Global Process Integration Of Combined Aromatics Unit And Studying On Application

Aromatics mainly mean benzene, toluene and xylene, which are basic raw materials of organic chemical industry. With the high-speed development of economy, the demand for aromatics has being very strong in China. However, aromatics combined unit is a high energy-comsumption due to the complicated process where there are many distillation columns, furnances and reactors, so the big attention is being focused on the issue of energy saving in aromatics. Although extensive researches have been undertaken, but they are mostly limited to a single device or unit, the overall optimization and integration are not sufficient, no significantl progress shown in energy consumption. In this paper, based on the overall processs integration crossing units and involing various energy-comsumers such as heat exchangers and columns as well as furnaces, a new energy integration strategies on aromatic combined unit are proposed as follows: analysis and identify distillation columns in view of process system integration, and optimization energy integration of aromatic combination unit in order to decrease total consumption of hot and cold utilities. Besides, heat pump be applied in aromatic distillation columns has been discussed. Finaly the strategies proposed in this paper are used in an aromatics combined unit with annual PX yield of 65×104t. After the exergy analysis and pinch analysis of tatrary unit, benzene-toluene distillation unit, xylene fractionation unit, adsorption separation unit and the isomar unit, three energy-saving measures are proposed as follows:①rising operating pressure of toluene column from 0.375MPag to 0.5Mpag, the overhead of benzene column is defined as heat source of bottom reboilers of toluene column and finishing column, originally the heat of finishing column only from xylene splitter's overhead, in new case some of them from toluene column, and the replaced heat of xylene splitter can be used as heat source of deheptanizer's bottom reboiler, totally resulting a saving of 0.43t/h fuel and 92KW electicity power;②establishing a new heat pump case, where the overhead of orthoxylene column is compressed and used as the heat resource of reformate splitter's reboiler. The result shows that a saving of 17.55t/h 3.5MPag steam and 0.34t/h fuel is available;③changing the heat transfer route of mixed xylene in isomar process unit, where the feed goes directly into the vertical heat exchanger to invoid the repeat heating and cooling, it reduces 0.56t/h of fuel and 238.3KW electricity power. Totally cost drop of about 270730 million yuan / year can be achieved benefiting from the above 3 revamps.