The bio-solids being fed to the incinerator are 18% to 22% solids. The bio-solids are pumped with a two piston concrete pump at the rate of 6 to 9 gpm into the fluidized sand bed of the incinerator. The sand bed is made up of approximately 16,000 lbs of green lightening sand. Diesel is used as an auxiliary fuel in order to maintain a bed temperature of 1400 degrees Fahrenheit. The air supply is preheated to 1200 degrees Fahrenheit by a heat exchanger in order to reduce the auxiliary fuel consumption. The pre-heated air is forced up through the bed of hot sand and causes the sand bed to be fluidized. When the sand bed is fluidized it acts like boiling water. 1000 gallons of bio-solids can be burnt and it will only generate two quarts of ash that will need to be disposed of.
The addition of 50 gpm of water at the inlet to the Venturi is used to encapsulate the ash particles of the exhaust gases and drop the ash and water out for ultimate disposal. The Venturi is used to create a pressure drop of 29" of water (1.03 psi). The exhaust gases are then forced through a 4 stage tray cooler that has 200 gpm of water flowing in the opposite direction of the exhaust gases. Each stage of the tray cooler has a plate with small holes in it that the air must flow through. The water runs across the top of each plate and the exhaust gases bubble through the water. The exhaust gases are reheated with a natural gas fired burner in order to eliminate the vapor plume for aesthetics.
June 16, 2020 Council Agenda Bill #4704 Narrative
The Wastewater Treatment Plant currently utilizes a Sanitary Sewage Sludge Incinerator (SSI) to combust solids before final disposal by landfilling. The SSI and all of its support equipment were originally installed 30 years ago and are well beyond their originally expected useful life. The cost of operating and maintaining this equipment has risen sharply in recent years due to increasingly stringent federal air quality regulations The goal of these regulations is to bring all of the SSI systems across the country up to New Source Performance Standards. They do this by limiting the expenditures an owner can incur to keep these older systems running. Once these investments exceed a certain percentage of the original installed cost of the system it must be replaced. We are already within 5 years of meeting this trigger. USEPA does not want to see these older incinerators continue to operate. The increased cost for regulatory compliance alone (sampling, testing, and reporting) currently exceeds $125,000 per year. It is estimated that yearly maintenance and operation of the existing SSI is approximately $800,000.
The bottom line is we are obligated to bring our air emissions up to the standards that a brand new incinerator must now meet. Our choices are limited to: 1) putting in a new, modern incinerator or, 2) using a more environmentally friendly biosolids management system. A new incinerator would likely be more expensive than systems using gasification and pyrolysis but these newer technologies will cost less to operate and maintain, at least one will have superior energy balances, and can significantly reduce the City’s carbon footprint. City Council Resolution No. 1389, which commits to achieving or exceeding, at the local level, the goals established in the Paris Climate Accord, adds additional motivation to begin development of the next generation biosolids processing and disposal system for our regional Wastewater Treatment Plant.
Initial research, technical information requests, and evaluation (established via an RFQ process that included proposals from across the USA) have revealed new technologies that can significantly improve the recovery of Carbon and are viable alternatives to incineration. The City has concluded that both Pyrolysis or partial Gasification could meet the goal and intent of Resolution No. 1389. In addition, either technology would significantly reduce operating, regulatory, and disposal expenses.
The idea of using Pyrolysis was first presented to WWTP staff in early 2019 (“Project A”). Project A involves a two-step process: sludge drying and Pyrolysis. This two-step process creates a Class A dried product and a “biochar” which are well established green renewable products. This two-step process is intended to be “net-zero” or energy neutral, and the biochar byproduct could be used in City parks and/or marketed as a soil conditioner or amendment. However, the details of Project A have since proven to be unworkable because 1) the cost as originally estimated has climbed dramatically, 2) current information tells us the process is not net-zero on energy consumption, and a new and expensive building would need to be built at the plant to house the equipment.
The project team (City, Ameresco, DES staff) have remained committed to providing the City with a project that meets the goals and intent of Resolution No. 1389 while also balancing both capital costs and O&M expense.
To this end, the City contracted with Ecoremedy, a gasification integrator, to conduct an initial design effort to determine if their technology could be successfully deployed in Edmonds. This effort, which we have referred to as Project B, also includes guaranteed performance language, a detailed and positive energy balance, and a commitment to a single source of responsibility during performance commissioning. Project B benefits from the lessons learned, the initial regulatory reports, and the modeling, engineering reports, and design work that was prepared for Project A. Most of this information is equally relevant to Project B. We estimate Project B is approximately 80% developed. Ecoremedy has funded half of this design effort to date due to their confidence in being able to achieve all defined project outcomes and bring additional value to the City.
With the help of our project design team, we have concluded this gasification approach offered by Ecoremedy would be a better fit for Edmonds than the pyrolysis-only technology offered by Bioforcetech and Centrisys. We are recommending the City move forward with finalizing a cost proposal to implement this technology. In order to reduce financial and operational risks, and build upon the recent success of prior energy-related projects, we are recommending use of an Energy Savings Performance contract (ESPC) through DES to complete the design, construct, and performance test Project B. ESPC projects are delivered with guaranteed not-to-exceed pricing, guaranteed performance of the new systems, and guaranteed energy savings that are measured and verified.
Governor Inslee recently signed the 2020 Supplemental State Capital Budget, which includes an appropriation of $250,000 for the Edmonds Carbon Recovery (Edmonds) Project.
Another benefit Project B will most likely provide to the City is a tax exemption from the Washington State Department of Revenue due to the fact that Biochar is considered a marketable product. All equipment and materials required to produce the sellable product qualify. We cannot at this point state specifically what other items may qualify but we believe at least 50% of this tax burden will ultimately be exempted.
Previous Action for this project included the following:
In August, 2014 City Council was presented with a plan to replace the Sanitary Sewage Sludge Incinerator with a gasification system.
On April 10th, 2018, the Parks and Public Works Committee reviewed the incinerator replacement project proposal and recommended it be placed on the April 17th City Council agenda for presentation, discussion, and action.
On April 17th, 2018, the City Council approved the pre-design contract with DES for the Carbon Recovery Project. The work was completed on time and within budget during 2018.
City Council authorized a contract and funding with the State Department of Enterprise Systems (DES) for design of the WWTP Phase 6 Energy Conservation Project - Carbon Recovery in the 2019 budget.
City Council appropriated $11,037,000 in the 2020 budget for construction to begin. Ameresco Presentation, April 17, 2018
On June 2nd, 2020 City Council received a presentation on the current status of the Incinerator Replacement Project (Carbon Recovery Project). The presentation presented a summary of work done to-date to identify and screen available options, described the significant design work done on the short-listed options, and presented a recommended option for City Council to consider as the preferred alternative. The comparisons included data on how the options actually work as well as how they compare on initial cost, on-going maintenance costs, and environmental performance.
On June 9th, 2020 City Council received an additional presentation on this recommended project. Staff was directed to again place the project on the Action Agenda for June 16th.
Attachments to this agenda bill include studies by Dr. David L. Parry, the City's 3rd Party Independent Reviewer for the Incinerator Replacement Project. The studies below offer a range of topics from biochar, pyrolisis, gasification and other wastewater solutions and energy projects. These resources were offered by Dr. David Parry.
Dr. David Parry Resume
Carbon Recovery Project Opinion 2020
Pros and Cons of Gas Production Through Pyrolysis
BioThermal Carbon Conversion
Biosolids Alternatives - Hamilton, Ontario
