In order to satisfy California’s unrelenting demand
for energy, Pacific Gas & Electric Company (PG&E) worked with
Environetics, Inc. of Lockport, Illinois on a $12 million project to increase
the capacity of their existing natural gas pipelines.
By reclassifying the existing pipeline, PG&E avoided the
enormous expense of laying 38 miles of new pipe. The primary objectives of the
project were to safely raise natural gas pipeline pressure without increasing
the release of nitrogen oxide (NOx) into the atmosphere. These objectives were
achieved by relocating two pressure limiting stations, retrofitting two
internal combustion compressors, and performing pipeline hydrotesting
operations.
Before PG&E could return these stretches of pipeline to
service, they had to establish the safety and integrity of the pipeline by
conducting eight separate hydrotests. This process involves removing all
natural gas from the line, cleaning the pipeline thoroughly, filling it with
water (in this case, about 10.7 million gallons), pressurizing the water to a
predetermined level, removing it and drying the pipeline. After the water is
removed from the pipeline, it must be cleaned and returned to its source.
According to PG&E’s Project Manager, obtaining all
this water, and disposing of it when the testing was finished, were the
project’s biggest challenges. “We had to find almost 8 acre-feet of
water somewhere and figure out where to safely dispose of it when we’re
done. Further, we had to do this at a flow rate of 4,000 gallons per minute to
minimize the pipeline outage duration,” he said. “That’s not
an easy thing to do in the middle of the Mojave Desert.”
The project team overcame this challenge by leasing property
from a nearby solar generating plant with a good well. Environmental experts
from PG&E’s Technical and Ecological Services (TES) and
Environmental, Health and Safety departments developed a plan to build their
own contiguous water system on plant property.
Environetics worked with PG&E to solve their demanding
water storage and reuse requirements. The solution highlighted the advantages
of the patented Porta Tank design. Because of its unique design, the Porta Tank
does not require a concrete foundation. This exclusive feature reduced
installation time and allowed the site to be returned to other uses after the
tanks were dismantled. The Porta Tank design also met California’s
stringent seismic zone 4 structural requirements, providing safe water storage
during a potential earthquake.
The specified water system incorporated three big tanks
— each 13.5 feet high and 129 feet in diameter — used to store the
water, and about 14,000 feet of 12 inch steel pipe to carry it to and from
hydrotest inlets and outlets. Each tank provided over 1.3 million gallons of
storage capacity for an overall volume of nearly 4 million gallons.
Environetics manufactured and shipped the tanks within two
weeks of approvals in order to meet PG&E’s fast paced schedule.
Furthermore, an accelerated installation schedule was implemented to minimize
the pipeline’s outage duration.
Field conditions were demanding however, with temperatures hovering
above 110 degrees and winds in excess of 35 miles per hour. The installation
crew also encountered a host of the local inhabitants including scorpions, black
widows, and sidewinders.
Even under these demanding conditions, Environetics was able
to complete the installation in only four weeks.
After the hydrotesting was completed, the water passed
through a portable activated carbon filtration system and was returned to the
solar generating plant for a fifth use, avoiding the expensive cleanup and
testing process normally mandated when hydrotest water is flushed back into a
stream or lake.
“We used that water four different times,” said
PG&E’s project manager, “and now we'll be giving it back to the
plant for yet another use. No extraordinary cleaning or testing was required
— even though we’re using over 3 million gallons of water.”
As a result of this huge project, the maximum allowable
pressure inside the pipeline was boosted from 573 psig to 688 psig (a gain of about 17 percent). With the rise in pressure, compressors can deliver a substantially larger volume of natural gas through their existing pipelines to California customers - without increasing the release of nitrogen oxide (NOx) into the atmosphere.
Through careful planning, coordination and hard work, the
project also beat the outage duration goal by 11 days and the outage start date
by four months.
