New Realization of Periodic Cycled Separation

Abstract

A new realization of periodic cycled gas/liquid separation is presented. Separation factors and column efficiencies are compared for a column stripping ammonia from water with air, using three different sets of internals: conventional sieve trays, Sulzer BX gauze packings, and periodically cycled trays. The proposed new periodic trays are shown to be advantageous compared to their continuous alternatives. It is demonstrated experimentally that periodic tray efficiencies of up to 300% are achievable. With the proposed new tray design, a new operation form is also introduced in which the trays are drained sequentially rather than simultaneously, such that the vapor flow is not interrupted during the liquid drainage. For different ratios of counter-current vapor/liquid flow rates, column efficiencies for periodically cycled columns are shown experimentally to be two times greater than those for columns with sieve trays.

Cyclic distillation technology - a mini-review

“…This means that separate phase movement and lack of mixing between the liquids from different trays (which have different compositions) will result in improved distillation performance. With a special tray design (shown in Fig. ), using cyclic operated perforated sheet or slate (COPS) type trays it is possible to introduce a new operational principle for periodic cycling separation based on sequential tray draining, where the trays are emptied sequentially rather than simultaneously, while the vapor flow is maintained throughout For stepwise periodic operation, each tray is fitted with an inlet and an outlet normally closed by on‐off valves and has a side reservoir large enough to contain one tray‐holdup – which makes the setup more expensive.…”

“…Thus the cyclic operation using sequential tray draining consists of a continuous vapor flow where sequential tray draining is initialized periodically. For this tray type a tray efficiency of 300% has been achieved in a stripper column …”

“…2), using cyclic operated perforated sheet or slate (COPS) type trays it is possible to introduce a new operational principle for periodic cycling separation based on sequential tray draining, where the trays are emptied sequentially rather than simultaneously, while the vapor flow is maintained throughout. 5,6 • For stepwise periodic operation, 7 each tray is fitted with an inlet and an outlet normally closed by on-off valves and has a side reservoir large enough to contain one tray-holdup -which makes the setup more expensive. The trays have no downcomers but they can be completely emptied through their outlet directly into the reboiler.…”

“…For this tray type a tray efficiency of 300% has been achieved in a stripper column. 6 In their three-tray column (0.47 m diameter) which can be equipped either with conventional sieve or with COPS type periodic tray designs, an overall column efficiency of 120% is obtained for periodic stripping, compared with 60% for conventional sieve trays. In those experiments the above mentioned tray efficiency was not fully exploited.…”

“…In order to obtain the theoretical performance, Toftegård et al recently developed trays based on a COPS type design where the tray is opened during liquid draining as illustrated in Fig. .…”