Hydrothermal Carbonization (HTC) for Solid Recovery of Organic Fractions in Municipal Solid Waste (OFMSW)

Transcription

1 Hydrothermal Carbonization (HTC) for Solid Recovery of Organic Fractions in Municipal Solid Waste (OFMSW) 5 th International Conference on Sustainable Solid Waste Management Tongji University, Shanghai, China College of Environmental Science & Technology Zhang Junting, Li Guangming*, He Wenzhi, Huang Juwen, Zhu Haochen Corresponding author: Li Guangming, ligm@tongji.edu.cn,

2 Increasing Amount of OFMSW The organic fractions in MSW (OFMSW) accounts for 47%-62% of MSW in developing countries (Figure 1) ; These kinds of waste mainly consist of organic matter along with high content of moisture since generation. Sludge Garden waste Food waste (High content of moisture, carbohydrates, lipid, salts and pathogens) Other package waste Figure 1. Composition of MSW in developing countries by region 01

3 Organic waste treatments Conventional treatments Lowers average heating value (HV) of MSW; Unexpected interactions during waste collection, transportation, and disposal. Bioconversion methods Generally time consuming and have strict requirements for precursors; High content of moisture, lipid, salts and pathogens are unfavorable. Thermochemical Recovery A series of thermochemical approaches including gasification, pyrolysis and hydrothermal carbonization (HTC) method 02

4 Char-deriving Treatments Table 1 compared process conditions and products between gasification, pyrolysis and hydrothermal carbonization. During these methods, energy is maintained within solid product known as biochar or hydrochar to obtain higher HV and maximize the added value of recovery products after treatment. HTC has been recognized as wet process that operates with moisture as heating medium on the country to pyrolysis and gasification. Hydrothermal methods are a sort of novel thermal conversion process, with wet, moisture as heating medium; relatively low temperature; autogenous pressure. Less requirement of feedstock drying process suggested HTC favorable for treating wet OFMSW like FW. Table 1. Comparison of gasification, pyrolysis and hydrothermal carbonization(htc) 03

5 HTC of OFMSW - Feedstocks The bromatological analysis of OFMSW shows various recyclable compounds, where carbohydrates as the most abundant components account for more than 40% in terms of dry basis (Figure 2). The composition of the OFMSW produced hydrochar suggests both dehydration and decarboxylation occur during carbonization. Figure 2. Elemental composition and bromatological analysis of OFMSW Decomposition route of cellulose assumed by M. Sevilla et.al 05

6 Table 2. Comparison of hydrochar generated from different organic feedstock 06

7 HTC of OFMSW Conditions Temperature Typical range of 15 60% dry-weight will decrease in the solid residue; Accelerates not only dissolution of feedstock but also decomposition; Organic N compounds of OFMSW were reported to hydrolysis and dissolution. Residence Time Optimization Hydrochar properties No significant high yield while specific structures like aromatic rings are formed; Restrain more thermal stable compounds within solid residues owing to the decrease in the amount of volatile compounds and thermo-sensitive molecules; Lower H/C and O/C atomic ratios indicating enhanced decarboxylation and dehydration reactions. Less significant impacts comparing with temperature; Though residence time varies from hours to days, most reactions take place in the first hour. Existing ions in process water Acid: accelerating cellulose dissolution; Alkali: decreasing dissolution of cellulose; Salt ions: Chlorine ions disrupt hydrogen bonding of cellulose and promotes dissolution. No obvious evidence that solids yields increase with increases in residence time; Longer reaction time may correlate to greater energy, which can be recovered from the gas-phase. Presence of ferric ions also shows impacts on morphologies of generated spheres 07

8 Feasible use of hydrochar I Carbon enriched char for cocombustion as energy supplement The combustion behaviors of hydrochar are controlled by the substances in majority of OFMSW feedstock. Most hydrochars presented good dewatering and drying properties. Thus the net calorific value of hydrochar is often higher than that first has to be dewatered or dried. Co-combustion of lignite and hydrochar generated from coconut fibers and eucalyptus leaves proved that both two kinds of hydrochar addition improved energy conversion by increasing the burnout, tensile strengths and shortened the combustion range of the blends. Energy balances associated with: (a) hydrothermal carbonization and (b) incineration, calculated by Liang Li et.al 08

9 Feasible use of hydrochar II Highly functional carbon material as soil amendment for carbon storage Small clusters of microspheres are found in pure carbohydrates-generated hydrochars in previous research with core and shell structures. The morphologies of the hybrid carbon materials derived from KW presented similar structure with those made by pure saccharides. Interesting products such as peat or humus can be gained for soil improvement. Approximately less than 10% of the carbon is released as gas (mainly carbon dioxide) after HTC Of OFMSW accordingly. Therefore, if using hydrochar as soil amendment for carbon storage, the total gas produced during HTC results in fewer emissions. Structure of hydrochar particles from cellulose by M. Sevilla et.al SEM picture of hydrochars generated from (a) cellulose and (b) kitchen waste, Presented by M. Sevilla and Fushen Zhang et.al 09

10 Industrial application of HTC Table 3. In-used industrial HTC plant 10

11 Industrial application of HTC Pending problems during industrial application of HTC 1 Uncertainty of aqueous phase utilization The aqueous phase from HTC is one of the main drawbacks: Reused to heat up the reactor or introduced for reaction optimization; Extraction of valuable in aqueous phase and recirculation is favorable. 2 Significant energy consumption during heating process Ingelia s HTC pilot plant by Martin Hitzl et.al The significant energy consumption during heating process need more efficiency and less environmental impacts: A local biorefinery concept to exploit solar energy into combustion energy employing wet organic waste as energy carrier; Application of microwave irradiation results in shorten of reaction time. 11

12 Conclusion This work summarized recent research progress of HTC using OFMSW as feedstocks and concludes as below: The high content of carbohydrates in OFMSW is quite promising for carbon enrichment during HTC treatment. The carbon content of recovered solid products (hydrochar) can be predicted with chemical properties of feedstock. Thus, OFMSW with high initial carbon content, such as food waste, is commonly favorable for energy-rich hydrochar generation. Besides initial properties of OFMSW, reaction conditions also have significant effects on hydrochar properties. To properly increase the reaction temperature and extent reaction time are both desirable for carbon recovery. Feasible use of hydrochar generated from OFMSW includes energy supplement and soil amendment. Co-combustion of lignite and hydrochar shows promising result. The application of hydrochars as soil amendment turns to has least environmental impact with limited gas emissions. Combustion of HTC-generated hydrochar as alternative fuel is the main industrial application for OFMSW treatment. Two main obstacles for HTC industrial application are the uncertainty of aqueous phase utilization and significant energy consumption during heating process. The HTC treatment can be improved with microwave assisted heating system and utilization of process water for future industrial application. 10

13 Thanks for your attention! For more info please contact us: 5 th International Conference on Sustainable Solid Waste Management Tongji University, Shanghai, China blubluooo@yeah.net College of Envitonmental Science & Engineering Corresponding author: Li Guangming, ligm@tongji.edu.cn,