An economic assessment of SO2 reduction from industrial sources on the highveld of South Africa

The costs and benefits associated with the implementation of an SO2 point source standard for solid fuel combustion installations (Category 1.1 sources, National Environmental Management: Air Quality Act: s21 List of Activities 2013) were evaluated to assess the desirability of implementation of the standards from an environmental as well as economic point of view. The study used a bottoms-up or impact pathway approach to analyse the impact of emission reduction. To reach the new plant (2020) SO2 emission standard of 500 mg/Nm3, the installation of wet flue gas desulfurisation (FGD) is the likely technology as it is a widely installed and well-developed technology. Costs and benefits associated with the installation of FGD were identified and ranked into four categories, based on the expected impact and the availability of information. All costs and benefits that could be quantified and monetized (Category 1 impacts) were included in the evaluation. A sensitivity analysis was conducted on the costs and benefits with the largest impact on NPV (net present value) or the largest uncertainty associated with the calculation to determine a range of feasible values. Site specific information was used where available, supplemented by benefit transfer where local data was not available. The impact on premature adult mortality was found to be the most significant benefit and dependent on the concentration response function selected and sensitive to the VSL (value of statistical life) estimate used (high R115 billion; low R36 billion). The choice of appropriate concentration response functions and the applicability thereof in the South African context are important considerations, likely requiring further study. The capital cost of FGD installations was found to be the most significant cost and was sensitive to the evaluation method (central R187 bil; high R306 bil; low R80 bil). Failure to account for operating costs would significantly impact the economic evaluation. The results of the study indicate that, given the information currently available, it is unlikely that the benefit of reducing SO2 emissions from existing sources to the required standard outweighs the cost of implementation on the Mpumalanga Highveld

Experimental investigation of biogas production from feedlot cattle manure

Biogas can be generated from biomass in an anaerobic digestion process and used to generate electricity and heat as an alternative energy source to fossil fuel-generated electricity. This study investigated biogas generation from cattle manure dried for periods up to 40 days. Manure samples were analysed for gas yield using the biochemical methane production test. The biogas volume produced by manure samples aged for periods up to 40 days after seeding with cattle rumen fluid was measured as a function of time until there was no further measurable gas production. The biogas was analysed for methane and carbon dioxide content using a gas chromatograph. The corresponding cumulative net biogas yield ranged from 154 to 369 Nml/g.VS respectively. The test results showed that an average of 240 Nml/g.VS of biogas can be produced from cattle manure that is less than 40 days old, with an average methane and carbon dioxide percentage of 63% and 31% respectively. Within 3 to 4 days the manure samples generated 80% of the final biogas volume. The drying process was found to occur at a constant rate per unit area, regardless of the manure thickness up to thickness of 200 mm. Biogas formation closely followed the Gompertz equation. There was no significant difference in the biogas production nor biogas production rate for cattle feedlot manure that was fresh up until aging to 40 days

Modeling the effects of biogenic NOX emissions on the South African Highveld and Waterberg regions

The Highveld and Waterberg regions in South Africa contain extensive coal fields and therefore have a high concentration of coal-fired power stations. Previous studies assessed the impact of atmospheric deposition of S- and N-containing species from anthropogenic sources in the region but did not include the effect of biogenic emissions. This study models biogenic NOX soil emissions for the regions and includes them in an atmospheric dispersion model to study the effects of biogenic emission on nitrogen deposition rates. Simulated sulfur deposition rates for the Highveld area are also reported on. Anthropogenic and biogenic sulfur and nitrogen emission sources were inventoried for the Highveld and Waterberg regions. Using previous work by Yienger and Levy, biogenic soil NOX emissions were quantified by constructing models for both areas using land use data, rainfall data, and atmospheric ground level temperatures from CALMET data. A CALPUFF dispersion model was used to predict deposition rates for S- and N-containing species with and without biogenic NOx emissions to determine the impact of biogenic emissions for the Highveld. As rainfall is highly variable in the region, meteorological data representative of high, average, and low rainfall years was used to determine the effect of rainfall on deposition rates for the various species. The biogenic NOx made up 3.96, 4.14, and 3.34% of total released NOx for 2001 (average rainfall), 2003 (low rainfall), and 2010 (high rainfall), respectively. Dry nitrogen deposition rates were affected most by the biogenic component, adding from 1.7 to 6.2% at various receptor locations. Wet deposition rates were affected very little (0.13 to 0.75%). Effect on total nitrogen deposition rates ranged from 0.32 to 1.77%. Biogenic emissions for the Waterberg area, being more arid, were calculated to be only 2.3% of total NOx emissions for the area and accordingly have little effect on deposition rates.http://link.springer.com/journal/112702018-09-30hj2017Chemical Engineerin

The economics of flue gas cooling technology for coal-fired power stations with flue gas desulfurisation

Developments in heat exchanger technology, specifically in the use of polymers as tube material, have allowed the use of gas to water heat exchangers under conditions previously not viable. Two applications in the flue gas cleaning circuit of coal-fired power stations are described in this paper. In conventional pulverised coal-fired boilers, cooling of gas prior to the wet flue gas desulfurisation (WFGD) absorber reduces water consumption for evaporative cooling of the flue gas and can recover heat for feed water preheating or for use elsewhere in the plant. In another application, circulating fluidised bed boilers, which are currently proposed for a few independent power producers and may not require wet FGD, heat recovery is still feasible upstream of the bag filter typically used for particulate emission control. The extracted heat can again be recovered for use in other power plant processes, in this case most economically for pre-heating combustion air. This paper presents case studies for each of the above applications, showing that the power station efficiency is typically increased by approximately 1% of its pre-installation value. An economic analysis is provided for each, including additional power sales, reduced water consumption, or reduced fuel use with a reduction in carbon tax. For the larger installations with WFGD, payback time can be in the order of 6 years

Magnetization dynamics in optically excited nanostructured nickel films

In this work, Laser-induced magnetization dynamics of nanostructured nickel films is investigated. The influence of the nanosize is discussed considering the time-scale of hundreds of femtoseconds as well as the GHz regime. While no nanosize effect is observed on the short time-scale, the excited magnetic mode in the GHz regime can be identified by comparison with micromagnetic simulations. The thickness dependence reveals insight on the dipole interaction between single nickel structures. Also, transient reflectivity changes are discussed

The design of electrostatically augmented moving bed granular gas filters

Granular gas bed filters have been used in industry for a considerable period and mathematical descriptions of dust capture have allowed rigorous design of static beds. Provision for bed movement and electrostatic augmentation, which allows much thinner continuous beds to be used, requires adaptation of design methods for these phenomena. Design methods that allow for this are developed for a cross-flow bed with vertical bed movement and a number of granule and dust types. Direct current charging is applied to the bed itself and to the particles before they enter the bed. In the case of electrostatic augmentation, it is shown that simple models of spherical particles describe the mechanism adequately. The advantages of pre-charging dust particles before they enter the bed are indicated by calculation and proved experimentally. Parameters to describe the enhancement of filtration efficiency by the collected dust are obtained experimentally. It is shown that the factors controlling re-entrainment vary with particle size. For the dust particles less than 1,5 micrometers in size, re-entrainment is linked closely to the electrostatic capture mechanism which is dominant in that size range. For particles approaching 10 micrometer, re-entrainment can be neglected as the impaction efficiency, which is dominant for particles of this size and larger, approaches unity. A complex situation exists between these particle sizes as the magnitude and predominance of capture mechanisms in this region are determined by a number of operational parameters. It did not prove possible to develop predictive equations for re-entrainment efficiency using the results of this study. A number of heuristics are however developed that allow rational design by the use of the empirical parameters found, and that will be valid for the range of parameters used in this work.Thesis (PhD(Chemical Engineering))--University of Pretoria, 2006.Chemical Engineeringunrestricte

The quantification of atmospheric emissions from complex configuration sources using reverse dispersion modelling

Reverse dispersion modelling was employed to quantify sulphur dioxide (SO2) and nitrogen dioxide (NO2) emissions from brick firing clamp kilns and spontaneous combustion from a coal discard dump. Reverse dispersion modelling technique integrates ambient monitoring and dispersion simulation to calculate actual emission rates from an assumed rate of 1 g per second (g/s). Emission rates and emission factors were successfully quantified for SO2, but not for NO2, due to the influence of external sources and the complexity regarding the varying proportion of nitrogen oxides released from the kiln. Quantified emission factor for clamp kiln firing ranged from 1.91–3.24 g of SO2 per brick fired and 0.67–1.14 g of SO2 per kilogram of bricks fired. The variation in SO2 emission factors was linked to high variability in energy input. The source configuration input to the dispersion model, assumed to represent the kiln, was changed from a volume source to a more effective “bi-point” source situated at the top of the kiln, with buoyancy calculated from the carbon combustion rate. In addition, SO2 emission rate for spontaneous combustion from the discard dump was quantified as 0.35 g/s. 274 tons of discard material was estimated to burn annually, assuming that the emission rate is consistent over a year. Consequently, the reverse dispersion modelling and the elevated “bi-point” source technique may be considered a novel approach for quantifying emissions from combustion of materials or mixture of materials where knowledge of source parameters is limited.The Clay Brick Association of South Africahttp://link.springer.com/journal/137622018-11-13hj2018Chemical Engineerin

Quantification of atmospheric emissions and energy metrics from simulated clamp kiln technology in the clay brick industry

Please read abstract in the article.The Clay Brick Association of South Africa and the National Research Foundation (NRF)http://www.elsevier.com/locate/envpol2019-05-01hj2018Chemical Engineerin