Double Reheat Unit Research Articles

Performance and Operation Strategy Analysis of BEST Cycle 1000MW Double Reheat unit under Different Operating Conditions

Improving steam parameters in a coal-fired power unit boosts cycle efficiency, lowers coal consumption, and reduces emissions. The backpressure extraction steam turbine (BEST) cycle addresses the problem of excessive superheating of extraction steam. This study analyzed a 1000 MW double reheating unit, finding that heat rate in the conventional and BEST cycle systems is heavily influenced by load under THA conditions. At 100% and 75% loads, the BEST cycle’s heat rate decreases but increases at 50% load. For safe operation during flow interruption and high load rates, a pairwise grouping method is recommended for high-pressure heater interruption. When multiple low-pressure heaters are simultaneously cut off, the unit load needs to be limited based on the number of heaters being removed. when multiple low-pressure heaters are simultaneously cut off, the unit load needs to be limited based on the number of heaters being removed. Removing two low-pressure heaters lowers the load to 90%, and three lowers it to 80%. These findings optimize the thermal system’s parameters and enhance overall efficiency.

Technical and economic study on improving parameters of double reheat units

Technical and economic study on improving parameters of double reheat units

Research and Application of Double-Reheat Boiler in China

The ultra-supercritical (USC) double-reheat technology is an immediate area of research focus in China, since the thermal efficiency of USC double-reheat unit is higher than the USC single-reheat unit. The parameters and capacity of USC double-reheat unit in China have made major breakthroughs, and the thermal efficiency of the units are as high as 47–48%, which is the highest in the world. USC double-reheat boiler is one of the most important devices for USC double-reheat unit, and the design concept and precision have a vital effect on the operation of boiler and power station. The most difficult and important factors in the design of double-reheat boiler are the layout of heating surface and the steam temperature regulation method. Therefore, this work summarizes the arrangement of heating surface and temperature regulation method of existing double-reheat boiler in China. It is hoped that the work will set a benchmark for the development of double-reheat boiler and the future 700 °C power generation unit in the world.

Thermal economy study on the waste heat utilization of a double reheat unit under coupled steam turbine and boiler

The waste heat utilization of flue gas has great potential, which is an effective measure to improve the thermal economy of the unit. This paper established the coupling model of boiler system and steam turbine system and studied the influence of boiler side parameters on thermal economy of double reheat waste heat utilization under coupled steam turbine and boiler. The study concluded that boiler load, Gas Recirculation Rate, r1 and the outlet temperature of primary air in the air preheater had an impact on the thermal economy of the advanced waste heat recovery system with double reheat. The thermal economy of the advanced waste heat recovery system with double reheat increased with the increase of boiler load and Gas Recirculation Rate, and decreased with the increase of r1 and the outlet temperature of primary air in the air preheater. The maximum coal-saving capacity of the advanced waste heat recovery system compared with the reference system is 1.5%.

Development and engineering application of high-precision and multi-function simulation system for double reheat ultra-supercritical units

Laiwu ultra-super critical double reheat unit is the highest ultra-super critical double reheat unit, with the highest parameters in China, from the safe and economical to run level put forward higher requirements. Taking ultra-super critical double reheat unit as the research object, a high-precision and multi-functional simulation system for ultra-super critical double reheat unit was developed before the unit was generated, to realize the dynamic analysis of ultra-super critical double reheat unit, control strategy verification and operation technique validation; and conduct operator operation and accident management training. provides technical support for the smooth construction, and safe and stable operation of the ultra-super critical double reheat unit.

Quantitative Analysis of Operating Economical Performance by Valve Leakage in Bypass System

In this paper, the influence of steam leakage of the control valve in bypass system on unit operating economy is analysed. Through quantitative analysis, the formulas for calculating the influence of the steam leakage of control valves in high-pressure, medium-pressure and low-pressure bypass systems on the parameters of unit work and heat absorption are obtained. In the end, combined with the design data, the thermal economy of 1000MW double reheat unit is analyzed in view of the internal leakage of control valve in high-pressure, medium-pressure and low-pressure bypass system.

Design and exergy analysis of 1000-MW double-reheat double-turbine regeneration system

The development of ultra-supercritical double-reheat technology is a practical choice to further improve the power generation efficiency, reduce coal consumption, reduce carbon emissions, and save resources. Currently, the outer-steam cooler system in double-reheat units has been typically adopted to solve the problem of prodigious superheat degree of an extraction steam. An increasing number of studies show that the double-turbine regeneration system achieves better economy and practicability in resolving the prodigious superheat degree of an extraction steam for double reheat. Through the thermal equilibrium analysis method and exergy analysis method, the performance of the three units under design conditions and off-design conditions is specifically analyzed, and the exergy loss and exergy efficiency of both the steam turbine and regenerative heater are further analyzed. The results show that the energy-saving performance of the double-turbine regeneration system is better than that of the outer-steam cooler system under the design conditions, and the energy-saving performance of the double-turbine regeneration system gradually decreases as the load decreases. At low loads, the performance of the regenerative turbine is significantly reduced, and the energy-saving effect of the double-turbine regeneration system is not as good as that of an outer-steam cooler system.

China’s national demonstration project achieves around 50% net efficiency with 600 °C class materials

The bottlenecks in developing high-efficiency ultra-super critical (USC) coal power technology are analyzed within the context of the growing pressure on the coal power industry to reduce carbon dioxide (CO2) emissions. To meet these demands, further improving the annual average operating efficiency of coal power is essential. A cross-compound double reheat unit design characterized by an elevated and conventional turbine layout is proposed in this paper. This new design can greatly shorten the length of expensive high-temperature piping required, significantly cut piping costs as well as reducing pressure drops and heat losses, resulting in a much higher efficiency and performance-price ratio than conventional double reheat design. The engineering study demonstrates the feasibility and advantages of this design. Now this new design is being implemented on Pingshan Phase II Project as a demonstration coal power unit in China. Despite the new turbine arrangement, Pingshan Phase II Project also adopts a series of energy saving, environmental protection, efficiency preservation and safety technologies, of which some have already gained success in Shanghai Waigaoqiao No. 3 Power Plant. Based on the new design and further optimization, the unit net efficiency of Pingshan Phase II is expected to achieve 49.8% under rated conditions on a lower heating value (LHV) basis. Combined with a series of innovative technologies that can keep the efficiency from decreasing under operational conditions, the annual average net efficiency can achieve 48.8% on LHV basis. This efficiency level is high enough to meet the strict CO2 emission standard proposed by United States Environment Protection Agency (U.S. EPA) based on the Pittsburgh #8 bituminous coal, showing significant potential for reducing CO2 emissions. A series of low-energy-consumption and even energy-saving pollutants removal technologies are also be applied on this project to harmonize high efficiency and low emissions.

Thermodynamic System Integration of Solar-coal-fired Power Plant

Solar-assisted coal-fired thermal power plant is an important direction to achieve large scale use of solar energy. Based on the exergy analysis theory, the 660MW double reheat unit is taken as an example to analyze the solar assisted feed water system and the solar assisted secondary air system. The results show that the performance of solar-assisted coal-fired units is better than that of coal-fired units alone, and the solar-assisted secondary air system efficiency is up to 47.15%. On the basis of this, the paper analyzes the exergy loss of the equipment of the coal-fired unit, the solar-assisted feed water system and the solar-assisted secondary air system. It reveals the exergy loss of the unit is mainly concentrated in the boiler side, the introduction of solar energy to reduce the boiler side of the loss, then the system's total loss is reduced. It also shows that changes in the feed water parameters in the solar assisted feed water system have an impact on the overall system.

Exergy analysis of the turbine system in a 1000 MW double reheat ultra-supercritical power plant

This study aims to achieve exergy distribution in a turbine system for a 1000 MW double reheat ultra-supercritical power plant. An exergy balance equation is used to identify the real points of energy loss in the turbine system, which can provide a reference for optimizing operation and conserving energy. Results show that irreversibilities yield the highest exergy loss in the turbine, particularly in the very high pressure (VHP) and low pressure (LP) cylinders. Compared with that in the turbine of a single reheat unit, exergy loss in the studied turbine is higher and exergy efficiency is lower. For the regenerative system, exergy loss is lower and exergy efficiency is higher in the double reheat unit than in the single reheat unit. Thus, the layout of the regenerative heaters in the double reheat unit is more reasonable. However, exergy loss in high pressure regenerative heater Nos. 3 and 6 and low pressure regenerative heater Nos. 7 and 10 in the heat recovery system is extraordinary because of different reasons. Exergy loss in the condenser of the double reheat unit is relatively smaller than that in the condenser of the single reheat unit.

Coal gasification for electric power generation

Since proven world coal resources are sufficient to produce electricity until well into the twenty-second century, coal will remain the primary fossil fuel for power generation. Growing concern about environmental pollution will inevitably lead to more advanced and cleaner cycles. Basic considerations for advanced coal fired plants are maximum availability and efficiency, minimum environmental emissions, optimal total costs (investment, operational and maintenance costs) and maximum utilization of waste products. The currently applied pulverized coal fired steam cycle plant will further develop from supercritical units in the early 1990s (27.5 MPa, 545°C/570°C) to ultrasupercritical double reheat units in the next century (35.0 MPa, 600°C/600°C). By additional improvements, such as increased feed-water temperature, improved turbine blading, waste heat recovery devices and better back-end designs, the net thermal efficiency can be increased further. Gas turbines and fuel cells provide a new basis for effic...

The Construction of 700 MW Units with Advanced Steam Conditions

High priority has been given to increase efficiency of power generation plants; therefore, the steam conditions of fossil fuelled plants have gradually been improved. Recent developments of material and design techniques, the accumulated experience of the operation and so on have enabled advancements to be made in steam conditions. Two units of 700 MW with advanced steam conditions were constructed at Kawagoe Power Station by Chubu Electric Power Company, Inc. in Japan. These two double reheat units are designed at elevated steam conditions of 310 bar, 5661566/566° C, to improve thermal efficiency by 5 per cent in relative values, as compared with conventional supercritical steam conditions (240 bar, 538/566° C). Considerable research and development has been carried out by the manufacturers of the boiler and the turbine to achieve highly reliable operation. This paper presents the design features, the result of the research and development and the result of the operation of these units.