Application of Unit Heat Integration in VFY Unit-A Case Study

Background/Objectives: Energy efficient technology selection for all the individual in site does not guarantee optimized energy consumption for total site. Synergy exist between two different technologies for heat recovery. Application of inter unit Pinch analysis opens up opportunities for step reduction in Energy consumption.

Methods/Statistical analysis: Viscose Filament Yarn process was chosen to demonstrate application of inter unit pinch analysis. Chlor-alkali units are integral part of viscose process units. Significant steam is consumed in viscose units for spin bath at 50 deg C. High grade steam at 150 deg C is normally used in graphite exchanger. There is general belief that graphite exchanger is expensive and use of low grade heat like hot water is not economical as area of exchanger increased and there by cost. Scheme was developed to compare spin bath heating using steam and hot water. Aspen EDR was used to size the exchangers. Costing for the scheme was done for analysis of project economics.

Findings:

• Inter unit use of low grade unit for spin bath heating is an economically viable option. Payback is very attractive at 8 months though the capex is very high. Leverage is in the operating cost i.e. Steam Vs Waste heat.

• Heat transfer co-efficient in hot water heating decreases only by 16% with respect to steam heating. Hence hot water availability at 125 °C would mean an increase in area only by 50% and not multifold.

• Reduction in water make up to cooling tower is additional benefit.

Improvements/Applications: Inter unit pinch analysis is applicable for any site having 2 or more process units.