Distillation column dynamics and control
Thesis DisciplineChemical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
A pilot plant scale, atmospheric pressure, sieve plate distillation column was constructed and fully instrumented. Novel speed controllable pumps were used to control liquid flows. A microcomputer was constructed to provide local and hierarchical control of the column. The microcomputer included an operator console, a 16 channel data acquisition unit, a 4 channel control output unit, and a hardware arithmetic processor. A software development system was assembled by linking the microcomputer to a minicomputer. Software written for the development system included a cross-assembler, a transfer program, and a microcomputer control program. A binary steady state distillation column model was developed, solved on a digital computer, and verified against experimental data using a binary mixture of methanol and water. Two control schemes were investigated using only the microcomputer resources. A multi-loop system using digital PI controllers was found to give excellent control within the accuracy of the instrumentation. An adaptive feedforward controller was proposed and verified using a steady state model, and experiments. The results were good, but because of the relatively simple dynamics of the experimental column, the feedforward controller was no better than the feedback controllers. A microcomputer control system has been shown to be an effective replacement for conventional analog control on a distillation column. The computing power of the microcomputer has enabled a sophisticated control scheme to be implemented at low cost.