Changhe Chen

Development of coal combustion pollution control for SO2 and NOx in China

Abstract Pollution control of coal combustion in China is a very urgent task. New low-NO x combustion and flue gas desulfurization (FGD) techniques suitable for China should be researched and developed. These techniques should be comparably effective, but have low investments, operating cost and water consumption, so that they can be widely used in China. To optimize the ecology of the coal-energy system and find new measures to rectify large areas of saline-alkali soil and deserts in China is important.

The future of hydrogen infrastructure for fuel cell vehicles in China and a case of application in Beijing

Abstract In the paper the future of hydrogen infrastructure for fuel cell vehicles in China is discussed. It is believed that, China should make different plans of hydrogen infrastructure during different periods and in different regions. Besides, a case of application in Beijing is studied to find the best plan for Beijing to develop hydrogen infrastructure in 2008 when Olympic Games will be held. In the study of that case, 11 feasible plans are designed at first according to the current technology of production, storage and transportation of hydrogen in China. After that, the energy, environmental and economic performances of these plans are evaluated with “life cycle assessment”. Finally, the best plan in the case is picked out from all the aspects of energy, environment and economy.

Evolution of pore fractal dimensions for burning porous chars

The evolution of pore fractal dimensions for three Chinese chars was investigated. The pores of porous chars can be classified into macro-, micro- and transition-pores based on their fractal dimensions. The radius ranges of the macro-, micro- and transition-pores may be different for various chars. For different conversions in the char combustion process, the fractal dimensions of the micro-pores for different chars are almost the same and the fractal dimensions of macro-pores for the same kind of chars are roughly unchanged. The effects of fractal structure on combustion rate are also discussed.

DRIFTS study of ammonia activation over CaO and sulfated CaO for NO reduction by NH3.

CaO catalyzes NH(3) oxidation, while sulfated CaO catalyzes NO reduction by NH(3) in the presence of O(2), and the adsorption and transformation of ammonia over CaO and sulfated CaO has been investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to understand their catalytic mechanism. It has been found that ammonia is first adsorbed over Lewis or Brönsted acid sites, and later undergoes hydrogen abstraction giving rise to either NH(2) amide or NH imide intermediates. The intermediates react with NO or lattice O to produce N(2) or NO. Comparing the DRIFTS of NH(3) adsorption over CaO and sulfated CaO, it is obvious that ammonia adsorbed over CaO is activated mainly in NH form apt to react with surface oxygen to produce NO, while ammonia adsorbed over sulfated CaO is activated mainly in NH(2) form apt to reduce NO. The DRIFTS results agree with experimental data and explain the catalytic mechanisms of CaO and sulfated CaO.

Modeling char combustion with fractal pore effects

The effects of char pores on char combustion has been studied with fractal theory. The fractal properties of different char samples were derived from mercury porosimetry measurements. Gas diffusion in pores affects combustion in char pores and this diffusion is affected by the geometrical complexity of pores. To explore gas diffusion and combustion in fractal pores, a fractal geometrical factor β is defined with pore fractal dimensions and other fractal geometrical factors. It has been found that both apparent activation energy and pre-exponential factor have linear relations with the factors β and the char combustion can be modeled with the fractal geometrical factor.

Thermogravimetric analysis of char combustion

Nine different char samples were tested in thermogravimetric analyzers with continuously rising temperatures and a global one-step kinetic reaction model was used to describe the char combustion. A mathematical method has been presented to deduce the activation energy and pre-exponential factor. The results show that this method has good convergence and is relatively easy for applications. The deduced apparent activation energies and pre-exponential factors will be used for analyzing diffusion effects within char pores in He, Sato, and Chen (2002).

Impact of Flue Gas Species and Temperature on Mercury Oxidation

Abstract Systematic experimental research has been conducted in a fix-bed reactor system to determine the impact of coal-fired flue gas species and temperature on mercury oxidation. This work focuses on the temperatures range of 200°C to 800°C to demonstrate that temperature is a critical factor for the effect of the gas components on the mercury oxidation process. Among the investigated gases, hydrogen chloride is essential for oxidizing the elemental mercury. Nitrogen oxide was also found to have a positive correlation with the mercury oxidation when hydrogen chloride was present. Sulfur dioxide can either promote or inhibit the oxidation depending on the conditions; however, when nitrogen oxide is also present, sulfur dioxide has a negative impact. Ammonia exhibits an strong inhibitory effect. Several plausible mercury oxidation pathways are suggested in this paper.

Carbon Dioxide Recovery from Flue Gases By Ammonia Scrubbing

Publisher Summary This chapter describes the significant researches on a novel CO2 removal approach—ammonia scrubbing. The preliminary experimental results are very promising. Under optimum conditions, the removal efficiencies are stable in the range from 95% to 99%, after one minute or so. This indicates a high potential for scrubbing with a fast absorption rate while using ammonia. The crystalline solids in the solution were analyzed by X-ray diffraction. It was proved that ammonium bicarbonate was the main product of the CO2–NH3 reaction in this study. Interest in CO2 removal has increased rapidly, mainly because of the growing awareness of the risks of a climate change due to greenhouse gas emissions, because CO2 is the largest component of greenhouse gases being emitted to air. The importance of carbon sequestration is now gradually being addressed by world nations. There are various technologies used to separate CO2 from flue gas streams—for example, chemical absorption, physical absorption, cryogenic methods, membrane separation, and biological fixation. Chemical absorption is generally recognized as the most effective technology among all the technologies at present. Although the MEA process is a promising system for the recovery of CO2 from flue gases, it has some shortcomings, including slow absorption rate and small solvent capacity. A novel approach that may provide another route of reducing CO2 emissions from power plants is separation by ammonia scrubbing.

Thermal Degradation of Ethanolamine in CO 2 Capture with SO 2

Amine degradation in the absorption/stripping process is one of the concerns in this technology. SO2 is reported to promote amine degradation in both bench scale and pilot scale. This work investigates the impact of SO2 on thermal degradation of MEA by preloading additives, which are Na2SO3, SO2 and H2SO4. 7 m (mol/kg H2O) MEA with 0.4 CO2 loading (mol CO2/mol MEA) at 135°C is the baseline condition. Initial sulfur concentration is 0.4 m in the experiments with additives. The experiment temperature varied from 120 to 150°C. Neither sulfite nor sulfate has significant impact on MEA degradation rate in thermal condition. There is no different cation product in the samples with additives compared to the baseline experiment. The main process of MEA thermal degradation is still carbamate polymerizing. Ammonium was induced by sulfite. The main organic acid product is formate for all the experiment conditions, while there are new anion products with sulfite. Formate formation was promoted by H2SO4. Ammonium and formate formation were promoted at higher temperature.

Catalytic Mechanism of NaY Zeolite Supported FeSO4 Catalyst for Selective Catalytic Reduction of NOx

The experimental results suggested that FeSO4-NaY and FeSO4-ZSM-5 prepared by impregnation method performed well in NOx removal. The NOx removal rates of the prepared catalyst were 20–35% higher than those of pure FeSO4, The effective temperature window was largely expanded with the best performance temperature shifted from 440 to 340°C. SO2 and H2O in flue gas had no obvious effect on catalyst performance. Mossbauer spectrometry, XPS and in-situ infrared spectra analysis had been employed to investigate the catalytic mechanism of catalysts. It had been found that FeSO4, Fe(OH)SO4 and Fe2O(SO4) were the major components existing in the prepared catalyst, with their portions related to carrier type and preparing condition. FeSO4 combined tighter with carriers after de-NOx reaction. Fe2O3 and the chemical bond between Fe and Al had been found. Fe(OH)SO4 was better in terms of NOx removal than that of Fe2O(SO4). NH3 absorbed on FeSO4-NaY catalyst generated the spectra of NH 4 + and NH3, suggesting the Eley-Rideal mechanism. FeSO4-ZSM-5 absorbed both NH3 and NO and the carrier (ZSM-5) itself demonstrated some catalytic effect, indicating a different reaction mechanism. \( {\text{SO}}_4^{{2 - }} \) from FeSO4 and hydroxyl from carrier jointly enhanced the adsorption of reaction gas. Fe provided the active sites for the reaction between NH3 and NO.