Determination of optimum vapor bleeding arrangements for sugar juice evaporation process

Abstract

The sugar juice evaporation process consists of juice heater, evaporator, and crystallizer. The juice heater increases the temperature of diluted sugar juice from the ambient temperature to the boiling point. The evaporator removes most water content of diluted sugar juice. The crystallizer removes the remaining water content, yielding raw sugar as the final product. Since both the juice heater and the crystallizer require vapor bled from the evaporator, there are interactions between the three components. A model of interactions between the three components of the sugar juice evaporation process is presented in this paper. The model yields a system of nonlinear equations that, under some specified assumptions and conditions, consists of only two free parameters. This implies that there is a unique distribution of a given total juice heater surface when vapor is bled from the first two effects of the evaporator. In contrast, if vapor is bled from the first three or four effects, there are many possible surface distributions. It is shown that there is an optimum surface distribution when vapor is bled from either the first three or four effects of the evaporator that minimizes the steam economy. The optimum four‐effect vapor bleeding arrangement results in the largest steam economy. However, the two‐effect vapor bleeding arrangement produces a larger mass flow rate of processed sugar juice than either three‐effect vapor bleeding arrangement or four‐effect vapor bleeding arrangement. Practical applications This paper presents a mathematical model of a sugar juice evaporation process. Although one specific process design is under consideration, the model can easily be adjusted for a different process design. This model will be useful for analysis and optimization of the process. One optimization problem mentioned in the paper is the optimum allocation of a fixed total surface among the four heat exchangers of the juice heater, which is used to increase juice temperature to the boiling point before entering the quintuple‐effect evaporator. It is found that there are two different optimum surface allocations corresponding to the maximum rate of processed juice and the minimum amount of steam required by the process. Results of this paper should provide a guideline to a process designer in selecting the juice heater that will both satisfy the required heating duty and yield the optimum performance.

Increased Energy Efficiency of a Backward-Feed Multiple-Effect Evaporator Compared with a Forward-Feed Multiple-Effect Evaporator in the Cogeneration System of a Sugar Factory

“…Steam consumption by a multiple-effect evaporator can also be minimized by distributing heating surface areas optimally in the process. Previous investigations by Chantasiriwan [6][7][8][9] have demonstrated the existence of the optimum distribution of heating surface areas that results in the minimum steam consumption.…”

Modification of Conventional Sugar Juice Evaporation Process for Increasing Energy Efficiency and Decreasing Sucrose Inversion Loss

“…Mechanical vapor compression [7] and thermal vapor compression [8] have been suggested as methods to increase the energy efficiency of the multiple-effect evaporator. The energy efficiency of the multiple-effect evaporator can also be increased by the optimum distribution of heating surface areas [9][10][11][12]. Recently, Chantasiriwan has shown that the energy efficiency of the cogeneration system, in which the evaporation process is a component, can be increased by replacing the forward-feed evaporator with the backward-feed evaporator [13].…”

Distribution of heating surface areas in sugar juice evaporation process for maximum energy efficiency

“…A more realistic model by Chantasiriwan () yields a similar conclusion that there exists the optimum distribution of evaporator surface area. For a specified distribution of evaporator surface area, it has also been shown that the minimum steam consumption occurs at the optimum distribution of juice heater surface area (Chantasiriwan, ). The previous works suggest that further reduction in steam consumption may be attained by simultaneously optimizing the distributions of evaporator and juice heater surface areas.…”

“…This article is an extension to the previous investigation by Chantasiriwan (2018), which is concerned with the optimum distribution of juice heater surface area in the sugar evaporation system with the quintuple-effect evaporator. It was shown that, for a specified distribution of evaporator surface area, there exist two different optimum distributions of a fixed surface area of juice heater corresponding to the maximum sugar juice flow rate and the minimum steam consumption.…”