Solids flow rates

Farbar [Trans. Am. Soc. Mech. Eng., 75,943-951 (1953)] describes how a venturi meter can be used to measure solids flow rate in a gas-solids mixture when the gas rate is held constant. Separate calibration curves (solids flowversus differential) are required for each gas rate of interest. 

Conveying systems normally use air as the transport medium to convey granular, crushed, or pulverized materials. Modelling the flow of pneumatic conveying and calculating its pressure loss is a problematic task. The greatest problem arises from the fact that different mass flow ratios, solid flow rate divided by the gas flow rate, imply different flow types in pneumatic conveying. Each of these flow types, which can be classified in many different ways, requires its own specific model in order to provide a concrete calculation method. 

Solid flow rate Recycling flow rate Eluent flow rate Extract flow rate Eeed flow rate Raffinate flow rate ... 

P ) Qpp- The specification of P and the solid flow rate (or, alternatively, one of the liquid flow rates) defines all the flow rates throughout the TMB system. The P parameter has a higher limit, since the feed flow rate must be higher than zero, 1 < /3 < v t. The case of /3 = 1 corresponds to the situation where dilution of species is minimal, and the extract and raffinate product concentrations approach the feed concentrations. In fact, for /3 = 1, we obtain = Qf = = ( - 1) = (Kg... 

The influence of the switch time interval on the purity is shown in Fig. 9-10. A change on the switch time interval will lead to a change on the equivalent solid flow rate throughout the system. In all runs the inlet and outlet flow rates, as well as the internal liquid flow rates in all the four sections of the SMB unit, are kept constant. 

Increasing the switch time interval is equivalent to decrease the solid flow rate and the net fluxes of components in all sections of the TMB unit will be pushed in the same direction of the liquid phase. This implies that, first, the more retained species will move upwards in section III and will contaminate the raffinate stream and the less retained species will move upwards in section IV, will be recycled to section I, and will contaminate also the extract stream. The decrease of the switch time interval will have similar consequences. The equivalent solid flow rate will increase and the net fluxes of component in all four sections of the TMB unit will be pushed in the opposite direction of the liquid phase. This implies that, first, the less-retained species will move downwards in section II and will contaminate the extract stream and the more retained component will also move downwards in section I, will be recycled with the solid to the section IV, and will contaminate the raffinate stream. It is possible to obtain simultaneously high purities and recoveries in a SMB, but the tuning must be carefully carried out. 

In addition, both the recycling and the solid flow rates are also kept constant. 

Considering that the separation system is fully characterized, i.e., adsorbent and mobile phases, column dimensions, SMB configuration and feed concentration, the optimization of the TMB operating conditions consists in setting the liquid flow rates in each section and also the solid flow rate. The resulting optimization problem with five variables will be certainly tedious and difficult to implement. Fortunately, the... 

Knowing that the feed flow rate should equal = 125 1 h one can estimate the required solid flow rate Q = = 149 1 h leading to all the inter-... 

Switch time interval Solid flow rate ... 

To construct a model which will give behavior similar to another bed, for example, a commercial bed, all of the dimensionless parameters listed in Eqs. (37) or (39) must have the same value for the two beds. The requirements of similar bed geometry is met by use of geometrically similar beds the ratio of all linear bed dimensions to a reference dimension such as the bed diameter must be the same for the model and the commercial bed. This includes the dimensions of the bed internals. The dimensions of elements external to the bed such as the particle return loop do not have to be matched as long as the return loop is designed to provide the proper external solids flow rate and size distribution and solid or gas flow fluctuations in the return loop do not influence the riser behavior (Rhodes and Laussman, 1992). 

S is coulombs/second or amps, coulombs/kg is given in Table 7-3, and kg/s is the solids flow rate. 

The performance of a reactor for a gas-solid reaction (A(g) + bB(s) -> products) is to be analyzed based on the following model solids in BMF, uniform gas composition, and no overhead loss of solid as a result of entrainment. Calculate the fractional conversion of B (fB) based on the following information and assumptions T = 800 K, pA = 2 bar the particles are cylindrical with a radius of 0.5 mm from a batch-reactor study, the time for 100% conversion of 2-mm particles is 40 min at 600 K and pA = 1 bar. Compare results for /b assuming (a) gas-film (mass-transfer) control (b) surface-reaction control and (c) ash-layer diffusion control. The solid flow rate is 1000 kg min-1, and the solid holdup (WB) in the reactor is 20,000 kg. Assume also that the SCM is valid, and the surface reaction is first-order with respect to A. 

As mentioned earlier in this section, each of these models must be solved for either sin or cos(p and tan as needed for Eq. 5.7 to predict the solids flow rate 0. The following two identities are used for the transformation ... 

Finally at the highest gas velocities we exceed what is called the choking velocity. Above this the bed is in pneumatic transport. This transition velocity depends on the solid flow rate, and according to Bi and Fan (1991) occurs at... 

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