Influence Of Ash Deposition Research Articles

Wake galloping energy harvesting in heat exchange systems under the influence of ash deposition

Since the fluid flows in heat exchange systems contain hydrokinetic energies, flow-induced vibration (FIV) energy harvesting technology can be potentially applied to collect electrical energy. Different from the applications in traditional scenarios, cylinder bluff bodies implemented in the heat exchange systems will inevitably suffer from ash deposition. This study proposes a wake galloping energy harvester to be used in heat exchange systems and focuses on investigating the effects of different ash deposition types on the energy harvesting performance. According to different ash deposition types, bell-shaped and horn-shaped cylinder bluff bodies are designed to consider the ash deposition effect. Wind tunnel experiments are conducted to investigate the performance of the wake galloping piezoelectric energy harvester (PEH) with different upstream ash deposit cylinders, at various space distances and under different wind speeds. The experimental results reveal that compared to the horn-shaped cylinder, the bell-shaped cylinder is more beneficial for energy harvesting. Among all tested cases, the optimal configuration is determined: the upstream cylinder is attached by bell-shaped ash deposition; and the space ratio between the upstream and the downstream cylinders is 1.5. The threshold wind speed of the optimal configuration is reduced and the maximum voltage output is improved by over 111%. It is learned that the two types of upstream ash deposit cylinders can both cause the quenching phenomenon to deteriorate the performance of the energy harvester. Guidelines based on the experimental results are provided to avoid the occurrence of the quenching phenomenon. Computational fluid dynamics (CFD) studies are conducted to reveal the underlying mechanisms to explain the experimental results. The CFD results corroborate that different ash deposit cylinders produce different wake vortices and the flow pattern changes with the space distance, which determines the dynamic response of the downstream cylinder.

Heat transfer and pressure drop characteristics of 3-D finned tube heat exchanger in ash-laden flue gas

As an efficient heat transfer enhancement element, 3-D finned tube has good potential in the field of waste heat utilization of industrial flue gas. However, the industrial flue gas often contains a large amount of ash particles. Meanwhile, ash deposition on the surface of heat exchanger can worsen the heat transfer performance and even shorten the service life of the heat exchanger. Therefore, the research of coupling effect of heat transfer and ash deposition on 3-D finned tube heat exchanger is very necessary, and it is bound to affect the further promotion and application of 3-D finned tube heat exchanger. In this paper, the influence of ash deposition on heat transfer process of 3-D finned tube heat exchanger was further studied. The effects of ash deposition time on heat transfer rate and relative pressure drop were discussed firstly. It was found that both ofheat transfer and relative pressure drop basically tended to be stable with the running time up to 6 hours. Then, the influences of fin height of 3-D finned tube, gas velocity and particle concentration on fouling characteristics, heat transfer and flow performance were studied according to the orthogonal array design method. The optimized parameters corresponding to the smallest fouling coefficient and the least relative pressure drop after fouling were determined. Besides, the performance of 3-D finned tube heat exchanger with the optimized parameters was also compared with other tested heat exchangers. The results showed that the heat exchanger with optimized parameters had better heat transfer performance than the other cases under the same condition. At last, a correlation of fouling coefficient of 3-D finned tube heat exchanger under the optimized parameters with ash deposition time was obtained, and it can be useful in the design and evaluation of heat exchanger in dusty environment.

Investigation on the ash deposition of a radiant syngas cooler using critical velocity model

Coal gasification technology is a very important industrial technology, in which the Radiant Syngas Cooler (RSC) plays a pivotal role in the heat storage and heat recovering process. Ash deposit in RSC is a critical factor which may seriously affect the performance of RSC or even result in a shutdown. Therefore, conducting research on the deposit process of RSC is extremely worthwhile. In this study, we create an RSC model with the application of an optimized Critical Velocity Model (CVM) and perform simulations using the CFD method. With the simulating method, we conduct a series of analysis to obtain a more detailed description of the ash distribution and heat transfer in the RSC. Research shows that the CVM proposed in this paper can be precisely applied to the heat transfer process in a RSC, and not only can this method obtain the distribution of ash deposit similar to other methods but also determine the conversion of the ash deposit thickness to heat resistance, which makes the forecast of the overall heat exchange more accurate. According to the study, the ash thickness changes with the vertical height of RSC. For the division wall and panels, the ash thickness increased from the bottom, and then reached a maximum value at about 2/3 of total height. Under the influence of ash deposition, the total heat transfer rate of RSC decreased by 10.4%, and the outlet temperature of syngas increased by 5.7%. This result can provide a reference for the predictive analysis of RSC.

The influence of potassium-rich biomass ashes on steel corrosion above 550 °C

The slagging, fouling and high temperature corrosion are major problems in biomass-firing units and lead to heat transfer limitation, bed agglomeration and metal surface degradation. This paper reports the results of the laboratory-scale corrosion studies of selected steel grades (16Mo3, 10CrMo9–10, X10CrMoVNb9–1, X7CrNiNb18–10) under biomass ash deposits. Five biomass ashes (3 agricultural biomass and 2 energy crops) were used for corrosion tests. Selected samples were doped with 0.1 and 0.5% wt. of KCl to simulate salt condensation process occurring in a real boiler. The corrosion experiments were carried out under oxidizing conditions, at 560 °C and 610 °C for 168 h. To determine the corrosion rate the mass of steel samples were measured after 24, 72 and 168 h. The corrosion products were analysed using SEM-EDS technique. The results showed that oxide scale formation rate determines the overall corrosion mechanism and the influence of ash deposits on steel. For low-chromium steels the oxidation rate is significant and a scale is a protective barrier between the deposit and metal surface limiting further oxidation process. The highest influence of ash on corrosion process was observed for high-chromium steels. However, high-chromium steels show the highest corrosion resistance.

Simulation of DPF with non-uniform grids and investigation of influence of ash deposition

Simulation of DPF with non-uniform grids and investigation of influence of ash deposition

Experimental study on 75 kW th downdraft (biomass) gasifier system

Experimental study on 75 kW th, downdraft (biomass) gasifier system has been carried out to obtain temperature profile, gas composition, calorific value and trends for pressure drop across the porous gasifier bed, cooling–cleaning train and across the system as a whole in both firing as well as non-firing mode. Some issues related to re-fabrication of damaged components/parts have been discussed in order to avoid any kind of leakage. In firing mode, the pressure drop across the porous bed, cooling–cleaning train, bed temperature profile, gas composition and gas calorific value are found to be sensitive to the gas flow rate. The rise in the bed temperature due to chemical reactions strongly influences the pressure drop through the porous gasifier bed. In non-firing mode, the extinguished gasifier bed arrangement (progressively decreasing particle size distribution) gives much higher resistance to flow as compared to a freshly charged gasifier bed (uniformly distributed particle size). The influence of ash deposition in fired-gasifier bed and tar deposition in sand filters is also examined on the pressure drop through them. The experimental data generated in this article may be useful for validation of any simulation codes for gasifiers and the pressure drop characteristics may be useful towards the coupling of a gasifier to the gas engine for motive power generation or decentralized electrification applications.

Influence of ash deposits on the heat resistance of materials for gas turbine engine blades

Influence of ash deposits on the heat resistance of materials for gas turbine engine blades