APPLICATION OF THE PINCH-ANALYSIS METHOD IN A THERMAL INTEGRATION OF THE MAGNESIUM CHLORIDE VAPORIZING PROCESS

Abstract

The thermal integration of the evaporation of magnesium chloride was carried out using the pinch analysis method. A table with streaming data has been generated to integrate the evaporation process based on calculations of the material and thermal balances of the process. Five thermal and four cold flows were selected for thermal integration. Hot flows are: condensates of the first and second frames, secondary steam of the first and second frames, one stripped off solution. Cold flows are: initial solution, solution evaporated in the first and second frames, water for technical needs. Composite flow curves are constructed, which are obtained for the selected value of the minimum temperature difference, the target energy values of hot and cold utilities are determined. It has been established that the pinch temperature of hot flows is 53 °C, and for cold flows is 45 °C. A grid diagram is constructed where heat exchangers are placed, using the N and CP rules. A decision was made to transfer heat through the pinch in the amount of 50,87 kW. It based on technological considerations, namely, on the temperature restrictions for the initial mixture, the temperature of which should not approach the boiling point in each of the streams that were formed as a result of splitting,. This has led to a change in the number of external utilities. It is calculated that as a result of thermal integration, the consumption values of hot utilities decreased from the initial QН=2527,1 kW to QНmin=1924 kW, i.e. by 603 kW. According to calculations the consumption of heating steam decreased by 23 % in comparison with the process according to the principle scheme. It is shown that the thermal load of the refrigerator corresponds to the thermal load of the barometric capacitor, which was obtained in the calculations. It is estimated that the amount of heat of recovery has increased for QRЕC=1734 kW before integration to QRЕC=2337,03 kW after integration. It was established that in order to realize the set target values of hot and cold utilities, it is necessary to install eight recuperative heat exchangers and one heater. Based on the grid diagram, an integrated technological scheme for the evaporation of magnesium chloride was obtained, which provides the necessary heat recovery.