High energy consumption

World resources of sulfur have been summarized (110,111). Sources, ie, elemental deposits, natural gas, petroleum, pyrites, and nonferrous sulfides are expected to last only to the end of the twenty-first century at the world consumption rate of 55.6 x 10 t/yr of the 1990s. However, vast additional resources of sulfur, in the form of gypsum, could provide much further extension but would require high energy consumption for processing. 

The Hall-Heroult process is a prodigious consumer of electrical energy. The energy required to produce 1 ton of aluminum from ore is more than twice that required to produce 1 ton of copper and ten times that for 1 ton of steel. More than 75% of this energy is consumed in the reduction of alumina to aluminum metal. The reasons for this high energy consumption have been presented in Table 6.18. The theoretical energy requirement for... 

Table 6.18 Reasons for high energy consumption in aluminum metal production.

Unfortunately, many new and old systems have not been designed properly and are being operated inefficiently. Some of the major consequences include high energy consumption, excessive system erosion, inadequate conveying capacity, unexpected pipeline blockages, excessive product damage and hence, poor quality control and/or increased maintenance. These problems have resulted mainly from... 

The ACH process has recently been improved, as stated by Mitsubishi Gas. Acetone-cyanohydrin is first hydrolized to 2-hydroxyisobutylamide with an Mn02 catalyst the amide is then reacted with methylformiate to produce the methyl ester of 2-hydroxyisobutyric acid, with coproduction of formamide (this reaction is catalyzed by Na methoxide). The ester is finally dehydrated with an Na-Y zeolite to methylmethacrylate. Formamide is converted to cyanhydric acid, which is used to produce acetone-cyanohydrin by reaction with acetone. The process is very elegant, since it avoids the coproduction of ammonium bisulphate, and there is no net income of HCN. Problems may derive from the many synthetic steps involved, and from the high energy consumption. 

Free product, suspended solids, and highly turbid waste streams lower UV reactor efficiency. The CAV-OX process does not treat metals. It may, however, oxidize metallic ions or reduce metallic salts while destroying organic contaminants. The disadvantages of the CAV-OX process include high energy consumption, not cost effective at high contaminant concentrations, and the process mechanisms are not well documented. 

Note that the carbon electrode takes part in the reaction. From the reaction stoichiometry, we can calculate that a current of 1 A must flow for 80 h to produce 1 mol A1 (27 g of aluminum, about enough for two soft-drink cans). The very high energy consumption can be greatly reduced by recycling, which requires less than 5% of the electricity needed to extract aluminum from bauxite (Box 14.1). Note also that the production of 1 tonne of aluminum is accompanied by the release of more than 1 tonne of carbon dioxide into the atmosphere. 

These shortcomings prevail also in Shelf cascade classifier [6], where instead of pipes, inclined shelves are mounted on the inner walls of a vertical vessel (Fig. 2b). Strong turbulence prevailing under the shelves cause high pressure drops (of up to 4-5 kPa) and high energy consumption of these devices. 

Proton transfer from the hydrogen peroxide molecule to His 74 is accompanied by O—H bond break and electron transfer to the oxygen atom. Then owing to the following O—H bond break and 0=0 bond formation this electron is transferred to the hydrogen atom with simultaneous hydride-ion transfer. The whole sequence of electron transfer in BRC is implemented without high-energy consumption. 

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