Common Design Deficiencies in Counterflow Cooling Towers

One of the best methods for insuring a power plant will produce its guaranteed base load is to have an excess of circulating cold water or at least the expected guaranteed cold water temperature throughout the year. Yet, within industry today, numerous mistakes continue to be made when purchasing a cooling tower, by both the Subcontractor, and the Contractor. Only following only normal design criteria established by cooling tower Subcontractors, or an industry association, is not sufficient. Guidelines in the cooling tower industry have been established to set forth minimum standards that have helped to eliminate obvious past deficiencies. They were not established to protect the Subcontractor. Nor were they established to guarantee the Contractor receives what is thermally and mechanically necessary for a given project. Design of a cogeneration or industrial plant does not always consider the necessary requirements on a cooling tower over the range of expected operation. This type of design for a cooling tower is more complicated than the single guarantee point operational design of a power plant that is the current norm. Just as the Contractor needs to consider how to meet the thermal energy requirements over the range of expected operation of the plant, the Subcontractor of the cooling tower must do the same. Contractors must be aware that the cooling tower designer does not consider aspects that are often applicable to cogeneration plants and therefore they must include exceptions to the Subcontractors’ optimized offering in their standard cooling tower specifications. These exceptions in no way disagree with the Codes and Standards adopted by the cooling tower industry or any governing agency. This paper will address exceptions that the power plant and cooling tower designer needs to take into consideration to ensure that a reliable supply of cold water relates to the thermal duty requirements from the plant throughout the year.

Steam Generator Replacement Project at TVA’s Sequoyah Unit 1 Nuclear Power Plant

Pressurized Water Reactor Power Plants have at times required that large components be replaced (steam generators weighing 750,000 lbs) which have necessitated performing first time modifications to the plant that were unintended during the original design. The steam generator replacement project at Tennessee Valley Authority (TVA’s) Sequoyah Nuclear Power Station necessitated (1) two large temporary openings (21’×45’) in the plant’s Shield Building roof (2’ thick concrete) by hydro-blasting to allow the removal of the old generators and installation of the new, (2) removal and repair of the concrete steam generator enclosure roofs (20’ diameter, 3’ thick) which were removed by wire saw cutting and (3) the seismic qualification of; the design and construction of an extensive ring foundation for; the use of one of the world largest cranes to remove these components through the roof. This removal and replacement process had to be performed in an expeditious manner to minimize the amount of time the plant is shutdown so the plant could return to providing power to the grid. This paper will address some of the many technical and construction considerations required to perform this demolition and repair work safely, efficiently and in a short as possible duration.

Cyclone Maintenance Improvement via Special Refractory Anchor Pin Studs

Since the inception of the cyclone style boiler, industry has become accustomed to performing routine maintenance during every scheduled shutdown occurring 12 months to 18 months between cycles. These maintenance cycles are influenced by service factor, loading and the type design. The same problems exist in both the standard and super critical cyclones; severe deterioration of refractory and the anchoring pin studs. This paper focuses on one type of refractory failure mechanism caused by the anchoring pin studs. Most operators have found that the most effective means of applying refractory in this type situation is to “ram” the refractory in and around the anchoring pin studs thus creating a dense lining with maximum integrity. Coupled with proper application of anchoring pin studs and a special designed coating, typical volumetric expansion of the pin studs from corrosion attack and oxidation is eliminated thus extending the life of the refractory. This mechanism is discussed along with the results of the coating performance as it relates to extreme heat oxidation and thermal cycling in laboratory tests. A protective coating was developed using a nano-cored thermal spray wire technology that produces a uniform, adherent protective layer against high temperature corrosion and oxidation. The coating yields similar thermal conductivity as a bare stud thus experiencing excellent thermal cycle performance. This specially designed thermal spray coating is applied to standard 430 stainless steel pin studs thus providing the necessary barrier against aggressive high temperature environments while maintaining excellent heat conductivity. The coating has a high amount of tungsten (40+%) in a nickel matrix with greatly reduced oxides at the substrate and throughout the coating. With these attributes for the anchoring pin studs in mind, a newly designed stud was evaluated in heat oxidation tests up to 2000°F and thermal cycling test and compared to 430 stainless steel, chromized and Alloy 625. The new stud out-performed all others even in the as-welded condition. Further corrosion testing in ferric chloride (ASTM G48) showed them to be superior to Alloy 72 and Alloy 625 in the thermal spray and welded condition. Proper welding equipment and welding techniques are also discussed since weld continuity impacts overall performance of anchoring pin studs with refractory linings. A major test site will be examined in the spring of 2004 for it’s full effectiveness in service and will be documented in order that all data retrieved would be available to the entire industry.

Thermodynamic Evaluation of Combined Cycle Using Different Methods of Steam Cooling

This paper deals with comparative study of the influence of different methods of steam cooling on the performance of simple combined gas/steam cycle plants. The topping cycle chosen is simple gas turbine while the bottoming cycle is a triple-pressure reheat steam cycle. Steam has been chosen as the cooling medium to be studied, as it is the most promising medium. All possible open and closed loop cooling with steam as the cooling medium have been considered. The prediction is based on the modeling of various elements of simple combined gas/steam cycle considering the real situation. The study shows that closed loop steam cooling is superior as compared to other steam cooling methods. However even though other two methods are slightly inferior technologically, but they do not suffer from the chances of problems of cogging of coolant holes if the steam is not ultra pure.

The Bioceanic Amazon Corridors: An Opportunity for Development of Sustainable Energy System

The bioceanic Amazon corridor represents a development opportunity for the Peruvian and Brazilian economy but this economic evolution is linked to the production and use of energy. Energy is a conditioning factor of economic growth and development and the application of conventional (or alternative) energy systems is strongly influenced by both quantitative and qualitative trends in energy consumption. Decentralized production of energy is necessary, and new decentralized energy technologies based on renewable sources could provide additional income opportunities, decreasing environmental risk along Amazon corridor, and providing clean fuel and electricity. It’s necessary that the bioceanic Amazon corridors call for the application of energy systems related to the renewable local resources in coast, mountain and forest. In Peru, firewood is the principal energy source for cooking and heating and this fuel is used in inefficient combustion system that increases the impact on ecosystems. Typical Peruvian biomass source are wood, agricultural residues, agro industrial waste and municipal solid waste. The most obvious it’s the availability of agricultural and agro industrial residues that could be used as a biomass fuel source in modern plant to produce electricity. Today, there is a growing interest for ethanol production from sugar cane, but it couldn’t be applied along bioceanic corridors; therefore it is necessary to integrate other renewable sources.

NOX Control Systems: SCR Bypass Systems — 20,000 MW of Case Studies

Correct design and layout of the SCR BYPASS SYSTEM is critically important to the efficiency and operation of power plants. Utilities have even had to consider closing down plants that could not efficiently operate their Bypass Systems. Numerous gas path configurations are available, which vary considerably based on site and space limitations, construction lifting capabilities and site construction limitations, as well as other key considerations specific to each plant site. This technical paper discusses a number of arrangements, technical selection and layout criteria. This paper discusses case studies and design details of approximately 20,000 MW of successful bypass system equipment which improve system performance, reduce pressure drop, reduce abrasive wear, substantially minimize maintenance costs and simplify operating requirements.

Common Electronic Platform for the Steam Turbine and Generator Controls: Upgrade Installed at the Mt. Poso Cogeneration Power Station — A Case Study

The scope of modern power plant controls usually includes plant DCS, boiler control and protection, steam/gas turbine governor and protection, auxiliaries control, automatic voltage controller, automatic synchronizer and operator/engineering stations. Usually these control packages come from different manufacturers (OEM). They are typically based on various electronic hardware and software platforms. Different communication protocols often present problems during system integration; and maintenance costs of these various electronic hardware and software platforms are normally greater than that of a stand alone system. Advantages of an integrated, distributed, open architecture, digital system, (Fig. 1) which covers all the power plant needs are discussed in this paper. A common electronic hardware/ software platform allows optimization of the new constructions and upgrades, shorten delivery and commissioning time, and improve availability and safety of the new and upgraded power plants. Specific benefits of this concept are presented in the Mt. Poso controls upgrade Case Study. The common electronic hardware/ software platform installed at Mt. Poso allowed optimization of the upgrade, shortened commissioning time, improved availability, reliability and safety and reduced maintenance cost of the control systems.

Optimizing Compliance Cost for Coal-Fired Electric Generating Facilities in a Multipollutant Control Environment

Higher natural gas prices have increased the importance of coal-fired generation at a time when environmental uncertainty is raising the risks of operating coal-fired units. The likely need for increased investment in environmental control technologies comes at a time when many electricity generators are under great financial stress. This combination of forces makes a structured and comprehensive approach to assessing compliance strategies essential to managing generating assets. The approach needs to incorporate the high degree of uncertainty that can be otherwise buried in key assumptions, such as regulatory requirements, market pricing of allowances, plant capacity factor, wholesale electric prices, etc. The approach should also facilitate testing of assumptions under a range of scenarios to allow for flexibility in possible compliance strategies. In this paper an approach for evaluating compliance risks and quantifying the potential costs under various scenarios will be described. The approach integrates market-based compliance mechanisms with capital improvements in control technology while providing methods to address the uncertainty of key assumptions. The approach facilitates optimizing the balance between market-based and technology-based compliance approaches so that the environmental compliance risk profile can be tailored to the specific situation. A unique feature of this approach is that it incorporates the effects of the market risk associated with emissions markets along with market derivative instruments designed to manage risk, while also incorporating comprehensive technology analysis so that costs and risks can be well quantified under any regulatory scenario. The approach lends itself to active scenario review to facilitate flexibility in decision making while avoiding premature commitments.

Finally: A Reliable, On-Line Carbon-in-Ash Analyzer

The paper describes the principle features necessary for reliable and representative on-line unburned carbon-in-ash (UBC) measurement. The paper shows how modern on-line technology has been applied to obtain truly representative and reliable data for the evaluation of fly ash quality and boiler performance. To assure accurate UBC data from which to make operating decisions, one must achieve representative sampling in the ash stream, comparability of unburned carbon to loss-on-ignition (LOI) with various fuel types, a quality control regime to ensure the accuracy of the on-line measurement system in comparison with laboratory standards and auditing of the QC process.

Enhancing Plant Start-Up Reliability: Independent Critical Equipment Evaluations

This paper describes a program instituted by Reliant Energy in 2002 to enhance the reliability of certain equipment that have been designated as being critical to the successful start-up of their plants under construction. The goal of the program is to reduce the risk of failing to meet forecasted Commercial Operation dates on plants under construction due to equipment failures during commissioning and start-up.