Slag Removal Research Articles

Evaluation of Metallurgical Quality of Master Heat IN-713C Nickel Alloy Ingots

Abstract The paper presents the results of evaluation of the metallurgical quality of master heat ingots and of the identification of non-metallic inclusions (oxides of Al., Zr, Hf, Cr, etc.), which have been found in the shrinkage cavities formed in these ingots. The inclusions penetrate into the liquid alloy, and on pouring of mould are transferred to the casting, especially when the filtering system is not sufficiently effective. The specific nature of the melting process of nickel and cobalt alloys, carried out in vacuum induction furnaces, excludes the possibility of alloy refining and slag removal from the melt surface. Therefore, to improve the quality of castings (parts of aircraft engines), it is so important to evaluate the quality of ingots before charging them into the crucible of an induction furnace. It has been proved that one of the methods for rapid quality evaluation is an ATD analysis of the sample solidification process, where samples are taken from different areas of the master heat ingot. The evaluation is based on a set of parameters plotted on the graph of the dT/dt derivative curve during the last stage of the solidification process in a range from TEut to Tsol.

Numerical Simulation of the Influence of Deposits on Heat Transfer Process in a Heat Recovery Steam Generator

Flue gas entrains a large number of ash particles which are composed of alkali substances into the heat recovery steam generator (HRSG). The deposition of particles on the tube surface of heat transfer can reduce the heat transfer efficiency significantly. In the present work, an Eulerian- Lagrangian model based on Computational Fluid Dynamics (CFD) is implemented to simulation flue gas turbulent flow, heat transfer and the particle transport in the HRSG. Several User-Defined Functions (UDFs) are developed to predict the particle deposition/ rebounding as well as the influence of physical properties and microstructure of deposits on the heat transfer process. The results show that only after one day deposition, the total heat transfer rate reduces 27.68% compared with the case no deposition. Furthermore, the total heat transfer rate reduces to only 238.74kW after 30 days of continuous operation without any slag removal manipulation. Both numerical simulation and field measurement identify that the deposits play an important role in the heat transfer in the HRSG. Especially, when the deposits can’t be removed designedly according to the actual operating conditions, the HRSG experiences a noticeable decline in heat transfer efficiency due to continuous fouling and slagging on the tube surface.

Development of caster slag detection system through imaging technique

Detection and removal of slag from the molten metal is an important aspect of steel making process. The application of infrared imaging, spectroscopic method and other contact type slag detection methods are inappropriate as far as caster slag detection is concerned. The detection of vibration due to slag flow has a major shortcoming. In the present article, a simple imaging technique is presented for caster slag detection. The imaging technique is based on the detection of sudden increase in the light intensity by a CCD camera as the slag floats immediately as it enters the tundish through the shroud in a casting operation. The camera is connected to a computer. As the detected light exceeds the predetermined limit, the system generates the indication of the onset of slag.

Problems of handling ashes and slags produced at Russian thermal power stations: Barriers, possibilities, and ways of solving them

The environmental indicators of ash and slag removal systems used at Russian thermal power stations are briefly estimated. The drawbacks inherent in the traditional hydraulic ash removal systems used at thermal power stations are discussed. Main barriers hindering the use of ashes and slags from thermal power stations are considered, and the possibilities of increasing the extent of their useful application are analyzed.

Stabilizing the outflow of liquid slag in the furnaces of boilers with slag-tap removal using plasma-energy technologies

Traditional methods for stabilizing outflow of liquid slag are analyzed. A method for stabilizing slag removal using plasma-energy technologies is proposed. Results from thermodynamic calculations and field tests of this technology on the BKZ-640 boiler at the Gusinoozersk district power station are presented.

Distribution of mercury in the combustion products of coal dust in boilers with liquid slag removal

The efficiency of trapping of solid particles and mercury compounds in the operation of wet centrifugal scrubbers with a closed-cycle water spray system at a thermal power plant was evaluated. Procedures were proposed for the monitoring of mercury at all of the steps of a process cycle. A balance on mercury in the combustion of coal dust in a TP-87 boiler was calculated. It was found that at least a half of mercury that entered in the firebox of boiler with coal was released as Hg0 vapor with flue gases into the atmosphere. It was demonstrated that the introduction of chemical oxidizing agents into scrubber spray water dramatically increased the efficiency of mercury trapping from flue gases.

Corrosion behaviour of chromium-free ceramics for liquid slag removal in Pressurized Pulverized Coal Combustion

The corrosion behaviour of HfO 2, HfSiO 4, ZrSiO 4, NiAl 2O 4 and, for comparison, a commercial Cr 2O 3-containing ceramic was investigated under Pressurized Pulverized Coal Combustion (PPCC) conditions at 1450 °C in the presence of liquid slag. Although Cr 2O 3-containing ceramics show sufficient corrosion resistance, they have the main disadvantage of vaporisation of toxic Cr(VI)-species. Among the investigated chromium-free ceramics, HfO 2 and HfSiO 4 showed relatively good corrosion resistance in laboratory investigations. The stability of the latter one depends not only on the microstructure of the ceramic but also on the slag composition. Technically produced ceramic balls of HfO 2 and ZrSiO 4 performed very well in the liquid slag separator of a PPCC test facility.

Application of pulse detonation technology for boiler slag removal

Pulse detonation technology for removing slag and fouling deposits in coal-fired utility power plant boilers offers great potential. This technology offers a potentially convenient, inexpensive, yet efficient way for on-line slag removal. This paper presents a feasibility study that includes both Computational Fluid Dynamics (CFD) simulations and laboratory experiments. CFD simulations provided visual and quantitative data to study the potential mechanisms for removal of slag. Mechanisms included direct impact, flow scrubbing, wave reflection and negative velocity impact on the back side of the tubes. Several experiments were carried out to verify the potential of the pulse detonation technology. Experiments were done using a pulse detonation engine and heat exchanger tubes with different types of slag placed in different orientations on the tubes. Tubes were placed at various distances from the detonation tube and in different configurations. The results present a strong case for the application of this technology for online slag removal. It is especially effective for removal of slag on the back sides of the tubes where other traditional methods are not very successful. A preliminary cost analysis indicated that the technology can be paid for within the first year itself and provide substantial savings in the subsequent years.

Erosive Wear in Pipelines at Pneumatic Conveying of Fine Silicon-Containing Materials

Erosive wear is a major operational problem in conveying of hard abrasive bulk materials like silica sand, fly ash, coal dust, etc., in pneumatic conveying systems. Erosion results in emergency downtime of pneumatic conveying installations of ash and slag removal and dust-preparation systems at TPPs caused by holes in pipelines. That leads to worsening of technical, economic, and ecological parameters of thermal power plants as a whole. In MPEI, a model of estimating erosion of rectilinear and curvilinear sections of pneumatic conveying pipelines has been developed. To validate the estimating model developed in the MPEI, experimental investigations in the Indian Institute of Technology Delhi (IITD) are being carried on. This paper presents the results of the first set of joint Indo Russian investigations carried out to study the influence of key operating variables on refinement of the erosion model. f 2009 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association All rights reserved. A R T I C L E I N F O Article history: Received 16 September 2009; Received in revised form 15 December 2009; Accepted 17 December 2009

Causes of damage to baffle pipes in high-pressure drum boilers at the Ust’-Ilimsk heat and electric power plant

The causes of damage to the baffle pipes in BKZ-420-140PT-2 high-pressure drum boilers during combustion of Irsha-Borodin and Zheronskii coals are analyzed. Damage to the salt module pipes was caused by the buildup of internal sediments and untimely chemical washing of the baffles. Flaws and bulging of the clean module pipes in the constriction region are caused by insufficient flow velocities in the 76/62-mm diameter pipes and high thermal loads during burning of Zheronskii coal. The fundamental solution for increasing the reliability of the boilers is to rebuild them with conversion to dry slag removal.

Formation processes and main properties of hollow aluminosilicate microspheres in fly ash from thermal power stations

The main parameters of aluminosilicate microspheres formed at thermal power stations in Russia were studied; these parameters are responsible for the prospective industrial application of these microspheres. A comparative analysis of the properties of mineral coal components, the conditions of coal combustion, and the effects of chemical and phase-mineralogical compositions of mineral impurities in coals from almost all of the main coal deposits on the formation of microspheres was performed. The effects of thermal treatment conditions on gas evolution processes in mineral particles and on the fraction of aluminosilicate microspheres in fly ash were considered. It was found that the yield of microspheres was higher in pulverized coal combustion in furnaces with liquid slag removal, all other factors being equal. The regularities of microsphere formation were analyzed, and the mechanism of microsphere formation in fly ash during the combustion of solid fuels was considered.

Modernizing the boiler installation for unit no. 3 at the Kashirskaya GRÉS to reduce nitrogen oxide emissions

The purpose of modernizing the Pp-1050-25-545 KGZh (P-50R) boiler is to reduce the emissions of nitrogen oxides (NOx) to levels consistent with modern requirements. The following engineering steps were taken, with liquid slag removal from the boiler, to attain NOx levels of 700–750 mg/m3 for operation with coal and 125 mg/m3 for operation with natural gas

Effect of Melting Temperature on the Wear Characteristics of Austenitic Manganese Steel

The practice in most manganese steel melting furnace is to raise the melting and pouring temperatures to 1500℃ and above so as to enhance fluidity of the molten metal and ease removal of slag. High temperature promotes micro and macro carbide segregation of alloy elements and formation of embritting transformation products. The presence of segregation at the grain boundaries, acts as barrier to dislocation movement. This could be responsible for uneven, inconsistent wear rate and pattern of the steel. This paper studies the effect of pouring/melting temperature on the propensity of carbide segregation of austenitic manganese steel and by translation on the wear characteristics of jaw crushers. Austenitic manganese steel (AMS) was subjected to different heat/melt temperatures ranging from 1380 to 1550℃ (H1-H3) in an induction furnace of 1-ton capacity. Samples obtained from the edge, middle and mounting section of the heat treated steel were examined by means of optical metallurgical microscope and the relative abundance of elements was determined by means of energy dispersed X-ray (EDX) elemental spectrometer. The results indicated high segregation of alloy elements at high melting temperatures. However, uniform dispersion of carbide particles in the base of the austenitic grains was noticed at pouring temperature range of 1400-1500℃.

Optimisation of hot metal desulphurisation at BOS2 Corus Strip Products IJmuiden

A project was started in 2002 to improve the hot metal desulphurisation by ladle treatment, whose underlying mechanism was analyzed by a process model based on fundamentals. This allowed a 10% reduction of reagent consumption. To reduce the treatment costs, calcium carbide was replaced by lime. Further results indicate the need to improve the absorption of reaction products into the slag. Lime post injection resulted in lower final sulfur content and improved slag removal.

豊島不法投棄廃棄物の溶融処理におけるスラブの再資源化(灰処理・有効利用,廃棄物処理技術)

Illegally dumped waste in Teshima includes a wide variety of substances such as ASR(Automobile Shredder Refuse), incineration ash, sludge, and soil deriving from granite, which permit some inclusions in the melted slag. Some treatments are shown to minimize the inclusions in the slag for the use of aggregate authorized by TR(Technical Report). They are, removal of slag containing soluble silicate followed by crushing and separation of aluminum and copper from crushed slag. The removed slag in appropriate for the aggregate is crushed and melted again to make them available, so that all the melting product may be recycled.

Entrainment of a two-layer liquid through a taphole

Entrainment through a taphole of a two-layer system has been investigated. The results showed that for liquids with low viscosities, the minimum dimensionless clearance from the taphole before entrainment occurs can be predicted theoretically and was related to the Froude number as Fr0.4. At low Froude numbers less than 1, fluids with low viscosities resulted in the entrainment showing a positive deviation from the critical Froude number. This allowed tapping to be carried out without entrainment occurring, even when the liquid-liquid interface was within the region of the taphole diameter. For liquids with appreciable viscosities, the entrainment showed a negative deviation from the critical Froude number. This occurs for the tapping of slag and results in entrainment at a higher liquid-liquid interface height than is predicted theoretically. Entrainment was more likely to happen for slag tapping than for matte tapping. A ledge below the taphole was found to reduce entrainment, enabling the liquid-liquid interface to be closer to the taphole during tapping. This resulted in improved slag removal efficiencies and reduced matte or metal entrainment, coupled with less slag left in the furnace after tapping. The length of the ledge from the taphole into the slag was found to be the controlling parameter for entrainment, while the ledge thickness had no effect on entrainment.

03/02468 Supercritical pressure steam boiler with 1000 t/h capacity for combustion of anthracite culm in a combustion chamber with removal of solid slag: Shapovalov, Y. I. Teploenergetika, 2002, (8), 2–8. (In Russian)

03/02468 Supercritical pressure steam boiler with 1000 t/h capacity for combustion of anthracite culm in a combustion chamber with removal of solid slag: Shapovalov, Y. I. Teploenergetika, 2002, (8), 2–8. (In Russian)

Investigation of a novel jet deflector to avoid slag accumulation around secondary air jets in incinerators and boilers

AbstractA major problem in the operation of incinerators is the build‐up of slag on the walls in the throat region of the plant between the furnace chamber and the radiation shaft. This slag can accumulate to a thickness of about one meter, with a weight of several tonnes. This accumulation reduces the availability of the plant, and poses a safety problem, since injury can occur when the material is removed by pneumatic drills during maintenance operations. The excessive downtime, labor, and other economic costs of the slag removal can be minimized by developing a novel, no‐moving‐part jet deflector that can prevent or minimize the accumulation of slag around the jets. The jet deflector was developed and designed by understanding the fundamental principles of the fluid and particle dynamics around the high‐speed jet.Two small‐scale laboratory rigs were constructed for this study. The first rig was a wind tunnel specially designed to minimize the turbulent intensity at the main flow inlet. The second was a combustion rig fitted with an ash/burner injection system, a mobile phone networked particle monitor, and a removable refractory panel onto which the jet and deflector were fitted. An extensive series of laboratory experiments were carried out on both rigs. In parallel with the laboratory investigation, computational fluid dynamic (CFD) analysis of the flow field around the jet and deflector under the same experimental conditions were also conducted. Optimization work on the deflector design was also carried out. Fully optimized jet deflectors were then manufactured and tested in a UK municipal waste incinerator plant. Visual inspections of the jets before and after the deflectors were fitted showed a very significant reduction in the slag formation.

Conversion of pulverized coal-fired boilers to ones with solid slag removal

The purpose of the present investigation is to explore the feasibility of applying the micromix combustion principle (MCP) to design low NOx burners using 100% H2 as fuel for domestic and industrial boilers. Previous investigations studying the MCP on stationary and aero gas turbine applications, showed low NOx emissions without flashback risk, which represent the two main issues when burning 100% H2. Since boiler burner operating conditions differ from gas turbine combustors, the present paper studies the MCP through CFD calculations under re-defined conditions for domestic and industrial burners, adapting the energy densities, air-fuel equivalence ratios and pre-heated air temperatures. A reference geometry was built to validate the selected numerical models with experimental results from literature. Afterwards, burners were re-dimensioned following an existing geometry-scaling methodology. The obtained results evidenced that MCP characteristics were still maintained for the defined cases, keeping low NOx values between 4 and 14 ppm. The numerical results were also validated through experimental NOx measurements in a laboratory scale micromix burner prototype. In order to assess the benefits of using hydrogen micromix burners in domestic and industrial boilers, the present work includes a final discussion with practical design considerations. The present study lays the groundwork for complementary experimental research work, which is being carried out in laboratory-scale prototypes.

The influence of electromagnetic stirring on Al-Ti-B master alloys

Electromagnetic stirring can improve the refining effect of Al-Ti-B master alloys by removing slag from the melt. When alternating-current magnetic intensity is 2,400 G, slag is removed after the melt has been stirred for three minutes. The magnetic field not only causes the melt to circulate, but also produces the secondary flow 1 cm away from the crucible wall that is the primary cause of slag removal. An alternating-current magnetic field removes slag more efficiently than a direct-current magnetic field.