Simultaneous Sulfur Dioxide and Nitrogen Dioxide Removal by Calcium Hydroxide and Calcium Silicate Solids

ABSTRACT

At conditions typical of a bag filter exposed to a coal-fired flue gas that has been adiabatically cooled with water, calcium hydroxide and calcium silicate solids were exposed to a dilute, humidified gas stream of nitrogen dioxide (NO₂) and sulfur dioxide (SO₂) in a packed-bed reactor. A prior study found that NO₂ reacted readily with surface water of alkaline and non-alkaline solids to produce nitrate, nitrite, and nitric oxide (NO). With SO₂ present in the gas stream, NO₂ also reacted with S(IV), a product of SO₂ removal, on the exterior of an alkaline solid. The oxidation of S(IV) to S(VI) by oxygen reduced the availability of S(IV) and lowered removal of NO₂. Subsequent acidification of the sorbent by the removal of NO₂ and SO₂ facilitated the production of NO. However, the conversion of nitrous acid to sulfur-nitrogen compounds reduced NO production and enhanced SO₂ removal. A reactor model based on empirical and semi-empirical rate expressions predicted rates of SO₂ removal, NO₂ removal, and NO production by calcium silicate solids. Rate expressions from the reactor model were inserted into a second program, which predicted the removal of SO₂ and NO_x by a continuous process, such as the collection of alkaline solids in a baghouse. The continuous process model, depending upon inlet conditions, predicted 30-40% removal for NO and 50-90% removal for SO₂. These x 2 results are relevant to dry scrubbing technology for combined SO₂ and NO_x removal that first oxidizes NO to NO₂ by the addition of methanol into the flue duct.     

Predicting the Performance of Particulate Control Equipment

A new probabilistic modeling environment is described which allows the explicit and quantitative representation of the uncertainties inherent in new environmental control processes for SO₂ and NO_x removal. Stochastic analyses provide additional insights into the uncertainties in process performance and cost not possible with conventional deterministic or sensitivity analysis. Applications of the probabilistic modeling framework are illustrated via an analysis of the performance and cost of the fluidized bed copper oxide process, an advanced technology for the control of SO₂ and NO_x emissions from coal-fired power plants. An engineering model of a conceptual commercial-scale system provides the basis for the analysis. The model also captures interactions between the power plant, the SO₂/NO_x removal process, and other components of the emission control system. Results of the analysis address payoffs from process design improvements; the dependence of system cost on process design conditions and the availability of byproduct markets; and the likelihood that the advanced process will yield cost savings relative to conventional technology. The implications of case study results for research planning and comparisons with alternative systems also are briefly discussed.     

Environmental assessment on a soil washing process of a Pb-contaminated shooting range site: a case study

In this study, an environmental assessment on a soil washing process for the remediation of a Pb-contaminated shooting range site was conducted, using a green and sustainable remediation tool, i.e., SiteWise ver. 2, based on data relating specifically to the actual remediation project. The entire soil washing process was classified into four major stages, consisting of soil excavation (stage I), physical separation (stage II), acid-based (0.2 N HCl) chemical extraction (stage III), and wastewater treatment (stage IV). Environmental footprints, including greenhouse gas (GHG) emissions, energy consumption, water consumption, and critical air pollutant productions such as PM₁₀, NO _x , and SO _x , were calculated, and the relative contribution of each stage was analyzed in the environmental assessment. In stage I, the relative contribution of the PM₁₀ emissions was 55.3 % because the soil excavation emitted the fine particles. In stage II, the relative contribution of NO _x and SO _x emissions was 42.5 and 52.5 %, respectively, which resulted from electricity consumption for the operation of the separator. Stage III was the main contributing factor to 63.1 % of the GHG emissions, 67.5 % of total energy used, and 37.4 % of water consumptions. The relatively high contribution of stage III comes from use of consumable chemicals such as HCl and water-based extraction processes. In stage IV, the relative contributions of GHG emissions, total energy used, and NO _x and SO _x emissions were 23.2, 19.4, 19.5, and 25.3 %, respectively, which were caused by chemical and electricity demands for system operation. In conclusion, consumable chemicals such as HCl and NaOH, electric energy consumption for system operation, and equipment use for soil excavation were determined to be the major sources of environmental pollution to occur during the soil washing process. Especially, the acid-based chemical extraction process should be avoided in order to improve the sustainability of soil washing processes.     

The aging process of naturally emitted aerosol (sea-salt and mineral aerosol) during long range transport

The aging processes of two representative natural aerosol, sea-salt and mineral aerosol, are investigated by using a box model equipped with a thermodynamic module (SCAPE). The model is shown to successfully describe the aging processes between the gas-phase anthropogenic pollutants (SO₂, NO_x, and NH₃) and primary aerosol particles, including self-neutralization process/chlorine depletion in the sea-salt aerosol; formation/dissipation of carbonate and bicarbonate ions in the mineral aerosol; irreversible dynamic deposition of SO₂ and H₂SO₄; and reversible thermodynamic distribution of inorganic volatile species. It is found that SO₂ and H₂SO₄ tend to deposit onto the mode with the largest surface area, and that ammonia deposition is controlled by preceding SO₂/H₂SO₄ deposition. During the SO₂/H₂SO₄ deposition, chloride and carbonate are continuously released from the sea-salt and mineral dust particles, respectively. The findings by the model predictions are consistent with field and observational studies.     

Comparison of life-cycle energy and emissions footprints of passenger transportation in metropolitan regions

A comparative life-cycle energy and emissions (greenhouse gas, CO, NO_X, SO₂, PM₁₀, and VOCs) inventory is created for three U.S. metropolitan regions (San Francisco, Chicago, and New York City). The inventory captures both vehicle operation (direct fuel or electricity consumption) and non-operation components (e.g., vehicle manufacturing, roadway maintenance, infrastructure operation, and material production among others). While urban transportation inventories have been continually improved, little information exists identifying the particular characteristics of metropolitan passenger transportation and why one region may differ from the next. Using travel surveys and recently developed transportation life-cycle inventories, metropolitan inventories are constructed and compared. Automobiles dominate total regional performance accounting for 86–96% of energy consumption and emissions. Comparing system-wide averages, New York City shows the lowest end-use energy and greenhouse gas footprint compared to San Francisco and Chicago and is influenced by the larger share of transit ridership. While automobile fuel combustion is a large component of emissions, diesel rail, electric rail, and ferry service can also have strong contributions. Additionally, the inclusion of life-cycle processes necessary for any transportation mode results in significant increases (as large as 20 times that of vehicle operation) for the region. In particular, emissions of CO₂ from cement production used in concrete throughout infrastructure, SO₂ from electricity generation in non-operational components (vehicle manufacturing, electricity for infrastructure materials, and fuel refining), PM₁₀ in fugitive dust releases in roadway construction, and VOCs from asphalt result in significant additional inventory. Private and public transportation are disaggregated as well as off-peak and peak travel times. Furthermore, emissions are joined with healthcare and greenhouse gas monetized externalities to evaluate the societal costs of passenger transportation in each region. Results are validated against existing studies. The dominating contribution of automobile end-use energy consumption and emissions is discussed and strategies for improving regional performance given private travel's disproportionate share are identified.     

Life cycle energy use,costs, and greenhouse gas emission of broiler farms in different production systems in Iran—a case study of Alborz province

In order to achieve sustainable development in agriculture, it is necessary to quantify and compare the energy, economic, and environmental aspects of products. This paper studied the energy, economic, and greenhouse gas (GHG) emission patterns in broiler chicken farms in the Alborz province of Iran. We studied the effect of the broiler farm size as different production systems on the energy, economic, and environmental indices. Energy use efficiency (EUE) and benefit-cost ratio (BCR) were 0.16 and 1.11, respectively. Diesel fuel and feed contributed the most in total energy inputs, while feed and chicks were the most important inputs in economic analysis. GHG emission calculations showed that production of 1000 birds produces 19.13 t CO_2-eq and feed had the highest share in total GHG emission. Total GHG emissions based on different functional units were 8.5 t CO_2-eq per t of carcass and 6.83 kg CO_2-eq per kg live weight. Results of farm size effect on EUE revealed that large farms had better energy management. For BCR, there was no significant difference between farms. Lower total GHG emissions were reported for large farms, caused by better management of inputs and fewer bird losses. Large farms with more investment had more efficient equipment, resulting in a decrease of the input consumption. In view of our study, it is recommended to support the small-scale broiler industry by providing subsidies to promote the use of high-efficiency equipment. To decrease the amount of energy usage and GHG emissions, replacing heaters (which use diesel fuel) with natural gas heaters can be considered. In addition to the above recommendations, the use of energy saving light bulbs may reduce broiler farm electricity consumption.     

Simultaneous Control of Hg0, SO2, and NOx by Novel Oxidized Calcium-Based Sorbents

Abstract

Efforts to develop multipollutant control strategies have demonstrated that adding certain oxidants to different classes of Ca-based sorbents leads to a significant improvement in elemental Hg vapor (Hg⁰), SO₂, and NO_x removal from simulated flue gases. In the study presented here, two classes of Ca-based sorbents (hydrated limes and silicate compounds) were investigated. A number of oxidizing additives at different concentrations were used in the Ca-based sorbent production process. The Hg⁰, SO₂, and NO_x capture capacities of these oxidant-enriched sorbents were evaluated and compared to those of a commercially available activated carbon in bench-scale, fixed-bed, and fluid-bed systems. Calcium-based sorbents prepared with two oxidants, designated C and M, exhibited Hg⁰ sorp-tion capacities (~100 μg/g) comparable to that of the activated carbon; they showed far superior SO₂ and NO_x sorption capacities. Preliminary cost estimates for the process utilizing these novel sorbents indicate potential for substantial lowering of control costs, as compared with other processes currently used or considered for control of Hg⁰, SO₂, and NO_x emissions from coal-fired boilers. The implications of these findings toward development of multipollutant control technologies and planned pilot and field evaluations of more promising multipollutant sorbents are summarily discussed.     

Control of Claus Plant Sulfur Compound Emissions

The body of information of this paper is directed to those individuals charged with selecting a process to control atmospheric sulfur emissions from Claus plants serving refineries, gas processing installations, and chemical plants. The TGT process developed by the French Petroleum Institute (IFP) is an extension of the Claus reaction itself in the liquid phase. Mixed H₂S and SO₂ in tail gas from Claus units is fed to a packed tower in which a solution of proprietary catalyst in a high BP polyglycol circulates countercurrent to the gas flow. The mixed gases react with the catalyst to form a complex, which in turn reacts with more gases to produce elemental sulfur. Reaction temperature keeps the sulfur above its melting point. Product accumulates in the boot of the tower and is drawn off continuously through a seal leg.

The IFP TGT process is simple in design and units have simple construction, characterized by use of low carbon steel and the use of very few pieces of equipment. Of all processes used today to take effluent sulfur values down to 1000 ppm SO₂ after incineration, the IFP TGT process requires the least capital investment and the lowest operating costs. Twenty-six full scale plants are operating or under design or construction: nine each in the U.S. and Japan, five in the U.S.S.R. and Poland, two in western Europe and one in Canada. Capacities of the Claus plants served range from 45 to 800 Lt/d sulfur.     

Assessment of Dry Sorbent Emission Control Technologies Part I. Fundamental Processes

The utility and industrial sectors continue to come under pressure from both national and local regulatory groups to reduce sulfur dioxide emissions. With a trend in the utility industry for life extension, retrofit technologies are likely to play an important role in any SO₂ emission reduction strategy. Potential retrofit technologies include, singly and in combination: coal switching or cleaning, wet or dry FGD, conversion to fluidized bed, and dry sorbent injection. The diversity within the utility industry in terms of unit size, unit age, fuel use, financial base, and geographic location dictates the need for a variety of technologies to address SO₂ emission control. Dry injection processes involving the injection of dry powders into either the furnace or post-furnace region offer the potential for low capital cost retrofitable technologies. However, compared to wet FGD processes, the dry calcium based processes will likely have lower SO₂ removal efficiencies and may pose more plant-wide integration issues that need to be addressed from both an applications and R&D perspective.

This paper provides a critical assessment of dry injection technologies, in two parts. Part 1 focuses on sorbent processes and science. An assessment of the different dry sorbent processes and the effect of process parameters is provided. Emphasis is placed on process limitations and potential avenues to enhance SO₂ removal. Part 2 will deal with applications of the technology, addressing cost, scale-up, and integration issues.

Much of the data included in this paper was presented at the 1986 Joint Symposium on Dry SO₂ and Simultaneous SO₂/NO_x Control Technologies, sponsored by the Electric Power Research Institute and the Environmental Protection Agency and held in June 1986. This paper provides both an overview and an evaluation of the technology, based largely on our analysis of the data and interpretations discussed at this symposium.     

Regional effects and efficiency of flue gas desulphurization in the Carpathian Basin

Although sulphur emissions (mainly as SO₂) have been continuously decreasing over the last 20 years in most western industrialized countries, localized SO₂ problems still exist in conjunction with strong local emission, meteorological, and topographical factors. In this study, the effect of supplementary installed flue gas desulphurization (FGD) units at high-capacity power plants on regional air pollution in the Carpathian Basin is investigated. The dispersion and accumulation of the SO₂ air pollutant are studied with the regional three-dimensional on-line atmosphere-chemistry model REMOTE. The changes in the SO₂ air pollution are investigated by parallel simulations in a case study, where the single modified parameter is the SO₂ emission rate. The results show that FGD units significantly reduce the horizontal and the vertical dispersion of the emitted SO₂, and its transboundary transport, too. Beside the SO₂ removal efficiency, the dispersion and accumulation also depend on the seasonal weather conditions. During winter, the dispersion and accumulation are higher than in other seasons. Due to this phenomenon, higher SO₂ removal efficiency is needed to guarantee similar air quality features like in the other seasons.     

转炉炼钢大气污染环境评价问题探讨

为了探讨转炉炼钢大气污染环境评价的关键问题,以某大型钢铁集团炼钢厂扩建项目为基础,分析了该类建设项目工艺流程和产污环节;确定了转炉炼钢的重点污染因子是粉尘、烟尘和SO2等.通过对转炉炼钢烟尘治理措施的有效性分析,得出了该扩建项目大气污染物粉尘、烟尘和SO2等能达标排放并满足总量控制指标,符合清洁生产要求.     

The aqueous oxidation of SO2 by OH radicals

The reaction of aqueous hydroxyl radicals with bisulphite ion has been proposed as a significant and in some cases a primary pathway by which SO₂ is oxidized to sulphate in tropospheric cloud. It is shown that many uncertainties still remain with regard to the kinetics and mechanism of this oxidation process. Illustrative computations indicate that reaction schemes taking account of the aqueous oxidation of SO₂ by OH in existing models of cloud chemistry are inconsistent with the mechanisms on which they are based and yield a wide range of oxidation rates. Calculations are presented which suggest that the reaction of the SO₅⁻ radical with bisulphite ion is rate determining, although the rate constant remains uncertain. The products of this reaction must be identified before the mechanism of sulphate production can be elucidated and the relevance of this process to tropospheric SO₂ oxidation reliably assessed.     

Supply Curves for Using Powder River Basin Coal to Reduce Sulfur Emissions

Abstract

Supply curves were prepared for coal-fired power plants in the contiguous United States switching to Wyoming's Powder River Basin (PRB) low-sulfur coal. Up to 625 plants, representing ～44% of the nameplate capacity of all coal-fired plants, could switch. If all switched, more than $8.8 billion additional capital would be required and the cost of electricity would increase by up to $5.9 billion per year, depending on levels of plant derating. Coal switching would result in sulfur dioxide (SO₂) emissions reduction of 4.5 million t/yr. Increase in cost of electricity would be in the range of 0.31-0.73 cents per kilowatt-hour. Average cost of S emissions reduction could be as high as $1298 per t of SO₂. Up to 367 plants, or 59% of selected plants with 32% of 44% nameplate capacity, could have marginal cost in excess of $1000 per t of SO₂. Up to 73 plants would appear to benefit from both a lowering of the annual cost and a lowering of SO₂ emissions by switching to the PRB coal.     

Nuclear and coal electric power generation strategies for control of acid rain at Ontario Hydro

Ontario Hydro is committed to achieving major reductions in atmospheric emissions of SO₂ and NO_x in accordance with regulations established by the Ontario Government. Information is provided on electricity demand in Ontario, on Ontario Hydro's generation capacity mix and on the forecast use of generation to meet demand. Emphasis is placed on the comparative economics and emissions of Ontario Hydro's nuclear and coal-fired generation and on the integration of each into a cost-effective emission control program. Emissions of SO₂ and NO_x will be reduced by about 25% by 1986 and by about 50% by 1990, primarily by using nuclear generation to replace coal, by purchasing hydroelectric generation from neighbouring utilities, by controlling coal sulphur levels and by selective application of emission control technology on coal-fired plants.     

Midwest/western/eastern U.S. precipitation and aerosol sulfate: Differences attributable to natural source inputs?

Factor analysis comparisons between the MAP3S network and Minnesota precipitation chemistry data show marked differences. An assessment of ambient aerosol and precipitation chemistry data obtained at several Colorado and Minnesota sites suggests that natural source inputs may contribute to the sulfate observed in ambient aerosol and at least partly, explain the marked differences of Minnesota and Colorado precipitation chemistry data from that of MAP3S (eastern U.S.). However, a recently proposed mechanism, SO₂ to SO₄ conversion on the surface of dust particles, may be more important than natural sources in explaining western and midwestern precipitation chemistry data. It is concluded that these predominantly non-acidic SO₄ sources may explain the poor association between the H⁺ and SO₄ in many western and some midwestern precipitation chemistry data sets.     

From Air Repair to EM: A&WMA’s Publications through a Century of Change

Abstract

This paper analyzes the natural desulfurization process taking place in coal-fired units using Greek lignite. The dry scrubbing capability of Greek lignite appears to be extremely high under special conditions, which can make it possible for the units to operate within the legislative limits of sulfur dioxide (SO₂) emissions. According to this study on several lignite-fired power stations in northern Greece, it was found that sulfur oxide emissions depend on coal rank, sulfur content, and calorific value. On the other hand, SO₂ emission is inversely proportional to the parameter y _CO2max, which is equal to the maximum carbon dioxide (CO₂) content by vol ume of dry flue gas under stoichiometric combustion. The desulfurization efficiency is positively correlated to the molar ratio of decomposed calcium carbonate to sulfur and negatively correlated to the free calcium oxide content of fly ash.     

Validation of Personal Exposure Models for Sulfafe and Aerosol Strong Acidity

Personal exposure models for sulfates (SO₄ ⁼) and aerosol strong acidity (H⁺) were previously developed using concentration and activity pattern data collected from a personal monitoring study conducted in Uniontown, Pennsylvania, during the summer of 1990. Models were constructed based on time-weighted microenvironmental exposures. For SO₄ ⁼, the “best-fit” model included a correction factor, while for H⁺, it included both a correction factor and a neutralization term.

In this paper, we present the validation of these models using data collected in a personal monitoring study conducted in State College, Pennsylvania, during the summer of 1991. Indoor and outdoor concentration and activity pattern data collected in this study were used as inputs for the “best-fit” models for SO₄ ⁼ and H⁺. Predicted personal exposures subsequently were compared to the measured personal exposures from State College to determine their accuracy and precision.

Predicted personal exposures for both SO₄ ⁼ and H⁺ were in excellent agreement with measured personal exposures from State College. The models explained 91 and 62 percent of the variability in personal SO₄ ⁼ and H⁺ exposures, respectively, and were able to estimate personal exposures substantially better than outdoor concentrations alone. Validation results suggest that the models' correction and neutralization factors are not site specific and support the models' future application as a technique to assess the personal acid aerosol exposures of children living in similar rural and semi-rural communities.     

Does agriculture-induced environmental Kuznets curve exist in developing countries?

Even though the economic growth and the increased agricultural production bring welfare increment, they could also load significant environmental costs to society. This study aims to investigate the existence of agriculture-induced EKC hypothesis in 47 developing countries during 1976–2017 by using dynamic panel data estimators. According to the long-run findings of the DOLS and the FMOLS estimators, there is an inverted U-shaped relationship that exists between income and the CO₂ emissions, while agricultural production has a negative impact on environmental quality. In addition, the PMG estimator is also employed for robustness check. Likewise the DOLS and the FMOLS findings, the long-run results of the PMG estimator also support the existence of agriculture-induced EKC for developing countries. The empirical findings of this study provide stimulus results of policy makers to re-consider their current production infrastructure of agricultural sector to achieve sustainable development.

     

Environmental assessment on electrokinetic remediation of multimetal-contaminated site: a case study

In this study, an environmental assessment on an electrokinetic (EK) system for the remediation of a multimetal-contaminated real site was conducted using a green and sustainable remediation (GSR) tool. The entire EK process was classified into major four phases consisting of remedial investigations (RIs), remedial action construction (RAC), remedial action operation (RAO), and long-term monitoring (LTM) for environmental assessment. The environmental footprints, including greenhouse gas (GHG) emissions, total energy used, air emissions of criteria pollutants, such as NO_x, SO_x, and PM₁₀, and water consumption, were calculated, and the relative contribution in each phase was analyzed in the environmental assessment. In the RAC phase, the relative contribution of the GHG emissions, total energy used, and PM₁₀ emissions were 77.3, 67.6, and 70.4 %, respectively, which were higher than those of the other phases because the material consumption and equipment used for system construction were high. In the RAO phase, the relative contributions of water consumption and NO_x and SO_x emissions were 94.7, 85.2, and 91.0 %, respectively, which were higher than those of the other phases, because the water and electricity consumption required for system operation was high. In the RIs and LTM phases, the environmental footprints were negligible because the material and energy consumption was less. In conclusion, the consumable materials and electrical energy consumption might be very important for GSR in the EK remediation process, because the production of consumable materials and electrical energy consumption highly affects the GHG emissions, total energy used, and air emissions such as NO_x and SO_x.     

A Simple Model for SO2 Removal in the Duct Injection Process

Abstract

In the In-Duct Injection Process, a lime slurry is sprayed into the flue gas between the air preheater and solids collection equipment, and about 30-60 percent removal of SO₂ is achieved. A simple model of this process has been developed based on heat and mass transfer theories, and this model was fitted to the data obtained at proof-of-concept test units. Data taken with separate injection of dry lime and water were also modeled, but the SO₂ removal was less than for slurry injection, probably because of incomplete capture of lime particles by the water droplets.