For predicting and relieving ash-related problems and harmful gas emissions during fluidized bed combustion, release of K and Cl and emissions of NOx and SO2 during reed black liquor (BL) combustion in a fluidized bed were investigated in this study. The effects of bed material (calcium-based zeolite and limestone) and bed temperatures (700–900 °C) were also studied. The results showed that higher temperature favored the K release for both calcium-based zeolite and limestone, and calcium-based zeolite caused lower K release due to the formation of K3Al(SO4)3, KAl(SO4)2, and K2O-Al2O3-SiO2 eutectic compounds. Cl was mainly released in the form of HCl above 700 °C. Moreover, high temperature facilitated Cl release for calcium-based zeolite, whereas it had a complicated effect on Cl release for limestone. Although higher temperature increased the NOx emission for both calcium-based zeolite and limestone, limestone resulted in higher NOx emission due to the conversion of fuel N to NOx under CaO catalysis. Temperature had a slight effect on SO2 emission for calcium-based zeolite, whereas it decreased the SO2 emission for limestone. Reed BL combustion generated lower SO2 emissions with the help of Na2CO3 and K2CO3, and limestone resulted in much lower SO2 emission with the help of CaCO3 and CaO.

For a reliable and efficient process for the recovery of energy and alkali of reed black liquor (BL), the experiments of reed BL combustion in a fluidized bed with limestone as bed material for direct causticization were conducted at temperatures from 700 to 900 °C. The products in the direct causticizing process were identified by XRD, and the recovery rate of alkali was measured. In addition, the mechanism of inhibiting bed material agglomeration was studied. The results show that a direct causticizing system successfully recovers NaOH when using limestone as bed material, and the recovery rate of NaOH is more than 87.4%. Na2O·2SiO2 produced in the combustion process is the main binder of agglomeration. The limestone has a strong effect on inhibiting bed agglomeration, as the decomposition of limestone can provide CaO for the reaction with silica forming high-melting Ca2SiO4 and 3CaO·Al2O3·3SiO2 instead of low-melting Na2O·2SiO2.

•Pyrolysis of dry reed black liquor particles in fluidized were been investigated in N2 atmosphere.•Effect of bed temperature on gas product characteristics was studied.•Special burr structure on the surface of RBLP char at low temperatures was detected.To improve the knowledge about pyrolysis behavior of reed black liquor (RBL), reed black liquor particles (RBLP) pyrolysis experiments were performed in nitrogen atmosphere at 530, 580, 630, 680, 730 and 780 °C in fluidized bed at atmospheric pressure. The effects of bed temperature on yields of pyrolysis product, gaseous product characteristics, carbon and hydrogen conversions, NOx and SO2 emissions, and the micro-morphology of RBLP char were investigated. The results showed that the main components of the gaseous products were CO, CH4, CO2 and H2. The contents (% by volume) of H2 and CO were increased with the increase of bed temperature, but CH4 and CO2 had an opposite trend. In addition, the combustible gases concentration increased with temperature increasing, which was from an initial 64.03% (at 530 °C) increase to 77.36% (at 780 °C). At last, the great impact of pyrolysis temperatures on micro-morphology of RBLP char had been found.

Experiments were carried out to investigate the agglomeration mechanism of neutral sulfite semi-chemical (NSSC) black liquor combusted in a bench-scale fluidized bed. The combustion experiments were focused on the influence of different operating conditions at temperatures ranging from 600 to 800 °C and at additive dosages from 0 to 30% with different additives (kaolin, calcium carbonate, and alumina). Defluidization resulting from agglomeration occurred frequently in the experiments. Samples of the bed material collected after the experiments were characterized by scanning electron microscopy, energy dispersive X-ray detection and X-ray diffractometry. There were explainable differences in the experimental phenomena and surface characteristics of the sinters depending on different operating conditions in this study, which can also be found in other studies. The mechanism has also explained that the additive is effective in solving the agglomeration problem. The experimental results indicate that the formation of the agglomeration in the fluidized bed burning NSSC black liquor depends mainly on the temperature, additive dosage, and additive species.

•This paper with the purpose of researching the control of heavy metal toxicity of MSWI fly ash with cement solidification.•Water washing pre-treatment as a method of removal of Cl− and SO3 from fly ash before being cement solidified.•PH value and leaching time as two variable conditions for study the effect of leaching toxicity.•Strength of cement added in MSWI fly ash as an evaluation term of recovery and utilization of compounds.Cement solidification technology can effectively reduce environmental pollution caused by municipal solid waste incineration (MSWI) fly ash. The present study aimed at investigating the impacts of three factors on the heavy metal leaching content, and the curing time on the strength of mortar specimens blended with MSWI fly ash. The factors are the quantity of cement, the PH value of leaching liquid and the vibrating leaching time. And the fly ash used in experiments is sampled from Harbin MSWI power plant. The results demonstrated that the leaching concentration of heavy metal of MSWI fly ash reduced significantly after being blended with cement, especially for Pb and Cd. As the PH value of the leaching liquid increased, the heavy metal leaching concentration quickly cut down to a very low value. The heavy metal leaching concentration significantly increased with leaching vibrating time in range of 16 h or 32 h. But conversely, both flexural strength and compressive strength of mortar specimens obviously dropped and the curing time of mortar specimens was delayed due to the addition of MSWI fly ash. Fortunately, the strength of mortar exceeds strength requirement of non-main building and base structure concrete and it can be recycled as base structure material.Download high-res image (175KB)Download full-size image