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As the global third-largest stationary source of carbon emissions, petroleum refineries have attracted much attention. Many investigations and methodologies have been used for the quantification of carbon emissions of refineries at the industry or enterprise scale. The granularity of current carbon emissions data impairs the reliability of precise mitigation, so analysis and identification of influencing factors for carbon emissions at a more micro-level, such as unit level, is essential. In this paper, four typical units, including fluid catalytic cracking, Continuous Catalytic Reforming, delayed coking, and hydrogen production, were chosen as objects. A typical 5-million-ton scale Chinese petroleum refinery was selected as an investigating object. The Redundancy analysis and multiple regression analysis were utilized to explore the relationship between the process parameters and carbon emissions. Three types of influencing factors include reaction conditions, processing scale, and materials property. The most important mitigation of carbon emission, in this case, can be summarized as measures of improving energy efficiency via optimizing equipment parameters or prompting mass efficiency by upgrading the scale for material and energy flow. [ABSTRACT FROM AUTHOR]

Fluid catalytic cracking (FCC) unit emits a large amount of flue gas, which is a major concern of environmental protection supervision. Wet flue gas desulfurization (WFGD) technologies have been widely used to control the emissions of SO2 in refineries. In this study, stack tests for pollutants emission of a typical FCC unit were conducted. The emission characteristics of the FCC unit indicated that WFGD would cause a large amount of water vapor in the flue gas, which indirectly leads to large quantities of salt pollutants entrained in the flue gas including ammonium sulfite ((NH4)2SO3) and ammonium sulfate ((NH4)2SO4). A strong correlation among the concentrations of SO2, NH3, and H2O was observed, and factor analysis shows that these concentrations are dominated by a common factor. It was also found that a mass quantity of NH4+ and SO32− existed in the condensate water of the flue gas. The TG-MS analysis shows that (NH4)2SO3 could be decomposed at 94.1 °C, and NH3, SO2, and H2O are released as reaction products in the form of gas. Therefore, a part of the NH3 and SO2 obtained by Fourier transform infrared spectroscopy (FTIR) monitoring may be derived from the decomposition of (NH4)2SO3 in the flue gas due to the high temperature during the sampling process, which was also confirmed in a lab experiment. The hot and wet sampling process will lead to overestimation of NH3 and SO2 emissions rather than FTIR method itself when monitoring the high-humidity FCC flue gas. Thus, the concentration of H2O in the flue gas and the type of sampling process need to be taken into consideration during the monitoring process. [ABSTRACT FROM AUTHOR]

• Main carbon, nitrogen and sulfur-precursors are indicated by XPS method. • The same precursors result in close temperatures at which characteristic pollutants occurred. • A full view of transformation mechanism of FCC pollutant emission is presented. Fluid catalytic cracking processes generate various gas pollutants, which are the major concern for environmental protection in refineries. However, the transformation mechanism from deposits to gas pollutants is not well understood. In this work, spent catalysts from different typical FCC units were analyzed to evaluate the effect of pollutant precursors on pollutant emission. The main carbon, nitrogen and sulfur precursors of FCC pollutant emission were identified. Regeneration experiments were conducted to assess the relationship between regeneration temperature and pollutant emission under partial combustion conditions. Results showed that the same precursors from different catalysts result in close temperatures at which characteristic pollutants occurred. VOCs are firstly generated by the coke branches cracking under low temperature. Then, nitrogen-containing compounds convert to NH 3 and HCN, and some of them are oxidized into NO x. After that, sulfur-containing compounds convert to C-S group and H-S group, which finally convert to SO 2 at high temperature. At last, a full view of transformation mechanism of FCC pollutant emission is presented, which will give a further insight into the prediction and control of pollutants. [ABSTRACT FROM AUTHOR]