Optimizing Sludge Incineration for Thermal Energy Recovery: A Sustainable Approach to Industrial Waste Management

Ash formation during fluidized-bed incineration of paper mill waste sludge

Comparing the greenhouse gas emissions from three alternative waste combustion concepts

Development of a circulating fluidized bed for a 100 kg/day waste plastic pyrolysis-combustion system

The gas-solid flow characteristics and fuel NOx formation mechanisms in a novel full-scale Dual Circulating Fluidized Bed (DCFB) was numerically studied. The DCFB was comprised of a bubbling fluidized bed (BFB) at reducing temperature for the release of fuel-N and a circulating fluidized bed (CFB) for combustion of the residue char. A dense discrete phase model coupled with kinetic theory of granular flow (DDPM-KTGF) model was used to determine the gas-solid flow characteristics of the DCFB, and a one-dimensional chemical reaction network (1D-CRN) with detailed chemical reaction mechanisms was used for understanding its NOx formation mechanisms. Results showed that bed particles in the CFB dense phase of DCFB were well-mixed and showed a typical “ring-core” structure in the dilute phase, proving good fluidization quality of bed materials. Meanwhile, circulation ash in BFB with sizes lager than 0.1 mm would pass through the designed overflow port, allowing mass flow from BFB to CFB. Investigation into NOx formation revealed that reactions such as R398, R1-N-1, R569, and R17 associating with O/O2 and volatile N would promote NOx formation in DCFB, whereas reactions mainly R411, R570, R571, R5, and R6 associating with NH2, soot, and char inhibited NOx formation. The overall NOx emission at the furnace outlet of DCFB was calculated to be 97.29 mg/Nm3, which was 56.66% lower than that in traditional CFB with the same configuration. Consequently, the novel DCFB design that separating fuel-N release and char combustion provides an alternative means for manipulating NOx emission during CFB combustion.

The production of synthetic natural gas (SNG) via methanation has been demonstrated by experiments in bench scale bubbling fluidized bed reactors. In the current work, we focus on the scale-up of the methanation reactor, and a circulating fluidized bed (CFB) is designed with variable diameter according to the characteristic of methanation. The critical issue is the removal of reaction heat during the strongly exothermic process of the methanation. As a result, an interconnected bubbling fluidized bed (BFB) is utilized and connected with the reactor in order to cool the particles and to maintain system temperature. A 3D model is built, and the influences of operating temperature on H2, CO conversion and CH4 yield are evaluated by numerical simulations. The instantaneous and time-averaged flow behaviors are obtained and analyzed. It turns out that the products with high concentrations of CH4 are received at the CFB reactor outlet. The temperature of the system is kept under control by using a cooling unit, and the steady state of thermal behavior is achieved under the cooling effect of BFB reactor. The circulating rate of particles and the cooling power of the BFB reactor significantly affect the performance of reactor. This investigation provides insight into the design and operation of a scale-up methanation reactor, and the feasibility of the CFB reactor for the methanation process is confirmed.

In this paper, a dual fluidized bed has been established. The effect of bed material build-up height and gas velocity on the solid circulation rate of CFB (circulating fluidized bed) and BFB (bubble fluidized bed) has been studied. The results show that the solid circulation rate is increased with the increasing of gas velocity Uc and the bed material build-up height. Bed material build-up height of BFB and CFB is changed with the changing of gas velocity Uc. The bed material heights of CFB and BFB have been also investigated in this experiment.

Development of 2nd Generation Oxyfuel CFB Technology – Small Scale Combustion Experiments and Model Development Under High Oxygen Concentrations

Carbon attrition during the circulating fluidized bed combustion of a packaging-derived fuel

Characterization of particulate matter in the hot product gas from atmospheric fluidized bed biomass gasifiers

00/03224 Low temperature CFB gasifier conceptual ideas and applications

A techno-economic feasibility study has been conducted to investigate the revamping of two 32 MWe Pulverised-Coal (PC) boilers with a number of firing options. The options investigated were: (1) conventional PC revamping, (2) replacement with a new PC boiler, (3) PC to Circulating Fluidised Bed (CFB) revamping, (4) replacement with a new CFB boiler, and (5) Bubbling Fluidised Bed (BFB) revamping. The study reveals that: (i) CFB revamping of the boilers is technically feasible and economically viable; (ii) Performance improvement of the plant is significant in terms of such indices as plant load factor, forced outage and auxiliary oil consumption; (iii) Significant improvement in emissions performance due to the reduction in emissions of NOx and fly ash is projected; (iv) CFB revamping option gives the highest return on investment compared to alternatives. Finally, to demonstrate the technical soundness and viability of the special design used in this revamping, a subscale CFB boiler has been designed and built at another power plant.

Analysis of the processes in fluidized bed boiler furnaces during load changes

Bubbling and turbulent fluidization are two typical fluidization regimes in fluidized beds . Under the Eulerian-Lagrangian framework, the heat transfer properties in a bubbling fluidized bed (BFB) and gas-solid behaviors in a three-dimensional (3-D) circulating fluidized bed (CFB) are investigated respectively by using Discrete Element Method-Large-eddy Simulation (DEM-LES ) coupling approach. The gas behavior is resolved at computational grid level and the solid behavior is handled at particle-scale level, moreover, inter-particle and inter-phase heat transfer are involved. Results show that the tube bundles make the solid distribution more uniform. Staggered tube bundle BFB achieves higher heat transfer performance. In the CFB, solid internal circulations are observed in the riser. Moreover, the inventories in six standpipes differ even though the geometry of the apparatus is symmetric. The solid back-mixing occurs mainly in the four corners of the riser. In each external circulating system, pressure drop forming between the inlet of riser and the surface of packed beds in standpipes becomes the driven force for solid circulations in the closed loop. In summary, all these crucial mechanisms shed light on the design, operation and scale-up of fluidized beds in practical engineering fields.

Development of fluidized bed combustion—An overview of trends, performance and cost

Carbon Capture and Storage (CCS) uses a combination of technologies to capture, transport and store carbon dioxide (CO2) emissions from large point sources such as coal or natural gas-fired power plants. Capturing CO2 from ambient air has been considered as a carbon-negative technology to mitigate anthropogenic CO2 emissions in the air. The performance of a mesoporous silica-supported polyethyleneimine (PEI)–silica adsorbent for CO2 capture from ambient air has been evaluated in a laboratory-scale Bubbling Fluidized Bed (BFB) reactor. The air capture tests lasted for between 4 and 14 days using 1kg of the PEI–silica adsorbent in the BFB reactor. Despite the low CO2 concentration in ambient air, nearly 100% CO2 capture efficiency has been achieved with a relatively short gas–solid contact time of 7.5s. The equilibrium CO2 adsorption capacity for air capture was found to be as high as 7.3wt%, which is amongst the highest values reported to date. A conceptual design is completed to evaluate the technological and economic feasibility of using PEI–silica adsorbent to capture CO2 from ambient air at a large scale of capturing 1Mt-CO2 per year. The proposed novel “PEI-CFB air capture system” mainly comprises a Circulating Fluidized Bed (CFB) adsorber and a BFB desorber with a CO2 capture capacity of 40t-CO2/day. Large pressure drop is required to drive the air through the CFB adsorber and also to suspend and circulate the solid adsorbents within the loop, resulting in higher electricity demand than other reported air capture systems. However, the Temperature Swing Adsorption (TSA) technology adopted for the regeneration strategy in the separate BFB desorber has resulted in much smaller thermal energy requirement. The total energy required is 6.6GJ/t-CO2 which is comparable to other reference air capture systems. By projecting a future scenario where decarbonization of large point energy sources has been largely implemented by integration of CCS technologies, the operating cost under this scenario is estimated to be $108/t-CO2 captured and $152/t-CO2 avoided with an avoided fraction of 0.71. Further research on the proposed 40t-CO2/day ‘PEI-CFB Air Capture System’ is still needed which should include the evaluation of the capital costs and the experimental investigation of air capture using a laboratory-scale CFB system with the PEI–silica adsorbent.