Energy Conservation in Alcohol Distillery with the Application of Pinch Technology

The energy audit of an operating distillery producing ethyl alcohol from low quality wine and wine dregs is presented. Three different processes were analyzed: the production of raw (unrefined) alcohol using stripping columns working at pressure lower than atmospheric, the same production using columns at higher pressure and the production of neutral (refined) alcohol. The operational and design data of these three processes were used to compute mass and energy balances. The liquid streams in a distillery are multicomponent nonideal solutions. The data reported in the literature for ethyl and methyl alcohol–water mixtures were utilized, together with purposely developed correlations for density, specific heat and vapor–liquid equilibrium and simplified exergy formulas. The methodologies used to study the alcohol production are based on the pinchtechnology approach: the detailed energy balances of the three industrial processes are presented. The main step was to present the heat sources and sinks of the production processes in the grand composite curve, laying out all the thermodynamic opportunities of any heat recovery. Thermodynamic analysis methods were used to minimize the heating energy needed by the production processes when using heat pump systems. The use of heat pump systems, mainly based on mechanical vapor re-compression, has proven to be effective in energy saving and profitable in other applications, as the concentration of gelatine, distillation of organic vapors, pulp drying and beer production. Different heat pump systems were investigated and compared with respect to fuel utilization and capital expenditures: electrical engine driven compressors, gas engine driven compressors, steam turbine driven compressors, gas absorption chillers, steam absorption chillers and thermo-vapor re-compression. It showed that the cogeneration of mechanical energy and heat to drive vapor compression (the so-called thermodynamic heating method of Frutschi et al.) is superior to other types of systems. Then, for mechanical vapor compression systems, two different applications to different production processes were analyzed: (a) a system using commercially available refrigerants and (b) a heat pump cycle using water from the bottom of the distillation columns or steam condensate as working fluid. The thermodynamic analysis, based on performance coefficients and fuel utilization, as well as the economic profitability in terms of costs, benefits and payback period, were discussed in detail.