Energy, saving recycling

The Overall Process. Each distillation column should be examined in context with the rest of the process as well as by itself. For example, an opportunity for energy saving may be a reduction of process recycles via a purer overhead or bottoms stream. Lowering or raising column pressure to facihtate interchange with other parts of the process is another possible opportunity. 

Fig. 1. A new process (Urea Technologies) developed for the Tennessee Valley Authority operates at considerable energy savings. Urea is produced in an overall exothermic reaction of ammonia and carbon dioxide at elevated pressure and temperature. In a highly exothermic reaction, ammonium carbamate is first formed as an intermediate compound, followed by its dehydration to urea and water, which is a slightly endothermic reaction. The conversion of CO2 and NH3 to urea depends oil the ammonia-to-caibon dioxide ratio, temperature, and water-to-carbon dioxide ratio, among other factors. The new process makes maximum use of the heat created in the initial reaction, including heat recycling. 1 Urea Technologies and Tennessee Valley Authority)...

The recycling of scrap steel contributes 310 million tonnes to the world supply of the alloy - 750 million tonnes. It has been calculated that the energy savings are equivalent to 160 million tonnes of coal. Also, it has been calculated that the raw materials conserved are equivalent to 200 million tonnes of iron ore. 

Heat recovery. Many process streams are hot. Ultrafiltration usually works better with hot feeds so hot feed solutions are not a problem. If the hot, clean permeate can be recycled without cooling, the energy savings can be considerable. If the water is 50 °C above ambient temperature, the energy savings amount to about US 4.00/1000 gal. 

Source Adapted from Pressurized ozone membrane ultrafiltration/nanofiltration methodology for TDS removal in the paper mill process water for energy saving, production efficiency, and environmental benefits. Available at http /www.recycle.com/linpac-nice3/documents/doefinalreport.pdf. 

More general environmental development interests than the details above relate to the capability of recycling several types of phosphates in a phosphorus plant, as long as these sources are low in iron, copper and zinc [26]. An automated system for determining the energy-saving potential in phosphorus production has been developed [27]. 

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