Research On Operational Economy Of Large-scale Circulating Fluidized Bed Boiler Unit

Due to the large scale of wind power and solar power accessed to power grid,the instability of power grid is increasing.Therefore,it is urgent for thermal power units to enhance flexible operation capacity to cope with grid connected problems of new energy.In recent years,a great quantity of large-scale Circulating Fluidized Bed(CFB)boiler units have been put into operation and grid connected.The frequent changes of AGC instruction lead to more variable load operations of units.However,due to the low utilization ratio of automatic control,the units have high energy consumption in operations.Meanwhile,the country's environmental requirements for thermal power units are increasing in recent years,which makes the pressure of SO2 and NOx emission control and the emission cost increasing.This paper shows the operation economy of CFB units through two aspects which are energy flow of unit load changing process and deep desulfurization and denitration economy.The main contents are as follows:(1)This paper studies on the energy flow and energy storage of CFB boiler unit,besides it establishes energy balance equation based on the fuel energy storage,conventional energy storage,energy supplied from coal and operation demand energy.According to the energy flow in the variable load operation,this paper establishes the operation economy index which is according to the comparison of the actual coal quantity and the economic coal quantity.This economic index can be used as a signal of controlling the ratio of coal to wind and stabilizing the main steam pressure to reduce the energy loss and ensure the safety of the units.This theory has been verified on the actual operating data of a 300MW CFB boiler unit.(2)This paper studies the mechanism of desulphurization and denitration in CFB boiler.The calculation method of desulfurization and denitration costs is established based on SO2 and NOx emission control technology of limestone desulfurization,wet flue gas desulfurization and selective non-catalytic reduction(SNCR)denitration.When the operation cost is established,the concept of active limestone is introduced to satisfy the dynamic operation requirements of the unit.Comprehensive economic index are no longer confined to the static operating conditions.Verification test has been carried out in a 330MW CFB boiler,which shows the connections between the ratio of calcium to sulfur with limestone in furnace,limestone outside furnace,cost of FGD electricity cost and denitration cost.According to the comprehensive cost,the most economical ratio of calcium to sulfur in the furnace can be obtained.It can provide some references for the selection of desulphurization tower of the new power plant through the construction cost of desulphurization tower and full load operation cost.