Zhongfa Hu

The Promotion Mechanism of Silicon–Aluminum on the Decomposition of Sulfates in Biomass Ash

The Si–Al additives shared positive effects on relieving the severe problems of slagging, fouling, and depositions by destructing the alkali sulfates and chlorides during biomass combustion. In the present study, the decomposition of sulfates in the biomass ash was studied by using XRD, XRF, and TG-DSC. Results showed that sulfates in the biomass ashes began to decompose over 1000 °C and almost completely at 1100 °C. The aluminum–silicon additives promoted the decomposition of sulfates, but the Kaolin addition showed a stronger promotion effect. It was further proved by the further analysis of thermo-equilibrium calculation and TG-DSC on the biomass ash and potassium sulfate.

Mechanisms of Inorganic Element Transfer During Zhundong Coal Combustion in Drop Tube Furnace

The recently discovered Zhundong coal field is one of the main energy bases in China for the huge prototyped coal reserve. However, the Zhundong coal causes seriously fouling and slagging problems during combustion for the high content of Na and Ca. In this study, the Zhundong coal combustion experiments were carried out in drop tube furnace and the ashes sampled at different temperature were analyzed by SEM–EDS (scanning electron microscope–energy dispersive spectrometer) to obtain the microstructure and composition of ashes. The results show that a lot of Na-based compounds and a part of CaO could be vaporized during the early stage of Zhundong coal combustion. With the fume temperature decreasing, the gaseous Na and Ca compounds react with SO2 to form Na2SO4 and CaSO4 which are divided into three parts. A part condensates on the ash particle surface, and the remainder forms to aerosol. A fraction of aerosol united to form flocculent particles and adhered ash particles and the others released to air as fine particles.

Mechanism Investigation on the Sulfation of Condensed Sodium Chloride at 523–1023 K

Sulfation of alkali chlorides has significant effects on relieving deposition and corrosion in the heat exchanging surfaces during combustion of fuels abundant in alkali and chloride. This paper studies the effects of sulfation temperature and reactants concentration on the sulfation of condensed sodium chloride in a fixed bed reactor. Results showed that only Na2SO4 was found in the products. The sulfation ratio for variation of temperature in 523–1023 K was divided into two stages, first almost no change below 773 K and exponential increase with temperature further increasing. It indicated a different sulfation mechanism existed between low and high temperatures, which was further validated by the kinetic analysis of the sulfation and results of the effects of reactant concentrations. The difference on the sulfation mechanism was mainly due to the formation of a eutectic of NaCl–Na2SO4 mixture at high temperatures, which was further confirmed by the results of scanning electron microscopy. The sulfation reaction rate of condensed NaCl at 823–1023 K is described by the expression \( {\text{d}}X/{\text{d}}t = 0.218\exp^{ - 10,320/T} (1 - X)^{2/3} \left( {C_{{{\text{O}}_{2} }} } \right)^{0.58} \left( {C_{{{\text{SO}}_{2} }} } \right)^{0.85} \left( {{\text{H}}_{2} {\text{O}}} \right)^{1.87} \).