Batch filter cycles simulation

In this chapter the equations and models previously described in detail (Wakeman and Tarleton, 2005 a) are summarised and brought together so that the various phases in a batch filter cycle can be related to one another and meaningful process engineering models obtained. These models facilitate sequential calculations to provide the basis for computer simulations. Whilst there is scope to predict the performance of most of the filter types described in Chapter 1, those shown in Table 6.1 are presented in sufficient detail to model their filter cycles. 

The calculations presented in Sections 6.4.1 and 6.4.2 illustrate the degree to which the operation of a filter can be predicted from the knowledge of suspension and cake properties as well as basic operational parameters. Simulations develop these procedures to allow the performance of batch filters to be investigated over a wide range of process conditions without the need to perform costly sequences of experiments. While any of the filters shown in Table 6.1 can be simulated with the aid of the equations and procedures presented throughout this chapter, the diaphragm filter press cycle considered in Section 6.4.1 is chosen to illustrate the process. 

The complexity of interacting variables is fiirther emphasised by the summary data in Table 6.17. While both the mass of solids processed per batch and the cycle time increase sequentially with formed cake thickness, for the chosen simulation conditions the nominal solids production rate, which is the ratio of these two parameters, passes through a minimum for a filter cycle with cakes initially formed at 30 mm thickness. For cakes formed at the maximum 40 mm thickness the durations of the filtration, compression and gas deliquoring phases are longer, however, these adverse effects are positively counteracted by the greater amount of solids processed per batch which results in the observed improvement in solids production rate. However, higher production rates are obtained when thinner cakes are processed which reinforces the findings presented in Section 6.5.1. 

The methods described in this chapter show how calculations can be performed for batch filters in a way that takes some account of physical properties and operating conditions. The models employed are based on fundamental theories and practical results of varying complexity, all of which are sufficiently well developed to facilitate filter design and optimisation. The simulations, which make use of the Filter Design Software described in Chapter 5, show how detailed calculation procedures can be implemented to investigate what if questions as well as the general influence of process variables on filter cycle performance. 

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