Large Coal-fired Power Station Research Articles

Evaluation of chemical stabilisation methods of coal-petcoke fly ash to reduce the mobility of Mo and Ni against environmental concerns

Reducing the potential leaching of Mo and Ni from the fly ash (FA) of petroleum coke is an increasingly important issue as Asia and Europe’s demand is expected to drastically intensify as continuing urbanisation and technological innovation demands ever more electricity. In the present study, we investigated coal combustion products (CCP) from a large coal-fired power station fed with a 56:44 coal/petroleum coke blend. Results revealed that leachable concentrations of Mo and Ni from FA were in the upper non-hazardous limit and in the inert limit, respectively (2003/33/EC). Whilst common prevention measures for Mo and Ni based on the adsorption capacity of boiler slag (BS), a mixture of BS: goethite, and jarosite, were considered insufficient to reduce the potential leaching of Mo into FA leachates, a novel chemical stabilisation method based on an aggregate product of portlandite and FA immobilised both Mo and Ni such that the resulting concentrations were below the limits established in the abovementioned 2003 EC Decision. Precipitation may be responsible for the fixation of Mo and Ni in the FA: portlandite aggregates as Ca(MoO4) and NiMoO4, respectively. The findings of this novel study support the use of this aggregate to reduce FA pollutants, which will be of particular interest to nations that remain largely coal/petroleum coke-dependant.

Study on Energy Requirement for CO2 Capture with Aqueous Ammonia Solution

As a CO2 absorber, ammonia solution has a good application prospect. However, the high energy consumption of the process of removing CO2 by ammonia water will bring a significant reduction in the power generation efficiency and a significant increase in the cost of power generation when it is used in coal-fired power plants. In this paper, the energy consumption of CO2 removal process with ammonia solution is studied, through parameter optimization, process design and absorbent improvement, the energy consumption of ammonia decarbonization process is reduced. Economic analysis of ammonia decarbonization system is done when it is used in large coal-fired power station.

Analysis of hourly generation patterns at large coal-fired units and implications of transitioning from baseload to load-following electricity supplier

Several factors have led to the decline of electricity generation from coal over the past decade, and projections forecast high rates of growth for wind and solar technologies in coming years. This analysis uses hourly generation data from large coal-fired power stations to determine how operations have been modified in recent years and describes the implications of these changes for plant equipment and unit reliability. The data shows increasing variability in intraday generation output that affects nearly all of the units in the sample, but the magnitude of increase varies widely among plants. Outage patterns were examined as was the relationship between renewable energy growth in a region and the changes in coal plant operations. Aggregate direct and indirect costs associated with running coal plants as load-following units have not yet been quantified in large-scale studies on a sector-wide basis, largely due to differences in how specific equipment responds to output fluctuations. Due to findings from the hourly generation data analysis and the high degree of potential impact on coal plant equipment, the study suggests the development of a new modeling tool that will represent the costs of running coal-fired power plants at lower capacity factors.

Climate change and hydropower in the Southern African Power Pool and Zambezi River Basin: System-wide impacts and policy implications

This paper examines climate change impact on hydropower will affect the expansion of the regional electricity system, as well as system costs and greenhouse gas emissions. The output from major Zambezi hydropower plants could decline by 10–20% under a drying climate, while wetting of the basin produces only a marginal increase. At a regional level, the increases in electricity generation costs are relatively small (less than 1% over the long term), but could reach 20–30% in the near term for hydro-dependent countries (e.g. Mozambique and Zambia). Because some hydropower could be displaced by coal, regional greenhouse gas emissions could increase by the equivalent of a large coal-fired power station. The risks to regional electricity systems highlight the need for strong cooperative governance arrangements to manage shared water resources in the region, which could be bolstered by recent political initiatives. Beyond the level of individual investments, a policy shift is needed to integrate climate change and upstream development considerations into national and regional electricity planning, supported by relevant tools. In addition, the potential for increased carbon emissions has implications for the commitments of southern African countries under the Paris Agreement to the UNFCCC.

Short introspections regarding the sawdust briquetting as sustainable solution for the environment

Wood pellets have only become an important part of this boom in the past few years. Owners of large coal-fired power stations in Europe started searching for a way to fulfill the new regulations and to find a solution for the declining economic relevance of traditional coal-fired power stations due to their high carbon dioxide emissions. The answer was to give the old dirty giants a green coat of paint by “co-firing” regular coal power plants with wood pellets. Wood pellets have similar burning qualities to traditional coal and the costs of converting boilers to burn wood pellets are low. The idea of declaring wood pellets as a carbon neutral energy source was based on the assumption that the released emissions of carbon dioxide during the burning process are neutralized by the carbon that is captured and stored in newly growing trees. The idea of using wood as a renewable source was backed by environment organizations. More recent pellet investment projects as well as facilities currently under construction show that the production of wood pellets is being outsourced by the energy firms to companies specialized in wood pellet production. These firms are 100-percent focused on sourcing the raw material, operating the wood pellet production plant and handling the logistics for transporting the renewable resource.

Estimating greenhouse gas emissions associated with achieving universal access to electricity for all households in South Africa

Climate change, energy security and achieving universal electricity access for all households are all pressing issues that South Africa must address. These objectives need not be trade-offs, however, and achieving electricity access for the poor does not justify the building of large coal-fired power stations or threaten South Africa’s climate change objectives. This paper estimates the electricity demand from the residential sector to 2020 resulting from universal access, and finds that electricity for low-income households would constitute only a small addition to total electricity demand and would represent only a minor portion of output from the coal-fired power station, Medupi. Furthermore, emissions from the additional electricity consumed by newly connected households would have a negligible impact on South Africa’s emissions profile.

Co-firing Bosnian coals with woody biomass: Experimental studies on a laboratory-scale furnace and 110 MWe power unit

This paper presents the findings of research into cofiring two Bosnian cola types, brown coal and lignite, with woody biomass, in this case spruce sawdust. The aim of the research was to find the optimal blend of coal and sawdust that may be substituted for 100% coal in large coal-fired power stations in Bosnia and Herzegovina. Two groups of experimental tests were performed in this study: laboratory testing of co-firing and trial runs on a large-scale plant based on the laboratory research results. A laboratory experiment was carried out in an electrically heated and entrained pulverized-fuel flow furnace. Coal-sawdust blends of 93:7% by weight and 80:20% by weight were tested. Co-firing trials were conducted over a range of the following process variables: process temperature, excess air ratio and air distribution. Neither of the two coal-sawdust blends used produced any significant ash-related problems provided the blend volume was 7% by weight sawdust and the process temperature did not exceed 1250?C. It was observed that in addition to the nitrogen content in the co-fired blend, the volatile content and particle size distribution of the mixture also influenced the level of NOx emissions. The brown coal-sawdust blend generated a further reduction of SO2 due to the higher sulphur capture rate than for coal alone. Based on and following the laboratory research findings, a trial run was carried out in a large-scale utility - the Kakanj power station, Unit 5 (110 MWe), using two mixtures; one in which 5%/wt and one in which 7%/wt of brown coal was replaced with sawdust. Compared to a reference firing process with 100% coal, these co-firing trials produced a more intensive redistribution of the alkaline components in the slag in the melting chamber, with a consequential beneficial effect on the deposition of ash on the superheater surfaces of the boiler. The outcome of the tests confirms the feasibility of using 7%wt of sawdust in combination with coal without risk to the efficiency of the unit, its combustion process and with the benefits of emissions reductions. Furthermore, they show that no modification to the existing coal transport system and boiler equipment is necessary to achieve this outcome.

Mercury wet deposition and coal-fired power station contributions: An Australian study

Regions that have large coal-fired power station regions may be prone to elevated mercury (Hg) deposition fluxes. Total mercury (THg) in daily rainfall samples at a near-field sampling site (Hunter Valley) and a far-field station (Sydney) has been monitored in this study employing ultra-clean sampling techniques and Cold Vapour Atomic Fluorescence Spectrometry (CVAFS) analysis. Measurements of THg range from 0.9 to 16.5 and from 1.2 to 18.9 ng/L for the far-field and near-field sites respectively. Average daily THg wet deposition fluxes were 49.9 and 79.8 ng/m 2 for the far and near-field sites respectively. A two-sample t-test reveals the near-field site to have higher rainfall mercury (significant at the 95% level) and deposition fluxes. At the far-field site, lower Hg deposition occurs during the cooler months, while the Hunter Valley site has higher winter deposition. It is believed that the higher winter values near-field may be due to the combined impact of prevailing wind direction and high pollutant build up brought on by lower mixing height. Based on this study, the first in the Southern Hemisphere, we conclude that rainfall THg concentrations and Hg wet deposition fluxes at the two sites are comparable to rural sites in North America.

Seasonal evaluation and spatial variability of suspended particulate matter in the vicinity of a large coal-fired power station in India?A case study

Coal combustion in the power sector gives rise to the emission of primary and secondary particulate pollutants. Since the emission of pollutants depends on coal quality and combustion technology, and given that transport, transformation and deposition of contaminants depend on regional climatic conditions, specific studies for the power stations is needed to evaluate their environmental impacts. Monitoring of ambient respirable suspended particulate matter (RSPM) and suspended particulate matter (SPM) levels around a large coal-fired power station in India was carried out. The specific objectives were the determination of spatial and seasonal variability in RSPM and SPM levels, and their relationship with meteorological parameters such as wind velocity and relative humidity. The results have shown a marked seasonal trend and spatial variability in RSPM and SPM levels in the study area. Higher concentrations of ambient RSPM and SPM were found in downwind monitoring stations compared to upwind direction. Ratios of RSPM to SPM and correlation coefficient values between RSPM and SPM along with meteorological parameters were also worked out. Relative humidity and wind velocity have shown an inverse relation with particulate deposition pattern.

A case study of spatial variation and enrichment of selected elements in ambient particulate matter around a large coal-fired power station in Central India

The dominant use of coal in power sectors has been associated with adverse environmental impacts. Ambient air monitoring for the two size fractions of particulate matter, respirable suspended particulate matter (RSPM) and non-respirable suspended particulate matter (NRSPM) in the downwind and upwind directions of a large coal-fired power station in central India, was carried out. Collected samples of ambient particulate matter were analysed atomic absorption spectrophotometrically for 15 elements. Spatial variability in elemental composition of RSPM and NRSPM and the degree of enrichment of these toxic metals in RSPM were investigated. A significant spatial variability for the elements in RSPM and NRSPM and higher degrees of enrichment of the elements were observed.

Wet-only sequential deposition in a rural area in north-eastern Spain

The present work summarises the results of a 2-year study of wet-only sequential deposition in 2 rural areas (Alcanñiz and Morella) located at different distances from a large coal-fired power station. Precipitation chemistry was characterised by relatively high, SO42-, Ca2+ and NH+4 average concentrations. Sequential study of single precipitation events showed that concentrations of most of the ions studied decreased exponentially throughout single precipitation events, with a sharper decrease in concentrations at the beginning of the event. Usually, 40 to 80% of the wet-only deposition of major ions occurred in the first 2 mm. pH measurements, ranging from 5.6 to 8.1, showed a decrease in the pH values throughout a precipitation event. Deposition levels of Ca2+ and NH+4 accounted for the neutralisation of major acidic species in the precipitation events except in 5 rain episodes sampled at Morella. The sequential study of the evolution of the (SO2-4 + NO-3)/(Ca2+ + NH+4) ratio during a single precipitation allowed us to identify potential acidic rainfall fractions after an initial volume of precipitation, after most of the Ca2+ in atmospheric particles had been scavenged. A higher neutralisation capacity was deduced for Alcanñiz owing to the higher atmospheric levels of natural carbonates and NH+4.

A novel prototype design for a transformer for high voltage, high frequency, high power use

A prototype transformer has been designed and built which is novel in its combination of high voltage (50 kV), high frequency (20 kHz) and high power (25 kVA) specifications. The design technique utilized a spreadsheet approach which facilitated an iterative design procedure. The transformer used a ferrite core, nylon insulated secondary bobbins and pressurized sulfur hexafluoride encapsulation. It was designed as part of a high-voltage switched-mode power supply for driving electrostatic precipitators. The transformer was field tested at a large coal-fired power station and was found to have an efficiency of better than 98%.

Bulk deposition in a rural area located around a large coal-fired power station, northeast Spain

This work focuses on bulk deposition in a rural area located around a large coal-fired power station in northeast Spain. Deposition chemistry was characterised by high concentrations of SO42−, Ca2+ and NH4+, which were relatively high when compared with other rural areas. Monthly bulk deposition evolution of major ions was the result of two superimposed patterns: one pattern related to the volume of precipitation and the other showed the seasonal influence of the major ionic sources. A major local origin was attributed to bulk deposition of SO42−, NH4+, and Ca2+, whereas a relatively higher contribution of an external source was deduced for NO3−, Na+ and Cl−. The SO42− concentrations showed a significant correlation with the local SO2 emissions. High levels of Ca2+ were due to the high alkalinity of soils in the study area, although an external origin was attributed to the frequent air mass intrusions from the Sahara. Sources of NH4+ were related to intensive livestock farming in the area. Total suspended particles exert a marked influence over bulk deposition and neutralisation. Thus, despite the high emissions of SO2 in the area, neutral pH values have always been attained given that the concentrations of Ca2+ and NH4+ account for the total neutralisation of NO3− and SO42−.

99/02270 Seasonal evolution of suspended particles around a large coal-fired power station: particulate levels and sources: Querol, X. et al. Atmos. Environ., 1998, 32, (11), 1963–1978

99/02270 Seasonal evolution of suspended particles around a large coal-fired power station: particulate levels and sources: Querol, X. et al. Atmos. Environ., 1998, 32, (11), 1963–1978

Rapid computation of the exit temperature of hot combustion gases flowing inside chimneys

This paper addresses the practical calculation of the thermal performance of industrial chimneys by means of recent results in forced convection heat transfer. Aside from its use in the estimation of static draft, the magnitude of the mean bulk temperature of combustion gases at the chimney exit is a key ingredient for the estimation of levels of air pollution in the vicinity of the stack. In addition, and depending on fuel and process characteristics, the wall temperature should be high enough to avoid acid condensation on the inner lining. The temperature decay of the combustion gases is a result of heat transfer processes involving both internal forced convection and external heat transfer to the surroundings. The coupling of these mechanisms renders highly difficult its accurate simulation. Possibly due to this fact, the analysis of the problem is scarcely treated in the energy- and environmental-related literature. Thermal design and performance estimations of chimneys are therefore based on engineering rules of thumb dictated by experience. The aim of this paper is to introduce rigorous heat transfer results into the subject, but from a framework accessible to design engineers. To this end, a 1-D lumped model of this kind of situations is used [1]. Although largely simplified, the model provided adequate estimates of the mean bulk temperatures when compared with those computed with a 2-D distributed model [2], thus satisfying the requirements of simplicity and accuracy for the present purpose. The paper describes the design criteria for thermal calculation of industrial chimneys, the application of the 1-D lumped model through the use of standard heat transfer correlations, and several examples. The sequence of calculations is easy to accomplish and it is explained in such a way that it can be directly employed by engineers engaged in the thermal design of tall chimneys. Comparison with experimental data measured at the stack of a large coal-fired power station is also discussed.

98/04244 Seasonal evolution of suspended particles around a large coal-fired power station: chemical characterization

The use of zeolitic material synthesized from coal fly ash for the immobilization of pollutants in contaminated soils was investigated in experimental plots in the Guadiamar Valley (SW Spain). This area was affected by a pyrite slurry spill in April 1998. Although reclamation activities were completed in a few months, residual pyrite slurry mixed with soil accounted for relatively high leachable levels of trace elements such as Zn, Pb, As, Cu, Sb, Co, Tl and Cd. Phytoremediation strategies were adopted for the final recovery of the polluted soils. The immobilization of metals had previously been undertaken to avoid leaching processes and the consequent groundwater pollution. To this end, 1100 kg of high NaP1 (Na6[(AlO2)6(SiO2)10] · 15H2O) zeolitic material was synthesized using fly ash from the Teruel power plant (NE Spain), in a 10 m3 reactor. This zeolitic material was manually applied using different doses (10 000–25 000 kg per hectare), into the 25 cm topsoil. Another plot (control) was maintained without zeolite. Sampling was carried out 1 and 2 years after the zeolite addition. The results show that the zeolitic material considerably decreases the leaching of Cd, Co, Cu, Ni, and Zn. The sorption of metals in soil clay minerals (illite) proved to be the main cause contributing to the immobilization of these pollutants. This sorption could be a consequence of the rise in pH from 3.3 to 7.6 owing to the alkalinity of the zeolitic material added (caused by traces of free lime in the fly ash, or residual NaOH from synthesis).

Seasonal evolution of suspended particles around a large coal-fired power station: particulate levels and sources

The present work focuses on the seasonal evolution of suspended particles (TSP and PM10) around the Teruel power station in NE Spain. The specific objectives are the determination of the spatial and time variability of levels of suspended particles, and their relationship with the power plant emissions and other natural or anthropogenic (local or external) particulate sources. The results show a marked seasonal trend, along the study period (July 1995–August 1996) which is characterized by particulate levels that were higher in spring–summer and decreased progressively towards winter. This trend may be related to (a) higher summer oxidation which increased levels of secondary particles, (b) higher convective circulation in summer which raised levels of soil-related particles and anthropogenic particles, (c) higher frequency of intrusion episodes of Sahara air masses in summer and spring, and (d) lower aerosol scavenging potential in summer. The similarity between the seasonal evolutions of daily mean levels of SO2 and particulates is due to the fact that both are partially controlled by the solar cycle. The long range transport particulate inputs affecting this area of the Mediterranean Basin (mainly Sahara air mass intrusions) account for major particulate peaks recorded at the monitoring stations. The influence of the emissions from the power plant in the PM10 and TSP levels is evidenced only in periods with a low background particulate levels. The results demonstrate that even PM10 levels are still highly influenced by the Saharian and European particulate inputs. Therefore, for an accurate environmental assessment, probably PM2.5 should be monitored instead of TSP or PM10, in order to quantify the influence of the power plant emissions on the bulk atmospheric particulate levels. The results obtained from the air back-trajectory analysis and their comparison with the time series of daily PM10 levels allowed the classification of the major external particulate inputs as a function of the particulate levels.

Seasonal evolution of suspended particles around a large coal-fired power station: Chemical characterization

Abstract The present work focuses on the seasonal evolution of total suspended particles (TSP) around the Teruel power station in Northeastern Spain. The results show a marked seasonal trend, along the sampling period (July 1995–July 1996), which is characterized by levels of the elements studied in TSP that were higher (up to one order of magnitude) in spring-summer and decreased progressively towards winter. This trend contrasts with the seasonal evolution reported by most of the studies carried out in industrial and urban areas in Central and Northern Europe. The origin of this seasonal TSP trend may be related to: (a) higher summer oxidation which increased levels of secondary TSP; (b) higher convective circulation in summer which raised levels of soil-related particles and primary anthropogenic particles; (c) higher frequency of intrusion episodes of Sahara air masses in summer and spring; and (d) lower aerosol scavenging potential in summer. A clear grain-size fractionation was observed for the different ions determined. SO 4 2− and NH 4 + were concentrated in the finest grain-size fraction (0.3−0.6 μm); NO 3 −, Cl −, K +, Mg 2+, Na + and minor amounts of NH 4 + were concentrated in the 1.2−5.0 μm fractions; and Ca 2+ increased with the particle diameter. S-bearing species were (NH 4) 2SO 4 (mascagnite), (NH 4) 2Ca(SO 4) 2 · H 2O (koktaite) and CaSO 4 · 2H 2O (gypsum). Mascagnite was the dominant species in the finest grain size fraction (0.3−0.6 μm), whereas koktaite was also present in the 0.6−1.2 μm fraction, and gypsum predominated in the other fractions.

Does environmental impact assessment really support technological change? Analyzing alternatives to coal-fired power stations in Denmark

Danish energy policy calls for development of decentralized, cleaner technologies to replace conventional power stations and, since 1990, aims to reduce CO 2 emissions in 2005 to 20% below their 1988 level. These political goals require a technological change, from conventional, central power stations to cleaner, decentralized technologies such as energy conservation, cogeneration, and renewable energy. In principle, environmental impact assessment (EIA) supports this change on a project-by-project basis. The EU directive on EIA (European Council 1985) was based on the preventive principle: to eliminate pollution source rather than attempting to counteract it subsequently. According to the Danish implementation of the directive, an EIA must review a project's main alternatives and the environmental consequences of the alternatives. If this were done properly, EIAs could assist Denmark in meeting its CO 2 reduction goals. However, because EIA is implemented on a restricted, regional basis, it does not support technological change. Responsibility for the preparation of the EIA is given to the regional authorities through a law which does not require alternatives to be assessed that extend geographically beyond the boundaries of a regional authority. Thus, there is no certainty of serious analysis of cleaner technology alternatives to large coal-fired power stations. This conclusion is based on examination of three case studies using a participatory research method.

Trace element contents in atmospheric suspended particles: inferences from instrumental neutron activation analysis

This study focuses on the determination of trace element concentrations in total suspended particles by instrumental neutron activation analysis (INAA) in two different areas in Northeastern Spain (a rural area influenced by the emissions of a large coal-fired power station, and the urban and industrial areas of Castellon). Total suspended particles were sampled by means of standard MCV high- and medium-volume captors, using cellulose membrane filters of 0.8 and 0.45 μm pore size. Preliminary research was performed on the homogeneous distribution of elements in the sample filters and on the study of blank filters for the calculations of the background average element contents. The results obtained allowed to distinguish different major anthropogenic sources of trace elements in the atmosphere at the sampling sites: a) Zr, Hf, Sc, U and Th are related to atmospheric pollution derived from the ceramic industry of the Castellon area; b) As, Cr, Cs, Rb, Sb, Se, Zn are related to traffic and other industrial emission in the Castellon area, and As, Cr, Sb and Zn to power generation emissions in the rural area.