The Unique Challenges of Cryogenic Distillation Column Control for Integrated Coal Gasification Combined Cycle Applications

Abstract

Abstract The world’s largest coal gasification plant for electricity generation is being built in Buggenum, The Netherlands and will be on-stream in 1993. Integrated coal gasification combined cycle (ICGCC) power plants are designed to convert coal to electricity in an environmentally superior and more efficient manner than conventional power plants. The ICGCC plant is characterized by the integration of a coal gasifier, steam and gas turbine units and an air separation unit (ASU) that provides oxygen and nitrogen. Because of the high degree of integration within the Buggenum facility, the ability of the air separation unit to respond to rapid changes in demand is a critical factor in the flexibility of the entire system. At the core of the air separation unit there is a system of tightly coupled, multicomponent, high-purity cryogenic distillation columns. This system will be subject to severe changes in process conditions including rapid product flow ramping rates, large pressure variations, and air supply pressures varying with the oxygen demand. Under all conditions tight purity specifications must be maintained on all the product streams. A program of dynamic modelling, simulation, and control system design was undertaken by Air Products at a very early stage in the plant design, prior to detailed equipment specification. This paper describes the approach taken to understand the dynamics of the proposed ASU under the expected load following conditions in order to verify the process design and to develop and optimise the control strategy. The work highlights the importance of incorporating control and operability considerations early during plant design.