Efforts by DTE Energy to cut methane greenhouse gas emissions by 80 percent progressed another step forward this week at the company’s Kalkaska Compressor Station, where the second of three natural gas compressor engines was overhauled, reducing methane escaping into the atmosphere. The first compressor unit was overhauled last year and work on the other two units will be finished this year.

Workers installing a new compressor rod and packing on a natural gas pumping engine in Kalkaska, Michigan

The piston-like rods on each compressor engine have bands of packing that seal the rod in the combustion chamber. The worker in the foreground is doing prep work on a seal to prevent fugitive methane escapes. The overhaul and rod packing work involves four technicians working six ten-hour days.

DTE is reducing fugitive methane escapes in two ways – replacing aging iron and steel gas lines with composite piping and changing seals known as rod packing on natural gas compressor engines like those in Kalkaska. Replacing the rod packing during routine compressor maintenance keeps the machines in top working condition with the added benefit of reducing escapes of fugitive methane.

“Operating in the most environmentally sustainable manner is a corporate, departmental, and Kalkaska goal,” said Karla Shawhan-Bonnee, operations manager at the Kalkaska station and a 34-year company employee. “Our 19 employees take pride in bringing about positive change by reducing fugitive methane emissions. They’ve identified multiple opportunities to reduce methane emissions from our station and this, in turn, enables our company to report lower companywide numbers. We’re literally all the better for it.”

Located about 25 miles east of Traverse City, the Kalkaska Transmission Station was established in the early 1970s. The Kalkaska Compressor Station was built in 1992 as a joint venture with ANR, one of the largest interstate natural gas pipeline systems in the United States, to compress gas piped to the nearby ANR Blue Lake Storage Field. Gas is pumped and stored there during the summer about 6,600 feet underground and withdrawn when demand peaks in the winter.

Huge natural gas compressor engines inside DTE' Energy's facility in Kalkaska, Michigan.

The Cooper GMVH 2700-horsepower compressor units were delivered to the Kalkaska station on a rail car in 1992.

Kalkaska is a hub of natural gas production and distribution. DTE’s Kalkaska facility keeps natural gas moving throughout northern Michigan by feeding multiple pipelines in the area as well as gas pumped directly from nearby production wells. The Antrim Shale Field that crosses northern lower Michigan is one of the nation’s top 100 natural gas fields. Michigan also has the largest underground natural gas storage capacity in the nation.

The three reciprocating compressor engines at Kalkaska are considered industry workhorses. One of the units operates 24/7, 365 days a year while the others crank up on demand. Including Kalkaska, DTE operates 10 natural gas compressor stations statewide housing 57 compressor engines.

“When doing the rod packing work, other maintenance is performed on the units including a complete compressor overhaul,” said Shawhan-Bonnee. “This includes inspecting critical parts and replacing everything that’s at the end of its service life. We attempt to restore, as close as we can, to like-new tolerances and install low-emission packing.”

Works remove new compressor rod assemblies from crates to install them as part of a natural gas compressor overhaul project at DTE Energy's facility in Kalkaska, Michigan.

Uncrating one of the compressor piston rod assemblies. Each compressor engine has three of these units.

The results are a terrific improvement. Before the overhaul, the compressor units had a 7.00 standard cubic feet per minute (SCFM) leakage rate resulting in 3679.2 thousand cubic feet (MCF) per year. Post-overhaul, the units have a 0.31 SCFM leakage rate, down to just 162.9 MCF per year.

The gas mains and valves on the exterior of DTE Energy's Kalkaska natural gas station.

Natural gas transmission mains leading into and out of the Kalkaska Compressor Station. DTE is the second largest taxpayer in Kalkaska County, operating several pipelines, taps, stations, and valve yards.

DTE’s methane reduction program is reducing carbon dioxide-equivalent emissions by about 16,300 metric tons per year. Using the EPA greenhouse gas calculator, that’s equivalent to the annual greenhouse gas emissions from 3,490 passenger vehicles, or the CO2 emissions from the energy use of 1,760 homes for a year.