(142b) Experimental Evaluation of a Concentric Tray HIDiC Performance

An internally heat integrated distillation column (HIDiC) is essentially a heat pump assisted distillation column that in conjunction with diabatic operation, i.e. a uniform distribution of heat transfer duty along the integrated parts of a hot rectification and a cold stripping section, enables minimization of energy requirement in demanding separations. It is a proven, but regarding the hardware a highly demanding energy conservation concept. Indeed, uncertainties related to both design & construction and operation of a HIDiC are the main reason for reluctance on the side of potential users that diminishes prospects for practical implementation.

In present, technical feasibility study a concentric column containing an 0.3 m diameter rectification section placed inside an 0.8 diameter stripping section, with five fully thermally integrated sieve trays, has been used to simulate experimentally operation of a HIDiC. Two heat integrated sections have been operated as two individual columns in parallel at total reflux conditions, using appropriate mixtures of cyclohexane and n-heptane. The inner, rectification column (section) of a HIDiC was operated at higher pressures, while the outer, stripping section was operated at atmospheric pressure. The heat transfer from hot rectification column (section) to cold stripping column (section) occurred via the surface of the inner column wall and the heat panels placed above active (bubbling) area of the annular sieve trays in the stripping column. The photograph shows design of equipment.                                                                             

The performance of the small diameter inner column (cartridge sieve trays) appeared to be more sensitive to the rate of internal heat transfer than the outer column, exhibiting a deteriorating trend in efficiency with increasing column vapor load. The outer column equipped with annular sieve trays exhibited a stable performance over the whole operating range and as expected the presence of heat transfer panels appeared to be beneficial to both hydraulics and mass transfer efficiency. However, the overall heat transfer coefficient exhibits a progressive increase with increasing vapor load, indicating that at lower loads insufficient wetting, i.e. vaporization occurs, which is a concern. This and other concentric tray HIDiC design and operation relevant considerations are discussed.