Combustion Optimisation using Methane Number and Wobbe Index as Evaluation Criteria

Abstract

One hundred and ten (110) streams have been identified in an oil refining process as contributors to the gas fuel net used in furnaces and boilers to supply power and steam to process. According to the origin of the gases and the previous treatment, these gas streams, have a different composition than the natural gas, which creates problems that affect the operational parameters and the integrity of equipment. It is due to this, which seeks to analyse how the fuel gas flows from a refining process, taking into account the energy efficiency, environmental and safety aspects in combustion process. Statistical analysis was developed in combustible gases to study their composition considering the origin of each of the streams represented by chromatographic analysis, which, provided the data for calculating the methane’s number (MN) via method radius ratio (H/C), and the Wobbe index as criteria for analysing the potential effect of gas fuel composition in efficiency, integrity and environmental emissions equipment. The methane’s number is a parameter which describes the behaviour of the explosive self-initiated and not controlled combustion in gas zone of the front flame (referred as knock Combustion). This knock resistance index, has two reference gases, methane and hydrogen; using a reference fuel mixture in which the methane works with a MN 100 and hydrogen with a MN 0. High numbers of MN means high efficiency and hence lower CO2. If MN is too low, knock can cause damage or loss in efficiency and performance. The results show that 45% of the streams of petrochemical area presented MN above 80 and 15% of streams presented low MN. Streams of cracking area showed lower MN. These results demonstrate the heterogeneity of currents, so that the methane number is an important reference when defining the logistic for combustible net in combustion process. Elaborating further on the effects that this variability can generate in the thermal efficiency of each of the currents, so as combustion efficiency and the stability of the operation was evaluated Wobbe Index, and the results showed that when applying these two methods and taking into account the current regulations, a comprehensive analysis can be performed of energy issues, environmental and security in combustion process of fuel variable composition. The principal result was a proposal for a fuel net.