Turnkey project approach
Fluor Enterprises Inc., a subsidiary of Fluor Corp., served as the engineer/procure/construct contractor for TSPP. The Babcock & Wilcox Co. (B&W) supplied the pulverized coal-fired radiant boiler fired by 18 DRB-4Z low-NOx burners with overfire air, three B&W roll wheel pulverizers; two primary, two forced draft, two induced draft, and two seal air fans with motors; regenerative air heater; two steam coil air heaters; and sootblowers. B&W also supplied the selective catalytic reduction system, spray dryer absorber (SDA), and pulse jet fabric filter to round out the project’s AQCS.
Of note is the very low NOx limit on this project: best available control technology was determined to be 0.067 lb per million Btu on a 24-hour rolling average. TSPP also is equipped with mercury control provisions built on B&W’s sorbent enhancement additive technology with halogenated powdered activated carbon (HPAC) injection upstream of the SDA and fabric filter.
As the turnkey contractor, Fluor also supplied the 350-foot stack and facilities for coal unloading, storage, crushing, and handling as well as storage silos for flyash, recycle ash, lime, and activated carbon for mercury control.
The steam turbine generator was supplied by Toshiba Corp. The plant’s distributed control system was supplied by ABB Inc.
Final cost of the project, including rail, transmission lines, water infrastructure, and owner’s costs was approximately $610 million.
The water supply for this high desert facility comes from groundwater less than 200 feet below the desert floor. One groundwater well supplies water to the plant’s raw water makeup pond via a 2-mile-long pipeline. An additional well is located at the raw water makeup pond as a backup well. This water is used as makeup for the mechanical draft cooling tower, service water, scrubber, and coal- and ash-handling systems.
Cooling tower blowdown, after nine cycles of concentration, is sent to one of the four lined evaporation ponds, each 21.5 acres in cross sectional area and 3 feet deep (Figure 3). A smaller on-site well supplies domestic water needs and boiler water makeup after passing through a reverse osmosis (RO) system and a mixed bed demineralizer. Boiler blowdown and RO reject water are discharged to the cooling tower and recycled.
3. Zero discharge. Cooling tower blowdown and plant wastewater are collected and transported to one of the plant’s four lined process discharge ponds to evaporate in the dry heat of Nevada’s high desert. In the foreground is the coal pile storm water runoff evaporation pond. Courtesy: Fluor Power
Removing mercury a priority
Regulatory uncertainty only slows the permitting phase of a project, so Newmont elected to proceed with maximum achievable control technology (MACT) because it was expected to be the most conservative regulatory approach under the then-soon-to-be-released Clean Air Mercury Rule (CAMR).
Under the assumption that mercury would be regulated by the Environmental Protection Agency (EPA) as a hazardous air pollutant with emissions limits based on MACT under Section 112 of the Clean Air Act, a permit emission limit was set at 20 x 10-6 lb/MWh over a 12-month rolling average based on the proposed MACT rule (January 2004). This limit was almost one-fourth of the CAMR limit later set under Section 111 by the EPA.
With CAMR recently vacated, the status of state programs regulating the heavy metal is unclear. However, Newmont took the high road and entered into an agreement with the Nevada Bureau of Air Pollution Control to use the mercury CEMS to optimize the mercury removal systems already installed at TSPP. The air permit issued by Nevada also requires a Method 29 source test to verify compliance.
Newmont’s TS Power Plant achieved full load on February 18, 2008. The plant staff were consumed with final commissioning and tuning of the facility during the first quarter of this year.
B&W then conducted field testing in May and June to evaluate enhanced mercury removal at various equipment operating conditions. First, the standard AQCS systems were evaluated and found to meet the permit limits. The SDA system reduced the boiler flue gas SO2 content during testing below the permitted level of 0.065 lb per million Btu and had a corresponding SO2 removal efficiency range of 87% to greater than 95%. The stack NOx emission levels were below the permitted level of 0.067 lb per million Btu and corresponded to a reduction across the selective catalytic reduction system ranging from 60% to 81%.
Next came full-scale mercury reduction testing over a seven-week period in May and June 2008 for a wide range of boiler operating conditions and mercury-reducing additive injection rates. The objective of the mercury testing was to maintain stack mercury emissions below the air permit requirement of 0.02 lb/GWh (~2.1 µg/dscm) with various combinations of reagent injection rates.
Two approaches to reducing stack mercury emissions were demonstrated: sorbent enhancement additive (SEA) to the coal and HPAC injection upstream of the SDA. Both the sorbent and reagent addition systems were supplied by contract, as part of the new boiler and AQCS (Figure 4). The summary results show that stack mercury emissions can be maintained below the permitted emissions levels with moderate additive injection rates of less than 400 ppm by weight of chloride added to the coal and less than 1 lb/Macf HPAC added to the air heater outlet flue gas for the particular Powder River Basin coal used.
4. Get the Hg out. Full-scale mercury reduction testing was completed over a seven-week period in May and June 2008 for a wide range of boiler operating conditions and mercury-reducing additive injection rates. The tests confirmed that mercury emissions were reduced to below the extremely low levels required by the plant’s air quality permit. Shown is a portion of the plant’s air quality control system equipment. Courtesy: Fluor Power
Further optimization testing showed that acceptable stack mercury emissions less than 0.02 lb/GWh were obtained with various combinations of chlorine addition less than 500 ppmw and HPAC injection less than 2.0 lb/Macf. This test data confirms that TSPP meets its demanding mercury emission permit limits.
The much lower relative cost of calcium chloride (compared with halogenated carbon) may mean that SEA is used before HPAC injection. The TSPP staff is continuing testing to determine the optimum combination of SEA and HPAC injection rates.
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