Coal oxidation at low temperatures: oxygen consumption, oxidation products, reaction mechanism and kinetic modelling

Coal oxidation at low temperatures (i.e. <100 °C) is the major heat source responsible for the self-heating and spontaneous combustion of coal and is an important source of greenhouse gas emissions. This review focuses on the chemical reactions occurring during low-temperature oxidation of coal. Current understanding indicates that this process involves consumption of O 2, formation of solid oxygenated complexes, thermal decomposition of solid oxygenated complexes and generation of gaseous oxidation products. Parameters, such as mass change, heat release, oxygen consumption, and formation of oxidation products in the gas or solid phase, have been used to qualitatively and quantitatively describe the oxidation process. Reaction mechanisms have been proposed to explain the characteristics of consumption of O2, and formation of oxidation products in the gas and solid phases. Various kinetic models have also been developed to describe the rate of oxygen consumption and the rates of formation of gaseous oxidation products in terms of the rate parameters of the relevant reactions, oxidation time, temperature, and initial concentration of oxygen in the oxidising medium. Further research emphasis should be placed on the formation of the complete reaction pathways proceeding in the oxidation process and on the development of kinetic models applicable for predicting the self-heating and gas emission in a coal seam or stockpile.

Coal oxidation at low temperatures: oxygen consumption, oxidation products, reaction mechanism and kinetic modelling, Pages 487-513

Coal fires in China over the last decade: A comprehensive review

Reaction pathway of coal oxidation at low temperatures: a model of cyclic chain reactions and kinetic characteristics

https://stacks.cdc.gov/view/cdc/9812/cdc_9812_DS1.pdf

Numerical study on effects of coal properties on spontaneous heating in longwall gob areas

Low-temperature oxidation of coal. 1. A single-particle reaction-diffusion model

Low-temperature oxidation of coal. 3. Modelling spontaneous combustion in coal stockpiles

Low-temperature oxidation of coal. 2. An experimental and modelling investigation using a fixed-bed isothermal flow reactor

The petroleum refining industry employs a wide variety of heat transfer-based equipment which tend to foul due to the complex nature of associated fluid streams and process conditions. Over the years, different test methods have been researched to understand fouling at the lab, pilot, and/or plant level. Several of these investigations have been limited to understanding fouling in static refinery streams or under non-practical operating conditions. The present study experimentally demonstrates the potential of a high-temperature batch stirred coupon test rig to characterize fouling under noncoking conditions for a specific refinery stream of interest. Experiments were conducted using a representative crude oil stream (obtained from a refinery) in a 2-liter batch autoclave system with a facility to immerse coupons attached to a rotating shaft into the stream during related test runs. The coupon Material of Construction (MOC) was chosen similar to the MOC of the tubes used in a refinery crude heat exchanger train. Experiments covered a range of bulk temperatures from 250°C to 300°C at 100 RPM. The foulant deposits obtained were found to have a strong (hard) and weakly (soft) adhering component. In the temperature range investigated, the hard and soft deposits were largely inorganic and organic in nature, respectively. The fluid bulk temperature was found to influence hard and soft deposit formation. The foulant deposits were characterized using TGA, CHNS, XRD, and SEM/EDAX, respectively. The iron and sulfur content in the hard deposit was more than 45% in total, indicating that the fouling mechanism was corrosion-based resulting from the formation of FeS on the surface. The thermal history of the soft deposit was distinct from the crude oil used. The results obtained confirm the potential of the coupon test rig for understanding fouling in refinery streams.

Crude Oil Foulant Deposition Studies on a Heated Surface Using a Novel Batch Stirred Coupon Test Rig

Ice based Freeze Desalination (FD) offers a potential alternative to recover fresh water from seawater. However, ice-water phase change data in saline water in the range of practical interest and of importance in FD process design is limited. In this study, reliable and accurate measurements related to ice–water phase change temperatures and specific enthalpies have been carried out using a Micro–Differential Scanning Calorimeter (μ–DSC). The runs were carried out using pure water, synthetic salt water (0.5 to 5 wt% NaCl) and seawater. The NaCl concentrations covered a range of values of practical interest in FD. In the case of pure water, the specific enthalpy value was found to be in excellent agreement to within ± 0.51% of the value reported in literature, i.e. 333 J/g which validated the experimental protocols adopted in this study. Phase change temperature and specific enthalpy values for salt water were found to decrease with an increase in salt concentration. Test runs conducted subsequently using seawater were consistent with the results obtained from the synthetic salt water test runs. The experimental protocol adopted and data presented in this study can be used in design of an ice based FD process. 

Srinivasan Krishnaswamy

Papers

Low-temperature oxidation of coal. 1. A single-particle reaction-diffusion model

Low-temperature oxidation of coal. 3. Modelling spontaneous combustion in coal stockpiles

Low-temperature oxidation of coal. 2. An experimental and modelling investigation using a fixed-bed isothermal flow reactor

Crude Oil Foulant Deposition Studies on a Heated Surface Using a Novel Batch Stirred Coupon Test Rig

Calorimetry based temperature and specific enthalpy measurements associated with ice-water phase change in saline systems for freeze desalination