Advanced Control of a Rotary Dryer

Abstract

Real knowledge is based on experience.(Chinese saying) AbstractDrying, especially rotary drying, is without doubt one of the oldest and most common unit operations in the process industries. Rotary dryers are workhorses which are easy and reliable to operate, but neither energy-efficient nor environmentally friendly. In order to conform better to the requirements of modern society concerning working conditions, safety practices and environmental aspects, the development of control systems can provide opportunities for improving dryer operation and efficiency. Our in depth understanding of rotary drying is poor, because it is a very complex process that includes the movement of solids in addition to thermal drying. Thus even today rotary dryers are controlled partly manually, based on the operator's "eye" and experience, and partly relying on conventional control methods. The control of a rotary dryer is difficult due to the long time delay, which means that accidental variations in the input variables can disturb the process for long periods of time before they are reflected in the output variables. To eliminate such disturbances at an early stage, increasing interest has been shown in more sophisticated control systems such as model-based constructs, fuzzy logic and neural nets in recent years. Although it has proved difficult and time-consuming to develop model-based control systems, due to the complexity of the process, intelligent control methods based on fuzzy logic and neural nets offer attractive solutions for improving dryer control. These methods make it possible to utilise experience, knowledge and historical data, large amounts of which are readily available.The aim of this research was to improve dryer control by developing new hybrid control systems, one consisting of a fuzzy logic controller (FLC) and PI controller and the other of a three-layer neural network (NN) and PI controller. The FLC and NN act as supervisory controllers giving set points for the PI controllers. The performance of each was examined both with simulations and in pilot plant experiments. The pilot plant dryer at the University of Oulu closely resembles a real industrial situation, so that the results are relevant. Evaluation of these results showed that the intelligent hybrid controllers are well suited for the control of a rotary dryer, giving a performance in which disturbances can be eliminated rapidly and operation of the dryer can thereby be improved, with the aim of enhancing its efficiency and environmental friendliness.

Преобразование Математической Модели Процесса Сушки Для Управления Сушильной Установкой Барабанного Типа

“…Ранее [1,3,5,6] преобразование общей модели своди-лось как к преобразованию левой части уравнений, так и к представлению коэффициента скорости сушки v R в виде: R в правой части модели [7].…”

“…Из экспериментальных данных видно [1], что 1-й этап сушки представляет собой процесс, где скорость сушки практически не зависит от времени. Этот этап, как показывают эксперименты, является самым про-должительным по времени и представляет собой соб-ственно сушку, т. е. испарение влаги из материала.…”

“…Изучение процесса сушки в установке барабанного типа проводилось рядом авторов [1][2][3][4] в течение мно-гих лет. Результатом исследований стал вывод, что общая модель сушильной барабанной установки со-ставлена из двух вспомогательных моделей, из кото-рых одна является подробным описанием поведения твердого материала, а другая описывает барабан [2].…”

“…Вторая модель, в свою очередь, является описанием оборудования и определяет время распределения ма-териала в барабане и тепловую передачу. При комби-нировании этих двух моделей получается несколько математических формул, решение которых дает пред-ставление о сушке твердого вещества в барабанной сушильной установке [1].…”

Fuzzy modelling of a rotary dryer

“…This model is based on simultaneous heat and transfer equations includes partial differential equations, which are complex and difficult to handle and to understand [1]. Furthermore, some parameters in the model are difficult to determine.…”