Abstract
Municipal solid waste (MSW)'s 40–60 % carbon content makes it a feedstock for biofuel production via pyrolysis. One challenge in the conversion process is MSW fouling due to thermal decomposition. The accumulated deposit on the injection screw often leads to plugging and constriction. This study examined the morphology and composition of the MSW fouling deposit and conducted a thermal simulation to understand the temperature gradience of the injection screw. Surface modifications including smoothening and anti-adhesion coating were proposed for the injection screw to address the deposit problem. For evaluating the candidate mitigations, a bench-scale fouling test was developed with the gas environment, temperature, and sliding speed relevant to the contact interface between the MSW particles and the screw. Results suggested that a smoother screw surface could reduce the grip and a non-metallic coating with a lower surface energy could decrease adhesion, consequently leading to less fouling. Specifically, reducing the roughness from 2 to 0.6 and then to 0.2 μm proportionally decreased the amount of deposit, and the diamond-like-carbon, CrN, and NiCr–CrC composite coatings effectively hindered the fouling process. This study provides fundamental insights into the MSW fouling and proof-of-concept of potential mitigations through the screw surface modification.
| Original language | English |
|---|---|
| Article number | 107337 |
| Journal | Biomass and Bioenergy |
| Volume | 188 |
| DOIs | |
| State | Published - Sep 2024 |
Funding
Notice: This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US Government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).The typical biochemical composition of the 1-inch (25.4 mm) ground MSW includes extractives: 15.19 %, lignin: 30.39 %, glucan: 29.70; xylan: 5.34 %, galactan: 0.83 %, arabinan: 0.77 %, and mannan: 2.95 % [4]. The 6.35 mm (1/4-inch) screen ground MSW has 81.89 % volatiles, 11.94 % ash, 6.17 % and fixed carbon, with a heating value of 19.45 MJ/kg. More information of the 1-inch and 1/4-inch screen size ground MSW, such as particle size distribution and bulk density, are given in Table S1 in the Supporting Information [18]. Tumuluru et al. [4] discussed the methods used by the American Society of Agricultural and Biological Engineers (ASABE) for measuring the moisture content, particle size distribution, and bulk density of ground MSW samples. For example, the 1-inch (25.4 mm) ground MSW has a bulk density of about 50 kg/m3, a mean particle size of 9.4 mm, and a moisture level of 30.4 wt%. Grinding MSW with about 13.5 % (w.b.) moisture content in a hammer mill fitted with a 1/4-inch (6.35 mm) screen decreased the mean particle size down to 2.4 mm but had a marginal impact on the bulk density [18]. The other particle dimensions such as d10, d50 and d90 were also significantly reduced after grinding MSW in a hammer mill fitted with a 6.35 mm screen size (Table S1). The MSW particle dimensions observed are way higher than any of the wood and herbaceous biomass that is typically used for bioenergy production. Their studies on pelleting of woody and herbaceous biomass such as wood and switchgrass reported that at ¼ inch hammer mill ground southern pine and switchgrass has about 0.91- and 1.25-mm mean particle size where MSW has about 1.78 mm mean particle size (Table 1). This higher mean particle size can be due to various fractions in the MSW having different grinding behaviors and creating particles with different mean particle sizes. The particle size distribution variability can impact the material's flow behavior in the screw-feeding system.Fig. 2a and S2 in Supporting Information show some pictures of a used injection screw pulled out of an MSW PDU steam reforming system at TRI. Note that the pictures were taken in the middle of the deposit removal process, and a lot of deposits had already been removed. The morphology and composition of some collected deposits were examined, as shown in Fig. 2b. The deposit appears to consist of scrambled particles in sizes from a few to tens of micrometers. The EDS spectrum indicates the deposit is carbon-based, containing small amounts of metal elements possibly in the form of oxides.Authors thank Ravi Chandran and Dave Newport from TRI for sharing field experience with MSW fouling, Kevin Cooley, Darren Loposser, and David Wilson from ORNL for help on the MSW fouling test setup and equipment repair. The research was sponsored by the Bioenergy Technologies Office (BETO), in part by the Feedstock-Conversion Interface Consortium (FCIC) of BETO, Office of Energy Efficiency and Renewable Energy (EERE), US Department of Energy (DOE).
Keywords
- Coating
- Deposit
- Fouling
- Municipal solid waste (MSW)
- Surface finish
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