In this study, energy-related operational parameters for modern and traditional (conventional) sugar mills are analyzed, with the goals of identifying improvements in energy efficiency and potential for surplus electricity export. Results show that the powerto-heat ratio of modern and traditional mills is clearly distinct, lying in the ranges of 0.3-0.5 and 0.04-0.07, respectively. Modifications under consideration for the traditional mills include the following upgrades: electric drives and higher capacity back-pressure turbine (case 1); high-pressure boiler, condensing extraction steam turbine and electric drives (case 2); and improvements in case 2 plus bagasse drying (case 3). The thermodynamic impact of these modifications shows that more power is generated as the modification becomes more advanced. Case 1 exhibits a modest increase in cogeneration efficiency (4%) as compared to the base case, while the cogeneration efficiency increase is more marked for cases 2 and 3 (21% and 31%, respectively). Surplus power was studied in a regional context, where it was found that the contribution of 19 retrofitted sugar mills in nine Brazilian regions could supply 30% or more power as compared to current installed power capacity. The economic analysis showed that levelized cost of electricity (LCOE) was lowest for case 1 (11 USD/MWh) and highest for cases 2 and 3 (58 USD/kWh).

It is known that there is a significant amount of thermal energy used for the sugar cane industry for the purpose of power production and for use in the sugar or ethanol processing in cane sugar industries. Likewise, it is understood that there are substantial amounts of waste heat that is not being recovered, in particular for traditional sugar mills. Regardless of this, energy conservation is given less consideration as compared to operational convenience due to the fact that sugar mills are self-sufficient in energy (heat and power). The identification of such potential heat loss areas (especially during transient conditions) suggests the sugar mills play a vital role in energy saving. In this study, a modified setup of the base case plant considered in part I of this paper is assessed for its energy potential and possible major heat losses during steady state and transient conditions where 2-h stoppage of the mill presses are considered to occur. For the modified setup, there are two major scenarios considered having two subscenarios each. The result of the assessment showed that the steady state assumption scenario of the modified plant (where bagasse drying is not considered) indicated a 20 % reduction in the losses considered which resulted in a 57 % power generation increase as compared to the steady state model of the base case plant. It is also possible to save excess bagasse by drying the bagasse for later use during unexpected stoppage. The carbon dioxide emission (amounting 29 t/day in case 2a of this study) that occurs during the use of fuel oil during such stoppages will thus be avoided. The simple economic analysis showed that it is only in case 2a where fuel oil cost is included in the operation cost that resulted in a negative NPV. Since the rest of the scenarios use bagasse as a fuel which is free, the NPV for all was positive. For the electricity price of 0.04 US $/kWh and discount rate of 15 %, the minimum payback period attained is about 3 years (case 1b) where the bagasse moisture content is 30 % whereas the maximum payback period is 6 years (case 1a) where there is no bagasse drying considered.

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This study is a comparison of four technological improvements proposed in previous works for the Cuban sugar mill Carlos Baliño. These technological options are: (1) utilization of excess wastewater for enhanced imbibition; (2) utilization of waste heat for thermally driven cooling; (3) utilization of excess bagasse for pellets; and (4) modification of the cogeneration unit for maximum electric power generation. The method used for the evaluation of the technological options involves using criteria such as energy saving, financial gains, and CO 2 emission saving potential. The results of the analysis show that the first three technological improvement options are attractive only during the crushing season. On the other hand, the last technological improvement option can be attractive if a year round generation of surplus power is sought. The first technological improvement option leads to only minor changes in energy utilization, but the increase in sugar yield of 8.7% leads to attractive profitability with an extremely low payback period. The CO 2 emissions saved due to the fourth technological improvement option are the highest (22,000 tonnes/year) and the cost of CO 2 emissions saved for the third technological improvement option (lowest) amount to 41 USD/tonne of CO 2 emissions saved. The cycle efficiencies of the third and fourth technological improvement options are 37.9% and 36.8%, respectively, with payback periods of 2.3 and 1.6 years. The second technological improvement option is the least attractive alternative of the group.