Process Intensification for Optimal Retrofit of a Multicomponent Distillation Plant -A Real Industrial Case Study
Special Symposium - EPIC-1: European Process Intensification Conference - 1
EPIC-1: Poster Session (EPIC - Poster) - P2
Keywords: Process intesification, thermal coupling, thermodinamically equivalent structures
Distillation is the mostly used separation technique in chemical and petrochemical plants. The mass separation agent used for the separation is the energy and for this reason the main disadvantage of the method is the high energy consumption. Due to the continuous increasing of energy price, plants where distillation is intensively used are always interested in improving their earnings with better energy utilization. The case studied in this paper is a real light ends separation plant where a four component hydrocarbon mixture is separated with a sequence of three simple columns.
One major task of plant retrofit is to propose new process alternatives which have the potential to replace or improve the existing plant. The proposed new process alternatives are expected to have the substantial improvement in the process performance. For distillation system, the new alternatives are expected to have the substantial savings on energy consumption. On the other hand, real plant retrofit is expected to have the minimum modification to the existing plant, and simultaneously to have the minimum investment of the capital cost. Currently, Process Intensification is regarded as the main trend to improve process performance. One major approach of process intensification is to reduce the number of pieces of equipment through new mechanisms of mass and heat transfers in the process. For distillation system, thermal coupling technique provides such a new mechanism to retrofit the traditional simple column configuration by the principle of process intensification. It is through the elimination of either the condenser or the reboiler or both in the traditional simple column configuration by thermal couplings. The thermal coupling will provide the simultaneous mass and heat transfers between different tasks in the separation sequence. Therefore, the thermal coupling technique provides a unique approach to intensify the traditional simple column configuration and have the advantages in several aspects: a) reduce the number of the heat exchangers, b) improve the separation efficiency, c) have the potential to save both energy and capital costs. Moreover, recent studies have shown that in many cases the thermally coupled configurations have the similar or better dynamic performance than the traditional simple column configurations.
In this work, starting from the existing plant of the simple column configuration, two groups of new alternatives are first proposed. One group consists of the alternatives that all of the condensers and reboilers involving the submixtures are eliminated which represent the theoretical modifications to the traditional simple column configuration. The second group consists of the alternatives in which either a condenser or a reboiler is eliminated at one time, which represent the minimum modification to the real plant. In addition, in order to investigate the capital investment for the modified plant, all of the alternatives through recombination of the column sections have been compared. The objective to study these thermodynamically equivalent structures is for the optimal equipment design through maximum use of the pieces of equipment in the existing plant. This includes the reallocation of the heat exchangers, as well as the use of the existing simple columns to construct the new column equipment.
For all of the proposed alternatives, Aspen Plus 12 has been used for the simulation to provide the parameters for energy and capital costs calculations. The alternatives in the two groups have been compared in detail with the energy costs, capital costs, as well as the total annual cost. It is shown that the optimal retrofit alternative was found in the second group where it has the minimum change to the existing plant.
Presented Thursday 20, 13:30 to 14:40, in session EPIC-1: Poster Session (EPIC - Poster) - P2.
