Buecker B.,Kiewit Power Engineers Co.
Chemical Engineering | Year: 2010
Some of the primary thermodynamics behind steam generator heat transfer are discussed. In many systems and especially steam generators, potential and kinetic energies are minor compared to other energy changes and can be neglected. In a steady flow process such as a steam generator, the system does not accumulate energy. The condensing steam generates the strong vacuum in the condenser, which actually acts as a driving force to pull steam through the turbine. Combined-cycle units are found to reach nearly 60% efficiency where electrical production is split between the combustion and steam turbines. Multiple feedwater heaters, especially in larger systems, increase efficiency of a stream generator, but at some point equipment costs offset efficiency gain. Six heaters are common in large, sub-critical, utility systems, where five might be closed heaters with one deaerator.
Liu Z.J.,Kiewit Power Engineers Corporation
Structures Congress 2014 - Proceedings of the 2014 Structures Congress | Year: 2014
Restrictions on power plant emissions have required owners and utilities to build and upgrade flue gas ductwork structures. Flue gas ductwork structures are generally designed as rectangular box-girders made of thin wall plates which are stiffened by W-shapes or Channels. Ductwork is designed for dead, ash, wind, live, and seismic loads at a high temperature and pressure. Better understanding of some critical issues, such as geometrically nonlinear analysis of ductwork, can help engineers to strengthen existing ductwork and design new ductwork more economically. This paper researches and compares different modeling methods per design experience and, for nonlinear analysis of ductwork, proposes an efficient approach to solve the problem. Ductwork is designed per ASCE "The Structural Design of Air and Gas Ducts for Power Stations and Industrial Boiler Applications". Since the guide was published in 1995, it hasn't been updated per current codes and developed finite element software. The linear small deflection theory and allowable stress design methods are proposed. Ductwork is generally made of thin steel plate, around 0.25 inch, with stiffener spacing L, around 3 feet. The ratio of span to thickness is larger than 80, which is the borderline used to consider the membrane force for a plate under lateral loads. The deflection to thickness is mostly above 0.5, which is the standard line from small deflection theory to large deflection theory per Timoshenko in 1959. Therefore, nonlinear analysis should be considered for most ductwork, especially when existing ductwork is to be evaluated for new loads. The nonlinear analysis is important because duct plate should support shear and axial membrane stresses instead of only bending stresses caused by flue gas pressure. For these cases, small deflection theory may not be the more conservative solution compared to large deflection theory. This paper summarizes flue gas ductwork design per ASCE design guide, and compares different solutions of fixed-edge-rectangular plates based on small and large deflection theories from recent technical papers and books to further understand the behavior of duct plate. This article discusses ductwork design loads per large deflection theory, and provides a typical example of finite element nonlinear analysis for a ductwork structure. This research can be used for similar structures using stiffened steel plates such as boiler casings, bridges, and other non-building structures. © 2014 American Society of Civil Engineers.
Kiewit Power Engineers Co. | Date: 2013-04-17
Air inlet chilling and/or intercooling systems, comprising of turbine inlet air coils, heat recovery vapor generator, an evaporative condenser, an absorber cooler and an ammonia recovery skid, for use in gas turbine electrical power plants.
Liu Z.J.,Kiewit Power Engineers Corporation
Structures Congress 2013: Bridging Your Passion with Your Profession - Proceedings of the 2013 Structures Congress | Year: 2013
Generally, foundations for large dynamic equipment are made of considerable amounts of concrete. Thus, they contribute to a significant percentage of a project's total concrete quantity. Designing these dynamic foundations requires a series of static and dynamic analyses to meet the vibration requirement of the equipment and any seismic requirements of the local building codes. This article researches and compares different modeling methods, and then proposes an efficient approach for their design in high seismic regions. For design optimization, two different types of foundations should be considered for these areas: mats and piles. Liquefaction, downdrag on piles, bearing pressure, spring constants, soil stratification, water table, soil types, bearing depth, and settlement, can all affect a foundation. Reviewing the geotech report and performing a cost/risk analysis with the contractor should make it clear which type of foundation should be considered at a given locale. Engineers should design these foundations using a finite element modeling software that can handle dynamic loading. Modal analysis can be used to provide frequencies and displacement amplitudes to verify vibration performance criteria based on ACI 351 and the manufacture's requirements. Modal analysis can also be used to analyze seismic response spectrum per SAP time history analysis. In addition, a model based on static and quasi-static loads as required by the applicable building code should be analyzed. The ability to combine these models into one can help to solve these problems more quickly and efficiently. A case study for a foundation of steam turbine generator is presented, in which, the analysis features and design procedures used are described in detail. This may help design engineers understand the different advantages and results of finite element models, to pick the best modeling option for any given situation. © 2013 American Society of Civil Engineers.