air into bubbles of uniform 1 mm diameter and mixes gas and liquid very rapidly. The reaction in the hquid phase has the stoichiometry A + 2O2 —> products with a rate r =... 

The bubble column and spray tower depend on nozzles to disperse the drop or bubble phase and thus provide the high area and small particle size necessary for a high rate. Drop and bubble coalescence are therefore problems except in dilute systems because coalescence reduces the surface area. An option is to use an impeller, which continuously redisperses the drop or bubble phase. For gases this is called a sparger reactor, which might look as shown in Figure 12-16. 

Figure 12-16 Sketch of sparger reactor in which an impeller continuously redisperses the bubble phase to maintain small bubble sizes and increase mass transfer. The impeller also recirculates the fluids in the reactor by placing it in a draft tube, which forces the fluids past the...

Kinetic system models are useful for visualizing the industrial operation (31,32). Stirred-tank and sparger reactor rates have been compared for this reaction and both are so high that they are negligible in the reaction s mathematical description. 

This case study on oxidation of sodium sulfide illustrates the design of a variety of gas-liquid reactors and compares their performances. Bubble column reactors are particularly attractive, as they offer advantages such as simplicity of construction and operation, but they suffer from such drawbacks as high pressure drop and backmixing in the liquid phase. To reduce the pressure drop, two modifications have been considered an external-loop air-lift reactor and a horizontal sparger reactor. Both result in substantial energy savings (because of low AP) under similar conditions of capacity and conversions in the gas and liquid phases. 

Fig. 19. TVA-type ammoniator—granulator incorporating a pipe cross reactor. 1, ammonia sparger, located at the 4 o clock position 11.4 cm from granulation shell with holes facing the rotating stream 2, phosphoric acid sparger, located to discharge phosphoric acid onto the top and near the center of the rotating bed of materials 3, pipe cross reactor 4, scmbber Hquor distributor, located above the bed in granulator to dribble scmbber Hquor onto bed.

Many initiators attack steels of the AISI 4300 series and the barrels of the intensifiers, which are usually of compound constmction to resist fatigue, have an inner liner of AISI 410 or austenitic stainless steel. The associated small bore pipework and fittings used to transfer the initiator to the sparger are usually made of cold worked austenitic stainless steel. The required pumping capacity varies considerably from one process to another, but an initiator flow rate 0.5 L / min is more than sufficient to supply a single injection point in a reactor nominally rated for 40 t/d of polyethylene. 

Bubble Reactors In bubble columns the gas is dispersed by nozzles or spargers without mechanical agitation. In order to improve the operation, redispersion at intei vals may be effected by static mixers, such as perforated plates. The liquid may be clear or be a slurry. 

Slurry Reactors with Mechanical Agitation The catalyst may be retained in the vessel or it may flow out with the fluid and be separated from the fluid downstream. In comparison with trickle beds, high heat transfer is feasible, and the residence time can be made veiy great. Pressure drop is due to sparger friction and hydrostatic head. Filtering cost is a major item. 

A bacterial fermentation was carried out in a reactor containing broth with average density p = 1200kg/m3 and viscosity 0.02N-s/m2. The broth was agitated at 90rpm and air was introduced through the sparger at a flow rate of 0.4 vvm. The fermenter was equipped with two sets of flat blade turbine impellers and four baffles. The dimensions of vessel, impellers and baffle width were ... 

A definite correlation of the results of the measurements can be achieved by using the adiabatic compressor power per unit volume of reactor according to Eq. (10) which is shown in Fig. 15 [27]. The experimentally determined loss factor is required in Eq. (10). The measured data for spargers with holes dL= 0.2 - 2 mm can be correlated with Eq. (24). 

Fig.2 and Fig.3 show the typical liquid velocity and gas hold up distribution in the ALR. From the figures, one notices that the cyclohexane circulates in the ALR under the density difference between the riser and the downcomer. An apparent large vortex appears near the air sparger when the circulating liquid flows fi om the downcomer to the riser at the bottom. In the riser, liquid velocity near the draft-tube is much larger than that near the reactor wall, the latter moved somewhat downward. The gas holdup is nonuniform in the reactor, most gas exists in the riser while only a little appears in the dowmcomer. 

Fig.8 illustrates the liquid velocity distribution at the bottom section of the reactor when the draft-tube diameter is 0.45m, 1.05m and 1.45m respectively. Results show that the liquid velocity at the outlet of the draft-tube lowers when the draft-tube diameter is raised, to subsequently influence the shape and size of the vortex at the bottom of the gas sparger. 

The reactor, a commercially supplied quartz photochemical reaction vessel, was fitted to meet the needs of this research (Figure 1). This included use of a Teflon-coated magnetic stirring bar in the reactor, a fiitted glass sparger, a nitrogen line used to cool the UV lany, and an injection port. Deionized water was distilled prior to use. 

A continuous, mechanically stirred tank reactor with a sparger located below the agitator or... 

The cost of specialised equipment, which cannot be found in the literature, can usually be estimated from the cost of the components that make up the equipment. For example, a reactor design is usually unique for a particular process but the design can be broken down into standard components (vessels, heat-exchange surfaces, spargers, agitators) the cost of which can be found in the literature and used to build up an estimate of the reactor cost. 

A sparger is used, since it is the most effective means of transferring heat. The water entering the reactor and that entering the steam boilers comes from the same source, so their cost and purity are similar. The meter that controls the amount of water entering the reactor must follow the sparger. Otherwise, the steam that is condensed would not be included in the amount of water added, and the wrong ratio of styrene to water would be obtained. 

There are at least two possible ways to preheat the water before it enters the reactors. One would be to use a heat exchanger similar to that designed for heating the styrene. A second would be to use a sparger in a tank. In the latter case the steam is intimately mixed with the water. 

Many factors affect gas holdup in three-phase fluidized systems, including bead size and density, liquid physical properties, temperature, sparger type, and fluid superficial velocities (Bly and Worden, 1990). System parameters such as reactor and gas distributor design can have... 

The pilot-scale SBCR unit with cross-flow filtration module is schematically represented in Figure 15.5. The SBCR has a 5.08 cm diameter and 2 m height with an effective reactor volume of 3.7 L. The synthesis gas passes continuously through the reactor and is distributed by a sparger near the bottom of the reactor vessel. The product gas and slurry exit at the top of the reactor and pass through an overhead gas/liquid separator, where the slurry is disengaged from the gas phase. Vapor products and unreacted syngas exit the gas/liquid separator and enter a warm trap (373 K) followed by a cold trap (273 K). A dry flow meter downstream of the cold trap measures the exit gas flow rate. 

Values of the ratio V(IVR given in Table 24.1 emphasize that most of the volume in a tower reactor (apart from a bubble column, data for which would be similar to a sparger-equipped tank) is occupied by the gas phase, and conversely for a tank reactor. This means that a, a in a tower and a, - a t in a tank. For mass transfer-controlled situations, a, is the more important quantity, and is much greater in a tower. For reaction-controlled situations, in which neither ai nor a is important, a sparger-equipped tank reactor, the cheapest arrangement, is sufficient. 

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