Comparison of flue gas desulphurization processes based on life cycle assessment

In this work, the environmental impact assessment is prepared for three different flue gas desulphurization (FGD) processes: (1) intra-furnace sulphur removal during coal combustion with limestone addition, (2) FGD with wet lime scrubbing, (3) regenerative copper oxide flue gas clean-up process. The evaluation and ranking of the three processes according to their environmental impacts is completed for the treatment of as much flue gas that contains 1 kg sulphur. The assessment of the environmental impacts is carried out with the Eco-indicator 99 life cycle impact assessment methodology based on life cycle inventories collected from existing coal fuelled power plants. The environmental assessment is prepared for three different scenarios according to degree of the utilization of the by-products obtained during the desulphurization: (1) zero utilization, (2) full utilization, (3) utilization according to industrial statistics. The results show that all the three investigated FGD processes have about 80% lower environmental impact than the uncontrolled release of sulphur oxides into air. Intra-furnace limestone addition and wet scrubbing processes use similar principal of physical chemistry and they have similar environmental indices. The basis of the regenerative process is a sorption/reduction/oxidation cycle that has higher SO2 removal efficiency than the two other processes. This higher efficiency results in a significantly lower environmental impact

Comparison of pervaporation models with simulation of hybrid separation processes

The industrial application of pervaporation as a membrane separation technology is increasing caused by the numerous advantages of this method. However, to complete engineering design, like in the cases of distillation, azeotropic distillation and absorption, reliable and adequate modelling of the process in flowsheeting environment is indispensable. A proper model is especially needed if the more complicated but more economical and environmentally sound hybrid separation methods are designed or investigated.In this study two pervaporation models, the solution-diffusion model of Rautenbach [1] and its developed form [2], are compared and evaluated with computer simulation on the dehydration processes of isobutanol-water and ethanol-water mixtures. Simulations of a hybrid separation method containing pervaporation for the separation of these mixtures are performed, thus proving the importance of using a proper pervaporation model regarding the discrepancies caused by the application of a false model

Ranking of rectification structures separating quaternary mixtures with exergy analysis

In this paper exergy analysis is applied to select the most efficient rectification structures for separation of quaternary hydrocarbon mixtures. The basis and usage of exergy analysis is shown, as well as the benefits of its application. Exergy loss and thermodynamic efficiency is calculated from basic equations of thermodynamics. The ranking, even based on exergy analysis, highly depends on the product purification prescription. Finally it is shown that heat integration of distillation columns is exergetically beneficial in a wide product purity range

New area for distillation: wastewater treatment

The protection of our environment is an actual and global problem in our time and the wastewater treatment is its important part. It is based on biological treatment. In certain cases, however, due to special regulations, the biological tools are not allowed and other options should be considered and selected. The incineration is an alternative but impact assessment studies show that it can make a serious burden upon the environment as well as it might be an expensive solution. Physico-chemical tools can mean a realistic alternative in such cases. In case of wastewater containing organic solvents (ethanol, ethyl-acetate, toluene, halogenated solvents, etc.), that is typical for wastewaters of medicine and fine chemical industries, the distillation is a powerful tool to remove the volatile polluting compounds. These volatile organic compounds (VOC) can contribute significantly to the chemical oxygen demand (COD) of the wastewater. This contribution we call VOC-COD. The Adsorbable Organically Bound Halogens (AO X) can be removed also with distillation. Industrial case studies show that the distillation offers a realistic alternative and the recovered solvents can be also utilised. The COD can be reduced in certain cases below the emission limit (1000 mg/lit) and the AOX, after the physico-chemical treatment, is less than 8 mg/lit

Application of the rough set data analysis for the development of the control structure of an FCC unit

The rough set data analysis (RSDA) is widely used for the determination of non-linear relationships in many different areas. In this paper it is applied to investigate the dependencies among the variables in fluid catalytic cracking unit (FCC) consisting of reactor and regenerator parts. The analysis has been performed to understand FFC behaviour and to develop its control structure. About 140 operating points of an industrial FCC unit are considered and analysed using the rough set methodology. The ROSETTA toolkit is applied to discover the dependencies among the controlled and the manipulated variables. It is determined that the temperature of the regenerated catalyst has a significant influence on the product quality (motor octane number) and it should be controlled. A new control loop is designed and its controlled variable is the temperature in the regenerator unit. To avoid afterburning in the regenerator part of the FCC unit, several temperature measurements are recommended with the use of a special control unit, a high selector (HS).The manipulated variable of the new control loop is the feed flow of the bottom product of the main distillation column (BMC) in the reactor part of the FCC unit

Modelling of wastewater ozonation - determination of reaction kinetic constants and effect of temperature

The direct ozonation is more and more used for waste water treatment. In this study the effect of temperature on the direct ozonation of a wastewater is studied. At constant pH and dissolved organic carbon concentration, the time-dependence of ozone concentration is measured in the function of different temperatures. Continuous experiments are carried out at two temperatures (8 and 17° C), batch experiments are carried out at three temperatures (8, 18 and 27° C). It is shown that with increasing temperature the ozone depletion is faster in both cases. In case of batch experiments the temperature dependence of the reaction kinetic constant is measured. It is found that if the temperature is increased by 10° C doubles the value of the reaction kinetic constant

Systematic Energy Optimization and Design of Process Alternatives for Separation of Quaternary Azeotropic Mixtures

The separation of homogeneous mixtures is an essential aspect of modern industrial processes that significantly relies on distillation operations. However, distillation has an elevated energy consumption and results in inefficiency in various cases. The non-ideal properties of certain mixtures render their separation unsuitable when employing a single distillation unit, increasing the necessary steps and energy requirements. Because of the relevant role of energy saving in sustainability, a systematic approach must be employed to select the most appropriate separation strategy and identify the operations that minimise energy requirements for product generation. This work employs a systematic approach that utilises residual curve maps to propose viable separation stages and determine the best separation sequence. Various separation strategies are identified via the P-graph framework, which identifies the n-best separation strategies and provides the designer with insightful information concerning the process and its performance. Such a methodology had been previously demonstrated for the separation of ternary mixtures; however, this work constitutes a first step in the development of a systematic approach for the separation of quaternary (or more complex) azeotropic mixtures. The range of separation options, including azeotropic distillation and extractive heterogeneous-azeotropic distillation, are identified by analysing the quaternary residual curves. The potential of this method is demonstrated through a case study involving a mixture of acetone, ethyl acetate, ethanol, and water. The initial set of structures comprises 37 alternative sequences for separation, out of which three interesting alternatives are discussed in detail. The case study demonstrates the potential of the method employed in assessing azeotropic distillation alternatives and facilitating informed decision-making for designers