Modularization Speeds Construction
By Gerald P. Burke and R.C. Miller,BVZ Power Partners
The Benefits of Using Modularization are Numerous:
Opportunities For Shorter Schedules, Lower Cost,
less risk, increased quality and greater construction flexibility for EPC (engineering, procurement and construction) power projects. It is an old strategy that has been used to the advantage of many projects in the power industry. Thousands of modular power skids have been used for gas turbines and auxiliaries, diesel engines, pump compressor skids and now, fuel cells. About 20 years ago, Ohio Edison and the Corps
of Engineers built coal-fired plants, hydroelectric power plants and lock components using modularization techniques.
What is new in modularization is the application of manufacturing techniques common in other industries to the power plant construction services industry, in the building of what are often one-of-a-kind plants. Innovations in modularization for design and construction activities are enabling a rise in the popularity of pre-packaged, prefabricated, installation-ready systems.
Finding the model
The BVZ Power Partners, a joint venture between Black & Veatch LLP and H.B. Zachry Co., assembled a modularization task team to advance modularization methods and achieve greater project savings. This team reviewed and reported on industries that use modularization extensively, including the shipbuilding and automobile industries, and several power-related industries in Japan. The BVZ team visited the Hitachi Plant Engineering and Construction Company Ltd. and the Toshiba Corp. in Japan to observe how modularization methods were being used in EPC power projects and how they could be adapted to U.S. combined-cycle projects. The team`s overall research goals were to identify areas in combined-cycle construction that provided an opportunity for modularization and then to implement the most beneficial modularization concepts into BVZ Power Partners projects.
Three general modularization techniques are available to achieve the prime benefit of parallel path construction on power projects. The first, prefabrication, is the common practice of work built according to an existing design in a shop environment, typically involving only a fabricator or vendor. The second, pre-assembly, is work built to an existing design but assembled on site. It generally involves only the on-site construction forces. The third, modularization, involves multiple disciplines of engineering and construction and can be performed wherever it is most advantageous to the project. BVZ Power Partners has utilized each of these modular construction techniques in recent EPC combined-cycle projects.
Combined-cycle projects are inherently modularized. The combustion turbine and generator, support equipment packages, and heat recovery steam generator (HRSG) pressure part components are shop-assembled and shipped as large units. The largest of these modules–some HRSG boiler modules can weigh in excess of 400,000 lb–requires special transportation methods and the use of heavy hauling and lifting equipment to place the modules into their final locations.
BVZ Power Partners` first modularization project was at the Cleburne Cogeneration Facility in Cleburne, Texas. This plant, which is managed by Tenaska IV Texas Partners Ltd., Omaha, Neb., incorporated both pre-assembly and prefabrication modular techniques. The Cleburne Cogeneration Facility is a nominal 260 MW gas-fired combined-cycle plant with a Westinghouse Electric Corp. 501F gas turbine and a Deltak Dino 6760 HRSG supplying steam to a Westinghouse Electric Corp. 104 MW steam turbine. Process steam is supplied to an on-site distilled water plant.
Through an aggressive engineering and procurement approach, BVZ provided pipe rack steel components and pipe supports to the construction site for simultaneous pre-assembly. First, an accurate bill of materials of pipe components was produced through an accelerated and integrated pipe routing, steel design, stress analysis and pipe supporting effort by the design team. This effort was so successful that the final location of the pipe supports could be entered on the support steel fabrication detail drawings before the shop even completed steel fabrication. It also allowed the steel fabricator to shop-weld the pipe hanger clips to the individual steel components before shipping.
Pipe support delivery to the site continued on schedule. Construction crews prefabricated the pipe support steel into assembly units on site and stacked the units in a staging area. The assembly units consisted of modularized, pre-assembled pipe rack bents. While the pipe rack bent frames were being put together, crews assembled the final pipe supports from the parts inventoried in the on-site pipe support trailer. Lisega Inc. supplied the support trailer as part of its pipe support purchase order. Once assembled, the pipe supports were permanently attached to the pre-assembled and staged pipe rack bents and temporarily tied off to facilitate subsequent erection. This modular effort for pipe rack steel enabled pipe erection to take place as soon as the steel was erected, eliminating the usual lead time required for pipe support installation.
The Cleburne project benefited from another modularization approach–the purchase of a prefabricated steam turbine electrical equipment building from Keystone Electrical Manufacturing Co. This building was shop-assembled and installed with all electrical equipment and building architectural features in place, including complete HVAC and lighting systems. Again, the project team sequenced the engineering and procurement effort so that the electrical equipment could be delivered to the shop for installation into the prefabricated building before shipment. At the site, the construction crew set the building on a cable vault foundation. Final wiring interconnection work with the plant could then proceed without the customary time for building erection and equipment setting activities.
BVZ Power Partners also recently performed modularization work for GPU International at the Mid-Georgia Cogeneration Plant in Kathleen, Georgia. The Mid-Georgia plant is a nominal 300 MW gas-fired combined-cycle facility comprised of two Westinghouse Electric Corp. 501D combustion turbines feeding two Nooter Erickson HRSGs. The HRSGs supply steam to a single Mitsubishi Heavy Industries 100 MW steam turbine (supplied by Westinghouse Electric Corp.). Process steam is supplied to the adjacent Frito-Lay plant.
In addition to the modular assemblies associated with the combustion turbine and HRSG, the project team utilized a creative approach for pipe installation. Taking the Cleburne experience with pipe rack pre-assemblies one step further, the Kathleen project team decided early in the project to modularize a substantial portion of the plant. Upon detailed review, BVZ Power Partners committed to modularizing five major pipe rack components for pre-assembly on site. The rack assemblies would then be transported as necessary and lifted into place. The design and construction team met often throughout the creation and implementation of the pipe rack planning, design, procurement, and installation phases to develop a workable plan for implementation of the module project scope.
The initial step in pipe rack modularization at Mid-Georgia consisted of determining the boundaries, or three-dimensional volumes, of the modules. Once these volumes were established, the BVZ project team utilized two computerized information management systems (POWRTRAK and ZMIS) to identify all work components that needed to be performed in each volume. As part of the volume creation process, an engineering-based control system assigned a volume designator to each of the design work components. Once assigned, detailed component information could be downloaded into the progress measurement and quantity installation systems. A construction-based control system then took the volume information and sorted it into work packages, thus providing a comprehensive listing of work to be performed in each volume.
By using this method of integrated work packaging, BVZ optimized the pipe rack modules for maximum pre-assembly. This included craft and discipline responsibilities for steel, pipe supports, pipe, electrical, instrumentation, insulation and painting. All pre-assembly activities took place on site with the racks assembled on the ground. This concept not only allowed for parallel path construction but also saved on labor and scaffolding costs. Once completed, cranes lifted the pipe rack modules into their final locations as assembled units that included finish-type construction items such as handrail, grating and insulation work.
Due to space constraints, the project team assembled four of the five pre-assembled pipe rack modules in open areas on the plant site prior to final positioning with cranes. The fifth and largest of the pipe rack modules was assembled on the ground at its final location. Once completed, construction crews lifted and held this 487,000-lb module in place using an E-Z Lift hydraulic jacking system while the permanent support columns were installed. The module was then lowered onto the foundation piers. Piping interconnection took place via specially designed interconnection volumes located at either end of the pipe rack modules, which allowed for the correction of any fit up or connection problems.
Keys to success
To make modularization work, multiple parallel construction schedule paths should be established. Potential peripheral construction sites for parallel path construction include laydown or shop space at the final site, special shops designed only for modularization and in the usual vendor or fabricator shops. To be successful, a modularization strategy must be incorporated at project inception. Reworking conventional plans to include modular design will not achieve the same schedule and cost reductions possible when modularization is made an integral component of design from the start.
An integrated approach to EPC contracting lends itself to successful modularization programs because it allows for the unrestrained involvement of the constructor and designer during the three prime phases of the work.
By implementing this coordinated approach, using task teams and continuing process improvement, modularization concepts can continue to be refined and successfully applied to combined-cycle projects. p
Modularized pipe rack being moved into place at the Mid-Georgia Congeneration Plant. Piping, hangers, instrumentation and the
auxiliary boiler deaerator are already integrated into the pipe rack
modules. Photo courtesy of Black & Veatch.
Modularized pipe rack systems were incorporated into the design and construction of the
Cleburne Cogeneration Facility. Photo
courtesy of Black & Veatch.
The Cleburne Cogeneration Facility includes a prefabricated steam turbine electrical equipment building. Photo courtesy of Black & Veatch.
Authors–Gerald P. Burke is the BV¥Power Partners business unit manager for H.B. Zachry Co. Burke has over 15 years of experience in power plant construction and holds a bachelor of science degree in civil engineering from Iowa State University.
R.C. Miller is a partner at Black & Veatch LLC and serves as a process executive for BV¥Power Partners. Miller has more than 29 years of experience in the power industry. He is a graduate of Kansas State University, Salina.