Romero, Mary Lou

Romero, Mary Lou

Mary Lou Romero is with Brown and Caldwell, based in California.

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About Romero, Mary Lou

Mary Lou Romero is with Brown and Caldwell, based in California.

Romero, Mary Lou

Mary Lou Romero is with Brown and Caldwell, based in California.

Titles from this speaker

Description: Biosolids Pyrolysis and Gasification: Technology Advancements and an Updated...

Biosolids Pyrolysis and Gasification: Technology Advancements and an Updated Assessment

Abstract

Introduction The potential for biosolids conversion into fuels and revenue-generating products has driven interest in biosolids pyrolysis and gasification for decades, yet technology adoption has been hampered by historical issues, operational complexity, and high capital outlay. A combination of market drivers, technology evolution, and an increased offering of technology manufacturers has reinvigorated interest in these technologies as a tool to address today's biosolids challenges. While previous work has been presented on the conceptual benefits of these technologies and their products, there has not yet been a biosolids pyrolysis and gasification state of the science review to provide a definitive mass and energy balance comparison among developing technologies, discuss the root cause of historical issues and define operational requirements, and outline best practices and future research for successful technology adoption. This presentation will identify key findings for each of these areas from a recent literature review and technology survey (Winchell et al., 2021) developed in collaboration with two utilities, Metropolitan Water Reclamation District of Greater Chicago (MWRD) and Great Lakes Water Authority (GLWA), who in addition provided insight into key considerations for technology evaluations in light of the evolving biosolids management landscape. Mass and Energy Balance Assessment Pyrolysis and gasification are thermochemical processes that apply high temperatures to dried wastewater solids (or biosolids when stabilized) to release organic content into a gaseous or liquid state and retain a condensed, solid product called char. The processes can be considered to proceed on a gradient with regards to oxidant mixing when assessed with a related process, incineration. While pyrolysis and gasification do produce fuel gases (or liquids when condensed) that can be considered for a variety of combustion applications, operational challenges (discussed further below), have limited current application to direct combustion in a thermal oxidizer for heat recovery and recycle to an upfront drying step (as noted below in Table 1). Consequently, the mass and energy balances, when considered with direct combustion and drying, can be compared directly to current sewage sludge incineration (SSI). Results from a technology survey of five pyrolysis and gasification manufacturers (excepts presented in Table 2) will be presented comparing targeted mass and energy balances to historical SSI operation with key insights presented regarding the amount of auxiliary fuel required and what parameters have the most critical impact (e.g. feed solids moisture content, heating value, or dryer and thermal oxidizer thermal efficiencies). Operational Requirements The primary operational concern around pyrolysis and gasification is the resulting condensable fraction of the off-gas, commonly referred to as tar, that forms as a liquid in low-temperature zones of the system (Iaconi et al., 2017). Tar is a viscous liquid that will plug downstream passages, is corrosive, and becomes increasingly viscous over time (Basu, 2013). As noted above, current operations of biosolids pyrolysis and gasification systems transfer the fuel gas at high temperatures directly into a thermal oxidizer where the volatile vapors are combusted before they have a chance to condense. However, future installations under development have proposed fuel gas or tar conditioning prior to utilization in internal combustion applications, where specialized equipment will be required to avoid the operational hazards inherent in the process. Biosolids as a feedstock also present inherent difficulties when compared to other biomass feedstocks such as woody waste, and especially fossil fuels. Example proximate analyses for a range of representative feedstocks will be compared to biosolids to demonstrate its unique qualities (comparatively high oxygen, nutrient, and ash content) and their impact on system operations. Special attention will be given to the presence of alkali and alkaline earth metals (AAEMs) which make biosolids at risk to slagging and corrosion within the system, and best practices for system operation to achieve stable temperature to avoid these issues. Variability in biosolids parameters and loading rates during operations also pose a notable challenge to pyrolysis and gasification. Coordinating operation of discreet drying, pyrolysis or gasification, and thermal oxidation parameters require upfront load leveling and adjustments to seasonal changes in solids parameters. Reactor feeding hopper and conveyor systems have been developed to address these challenges on a micro-scale and its expected that further system development will be required to optimize operational resiliency to larger changes in solids production and processing trends upstream. Furthermore, an overview of required monitoring and operational points will be presented as an indicator for operational and staffing requirements for any project. Conclusions and Next Steps The technology review findings show that pyrolysis and gasification, as deployed today with direct combustion, can address historical operating challenges, but do entail a substantial demand on operations staff. As these technologies convert all the fuel gas into usable heat onsite, they are primarily differentiated from SSI by the characteristics, and end use opportunities afforded by the solid char product. Consequently, further work to identify the environmental and economic benefits from char, and impact of upstream processing steps on its beneficial use, will be critical to determining their viability. In addition, potential exists for improved combustion conditions compared to SSI in the thermal oxidizer, but emission characterization, especially for emerging contaminants like per- and polyfluorinated alkyl substances (PFAS) will be required to verify their effectiveness. For systems considering fuel gas processing and alternative uses, such as oil production, a careful study of fundamental operating principles and requirements will be required to address challenges inherent in the biosolids feedstock. Finally, opportunities exist for process intensification, including carbon diversion in wastewater treatment, co-processing with alternative dried feedstocks, and high efficiency drying technologies. Of all these options, high-efficiency drying is shown to have the highest potential impact and further development in this area could lead to a greater breakthrough in technology adoption.

This paper was presented at the WEF Residuals and Biosolids Conference in Columbus, Ohio, May 24-27, 2022.

SpeakerRomero, Mary Lou

Presentation time

8:30:00

9:00:00

Session time

8:30:00

11:45:00

Session number06

Session locationGreater Columbus Convention Center, Columbus, Ohio

TopicBiosolids To Energy, incineration, Thermal Processes

Author(s)

M. Romero

Author(s)M. Romero1; J. Ross2; L. Winchell3; D. Brose4; T. Bremm Pluth5; X. Fonoll Almansa6; J. Norton7

Author affiliation(s)Brown and Caldwell; 1Brown and Caldwell; 2Brown and Caldwell; 3MWRDGC; 4MWRDGC; 5GLWA; 6Great Lakes Water Authority; 7

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May, 2022

DOI10.2175/193864718825158384

Volume / Issue

Content sourceResiduals and Biosolids

Word count11

Pyrolyis Gas Thermal Oxidation: PFAS and Emissions Control

Abstract

Introduction Biosolids pyrolysis and gasification are gaining interest as a means to remove per- and polyfluoroalkyl substances (PFAS) from biosolids, however PFAS destruction has yet to be proven from the gas phase emissions. In 2020, the USEPA demonstrated that PFAS were removed to below reporting limits in biochar, the solid phase residual product from the Silicon Valley Clean Water (SVCW) biosolids pyrolysis system, but analytical techniques had not matured at the time for gas phase analysis (Thoma et al., 2021). Later bench scale studies showed that appreciable amounts of PFAS could be transferred from biochar to the gas phase at typical pyrolysis temperatures (500°-700°C) (McNamara et al., 2023; Williams et al., 2021). Pyrolysis gas contains an appreciable energy density and can be combusted for energy recovery and the industry has long postulated that gas-phase PFAS would be destroyed in the gas phase when combusted (Winchell et al., 2022). However, no studies had been conducted to date to demonstrate the extent of destruction. This presentation presents results from a Water Environment Federation (WEF) research study lead by Brown and Caldwell with five utility and industry partners to develop a bench-scale biosolids pyrolysis and thermal oxidation laboratory scale reactor to evaluate PFAS inputs and outputs, including flue gas emissions from the pyrolysis gas thermal oxidizer. The lab-scale reactor was created in partnership with Western University and BioForceTech, the pyrolysis system supplier for SVCW, to mimic the pyrolysis and thermal oxidation parameters from the full-scale installation. This presentation provides results from the study and lessons learned from operational issues and proposed mitigation steps for thermal oxidation at full-scale. Methodology The bench scale biosolids pyrolysis and thermal oxidation system were manufactured and commissioned by Western University over a twelve-month period starting Spring of 2022. The thermal oxidizer was configured by installing a forced air gas burner in a steel-lined combustion chamber. The burner and combustion chamber were configured with a propane pilot system that ignited the pyrolysis gas mixture, creating a self-sufficient flame when pyrolysis gas is available. The chamber was configured to provide sufficient residence time and turbulence to match the SVCW system parameters (1,000°C at two seconds). Once the system was found to meet key performance requirements the PFAS sampling event was conducted May 2023. Dried biosolids from SVCW were processed in the lab-scale biosolids pyrolysis and thermal oxidation system over three operating days for a continuous four-hour sampling campaign each operating day. Biosolids were loaded at a rate of 15 grams per minute at a solids residence time of 20 minutes and processed at a pyrolysis reactor temperature of 620°C. PFAS were analyzed in the biosolids, biochar and gas phase extracts by Eurofins. Gas-phase sampling was conducted by a commercial stack sampler, Ortech, using a modified OTM-45 PFAS sampling train. The PFAS data was received in August and September 2023 and are currently being evaluated using the data quality analysis plan developed under the Brown and Caldwell lead Water Research Foundation Tailored Collaboration program project (WRF 5111). Results and Discussion PFAS sampling data is under review and will be available for detailed comparison by 2024 WEF RBC. An initial review of preliminary findings and their comparison to a 2019 BioForceTech study is provided below. - No clear trend was observed between PFAS in the dewatered and dried biosolids. A wide range of variability in PFAS concentrations was observed indicating potential PFAS transformation in the dryer, some PFAS transfer to gas-phase, or sampling variability. - Except for PFBA at 0.7 ng/g, PFAS were below reporting limits in biochar. The reporting limit for the 2023 data was 0.4 ng/g, an order of magnitude lower than the 2-4 ng/g reporting limits available in 2019. - The loading for each PFAS to the bench-scale system ranged from 0.1 - 15 ng per second and the individual PFAS emissions rates in the flue gas ranged from 0.0001 - 0.008 ng per second, indicating individual destruction and removal efficiencies (DRE) will generally exceed 99% for PFAS in the thermal oxidizer flue gas. Conclusions This study is the first to demonstrate PFAS destruction and removal from combustion of biosolids pyrolysis gas. This data can support PFAS air permitting from biosolids pyrolysis projects under consideration by state permitting agencies such as Maine Department of Environmental Protection. While the study demonstrates the efficacy of thermal oxidation for PFAS treatment at bench scale, several lessons learned have been identified from operational issues at the full scale SVCW pyrolysis system that should be considered before widespread adoption. The main issue faced by SVCW is excessive dust from the pyrolysis reactor transferred into the combustion chamber, coating the interior of the burner and chamber. This requires a regular shutdown and cleaning cycle that takes two to three days for cooling, cleaning and reheating. This presentation will provide insights gained into dust creation and mitigation measures under consideration by SVCW and BioForceTech to improve operational uptime.

This paper was presented at the WEF Residuals and Biosolids Conference, June 18-21, 2024.

SpeakerRoss, John

Presentation time

13:30:00

14:00:00

Session time

13:30:00

15:00:00

SessionCarbonization

Session number19

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

TopicPFAS, pyrolysis

Author(s)

Ross, John

Author(s)J. Ross1, L. Winchell1, M. Romero1, F. Kakar1, A. Miot2, J. Norton3, M. Magruder4, K. Bell1

Author affiliation(s)Brown and Caldwell 1; Brown and Caldwell 1; Brown and Caldwell 1; Brown & Caldwell 1; Silicon Valley Clean Water 2; Great Lakes Water Authority 3; Milwaukee Metropolitan Sewerage District 4; Brown and Caldwell 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159452

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count9

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Romero, Mary Lou

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