• Plant Journal
• /
• v.17 no.1
• /
• pp.38-49
• /
• 2021

In order to increase power plant efficiency, the steam temperature was increased to 610 ℃ which deteriorates the durability of the boiler tube and as the use of low-calorie coal increases the post combustion and delayed combustion phenomenon, the overheating of the final reheater and the tube rupture are becoming frequent. In order to prevent overheating of the final reheater, desuperheater water injection was increased, leading to a decrease in boiler efficiency. In this study install a baffle plate at the back of some overheated tube groups, thereby reduce the temperature of the tube by reducing the amount of combustion gas, and the reduced combustion gas moves to an adjacent place to increase the temperature of other tubes. As a result of the study, the temperature deviation between tubes decreased 1.5. And the heat-reducing injection amount was reduced to 6,929 kg/h and the maximum tube temperature was reduced to 623.4℃ which is 6.6℃ more below than the control standard of 630℃.

• KIEE International Transaction on Systems and Control
• /
• v.2D no.2
• /
• pp.78-91
• /
• 2002

In the thermal power plant, there are six manipulated variables: main steam flow, feedwater flow, fuel flow, air flow, spray flow, and gas recirculation flow. There are five controlled variables: generator output, main steam pressure, main steam temperature, exhaust gas density, and reheater steam temperature. Therefore, the thermal power plant control system is a multinput and output system. In the control system, the main steam temperature is typically regulated by the fuel flow rate and the spray flow rate, and the reheater steam temperature is regulated by the gas recirculation flow rate. However, strict control of the steam temperature must be maintained to avoid thermal stress. Maintaining the steam temperature can be difficult due to heating value variation to the fuel source, time delay changes in the main steam temperature versus changes in fuel flow rate, difficulty of control of the main steam temperature control and the reheater steam temperature control system owing to the dynamic response characteristics of changes in steam temperature and the reheater steam temperature, and the fluctuation of inner fluid water and steam flow rates during the load-following operation. Up to the present time, the Proportional-Integral-Derivative Controller has been used to operate this system. However, it is very difficult to achieve an optimal PID gain with no experience, since the gain of the PID controller has to be manually tuned by trial and error. This paper focuses on the characteristic comparison of the PID controller and the modified 2-DOF PID Controller (Two-Degrees-Freedom Proportional-Integral-Derivative) on the DCS (Distributed Control System). The method is to design an optimal controller that can be operated on the thermal generating plant in Seoul, Korea. The modified 2-DOF PID controller is designed to enable parameters to fit into the thermal plant during disturbances. To attain an optimal control method, transfer function and operating data from start-up, running, and stop procedures of the thermal plant have been acquired. Through this research, the stable range of a 2-DOF parameter for only this system could be found for the start-up procedure and this parameter could be used for the tuning problem. Also, this paper addressed whether an intelligent tuning method based on immune network algorithms can be used effectively in tuning these controllers.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2012.05a
• /
• pp.953-954
• /
• 2012

• Journal of the Korean Society of Combustion
• /
• v.18 no.4
• /
• pp.1-11
• /
• 2013

The oxy-fuel combustion is $CO_2$ capture technology that uses mixture of pure $O_2$ and recirculated exhaust as oxidizer. Currently some Oxy-fuel power plants demonstration project is underway in worldwide. Meanwhile research project for converting 125 MWe Young-Dong power plant to 100 MWe oxy-fuel power plants is progress. In this paper, 1 D process analytical approach was applied for conducting process design and operating parameters sensitivity analysis for oxy-fuel combustion of Young-Dong power plant. As a result, appropriate gas recirculation rates was 74.3% that in order to maintain normal rating superheater, reheater steam temperature and boiler heat transfer patterns. And boiler efficiency 85.0%, CPU inlet $CO_2$ mole concentration 71.34% was predicted for retrofitted boiler. The oxygen concentration in the secondary recycle gas is predicted as 27.1%. Meanwhile the oxygen concentration 22.4% and moisture concentration 5.3% predicted for primary recycle gas. As the primary and secondary gas recirculation increases, then heat absorption of the reheater is tends to increases whereas superheater side is decreased, and also the efficiency is tends to decrease, according to results of sensitivity analysis for operating parameters. In addition, the ambient air ingression have a tendency to lead to decline of efficiency for boiler as well as decline of $CO_2$ purity of CPU inlet.

• Journal of Advanced Marine Engineering and Technology
• /
• v.35 no.1
• /
• pp.46-52
• /
• 2011

A study on the improvement for cycle efficiency of closed-type ocean thermal energy conversion (OTEC) was studied to obtain the basic data for the optimal design of cycle. For that, OTEC cycle with a generator, a reheater and a multi-turbine was simulated and analyzed. The basic thermodynamic model for OTEC is Rankine cycle and the surface seawater of $26^{\circ}C$ and deep seawater of $5^{\circ}C$ were used for the heat source of evaporator and condenser, respectively. Ammonia is used as the working fluid. The cycle efficiency increased when generator is added with 0.9 generator effectiveness. When the reheater and multi-turbine are applied in the basic cycle, the cycle efficiency showed 3.14% and the capacity of heat exchanger decreased for same total cycle power. For the OTEC cycle with the generator, the reheater and the multi-turbine showed the highest cycle efficiency and increased the efficiency by more than 6.5% comparing with the basic OTEC cycle.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.5
• /
• pp.563-569
• /
• 2012

The superheater and reheater tubes of a heavy-load fossil power plant boiler can be damaged by overheating, and therefore, the degree of overheating is assessed by measuring the oxide scale thickness inside the tube during outages. The tube temperature prediction from the oxide scale thickness measurement is necessarily accompanied by destructive tube sampling, and the result of tube temperature prediction cannot be expected to be accurate unless the selection of the overheated point is precise and the initial-operation tube temperature has been obtained. In contrast, if the tube temperature is to be predicted analytically, considerable effort (to carry out the analysis of combustion, radiation, convection heat transfer, and turbulence fluid dynamics of the gas outside the tube) is required. In addition, in the case of analytical tube temperature prediction, load changes, variations in the fuel composition, and operation mode changes are hardly considered, thus impeding the continuous monitoring of the tube temperature. This paper proposes a method for the short-term prediction of tube temperature; the method involves the use of boiler operation information and flow-network-analysis-based tube heat flux. This method can help in high-temperaturedamage monitoring when it is integrated with a practical tube-damage-assessment method such as the Larson-Miller Parameter.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.643-647
• /
• 2003

Power plant Piping operating at elevated temperature often fails prematurely by the growth of microcracks under creep conditions. Therefore, the life assessment of high temperature components that contain cracks is an important technological problem. The mechanisms of crack growth in simple metals and alloys have been investigated using both mechanical and microstructural approaches. In this study, life prediction accounting for creep, crack growth and thermal stress is analyzed.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.23 no.4
• /
• pp.328-333
• /
• 2003

It has been widely recognized that the residual stress of the weldment affect the integrity of steel structures and cause an initiation of crack in the welded regions. Since the power plants adopt a variety of welding processes, it is necessary to know the distribution and magnitude of residual stresses. This paper has attempted to investigate the validity of the saw cutting method and the indentation method to measure the residual stresses in the steel plates. The residual stresses in the specimens of hot reheater pipes, cold reheater pipes and feed water lines in power plants were determined by the saw cutting method and the indentation method. The data were compared and reviewed for the validity of the methods.

• Clean Technology
• /
• v.23 no.3
• /
• pp.223-236
• /
• 2017

As the use of waste and biomass increases in a power generation boiler, high temperature corrosion (HTC) problems of boiler heat exchangers are becoming very important. Chlorine of the low-rank fuels is mainly responsible for the HTC issues, which typically occur in the surface of high temperature heat exchanger like a superheater or reheater. In order to mitigate the problem, various approaches have been proposed in terms of design modification, material improvement, fuel pre-treatment and additive utilization. In this study, the current state of research and development focused on the additive method was investigated.

• Journal of the Korean Institute of Gas
• /
• v.17 no.2
• /
• pp.70-77
• /
• 2013

The present study has been carried out to analyze the effect of steam hammering on the steam piping system including the final superheater, the high pressure turbine, check valve and the first reheater by sudden stoping of main stop valve in a power plant. For the present steam hammering analysis, the well known Flowmaster software has been used to model the steam piping system and the time dependent characteristics of pressure and steam mass flow rate has been conducted. Using the result of the unsteady pressure and steam mass flow rate, the forces acting on the elbows in the piping system has been derived. From the present analysis, it has been elucidated that the elbow just before the main stop valve and the elbow near the connection pipe between bypass pipe and check valve had the largest force among the elbows in the steam piping system. The structural safety diagnostics study on the elbow and the supporting structures of the steam piping system of a power plant will be conducted in the future by the present results of the forces acting on the elbow.