Match Characteristics And Influence Factors Of Dongfang Double Reheat Boiler Reheating Surface

As coal is the main primary energy in China, thermal power generation has been placed in a dominant position in the power field. With the depletion of fossil energy and the increasing recognition of international society to CO2 reduction, the development of high parameters and large capacity(ultra) supercritical coal-fired unit is highly recognized by the research institutions and manufacture organizations for the further implementation of saving energy and reducing CO2 emissions. Contrast with traditional(ultra) supercritical coal-fired unit, the double reheat unit has the obvious characteristics which are increasing efficiency by 3%~4% and saving coal resource. For that, the double reheat unit is necessary development trend of China thermal power field. However, there are some problems extremely need to be solved in the developing process of double reheat technology. They are deciding reasonable distribution of the heating surface, choosing reasonable adjusting modes of steam temperature and analysing influence factors of heating surface match characteristics. So the research of heating surface match characteristics and its influence factors is importantly significant to the unit running under the design parameters and good performance index, and long term safe and steady run without the phenomena of exorbitant tube temperature and tube crack. Then, that will promote the development and domestic of the double reheat unit, so it has very important engineering significance and value.Combining with the characteristics of domestic DBC 1000 MW and 660MW(ultra) supercritical coal-fired unit, the research contents of this thesis include furnace type and heat transfer characteristic of DBC double reheat boiler, superheater and reheater heating surface match characteristic of double reheat boiler, and steam temperature adjusting modes and its effect on heating match characteristic of double reheat boiler. The research contents of this thesis are carried out based on three double reheat boiler engineering projects(Huilai 1000 MW, Bengbu 660 MW and Luoyuanwan 660MW).Through research and practice, some conclusions can be required as below.① The proportion of heat absorbed by superheated steam to reheat steam is about 72% to 28%, the proportion of heat absorbed by the first reheat steam to the second reheat steam is about 16% to 12%. The configuration of heating surfaces of the double reheat boiler must be matched to the heat absorbing proportions. If this is complied strictly, the boiler will have reasonable design and run under the design parameters at all loads with good reasonable adjusting modes of steam temperature.② The reasonable choice of the unit steam parameters is the main factor to affect the heat absorbing match characteristics of reheater surface. The research steam parameters of the boiler outside is 32.6MPa(a)/605℃/623℃/623℃, and accordance to the turbine inside is 31MPa(a)/600℃/620℃/620℃ in this thesis.The adjusting mode of reheat steam temperature is the important influence factor to the heat absorbing match characteristics of reheater surface. Because the second reheat system is added in the double reheat boiler, the adjusting mode of reheat steam temperature is very complex and important. The different adjusting mode of reheat steam temperature has the great influence to the heat absorbing match characteristics of reheater surface. The adjusting mode of superheated steam temperature is adjusting the proportion of coal to water and two grade water spray configuration. The determination of the adjusting mode of the reheat steam temperature must be accordance with the boiler type characteristic and the type of the unit run, and consider the initial investment and the run economy of power plant.③ The double reheat boiler can be developed based on the ultra supercritical single reheat boiler in which numerous rich design and running experiences are accumulated. In the development progress of double reheat boiler, we should keep the mature structure and technology of single reheat boiler as far as possible, such as the П-type layout, the spiral furnace with internal thread pipe, the wall fired or tangentially-fired combustion type, the low NOX combustion technology with excellent performance, the advanced superheater and reheater system design, the two-pass or three-pass boiler,the adjusting type of reheat steam temperature with flue gas recirculation, flue gas baffle or burner swing. Then the advanced and reliable double reheat technology with good succession can be acquired.④ The engineering applications of Dongfang double reheat boiler: Huilai 1000 MW double reheat boiler with the П-type layout, the single furnace, the wall fired combustion type, the two-pass, the adjusting type of reheat steam temperature with flue gas recirculation; Bengbu 660 MW double reheat boiler with the П-type layout, the single furnace, the wall fired combustion type, the three-pass, the adjusting type of reheat steam temperature with flue gas baffle; Luoyuanwan 660 MW with the П-type layout, the single furnace, the double tangentially-fired combustion type, two passes distributed right-and-left, the adjusting type of reheat steam temperature with burner swing.