Level Heat Recovery Steam Generator Research Articles

ASPEN dynamics simulation for combined cycle power plant – Validation with hot start-up measurement

Since the beginning of energy market liberalization, shutdown and start-up phases of thermal power plants have acquired greater importance. Dynamic simulation is a helpful tool due to its possibility of predicting the behaviour of the power plant with a good degree of accuracy. This paper goes into the details of the hot start-up phase of a combined cycle power plant with three-pressure level heat recovery steam generator, analysing the capability of the software ASPEN Plus Dynamic through a dynamic comparison between the numerical results and the real operation data. The developed model is built according to the design data of an actual plant including heat exchangers, pipes, turbines, valves, pumps and so on. Good agreements between measurement and simulation results, with some discrepancies in the first phase of the start-up, have been found and then discussed. Best deviation values are obtained for the temperature where the maximum relative error is 3.62% in the re-heater section. Worst deviation values are obtained for the pressure where the maximum relative error shown is 10.8%. Further possible improvements of the model and future applications are suggested.

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.

Superheater and Drum Lifetime Estimation: An Approach Based on Dynamic Analysis

The increasing penetration of variable and unpredictable renewable energy sources into the liberalized electricity market brings about significant changes in the management strategies of fossil fuel power plants. These new operation modes cause remarkable effects on the lifetime of the plants. Consequently, the operators of the plants need to be assisted by effective procedures, which are able to define suitable production plans. In the present paper, the authors propose a dynamic model which can be used to estimate the effects of the variations of thermodynamic and mechanical parameters during transient operation, start-ups and shut-downs. To check the effectiveness of the model, a combined cycle plant with a three-pressure level heat recovery steam generator has been selected. The geometry of the components, the influence of the environmental conditions, and the control strategies are included in the model. In this way, the residual lifetime of the most critical components can be predicted.

Thermo-economic optimization of heat recovery steam generator for a range of gas turbine exhaust temperatures

This paper illustrates the effect of selling price on the optimum design parameters of a heat recovery steam generator (HRSG) and the selection of its ideal configuration for an outlet temperature range of 350–650°C. The Particle Swarm Optimization (PSO) method was used, considering the steam cycle specific work as an objective to be maximized, the net present value as another objective to be maximized for the economic optimization and a combination of both. Three configurations of heat recovery steam generators are considered with one, two and three pressure levels and a reheat. The results show that, the three pressure level system is the best configuration from a thermodynamic point of view, but with respect to the economical aspect the two pressure levels is the best configuration for the low and medium selling prices (0.04$/kWh, 0.08$/kWh and 0.2$/kWh), whereas the three pressure level configuration would only be interesting for a high selling price of 0.3$/kWh and a temperature range 450–600°C. For a temperature of 650°C, the high cost of the three level system leads to a decrease in the net present value. As the selling price increases the optimized design parameters of the three pressure level HRSG based on economic or thermodynamic optimization are similar. The obtained results are used to elaborate a new correlation relating the net present value with the gas turbine outlet temperature, gas mass flow rate, number of levels of HRSG and selling price.

Thermoeconomic Analysis of a One-Pressure Level Heat Recovery Steam Generator Considering Real Steam Turbine Cost

Nowadays, gradual depletion of fossil fuels associated with emissions constraints due to greenhouse gases, leads to reuse wasted heat from power plant in order to increase the global efficiency. One of the implemented technologies for improvements is the application of combined cycles. In this scenario, the steam cycle is frequently combined with a Brayton cycle and the power plant performances and costs are competitive in the global market.Often, an energetic engineering company defines and studies the performance of the bottom steam cycle, thus it imposes operational conditions of steam turbine and heat recovery boiler and requires these components are built by two different manufacturers. For this reason, the plant cannot be globally optimized.From a steam turbines manufacturer point of view, the integration between proprietary simulation code and an energy balance code is an opportunity to simulate a complete bottom-cycle in order to define the best plant configuration.In the present paper, aone-pressure level heat recovery steam generator is studied in term of thermodynamic performance and cost analysis. The thermodynamic analysis is realized using a fixed steam turbine isentropic efficiency (as an energetic engineering company can do) and using anisentropic efficiency determined from steam turbine industrial tool, so a different best performance can be determined. Moreover, a comparison between two academic steam turbine cost correlations and steam turbine cost suggested by industrial cost is carried out.

Dynamic behaviour analysis of a three pressure level heat recovery steam generator during transient operation

The context of the deregulated energy market and the rapid expansion of the non-predictable energy sources, are stressing the necessity of improving the flexibility of traditional power plants. Cyclic operation guarantees high profits in the short term but causes a lifetime reduction due to thermo-mechanical fatigue, creep and corrosion. In this context, combined cycle gas turbine power plants are the most concerned in flexible operation. However, the most stressed devices are in the Heat Recovery Steam Generator. For these reasons, in the present work, a procedure able to estimate the most stressed devices lifetime reduction is proposed. The core of the procedure is the power plant dynamic model. The selected test case is a 380 MW combined cycle gas turbine power plant composed by a gas turbine and a three pressure level Heat Recovery Steam Generator with reheat. The model's peculiarity is the full implementation of the components geometry. The model is able to predict the plant steady-state, part-load and dynamic behaviour. Different transient conditions are tested and the superheater lifetime reduction computed. Results show that the procedure can be considered as valuable innovative instrument to assist power plant designers and operators in order to improve the plant's flexibility.

Design criteria and optimization of heat recovery steam cycles for integrated reforming combined cycles with CO 2 capture

One option for pre-combustion CO 2 capture in power plants is the integrated reforming combined cycle (IRCC). IRCCs have previously been studied from multiple viewpoints: thermo-economic analysis, process optimization, environmental impact, and plant flexibility. This paper is focused on the design of the heat recovery steam cycle (HRSC), including the heat recovery steam generator (HRSG), and aims to define the optimal steam cycle configurations for plant efficiency and dual-fuel flexibility. A recently developed optimization algorithm was successfully applied to obtain a set of flexible and efficient designs for IRCCs. Results showed that the preferred designs consisted of a dual-pressure level HRSG with reheat and limited supplementary firing in duct burners, high-pressure evaporators and economizers in the syngas coolers, limited high-pressure level (140–154 bar), and feedwater preheating. The most attractive optimized dual-pressure designs showed improvements of approximately 0.5% points in the net plant efficiency compared to the non-optimized base case. The resulting net plant efficiency was about 45.8% with a net power output of around 425 MW for the best cases.

Exergetic optimization of single level combined gas–steam power plants considering different objective functions

Combined cycle power plants have been studied in this paper with the aim of optimizing the heat recovery steam generator using a first and second law approach. To this end, a mathematical model has been developed for determining the optimal steam pressure in a one pressure level heat recovery steam generator, considering that the gas turbine is known. Different objective functions have been analysed in this study, some of which refer only to the exergy balance of the heat recovery steam generator while others involve the whole bottoming cycle. Some constraints for the operating parameters of the power plant have also been taken into account, regarding for instance the steam quality at the turbine outlet and the steam turbine blade height. Some numerical results have been reported in the paper, comparing the different objective functions for heat recovery steam generators coupled with several gas turbines; the developed parametric analysis has been performed in order to evaluate the influence of some parameters on both the heat recovery steam generator and the whole bottoming cycle.

Heat recovery steam generator performance and degradation in a 400 MW combined cycle

This article presents a research project carried out by the Thermochemical Power Group of the University of Genoa and is concerned with the monitoring of a three pressure level heat recovery steam generator (HRSG). The work consists of the development of an original computer code using Matlab software that calculates the performance of heat exchangers, at different power plant operating conditions. This kind of software was developed with a twofold objective: to calculate the actual gas path inside the HRSG starting from the available measurements, thus obtaining the current effectiveness of all the heat exchangers in the HRSG, and to estimate the expected performance of each heat exchanger to be compared with the actual ones. Once the actual effectiveness and the expected effectiveness of the heat exchanger are defined, non-dimensional performance parameters suitable for degradation assessment can be defined. As a result of the sensitivity analysis, each performance parameter is coupled with an accuracy factor. The developed methodology has been successfully applied to historical logged data (3 years) of an existing large size (400 MW) combined cycle, showing good capabilities in estimating the degradation of the HRSG throughout plant life.

Modelling the Transient Behaviour of Heat Recovery Steam Generators

This paper describes a method used to compute the transient performances of assisted circulation heat recovery steam generators. These heat recovery steam generators are composed of several heat exchangers, each of which is a bundle of tubes. The method presented here treats each heat exchanger in a similar way, replacing the bundle of tubes with an ‘equivalent’ linear heat exchanger. This equivalent linear heat exchanger is then discretized in as many slices as required by the accuracy. The mass and enthalpy equations on each of these control volumes are solved by a fully explicit numerical method, adapted for the special conditions encountered in this kind of problem, allowing a considerable reduction of the computation time compared to other methods. Some emphasis is put on the modifications required to solve the equations for the evaporators because they are two-phase heat exchangers. A model for the steam drums is also presented together with simple models for the main control loops used in such systems. An example is presented in which an existing dual pressure level heat recovery steam generator is started from a cold state. The numerical predictions are in good agreement with measurements.