Agitators anchor

Close-Clearance Stirrers For some pseiidoplastic fluid systems stagnant fluid may be found next to the -essel walls in parts remote from propeller or turbine impellers. In such cases, an anchor impeller maybe used (Fig, 18-6), The fluid flow is principally circular or helical (see Fig, 18-7) in the direction of rotation of the anchor. Whether substantial axial or radial fluid motion also occurs depends on the fluid iscosity and the design of the upper blade-supporting spokes. Anchor agitators are used particularly to obtain irnpro ed heat transfer in high-consistency fluids,... 

This procedure can be repeated for different values of N. A compilation of the experimental values of ks for a variety of impellers, turbine, propeller, paddle, anchor, and so on, has been given by Skelland(16), and an examination of Table 7.1 suggesLs that for pseudo-plastic liquids, ks lies approximately in the range of 10-13 for most configurations of practical interest/22 231 SKELLAND l6) has also correlated much of the data on the agitation of purely viscous non-Newtonian fluids, and this is shown in Figure 7.8. 

Figure 7.14. Single-celled secondary flow with an anchor agitator...

Figure 7.20 shows some of the impellers which are frequently used. Propellers, turbines, paddles, anchors, helical ribbons and screws are usually mounted on a central vertical shaft in a cylindrical tank, and they are selected for a particular duty largely on the basis of liquid viscosity. By and large, it is necessary to move from a propeller to a turbine and then, in order, to a paddle, to an anchor and then to a helical ribbon and finally to a screw as the viscosity of the fluids to be mixed increases. In so doing the speed of agitation or rotation decreases. 

Bhi KNER. J. L. and Smith, J. M- Trans. Inst. Chem. Eng. 44 (1966) T224. Anchor-agitated systems Power input with Newtonian and pseudo-plastic fluids. 

A simple jacketed pan or kettle is very commonly used in the processing industries as a reaction vessel. In many cases, such as in nitration or sulphonation reactions, heat has to be removed or added to the mixture in order either to control the rate of reaction or to bring it to completion. The addition or removal of heat is conveniently arranged by passing steam or water through a jacket fitted to the outside of the vessel or through a helical coil fitted inside the vessel. In either case some form of agitator is used to obtain even distribution in the vessel. This may be of the anchor type for very thick pastes or a propeller or turbine if the contents are not too viscous. 

BROWN et al.i95) have given data on the performance of 1.5 m diameter sulphonators and nitrators of 3.4 m3 capacity as used in the dyestuffs industry. The sulphonators were of cast iron and had a wall thickness of 25.4 mm the annular space in the jacket being also 25.4 mm. The agitator of the sulphonator was of the anchor type with a 127 mm clearance at the walls and was driven at 0.67 Hz. The nitrators were fitted with four-bladed propellers of 0.61 m diameter driven at 2 Hz. For cooling, the film coefficient hb for the inside of the vessel was given by ... 

An example of a low conversion reactor would be a conventionally agitated kettle with large turbine agitators and jacket cooling. The utility of this type of reactor can be extended to intermediate conversions by the use of anchor or helical agitators to partially overcome heat transfer and mixing problems at higher viscosities. 

Because of their proximity to the wall, anchor agitators are more effective in maintaining heat transfer coefficients to higher viscosities. Relatively high torques and larger gear reducers are required, however. Studies by Uhl and Voznick ( ) correlated the heat transfer coefficient in a manner similar to that used with turbine agitators ... 

Heat transfer can, of course, be increased by increasing the agitator speed. An increase in speed by 10 will increase the relative heat transfer by 10. The relative power input, however, will increase by 10In viscous systems, therefore, one rapidly reaches the speed of maximum net heat removal beyond which the power input into the batch increases faster than the rate of heat removal out of the batch. In polymerization systems, the practical optimum will be significantly below this speed. The relative decrease in heat transfer coefficient for anchor and turbine agitated systems is shown in Fig. 9 as a function of conversion in polystyrene this was calculated from the previous viscosity relationships. Note that the relative heat transfer coefficient falls off less rapidly with the anchor than with the turbine. The relative heat transfer coefficient falls off very little for the anchor at low Reynolds numbers however, this means a relatively small decrease in ah already low heat transfer coefficient in the laminar region. In the regions where a turbine is effective,... 

The time required to pass through the high shear zone will be proportional to the volume of the vessel divided by the flow from the turbine. This will be porportional to 1/ND. With a turbine in turbulent flow, turnover is relatively rapid and all the fluid will pass through the impeller region in a relatively short period of time. The flow regime in an anchor or helically agitated vessel can be inferred from the flow studies by Smith and Peters (], 13j. These indicated... 

Figure 10. Pure drag flow of polymer syrup in the wall-blade clearance C of an anchor agitator in creeping flow. All velocities relative to the blade (12),...

Figure 11. Flow patterns with an anchor agitator as in Figure 10 but at higher Reynolds numbers (above 10-20) where inertial effects become significant. Streamline schematic (12) shows stable trailing vortex.

Monsanto Patents. A process for HIPS is described in the patent issued to Carter and Simon (35)and is illustrated in Fig. 20. There are two reactors an anchor agitated CSTR and a reflux cooled LFR. Both reactors can be operated at variable and controllable tillage so that a given product can be made over a range of rates. 

A typical stirred-tank reactor is shown in Fig. 5.4-3. It is a cylindrical vessel with elliptical or torospherical bottom and cover. It is equipped with an axially mounted stirrer rotating with a speed from 25 rpm (large scale) to 2000 rpm (laboratory). Fig. 5.4-4 shows the stirrers that are mostly used in fine chemicals manufacture, viz. the marine propeller, turbine, flat- or pitched-blade agitator, and anchor. Agitators move the fluid into axial and radial direction. Marine propellers and pitched-blade stirrers predominantly impose axial motion. 

Paddle, anchor and helical ribbon agitators (Figures 10.56a, b, c), and other special shapes, are used for more viscous fluids. 

Figure 10.56. Low-speed agitators (a) Paddle (b) Anchor (c) Helical ribbon...

For turbine agitators, impeller to tank diameter ratios of up to about 0.6 are used, with the depth of liquid equal to the tank diameter. Baffles are normally used, to improve the mixing and reduce problems from vortex formation. Anchor agitators are used with close clearance between the blades and vessel wall, anchor to tank diameter ratios of... 

Ag-301 to Ag-308 8 Agitators for reactors, 120 hp, anchor type, stainless steel, 40 rpm. 

Church27 suggest using a paddle or anchor type stirrer of medium speed at 20-60 rpm. Since styrene is only slightly soluble in water and all the other substances are present in very small quantities, it is assumed that the properties of water, the continuous medium, can be used in the design of the agitator. The size of the motor will then be doubled to correct for any errors and then doubled again to obtain the necessary power for startup. 

No specific costs could be found for the cutter, Cu-201 an anchor-type agitator, Ag-301 an epoxy-lined tank, D-101 and the waste treatment system, WTS-801. Further, the F O B. costs of the sand filter, WTS-701, and the extruders, EXT-501, had to be calculated from the installed costs. 

One way to estimate prices of items when they cannot be found is to compare them with other items that might be similar or to items that might be expected to cost about the same. To be conservative for the cutter, it was assumed that a blender would cost at least as much and probably more. Its price was equated to that of a similar size blender ( 5,000). In place of an anchor-type agitator, the costs for a propeller-type agitator was used. Similarly, it was assumed that an epoxy-lined tank would cost the same as a rubber-lined tank. 

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