Pulverized coal-fired boilers applying low-NO x combustion technologies commonly suffer from high-temperature corrosion due to high-concentration H 2 S. Accurate prediction of sulfur species, especially H 2 S, is of great importance for the optimized design and operation of boilers and burners to reduce such problems. The sulfur release characteristics from coal and subsequent sulfur species gas-phase reaction mechanism are two critical steps controlling sulfur species evolution. In this study, first, a global sulfur species gas-phase reaction mechanism consisting of 10 reactions is proposed based on a detailed mechanism considering hundreds of elementary reactions. Kinetic parameters of the global mechanism are determined via a rigorous mathematical optimization process. Second, the sulfur release characteristics during coal pyrolysis and char burning of five kinds of sub-bituminous coals are investigated in a drop tube furnace (DTF). Equations describing the relationship between sulfur release and coal consumption are proposed and fitted to experimental data. Third, a novel integrated sulfur species prediction model is developed by implementing the global sulfur species gas-phase reaction mechanism and the sulfur release submodel into computational fluid dynamics (CFD )software, Fluent. Finally, combustion experiments of three kinds of sub-bituminous coals are conducted in the DTF at different temperatures with different stoichiometric ratios to validate the developed model. The results show that the prediction errors of sulfur species, including SO 2 , H 2 S, and COS, are within ±25%, which indicates that the novel sulfur species prediction model is of great assistance for actual engineering applications.

In chemical looping combustion of solid fuels, carbon slip from the fuel reactor to the air reactor is a critical issue. This paper presents the design and experimental evaluation of a carbon stripper (CS) in a cold flow model of a 70 kW chemical looping combustor of solid fuels. In the dual fluidized bed system, stable long-term operation was achieved. Plexiglas beads simulating the behavior of fuel particles were mixed with ilmenite particles to study the separation characteristics of the carbon stripper. The factors affecting the carbon stripper performance, such as the gas velocity in the carbon stripper, the solids circulation rates, and the inner structure of the carbon stripper, were experimentally investigated. The results showed that the separation efficiency of the Plexiglas beads was in the range of 0 to 60%. The carbon stripper added 160% additional residence time in the reducing atmosphere for the fuel particles.

Experiments were carried out in a pilot-scale entrained flow reactor (EFR) to investigate the reaction of SO3 with Ca­(OH)2 as a method of dry sorbent injection (DSI) for SO3 removal from flue gas. The results indicate that SO3 can be removed by Ca­(OH)2 with an efficiency that can reach 80%, and it was found that the molar ratio of Ca­(OH)2 to SO3 ([Ca]/[S]) and reaction temperature have a significant effect on SO3 removal efficiency. The experimental data measured inside the EFR were analyzed with a computing fluid dynamic (CFD) simulation, in which the Euler–Lagrangian frames were used for gas- and discrete-phase modeling. The CFD models were validated and applied to analyze the effects of certain parameters on SO3 removal efficiency, such as particle velocity, [Ca]/[S], temperature and residence time. It was found that the sorbent diameter has a significant influence on SO3 removal efficiency, with an obvious decrease in efficiency if the Ca­(OH)2 particle diameter increases. For example, if the sorbent diameter increases from 3 to 10 μm, the SO3 removal efficiency at the reactor outlet will decrease from 99% to 55%. A detailed comparison and theoretical analysis indicated that external diffusion of SO3 from the gas phase to the particle surface is the rate controlling step for larger Ca­(OH)2 particles, and more attention should be paid to the competition between external diffusion and surface reaction when applying the DSI method for removing SO3 from flue gas.

No abstract

No abstract