POWER PLANTS GO MODULAR
By Brian K. Schimmoller,Associate Editor
From component fabrication to overall plant design, modularization is being used to cut costs and accelerate development schedules.
Power plants are somewhat like snowflakes. There are no two alike. Traditionally, every time a new power plant was built, engineers developed a unique design catered to the specific needs and requirements of the customer. Today, engineers are attempting to duplicate their snowflakes by incorporating modularization concepts into plant design, fabrication and construction. One-of-a-kind plant design and construction is giving way to the development of pre-designed plants–or at least pre-designed, prefabricated components–that can be customized and modified to meet individual specifications. “The industry is moving from a `sell, design, build` framework to a `design, sell, build` approach,” according to Ed Dalmasso, manager of the fossil technology group at Bechtel Power Co.
The move to modularization is primarily a reaction to the highly competitive, low-margin, short lead-time nature of today`s power plant design and construction market. Particularly in the emerging markets of southeast Asia, where baseload capacity needs are greatest, the ability to rapidly design and replicate power plants is appealing. In countries where capacity requirements are less severe, modularization enables utilities and power providers to respond to incremental load demand more quickly, at lower cost and with reduced risk, either through new plant construction or the repowering of aging facilities.
Chocolate and Vanilla
Modularization comes in two main flavors. Total plant modularization involves the development of fully functional, standard plants that can be plugged in where needed to satisfy a given energy demand. Component modularization entails the use of pre-designed plant components–such as pre-assembled, factory-instrumented pipe racks–to streamline project execution and reduce design and construction costs. Component modularization will likely be used to some degree in all new plant designs; total plant modularization, while increasing in popularity, will likely find more favor with clients with well-defined power demands.
Total plant modularization is typically achieved through the following steps: base model selection, standard option selection and customization. Base model selection requires a choice to be made regarding how much capacity is required and what fuel is desired (and available). A fully functional base plant design is selected to meet the client`s requirements. The following deliverables are typically provided with a base plant design package: technical scope book, major equipment lists, predicted performance, site layout, general arrangement drawings, 3D models of critical components, piping and instrument diagrams (P&IDs), heat and water balance diagrams, single-line diagrams, capital cost model and construction schedule.
The client then has the opportunity to incorporate standard option components into the plant. These include items such as alternate gas turbines, selective catalytic reduction for NOx control, black start diesel generators and dual fuel capability. Equipment lists, general arrangements, P&IDs and installed costs are provided with each of the standard option components. Critical at this stage is adjusting the base cost to accommodate the standard options. For example, additional engineering and construction costs will be incurred if an auxiliary boiler is desired and gas turbine price adjustments will be necessary to account for dual fuel firing
Customization cannot be completely eliminated from modularized design. There always will be site-specific issues that necessitate modifications to reflect site-specific and client-specific requirements. These include wind speed, local precipitation, seismic conditions and various other local regulations and constraints (noise, building codes, soils, etc.). The objective of total plant modularization is to minimize the amount of time and effort devoted to the customization portion of plant design (Figure 1).
Bechtel is actively pursuing the total plant modularization concept through its PowerLine suite of modularized power plants. PowerLine consists of ten, low-cost, standard plant designs (models): four gas-fired combined cycle plants, one gas-fired cogeneration plant, four pulverized-coal plants and one petroleum coke-fired fluidized bed plant. Capacities range from 80 MW up to 1,400 MW. The Hermiston Generating Plant, a two-train 474 MW combined-cycle facility managed and operated by U.S. Generating Co. in northeast Oregon, was the first U.S. application of PowerLine (Power Engineering, Jan. 1996). The Rocksavage plant, a 740 MW combined-cycle facility in Runcorn, England, also uses a PowerLine design. Additional modularized plants are under development.
Siemens and ABB also offer several standard plant designs. One of Siemens` “reference plants,” denoted GUD 1S.84.3A, integrates a V84.3A gas turbine into a single-shaft combined-cycle arrangement. ABB has developed a pre-engineered, modularized single-shaft combined-cycle power plant. The KA8C2-1 reference plant integrates the recently upgraded GT8C2 gas turbine with a dual pressure non-reheat steam cycle. The IP Co-Gen plant in Thailand, a 137.5 MW facility that came on-line in October 1997, was the first ABB reference plant application.
Some attractive numbers back up the value of total plant modularization. The time between request for proposal and preliminary design is significantly reduced through the use of standard plant modules. A process that used to take several months can now be accomplished in about 3 weeks. For customers with a well-defined set of conditions and site characteristics, turnaround times as short as 1 week are feasible.
Modularized design results in lower labor and overhead costs for engineering. “We`ve been able to cut the engineering hours devoted to a given plant design project by up to 30 percent,” said Bechtel`s Dalmasso. Although some of this total is not directly attributable to modularization–e.g., efficiencies achieved through better use of information systems (see sidebar)–there is a strong correlation between modularization and engineering costs.
The pressure to minimize costs and respond quickly to capacity demand requirements has also led to a reduction in plant design and construction times. For example, completion times for Bechtel`s PowerLine plants range from about 20 months up to 34 months. Some industry experts envision a further reduction in completion times for power plants. Siemens projects completion times for gas turbine and combined-cycle plants–which, under ideal conditions, run 12 and 22 months today–to fall to 10 and 18 months in the near future.1 Additional modularization and pre-designed component packaging will be needed to accomplish this goal.
Piece by Piece
Component modularization represents a less ambitious and less risky form of modularization than total plant modularization because only selected parts of the plant are modularized. Clients with unusual site conditions or with unclear capacity requirements may be wary of committing to a completely modularized plant design. They can benefit, however, from the application of modularized concepts to component design and fabrication, reducing costs and compressing schedules.
The chemical industry has been relying more and more on component modularization. Foster Wheeler, for example, used 213 modules–some as long as 250 feet, weighing more than 1,200 tons–in the construction of an aromatics plant in Singapore.2 Electric power plants can also benefit from such component modularization. Heat recovery steam generators also have been assembled in modular sections–with stair towers attached–to reduce construction schedules and costs. Combustion turbines are often shipped with gas combustors and manifold piping already installed. Even stacks can be modularized into 40-foot sections to eliminate awkward fabrication high in the air.3
Design and construction firms have scrutinized the plant footprint for additional modularization opportunities. Any design or construction modification that results in lesser quantities of bulk materials (concrete, steel, etc.) is fair game, as long as it does not impact subsequent operation and maintenance. Plant control rooms, which historically have been large, open buildings, can be replaced with much smaller structures that can easily accommodate the handful of PCs and display terminals necessary to operate modern control systems. Steam turbines can be modified from down-exhaust designs to axial-exhaust designs to reduce pedestal support costs. “Compared with conventional plant designs, newer designs incorporating modularization concepts can reduce plant footprints by 30 to 40 percent and bulk materials costs by a similar margin,” said John Hollett, Bechtel construction manager.
Old Dog, New Tricks
Modularization is more suited to new construction applications than repowered applications. With new construction, fewer design constraints exist and the full benefits of modularization can be achieved. Repowering applications can still effectively utilize modularization concepts, but modifications must be made. At a southern power generation facility, for example, Bechtel adapted one of its PowerLine plants to increase the reliability of the 1.6 million lb/hr steam supply to an adjacent refinery complex while simultaneously generating additional electrical output (150 MW). Because the generating plant had an existing steam turbine, the steam turbine was stripped from a combined cycle PowerLine design and the remaining gas turbine system was integrated into the plant with a supplementary-fired heat recovery steam generator.
ABB is also applying modularization to repowering applications. One concept involves the use of pressurized fluidized bed combustion (PFBC) as the combustor for a gas turbine in a combined-cycle configuration. Two base modules have been developed, one at 100 MW and one at 400 MW. A PFBC island consists of a fluid bed boiler contained within a pressurized vessel and a PFBC machine (compressor and hot gas expander), forming a coal-fired combined-cycle power plant. Mainly fixed by the compressor-expander characteristics, and being relatively insensitive to fuel type (heating value and sulfur content), all systems can be standardized with only the steam conditions having an influence on boiler design.
Standardization has enabled the development of PFBC modules consisting of the pressure vessel, internal components (including the boiler), the compressor/expander, and associated fuel, sorbent and auxiliary systems. Multiple modules can be employed to provide steam to one or more steam turbines. The 400 MW unit is produced by combining multiple 100 MW units. For repowering with PFBC modules, ABB projects 20 percent higher plant output, 20 percent lower heat rate and a low marginal cost that will increase plant capacity factor above 80 percent. The target markets are aging (>30 years old) gas- and oil-fired steam plants that are worn out, uneconomic or unable to meet emissions limits–especially those licensed to burn high-sulfur oils.
Modularization–total plant modularization in particular–fits with gas-turbine technology better than coal-fired technology. Because gas turbines are essentially “catalog” items, available from the major manufacturers in set capacities and configurations, standard plant designs are more easily developed. The PowerLine plants were originally designed around GE gas turbines; because of the worldwide surge in demand for gas turbines (of various makes), however, Bechtel now offers Westinghouse, ABB and Siemens gas turbines as standard options to its base gas turbine plant designs. Coal-fired power plants are somewhat less amenable to modularization; “catalog” systems akin to the gas turbine classes do not exist and more attention often must be paid to environmental regulations. Nonetheless, because of exploding demand in developing countries for coal-based power, modularization is viable. One option is to fashion standard plant designs to match the “boiler-plate” plants prevalent in India and China.
Vendor participation is critical to the success of modularized plant design and construction programs. Conventional practice entailed calling up suppliers after a project had been awarded and purchasing all equipment individually for that project. Today, some design and construction firms contract with vendors to supply equipment and materials for multiple projects. For example, rates may be negotiated with a pipe supplier for various grades of pipe that will be needed at several plants over a given length of time. Or an air compressor manufacturer may provide 4 or 5 standard models of varying capacity that can be used in various plant designs. Key to this relationship is prior approval of available products from the vendor; this is often facilitated by the use of compatible information systems that permit ready access to component drawings, material lists, etc. p
Total plant modularization achieves final scope finalization through three design phases. By eliminating the variability associated with 80 percent of the plant design, equipment order lead times can be reduced, construction schedules
can be moved forward and labor costs–white and blue collar–can be minimized.
U.S. Generating Co.`s Hermiston plant is based on Bechtel`s CC1240 PowerLine design, which incorporates a gas turbine, a heat recovery steam generator and a steam turbine in a train. Hermiston uses a two-train CC1240
for its combined-cycle configuration. Photo courtesy of U.S. Generating Co.
1Bohm, H., “Structure and Technology of Future Power Supply,” Siemens Power Journal, Number 2, 1997, pp. 14-18.
2Foster Wheeler Corp., “A Major Modular Plant,” Heat Engineering, Fall 1997, pp. 2-11.
3Narula, R.G. and A. Walker, “PowerLine for Independent Power in the United Kingdom,” Proceedings of POWER-GEN Europe 1997, Madrid, Volume 1, pp. 365-379.
Modularized design, fabrication and construction would not be possible without the use of sophisticated computer information management systems and databases that enable: (1) multiple users to share data; (2) alternate plant designs to be evaluated almost immediately; (3) equipment lists, cost tables and drawings to be updated as changes are made; (4) real-time communication and information exchange between vendors and design firms; and (5) lessons learned from previous project experience. These systems reduce project costs and effectively maintain project information.
Most of the larger design and construction firms have programs or systems in place for managing and coordinating power plant design and construction efforts. Black & Veatch uses POWRTRAK. Siemens relies on the SIGMA IT system. And Bechtel uses its ProjectWorks system. These systems connect users in various disciplines and various locations through integrated applications related to engineering, procurement, construction and project management. Applications include scheduling, 3-D modeling, construction control, computer automated engineering, document management, engineering design, procurement control and cost control.
The early versions of power plant project management systems were mainframe-based. With the ubiquity of personal computers, however, most systems are moving to a client/server architecture. This separates the front-end (PC) from the back-end (server) and provides substantial flexibility in operating and maintaining the system. ProjectWorks operates using a three-tiered client/server structure; project information and data is shared and transported across an Information Exchange Layer. POWRTRAK, originally established for use with a Sun Microstation, is being converted into a PC-based system as well.
“The move from a paper-thinking environment to a data-centric environment is real in the power industry,” said Stan Pietrzyk, Bechtel project engineering manager. “We still have to print out certain documents, but at fewer points along the way, saving time and money.” In this new environment, information ownership and data security become critical issues. “Everyone has read-only access to project information and data, but only select individuals and groups with specific project responsibilities have write access,” said Brad Vaughan, Black & Veatch manager of office operations for power. When the plant designers make a change–a different pipe diameter, for example–all downstream users of this information, such as the construction and procurement personnel, need to be informed. Information systems automate and accelerate this process.
Computerized information management systems are essential to realizing the benefits of modularized plant design. Graphic courtesy of Bechtel Power Co.