Research on the Influence of Combustion Methods on NO x Emissions from Co-combustion of Various Tannery Wastes.

To further increase combustion efficiency and reduce nitrogen oxide pollution caused by tannery wastes, three raw materials, including tannery sludge, chrome-tanned buffing dust, and chrome shavings, were burned together in a dual-bed model reactor under various conditions. In addition, a thermogravimetric analysis of co-combustion of three tannery wastes was studied in this study, which was conducive to understanding the combustion characteristics and positive effects. The comprehensive combustibility index S, the flammability index K r, and the stable combustion characteristic index G b all increased when the tannery sludge was blended with chrome-tanned buffing dust and chrome shavings, indicating that the combustion behavior was improved by co-combustion. For normal combustion, decreasing the gas volume flow and temperature resulted in a decrease in the oxidation of nitrogen compounds, consequently lowering the NO x emission. During air staged combustion, at an appropriate secondary gas ratio of about 10-40%, the NO x reduction would be increased from 10.9 to 19.3%. By increasing the tertiary gas volume flow from 0.2 to 1.1 L/min in decoupling combustion, an average relative NO x reduction efficiency of 47% was attained compared with normal combustion. The results offered a viable technology that resulted in a lower NO x emission and realized the application of decoupling combustion.

Recovery of Fe and Al from red mud by a novel fractional precipitation process.

The development of cheap and effective approach for utilizing red mud (RM) waste is a long and arduous task. This work provided a technically and economically feasible route to utilize RM waste for the production of high valuable chemicals by use of the industrial wastes as cheap raw materials. The Fe and Al elements were first leached from RM through hydrothermal reaction and then were separated by precipitation after the Fe(III) in leachate was reduced to Fe(II) by iron powder. Above 90% Fe and Al were extracted from RM with the Fe and Al purity of about 95% and 45%, respectively. The control test revealed that the main impurity of Al product was caused by the adsorbed SO42- during the precipitation of the Al3+. The structural characterization demonstrated that the obtained Fe products were in nanoscale, and the Ti-Si residue has high BET area of 203.7 m2/g. Four products of nano-Fe3O4/nano-Fe, aluminum oxide, Ti-Si residue, and (NH4)2SO4 were obtained as valuable chemical materials for industry. This demonstrated utilization of industrial waste to produce high added-value products with high efficiency and low cost will possess promising application prospect for the resource utilization of RM in industry.

The utilization of red mud waste as industrial honeycomb catalyst for selective catalytic reduction of NO.

As a new way for the high-value utilization of red mud (RM) waste, we proposed an improved approach to prepare the RM-based sludge/powder via the sulfuric acid hydrothermal dissolution and NH3 aqueous precipitation route and then the RM-based industrial-sized honeycomb (150 × 150 × 600 mm) was successfully produced by the extrusion moulding method in pilot scale. The synthesized RM-based powdery/honeycomb catalyst exhibited more than 80% deNO x activity and good durability of H2O and SO2 above 350°C. But the decline of NO conversion was also observed above 350°C, which was confirmed to result from the increased oxygenation of NH3 at high temperature. To improve the NO conversion at high temperature, NH3 was shunted and injected into the catalyst bed at two different places (entrance and centre) to facilitate its uniform distribution, which relieved the oxidation of NH3 and increased deNO x efficiency with 98% NO conversion at 400°C. This work explored the industrial application feasibility for the RM-based honeycomb catalyst as well as the possible solution to decrease the oxygenation of NH3 at high temperature, which presented a valuable reference for the further pilot tests of RM catalyst in industry.

The industrial feasibility of low temperature DeNO x in the presence of SO x : a project case in a medium coking plant.

Catalyst poisoning by SO x has hindered the industrial application of selective catalytic reduction (SCR) technology for the DeNO x of low temperature flue gas for many decades. The current engineering process of placing the SCR unit after the desulphurization and dedusting units can lead to high project and operational costs owing to low DeNO x efficiency at low temperatures. Based on our previous pilot results, a DeNO x project case was built before the desulfurization unit in a medium coking plant to explore the industrial feasibility of low temperature DeNO x in the presence of SO x . A new engineering process was considered and designed to overcome the problem of SO x , including the elimination of SO3 with NH3 before the SCR reactor, the filtration of ash by a foam metal plate and in situ regeneration technology. The project case could run continuously for six months with above 70% DeNO x efficiency and less than 10 ppm NH3 slip at 250 °C and a space velocity of 4000 h-1 in the presence of 260-300 mg m-3 SO x . The activity loss for the catalyst itself was not obvious after it had been running for six months, but blocking of the honeycomb channels by the sedimentary ash on the honeycomb catalyst modules owing to the low linear velocity resulted in decreased DeNO x efficiency and an increased pressure drop. A improved DeNO x process with gravitational dust collectors was also proposed to upgrade the present DeNO x project case for further continuous and stable operation.