Online Heat Transfer Measurement and Analysis for Sugar Mill Evaporators
Fouling and scaling in evaporators has been an area of great interest to raw sugar mills for a number of years and many of the mechanisms causing the scale and the rates of scaling are unknown. In an attempt to quantify the scaling rates and measure the scaling, an online model has been developed to model a system of evaporators. Monitoring the heat transfer coefficient as a function of time enabled measurement of the scaling rate by monitoring the heat transfer coefficient as it decreased with time. It is assumed that the scaling on the juice side of the evaporators with time is the only contributor to the drop in heat transfer and that other effects such as the fouling of the steam side are negligible.
A large problem in the past was reliable measurements of the heat transfer coefficient on evaporators. This was usually because the procedure required multiple measurements that needed to be taken by expensive equipment, which meant large amounts of capital to set up the monitoring systems. Another issue in the past was the iterative nature of the calculations, but with the advancements in computer processing and control systems, it is now possible to setup a control system that requires fewer inputs and low-cost instrumentation to get accurate measurements of the heat transfer coefficient. Utilizing the processing power of the control computer to perform multiple iterations allows for quick convergence to the solution of the heat transfer coefficient for the system.
The scaling rates are measured on a simple quadruple effect evaporator with no vapor bleeds at the St James sugar mill in Louisiana. A model was developed to predict the scaling rates of the individual effects based on the heat transfer coefficient measurements.
Analysis of the juice and syrup streams to and from the evaporators was performed to quantify the scale components in the scale that accumulates in the evaporators.
The measurement of the heat transfer coefficient shows, as is sometimes seen in practice, that the final effect is the effect that will scale the most and determines the need for the effect to come offline to be cleaned. This information on the degree of scaling is useful for the mills as they can use this to optimize cleaning of the effects.
The measured values of the heat transfer coefficients fell within measured values from other sugar milling countries. The results show that the use of computers enables one to calculate a heat transfer coefficient for a system of evaporators in real time.
Advisor:Peter W.Rein; Kalliat T. Valsaraj; Karsten E. Thompson
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Date of Publication:11/16/2004