Effects of fine ash particles and alkali metals on ash deposition characteristics at the initial stage of ash deposition determined in 1.5MWth pilot plant tests

Shimogori, Miki; Mine, Toshihiko; Ohyatsu, Noriyuki; Takarayama, Noboru; Matsumura, Yukihiko

doi:10.1016/j.fuel.2012.01.036

Cited by 32 publications

(31 citation statements)

References 25 publications

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“…Measurements of steady-state heat flux and heat transfer coefficient are subject of many current studies [3][4][5][6][7][8][9][10]. Heat flux measurements absorbed by the water walls of the combustion chamber are used in the design of the steam boilers or in the control systems of the soot blowers.…”

Section: Measurements Of Heat Flux Absorbed By Water Walls In Combustmentioning

confidence: 99%

Solving Inverse Heat Transfer Problems When Using CFD Modeling

Ludowski¹,

Taler²,

Taler³

2016

Numerical Simulation - From Brain Imaging to Turbulent Flows

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The chapter presents solving steady-state inverse heat transfer problems using Computational Fluid Dynamics (CFD) software. Two examples illustrate the application of the proposed method. As the first inverse problem determining the absorbed heat flux to water walls in furnaces of steam boilers is presented in detail. Three different measurement devices (flux tubes) were designed to identify steady-state boundary conditions in water wall tubes of combustion chambers. The first meter is made of a short eccentric tube in which four thermocouples on the fire side below the inner and outer tube surfaces are installed. The fifth thermocouple is situated at the rear of the tube on the housing side of the water wall tube. The second meter has two longitudinal fins that are welded to the bare eccentric tube. In the third option of the instrument, the fins are attached to the water wall tubes but not to the flux tubes as in the second version of the flux tubes. The first instrument is used to measure the heat flux to water walls made from bare tubes, while another two heat flux tubes are designated for measuring the heat flux to membrane walls. Unlike the existing devices, the flux tube is not attached to neighboring water-wall tubes. The absorbed heat flux on the outer surface and the heat transfer coefficient at the inner surface of the flux tube are determined from temperature measurements at internal points. The thermal conductivity of the flux-tube material is a function of temperature. The nonlinear inverse problem of heat conduction (IHCP) is solved using the least-squares method. Three unknown parameters are determined using the Levenberg-Marquardt method. In each iteration, the temperature distribution in the cross section of the heat flux instrument is determined using the ANSYS/CFX software.Another inverse heat transfer problem will be a CFD simulation carried out for the platen superheater placed in the combustion chamber of the circulating fluidized bed (CFB) boiler. Velocity, pressure, and temperature of the steam, as well as the temperature of the tube wall with the complex cross section, were computed using the ANSYS/ CFX software. The direct and inverse problems were solved. In the first inverse problem, the heat transfer coefficient on the flue-gas side was determined based on the meas- ured steam temperature at the inlet and outlet of the three pass steam superheater. In the second inverse problem, the inlet steam temperature and the heat transfer coefficient on the flue-gas side were estimated using measured steam temperatures at selected locations of the superheater. The Levenberg-Marquardt method was also used to solve the second inverse problem. At every iteration step, a direct conjugate heat transfer problem was solved using the ANSYS/CFX software. The CFX program was called and controlled by an external program written in Python language. The LevenbergMarquardt algorithm was also included in the Python program.

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Section: Measurements Of Heat Flux Absorbed By Water Walls In Combustmentioning

confidence: 99%

Solving Inverse Heat Transfer Problems When Using CFD Modeling

Ludowski¹,

Taler²,

Taler³

2016

Numerical Simulation - From Brain Imaging to Turbulent Flows

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“…A lot of research has shown that the slagging and fouling on heating surfaces during coal combustion are usually related to alkali metal elements Na and K [16][17][18][19][20][21][22]. As shown in Table 4, the ash in the flue gas exhausted from the ferrosilicon electric furnace has high Na and K contents, which leads to easy slagging and fouling.…”

Section: Slagging Mechanismmentioning

confidence: 99%

Slagging and Fouling Characteristics of HRSG for Ferrosilicon Electric Furnaces

Wang

Chen

et al. 2015

Energies

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Abstract:The slagging and fouling characteristics of the heat recovery steam generator (HRSG) for ferrosilicon electric furnaces are discussed in this paper. Three ash samples were taken from the HRSG of a ferrosilicon furnace in Ningxia Province, China, which suffered from serious slagging and fouling. X-ray fluorescence (XRF), X-ray powder diffraction (XRD) and scanning electron microscope (SEM) were used to analyze the ash samples. The results show that low melting point salt Na2SO4 and composite salts Na (AlSi3O8) and 3K2SO4· CaSO4 deposit on the superheater tube walls in aerosol form and solidify to form the initial slag layer. With the continuous deposition of the low melting point compounds, more and more ash particles in the flue gas adhere to the slag surface to form a thicker slag. Low melting point composite salt NaO· Al2O3· SiO2 is absorbed on the evaporator tube walls in aerosol form. With the deposition of NaO· Al2O3· SiO2, more and more ash particles are absorbed to form the fouling. Since there is less space between pin-finned tubes, the large iron-rich slag particles are easily deposited on tube walls and fin surfaces, which is advantageous to the fouling process. There are large quantities of superfine ash particles in the flue gas that easily adhere to other particles or tube walls, which facilitates the slagging and fouling process. OPEN ACCESSEnergies 2015, 8 1102

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“…Fryda and colleagues developed an advanced sensor probe, which measured heat flux data online and the collected data were used to calculate fouling factor under oxy‐fuel combustion and air combustion. Shimogori and colleagues used a slagging probe to evaluate the effects of fine particles and alkali metals on heat transfer characteristics at the initial stage of ash deposition. The surface temperature of ash deposit has an obvious effect on ash deposition .…”

Section: Introductionmentioning

confidence: 99%

A novel method used to study growth of ash deposition and in situ measurement of effective thermal conductivity of ash deposit

Zheng

Wang

Cai

et al. 2017

Heat Trans. Asian Res.

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Ash deposition always brings boilers some trouble due to fouling or slagging. In this paper, a completely controlled system was developed to study the growth of ash deposit. A novel sampling probe was designed to online measure the heat flux through ash deposit. Additionally, the thickness of ash deposit can be obtained by an online figure collecting system. The results of this research showed that as the thickness of ash deposit increased, the heat flux decreased. It was also found that at the initial stage of ash deposition when the thickness of ash deposit is approximately 1 mm, the heat flux through ash deposit had a sharp reduction. An effective method was attempted to situ measure the effective thermal conductivity of the ash deposit in the simulated combustion flue gas. It was found that temperature of the ash deposit layer had no obvious effect on its value. It was concluded that the structure of ash deposit had no obvious change in a short deposition time of 30 min with varied surface temperatures of the probe head between 400 °C and 600 °C.

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Effects of fine ash particles and alkali metals on ash deposition characteristics at the initial stage of ash deposition determined in 1.5MWth pilot plant tests

Cited by 32 publications

References 25 publications

Solving Inverse Heat Transfer Problems When Using CFD Modeling

Solving Inverse Heat Transfer Problems When Using CFD Modeling

Slagging and Fouling Characteristics of HRSG for Ferrosilicon Electric Furnaces

A novel method used to study growth of ash deposition and in situ measurement of effective thermal conductivity of ash deposit

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