Avaliação termodinâmica de alternativas de tratamento de resíduos de borra de petróleo a partir da gaseificação

Abstract

In this study, gasification of oil sludge (OS) from crude oil refinery process has been investigated. Gasification process was simulated by Aspen-Hysys® (v.8.6) tools to evaluate the possibilities of hydrogen-enriched syngas production and its potential use in thermochemical conversion process. Five cases of study were evaluated in order to valorize OS wastes from oil refining. These cases include hydrogen production from syngas reforming and its potential use in the diesel oil hydrodesulphurization process (Case 1), synthetic liquid fuels production (Case 2), power electric generation (Case 3), ammonia (Case 4) and methanol (Case 5) production. Simulation of OS gasification process was carried out considering a kinetic model for main chemical reaction rate, according to OS compounds. Air and superheated steam mixtures were used as gasifying agents and its influence over gasification temperature, gas yield, chemical composition and heating value of gas, ash specific production, hot and cold gasification efficiencies were evaluated. Results from simulation work showed that OS thermochemical conversion require an operational temperature of gasifier above 1300 °C in order to ensure high conversion (> 90%) of heavy hydrocarbons content in OS waste. Thermal energy requirement for gasification was estimated between 0,80 and 1,25 kWh/kg OS, considering equivalence ratio (ER) and steam/oil sludge (SOS) ratio between 0,25-0,37 and 0,20-1,50 kg steam/kg OS, respectively. Specific gas yield from OS gasification between 2,14 and 3,34 Nm3/kg OS is expected, with hydrogen molar composition of about 10-25,0 mol%, indicating that a specific hydrogen production in the range of 0,21-0,84 Nm3 H2/kg OS gasified could be obtained as syngas reforming is reformed. Furthermore, a lower heating value (LHV) of produced gas in the range of 7,0-11,1 MJ/Nm3 was achieved, while ash production ranged between 0,10 and 0,17 kg ash/kg OS. For Case 1, hydrogen potential production was found to be 1,87 Nm3/kg OS, indicating that 28% of total hydrogen required for diesel oil hydrodesulphurization process could be replaced by hydrogen from OS gasification. For Case 2 and Case 3, a specific production of synthetic liquid fuels and electricity index close to 0,48 L/kg OS and 1,54 kWh/kg OS were calculated, respectively. Likewise, for Case 4 and Case 5, simulation results showed a synthetic ammonia and methanol production of about 1,41 L NH3/kg OS and 1,61 L CH3OH/kg OS, respectively. Finally, the five cases analyzed in this work represent promising technological alternatives to treatment and environmental management of OS wastes from crude oil refinery and its energetic added value before final disposal.