Data-driven optimization of pollutant emission and operational efficiency for circulating fluidized bed unit

Modeling for the bed temperature 2D-interval prediction of CFB boilers based on long-short term memory network

A pressure balance model for a circulating fluidized bed (CFB) unit that incorporates a downer has been proposed. A comparison of the operation stability between a CFB downer and a CFB riser showed that, although only one critical operating gas velocity exists in the CFB riser for a given riser solids flux, there can be many critical gas velocities for the operation of a CFB downer. Therefore, it is possible to achieve high solids concentration in a CFB downer if appropriate operating conditions are used. Parameters that affect the solids concentration in the CFB downer have been studied using the model and have been validated with experimental data obtained from a special CFB unit that incorporates a downer. Measures to increase the solids concentration in the downer have been proposed.

Three-dimensional numerical simulation of coal and papermaking trash co-combustion in a circulating fluidized bed

Circulating fluidized bed (CFB) is becoming the main coal combustion technique all over the world for its high combustion efficiency, low pollution, fuel flexibility and good load-following capability, but its combustion process characteristic is highly non-linear, time-varying, large time delay and multi-variable strong coupling. The conventional control proposal divides the bed temperature control system and main steam pressure control system into two separate PID single-loops without consideration of inter-circuit coupling, which results in low automatism operation rate and often manual operation required. To solve this problem, a multi-variable adaptive neural network decoupling controller with PID structure is introduced based on the principle of NN control and decoupling compensation. The decoupling and control capability of PID NN decoupling controller are from the NN cross-tie structure and the nonlinear mapping properties, as well as the PID style processing of the hidden layer node. The weights of the NN are learned and optimized by the particle swarm optimization (PSO) algorithm, which is known for its searching ability in the total parameter space concurrently and efficiently. These NN weights will not only eliminate the coupling relations between circuits, but also strengthen the PID-NN controller's adaptability. This multivariable decoupling control method is used to control the two-dimensional transfer function matrix of the bed temperature and main steam pressure system in the CFB combustion system. Simulation results show that the new control strategy could overcome nonlinear and strong coupling features of CFB combustion system in a wide range and is expected to have great potential for engineering application.

With the increasing global focus on sustainable development, circulating fluidized bed (CFB) boilers, as highly efficient and low-pollution combustion equipment, play an important role in energy production and environmental protection. However, the combustion efficiency and emission control of CFB boilers still face challenges, and there is an urgent need for multi-objective optimization through advanced technologies to support the goal of sustainable development. This study proposes an intelligent framework integrating Bidirectional Temporal Convolutional Network (BiTCN) and Hybrid Dung Beetle Optimizer (HDBO) for multi-objective optimization of combustion efficiency and NOx/SO2 emissions in CFB boilers. The BiTCN model captures bidirectional temporal dependencies between dynamic parameters (e.g., air-coal ratio, bed temperature) and target variables through operational data analysis. Three key improvements are implemented in DBO: (1) Chaotic initialization via sequential pattern mining (SPM) enhances population diversity and spatial coverage; (2) The osprey optimization algorithm (OOA) hunting mechanism replaces the original rolling update strategy, improving global exploration; (3) t-Distribution perturbation is applied to foraging beetles in later iterations, leveraging its “sharp peak and thick tail” characteristics to dynamically balance exploitation and exploration. Experimental results demonstrate 0.5–1% combustion efficiency improvement and 15.1%/30% reductions in NOx/SO2 emissions for a typical CFB boiler.

Oxidation mechanism of pyrite concentrates (PCs) under typical circulating fluidized bed (CFB) roasting conditions and design principles of PCs’ CFB roaster

The interrelation between fuzzy logic and cluster renewal approaches for heat transfer modeling in a circulating fluidized bed (CFB) has been established based on a local furnace data. The furnace data have been measured in a 1296 t/h CFB boiler with low level of flue gas recirculation. In the present study, the bed temperature and suspension density were treated as experimental variables along the furnace height. The measured bed temperature and suspension density were varied in the range of 1131-1156 K and 1.93-6.32 kg/m3, respectively. Using the heat transfer coefficient for commercial CFB combustor, two empirical heat transfer correlation were developed in terms of important operating parameters including bed temperature and also suspension density. The fuzzy logic results were found to be in good agreement with the corresponding experimental heat transfer data obtained based on cluster renewal approach. The predicted bed-to-wall heat transfer coefficient covered a range of 109-241 W/(m2K) and 111-240 W/(m2K), for fuzzy logic and cluster renewal approach respectively. The divergence in calculated heat flux recovery along the furnace height between fuzzy logic and cluster renewal approach did not exceeded ±2%.

Fluidization of sawdust in a cold model circulating fluidized bed: Experimental study

An intelligent coordinated control strategy has been proposed and successfully applied to 135∼300MW circulating fluidized bed (CFB) boiler-turbine units in China. Because the combustion system of the CFB is a complex object characterized, it is difficult to build precise mathematic model and control it with traditional control theory. The paper describes intelligent coordinated control (ICC) system for the circulating fluidized bed (CFB) unit. ICC is based on both fuzzy feedforward control and the fuzzy-PID feedback control. The feedforward control path contains a set of multi-input single-output fuzzy inference systems. The control ouput is mainly determined by the feedforward path, diminishing the control effort on the PID controllers. The fuzzy-PID controller supplies the complementary control signal component for regulation and disturbance rejection in small neighborhoods about the commanded trajectories. The scheme is implemented based on the Function Code on many typical DCS (INFI-90, XDPS, etc). The industrial application results show that this design scheme works well for the specific range of load variations.

Investigation on lateral dispersion characteristics of fuel particles in dense phase zone of a large-scale circulating fluidized bed boiler under combustion conditions

With the pollutant emission standards becoming increasingly stringent and considering the pressure of carbon neutral by 2060, the low pollutant emission potential of circulating fluidized bed (CFB) combustion technology needs to be further exploited, thus to promote the market competitiveness of CFB boilers; this is critical for the clean and efficient utilization of coal as well as for the energy transformation in China. In this article, we summarize the pollutant emission characteristics of CFB combustion, and review the development of major technologies for CFB boiler emission control. Based on the energy development strategies and corresponding policies in China, development suggestions are proposed for reducing pollutant emission of the CFB combustion technology. The most significant approach is to push the limits of original pollutant emission for CFB combustion by re-specifying the fluidization state and through in-furnace combustion adjustment, while the boiler thermal efficiency should be ensured. For the long-term development of coal energy, the new-generation CFB combustion technology with ultra-low emission should be researched and developed while combining with technologies such as supercritical/ultra-supercritical, intelligent operation, carbon capture, utilization, and storage, and energy storage technologies. The existing CFB boilers with small or medium capacity should also be upgraded. Considering the fuel flexibility of CFB combustion, biomass power generation should be promoted to realize low-cost and high-efficiency consumption of low-heat value fuels, urban refuse, industrial wastes, etc. The peak load regulation capacity and low pollutant emission property of the CFB boilers should be promoted to improve operation flexibility and renewable energy consumption. Moreover, the desulphurization ash produced in CFB combustion should be comprehensively utilized, and the N2O emission problem is also significant. The pollutant emission standards and related policies need to be formulated from an overall perspective to guide the healthy development of the energy industry.

Modeling of axial bed-to-wall heat transfer in a CFB combustor with abrupt riser exit geometry

High-density circulating fluidized beds (CFB) differ in several respects from low-density CFB systems. In high-density CFB risers, solids move upward throughout the entire riser cross-section, and the net downflow of particles at the wall, a commonly observed feature of fast fluidized beds, is absent. Hence there exists a transition regime from the low density to high density CFB where the net particle motion in the vicinity of the wall is changing from downwards to upwards. This was confirmed by experiments carried in a dual-loop high-density CFB facility with concentric-tube heat exchanger installed in the riser. Local suspension-to-wall heat transfer coefficient and suspension temperature distribution below and above the heat exchange section were measured. Experimental results elucidated that particles move both upwards and downwards in the vicinity of the wall for the operation conditions studied. This alternation of direction leads to higher heat transfer coefficients at both ends of the heat exchange.

The capability of Fluent 6.2.16 to simulate particle mixtures in a laboratory scale 2D circulating fluidized bed (CFB) unit has been tested. In the simulations, the solids were described as one or two particle phases. The loading ratio of small to large particles, particle diameters and the gas inflow velocity were varied. The 40 cm wide and 3 m high 2D CFB was modeled using a grid with 31080 cells. The outflow of particles at the top of the CFB was monitored and emanated particles were fed back to the riser through a return duct. The paper presents the segregation patterns of the particle phases obtained from the simulations. When the fraction of large particles was 50% or larger, large particles segregated, as expected, to the wall regions and to the bottom part of the riser. However, when the fraction of large particles was 10%, an excess of large particles was found in the upper half of the riser. The explanation for this unexpected phenomenon was found in the distribution of the large particles between the slow clusters and the faster moving lean suspension.

Mixed incineration of municipal solid waste (MSW) in existing coal gangue power plant is a potentially high-efficiency and low-cost MSW disposal way. In this paper, the co-combustion and pollutants emission characteristic of MSW and coal gangue was investigated in a circulating fluidized bed (CFB) combustor. The effect of MSW blend ratio, bed temperature and excess air ratio was detailedly studied. The results show the NOx and HCl emission increases with the increasing MSW blend ratio and the SO2 emission decreases. With the increase of bed temperature, the CO emission decreases while the NOx and SO2 emission increases. The HCl emission is nearly stable in the temperature range of 850–950 °C. The increase of excess air ratio gradually increases the NOx emission but has no significant effect on the SO2 emission. The HCl emission firstly increases and then decreases with the increase of excess air ratio. For a typical CFB operating condition with excess air ratio of 1.4, bed temperature of 900 °C and MSW blend ratio of 10%, the original CO, NOx, SO2 and HCl emissions are 52, 181, 3373 and 58 mg/N m3 respectively.