Search

The development and performance in practice of a commercial automatically controlled wood stove is described. The digital control system controls the three combustion air inlets individually, based on the combustion phase, measured flue gas temperature, measured O2 outlet concentration and desired room temperature. The control system ensured a well-controlled combustion cycle with respect to temperature and oxygen concentration, yielding improved thermal efficiency and minimized carbon monoxide emissions. A minimum in CO emissions was identified for the oxygen operation range 10–13% O2. The improved performance has been verified by field tests in 5 private homes, demonstrating more stable and optimal O2 concentrations and temperatures compared to manual operation. This resulted in significant lower CO concentrations (up to 27%) alongside higher thermal efficiency (up to 20%) when comparing manually and automatically controlled wood stoves. This new technology has a great potential for improving the stove efficiency/biomass utilisation and reducing the emissions of pollutants at low altitude close to private homes.

The selective catalytic reduction (SCR) of NOx using NH3 was studied at pressures up to 5 bar over a vanadium-based SCR catalyst (~1 wt% V2O5 and 10 wt% WO3/TiO2), relevant for the installation of SCR reactors upstream of the turbocharger at marine engines. Experiments were performed using both granulated catalyst in a lab-scale fixed-bed reactor and a monolith catalyst in a bench-scale setup. The residence time across the catalytic bed was kept constant, by increasing the (normalized (0 °C, 1 atm)) volumetric flow rate proportionally to the pressure. The results show that for the granulated catalyst, the NOx conversion was independent of the pressure, indicating that the SCR kinetics are not affected by the increased pressure up to 5 bar. NH3 temperature-programmed desorption experiments showed that the catalyst NH3 adsorption increased with more than 30% when the pressure was increased from 1 bar to 4.5 bar. On the other hand, when the adsorption temperature was increased from 150 to 300 °C, the adsorption capacity decreased by approximately 60% independent on the pressure. The SCR reaction was unaffected by the increased NH3 uptake caused by the increased pressure, because only a certain fraction of the sites ( $$ {\theta}_{N{H}_3}^{\ast } $$ = 0.14) was found to be active in the SCR reaction, and these are filled up at lower NH3 partial pressure than the total number of sites. Experiments using a monolithic catalyst showed that at temperatures above 250 °C, the NOx conversion was lower at an increased pressure (3.1 bar) when the residence time was held constant. This decrease was ascribed to increased internal and external diffusion limitations at the elevated pressure.

Ammonia slip catalysts (ASC) are used downstream of the NH3-selective catalytic NOx reduction (SCR) system, to minimize ammonia slip from transport sector SCR units. The ASC may consist of an SCR active layer for NOx control, a layer with oxidation functionality for ammonia conversion, or a combination thereof, either as individual layers or as a single mixed layer. Mathematical models of such systems involve flow and mass transfer in the monolithic channels as well as coupled reaction/diffusion processes in the catalytic layers. In this work, we develop a single channel 1D-1D (pseudo 2D) steady-state tank-in-series mathematical model for monolithic ammonia slip catalysts with up to two layers. Kinetics of relevant reactions over the Cu-Beta zeolite and the Pt/TiO2 layer, including SCR, ammonia oxidation and the formation of N2O, were derived based on an extensive flow reactor study. The model was validated based on experiments using four different small-scale ASC monoliths, showing good agreement between the model predictions and the experimental results. Comparison of ten ASC configurations for the oxidation of 200 ppm NH3 at 300°C, show that configurations with a pure layer of NH3 oxidation catalyst, generate undesirable high N2O and NOx levels. The best ASC configurations feature fast diffusion in the catalytic layers (a high effective diffusion coefficient), a thin top layer loading with some ammonia oxidation catalyst, and a mixed layer of ammonia oxidation catalyst and the SCR catalyst to limit the formation of N2O and NOx.

The undesired oxidation of SO2 was studied experimentally at elevated pressures of up to 4.5 bar across two commercial vanadium-based (1.2 and 3 wt% V2O5) selective catalytic reduction (SCR) catalysts. This pressure range is of interest for preturbine SCR reactor configuration for NOx reduction on ships. The residence time in the catalyst was kept constant, independent on pressure, by adjusting the total flow rate. The conversion of SO2 was of the order 0.2–3% at temperatures of 300–400 °C and was independent of the pressure. Based on the measured conversion of SO2, the kinetics were fitted using an nth order rate expression. The reaction order of SO2 was found close to 1, and the reaction order of SO3 was found close to 0, also at increased pressures of up to 4.5 bar. The rate of SO2 oxidation was clearly promoted by the presence of 1000 ppm NOx at elevated pressure; however, at atmospheric pressure, the effect was within experimental uncertainty. The promoting effect is explained by a catalyzed redox reaction between SO2 and NO2, and since more NO2 is formed at elevated pressure, a higher degree of promotion by NOx is observed at elevated pressures.

Platinum-based oxidation catalysts applied for diesel exhaust aftertreatment constitute a significant part of system costs. Effective utilization of platinum is therefore relevant to reduce costs while retaining performance. To this end, the influence of Pt particle size on catalytic activity for CO, hydrocarbon, and NO oxidation was studied. 1 wt% Pt/Al2O3 catalysts were prepared by wet impregnation, drying, and different calcination and thermal treatments, yielding Pt particles with diameters between 1.3 and 18.7 nm, as determined by CO pulse titration and transmission electron microscopy. Activity measurements for CO, C3H6, and NO oxidation showed an optimal Pt particle size with respect to the mass based activity between 2 and 4 nm for all three reactions. From measured turnover frequencies and site statistics of Pt particles, the reactions appear to be mainly catalyzed by terrace atoms, which are most abundant between 2 and 4 nm. The decrease in catalytic activity for large Pt particles is therefore due to the diminishing Pt surface area, while the decrease in activity for small particles is due to the lack of terrace atoms required for CO, HC, and NO oxidation.

The release of chlorine (Cl) and sulfur (S) during biomass torrefaction and pyrolysis has been investigated via experiments in two laboratory-scale reactors: a rotating reactor and a fixed bed reactor. Six biomasses with different chemical compositions covering a wide range of ash content and ash-forming elements were torrefied/pyrolyzed in the temperature range of 150–500 °C. The relative release of chlorine and sulfur was calculated based on mass balance and analysis of the biomass before and after torrefaction. In selected cases, measurement of methyl chloride (CH3Cl) in the gas from straw torrefaction has furthermore been conducted. The release of chlorine from straw was first observed at 250 °C and peaked with about 60–70% at 350 °C. Analysis of the released gas showed that most of the chlorine was released as methyl chloride. Increasing the straw content in the reactor resulted in a lower fractional release of Cl, probably due to more reactive sites in contact with gas phase Cl species leading to se...

Foaming is a common phenomenon in industrial processes, including wet flue gas desulfurization (FGD) plants. A systemic investigation of the influence of two foaming agents, sodium dodecyl sulphate (SDS) and egg white albumin (protein), and two commercial antifoams on a wet FGD pilot plant operation has been carried out. Foaming caused by 0.03 g SDS/(L slurry) reduced the desulfurization degree from 84 to 74% and the solids and limestone concentrations of the slurry from 58 to 48 g/(L slurry) and from 1.4 to 1.0 g/(L slurry), respectively. These effects were attributed to the foaming transferring small particles to the foam layer present on top of the slurry in the holding tank. The addition of 0.03 g antifoams/(L slurry) to SDS foam eliminated the foam, but the desulfurization degree remained low. Potential mechanisms for the observed behavior are analyzed. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2382–2388, 2014

Different biomass types may differ with respect to torrefaction characteristics, and an improved understanding and ability to predict the torrefaction performance is, therefore, desired. In this study, the influence of the chemical properties (lignocellulose composition and alkali content) on the torrefaction behavior with respect to mass loss and grindability is investigated by simultaneous thermal analysis (STA) and by using a combined torrefaction and grinding reactor. The torrefaction behavior of six raw biomass samples and selected pretreated samples (washed and impregnated with KCl and K2CO3) has been studied. The investigated biomasses have reasonably similar carbohydrate compositions (hemicelluloses 18–25 wt % db; cellulose 38–48 wt % db; lignin 17–29 wt % db) with the exception of spruce bark, which is lower in hemicellulose content (12.9 wt % db) and cellulose content (24 wt % db), and higher in lignin content (36.8 wt % db). An increasing biomass potassium (K) content decreases the temperature ...

Combining torrefaction and grinding of biomass in one reactor may be an attractive fuel pretreatment process. A combined laboratory torrefaction and ball mill reactor has been constructed for studies of the influence of temperature and residence time on the product yields and particle size reductions of Danish wheat straw, spruce chips, and pine chips. On the basis of initial experiments, which evaluated the influence of reactor mass loading, gas flow, and grinding ball size and material, a standard experimental procedure was developed. The particle size reduction capability of the torrefaction process has been evaluated by the relative change in d50, and this method was compared to the Hardgrove grindability index (HGI), showing reasonably similar results. Significant differences in torrefaction behavior have been observed for straw and spruce chips torrefied at 270–330 °C. Torrefaction of straw for 90 min yielded a higher mass loss (27–60 wt %) and relative size reduction (59–95%) compared with spruce (...

Spontaneous foaming can cause a range of operational problems in industrial processes such as wet flue gas desulfurization (FGD). This work investigates the performance of selected antifoaming agents (Nalco FM-37, Foamtrol 2290, and rapeseed oil) on foams generated by egg white albumin (protein), sodium dodecyl sulfate, and adipic acid at conditions of relevance for wet FGD plants. The addition of antifoaming agents breaks any existing foam and causes an induction period without foaming, after which the foam gradually will begin to reappear. Foaming by egg white albumin (2 g/L) at 0.014 m/s could be controlled by both commercial antifoaming agents (6.4 g/L), but not by rapeseed oil addition. Foaming by pure commercial antifoaming agents has also been demonstrated: up to 7 × 10−2 m foam was observed with 6.4 g/L Nalco FM-37. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3741–3747, 2013

The utilization of bio-fuels, such as biodiesel, is expected to contribute significantly towards the planned 10% of renewable energy within the EU transport sector by 2020. Increased biodiesel blend percentages may change engine exit flue gas ash composition and affect the long-term performance of cleaning technologies, such as oxidation catalysts and diesel particulate filters. In this work the performance of a commercial catalyst has been studied for conversion of diesel particulate matter (SRM 2975) at 10% O 2 , in the presence of salts simulating ash species derived from engine oil and biodiesel. Simultaneous thermal analysis experiments of the diesel particulate matter showed that it was dominated by soot with approximately 10 wt.% condensed hydrocarbons. The presence of a commercial catalyst (5:1 wt. ratio of catalyst to soot), in tight contact with the diesel particulate matter, decreased the temperature at which the oxidation rate peaked from 662 ± 1 °C to 526 ± 19 °C. The introduction of biodiesel ash species such as Na 2 CO 3 , K 2 CO 3 or K 3 PO 4 decreased the peak conversion temperature further (422 ± 12; 404 ± 4 and 423 ± 7 °C), with a limited dependence on ash concentration. A deterioration in catalytic conversion, i.e. increased peak conversion temperatures, was seen for two engine oil ash species and one mixed ash species (from engine oil and biodiesel) – CaSO 4 (569 ± 6 °C), Ca(H 2 PO 4 ) 2 (699 ± 13 °C) and K 2 SO 4 (581 ± 16 °C). Kinetic parameters ( A and E a ), obtained from Arrhenius plots of the data, showed a lower activation energy in the presence of the commercial catalyst ( E a = 91 ± 5 kJ/mol) or CeO 2 ( E a = 62 ± 8 kJ/mol) compared to pure SRM 2975 ( E a = 220 ± 3 kJ/mol). The obtained kinetic data were able to describe the peak conversion temperature and the associated part of the mass loss curve, but an initial low-temperature gradual increase in conversion was not adequately described.

Wet flue gas desulphurization (FGD) plants with forced oxidation, installed at coal and oil fired power plants for removal of SO2(g), must produce gypsum of high quality. However, quality issues such as an excessive moisture content, due to poor gypsum dewatering properties, may occur from time to time. In this work, the particle size distribution, morphology, and filtration rate of wet FGD gypsum formed in a pilot-scale experimental setup, operated in forced oxidation mode, have been studied. The influence of holding tank residence time (10–408 h), solids content (30–169 g/L), and the presence of impurities (0.002 M Al2F6; 50 g quartz/L; 0.02 M Al3+, and 0.040 M Mg2+) were investigated. In addition, slurry from a full-scale wet FGD plant, experiencing formation of flat shaped crystals and poor gypsum dewatering properties, was transferred to the pilot plant to test if the plant would now start to produce low quality gypsum. The crystals formed in the pilot plant, on the basis of the full-scale slurry did, however, show acceptable filtration rates and crystal morphologies closer to the prismatic crystals from after pilot plant experiments with demineralized water. The gypsum slurry filtration rates were generally high, but a shorter residence time (10 h) and gypsum crystals experiencing breakage and/or attrition (408 h) showed slightly lower filtration rates. Both these experiments contained a higher fraction of fines, which may explain the slightly lower filtration rates. Crystals formed at a higher solids concentration and longer residence time (169 g/L and 120 h) showed a higher proportion of flat crystals, and the XRD pattern contained strong peaks at 31.1° (as the full-scale gypsum) and 29.1°, but no change in the filtration rate was obtained. It has not been possible in the pilot plant to form flat gypsum flakes with poor dewatering properties similar to those observed in full-scale plants.

In the present study the gypsum (CaSO 4 ·2H 2 O) quality at three full-scale wet flue gas desulphurisation (FGD) plants and a pilot plant were examined and compared. Gypsum quality can be expressed in terms of moisture content (particle size and morphology dependent) and the concentration of residual limestone and other impurities. The particle size distributions (PSD) in the holding tanks of the investigated plants were similar, apart from a slightly higher fraction of small particles in the full-scale plants. These high levels of small particles could originate from nucleation, attrition or accumulation of fly ash and impurities from the sorbent. The crystal morphology obtained in the pilot plant was columnar with distinct crystal faces as opposed to the rounded shapes found at the full-scale plants. All the investigated full-scale plants consistently produced high quality gypsum (High purity, low moisture content and low impurity content). An episode concerning a sudden deterioration in the gypsum dewatering properties was furthermore investigated, and a change in crystal morphology, as well as an increased impurity content (aluminium, iron and fluoride), was detected.

Oxy-fuel firing is a promising technology that should enable the capture and storage of anthropogenic CO2 emissions from large stationary sources such as power plants and heavy industry. However, this new technology has a high energy demand for air separation and CO2 compression and storage. Unresolved issues, such as determination of the optimal recycle location of flue gas, the flue gas cleaning steps required (SO2, NOx, and particles), and the impact of an oxy-fuel flue gas on the cleaning steps, also persist. The aim of this work was to study the performance of the wet flue gas desulfurization (FGD) process under operating conditions corresponding to oxy-fuel firing. The most important output parameters were the overall degree of desulfurization and the residual limestone concentration in the gypsum slurry. Pilot-scale experiments quantified that the introduction of a flue gas with 90 vol % CO2, at a holding tank pH 5.4, reduced the limestone dissolution rate significantly and thereby increased the re...

The aim of this work is to study the influence of nucleation, growth and breakage on the particle size distribution (PSD) of gypsum crystals produced by the wet flue gas desulfurization (FGD) process. The steady state PSD, obtained in a falling film wet FGD pilot plant during desulfurization of a 1000 ppm(v) SO2 gas stream, displayed a strong nonlinear behaviour (in a ln(n(l)) vs. l plot) at the lower end of the particle size range, compared to the well-known linear mixed suspension mixed product removal model. A transient population balance breakage model, fitted to experimental data, was able to model an increase in the fraction of small particles, but not to the extent observed experimentally. A three-parameter, size-dependent growth model, previously used for sodium sulphate decahydrate and potash alum, was able to describe the experimental data, indicating either size-dependent integration kinetics or growth rate dispersion. © 2009 American Institute of Chemical Engineers AIChE J, 2009

The objective of this work is to study the influence of particles, electrolytes, and buffers on the foaming ability of wet flue gas desulfurization (FGD) slurries. Foaming within this industrial process has been associated with a range of operational problems, as well as an increased degree of absorption. The foaminess of selected process parameters has been assessed, systematically, using laboratory-scale Bikerman experiments. Adipic acid alone, as well as a combination of small particles and an electrolyte, have been demonstrated to generate weak transient foams (with a Bikerman coefficient (Σ) of ≤7 s), that potentially can interfere with process monitoring equipment. Additional experiments with a wet FGD pilot plant showed an increased absorption efficiency of sulfur dioxide (SO2) by a tap water solution with small quartz particles and calcium chloride (CaCl2), compared to a solution of pure tap water.

Single droplet combustion characteristics has been investigated for bio-oil slurries, containing biomass residue, and compared to conventional fuels for pulverized burners, such as fuel oil (start up) and wood chips (solid biomass fuel). The investigated fuels ignition delays and pyrolysis behavior was tested in a single particle reactor at conditions relevant for suspension firing (A: 1200 °C, 5.5 % O2; B: 1200 °C, 2.9 % O2 and C: 990 °C, 5.5 % O2). The slurries were tested to optimize the bio-oil composition for use as an alternative power plant start-up fuel. Pyrolysis times for 5 mg bio-oil samples (app. dp 1 mm) were generally in a similar range (1300 to 2700 ms) as fuel oil, (app 1800 ms) and wood blocks (app 2400 ms), within the 600 ms standard deviation. The 5 different bio-oil slurries samples showed considerable data variability, indicating some extent of sample heterogeneity. With respect to the ignition delay, the bio-oils were in contrast to the fuel oil (125±70 ms), associated with either a longer ignition delay or an ignition phase with sporadic gas phase ignitions (350 to 1050 ms with no stable flame), which could be a cause for concern for a start-up fuel, due to flame lift above the nozzles and thereby decreased flame stability. Most promising were oil or diesel (not palm oil) containing slurries (1 and 5) with heating values in the range of 15 MJ/kg.

Et forskningsprojekt mellem HWAM A/S og DTU Kemiteknik har førttil udvikling af mere energieffektive og miljøvenlige brændeovne. Projektet – der er et EUDP-projekt – har bidraget til, at HWAM A/S har introduceret den første digitale styrede brændeovn på markedet.