BELYALOV ALEXANDERMaster's Work |
| "Heating work development of CFB boiler of Starobeshevo Power Plant" |
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Importance of this work is in the theoretical grounds of process variables of the combustion procedure in CFB boiler and modeling of the boiler according to results of experiment and determine the dust loss speed from the bed too.
Aim and tasks of this work:develop of the CFB heating rate, research furnace aerodynamic performances, calculate the dust loss speed and coal particles fluidization and bed substance.
The most part of Ukrainian coal deposits concern to low rank class and their usage in power industry demand the application of the special technologies.
World experience indicates that not only possibility in principle of burning low rank fuel grade but also the high efficiency and ecolgical purity of these technologies. Similar technologies have been used in the USA, Germany, France, Sweden, Spain, Canada, China and in many other countries for a long time.
Developinfg of future trends of Ukraine power industry concern the usage of the coal which is the main energy carrier of organic origin. Today the solid fuel power industry is in critiacal situation due to the insufficient coal production and high ash content of thermal coal on the one hand and depreciation and obsolescence of the generating equipment on the other hand. Boilers of Power Plants were built in the sixties - seventies of the twentieth century with pulverized burning and ash tapping process. They can burn coal with high ash content together with natural gas or heavy oil and their parts increase due to solid fuel enlargement. Besides they do not correspond to the modern ecological standarts (desulphurization and nitric purification systems are absent). That's why the boilers reconstruction question is one of the urgent question. These boilers exhausted all their resources whereas the modern high-performance and ecologically clean methods of processing of power-generating coal are used. Above all the technology of burning in CFB bed concerns to these methods.
Burning process in CFB is the result of low temperatures (850-900°Ñ)and characterized by equal distribution of temperatures in the bed and its thermal inertance and stability. Besides, it is possible the guaranteeing stringent ecological requirements concerning the emissions of nitric oxide and sulfur without usage of the expensive harmful emissions refiners. The feature of solid fuel burning in FB and CFB is the burning process as in the bed as in above-bed level with futher return and frequent circulation of fuel particles in the reaction zone.
For the 10-20 years immediately ahead utilization of CFB technology is the most promising technique of reconstruction and erection of new boilers and industrial boilers with output from 6-10 to 800 t/h. Doubtless advantages of CFB and CB are: ecological cleanness, utilization of coal with high ash level (40-55%) and low heating value (up-to-date 30-100%Nnom), maneuvering regime work.
The most important advantage of new burning technology is the possibility of utilization waste coal. About 6,5 million tons of waste coal are prodused on the concentration plant of Ukraine. It is possible to burn waste coal in CFB furnace with appropriate preporation.
In conditions of deficiency circulating and investing assets for fundamental reconstruction seems that low costs for renovationf of Power Plant by replacement of separate units would be the most economically sound method of cost minimization for their renovation. It should be mantioned that execution of maintanance based only on overhaul-period renewal would lead to the accomulation of obsolete equipment and its maturing, degradation of work and growth repair bill, fuel overdraft would be commensurable with the cost of fundamental reconstruction.
The main point of CFB technology consists in ensuring of circulation of disperse material consits on 97...99% of ash particles in closed loop: furnace -separator - recirculation circuit - furnace. The speed of gas rate in the furnace exceeds the speed of dust loss for most part of disperse material. In contrast to the bubbling bed there is no sharply defined bound between the boiling bed and upper-bed level. The whole furnace is filled up with the disperse material which concentration without pronounced jump vary from the peak on the grill to the minimum in the upper part of the furnace. Such variation concerns with intrafurnace circulation of solid phase and it allows to smooth the temperature gradients within the bounds of the furnace. There is so-called dense bed on the grill which consists from the large particles. It provides the equal distribution of returned disperse material from the separator over the grill and its height and accordengly resistance define the greater part (70...80%) of furnace aerodynamic resistance.
The CFB technology provides the effective and stable operation of boiler with wide range of fuel (Ar = 10...80%; Wr = 0...60%; Qn = 8...29 Mj/kg; Vg = 3...90%). The CFB technology among the other methods of fuel buring supplies the deep intrafurnace suppression of NOx and SO2. NOx content in smoke fumes (equate α = 1,4) does not exceed 400 mg/m³ and the binding degree SO2 is 85...95%.
There are some industrial adjusted CFB technologies such as "LURGI" (Germany), "PYROFLOW" ALSTREM (Finland), "Cyclefluid" Douche Babcock (Germany) etc. The biggest technologies which are in operation are presented in the first and second technologies. The circuit diagram of CFB boilers of LURGI and PYROFLOW are given in the picture 1 and 2 accordingly.
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