CommonWealth is the developer and sole owner/operator of two projects at the Crapo Hill Landfill in Dartmouth, MA:
- A 3.3-MW landfill gas-to-electricity project known as the Greater New Bedford LFG Utilization Project (the LFG Project).
- A 100,000-gallon anaerobic digestion project for converting liquid organic wastes to bio-gas, known as the CRMC Bioenergy Project (the AD Project).
(CNBE) The LFG Project generates electricity from combustion of landfill gas in four Caterpillar 3516 LE internal combustion engines. This facility is located on a site adjacent to the Crapo Hill Landfill in Dartmouth, MA, and leased from the Greater New Bedford Regional Refuse District, which owns and operates the landfill. The LFG Project is owned by CommonWealth New Bedford Energy, LLC (CNBE), which is owned by CommonWealth.
Landfill gas is collected from a series of vertical and horizontal extraction wells connected by piping and forming a network that covers the entire volume of the Crapo Hill Landfill. The gas typically consists of 48% to 55% methane, up to 40% carbon dioxide and less than 1% oxygen, with the balance mostly nitrogen drawn in from ambient air.
Two vacuum blowers connected to the collection network bring the gas from the landfill to the LFG Project, then through a media-based system to remove hydrogen sulfide and a condensate knock-out to remove moisture. The blowers then push the pressurized gas through a radiative cooler and coalescing filter before delivery to the engines for combustion. The engines drive generators rated at 825 kW each.
The electricity is delivered to the regional grid through the Eversource 13.2 kV local distribution system. Air emissions are controlled by ensuring efficient combustion, aided by a state-of-the-art air-to-fuel ratio controller on each engine for optimized control of NOx and CO emissions.
The LFG Project was constructed starting in March 2005 and achieved commercial operation in December 2005. The sulfur removal system, supplied by MV technologies, Inc., was added in 2016.
Development was supported in part by loan programs of the Massachusetts Renewable Energy Trust (now the Massachusetts Clean Energy Center) and private investments of debt and equity.
Environmental benefits of the LFG Project include the following:
- Supports efficient collection of methane gas from the landfill, thereby preventing its emission to the atmosphere. Methane has 28 times more impact on global warming than emission of an equal volume of carbon dioxide.
- Destroys the methane by combustion with an effectiveness that exceeds 99.8 percent.
- Controls landfill odors by removing the hydrogen sulfide and destroying VOCs and other odorous compounds generated as a part of the landfill gas.
- Displaces electricity that would otherwise be generated from fossil fuels.
- Avoids losses and adverse reliability impacts of long-distance transmission of electricity generated from remote sources.
(CRMC) The AD Project generates bio-gas from anaerobic digestion of liquid organic wastes in a 100,000-gallon digester tank. The digestion facility is located adjacent to the Crapo Hill Landfill in Dartmouth, MA, on a portion of the site leased to CNBE for the LFG Project. The AD Project is owned by CRMC Bio-energy, LLC, which is owned by CommonWealth.
The AD Project accepts liquid wastes that have included dairy waste, fermentation process wastes, other food processing wastes, compost facility tea and pumpable biosolids from wastewater treatment plant sludge. Liquid wastes are delivered by tanker trucks into any of three feedstock storage tanks, combined in a mixing tank, then injected into the digestion tank. Tank temperature is maintained by pre-heating feedstock with heat recovered from engine jacket water or, as appropriate, by using the radiators to pre-cool feedstock Active bugs in the tank convert the organic material to bio-gas, which typically consists of 55% to 70% methane, the remainder being predominantly carbon dioxide. The bio-gas is piped to be combined and mixed with the landfill gas upstream of the sulfur removal system for eventual delivery to the engine-generator sets, where the mixture is combusted to generate electricity. Although the composition of the bio-gas is somewhat different than the landfill gas, the engine controls and air-to-fuel ratio controller support efficient combustion and minimize emissions. Residual liquids from the digestor are pumped to a fourth storage tank, then either (i) returned to the landfill to stimulate additional generation of gas for collection; or (ii) discharged to the sewer.
The AD Project was constructed over the summer and achieved commercial operation in November 2014. Construction was supported in part by a loan from the Massachusetts Business Development Corporation and grants from the Massachusetts Department of Environmental Protection and the Rural Development Authority of the U.S. Department of Agriculture along with equity investment by CRMC.
Environmental benefits of the AD Project include the following:
- Collects and destroys all the methane that the liquid organic wastes can generate.
- Provides a local outlet for management of liquid organic wastes other than a landfill or incinerator and avoids the emissions that would otherwise occur.
- Supports generation and collection of additional landfill gas from the landfill.