Sieve-plate columns design

Prepare a sieve-plate column design for the chlorobenzene distillation and make dimensioned sketches showing details of the plate layout including the weir and the downcomer. 

Design a sieve plate column to perform this separation, for a feed rate of 10,000 kg/hour. Treat the feed as a binary mixture of ethanol and water. 

The specification for of a sieve plate column is given below. Make a preliminary mechanical design for the column. You design should include ... 

NORMAL OPERATION OF SIEVE PLATE. A sieve plate is designed to bring a rising stream of vapor into intimate contact with a descending stream of liquid. The liquid flows across the plate and passes over a weir to a downcomer leading to the plate below. The flow pattern on each plate is therefore crossflow rather than countercurrent flow, but the column as a whole is still considered to have countercurrent flow of liquid and vapor. The fact that there is crossflow of liquid on the plate is important in analyzing the hydraulic behavior of the column and in predicting the plate efficiency. 

Since the behavior of packed columns [2,3,4, 5] and bubble cap columns [6] has been previously reported, this research at the National Bureau of Standards was primarily concerned with the characteristics of perforated or sieve plate columns. Such parameters as plate spacing, plate geometry, maximum allowable vapor velocity, weir height and downcomer area were investigated, and the results of these investigations were applied to the design of a pilot plant column. 

The design of downcomers for sieve plate columns is reviewed by Biddulph et al. (1993). These authors present the following four rules of thumb for downcomer sizing based on years of experience ... 

Solvent recovery column plate column, diameter 0.6 m, height 6 m, 10 stainless steel sieve plates, design pressure 2 bar, column material carbon steel. 

Pressure drop. The pressure drop over the plates can be an important design consideration, particularly for vacuum columns. The plate pressure drop will depend on the detailed design of the plate but, in general, sieve plates give the lowest pressure drop, followed by valves, with bubble-caps giving the highest. 

Design the plates for the column specified in Example 11.2. Take the minimum feed rate as 70 per cent of the maximum (maximum feed 10,000 kg/h). Use sieve plates. 

The feed temperature will range from 10 to 25 °C. The column will operate at atmospheric pressure. For a feed of 7500 kg/h, compare the designs for a sieve plate and packed column, for this duty. Use a reflux ratio of 3. Compare the capital and utility cost for the two designs. 

A sieve tray-type absorption column is proposed. The design specifies a column 1.8 m diameter, approximately 32 m high, and containing 59 sieve plates. Weak-acid condensate is added to tray 13 and make-up water is added at tray 59 (the top tray). Crossflow-type trays are employed from plates 1 to 13, however, a decreased liquid loading demands reverse flow-type trays for plates 14 to 59. The operating pressure is approximately 950 kPa and the operating temperature range is from 8°C to 65°C. 

After selection of the column internal diameter (the fundamental column specification), the sieve plates must then be designed. This involves a trial and error approach. A preliminary plate design is proposed based upon typical tray configurations, then the hydraulic... 

Sieve trays are used throughout the absorption column, however two distinct hydraulic designs are required. The first sieve plate design is required for trays below the weak-acid feed point. Above the weak-acid feed point, the downcoming liquid flowrate is diminished. The vapour flowrate essentially remains constant throughout the column. Different vapour to liquid ratios above and below the weak-add feed point require a second hydraulic design to be considered. 

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