Performance Characteristics of Centrifugal Slurry Pump with Multi-Sized Particulate Bottom and Fly Ash Mixtures

The present study reports on the performance characteristics of the centrifugal slurry pump with multi-sized particulate slurry of bottom ash and fly ash mixtures. The performance characteristic of the pump was experimentally evaluated at rotational speed 1450 rpm for bottom ash slurries with and without the addition of fly ash in the concentration range of 10% to 50% (by weight). Addition of fly ash in the bottom ash was varied from 10% to 30% (by weight). The pump total head, overall efficiency, and pump input power at different flow rates were evaluated. The performance characteristics results show that the value of head and the efficiency of the pump depend on the solid concentration. It was also observed that the performance parameter of the pump strongly depends on slurry properties. The addition of fine particles fly ash in the coarser particles of bottom ash slurry, leads to reduce the additional head losses in the pump. The pump performance in terms of head and efficiency improved with addition of fly ash in bottom ash slurry.     

Effect of particle size distribution on performance and particle kinetics in a centrifugal slurry pump handling multi-size particulate slurry

A significant variation in particle size distribution (PSD) is generally encountered in slurry transportation. The goal of this work is to establish the effect of variation in PSD on the centrifugal slurry pump (CSP) performance and particle kinetics. Computational fluid dynamics (CFD) modeling of a CSP with multi-size particulate slurry has been performed with a sliding mesh approach using the granular Eulerian-Eulerian model. The numerical model is validated with the experimental data of the pump performance for multi-size particulate fly ash slurry. The maximum deviations in the predicted head and efficiency compared to the measured values are of the order of ±2% and ±3.5%, respectively. Simulations with a single representative particle size for multi-size particulate slurry using median and weighted mean diameter approach are also carried out to understand the difference in performance prediction with equi-size and multi-size slurry. The predicted trend of pump performance variation with PSD is linear and non-linear with equi-size and multi-size slurries, respectively. The median and weighted mean approaches showed error in capturing the effect of variation in PSD on pump performance. The variation in PSD significantly affects the flow of particles inside the impeller and casing flow passages due to particle kinetics. Reduction in the intensity of granular pressure, maximum granular viscosity, and the head loss due to friction in impeller and casing flow passages are found with the increase in the fine size particles.     

Performance prediction of a centrifugal pump delivering non-Newtonian slurry

Centrifugal pump has been used for the transport of the multiphases particularly slurry (solid–liquid mixture) in the petroleum and chemical industry. The present article describes the experimental analysis of a centrifugal pump delivering non-Newtonian fluids and reports the pump’s performance characteristics under different flow conditions. The mixture is prepared by mixing right quantities of bentonite powder, water, and Na₂CO₃ to give the desired fluids having different viscosities. It was observed that the head and the efficiency of the pump decrease with the increase in fluid viscosity at the rated speed. The pump performance depends on the bentonite concentration in water, which changes rheological property of the fluid. To avoid experimental difficulties and to find correlations among the parameters, a polynomial regression (PR) model was fit to predict the head and efficiency. The PR models predict head and efficiency with relative percentage error of 3.137% and 5.096%, respectively.     

Numerical simulation of a centrifugal slurry pump handling solid-liquid mixture: Effect of solids on flow field and performance

The effect of solids on a centrifugal slurry pump performance is a major concern to the design of slurry transportation system. In the present study, the multiphase modeling of centrifugal slurry pump is performed using two models, Mixture and Eulerian-Eulerian multiphase. Sliding mesh approach is employed for unsteady simulation of the pump. The accuracy of the simulations is ascertained by comparing the performance characteristics of the pump obtained numerically and experimentally. Experimental results are obtained by measurements in a pilot plant test rig with three different mean size sand particulate slurries. The Eulerian-Eulerian multiphase model predicted the effect of the solids on pump performance close to the experimental results as compared to Mixture model. The obtained accuracy with Eulerian-Eulerian model for predicting the effect of solids on head and efficiency is around ±2% and ±3%, respectively. The predicted results using Eulerian-Eulerian model confirm that the head and efficiency of the pump decrease with the increase in particle size and concentration. The particles of high specific gravity show less reduction in head and efficiency of the pump. Further, the effect of variation in particle size and concentration on the flow field in the impeller and casing has also been analyzed at best efficiency point operation. Non-homogeneous suspension of particles inside the blade channels and casing passages is examined. The particulate concentration is observed higher near the impeller back shroud, pressure side of the blades, and non-suction side of the casing as compared to other locations.     

Variation of physical and rheological properties of fly ash slurries with particle size and its effect on hydraulic transportation at high concentrations

In thermal power plants, fly ash is collected at the bottom of electrostatic precipitator (ESP) hoppers and transported to common sump for further disposal to the ash pond by slurry pipelines. The fly ash from different fields of ESP hoppers vary widely in particle size as well as quantity. Depending on the sequence of evacuation, the overall particle size distribution (PSD) would vary with time which in turn would affect the head requirement in the high concentration slurry disposal (HCSD) system. Fly ash samples from different fields of ESP hoppers of a thermal power plant have been analyzed for their physical properties namely the PSD, specific gravity, settling characteristics, pH of the slurry, etc. and for rheological properties in the concentration range of 60–70% (by weight). The particle size (d_wm) of the fly ash samples decreases with the increase in ESP field, whereas the static settled concentration and specific density increase. The pH values of all samples are almost constant and nonreactive in nature. The rheological properties namely yield stress and Bingham viscosity of the fly ash slurries from different fields of ESP hoppers increase with increase in concentration. Further at any given concentration, these parameters exhibit a strong dependence on particle size. Using these properties and treating the distribution of particles across the pipe cross section as homogeneous in the concentration range of 60–70% (by weight), CFD computations are made to evaluate the head requirement in a HCSD pipeline. The head loss increases with increase in concentration for all fields of ESP hoppers. The present study also shows that head requirement varies significantly by mixing different proportion of fly ash from different ESP fields.     

Conveying of Solid Particles in Newtonian and Non-Newtonian Carriers

This article deals with the effect of slurry composition and volumetric concentration on the flow behavior of slurries containing fine-grained and coarse-grained particles. Fluidic fly and bottom ash slurries and sand slurries were experimentally investigated. Kaolin slurries with and without a peptizing agent were used as the carrier liquid for the sand slurries to compare the effect of Newtonian and non-Newtonian carriers. The study revealed a time-dependent yield pseudo-plastic behavior of fluidic fly and fly/bottom ash slurries and the possibility of substantial reduction of the flow resistance by mechanical treatment or by the arrangement of particle size distribution. The flow behavior of fluidic ash slurries can be approximated by the Bulkley-Herschel model in the laminar region. In the turbulent region, the Wilson or Slatter models can be used. The effect of the size distribution of the sand slurry on the hydraulic gradient depends on the flow velocity. The coarse sand slurry reaches a higher hydraulic gradient than the fine sand slurry: the difference decreases with growing velocity. The highly concentrated sand-kaolin slurries show non-Newtonian behavior. When the carrier kaolin slurry is peptized, the hydraulic gradient in the laminar region becomes markedly lower, and the favorable effect vanishes in the transitional and turbulent regions. The addition of small amounts of kaolin favorably affects the flow behavior of the sand slurry.     

Comprehensive Characterization of Pond Ash and Pond Ash Slurries for Hydraulic Stowing in Underground Coal Mines

In this study, the physicochemical and self-heating characteristics of pond ashes from Talcher Thermal Power Station (TTPS), located in the Angul district of the Indian state of Odisha are studied. The study revealed that the TTPS pond ashes belong to Class F fly ash category consisting mainly of SiO₂, Al₂O₃, and Fe₂O₃, with a small amount of CaO. The presence of mineral phases, namely, quartz, mullite, magnetite, and hematite in the pond ash are confirmed by x-ray diffraction. Based on the pond ash properties, various properties of the slurries of one representative pond ash, namely, density, volume concentration, and viscosity are determined by varying the ash concentration from 45% to 65% with an increment of 5%. As well, the critical deposition velocities of slurries as a function of slurry concentration and pipe diameter are determined. The results showed that the slurry viscosity increases exponentially with increase in solid content and the critical velocity increases linearly with increase in slurry concentration and pipe diameter. The relationships generated through regression analysis can be used to quickly predict the critical velocity of similar types of ash slurries for any known slurry concentrations and pipe sizes.     

Deposition characteristics of coal ash slurries at higher concentrations

High concentration slurry disposal system (HCSD) for transportation of coal ash to ash ponds from coal fired thermal power plants using pipelines has emerged as an economical and environmental friendly method. Coal Ash in slurry form is deposited in the ash pond and hence the deposition characteristics at higher concentrations (C_w >60% by weight) are very important. The settled solid profile in the ash pond at high concentrations is of great interest to the ash pond designers. The present study is an attempt to establish the relationship between the settled solid profile and the physical/rheological properties of coal ash slurry at high concentrations. The settled solid profile is experimentally measured in terms of cone angle for slurries of fly ash as well as mixture of fly ash (FA) and bottom ash (BA) in the ratio of 4:1 at high concentrations. The values of cone angle if the slurries are poured on either a pervious or impervious bed have also been measured. The results obtained from the experiments show that the cone angle depends on rheological properties like yield stress and Bingham plastic viscosity which in turn depend on various properties like solid concentration, particle size distribution etc. Also, cone angle for fly ash slurry is higher than that for the mixture of FA and BA slurry at any given concentration. Further, it was also observed from the experiments that cone angle is higher for pervious bed as compared to impervious bed for both types of slurries.     

Bulk Hydraulic Disposal of Highly Concentrated Fly Ash and Bottom Ash–Water Slurries

Mine backfilling with power plant ash is gaining increasing attention from the power and mining industries for its bulk disposal. In the USA and other countries, mine backfilling with ash is considered as a viable option for stability improvement, subsidence control, and mine site rehabilitation. This paper presents the results of rheological studies conducted on fly ash and mixtures of fly ash and bottom ash samples collected from NTPC Talcher, Odisha. The complex hydro-mixture slurry indicated non-Newtonian pseudo-plastic behavior in the mass concentration range of 60–67.5%. A non-Newtonian power law head loss model was used to evaluate the head loss of ash slurry in pipelines having nominal bores in the range of 100–300 mm. The results indicated that the addition of bottom ash to fly ash slurry at a given solids concentration has a beneficial effect in reducing the pumping power requirement. A design chart for the fly ash mixture slurry has been formulated indicating the variation in backfilling rate with relative head requirements for a given length of pipeline for a range of pipe sizes and transport velocities. This is expected to provide relevant pipe flow and operational conditions for bulk disposal of fly ash for mine backfilling purpose.     

旁通装置控制离心泵空化特性的数值模拟与试验

为了研究旁通水路对离心泵空化性能的影响规律,以一台比转速为32的低比转速离心泵为研究对象,在蜗壳第八断面靠进口侧位置处至吸入段搭建一旁通管路.采用修正的SST k-ω湍流模型和Kubota空化模型,在不同空化数下,对原型泵和带有旁通水路的离心泵进行三维非定常数值模拟,并同试验结果进行对比.结果表明:低比转速离心泵在搭建...     

Development of new models of performance correction factors of centrifugal pumps as a function of Reynolds number and specific speed

The performance characteristics of a small centrifugal pump having a specific speed of 20 min^?1 are measured when pumping two industrial Newtonian oils of viscosities 75 and 646 cSt, at value of Reynolds number near 10³. The diminishing of the performance in the case of these oils compared to water is about 50 to 80 %. It decreases with the reduction of Reynolds number. The correction factors of head, of flow rate and efficiency, are determined depending on Reynolds number, and they are compared with those obtained using the European KSB empirical method, the American method ANSI/HI and the semi-empirical method based on the analysis of power losses. For centrifugal pumps of a specific speed below 50 min^?1, the fall in performance increases with the decrease of Reynolds number and specific speed. The fall in efficiency is more important than the fall of the other performance parameters. A good agreement is obtained between experimental results and predicted results using the three above mentioned methods, with the exception of the efficiency correction factor obtained by the method of power losses analysis, in the range of Reynolds numbers between 10³ and 10⁵. The expression of correction performance factors based on the Reynolds number is universal. It allows to distinguish the ranges of correction factors falls, and to know the economic limitations of the use of centrifugal pumps. A fall of head and flow rate correction factors of over 10 % occurs at values of Reynolds number below 10⁴. But, the fall of efficiency correction factor of over 10 % occurs at values of Reynolds number below 10⁵. To facilitate to the professionals the calculation of the performance correction factors of centrifugal pumps, new models are proposed in this study according to Reynolds number and specific speed.     

盐离子对纳米氧化锆浆料流变性能的影响

通过测定浆料的Ｚｅｔａ电位和粘度曲线,研究了含高浓度盐溶液电解质对纳米氧化锆浆料电动性能和流变性能的影响。研究结果表明,盐离子的加入可显著改变浆料的悬浮特性,增加盐离子的浓度,氧化锆浆料的Ｚｅｔａ电位降低,粘度增大,对同一种电解质而言,浆料的等电点并不随离子浓度的改变而改变,说明氧化锆浆料对这些盐离子无特性吸附,从浆料 的粘度贡线可以看出,盐离子的加入均对浆料产生絮凝作用,使颗粒间产生一种相互相吸     

STUDY ON CASING PERFORMANCES IN CENTRIFUGAL SLURRY PUMPS

ABSTRACT

The pump casing is the most expensive wear component of a centrifugal slurry pump. It determines to a large extent the hydraulic performance of the pump and plays a major role in the overall wear life of the unit.

This paper suggests a new approach to compute the mixture velocity and solid particle dynamics in the casing, and on this basis the erosion wear distribution inside the pump casing. Numerical analysis was performed using the finite element method. The model was tested using Georgia Iron Works (GIW) pump casings, at flowrates between 2000 and 4000 US-GPM (US gallons ner minute). The experimental results were obtained in the Hydrualic Laboratory and in field applications in mining and dredging industries. The suggested techniques are useful for estimating casing wear rates and for the optimal design and selection of slurry pumps.     

STUDY ON CASING PERFORMANCES IN CENTRIFUGAL SLURRY PUMPS

The pump casing is the most expensive wear component of a centrifugal slurry pump. It determines to a large extent the hydraulic performance of the pump and plays a major role in the overall wear life of the unit.

This paper suggests a new approach to compute the mixture velocity and solid particle dynamics in the casing, and on this basis the erosion wear distribution inside the pump casing. Numerical analysis was performed using the finite element method. The model was tested using Georgia Iron Works (GIW) pump casings, at flowrates between 2000 and 4000 US-GPM (US gallons ner minute). The experimental results were obtained in the Hydrualic Laboratory and in field applications in mining and dredging industries. The suggested techniques are useful for estimating casing wear rates and for the optimal design and selection of slurry pumps.     

Kennfeldanalyse einer Schraubenvakuumpumpe

Operating Performance of Screw Vacuum Pumps This paper presents detailed analyses of the operating performance of a dry‐running screw vacuum pump. The characteristic parameters, suction speed and final attainable pressure ‐ which primarily define the operating performance of screw vacuum pumps ‐ are explored in experimental and theoretical investigations. Experiment and simulation in combination are used to show the correlation between the main physical and technical characteristics and the operating performance of screw vacuum pumps. This basic knowledge is essential for understanding the specific machine physics of positive displacement vacuum pumps, especially for screw vacuum pumps, and is useful in view of further design and optimization processes. The experiment covers measurements of the operating performance of the investigated isochoric screw vacuum pump working against ambient pressure. As operating parameters intake pressure (1000mbar to 10^‐3mbar) and rotor speed are varied over a wide range. The theoretical analysis of the operating performance contains simplifying models as well as simulations of the thermodynamic processing. The impact of external leakages, clearance vacuum flows and further losses on operating performance are described in detail.     

适用于化工工业的真空泵

真空泵在化工企业如水、电、压缩空气一样是不可缺少的公用设施。用于化工行业的真空泵必须结实、可靠,能处理大量蒸汽、腐蚀性气体和可燃性气体。本文介绍了各种真空泵的结构与性能,认为液环泵和螺杆真空泵最适合于化学工艺应用。     

PARTICULATE MOTION AND CONCENTRATION FIELDS IN CENTRIFUGAL SLURRY PUMPS

Erosion wear of centrifugal slurry pumps is primarily governed by the particulate motion and concentration as well as their physical properties. This paper presents a quasi-3D approach to predict particulate phase motion and concentration in an arbitrary radial section of a centrifugal slurry pump. A brief discussion of the fully developed turbulent flow solution of the carrier fluid is followed by a computation of the particulate phase velocity resulting from a force balance between the pressure, gravity, viscous and inertial effects. The concentration distribution is obtained by invoking the convection-diffusion equation. The governing partial differential equation is cast into a weak Galerkin finite element form. The system of algebraic equations is solved by a Newton-Raphson scheme via a frontal solver. An iterative solution scheme is employed to alternate between the fields of particle motion and concentration. Numerical solutions are examined in light of their applicability to the solution of the pump wear problem.     

电厂脱硫泵用机械密封故障分析和维修

以可门电厂脱硫浆液泵的维修为例,总体上分析了脱硫浆液泵机械密封失效的原因;阐述了在调试和维护中出现的故障,并分析了一些值得注意的问题,提出一些维修方面的相应对策。     

Preparation of coal slurry with 2-propanol

This study explored the feasibility of using waste organic solvents as substitutes for water to prepare coal slurries. The rheological properties of coal-2-propanol slurries were examined and compared with that of coal-water slurry (CWS). The good compatibility between coal particles and 2-propanol resulted in stable particle suspension in slurry which usually exhibit Newtonian behaviour. However, coal-2-propanol slurries usually shown higher viscosities comparing to CWSs at a fixed solid loading due to swelling of coal by 2-propanol. In addition, coal-2-propanol slurries demonstrated lower settling rates (higher stability) compared to CWSs presumably due to good compatibility between coal particles and 2-propanol. Finally, coal-2-propanol slurries formed bulky sediment with loose structure even coal particles suspended in 2-propanol were more stable than coal particles in CWSs.     

HEMA-TBA凝胶体系制备多孔氧化铝陶瓷

采用HEMA-TBA凝胶体系制备具有高气孔率, 高强度的多孔氧化铝陶瓷, 研究多孔氧化铝陶瓷的浆料和坯体制备工艺, 并系统研究了分散剂含量和固相体积分数对浆料粘度和悬浮稳定性的影响、干燥和单体含量对生坯性能的影响以及固相体积分数和烧结温度对烧结体微观结构的影响。结果表明: 加入柠檬酸可以使浆料粘度降低, 稳定性提高, 柠檬酸加入量达到2wt%后浆料粘度和稳定性趋于稳定; 固相体积分数的增加会导致浆料粘度和稳定性的增加; 生坯在干燥过程中的收缩比水基体系小很多, 干燥时间也相对更短; 单体含量对生坯强度影响较大, 当单体含量为25wt%时, 生坯强度较高; 通过选择不同的固相体积分数和烧结温度, 可以有效地控制烧结体的微观结构, 气孔率的变化范围在40%~65%, 同时烧结体强度也会随之发生变化, 变化范围在5.7~91.2 MPa。