Table 2.

Different types of reactors used in pyrolysis process for the treatment of CW.

S. No.	Types of reactors	Functions	Advantages	Disadvantages	References
1	Fixed bed reactor	The feedstock is mounted in the stainless-steel reactor, which is externally heated by an electric furnace. It is flushed by inert gas such as nitrogen or argon until the reactor becomes useable and this gas flow is retained throughout the entire process to provide an anaerobic atmosphere. During pyrolysis, the obtained gases and vapours are discharged from the reactor, but char is normally extracted after the process. Low heating rate is defined for the fixed bed reactor.	1. Best suited for laboratory-scale. 2. Simplicity in design 3. Consistent in their outcomes.	1. Feedstock does not shift in the reactor, which makes it impossible on an industrial scale to uniformly heat a significant portion of MSW. 2. It’s really challenging to remove char. 3. High conservation of carbon. 4. Long solid residence time.	Jouhara et al. (2017); Czajczyńska et al. (2017)
2	Fluidized bed reactor	The reactor consists of a two-phase mixture, solid and liquid, which is normally done by moving a pressurized fluid through the solid material. A high heating rate and a strong mixing of the feedstock defines these reactors. A successful solution for waste polymer pyrolysis tends to be this sort of reactor.	1. They are more appropriate for studying the behaviour of fast pyrolysis solid particles. 2. Analysis of secondary oil cracking at longer residence times. 3. In laboratory studies, these reactors are generally used to explain the effect of temperature and residence time on pyrolysis behaviour and products.	1. There are issues with the use of fluidized-bed reactors for MSW handling. 2. The raw material delivered to the reactor must be thin, so that it can float in the fluid. 3. With the separation of the char from the bed material is the major problem in using this reactor. 4. Occasionally used in large-scale projects	Chen et al. (2014); Ding et al. (2016)
3	Spouted bed reactor	The reactor provides the solids with excellent movement, leading to high transfer rates of heat between phases, making them ideal for flash pyrolysis. In addition, the conical sputter bed reactor is ideal for continuous operation, which is particularly important for the larger-scale implementation of biomass pyrolysis. Spouted beds have been successfully implemented for pyrolysis of a number of polymers including polystyrene, polyethylene, polypropylene and polyethylene terephthalate. In this type of reactor, waste plastics melt as they are fed into the reactor and, due to their cyclic movement, provide a uniform coating around the sand particles. It also provides high heat transfer with sticky solids from plastics between phases and smaller defluidization problems.	1. In comparison with the bubbling fluidized bed, the spouted bed reactor presents interesting conditions for the pyrolysis of waste plastics due to low bed segregation and lower attrition. 2. This reactor is ideal for the handling of irregularly textured particles, fine particles, sticky solids and broadly dispersed particles. 3. In addition, with respect to gas flow, the device has great flexibility, allowing operation with short residence times for gas. 4. The pattern of solid flow and the spout’s action reduces the agglomerate formation.	1. There is still no data on the use of this reactor with mixed MSW. 2. They need very tiny pieces of feedstock.	Amutio et al. (2012); Çepelioǧ; ullar and Pütün, 2013; Niksiar et al. (2015)
4	Rotary kiln reactor	In the slow pyrolysis of MSW, rotary kiln reactors were used and normally performed at temperatures of around 500 C with a residence time of around 1 h. It is vital that solid waste of different shapes, sizes and heating values can be fed either in batches or continuously into a rotating kiln; this feature makes it possible to use this type of reactor extensively. Rotary kilns provide improved heat transfer to the feedstock than fixed beds and are less difficult to run than fluidized beds at the same time. In the pyrolysis process, the residence time of the feedstock in the reactor is a very significant parameter since it defines the energy obtained at a given heating rate by the charge. Residence time is usually a function of the mean volumetric flow and the rotational speed of the kiln in rotary kilns.	1. This is the only type of reactor that has so far been successfully implemented on different scales as a practical industrial solution. 2. The slow rotation of an inclined kiln causes the waste to be blended well more uniform pyrolytic products can therefore be obtained. 3. The versatile residence time change will make the pyrolysis reaction easy to conduct under optimum circumstances.	1. Feedstock needs some pre-treatment of MSW before pyrolysis. 2. Waste should be sorted and then shredded to remove unwanted materials. 3. Large-scale implementation is tough.	Li et al. (2002); Fantozzi et al. (2007)
5	Microwave assisted reactors	Microwave energy is derived from electrical energy and most of the domestic microwave ovens use the frequency of 2.45 GHz. The transfer of energy occurs as a result of interaction between the molecules and atoms using microwave. The whole process of drying and pyrolysis are carried out in a microwave oven chamber connected to electricity source. The carrier gas is inert and is also used to create oxygen-free chamber. The reactor has proven to be highly effective in chemical recovery from biomass.	1. Microwaves are the uniform and fast internal heating of large particles of biomass. 2. Immediate reaction to fast start-up and shut-down. 3. High energy efficiency. 4. No need for controllability and agitation.	1. The particles in the feedstock must be very small. 2. To avoid secondary cracking reactions, the organic vapours should be removed very quickly from the reactor. 3. High running costs due to the high consumption of electrical fuel.	Lam and Chase (2012); Zhang et al. (2014)
6	Plasma reactors	Plasma is a gaseous mixture of negatively charged electrons and positively charged ions produced by intensively heating a gas or by exposing a gas to a powerful electromagnetic field. Two major plasma classes exsist, namely plasma fusion and gas discharges. A direct current or alternating current electrical discharge or radio frequency induction or microwave discharge may be used to produce thermal plasma. To generate plasma, also a 2.45 GHz magnetron available from a commercial microwave oven can be used. As carbonaceous waste-derived particles are pumped into a plasma, they are heated very quickly, releasing and cracking the volatile matter, resulting in hydrogen and light hydrocarbons such as methane and acetylene. Only two streams are formed by thermal plasma pyrolysis of organic waste: a combustible gas and a solid residue, all of which are useful products and simple to handle. Gas yields range between 50 and 98 percent by weight.	1. Easy manageability. 2. Enables fast heating. 3. Work effectively at relatively 4. low power consumption	1. High operating costs. 2. Small particle sizes required.	Tang and Huang (2005); Huang and Tang (2007)
7	Solar reactors	The method was performed under an argon flow in a transparent Pyrex balloon reactor. The feedstock was mounted in a black foam insulated graphite crucible located at the centre of a 1.5 kW vertical-axis solar furnace. Without any external heating sources, this construction enables the device to achieve temperatures between 600 °C and 2000 °C.	1. Solar reactors have to be given more attention for their ability of using renewable energy resources to provide energy to endothermic reactions makes pyrolysis more environmentally friendly. 2. Char composition decreases with high temperatures and heating rate.	1. Still in laboratory-scale study only. 2. Weather dependent	Zeng et al., (2015)
8	Vacuum pyrolysis reactor	In this reactor the feedstock is conveyed into the vacuum chamber with a high temperature with the aid of a conveyor metal belt with periodical stirring by mechanical agitation. The heat carrier normally consists of a burner while the feedstock is melted using molten salts by heating inductively. It has the potential to process feedstock of larger particle size, but needs special solids feeds to specialised discharge devices to provide an efficient seal all the time. Under very low pressures, which can be around 5 kPa, vacuum pyrolysis is performed. This is a slow pyrolysis reactor with a very low rate of heat transfer. This usually results in lower bio-oil yields in the range of 35–50 percent by weight.	1. They have a short organic vapour residence time in the reactor. 2. Low temperature of decomposition. 3. These two factors decrease the frequency and strength of secondary reactions.	1. The design is extremely complicated. 2. Expenditure and maintenance requirements are often heavy, rendering the technology uneconomically acceptable.	Garcìa-Pérez et al. (2007); Zhou and Qiu (2010).