SUSTAINABLE ENERGY MANAGEMENT USING IN-HOUSE RESOURCES

Thomas R. Alspaugh, PE

Senior Mechanical Engineer

City of San Diego

Metropolitan Wastewater Department

9192 Topaz Way

San Diego, CA 92123

ABSTRACT

This paper presents the energy management program the City of San Diego Metropolitan Wastewater Department has developed utilizing in-house staff. It discusses how the program began, how the Department Energy Plan was developed and the many resulting successful and innovative sustainable energy projects that have been conceived and developed.

KEYWORDS

Energy management, digester gas, cogeneration, photovoltaics, in-house engineering, renewable energy, hydroelectric, landfill gas, fuel cell.

INTRODUCTION

The City of San Diego’s Metropolitan Wastewater Department (MWWD) treats the wastewater from the City of San Diego and 15 other cities and districts in a 450 square mile area with a population of over 2.2 million people. An average of 180 million gallons of wastewater is treated daily. The system’s peak capacity is 477 million gallons per day (MGD).

MWWD owns and operates four wastewater treatment plants and 90 pump stations. The treatment plants include the 240 MGD advanced primary Point Loma Wastewater Treatment Plant, the 30 MGD North City Water Reclamation Plant, the 15 MGD South Bay Water Reclamation Plant and the 250 dry ton per day Metro Biosolids Center. It also includes nine large pump stations with capacities from 15 MGD to 432 MGD with pumps ranging from 150 to 2250 horsepower (hp). MWWD is managed from a complex of 6 buildings in San Diego’s Kearny Mesa area called the Metro Operations Complex or MOC.

The MWWD utilizes in-house engineers, operations personal and interested staff members to implement its Energy Management Plan. This Energy Plan, written by in-house staff in 2000, is updated annually and helps MWWD prioritize its energy audits, energy generation projects and energy management issues. MWWD has performed 19 energy audits of its largest facilities utilizing an in-house energy audit team trained with a special state grant for wastewater energy education. The Department has received state energy incentives for lighting, fan variable frequency drives (VFDs), centrifuge back drives, aeration systems and many other projects. State grants have helped to fund a 1.35 megawatt (MW) hydropower plant and 1.2 MW digester gas fueled emergency generator/peaking shaving system at the Pt. Loma Wastewater Treatment Plant (PLWTP). State grants also encouraged the first commercial 30 kW cadmium telluride photovoltaic system as manufactured by 1st Solar to be installed on one of MWWD’s central office buildings.

The MWWD also owns and operates a 4.53 MW digester gas cogeneration plant at the PLWTP. MWWD’s energy engineering staff has also developed and currently oversees a 6.4MW privatized landfill gas and digester gas fuel cogeneration system at the Metro Biosolids Center (MBC) and a 3.8 MW privatized landfill gas fueled small power producer at the North City Water Reclamation Plant (NCWRP). MWWD also owns and operates two natural gas 2250 hp direct drive engine driven pumps at its Pump Station 2 (PS 2) facility.

MWWD generates renewable energy at four locations from four different sources: digester gas, landfill gas, hydro and solar energy. Four of these renewable energy power generation systems are City owned and operated. The two landfill gas systems are privately owned.

The City of San Diego Metropolitan Wastewater Department has obtained millions of dollars of energy grants and incentives to compliment its in-house technical resources and its many renewable resources to control its energy costs. This paper will discuss MWWD’s energy programs and the major energy projects that have been completed and that are being planned.

THE BEGINNING

Energy is MWWD’s second largest expenditure next to personnel. This major expense has been a Department focus since the 1980’s when the PLWTP designed and constructed a 2.7 MW digester gas fuel power generation facility and a 1.35 MW hydro electric plant on the treatment plant’s ocean outfall, which has a 90 ft elevation drop to the ocean.

In 1991, as part of a major upgrade planned for the whole system, the Department had an agreement with the Navy to relocate its Fiesta Island Biosolids Processing Facility to the Marine Corps Air Station at Miramar. The City operated a major landfill on Miramar land leased from the Navy adjacent to the location were the new Metro Biosolids Center (MBC) was to be located. The US Navy, being the landowner, was being cited by the Air Pollution Control District for landfill gas emissions. The Navy had kept all landfill gas rights as part of the landfill lease, but did not have the ability to economically utilize the gas. MWWD offered to assist by taking ownership of the landfill gas and building a power plant on the new MBC site.

At the same time, the City’s PLWTP digester Gas Utilization Facility (GUF) needed to expand in order to meet the increased demands of the PLWTP as a $250 million upgrade occurred to this 30 year old facility.

THE PRIVATIZED LANDFILL GAS FACILITIES

Because the IRS offered substantial tax credits in the early ‘90’s, (small credits are still available) for the development of new biogas generation systems, the City utilized a request for proposals process to select a firm to design, build, manage and operate a 6.4 MW cogeneration system at the new MBC facility as it was being designed. The selected privatizer would also be responsible for installing the required landfill gas (LFG) collection system. Firms were also offered an option to utilize the Miramar LFG to fuel a power plant at the Department’s North City Water Reclamation Plant (NCWRP) that was under construction only three miles from the landfill. Additionally, since the MBC had digesters to process the NCWRP wastewater solids, this digester gas would also be leased to the private firm. Minnesota Methane (MM) was chosen to install these systems and provide the required services to the City.

These projects provided the City with $7.3 million worth of LFG systems, avoided $4 million in construction costs at MBC and provides electricity to MBC at 5¢/kWh and heat at 14¢ per therm, saving MBC over $2 million per year in current utility costs. The 3.8 MW North City Cogeneration Facility (NCCF) was also constructed by MM at the NCWRP where they also pay 5¢/kWh for their electricity and they also save about $2 million/yr on their electric bill.

THE PLWTP’S UNIQUE RENEWABLE POWER PRODUCTION SYSTEM

The 1350kW DeLavalve 600 rpm engines installed at the PLWTP to utilize the digester gas in the 1980’s were not reliable and many parts were no longer available. The digester gas production was expected to double with the upgraded treatment plant and space was a significant issue. It was decided to consolidate four boiler facilities into one boiler house next to the existing engine building call the GUF. The two 1350kW engine generators were replaced with two new, state-of-the-art 2585kW Caterpillar model 3516 cogeneration systems. The 1350kW hydroelectric facility (Hydro), built in the 1980’s, was never commissioned due to start up problems. In 2000, MWWD received state grants and incentives of $800,000 and invested $500,000 of the Department’s capital into a design/build and start-up contract to refurbish and commission the Hydro. The Hydro produced its first electricity in May 2001. In December 2001, MWWD received a state grant to fully fund the upgrade of PLWTP’s 1.5 MW Caterpillar model 3512 backup diesel generator so that it could operate on 80% digester gas and 20% diesel fuel. These units form the quartet of renewable power generators that supply the treatment plant with its average load of2 MW. The PLWTP sells up to 4.8MW of renewable energy to the local utility, San Diego Gas & Electric Company (SDG&E), at a preferred wholesale electric rate. This unique renewable power system “saves” the plant approximately $2.8 million per year when revenues are included.

PHOTOVOLTAIC

The first commercial installation of a cadmium telluride photovoltaic system (PV) as manufactured by 1st Solar was installed on MWWD’s MOC III facility with a state grant of $146,000 in 2003. This 30kW system provides over 20% of the building’s electrical requirements and cost the City $174,000 after the grant. The PV system saves about $11,000 per year. MWWD management directed Engineering to pilot innovative renewable technologies as this design build project was being scoped. MWWD was rewarded with 20% higher electrical production than comparable standard silicon based PV systems.

NATURAL GAS ENGINES

In 1992, Pump Station 2 (PS 2) had two 2250 hp natural gas fired Caterpillar model 3612 engines installed to direct drive two of the station’s wastewater pumps. These engine-driven pumps were programmed and permitted to operate to protect the force main in special flow situations and in a constant flow mode. In 1996, the pump station staff was having problems reliably starting the engines. It was decided the pump station would be more reliable if the engines could be started and stopped less frequently and if they could be run at variable engine speeds and provide variable flows rates. MWWD would also benefit with substantially more electrical savings. The air pollution control permits and engine control systems were successfully changed to allow continuous operation as well as variable speed operation of the engines. The pump station now runs these units as much as operationally allowed, currently saving Pump Station 2 about $600,000 per year, even with the recent escalation in natural gas prices.

ENERGY ENGINEERING AND CONSERVATION

In 1995, an additional energy engineer was hired dedicated to energy conservation and grant procurement. Not long after this, an existing power plant operator with Navy teaching experience became available to assist with managing the power contracts associated with the plants being built at Miramar landfill and the PLWTP. This became the nucleus of a group of plus or minus four people that spent between 50% to 100% of their time managing the Department’s power generation, energy projects, energy data, and energy reports, as well as obtaining energy grants and incentives. The early years were spent reviewing designs of new projects to encourage energy conservation, applying for and managing new construction energy incentives and getting power plants built. Since 1991, over $2.7 million worth of new construction energy conservation incentives, grants, and energy production incentives have been received by the Department.

These energy engineers in the Department’s Energy Section also analyzed prospective energy projects, managed energy audits, managed and negotiated energy contracts, assisted with wholesale energy sales coordination and generated and analyzed energy budgets.

In 1999, with the major power plant construction projects being completed, a consolidation of the Department’s engineering divisions occurred and the new Deputy Director wanted to make a major push to encourage the operating divisions to be a more active partner in the Department’s energy conservation and power generation efforts. Up until this time, it was felt that energy projects were “Downtown” Engineering’s projects being pushed onto the operating divisions. To remedy this, the new Deputy Director decided to have a Department Energy Plan written by the operating divisions. It would be a ground up effort. A treatment plant superintendent was selected in January 2000 to be the Department’s Energy Manager and to lead the writing and implementation of the Plan. The energy engineers were there to support them in this effort.

The MWWD Energy Plan was completed in June of 2000. It included discussions of:

1.Formation of a new Department Energy Committee

2.Implementation of regular energy meetings with the Assistant Director, the Department’s Energy Managers, Engineering and the Attorney.

3.Assignment of Facility Energy Coordinators to each major facility and made all of them part of the Department Energy Committee

4.Definition of energy responsibilities down to the section level

5.Development of an internal Energy Audit Team and procedure for approval of audit reports and projects (see next section)

6.The status of energy projects

7.Energy use and demand costs for each facility and Department wide

8.The status of the electrical industry in California

9.The Department power plant sales and purchase contracts

10.Definition of energy terms

11.Energy Grants and Incentives available

12.Potential future energy opportunities

13.Implementation of the Energy Plan

Yearly updates to the Plan are issued.

In June of 2003, Department management requested an assessment of the progress being made toward the implementation of the Department Energy Plan. Issued by the Department’s Energy Committee in December of 2003, this assessment addressed the Department’s accomplishments and its need for improvement on over 25 different items. The long list of accomplishments and the frank discussion of issues to be solved indicated to management that this ground up approach was working, projects were moving forward, operational changes were being made and the overall Department culture of energy awareness was changing for the better. One suggestion that came out of this process was an energy “Pay for Performance” goal. As a part of an existing Department performance incentive plan, a new goal was established. If the Department lowered its energy use and/or demand annually by 3%, then each person in the Department received a small bonus. While this goal has changed over the years, it still exist and encourages energy awareness for all MWWD Personnel.

ENERGY AUDITS

The Department Energy Plan formed a core energy audit team that would audit each facility in order of priority listed in the Plan. The core team would consist of the energy engineers from the Energy Section and a group of Department staff members who volunteered to be trained to be energy auditors. Most of them were Facility Energy Coordinators. A special grant was received from the State to pay for our energy audit team to be trained by wastewater energy consultants.

Each energy audit is begun with the Facility Energy Coordinator providing the data, and an energy engineer coordinating the audit team. Usually, at least one facility operator provides on site assistance. The facility site inspection is immediately followed by a brain storming session where a draft list of credible energy saving ideas is generated for additional study. A draft report is issued by the team after “back of the envelope” type calculations are made by the audit team and reviewed by the energy engineers.

Most suggestions that require an investment of more than a few hundred dollars are more thoroughly analyzed in detail by the energy engineers to see if a capital project can be justified. The energy engineer that performs the analysis then tracks and implements these projects.

The Department Energy Manager leads follow-up facility energy suggestion implementation meetings about every two to three years. Currently:

19 facilities have been audited

169 potential energy improvements have been identified

44 energy improvements have been completed

20 energy improvements have been analyzed and are proceeding

12 energy suggestions have been analyzed and are not proceeding

93 are pending additional analysis, testing, or an appropriate funding source

SPECIAL RECOGNITION

MWWD is proud that in 1997, The San Diego County Tax Payers Association awarded the City of San Diego with its Golden Watch Dog Award for the money that the MBC Cogeneration system and Landfill Gas Facilities saved the City of San Diego sewer and landfill rate payers.

In 2002, the PLWTP hydroelectric plant’s commissioning project received the City of San Diego’s William Earl Hayden Award for the Industrial Project of the Year.

In 2006, the U.S. Environmental Protection Agency listed the City of San Diego as the government agency consuming the most renewable energy in the country. Twenty five percent (25%) of the energy the City of San Diego consumes is renewable, and 96% of that is consumed and caused to be produced by MWWD.

LOOKING FORWARD

Currently, the MWWD’s major plans are expected to include:

A 900kW expansion to the NCWRP’s landfill gas fired privatized (Minnesota Methane) NCCF. It is expected to save the City $150,000/yr starting in 2008.

Participation in a privatized remote controlled backup generator demand response program by ENERNOCand SDG&E that will bring six of our backup generators on line (6.3 MW total) to prevent rolling blackouts in the SDG&E territory. In return, ENERNOCwill provide free generator maintenance to MWWD on these six (6) units.

A one megawatt privatized Photovoltaic system is being considered for our South Bay Water Reclamation Plant. (Privatizer has been selected) (Sun Edison, 1st Solar, Cadmium Telluride)

A privatized Beneficial Use of Digester Gas (BUDG) project is being designed to utilize excess PLWTP digester gas that is currently being flared. The gas will be compressed and trucked to off-site locations to be utilized in 3.6 MWfuel cells. The project is expected to include a 300 kW fuel cell on the PLWTP site to service the digester gas compression system. (Privatizer (BOC) has been selected).