Cake temperature

At the end of the run, measure and record the filtrate volume (and weight, if appropriate), cake thickness, final cake temperature (if appropriate), wet cake weight, and note the cake discharge characteristics (roU, sticks to media, etc.). 

For the refiner trying to mitigate the problem of spontaneous combustion, probably the two most important parameters to control are as follows (1) spent filter cake temperature and (2) oil content. Although the actual temperature marking the onset of second-stage charring will vary from plant to plant depending on type of oil and clay activity, the most important point is that spontaneous combustion should not occur if the spent filter cake temperature can be sufficiently lowered before exposure to the atmosphere. Obviously, water addition is one way to lower temperature and this approach is probably the simplest and most reliable method. 

The temperature difference ( d t) was obtained from the difference between cake temperature (95°C constant) and steam temperature. 

Initial adjustment period—is the stage at which the wet feed material heats up or cools down to the starting drying temperature which is basically referred to as the wet cake temperature. For example, the wet feed is introduced to the heated dryer at ambient temperature. During this period the material temperature will start to rise to the wet bulb temperature which may be different from the initial feed temperature. The reason the temperature of the wet cake remains low relative to the gas temperature is a phenomenon known as evaporative cooling. 

Although elevated temperatures reduce oil viscosity and enhance diffusion, hexane vapor pressure limits the practical operating temperature of the extractor and its contents to about 55°-60°C. Higher temperatures and the consequent higher vapor pressures unduly increase the volume of vapor which the recovery systems must capture and recycle. Futhermore, if the cake temperature is at or near the boiling temperature of the solvent, a vapor phase may occur at the interface between cake fragment and solvent (mis-cella), effectively thwarting liquid diffusion. 

Except on start-up, the solvent does not normally require heating since the hot cake from the prepress process often provides more than sufficient heat to maintain the required extraction temperature. It has, in fact, been found necessary to allow the cake to dissipate as much heat as possible while in transit from the preparation process to the extraction plant. In addition, subcooling the solvent below the ambient temperature of the solvent work tank has been used successfully to control extractor temperatures. Notwithstanding the reduced cake temperatures resulting from the generally lower temperatures used to cook the current "double low" rapeseed varieties, some cooling of cake and/or subcooling of solvent is still found to be necessary in some plants. 

In a 500 ml. bolt-head flask, provided with a mechanical stirrer, place 70 ml. of oleum (20 per cent. SO3) and heat it in an oil bath to 70°. By means of a separatory funnel, supported so that the stem is just above the surface of the acid, introduce 41 g. (34 ml.) of nitrobenzene slowly and at such a rate that the temperature of the well-stirred mixture does not rise above 100-105°. When all the nitrobenzene has been introduced, continue the heating at 110-115° for 30 minutes. Remove a test portion and add it to the excess of water. If the odour of nitrobenzene is still apparent, add a further 10 ml. of fuming sulphuric acid, and heat at 110-115° for 15 minutes the reaction mixture should then be free from nitrobenzene. Allow the mixture to cool and pour it with good mechanical stirring on to 200 g. of finely-crushed ice contained in a beaker. AU the nitrobenzenesulphonic acid passes into solution if a little sulphone is present, remove this by filtration. Stir the solution mechanically and add 70 g. of sodium chloride in small portions the sodium salt of m-nitro-benzenesulphonic acid separates as a pasty mass. Continue the stirring for about 30 minutes, allow to stand overnight, filter and press the cake well. The latter will retain sufficient acid to render unnecessary the addition of acid in the subsequent reduction with iron. Spread upon filter paper to dry partially. 

Phthalide. In a 1 litre bolt-head flask stir 90 g. of a high quality zinc powder to a thick paste with a solution of 0 5 g. of crystallised copper sulphate in 20 ml. of water (this serves to activate the zinc), and then add 165 ml. of 20 per cent, sodium hydroxide solution. Cool the flask in an ice bath to 5°, stir the contents mechanically, and add 73-5 g. of phthalimide in small portions at such a rate that the temperature does not rise above 8° (about 30 minutes are required for the addition). Continue the stirring for half an hour, dilute with 200 ml. of water, warm on a water bath imtil the evolution of ammonia ceases (about 3 hours), and concentrate to a volume of about 200 ml. by distillation vmder reduced pressure (tig. 11,37, 1). Filter, and render the flltrate acid to Congo red paper with concentrated hydrochloric acid (about 75 ml. are required). Much of the phthalide separates as an oil, but, in order to complete the lactonisation of the hydroxymethylbenzoic acid, boil for an hour transfer while hot to a beaker. The oil solidifles on cooling to a hard red-brown cake. Leave overnight in an ice chest or refrigerator, and than filter at the pump. The crude phthalide contains much sodium chloride. RecrystaUise it in 10 g. portions from 750 ml. of water use the mother liquor from the first crop for the recrystaUisation of the subsequent portion. Filter each portion while hot, cool in ice below 5°, filter and wash with small quantities of ice-cold water. Dry in the air upon filter paper. The yield of phthalide (transparent plates), m.p. 72-73°, is 47 g. 

Cakes are dried in low temperature, high humidity conditions for a long time in order to minimize strain and absorbency variabiUty. The continuing usage of the cake system almost a century after its invention owes much to the desirable strain-free yam arising from its washing and drying operations. 

Reaction times can be as short as 10 minutes in a continuous flow reactor (1). In a typical batch cycle, the slurry is heated to the reaction temperature and held for up to 24 hours, although hold times can be less than an hour for many processes. After reaction is complete, the material is cooled, either by batch cooling or by pumping the product slurry through a double-pipe heat exchanger. Once the temperature is reduced below approximately 100°C, the slurry can be released through a pressure letdown system to ambient pressure. The product is then recovered by filtration (qv). A series of wash steps may be required to remove any salts that are formed as by-products. The clean filter cake is then dried in a tray or tunnel dryer or reslurried with water and spray dried. 

Shipping and Storage. MaHc acid is shipped in 50-lb, 100-lb, and 25-kg, multiwall paper bags or 100-lb (45.5 kg) fiber dmms. A technical-grade, 50% solution may be shipped in tank cars or tank tmcks. MaHc acid can be stored in dry form without difficulty, although conditions of high humidity and elevated temperatures should be avoided to prevent caking. 

The newly formed y-Mn02 actually coats the surfaces of the particles of the soHd phase the MnSO dissolves in the Hquid phase, along with the majority of the ore impurities. The effective surface area is expanded by the etching action of the sulfuric acid. Following the acid treatment step, the slurry is filtered and the cake is carefiiUy washed and dried at a controlled temperature. 

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