Power Consumption and Pressure Drop

The power consumption is made up of the work of compression of the air and the frictional losses due to the flows of air and solid through the line. The work of compression of air at a flow rate m a and CP/C = 1.4 is given by 

Frictional losses are evaluated separately for the air and the solid. To each of these, contributions are made by the line itself, the elbows and other fittings, and the receiving equipment. It is conservative to assume that the linear velocities of the air and solid are the same. Since the air flow normally is at a high Reynolds number, the friction factor may be taken constant at f, = 0.015. Accordingly the frictional power loss of the air is given by 

The work being done on the solid at the rate of m s lb/sec is made up of the kinetic gain at the entrance (w2), the lift (vv3) through an elevation Az, friction in the line (wA), and friction in the elbow (ws). Accordingly, 

The coefficient of sliding friction fs of the solid equals the tangent of the angle of repose. For most substances this angle is 30-45° and 

Friction in the curved elbows is enhanced because of centrifugal force so that 

Figore 5.5. Concept of dense phase transfer of firiable materials, by intermittent injection of material and air pulses, air pressures normally 10-30 psig and up to 90psig Sturtevant Engineering Co., Boston, MA). 

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The most important variables which must be considered in estimating power consumption and pressure drop are ... 

For transport of a gas-solid suspension, it is important to be able to evaluate the pressure drop in order to estimate the power consumption. In a pneumatic conveying system, particles are usually fed into the carrying gas and accelerated by the gas flow. The power consumption (or pressure drop per unit pipe length) for the acceleration of particles can be significant compared with that for a fully developed flow condition. Moreover, the pressure... 

Estimation of power consumption and power efficiency of the use of moving moulding elements is important both from the theoretical and the practical point of view. It is also rather complicated. In the end of Sect. 2.2 we stated that the theoretical power consumed for extrusion of a melt through the head and that consumed by rotation (or vibration) of the core are strictly increasing functions of frequency (oo or 2) at a fixed specific pressure drop across the f = P/l (see Fig. 6). 

Finally, the rotating-disk reactor provides efficient gas-liquid mass transfer by constant renewal of the gas-liquid film on the rotating disk. The mass-transfer coefficient in such a reactor can be calculated using Eq. (6.49). The reactor provides a low pressure drop and partially backmixed gas and liquid phases. The extent of backmixing can be further reduced by the use of baffles. Once again, power consumption and mechanical difficulties may limit the size of such vessels. 

Many scale model measurements include quantitative measurement of pressure drops throughout the system. Maximum allowable system pressure drop is frequently a major constraint from the equipment manufacturer or end user when flow correction solutions are sought. System pressure drop directly relates to the operating cost due to blower/fan power consumption and the hydraulic head available for downstream power or steam generation. For scale model testing, pressure... 

The devices sending air to the stack can be fans, blowers, or compressors. They must meet two requirements (1) being able to send enough air to the stack for reaction (typically 2.5 to 3.0 times stoichiometric ratio), (2) being able to overcome the pressure drop caused by the stack. Fans can only be used for air-cooled stacks because their pressure boost is lower than several kPa. The advantages of fans are that they have the lowest power consumption and noise levels. Blowers and compressors are used for liquid-cooled stacks. Compressors have the highest power consumption and noise levels. Whenever possible, blowers should be used over compressors. A blower can achieve a pressure boost up to about 25 kPa. When the pressure need is more than a blower can provide, a compressor must be used. 

The particle size of catalyst is an important parameter for an industrial catalyst. It not only significantly affects the pressure drop of the reaction gas through the catalyst bed, but also affects the diffusion rate, and thus the macro reaction rate. Reducing the size of catalyst can increase the utilization ratio of the inner surface of catalyst and decrease the influence of intraparticle diffusion, improve the macro reaction rate, and reduce the needed amount of catalyst. Reducing the amount of catalyst can reduce the height of catalyst bed and pressure drop. However, if the particle size of catalysts is reduced, the resistance of unit bed of catalyst to gas flow increases and power consumption for gas transmission also increases. Thus the particle size of catalyst has contradictory effects on a reactor. 

A technique which avoids this problem is to decouple mixing from extrusion. An arrangement used by the author is shown in Figure 8.17 [17]. The primary objective was to obtain data on the influence of cavity size of the cavity transfer mixer (CTM) (described in Section 9.3). At the same time a variety of mixers were evaluated in an attempt to compare this particular mixer with a range of known mixing devices. An equal length of screw and a plain annulus (like the Couette model in Chapter 2) were used as controls. In addition to mixing performance, data was required on power consumption, temperature rise, and pressure drop. 

Dust Filter. The cloth or bag dust filter is the oldest and often the most reHable of the many methods for removing dusts from an air stream. Among their advantages are high (often 99+%) collection efficiency, moderate pressure drop and power consumption, recovery of the dust in a dry and often reusable form, and no water to saturate the exhaust gases as when a wet scmbber is used. There are also numerous disadvantages maintenance for bag replacement can be expensive as well as a sometimes unpleasant task these filters are suitable only for low to moderate temperature use they cannot be used where Hquid condensation may occur they may be hazardous with combustible and explosive dusts and they are bulky, requiring considerable installation space. 

Ttbles 9.20 and 9.21 present recommendations for maximum pressure drops of components in the supply and extract air systems in order to achieve a certain target level for power consumption in the whole system. In category Low," this target level is 1500 in Normal, 2500 and in High 4000 W/(mVs),... 

Stepped-diameter pipelines to minimize pressure drop, velocity, wear and power consumption. 

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