Capital and Operating Costs of Selected Air Pollution Control Systems—IV

Previous articles in this series discussed the equipment costs of control devices, gas conditioning equipment, hoods, ductwork, and dampers. In this article, the discussion will concern the fans and associated components required to convey the gas stream from the initial pollutant source to the control device.     

Impaction and Particle Bounce at High Stokes Numbers

The information in this paper is directed to those concerned with controlling SO₂ emissions from power plants, and particularly with retrofitting controls onto existing plants. The paper describes an FGD system based on the dolomitic lime process and the scrubber design that have proved successful at the Colstrip plant in eastern Montana. A single scrubber vessel sized to treat all the gas from a 350-MWe coal-fired unit combines the functions of prequenching, absorption, washing, mist elimination, and recycle storage. Downflow Injection of gas along the vessel centerline and regulation of gas flow by the wash tray make the gas velocity uniform and permit scaling up to this large size. A high concentration of dissolved alkalinity in the scrubbing slurry provides rapid absorption and permits low L/G—40 gal/1000 acf—when coal with 2.5% sulfur is burned. Complete oxidation of sulfite makes gypsum of wallboard quality and the process can discharge clarified liquor low in COD if necessary to control chlorides. Since only the single scrubber vessel and the recycle pumps must be located close to the back end of the boiler, the system is particularly well suited for retrofit applications.     

VOC Recovery through Microwave Regeneration of Adsorbents: Comparative Economic Feasibility Studies

ABSTRACT

Microwave regeneration of adsorbents facilitates the recovery of volatile organic compounds (VOCs) by decoupling the bed heating from the stripping gas. This makes possible the creation of a highly-concentrated regeneration effluent from which the VOCs can be recovered by condensation at near-ambient temperatures. The economic feasibility of two novel microwave-regenerated adsorption systems was evaluated by systematically comparing the capital and operating costs of the proposed systems with 10 conventional VOC control technologies. The microwave systems were found to have similar capital and operating costs to conventional steam regeneration systems and, therefore, may present an attractive alternative for recovering water-miscible solvents. In general, the cost of the microwave subsystem is a relatively small component of the overall system costs, and the microwave power requirements are within the range of commercially available generators, even for large emission streams.     

Determination of chlorinated paraffins in sediments from the Firth of Clyde by gas chromatography with electron capture negative ionisation mass spectrometry and carbon skeleton analysis by gas chromatography with flame ionisation detection

Short chain chlorinated paraffins (SCCPs) are a group of persistent organic pollutants (POPs) of increasing concern, but are to date not widely investigated in the environment, largely due to the challenges involved in their quantification. Here, SCCPs were quantified in marine sediments from the Firth of Clyde, Scotland, by gas chromatography with electron capture negative ionisation mass spectrometry (GC-ECNIMS) and through carbon skeleton analysis by gas chromatography with flame ionisation detection (GC-FID), and the analytical challenges encountered are discussed. Concentrations in the sediments ranged from 0.4 to 69 μg kg⁻¹ when determined by GC-ECNIMS, and from 5.6 to 379 μg kg⁻¹ when determined by GC-FID. For 8 out of 11 samples, analysis by GC-FID gave higher results than analysis by GC-ECNIMS. Unexpected aspects of the analysis, such as the presence of high concentrations of longer chain chlorinated paraffins in the samples, are also presented.     

Influence of alumina coating on characteristics and effects of SiO2 nanoparticles in algal growth inhibition assays at various pH and organic matter contents

Silica nanoparticles (NPs) belong to the industrially most important NP types. In a previous study it was shown that amorphous SiO(2) NPs of 12.5 and 27.0 nm are stable in algal growth inhibition assays and that their ecotoxic effects are related to NP surface area. Here, it was hypothesized and demonstrated that an alumina coating completely alters the particle-particle, particle-test medium and particle-algae interactions of SiO(2) NPs. Therefore, stability and surface characteristics, dissolution, nutrient adsorption and effects on algal growth rate of both alumina coated SiO(2) NPs and bare SiO(2) NPs in OECD algal test medium as a function of pH (6.0-8.6) and natural organic matter (NOM) contents (0-12 mg C/l) were investigated. Alumina coated SiO(2) NPs aggregated in all media and adsorbed phosphate depending on pH and NOM concentration. On the other hand, no aggregation or nutrient adsorption was observed for the bare SiO(2) NPs. Due to their positive surface charge, alumina coated SiO(2) NPs agglomerated with Pseudokirchneriella subcapitata. Consequently, algal cell density measurements based on cell counts were unreliable and hence fluorescent detection of extracted chlorophyll was the preferred method. Alumina coated SiO(2) NPs showed lower toxicity than bare SiO(2) NPs at concentrations ≥46 mg/l, except at pH 6.0. At low concentrations, no clear pH effect was observed for alumina coated SiO(2) NPs, while at higher concentrations phosphate deficiency could have contributed to the higher toxicity of those particles at pH 6.0-6.8 compared to higher pH values. Bare SiO(2) NPs were not toxic at pH 6.0 up to 220 mg/l. Addition of NOM decreased toxicity of both particles. For SiO(2) NPs the 48 h 20% effect concentration of 21.8 mg/l increased 2.6-21 fold and a linear relationship was observed between NOM concentration and effective concentrations. No effect was observed for alumina coated SiO(2) NPs in presence of NOM up to 1000 mg/l. All experiments point out that the alumina coating completely altered NP interactions. Due to the difference in surface composition the SiO(2) NPs, which had the smallest surface area, were more toxic to the alga than the alumina coated SiO(2) NPs. Hence, surface modification can dominate the effect of surface area on toxicity.     

Four Decades of Plant Community Change in the Alpine Tundra of Southwest Yukon,Canada

Repeat measurements from long-term plots provide precise data for studying plant community change. In 2010, we visited a remote location in Yukon, Canada, where a detailed survey of alpine tundra communities was conducted in 1968. Plant community composition was resurveyed on the same four slopes using the same methods as the original study. Species richness and diversity increased significantly over the 42 years and non-metric multidimensional scaling indicated that community composition had also changed significantly. However, the direction and magnitude of change varied with aspect. Dominant species were not replaced or eliminated but, instead, declined in relative importance. Fine-scale changes in vegetation were evident from repeat photography and dendro-ecological analysis of erect shrubs, supporting the community-level analysis. The period of study corresponds to a mean annual temperature increase of 2°C, suggesting that climate warming has influenced these changes.     

Partitioning of aromatic and oxygenated constituents into water from regular and ethanol-blended gasolines

Variability in gasoline-water partitioning of major aromatic constituents (benzene, toluene, ethylbenzene, and xylenes (BTEX)) and methyl tert-butyl ether (MTBE) were examined for regular and ethanol-blended gasolines. By use of a two-phase liquid-liquid equilibrium model, the distribution of nonpolar solutes between fuel phase and water was related to principles of equilibrium. The models derived using Raoult's law convention for activity coefficients and liquid solubility is presented. The observed inverse log-log linear dependence of K_fw values on aqueous solubility, could be well predicted by assuming gasoline to be an ideal solvent mixture. Oxygenated additives (i.e., ethanol and MTBE), in the low percent range (below 5%), were shown to have minimal or negligible cosolvent effects on hydrocarbon partitioning. In the case of high fuel-to-water ratio (e.g., 1:1) or near contaminant source zone, the cosolvent effect of oxygenated gasoline with high content of ethanol (e.g., E85) will be environmentally significant.     

Emission projections for the U.S. Environmental Protection Agency Section 812 second prospective Clean Air Act cost/benefit analysis

Section 812 of the Clean Air Act Amendments (CAAA) of 1990 requires the U.S. Environmental Protection Agency (EPA) to perform periodic, comprehensive analyses of the total costs and total benefits of programs implemented pursuant to the CAAA. The first prospective analysis was completed in 1999. The second prospective analysis was initiated during 2005. The first step in the second prospective analysis was the development of base and projection year emission estimates that will be used to generate benefit estimates of CAAA programs. This paper describes the analysis, methods, and results of the recently completed emission projections. There are several unique features of this analysis. One is the use of consistent economic assumptions from the Department of Energy's Annual Energy Outlook 2005 (AEO 2005) projections as the basis for estimating 2010 and 2020 emissions for all sectors. Another is the analysis of the different emissions paths for both with and without CAAA scenarios. Other features of this analysis include being the first EPA analysis that uses the 2002 National Emission Inventory files as the basis for making 48-state emission projections, incorporating control factor files from the Regional Planning Organizations (RPOs) that had completed emission projections at the time the analysis was performed, and modeling the emission benefits of the expected adoption of measures to meet the 8-hr ozone National Ambient Air Quality Standards (NAAQS), the Clean Air Visibility Rule, and the PM2.5 NAAQS. This analysis shows that the 1990 CAAA have produced significant reductions in criteria pollutant emissions since 1990 and that these emission reductions are expected to continue through 2020. CAAA provisions have reduced volatile organic compound (VOC) emissions by approximately 7 million t/yr by 2000, and are estimated to produce associated VOC emission reductions of 16.7 million t by 2020. Total oxides of nitrogen (NO(x)) emission reductions attributable to the CAAA are 5, 12, and 17 million t in 2000, 2010, and 2020, respectively. Sulfur dioxide (SO2) emission benefits during the study period are dominated by electricity-generating unit (EGU) SO2 emission reductions. These EGU emission benefits go from 7.5 million t reduced in 2000 to 15 million t reduced in 2020.     

The call of different wilds: the importance of definition and perception in protecting and managing Scottish wild landscapes

Concepts of wild land have recreational, ecological and cultural dimensions, and place varying emphasis on physical landscape attributes and the perceptions of users. In Scotland, national and NGO policies show reasonable consistency in interpreting and defining ‘wild land’, emphasising the (perception of) lack of current human influence as a key criterion. This research used semi-structured interviews with key individuals and a questionnaire survey of land managers to evaluate concepts and perceptions of wild land in Scotland. Recognising that the conceptual and spatial definition of wild land is a key issue, a new typology is proposed. Weaknesses in the policy framework, as well as key potential threats to, and opportunities associated with, wild landscapes are identified. Management initiatives are fitted to the typology and divided into four management themes. Key recommendations are: (i) that national policy for wild landscapes needs to incorporate criteria, which recognise the multiple values deriving from such areas; and (ii) that future research should combine user group preferences with physical attribute information in determining what constitutes wild landscapes.