[en] Highlights: • Ash transformation and slagging of co-firing aquatic biomass with coal were studied. • Pretreatment strategies of water washing and acid washing were applied. • Water washing was more proper for Ulva lactuca to alleviate slagging propensity. • SCK and Factsage estimations are not fully consistent with the analytical results. • There is a synergistic effect on reducing SO₂ emission during co-firing process. In this study, bituminous coal and two aquatic biomasses, Ulva lactuca and Hydrilla verticillate, were selected as the raw materials for studying the ash slagging behavior. Furthermore, Ulva lactuca was pretreated by washing with water and acid; the influence of pretreatment on ash transformation was subsequently studied. Co-firing tests were performed in a drop tube furnace and the SO₂ content in the flue gas was determined using a flue gas analyzer. The chemical compositions and mineral phase properties of the collected ash were studied using several analytical techniques, including ICP, XRF, SEM-EDS, and XRD, as well as thermochemical software Factsage 7.2. The results indicated that the most extreme agglomeration of coal co-fired with Ulva lactuca was due to the increased content of alkali metals, especially K. Pretreatment can effectively reduce the slagging trend of co-fired ash. Acid washing had a higher removal rate of S and alkali and alkaline earth metals but did not show a lower slagging tendency when co-firing with coal. The SO₂ emissions during co-firing were less than the value calculated by linear interpolation but much higher than the SO₂ emissions when coal was burned alone.

[en] Highlights: • Surface tension and contact angle decrease markedly by adding alcohol into water. • Numerous bubbles can be seen by adding alcohol even at a low surface temperature. • The heat transfer enhancement degree is most evident at a certain alcohol content. • The best volume fractions of ethanol, n-propanol and isopropanol are 4%, 4% and 2%. • The correlation of Nusselt number with an error of 15% is presented. -- Abstract: In the present study, the spray-wall impingement characteristics and heat transfer performance during spray cooling were experimentally investigated to ascertain the effect of different low-alcohol additives in water. The surface tension and contact angle on the heating surface were measured and the images of spray wall interaction were taken. The spray cooling performance of alcohol-water mixtures were compared with pure water. The results indicated that adding a small amount of alcohol to water can significantly decrease the surface tension and contact angle. It is also an effective way to enhance the heat dissipation and to control the surface temperature simultaneously. As the alcohol content increases, the intensity of heat transfer capacity enhancement increases first and then weakens slightly. The optimal concentrations of ethanol, n-propanol and iso-propanol corresponding to the best heat transfer performance are respectively 4 vol%, 4 vol% and 2 vol%, and the maximum heat transfer coefficient is achieved with 4 vol% ethanol-water mixture. The correlation of Nusselt number, which is associated with the physical properties, the Weber, Prandtl, Jacob as well as Reynolds numbers, is also presented with an error of 15%.

[en] Ash related problems such as fouling and slagging are crucial for operation of the heat recovery steam generator (HRSG) of the wastewater incinerator. In this paper, numerical studies of the characteristics of ash particle deposition and distribution under different operating conditions in the HRSG of a wastewater incinerator have been performed using numerical deposition model coupled with gas–solid two phase turbulent flow model. Based on ash melting thermo-analysis and critical moment theory, a numerical deposition model was adopted to predict ash particle sticking and rebounding in the thermal boundary layer, as well as shedding of deposited particles from tube surfaces, using the commercial computational fluid dynamic code FLUENT 6.3.26. Field measurements from an industrial-scale HRSG of the wastewater incinerator in Acrylic Fiber Plant, Sinopec Qilu Petrochemical Corporation Group, China, have been used to validate the model. The predicted results under different operating conditions are in good agreement with the measured data. The results show that ash deposition and distribution have significant particle size and temperature dependence. Strong deposition propensity of large particles on the windward side of tube surfaces should be responsible for the formation of serious fouling deposits near the entrance of the furnace. High temperature will accelerate ash particle deposition in the furnace. - Highlights: ► Deposition of ash particles originated from wastewater incineration is predicted. ► Both melting curve model and critical moment theory are used to predict deposition. ► Reasonably good agreement was obtained by field observations and measurements. ► Ash particle sizes play important role in ash deposition and distribution. ► The calculated results show that the deposition rate is the temperature dependence.

[en] Highlights: • An enhanced conceptual design for CACRS-ORC integrated system is developed. • An optimization-based method is proposed to achieve the optimal design. • The configuration and operating parameters are optimized simultaneously. • Multi-objective optimization and sensitive analysis have been carried out. Waste heat recovery techniques can greatly improve the energy efficiency and relieve the energy crisis. The integration of compression-absorption cascade refrigeration system (CACRS) and Organic Rankine Cycle (ORC) can achieve cooling and power cogeneration utilizing waste heat. However, the simultaneous optimization of integrating configuration and operating parameters has not been considered in recent studies, neglecting the complex interactive relationship within the integrated system consequently. To overcome these limitations, an enhanced CACRS-ORC integrated system, containing more coupling possibilities and more routes in driving the integrated system with waste heat, is proposed and investigated in this paper. To examine the trade-off in the economic and thermodynamic performances, a multi-objective optimization-based method, aiming at the simultaneous minimization of the total annualized cost (TAC) and the total exergy destroy (${\mathit{Ex}}_{\mathit{destroy}}^{\mathit{total}}$), is developed to determine the optimal configuration and operating parameters of the integrated system. The derived Pareto solutions reveal the contradictory relationship between the two objectives, and the thermo-economic analysis is executed to show the impact of system configuration and operating parameters on economy and thermodynamics. Sensitive analysis is also performed to reveal the effects of key parameters on the structural configuration and thermo-economic performances.

[en] Highlights: • Wastewater was mixed with lignite and the co-combustion behaviors were studied. • Effects of blending ratio and heating rate on the combustion process were evaluated. • The interactions between RS and HL were inhibitive effects during main combustion. • Surface morphology and minerals of residues were separately detected by SEM and XRD. • The activation energies were calculated by using the KAS and FWO method. - Abstract: Co-combustion characteristics of refining and chemicals wastewater solid (RS) and Huolinhe lignite (HL) were studied through thermogravimetric analysis (TGA). The combustion behaviors of the blends at various RS to HL ratios were compared with those of the individual samples. Co-combustion experiments showed that the combustion performance of the blends would be improved with the percentage of RS rising. The interactions between RS and HL during the co-combustion could be divided into four phases, and there were no interactions below 120 °C (PH 1) and beyond 700 °C (PH 4), inhibitive effects at the temperature range of 120–700 °C (PH 2 and PH 3). The results of SEM and XRD indicated that the sintering and fusion degree of residues after combustion became more severe with the percentage of RS increasing. The iso-conversional methods, Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO), were used for the kinetic analysis of the combustion process. The results showed that the activation energy of RS was higher than that of HL, and the minimum value was obtained at 75HL/25RS