Red mud-based perovskite oxygen carrier preparation for chemical looping gasification of municipal sludge.

Chemical looping gasification (CLG) is a promising technology that utilizes lattice oxygen for partial oxidation of solid organic waste to produce high-quality syngas. The utilization of low-cost and high-performance oxygen carriers (OCs) is important for the success of this technology. The red mud from aluminum production was mixed with calcium and manganese oxides to prepare CaMn0.5Fe0.5O3-δ perovskite OCs. The comparative redox tests were carried out to analyze the reactivity using a thermogravimetric analyzer (TGA). Multiple cycle CLG experiments were conducted on a wet municipal sludge in a lab-scale fluidized bed to produce the hydrogen-rich gas. The results showed that the CaMn0.5Fe0.5O3-δ-washed demonstrated higher oxygen transfer capacity and better cycling stability with a maximum weight loss of 7.3096 %. After the 5th cycle in CLG, the syngas obtained using CaMn0.5Fe0.5O3-δ-washed maintained a H2 volume fraction exceeding 40%. However, an increase in CO2 production was also observed, which could be due to the catalytic effect of MnO in the OC on the steam-reforming reaction. The XRD curves showed that fresh CaMn0.5Fe0.5O3-δ-washed exhibited prominent diffraction peaks characteristic of perovskite. It was observed that after undergoing 5 cycles, the presence of iron calcium silicate structures containing Mn became evident due to the attachment of sludge ash, leading to the increased impurities on the surface of OCs with a decrease in the specific surface area. Additionally, some of the reacted OC particles exhibited a hollow structure, facilitating the fluidization. This preliminary study provides the basis for the improvement of the OC performance in sludge gasification.

Mechanism and Performance of Composite Phase Change Materials from the Direct Hydrolysis Residue of Municipal Sludge Loaded with Sodium Acetate Trihydrate.

The direct hydrolysis of municipal sludge for the production of oil and gas has become a key research focus, despite the application of hydrolysis residues presenting a challenge. In this study, municipal sludge was directly hydrolyzed in a high-pressure reaction kettle and the hydrolysis residue byproduct was used as a carrier to prepare a composite phase change heat storage material (CPCM), utilizing vacuum impregnation for sodium acetate trihydrate (SAT) loading. The results of Brunauer-Emmett-Teller (BET) and particle size analyses showed that the residue obtained by the hydrolysis of sludge and sawdust with a dry basis ratio of 4:1 had a higher pore volume and a uniform particle size. The adsorption capacity of the hydrolysis residue to SAT reached 600 wt %; the phase change temperature of the CPCM was 56.9 °C, and its latent heat reached 217.9 kJ/kg. The CPCM remained stable during 150 cycles of the melting-solidification process in a water bath and maintained excellent phase change characteristics. The hydrolysis residue can effectively improve the undercooling and phase separation of SAT without other additives.

Simulation of biomass-steam gasification in fluidized bed reactors: Model setup, comparisons and preliminary predictions.

A user-defined solver integrating the solid-gas surface reactions and the multi-phase particle-in-cell (MP-PIC) approach is built based on the OpenFOAM software. The solver is tested against experiments. Then, biomass-steam gasification in a dual fluidized bed (DFB) gasifier is preliminarily predicted. It is found that the predictions agree well with the experimental results. The bed material circulation loop in the DFB can form automatically and the bed height is about 1m. The voidage gradually increases along the height of the bed zone in the bubbling fluidized bed (BFB) of the DFB. The U-bend and cyclone can separate the syngas in the BFB and the flue gas in the circulating fluidized bed. The concentration of the gasification products is relatively higher in the conical transition section, and the dry and nitrogen-free syngas at the BFB outlet is predicted to be composed of 55% H2, 20% CO, 20% CO2 and 5% CH4.

Thermodynamic analyses of a biomass-coal co-gasification power generation system.

A novel chemical looping power generation system is presented based on the biomass-coal co-gasification with steam. The effects of different key operation parameters including biomass mass fraction (Rb), steam to carbon mole ratio (Rsc), gasification temperature (Tg) and iron to fuel mole ratio (Rif) on the system performances like energy efficiency (ηe), total energy efficiency (ηte), exergy efficiency (ηex), total exergy efficiency (ηtex) and carbon capture rate (ηcc) are analyzed. A benchmark condition is set, under which ηte, ηtex and ηcc are found to be 39.9%, 37.6% and 96.0%, respectively. Furthermore, detailed energy Sankey diagram and exergy Grassmann diagram are drawn for the entire system operating under the benchmark condition. The energy and exergy efficiencies of the units composing the system are also predicted.

Effects of the updated national emission regulation in China on circulating fluidized bed boilers and the solutions to meet them.

The advantage of circulating fluidized bed (CFB) boilers in China is their ability to utilize low rank coal with low cost emission control. However, the new National Emission Regulation (NER) issued in early 2012 brings much more stringent challenges on the CFB industries, which also causes much attention from other countries. Based on the principle of a CFB boiler and previous operating experience, it is possible for the CFB boilers to meet the new NER and maintain the advantage of low cost emission control, while, more influences should be considered in their design and operation. To meet the requirement of the new NER, the fly ash collector should adopt a bag house or combination of electrostatic precipitator and bag filter to ensure dust emissions of less than 30 mg · Nm(-3). For SO2 emission control, the bed temperature should be strictly lower than 900 °C to maintain high reactivity and pores. The limestone particle size distribution should be ranged within a special scope to optimize the residence time and gas-solid reaction. At the same time, the injecting point should be optimized to ensure fast contact of lime with oxygen. In such conditions, the desulfurization efficiency could be increased more than 90%. For lower sulfur content fuels (<1.5%, referred value based on the heating value of standard coal of China), increasing Ca/S enough could decrease SO2 emissions lower than that of the new NER, 100 mg · Nm(-3). For fuels with sulfur content higher than 1.5%, some simplified systems for flue gas desulfurization, such as flash dryer absorber (FDA), are needed. And the NOx emissions of a CFB can be controlled to less than 100 mg · Nm(-3) without any equipment at a bed temperature lower than 900 °C for fuels with low volatiles content (<12%), while for fuels with high volatiles, selective non-catalytic reduction (SNCR) should be considered. Due to the unique temperature in CFB as well as the circulating ash, the efficiency of SNCR could reach as high as 70%. The Hg emission of CFB is very low for the new NER due to its innate property.