Caking Mechanism Research Articles

Granular fertilizer caking: A research on the performance evaluation of coating agents

Caking formation in fertilizer products during handling and storage is a frequently encountered problem. Caked fertilizers become together as lumps, lose their free- flowing properties, and create inefficient applications. Several parameters such as relative humidity and temperature of the environment, pressure by pile height, and physicochemical properties of fertilizer product such as moisture content, presence of fines and chemical composition, etc. cause or accelerate caking mechanism. Internal or external anticaking products have been proved to be effective in preventing the caking of fertilizer particles. Liquid or wax anticaking agents are applied externally as coatings on the fertilizer surface. This study focuses on the performance evaluation of commercially available liquid- wax anticaking agents coated on NP 20-20-0 fertilizer, classified as three main groups: petroleum-derived, alkyl amine-fatty acid containing mixtures and bio- based composition. Caking performance of coating products are evaluated via small-bag storage test in 4 sets, according to the results, petroleum derived and alkyl amine- fatty acid containing anticaking products show similar performance, whereas bio-based products’ performance is moderate. This study focuses on a practical approach that will help fertilizer industry about which type of coating product will be effective on the anticaking properties of nitrogenous fertilizers and gives brief results of the effect of commercially available products with various ranges of chemical composition on the caking process.

Understanding Caking Phenomena in Industrial Fertilizers

One of the most important problems of the fertilizer industry is that fertilizers show caking tendency during transportation and storage. Caking occurs as a result of interaction at the contact points formed between solid fertilizer particles. These interactions, also called contact mechanisms, are activated by a number of properties that fertilizers have and by environmental conditions. Prevention of caking mechanism is a substantial research subject that directly affects the quality and financial value of the final product and ensures its applicability. Fertilizer in good quality can provide ease in agricultural applications, and directly affect plant nutrition and crop productivity. At this point, there are various promoter practices for obtaining the free-flowing property in fertilizers that can be maintained or suggested during or after production, both in industry and in R&D studies. In order to develop new process control points in the industry, it is important to understand the factors that cause caking and the mechanism of physicochemical interactions that progress depending on these factors. In addition, it is essential to improve the storage conditions of the fertilizer, as well as to maintain its quality until end-use. This paper focuses on the caking behavior of fertilizers in detail, giving brief information about the prevention of caking and various types of anticaking agents.

Improving the Coke Property through Adding HPC Extracted from the Mixture of Low-Rank Coal and Biomass

To effectively utilize low-rank coal and biomass in the coking process, through the dissolution method, hypercoal (HPC) was produced, and its performance as an additional component in the coking process was also investigated. The cold strength of coke was tested using an I-type tumble tester and a universal testing machine; the carbon structure of the HPCs was examined via thermogravimetry (TG), X-ray diffraction (XRD), and Fourier transform infrared spectrometry (FT-IR) analyses. The results revealed that the thermoplastic properties of HPCs and the coke cold strength increased compared to raw coal. There is a positive linear relationship between the cold strength of coke and the order degree of the HPCs. As the biomass amount increased, the order degree of the HPCs greatly decreased, resulting in a decrease in the coke cold strength. When the amount of biomass was 20%, the caking index (G), drum strength, and compressive strength achieved maximum values of 95.21%, 83%, and 7.13 MPa, respectively. In addition, a caking mechanism of the HPCs is proposed.

Modification mechanism of caking and coking properties of Shenmu subbituminous coal by low-temperature rapid pyrolysis treatment

Shenmu (SM) subbituminous coal without caking property was treated by low-temperature rapid pyrolysis (LTRP) to modify its caking and coking properties. The treated samples were characterized by Fourier transform infrared spectrometry, vitrinite reflectance, and X-ray diffraction to determine the modification mechanism. Moreover, caking index (G) and coking indices (mechanical strength, coke reactivity, and coke strength after reaction) were employed to evaluate caking and coking properties, respectively. The results showed that SM coal was gradually upgraded with increasing processing temperature. Furthermore, the G values for the treated samples were significantly higher than that for SM coal, and G reached the maximum value at 450 °C, implying the modification of caking property and the existence of an optimum temperature (450 °C). Additionally, laboratory coking determinations showed that LTRP increased the mechanical strength of coke and coke strength after reaction and decreased coke reactivity when the treated coals were used in the coal blends instead of raw SM coal. Overall, LTRP treatment is effective to improve the caking and coking properties of SM coal. A mechanism was proposed for the modification. Suitable upgrading degree with suitable molecular masses and some releasable hydrogen-rich donor species present within the coal, which dominate the development of caking property, is important.

Caking of crystals: Characterization, mechanisms and prevention

Caking of crystals leads to a great deal of negative impact on the quality of products leading to extra cost to restore the products to its original state before caking. It is therefore an undesired phenomenon that should be investigated and inhibited. This review considers particle issues (particle science and technology) in a crystallization view (crystallization science and engineering). 1. Characterization. Caking indices and the relevant characterization methods are classified. Their advantages and disadvantages are summarized. Particularly, potential novel characterization methods, e.g. image analysis technique and its application in analysis of caking ratio, are discussed. 2. Mechanisms. Caking process is organized into three stages: moisture sorption, then liquid bridge, and finally crystal bridge. The mechanisms are reconsidered with recent studies (e.g. mass transfer, adhesion effect of liquid bridge, kinetic of crystal caking) and crystallization science (e.g. nucleation and growth theory, polymorphism, and phase transition). 3. Prevention. Based on particle and crystal engineering, prevention of crystals caking is discussed through controlling ambient conditions (relative humidity, temperature, liquids screening, and pressure) and improving anticaking property of crystals (particles size, particles shape, impurity, and anticaking agent). A potential method of simulating crystal caking behavior based on discrete element method (DEM) and caking mechanisms is presented. With the aid of simulation, the enhanced design of particle and crystal engineering would be available, which could be a key to control these factors systematically.

Assessment of surface caking of powders using the ball indentation method

Powder caking is a ubiquitous problem, which could significantly decrease product quality and lead to economic losses. Hence it is important to know the conditions under which it occurs. The caking behaviour of three powder materials (PVP, HPC and CaHPO4) has been investigated by the ball indentation method (BIM) as affected by relative humidity (RH), temperature and time. The resistance to powder flow, as indicated by the hardness is measured by a ball indenting the powder bed surface. The surface hardness increases with increasing RH and temperature, indicating caking of the powder bed. Moreover, the temperature and RH show a coupled effect on powder caking. Irreversible caking is formed in PVP and HPC at 75% RH; the particles coalesce and the volume of powder bed is significantly reduced with time. However, the caking of CaHPO4 is reversible. To examine the caking mechanism of PVP and HPC, the critical glass transition RH is determined at 25°C and 45°C. The values are 63% and 53% RH for PVP and 61% and 50% RH for HPC, respectively. The glass transition moisture content in the ball indentation experiments is comparable with that determined by the dynamic vapor sorption measurement. BIM could be a fast and effective method for the assessment of powder surface caking.

Storage-induced caking of cocoa powder

Cocoa powders are highly subjected to caking, a phenomenon of solid particles agglomeration that impairs powder functionalities such as rehydration and flowing properties. This study aimed at identifying the main caking mechanisms occurring during storage of cocoa powders, according to their fat content and water activity, as well as storage temperature. The formation of caked powder was monitored at macroscopic scale by sieve analysis, showing that caking was significant only for fatty powders at 40 °C, in agreement with a caking mechanism controlled by fat melting. The similarity of results obtained at 0.2 and 0.7 water activity indicated that the humidity caking mechanism was not significant for these powders. Observations performed by TEM evidenced the formation of fat bridges, confirming the occurrence of the fat melting mechanism. Then, solvent extraction techniques designed to quantify fat fractions permitted to highlight that storage caused the conversion of encapsulated fat into free fat. At temperatures sufficient to melt cocoa fat (40 °C), this newly formed free fat migrates toward cocoa particle surface, enhancing its fat coverage, hence making cocoa particle sticky and prone to cake. Finally, XPS analysis of the extreme surface of cocoa powders confirmed that two conditions should be met to trigger significant cocoa powder caking: high fat content and elevated storage temperature.

Caking and adhesion free energy of maltitol: Studying of mechanism in adhesion process

Caking is a common phenomenon of maltitol that causes problems of separation, processing and transportation. To study the mechanism of caking, method of capillary rise was used to measure the contact angles between maltitol particles and relevant liquids. Based on the calculation of adhesion free energy of maltitol particles in different liquids by Lifshitz–van der Waals acid-base theory, the relationship between adhesion free energy and the maltitol particles size has been established. It is concluded that the adhesion free energy of maltitol with rinsing liquid plays a key role in caking. When the adhesion free energy is higher than a critical value (about 60mJ/m2), the repulsion between the particles can avoid caking. In general, the adhesion free energy depends on the rinsing liquid used and maltitol particles size. The adhesion free energy increases with increasing the particles size of maltitol and type of liquids (water, ethyl acetate, formamide, ethylene glycol, ethanol, methanol in sequence). Hence, controlling particles size distribution and screening of rinsing liquid are crucial factors to avoid caking.

Understanding Powder Caking as a Consequence of a Range of Mechanisms by Means of Powder Rheometry

Over 70% of materials in the food, chemical, and pharmaceutical industries (from raw materials, additives, and intermediates through to manufactured products) are supplied as relatively free-flowing powders, intended to be suitable for the manufacturing process or final application. For logistical reasons however these materials will often have to be stored for extended periods during which time some powders have the potential to gain strength due to prolonged and undisturbed particle/particle interactions. This is generally referred to as “caking” and can significantly limit the ability of a powder to pass through the process train without interruption as well as detrimentally impacting product quality.This paper will present case studies that evaluate the flow properties of different powder systems that are affected by chemical-, moisture-, and temperature-based caking mechanisms. It will show how the propensity to cake can be effectively quantified with respect to the powders’ flow properties and how this can assist in understanding and adapting the processing environment to retain optimal processability.

Influence of environmental conditions on caking mechanisms in individual amorphous food particle contacts

Caking of amorphous powders creates severe problems such as product loss and additional costs in the food industry. Among the main factors causing this unwanted agglomeration process are fluctuations of the environmental conditions, that is, a rise in temperature and humidity. There is correspondingly a need to identify and, if possible, avoid the environmental conditions inducing strong interparticle cohesion based on particle contact mechanisms like viscoelastic flattening and sintering. For this reason, a novel micromanipulation approach focusing on the interactions between individual amorphous food particles in contact under load in a controlled environment is introduced. It was possible to identify the dominant caking mechanism under defined conditions, such as temperature and humidity, particle deformation, as well as contact holding time, and to quantify interparticle cohesion. Furthermore, the mechanical behavior of rubbery spherical model particles is presented and a theoretical approach to describe the contact zone formation kinetics is proposed. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2774–2787, 2014

The Use of Atomic Force Microscopy in Investigating Particle Caking Mechanisms

AbstractSpray‐dried materials are being used increasingly in industries such as food, detergent and pharmaceutical manufacture. Spray‐dried sodium carbonate is an important product that has a great propensity to cake; its moisture‐sorption properties are very different to the crystalline and amorphous species, with a great affinity for atmospheric moisture. This work demonstrates how the noncontact surface analysis of individual particles using atomic force microscopy can highlight the possible mechanisms of unwanted agglomeration. The nondestructive nature of this method allows cycling of localised humidity in situ and repeated scanning of the same particle area. The resulting topography and phase scans showed that humidity cycling caused changes in the distribution of material phases that were not solely dependent on topographical changes.

Visualization of the Caking Behavior Between Two Powder Particles

The handling of powders in industry has been laden with problems caused by caking during storage and handling, whereby free flowing materials are transformed into lumps and agglomerates. It is of great importance for the manufacturers of bulk solid products to know whether and under what conditions the products are prone to cake. The objective of the work in this paper was to visually investigate the influence of relative humidity (RH) and humidity cycling on the caking behavior of powder particles in contact and to interpret the caking mechanism. A light microscope equipped with a digital camera was used to visually observe the caking of two particles in contact over time by taking a series of photographs. The following four food powders were studied: maltodextrin DE 21, sodium chloride (NaCl), skim milk powder (SMP), and a baby food powder. The maltodextrin and the baby food powders behaved similarly with sinter bridge formation being the caking mechanism. The NaCl and SMP behaved similarly with the caking mechanism being due to water bridge formation and solid bridge formation during low humidity exposure when the water vaporized leaving behind the dissolved solids in the bridge.

Comparing the caking behaviours of skim milk powder, amorphous maltodextrin and crystalline common salt

This work examined and compared the caking behaviour of three physically and chemically different food powders. The food powders studied were maltodextrin DE21 which is an amorphous powder, common salt which consists of crystalline NaCl, and skim milk powder (SMP) which contains a mixture of components including 51% lactose. The three powders were all exposed to high relative humidities (76% or 100%) over a 1-week period and to a humidity cycle to investigate their caking behaviour and interpret their caking mechanisms. The humidity cycle consisted of 2-day exposure to a high relative humidity (RH) followed by 2-day exposure to low RH of 11% and finally 2-day exposure to the original high RH. At the end of each day, cake strength was measured using a force displacement tester and cake water content was also measured. All three powders sorbed much water when exposed to high relative humidities; however, their cake strengths were very different. Cake strength was influenced by glass transition and the ability of the powders to form sinter bridges. All three powders had similar water content profiles during the humidity cycle with water gain at high RH and loss at low RH. The cake strength profile of the amorphous maltodextrin powder and amorphous SMP were different even though the maltodextrin and lactose glass transition temperatures were reduced below the powder temperature during exposure to high RH. The cake strength of maltodextrin decreased during low RH exposure while it increased for SMP. The cake strength profile of the SMP was similar to the crystalline NaCl. The paper presents an interpretation of the caking mechanisms behind the caking behaviour of each powder.

Aggregation and Caking Processes of Granular Materials: Continuum Model and Numerical Simulation with Application to Sugar

Aggregation and caking of particles are common severe problems in many operations and processing of granular materials, where granulated sugar is an important example. Prevention of aggregation and caking of granular materials requires a good understanding of moisture migration and caking mechanisms. In this paper, the modeling of solid bridge formation between particles is introduced, based on moisture migration of atmospheric moisture into containers packed with granular materials through vapor evaporation and condensation. A model for the caking process is then developed, based on the growth of liquid bridges (during condensation), and their hardening and subsequent creation of solid bridges (during evaporation). The predicted caking strengths agree well with some available experimental data on granulated sugar under storage conditions.

Aggregation and caking processes of granular materials: continuum model and numerical simulation with application to sugar

AbstractAggregation and caking of particles are common severe problems in many operations and processing of granular materials, where granulated sugar is an important example. Prevention of aggregation and caking of granular materials requires a good understanding of moisture migration and caking mechanisms. In this paper, the modeling of solid bridge formation between particles is introduced, based on moisture migration of atmospheric moisture into containers packed with granular materials through vapor evaporation and condensation. A model for the caking process is then developed, based on the growth of liquid bridges (during condensation), and their hardening and subsequent creation of solid bridges (during evaporation). The predicted caking strengths agree well with some available experimental data on granulated sugar under storage conditions.

Moisture-induced caking of boric acid powder

There is a need to establish a caking test that gives a measure of the caking propensity of powders due to the presence of moisture in a relatively short time. A suitable test has been developed for materials that cake by the partial dissolution and recrystallisation of material to form solid bridges between particles. Boric acid (H 3BO 3) has been used as a candidate material due to its modest tendency to cake. The developed test involves addition of a specific amount of water to a powder, and then subjecting the contained powder to temperature cycling. The amount of water for addition is determined by independent measurement of the equilibrium moisture sorption isotherm. A caking index can be obtained by comparing the mass of cake formed to the mass of original sample. Tests in which the temperature of the sample was held constant yielded cakes that were comparable in size and strength to the cakes formed during temperature cycling. This interesting anomaly has been explained by the enhanced solubility of submicron surface features. The resulting supersaturated solution promotes crystal growth on surfaces of larger radii of curvature. This phenomenon can be termed Ostwald caking after the analogous process of “ripening” during crystallisation processes. Evidence to support this proposed caking mechanism has been gathered by scanning electron microscopy (SEM), by inducing caking in boric acid by condensation of water from the vapour phase at constant temperature, and by visualizing the disappearance of submicron surface features after exposure to humid air, using atomic force microscopy (AFM).

重炭酸ナトリウムの固結メカニズ

Sodium bicarbonate easily forms cakes during the storage and / or transport process after production, due to the influence of conditions such as humidity, temperature, compaction etc. Caking causes serious degradation of the material in the commercial value. To overcome the problem, the caking mechanism must be clarified first, and thereafter the effective treatment should be considered to avoid caking. Weak caking strength of sodium bicarbonate powder at the initial stage of caking was measured and evaluated in relation to amounts of various components and physical properties of the powder. Caking under the high humidity (RH80%) of sodium bicarbonate found to occur due to the bridging among particles during the process of changing of sodium carbonate to sodium sesquicarbonate. The caking under the conditions of low humidity (RH40%) and high temperature (40 ∼ 50 °C) however owes bridging accompanied by the change from sodium carbonate to Wegscheider's salt. Caking strengths measured for sodium bicarbonate samples with various particle sizes were correlated with contacting numbers among particles. The caking strength, BL, was found to be expressed with the equation: BL = k·Sc·F, where Sc is the contact area per unit surface area of sodium bicarbonate particles, and F is the formation quantity per the unit surface area, of the double salts such as sodium sesquicarbonate and Wegscheider's salt. We have found finally an effective method to avoid caking through the process of analyzing the caking mechanism of sodium bicarbonate.

Mechanism of caking of granules containing oily materials

Caking of granules containing oily materials was studied. It was found that caking occured on storage below the melting point of the oily materials and it was particularly marked for granules with fresh surfaces. However, the caking tendency diminished or disappeared on heat treatment, even in the case of granules with fresh surfaces. The dependence of the penetration rate of oily materials on temperature and the amount of oily materials on the fresh surfaces of granules with or without heat treatment was determined. Direct observation of these surfaces under a stereoscopic microscope was further conducted. Based on these results, a schematic model of the caking of granules containing oily materials was presented: oily materials are present in thick layers on the fresh surfaces immediately after the crushing process, however, heat treatment increases the fluidity of the oily materials and facilitates their penetration into wedges between carrier particles. Thus, heat treatment shows an effective anti-caking action.

Fertilizer caking: Mechanisms, influential factors, and methods of prevention

Most fertilizers have some tendency to form lumps or agglomerates (caking) during storage. The mechanism of caking in fertilizers is most often attributed to the formation of salt bridges and/or capillary adhesion. The severity of caking can be influenced by a number of factors, such as chemical composition, moisture content, particle structure, mechanical strength, hygroscopic properties, product temperature, ambient conditions, storage time, and storage pressure. The various methods of reducing or eliminating caking in fertilizers basically involve process control, storage/packaging conditions, and/or addition of anticaking agents.

Mechanism of caking of ammonium nitrate (NH4NO3) prills

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMechanism of caking of ammonium nitrate (NH4NO3) prillsChrister SjolinCite this: J. Agric. Food Chem. 1972, 20, 4, 895–900Publication Date (Print):July 1, 1972Publication History Published online1 May 2002Published inissue 1 July 1972https://doi.org/10.1021/jf60182a025RIGHTS & PERMISSIONSArticle Views301Altmetric-Citations10LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (5 MB) Get e-Alerts Get e-Alerts