analise dinâmica de um chiller de absorção de brometo de lítio ...

100inhibition coefficient, E max is the maximum ethanol concentrationat which yeast cell growth is completely inhibitedand n is the product inhibition power. Cell inhibitionand death are not taken into account in the modeldue to the dilution effect in the fed-batch mode andthe short residence time. This inhibition occurs at highyeast cell concentration, with cell recycling (Jarzebskiand Malinowski 1989; Lee et al. 1983). Under industrialconditions, the microorganism is a yeast isolatedfrom the industrial environment and therefore adaptedto fermentation stress. In addition, in each fermentationcycle the yeast receives an acid treatment for 2 to 3h,when nutrients are also supplied.The parameters used in the model shown above weretaken from the literature Atala et al. (2001) and are presentedin Table 3. These expressions were determinedfor the temperature range of 28 to 40 ◦ C, using an industrialyeast Saccharomyces cerevisiae (Pedra-2) andcane molasses as the substrate.Table 3. Kinetic Parameters as a Function of Temperature.Par.Expression or Value(μ max 1.6· exp − 41.5)(− 1.3·10 4 · exp − 431.4)T 21 T 21E max −0.4421·T21 2 + 26.41·T21 − 279.75Y X/S 2.704· exp(−0.1225·T 21)Y E/S 0.6911· exp(−0.0139·T 21)K i 1.393·10 −4 · exp(0.1004·T 21)K S 4.1m E 0.1m X 0.2n 1.5The heat flow rate released during the fermentationprocess ˙Q f is calculated as follows[ ]Vt−Δt · (S˙Q f = ΔH S ·t−Δt + S in) −V ·S(11)3600·Δtwhere S t−Δt and V t−Δt represent the substrate concentrationand the working volume of the fermentation vatat time t − Δt, S and V being the substrate concentrationand the working volume at the present time and Δtrepresenting the time difference.The fermentation heat exchanger is modeled usingthe Logarithm Mean Temperature Difference (LMTD)method and the energy balance as described in Bejanand Kraus (2003).The fermentation efficiency may be written as{}E ·V − Eη = 100·0 ·V 0(12)0.511· [V · (S in − S) −V 0 · (S in − S 0)]where 0.511 is the sugar to ethanol conversion factorbased on the theoretical maximum yield.The ethanol productivity is calculated by the followingexpressionE ·V − E0 ·V0φ E = (13)V ·t2.3 SimulationThe data collected in a sugar and ethanol productionplant (Usina Cerradinho Açúcar e Álcool S/A) areshown in Table 4 and they are used as the initial conditionsfor the simulation of the industrial fermentationprocess. For the fermentation, the feed flow rate of themust Ḟ and the inlet must temperature T in change accordingto the expressions given in the table. The valuesfor the feed substrate concentration S in, initialcellX 0 and ethanol E 0 concentrations, initial temperature T 0and initial volume V 0 are shown. The initial time of therefrigeration process is 0.45 h. The water temperatureof the cooling tower T 23 and volume flow rate ˙V 19 weretaken during the fermentation process under industrialconditions at the above-mentioned plant and the temperaturesvary according to the expression shown.Table 4. Fermentation Data Collected at Usina CerradinhoAçúcar e Álcool S/A.ParameterExpression or ValueḞ 8.73·t + 76.29S in 200E 0 34.56X 0 71.6T 0 28.37T in 0.15·t + 31.43T 23 −0.05·t 2 + 0.78·t + 26.03V 0 210˙V 19 −60.0·t + 1030.1˙V 21 1000The simulations were performed using the softwareEngineering Equation Solver (EES R , Klein and Alvarado(2008)). The properties of the water are wereevaluated with the correlations given by IAPWS (1995).The specific enthalpy of the aqueous lithium bromidesolution is was calculated in terms of the solution temperatureand lithium bromide mass fraction using thecorrelation given by ASHRAE (2001). The density andthe heat capacity of the aqueous lithium bromide solutionare given by the equations of Patterson and Perez-Blanco (1988)andYuan and Herold (2005), respectively.The correlations of the heat capacity and density of thesugarcane juice used in this work are were calculated byRao et al. (2009).3 Results and DiscussionFigure 2 shows the behavior of the fermentation processusing only water from cooling tower to chill thevat, where cell X, substrateS and ethanol E concentrationprofiles are detailed. The fermentation temperatureprofile (T 21) is also presented. The final concentrationof ethanol in the simulated fermentation reaches114 / Vol. 13 (No. 3) Int. Centre for Applied Thermodynamics (ICAT)