Thermal Design of Heat Exchangers of a Dual Mode LOX-LIN Plant at BARC

An air separation plant with a liquid oxygen (LOX) and liquid nitrogen (LIN) generation capacity of 50 l/hr and 75 l/hr, respectively, is being developed at the Bhabha Atomic Research Centre (BARC), Mumbai. The plant will be capable of working in either LOX or LIN generation modes as needed. The targeted minimum purity values for LOX and LIN are 96% and 99% by volume, respectively. A modified Claude cycle-based liquefaction process is designed to cater to the simultaneous demands of liquid and gas products. For the feasibility of this process, along with the turboexpander and rectification column, high-effectiveness heat exchangers (HEX) are required. Three-stream HEXs are required for the mixed (liquid + gas) mode of operation. Plate fin heat exchangers (PFHEs) are selected for the dual-mode LOX/ LIN plant being developed. The thermal design of the multi-stream plate fin heat exchanger is based on bypass fin efficiency and a layer-by-layer analysis method. Sizes required for the different modes are evaluated for the PFHEs, followed by the selection of optimum sizes to suit all the operating modes. The sizing calculations for the required PFHEs are detailed in the current article.