Hydrating plant

Huang CX, Canny MJ, Oates K, McCully ME. Planning frozen hydrated plant specimens for SEM observation and EDX microanalysis. Microsc Res Technol 1994 28 67-74. 

Traditionally, ethanol has been made from ethylene by sulfation followed by hydrolysis of the ethyl sulfate so produced. This type of process has the disadvantages of severe corrosion problems, the requirement for sulfuric acid reconcentration, and loss of yield caused by ethyl ether formation. Recently a successful direct catalytic hydration of ethylene has been accomplished on a commercial scale. This process, developed by Veba-Chemie in Germany, uses a fixed bed catalytic reaction system. Although direct hydration plants have been operated by Shell Chemical and Texas Eastman, Veba claims technical and economic superiority because of new catalyst developments. Because of its economic superiority, it is now replacing the sulfuric acid based process and has been licensed to British Petroleum in the United Kingdom, Publicker Industries in the United States, and others. By including ethanol dehydrogenation facilities, Veba claims that acetaldehyde can be produced indirectly from ethylene by this combined process at costs competitive with the catalytic oxidation of ethylene. 

The term marijuana is thought to be based on the Portuguese word mari uan o, which translates as intoxicant. Marijuana, incidentally, is not the same as hashish, although both arc derived from the Cannabis saliva plant. Marijuana is the leafy top portion of the plant, whereas hashish is made from the dust of the resin that the hemp plant produces to protect it from the sun and heat and to maintain hydration. Plants that grow in warmer climates produce greater amounts of the resin, which generally has stronger psychoactivc effects. 

Rotary kilns were developed for the manufacture of cement, and were first used for lime burning in 1885. Their high capital cost, however, limited their use to relatively large productive capacities. They could only calcine small limestone (e.g. with a top size of 60 mm), but, while this was an advantage in terms of the stone balance of the quarry, the small lime produced was not as marketable as lump lime. For many years, rotary kilns were largely used to feed hydrating plants. 

Others keep the two products separate, with the primary fines being sent to less demanding customers (including in-house ground lime and hydrating plants). 

Generally, the best outlets for both primary and secondary fines are as a feed to ground lime and hydrating plants. They have also been used as a source of calcium oxide in dry process cement plants, where their use resulted in a significant reduction in heat requirements [17.1]. 

Reaction with metals. Hydrated lime does not react with iron or steel, which are commonly used as materials of construction for hydrating plants and hydrated lime handling systems. It reacts readily with aluminium and also attacks lead and brass [19.2], which should not be used as storage containers. 

An estimated 10 to 15 % of the quicklime produced in developed countries is converted into hydrated lime and the percentage may be higher in countries which do not have a large steel industry. Because hydrating plants are relatively complex and can be fed with surplus grades of quicklime, there are relatively few of them and they are normally located at a lime works. 

Because of the above complexities, before deciding to invest in a hydrating plant, the hydration characteristics of the available grades of quicklime should be evaluated. The quality of the water supply should also be assessed, bearing in mind any seasonal variations. 

Some buffer storage of quicklime is usually provided between the lime kilns and the hydrating plant to provide operating flexibility. Where the removal of impurities in the hydrating plant is not important, the quicklime is generally reduced in size using impact breakers. Otherwise, rolls and jaw crushers, or cone mills may be used (see section 5.2). 

A typical pressure hydration plant is illustrated in Fig. 20.4. The quicklime is generally ground or pulverised. In some plants the lime and water are blended in... 

O. Collarini, T. Christiansen, New lime hydration plant in northern Italy , Zement Kalk Gips 9,1996, 540-544. 

As with limestone, minimising wastage is an important factor in the economics of quicklime production. Integrated hme works often feed surplus grades to a hydrating plant or to a ground lime plant. Products which cannot be used are often blended into selected products, or sold as agricultural lime. 

The processing stage of a hydration plant includes conveyors, elevators, air classifiers, chutes and mills. It is all effectively enclosed. Dust extraction and filtration equipment is provided for all discharges to atmosphere and for pressure relief, at, for example, the top of elevators. The collected dust is returned to the process. Hydrated lime and any rejects from the process are stored in enclosed bunkers fitted with filters to de-dust displaced air. 

Desiccation of plant tissues presents a shift of the water from the liquid to the vapour phase (Sun, 2002). Temperature influences evaporation, as well as the partial water vapour pressure in the air and the energy status of water in plant tissue, both in dry and hydrated plant tissue. An increase in temperature results in a decrease in the equilibrium water content at a given relative humidity (water activity) or an increase in the equilibrium water activity for a given tissue water content (Fig. 1). Water activity can be described as the effective water content, which is thermodynamically available for various physiological processes in cells. The temperature dependence of the isotherm shift is described by the Clausius-Clapeyron Equation ... 

Tab.l - Effects of water stress on the molecular species composition of polar lipids from Vigna leaves. C=well-hydrated plants S=water-stressed plants... 

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