OPTIMIZATION IZATION OF HEAT INTEGR. TED DISTILLATION COLUMN

Abstract

With the continuous rise in energy cost, depletion of conventional energy resources and growing environmental concern, there is need to reduce the energy consumption by optimization of existing processes. In refineries besides the cost of crude, energy is the largest cost which can be influenced by improved operation and/or capital investment, and has therefore become a primary focus. Process-integration techniques based on pinch technology represent a new and powerful way to optimize process designs, yielding results superior to those achievable using conventional methods. These new techniques permit the design engineer to track the energy flows in a manufacturing process more clearly and to modify the process to reduce energy consumption. Pinch technology also enables the design of an optimum interface between the process and the utility systems. Heat integration of a given process can give higher benefits to an existing industry. The use of heat integration for distillation columns holds a great promise of energy savings up to 45-50%. In addition to saving energy, heat integration reduces the environmental impact of a process, reduces site utility costs and can give possible reduction in capital costs. There are several approaches for the analysis of heat integrated distillation systems, with their specific merits and demerits. These approaches are Pinch Technology, Evolutionary Algorithm Approach, Linear Programming (LP), Nonlinear Programming (NLP) and Mixed Integer Nonlinear programming (MINLP). Out of these tools Pinch Technology is a prominent tool because it allows the operator and designer to take part in each step of process integration. The present work is related to heat integration of different processes available in Crude Distillation unit by carrying out Pinch study and identifying schemes that enable maximum energy recovery. Two possibilities are conceptualized to increase furnace inlet temperature of crude by heat integrating distillation column pump around and circulating reflux streams with preheat exchanger train in existing unit. 111 Target crude furnace inlet temperature of around 267 °C is achievable by introducing new heat exchanger matches i.e. Crude/ LVGO CR, Crude/ Column overhead vapors and Crude/ Sweet VGO. By doing new heat exchanger matches reduction in furnace duty can be achieved corresponding to the heat recovered at lower temperature. However additional heat exchanger area needs to be provided. The economic analysis for both cases indicates the annual saving of Rupee 32.5 Crores and 61.8 Crores with payback period of 1.28 years and 0.88 years respectively. iv