Correlation Study on Operation of the Wet FGD System and Incomplete Coal Combustion

A Wet Flue Gas Desulfurization (WFGD) system operating at thermal power plant Rovinari (Romania), was considered in this study in an attempt to establish mutual or uni-directional influences between the performance of the sulphur removal process and the quality of the combustion process. Although in theory the WFGD system operates automatically with parameters controlled in such way that optimum removal efficiency is obtained, some parameters cannot be fully controlled, especially those that could not be anticipated at the design of the WFGD system. Sulphur removal systems are customizable to some extent but cannot provide an optimum solution for any plant, given the large range of differences between various plants. Coal quality is such a parameter, for which a large range of values and high standard deviation exists. Incomplete combustion is a serious issue caused by low coal quality resulting in significant losses. Briefly, incomplete combustion process is equivalent to coal that is injected in the furnace but does not undergo combustion or undergoes a partial combustion, being eventually evacuated from the boiler. This study attempts to identify quantitative and qualitative influence of incomplete combustion on the operation of the FGD system

Optimalization of the Ferronickel Production Process through Improving Desulfurization Effectiveness

Desulphurization of Ferronickel in the converters with oxygen is the most complex part of the technological process in the Drenas foundry. Sulphur in the ferronickel melting is mostly in the form of FeS, with a melting temperature of 1195oC, and it has tendency to dissolve indefinitely in liquid iron. Our objective is to determine the sulphur removal coefficient, as a key indicator of the desulphurization efficiency in the converter, by measuring the activity and concentration of sulphur and other elements in liquid Fe and melting. Determination of this coefficient is done according to the analytical method, while comparing the current process parameters with those of the new desulfurization methods, other indicators of the refining process are determined. The refining process and the effective conduct of the study depend on the XRD analysis database of metal and slag, and as well of the technological refining process analysis data. Research has shown that desulfurization efficiency is a function of the sulphur removal coefficient, respectively; metal composition, slag, oxygen activity, CaO/SiO2 ratio, sulphide capacity, fluidity, surface pressure, etc.). In addition to this coefficient, other indicators of refining process optimization are defined.

Oxidation Desulphurization of Heavy Naphtha Improved by Ultrasound Waves

The oxidation desulphurization assisted by ultrasound waves was applied to the desulphurization of heavy naphtha. Hydrogen peroxide and acetic acid were used as oxidants, ultrasound waves as phase dispersion, and activated carbon as solid adsorbent. When the oxidation desulphurization (ODS) process was followed by a solid adsorption step, the performance of overall Sulphur removal was 89% for heavy naphtha at the normal condition of pressure and temperature. The process of (ODS) converts the compounds of Sulphur to sulfoxides/ sulfones, and these oxidizing compounds can be removed by activated carbon to produce fuel with low Sulphur content. The absence of any components (hydrogen peroxide, acetic acid, ultrasound waves and activated carbon) from the ODS process leading to reduce the performance of removal, hydrogen peroxide was the most crucial factor. The ultrasound waves increase the dispersion of carbon, water and oil phase, promotes the interfacial mass transfer, and this leads to accelerates the reaction. The ultrasound waves did not affect the chemical or physical properties of the fuel. The chemical analysis of treated fuel oil showed that <1% of the hydrocarbon fuel compounds were oxidized in the ODS process. In this work, desulphurization by oxidation is the main mechanism was tested with several parameters that effects desulphurization efficiency such as sonication time (5-40) min, activated carbon (0.01-0.5) gm, hydrogen peroxide (1-30) ml, and acetic acid (1-15) ml. It was found that the hydrogen peroxide amounts lead to increase oxidation rates of Sulphur compounds so, the desulphurization efficiency increases. The optimum amounts of oxidants are 10 ml hydrogen peroxide per 100 ml of heavy naphtha. Increasing the amount of acid catalyst lead to increase Sulphur removal, it was found that7.5 ml acid per 10 ml oxidant was the optimum amount. Activated carbon as a solid adsorbent and reaction enhancer with 0.1gm weight was found as the optimum amount for 100 ml heavy naphtha. Increasing sonication time lead to increase desulphurization rate, it was found that (10 min) is the optimum period. By applying the optimum parameters 89% of sulfur can be removed from heavy naphtha with 598.4 ppm Sulphur content.

Modelling and optimisation of oxidative desulphurisation of tyre-derived oil via central composite design approach

The aim of this study was to apply the central composite design technique to study the interaction of the amount of formic acid (6-12 mL), amount of hydrogen peroxide (6-10 mL), temperature (54-58°C) and reaction time (40-60 min) during the oxidative desulphurisation (ODS) of tyre-derived oil (TDO). The TDO was oxidised at various parametric interactions before being subjected to solvent extraction using acetonitrile. The acetonitrile to oil ratios used during the extraction were 1:1 and 1:2. The content of sulphur before and after desulphurisation was analysed using ICP-AES. The maximum sulphur removal achieved using a 1:1 acetonitrile to oxidised oil ratio was 86.05%, and this was achieved at formic acid amount, hydrogen peroxide amount, temperature and a reaction time of 9 mL, 8 mL, 54°C and 50 min respectively. Analysis of variance (ANOVA) indicated that the reduced cubic model could best predict the sulphur removal for the ODS process. Coefficient of determination (R2 = 0.9776), adjusted R2 = 0.9254, predicted R2 = 0.8356 all indicated that the model was significant. In addition, the p-value of lack of fit (LOF) was 0.8926, an indication of its insignificance relative to pure error.

Kinetic modelling of scrap tyre pyrolysis and oxidative desulphurisation of tyre-derived oil

The amount of tyres generated around the world has been on the rise. This has prompted the need to explore ways in which waste tyres can be disposed. One of the ways of recycling waste tyres is through pyrolysis, a process that has the potential to produce oil products with high calorific value. However, the oil produced from waste tyre pyrolysis has a high sulphur content, resulting in high levels of toxic emissions during combustion. This research study focuses on two aspects associated with waste tyre pyrolysis. The first aspect deals with the establishment of the kinetics of scrap tyre pyrolysis while the second aspect involves the oxidative desulphurisation (ODS) of tyre-derived oil (TDO). The ODS was carried out with incorporation of the central composite design (CCD) technique of the response surface methodology (RSM) in order to model the desulphurisation process. In order to study the kinetics of the scrap tyre pyrolysis, three different models were applied to thermogravimetric data. The thermogravimetric (TG) experiments were carried out in a nitrogen environment and a temperature range of 20°C to 600°C at heating rates of 2, 5, 10, and 20 °C min-1. The models used to determine the activation energy (Ea) were Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO) and Friedman (FR) whereas the Coats-Redfern (CR) model aided in the determination of the pre-exponential factor. The FWO model had the highest average value (R2 = 0.9847) of the coefficient of determination, and therefore the Ea values from this model were loaded into the CR model to determine the pre-exponential factors and the order of the reaction model. The thermal decomposition started at a mean temperature of about 285°C and was complete at about 482 °C for the four heating rates. Results indicate that the mass losses become greater with increasing heating rates. The thermogravimetric analysis results revealed that tyre pyrolysis involves three stages i.e. removal of lubricants and oil in the scrap tyre, breakdown of natural rubber and breakdown of butadiene rubber and styrene-butadiene rubber. The average activation energies obtained were 206.01 kJ mol-1, 206.08 kJ mol-1 and 204.82 kJ mol-1 using KAS, FWO and FR models respectively. A mean pre-exponential factor of 1.27E+10 min-1 was obtained. In addition, the results showed that the pyrolysis of the tyre crumb conforms to the second order reaction model (F2). The second objective of the study involved the use of the CCD methodology to investigate the interaction of parameters during the ODS of tyre-derived oil. The oxidative desulphurisation involved the investigation of the interaction of formic acid and hydrogen peroxide amounts, reaction time and temperature. The liquid-liquid extraction was carried out using two different solvents. In addition, for one of the solvents (acetonitrile), two solvent to oil ratios were used, bringing the total number of solvent extraction scenarios to three. The three extraction scenarios were acetonitrile to oil ratio of 1:1, acetonitrile to oil ratio of 1:2 and dimethylformamide to oil ratio of 1:1. The ODS for each of the solvent extraction scenarios consisted of 21 experiments. Therefore, the total number of experiments for the three solvent extraction scenarios was 84 i.e. 21 runs for the oxidation stage and 63 runs for the solvent extraction. The maximum sulphur removal achieved was 86.05, 52.77 and 35.00 % respectively for oxidised oils extracted using 1:1 acetonitrile to oil ratio, 1:2 acetonitrile to oil ratio and 1:1 dimethylformamide to oil ratio while the corresponding minimum sulphur removal values were 34.02, 27.91 and 3.8 %. The results of the sulphur removal in which extraction was carried out at 1:1 acetonitrile to oil ratio were further analysed and modelled. From the analysis of variance (ANOVA), the reduced cubic model was found to be the best predictor of sulphur removal during the ODS process. Coefficient of determination (R2 = 0.9776), adjusted R2 = 0.9254, predicted R2 = 0.8356 all showed that the model was significant. Moreover, the p-value for the lack of fit was 0.8926, which is indication of its insignificance relative to pure error. In summary, the data obtained from the kinetic study of the scrap tyre pyrolysis could play an important role in the design and optimisation of industrial scale scrap tyre pyrolysis units. The findings could provide an insight for improvement of the general operability of scrap tyre thermal conversion processes via pyrolysis. Further research should be carried out to obtain thermogravimetric data at higher heating rates, which can then be used to model the process via the non-isothermal means. On the other hand, the findings from the oxidative desulphurisation of tyre-derived oil obtained from this research can play a key role in minimising the levels of emission during the combustion of oils obtained from the pyrolysis of waste tyres. In addition, the knowledge from the present study could be useful in commercialisation of efficient sulphur removal technology in tyre-derived oils, which can then be blended with other fuels such as diesel for use in real combustion processes. Further work with incorporation of a different organic acid, such as acetic acid and hydrogen peroxide as part of the oxidation system may be carried out to investigate the change in the extent of sulphur removal.