Evacuation with Steam Jets

Typically, a suspension of starch in water (35% of solids), containing a small quantity of bacterial alpha-amylase, and adjusted to a pH of 6.5 with slaked lime (calcium hydroxide), is drawn into a steam jet that raises the temperature almost instantaneously to 82.2°C (180°F). This temperature is maintained for 20 minutes, and then the liquor is drawn into a partially evacuated space where the liquor is cooled by evaporation to 60°C (140°F). The treatment with alpha-amylase and the cooling operations are continuous. It is sometimes desirable to heat the liquor under super-atmospheric pressure in between the treatment with alpha-amylase and the cooling, in order to break up small amounts of residual granule-structure which would interfere with refining operations at a later stage in the process. The treatment with alpha-amylase results in a cloudy liquor of 20 d.e., containing... 

There is considerable information available in the hterature on the design of ejectors (steam jet ejectors, water jet pumps, air injectors, etc.) supported by extensive experimental data. Most of this information deals with its use as an evacuator and the focus is on ejector optimization for maximizing the gas pumping efficiency. The major advantage of the venturi loop reactor is its relatively very high mass transfer coefficient due to the excellent gas-liquid contact achieved in the ejector section. Therefore, the ejector section needs careful consideration to achieve this aim. The major mass transfer parameter is the volumetric liquid side mass transfer coefficient, k a. The variables that decide k a are (i) the effective gas-hquid interfacial area, a, that is related to the gas holdup, e. The gas induction rate and the shear field generated in the ejector determine the vine of and, consequently, the value of a. (ii) the trae liquid side mass transfer coefficient, k. The mass ratio of the secondary to primary fluid in turn decides both k and a. For the venturi loop reactor the volumetric induction efficiency parameter is more relevant. This definition has a built in energy... 

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