By Teresa Hansen, Senior Editor
Searles Valley Minerals Operations Inc. (SVM) is located in the California high desert near the town of Trona. The company mines minerals out of the Searles dry lake named for its founder, John Searles, who discovered the minerals more than 130 years ago. At the site, SVM operates three mineral processing plants, two power plants and a mining operation to manufacture soda ash, borate and sodium sulfate.
One of the power plants, known as Westend, was originally a gas-fired plant that included a 45-year-old GE Frame 5 turbine generator and heat recovery steam generator (HRSG) that produced 16 MW of electricity and 100 kilopounds per hour (kpph) of 250 psig steam. It also included a gas-fired packaged boiler that produced up to 60 kpph of 250 psig steam. The second power plant, named Argus, is a coal-fired plant that includes two 30-year-old, 700 kpph, 1,500 psig Combustion Engineering VU40 steam generators and two 27.5 MW GE medium pressure steam turbines. SVM operates both plants, which provide baseload electricity for its mineral mining and processing operations.
 The steam transfer pipeline between the Westend and Argus plants crosses a dry lakebed and includes multiple expansion loops (shown) along its five-mile length. |
In 2007, SVM began a project to shut down the gas-fired power and steam production at its Westend plant and provide coal-fired steam from its Argus plant. The project, which earned a $3.6 million incentive rebate from Pacific Gas & Electric Co., was the largest natural gas savings project awarded in the rebate program’s history, said Roland Buchs, SVM’s director of utilities and engineering. “By shutting down gas-fired steam and power generating equipment at the Westend plant, the project saves about 4,500,000 therms of natural gas each year,” he said.
The distance between the two plants is a little more than four miles. The pipeline SVM installed to transfer the steam, however, is just over five miles long, the result of routing and expansion loops. A steam supply line and a condensate return line run parallel to each other across the dry floor of Searles Lake. These lines stand a few feet above ground level with the help of steel pipe supports. The vertical expansion loops also serve as crossing locations for roads that occasionally cut across the pipeline. Bridges are used where the pipe crosses railroad tracks, and a single underground crossing accommodates a county highway. Altogether, there are more than 60 steam pipe loops in the system. There is also one condensate pipe vertical expansion loop for every two steam pipe expansion loops.
SVM built a condensate recovery and delivery system at the Westend plant and a condensate receiving system at the Argus plant. These systems include instrumentation for monitoring and controlling water quality and chemical treatment for corrosion control. Vertical pumps return condensate the entire distance from the Westend condensate collection receiver to the Argus condensate receiver. Foxboro DCIS systems in the plants provide monitoring and system control for all facets of the project.
About 150 kpph of steam is supplied from the 450 psig header at the Argus plant at around 430 psig and 620 F. The steam is transported via a 12-inch insulated carbon steel line to the Westend plant at about 270 psig and 500 F. There it connects to a pressure control valve, which maintains the Westend plant main steam header at 250 psig. A six-inch insulated carbon steel line returns steam condensate to the Argus plant’s coal-fired boilers.
Although replacement steam for Westend is supplied from Argus coal boilers, no additional coal burning was required. Several conservation projects were completed in parallel with the steam line construction ensuring that enough steam would be available to Westend. “The idea is to use the steam conservation project so that no generating capacity is lost,” Buchs said. “Reduced consumption was the target and it is being achieved. There is a smaller amount of gas used in the mineral plant processes which will continue to be used.”
The project included installing a thermo-compressor and 90-pound flash system on rotary steam dryers at Argus. The thermo-compressors optimize 450 psig steam usage to the rotary dryers The 90-pound system flashes the high-pressure condensate from the dryers. This replaces 450 psig steam that had been used to heat two fluid bed dryers. In addition, a new heat exchanger preheats feed brine from the lake injection mining operation, using the warmer’s spent brine that is returned to the lake rather than steam.
A third conservation project currently in progress will cool the gases being compressed by a series of steam-driven compressors so that the volume of compressed gas is reduced, resulting in less steam to drive the compressors.
The project required no reviews or revisions to the Argus plant’s environmental New Source Review status. SVM was required, however, to obtain a review of issues involving pipeline construction from the federal Bureau of Land Management before rights-of-way were issued for pipeline construction across public lands.
 The steam supply line and the condensate return line run parallel to each other. |
Because this was a unique project, many challenges were encountered. Designing and routing the steam and condensate lines posed some problems, especially resolving how to handle pipe expansion and road crossings for such a long line. In addition, dealing with soils in the dry lakebed proved challenging. So were tasks related to completing environmental studies and securing the necessary rights-of-way.
Determining how to collect and obtain good quality condensate recovery for high-pressure boilers from an old plant was also difficult. The thermo-compressor project technology was essentially developed on the fly, said Buchs.
“There was just a lot of overall coordination involved in getting all the pieces to fit: pipeline, tie-ins in both plants, condensate handling systems and three innovative conservation projects,” he said.
Even before the project was completed, some unique maintenance issues arose. “How do you clean a five-mile pipeline if you expect to deliver quality steam on the other end and how do you test its integrity before starting?,” Buchs said. Issues such as these were addressed throughout the design phase and much of the construction phase.
“We ended up doing spot x-rays and weld inspection for quality control, a lot of pigging for initial cleaning and then a hydro pressure test and some steam blowing for final cleanup and pressure testing,” he said. In the end, the line started up with fewer problems than expected. Buchs said only a few leaks and some expansion joint issues needed to be fixed.
Much of the project was completed with in-house engineering and local contractors. The detailed pipeline design was completed by Veizades and Associates and construction was completed by PCL Industrial Services.
PG&E estimated that the project reduces 26,325 tons of CO2 emissions and 22 tons of NOX emissions per year. These estimates do not include the direct CO2 and NOX reductions associated with shutting down the Westend gas turbine and package boiler.
Buchs said SVM expects to recover the investment within two years.