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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]

District heating and cooling (DHC) systems, modified or retrofitted with integration of gasifiers and gas upgrading equipment, represent promising alternatives to traditional approaches since various scenarios of products complementary to heat, cold, and electricity can be realized, namely: char only; char and syngas; char, synthetic natural gas (SNG) and hydrogen (H 2 ); and char, syngas, SNG and H 2 . This manuscript evaluates a polygeneration-enabled DHC system in detail (operation during a typical year) from exergetic and exergoeconomic perspectives. The base DHC system utilizes natural gas as fuel with a nominal capacity of 29 MW heat, 35 MW of cold, and 5 MW of electricity. The retrofit employs refuse derived fuel (RDF) as feedstock to an atmospheric gasifier with downstream gas clean-up, a gas turbine, and a heat recovery steam generator along with heat exchangers for integration with the base DHC system. The exergy analysis revealed that the polygeneration system presents adequate performance at all scenarios established. Among the sets of value-added products the combination of char and syngas is the most beneficial as the system efficiency reaches a value of ∼72%. The outcomes of the exergoeconomic analysis support the exergy results. The lower production costs for value-added products are achieved for the maximum simultaneous char and syngas production, with each of these costs estimated to be 6.1 USD/GJ. [ABSTRACT FROM AUTHOR]

Highlight: [•] A thermodynamic analysis was conducted to evaluate the characteristics of the PGM. [•] Energy recovery using gas furnaces is suggested due to high total energy and exergy. [•] Gas turbines are not recommended due to high tar yield. [•] Increasing heat to the PGM is beneficial for cold gas energy and exergy efficiencies. [•] A small steam addition is beneficial for PGM energy and exergy efficiencies. [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]