Control Boiling point rise

Product Concentration Control. Product concentration is one of the most important evaporator system control parameters. It can be determined from the solution density, as assumed in the discussion above, or the boiling point rise (BPR). 

Product concentration can be controlled by measuring a number of physical properties. On-stream composition analyzers are often used. Commonly used physical properties include density, boiling point rise, temperature/pressure combinations, temperature difference, conductivity, differential pressure, refractive index, buoyancy float, and viscosity. Each method has certain advantages as well as limitations. In all cases, however, a representative measurement location must be carefully selected to eliminate entrained air bubbles or excessive vibration, and the instrument must be mounted in an accessible location for cleaning and calibration. The location of the product quality transmitter with respect to the final effect should be considered also. Long piping runs between the product and the instrument increase deadtime, which in turn reduces the effectiveness of the control loop. 

Water in Oven Cooked Products. In oven baked products the inside of the product is not going to reach boiling point, indeed one of the simplest ways of obtaining a well-controlled temperature is to rely on holding a liquid at its boiling point. However, in a baked product, as the temperature rises the vapour pressure of the water rises, causing water to be lost by evaporation. 

Because of impurities in the liquid feed, it may be necessary to purge or blowdown the vaporizer periodically, as indicated by a rising boiling point temperature or the steam valve approaching a full open position. Although not shown, vaporizers often have a separate, temperature-controlled superheater to ensure the vaporization of any entrained droplets and to prevent condensation. 

In a Pasteur pipette loosely place a very small piece of cotton followed by 2.5 g of alumina. Add to the top of the pipette 1.5 mL of styrene and collect 1 mL in a disposable 10 x 75-mm test tube. Add to the tube 50 mg of benzoyl peroxide and a thermometer and heat the tube over a hot sand bath. When the temperature reaches about 135°C polymerization begins and, since it is an exothermic process, the temperature rises. Keep the reaction under control by cautious heating. The temperature rises, perhaps to 180°C, well above the boiling point of styrene (145°C) the viscosity also increases. Pull the thermometer from the melt from time to time to form fibers when a cool fiber is found to be brittle remove the thermometer. A boiling stick can be added to the tube and the polymer allowed to cool. It can then be removed from the tube or the tube can be broken from the polymer. Should the polymer be sticky the polymerization can be completed in an oven overnight at a temperature of about 85°C. 

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