Peter Mizsey

Rigorous investigation of heat pump assisted distillation

Abstract In this work a propylene-propane splitter assisted by a heat pump of the vapour recompression type is investigated by rigorous methods. Two schemes, a single compressor scheme and a double compressor scheme in parallel arrangement, are scrutinised and compared to the conventional stand alone column. The investigation includes parametric study, operability assessment and an estimation of the role of heat pump in minimising flue gas emissions. The parametric study of the influences of the column top pressure and the pressure lift of the heat pump on the economics shows, for both schemes at the optimal conditions, practically the same annual total cost, which is about 37% cheaper than the conventional stand alone column. The operability of the system is investigated by degrees of freedom analysis and steady state controllability parameters. The operability considerations show that in the case of the double compressor scheme, the column pressure can be independent of the threshold temperature of the condenser. Thus the column pressure can be determined to satisfy the optimum separation parameters. Due to this operability reason, the double compressor scheme is preferred to the single compressor scheme. The heat pump share in reducing flue gas emissions is estimated. It is found that about 60% of the flue gas emissions can be minimised when using a heat pump.

Energy savings of integrated and coupled distillation systems

Abstract Direct separation sequence without, with forward, and with backward energy integration, indirect separation sequence without, with forward, and with backward energy integration, sloppy separation sequence without (preflash system), with forward, with backward, and with double energy integration, and thermally coupled sloppy separation sequence (Petlyuk system) are compared with short-cut and rigorous modelling. Based on theoretical considerations and economically evaluated rigorous case studies for ternary mixtures it is demonstrated that in the most cases the Petlyuk system is not superior to the energy integrated configurations even in energy savings. According to the energy consumption of sharp separation determined by short-cut methodology, all the sloppy sequence structures are equivalent. According to the energy losses determined by short-cut methodology, derived here, the energy-integrated structures win almost everywhere in the studied conditions that include a range of relative volatility ratios and the whole feed composition triangle. According to rigorously simulated and optimised results, together with controllability studies, the advantageous application of the thermally coupled (Petlyuk) systems is constrained to a very small range of relative volatility ratio, feed composition, and price structure. This small range is situated somewhere around balanced relative volatility ratio A/B to B/C, small amount of the middle component B, balanced presence of the two swing components A and C in the feed, and high energy costs to investment costs ratio or slow depreciation rate.

Comparison of different vehicle power trains

Abstract Four different alternatives of mobile power train developments (hybrid diesel, fuel cell operating with hydrogen produced on a petrochemical basis, methanol reformer-fuel cell system, gasoline reformer-fuel cell system), are compared with the gasoline internal combustion engine (ICE), for well-to-wheel efficiencies, CO 2 emissions, and investment costs. Although the ICE requires the lowest investment cost, it is not competitive in well-to-wheel efficiencies and less favourable than the above alternatives for CO 2 emissions. The hybrid diesel power train has the highest well-to-wheel efficiency (30%), but its well-to-wheel carbon dioxide emission is similar to that of the fuel cell power train operated with compressed hydrogen produced on a centralised petrochemical basis. This latter case, however, has the advantage over the hybrid diesel power train that the carbon dioxide emission is concentrated and easier to control than the several point-like sources of emissions. Among the five cases studied only the on-board reforming of methanol offers the possibility of using a renewable energy source (biomass).

Process control for energy integrated distillation schemes

Abstract Two energy integrated distillation schemes for the separation of three different ternary mixtures of four typical feed compositions have been rigorously investigated and compared to the best conventional two-column distillation scheme. The two energy integrated schemes are: the heat integrated two column system and the fully thermally coupled distillation column (FTCDC), also known as Petlyuk column. The comparison of the energy savings and the total costs of the investigated schemes show that the heat integrated two column scheme is economically always better than the conventional scheme. The FTCDC shows considerable energy savings in several cases, however, it can be competitive with the heat integrated two column system only in those rare cases where the concentration of the middle component is high, the split between the first and second components is harder than the split between the second and third components, and the separation is not too sharp (Annakou and Mizsey, 1996). The rigorous economic study is supported by controllability studies for the two energy integrated distillation schemes. Degrees of freedom analysis and steady-state multivariable control structure synthesis tools show that both investigated schemes can be controlled by conventional decentralised control structures, however, in the case of the heat integrated two column scheme heuristics and also the steady-state control indices show that the interaction among the control loops is less than in the case of the FTCDC. The dynamic simulations of the two energy integrated schemes without and with the most promising control structures support the steady-state analysis. They also demonstrate that in the case of the control of the FTCDC due to the significant interaction among the control loops detuning of the controllers is necessary. Higher overshoots, longer settling time and more sluggish behaviour are expected compared to the heat integrated two column system.

Production of platform molecules from sweet sorghum

This study proves that the non-food dedicated sweet sorghum (Sorghum bicolor) can be a possible source and/or raw material of platform molecules such as levulinic acid (LA) and 5-hydroxymethyl-2-furaldehyde (5-HMF). The high sugar-containing juice derived from sweet sorghum can be efficiently converted to LA and 5-HMF by using microwave dielectric heating. Centrifugal separation was proposed as a first step of the technology to remove the insoluble materials (fibers, starch, and sand) to obtain high sugar containing feedstock for acid-catalyzed dehydration. The effects of pretreatment by centrifugal separation and reaction conditions (irradiation time, acid concentration and reaction temperature) on the formation of levulinic acid were studied. The conversions were monitored by in situ NMR spectroscopy. It was shown that maximum yield (31.4%) of LA was achieved in the presence of 2 M sulfuric acid by applying 30 min irradiation at 160 °C to the sorghum sample treated for 20 min in a centrifuge at a rotational force of 5870. It was also revealed that 5-HMF can be produced from the sweet sorghum juice in the presence of 0.05 M sulfuric acid at 120 °C.

Effects of recycle on control of chemical processes

The effects of the recycle of mass or energy on the control of chemical processes are studied. The recycle can be considered analogous to a feedback and significantly changes the characteristics of the process. The study on simple transfer function models indicates that the recycle loop gain strongly and time constant of the recycle unit somewhat less strongly influence the behaviour and the controllability of the process. Higher time constants of the recycle, the use of large surge tanks, and the control of the recycle unit of smaller time constants improves the range of stability. Two case studies, the distillation train of the manufacture of styrene and a simple reactor-distillation column system, demonstrate that chemical processes with internal recycle can usually be controlled with decentralised control structure with individually tuned controllers. The case studies also show that in the case of the control structure design the connections of the different units should be considered and the control of the recycle unit is also important.

Rigorous modelling and optimization of hybrid separation processes based on pervaporation

Hybrid separation processes are becoming more and more important in the practice if membrane technologies are also involved. In this work, a systematic investigation is completed for three sequence alternatives of distillation and pervaporation. These are the following: pervaporation followed with distillation (PV+D), distillation followed with pervaporation (D+PV), two distillation columns and a pervaporation unit between them (D+PV+D). The hybrid separation process alternatives are evaluated with rigorous modelling tools, but first, a rigorous simulation algorithm is determined for the pervaporation. The three hybrid separation processes are rigorously modelled with CHEMCAD, and optimized with the dynamic programming optimization method for the case of the separation of ethanol-water mixture. The objective function is the total annual cost (TAC). The energy consumption is also investigated. The selection of the ethanol-water mixture has two motivations: (i) it is quite often studied and well known, and (ii) to make biofuel (ethanol) production more economical, membrane technologies might also be applied. The results are compared with each other and with the classical separation completed with heteroazeotropic distillation. The optimized TAC shows that the distillation column followed with pervaporation is the most economical hybrid separation process alternative. Its TAC is about 66% of that of the classical separation.

Waste reduction in the chemical industry: a two level problem

Abstract The waste minimisation in the chemical industry has shifted from the end-of-pipe treatment to the elimination of wastes at the source as well as environmentally sound internal recycling. Several systematic strategies based on the hierarchical process design have been developed and used in the practice. In the case of a chemical company that consists of several processes or plants it is necessary to co-ordinate the waste minimisation incentives on the company level. The main goal is to utilise the waste of a plant in another plant that is to design closed-cycle processing. This article describes a systematic two level procedure for the reduction of the global emission of a chemical company.

Effect of fossil fuels on the parameters of CO2 capture

The carbon dioxide capture is a more and more important issue in the design and operation of boilers and/or power stations because of increasing environmental considerations. Such processes, absorber desorber should be able to cope with flue gases from the use of different fossil primary energy sources, in order to guarantee a flexible, stable, and secure energy supply operation. The changing flue gases have significant influence on the optimal operation of the capture process, that is, where the required heating of the desorber is the minimal. Therefore special considerations are devoted to the proper design and control of such boiler and/or power stations equipped with CO2 capture process.

Novel hybrid separation processes for solvent recovery based on positioning the extractive heterogeneous-azeotropic distillation

The solvent recovery is often the separation of highly non-ideal mixtures. The separation and recovery of quaternary solvent mixtures coming from printing and medicine factories are investigated. The components of the six quaternary mixtures studied in form of heterogeneous and homogeneous azeotropes of minimum boiling point. The mixtures can be categorised into three groups according to their VLLE behaviours. After studying their behaviours, three novel hybrid separation processes based on the extractive heterogeneous-azeotropic distillation, a special kind of new distillation, are developed and recommended for each group of solvents. In the novel processes, beside the extractive heterogeneous-azeotropic distillation, ordinary distillations and phase separation units are also used utilising the fact that the combination of such units, the hybrid processes, offer a higher variety of the possibilities for the separation of highly non-ideal mixtures. The separation processes are verified experimentally and the agreements between the simulated and measured data prove to be rather favourable. A strategy is recommended for the use of the novel hybrid processes developed according to the VLLE behaviour of the non-ideal quaternary mixtures.