Abstract:

In order to utilize energy fully a mathematical model of parallel-feed multi-effect evaporation system for conventional design was established.The model included two sequential system—multi-evaporation system and multi-level preheating system.In this model, the energy-saving measures, such as condensate flash, using extra steam and thick liquor of each effect to preheat raw liquid were adopted.Solid separation was also considered in the process of evaporation.Material balance and energy balance equations of complex parallel-feed multi-effect evaporation system were expressed in matrix equation.By holding or omitting correlated block-matrix, the matrix equation could be used to describe the difference of parallel-feed multi-effect evaporation system with and without solid separation, with and without condensate flash, with and without preheating raw liquid.The model could also be used in the calculation of different effects to realize the universality of the model.The solid-liquid equilibrium data in the multi-effect evaporation system with solid separation was fitted by the intelligent fitting method, which helped to solve this problem by computer.The model was solved by the iterative method and matrix method.The result showed that the model had universality.Using extra steam to preheat raw liquid and condensate flash were effective methods to save energy.The steam consumption of four-effect parallel-feed evaporation with former energy saving methods was decreased by about 30% for evaporation of NaOH solution containing NaCl.The algorithm increased the convergence speed and stability.

Key words:

平流多效蒸发, 常规设计, 数学模型, 矩阵法

摘要：

为了充分利用能量，采用冷凝水闪蒸、引出额外蒸汽及引出各效完成液预热原料液等节能措施，考虑蒸发过程有固相析出的情况，建立了由多效蒸发和多级预热两个子系统构成的平流多效蒸发系统数学模型。将物料衡算和热量衡算方程组写成矩阵方程的形式，保留或舍弃矩阵方程中的相关块矩阵，模型就能代表有或无固相析出、有或无冷凝水闪蒸、有或无引出各效完成液预热原料液以及不同情况任意组合的平流多效蒸发过程，该模型还可以用于计算不同效数的平流多效蒸发过程，实现模型的通用。利用智能拟合法，将系统的固液相平衡数据拟合成相平衡方程，实现模型的计算机编程求解。用迭代法结合矩阵法求解模型，研究结果表明，平流多效蒸发系统常规设计的数学模型具有通用性，采用冷凝水闪蒸、引出额外蒸汽预热原料液、引出各效完成液预热原料液是有效的节能技术，对四效平流蒸发含NaCl的NaOH溶液系统，采用以上节能措施可节省加热生蒸汽30%左右，节能效果显著。求解模型的算法稳定且高效。

关键词:

平流多效蒸发, 常规设计, 数学模型, 矩阵法