In this research, the waste tail gas emitted from petrochemical processes, e.g. catalytic reforming unit, catalytic cracking unit and residue desulfurization unit, was recovered and reused as a replacement of natural gas (NG). On-site experimental results show that both the flame length and orange-yellowish brightness decrease with more proportion of waste gas fuel added to the natural gas, and that the adiabatic temperature of the mixed fuel is greater than 1800 degrees C. A complete replacement of natural gas by the recovered waste gas fuel will save 5.8 x 10(6) m(3) of natural gas consumption, and 3.5 x 10(4) tons of CO2 emission annually. In addition, the reduction of residual 02 concentration in flue gases from 4% to 3% will save 1.1 x 10(6) m(3) of natural gas consumption, reduce 43.0% of NOx emission, and 1.3 x 10(3) tons of CO2 emission annually. Thus, from the viewpoint of the overall economics and sustainable energy policy, recovering the waste tail gas energy as an independent fuel source to replace natural gas is of great importance for saving energy, reducing CO2 emission reduction, and lowering environmental impact. (C) 2009 Elsevier Ltd. All rights reserved.