Chouinard, Tracy

Tracy Chouinard has over 10 years’ experience in wastewater process, focusing on solids and energy. Tracy currently serves as a solids and energy process engineer specializing in data analysis, visualization and solids and energy systems process modelling and model development. Her project roles range from solids master planning to detailed design and process assessment and optimization, supporting clients nationally.

Titles from this speaker

Designing Cogeneration for the Real-world: A Comprehensive Approach

Abstract

Digester gas is an asset utilities’ can use to maximize beneficial reuse of their resources and reduce their climate impact. In Fairfield, CA, the Fairfield-Suisun Sewer District (District) plant is already an industry leader by employing cogeneration, solar photovoltaics, and wind turbine sources to generate renewable energy and produce the majority of its electricity demands onsite. When looking to replace systems and further advance their energy program, the District engaged Brown and Caldwell to complete a digester gas utilization study. Due to increasing complexity of electric utility rate schedules, the existing varied energy resources at the facility, net metering/export limitations, and potential gas/energy storage, the typical annual average evaluation approach was no longer sufficient to reach realistic conclusions. New tools and methods were required that incorporated time-domain analysis and plant-level energy balance. Simulating minute-resolution digester gas production, real time energy production, and gas storage, allowed for a more accurate evaluation for the District, while using annual averages caused an over estimation of the benefits of the various scenarios evaluated. The selected design was one 1,100 kW engine with natural gas blending to accommodate variability in gas production, take advantage of spark spread, and reduce flaring.

Biogas utilization maximizes resource recovery and reduces climate impact. Fairfield-Suisun Sewer District employs renewable energy generation sources and produces most of its electricity onsite. To evaluate and size a biogas engine, a new method was developed that incorporated a time-domain analysis balancing generation sources, plant demands, and simulated real time biogas and resulting engine output.

SpeakerChouinard, Tracy

Presentation time

15:30:00

15:50:00

Session time

15:30:00

17:00:00

SessionOptimizing Energy Investments Part II: Energy Use is in the Details

Session locationRoom S402b - Level 4

TopicEnergy Production, Conservation, and Management, Facility Operations and Maintenance, Intermediate Level, Utility Management and Leadership

Author(s)

Chouinard, Tracy

Author(s)T. Chouinard 1; K. Klittich 2 ; A. Nojima 3; T. Chouinard 1;

Author affiliation(s)Brown and Caldwell 1; Brown and Caldwell 2 ; Brown and Caldwell 3; Brown and Caldwell 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159040

Volume / Issue

Content sourceWEFTEC

Word count9

Description: When Average isn't Good Enough: Cogeneration Evaluation and the Value of...

When Average isn't Good Enough: Cogeneration Evaluation and the Value of Electricity

Abstract

As utilities nationwide plan to increase their sustainable practices into the future, they are evaluating various methods to maximize beneficial use of their resources, especially biogas. Such biogas utilization programs primarily consist of boilers or cogeneration but can also be coupled with wind or solar programs. In Fairfield, CA, the Fairfield-Suisun Sewer District (District) plant is already an industry leader by employing biogas cogeneration, solar photovoltaics (PV), and wind turbine sources to generate renewable energy and produce the majority of its electricity use onsite. When looking to replace systems and further advance their energy program, the traditional simple business case evaluation was not sufficient and new analysis tools and methods were required. The District treats an average of 14 million gallons per day of wastewater collected from its sewer shed. Plant influent is a combination of both domestic and industrial sources. The District has two mesophilic anaerobic digesters that process the primary sludge and waste activated sludge. Furthermore, the plant loads approximately 8,200 gallons per day of a mix of candy waste and dairy sludge to its digesters as part of the high-strength waste (HSW) program to enhance the digesters' energy yield that generates revenues at the plant. the District currently operates an aging 900 kilowatts (kW) cogeneration engine. Recently Brown and Caldwell (BC) completed a Digester Gas Utilization Master Plan for the District. This analysis faced many complicating factors: - Multiple electrical generating system, including existing net-metered solar PV - Pacific Gas & Electric (PG&E) time-of-use rate schedule - Other potential electric tariffs, such as bioenergy market adjusting tariff (BioMAT), net energy metering (NEM2), and net energy metering multiple tariff (NEM-MT) - Standby charges for new installed capacity - Grant funding opportunities - Variable facility electric load The core of any financial energy evaluation is the value of produced electricity. A behind the meter energy production system offsets imported utility power and derives value by reducing the electric bill. With electric rate schedules growing more complicated and relying on time-of-use rates and larger demand charges, calculating a more accurate estimate of the value of produced electricity requires a much more in depth and comprehensive analysis & the average cost of electricity using 12 months of utility bills is often misleading. The method BC developed to size and evaluate the benefits from a new cogeneration system included: - Minute by minute data for digester gas production - Solar and wind generation profiles - Facility load electricity usage profiles - Variable quantities of HSW and resulting digester gas production - Natural gas supplemental fuel to the engine system - Medium- and low-pressure digester gas storage - Internal combustion engine output based on part load efficiency - Hourly electricity generation, use and import/export calculations - Costs and value derived from the energy system This manuscript will present the methodology used to complete this novel approach to engine evaluation as well as the benefits and drawbacks to this approach relative to the industry standard method for engine evaluation. Finally, this manuscript will discuss the economic impacts and biogas utilization, which minimized flaring while optimizing time of use with energy production, based on this analysis. The basis of design for sizing equipment is based on historical digester gas (DG) production data with additional capacity for future increases in DG produced by increased HSW receiving. Historical and anticipated DG production is presented in Table 1. This table summarizes the anticipated annual average and 90th percentile DG production. It also provides the maximum fuel requirement for the gas conditioning system design basis. Figures 1 and 2 provide a frequency analysis of the historical and anticipated ranges of DG production without and with HSW addition, respectively. As noted in Figure 2, the addition of HSW causes bimodal distribution in the frequency analysis. To perform the engine sizing analysis, the minute fluctuations observed in DG production were simulated to reflect the dynamic operating conditions of the engine(s). DG generated from HSW codigestion was simulated on a minute-by-minute basis and layered on top of the current DG production for small (70,000 gallons per week) and large (140,000 gallons per week) HSW scenarios to simulate engine power output. It was assumed that HSW deliveries only occurred during weekdays, which influence the amount of HSW available for the weekends, shown in Figure 3. Ideally HSW is fed continuously over a 24-hour period, the analysis assumed a less than perfect distribution after morning deliveries as shown in Figure 4, which is similar to the District's current HSW feed strategy. Figures 3 and 4 show simulated above average DG production from HSW during weekdays and midday. These normalized data distributions were implemented for both HSW programs and adjusted based on the incoming HSW volume. These simulated DG data were used to assess four engine size scenarios with and without natural gas blending. Additionally, these scenarios were evaluated under two different DG storage options (high and medium pressure). Based on the DG storage and utilization analysis along with the economic analysis, the District elected to move forward with the one 1,100 kW engine design. Based on the assumptions used in the analysis and the best information available at the time of the analysis, this engine design provides the greatest net present value over the range of HSW programs. This allows the District to ramp up the HSW program at a preferred rate. Additionally, the District decided that the design will not include gas storage and will rely on natural gas blending to smooth out peaks in gas production, take advantage of spark spread, and reduce flaring due to insufficient DG fuel to operate the engine at its minimum capacity.

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

SpeakerChouinard, Tracy

Presentation time

10:15:00

10:45:00

Session time

8:30:00

11:15:00

Session number18

Session locationGreater Columbus Convention Center, Columbus, Ohio

TopicBiogas Energy, business case evaluation, Cogeneration

Author(s)