Slurry Supply Research Articles

Prediction of SO2 concentration in WFGD system based on GWO optimized CNN‐BiLSTM‐attention

AbstractDue to external disturbances, the parameters of the desulphurization system are uncertain, and their relationships are complex, which makes it difficult to predict the concentration of SO2 at the desulphurization system outlet. In this paper, grey wolf optimization (GWO) optimized convolutional neural network (CNN)‐bi‐directional long short‐term memory (BiLSTM)‐Attention algorithm was used for prediction, and the problem of low SO2 concentration prediction accuracy at outlet has been resolved. First, the outliers of the thermal power plant desulphurization data were processed using the local outlier factor (LOF) algorithm. Secondly, CNN‐BiLSTM model was constructed using CNN and BiLSTM, and attention module was added to realize feature extraction and better capture the regularity of input data. Then, the CNN‐BiLSTM‐Attention model was optimized using GWO and its hyperparameters were improved. Finally, based on the Matlab R2023a platform, the prediction comparison as well as the error analysis of the desulphurization data were carried out. In the prediction of SO2 concentration in low‐flow continuous slurry supply mode, the error of the combined model decreased by 23.2% on average compared to the CNN‐BiLSTM‐Attention model. In the prediction of SO2 concentration in the high‐flow intermittent slurry supply mode, the error of the combined model decreased by 20.8% on average. According to the results, the combined model surpasses both the single model and several other algorithmic combination models in terms of performance metrics, and the predictions are more accurate.

Control-oriented dynamic modeling and GPC for single-tower double-circulation wet flue gas desulfurization system

In China, the current situation of large-scale grid integration of renewable energy generation and the government's introduction of capacity-based electricity pricing policies have compelled coal-fired power plants to gradually enhance their load adjustment capabilities and expand their load adjustment ranges. Simultaneously, the national environmental requirements for these plants have become increasingly stringent. However, the economic control of wet flue gas desulfurization (WFGD) systems is still far from meeting practical requirements. In this paper, starting from practical engineering applications and utilizing historical operational data, considering the actual system operation process, the impact of the absorption tower variable-frequency slurry circulation pump on the concentration of sulfur dioxide (SO2) in flue gas under different slurry pH values is investigated. This led to the establishment of a dynamic model for a single-tower double-circulation wet flue gas desulfurization (SD-WFGD) system. Recognizing the significant delay and inertia characteristics of pH value control in the SO2 absorption tank, a desulfurization system pH value desulfurization capacity-based optimization control scheme for the SD-WFGD system is proposed, termed as the Direct Sulfur Control (DSC) strategy. Based on the established dynamic model, a SD-WFGD system series control system is developed using a step generalized predictive control algorithm (GPC) combined with the DSC strategy. Validation results indicate that, compared to SGPC control schemes and traditional PID control schemes, this approach reduces fluctuations in slurry supply and outlet SO2 concentration, significantly enhancing the control performance of the SD-WFGD system. This ensures the safe, stable, economical, and flexible operation of the desulfurization system against the backdrop of flexible operation in coal-fired power plants.

Center-injected Polishing for Efficient Slurry Utilization

Polishing is one of the most crucial finishing processes and usually consumes a sufficient slurry to achieve an ultra-fine surface. However, excess slurry consumption is environmentally costly, as it generates a large amount of wastewater. Given the growing environmental concerns, it is essential to improve the process efficiency and minimize the environmental burdens. Considering this, a novel polishing system, herein referred to as center-injected polishing, is proposed by injecting slurry into the center of the polishing pad. Here, it is aimed to utilize the centrifugal force of the rotating pad, with the aim of efficient slurry utilization. The slurry is directly introduced between the pad and the workpiece, then dispersed across the pad by centrifugal force. A simple experiment was conducted with computational analysis using the specially designed polishing tool to prove the concept; slurry was distributed more uniformly in center-injected polishing when compared to the conventional process. The polishing system was then constructed to evaluate polishing performances. Based on sets of experiments in the polishing of silicon carbide (SiC), slurry efficiencies and productivity were analyzed with respect to different rotational speeds and slurry supply rates. The material removal rate (MRR) was more than twice the rate achieved by conventional polishing at the same processing conditions; whereas the slurry consumption was approximately 60% less at the same MRR. The extended Preston equation was used to predict the MRR of the new process. It is expected that efficient slurry utilization will reduce the environmental footprint of abrasive processes.

Oxidation-free thiourea leaching of gold uthig sulphur dioxide

The paper summarizes research on gold recovery by the Carbon in Leach (CIL) process using thiourea by feeding sulphur dioxide by a hydroacoustic emitter. It was found that the use of such a device favors the formation of the radical OH*. The latter is the strongest oxidizing agent. One of the main regulated parameters of the plant is the pressure of pulp supply to the inlet device, which was studied. According to the results of the study, it was found that a high degree of gold recovery is achieved under the following conditions: initial concentration of H2SO4 – 0.5%, thiourea loading – 1.5 kg/t, coal loading 10 g/kg, sulphur dioxide feed –0.13 kg/t*min, ratio L:S – 1:3, slurry supply pressure to the inlet – 1.5 atm, CIL process time – 60 min. Thiourea consumption amounted to 0.57 kg/t, and sulphur dioxide – 8 kg/t. Gold recovery reached 93.5%.

Enhancing deep learning for the comprehensive forecast model in flue gas desulfurization systems

The sulfur dioxide (SO2) emissions contribute to severe environmental pollution and respiratory problems, which make the limestone–gypsum wet flue gas desulfurization (WFGD) an increasingly important issue. The WFGD system consists of the flue gas system, the limestone slurry supply system, the oxidation air supply system, and the gypsum slurry discharge system, which have the characteristics of multivariable coupling, high dimension, nonlinear, large delay, and difficulty for parameters measurement, bringing great challenges and limitations for the traditional mechanism modeling of the WFGD system. To solve those issues above, in this study, an enhancing modeling method that integrates feature fusion and deep learning is proposed to predict the dynamics of SO2 emission in a WFGD system. Aiming at the problem that most of the existing modeling methods cannot fully and accurately extract the hidden features in WFGD system data, the convolutional neural network (CNN) method is responsible for extracting multiple spatial features including the local and global spatial features from WFGD system data, and the long short-term memory (LSTM) method mines the temporal relationship from the previous and current state of the WFGD system. Finally, the attention mechanism (AM) method is enhanced for the effective improvement of crucial information. Taking an actual coal-fired boiler as an illustration, the SO2 emissions at different time steps are predicted. The experiment results reveal that the proposed CNN-LSTM-AM model can fully and accurately extract system features and outperform other approaches in terms of prediction accuracy.

Slurry Conditions for Reaction-Induced Slurry-Assisted Grinding of Optical Glass Lens

The demand for optical glass lenses is rising owing to the increase in image resolution. Optical glass is a hard and brittle material. Thus, an efficient and precise grinding method is required for optical glass to improve lens quality and productivity. There are a few methods of producing crack-free machined surfaces; however, they provide only limited grinding efficiency. To resolve this issue, the authors’ group has proposed the reaction-induced slurry-assisted (RISA) grinding method, which expands the range of ductile-regime grinding by utilizing the chemical–mechanical action of a cerium oxide slurry. In this study, the grinding performance of RISA grinding is experimentally evaluated for different pH levels. The results are compared using Tukey’s test, where surface roughness is considered as the characteristic value and the pH value as the analyzed factor. The result shows that RISA grinding efficiently produces a high-quality surface when the slurry is alkaline. The adhesion of cerium oxide abrasives to the wheel in RISA grinding follows the same mechanism as slurry aggregation. In addition, adhesion is more likely to occur when the alkalization of the slurry promotes aggregation. The tank in the slurry supply unit is replaced with a rotating tank to ensure stable RISA grinding with a highly aggregable slurry while preventing aggregation. The performance evaluation shows that a high-quality surface with a surface roughness of less than 10 nm in most parts is obtained. Moreover, the critical depth of cut stably increases by a factor of 5.8.

Farmers’ willingness to engage in a deposit-refund system for animal manure in biogas production: A discrete choice experiment in Germany

This article reports the results of a discrete choice experiment with 101 German livestock farmers designed to establish the factors affecting the respondents’ acceptance of a deposit-refund system for animal manure. Farmers entering into a manure supply contract with a biogas plant would offer their entire slurry to the plant and pay a deposit which is refunded if and when the farmer takes back the same quantity of nutrients as initially supplied. Such a system can secure the supply of slurry for biogas plants and help farmers reduce greenhouse gas and ammonia emissions. A mixed-logit model revealed a very high overall willingness to participate in such a scheme. The average probability of participation is 70%. With an average of 73% of nutrients taken back the deposit-refund system can be a good way to distribute nutrients regionally. The remaining nutrient quantities are transferred to crop farms - if necessary for a fee, financed by the retained deposit. Low deposit rates and cost-reducing complimentary services offered by the biogas plant in the field of nutrient management improve participation. Free slurry storage with a WTP of €4.15 per m3 and free digestate spreading with a WTP of €7.14 per m³ can be very effective in enticing farmers into the scheme. Less tangible services such as the certification of greenhouse gas reductions appear less important for participation decisions. While high deposit amounts could increase nutrient redemption or additional intake, the probability of choice decreases as the amount increases. Based on the simulated acceptance rate, 8–10 €/t seems to represent a critical deposit level up to which a high probability of participation can be achieved.

A Novel Polishing Method for Extending the Service Life of Magnetic Compound Fluid

Magnetic field-assisted magnetic compound fluid (MCF) ultra-precision machining technology is regarded as an effective method to obtain a smooth surface. However, due to the evaporation and splashing of water in the polishing fluid during processing, the service life of the MCF slurry is reduced. This paper presents a material removal model for MCF polishing, and a novel experimental apparatus is proposed to extend the service life by supplying MCF components into the MCF slurry. Firstly, in order to obtain the ideal polishing tool, the appearance morphologies and the formation process of the MCF slurry were observed by an industrial camera. On this basis, the optimum parameters were determined by multi-factor and multi-level orthogonal experiments. Finally, the investigation of the MCF service life was carried out under the optimal processing parameters. The main findings are summarized as follows. (1) Excellent MCF polishing tools are obtained when the eccentric distance r is 4 mm and the MCF slurry supply V is 1 mL. (2) When the eccentric distance increases from 2 mm to 4 mm, the forming time of the MCF tool decreases sharply, but when the eccentricity exceeds 4 mm, the decreasing trend becomes slow. The molding time grows steadily as the supply is increased. (3) When the machining gap Δ, the MCF carrier speed nc, the eccentricity r, and the revolution speed of magnetic nm are 1 mm, 500 rpm, 4 mm, and 600 rpm, respectively, the ideal machining effect can be obtained. (4) It could be proven that the polishing device is feasible to extend the service time of the MCF slurry by adding MCF components.

Novel method to visualize Preston’s coefficient distribution for chemical mechanical polishing process

Preston’s law is widely used in polishing simulations in which the distribution of Preston’s coefficients on an entire wafer surface is generally assumed to be uniform. However, it is more likely that the distribution is not uniform and depends on several factors. To clarify Preston’s coefficient distribution in chemical mechanical polishing (CMP), we propose a novel experimental technique. In the proposed method, the unique experimental approach “stop polishing,” where the wafer does not rotate, and thus the circumferential variation of the coefficient is not averaged, is applied. Oxide-CMP experiments verified the uneven Preston’s coefficient distribution depending on the distance from the pad rotation center. Furthermore, we investigated the influence of slurry supply position on Preston’s coefficient distribution, and clarified that the distribution depends on slurry flow condition. Therefore, the proposed method is expected to be a novel tool for analyzing the CMP process from the perspective of Preston’s coefficient distribution.

Origins of wear-induced tungsten corrosion defects in semiconductor manufacturing during tungsten chemical mechanical polishing

During chemical mechanical polishing (CMP) process optimization, a unique corrosion defect was identified in the tungsten (W) contact plugs, which were investigated to develop practical solutions to improve CMP mass productivity. The corrosion defect occurred in the absence of external incident energy and was observed to occur only at the W plugs connected to the P+/n-well close to the wafer edge. To examine the root cause of the corrosion, a series of experiments was carried out at each W CMP step, using in-line defect inspection. Additional experiments were conducted using on-line inductively coupled plasma mass spectrometry (ICP-MS) to understand pH- and potential-dependent electrochemical dissolution behaviors of W. Experimentally, W corrosion was confirmed to be exacerbated if the surface oxide of the W plugs is removed by the deionized water (DIW) rinsing step under wafer pressurization, then exposed to DIW and alkaline cleaning solution. Although the DIW rinsing step is commonly performed to clean polishing pads right after the main polishing, a small amount of applied pressure (0.5 psi) without slurry supply can lead to corrosion defects. This wear-induced corrosion of the W plugs can be prevented by removing the applied pressure during the post DIW rinsing step of W CMP.

Simulation and Experimental Investigation of the Radial Groove Effect on Slurry Flow in Oxide Chemical Mechanical Polishing

Slurry flow on the pad surface and its effects on oxide chemical mechanical polishing (CMP) performance were investigated in simulations and experiments. A concentric groove pad and the same pad with radial grooves were used to quantitatively compare the slurry saturation time (SST), material removal rate (MRR), and non-uniformity (NU) in polishing. The monitored coefficient of friction (COF) and its slope were analyzed and used to determine SSTs of 25.52 s for the concentric groove pad and 16.06 s for a certain radial groove pad. These values were well correlated with the simulation prediction, with around 5% error. Both the laminar flow and turbulent flow were included in the sliding mesh model. The back mixing effect, which delays fresh slurry supply, was found in the pressure distribution of the wafer–pad interface.

An Analysis of the Formation Mechanisms of Abrasive Particles and Their Effects on Cutting Efficiency

Magnetic induction-free abrasive wire sawing (MIFAWS) is a method that combines magnetic fields with traditional free abrasive wire sawing technologies. Magnetic abrasive particles (MAPs) are attracted on a magnetized wire, thus leading to an increase in their number into the cutting zone. The number of instantaneous-effective abrasive particles (IEAPs) adsorbed on the wire surface has a great influence on the cutting efficiency of the saw wire. In this study, a mathematic model of the movement of the MAP is presented, and the factors influencing the IEAPs number, including slurry-supply speed and slurry dynamic viscosity, are investigated both by means of simulation analysis and experiments. The results indicate that the number of IEAPs decreases with an increase in the slurry supply speed. The cutting efficiency increases gradually with the increase of slurry supply speed, but the growth rate of wire saw cutting efficiency slows down when the slurry supply speed exceeds a given threshold. The number of IEAPs adsorbed by saw wire increases with a decrease in the dynamic viscosity of the cutting fluid, while the cutting efficiency first increases and then decreases. The cutting efficiency attains its highest value when the dynamic viscosity of the cutting fluid is 0.0047 Pa⋅s. The experimental results agree with the simulation results, and provide some guidance for the practical application of the MIFAWS process.

Investigation of 2-Way Injection Method on Cu CMP Process

Chemical mechanical polishing (CMP) is one of the process for planarization in semiconductor manufacturing. With the decrease of device size, copper (Cu) has been accepted as the material of interconnect for good performance. After electroplating process of Cu, overburden Cu surface is polished for planarization using CMP process. Generally, oxidants, dispersants, abrasive particles, chelating agents, and corrosion inhibitors are used in the Cu CMP slurry, and planarization of Cu is achieved by reaction of slurry components. Hydrogen peroxide is one of the oxidants which is widely used in Cu CMP slurry and react with Cu surface to form a passivation layer. In general, it is known that hydrogen peroxide is easily decomposed in the alkaline state. Therefore, in the alkaline slurry, decomposition of hydrogen peroxide can occur, which leads to deterioration of CMP performance.In this study, a new slurry injection method is proposed as an alternative to prevent the decomposition of hydrogen peroxide that may occur when hydrogen peroxide and slurry are mixed. The concentration of hydrogen peroxide decreased when hydrogen peroxide and slurry are mixed, and accordingly, the removal rate decreased (Fig. 1(a)). It indicates that hydrogen peroxide is decomposed in alkaline state, and this affects the CMP performance. In order to prevent the decomposition of hydrogen peroxide, hydrogen peroxide and slurry were separately injected (2-way injection) during the CMP process. Fig. 1(b) shows the comparison of the removal rate between the general method and the 2-way injection method in the slurry supply system. As shown in the graph, when using the 2-way injection method, the removal rate is almost similar to that of the general injection method. Therefore, the 2-way injection method can replace the general injection method.Figure 1. (a) the removal rate and concentration of hydrogen peroxide with slurry aging time, (b) the removal rate of general and 2-way injection method Figure 1

Hybrid CMP Slurry Supply System Using Ionization and Atomization

Chemical mechanical planarization (CMP) is frequently used in semiconductor manufacturing to polish the surfaces of multiple layers in a wafer. The CMP uses a slurry that aids in fabricating a smooth surface by removing the excess materials. However, excessive use of slurry affects the environment and is expensive. Therefore, we propose a hybrid slurry supply system that combines ionization and atomization to reduce slurry consumption and improve the polishing quality. The proposed hybrid system atomizes the ionized slurry using electrolysis and a spray slurry nozzle. We compared the material removal rate (MRR) and polishing uniformity based on the slurry supply systems used in Cu and SiO2 non-patterned wafers. Additionally, the step height reduction and dishing were compared in the Cu-patterned wafers. The experimental analysis using the hybrid system confirmed a 23% and 25% improvement in the MRR and uniformity, respectively, in comparison with the conventional slurry supply system. This improvement can be attributed to the chemical activation and uniform supply of the ionized and atomized slurries, respectively. Moreover, a significant reduction was observed in dishing and pitch-size dependence. Furthermore, the proposed system prevents heat accumulation between the CMP processes, serving as a cooling system.

Preliminary preparation of water supply system for the headbox through Pulsar water treatment plant

Today, the main quality criterion in the production of fiberboards is a uniform supply of mixed wood fiber slurry to the mesh part of the press using a high pressure headbox. The interaction of water, various inclusions of waste water, wood-fiber semi-finished product, as well as stainless steel provokes occurrence of chemical reactions that cause intense corrosive destruction of working parts of the inlet. At present, the study of corrosion of the inlet structure pursues the goal of determining characteristic factors caused by the aggressive environment arising at the time of mixing the wood-fiber suspension with the water flow. The analysis of fiberboard production by the wet method examines the possibility of introducing equipment designed for high-quality water treatment with the possibility of cleaning it from various impurities. Pulsar water treatment system is designed for oxidation of soluble metals with their conversion into filterable forms, cleaning from organic and inorganic contaminants due to filters of soft and coarse cleaning using AS sorbents. The station operates autonomously with control of the output gravity for up to 10 years with annual losses of no more than 10% of filter elements.

슬러리 공급 조건에 의한 패드 온도 분포의 변화

슬러리 공급 조건에 의한 패드 온도 분포의 변화

Use of Air Cooling Method for Slurry Cooling for WPA Production Units

One of the most important issues in wet phosphoric acid technology is maintenance of the set temperature of slurry. Excess process heat is taken away mainly by evaporation of water from slurry. There are two main ways of cooling – evaporation under vacuum and air cooling method. Both ways have advantages and disadvantages. The main advantages of air cooling method are: it’s rather simple, and requires low capital cost for implementation, use of cooling water for condensation of secondary steam is excluded, cooling tower isn't required for cooling water, etc. Since 1980-s JSC “NIUIF” is engaged in elaboration and improvement of air cooling systems for slurry cooling. As a result of these researches air cooling units of various types for dihydrate and hemi-hydrate processes of WPA were constructed. Use of air cooling method is an essential part of elaborated by JSC “NIUIF” hemi-hydrate WPA process technology from Kola apatite concentrate, as well as high-temperature dihydrate process from Karatau phosphate rock which are carried out at temperatures of 90-94°C. Modern system of air cooling is comprised of: low pressure (LP 800-1000 mm) slurry supply axial pump of high capacity (5000-10000 m3/h), air cooling unit, FDF and/or IDF. Due to optimization of heat&mass exchange conditions and design of air cooling unit (ACA), moisture saturation of cooling air can be achieved up to high extent (up to 400 g/kg of dry air) that allows to minimize its consumption. High consumption of slurry for cooling provides rather low gradient of temperatures (∆t ≤ 3°C) at inlet and outlet from ACA and rather low manual labor efforts for cleaning of the equipment from incrusting sediment. The loop of supply for cooling can be combined with circulation loop inside the reactor that contributes to homogenization of slurry in reactionary volume. Air cooling units for slurry cooling based on researches by JSC “NIUIF” are successfully introduced at modernized and newly constructed WPA systems in Russia, Belarus, Kazakhstan, Lithuania. WPA single line process system capacity with air cooling of reactors reaches 1500 tpd of Р2О5.

Study on Performance Optimization of Wet Desulfurization of an Ultra-low Emission Coal-fired Power Unit

The operation mode of slurry recirculation pump and the limestone slurry feed were optimized in order to reduce the power consumption and material consumption of the wet flue gas desulfurization facility in a 330MW ultra low emission coal-fired power unit. The results show that the electricity consumption of WFGD has decreased by optimizing the operation mode of the slurry recirculating pumps. The operating current of the slurry recirculation pumps decreased by 33.25A on average and the electricity charge could be saved 441,000 yuan per year. A feed-forward PID control strategy of limestone slurry feed has been successfully used in the WFGD. A desired tracking performance is achieved and the limestone slurry supply was reduced by 0.0187 ton/(ten thousand of kWh).

Study on polishing slurry waste reduction in polishing monocrystalline silicon based on ultrasonic atomization

It is found that in order to ensure the polishing slurry involved in polishing process is sufficient, the supply of polishing slurry has to be excessive in conventional polishing process. However, actually only a limited amount of polishing slurry is involved in polishing process compared with the supplied polishing slurry, and the overwhelming majority is directly discharged which increases waste emissions. On the other hand, the issue of industrial waste is increasingly attracting scientific and public attention due to the magnitude of the problem in China, and various types of polishing slurries will cause serious pollution to rivers and soils. This paper focuses on a novel and successful polishing slurry waste reduction method which realizes waste reduction on the premise of ensuring the polishing performance. The proposed method is based on ultrasonic atomization, which can make the polishing slurry with low supply rate form a soft and low velocity fine mist spray and realize the even distribution of abrasive particles in slurry, and is called ultrasonic atomization polishing. In order to prove the feasibility of this waste reduction method, this paper has proved that (i) the introduction of ultrasonic atomization contributes the improvement of surface quality and polishing efficiency and (ii) ultrasonic atomization polishing can greatly realize polishing slurry waste reduction, moreover, multi-objective optimization scheme of polishing parameters for ultrasonic atomization polishing is obtained, which are all of great significance to guide the waste reduction in actual production.

Slurry Supply Mechanism Utilizing Capillary Effect in Chemical Mechanical Planarization

A novel slurry supply mechanism that utilizes the capillary effect was designed. In the mechanism, a fiber array is positioned on the pad, and the slurry is evenly distributed along the radius of the pad by exploiting the capillary effect. Setting the proper height of the slurry supply mechanism from the pad surface and grooves enables selective slurry supply only to the pad surface, so that old slurry fallen into the grooves does not mix with newly supplied slurry. Experimental evaluation revealed that, in the case of concentrically grooved pads, the removal rate did not differ significantly between the proposed slurry supply mechanism with fiber array and the point-use supply mechanism. In the case of polishing pads with orthogonal grooves, the removal rate of the proposed mechanism using a wafer of 300 mm in diameter at a slurry supply rate of 50 ml/sec was greater than that of the conventional slurry-nozzle supply mechanism. Finally, in the case of pads with orthogonal grooves deepened from 0.5mm to 0.7mm, the proposed mechanism again had a higher removal rate than the conventional mechanism. It was demonstrated that the proposed slurry supply mechanism made efficient use of slurry for polishing.