Deactivation of V2O5-WO3-TiO2 SCR catalyst at biomass fired power plants: Elucidation of mechanisms by lab- and pilot-scale experiments

In this work, deactivation of a commercial type V₂O₅-WO₃-TiO₂ catalyst by aerosols of potassium compounds was investigated in two ways: (1) by exposing the catalyst in a lab-scale reactor to a layer of KCl particles or fly ash from biomass combustion; (2) by exposing full-length monolith catalysts to pure KCl or K₂SO₄ aerosols in a bench-scale reactor. Exposed samples were characterized by activity measurements, SEM-EDX, BET/Hg-porosimetry, and NH₃ chemisorption. The work was carried out to support the interpretation of observations of a previous study in which catalysts were exposed on a full-scale biomass fired power plant and to reveal the mechanisms of catalyst deactivation.Slight deactivation (about 10%) was observed for catalyst plates exposed to a layer of KCl particles at 350 °C for 2397 h. No deactivation was found for catalyst plates exposed for 2970 h to fly ash (consisting mainly of KCl and K₂SO₄) collected from an SCR pilot plant installed on a straw-fired power plant. A fast deactivation was observed for catalysts exposed to pure KCl or K₂SO₄ aerosols at 350 °C in the bench-scale reactor. The deactivation rates for KCl aerosol and K₂SO₄ aerosol exposed catalysts were about 1% per day and 0.4% per day, respectively.SEM analysis of potassium-containing aerosol exposed catalysts revealed that the potassium salt partly deposited on the catalyst outer wall which may decrease the diffusion rate of NO and NH₃ into the catalyst. However, potassium also penetrated into the catalyst wall and the average K/V ratios (0.5–0.75) in the catalyst structure are high enough to explain the level of deactivation observed. The catalyst capacity for NH₃ chemisorption decreased as a function of exposure time, which reveals that Brønsted acid sites had reacted with potassium compounds and thereby rendered inactive in the catalytic cycle. The conclusion is that chemical poisoning of active sites is the dominating deactivation mechanism, but physical blocking of the surface area may also contribute to the loss of activity in a practical application. The results support the observation and mechanisms of deactivation of SCR catalysts in biomass fired systems proposed in a previous study [Y. Zheng, A.D. Jensen, J.E. Johnsson, Appl. Catal. B 60 (2005) 253].     

The diarylprolinol silyl ether system: a general organocatalyst

The past few decades have witnessed some of the most important and revolutionizing advances in the field of asymmetric catalysis. Chemists no longer rely solely on natural sources as the starting point of their synthetic strategy, as in chiral pool or auxiliary-based synthesis. Instead, naturally occurring chiral motifs are selected and, either unchanged or after modification, used in substoichiometric amounts as chiral catalysts or ligands. In this way, they effectively transfer their chirality to prochiral substrates, thereby rapidly amplifying and diversifying the arsenal of useful chiral building blocks available to the synthetic community. A long-standing goal in the pursuit of new catalytic systems is the discovery of general catalysts. Ideally, such catalytic systems should be capable of promoting a large number of enantioselective reactions, via multiple modes of activation, with good substrate tolerance and high stereoselectivity. In this Account, we describe the synthetic usefulness, efficiency, selectivity, and robustness of the diarylprolinol silyl ether system as the catalyst in various reactions of aldehydes. Based on the diarylprolinol silyl ether system, several studies on enamine-mediated transformations of saturated aldehydes have resulted in the introduction of different functionalities into the α-position of aldehydes in a highly stereoselective manner. This HOMO-activation concept was later extended to include α,β-unsaturated aldehydes, which after condensation with the aminocatalyst generate a dienamine species capable of undergoing stereoselective Diels-Alder-type reactions. As a result, the effective functionalization of the γ-position of the aldehyde is achieved. Recently, the activation principle was further developed to include 2,4-dienals, which form trienamine intermediates upon condensation with the aminocatalyst. The trienamines effectively react with carbon-centered dienophiles, forming aldehyde products having up to four contiguous stereocenters. Because of the concerted nature of the reaction and the efficient catalyst shielding of the β-position, the stereoinduction is achieved at the remote ε-position of the original aldehyde. Complementary to the enamine-mediated activations, α,β-unsaturated aldehydes can also be efficiently functionalized by applying the diarylprolinol silyl ether system via conjugate addition through iminium-ion-mediated processes, that is, LUMO-activation. In such reactions, the aminocatalyst not only effectively shields one of the enantiotopic faces of the enal, it also ensures excellent chemoselectivity, affording 1,4-adducts as the only products. Several different carbon and heteroatom nucleophiles can be added in a highly stereoselective fashion. The ability of the catalysts to participate in various enamine- and iminium-ion-mediated processes also makes them ideal for the sequential addition of nucleophiles and electrophiles in a cascade manner. These cascade reactions thereby afford access to products having at least two stereocenters. In the years to come, the diarylprolinol silyl ether catalysts will probably maintain their prominent position as general catalysts in the field of aminocatalysis. Moreover, recent efforts devoted to mechanistic studies might soon engender further advances with this versatile catalytic system, particularly in the areas of activation modes, catalyst loadings, and industrial applications.     

Investigation of potential extreme load reduction for a two‐bladed upwind turbine with partial pitch

This paper presents a wind turbine concept with an innovative design combining partial pitch with a two‐bladed (PP‐2B) turbine configuration. Special emphasis is on extreme load reduction during storm situations at standstill, but operational loads are also investigated. In order to compare the loads and dynamics of the PP‐2B turbine, a partial pitch three‐bladed (PP‐3B) turbine and a normal pitch regulated three‐bladed (3B) turbine are introduced on the basis of solidity similarity scaling. From the dynamic comparisons between two‐ and three‐bladed turbines, it has been observed that the blade vibrations are transferred differently from the rotor to the tower. For a three‐bladed turbine, blade vibrations seen in a fixed frame of reference are split with ±1P only. A two‐bladed turbine has a similar split of ±1P but also includes contributions on higher harmonics (±2P, ±3P, … etc.). Further on, frequency split is also seen for the tower vibrations, where an additional ±2P contribution has been observed for the two‐bladed turbine. Regarding load comparisons, the PP‐2B turbine produces larger tower load variations because of 2P excitation during the operational cases. However, extreme loads are reduced by approximately 20% for the PP‐2B and 18% for the PP‐3B compared with the 3B turbine for the parked condition in a storm situation. Moreover, a huge potential of 60% is observed for the reduction of the extreme tower bottom bending moment for the PP‐2B turbine, when the wind direction is from ±90° to the turbine, but this also requires that the turbine is parked in a T‐configuration. © 2014 The Authors. Wind Energy published by John Wiley & Sons, Ltd.     

Technical Due Diligence: Study of Building Evaluation Practice

Technical due diligence (TDD) as an evaluation of the performance of constructed facilities has become an important new field of practice for consultants. Before the financial crisis started in autumn 2008, TDD represented the fastest growing activity in some consulting companies. TDD is usually carried out for buyers or sellers involved in real estate transactions. It can also be part of mergers, including real estate and other assets, or part of facilities management outsourcing. This paper is based on a case study and an interview survey of companies involved in TDD consulting in Denmark and Italy during 2009. The research identifies the current practice and compares it with the recommended practice in international guidelines. The current practice is very diverse and could, in many cases, be improved by a more structured approach and stricter adherence to international guidelines. However, the investigation of the current practice also identifies examples of value-adding practices, which can give the companies in question competitive advantages by differentiation and/or give input to improvements of the recommended practice guidelines.     

Activation effects during hydrogen release and uptake of MgH2

Scandium(II)hydride, ScH₂, and scandium(III)chloride, ScCl₃, are explored as additives to facilitate hydrogen release and uptake for magnesium hydride. These additives are expected to form more homogeneous composites with Mg/MgH₂ as compared to metallic scandium. However, scandium(III)chloride, reacts with MgH₂ during mechano-chemical treatment and form ScH₂ and MgCl₂ (that later crystallise during heat treatment). The composite MgH₂−ScH₂ was investigated using in-situ synchrotron radiation powder X-ray diffraction during up to five cycles of continuous release and uptake of hydrogen at isothermal conditions at 320, 400 and 450 °C and p(H₂) = 100–150 or 10⁻² bar. The data were analysed by Rietveld refinement and no reaction is observed between either MgH₂/ScH₂ or Mg/ScH₂ during cycling. The extracted sigmoidal shaped curves for formation or decomposition of Mg/MgH₂ suggest that a nucleation process is preceding the crystal growth. The reaction rate increases with increasing number of cycles of hydrogen release and uptake at isothermal conditions possibly due to activation effects. This kinetic enhancement is strongest between the first cycles and may be denoted an activation effect.     

Simple tool to evaluate the impact of daylight on building energy consumption

This paper presents a simple building simulation tool for integrated daylight and thermal analysis. The tool is capable of importing the thermal and visual properties for different glazings and shading positions from the Window Information System (WIS) program. A coupled ray-tracing and radiosity methodology is used to derive the daylight levels for different sky conditions. Both detailed daylight distribution for a particular day and time and hourly discrete values on a yearly basis may be obtained. For an integrated simulation the hourly daylight levels are fed into an existing simple thermal simulation program capable of calculating energy demand and the indoor environment. Straightforward control systems for general and task lighting systems have been implemented together with a shading control strategy that adjusts the shading according to the indoor operative temperature, the risk of glare and the profile angle of the sun. The implemented daylight calculation method allows for shades from the window recess and overhang, and for distant shades blocking the sky vault. Comparisons with the ray-tracing program Radiance show that the accuracy of this approach is adequate for predicting the energy implications of photoresponsive lighting control. The amount of input is small, which makes the tool useful for integrated daylight optimisation in the early design process.     

Characterizing delamination of fibre composites by mixed mode cohesive laws

A novel method is used for the determination of mixed mode cohesive laws and bridging laws for the characterisation of crack bridging in composites. The approach is based on an application of the J integral. The obtained cohesive laws were found to possess high peak stress values. Mixed mode cohesive stresses were found to depend on both the normal and tangential crack opening displacements. The bridging laws, which are to be used together with a mode mixity dependent crack tip fracture energy, were found to possess relative low bridging stresses; the peak normal bridging stress was approximately 2 MPa during pure Mode I and the maximum shear stress during pure Mode II was about 10 MPa.     

Heavy Metal and PAH Concentrations in Highway Runoff Deposits Fractionated on Settling Velocities

The correlation between settling velocity and associated pollutant concentrations is of major importance for best management practice in designing, redesigning, or evaluation of the efficiency of existing pond facilities for retaining unwanted pollutants. The prospect of this note is to state the relationship between the settling velocity of the runoff particles and the corresponding metal and polyaromatic hydrocarbon (PAH) concentration directly instead of dealing with two unknowns—the density and the shape of a single particle fraction in a settling velocity calculations. The measurements show that the highest cadmium, chromium, zinc, and nickel concentrations is associated with the most slowly falling particles and the lowest concentration associated within the faster falling fraction. This tendency is not clear for some of the sediments due to high content of organic matter and clearly not for lead and copper and there is no significant correlation between PAH concentration and settling velocity. The largest mass of metals and PAH within each pond can be found on the particle fraction with a settling velocity of 5.5–2.5 mm/s.     

Climate-change impacts on hydrology and nutrients in a Danish lowland river basin

The Mike 11-TRANS modelling system was applied to the lowland Gjern river basin in Denmark to assess climate-change impacts on hydrology and nitrogen retention processes in watercourses, lakes and riparian wetlands. Nutrient losses from land to surface waters were assessed using statistical models incorporating the effect of changed hydrology. Climate-change was predicted by the ECHAM4/OPYC General Circulation Model (IPCC A2 scenario) dynamically downscaled by the Danish HIRHAM regional climate model (25 km grid) for two time slices: 1961-1990 (control) and 2071-2100 (scenario). HIRHAM predicts an increase in mean annual precipitation of 47 mm (5%) and an increase in mean annual air temperature of 3.2 degrees C (43%). The HIRHAM predictions were used as external forcings to the rainfall-runoff model NAM, which was set up and run for 6 subcatchments within and for the entire, Gjern river basin. Mean annual runoff from the river basin increases 27 mm (7.5%, p<0.05) when comparing the scenario to the control. Larger changes, however, were found regarding the extremes; runoff during the wettest year in the 30-year period increased by 58 mm (12.3%). The seasonal pattern is expected to change with significantly higher runoff during winter. Summer runoff is expected to increase in predominantly groundwater fed streams and decrease in streams with a low base-flow index. The modelled change in the seasonal hydrological pattern is most pronounced in first- or second-order streams draining loamy catchments, which currently have a low base-flow during the summer period. Reductions of 40-70% in summer runoff are predicted for this stream type. A statistical nutrient loss model was developed for simulating the impact of changed hydrology on diffuse nutrient losses (i.e. losses from land to surface waters) and applied to the river basin. The simulated mean annual changes in TN loads in a loamy and a sandy subcatchment were, respectively, +2.3 kg N ha(-1) (8.5%) and +1.6 kg N ha(-1) (6.9%). The rainfall-runoff model and the nutrient loss model were chained with Mike 11-TRANS to simulate the combined effects of climate-change on hydrology, nutrient losses and nitrogen retention processes at the scale of the river basin. The mean annual TN export from the river basin increased from the control to the scenario period by 7.7%. Even though an increase in nitrogen retention in the river system of 4.2% was simulated in the scenario period, an increased in-stream TN export resulted because of the simulated increase in the diffuse TN transfer from the land to the surface-waters.     

Acute health effects from exposure to indoor ultrafine particles—A randomized controlled crossover study among young mild asthmatics

Particulate matter is linked to adverse health effects, however, little is known about health effects of particles emitted from typical indoor sources. We examined acute health effects of short-term exposure to emissions from cooking and candles among asthmatics. In a randomized controlled double-blinded crossover study, 36 young non-smoking asthmatics attended three exposure sessions lasting 5 h: (a) air mixed with emissions from cooking (fine particle mass concentration): (PM_2.5: 96.1 μg/m³), (b) air mixed with emissions from candles (PM_2.5: 89.8 μg/m³), and c) clean filtered air (PM_2.5: 5.8 μg/m³). Health effects (spirometry, fractional exhaled Nitric Oxide [FeNO], nasal volume and self-reported symptoms) were evaluated before exposure start, then 5 and 24 h after. During exposures volatile organic compounds (VOCs), particle size distributions, number concentrations and optical properties were measured. Generally, no statistically significant changes were observed in spirometry, FeNO, or nasal volume comparing cooking and candle exposures to clean air. In males, nasal volume and FeNO decreased after exposure to cooking and candles, respectively. Participants reported additional and more pronounced symptoms during exposure to cooking and candles compared to clean air. The results indicate that emissions from cooking and candles exert mild inflammation in asthmatic males and decrease comfort among asthmatic males and females.