Boshu He

Temperature impact on SO2 removal efficiency by ammonia gas scrubbing

Abstract Emissions reduction in industrial processes, i.e. clean production, is an essential requirement for sustainable development. Fossil fuel combustion is the main emission source for gas pollutants, such as NO X , SO 2 and CO 2 , and coal is now a primary energy source used worldwide with coal combustion being the greatest atmospheric pollution source in China. This paper analyzes flue gas cleaning by ammonia scrubbing (FGCAS) for power plants to remove gaseous pollutants, such as NO X , SO 2 and CO 2 , and presents the conceptual zero emission design for power plants. The byproducts from the FGCAS process can be used in agriculture or for gas recovery. Experimental results presented for SO 2 removal from the simulated flue gas in a continuous flow experiment, which was similar to an actual flue gas system, showed that the effectiveness of the ammonia injection or scrubbing depends on the temperature. The FGCAS process can effectively remove SO 2 , but the process temperature should be below 60 °C or above 80 °C for SO 2 reduction by NH 3 scrubbing.

Thermodynamic analyses of a biomass-coal co-gasification power generation system.

A novel chemical looping power generation system is presented based on the biomass-coal co-gasification with steam. The effects of different key operation parameters including biomass mass fraction (Rb), steam to carbon mole ratio (Rsc), gasification temperature (Tg) and iron to fuel mole ratio (Rif) on the system performances like energy efficiency (ηe), total energy efficiency (ηte), exergy efficiency (ηex), total exergy efficiency (ηtex) and carbon capture rate (ηcc) are analyzed. A benchmark condition is set, under which ηte, ηtex and ηcc are found to be 39.9%, 37.6% and 96.0%, respectively. Furthermore, detailed energy Sankey diagram and exergy Grassmann diagram are drawn for the entire system operating under the benchmark condition. The energy and exergy efficiencies of the units composing the system are also predicted.

On a clean power generation system with the co-gasification of biomass and coal in a quadruple fluidized bed gasifier

A clean power generation system was built based on the steam co-gasification of biomass and coal in a quadruple fluidized bed gasifier. The chemical looping with oxygen uncoupling technology was used to supply oxygen for the calciner. The solid oxide fuel cell and the steam turbine were combined to generate power. The calcium looping and mineral carbonation were used for CO2 capture and sequestration. The aim of this work was to study the characteristics of this system. The effects of key operation parameters on the system total energy efficiency (ŋten), total exergy efficiency (ŋtex) and carbon sequestration rate (Rcs) were detected. The energy and exergy balance calculations were implemented and the corresponding Sankey and Grassmann diagrams were drawn. It was found that the maximum energy and exergy losses occurred in the steam turbine. The system ŋten and ŋtex could be ∼50% and ∼47%, and Rcs could be over unit.

Simulation of biomass-steam gasification in fluidized bed reactors: Model setup, comparisons and preliminary predictions.

A user-defined solver integrating the solid-gas surface reactions and the multi-phase particle-in-cell (MP-PIC) approach is built based on the OpenFOAM software. The solver is tested against experiments. Then, biomass-steam gasification in a dual fluidized bed (DFB) gasifier is preliminarily predicted. It is found that the predictions agree well with the experimental results. The bed material circulation loop in the DFB can form automatically and the bed height is about 1m. The voidage gradually increases along the height of the bed zone in the bubbling fluidized bed (BFB) of the DFB. The U-bend and cyclone can separate the syngas in the BFB and the flue gas in the circulating fluidized bed. The concentration of the gasification products is relatively higher in the conical transition section, and the dry and nitrogen-free syngas at the BFB outlet is predicted to be composed of 55% H2, 20% CO, 20% CO2 and 5% CH4.

Carbon Dioxide Recovery from Flue Gases By Ammonia Scrubbing

Publisher Summary This chapter describes the significant researches on a novel CO2 removal approach—ammonia scrubbing. The preliminary experimental results are very promising. Under optimum conditions, the removal efficiencies are stable in the range from 95% to 99%, after one minute or so. This indicates a high potential for scrubbing with a fast absorption rate while using ammonia. The crystalline solids in the solution were analyzed by X-ray diffraction. It was proved that ammonium bicarbonate was the main product of the CO2–NH3 reaction in this study. Interest in CO2 removal has increased rapidly, mainly because of the growing awareness of the risks of a climate change due to greenhouse gas emissions, because CO2 is the largest component of greenhouse gases being emitted to air. The importance of carbon sequestration is now gradually being addressed by world nations. There are various technologies used to separate CO2 from flue gas streams—for example, chemical absorption, physical absorption, cryogenic methods, membrane separation, and biological fixation. Chemical absorption is generally recognized as the most effective technology among all the technologies at present. Although the MEA process is a promising system for the recovery of CO2 from flue gases, it has some shortcomings, including slow absorption rate and small solvent capacity. A novel approach that may provide another route of reducing CO2 emissions from power plants is separation by ammonia scrubbing.

Characterization of a dual fluidized bed gasifier with blended biomass/coal as feedstock

A one-dimensional model is built based on the commercial Aspen Plus software to kinetically simulate the biomass/coal co-gasification process in a dual fluidized bed gasifier. The synergistic effect on the co-gasification kinetics is allowed for, and is coupled with the gas-solid flow hydrodynamics. With the developed model, the effects of different key operating parameters including the biomass blending ratio (Rb), the initial bed temperature (Tg), the feedstock mass flow rate (Ffs), the bed material flux (Fbm) and the steam to carbon ratio (Rsc) on the resultant syngas composition and the supplemental fuel mass flow rate (Fsf) are investigated, and the operation parameters are optimized. It is found that increasing Rb and Tg can enhance the gasification, while increasing Ffs and Rsc restricts the gasification. Increasing Fbm has slight effect on the gasification results but can reduce Fsf. The cold gas efficiency is up to 78.9% under the proposed optimum condition.

Investigation on biomass steam gasification in a dual fluidized bed reactor with the granular kinetic theory

The dual fluidized bed (DFB) reactor is promising to convert biomass into high-quality syngas efficiently. In this work, a three-dimensional model is built based on the granular kinetic theory to predict the biomass steam gasification in dual fluidized bed reactors. The model is firstly validated against a series of experimental results. Then, the effects of some essential operation parameters including the biomass flow rate (Fb), the steam to fuel ratio (Rsf) and the gasification temperature (Tg) on the biomass steam gasification properties in a DFB reactor are comprehensively analyzed with the orthogonal method. In the concerned ranges of the operation parameters, the cold gas efficiency is found to be the most sensitive to Fb and least sensitive to Tg. The optimal cold gas efficiency of the DFB gasifier is 82.9% when Fb, Rsf and Tg are 15 kg/h, 1.5 and 900 °C, respectively, and the H2 mole fraction is 46.62%.