April 2010 Vol. 237 No. 4
Features
Gas Utilities Should Ask A Simple Question: Whats In Your Pipeline?
Alternative sources of methane gas often get overlooked in America’s ongoing quest to relieve its dependence on finite fossil fuels and decrease its greenhouse gas emissions. However, what should not be overlooked is the reality that biogas can be a supplement to natural gas in this country’s natural gas transmission and distribution systems.
Across the country, municipalities are making that valuable discovery. Over the last several years, many cities and towns have become involved with alternative energy and renewable energy projects that deliver an alternative source of methane gas from non-traditional sources. And as a result, these communities are demonstrating how to be both economically savvy and environmentally friendly.
Landfill methane can provide fuel for a cogeneration (COGEN) plant. The organic matter in landfill waste is consumed by bacteria that give off gas rich in methane. Landfill methane becomes a greenhouse gas at least 20 times more potent than carbon dioxide – the principal greenhouse gas – when it is released into the atmosphere. In some instances, methane is burned off, or flared, to minimize the release of methane gas into the environment, but that approach is fast becoming archaic, as operators of landfill facilities are coming to realize it is a waste of potential energy. Capturing that gas and using it to generate electricity and heat is becoming a popular alternative.
According to the Environmental Protection Agency, there are 480 operational landfill gas-to-energy projects in the U.S. In addition, about 130 projects are under construction or under study.
One completed project is at the University of New Hampshire (UNH) in Durham. The recently launched EcoLine project gave the university the distinction of being the first in the country to depend on landfill gas for its primary fuel source. UNH purchases methane gas from the nearby Turnkey Recycling and Environmental Enterprise facility in Rochester, NH. The gas used to produce roughly 85% of the electricity and heat consumed on the university’s 5 million square-foot campus.
The methane gas produced at Turnkey is used to power UNH’s $28 million combined heat and power facility, or COGEN plant, which features a chilled water plant. The COGEN plant takes waste heat typically lost during the production of electricity and uses it to heat campus buildings, thus making more efficient use of the university’s energy resources.
At the landfill, 300 extraction wells, as well as a series of collection pipes, capture the methane-rich landfill gas, which is then cleaned of compounds such as siloxanes (typically produced by the decomposition of various materials, most notably health and beauty care products) through a variety of different methods, particularly compression refrigeration and heating, and activated charcoal.
Once it has been enriched and purified, the gas is odorized at the landfill site before being sent the roughly 12.7 miles from Turnkey to UNH.
Digester Gas
Another popular alternative to traditional fossil fuels is the use of combined heat and power (CHP) systems. Pittsfield, MA, recently completed the final design for an upgrade to its wastewater treatment facility, which anaerobically digests sludge as part of its secondary waste treatment. Some of the digester gas being produced in this digestion process is flared. With the proposed modifications, a CHP system will be installed, using three 65-kW rated microturbines for a total rating of 195 kW. The microturbines will be fueled by the digester gas.
Under the proposed CHP system, the digester gas – a byproduct of the facility’s anaerobic sludge digestion process – will be sent through a fuel gas-conditioning system that removes contaminants from the digester gas and boosts the pressure of the gas to the microturbines. The target contaminants of the fuel gas-conditioning system include water vapor, hydrogen sulfide, and siloxanes, which are silicone-based compounds contained in many health and beauty care products.
The conditioned digester gas will then be used to fuel the microturbines which will generate heat and electricity to meet the plant’s baseload demands. The waste heat in the exhaust of the CHP system will be utilized in a heat exchanger to produce hot water. This hot water’s purpose is to heat the sludge in the primary digester and serve as building heat in the digester building.
And while it is anticipated there will not be enough heat generated to meet the peak sludge heating requirements under design winter conditions – making use of the existing boilers in the pump and power building for sludge heating and building heat a possible necessity – the microturbine system is expected to reduce the operating time of these boilers and thus, the volume of required diesel fuel for operation of the existing boilers, as well as minimize significantly the amount of digester gas diverted to a flare-gas burner.
The benefits of natural gas alternatives are several. Thanks to the aforementioned proposed upgrades, the Pittsfield wastewater treatment facility is expected to reduce the flaring of the digester gas and consumption of diesel fuel, and decrease the plant’s electric bill by an estimated 30% (saving taxpayers over $200,000 a year). The CHP project is expected to have a payback period ranging from five to eight years, prior to receiving funding from The American Recovery and Reinvestment Act of 2009 (ARRA).
Meanwhile, the EcoLine project will provide UNH with much-needed energy stability. By replacing commercial gas with renewable, carbon-neutral landfill gas as the primary fuel, the COGEN plant will stabilize energy costs for the university and ensure the plant has a dependable source of fuel for decades to come. The landfill gas project costs an estimated $49 million with an anticipated payback of 10 years.
Projects such as these have gas utilities, both domestic and international, considering one simple question: “What’s in your pipeline?” By considering alternatives to natural gas, suppliers are creating new paths that can help the country meet its ambitious renewable energy goals.
Authors
Michael A. Nicoloro, P.E., is a registered professional engineer (Massachusetts and New Hampshire). He is director of energy services for S E A Consultants Inc., which is headquartered in Cambridge, MA. His focus is in the renewables and natural gas arenas. He has 31 years of diverse experience working in plant and process environments. He is the former manager of Gas Supply and LNG/SCADA Operations for Commonwealth Gas Co. (now N-Star), and managing director for the City of Cambridge Water Department.
Joan Fontaine, P.E., is a principal engineer in S E A Consultants’ Energy Sector. She has over 20 years of engineering experience, 12 years of which have been focused in the energy sector performing mechanical and process design, and analysis for numerous utility projects, as well as managing an array of projects, including both design and design/build projects. Her project experience includes propane, natural gas, LNG, and alternative fuel applications. The majority of the balance of her professional experience has been with two General Electric facilities.
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