Geração de bioenergia com captura intríseca de CO2 via processo de iG-CLC em planta piloto contínua

Abstract

The continuous increase in CO2 emissions and its effect on global warming imposes the need for collaborative actions between scientists and government to implement strategies aimed at reducing CO2 emissions. Among these strategies, carbon capture and storage technologies stand out that, especially when associated with the use of biofuels, as they can achieve a negative balance of CO2 emissions. Chemical looping (CL) is recognized as an energy-efficient approach to capture and store CO2 and has high technological maturity. In these processes, the search for low-cost solid oxygen carriers (OC) is motivated by the loss of OC incurred when solid biofuels are employed. In this context, this study aims to select, characterize and evaluate the energy potential of different biomasses and the reactivity of low-cost mineral materials as solid oxygen carriers for application in chemical looping combustion process with gasification in situ (iG-CLC) in pilot plant with continuous power supply with a technology readiness level (TRL) 4. The biomasses were characterized by proximate, ultimate, thermogravimetric analysis, analytical flash pyrolysis and determination of calorific value. The OCs were characterized using X-ray diffraction and fluorescence techniques, scanning electron microscopy, determination of crushing strength, and attrition rate. Their reactivities with CH4, H2 and CO were evaluated in thermobalance performing redox cycles at 900 °C and in a semi-continuous fluidized bed reactor (FBR) at 850, 900 and 950 °C. The reactivity during iG-CLC process of the selected OC was evaluated in FBR at 900°C feeding char of the selected biomass; and in a 0.5 kWh pilot plant with continuous biomass feed. The selected biomass showed high calorific value (18 MJ/kg), high volatile + fixed carbon content (67%) and ashes with high K and Ca content, which can catalyze gasification reactions. All OCs showed low friction rate and good crushing strength, except for Mn, which is why it was submitted to calcination. The OCs Fe2, Fe3 and MnT1000 (Mn calcined at 1000 °C) demonstrated favorable attributes such as adequate crushing strength (>1 N), minimum attrition rate (<7%), good oxygen transport capacity (3.3%, 1.7% and 3.4%, respectively) and high reactivity in thermobalance. They also showed excellent performance in FBR with CO and H2, without agglomeration, good reoxidation rate and lifetime ranging from 3000h to 10500 hours. Notably, due to the excellent performance of the MnT1000 with CO and H2, it is a promising candidate for application in the iGCLC process. The iG-CLC tests in FBR indicates that an oxygen-to-biomass ratio greater than 30 promotes complete combustion of the gasification products, while lower values promote incomplete combustion. The iG-CLC tests in a continuous pilot plant indicate that an increase of the temperature of the fuel reactor or a decrease in the oxygen-biomass ratio increases the CO2 capture efficiency (>87%) and the combustion efficiency (>85%) while the excess oxygen has little influence on the process. The MnT1000 stood out as an oxygen carrier, did not suffer agglomeration in any of the tests, presented high performance, high reactivity, resistance, is environmentally friendly and low-cost. The application of a highly reactive low-cost TSO in iG-CLC processes using biomass stands out as an energy-efficient alternative to produce energy with intrinsic CO2 capture with a negative CO2 emissions balance.