IMECE2002-32095 CFD ANALYSIS OF LIQUID-COOLED EXHAUST MANIFOLDS IN A REAL ENGINE CYCLE

ABSTRACT Liquid-cooled exhaust manifolds are used in turbocharged diesel and gas engines in the marine and various industrial applications in order to minimize heat rejection to surrounding areas, maximize energy to the turbocharger, and maintain a maximum allowable skin temperature. A commercial CFD software FLUENT ® was used to analyze liquid-cooled exhaust manifolds in a real time engine cycle. Detailed information of flow property distributions and heat transfer were obtained in order to provide a fundamental understanding of the manifold operation. Experimental data was compared with the CFD results to validate the numerical simulation. Computations were performed to investigate the parametric effects of operating conditions on the performance of the manifold. Two different geometries were compared. One of them was found to have better performance, resulting in an approximately 2 to 3% fuel consumption improvement. INTRODUCTION Liquid-cooled exhaust manifolds are used on turbocharged diesel engines for marine, oilrig, and other industrial applications. The purpose of cooling the manifold is to prevent possible fire hazards by maintaining a maximum safe temperature on the exposed surfaces or "skin" of the manifold. The adverse effec

Pyrolysis of end-of-life polystyrene in a pilot-scale reactor: Maximizing styrene production

Chemical recycling of polystyrene (PS) via pyrolysis is of great industrial, and academic interest, with styrene being the primary product of interest. To identify the optimal process conditions, the pyrolysis of end-of-life PS was studied in a pilot-scale unit consisting of an extruder, and a continuous stirred tank reactor (CSTR). The PS was pyrolyzed with continuous feeding at a pressure range from 0.02 to 1.0 bara, and a temperature range from 450 to 600 ◦C, giving primarily styrene, other mono-aromatics, and oligomers. The comprehensive twodimensional gas chromatography (GC × GC) coupled with flame ionization detector (FID), and time-of-flight mass spectrometer (ToF-MS) as well as GC with thermal conductivity detector (TCD) were used to characterize the liquid, and gaseous products exhaustively. The styrene yield increased from 36 wt% at 1.0 bara, and 450 ◦C to 56 wt% at 0.02 bara, and 550 ◦C. Working under a vacuum enhanced the styrene recovery at all corresponding temperature levels. The yield of benzene, toluene, ethylbenzene, and xylene (BTEX) increased from 4 wt% at 450 ◦C, and 0.02 bara to 17 wt% at 450 ◦C, and 1.0 bara. The experimental results have been used in a mathematical model that can explain the combined effect of temperature, and pressure on the yield of the primary products. The present work illustrates the potential of a continuous pyrolysis process for end-of-life PS, and paves the way for this technology to be rapidly transferred from mere laboratory use to industrial processes in the circular (petro-) chemical industry

Assessing the feasibility of chemical recycling via steam cracking of untreated plastic waste pyrolysis oils : feedstock impurities, product yields and coke formation

In this work, the use of biomethane produced from local biogas plants is proposed as renewable fuel for light marine transport. A profitability analysis is performed for three real biogas production plants located in Cornwall (United Kingdom), considering a total of 66 different scenarios where critical parameters such as distance from production point to gas grid, subsidies, etcetera, were evaluated. Even though the idea is promising to decarbonize the marine transport sector, under the current conditions, the approach is not profitable. The results show that profitability depends on the size of the biogas plant. The largest biogas plant studied can be profitable if feed-in tariffs subsidies between 36.6 and 45.7 euro/MWh are reached, while for the smallest plant, subsidies should range between 65 and 82.7 euro/MWh. The tax to be paid per ton of CO2 emitted by the shipping owner, was also examined given its impact in this green route profitability. Values seven times greater than current taxes are needed to reach profitability, revealing the lack of competitiveness of renewable fuels vs traditional fuels in this application. Subsidies to make up a percentage of the investment are also proposed, revealing that even at 100% of investment subsidized, this green approach is still not profitable. The results highlight the need for further ambitious political actions in the pursuit of sustainable societies

Mixed plastic waste to olefins : from sorting, over impurities to product yields and coke formation

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Moving from linear to circular household plastic packaging in Belgium : prospective life cycle assessment of mechanical and thermochemical recycling

Currently, Belgium is in a transition period after which more household plastic packaging waste will be collected separately in function of increased recycling. The challenge is to identify the most environmentally sound treatment option for the increased selectively collected plastic waste. In this study, mechanical recycling (MR) and thermochemical recycling (TCR) of four newly collected subfractions, being polypropylene (PP), polystyrene (PS), mixed polyolefins (MPO) rigids and polyethylene (PE) films, were investigated through prospective Life Cycle Assessment (LCA), in comparison to incineration with energy recovery. Results showed clear benefits of recycling over incineration with energy recovery. Generally, MR showed a better net environmental impact compared to TCR (for PP, PS, MPO rigids and PE films, respectively, e.g., a global warming impact of 100, -1580, 539 and 101 kg CO2 eq. per ton by TCR, and -1183, -3096, -319 and -1162 kg CO2 eq. per ton by MR, and 2339, 2494, 2108 and 2141 kg CO2 eq. per ton by incineration). This could mainly be explained by the avoided burdens of virgin materials. Whereas TCR avoids the virgin supply of the feedstock for polymer production, MR avoids additionally polymerisation and granulation. MR products, i.e. regranulates or flakes, can be directly used in manufacturing, whereas TCR products require first processes like steam cracking, polymerisation and granulation before being used in manufacturing. As this study assumed a 1:1 substitution ratio between MR regranulates and their virgin alternatives, it presents the most favourable results for MR, which should be kept in mind and further investigated

A comprehensive experimental investigation of plastic waste pyrolysis oil quality and its dependence on the plastic waste composition

Pyrolysis of plastic packaging waste yields a liquid product that can be processed in steam crackers producing light olefins and hence closing the loop towards new virgin plastics. However, there is a lack of knowledge on how the plastic waste composition affects the pyrolysis oil quality regarding hydrocarbon composition and contaminant concentrations. The associated uncertainty is a key reason why thermochemical recycling of contaminated plastic waste is not yet industrially established. In this study, post-consumer plastic packaging waste fractions, namely mixed polyolefins (MPO), polyethylene (PE), and polypropylene (PP) were processed in a continuous pilot-scale pyrolysis unit and the pyrolysis oils subsequently characterized using advanced analytical techniques such as two-dimensional gas chromatography. Substantial amounts of branched olefins (~63 wt%) and diolefins (~20 wt%) were detected in the pyrolysis oil of PP-rich waste, while PE-rich waste produced high amounts of linear paraffins (~34 wt%) and olefins (~26 wt%). Furthermore, significant amounts of nitrogen, oxygen, chlorine, iron, sodium and silicon were detected in the pyrolysis oils exceeding feedstock specifications for industrial steam crackers by orders of magnitude. The results show that next to improved waste sorting and separation processes, pre- and post-treatment techniques are required to produce pyrolysis products suitable for chemical processing

Fractional distillation of waste plastic pyrolysis oil for isolating narrow hydrocarbons cuts

Pyrolysis of polyolefins generates a large amount of olefins, which can serve as a valuable feedstock for the synthesis of chemicals. Nevertheless, their effective utilization requires refining owing to their diverse carbon distribution. This study performed a comprehensive GCxGC analysis of pyrolysis oils derived from waste polypropylene (PP) and waste high-density polyethylene (HDPE). The chemical composition of PP pyrolysis oil exhibited a high content of iso-olefins, whereas HDPE pyrolysis oil contained mainly alpha-olefins. Experimental batch distillation of PP pyrolysis oil yielded narrow hydrocarbon cuts with iso-olefins content exceeding 70 wt%. In contrast, distillation of HDPE resulted in cuts with more than 25 wt% alpha-olefins content. To perform ASPEN simulations, the physical properties (density, viscosity) of the oil were determined, two ways for obtaining boiling curves (ASTM D2887 and ASTM D86) were compared and two property methods (Peng-Robinson and Soave-Redlich-Kwong) were compared. It was concluded that the ASTM D2887 boiling curve and the Peng-Robinson property method present better experimental agreement for pyrolysis oils using the Theil's Inequality Coefficients test. Based on the validated batch simulation, continuous distillation process schemes for isolating narrow carbon cuts in the refinery atmospheric tower indicate that a side draw configuration provides a better yield of (19.1 wt%) compared to a dedicated separate distillation column of (11.9 wt%) for the same number of trays, while the dedicated column allows the possibility to achieve higher purity

Thermal pyrolysis of waste versus virgin polyolefin feedstocks: The role of pressure, temperature and waste composition

Due to the complexity and diversity of polyolefinic plastic waste streams and the inherent non-selective nature of the pyrolysis chemistry, the chemical decomposition of plastic waste is still not fully understood. Accurate data of feedstock and products that also consider impurities is, in this context, quite scarce. Therefore this work focuses on the thermochemical recycling via pyrolysis of different virgin and contaminated waste-derived polyolefin feedstocks (i.e., low-density polyethylene (LDPE), polypropylene (PP) as main components), along with an investigation of the decomposition mechanisms based on the detailed composition of the pyrolysis oils. Crucial in this work is the detailed chemical analysis of the resulting pyrolysis oils by comprehensive two-dimensional gas chromatography (GC × GC) and ICP-OES, among others. Different feedstocks were pyrolyzed at a temperature range of 430–490 °C and at pressures between 0.1 and 2 bar in a continuous pilot-scale pyrolysis unit. At the lowest pressure, the pyrolysis oil yield of the studied polyolefins reached up to 95 wt%. The pyrolysis oil consists of primarily α-olefins (37–42 %) and n-paraffins (32–35 %) for LDPE pyrolysis, while isoolefins (mostly C9 and C15) and diolefins accounted for 84–91 % of the PP-based pyrolysis oils. The post-consumer waste feedstocks led to significantly less pyrolysis oil yields and more char formation compared to their virgin equivalents. It was found that plastic aging, polyvinyl chloride (PVC) (3 wt%), and metal contamination were the main causes of char formation during the pyrolysis of polyolefin waste (4.9 wt%)