Ground level concentration of some air pollutants from Nigeria thermal power plants

Power sector in Nigeria is undergoing structural reforms aimed at improving and expanding the current generation capacity, using thermal power plants. Ground level concentrations of air pollutants emitted from natural gas-powered thermal power plants were estimated using the American Meteorological Society-Environmental Protection Agency Regulatory Model (AERMOD). The average 24-h ground level concentrations of CO, NO_x, SO₂, particulate matter (PM), and volatile organic compounds (VOCs) were 31.88–72.79; 61.33–104; 0.61–3.91; 0.21–1.52; and 0.19–1.09 µg/m^3, respectively. There is need for continuous monitoring of ground level concentration of pollutants around the thermal power plants to guarantee the safety of the environment in the host communities.     

Influence of high rates of supplemental cooled EGR on NOx and PM emissions of an automotive HSDI diesel engine using an LP EGR loop

Previous experimental studies on diesel engine have demonstrated the potential of exhaust gas recirculation (EGR) as an in‐cylinder NO_x control method. Although an increase in EGR at constant boost pressure (substitution EGR) is accompanied with an increase in particulate matter (PM) emissions in the conventional diesel high‐temperature combustion (HTC), the recirculation of exhaust gases supplementary to air inlet gas (supplemental EGR) by increasing the boost pressure has been suggested as a way to reduce NO_x emissions while limiting the negative impact of EGR on PM emissions. In the present work, a low‐pressure (LP) EGR loop is implemented on a standard 2.0 l automotive high‐speed direct injection (HSDI) turbocharged diesel engine to study the influence of high rates of supplemental cooled EGR on NO_x and PM emissions. Contrary to initial high‐pressure (HP) EGR loop, the gas flow through the turbine is unchanged while varying the EGR rate. Thus, by closing the variable geometry turbine (VGT) vanes, higher boost pressure can be reached, allowing the use of high rates of supplemental EGR. Furthermore, recirculated exhaust gases are cooled under 50°C and water vapour is condensed and taken off from the recirculated gases. An increase in the boost pressure at a given inlet temperature and dilution ratio (DR) results in most cases an increase in NO_x emissions and a decrease in PM emissions. The result of NO_x–PM trade‐off, while varying the EGR rate at fixed inlet temperature and boost pressure depends on the operating point: it deteriorates at low load conditions, but improves at higher loads. Further improvement can be obtained by increasing the injection pressure. A decrease by approximately 50% of NO_x emissions while maintaining PM emission level, and brake specific fuel consumption can be obtained with supplemental cooled EGR owing to an LP EGR loop, compared with the initial engine configuration (HP moderately cooled EGR). Copyright © 2008 John Wiley & Sons, Ltd.     

Ecological efficiency in CHP: Biodiesel case

This paper evaluates and quantifies the environmental impact resulting from the combination of biodiesel fuel (pure or blended with diesel), and diesel combustion in thermoelectric power plants that utilize combined cycle technology (CC). In regions without natural gas, the option was to utilize diesel fuel; the consequence would be a greater emission of pollutants. Biodiesel is a renewable fuel which has been considerably interesting in Brazil power matrix in recent years. The concept of ecological efficiency, largely evaluates the environmental impact caused by CO₂, SO₂, NO_x and particle matter (PM) emissions. The pollution resulting from biodiesel and diesel combustion is analyzed, separately considering CO₂, SO₂, NO_x and particulate matter gas emissions, and comparing them international standards currently used regarding air quality. It can be concluded that it is possible to calculate the qualitative environmental factor, and the ecological effect, from a thermoelectric power plant utilizing central heat power (CHP) of combined cycle. The ecological efficiency for pure biodiesel fuel (B100) is 98.16%; for biodiesel blended with conventional diesel fuel, B20 (20% biodiesel and 80% diesel) is 93.19%. Finally, ecological efficiency for conventional diesel is 92.18%, as long as a thermal efficiency of 55% for thermoelectric power plants occurs.     

Ecological efficiency in thermoelectric power plants

This work evaluates the environmental impact resulting from the natural gas and diesel combustion in thermoelectric power plants that utilize the combined cycle technology (CC), as regarding to Brazilian conditions according to Thermopower Priority Plan (TPP). In the regions where there are not natural gas the option has been the utilization of diesel and consequentily there are more emission of pollutants. The ecological efficiency concept, which evaluates by and large the environmental impact, caused by CO₂, SO₂, NO_x and particulate matter (PM) emissions. The combustion gases of the thermoelectric power plants working with natural gas (less pollutant) and diesel (more pollutant) cause problems to the environment, for their components harm the human being life, animals and directly the plants. The resulting pollution from natural gas and diesel combustion is analyzed, considering separately the CO₂, SO₂, NO_x and particulate matter gas emission and comparing them with the in use international standards regarding the air quality. It can be concluded that it is possible to calculate thermoelectric power plant quantitative and qualitative environment factor, and on the ecological standpoint, for plant with total power of 41 441 kW, being 27 170 kW for the gas turbine and 14271 kW for the steam turbine. The natural gas used as fuel is better than the diesel, presenting ecological efficiency of 0.944 versus 0.914 for the latter, considering a thermal efficiency of 54% for the combined cycle.     

3‐E analysis of advanced power plants based on high ash coal

The objective of the study is to identify the ‘best’ possible power plant configuration based on 3‐E (namely energy, exergy, and environmental) analysis of coal‐based thermal power plants involving conventional (subcritical (SubC)) and advanced steam parameters (supercritical (SupC) and ultrasupercritical (USC)) in Indian climatic conditions using high ash (HA) coal. The analysis is made for unit configurations of three power plants, specifically, an operating SubC steam power plant, a SupC steam power plant, and the AD700 (advanced 700°C) power plant involving USC steam conditions. In particular, the effect of HA Indian coal and low ash (LA) reference coal on the performance of these power plants is studied. The environmental impact of the power plants is estimated in terms of specific emissions of CO₂, SO_x, NO_x, and particulates. From the study, it is concluded that the maximum possible plant energy efficiency under the Indian climatic conditions using HA Indian coal is about 42.3% with USC steam conditions. The results disclose that the major energy loss is associated with the heat rejection in the cooling water, whereas the maximum exergy destruction takes place in the combustor. Further, the sliding pressure control technique of load following results in higher plant energy and exergy efficiencies compared to throttle control in part‐load operation. Copyright © 2009 John Wiley & Sons, Ltd.     

Estimate of ecological efficiency for thermal power plants in Brazil

Global warming and the consequent climatic changes that will come as a result of the increase of CO₂ concentration in the atmosphere have increased the world’s concern regarding reduction of these emissions, mainly in developed countries that pollute the most. Electricity generation in thermal power plants, as well as other industrial activities, such as chemical and petrochemical ones, entail the emission of pollutants that are harmful to humans, animals and plants. The emissions of carbon oxides (CO and CO₂) and nitrous oxide (N₂O) are directly related to the greenhouse effect. The negative effects of sulfur oxides (SO₂ and SO₃ named SO_x) and nitrogen oxides (NO_x) are their contribution to the formation of acid rain and their impacts on human health and on the biota in general. This study intends to evaluate the environmental impacts of the atmospheric pollution resulting from the burning of fossil fuels. This study considers the emissions of CO₂, SO_x, NO_x and PM in an integral way, and they are compared to the international air quality standards that are in force using a parameter called ecological efficiency (ε).     

Methods for in-cylinder EGR stratification and its effects on combustion and emission characteristics in a diesel engine

The effects of in-cylinder EGR stratification on combustion and emission characteristics are investigated in a single cylinder direct injection diesel engine. To achieve in-cylinder EGR stratification, external EGR rates of two intake ports are varied by supplying EGR asymmetrically using a separated intake runner. The EGR stratification pattern is improved using a 2-step bowl piston and an offset chamfer at the tangential intake port. When high EGR gas is supplied to the left (tangential) port, a high EGR region is formed at the central upper region of the combustion chamber. Consequently, combustion is initiated in the low EGR region, and PM is reduced significantly. When high EGR gas is supplied to the right (helical) port, a high EGR region is formed at the lower periphery of the combustion chamber. Therefore, combustion is initiated in the high EGR region, and NO_x is reduced without PM penalty. Stratified EGR potentially reduces NO_x by maximum 45%, without penalties of performance and other emissions. A proper in-cylinder swirl with stratified EGR maximizes the effects and achieves simultaneous reduction of NO_x by 7% and PM by 23%. Moreover, the robustness of stratified EGR is evaluated under various operating conditions and injection strategies.     

A system performance and economics analysis of IGCC with supercritical steam bottom cycle supplied with varying blends of coal and biomass feedstock

In recent years, Integrated Gasification Combined Cycle Technology (IGCC) has been gaining popularity for use in clean coal power operations with carbon capture and sequestration. Great efforts have been continuously spent on investigating ways to improve the efficiency and further reduce the greenhouse gas emissions of such plants. This study focuses on investigating two approaches to achieve these goals. First, replace the traditional subcritical Rankine cycle portion of the overall plant with a supercritical steam cycle. Second, add biomass as co‐feedstock to reduce carbon footprint as well as SO_x and NO_x emissions. In fact, plants that use biomass alone can be carbon neutral and even become carbon negative if CO₂ is captured. Due to a limited supply of feedstock, biomass plants are usually small, which results in higher capital and production costs. In addition, biomass can only be obtained at specific times in the year, resulting in fairly low capacity factors. Considering these challenges, it is more economically attractive and less technically challenging to co‐gasify biomass wastes with coal. The results show that for supercritical IGCC, the net efficiency increases with increased biomass in all cases. For both subcritical and supercritical cases, the efficiency increases from 0% to 10% (wt.) biomass and decreases thereafter. However, the efficiency of the blended cases always remains higher than that of the pure‐coal baseline cases. The emissions (NO_x, SO_x, and effective CO₂) and the capital costs decrease as biomass ratio (BMR) increases, but the cost of electricity (CoE) increases with BMR due to the high cost of the biomass used. Finally, implementing a supercritical steam cycle is shown to increase the net plant output power by 13% and the thermal efficiency by about 1.6 percentage points (or 4.56%) with a 6.7% reduction in capital cost, and a 3.5% decrease in CoE. Copyright © 2013 John Wiley & Sons, Ltd.     

Experimental study on combustion of torrefied palm kernel shell (PKS) in oxy‐fuel environment

Oxy‐combustion of biomass can be a major candidate to achieve negative emission of CO₂ from a pulverized fuel (pf)‐firing power generation plants. Understanding combustion behavior of biomass fuels in oxy‐firing conditions is a key for design of oxy‐combustion retrofit of pulverized fuel power plant. This study aims to investigate a lab‐scale combustion behavior of torrefied palm kernel shell (PKS) in oxy‐combustion environments in comparison with the reference bituminous coal. A 20 kW_th‐scale, down‐firing furnace was used to conduct the experiments using both air (conventional) and O₂/CO₂ (30 vol% for O₂) as an oxidant. A bituminous coal (Sebuku coal) was also combusted in both air‐ and oxy‐firing condition with the same conditions of oxidizers and thermal heat inputs. Distributions of gas temperature, unburned carbon, and NO_x concentration were measured through sampling of gases and particles along axial directions. Moreover, the concentrations of SO_x and HCl were measured at the exit of the furnace. Experimental results showed that burnout rate was enhanced during oxy‐fuel combustion. The unburnt carbon in the flue gas was reduced considerably (~75%) during combustion of torrefied PKS in oxy‐fuel environment as compared with air‐firing condition. In addition, NO emission was reduced by 16.5% during combustion of PKS in oxy‐fuel environment as compared with air‐firing condition.     

Study on using hydrogen and ammonia as fuels: Combustion characteristics and NOx formation

This paper evaluates the potential of hydrogen (H₂) and ammonia (NH₃) as carbon‐free fuels. The combustion characteristics and NO_x formation in the combustion of H₂ and NH₃ at different air‐fuel equivalence ratios and initial H₂ concentrations in the fuel gas were experimentally studied. NH₃ burning velocity improved because of increased amounts of H₂ atom in flame with the addition of H₂. NH₃ burning velocity could be moderately improved and could be applied to the commercial gas engine together with H₂ as fuels. H₂ has an accelerant role in H₂–NH₃–air combustion, whereas NH₃ has a major effect on the maximum burning velocity of H₂–NH₃–air. In addition, fuel‐NO_x has a dominant role and thermal‐NO_x has a negligible role in H₂–NH₃–air combustion. Thermal‐NO_x decreases in H₂–NH₃–air combustion compared with pure H₂–air combustion. NO_x concentration reaches its maximum at stoichiometric combustion. Furthermore, H₂ is detected at an air‐fuel equivalence ratio of 1.00 for the decomposition of NH₃ in flame. Hence, the stoichiometric combustion of H₂ and NH₃ should be carefully considered in the practical utilization of H₂ and NH₃ as fuels. H₂ as fuel for improving burning performance with moderate burning velocity and NO_x emission enables the utilization of H₂ and NH₃ as promising fuels. Copyright © 2014 John Wiley & Sons, Ltd.     

Impact of EGR fraction on diesel engine performance considering heat loss and temperature‐dependent properties of the working fluid

Exhaust gas recirculation (EGR) to reduce feed gas NO_x emission is common practice in modern diesel engines. Dilution of the intake air with cooled recirculated exhaust gas limits the production of in‐cylinder NO_x due to a lowering of the adiabatic flame temperature and a reduction in oxygen content of the intake mixture. EGR also reduces the mixture‐averaged ratio of specific heats (γ) of the combustion charge leading to a reduction in the thermodynamic cycle efficiency. This trade‐off between minimizing NO_x production and maximizing cycle efficiency is of critical importance when calibrating EGR control schemes. Modeling tools that allow a quantitative analysis of this trade‐off can be very beneficial in tuning EGR systems over a range of operating conditions. In this study, the systematic development of a model that allows an assessment of the impact of EGR on three parameters, namely (a) the thermodynamic cycle efficiency, (b) the mixture temperatures during the cycle and (c) the mixture‐averaged γ, is presented. This is accomplished through a numerical solution of the energy equation while considering the effects of heat loss and temporally varying mixture‐averaged values of γ. Results for a simple phenomenological model relating fuel‐burn rate with EGR fraction and the impact of EGR fraction on NO_x reduction are also included. Copyright © 2008 John Wiley & Sons, Ltd.     

Reduction of greenhouse gas emission on a medium-pressure boiler using hydrogen-rich fuel control

The increasing emission of greenhouse gases from the combustion of fossil fuel is believed to be responsible for global warming. A study was carried out to probe the influence of replacing fuel gas with hydrogen-rich refinery gas (R.G.) on the reduction of gas emission (CO₂ and NO_x) and energy saving. Test results show that the emission of CO₂ can be reduced by 16.4% annually (or 21,500 tons per year). The NO_x emission can be 8.2% lower, or 75 tons less per year. Furthermore, the use of refinery gas leads to a saving of NT$57 million (approximately US$1.73 million) on fuel costs each year. There are no CO₂, CO, SO_x, unburned hydrocarbon, or particles generated from the combustion of added hydrogen. The hydrogen content in R.G. employed in this study was between 50 and 80 mol%, so the C/H ratio of the feeding fuel was reduced. Therefore, the use of hydrogen-rich fuel has practical benefits for both energy saving and the reduction of greenhouse gas emission.     

Determination of ecological efficiency in internal combustion engines: The use of biodiesel

This paper evaluates and quantifies the environmental impact from the use of some renewable fuels and fossils fuels in internal combustion engines. The following fuels are evaluated: gasoline blended with anhydrous ethyl alcohol (anhydrous ethanol), conventional diesel fuel, biodiesel in pure form and blended with diesel fuel, and natural gas. For the case of biodiesel, its complete life cycle and the closed carbon cycle (photosynthesis) were considered. The ecological efficiency concept depends on the environmental impact caused by CO₂, SO₂, NO_x and particulate material (PM) emissions. The exhaust gases from internal combustion engines, in the case of the gasoline (blended with alcohol), biodiesel and biodiesel blended with conventional diesel, are the less polluting; on the other hand, the most polluting are those related to conventional diesel. They can cause serious problems to the environment because of their dangerous components for the human, animal and vegetable life. The resultant pollution of each one of the mentioned fuels are analyzed, considering separately CO₂, SO₂, NO_x and particulate material (PM) emissions. As conclusion, it is possible to calculate an environmental factor that represents, qualitatively and quantitative, the emissions in internal combustion engines that are mostly used in urban transport. Biodiesel in pure form (B100) and blended with conventional diesel as fuel for engines pollute less than conventional diesel fuel. The ecological efficiency for pure biodiesel (B100) is 86.75%; for biodiesel blended with conventional diesel fuel (B20, 20% biodiesel and 80% diesel), it is 78.79%. Finally, the ecological efficiency for conventional diesel, when used in engines, is 77.34%; for gasoline, it is 82.52%, and for natural gas, it is 91.95%. All these figures considered a thermal efficiency of 30% for the internal combustion engine.     

LCI (Life cycle inventory) analysis of fuels and electricity generation in Singapore

This article offers a unique three-stage approach in LCI analysis for generating the environmental profile of electricity generation in Singapore. The first stage focuses on fuels delivered to Singapore, next on electricity generated from various types of power production plants. The third stage integrates the entire life cycle study. The final gate-to-gate results show that the total CO₂ emissions from the national grid are 455.6 kg CO₂ per MWh without any loss in transmission and 467.0 kg CO₂ per MWh with 2.5% losses. The results for the entire cradle-to-gate energy production are: 586.3 kg CO₂ per MWh without considering any losses and 601.0 kg CO₂ per MWh with 2.5% transmission loss. For the rest of the LCI, the cradle-to-gate results (per MWh) are kg 0.19 CO (carbon monoxide), 0.06 kg N₂O (nitrous oxide), 1.94–1.99 kg NO_x (nitrogen oxides), 2.94–3.01 kg SO_x (sulphur oxides), 0.064–0.066 kg VOC (volatile organic compounds) and 0.078–0.080 kg PM (particulate matters). From gate-to-gate, the results are 0.12 kg CO, 0.0016 kg N₂O, 1.42–1.46 kg NO_x, 2.56–2.62 kg SO_x, 0.033–0.034 kg VOC and 0.067–0.069 kg PM. Emissions of CO₂ from energy generation, climate change mitigation and policies for energy security are also discussed.     

Solid fuel burning in steady,strained, premixed flow fields: the graphite/air/methane system

A detailed numerical investigation was conducted on the simultaneous burning of laminar premixed CH₄/air flames and solid graphite in a stagnation flow configuration. The graphite and methane were chosen for this model, given that they are practical fuels and their chemical kinetics are considered as the most reliable ones among solid and hydrocarbon fuels, respectively. The simulation was performed by solving the quasi‐one‐dimensional equations of mass, momentum, energy, and species. The GRI 2.1 scheme was used for the gas‐phase kinetics, while the heterogeneous kinetics were described by a six‐step mechanism including stable and radical species. The effects of the graphite surface temperature, the gas‐phase equivalence ratio, and the aerodynamic strain rate on the graphite burning rate and NO_x production and destruction mechanisms were assessed. Results indicate that as the graphite temperature increases, its burning rate as well as the NO_x concentration increase. Furthermore, it was found that by increasing the strain rate, the graphite burning rate increases as a result of the augmented supply of the gas‐phase reactants towards the surface, while the NO_x concentration decreases as a result of the reduced residence time. The effect of the equivalence ratio on both the graphite burning rate and NO_x concentration was found to be non‐monotonic and strongly dependent on the graphite temperature. Comparisons between results obtained for a graphite and a chemically inert surface revealed that the chemical activity of the graphite surface can result in the reduction of NO through reactions of the CH₃, CH₂, CH, and N radicals with NO. Copyright © 2000 John Wiley & Sons, Ltd.     

Experimental study on combustion and pollutants emissions of oil sludge blended with microalgae residue

Experimental study on co-combustion of oil sludge (OS) and microalgae residue (MR) was conducted with a thermogravimetric analyzer and a designed fluidized bed reactor system. Combustion process of OS blended with MR could be divided into four stages, water evaporation, volatiles release and combustion, fixed carbon combustion and minerals decomposition. With MR ratio increasing, combustion performance of the mixture became better. MR addition can help improve the combustion performance of OS. NO_x and SO₂ concentrations increased firstly and then decreased with the increase of combustion temperature which ranged from 800 to 1100?°C. With the increase of excess air ratio α, NO_x and SO₂ emissions increased. Generally, NO_x and SO₂ emissions decreased with MR ratio increased at 800?°C, which is caused by the catalysis effect of ash and heavy metals in OS. OS blended with MR could both improve combustion performance and help reduce NO_x and SO₂ emissions during OS combustion, which provides an effective approach to massive synergistic disposal of waste resources.     

Experimental determination and analysis of CO2, SO2 and NOx emission factors in Iran’s thermal power plants

Emission factors of CO₂, SO₂ and NO_x emitted from Iran’s thermal power plants are fully covered in this paper. To start with, emission factors of flue gases were calculated for fifty thermal power plants with the total installed capacity of 34,863 MW over the period 2007–2008 with regard to the power plants’ operation characteristics including generation capacity, fuel type and amount and the corresponding alterations, stack specifications, analysis of flue gases and physical details of combustion gases in terms of g kWh⁻¹. This factor was calculated as 620, 2.57 and 2.31 g kWh⁻¹ for CO₂, SO₂ and NO_x respectively. Regarding these results, total emissions of CO₂, SO₂ and NO_x were found to be 125.34, 0.552 and 0.465 Tg in turn. To achieve an accurate comparison, these values were compared with their alternatives in North American countries. According to this comparison, emission factor of flue gases emitted from Iran’s thermal power plants will experience an intensive decline if renewable, hydroelectric and nuclear types of energy are more used, power plants’ efficiency is increased and continuous emission monitoring systems and power plant pollution reduction systems are utilized.     

Tributyl phosphate additive enhancing catalytic absorption of NO2 for simultaneous removal of SO2/NOx in wet desulfurization system

Removal of SO₂ and NO emissions from coal-fired power plants have always been the focus in coal's utilization industries for which traditional wet desulfurization system hold the potential to achieve simultaneous removal of SO₂/NO_x. In this work, a novel liquid catalyst (tributyl phosphate, TBP) was investigated for the simultaneous removal of SO₂ and NO_x in a NO pre-oxidation (ozone oxidation) assisted process. The absorption process and reaction mechanism of SO₂ and NO₂ were studied in a small-scale experimental system, and the removal efficiency of pollutant and the key parameters were examined in a pilot-scale system. The results show that the removal efficiency of NO₂ in traditional wet desulfurization system is only 20–40%; however greatly increases to >90% when TBP is added. Moreover, TBP can enhance the NO₂ removal performance in the presence of SO₂ due to the formation of TBP–NO₂–SO₃²⁻ complex. Considering the oily nature of TBP that can be easily separated, such addition strategy hold great potential for industrial SO₂/NO_x simultaneously removal.     

Ecological aspects concerning the combustion of lignite in Romanian thermopower plants

This paper focuses on the analysis of thermopower plants emissions with regard to a new indicator, SONOX (SO from SO₂ and NOX from NO_x), which is symbolized by Σ. Based on this method, analysis is accomplished for several Romanian thermopower plants fuelled by lignite.Conclusions are drawn concerning the possibilities of reduction of the reaction agents for desulphurisation of the flue gas exhausted by the thermopower plants.     

Environmental impact of alternative fuel mix in electricity generation in Malaysia

The Fuel Diversification Strategy was incorporated into the Malaysian National Energy Policy in order to achieve a more balanced consumption of fuel, namely gas, hydro, coal and petroleum. The objective of this paper is to evaluate changes in CO_2, SO₂ and NO_x emission due to changes in the fuel mix specified in the Fuel Diversification Strategy. Using the environmental extended Leontief's input–output framework it was found that the fuel mix as envisioned by the Fuel Diversification Strategy generates higher CO_2, SO₂ and NO_x emissions. As such, to ensure a sustainable energy policy, the proposed fuel mix must be accompanied by efficiency gain so that the negative impact on the environment could be mitigated.