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Polygeneration is a promising technology for enhancing the performance of traditional centralized district heating and cooling (DHC) systems since it enables the use of renewable energy sources and provides flexibility in supplying a range of value-added products. The main objective of this study is to evaluate how a reduction in heating, cooling and electricity loads would impact on the performance of a polygeneration DHC system based on waste gasification from thermodynamic, exergy, economic and environmental perspectives. To this end, system models considering hourly performance for a typical year of operation were established with either refuse derived fuel (RDF) or municipal solid waste (MSW) as feedstocks. The study reveals that with a decrease in heating, cooling and electricity loads the system, using RDF or MSW as the main fuel, is still capable of delivering energy services, but with reduced amounts of value-added products and less favourable overall system performance. For example, with RDF as the main fuel, when char, syngas, synthetic natural gas and hydrogen are produced with the gas turbine operating at 25% of its nominal value, with no heating and cooling supplies, the system thermodynamic efficiency is only 3.9%, as compared with 31.5% for the maximal heating, cooling and electricity supplies for the same group of value-added products. Nevertheless, under these conditions the system operation is still feasible and economically viable; specifically, annual revenues and discounted net cash flows are 6.4 and 11.1 mln USD, respectively. [ABSTRACT FROM AUTHOR]

Catalytic tar removal from producer gas is critical for the economic feasibility of Municipal Solid Waste (MSW) gasification in the waste-to-energy(WtE) approach. Nickel- and noble-metal catalysts have the highest tar cracking activities, but they increase costs, use scarce materials, and generate dangerous byproducts. To overcome these drawbacks, naturally occurring materials should be used for tar cracking. In this paper, two nanomaterials, synthesized from oyster and mussel waste shells respectively, are used to clean syngas from MSW in a secondary tar cracking unit. We observed that they reform class 1 tar (heavy tars that condense at high temperatures at very low concentrations) into class 3 tar (light hydrocarbons that are not important in condensation) and benzene. Although both catalysts' composition and textural properties were identical, crystallite size and especially specific surface area variation was enough to generate a change in product selectivity. A larger crystallite size and SSA shows a soot yield reduction of 95% with respect to the non-catalytic case, simultaneously increasing the H 2 /CO at 1000 °C. • Two CaO rich catalysts doped with Sr were synthesized from oyster and mussels waste shells. • Both catalysts improve syngas H2:CO ratio, reduce class 1 tar and soot yield at high temperatures. • Soot reduction is accompanied by a class 5 tar reduction and by an increase in class 3 tar. • The crystallite size and specific surface area of the two catalysts directly affect the tar cracking product selectivity. • The syngas quality obtained using the oyster derived catalyst makes it ideal to use in tandem with Ni and noble-metal catalysts. [ABSTRACT FROM AUTHOR]

• MSW gasification was performed under air and steam in a fixed-bed gasifier. • Naphthalene is the most stable compound in secondary tar thermal cracking. • Corona plasma-aided thermal cracking achieved naphthalene complete removal at 800 °C. • With a fixed energy input, the SEI increased when temperature increased. • Corona and plasma cracking have a synergistic effect below 800 °C. Gasification has been proposed as a good solution for recovering energy from waste and biomass in the form of syngas. However, the presence of tar limits syngas applications. Tar model molecules have been removed by cold plasmas up to 400 ° C, but to avoid syngas cooling tar removal above 600 ° C is required. To investigate tar removal by cold plasma at higher temperatures, two sets of experiments were done, one to identify tar composition from MSW gasification, and a second one to crack in a nanosecond-pulsed corona plasma at high temperatures the most refractory tar compound found, naphthalene. In this paper, we report the first results of cold plasma for tar cracking at temperatures up to 1100 ° C, revealing that this tandem can remove naphthalene completely at 800 ° C, compared to the 1000 ° C needed in case of thermal cracking alone. The synergy between plasma and thermal cracking is driven by higher energy densities when temperatures increase. However, this synergy stops when thermal cracking reactions predominate. [ABSTRACT FROM AUTHOR]

Highlights: [•] CaO shows a good capacity of CO2 adsorption at devolatilization stage of MSW. [•] CaO acted as a catalyst both in MSW devolatilization and char steam gasification. [•] Good dispersion and mobility of calcium in char were observed. [•] Catalytic mechanism during devolatilization and char gasification were discussed. [ABSTRACT FROM AUTHOR]

Primary fragmentation during rapid pyrolysis is considered to be the critical size reduction mechanism as it determines the particle size distribution and char conversion rates in the fixed bed gasifier. This study aims to investigate the primary fragmentation behavior of Refuse Derived Fuel (RDF) pellets during a rapid pyrolysis process. RDF pellets consisted of different blending ratios of cardboard and polyethylene (PE) were produced by a single-pellet densification process. Pyrolysis tests at temperature ranges of 500–700 °C were performed for each pellet type, and the number and particle size of the fragmented particles were analyzed. The results demonstrate that the different composition of RDF causes different particle binding mechanisms that behave differently during pyrolysis. Densification of cardboard particles can maintain the structure of the pellet char at higher temperatures compared to PE, due to the more stable lignin binding mechanism. A modified Fragmentation Ratio (FR) is introduced to quantify the degree of fragmentation. It is shown that a raise of the concentration of PE from 25 to 75 wt% increases the FR value by up to 4.2 times, whereas an increase in pyrolysis temperature from 500 to 700 °C only slightly changes the FR values. It can be concluded that the type of materials in the RDF pellet has a more dominating effect on the fragmentation compared to the pyrolysis temperature. Further, the volatile matter content of pellets shows a linear correlation with the FR value, whereas no clear relation is found in the case of the pellet's mechanical strength. • Fragmentation RDF pellets were examined during pyrolysis tests at 500–700 °C. • Effects of pyrolysis temperature and pellet compositions were investigated. • Pellets with high cardboard and low plastic contents are less fragmented. • Volatile matter content of pellets shows a linear relation with the fragmentation degree. [ABSTRACT FROM AUTHOR]