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Low-cost multi-pollutant collaborative removal technology for large circulating fluidized bed units
Applicating Company
Guoneng (Shandong) Energy & Environment Co., Ltd.
Technology Name
Low-cost multi-pollutant collaborative removal technology for large circulating fluidized bed units
Technical principle
(1) Ultra-low flue gas pollutants emission control technology for 600MW supercritical CFB units
The electric area of the electric-bag filter at the tail of CFB boiler is reserved as the pre dust remover to reduce the dust concentration in the flue gas. CFB-FGD is added outside CFB boiler, and high-efficiency bag filter is set at the same time. "One boiler and two towers" technology is adopted for CFB units of 600MW grade and above, that is, one boiler corresponds to two sets of semi-dry CFB-FGD, each set of semi dry process system handles 50% of flue gas. The stable switching control technology of "one boiler and two towers" is adopted to realize the switching operation of single and double towers when the load of CFB unit increases or decreases.
(2) Two stage collaborative desulfurization technology of limestone in furnace and semi dry method outside furnace of CFB unit
Focus on solving the problem that the automatic control system of CFB unit desulfurization inside and outside the furnace is affected by the characteristics of boiler combustion conditions, such as large delay, variable coal quality and nonlinearity, so as to achieve coordination between desulfurization processes inside and outside the furnace. The two-stage collaborative desulfurization optimization control system is complementary to the control scheme of the original DCS inside furnace/outside furnace desulfurization system. Specifically, it includes the automatic control of limestone feeding inside the furnace and the automatic control of slaked lime feeding outside the furnace. Through fuzzy control and predictive control, the advance of feeding and stop feeding, the reduction of SO2 concentration fluctuation are realized, taking the current value and change trend of the controlled variable into account.
(3) Collaborative optimization control technology of hierarchical cascade desulfurization and dust removal with disturbance compensation for pulverized coal fired units.
Bring into play the "triple" optimization control mechanism. The first optimization mechanism, anti-disturbance closed-loop control of dry electrostatic dust filter + advanced predictive control of wet electrostatic dust filter. The second optimization mechanism, collaborative optimization mechanism of dry and wet electrostatic dust filters. The third optimization mechanism, safety protection mechanism for reaching the standard of dust concentration at the outlet. And finally realize 100% automatic input rate of dust removal control system. Based on big data analysis, the economic operation of the system is optimized, the precise control system of the desulfurization and dust removal is developed adopting advanced algorithms, and the intelligent adjustment, precise control and economic operation of the desulfurization and dust removal system are realized.
Scope of application
This technology is applicable to the ultra-low emission control of flue gas pollutants for circulating fluidized bed units, or the coal-fired units and industrial boilers with the original boiler outlet flue gas SO2 concentration≤1600mg/Nm3. The goal of SO2 emission concentration≤35mg/Nm3 and the dust emission concentration≤5mg/Nm3 can be achieved adopting this technology.
Process flow and description
The semi-dry CFB-FGD technology is based on the mechanism of gas-solid two-phase flow reaction. The flue gas enters the bed through the acceleration of the Venturi tube at the bottom of the desulfurization tower. The materials are fully contacted in the circulating fluidized bed for reaction. A water spray device is set on the top of the Venturi tube to increase the desulphurization agent moisture and reduce the flue gas temperature in the tower, so that the reaction between SO2 and Ca(OH)2 can be converted into ionic reaction.
The two stage collaborative desulfurization control system includes hardware architecture and closed-loop control algorithm. The hardware architecture includes three parts: the upper industrial computer, the middle PLC and the bottom DCS. Closed loop control algorithm adopts a nonlinear predictive control strategy combined with a variety of advanced control strategies targeting the relevant control loops.
Promotion prospects
The layout of "one boiler and two towers" is adopted for the technical route of desulfurization and dust removal of 600MW supercritical CFB unit，and the single/double tower switching technology is adopted when the unit load changes. The key and difficult point of the project research is to ensure that the flue gas emission reaches standards during the switching process. Through basic research, experimental research, project implementation and commissioning and a certain period of operation, our company has mastered the key technologies such as "one boiler and two towers" design, stable switching between single and double towers, and SNCR denitration optimization. The application of two-stage collaborative desulfurization control technology based on advanced control strategies effectively improves the economic operation of the system and reduces system maintenance. The achievements will help protect the ecological environment of "the Belt and Road" region and achieve the goal of energy saving and carbon reduction.