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Master of Science / Department of Biological and Agricultural Engineering / Stacy L. Hutchinson / Coal-fired generation accounts for 45% of the United States electricity and generates harmful emissions, such as sulfur dioxide. With the implementation of Flue Gas Desulfurization (FGD) systems, sulfur dioxide is removed as an air pollutant and becomes a water pollutant. Basic physical/chemical wastewater treatment can be used to treat FGD wastewater, but increased regulations of effluent water quality have created a need for better, more economical wastewater treatment systems, such as constructed wetlands. At Jeffrey Energy Center, north of St. Mary’s, KS, a pilot-scale constructed wetland treatment system (CWTS) was implemented to treat FGD wastewater before releasing the effluent into the Kansas River. The objectives of this study were to 1.) determine if a portable water quality meter could be used to assess water quality and track pollutant concentrations, 2.) develop a water balance of the CTWS, 3.) generate a water use coefficient for the CWTS, and 4.) create a mass balance on the pollutants of concern. Water quality measurements were taken with a HORIBA U-50 Series Multi Water Quality Checker and compared to analytical water tests provided by Continental Analytic Services, Inc. (CAS) (Salina, KS). The water balance was created by comparing inflows and outflows of data determined through flow meters and a Vantage Pro2™ weather station. Information from the on-site weather station was also used to compute the system water use coefficient. Water sampling was conducted from date to date at 10 locations within the CWTS. In general, there was little to no relationship between the HORIBA water quality measurements and the analytical water tests. Therefore, it was recommended that JEC continue to send water samples on a regular basis to an analytical testing laboratory to assess the CWTS function and track pollutants of concern. Because the water balance was conducted during system initiation, there was a great deal of fluctuation due to problems with the pumping system, issues with the upstream FGD treatment system, extreme weather events, and immature vegetation. This fluctuation resulted in the system having a non-steady state operation, which weakened the ability to calculate a system water use coefficient. However, during periods of strong system function, the water use coefficient was similar to previous studies with maximum water use being approximately equal to the reference evapotranspiration. The results of the mass balance indicated high removals mercury, selenium, and fluoride, but low removals of boron, manganese, chloride, and sulfate were exported from the CWTS.

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Processindustrin är den största källan för utsläpp av svaveldioxid (SO2) i Sverige, vilket även inkluderar icke­järnmetallindustrin. Kopparsmältverket Boliden Rönnskär har ett miljötillstånd som tillåter SO2­-utsläpp på maximalt 3500 ton/år, en gräns som Rönnskär har legat nära under de senaste åren. För att minska svaveldioxidutsläppen på Rönnskär så har våtskrubbning (tillsammans med ett bagfilter för stoftrening) föreslagits som en metod för att rena de SO2-­bärande och intermittenta tappgaserna från flashugnen. För att göra ett optimalt val av våtskrubberteknik för ändamålet, undersöktes, utvärderas och jämfördes våtskrubbningstekniker baserade på de följande kemikalierna i denna rapport: lut, soda, peroxid, kalk and zinkoxid. Mätningar gjordes också på sekundärhuvsgaserna från konvertrarna, som också kan användas i skrubbern då flashugnens tappgaser har ett fluktuerande flöde. Vidare gjordes tester på olika processvatten på Rönnskär, som skulle kunna återanvändas i skrubbern. Skrubbrarna utvärderades sedan baserat på indata och olika systemkrav med hjälp av simulerings­ och designprogram samt teoretiska beräkningar. Resultaten visade att det är rimligt att rena sekundärhuvsgaser i skrubbern, då de innehöll ca 280 ton SO2/år. Detta kan jämföras med flashugnens tappgaser som innehöll ca 445 ton SO2/år. Bland skrubbrarna, så utvecklade peroxidskrubbern sig till att vara den mest attraktiva tekniken på grund av dess relativt låga livscykelkostnader och dess lämplighet med både lakverket och flashkyltornsprocessvattnet. De andra teknikerna med packade torn, lut­ och sodaskrubbern, hade högst livscykelkostnader, huvudsakligen på grund av deras höga kemikaliekostnader. Sodaskrubbern, som var den billigare av de två natriumbaserade skrubbarna, skulle kunna vara lämplig ändå på grund av teknikens enkelhet. De öppna tornen hade lägre livscykelkostnader jämfört med de packade tornen. Dock så hade kalkskrubbern flera nackdelar som gör att den inte är ett lämpligt alternativ. Zinkoxidskrubbning har i sin tur inte studerats tillräckligt och är en relativt oprövad teknik, men den bör studeras vidare då den skulle kunna integreras med zinksmältningsprocessen på Rönnskär. Användningen av processvatten i skrubbern skulle leda till en nettominskning av processvatten till reningsverket. Det skulle även leda till minskade reagentkostnader ifall en stripper installeras för att ta bort SO2 från processvattnen innan de går in i skrubbern. / The processing industry is the largest source of sulfur dioxide (SO2) emissions in Sweden, which includes the non­ferrous metals industry. The copper smelter Boliden Rönnskär has an environmental permit to emit a maximum of 3500 tonnes of SO2/year, a limit that the smelter has been close to in recent years. To reduce the SO2 emissions at Rönnskär, wet scrubbing (together with a bag filter for dust cleaning) has been proposed as a method for cleaning the SO2­-bearing, intermittent tapping gases from the flash furnace. To find the optimal wet scrubbing technique for the purpose, wet scrubbing techniques based on the following reagents were investigated, evaluated and compared in this report: caustic soda, soda ash, peroxide, lime and zinc oxide. Measurements were also done on the secondary hood gases from the converters, which could make use of the remaining capacity in the scrubber. Further, tests were conducted on various process waters from other processes at Rönnskär, waters that could be reused in the scrubber. The scrubber techniques were then evaluated based on the input data and system requirements using simulation and design software as well as theoretical calculations. The results suggested that it is reasonable to clean secondary hood gases in the scrubber, as they contained approximately 280 tonnes of SO2/year. This could be compared to the flash tapping gases that contained approximately 445 tonnes of SO2/year. Among the scrubbers, the peroxide scrubber evolved as the most attractive technique due to its relatively low life cycle cost and due to its suitability with the leaching plant and the flash cooling tower process water. The other packed tower techniques, caustic soda and soda ash had the highest life cycle costs, mainly due to their high reagent costs. The soda ash scrubber, which was the cheaper of the two sodium­-based scrubbers, could still be a suitable alternative due to its simplicity. The open spray towers had lower life cycle costs than the packed towers. However, the lime scrubber had several disadvantages that makes it an unsuitable alternative. In turn, the zinc oxide scrubber is a relatively under­researched and unproven technique, but should still be studied further as it could be integrated with the zinc smelting process at Rönnskär. The use of process waters in the scrubber would lead to a net reduction of process water to the process water treatment plant and would lead to reduced reagent costs if a stripper is installed to remove the SO2 from the process waters before entering the scrubber.

Experiments with both quantitative and qualitative factors always complicate the selections of experimental settings and the statistical analysis for data. Response surface methodology (RSM) provides the systematic procedures such as the steepest ascent method to develop and improve the response models through the optimal settings of quantitative factors. However the sequential method lacks of exploring the direction of the maximum increase in the response among the qualitative levels. In this dissertation the optimal designs for experiments with both qualitative and quantitative factors are investigated. Focused on the second-order response surface model for quantitative factors, which is widely used in RSM as a good approximation for the true response surface, the approximate and exact D-optimal designs are proposed for the model containing the qualitative effects. On spherical design regions, the D-optimal designs have particular structures for considering the qualitative effects to be fixed or random. In this study, the exact D-optimal designs for a second-order response surface model on a circular design region with qualitative factors are proposed. For this model, the interactions between the quantitative and qualitative factors are assumed to be negligible. Based on this design region, an exact D-optimal design with regular polygon structure is made up according to the remainder terms of the numbers of experimental trials at each qualitative levels divided by 6. The complete proofs of exact D-optimality for models including two quantitative factors and one 2-level qualitative factor are presented as well as those for a model with only quantitative factors. When the qualitative factor has more than 2 levels, a method is proposed for constructing exact designs based on the polygonal structure with high efficiency. Furthermore, a procedure for minimizing the number of support points for the quantitative factors of exact D-optimal designs is also proposed for practical consideration. There are no more than 13 support points for the quantitative factors at an individual qualitative level. When the effects between the quantitative and qualitative factors are taken into consideration, approximate D-optimal designs are investigated for models in which the qualitative effects interact with, respectively, the linear quantitative effects, or the linear effects and 2-factor interactions of the quantitative factors or quadratic effects of the quantitative factors. It is shown that, at each qualitative level, the corresponding D-optimal design consists of three portions as a central composite design but with different weights on the cube portion, star portion and center points. Central composite design (CCD) is widely applied in many fields to construct a second-order response surface model with quantitative factors to help to increase the precision of the estimated model. A chemical study is illustrated to show that the effects of the qualitative factor interacts with 2-factor interactions of the quantitative factors are important but absent in a second-order model including a qualitative factor treated as a coded variable. The verification of the D-optimality for exact designs has become more and more intricate when the qualitative levels or the number of quantitative factors increase, even when the patterns of the exact optimal designs have been speculated. The efficient rounding method proposed by Pukelsheim and Rieder (1992) is a model-free approach and it generates an exact design by apportioning the number of trials on the same support points of a given design. For constructing the exact designs with high efficiencies, a modified efficient rounding method is proposed and is based on the polygonal structure of the approximate D-optimal design on a circular design region. This modification is still based on the same rounding approach by apportioning the number of trials to the concentric circles where the support points of the given design are standing on. Then a regular polygon design will be assigned on the circles by the apportionments. For illustration, the exact designs for a third-order response surface model with qualitative factors are presented as well as those for the second-order model. The results show that nearly D-optimal designs are obtained by the modified procedure and the improvement in D-efficiency is very significant. When the factors with the levels selected randomly from a population, they are treated as with random effects. Especially for the qualitative effects caused by the experimental units that the experimenter is not interested in, one should consider the model with random block effects. In this model, the observations on the same unit are assumed to be correlated and they are uncorrelated between different units. Then the mean response surface is still considered as second-order for quantitative factors but the covariance matrix of the observations is different from the identity matrix. In the fourth part of this dissertation, the locally D-optimal designs on a circular design region are proposed for given the value of the correlations. These optimal designs with the structures based on the regular polygons are similar to the D-optimal designs for the uncorrelated model.

[pt] SO2 é conhecido com um grande contaminante ambiental e muitos países estabeleceram regras para o controle da sua emissão para a atmosfera. Como resultado a maioria das plantas fornecedoras de energia foram equipadas com instalações de dessulfurização de gases de combustão. Embora esta tecnologia seja bem sucedida no abate de SO2, ela gera uma grande quantidade de gesso FGD (flue gas desulfurization) como resíduo. Grandes esforços estão sendo feitos para aproveitar este resíduo (gesso FGD). No presente estudo o gesso FGD foi avaliado como aditivo retardador do tempo de pega substituindo o gesso natural na fabricação do cimento Portland (CP II E-32). Os resultados da caracterização físico-química e morfológica do gesso natural e de gesso FGD identificam um material de alta pureza, sulfato de cálcio di-hidratado para o gesso natural, e presença principalmente de bassanita (CaSO4.0,6H2O) e hannebachite (CaSO3.0,5H2O) com baixas concentrações de impurezas no gesso FGD. Baseado nos resultados, o gesso FGD é uma alternativa adequada para substituir o gesso natural. O tempo de pega mostrou cerca de uma hora de retardo em comparação com gesso natural e seu efeito sobre a resistência à compressão para as amostras de 3, 7 e 28 dias depende da composição das misturas, atingindo um valor máximo para a argamassa com 2,1 porcento de gesso FGD e 1,4 porcentode gesso natural. Também foi estimado o impacto ambiental do gesso FGD, examinando a liberação de seus constituintes inorgânicos seguindo a norma ABNT NBR 10004:2004 e classificando o resíduo como não perigoso e não inerte. / [en] The SO2 is well known as an important environmental contaminant and many countries have established rules to control its emission to the atmosphere and as result most of power supply plants were equipped with flue gas desulfurization systems. Although this technology is successful in the discharge of SO2, its generates a large amount of gypsum FGD (flue gas desulfurization) as a residue. Great efforts are being made to find destinations for this residue. In the present study, the FGD gypsum was evaluated as setting retarder to replace the natural gypsum in the production of Portland cement (CP II E-32). The results of physical-chemistry and morphological characterization of both products, natural and FGD gypsum showed a material of high purity, calcium sulfate dehydrate for natural gypsum, and the presence of bassanite (CaSO4.0,6H2O) and hannebachite (CaSO3.0,5H2O) with low concentrations of impurities for FGD gypsum. Based on the results, the FGD gypsum is a suitable alternative to replace natural gypsum. The setting time with FGD gypsum showed about 1 hour delay compared with natural gypsum and its effect on compressive strength, for samples of 3, 7 e 28 days, depend the composition of the mixtures, reaching the maximum value for the mixture of 1,4 weight percent natural gypsum and 2,1 weight percent FGD gypsum. The FGD gypsum environmental impact was evaluated by determining its potential in releasing inorganic constituents, following the standard ABNT NBR 10004:2004, and it was classified as a non-hazardous and non-inert.

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