Study on the corrosion of refractory materials by coal blended with the extraction residue of direct coal liquefaction in a simulated gasification atmosphere

Utilizing the extraction residue (ER) of direct coal liquefaction residue as a gasification feedstock has significant economic value. But the characteristic of high ash and iron in the ER would increase the risk of corrosion of the refractory materials and affect the long-term operation of the gasifier. In this work, corrosion experiments of molten slag derived from a mixture of 20 wt% ER and 80 wt% coal on a high-chromia refractory brick and SiC brick were carried out using a rotary-drum furnace in a simulated gasification atmosphere. The experimental results show that the viscosity of the poured slag is larger as compared to the initial ash sample at the same temperature, which suggests that the viscosity–temperature relationship of the poured slag should be used as the reference for the operation temperature of the gasifier to ensure that the slag can flow during operation. For a high-chromia refractory brick, iron oxides in molten slag could react with Cr2O3 in the refractory matrix but, because the aggregate was not found to be damaged, the damage to the matrix structure was the key factor for causing the corrosion of the high-chromia refractory brick. Metallic iron was observed in the exposed SiC brick, which indicated that the reaction between the iron oxides in the slag and SiC occurred, forming metallic iron and SiO2. The corrosion of a SiC brick by molten slag depended mainly on the dissolution of Al2O3 particles and the reaction between iron oxides in the molten slag and SiC particles. Therefore, the high iron content in coal ash had a serious influence on the corrosion of refractory materials. More efforts need to be made on coal blended with ER as a gasification feedstock in the future.

Effects of diesel from direct and indirect coal liquefaction on combustion and emissions in a six-cylinder turbocharged diesel engine

The aim of this study is to evaluate the effects of diesel from direct coal liquefaction (DDCL) and diesel from indirect coal liquefaction (DICL) on combustion and emissions. A six-cylinder turbocharged diesel engine fueled with DDCL, DICL, petroleum diesel (PD), 58% DDCL, and 42% DICL blended by volume (BD58) is used. The experiments are carried out at 1400 and 2300rpm engine speeds and various engine loads (10%, 25%, 50%, 75%, and 90% of the full-load). The results show that the brake thermal efficiency (BTE) of PD was higher than that of CTL (the maximum difference was 2%) at medium and high loads. At 10% load of 1400 rpm, the CO, HC and formaldehyde emissions of DDCL are 88.9%, 44.3% and 26.5% higher than those of PD respectively, and the CO, HC, and formaldehyde emissions of DICL are 30.1%, 15.3%, and 15.2% lower than those of PD. The differences among four fuels decrease rapidly with the increase of load. The NOX emissions of PD are the highest due to high nitrogen content (102.3 μg/g) and low hydrogen-carbon (H/C) ratio. The fuel with higher cetane number has less formaldehyde emission at low loads, while the fuel with lower H/C has less formaldehyde emission at high loads. The particle size distribution shows a bimodal shape at different loads and the peak particle size of accumulation mode and nucleation mode all increases with the increase of load. The particulate emission of different fuels from high to low is the order of PD > DDCL > BD58 > DICL. In addition, the emissions of polycyclic aromatic hydrocarbons (PAHs) and toxicity equivalent (TE) of PD are highest at all loads. The proportion of soluble organic fractions (SOF) from DDCL, DICL, and BD58 is higher than that of PD.