Heat Recovery Steam Generator Configuration Research Articles

Evaluation of supply boiler repowering of an existing natural gas-fired steam power plant

Using supply boiler to repower existing steam power plants (also known as parallel repowering) is one of the awesome repowering methods for almost all types of steam power plants. In this way, the capacity of the gas turbine and heat recovery steam generator (HRSG) can be designed in different ranges. Choosing the best number of HRSG pressure levels and the appropriate way to integrate the generated steam in the HRSG with the existing cycle are important steps during the cycle design. In this paper, we analyse the effects of HRSG pressure levels on the performance of existing boiler and turbines for Montazeri Steam Power Plant in Iran. To do this, we present three separate HRSG configurations and a multi-parameter analysis is provided. For each case, the effects on existing boiler, steam turbines and the condenser are examined. The results show that using HRSG with higher pressure levels (2 or 3) are caused an imbalance in mass flow rate of steam in steam turbines and different parts of the existing boiler. Therefore, using a single-pressure level HRSG with a reheat is recommended for this aim. If we use one HRSG and a gas turbine model Mitsubishi-701G2, net energy and exergy efficiencies and produced power will increases %52.19, %50.9 and 485.8MW, respectively.

Method for CFD facilitated pressure rise calculation due to deflagration in heat recovery steam generator

For combined cycle operations, especially during startup and shutdown, safety concerns have always been the top priority. Residual fuels can escape to and accumulate in the downstream heat recovery steam generator (HRSG) if appropriate purge is not taken, which may cause deflagration, an explosion at subsonic condition, during startup when heat source exists. Residual fuel deflagration will lead to pressure rise and therefore, structural and or tube damages depending on the level of pressure increase. Therefore, a careful study of the residual fuel distribution in HRSG and the pressure rise due to possible deflagration is wanted.Historically, thermodynamics relationships and chemical equilibrium calculations are used to estimate the pressure rise. These approaches either assume that all fuel energy is converted into heat, or make assumptions on the amount of fuel in chemical equilibrium that contributes to the pressure rise. These assumptions tend to overestimate the pressure rise. With the development of computational fluid dynamics (CFD) simulation, a more accurate prediction of the fuel concentration in HRSG during transient startup and/or shutdown process is possible. The local fuel concentrations can now be calculated and therefore, how much fuel that are within the explosion limits and contribute to the pressure rise can be detected readily.This article presents the transient CFD modeling results of residual fuel concentration in a typical HRSG configuration during a gas turbine/combined cycle startup failure process. The article then refines the adiabatic mixing model with the predicted local fuel concentrations to provide a better estimation of the pressure rise due to deflagration. © 2017 American Institute of Chemical Engineers Process Saf Prog 36: 408–413, 2017

Optimizing heat integration in a flexible coal–natural gas power station with CO2 capture

Computational optimization is used to simultaneously determine the design and planned operating profile of a flexible coal–natural gas power station with CO2 capture, under a CO2 emission performance standard. The facility consists of a coal-fired power station undergoing retrofit with CO2 capture. The CO2 capture energy demand is provided by a specially designed combined cycle gas turbine (CCGT). The heat recovery steam generator (HRSG) component of the CCGT is modeled and optimized in detail, with explicit treatment of the discrete aspects of the HRSG configuration, including the number and sequential arrangement of HRSG internal components. Variable facility operations are represented by discrete operating modes selected based on the electricity price–duration curve. Two objectives, the minimization of capital requirement and the maximization of net present value, are considered in a bi-objective mixed-integer nonlinear programming formulation. Pareto frontiers, which define the optimal tradeoffs between these two objectives, are generated for six scenarios constructed from recent historical data from West Texas, the United Kingdom, and India.For a 440MW coal plant in a scenario based on 2011 West Texas data, the minimum effective net present cost required for the retrofit (which meets the CO2 emission performance standard) varies from $278 to 383million, and the minimum total capital investment requirement ranges from $346 to 517million. The variations in these optimized values correspond to the range of the Pareto frontier within the bounds of the problem. The net present cost of the retrofit is less than the present value of the existing coal plant, $476million, indicating that a retrofit is preferred over decommissioning. In the case of very low energy prices, however, decommissioning is shown to be the preferred option. The UK and India scenarios demonstrate that optimal designs can vary greatly depending upon location-specific economic conditions.

Optimal Heat Integration in a Coal-Natural Gas Energy Park with CO2 Capture

Computational techniques are used to optimize the design of an integrated energy park consisting of a coal-fired power plant, a CO2 capture system, and an auxiliary natural gas combined cycle plant. Emphasis is placed on the design of heat integration in the combined cycle system, as this heat constitutes most of the energy required for temperature-swing CO2 capture. The facility is constrained to meet a maximum CO2 emission intensity limit while flexibly capturing CO2 to maximize profit. The process and capital cost models of the facility include a detailed treatment of the heat recovery steam generator (HRSG). Computational optimization techniques are used to select gas turbine size, CO2 capture capacity, and the sizes and pressures of HRSG components for HRSG configurations with one, two, and three pressure levels. Facility design is jointly optimized with dispatch using an electricity price- duration curve and natural gas price scenarios of $3/MMBtu, $4.50/MMBtu and $6/MMBtu. System configuration is shown to have a significant impact on economics, with spread in net present value (NPV) among configurations of $39-54 million (2.6-26% of NPV). Joint optimization of design with optimized flexible dispatch is observed to improve NPV by $18-56 million (1.2-27%) as compared to optimization with constant dispatch. Gains from optimization increase with higher natural gas price. Optimal capital cost, approximately $2.1-2.2 billion in all configurations, is higher for configurations with higher number of pressure levels, but does not exhibit strong trends with gas price.

Thermodynamic analysis of heat recovery steam generator in combined cycle power plant

Combined cycle power plants play an important role in the present energy sector. The main challenge in designing a combined cycle power plant is proper utilization of gas turbine exhaust heat in the steam cycle in order to achieve optimum steam turbine output. Most of the combined cycle developers focused on the gas turbine output and neglected the role of the heat recovery steam generator which strongly affects the overall performance of the combined cycle power plant. The present paper is aimed at optimal utilization of the flue gas recovery heat with different heat recovery steam generator configurations of single pressure and dual pressure. The combined cycle efficiency with different heat recovery steam generator configurations have been analyzed parametrically by using first law and second law of thermodynamics. It is observed that in the dual cycle high pressure steam turbine pressure must be high and low pressure steam turbine pressure must be low for better heat recovery from heat recovery steam generator.

Performance Simulation of Dual Pressure HRSG in Combined Cycle Power Plant

ABSTRACT Combined cycle power plants play an important role in the present energy sector. The main challenge in designing a combined cycle power plant is how to transfer gas turbine exhaust heat to the steam cycle to achieve optimum steam turbine output. Most of the combined cycle developers focus on the gas turbine and steam turbine, but the performance of the heat recovery steam generator (HRSG) strongly affects the overall performance of the combined cycle power plant. Therefore, the present article undertakes the problem of optimal utilization of the waste heat from gas turbine exhaust with dual pressure HRSG configuration. The combined cycle efficiency has been analyzed parametrically from both the first and second law of thermodynamics. It is observed that in the dual cycle the high-pressure steam pressure must be relatively high, and low-pressure steam pressure must be low for better heat recovery from HRSG.

Influence of the heat recovery steam generator design parameters on the thermoeconomic performances of combined cycle gas turbine power plants

This paper proposes a methodology to identify the most relevant design parameters that impact on the thermal efficiency and the economic results of combined cycle gas turbine power plants. The analysis focuses on the heat recovery steam generator (HRSG) design and more specifically on those operating parameters that have a direct influence on the economic results of the power plant. These results are obtained both at full and part load conditions using a dedicated code capable of simulating a wide number of different plant configurations. Two different thermoeconomic models aimed to select the best design point are proposed and compared: the first one analyzes the generating cost of the energy while the second one analyzes the annual cash flow of the plant. Their objective is to determine whether an increase in the investment in order to improve the thermal efficiency is worth from an economic point of view. Both models and the different HRSG configurations analysed are compared in the results section. Some parametric analysis show how the design parameters might be varied in order to improve the power plant efficiency or the economic results. Copyright © 2004 John Wiley & Sons, Ltd.

Combined cycle plant efficiency increase based on the optimization of the heat recovery steam generator operating parameters

At the present time combined cycle (CC) power plants allow to meet the growing energy demand with the least fuel consumption. Thus it is of great interest to define a strategy for the optimization of these systems, in order to get greater performances and efficiency from them. The purpose of the most part of the world manufactures involved in this sector is to reach overall thermal efficiency of 60% in the short term period, above all by improving the gas turbine inlet temperature. In the present work, it is shown how it could be possible to reach the same performances by best fitting the existing technology. In particular we point our attention to the optimization of the heat recovery steam generator (HRSG), as a first step in the analysis of the whole plant, according to a hierarchical strategy. We handle this problem adopting both a thermodynamic and a thermoeconomic objective function instead that with the usual pinch point method. Thermodynamic optimization has the purpose to diminish energy losses, expressed on exergy basis, while the aim of the thermoeconomic optimization is the minimization of a cost function, sum of the cost of exergy inefficiencies and the cost of the HRSG. Proposed methods have been applied to some HRSG configurations, including some present commercial plants. The results of the application of the thermoeconomic optimization leads to a meaningful increase of the thermal efficiency of the plant that approaches the 60%, obtained with and increases of the heat surface and a decrease of the pinch-points. The economic evaluations are referred to US dollars ($) even if the costs are referred to European scenario, assuming 1 US $ = 1.1 euro.

Thermodynamic Optimization of the Operative Parameters for the Heat Recovery in Combined Power Plants

For the combined power plants, the optimization of the heat recovery steam generator (HRSG) is of particular interest in order to improve the efficiency of the heat recovery from turbine exhaust gas and to maximize the power production in the steam cycle. The thermodynamic optimization is the first step of a power plant design optimization process. The aim of this paper is to provide thermodynamic tools for the optimal selection of the operative parameters of the HRSG, starting from which a detailed optimization of its design variables can be carried out. For the thermodynamic analysis, the selected objective is the minimization of thermal exergy losses, taking into account only the irreversibility due to the temperature difference between the hot and cold streams. Various HRSG configurations have been analyzed, from the simpler, a single evaporator to the common configuration of two-pressure steam generator with five different sections. This paper was presented at the ECOS'00 Conference in Enschede, July 5-7, 2000