Agitated reactors impeller power

Repeat Example 24-2 for the xylene (B) oxidation reaction carried out in an agitated tank reactor (instead of a bubble-column reactor). Use the data given in Example 24-2 as required, but assume the diameter D is unknown. Additional data are the power input without any gas flow is 8.5 kW the impeller rotates at 2.5 Hz the height and diameter of the tank are the same (h = D) the impeller diameter is DI3, and the impeller contains 6 blades assume ubr = 1.25usg. In addition to the vessel dimensions for the conversion specified (/B = 0.16), determine the power input to the agitator (P,). 

Determine the reactor volume required for one reactor and that for two equal-sized reactors in series for 80 percent conversion of A. And if the capital cost of a continuous-flow stirred-tank reactor unit is given by 200,000(17/100)° 6 (where V is reactor volume in m3), the life is 20 years with no salvage value, and power costs 3 cents per kilowatt-hour, determine which system has the economic advantage. Assume that overhead, personnel, and other operating costs, except agitation, are constant. The operating year is 340 days. Each reactor is baffled (with a baffle width to tank diameter of 1/12) and equipped with an impeller whose diameter is one-third the tank diameter. The impeller is a six-bladed turbine having a width-to-diameter ratio of 1 /5. The impeller is located at one-third the liquid depth from the bottom. The tank liquid-depth-to-diameter ratio is unity. 

Mechanically stirred hybrid airlift reactors (see Fig. 6) are well suited for use with shear sensitive fermentations that require better oxygen transfer and mixing than is provided by a conventional airlift reactor. Use of a low-power axial flow impeller in the downcomer of an airlift bioreactor can substantially enhance liquid circulation rates, mixing, and gas-liquid mass transfer relative to operation without the agitator. This enhancement increases power consumption disproportionately and also adds other disadvantages of a mechanical agitation system. 

A pilot-plant reactor, a scale model of a production unit, is of such size that 1 g charged to the pilot-plant reactor is equivalent to 500 g of the same material charged to the production unit The production unit is 2 m in diameter and 2 m deep and contains a six-blade turbine agitator 0,6 m in diameter. The optimum agitator speed in the pilot-plant reactor is found by experiment to be 330 r/min. a) What are the significant dimensions of the pilot-plant reactor (b) If the reaction mass has the properties of water at 70°C and the power input per unit volume is to be constant, at what speed should the impeller turn in the large reactor (c) At what speed should... 

In a polymerisation reactor, a monomer/polymer solution is to be agitated in a baffled mixing vessel using a double turbine (6 fiat blades) impeller, with the configuration B-B in Table 8.1, at a rotational speed of 2Hz. The solution exhibits power-law behaviour with n = 0.6 and m = 12 Pa-s° . Estimate the power required for a 300 mm diameter impeller. The density of the solution is 950kg/m. ... 

Bouaifi, M., and Roustan, M. (2001), Power consumption, mixing time and homogenisation energy in dual-impeller agitated gas-liquid reactors, Chemical Engineering and Processing, 40(2) 87-95. 

This means that the aggregate size distribution mirrors the turbulence spectrum of the reactor. Variables that determine mixing are reactor design, number and design of baffles, impeller design, power input, feed concentration, feed rate, location and number of inlet tubes, and so on. The position of the inlet tube(s) and the conditions near these feed points are also important and generally the solutions should be introduced close to the agitator [23, 24]. 

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