A rigorous pressure-driven dynamic model for a heat-integrated double-column air separation unit (ASU) has been developed in a process simulator environment to investigate feasibility and applicability of high ramp-rate demands posed by gasification island within the integrated gasification combined cycle (IGCC) power plant, while maintaining the oxygen purity constraints. Some of the operability and controllability issues, including the "snowball effect" observed due to ASU's condenser-reboiler and feed-product heat integration, which may be extended to many heat-integrated processes, have been identified and addressed. Initial model based PID control structures were proposed and implemented in pure feedback, pure feedforward/ratio, and feedforward-feedback modes and corresponding responses were assayed and compared. In addition, the importance of oxygen storage and degradation of controllability when fast-refrigeration is actively enabled during large ramp-changes has been discussed in detail, in view of promoting faster load-following operations.