This paper presents a comparison of impacts of halogen species on the elemental mercury (Hg(0)) oxidation in a real coal-derived flue gas atmosphere. It is reported there is a higher percentage of Hg(0) in the flue gas when burning sub-bituminous coal (herein Powder River Basin (PRB) coal) and lignite, even with the use of selective catalytic reduction (SCR). The higher Hg(0)concentration in the flue gas makes it difficult to use the wet-FGD process for the mercury emission control in coal-fired utility boilers. Investigation of enhanced Hg(0) oxidation by addition of hydrogen halogens (HF, HCl, HBr, and HI) was conducted in a slipstream reactor with and without SCR catalysts when burning PRB coal. Two commercial SCR catalysts were evaluated. SCR catalyst no. 1 showed higher efficiencies of both NO reduction and Hg(0) oxidation than those of SCR catalyst no. 2. NH3 addition seemed to inhibit the Hg(0) oxidation, which indicated competitive processes between NH3 reduction and Hg(0) oxidation on the surface of SCR catalysts. The hydrogen halogens, in the order of impact on Hg(0) oxidation, were HBr, HI, and HCl or HF. Addition of HBr at approximately 3 ppm could achieve 80% Hg(0) oxidation. Addition of HI at approximately 5 ppm could achieve 40% Hg(0) oxidation. In comparison to the empty reactor, 40% Hg(0) oxidation could be achieved when HCl addition was up to 300 ppm. The enhanced Hg(0) oxidation by addition of HBr and HI seemed not to be correlated to the catalytic effects by both evaluated SCR catalysts. The effectiveness of conversion of hydrogen halogens to halogen molecules or interhalogens seemed to be attributed to their impacts on Hg(0) oxidation.

A systematic investigation of sorbent-trap sampling, which is a method that uses paired sorbent traps to measure total vapor phase mercury (Hg), was carried out at two coal-fired power plants. The objective of the study was to evaluate the effects (if any) on data quality when the following aspects of the sorbent trap method are varied: (a) sorbent trap configuration; (b) sampling time; and (c) analytical technique. Also, the performance of a speciating sorbent trap (i.e., a trap capable of separating elemental Hg from oxidized Hg), developed by the Western Kentucky University's Institute for Combustion Science and Environmental Technology (ICSET), was evaluated by direct comparison against the Ontario Hydro (OH) reference method. Flue gas samples were taken using both "regular" and modified sorbent trap measurement systems. The regular sorbent trap systems used a dual-trap, in-stack sampling technique. The modified systems were equipped with either inertial or cyclone probes and used paired, out-of-stack sorbent traps. Both short-term (1.5 h) and long-term (18 h to 10 days) samples were collected. The OH method was run concurrently during the short-term test runs, to provide reference Hg concentrations. At one facility, mercury concentration data from continuous emission monitoring systems were also recorded during the sorbent trap sampling runs. After sampling, the conventional (nonspeciating) sorbent traps were analyzed for Hg, using either a direct combustion method or a wet-chemistry analytical method (i.e., microwaveassisted digestion coupled with cold vapor atomic absorption spectroscopy). The speciating traps were analyzed only by the direct combustion method. All of the sorbent trap data collected in the study were evaluated with respect to relative accuracy, relative deviation of paired traps, and mercury breakthrough. The in-stack and out-of-stack sampling methods produced satisfactory relative accuracy results for both the short-term and long-term testing. For the short-term tests, the in-stack sampling results compared more favorably to the OH method than did the out-of-stack results. The relative deviation between the paired traps was considerably higher for the short-term out-of-stack tests than for the long-term tests. A one-way analysis of variance (ANOVA), showed a statistically significant difference (p < 0.1) between the direct combustion and wet-chemistry analytical methods used in the study; the results from the direct combustion method were consistently higher than the wet-chemistry results. The evaluation of the speciating mercury sorbent trap demonstrated that the trap is capable of providing reasonably accurate total mercury concentrations and speciation data that are somewhat comparable to data obtained with the OH method. Although the results of the study were informative and promising, further evaluation of both the out-of-stack sampling methods and the speciating sorbent trap is recommended. † Progress in Coal-Based Energy and Fuel Production.

A radio frequency pulse width modulation (RF-PWM) scheme based on phase-shift control and mapping PWM (MPWM) is described. Pulse coding is the key to improving the coding efficiency, flexibility, and configurability of the all-digital transmitter (ADTx). To solve the problem that the real-time performance of the system is limited by the time resolution, the phase-shift control principle is adopted to constrain the output pulse state. It decomposes the original signal into two phase-modulated constant envelope signals, and directly converts the two-level pulse waveform by MPWM. Finally, the fast generation of the three-level digital RF modulated signal is completed by vector synthesis. In this way, the rear power amplifier can be directly driven, and the difficulty of physical implementation is greatly reduced. Different from the traditional mapping strategy of traversal search, the proposed scheme does not require complicated error calculation and comparison. Simulation and offline experiments show that the proposed scheme has better comprehensive performance than other mapping schemes. For 16QAM modulated signals at a 300 MHz carrier, the proposed scheme can achieve nearly 70% coding efficiency (CE), less than −50 dBc, and 1% adjacent channel power ratio (ACPR) and error vector magnitude (EVM).

Photocatalysis has become the forefront of international chemical research due to its green and environmentally friendly characteristics. A new protocol to construct S-S(O)2 bonds using selectfluor as oxidant and eosin Y as photocatalyst under blue light irradiation was reported. This method has advantages of mild conditions, good compatibility of functional groups, and easily preparation of various symmetric or asymmetric thiosulfonates various from the corresponding mercaptans with good conversion rates. Thus, this protocol provides a very valuable reference for developing a catalytic system with mild conditions, high atomic economy and strong universality to achieve efficient and controllable conversion of sulfur-containing organic compounds.

No abstract