Owner/operator: Xcel Energy
Located in a semi-arid region, this “Texas tough” coal-fired power plant uses a number of smart practices to increase water-use efficiency. For example, a pipeline was constructed to send blowdown water from nearby Plant X for treatment and recycling at the 1,080-MW Tolk Station, making both plants “zero-discharge” facilities. For its environmental stewardship and superior plant operations, the Powder River Coal Users’ Group named Tolk Station its 2010 Plant of the Year.
With a backdrop that looks like the set of the Lonesome Dove television miniseries, Tolk Station delivers power not only to Xcel Energy customers in Texas and New Mexico but also to customers of rural cooperatives and municipal utilities in the region. The facility is situated on the western edge of the Texas Panhandle, which is traditional ranching country. Specifically, the plant is located near what was once the XIT Ranch, which, when it was one of the largest ranches in U.S. history, covered more than 3 million acres.
Tolk Station was designed in-house in the late 1970s by the generation plant design group at Southwestern Public Service Co. (Xcel Energy’s Texas-based operating company). Total construction cost was $571 million, or $506/kW (about half the national average), according to David Low, Tolk and Plant X plant director. A single general mechanical contractor was used, along with four subcontractors. The plant was designed to burn Powder River Basin (PRB) coal.
“The plant was designed for low station loads by using variable-frequency drive fans, two-speed main circulating pumps, and rifle tubes on the waterwall, which reduced horsepower requirements from boiler circulating pumps,” Low said. “The units had the first submerged scraper conveyor design in the U.S. The Unit 1 and Unit 2 cooling towers, as well as the Unit 2 baghouses, were in–house designs. The plant layout was designed for ease of maintenance due to fact that the design group had visited with plant personnel.”
Other features include a separate economizer ash collection system, economizer in-line tubing to ease cleaning, a rotary dumper building, an Amertap system to keep the condenser clean, twin 4,160 V start-up boiler feedpump motors (not 6,900 V switchgear), cooling tower riser valves, an auxiliary circulating water plate heat exchanger, air preheater sector seals, and a control room simulator for training.
Each of the plant’s two units, completed in 1982 and 1985, has a generating capacity of 540 MW. Tolk Station is the largest generating plant in the Texas Panhandle-Plains region.
Low described the following operations of the plant:
- Overall efficiency rate: Unit 1—530 MW net, 9,574 Btu/kWh (tested in 2009); Unit 2—535 MW net, 9,870 Btu/kWh (tested in 2008).
- Forced outage rate: 2.75% for 2009.
- The equivalent forced outage rate for the past five years (2005 to 2009) ranged from 4.66% to 3.21%.
- Equivalent availability factor during the past five years ranged from 87.01% to 83.88%.
- Gross capacity factor during the past five years ranged from 76.18% to 82.17%.
- Net capacity factor during the past five years ranged from 75.32% to 81.74%.
Xcel has 106 employees at the facility handling operation and maintenance duties. In addition, Savage Companies provides coal-handling services for the Tolk Station and employs 26 workers at the facility. “We have a very devoted crew that keeps the plant safe, clean, and running efficiently,” Low said.
During the past decade, the Savage Companies have carried out the following capital improvement projects at the facility:
- New fire suppression systems for mobile equipment: 2006
- Controls upgrade: 2006
- Replacement baghouses: 2005
- Replacement fire suppression system: 2005
- Railcar dumper refurbishment: 2002 to 2005
- Carbon monoxide (CO) monitoring system: 2003
- Pile discharger refurbishment: 2003
- Tramp metal magnet replacement/upgrade: 2003
- Replacement automatic sampler system: 2002
Water Conservation Measures
“Operating in a semi-arid region, we have developed a unique solution to reduce water supplies at two of our facilities, Tolk Station and nearby Plant X,” Low said. “By creating a pipeline to send Plant X’s blowdown water for recycling and additional freshwater to Tolk Station for treatment, we increased water recovery from Plant X and eliminated the need for new sludge and disposal ponds and a wastewater treatment system at the facility. As a result, the combined plants’ water consumption was reduced by about 180 million gallons per year” (Figure 1).
|1. Riding herd over water supplies. The Tolk Station is shown with its evaporation pond in the foreground. It is a zero-discharge plant, which means that no process waters are discharged off-site. The facility collaborates with nearby Plant X to treat its blowdown water. As a result, the combined plants’ water consumption has been reduced by about 180 million gallons per year. Courtesy: Xcel Energy|
Tolk Station is a zero-discharge plant, which means that no process waters are discharged off-site. For example, water is cycled through the cooling tower 20 times to maximize its usage.
Air emissions are controlled at Tolk Station with the help of the low-sulfur PRB coal and baghouses. The baghouses remove approximately 99% of particulate emissions from the flue gas. The particulate or ash collected at the Tolk Station is recycled as by-products for construction, oil well “mud,” and other uses rather than sending it to a landfill.
“In order to improve the plant’s environmental performance, in 2009 we purchased the Neuco Neural Net for both units and the Zolo Boss system for Unit 2,” Low said. “MIC adjustable fuel orifices were installed in 2008 to 2009. This equipment has helped the plant lower NOx emissions.”
The Powder River Basin Coal Users’ Group (PRBCUG) named the Tolk Station as its 2010 Plant of the Year, citing its safe operations, high reliability, and environmental stewardship. The PRBCUG is a trade group that promotes the safe, efficient, and economic use of Wyoming’s PRB coals by generating companies.
“Our employees and Savage have strived for excellence over the past few years, and this national recognition reflects that effort,” said Low. “Savage played a big role in winning this award by operating a well-run coal-handling facility.”
The facility has been proactive in dealing with the challenges related to handling large quantities of coal. For example, significant work was done in-house to reduce spills and contain dust throughout the facility at several transfer points, according to Low. Modifications and upgrades were made to the chute work, dust-settling chambers, skirting, as well as “slider-beds” and belt-scrapers. In addition, the staff recently revamped the water suppression system, which included relocating and reducing the number of spray nozzles. The result has been a system with minimal spillage and dust.
The staff deals with a variety of other challenges related to burning coal. For example, on occasion a batch of poor-quality PRB coal will be blended with a higher-quality PRB coal to meet operational restrictions on ash, sulfur, and/or sodium. In addition, to deal with boiler slagging problems, plant personnel conduct slag surveys during the normal rounds and as needed.
Due to the higher volatility of PRB coal, the Tolk Station has taken a number of measures to ensure safe work practices. For example, the plant installed the Conspec CO monitoring system and bunker baghouse fire suppression system.
The plant has an Xcel Energy/Savage emergency response team (ERT), which has 24 members. As a result of the plant’s rural location, ERT members have received extensive training for fighting fires. In addition, a few of the ERT members participate in their local volunteer fire department crews.
“We also have a mill steam inerting system that uses turbine extraction steam. The system is used as a last resort only to control a coal mill fire. There are no interlocks,” Low said.
— Angela Neville, JD, is POWER’s senior editor.