Crystallizers discharge lines

Normally, the product made in a crystallizer is for customer use and, therefore, the product size must be carefully monitored in order to stay within the prescribed limits. Typically, the product from a crystallizer will be sampled every l-2h during conditions when the operation is monitored to make adjustments in product size or characteristics. Ideally, the best place to sample the product is before it enters the slurry discharge pump and preferably from the slurry discharge line. 

Fig. 4. Drainage of salt crystals in a cylindrical screen pusher-discharge centrifuge (8), where the cake thickness is 3.3 cm, the centrifugal field = 320 U, and the crystals 14 wt % <250 p.m. ( ) Represents moisture in the discharge cake, and (° ) moisture in the cake by material balance with drainage flows line A...

Low-pressure mercury lamp Low-pressure glow discharge 254 and 185 O.l-l.O Liquid crystal displays, photoresist technology Weaker emission lines at 313 and 578 nm... 

Bamford and Ward (1961) have obtained evidence which supports this conclusion, although the systems studied are somewhat different. They used an electric discharge to produce radicals in methacrylic acid (monomer) crystals and in various salts of this acid at 77°K. In some cases relatively narrow lines were obtained, and generally the characteristic nine-line spectrum was observed. Perhaps their most striking result was for the barium salt. At 77°K the four lines were weak and broad, whilst at room temperature a nine-line spectrum of intensity ratio very close to 1 2 4 6 6 6 4 2 1 resulted. These changes were reversed on cooling. 

Ethylene glycol and urea under pressure. Two charges, each composed of 60 g. (1 mole) of urea and 62 g. (1 mole) of ethylene glycol, were processed in similar silver-lined bombs of 325-cc. capacity at 275° and a pressure estimated to have been 400 atm. for 3 hrs. The bombs were allowed to cool to room temperature and discharged. The combined products were distilled under reduced pressure and 35% of the ethylene glycol was recovered. Ethyleneurea, b.p. 150—170°/1—2 mm., was obtained which, after crystallization from chloroform, amounted to 51 g. for a net yield of 47%, based on ethylene glycol. 

Peelers are characterized by conical baskets (Fig. 9) that are fitted with a heavy-duty plow mechanism that peels the cake away from the bowl for discharging at operating speed. This minimizes the batch cycle time and is normally used to process more rugged crystals. Peelers may provide cake rinse and may be equipped to dissolve the residual heel cake on line, promote drainage, and maintain short cycle times. 

A stirred vessel crystallizer is shown in Fig. 6-4. Included are a dual-impeller pitched-blade turbine with a tickler blade (see Section 6.6.1.6), a subsurface addition line, baffles, and a ram-type bottom outlet valve to aid in discharge of slurries. 

Start-up methods. In this study, methods of start-up of a continuous cooling crystallizer are considered. Although several start-up methods are possible two typical ones as shown in Figure 2 were chosen. This description is based on the SFC (Sequential Function Chart). The SFC is conq)Osed of step and transition . Step , which is denoted with a box, shows the state of apparatus. Transition with a bold line indicates a condition that makes a move of the step . The items on the side of step are actual operations. The feed solution was charged to the crystallizer from the feed line. The feed was stopped when the liquid level arrived at the set up value, i.e. the hold up was fulfilled, l en, the solution was cooled to the operating temperature. Seed crystals were added when the solution temperature became constant at the set up value. After that, the continuous feeding and discharge were started. In this study, the experimental duration was more than 10 residence times in order to ensure the attainment of steady state. This method of start-up is defined as SU Method 1. 

Semicontinuous crystallization processes often eombine the best features of both batch and continuous operation. For example, a rapid mixer with a short residence time (possibly an on-line deviee, e.g. Figure 9.14) can discharge its product slurry into an agitated residenee tank. In many eases, a series of tanks may have to be installed, whieh can then be operated as individual units or arranged in cascade (section 9.1.2). 

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