Multiple Hearth Research Articles

Residence time distribution of wood chips in a semi-industrial multiple hearth furnace using RFID tracers

In continuous biomass torrefaction plants, the products' yields, composition and homogeneity highly depend on the residence time of particles. A characterization of particle residence time distribution (RTD) was therefore carried out in an industrial-scale multiple hearth furnace on poplar wood chips using radio frequency identification tracers. The effects of operating conditions, namely, mass flow rate of biomass, shaft speed of the rabbling system and interdental length on the RTD were studied. The increase of shaft speed and mass flow rate reduces particles’ mean residence time. Lowering the length between two successive teeth also increases the bed speed. Uncontrollable biomass accumulation (also called “bulldozing”) was observed during several tests. This phenomenon is favored by a high mass flow rate of resources, a small interdental length between the teeth and a low shaft speed. RTD measurements were compared to the axial dispersion model. For all tests, the Peclet number is ranging between 20 and 62, indicating that the multiple hearth furnace cannot be modelled as an ideal plug flow reactor.

Fate of perfluoroalkyl and polyfluoroalkyl substances (PFAS) through two full-scale wastewater sludge incinerators.

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are an emerging issue in wastewater treatment. High-temperature thermal processes, incineration being time-tested, offer the opportunity to destroy and change the composition of PFAS. The fate of PFAS has been documented through wastewater sludge incinerators, including a multiple hearth furnace (MHF) and a fluidized bed furnace (FBF). The dewatered wastewater sludge feedstock averaged 247- and 1280-μmol targeted PFAS per sample run in MHF and FBF feed, respectively. Stack emissions (reportable for all targeted PFAS from MHF only) averaged 5% of that value with shorter alkyl chain compounds comprising the majority of the targeted PFAS. Wet scrubber water streams accumulated nonpolar fluorinated organics from the furnace exhaust with an average of 0.740- and 0.114-mol F- per sample run, for the MHF and FBF, respectively. Simple alkane PFAS measured at the stack represented 0.5%-4.5% of the total estimated facility greenhouse gas emissions. PRACTITIONER POINTS: The MHF emitted six short chain PFAS from the stack, which were shorter alkyl chain compounds compared with sludge PFAS. The FBF did not consistently emit reportable PFAS from the stack, but contamination complicated the assessment. Five percent of the MHF sludge molar PFAS load was reported in the stack. MHF and FBF wet scrubber water streams accumulated nonpolar fluorinated organics from the furnace exhaust. Ultra-short volatile alkane PFAS measured at the stack represented 0.5%-4.5% of the estimated facility greenhouse gas emissions.

Discrete Element Simulations of Contact Heat Transfer on a Batch-Operated Single Floor of a Multiple Hearth Furnace

The multiple hearth furnace is a common industrial reactor for the thermal treatment of particulate material. The present contribution concentrates on a numerical analysis of contact heat transfer on a batch-operated single floor of a multiple hearth furnace employing the Discrete Element Method (DEM). The particles are agitated on an electrically heated circular floor by a single rotating rabble arm equipped with three flat blades. Blade angles have been varied from 0° to 90°. The DEM simulations (particle mechanics and contact heat transfer) were validated against experimental data. The transient heating of 20 mm diameter polyoxymethylene (POM) spheres was analysed. As the simulations did not consider natural convection inherently leading to time-varying heat losses, an averaged heat loss parameter was determined to represent heat dissipation from the particles to the surrounding gas and incorporated into the DEM simulations. With this approach, a good agreement with measurements was obtained. The DEM simulations and experiments do not show a large influence of the blade angle on the temporal evolution of the mean particle temperatures. However, the frequency distribution of particle temperature is dependent on the blade angle, revealing an increase in the standard deviation of the frequency distribution with an increasing blade angle.

Experimental study on influence of blade angle and particle size on particle mechanics on a batch-operated single floor of a multiple hearth furnace

In industry, multiple hearth furnaces are used for the thermal treatment of particulate material. The current contribution concentrates on the experimental analysis of particle mechanics for a batch-operated single floor of a multiple hearth furnace. The particles are agitated on the circular floor by a single, rotating rabble arm equipped with three flat rabble blades of 10 mm thickness. The blade angle, defined as the angle, which the blade is inclined against the tangential direction, is varied from 0° to 90°. A single layer of spherical polyoxymethylene (POM) particles with three different diameters (5, 10 and 20 mm) is placed on the floor. To analyze the results, two parameters have been extracted from image analysis when the bed of particles is agitated, first, the area not covered by particles and second, the frequency distribution of the mean distance among the particles. The particle free surface area increases with the inclination of the blades. The evolution of the particle free surface area differs for the different particle diameters. In general, the maximum particle free area for all blade angles is the largest for the 5 mm particles followed by the 20 mm particles. For the 10 mm particles, the particle free surface area starts for a blade angle of 0° at larger values than for the 20 mm particles but the values fall below the values for the 20 mm particles for larger blade angles. The reason for this behavior is discussed in detail. The mean distance among the particles is a parameter characterizing the length scales dominating the effects on the floor. The frequency distribution of the mean distance among particles provides information about the morphology of the particle bulk, for example, whether the free surface area is interspersed with particles.

OPTIMIZATION DESIGN OF GRANULAR ACTIVAED CARBON USING GENETIC ALGORITHM

Integrated advanced wastewater treatment provides important fundamental solutions to problems associated with water scarcity prevailing in arid and semi arid climatic regions. This was accomplished through treated water with specific specification and characteristics suitable to be used for agricultural, domestic, and industrial purposes. This study is concerned with the use of genetic algorithm procedure for the optimum design of integrated advance wastewater treatment units, with their various types and characteristics. The aim of optimum wastewater treatment units design is to attain optimum values of certain pre defined objective function. Based on the results of applying genetic algorithm on activated carbon treatment plant, it was found that the optimum values of empty bed contact time, dose of activated carbon, diameter of contractor, and loading rate of multiple hearth furnaces are 10min, 25mg/l, 2.4m, and 30 m/min, respectively

Post-combustion artificial neural network modeling of nickel-producing multiple hearth furnace

AbstractIn a nickel-producing multiple hearth furnace, there is a problem associated to the automatic operation of the temperature control loops in two of the hearths, since the same flow of air is split into two branches. A neural model of the post-combustion sub-process is built and served to increase the process efficiency of the industrial furnace. Data was taken for a three-months operating time period to identify the main variables characterizing the process and a model of multilayer perceptron type is built. For the validation of this model, process data from a four-months operating time period in 2018 was used and prediction errors based on a measure of closeness in terms of a mean square error criterion measured through its weights for the temperature of two of the hearths (four and six) versus the air flow to these hearths. Based on a rigorous testing and analysis of the process, the model is capable of predicting the temperature of hearth four and six with errors of 0.6 and 0.3 °C, respectively. In addition, the emissions by high concentration of carbon monoxide in the exhaust gases are reduced, thus contributing to the health of the ecosystem.

The Applied Artificial Intelligence to the ControlElectronics Improving the Energy Efficiency ofVentilation Systems in the Industry

In the furnaces of multiple hearths there is a problem related to the inefficiency of the current control of the combustion air system and the energy reserves present, since manually the excess air flow is regulated, while the fans work at full capacity all the time what produces an unnecessary expenditure of electrical energy. The experimental identification of the air supply system through artificial neural networks and fuzzy logic is executed for the future implementation of a control architecture with a view to increasing the energy efficiency of said process. Several experiments were carried out: first, in a laboratory, on an air flow test bench simulating in miniature the real process with a possible closed loop that links the input variables (sensors) with the speed of the motor (actuator: speed variator) ) and second, field, on one of the actual slabs of the plant, varying the number of revolutions of the motors in a staggered way around an operating point, alternating the operation of the fans with manual adjustment of the variable speed drives that they were installed previously. Of all the configurations tested, the most energy efficient variant resulted in the use of the two fans farthest from the common manifold (seven and eight), keeping the reserve nine. The proposed artificial neural model predicts the air pressure in the collector with 98 % correlation and 71 % in its generalization.

Handling uncertainties inherited in life cycle inventory and life cycle impact assessment method for improved life cycle assessment of wastewater sludge treatment

Life cycle assessment (LCA) has been used to evaluate environmental impacts of products or processes including wastewater treatment. Uncertainty has not received adequate attention in LCA studies. Uncertainty inherited in LCA steps such as the life cycle inventory (LCI) or the life cycle impact assessment (LCIA) method use is unavoidable, but it affects LCA outcomes and associated decision-making. The objective of this paper was to show the impact of uncertainty from LCI and LCIA method on LCA outcomes by using a case study base approach on wastewater sludge treatment processes. A qualitative analysis included setting criteria about what data to be included in LCI, characterization of data, differentiating between major and minor contributors in LCI modeling, evaluation of data quality indicators, setting achievable alternative scenarios, and selecting proper LCIA method were used, in addition to quantitative analysis included assigning most appropriate values for data gaps and proper distribution, and conducting probabilistic analysis to evaluate overall uncertainty. This research used a full-scale wastewater treatment plant in Missouri, USA for case study in which multiple hearth incineration (MHI) is the existing process, while fluid bed incineration (FBI) and anaerobic digestion (AD) were proposed as the alternatives. Using ReCipe method, the study revealed that variation in LCA results of MHI is 63.4% for a single end-point score of 57.9 mPt. On the two alternative processes, it is 54.6% probable that FBI would have more environmental impact than AD. The case study showed that the proposed steps were able to address issues of data uncertainty. Due to differences in characterization, normalization, and weighting factors, different LCIA methods may point out different conclusions and need to be addressed in evaluation.

Statistical Model of The Postcombustion Subprocess in an Oven of Multiple Hearth Furnace

Nickel-producing companies are characterized by continuous processes of great complexity; that require automation to achieve...

Control strategy for a multiple hearth furnace in kaolin production

In the face of strong competition, the kaolin calcination industry is aiming at higher profitability through increased productivity and reduction of costs. Specifically, the industry is facing market demands to maintain product quality with the depletion of high-quality ore. Therefore, considerable research is being conducted to enhance existing processes and their operation and control. In this paper, the concept of a mineralogy-driven control strategy for multiple hearth furnaces for kaolin production is presented and discussed. The aim of the advanced control concept is to increase capacity and to reduce energy consumption while maintaining the desired product quality. The control is based on two main soft sensors: the spinel phase reaction rate indicator for energy use reduction and the mullite content indicator for capacity improvement. In this simulation study, the control strategy is tested and compared with an industrial controller based on a proportional–integral scheme as a benchmark. The results show that the capacity of the process is considerably improved and energy use is remarkably reduced.

Simplified Mechanistic Model of the Multiple Hearth Furnace for Control Development

Simplified Mechanistic Model of the Multiple Hearth Furnace for Control Development

Control Strategy For A Multiple Hearth Furnace

This paper presents and discusses a mineralogy-driven control strategy for a multiple hearth furnaces in kaolin production. The objective of the advanced control is to maximize capacity and to minimize energy consumption while preserving the desired product quality. The control is based on two main soft sensors: the mullite content indicator for capacity improvement and the spinel phase reaction rate indicator for energy use reduction. In this simulation study, the control strategy is tested and compared with an industrial controller based on a proportional-integral scheme as a benchmark. The results show that the capacity of the process is significantly improved and the energy use is notably diminished.

Two-Stage Thermal oxidization: A Cost-Effective, Environmentally Sound Alternative for BioEnergy Recovery from Multiple Hearth Furnaces

Two-Stage Thermal oxidization: A Cost-Effective, Environmentally Sound Alternative for BioEnergy Recovery from Multiple Hearth Furnaces

Influences of Different Components on Agglomeration Behavior of MoS2 During Oxidation Roasting Process in Air

An agglomeration of the furnace charge always takes place during the oxidation roasting process of molybdenite concentrate (with the main component of MoS2) in multiple hearth furnaces, which greatly affects the production process and furnace service life. In the present work, a preliminary study about the influence of various components on the agglomeration phenomenon of pure MoS2 have been carried out. The results show that reaction temperature, impurity content, and air flow rate have significant effects on the agglomeration extent. Meanwhile, the impurity type added into the pure MoS2 plays a crucial role. It was found that CaO and MgO have a stronger sulfur-fixing effect and that the desulphurization of the roasted product was uncompleted. It was also concluded that the agglomeration is due to the formation of low-melting-point eutectics, including that between MoO3 and impurities and that between MoO3 and Mo4O11. It is suggested that decreasing the impurities contents, especially K, Cu, Pb, and Fe, is an effective method for reducing the extent of agglomeration.

Lithic Technology at Linda's Point, Healy Lake, Alaska

<p class="Pa5" style="text-align: justify; text-justify: inter-ideograph;"><span style="font-size: 10.0pt; color: #221e1f;">Interior Alaska’s Healy Lake archaeological locality contains a cultural sequence spanning 13 500 years, beginning with some of the oldest known human occupations in Alaska. From 2011 to 2014, we conducted archaeological excavations at the Linda’s Point site. Detailed recording has clearly separated the lowest cultural component at the site and begun to clarify the contentious culture history of the Healy Lake area. The lower component, associated with a thick paleosol, contains multiple hearths, debitage, and small triangular points similar to those seen at the Healy Lake Village site. The upper silt deposits contain a variety of lithic tool types within a dense scatter of debitage and bone fragments spanning a wide time range. Linda’s Point appears to have been used as a habitation site throughout its history, changing from recurring short-term occupations in the terminal Pleistocene to more intensive site habitation and greater reliance on local lithic resources during the Holocene.</span></p>

Dynamic modelling of a multiple hearth furnace for kaolin calcination with a sensitivity analysis with respect to reaction rates

Abstract: This paper is devoted to dynamic modeling of a multiple hearth kaolin calciner. The physical-chemical phenomena taking place in the six furnace parts, including the solid phase, gas phase, walls, cooling air, rabble arms and the central shaft, are described by the model. In particular, a mixing model is developed to describe the solid phase movement, dividing the solid bed in a hearth into volumes and considering the distribution of their contents after one full central shaft rotation. Step changes are introduced to the feed rate to study the responses of the gas phase temperature and solid bed component profiles in the multiple hearth furnace (MHF). In addition, the sensitivity analysis of the temperature profile with respect to the reaction kinetics is provided.

Study of the Reasons of Emergency Shutdown of Multiple Hearth Furnace for Production of the Magnesia Binding Material

The results of chemical, mechanical and metallographic studies of elements of the design of a multiple hearth furnace from the steel 1.4837 and 1.4857 according to EN 10295: 2002 are given in order to establish possible causes of its emergency shutdown. Among the possible causes of failures of elements the following ones are considered: non-operation of the safety device, degradation of material properties, as well as development of cracks in these surfaces caused by the high temperature and force action.The study has found out that the basic chemical composition, structure, and mechanical properties of the construction material ensure normal operation of the furnace to a temperature of up to 10500С. Exceeding this temperature and periodical heating and cooling of the basic elements (thermal cycles) leads to emission of complex carbide inclusions on the dendrite boundaries. Frequent thermal cycles as well as the significant heterogeneity in distribution of non-metallic inclusions and carbides leads to degradation of material properties.While establishing causes of a failure of a safety device, the authors have found out that the increase of the gap between the sleeves results in a relatively small change in the cutoff force by increasing the proportion of normal stresses from bending. A more significant increase in the shear force occurs at the minimum cross section of the pin offset from the edge of the plane.The results of the study suggest a modification of a chemical composition of the used steel grades and change of the design of a safety device pin.

Dynamic modeling of a multiple hearth furnace for kaolin calcination

A dynamic model of a multiple hearth kaolin calciner has been developed and is presented in this article. This model describes the physical‐chemical phenomena taking place in the six furnace parts: the solid phase, gas phase, walls, cooling air, rabble arms, and the central shaft. The solid phase movement, in particular, is described by a novel mixing model. The mixing model divides the solid bed in a hearth into volumes and the distribution of their contents, after one full central shaft rotation, is identified by the pilot experiments. First, the model is validated by the industrial data, and then the dynamics of the multiple hearth furnace is studied by introducing step changes to the three manipulated variables: the feed rate, and the gas, and air flows supplied. The responses of the gas phase temperature and solid bed component profiles are analysed and the results are discussed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3683–3698, 2015

The City of Palo Alto is Applying Sustainability to Develop a 50-Year Plan for Solids Handling

The City of Palo Alto is Applying Sustainability to Develop a 50-Year Plan for Solids HandlingLong-range planning for the City of Palo Alto's Regional Water Quality Control Plant (RWQCP) considered aging infrastructure, current and future regulations, and community values in evaluation of biosolids treatment and disposal strategies. Ultimately, the decision was made to develop an implementation plan to replace the aging multiple hearth incinerator with a biosolids process that will meet...Author(s)Bob GilletteLydia HolmesSarah DeslauriersJames AllenSourceProceedings of the Water Environment FederationDocument typeConference PaperPublisherWater Environment FederationPrint publication date Oct, 2013ISSN1938-6478DOI10.2175/193864713813715913Volume / Issue2013 / 9Content sourceWEFTECCopyright2013Word count78

The Greener Solution to Biosolids Incineration: Cincinnati's Switch from Multiple Hearth to Fluidized Bed Incineration

The Greener Solution to Biosolids Incineration: Cincinnati's Switch from Multiple Hearth to Fluidized Bed Incineration