Assessment of gaseous,PM and trace element emissions from a 300-MW lignite-fired boiler unit for various fuel qualities

Modeling of effects of fuel quality on the emissions of major pollutants (NO_x, SO₂, CO₂ and PM) and eight trace elements (As, Co, Cr, La, Mo, Ni, Sb and U) from a 300-MW boiler unit fired with Thai lignite was the main focus of this study. The NO_x and SO₂ emission models were validated with the use of experimental data. Emission rates and specific emissions (per MW h) of the major pollutants and trace elements were quantified by including efficiencies of the flue gas desulphurization system and electrostatic precipitators in the computations. As shown in this work, the contributions of 300-MW boiler units fired with Thai lignite to the “greenhouse” and “acid rain” gas emissions in the region are significant. Additionally, substantial amounts of hazardous As, Cr and Ni are emitted from the boiler units into the atmosphere via fly ash particles.     

Electron beam flue gas treatment (EBFGT) technology for simultaneous removal of SO2 and NOx from combustion of liquid fuels

Electron beam flue gas treatment technology was applied for removal of SO₂ and NO_x from flue gas, emitted from combustion of high-sulfur fuel oils. The detailed study of this process was performed in a laboratory by irradiating the exhaust gas from the combustion of three grades of Arabian fuels with an electron beam from accelerator (800 keV, max. beam power 20 kW). SO₂ removal is mainly dependent on ammonia stoichiometry, flue gas temperature and humidity and irradiation doses up to 8 kGy. NO_x removal depends primarily on irradiation dose. High removal efficiencies up to 98% for SO₂ and up to 82% for NO_x were obtained under optimal conditions. The flue gas emitted from combustion of high-sulfur fuel oils, after electron beam irradiation, meets the stringent emission standards for both pollutants. The by-product, which is a mixture of ammonium sulphate and nitrate, can be used as a fertilizer as such or blended with other components to produce commercial agricultural fertilizer.     

Absorption enhanced reforming of lignite integrated with molten carbonate fuel cell

A technical-economic assessment of an innovative system which integrates absorption enhanced reforming (AER) of lignite with molten carbonate fuel cell (MCFC) for electricity generation is investigated using the ECLIPSE process simulator.The simulation results show that the proposed system of combining AER with MCFC has the electricity output of 206 kW, with the electrical efficiency of 44.7% (low heating value – LHV) and CO₂ emissions of 751 g/kW h, when fuelled with lignite. The system has a specific investment (SI) of £11 642 and a break even electricity selling price (BESP) 21 p/kW e, compared to the SI of £10 477 and the BESP of 19 p/kW e for the basic case of MCFC fuelled with natural gas.A sensitivity analysis of the break even selling price (BESP) of electricity and the specific investment (SI) versus the capital cost show that capital costs have a significant effect on BESP and SI. Based on the basic case of capital cost of £2 398 000, when the capital cost of the system reduces 50%, the relevant BESP lowers down to 10.8 p/kW e, the SI also reduces by 50%, to £5864/kW e.A sensitivity analysis of fuel cost versus BESP show that the fuel cost has a little effect on BESP. For the basic case of the system with the cost of lignite £20/ton, the BESP is 21.1 p/kW e. While the fuel cost reduces by 50%, to £10/ton, the BESP lower down to 20.9 p/kW e, only reduces 0.2 p/kW e, the change is 0.9%.Although the BESP and SI are high for the AER + MCFC system, there are no nitrogen oxides (NO_x) and sulphur oxides (SO_x) emissions from the system; the CO₂ gas stream produced in the AER process is suitable for subsequent sequestration. Thus the combination system may become a power generation with zero greenhouse gas emissions.     

Impact of support oxide and Ba loading on the NOx storage properties of Pt/Ba/support catalysts: CO2 and H2O effects

A series of 1 wt.%Pt/_xBa/Support (Support = Al₂O₃, SiO₂, Al₂O₃-5.5 wt.%SiO₂ and Ce_0.7Zr_0.3O₂, x = 5–30 wt.% BaO) catalysts was investigated regarding the influence of the support oxide on Ba properties for the rapid NO_x trapping (100 s). Catalysts were treated at 700 °C under wet oxidizing atmosphere. The nature of the support oxide and the Ba loading influenced the Pt–Ba proximity, the Ba dispersion and then the surface basicity of the catalysts estimated by CO₂-TPD. At high temperature (400 °C) in the absence of CO₂ and H₂O, the NO_x storage capacity increased with the catalyst basicity: Pt/20Ba/Si < Pt/20Ba/Al5.5Si < Pt/10Ba/Al < Pt/5Ba/CeZr < Pt/30Ba/Al5.5Si < Pt/20Ba/Al < Pt/10BaCeZr. Addition of CO₂ decreased catalyst performances. The inhibiting effect of CO₂ on the NO_x uptake increased generally with both the catalyst basicity and the storage temperature. Water negatively affected the NO_x storage capacity, this effect being higher on alumina containing catalysts than on ceria–zirconia samples. When both CO₂ and H₂O were present in the inlet gas, a cumulative effect was observed at low temperatures (200 °C and 300 °C) whereas mainly CO₂ was responsible for the loss of NO_x storage capacity at 400 °C. Finally, under realistic conditions (H₂O and CO₂) the Pt/20Ba/Al5.5Si catalyst showed the best performances for the rapid NO_x uptake in the 200–400 °C temperature range. It resulted mainly from: (i) enhanced dispersions of platinum and barium on the alumina–silica support, (ii) a high Pt–Ba proximity and (iii) a low basicity of the catalyst which limits the CO₂ competition for the storage sites.     

Comparisons of pulverized coal combustion in air and in mixtures of O2/CO2

Pulverized coal combustion in air and the mixtures of O₂/CO₂ has been experimentally investigated in a 20 kW down-fired combustor (190 mm id×3 m). Detailed comparisons of gas temperature profiles, gas composition profiles, char burnouts, conversions of coal–N to NO_x and coal–S to SO₂ and CO emissions have been made between coal combustion in air and coal combustion in various O₂/CO₂ mixtures. The effectiveness of air/oxidant staging on reducing NO_x emissions has also been investigated for coal combustion in air and O₂/CO₂ mixtures. The results show that simply replacing the N₂ in the combustion air with CO₂ will result in a significant decrease of combustion gas temperatures. However, coal combustion in 30% O₂/70% CO₂ can produce matching gas temperature profiles to those of coal combustion in air while having a lower coal–N to NO_x conversion, a better char burnout and a lower CO emission. The results also confirm that air/oxidant staging is very effective in reducing NO_x emissions for coal combustion in both air and a 30% O₂/70% CO₂ mixture. SO₂ emissions are proved to be almost independent of the combustion media investigated.     

Optimization of coal reburning in a 1 MW tangentially fired furnace

This paper deals with an experimental study on the influence of coal reburn on NO_x reduction efficiency, unburned carbon in fly ash and the furnace temperature distribution along the height in a 1 MW (heat input power) tangentially firing furnace with multiple low NO_x control technologies. Several variables associated with the reburn system have been investigated in the experiment which includes the air stoichiometry in reburn zone, the location of reburn burner and reburn coal fineness. The optimum location of reburn nozzles has been found where NO_x reduction efficiency is highest. With the decrease of reburn coal size (average diameter from 53.69 μm to 11.47 μm), NO_x reduction efficiency increases slightly, but the burnout performance of coal is improved noticeably. In the process of coal reburning, the temperature of flue gas is 70–90 °C lower in primary combustion, but 130–150 °C higher at the top of furnace as compared to baseline.     

Experimental study on effects of operating conditions and fuel quality on thermal efficiency and emission performance of a 300-MW boiler unit firing Thai lignite

This paper presents the results of an experimental study on a 300-MW boiler unit fired with Thai lignite. Effects of operating conditions (excess air ratio and unit load) and fuel quality on the boiler heat losses and thermal efficiency as well as on the gaseous (CO₂, CO, NO_x and SO₂) and particulate matter (PM) emissions from the boiler unit are discussed. The boiler thermal efficiency was weakly affected by the excess air ratio, unit load and fuel lower heating value, varying from 90.3 to 92.3% for wide ranges of the above variables. In all the tests, the NO_x, SO₂ and PM emissions were below the national emission standards for these pollutants. Quite low level of the SO₂ emission was secured by the high-efficiency flue gas desulphurization system. The CO emissions of rather small values were detected only at extremely low excess air ratios. The emission rate and specific emission (i.e. per MWh of electricity produced) for NO_x, SO₂ and CO were quantified using experimental emission concentrations of the pollutants. Meanwhile, the emission characteristics for CO₂ were determined with the use of fuel-C and fuel consumption by the boiler. In addition, the emission rate and specific emission for PM were estimated by taking into account the actual fuel-ash content and fuel consumption by the boiler, as well as the effects of SO₂ adsorption by fly ash in the boiler gas ducts and overall ash-collecting efficiency of the electrostatic precipitators and flue gas desulphurization system. Elevated CO₂ and NO_x emissions from the 300-MW boiler units firing Thai lignite are of great concern.     

Effects of emulsification variables on fuel properties of two- and three-phase biodiesel emulsions

Biodiesel has attractive fuel properties such as excellent biodegradability and lubricity, almost no emissions of sulfur oxides, PAH and n-PAH, reduced CO₂, PM and CO emission, superior combustion efficiency, etc. However, burning of biodiesel generally produces higher levels of NO_x emissions, primarily due to its high oxygen content. In this study, the emulsification technology has been considered to reduce the NO_x emission level of fossil fuel. Biodiesel, produced by means of transesterification reaction accompanied with a peroxidation process, was emulsified to form two-phase W/O and three-phase O/W/O emulsions. The effects of the emulsification variables such as hydrophilic lipophilic balance (HLB), and water content on the fuel properties and emulsion characteristics of W/O and O/W/O emulsions were investigated in this study. The experimental results show that the surfactant mixture with HLB = 13 produced the highest emulsification stability while HLB = 6 produced the lowest emulsification stability and the most significant extent of water–oil separation among the various HLB values for O/W/O biodiesel emulsion. The kinematic viscosity, specific gravity and carbon residual of the biodiesel emulsions were larger than those of the neat biodiesel. In addition, the W/O biodiesel emulsion was found to have a smaller mean droplet size, lower volumetric fraction of the dispersed phase than the O/W/O biodiesel emulsion, and the highest heating value among the test fuels, if the water content is deducted from the calculation of the heating value.     

Soot oxidation on a catalytic NOx trap: Beneficial effect of the Ba–K interaction on the sulfated Ba,K/CeO2 catalyst

The Ba,K/CeO₂ catalyst is active both for NO_x trapping and soot combustion. In this work we report a Ba–K interaction that prevents K sulfation when NO_x is present, thus preserving the activity of K towards soot combustion during the working period of the trap. This effect is originated in the K₂SO₄(s) + Ba(NO₃)₂(s) → 2KNO₃(s) + BaSO₄(s) reaction, which is thermodynamically favored. In the absence of NO_x, the soot combustion reaction is strongly depressed by SO₂ whereas when NO_x is present both the sulfated and the non-sulfated catalysts present similar TPO patterns.     

The effects of fuel characteristics and engine operating conditions on the elemental composition of emissions from heavy duty diesel buses

The effects of fuel characteristics and engine operating conditions on elemental composition of emissions from twelve heavy duty diesel buses have been investigated. Two types of diesel fuels – low sulfur diesel (LSD) and ultra low sulfur diesel (ULSD) fuels with 500 ppm and 50 ppm sulfur contents respectively and 3 driving modes corresponding to 25%, 50% and 100% power were used. Elements present in the tailpipe emissions were quantified by inductively coupled plasma mass spectrometry (ICPMS) and those found in measurable quantities included Mg, Ca, Cr, Fe, Cu, Zn, Ti, Ni, Pb, Be, P, Se, Ti and Ge. Multivariate analyses using multi-criteria decision making methods (MCDM), principal component analysis (PCA) and partial least squares (PLS) facilitated the extraction of information about the structure of the data. MCDM showed that the emissions of the elements were strongly influenced by the engine driving conditions while the PCA loadings plots showed that the emission factors of the elements were correlated with those of other pollutants such as particle number, total suspended particles, CO, CO₂ and NO_x. Partial least square analysis revealed that the emission factors of the elements were strongly dependent on the fuel parameters such as the fuel sulfur content, fuel density, distillation point and cetane index. Strong correlations were also observed between these pollutants and the engine power or exhaust temperature. The study provides insights into the possible role of fuel sulfur content in the emission of inorganic elements from heavy duty diesel vehicles.     

Exhaust emissions of a H2-enriched heavy-duty diesel engine equipped with cooled EGR and variable geometry turbocharger

This paper investigates the impact of hydrogen (H₂) addition on the exhaust emissions of a 2004 Mack MP7 355E heavy-duty diesel engine. As expected, the addition of H₂ reduced substantially the emissions of particulate matter (PM), unburned hydrocarbon (HC), and carbon dioxide (CO₂). However, the effects of H₂ addition on the emissions of carbon monoxide (CO) and oxides of nitrogen (NO_x) depended on the amount of H₂ added and engine load. For measurements using the 13-mode European Stationary Cycle (ESC), the addition of 2% and 4% H₂ (vol.% in intake mixture) increased substantially the nitrogen dioxide (NO₂) emissions but reduced the emissions of nitric oxide (NO). The addition of H₂ only minimally affected NO_x emissions. The detailed effects of H₂ addition on the exhaust emissions were investigated for various loads at 1200 rpm. The addition of H₂ at low load mildly influenced NO_x emissions, with the exception of 10% load. Adding over 4% H₂ at 10% load began to reduce NO_x emissions. When operated at medium to high loads, the addition of a relatively small amount of H₂ slightly reduced NO_x emissions. The expected increase in NO_x emissions was observed only with the addition of a large amount of H₂ at medium to high loads. When operated at full load, the addition of H₂ had a negligible effect on NO_x emissions. In a few cases, a minor change in H₂ flow rate suddenly increased NO_x emissions. By further increasing or reducing the amount of H₂ added, NO_x emissions resumed to the expected values. This discrepancy was attributed to the unexpected change in the flow rate of the recirculated exhaust gas. Based on the data obtained, it seems infeasible to substantially reduce the exhaust emissions of this diesel engine through the addition of a small amount of H₂ such as that produced on-board using a small H₂O electrolyzer, or diesel fuel reformer.     

Preferential CO oxidation over activated carbon supported catalysts in H2-rich gas streams containing CO2 and H2O

Selective CO oxidation (PROX) was studied at 423 K over 1% Pt–0.25% SnO_x and 1% Pt–1% CeO_x catalysts supported on un-oxidized and oxidized activated carbon (AC) using feed mixtures simulating the reformate coming from fuel processors. Effects of the addition of 15% CO₂ or (15% CO₂ + 10% H₂O) into feed mixtures containing 1% CO, 1% O₂, 60% H₂ and He were determined for nine different AC-supported catalysts, and the results were compared with those obtained with pure H₂-rich feed. Unlike other PROX catalysts having oxide supports, introduction of CO₂ into pure feed drastically increased CO conversion on all nine catalysts supported on oxidized or un-oxidized AC regardless of impregnation strategy.1% Pt–0.25% SnO_x supported on HNO₃-oxidized AC stands out as a potential candidate for commercial use in PROX since it yields 100% CO conversion under realistic feed conditions. 1% Pt–1% CeO_x catalysts prepared by sequential or co-impregnation and supported on air-oxidized AC also give 100% CO conversion in H₂-rich feed containing (CO₂ + H₂O) during extended run times and hence hold promise as PROX catalysts.     

Regeneration of sulfur-poisoned CeO2 catalyst for NH3-SCR of NOx

The effects of regeneration on the activities and structure of CeO₂ catalysts for NH₃-SCR of NO_x have been studied in this article. CeO₂ catalyst is deactivated by SO₂ for NH₃-SCR of NO_x in a 200 h long-term operation at 350 °C due to the formation of sulfates, and its NO_x conversion decreases from 100% to 83% gradually. However, sulfates can be removed from sulfur-poisoned CeO₂ catalysts under high temperature thermal treatment in air. After regeneration, NO_x conversion of sulfur-poisoned CeO₂ catalyst is recovered to about 100% at 350 °C. Moreover, the regeneration temperature is related to the nature of the sulfates formed on the sulfur-poisoned CeO₂ catalysts.     

NOx removal by low-cost char pellets: Factors influencing the activity and selectivity towards NOx reduction

The activity of potassium-containing char pellets prepared from different low-cost carbon precursors towards NO_x reduction in an oxygen-rich environment has been investigated by isothermal reactions at 325 °C. From the overall data, it can be asserted that high potassium content is a key factor in allowing carbon-based pellets to achieve better NO_x reduction capacities whilst exhibiting higher selectivity to NO_x reduction and inhibiting carbon burn-off, but the intrinsic characteristics of the carbon precursor must also be taken into account (mineral matter content, carbon nature…).Having chosen the most appropriate formulation for pellet preparation (high potassium content and suitable carbon precursor, a metallurgical coke), the 3HT-C pellets demonstrated the most promise for consideration for NO_x removal. This sample, when tested as a packed bed of pellets at 325 °C, gave more moderate and very constant NO_x reduction rates in combination with very high selectivity towards NO_x. On the other hand, when tested at 400–450 °C, very high and constant NO_x reduction rates were achieved, with decreased but still acceptable selectivity. Reaction data from a lifetime test were not significantly worse than those from a 2 h reaction, which is very encouraging. Neither was sample efficiency compromised in the lifetime test, in which only 18% (maximum) of oxygen was consumed compared with 84.1% (maximum) NO_x converted.     

Effects of WO3 doping on stability and N2O escape of MnOx–CeO2 mixed oxides as a low-temperature SCR catalyst

MnO_x–WO_x–CeO₂ catalysts synthesized using a sol–gel method were investigated for the low-temperature NH₃-SCR reaction. Among them, W_0.1Mn_0.4Ce_0.5 mixed oxides exhibited above 80% NO_x conversion from 140 to 300 °C. In addition, this catalyst exhibited high stability and CO₂ tolerance in a 50 h activity test at 150 °C. Substantially reduced N₂O production and enhanced N₂ selectivity were achieved by WO₃ doping, which was due to the weakened reducibility and increased number of acid sites. The decreased SO₂ oxidation activity as well as the reduced formation of ammonium and manganese sulfates resulted in a high SO₂ resistance of this catalyst.     

Loss of NOx storage capacity of Pt–Ba/Al2O3 catalysts due to incorporation of phosphorous

This work aims at determining the effect of the incorporation of P on NO_x storage capacity by NO_x storage-reduction (NSR) catalysts. Different amounts of phosphorous were deposited on a Pt–Ba/Al₂O₃ catalyst (1 wt% Pt and 17 wt% Ba) by impregnation of a phosphate salt. Samples were calcined at 723 K and characterized using X-ray diffraction (XRD), N₂ adsorption isotherms and X-ray photoelectron spectroscopy (XPS). Their NO_x storage capacity was also measured. It was observed that storage capacity decreased almost linearly with the P/Ba ratio and besides at a phosphorous concentration P/Ba ratio of <0.1 deterioration was low. At higher P concentrations (P/Ba ratio = 0.7) the NO_x storage was significantly reduced. It is proposed that the cause of the decline in NO_x retention capacity would be the formation of Ba–P phases (very likely Ba phosphates) at the expense of Ba carbonate or Ba oxide. These new phases would be unable to exchange NO_x.     

Continuous hydrothermal synthesis of Ca1−xSrxTiO3 solid-solution nanoparticles using a T-type micromixer

In this work, a continuous hydrothermal synthesis method in supercritical water was applied to environmentally benign production of Ca_1−xSr_xTiO₃ (x = 0.0–1.0) solid-solution nanoparticles as key materials in conducting, electric, magnetic, and photocatalytic fields. A T-type micromixer (330 μm id) was introduced for rapid heating of stating solutions of Ca(NO₃)₂, Sr(NO₃)₂, and TiO₂ sol using turbulent flow mixing with preheated NaOH aqueous solution and also for exact control of reaction temperature. At 673 K and 30 MPa for 5.0 s mean residence time, Ca_1−xSr_xTiO₃ solid-solution nanoparticles having crystallite diameters of around 20 nm with monomodal diameter distributions were obtained without byproducts and production of CaTiO₃ and SrTiO₃ separately over the whole composition range. Effects of NaOH molality, Ca and Sr compositions in the starting solutions, and mean residence time on the reaction were examined. The results showed that TiO₂ sol dissolution and Ca_1−xSr_xTiO₃ precipitation were almost finished within 0.25 s mean residence time, and after that Ostwald ripening proceeded.     

Biodiesel production from tall oil with synthesized Mn and Ni based additives: Effects of the additives on fuel consumption and emissions

In this study, biodiesel fuel and fuel additives were produced from crude tall oil that is a by-product in the pulp manufacturing by craft or sulphate pulping process. Fatty acids and resinic acids were obtained from crude tall oil by distillation method. Tall oil methyl ester (biodiesel) was produced from fatty acids. Resinic acids were reacted with NiO and MnO₂ stoichiometrically for production of metallic fuel additives. Each metallic fuel additive was added at the rate of 8 μmol/l and 12 μmol/l to make mixtures of 60% tall oil methyl ester/40% diesel fuel (TE60) for preparing test fuels. Metallic fuel additives improved properties of biodiesel fuels, such as pour point and viscosity values. Biodiesel fuels were tested in an unmodified direct injection diesel engine at full load condition. Specific fuel consumption of biodiesel fuels increased by 6.00%, however, in comparison with TE60, it showed trend of decreasing with adding of additives. Exhaust emission profile of biodiesel fuels improved. CO emissions and smoke opacity decreased up to 64.28% and 30.91% respectively. Low NO_x emission was also observed in general for the biodiesel fuels.     

Characterization and optimization of an autothermal diesel and jet fuel reformer for 5 kWe mobile fuel cell applications

The present paper describes the characterization of an autothermal reformer designed to generate hydrogen by autothermal reforming (ATR) from commercial diesel fuel (～10 ppm S) and jet fuel (～200 ppm S) for a 5 kW_e polymer electrolyte fuel cell (PEFC). Commercial noble metal-based catalysts supported on 900 cpsi cordierite monoliths substrates were used for ATR with reproducible results. Parameters investigated in this study were the variation of the fuel inlet temperature, fuel flow and the H₂O/C and O₂/C ratios. Temperature profiles were studied both in the axial and radial directions of the reformer. Product gas composition was analyzed using gas chromatography.It was concluded from the experiments that an elevated fuel inlet temperature (≥60 °C) and a higher degree of fuel dispersion, generated via a single-fluid pressurized-swirl nozzle at high fuel flow, significantly improved the performance of the reformer. Complete fuel conversion, a reforming efficiency of 81% and an H₂ selectivity of 96% were established for ATR of diesel at P = 5 kW_e, H₂O/C = 2.5, O₂/C = 0.49 and a fuel inlet temperature of 60 °C. No hot-spot formation and negligible coke formation were observed in the reactor at these operating conditions. The reforming of jet fuel resulted in a reforming efficiency of only 42%. A plausible cause is the coke deposition, originating from the aromatics present in the fuel, and the adsorption of S-compounds on the active sites of the reforming catalyst.Our results indicate possibilities for the developed catalytic reformer to be used in mobile fuel cell applications for energy-efficient hydrogen production from diesel fuel.     

Experimental investigation and mathematical modelling of wood combustion in a moving grate boiler

The use of biomass to generate energy offers significant environmental advantages for the reduction in emissions of greenhouse gases. The main objective of this study was to investigate the performance of a small scale biomass heating plant: i.e. combustion characteristics and emissions. An extensive series of experimental tests was carried out at a small scale residential biomass heating plant i.e. wood chip fired boiler. The concentrations of CO, NO_x, particulate matter in the flue gas were measured. In addition, mathematical modelling work using FLIC and FLUENT codes was carried out in order to simulate the overall performance of the wood fired heating system. Results showed that pollutant emissions from the boiler were within the relative emission limits. Mass concentration of CO emission was 550-1600 mg/m³ (10% O₂). NO_x concentration in the flue gas from the wood chips combustion varied slightly between 28 and 60 ppmv. Mass concentration of PM₁₀ in the flue gas was 205 mg/m³ (10% O₂) The modelling results showed that most of the fuel was burnt inside the furnace and little CO was released from the system due to the high flue gas temperature in the furnace. The injection of the secondary air provided adequate mixing and favourable combustion conditions in the over-bed chamber in the wood chips fired boiler. This study has shown that the use of wood heating system result in much lower CO₂ emissions than from a fossil fuel e.g. coal fired heating system.