Industrial-scale Measurements Research Articles

Novel efficient energy saving approach for liquid ring vacuum pump in coal mine gas drainage

Liquid ring vacuum (LRV) pumps used in the coal mine gas drainage system waste a considerable amount of electrical energy due to the extremely low efficiency, which has been a dramatic limitation over many decades not effectively solved using the conventional structural optimization method. Here a novel approach for drastic improvement of LRV pump efficiency, based on turbulent drag reduction theory, is proposed to reduce the useless energy consumption. Furthermore, a new kind of drag-reducing working fluid (DRWF) for the LRV pump and a supporting closed energy-efficiency system, are developed. Industrial-scale measurements are conducted on the LRV pumps with various models to evaluate the influence of the new DRWF on the overall pump performance. The experimental results show that the new approach can achieve approximately 10% pump efficiency improvement and maximally 21–24% energy-saving rate at an optimum concentration of xanthan gum of 4000 ppm in the DRWF. A cost-effectiveness analysis shows the economic viability of this approach. This technology has been commercially applied to reduce the electricity waste in coal mine gas drainage system, and the energy-saving rate reaches 15–22%, and the carbon emissions reduction for Gucheng mine in China can reach 987 tons per year, which is proved to be an effective approach to achieve China's carbon peak and neutrality goals.

Physical Modelling of Nitrogen Variation in Continuously Cast Blooms Resulting from Atmospheric Exposure of Steel in Tundish during Initial Stages of Teeming

Exposure of liquid steel to air, consequent re-oxidation as well as nitrogen absorption are common in steelmaking and produce unacceptable variations in product chemistry. The phenomena, during continuous casting of the lead or first heat, have been investigated in a full-scale water model of a two-strand, bloom casting shroud-tundish system. Physical modelling results supported by industrial scale measurements have demonstrated that exposure of liquid steel to tundish atmosphere during initial period of ladle teeming and consequent nitrogen absorption, manifest over substantial period, influencing predominantly the first three blooms.

A Multiscale-Based Approach to Understand Dendrite Deflection in Continuously Cast Steel Slab Samples

Dendrite bending angle measurements were conducted along two different directions on four steel slab samples collected from a conventional caster. The primary dendrites growing at the slab surface showed a transition in their growth direction as the distance from the surface increased. Numerical fluid flow simulation showed changes in the flow directions that might have caused the change in the growth direction. The bending angle measurements were also correlated with the casting process parameters. Thereafter, a multiscale approach was adopted to predict the dendrite deflection angles by correlating the macro-scale flow profile with the micro-scale bending angle formulation and subsequently corroborated with the industrial scale measurements.

Tundish Process Performance Parameters and Their Direct Estimation from a New, Plant Measurement-Based Formalism

A mathematical frame work has been developed to quantitatively investigate inclusion floatation and generation phenomena in a tundish during continuous casting of LCAK (low carbon aluminum killed) steel. Embodying industrial scale measurements of dissolved and total aluminum in VD (vacuum degasser), tundish and bloom in a materials balance frame work, two key dimensionless parameters, viz., inclusion generation (GI) and floatation (FI) indices, have been formulated. To demonstrate their adequacy, as a test case, a 13 metric ton bloom casting tundish has been considered and plant scale data from nearly fifty heats applied. The analysis reveals barely satisfactory inclusion floatation coupled with significant generation, indicating essentially sub-optimal tundish process performance.

Upscaling Effects on Char Conversion in Dual Fluidized Bed Gasification

Dual fluidized bed gasification (DFBG) is an emerging technology that can be employed as a first step in the transformation of lignocellulosic materials into transportation fuels such as substitute natural gas, dimethyl ether, methanol, and Fischer-Tropsch diesel. The present work aims at (i) identifying challenges that arise in the upscaling of DFBG plants, (ii) determining whether the increased fuel residence time that results from the upscaling is sufficient for process optimization, and (iii) evaluating the impact of measures to mechanically control the fuel residence time. The investigations use a semiempirical 1-dimensional model, which is validated with industrial-scale measurements. The scope includes both DFBG units delivering gas as the main product and those in which the product gas is a byproduct in a heat and power plant. Moreover, both new designs and retrofit cases of existing CFB combustion plants (i.e., adding a gasifier to the return leg) are considered. Modeling results show that although there is an initial increase in the fuel residence time as the size of the gasifier increases, further upscaling eventually leads to a decrease in the degree of char gasification due to (i) a decrease in the fuel residence time, as there is a transition in lateral fuel mixing from the dispersion-dominant regime to the convection-dominant regime; and (ii) a decrease in the char gasification rate due to an increased bed material velocity, which increases the probability that pyrolysis occurs on the bed surface (leading to a less reactive char as the heat transfer is lower there compared to inside the dense bed). For DFBG units of around 100 MW, proper combinations of operational conditions (e.g., the solids circulation, the steam-fuel ratio, and the temperature of the circulating solids) result in an optimized process when heat and power is the main product, with gas as a byproduct. However, when gas is the sole targeted product, it is likely that baffles are also necessary to achieve sufficient fuel conversion for process optimization.

Industrial-scale investigations of anthracite combustion characteristics and NOx emissions in a retrofitted 300 MWe down-fired utility boiler with swirl burners

To burn anthracite and reduce NOx emissions, a new combustion system was applied to a 300 MWe Babcock & Wilcox (B&W) down-fired boiler that included overfire air (OFA) and a decreased flow area of the inner and outer secondary air ducts of the installed swirl burners. Industrial-scale measurements (adjusting OFA ratios from 15.4% to 22.6%) were conducted to evaluate the overall performance of the retrofitted boiler. The experimental results demonstrated that the new combustion system promoted coal/air flow ignition and combustion stability. When the OFA ratio was less than 19.7%, the influence of the burner secondary air ratio on coal/air flow ignition was greater than that of the recirculation region below the arches. The overall combustion level in the primary combustion zone depended on the oxygen content and the recirculation region in the lower furnace instead of the early or late ignition of the coal/air flow. Oxygen and carbon monoxide concentration measurements in the near-sidewall region revealed that the fullness degree of the coal flame varied under different OFA ratios. Considering both environmental and economic effects, 19.7% was chosen as the optimal OFA ratio, thereby achieving a significant NOx reduction of 47% without increasing carbon content in the fly ash.

Heat Flow and Solidification Modeling of Industrial Scale, Ingot Casting Operation

A model, based on the concept of effective thermal conductivity, was developed to study thermal fields and the resultant solidification behavior of large, round, industrial size ingots. In this, flow and turbulence phenomena during mold filling as well as subsequent solidification were not modeled explicitly but their influence was accounted for by artificially raising the thermal conductivity of solidifying steel. Thus, a conduction like equation embodying a conjugate approach was applied to simultaneously predict the evolution of temperature fields in the mold as well as in the solidifying ingot following teeming. Prior to comparing model predictions against industrial scale measurements, sensitivity of calculations to grid size, time step height, convergence criterion etc. were rigorously assessed. Similarly, modeling of interfacial resistance, chemical reactions and heat effects in the hot top as well as their influence on predicted results were evaluated computationally. Embodying mixed thermal boundary conditions (free convection + radiation) at the mold wall, temperature fields during solidification of two different industrial large ingots were predicted numerically. Parallely, mold wall temperature was monitored as a function of time and surface temperature of ingot was measured at the instant of mold stripping using hand held, radiation pyrometers. Incorporating relevant operating conditions (viz., mold dimensions and size, ingot and hot top dimensions and material, initial mold and liquid temperature etc.) into the calculation scheme, predictions were made via a computational procedure developed in-house and results thus obtained were compared against equivalent industrial scale measurements. Very reasonable agreement between the two was demonstrated.

Prediction of coking dynamics for wet coal charge

Abstract A one-dimensional transient mathematical model describing thermal and flow phenomena during coal coking in an oven chamber was studied in the paper. It also accounts for heat conduction in the ceramic oven wall when assuming a constant temperature at the heating channel side. The model was solved numerically using partly implicit methods for gas flow and heat transfer problems. The histories of temperature, gas evolution and internal pressure were presented and analysed. The theoretical predictions of temperature change in the centre plane of the coke oven were compared with industrialscale measurements. Both, the experimental data and obtained numerical results show that moisture content determines the coking process dynamics, lagging the temperature increase above the water steam evaporation temperature and in consequence the total coking time. The phenomenon of internal pressure generation in the context of overlapping effects of simultaneously occurring coal transitions - devolatilisation and coal permeability decrease under plastic stage - was also discussed.

Three phase transient model of wet coal pyrolysis

A one-dimensional transient mathematical model was developed to describe the thermal and flow phenomena during coal pyrolysis in a coke oven. The model was solved numerically using partly implicit methods for gas flow and heat transfer problems. It was successfully validated with industrial-scale measurements of temperature change in the middle-plane of the coke oven chamber. The evolution of temperature and pressure, distributions of gas and steam generation rates were presented and analyzed. Special emphasis is put on the progress of vaporization and condensation fronts and their impact on the moisture levels within the coal charge. The obtained results show that moisture content determines the coking process dynamics, lagging the temperature increase above the boiling temperature and in consequence the start up of pyrolysis. The effect of low permeability of coal in its plastic stage on the internal pressure peaks in a coke oven is discussed.

New dynamic models for simulation of industrial SO2 oxidation reactors and wet gas sulfuric acid plants

Simulation of plant performance during start-up, shutdown, and changes in the feed for industrial sulfuric acid plants requires dynamic modeling of the complete plant. A dynamic tanks-in-series model has been set up for the SO2 oxidation reactor with accumulation terms accounting for absorption and desorption of SO3 in the catalyst melt, which can have significant effect on operation due to the large absorption capacity of the SO2 oxidation catalyst. Simulations are compared with pilot and industrial scale measurements, and good agreement is found for temperatures, SO2, and SO3 concentrations when flow rate, temperature, and composition of the feed are changed. A corresponding model for the transient operation of a sulfuric acid condenser has also been developed. Implementation of the models in a commercial dynamic simulator has enabled full closed-loop simulation of industrial SO2 oxidation reactors and complete WSA plants.

Grinding and combustion characteristics of woody biomass for co-firing with coal in pulverised coal boilers

This paper presents results of grinding experiments and development of woody biomass mill for co-firing in pulverised coal fired boilers. Woody biomass co-firing with coal is already realised since it can be easily handled as a carbon–neutral fuel. Three steps have been carried out to understand the grinding and combustion characteristics of woody biomass. A suitable mill type for woody biomass grinding has been sought in laboratory-scale experiments. The selected industrial-scale mill has been modified to increase the capacity.The objective of this experimental study is to establish and demonstrate the woody biomass firing system including mill and burner for pulverised coal fired boilers. Both, laboratory- and industrial-scale measurements, provide good understanding of woody biomass grinding and firing performance. The proper burner arrangement is found by use of Computational Fluid Dynamics (CFD) to maintain high burnout efficiency in the boiler. The study proves that the proposed mill and burner positioning is promising to utilise woody biomass with high co-firing ratio. The combination of furnace experiments and CFD modelling results in a satisfying specification of a co-firing system for woody biomass with pulverised coal in sufficient ratio whilst reducing CO2 emissions.

Arch- and wall-air distribution optimization for a down-fired 350 MWe utility boiler: A cold-modeling experimental study accompanied by real-furnace measurements

To determine the effect of the arch- and wall-air distribution on flow characteristics, experiments were conducted within a 1:15-scaled model for a down-fired 350 MWe furnace at various settings, i.e. ratios (denoted by Rd) of the mass flow rate of staged air to that of total secondary air of 0%, 7%, 16%, 23%, and 29%. Meanwhile, industrial scale measurements were performed at full load with staged-air damper openings of 15% and 35% (equaling to Rd at about 10% and 20%), respectively. At settings of Rd = 0% and 7%, an essentially symmetric flow field appeared. At the left three higher settings (i.e., Rd = 16%, 23%, and 29%), a deflected flow field developed, with the airflow near the front wall penetrating much further than that near the rear wall. At this time, increasing Rd deteriorates the flow-field deflection. By means of cold-modeling experiments to evaluate the flow-field symmetric extent and downward airflow penetration depths in the lower furnace, the appropriate Rd was found to be in the range of 7–16%. Real-furnace measurements revealed that although the 15% opening was inapplicable in boiler operations for a long time, relatively symmetric combustion could developed at the this opening setting. At the 35% opening setting, an asymmetric combustion pattern developed in the furnace, with temperatures near the front wall being clearly higher that those near the rear wall. However, particularly high NOx emissions and good burnout developed at both two openings. In considering that numerical simulations and industrial scale measurements in published work have confirmed the validity of a previously-proposed deep-air-staging combustion technology in achieving excellent furnace performance within down-fired furnaces, retrofitting the present furnace with the technology is thus recommended if symmetric combustion, good burnout, and low NOx emissions are to be achieved.

CFD–DEM study of the effect of particle density distribution on the multiphase flow and performance of dense medium cyclone

A mathematical model is developed to study the coal-medium flow in a dense medium cyclone (DMC) of 1000 mm body diameter. In the model, the motion of coal particles is obtained using the Discrete Element Method (DEM) facilitated with the concept of “parcel–particle” while the flow of medium as a liquid-magnetite mixture Computational Fluid Dynamics (CFD) based on the local averaged Navier–Stokes equations. In addition the Reynolds Stress Model (RSM) is adopted to describe the anisotropic turbulence, the Volume of Fluid (VOF) model is used to describe the air-core position and multiphase mixture model used to estimate the flow of fine magnetite particles. The simulated medium and coal flows allow estimates to be made of pressure drop, efflux stream medium densities and partition curves for coal particles of different sizes and densities. These estimates are compared favourably with industrial scale measurements of a 1000 mm DMC operating under similar conditions. On this base, the effect of particle density distribution that represents the major difference between two major coal type, i.e., coking coal and thermal coal, is studied. The results are analysed in terms of medium flow pattern, particle flow pattern, partition performance and particle–fluid, particle–wall and particle–particle interaction forces.

Monitoring grinding parameters by vibration signal measurement - a primary application

Grinding plays an important role on energy consumption and subsequent separation stage in a mineral processing plant. To maintain higher grinding efficiency, the operating parameters must be continuously monitored and adjusted close to the setup of the optimal operating conditions. It is difficult and expensive to trace the frequent variations of the grinding parameters by traditional methods in commercial scale operation. Since mechanical grinding emits strong vibration signals, it can be picked up by commercially available instrument in the form of time-domain waveform. The variations of the vibration signals were governed by the changes of the grinding state. A primary application was studied based on industrial scale measurements, where the mechanical vibration was picked up by an accelerometer and acoustic pressure changes by a microphone. The digitised time-domain source signals were processed by digital signal processing technique. The variable grinding parameters were the power draw, the feed rate, the pulp density, and the particle sizes of the mill feed and ground product. By principal component analysis and parameter identification, the variations of the grinding parameters were related to the changes of the source vibration signals. By vibration measurement, a new alternative could be developed for monitoring the operating parameters in grinding.