Pressurized Thermogravimetric Study on the Hydropyrolysis and Hydrogasification Kinetics of a Bituminous Coal

Abstract

Coal hydropyrolysis (CHP) and coal hydrogasification (CHG) are two important processes during coal conversion in a hydrogen atmosphere. Much attention has been paid on this clean coal conversion technology because of its advantages. In this work, the CHP and CHG kinetic characteristics of a bituminous coal are studied in a pressurized thermogravimetric analyzer (P-TGA). The effects of the pressure on the CHP and CHG kinetics of the bituminous coal are detected with the non-isothermal thermogravimetric method. In addition, the kinetic compensation effect (KCE) and isokinetic points of the two processes are investigated. Besides, the kinetic triplets, including the pre-exponent factor, the activation energy and mechanism function are also calculated and defined for all of the cases during the CHP and CHG processes. Meaningful and interesting conclusions are finally obtained from this study. The initial pyrolysis temperature will increase with the reaction pressure when the pressure is within 3 MPa. The appearing time of the weight loss peak rate will be delayed when the pressure is lower than 2 MPa, and then it will become earlier gradually with the pressure increment. The weight loss peak rate will decrease sharply when the pressure is increased from 0.1 to 1 MPa, and then it will increase gradually with the reaction pressure increment. The KCE phenomenon during the CHP process is not detected, and the isokinetic point is not found. The KCE can be detected during the CHG process when the reaction pressure is within 3 MPa and the isokinetic point temperature is found as 1041.0 K.

Kinetic and thermodynamic modelling of thermal decomposition of bitumen under high pressure enhanced with simulated annealing and artificial intelligence

“…However, these observations are possibly due to higher heat and mass transfer efficiency at lower pressure and heating rates (under inert condition), which eventually leads to higher cracking and weight loss in form of volatiles. [ 9 ] As reported in the literature, [ 17,23,25,27,28,31,46,53,54 ] the weight loss increases with increasing partial pressure of oxygen during TGA experiments. On the contrary, the observation from the present work indicates decreasing reactivity as the pressure increases under inert environment.…”

“…From previous studies, the kinetic parameters, in most cases, were observed to decrease with increasing partial pressure of the oxidants during gasification and combustion experiments. [ 17,23,25,27,31,46,54 ] The behaviour of the kinetic parameters with respect to pressure, as observed in the present study, may be due to reduced reactivity under pyrolysis environment, likely because of reduced heat and mass transfer. This observation is comparable to those observed from similar investigations.…”

“…[17] Thehigh-pressure TGA have been employed to study effects of pressure on the activation energy and frequency factor of crude oils, [17,18,[21][22][23][24][25] and other hydrocarbons including asphaltene, [26] petroleum coke, [27] oil shale, [28] and coal. [29][30][31] Bagci, [25] using the ramped temperature experiments (RTO), studied the kinetics of oxidation of crude oil in the presence of limestone particles under high pressure. The author reported that CO 2 /CO ratios and activation energy increase with operating pressure.…”

Structure and CO2 Gasification Reactivity of Char Derived through Pressured Hydropyrolysis from Low-Rank Coal

“…Hydropyrolysis of coal is a hydrothermal devolatilization process under the hydrogen atmosphere. It can significantly increase the tar yield and improve tar quality and further produce high calorific value gas and clean semicoke. − The merits of hydropyrolysis attracted great attention, and extensive studies have been carried out to clarify the relationship between the tar yield and coal property, as well as the influence of operating conditions on hydropyrolysis products. − A novel multistage hydropyrolysis of lignite was introduced, and the results showed that the tar yield and tar quality improved remarkably compared with the hydropyrolysis. , It was found that the yield of total liquids was apparently correlated with the H/C atomic ratio of raw coal . Temperature was the most essential factor affecting the tar yield and quality; higher pressure and lower heating rate facilitated higher tar yield.…”