Thermal Treatment of Biomass: A Bibliometric Analysis—The Torrefaction Case

Abstract

The aim of the paper was to summarize and discuss current research trends in biomass thermal treatment (torrefaction process). Quantitative analyses were carried out, in which the main countries, research units and scientists were indicated. The analysis showed a clear upward trend in number of publications after 2010. Most scientists on selected topics come from China, USA, Canada, South Korea, Republic of China, Poland (Web od Science—Core Collection (WoS-CC) and Scopus databases). Quantitative analysis also showed that the most relevant WoS-CC categories in the summary are: Energy Fuels, Engineering Chemical, Agricultural Engineering, Biotechnology Applied Microbiology and Thermodynamics and Scopus Subject area: Energy, Chemical Engineering, Environmental Science, Engineering and Chemistry. Thematic analysis included research topics, process parameters and raw materials used. Thematic groups were separated: torrefaction process (temp.: 150–400 °C), hydrothermal carbonization process (HTC) (temp: 120–500 °C), pyrolysis process (temp.: 200–650 °C) and gasification and co-combustion process (temp.: 350–1600 °C). In the years 2015–2019, current research topics were: new torrefaction technologies (e.g., HTC), improvement of the physico-mechanical, chemical and energetic properties of produced fuel as well as the use of torrefied biomass in the process of pyrolysis, gasification and co-combustion. The raw materials used in all types of biomass thermal treatment were: energy crops, wood from fast-growing and exotic trees, waste from the agri-food industry, sewage sludge and microalgae.

Fuel Properties of Torrefied Biomass from Sapindus Pericarp Extraction Residue under a Wide Range of Pyrolysis Conditions

“…Based on the values of molar H/C and O/C (i.e., 1.02 and 0.28, respectively), the optimal SP-torrefied product (i.e., T-SP-280-30) should belong to the class of lignite [1]. The results were in accordance with those reported previously [20,21,28] and recently reviewed [4][5][6][7][8][9]. In addition, the feedstock SP has the highest values of atomic O/C and H/C (Table 3), making it difficult to transform the biomass into liquid fuels.…”

“…Among the lignocellulosic constituents (i.e., cellulose, hemicellulose and lignin) in biomass, the hemicellulose constituent has the highest moisture absorption capacity [2]. In this regard, a pretreatment process, also known as torrefaction, was extensively studied to produce a torrefied biomass for further use in the energy, metallurgical and chemical fields instead of direct use in its original form [3][4][5][6][7][8][9]. To maximize the energy density and mass yield of biomass by reducing the contents of noncarbon elements, the typical temperature range for the torrefaction process is between 200 • C and 300 • C [1], where hemicellulose can be thermally decomposed but cellulose and lignin will be partly repolymerized or degraded to some extent.…”

Effect of Compaction Pressure and Moisture Content on Post-Agglomeration Elastic Springback of Pellets

“…The resulting products have various applications, such as biofuels, fertilization, soil remediation, and biosorbents [11]. As a result of processing, the products can be used directly or serve as a raw material for further processing [12][13][14].…”

Synergetic Co-Production of Beer Colouring Agent and Solid Fuel from Brewers’ Spent Grain in the Circular Economy Perspective

“…The torrefaction process is used for thermal valorization of solid fuels, thus improving their properties, and in consequence, promoting sustainability in the energy generation sector [41][42][43]. Torrefaction is sometimes called slow pyrolysis, and it typically takes place at temperatures between 250 • C and 300 • C [44][45][46][47], with residence times ranging between 10 and 60 min [48][49][50][51]. Torrefied biomass can be an attractive fuel for the power industry for combustion and co-firing [52][53][54][55], mainly due to increased grindability [56,57], which extends the time between renovations of the mill [58], and energy density [59][60][61][62].…”