This work details the findings from sizing and costing of a 250MW hydrogen plant capable of purifying hydrogen from a coal gasifier using high temperature silica membranes. The plant was designed around 40 mol% hydrogen feed (balance CO2) at 3MPa, operating at up to 500°C. Flow was split into 10 parallel membrane trains with membranes staged in each train in series or parallel arrangements. Each stage was a fixed module of 100m2. Membrane system modelling revealed that at least 4 stages is needed to ensure plant feed flow is kept to a minimum (large feed flows put demand on gasifier size). The series train achieved lower feed flows and better total recovery of H2 as compared to the parallel train. The parallel train did however achieve better outlet concentration of H2 (i.e. 77 mol% vs. 64 mol% for 4 stage systems), but this improvement appeared outweighed by the lower feed flow required (27% lower) and better permeate H2 recovery. The capital cost of constructing a 4-stage train (40 stages total) system was estimated at over AUD$20M, being mostly made up of membrane cost (38%) and the membrane vessel (36%). The operating cost was estimated at AUD$4M per year, mostly made up of membrane replacement cost (68%).