Washing phase

The displacement washing phase is performed at a constant pressure of 600 kPa and specifications require a fractional solute recovery (F) of 91%. Assume that the cake thickness, solids volume fraction (and hence porosity), specific resistance and wash flow rate are constant throughout washing and the active filter area is = Af/2 = 150 m.  

Using values from the end of the previous consolidation phase for (CJg = 1 -(e v)e, (Oe and (4)g = L , the superficial wash velocity and mean 

The mass of solids in the cakes remains constant throughout washing and is equal to the value at the end of compression deliquoring (M = 4527 kg). The mass of liquid in the cakes, as given by equation (6.63), also remains the same as the density of filtrate and wash are equal (M = 3920 kg). The data sequences shown in Table 6.8 provide information for the washing phase where  

The cake moisture content at the end of washing is the same as at the end of consolidation (i.e. = 46.41%). Although no corrections have been applied 

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The system control is based on a series of six cam timers, which control the following sample introduction unit, sampling phase sample introduction unit, refilling phase neutralization unit, neutralization phase neutralization unit, wash phase chelation— extraction unit, extraction phase and chelation—extraction unit, collection and wash phase. 

Benzofuran. Heat under reflux for 8 hours a mixture of 20 g (0.11 mol) of o-formylphenoxyacetic acid, 40 g of anhydrous sodium acetate, 100 ml of acetic anhydride and 100 ml glacial acetic acid. Pour the light brown solution into 600 ml of iced water, and allow to stand for a few hours with occasional stirring to aid the hydrolysis of acetic anhydride. Extract the solution with three 150 ml portions of ether and wash the combined ether extracts with 5 per cent aqueous sodium hydroxide until the aqueous layer is basic the final basic washing phase acquires a yellow colour. Wash the ether layer with water until the washings are neutral, dry the ethereal solution over anhydrous calcium chloride and remove the ether on a rotary evaporator. Distil the residue and collect the benzofuran as a fraction of b.p. 170-172°C. The yield of colourless product is 9.5 g (91%). 

In the final five wash phases the bed is connected in series with the four other beds that preceded it in flow sequence and washed with water in countercurrent flow sequence to recover ammonium carbonate and prepare the bed to receive seawater at the start of the next cycle. 

Weight (or mass flow rate) of wash phase or stream Weight (or mass flow rate) of wash solvent alone Weight solute/weight feed solvent in feed (raffinate) phase... 

When it comes to the washing temperatures, 30% reduction of the washing phase emissions can he achieved at 40 °C compared to washing at 60 °C. 

Washing Parameters specific to a washing phase including washing pressure, wash liquid density, viscosity and surface tension, solute concentration in the wash liquid and the required washing model/curve. 

Depending on the type and mode of operation of a batch filter, a cycle may comprise up to two filtration phases followed by a number of compression, gas deliquoring and washing phases, essentially in any order, as well as a cake discharge operation (see also Tarleton and Hancock, 1997 , Tarleton and Wakeman, 1994c, 2005b Wakeman and Tarleton, 1994a,b, 1999). 

Calculations for a washing phase are based on the dispersion model (Wakeman, 1986a Wakeman and Attwood, 1988, 1990). The model requires the determination of a dispersion number (Z) ) that characterises the washing process and use of a design chart (Figure 6.7), which allows the number of wash ratios (W) and fractional solute recovery F) to be found. The pressure (A/ ) is fixed throughout washing and several properties of... 

Table 6.8 i Data sequences for the washing phase of a diaphragm press cycle. ... 

Using relevant values from the end of the previous washing phase, i.e. 

Filtration phase durations Compression deliquoring phase duration Washing phase duration Gas deliquoring phase duration... 

The dispersion model is again used to model the washing phase in the cycle. The initial step, i.e. the calculation of the dispersion number (D ), follows the procedure shown for the diaphragm filter press in Section 6.4.1. 

The end of the washing phase is denoted (in this particular example) by a fixed number of wash ratios. The data sequences shown in Table 6.13 provide information for the washing phase such that ... 

To describe the washing phase on a continuous filter cycle the dispersion model is preferred (Wakeman, 1986a Wakeman and Attwood, 1988,1990). A dispersion number (D ) that characterises the cake washing process is calculated and for a known number of wash ratios (IT) the fractional solute recovery (F) can be found. The applied vacuum (ApJ is fixed throughout washing and several properties of the cake are assumed to remain constant and equal to the values at the end of the previous phase in the cycle, i.e. K=Lpr==( <,vV Qv=(CJpr = 1 (ejpr nd M/t)=(M,(t))p ... 

Solid/Liquid Separation Equipment Selection and Process Design 7.3.1.2 Washing phase... 

The displacement washing phase is performed at the same level of vacuum as the filtration phase. From equations (7.2) and (7.4)... 

Values at the end of the washing phase are given in the bottom row of Table 7.4. Although no corrections have been applied to the wash ratio to account for splashing and other losses, in practice the wash ratio is likely to be greater than the values shown. If the losses can be quantified (no theory currently exists) then a correction factor >1 is applied to column (4) to account for the additional wash volumes required. 

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