Optimizing Fluid Bed Combustion

The Northeast Ohio Regional Sewer District operates the Renewable Energy Facility (REF) at the Southerly Wastewater Treatment Center. Commissioned in 2014, the REF includes sludge dewatering, incineration, and energy recovery processes. The facility receives an average of 120 dry tons per day of biosolids from two of the District's three treatment plants. Combustion in a fluidized bed incinerator is a complex process with many factors that affect operation. The incineration process at REF faces two primary challenges to realizing efficient process operation: first, the biosolids loading is approximately 20% lower than the projections used for design conditions and second, the volatile solids proportion is relatively low as a result of the District's majority combined sewer collection system. In order to overcome these challenges and maximize autogenous operation, the following three strategies are in various stages of deployment: 1.Implementation of informational tools to fully optimize combustion process 2. Full use of a Grease Merchant Facility 3. Exploration of an Intermittent Operating Strategy In 2021, operations and engineering staff began an FBI optimization effort. As part of this work, a mass and energy balance was developed to represent operating conditions in the process. This tool is able to be implemented in real time by integrating with the Plant's process management software to quickly pull in new data as it becomes available. By using this tool, operations staff is able to build a more robust understanding of the process and predict the effect of various operational changes when deciding on a course of action to take. In 2016, the Grease Unloading Station (GUS) was completed. This is a merchant facility that allows the grease processing system to receive a higher volume of loads from grease trap haulers. This is a significant benefit to the incineration process which allows grease addition to the cake feed system. Despite representing about 5% of the biosolids feed by weight, the grease can account for 20-30% of the chemical energy in the feed. Currently District operations staff are planning a full pilot of an intermittent operating strategy for the three incinerator trains at the REF. Each train is rated to process 100 dry tons of biosolids per day and the average daily loading to the facility is 120 dtpd. This means that, when running at a steady state, our units are loaded at approximately 60% of capacity. In order to maintain a higher uptime of operation without supplemental fuel addition, intermittently operating one and two units at a time would fully load each incinerator that is operating. Past attempts at this strategy have not fully utilized the capacity of the incinerators and it's expected that an updated implementation of this operating strategy would yield much improved results from past attempts. Note to reviewers: There are two main components to this prospective presentation: (A) an introduction/overview of the mass and energy inputs/outputs to the fluid bed combustion process and (B) a demonstration of how we use this understanding to optimize operation at our facility with the three parts I discuss above. Part A is more a presentation on the fundamentals of the process and Part B is geared towards presenting data and a unique challenge at our facility. If selected, I can tailor the presentation towards one end or the other depending on feedback from the conference program committee and how it is intended to fit with other sessions.