Coal - back on the critical list?1 April 2007
Increased thermal efficiency, high gas prices, supply security and the availability of better materials all help to explain the rebirth in the USA of supercritical technology, which is being carried along in the general resurgence of coal firing. The first of these plants to come on line will be Council Bluffs 4, a 790 MW supercritical situated in Iowa and scheduled to complete its test phase in time for a 1 June start up.
Construction is almost complete at MidAmerican Energy’s 790 MWe Council Bluffs Energy Centre unit 4, a plant of some significance because when it comes on line on 1 June, as it is scheduled to do, this PF (pulverised fuel) supercritical plant will be the first of its type to be built in the USA for many years, and the first ever to be built there using advanced supercritical technology. ‘Advanced’ in this context means a combination of new materials for the high temperature components, and state-of-the-art environmental control technology, including NOx, SO2 and mercury emissions controls. It also has the distinction of being the first plant in the USA – and perhaps anywhere – to have a mercury limit specifically noted in its air pollution permit, namely 0.0000017 lb/MMBtu.
Council Bluffs (see MPS, April 2004 for a fuller description) may be the first, but it isn’t the only. By 2011 eight more units will have come on line, including the 790 MW Red Rock ultrasupercritical, four of them in construction at this moment.
American utilities embraced supercritical coal plant technology early, and indeed pioneered the concept in the 1950s. Many supercritical coal fired plants were built in the USA in the 60s and 70s. But despite this auspicious start supercriticals have had a bumpy ride in the US. They took off in the late 1950s and reputedly 170 were built, but the technology was ahead of the materials available for it and operational problems gradually took their toll. By the seventies the technology had been abandoned in the USA and no more were built until the present day. Operators limited steam temperatures to 1000ºF and pressures to 2400 psi. Known as sub-critical boilers, they became the workhorses of American utility generation, and with abundant coal supplies US utilities had little incentive to do anything else.
Research into more suitable materials however did not stop, and outside the US supercritical plants continued to be built as development of the existing high temperature ferritic-martensitic 9%Cr and 12%CrMoV (chrome-molybdenum-vanadium) steels for the production of rotors, headers, pipes and casings capable of resisting 650ºC continued apace. European and Japanese manufacturers in particular persevered, and the competitive edge that this gave them represented a grave enough threat for industry leaders in the States to see a need to respond collaboratively. In 2001 Electric Power Research Institute, with funding from the US DoE, organised an R&D effort with four major boilermakers (Alstom, McDermott Technologies with its affiliate Babcock and Wilcox, Foster Wheeler, and Babcock Borsig) with the aim of developing a family of pipes and components made of advanced steel capable of withstanding operating temperatures up to 1400 ° F and pressures up to 5000 psi. The project also contained provisions for developing advanced alloys suited to 1600 °F if needed.
This, together with the results of US boilermakers’ collaborating with manufacturers outside the country, resulted in a technology new to the US. Joint studies showed that with minor changes in boiler materials, steam plants operating at 1100° F and 4500 psi could be built. Manufacturers learned, among other things, that high-strength ferritic stainless steels for heavier components would avoid heat-related failures, that high-chromium creep-resistant stainless steel for superheater and reheater tubes resists corrosion, and that higher-strength low-alloy steels make better waterwalls.
Coal is back
The commercial case has changed in recent years in that the emphasis in the USA has shifted strongly towards combustion efficiency in order to reduce unit costs and help in meeting emissions legislation and electricity demand, all of which strongly favours the development and installation of SC steam units.
Now coal is back. Although over the last decade only about 2.5 % of new electricity generation capacity in the United States has been coal-fired, the US Department of Energy predicts that over the next two decades that number will jump to nearly 40 %. Long-term price predictability coupled with improvements in technology have reignited power producers’ interest in coal.
An indicator of the continued hegemony of coal-fired generation is the rush by developers and utilities to make it their preferred option for near-term baseload capacity. According to the US National Energy Technology Laboratory, 159 proposed new coal units totalling 96 GW are in some stage of development in 40 states (Figure2). Industrial Info Resources Inc. (www.industrialinfo.com) puts the total even higher, saying that it is tracking 180 coal projects.
Of the 159 named by NETL (now only 151, with the likely loss of eight units proposed by TXU) 26 are listed as supercritical units, 5 of them USC, at 20 plants (Table 1). Five units are under construction, six are very close to starting, eight are in the permitting stage and eight more are still at the ‘proposal’ stage. The very first SC to be proposed in the ‘New Wave’, Council Bluffs, will, as mentioned, come on line this year, with 18 of the rest following between 2009 and 2012, provided of course that there are no cancellations of the seven still in permitting.
This is not such an unlikely eventuality. Many of the 150 odd proposed plants will never get off the drawing board, and it is true that there is not universal approval of this return to coal, as evidenced by recent events at Texas utility TXU. The largest single tranche of the 159 is TXU’s proposed development of 11 coal fired plants, eight of them a bulk buy of identical 858 MW units, but these eight have been suspended, pending cancellation, following the ‘green takeover’ of TXU by the private equity firms Kohlberg Kravis Roberts & Co (KKR) and Texas Pacific (TPG) in February. That is, if the deal is approved by shareholders, and as it is a very good deal, offering a price 17% ($70 for $60) above the pre-offer level, they are likely to, or likely to have done by the time this report is published.
Of the 11, ten were to be supercriticals. The only three that are now likely to be built are two at the 1720 MW Oak Grove, Robertson County plant, along with the subcritical Sandow plant. TXU will also be sticking to its plan to build 6 GW of nuclear plant (it already has two reactors at Comanche Peak) fuelling speculation that it is to order two more in the near future, or at least try to obtain licences for them. It seems that KKR has bought into Texas style nimby-ism which is strongly anti-coal, and does not make much of a distinction between ‘clean’ coal and conventional burn, as the number and methods of organised protest groups indicates. Indeed it has become more or less routine practice to oppose new coal firing proposals, often quite effectively in terms of winning emissions concessions, as some of the examples below illustrate.
Nor is there universal approval of new technologies. Of the 159 units listed by NETL, and again excluding the bulk buy TXU eight, 32 are gasification plants, 22 CFB, 26 supercritical ultrasupercritical. So 79, about half the total, are to be conventional subcritical.
The commercial advantage to be gained by going critical derives from the properties of steam as a working medium, namely that the efficiency (aka heat rate) of conventional boiler/steam turbine fossil power plants is strongly dependent on steam temperature and pressure. Figure 3 illustrates the improvement that can be achieved by raising the steam condition. For example, compared to a 538°C, 18.5 MPa (1000ºF, 2600 psi) steam plant as a base case, an efficiency increase of 6% is achieved by changing the steam conditions to about 593ºC and 30 MPa (1100ºF, 4300 psi). At 650ºC the increase is as much as 8%.
This desire for increased efficiency led in the late nineteen fifties to the introduction of numerous supercritical boilers operating at or above 565ºC and 24 MPa. One of these, Eddystone 1, built in 1959, is still operating today, making it the oldest operating supercritical, although for most of its service life it has been de-rated to 32.4 MPa, 605ºC. It was originally designed to run at 34.5 MPA and 650/565/565ºC in a double re-heat cycle but as with all its contemporaries its availability was unacceptably low owing mainly to the inadequacy of the austenitic steel from which were fabricated the heavy section components operating at high steam temperatures. This steel has a low thermal conductivity and high thermal expansion resulting in high thermal stresses and fatigue cracking, leading to unexpected problems such as superheater corrosion and creep cracking – which occurs when pipes are stretched out of shape and weakened because of excessive temperatures and pressures. These problems and the general low availability resulted in a cooling of interest among the utilities and most of them had returned by the late sixties to building sub-critical plants. That phase is now in the past and the star of SC technology has risen high enough to be visible on the American horizon.
Following closely on Council Bluffs, in 2008 Wisconsin Public Service Corporation in partnership with Dairyland Power is adding a fourth coal-fired generator, a 530 MW supercritical pulverised coal-fired base load power plant, to its Weston site.
Black & Veatch have been contracted to provide the conceptual and detailed design, procurement, site management, field engineering and startup management. The plant is to offer ‘the most advanced environmental control technologies available, with the ability to capture mercury, nitrogen oxide, sulphur dioxide and particulate matter from exhaust gases before they leave the plant’.
The intention is that Weston will be a ‘good neighbour and responsible corporate citizen’ complying not just with the letter of the applicable federal, state and local laws, and related regulations but the intent too.
The first and most significant decision regarding its configuration was the determination that the facility would be a supercritical base load unit with an expected capacity factor of 80 % or more, and for the purpose of the economic analyses, a 40-year plant life was assumed.
Weston 4’s ‘cleaner coal technology’ is to include SCR and low NOx burners, sorbent injection (a proven mercury control technique that will make Weston 4 the first power plant in Wisconsin to use advanced mercury reduction technology), dry FGD, and fabric filters to collect particulates. The emission control system will cost $120 million, 16 % of the total construction cost, but is expected to result in 80 to 93 % less particulate matter, 72 to 90 % less NOx and 76 to 85 % less SO2 compared to other WPSC units.
Kansas City Power & Light appointed Burns & McDonnell as owner’s engineer for its 850 MW Iatan unit 2 supercritical currently being built on the existing Iatan site near Weston, Missouri, and awarded Alstom the $700 m contract for the engineering, design and construction of the boiler and air quality control equipment (Figure 4). Although KCP&L was always aiming to be environmentally aware the project attracted considerable opposition from environmental groups including Sierra Club who alleged Clean Air Act violations at Iatan 1 as part of its appeal against the Iatan 2 unit's air permit in a state administrative proceeding. KCP&L was driven to the lengths of filing a federal lawsuit for a declaratory judgment for the operation of the 651 MW unit, asking the court to find that the operation of the plant, which has been in operation since 1980, has complied with the federal Clean Air Act. Nonetheless this opposition has brought several concessions. KCP&L have agreed on a set of initiatives to offset carbon dioxide and reduce other emissions and have committed the company to pursuing offsets for all global warming emissions associated with Iatan 2 through investments in energy efficiency and renewable energy, and cut pollution from its existing plants. The agreement resolves four appeals pending between the environmental groups and KCP&L.
In February TXU signed contracts with Babcock Power subsidiary Thermal Engineering International (TEi) to supply the condensers for the 2x860 MWe supercritical lignite fired Oak Grove power plant near Hearne, Texas. Fluor Corporation is to be the EPC for the two new units. TEi’s scope includes the design and fabrication of two twin shell, single pressure condensers. TEi intends to produce a condenser with ‘superior mechanical design that offers maximum thermal efficiency’. The intention is that Oak Grove 1 & 2 will apply ‘best available technology’ philosophy to its air pollution control supplied by TEi’s sister company Babcock Power Environmental, partly in response to public opposition to more coal plants. TXU now intends this as a reference plant design, one that will be ‘the most advanced supercritical coal technology of any plant under construction in the US today’ and meet carbon capture and storage-ready criteria.
But the plan in its first form attracted fierce opposition from Texans, large numbers of whom do not want any more pollutants on any scale. After receiving applications for a slew of new coal plants, mostly from TXU, state governor Perry issued an executive order expediting the permitting of these plants, potentially allowing them to slip in under the wire and avoid pollution reduction rules that were still pending at the TCEQ (Texas Commission on Environmental Quality). TXU has earned a notoriety among industrial plant operators in Texas, according to lobbyists the Lone Star Sierra Club. Based on TCEQ annual emissions inventory data for 2003, TXU operates the top three coal (lignite) polluters in Texas, emitting in that year about 440 000 tons of pollutants. At the time of its original Oak Grove application it would have emitted a further 41400 tons. The intervention of KKR and TGR has turned that situation on its head.
Xcel Energy is constructing its first new coal-fired generating unit in nearly 30 years at the Comanche Station site (Figures 5,6) near Pueblo, Colorado. The 750 MWe supercritical PC fired unit will accompany two existing units that together generate about 660 MW. When the Comanche 3 unit is complete, the site will provide enough electricity for about one third of Colorado’s communities. The project is estimated to cost about $1.3 billion.
Alstom won the contract from Public Service Co. of Colorado, aka Xcel Energy and will design, supply, erect and commission the supercritical boiler. Mitsubishi Heavy Industries will supply the steam turbine, MHI’s first such order from the US. Delivery is planned for June 2007 and commercial operation for 2009.
Comanche 3 will feature advanced emission controls, with additional controls also being fitted on the two existing units at the plant. These will help reduce overall emissions of SO2 by 65% and NOx by 30%, even with the doubling in overall electric generation.
Alstom says that its boiler will be the core of one of the most advanced steam plants ever to have been built in the US. It will burn low-sulphur PRB coal and has the company’s TFS 2000 firing system. With an SCR added it will have, Alstom says, one of the lowest NOx emissions rates in the USA. A low water-use system for Comanche 3 will use both water and air for cooling, reducing water use by about 50%.
Oak Creek expansion, Elm Road
WE Energies is a Milwaukee-based utility, a subsidiary of Wisconsin Energy Corp and operator of the new 2x750 MW supercritical Oak Creek unit, (aka Elm Road), to be located on the west shore of Lake Michigan in Oak Creek Wisconsin. These units are important to increasing the generation capacity within Wisconsin, a state that has historically been a net importer of electricity.
They will also be equipped with themost advanced emission-control technology available, says WE, making the facility one of the cleanest plants of its type in the United States. The result will be a system-wide reduction of emissions of more than 65 % by 2013, while at the same time generating 50 % more electricity.
The control system is by Emerson, which is installing its PlantWeb digital plant architecture with an Ovation expert control system. Bechtel, the project’s EP contractor, selected the
system to provide control for the units’ Hitachi once-through, supercritical boilers, the selective catalytic reduction system, and other equipment and processes. The Ovation system will also provide monitoring and control for each boiler’s burner management system, and interface to the turbine and balance of plant controls. Integration of the BMS, turbine and BOP controls will take place as part of the Ovation system factory acceptance test prior to installation.
Alstom’s Brno facility Boiler Manufacturing Operations has been awarded the pressure parts order by main steam side supplier Hitachi Europe. The order includes the supply of several parts, in particular the spiral panels of two 750 MWe coal-fired generating units.
Construction of the 1230 MWe Elm Road station began in 2005. The first unit is expected to begin commercial operation in 2009, with unit 2 scheduled to come on line one year later.
Red Rock USC
The first ultrasupercritical plant got under way in February when OG&E Electric Services, Public Service Company of Oklahoma and the Oklahoma Municipal Power Authority signed an agreement with Red Rock Power Partners (RRPP) a joint venture that includes Black & Veatch subsidiary Overland Contracting Inc, to begin the first phase of a project to build a 950 MW generating unit near Red Rock, Oklahoma.
The design is to feature the most efficient proven coal-fired technology available for around-the-clock base load power generation. Estimated cost of the plant is $1.8 billion. Regulatory approval and conditions in the construction market will be key factors in determining when the Red Rock unit begins commercial operation. Under an agreement announced last year, PSO will own 50 % of the plant; OG&E will operate the facility and own 42 % and OMPA, which provides electric power to about three dozen communities in the state, will own 8 %.
Imminent start at Longview
GenPower Holdings, a joint venture between GenPower and First Reserve Corporation, has awarded a consortium of Aker Kvaerner Songer and Siemens Power Generation the contract to engineer, build, and supply equipment for the Longview project, a 695 MW supercritical pulverised coal-fired facility in Monongalia County, West Virginia where construction work is about to get under way. Foster Wheeler North America will supply the boiler and Siemens the steam turbine, a Benson vertical tube supercritical steam unit, and the air quality control system.
The consortium contracts have a total combined value of approximately USD1.3 billion, with the Aker Kvaerner individual contract valued at approximately USD 654 million.
The Longview project, scheduled to finish in spring 2011, will be one of the largest investments in the history of West Virginia. Fitted with ‘the best available pollution control technology’ it is expected to be one of the cleanest and most efficient coal-fired plants in the USA.
Figure 1. Comanche 3 construction site Figure 2. Proposed and planned coal fired build in the USA at January 2007. Source – NETL Figure 3. Effect on efficiency of more energetic steam conditions Figure 4. The Alstom PC double pass boiler that is being constructed for Iatan 2. (Illustration courtesy of Alstom) Figure 5. Lifting the coal silo sub-assembly into position at Comanche 3. (Photograph courtesy of Alstom) Figures 6. Lifting the coal silo sub-assembly into position at Comanche 3. (Photograph courtesy of Alstom)