Energy 239 (2022) 121925
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Energy
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Paper mill sludge biochar to enhance energy recovery from pyrolysis: A comprehensive evaluation and comparison Zhongzhe Liu a , * , Matthew Hughes b , Yiran Tong c , Jizhi Zhou d , William Kreutter b , Hugo Cortes Lopez a , Simcha Singer b , Daniel Zitomer c , Patrick McNamara c , ** a Department of Physics and Engineering, California State University-Bakers fi eld, 9001 Stockdale Highway, Bakers fi eld, CA, 93311, USA b Department of Mechanical Engineering, Marquette University, Milwaukee, WI, 53233, USA c Department of Civil, Construction and Environmental Engineering, Marquette University, Milwaukee, WI, 53233, USA d School of Economics, Shanghai University, Shanghai, 200444, China
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a b s t r a c t
Article history: Received 23 April 2021 Received in revised form 25 August 2021 Accepted 26 August 2021 Available online 3 September 2021
Bio-oil and pyrolysis gas (py-gas) are two pyrolysis products available for potential energy recovery. Crude bio-oil, however, is typically corrosive and unstable, requiring special combustion equipment or catalytic upgrading to produce drop-in-grade fuel. In contrast, py-gas is readily useable in standard equipment for energy recovery. Previous research revealed that Ca-impregnated biochar catalyst improved bio-oil to py-gas conversion. Biochar produced from paper mill sludge (p-sludge) has very high Ca content. In this study, the catalytic ability of p-sludge biochar was systematically evaluated for the fi rst time in pyrolysis. P-sludge biochar resulted in higher py-gas yield (40 wt% of total pyrolysis products) and py-gas energy (8400 kJ of py-gas per biosolids pyrolyzed) than other biochar catalysts (e.g. wood and corn stover biochars) and mineral catalysts (e.g. calcined dolomite). Under some conditions (e.g. high temperature and catalyst loading), catalysis completely eliminated the nonaqueous phase condensate. A lower catalyst-to-feedstock ratio was required using p-sludge biochar compared to other biochars for similar performance. P-sludge biochar also had a longer catalyst lifetime based on the effectiveness over fi ve reuse cycles. Bio-oil catalyzed by p-sludge biochar contained fewer organic constituents based on GC-MS and GC-FID analyses (e.g. toluene, ethylbenzene, styrene, phenol, cresol, and indole were not identi fi ed after catalysis). © 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: Biomass Bio-oil Catalytic pyrolysis Tar reduction Wastewater solids Industrial waste
1. Introduction
and corrosiveness that requires special equipment for direct com- bustion or costly upgrading to produce drop-in-grade fuel [7 e 9]. In contrast, py-gas can more easily be used in conventional power generators such as internal combustion engines [10]. In particular, for slow pyrolysis, the target product is biochar, whereas py-gas can be used for on-site energy recovery to provide heat to the process. Thus, processes that improve py-gas yield while minimizing bio-oil production are bene fi cial for slow pyrolysis energy recovery. Cat- alytic pyrolysis, speci fi cally, could be an ef fi cient means to mini- mize bio-oil production while increasing py-gas yield and maintaining biochar production. Organic wastewater solids such as biosolids are a major byproduct from water resource recovery facilities, and solids pro- duction has been increasing [11]. Our previous research showed that pyrolysis of dried wastewater biosolids can recover energy [12]. Biosolids-derived biochar with sorbed nutrients can increase grass growth rates comparable to that of commercial inorganic fertilizer [13]. Moreover, biosolids pyrolysis can remove
Thermochemical treatment is an ef fi cient process that can be used to recover energy and resources from carbonaceous wastes. Mainstream thermochemical technologies include incineration, gasi fi cation, and pyrolysis [1 e 5]. Pyrolysis is gaining attention because it can produce crude bio-oil (i.e. pyrolysis condensate, hereafter referred to as bio-oil) and pyrolysis gas (py-gas) as renewable fuels, and biochar as a valuable soil amendment product [6]. However, all pyrolysis technologies (i.e. fast, intermediate, and slow pyrolysis classi fi ed by heating rates) produce bio-oil with undesired properties such as high viscosity, water content, acidity,
* Corresponding author. ** Corresponding author. E-mail addresses: zliu006@ucr.edu (Z. Liu), patrick.mcnamara@marquette.edu (P. McNamara).
https://doi.org/10.1016/j.energy.2021.121925 0360-5442/ © 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/ ).
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