The cogeneration boiler has been applied extensively for simultaneously supplying electrical power and high-pressure steam. In this study, the performance of a high-pressure cogeneration boiler (max 280 tons/h boiler capacity) that burnt fuel oil (FO) and natural gas (NG) in a full-scale petrochemical plant was enhanced by partially replacing the NG with a waste hydrogen-rich refinery gas (RG), a byproduct from catalytic reforming and catalytic cracking operations. The addition of RG does not influence the boiler efficiency; it results in saving the energy consumption and significantly decreasing the greenhouse gas emission. if the inlet FO/NG/RG volumetric flow rate ratio is maintained at 50:33:17, adding RG will save 14,500,000 m(3)/year of NG and reduce 12,900 tons/year of CO2 emission. Therefore, the use of RG to partially replace NG has practical benefits for reducing energy consumption and greenhouse gas emission. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.