The Optlmal Design And Dynamic Control Of Heat-integrated Distillation Column

Distillation is widely used in the chemical industry.Its energy consumption accounts for about 30% in the chemical production process,and its thermodynamic efficiency is only 5%-20%.Distillation is a unit operation process of low energy utilization and high energy consumption.The internally heat-integrated distillation column(HIDiC)can reduce the irreversibility of the process and improve the thermodynamic efficiency.The experimental was carried out with ethanol-water as the separation system in internally heat-integrated distillation column.Under the continuous operation condition,the temperature distribution in the column was obtained.By calculating the heat transfer coefficient and the temperature difference,the heat transfer rate between the rectifying section and the stripping section was obtained.Compared with the common distillation column,when the compression ratio was 2.2,the energy saving of the HIDiC was 62.6% and the operating cost was reduced by 23.46%.Based on the separation of benzene and toluene mixture,the compression ratio and feed thermal condition were studied on heat pump distillation,pressure-swing distillation and HIDiC.The results showed that for heat pump distillation,when the compression ratio was 2.4 and the vapor fraction of feed was 0.2,its operation cost reached the minimum value.For pressure-swing distillation,when the compression ratio was 2.4 and the vapor fraction of feed was 0,its operation cost reached the minimum value.For HIDiC,when the compression ratio was 2.1 and the vapor fraction of feed was 0.2,its operation cost reached the minimum value.On this basis,the calculation of the total annual cost(TAC)was carried out for three types of distillation processes.The results showed the energy saving effect of heat pump,pressure-swing and HIDiC was obvious,and HIDiC reached to the minimum TAC when the vapor fraction of feed was 0.2.As the feed thermal condition has a great impact on the energy saving of HIDiC,the gas and liquid phase The gas and liquid are separated from the feed,and the gas phase enters from the stripping section and the liquid phase enters from the rectification section.The effects of feed vapor fraction and gas-liquid feed location were studied using near boiling range n-butanol and isobutanol as the separation system.The results showed that the operation cost of the double feed was lower than one feed of HIDiC,and the most energy saving point was when the vapor fraction was 0.2.By optimizing the vapor and liquid feed location,when NF=2,the operation cost of double feed reached the minimum.The HIDiC for double feeds used a control scheme based on composition control,but the fluctuation peak was large and the recovery period was longer.According to this,the temperature cascade control scheme is proposed.The peak value of the purity fluctuation of the overhead and the bottom product was obviously reduced,and the time required to reach the steady state was shortened significantly;finally an improved temperature cascade control scheme for controlling the impurity(isobutanol)concentration in the bottom was proposed,which further reduced the stabilization time of the bottom product and achieved the best control effect of product purity and temperature recovery.