Heating surfaces continuously cleaning

In distillation the water closest to the heating surface is hottest and it is there that calcium sulfate is least soluble. Thus, calcium sulfate deposits, forming an adhering film that increases the thermal resistance and decreases the heat flux. The scale is continuously deposited until the tubes are cleaned or become plugged. For scale deposition the local concentration must be at least saturated in calcium sulfate. At 100° C. this occurs in concentrated sea water at a concentration 3.1 times that of ordinary sea water. A plant has been successfully operated continuously without calcium sulfate deposition by taking only part of the available water from the sea water, so that the liquid in the evaporator is never more than 1.8 times the concentration of sea water and the wall temperature is below about 250° F. ( ). This imposes technical and economic limitations on distillation plants. Similar considerations hold for plants distilling brackish water containing calcium sulfate. 

As we have already explained in section 4.1.1., if the condensate does not completely wet the wall, individual liquid droplets form instead of a continuous condensate him. Heat transfer coefficients in dropwise condensation are significantly larger than in film condensation. In the condensation of steam, the heat transfer coefficients measured have been a factor of four to eight times larger. However, it has been shown that all investigated substances, in particular water, which condense on commonly used heating surfaces, will completely wet the surface. This is true as long as the material of the heated surface and the liquid have not been contaminated. This also corresponds to the experience that the formation of a water film is taken to be an indication that laboratory equipment is well cleaned. 

A pneumatically operated acoustic cleaning system (140 dBA, 200-300 Hz) for the boiler heating surfaces has been installed. It can, however, only cope with major fouling of these surfaces. A certain amount of permanent fouling under continuous operating conditions is unavoidable. 

For the determination of copper, weigh out accurately about 0.5 g of your preparation into a conical flask. Add 30 cm dilute sulphuric acid and 2.5 g ammonium persulphate and shake well to dissolve the solids. Heat the solution gradually to the boiling point. Continue until all the copper appears as the blue copper(II) sulphate disregarding a small residue of sulphur which floats on the surface. Continue boiling for 15 minutes to decompose any remaining persulphate. Filter into a clean conical flask and wash on the filter with water. Add to the filtrate concentrated ammonia until the deep blue copper(lI) complex is formed. Ttien add dilute acetic acid to restore the pale blue colour of aqueous Cu(II) ions and then add an equal volume of the acid already added. Dissolve 2 g of KI and titrate the liberated iodine with standardised 0.05 M sodium diiosulphate until the solution is straw yellow. Dilute with 100 cm water, add 2 cm ficshly prepared starch solution and continue titration. When the blue colour fades add 1 g of purest ammonium thiocyanate and continue titration rapidly until the blue colour disappears for 1 minutes. The pale flesh-coloured Cul remains as a precipitate. Calculate the molar ratio Cu thiosulphate. 

Ethyl phenylethylmalonate. In a dry 500 ml. round-bottomed flask, fitted with a reflux condenser and guard tube, prepare a solution of sodium ethoxide from 7 0 g. of clean sodium and 150 ml. of super dry ethyl alcohol in the usual manner add 1 5 ml. of pure ethyl acetate (dried over anhydrous calcium sulphate) to the solution at 60° and maintain this temperature for 30 minutes. Meanwhile equip a 1 litre threenecked flask with a dropping funnel, a mercury-sealed mechanical stirrer and a double surface reflux condenser the apparatus must be perfectly dry and guard tubes should be inserted in the funnel and condenser respectively. Place a mixture of 74 g. of ethyl phenylmalonate and 60 g. of ethyl iodide in the flask. Heat the apparatus in a bath at 80° and add the sodium ethoxide solution, with stirring, at such a rate that a drop of the reaction mixture when mixed with a drop of phenolphthalein indieator is never more than faintly pink. The addition occupies 2-2 -5 hoius continue the stirring for a fiuther 1 hour at 80°. Allow the flask to cool, equip it for distillation under reduced pressure (water pump) and distil off the alcohol. Add 100 ml. of water to the residue in the flask and extract the ester with three 100 ml. portions of benzene. Dry the combined extracts with anhydrous magnesium sulphate, distil off the benzene at atmospheric pressure and the residue under diminished pressure. C ollect the ethyl phenylethylmalonate at 159-160°/8 mm. The yield is 72 g. 

The cracked products leave as overhead materials, and coke deposits form on the inner surface of the dmm. To provide continuous operation, two dmms are used while one dmm is on-stream, the one off-stream is being cleaned, steamed, water-cooled, and decoked in the same time interval. The temperature in the coke dmm is in the range of 415—450°C with pressures in the range of 103—621 kPa (15—90 psi). Overhead products go to the fractionator, where naphtha and heating oil fractions are recovered. The nonvolatile material is combined with preheated fresh feed and returned to the furnace. The coke dmm is usually on stream for about 24 hours before becoming filled with porous coke, after which the coke is removed hydraulically. 

For some processes, though they would not be classified as batch processes, the period of continuous production will be limited by gradual changes in process conditions such as, the deactivation of catalysts or the fouling of heat-exchange surfaces. Production will be lost during the periods when the plant is shut down for catalyst renewal or equipment clean-up, and, as with batch process, there will be an optimum cycle time to give the minimum production cost. 

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