STEADY-STATE DETERMINATION OF FUEL-BOND NITROGEN IN DIESEL AND INDUSTRIAL GAS OIL

A new method for the determination of fuel-bond nitrogen in Industrial Gas Oil (IGO) has been developed by means of a low heat input pre-mixing burner. The need to understand the NO-mechanism and its influencing factors with the objective of achieving precise measurements of fuel bond nitrogen, in the range over 100 mg/kg is the primary motivation of this work. Results of the variation of the equivalence ratio φ show that by increasing φ the conversion rate rN decreases. The experiments with indoline reveal a higher conversion rate rN as quinaldine, quinoline and 2,4,6-trimethylpyridine. The heterocyclic non-aromatic nitrogen bonds and the lower boiling point are the main arguments for this behaviour. The increase of the heat load of the burner surface results in the increase of the conversion rate rN. Introduction Over the last years, the reduction of the emission of nitrogen oxides has been clearly achieved by implementation of primary measures to constrict the thermal NOX. Due to the mentioned reductions, other main NOX sources (fuel-bond and prompt NOX) gained relevancy. A further reduction potential is in the fuel-bond NOX. It represents up to 60 % of the total emissions and can be achieved by reducing the fuel bond nitrogen content. Therefore it’s necessary to accurately known the nitrogen content and understand the fuel bond NOX Mechanism. Which parameters and how they influence the fuel bond nitrogen conversion to nitrogen oxides are the questions to be answered in this paper. The influential parameters are valid for the majority of the current nitrogen analysis equipment due to the similarity of the sample processing (vaporization and oxidation) and analysing (chemoluminescence detector) methods. The equivalence ratio, heat input, chemical structure and content of the nitrogen compounds are some of the test parameters. Objectives One of the main objectives of this paper is to identify the factors that influence the conversion of the fuelbond nitrogen to nitrogen oxides. With all the other sources of nitrogen excluded, except the fuel nitrogen, it allows focusing on the mechanism and its influence parameters. A further objective is to improve the actual detection methods which experienced irregularities for fuel nitrogen contents higher than 100 mg/kg. The developed method should be a pre-mixed IGO burner [1] for low heat inputs (mass flow rate 6 10 33 . 23 − ⋅ = m& kg/s) and with reduced dimensions. Experimental Method The developed equipment uses a steady state measurement methodology contrary to the existing transient methods. The terms steady state and transient are related to the measurement time of the sample. In current methods the sample is injected and oxidised at 1000 °C in an inert atmosphere until the measured value reaches 90 % of the maximal value (T90). Then the sample injection is interrupted and the measurement is terminated when the value returns to zero. The corresponding area filled below the measurement trend line is correlated to the nitrogen content in the sample. The method described in this paper uses a steady state oxidation process. The sample is continually conveyed to the equipment, oxidised and with the measured NOX value in the CL detector, a nitrogen mass balance is established, delivering the corresponding nitrogen content of the sample. The system is divided into vaporiser, mixing and oxidation zone coupled to a standard CL detector (s. Figure 1). The sample and a primary argon flow are sprayed into the vaporizer by means of a two fluids nozzle with an additional secondary preheated argon flow. The sample and the argon mixture leave the vaporizer with a temperature of Tvap. = 300 °C, completely in the gas phase proceeding to the mixing zone where oxygen is pre-mixed with the main flow. The final gas mixture consists of the vaporized sample and a mixture of 79 % argon with 21 % oxygen. The only nitrogen source for the nitrogen oxides formation in the system is the fuel bond nitrogen. The completely premixed flow proceeds to a surface burner where the sample is oxidised at temperatures of Tflame = 1550 K and the fuelbond nitrogen is converted to NOX. The nitrogen content in the sample is calculated from the stationary nitrogen oxide value in the exhaust gas measured by means of a chemoluminescence detector. The NOX in the flue gas consists of approximately 90 % nitrogen monoxide (NO) and 10 % nitrogen dioxide (NO2). To avoid information losses due to the solubility of NO2 in water, a NO2 to NO converter is assembled prior to the condensing unit which is part of the exhaust gas pretreatment. In a further stage the NO is combined with Ozone to yield NO2 in an active state. Afterwards the reversion of NO2 to a lower energy state causes photon dislocation detected by a photomultiplier (CL detector) which is proportional to the amount of nitrogen oxide in the exhaust gas. THIRD EUROPEAN COMBUSTION MEETING ECM 2007