Example 6.2 Nutsche filter

Variations in upstream formulation mean that crystallisation of the j8-form, which is more difficult to filter, can occur in place of the a-form. In each batch, 50 kg of solids are present at a concentration of 6% v/v and it is envisaged that cake formation will occur to a maximum depth of 50 mm. In order to meet product specifications this new filter installation requires a sequential cycle comprising filtration, displacement washing and gas deliquoring. Preliminary 

The characteristics for both the a and P particle forms in suspension have been measured experimentally and these are shown in Table 6.11 along with other suggested operational parameters. For the a-form, determine the required filter area, the solid, liquid and solute throughput rates, the filter cycle time and other performance indicators. Assess the impact on the filter cycle if )S-form crystallisation occurs. 

For a filter cycle following the sequence filtration - washing - gas deliquoring, and with reference to the procedures outlined in Section 6.2, calculations 

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Design Example for a Batch Nutsche Filter Operation A batch Nutsche filter operates under constant pressure and maximum capacity with three stages filtration, washing and drying. The Nutsche filter with a 1 m filtration area operates under the following set of conditions ... 

The calculations presented in this section illustrate the level of detail that can be achieved when appropriate design equations and procedures are used to predict the performance of batch filters. Although the examples of the diaphragm filter press and the pressure Nutsche filter have been chosen for illustrative purposes, the methodologies can be readily adapted with the aid of the equations shown in Section 6.2 to analyse the performance of most other filters. 

The pentaerythritol was introduced into the acid in finely divided and well-dispersed particles and not in large unitary quantities. The entire 92 parts of pentaerythritol tetranitrate was introduced in 35 to 40 minutes. The pentaerythritol thus obtained was separated from the spent acid by filtering or drowning in water. To recover the spent acid the charge was passed onto a nutsch and filtered. The crude product was washed with water, then with a weak water-soluble alkali solution, such as sodium carbonate for example, and subsequently with water in order to remove the acid. 

As shovm in Table 7.3, the residual moisture content decreases significantly from sedimentation to filtration, with best results for centrifugation, where still 4-8% residual moisture remain in the product. These data stem from experiences of the potash industry, a very optimistic case in particular with regard to the filtration results. Since the quality of filtration also depends on particle properties (size and shape), the residual moisture content can vary in a wide range. For example, there are also references to residual moisture contents between 30% and 50% for nutsche or pressure filters. For highly disperse materials such as Al(OH)3 or Fe(OH)3 the residual moisture content can reach 70-90%. 

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