Cold Reheat Research Articles

Numerical investigation of condensation-induced water hammer effects in horizontal and vertical cold reheat pipes

Condensation-induced water hammer (CIWH) is an unavoidable phenomenon in power generation facilities and must be properly adjusted for the thermal efficiency and safety of the system. This study simulated CIWH in a realistic steam pipe to analyze its characteristics in horizontal and vertical pipe sections. Additionally, CIWH intensities with respect to key parameter changes were explored for its mitigation. Numerical simulations for the CIWH were performed using an OpenFOAM solver, ICFMCondFOAM, which was validated for multiple phase change computational fluid dynamics (CFD) problems. The geometric and operating conditions of the cold reheat pipe of our partner company were used for CFD simulations. To assess the intensity of the water hammer effect, various inlet water flow rates and steam temperatures were employed and pressure over time was recorded at two measurement points: horizontal and vertical sections. Results of the CFD simulation show that the CIWH phenomenon behaves differently in horizontal and vertical pipes. CIWH strength was also evaluated using the Froude (Fr) and modified Jakob (Ja) numbers. Smaller Fr and larger Ja were found to be desirable for lowering the pressure increase ratios caused by the CIWH in both the horizontal and vertical pipe sections.

Improving the Performance of Steam Power Plant by Applying Energy and Exergy Analysis at Altering Operating Parameters

This study presents the energy and exergy analysis for unit three of the Al-Mosyab thermal power plant, which has a capacity of 225 MW. The energy losses, exergy destruction and second law efficiency, are computed. The objective is to obtain a comprehensive prediction of improvement that will happen in the performance. Results showed that the second law efficiency of the cycle is 34.91%, and the maximum exergy destruction was at the boiler by 86%. The plant's second law efficiency improves successfully to 37.65%, and 0.67 kg/s of the fuel mass flow rate can be saved. As well as, the total exergy destruction decreased by 10.8% at increasing the feedwater temperature to 230 °C. The second law efficiency has enhanced to 35.74% and 1.32% of the exergy destruction drops when reducing the mass flow rate of the desuperheater spray water of the main steam. The second law efficiency increased by 2.27%, and 1.25% of the total exergy destruction was reduced when the hot reheat pressure increased. Moreover, the analysis reveals that the plant's second law efficiency has grown by 6.45% and that the total exergy destruction has fallen by 3.31% when cold reheat steam temperature is reduced.

Operational flexibility and operation optimization of CHP units supplying electricity and two-pressure steam

Combined heat and power (CHP) is an effective way of enhancing the energy efficiency of thermal power plants. Double-extraction CHP, a typical kind of CHP unit, can supply two-pressure steam to district heating and industry users. The feasible operation domain of a double-extraction CHP unit, which has many constraints, is essential for the flexible operation enhancement and operation optimization of CHP units. In this study, a method is proposed to express the feasible operation domain of the double-extraction CHP unit with a 3D operation domain with six boundary surfaces, and the operating boundary constraints of the double-extraction unit are elaborated. Then, a reference 1000-MW double-extraction CHP case is analyzed, and the operation domains and energy consumption characteristics of three typical heating modes are analyzed. The optimal scheme of heating modes is obtained under different power loads. When the power load is between 783.09 MW and 936.06 MW, Heating Mode 4 (cold reheat steam for HLS1, hot reheat steam for HLS2) has the highest exergy efficiency. This research provides theoretical guidance and a basis for the operation of the CHP unit supplying power load and two heat loads simultaneously.

Performance Analysis of a Waste-to-Energy System Integrated with the Steam–Water Cycle and Urea Hydrolysis Process of a Coal-Fired Power Unit

An innovative hybrid energy system consisting of a waste-to-energy unit and a coal-fired power unit is designed to enhance the energy recovery of waste and decrease the investment costs of waste-to-energy unit. In this integrated design, partial cold reheat steam of the coal-fired unit is heated by the waste-to-energy boiler’s superheater. The heat required for partial preheated air of waste-to-energy unit and its feedwater are supplied by the feedwater of CFPU. In addition, an additional evaporator is deployed in the waste-to-energy boiler, of which the outlet stream is utilized to provide the heat source for the urea hydrolysis unit of coal-fired power plant. The stand-alone and proposed designs are analyzed and compared through thermodynamic and economic methods. Results indicate that the net total energy efficiency increases from 41.84% to 42.12%, and the net total exergy efficiency rises from 41.19% to 41.46% after system integration. Moreover, the energy efficiency and exergy efficiency of waste-to-energy system are enhanced by 10.48% and 9.92%, respectively. The dynamic payback period of new waste-to-energy system is cut down from 11.39 years to 5.48 years, and an additional net present value of $14.42 million is got than before.

Numerical Investigation of Condensation-Induced Water Hammer Effects in Horizontal and Vertical Cold Reheat Pipes

Numerical Investigation of Condensation-Induced Water Hammer Effects in Horizontal and Vertical Cold Reheat Pipes

Performance analysis of turbine extraction superheat utilization schemes of built power plant

The system optimization scheme of adopting outer steam coolers (OSCs) to utilize turbine extraction superheat (conventional scheme) is considered an effective way to improve the thermal efficiency of power plants. However, adopting the conventional scheme in a built unit would increase the feedwater temperature, thus generating under-temperature reheat steam for some units. A novel system optimization scheme was proposed with turbine extraction for preheating feedwater and cold reheat steam simultaneously. Case analysis shows that the proposed scheme attains a better energy-saving effect than the conventional scheme under the considered load conditions. The investment payback period (IPP) of the novel scheme is 3.98 years, which is better than the attained 6.93 years of the conventional scheme.

An innovative waste-to-energy system integrated with a coal-fired power plant

An advanced waste-to-energy system integrated with a coal-fired power plant has been proposed to improve the energy utilization of municipal solid waste. In the new design, the energy gained from the waste-to-energy boiler is employed to heat the feedwater and partial cold reheat steam of the coal power plant, and the feedwater of the waste-to-energy boiler is provided by the heat regeneration system of the coal power plant. Consequently, the energy obtained from the waste incineration products is injected into the steam cycle of the coal power plant, and the waste-to-electricity efficiency can be significantly boosted. Based on a 500 t/day waste-to-energy plant and a 630 MW coal power plant, the proposed hybrid scheme was evaluated compared with the conventional separate one. The results show that the waste-to-electricity efficiency is promoted by 9.16% points with an additional net power output of 3.71 MW, attributed to the suggested integration. Furthermore, the energy-saving mechanism of the novel concept was revealed by energy and exergy analyses. Finally, the new design was economically examined, which indicates that the dynamic payback period of the proposed waste-to-energy plant is only 3.55 years, which is 5.87 years shorter than that of the conventional one.

A Performance Evaluation and Optimization of a 135-Mw Circulating Fluidized Bed (Cfb) Coal Based Thermal Power Plant Turbine Cycle Using Exergy Analysis

This study aims to conduct a performance evaluation of a 135 MW Circulating Fluidized Bed (CFB) Coal Based Thermal Power Plant using exergy analysis and use these assessments in order to provide an optimum operation of the said plant. The study includes on determining the effects of ambient condition on the exergy analysis of the plant. The necessary parameters such as temperature, pressure and mass flow rates were collected from the DCS (Distributed Control System) of the plant. These parameters are then inputted in the excel file prepared by the proponent in order to arrive at necessary thermodynamic values. The results in the exergy analysis of the plant showed that most of the exergy losses occur in the boiler with a total of 172222.8 kJ/s under low temperature ambient and 182602.3 kJ/s at high temperature ambient. The high exergy loss in boiler is caused by unutilized heat that was not fully transferred in to turbine cycle system and is just venter out in the atmosphere. Turbine cycle exergy only accounts to 5 to 6 percent of the total initial exergy available. Most of these exergy losses are located at IP/LP turbine (8564.64 kJ/s), condenser (4818.07 kJ/s), cold reheat pipe (4690.16 kJ/s), HP turbine (1697kJ/s) and Deaerator (1055.82 kJ/s). Moreover, based the exergetic efficiency, most of the components in the turbine cycle that involve phase change are most likely to have low efficiency these include the boiler (50.97%), condenser (42.68%), gland steam cooler (75.34%) and LPH no.7 (13.46%). The effect of ambient temperature on the generation of irreversibility in the plant is considerable. During high ambient temperatures, the boiler produces high irreversibility than that of the low ambient temperatures. However, if we look into the turbine cycle side, the most irrversibilities are seen during low ambient conditions which are around 6.54 percent whilst the hotter ambient condition poses only a tad lower value of 5.79 percent. The optimized parameter in maximizing the load is suggested on the results which are: Unit load = 40 MW and main steam temperature = 530 Mpa. Heat exchange between the component and the system is a significant part in the exergy analysis of the plant. Thus an exact approximation of the actual heat transfer would decently make the exergy analysis more accurate. Moreover, the program for thermodynamic value determination can be made from other programming platform aside from excel in order to create a faster generation of data and can be easily organize accordingly. Lastly based on the results provided by the exergy analysis on the plant, it recommended to formulate plans for improvements on plant components with high exergy loses especially the cold reheat pipe.

Comparison of three cold water reheat test methods for arms vibration

目的： 探讨3种冷水复温试验方法对手臂振动病的判断效果。 方法： 选取2015年12月至2016年2月烟台市某大型金矿矿工154人为研究对象，随机分组进行冷水复温试验，分别给予10 ℃冷水浸手10 min、15 ℃冷水浸手5 min、12 ℃冷水浸手5 min，分析3种冷水复温试验方法的效果。 结果： 10 ℃冷水浸手10 min、15 ℃冷水浸手5 min和12 ℃冷水浸手5 min方法的灵敏度分别为0.61、1.00、0.91，特异度分别为0.77、0.53、0.71，阳性预测值分别为0.34、0.22、0.29，阴性预测值分别为0.47、1.00、0.91；15 ℃冷水浸手5 min、12 ℃冷水浸手5 min和10 ℃冷水浸手10 min的ROC曲线下面积分别为0.809、0.562、0.529。 结论： 15 ℃冷水浸手5 min方法的诊断灵敏度更高，更适合用于手臂振动病的评价。.

Modeling and analysis of process configurations for hybrid concentrated solar power and conventional steam power plants

Availability and flexibility of variable renewable energy production can be increased without thermal energy storages by integrating intermittent energy production with load following energy production. This paper focuses on modeling, analysis and comparison of three hybrid configurations for concentrated solar power and conventional steam power plants. The configurations include feedwater preheating, cold reheat line and high pressure turbine concepts, in which linear Fresnel collector solar field with direct steam generation is applied to generate steam parallel with the steam boiler. The modeling is conducted using dynamic simulation software Apros®, which enables investigation of the system operation under varying process conditions. In particular, the focus is on the comparison of thermal load balance and interdependencies of the subsystems. In addition, the focus is on increasing the solar contribution, as the solar share is low in current commercial concepts. As a main conclusion, the more solar steam is fed to the system, the more different turbine sections and heat surfaces of the steam boiler are imbalanced, which leads to challenging system design. In addition, the maximum fuel and emission savings are not only determined by the achievable solar share, but also by the hybrid process design. The design of the hybrid system has to be optimized and modified according to the configuration in order to achieve higher peak solar share and fuel and emission savings than 20% achieved in this study.

Simulation study on 660 MW coal-fired power plant coupled with a steam ejector to ensure NOx reduction ability

A 660MW supercritical coal-fired power plant coupled with a steam ejector is proposed to increase the feedwater temperature, which is used to ensure the NOx reduction ability under a low load. The simulation work for the system performance under different steam sources of feedwater heater, feedwater regenerative heating systems and steam sources of steam ejector is carried out. Results indicate that it’s a favorable choice to increase the water temperature through adding No. 0 feedwater heater coupled with steam ejector, because NOx removal efficiency increases from 68.97% (benchmark condition) to 74.66% under 50% THA condition, and it would improve the plant thermal efficiency while the standard coal consumption rate would decrease 0.5g(kWh)−1. Meanwhile, results conclude that it has superior performance than the system by No. 1 feedwater heater coupled with steam ejector. Finally, it’s found that it is more suitable when the primary flow is from the platen superheater outlet. It also finds that the system performance (the induced flow is from No. 1 steam extraction) is more efficient compared with systems that the induced flow is from the cold or hot reheat steam.

Analysis on Welding Crack of Subcritical Power Station Boiler Platen Superheater Header

Welding crack analysis was carried out on tee joint crack of boiler platen superheater header (12Cr1MoV) of subcritical power station applying finite element analysis,microanalysis, mechanical properties test, chemical composition analysis, metallography examination and SEM observation etc. Results indicated that the improper structure, the original welding defects, higher welding heat input, excessive welding residual stress and improper heat treatment led to cold crack and reheat crack ,then induced to the leakage failure while operating.the welding crack originated at the original defects, connected with reheat cracks during propagation and led to leakage finally.

Diverse configurations of the boiler feed pump drive for the ultra-supercritical 900-MW steam plant

Coal-based electric power generation remains the basic source of obtaining energy. With increasing pressure to reduce CO2 emissions, improving power unit efficiency has become an issue of utmost significance. Surely, one of the possibilities to improve the efficiency of new power units is raising the steam parameters. With improved power plant efficiency, there is a lower demand for power of almost all auxiliary equipment except the boiler feed pump. The reason for this is that the power needed to drive the feed pump is an almost linear function of the steam pressure. This means that, even though the steam mass flow (and, consequently, the feed water mass flow) is reduced and the efficiency of feed pumps is improved, their power increases. For this reason, it is very important to find the optimum drive of the boiler feed pump. The main aim of the conducted analysis was to compare various drive options of the boiler feed pump for a conceptual ultra-supercritical 900-MW steam power unit. The following drive configurations of the boiler feed pump were presented and compared: · A frequency-controlled electric motor · A condensing turbine fed with steam extraction from the immediate-pressure turbine · An extraction-backpressure turbine fed with steam from a cold reheat steam line with bleeds shifted from the low-pressure turbine · A backpressure turbine fed with steam from a hot reheat steam line operating in parallel with the intermediate-pressure turbine · An extraction-backpressure turbine fed with steam from a cold reheat steam line with bleeds shifted from the intermediate-pressure turbine (the master cycle idea). The analysis of the operation of the 900-MW unit with various configurations of the feed pump drive was carried out for three load levels: for the nominal mass flow of live steam and for the partial mass flow of 75% and 50%.

Reduction of CO2 emissions of coal fired power plants by optimizing steam water cycle

Abstract To fulfill the energy demand now and in the next decades, coal-fired power plants will be an essential part of the portfolio of power plants that supply electricity cheaply and in a reliable way. The specific CO2 emissions of these plants can be reduced by increasing the efficiency. For that reason KEMA did optimize the steam water cycle of ultra super critical (USC) coal-fired power plants within the EOS program. The improvements are based on the application of the so-called Master Cycle, and on the application of higher steam temperatures. In the Master Cycle cold reheat steam is used in an extra turbine and with steam extraction of this turbine feed water preheating is realized with reduced exergy losses. The turbine is called a tuning turbine reflecting the improved possibilities to tune and optimize the steam cycle with the new coupling where the regenerative heater train and the re-heaters have been decoupled. The Master Cycle is proposed by Dong Energy . The first approach deals with the USC technology with a steam temperature of 600 °C and reheat temperatures of 620 °C. This technology is available at the moment and is applied in new built coal-fired power plants. The second approach deals with the USC technology with a steam temperature of 700 °C and reheat temperature of 720 °C. The expectation is that this technology can be applied around 2025 with the same availability as the USC units with 600 °C. The thermodynamic analyzes are carried out with KEMA’s flow sheeting package SPENCE®. In all considered cases the thermal input was 2400 MWth. In case of the application of the Master Cycle a second reheat is introduced. Results will be discussed and presented in tables, t-s diagrams and h-p diagrams. Improvement of efficiency of coal fired power station technology can reduce the amount of CO2 emitted significantly. This paper shows that with current available technology and improvements an additional emission reduction of almost 10% can be realised by applying the USC 700 + MC. Compared to the world wide average an emission reduction of 66% can be achieved without CCS. In the continuation of the analysis post combustion technology will be integrated in the concept to analyze possible additional benefits of the master cycle with respect to steam supply for the regeneration of the solvents.

Outdoor noise of fossil-fuel power plants

Outdoor noise of several fossil-fuel power plants was measured for varying purposes. Typical continuous noises were generated by water circulation pumps, forced-draft fans and induced-draft fans, emergency diesel engine generators, stacker-reclaimers, SO2 systems, and gas-turbine peaking units. Transient noises included the bumping of coal cars and coal unloading. Another transient noise source was the main steam and cold reheat lines during steam purge. All noises were recorded on magnetic tapes and analyzed using a 1/3-octave band-filter system and in terms of statistical data. Noise propagation was interpreted from topographic conditions, meteorologic effects and sound attenuation factors. The community noise impacts for both continuous noises and transient noises are discussed along with necessary noise controls. One outdoor noise survey of an existing power plant served as a baseline ambient noise measurement for further expansion of the plant. The environmental noise of the expanded plant was also predicted.