See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/328037726 Presentation of Reactor Types for Thermo-Catalytic Thermal Cracking Conference Paper · January 2017 DOI: 10.26649/musci.2017.066 CITATIONS READS 0 20 3 authors , including: Zoltán Siménfalvi Arpad B Palotas University of Miskolc University of Miskolc 51 PUBLICATIONS 44 CITATIONS 58 PUBLICATIONS 488 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Particulate Matter Sensing - AQM 2.0 View project Complete Life Cycle Model for Plastic Products. LCA-based development of innovative and enviro-friendly concrete structural elements by recycling secondary raw materials or waste. Advanced Materials and Smart Technologies Creating HEICC at the University of Miskolc (GINOP-2.3.4-15-2016-00004) View project All content following this page was uploaded by Zoltán Siménfalvi on 26 March 2020. The user has requested enhancement of the downloaded file.
University of Miskolc, Hungary, 20-21 April 2017 MultiScience - XXXI. microCAD International Multidisciplinary Scientific Conference ISBN 978-963-358-132-2 PRESENTATION OF REACTOR TYPES FOR THERMO- CATALYTIC THERMAL CRACKING Andor Zsemberi 1 , Zoltán Károly Siménfalvi 2 , Árpád Bence Palotás 3 1 PhD student, 2 associate professor, 3 professor 1,2 Institute of Energy Engineering and Chemical Machinery, University of Miskolc 3 Institute of Energy and Quality Affairs, Department of Combustion Technology, University of Miskolc ABSTRACT Thermo-catalytic thermal cracking processes refer to processes of the chemical industry whose input raw material are solid, liquid or gas state hydrocarbons. The purpose of technology is to produce a liquid and gas state hydrocarbon fraction with higher value. As a starting point in our research, we examined thermal cracking of solid and/or rubber waste by means of a fixed and fluid-bed (semi-batch) complex reactor system using a catalyst at 450 °C. Common features of these operations of the chemical industry are the inertised atmosphere, temperatures between 400 and 450 °C and a pressure range close to the atmosphere. However, the selected reactor design may imply a considerable difference as it largely determines the distribution and quality parameters of the valuable products formed. Our publication discusses the optimisation possibilities of reactor constructions of diverse types based on the values measured with the equipment constructed by us and experiences. 1. PRESENTATION OF THERMAL CRACKING PROCESSES Recycling various plastic and rubber waste sorts thermo-catalytically has been drawing more and more attention in the last years as valuable raw materials for the chemical industry and energy carriers can be generated this way. Moreover, it is worth noting that considerable environmental and waste-treatment issues can become resolvable, too. One of the most important operational units of the process is the reactor, in which the degradation, more precisely the chemical conversion of the solid raw material occurs with the impact of a catalyst and inert fluid mixer. However, it is a relevant fact that solid raw material-processing thermal cracking technologies face a number of important challenges. The design and operation of catalytic cracking reactors is difficult due to the poor thermal conductivity factor and extremely high viscosity of molten polymer. Types used in a broad range applications are the following: batch/semi-batch reactors; fixed-bed reactors; fluid-bed reactors; DOI: 10.26649/musci.2017.066
streamed-bed reactors; screw press (extruder) reactors. Our work leveraged a combined-design laboratory-scale (capacity: 40 g/h) semi- batch operated fluid and fixed-bed reactor system by means of which experimental measurements were performed under thermal and thermo-catalytic circumstances at 450 °C. 2. ANALYSIS OF REACTOR TYPES OF THE THERMAL AND THERMO- CATALYTIC THERMAL CRACKING PROCESSES The selection of reactor type(s) appropriate for the solid raw material to be processed is key in the process as it affects directly both the quality and quantity of the product formed. 2.1. Batch/semi-batch reactors Many studies on thermo-catalytic plastics cracking in mixed (not in each case) batch or semi-batch reactor are available in the professional literature [1]. The main reason for this is principally the easy designability and operability. In the case of semi-batch reactors, a stream of continuous inert gas (nitrogen in general) is generated, which removes the volatile components from the vapour space at the temperature of reaction. The removal of volatile products minimises the possibility of the secondary cracking (e.g. via oligomerisation, cyclisation and aromatization) of primary cracking products. This process ‘takes a back seat’ in a batch reactor as there the secondary cracking is ‘brought to the fore’ [2]. Lee et al. examined the catalytic degradation of plastic waste ((HDPE high density polyethylene), LDPE (low density polyethylene), PP (polypropylene) and PS (polystyrene) on FCC (fluid catalytic cracking) catalyst in a semi-batch mixed reactor [3]. The yield of liquid products depending on the plastics of various types at 400 °C was as follows: PS > PP > PE (HDPE, LDPE). The quantity of liquid products was over 60 % in each case. In the catalytic case, the solid remains were below 1 m/m% except for PS, where it was about 5 m/m%. To avoid the mentioned secondary cracking, we decided to operate the vertically- positioned fluid-bed tube reactor in our work in a semi-batch manner with the continuous stream-in of nitrogen. 2.2. Fixed-bed reactors Fixed-bed reactors are probably listed among the most classic reactors. However, there use with plastics is not easy as these materials have an elevated viscosity and low thermal conductivity factor, due to which extremely serious issues can arise even at the feed-in. In specific cases, the molten polymer fraction is introduced to the reactor [4] via a capillary tube from the tank under overpressure. The most frequent technical solution is to perform a so-called preventive thermal cracking. Next, the liquid or gas components – originating from the thermal cracking – can be simply transferred onto the fixed-bed [5, 6] in a simple fashion.
In our experiments, the role of the fixed-bed outlined above was played by the horizontal tube reactor opera ted at 300 °C as the product vapours formed coming from the vertically-positioned operational unit were transferred directly in here, which can actually be regarded as a preventive thermo-catalytic cracking as well. 2.3. Fluid-bed reactors Fluid-bed reactors are characterised by homogeneity in terms of temperature and product composition. This is a remarkable advantage in the cracking of polymers as a thermal gradient develops due to the generally low thermal conductivity factor and high viscosity, leading to developing other reaction systems as heat does not transfer uniformly everywhere. One of the most known processes for the pyrolysis of plastic waste is the Hamburg process developed by Kaminsky et al. [7]. The reactor was heated with a heating filament with a power of 5 kW. The raw material was in-fed by two screw conveyor belts. The products produced in this way underwent a thorough separation, composed of a cyclone, coolers and electrostatic separators, too. Initially this system was used for thermal cracking of waste polymers exclusively, thereby using nitrogen or pre-heated vapour as fluidising agent [7]. At a conversion of 90 m/m% oil and waxy products formed, whereas oil had 40% BTX (benzene, toluene, xylene) at higher temperatures (690 to 735 °C) [7]. In our work, we noticed that the conversion was almost 90% already at 450 °C with the reactor combination selected by us as we mixed 10 w% catalyst into the raw material and the NiO-coated metal mesh, which was also responsible for the establishment of the homogeneous temperature field. The oil produced in our case contained 40% BTX fraction, too (Table 1) because the product vapours could be in direct contact with the catalyst attachment in the horizontal tube reactor. 2.4. Streamed-bed reactors One of the first proposals to recycle plastic waste was to crack them directly together with standard FCC raw materials in a combined material flow in FCC refining units. In this line of thinking, a new reaction system is established in a streamed-bed. The in-feeding contains normally mixed plastic (PE, PP, PS) at 5-10 m/m%, light oil (LCO), vacuum gas oil (VGO) or benzene [8]. The key element of the process is the internal recirculation reactor, which can ensure little contact time (1 to 10 s) and can operate at a ratio of C/O = 6 (catalyst/oil ratio). The catalyst is placed in a basket and gases circulate through the basket via a streaming enforced by a turbine. At time 0, in-feeding takes place by injection, when the reaction is finished, the valve opens and the products flow into a vacuum chamber [8]. Cracking PE/LCO and PP/LCO mixtures on a HZSM-5 catalyst resulted in the formation of mainly C5-C12 hydrocarbon and aromatic-type product as well as small quantity of C1- C2 gas and chark at 450 °C in the asce nding simulator [8].
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