CFD Modeling of Cogeneration Burner Applications and the Significance of Thermal Radiative Heat Transfer Effects

Industrial burners provide process heat for a wide range of applications including cogeneration power production. In such applications a (typically) natural gas fired stationary turbine powers an electric generator and indirectly powers a heat recover steam generator (HRSG). The HRSG steam cycle operates by reclaiming the residual thermal energy of the gas turbine exhaust (GTE) flow. Burners are used to reheat the GTE and increase plant capacity during peak demand periods. CFD modeling is used in the design of burner systems for HRSG applications. GTE flow exiting the turbine unit is passed through a diffuser and then expanded into ductwork where the steam system heat exchangers are located. The expansion of the GTE flow from the turbine diffuser to the full cross section of the ductwork is usually severe and creates an uneven flow distribution. Flow correcting structure may be needed to distribute the flow depending upon the severity of the duct expansion. CFD modeling is used to predict the flow distribution of the GTE and guide the design of any necessary flow correcting structure. Burners are typically installed in an array upstream of the application heat exchanger inlet. CFD combustion, heat transfer, and flow analysis is employed in the burner system design process to locate the burner array, determine any necessary flow baffling, and to ensure and provide a uniform thermal distribution at the downstream heat exchanger inlet. Excessive thermal variation in the GTE flow entering the heat exchanger results in large temperature gradients that can lead to thermal cracking and fatigue of the heat exchanger surfaces. CFD modeling is used to ensure that the burner system design produces a uniform flow and temperature distribution at the heat exchanger inlet region downstream of the burners. This report presents a case study of a CFD flow, heat-transfer, and combustion analysis for a typical HRSG burner application. Two CFD models were constructed for the analysis. The first model included the coupled effects of flow, heat transfer, and combustion for the entire HRSG model volume, but excluded the effects of thermal radiation. The second model included a sub-domain of the HRSG volume near the burner and included the additional effects of thermal radiation, both surface radiation and the effects of the radiatively participating flue gas. Radiative effects were included in the second model by employing the Discrete Transfer Method. Results of the study showed the significant role thermal radiative heat transfer had on the resulting temperature predictions downstream of the flame zone.

Combustion Improvement System in Boilers and Incinerators

This work presents the main features, advantages and evaluation of applications of the novel “Ecotube” combustion improvement and emission reduction system by Ecomb AB of Sweden and Synterprise, LLC of Chattanooga, Tennessee. In the Ecotube system, the nozzles used for mixing are put on the suitable position inside the combustion chamber to control uniformity of temperature, mixing and reactants distribution in boilers and incinerators since the formation and reduction of pollutants (NO, CO and VOC) and in-furnace reduction processes (Air/Fuel staging, SNCR, flue gas recirculation and SOx reduction by dry sorbent injection) are related directly to mixing in a combustion chamber. The novel Ecotube combustion improvement system allows better control of mixing of the gases for example from a primary combustion zone with secondary combustion air or a recirculated flue gas. By means of the novel system it is possible to better control the residence time and to some degree gas phase temperature distribution as well as the heat release distribution in the furnace of the waste incinerators or boilers. This new combustion improvement system can be applied to supply different gas or liquid media — for example air, fuel, urea or even solid powder. Using the system a more efficient and environmentally clean combustion or incineration process can be performed. The Ecotube System may be used to meet increasingly stringent environmental emissions regulations, such as NOx SIP Call, while it delivers added benefits of reduced and stabilized CO and reduced fly ash and improved boiler efficiency. The study tool used in this work to present influence of the Ecotube system design on temperature as well as uniformity of reactants and flow field is numerical modeling. Using this tool, the influence of the position of the Ecotube system and the injection angle of the nozzles are studied. The studied boilers included the biomass waste incinerator, municipal solid waste incinerator and coal fired boiler. The concept of the Heat Release Distribution Ratio is proposed to classify the heat release inside the upper furnace of the boilers or incinerators. The results show that Ecotube spreads reaction zone over a larger furnace volume. The furnace flame occupation coefficient can be as high as 45% with the Ecotube system and it is around 40% higher comparing with the conventional multinozzle mixing system. Ecotube system allows keeping far more uniform heat release distribution, more uniform temperature distribution, and thus longer life of the heat transfer surfaces inside the furnace. Position of the Ecotube system and the injection angle of the nozzles are of primary importance and can be used as a technical parameter to control the boiler operation at different loads and varying operating conditions.

H2/O2 Cycles: Thermodynamic Potentialities and Limits

In this paper, the thermodynamic potentialities and limits of the H2/O2 cycles are investigated. Starting from the conventional gas turbine and steam turbine technology, the paper qualitatively tackles problems related to a change of oxidizer and fuel: from these considerations, an internal combustion steam cycle (ICSC) is analyzed where steam, injected in the combustion chamber together with oxygen and hydrogen, is produced in a regenerative way and plays the important role of inert. A proper parametric analysis is then performed in order to evaluate the influence of the main working parameters on the overall performance of H2/O2 cycles. All the results are carried out neglecting the energy requirements for O2 and H2 production systems, but taking into account their work compression only. This choice permits great freedom in the definition of these thermodynamic cycles and allows general considerations because there is no need of any specification about H2 and/or O2 production systems and their integration with thermodynamic cycles. Therefore this paper can be framed in a context of oxygen and hydrogen centralized production (by nuclear or renewable energy sources for example) and in their distribution as pure gases in the utilization place. Adopting realistic assumptions, TIT of about 1350°C, the potentialities of H2/O2 cycles are very limited: the net efficiency attains a value of about 50%. Instead, adopting futurist assumptions, TIT = I700°C, a different H2/O2 cycle scheme can be proposed and more interesting performance is attained (a net efficiency value over 60%). The thermodynamic and technological aspects are completely addressed in the paper, underlining the great importance of the choice of the main working parameters.

Nuclear Power: Time to Start Again

One of America’s best kept secrets is the success of its nuclear electric power industry. This paper presents data which support the construction and operating successes enjoyed by energy companies that operate nuclear power plants in the US. The result—the US nuclear industry is alive and well. Perhaps it’s time to start anew the building of nuclear power plants. Let’s take the wraps off the major successes achieved in the nuclear power industry. Over 20% of the electricity generated in the United States comes from nuclear power plants. An adequate, reliable supply of reasonably priced electric energy is not a consequence of an expanding economy and gross national product; it is an absolute necessity before such expansion can occur. It is hard to imagine any aspect of our business or personal lives not, in some way, dependent upon electricity. All over the world (in 34 countries) nuclear power is a low-cost, secure, safe, dependable, and environmentally friendly form of electric power generation. Nuclear plants in these countries are built in six to eight years using technology developed in the US, with good performance and safety records. This treatise addresses the success experienced by the US nuclear industry over the last 40 years, and makes the case that this reliable, cost-competitive source of electric power can help support the economic engine of the country and help prevent experiences like the recent crisis in California. Traditionally, the evaluation of electric power generation facility performance has focused on the ability of plants to produce at design capacity for high percentages of the time. Successful operation of nuclear facilities is determined by examining capacity or load factors. Load factor is the percentage of design generating capacity that a power plant actually produces over the course of a year’s operation. This paper makes the case that these operating performance indicators warrant renewed consideration of the nuclear option. Usage of electricity in the US now approaches total generating capacity. The Nuclear Regulatory Commission has pre-approved construction and operating licenses for several nuclear plant designs. State public service commissions are beginning to understand that dramatic reform is required. The economy is recovering and inflation is minimal. It’s time, once more, to turn to the safe, reliable, environmentally friendly nuclear power alternative.

Thermo-Economic Analysis of Combined Cycles

The paper presents a thermo-economic analysis of gas/steam combined cycle. The stated objective is achieved by optimizing thermo-economic parameters for simple combined cycle (large and medium range) and to apply this to economic model of these cycles. The economic parameters evaluated in the present study include discount cash flow rate of return (DCRR) and gross payout period (GPO), two terms commonly employed in engineering economic analysis. DCRR and GPO are calculated for various electric sale and fuel prices. It has been found that maximum value of DCRR and minimum value of GPO are found with large size plant.

Hot Gas Filtration in Co-Generation Power Plants

This paper reports a computational study using CFD on a hot gas filter in cross flow arrangement. The filter generally operates with the dirty gases passing through the filter elements, the particulate material being deposited on the outside of the filter. However, in power co-generation plants, hot gas filtration is needed to allow the hot exhaust gases to be fed to a turbine without causing any physical damage to the blades. The aim of this work is to increase understanding of the deposition process and the factors that affect the build up of the filter cake. A parametric investigation is undertaken with particular emphasis on the effects of the ratio of the approach cross flow velocity to filter face velocity on the deposition pattern as a function of the particle size (1 to 100 microns). Velocity fields and particle tracks are presented, in addition to the radius of convergence which is a parameter that characterizes the deposition process for each flow regime.

Recent New Combined Cycle and Gas Turbine Plant Acceptance Test Experience

In the past year, Constellation Power Source Generation (CPSG) has commissioned (or is commissioning) four new combined cycle and simple cycle gas turbine plants. Each of these plants involved different equipment, vendors and architect engineers. Acceptance testing was done for these plants in accordance with ASME PTCs 46 and 22 with support from Fossil Consulting Services, Inc. (FCS). The Performance Test Codes provided the framework for the testing done, but considerable work was required to apply the codes in accordance with relevant contracts. Problems in acceptance testing can result in costly delay and retesting. This paper describes the lessons learned in resolving issues and problems that can help others in planning for and executing similar tests. These lessons learned can also help in writing effective contracts between owners, vendors and architect engineers.

Advanced Aerodynamic Sealing System for Thermo Turbo Machinery

This paper presents the feasibility of using advanced aerodynamic sealing systems to replace aged labyrinth seals in gas & steam turbines for the electric power generating and aerospace industry. Focus is on promoting new technologies in the power generating industry to reduce pollutant emissions.

Application of Rough Set Theory to Data Mining of Condenser Diagnosis in Power Plants

Rough set theory is a powerful tool in deal with vagueness and uncertainty. It is particularly suitable to discover hidden and potentially useful knowledge in data and can be used to reduce features and extract rules. This paper introduces the basic concepts and fundamental elements of the rough set theory. A reduction algorithm that integrates a priori with significance is proposed to illustrate how the rough set theory could be used to extract fault features of the condenser in a power plant. Two testing examples are then presented to demonstrate the effectiveness of the theory in fault diagnosis.

Graphical User Interface (GUI) for Stochastic Optimal Power Flow in the Deregulated Power Markets

This paper presents the Graphical User Interface (GUI) for the Stochastic Optimal Power Flow (SOPF) in deregulated power markets. SOPF is a C++ software package that incorporates a probabilistic approach for the evaluation of composite reliability of generation, load forecast and fuel prices using different probability distributions. GUI is a Visual Basic package incorporated with Microsoft Access and PowerPoint for visualization. GUI provides several simple user interface screens for handling the inputs, processes, and results. Several screens are designed and presented in this paper to show the crucial role for the GUI.