Water Wall Research Articles

Heat Transfer Analysis Using Thermofluid Network Models for Industrial Biomass and Utility Scale Coal-Fired Boilers

Integrated whole-boiler process models are useful in the design of biomass and coal-fired boilers, and they can also be used to analyse different scenarios such as low load operation and alternate fuel firing. Whereas CFD models are typically applied to analyse the detail heat transfer phenomena in furnaces, analysis of the integrated whole-boiler performance requires one-dimensional thermofluid network models. These incorporate zero-dimensional furnace models combined with the solution of the fundamental mass, energy, and momentum balance equations for the different heat exchangers and fluid streams. This approach is not new, and there is a large amount of information available in textbooks and technical papers. However, the information is fragmented and incomplete and therefore difficult to follow and apply. The aim of this review paper is therefore to: (i) provide a review of recent literature to show how the different approaches to boiler modelling have been applied; (ii) to provide a review and clear description of the thermofluid network modelling methodology, including the simplifying assumptions and its implications; and (iii) to demonstrate the methodology by applying it to two case study boilers with different geometries, firing systems and fuels at various loads, and comparing the results to site measurements, which highlight important aspects of the methodology. The model results compare well with values obtained from site measurements and detail CFD models for full load and part load operation. The results show the importance of utilising the high particle load model for the effective emissivity and absorptivity of the flue gas and particle suspension rather than the standard model, especially in the case of a high ash fuel. It also shows that the projected method provides better results than the direct method for the furnace water wall heat transfer.

Design and analysis of fixture for easy lug plate fit up at bend portion of first pass and second pass gang bend water wall panels phase I

With the technological evolution of “high-pressure steam generators” from sub-critical to the super-critical stage, the “Water-wall Panels” is transformed from “straight panels” to “terminal bend panels” and “gang bend panels”. The lug plates are fitted at the bend portion of the terminal and gang bend panels as per the design. The traditional method of lug plate fit up has an awkward impact on the working method, productivity, quality, and re-work. This paper aims to discuss the design and analysis of the fixture to avoid the manual lug plate fit up. With the proposed design of the fixture, the lug plate fit up can be done easily at the bend portion of tubes of gang bend and terminal bend “Water-wall Panels”. Proposed design not only solves the problems being faced while giving the easy fit up but also brings in marked improvements in workplace-safety, productivity, working environment coupled with a considerable reduction in manpower and operational risks.

Simulation analysis of instantaneous impact on the radiant syngas cooler by rapping vibrators

AbstractSlag or ash removal from water wall tubes in a radiant syngas cooler (RSC) is a routine task in operation, which can effectively increase the overall thermal efficiency. Rapping ash removal is one of the valid methods for shedding off the ash deposits in the high‐pressure surroundings of the RSC. In this study, the model of a real RSC was established by a numerical simulation based on the finite element software ABAQUS, and modal analysis and instantaneous response analysis (IRA) were researched to reveal the natural vibration characteristics of the RSC and aid the design of rapping ash removal. On the basis of the results of natural vibration characteristics and a subsequent harmony response, 16 Hz was set as the impact frequency, balancing off the vibrator number and the water‐tube displacement effect. It was indicated that ash deposit in the area around 1/2 longitudinal position was easy to remove due to great response to rapping action. Moreover, rapping at ½ position generally obtained greater displacement response in the whole RSC. A rapping design was proposed with six vibrators at the ½ longitudinal position and 16 Hz frequency, and then two rapping intervals were investigated comparatively. The case with a half‐cycle interval had a slightly larger response than the one‐cycle case, with a larger displacement in more circumferential tubes as well as with a greater sound pressure response in the RSC.

Effect of an algae integrated water wall on energy consumption and CO<SUB align="right">2 emission

This study develops a transient thermal model for an indoor in which a photobioreactor (PBR) is integrated into one of its facades. Thermal comfort, energy consumption, and carbon dioxide (CO2) emissions were interpreted in different design scenarios for Izmir, Turkey. As a result, it was determined that a 20% window-to-wall ratio (WWR) provides the most comfortable results, and the algae usage increases the annual comfort by 19% and reduces the heating/cooling demand. Compared to a water wall, it provides a 17% reduction in energy consumption and CO2 emissions.

Different modes of bubble migration near a vertical wall in pure water

Different modes of bubble migration near a vertical wall in pure water

Adhesion dynamics of functionalized nanocarriers to endothelial cells: a dissipative particle dynamics study.

Targeted drug delivery to endothelial cells utilizing functionalized nanocarriers (NCs) is an essential procedure in therapeutic and diagnosis therapies. Using dissipative particle dynamics simulation, NCs have been designed and combined with an endothelial environment, such as the endothelial glycocalyx (EG) layer, receptors, water, and cell wall. Furthermore, the energy landscapes of the functionalized NC with the endothelial cell have been analyzed as a function of properties such as the shape, size, initial orientation, and ligand density of NCs. Our results show that an appropriate higher ligand density for each particular NC provides more driving forces than barriers for the penetration of the NCs. Herein we report the importance of shell entropy loss for the NC shape effect on the adhesion and penetration into the EG layer. Moreover, the rotation of the disc shape NC as a wheel during the penetration is an extra driving force for its further inclusion. By increasing the NCs' size larger than the appropriate size for each particular ligand density, due to an increase in the NCs' shell entropy loss, the barriers surpass the driving forces for NC penetration. Furthermore, the parallel orientation provides the NCs with the best penetration capabilities. However, the rotation of the disc shape NCs enhances their diffusion in the perpendicular orientation too. Overall, our findings highlight the crucial role of the shell entropy loss in governing the penetration of NCs. Besides, studying NCs with a homogeneous ligand composition enabled us to cross barriers and probe energetics after the complete inclusion of the NCs.

Failure Analysis of a Deep Pit on the Inner Wall of Water Wall Tube in a Power Plant

A deep pit on the inner wall of a water wall tube of a 600MW boiler was found at the extension end of the front of the furnace during an overhaul after 200 thousand hours of operation. To investigate the causes of the failure, various techniques including macroscopic inspection, chemical composition analysis, microstructural analysis, mechanical performance testing, scanning electron microscope (SEM) observation and energy dispersive spectroscopy (EDS) analysis were carried out. The results of investigations showed that the chemical composition of the as-received tube conformed with SA-178 Grade C and the mechanical properties were qualified. EDS analysis revealed that the main elements of the deposit on the surface of the pit were iron and oxygen, along with phosphorus, potassium and aluminium, which were identified with the constitutes of the under deposit corrosion products. Based on the results, the cause of the failure is under deposit corrosion. Possible measures to combat the corrosion were proposed.

Effect of an algae integrated water wall on energy consumption and CO<SUB align="right">2 emission

Effect of an algae integrated water wall on energy consumption and CO<SUB align="right">2 emission

Model tests of geosynthetic-reinforced soil walls with marginal backfill subjected to rainfall

A series of model tests were conducted to investigate the performance of geosynthetic-reinforced soil (GRS) walls with marginal backfill subjected to rainfall infiltration. The effectiveness of improvement measures—such as decreasing reinforcement spacing and increasing sand cushion thickness—to prevent the GRS wall failure due to heavy rainfall was evaluated. The distribution and variation of the volumetric water content, porewater pressure, wall deformation, and reinforcement tensile strain were monitored during the test. The advancement of the wetting front and the drainage function of sand cushions were visually observed using the fluorescent dyeing technique. For the baseline case, the wall began to deform as rainfall proceeded, causing the potential failure surface to gradually move backward. When the potential failure surface moved beyond the reinforced zone, the pullout of the topmost reinforcement layers occurred, resulting in the collapse of the GRS wall in a compound failure mode. Decreases in reinforcement spacing and increases in sand cushion thickness effectively reduced wall deformation and enhanced wall stability. The placing of sand cushions between the reinforcement layers can also delay water infiltration and reduce the accumulation of porewater pressure inside the wall. Suggestions for designing rain-resistant GRS walls are also proposed based on the findings.

Cause analysis of corrosion and burst of water wall of utility boiler

During the operation of a boiler in a power plant, the water wall tube burst and leaked. In order to find out the reason of tube rupture, a comprehensive experimental study was made on the sample with macro morphology, chemical composition, metallography, SEM and EDS. The results show that due to the high sulfur content in the combustion medium of the boiler, a large amount of sulfate containing sulfur elements will deposit on the outer wall of the water wall tube during the long-term operation. In the high temperature environment of the boiler, the thermal corrosion of sulfate deposit, that is, high temperature sulphur corrosion, is formed on the side of the water wall wall steel tube, which leads to the continuous thinning of the wall thickness. And finally, explosion leakage occurs under the action of the internal high-temperature and high-pressure medium.

Condition Assessment of Boiler Water Wall Tubes using Robotics

Boiler tube failures continues to be the primary cause for forced outages in boilers. To get the boiler back on line and reduce (eliminate) future forced outages due to tube failure, it is extremely important to determine and correct the failure root cause. Detecting and sizing flaws before they cause failures is of critical importance in boiler maintenance. Localized and general wall thinning due to corrosion & erosion in boiler water-wall tubing is a significant inspection concern for boiler operators. There are at least four (4) other methods used for the inspection of Boiler Water walls. These methods are Spot Check UT, A-Scan UT, EMAT, and Scanning Thermograpy. Spot Check UT only gives thickness readings and gets very minimal coverage of the total surface area of the furnace water walls; the chances of finding I.D. flaw mechanisms using Spot Check UT are minimal at best. If Boiler Water walls have been sandblasted, A-Scan UT may be used to inspected larger areas of the furnace walls; in these cases, a steady flow of water is most often used as the couplant. The EMAT technique requires that any Boiler Water wall surfaces be sandblasted. This paper will present a discussion on the deployment of robotic wall crawler using electromagnetic technique to inspect boiler water walls from outside of the tube together with the theoretical background of the technique which explains the quantitative nature of the inspection. Further, case studies will be presented for the technique that allows the extraction of tube wall thickness information from the inspection data.

Failure analysis of the water-wall tube in once through Benson boiler

Failure analysis of a water wall tube of a once-through Benson boiler after 100,000 h of use of service is presented. A 15Mo3 material was used in the manufacture of the tube. In order to identify the root cause of the rupture, visual inspection, optical emission spectroscopy, microscopic examinations, mechanical strength measurements, and tube wall thickness measurements at various locations were performed on the failed tubes. Visual inspection revealed a fish mouth puncture opening with thin lips. As a result of optical spectroscopy, mechanical testing, and hardness measurements, the material was found to meet the requirements. Based on microstructure analysis, it appears that the pearlite spheroidized near the rupture site as a result of localized high temperatures. The failure mechanism of the tube was identified as a localized short-term overheating caused by high heat flux based on the results of all the tests and analyses conducted in this study.

Protective water curtains as wave attenuators for blast-resistant tunnels

Tunnels, as highly cost-demanding infrastructures which facilitate the transportation of people and goods, have been a target of terrorist attacks within the past few decades. The significance of the destructive impact of explosives on these structures has resulted in research on the development of blast-resistant design approaches. In this paper, water curtains are proposed as a blast-resistant system due to the established performance of water against explosives in free fields in previous studies as well as its capability to mitigate the potential incoming fire after an explosion. A parametric study was conducted for this purpose, considering the effects of curtain thickness, the distance of the curtain from the tunnel opening, and the amount of TNT charge. Accordingly, fifty-two finite element (FE) models were created in the FE package ABAQUS to investigate the performance of a water wall in a typical tunnel through the Eulerian approach to simulation. The water curtains had four different thicknesses and were located at three different distances from the reference point. TNT explosive charges were placed at the tunnel opening with four different masses. The thicker walls nearer to the tunnel opening were found to be more effective. However, the peak pressure reduction in all charges was in a desirable range of 53 to 80%. The parametric study also illustrated that the peak pressures were more sensitive to wall thickness rather than TNT charges mass and the wall distance from the explosives. We anticipate this preliminary study to be a starting point for the further development of the concept of water curtains for blast mitigation.

Effect of metal anti-wear device on the water wall erosion in CFB boiler

The erosion of water wall tube induced by the flushing of ash is one of the safest factors in the operation of the circulating fluidized bed (CFB) boiler. The reasonable installation of a metal anti-wear device on the water wall provides an effective protection method for reducing particle erosion on the wall surface. Seven metal anti-wear devices were designed and evaluated by comparing the erosion distribution of the local water wall surface in this work. The results show the type with an angle between the windward side and the water wall greater than 90° and the leeward side perpendicular to the water wall can obtain a good anti-wear effect. The erosion rate of water wall increases correspondingly with the increasing inlet velocity and particle size, but decreases to some extent by adding cohesive particles. The height of the ash deposition zone decreases correspondingly with the decreasing particle diameter and proportion of cohesive particles. The type G metal anti-wear device was preferably applied and tested in a CFD boiler for half a year according to its simple structure and its behavior of reducing erosion rates. The Type G anti-wear device can well protect the water wall of CFB boilers at the power plants.

Effect of hydrophobic groups on adsorption of arginine-based amino acids to solid surfaces in water

We calculate the free energies of adsorption between a solid wall and various arginine derivatives in water using molecular dynamics simulations. We vary the hydrophobic group size of the amino acids in two ways and the hydrophilicity of the solid wall in five ways. The free energy of adsorption decreases by increasing the hydrophilicity of the solid wall, regardless of the size of the hydrophobic group. Amino acids with small hydrophobic groups are adsorbed on the solid wall with the strongest hydrophilicity, but the free energy of the amino acids with large hydrophobic groups is relatively small. The free energy of adsorption in benzene solvent is increased by increasing the hydrophilicity of the solid wall; however, analogous to results in water solvent, it is independent of the size of the hydrophobic group. We attribute these differences in free energy to the effect of solvent molecules localized on the solid wall. Thus, these results may modulate peptide adsorption on a solid surface by the size of the peptide’s hydrophobic groups.

Fouling and Slagging Investigation on Ash Derived from Sasol Coal Using ICP and XRF Analytical Techniques

During coal combustion in boilers, light fly ash particles are carried away along with the hot flue gases and the heavier bottom ash particles fall to the bottom of the boiler. The fly ash particles stick on the convective heat transfer surfaces and the furnace wall, causing fouling and slagging deposition problems during the boiler operation. The fouling and slagging effect reduces the boiler’s operational efficiency. This study was motivated by the decline in the operational efficiency of the installed boilers at Sasol synfuel operations in Secunda, Mpumalanga province in the Republic of South Africa. It was assumed that the drop in the boiler efficiency was caused by the coal ash deposition during the boiler operations. The rate of ash deposition and accumulation in the convective heat transfer tubes and furnace water walls during the boiler operation depends on the chemical composition of the coal ash produced during combustion. Coal fly and bottom ash samples were collected from the operational site for laboratory analysis to determine their chemical composition using induced coupled plasma optical emission spectroscopy, induced coupled plasma mass spectroscopy (ICP-OES, ICP-MS) and X-ray fluorescence (XRF) analytical methods. The major, minor and trace elements by mass (%) in the ash samples were obtained from the ICP-OES and ICP-MS, whereas the elemental composition in an oxidised atmosphere was obtained from the XRF analysis. The amount of unburnt coal particles within the ash samples was determined from the loss on ignition (LOI) test. The fouling and slagging prediction during Sasol boiler operation was evaluated using previously developed fouling and slagging indices as a guide using the analysed ash chemical composition results obtained in this study. It was concluded from the analysed results using the guided evaluated indices from the analysed coal ash chemistry that during the operations of Sasol boiler(s) there is a low to medium fouling prediction occurrence on the convective heat transfer tubes and a low slagging in the boiler furnace walls.

Study of an air bubble curtain along a wall in water and radiated noise mitigation

The injection of air bubbles into the liquid phase of a freestream flow has several impacts on the flow structure, which depends on the volume and size of the bubbles. This work experimentally investigates the characteristics of air bubble injection into freestream flow using three different injector models. The effects of the bubble curtain on the sound wave attention are studied. A wide range of air injection rates from 2 to 50 standard liters per minute is injected into the freestream water at Froude numbers (Fr) of 50.5, 70.7, and 90.9. The injector model is placed on the sidewall, which is where the bubble curtain is generated. High-speed cameras and an image processing technique are used to visualize and quantify the projected void fraction (PVF) of air bubbles. The sound measurement system consists of two hydrophones. The first hydrophone projects sound waves at discrete frequencies ranging from 17 to 50 kHz, and the second receives the transmitted sound waves. The bubble PVF is observed to increase with the air injection rate as the Froude number increases. There is no significant increment in the thickness of the bubbly curtain when the air injection rate or Froude number increases. The different air injector models produce various air bubble flow patterns, and model II provides the highest PVF. The bubble curtain greatly suppresses sound waves at all frequency ranges. However, the sound attenuation rate varies along the frequency range. The insertion loss increases depending on the PVF of the bubbles, freestream velocity, and frequency range. At a high Froude number of 90.9, the increased air injection rate does not affect the insertion loss. Model II has a relatively higher insertion loss rate at frequencies >26 kHz.

Safety Analysis on the Heating Surfaces in the 660 MW Ultra-Supercritical CFB Boiler under Sudden Electricity Failure

Ultra-supercritical circulating fluidized bed (CFB) boilers are taking up an increasing proportion of the CFB boiler fleet in China, making the safety concern about the heating surfaces in this type of boilers under sudden electricity failure draw more and more attention from the industry. For the time being, however, few studies have made efforts to resolve this concern. Given this, the physical process in a 660 MW ultra-supercritical boiler during the electricity failure accident was precited with a comprehensive model composed of mass and energy conservation equations in this work. The tube temperature of the boiler components with the highest safety risk, i.e., the water wall and a superheater, was obtained to evaluate the safety of the heating surfaces. The results revealed that the tube temperature (about 516 °C and 544 °C) would be obviously lower than the maximum permissible temperature of the tube material (600 °C and 630 °C) even when electricity could be restored at the power plant, indicating that the heating surfaces in the 660 MW ultra-supercritical CFB boilers would generally be recognized to be safe under sudden electricity failure.

Numerical analysis on the flow instability of a 700 °C ultra-supercritical tower boiler

The boiler equipment should be able to adapt to the load requirements and overcome the interference of various external conditions. By establishing a one-dimensional single-channel general numerical calculation model suitable for flow instability analysis of ultra-supercritical boilers at 700 °C, the rules of flow in the tubes are calculated. The 7th loop and the 22nd loop of the boiler water wall are selected as typical loops, and the dynamic characteristics of the two loops are calculated. The results show that after applying different multiples of heat flux disturbance, regardless of whether metal heat storage is considered, the inlet and outlet mass flow rates of the two circuits show inverse dynamic responses and eventually return to a steady state. When considering heat storage, it takes about 63 s for the 7th loop to return to stability. The recovery and stabilization time of the 22nd loop is about 60 s. Metal thermal storage has a positive effect on the settling time of the pipe section after heat flux disturbance. And when the maximum heat flux disturbance is applied, the maximum wall temperatures of the two loops are 443.9 °C and 446.5 °C, and the boiler can operate safely and stably.

Discussion on the Feasibility of Deep Peak Regulation for Ultra-Supercritical Circulating Fluidized Bed Boiler

In order to meet the flexibility operation needs of coal-fired units under the goal of carbon peak and carbon neutralization, it is imperative for circulating fluidized bed (CFB) units to participate in deep peak regulation. By systematically summarizing deep peak regulation operation practice of existing SC and subcritical-parameter-levels CFB units, the feasibility of deep peak regulation technology of an ultra-supercritical (USC) CFB unit under development and being built is analyzed and demonstrated; meanwhile, the deep peak regulation capacity of the boiler is also predicted. The results show that by analyzing the structural characteristics and design performance of the USC-CFB boiler, for technical problems such as stable combustion under low load, hydrodynamic safety, denitration performance under wide load, and rapid boiler load change rate existing in deep peak regulation, technical measures were implemented by selecting advanced boiler furnace type, adopting good design technology of the secondary rising water wall and uniformity design of bed temperature and bed pressure, strengthening the reducing atmosphere inside the furnace, improving the performance of wear-resistant refractory materials, quickly controlling the furnace bed material stock under variable load, optimizing the control strategy of CFB unit, and so on. The boiler achieved good operation characteristics and good deep peak regulation performance, and the pollutant emissions can steadily achieve ultra-low emission standards. When the USC-CFB unit participates in deep peak regulation, the minimum stable combustion load of the boiler can reach 20~30% BMCR, and a boiler load change rate under 30% BMCR or above could reach 1.5~2% BMCR/min, while that below 30% BMCR could reach 1% BMCR/min. The research results can provide references for the deep peak regulation of in-service supercritical (SC) CFB units and design optimization of similar USC-CFB units.