Nutsche filters/filter cycles

Batch Percolators The batch tank is not unlike a big nutsche filter it is a large circiilar or rectangiilar tank with a false bottom. The solids to be leached are dumped into the tank to a uniform depth. They are sprayed with solvent until their solute content is reduced to an economic minimum and are then excavated. Countercurrent flow of the solvent through a series of tanks is common, with fresh solvent entering the tank containing most nearly exhausted material. In a typical ore-dressing operation the tanks are 53 by 20 by 5.5 m (175 by 67 by 18 ft) and extract about 8200 Mg (9000 U.S. tons) of ore on a 13-day cycle. Some tanks operate under pressure, to contain volatile solvents or increase the percolation rate. A series of pressure tanks operating with countercurrent solvent flow is called a diffusion battery. 

A suspension of aluminum hydroxide in water is to be filtered imder constant pressure in a batch Nutsch filter having a filtering area of 1 m. Each filter cycle is estimated to separate out 0.5 m of suspension. The operating temperature is 25° C. The following expression for the cake resistance was empirically determined from pilot tests ... 

The next step.was the removal of ammonia from the crude soln , which was done by steam-stripping in an evaporator to an ammonia recovery system, where NH, was absorbed in w. The resultant NH,-free crude soln was filtered through a Nutsch type filter to remove the catalyst and other insol impurities. The filtrate referred to as clear liquor was stored in a 1000 gal tank from which it could be transferred by suction into either of two 280 gal jacketed evaporators. The evaporation was conducted under 24" vacuum with 50 lb steam press in the jacket. A total of 425 gal of "clear liquor was concentrated until a sample of its "mother liquor showed the strength of 35% NaOH. During this operation the bulk of NaN, being less sol in w than NaOH, pptd. Then the mixt was cooled to 80-90°F (27-32°) (to cause the pptn of addnl NaN,) and dropped to a wringer. The yield was ca 75% NaN, and the overall cycling time was 5 6 hrs... 

Figure 1.28 Photographs, with permission from Pope Scientific, of a 0.15 m capacity pressure Nutsche filter assembled (/eft) and disassembled showing the filter medium and sealing arrangements right). A schematic of the typical pressure Nutsche filter cycle is shown in Figure 6.1.

Figure 6.1 Schematic diagram of a simple pressure Nutsche filter cycle, (a) Filtration (b) displacement washing (c) gas deliquoring (d) cake discharge by plough.

Table 6.12 Data sequences for the filtration phase of a Nutsche filter cycle. ...

Table 6.15 Comparison of filter cycle performance for two particle forms in a Nutsche filter.

The addition of R-103 reduces the cycle time of the process to 55 h, resulting in 143 batches per year and aimual throughput of 24,753 kg. Under these conditions the bottleneck shifts to NFD-101. Since the aimual throughput is still below the desired amount of 27,000 kg/year, addition of an extra Nutsche filter to eliminate the current bottleneck is the next logical step. Figure 15.7 shows the results of that scenario. Under these conditions, the first Nutsche filter (NFD-101) is used for the first three filtration procedures (P-3, P-5, and P-7) and the second filter (NFD-102)... 

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