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MINING







AGITATORS IN MINING AND MINERAL PROCESSING

Agitators are the mechanical equipment employed during the chemical processing of excavated ores whereby the valuable minerals and metals are extracted. Extractive metallurgy focuses on the processes and methods of extracting metals from their mineral deposits. Ferrous and Non-Ferrous extractive metallurgy have common specialties, which are categorized as follows Mineral processing, Hydrometallurgy, Pyrometallurgy and Electrometallurgy; according to the processes adopted to extract the metal. Certain metals undergo several extraction processes, which are determined by the metals occurrence as well as chemical requirements.

The exploration and extraction of gold, platinum, nickel, copper and uranium alongside other base metals, provides for a large variation of different process applications where the agitators are carefully calculated and designed. Ensuring that the individual processes are understood, AFX engineers have spent time on site and continuously work closely with process engineers that we offer the best solutions.

AFX has an exceptional track record throughout mining and mineral processing. Our attention to detail as well as the years of accumulated knowledge has allowed AFX to become the preferred supplier of specialized  SX pumper mixers, Bioleaching, Cyanide Detoxification, Leach and CIP/ CIL, Iron Removal, High-pressure Autoclave agitators, Backfill agitators and many other applications requiring unique solutions.

Although the spans of mining and mineral processing are more extensive than what we have listed below, we have elected only a few specialized and specific processes below to highlight not only the extensive knowledge around the process application, but to offer peace of mind relating to our agitator and engineering solutions.

All metallurgical treatments have a common outcome namely the extraction of the mineral ore from the rock. The first step in the circuit would be the accurate grinding, comminution, into small particles.


GOLD EXTRACTION & PROCESSING

Principally, gold occurs as a native metal usually alloyed with silver as an electrum or with mercury as an amalgam. Gold may occur as sizeable nuggets, fine grains or flakes in alluvial deposits or microscopic particles embedded in rock minerals. Although comparatively rare, gold occurs in chemical compositions with other elements such as calaverite, sylvanite and petzite to name a few.

Historically, the extraction of the metal relied on gravity concentration, where simple tools such as pans and wash tables were used. Gravity concentration could be directly smelted too for gold bars, if the gold was present in the ore as coarse particles.

In todays’ era, which is continually demanding maximum yield and concentration from the mining process, there are a series of chemical procedures employed to extract the gold from the ore.


CYANIDE LEACHING

This is commonly used metallurgical extraction processing method. The process itself falls into the Hydrometallurgy category, which is the use of an aqueous solution to extract the gold from the ore. Most leaching applications sparge oxygen into the leach tanks. Cyanide is a lixiviant, which is used to leach gold from solid matrixes to form a gold-cyanide complex. The concentration and dose of cyanide used is very low in comparison to the live liquid volume in the tank. The pH of the resulting slurry would be carefully controlled by means of adding lime or another alkali ensuring that the cyanide ions do not change into toxic cyanide gas. AFX carefully calculate and design the required agitators for the process, knowing that the slurry requires the solids to be in full suspension throughout the tank for the chemical process to efficiently take place. The agitator will also ensure the thorough distribution of the alkali chemical(s) being dosed into the mixing environment. AFX are able to offer advice on the sizing and installation configuration of baffles within the mixing tanks, which are vital for the mixing process. An adsorption process is employed after cyanide leaching, where activated carbon or an organic carbon maybe used, depending on the ore.

The below processes refer either to a particular process in a metallurgic extraction or through various metallurgical applications.


CIL and CIP

Adsorption is most commonly recognized as Carbon in Leach (CIL) or Carbon in Pulp (CIP) the processes use activated carbon for the gold to leach onto.

CIL is a process of cyanidation as the carbon is added into the leach or reactor tanks. Leaching as well as adsorption will take place in the same leach tanks. CIL is the simultaneous process of leaching and adsorption. This process was specifically developed for the processing of gold ores containing “preg-robbing” materials i.e. organic carbon. These materials reduce the gold yield by attracting the gold meant for the activated carbon. The employment of leaching and adsorption assists in minimizing this problem.

CIP differs from CIL in that the leaching process and the adsorption process take place in separate reactors or tanks. During the CIP process, pulp flows through several agitated tanks. The addition of oxygen and sodium cyanide is done prior to the CIP circuit so in order to dissolve the gold into a solution, this is commonly known as gold dissolution. Activated carbon is present in the adsorption tanks, which the gold adsorbs onto. The activated carbon flows counter currently to the pulp. Separation screens sort the barren pulp from the gold loaded carbon.

Absorption onto activated carbon is commonly categorized as recovery. Preceding recovery one would expect to encounter solution concentration, stripping or electro-winning.

AFX have a countless number of successful installations in Leach, CIL and CIP applications worldwide, using our F3 hydrofoil impeller system, our agitators are robust in design and mechanically sound to withstand the harsh operating conditions some of these plants undergo.


BIOLEACHING

Bioleaching is a method of extracting metals from their ores with the use of living organisms. Bioleaching is a cleaner and more environmentally accepted means of extraction when compared to traditional cyanide leaching. Bioleaching is categorized under biohydrometallurgy and can be used in the recovery of copper, zinc, lead, gold silver, cobalt and nickel to name a few. Bioleaching also known as Bio-oxidation, uses bacteria for the further oxidization of the ore. The bacteria oxidize the ore, whilst regenerating the chemical oxidant. Bioleaching or Bio-oxidation applications require the induction of oxygen into the process tanks, as the bacteria use the oxygen in order to carry out their required oxidizing tasks. As exploration into bioleaching’s possibilities has expanded, AFX working hand in hand with specialist, have been at the forefront of innovative solutions.  In order to deliver the most calculated solution for optimal output results. AFX designed and commissioned pilot plants, which were used for testing. Once the testing was completed and the client satisfied with the results of the agitators and spargingequipment, AFX was awarded the contract for the full-scale plant.


AUTOCLAVES

Pressure oxidation, POX, can be employed for the leaching of ores and concentrates in the mining and mineral processing industry. Autoclaves operate under pressure as well as high temperature conditions in the presence of pure oxygen gas being required in order for the chemical reactions to take place. Efficient oxygen uptake as well as dispersion throughout the autoclaves is of utmost importance. AFX have spent time focusing on a mechanical solution of the autoclave systems. A dual agitator impeller system, with a P4 and P3 impeller are installed with a mechanical seal, housed in a pedestal. The mechanical seal is rated to withstand the high temperatures as well as pressure of the autoclave systems. AFX provide the solution, which has a proven industry track record throughout the mining and mineral processing groups, internationally.


SOLVENT EXTRACTION (SX)

Solvent extraction is the process used to recover base metals and uranium from solutions generated in atmospheric leaching reactors, as well as in pressure oxidation autoclaves.  This solution is always referred to as the pregnant leach solution (PLS) and contains copper, nickel, uranium and other minerals in the solution.  The metals are removed from the solution using the solvent extraction (SX) process.  The SX plant consists of three or four mixer or settler units which is a mixing tank, attached to a large circular or rectangular settler.


The organic solvent used in the application, extracts the metal from the solutions and at the same time concentrates it into a much smaller volume, similar to the gold CIP process, where the gold absorbs onto the carbon.  As an example, copper PLS is contacted with an organic solvent in the extraction settlers of the SX plant. The extraction is normally carried out in three to four stages, with the two-phase (PLS aqueous and organic solvent) moving counter currently.  The two phases need to be mixed thoroughly with the organic solvent to extract from the metal.  The aqueous phase gravitates, while the organic is pumped.  Extraction mixers operate in the organic phase.  The two phases then separate in the settlers, with the lighter organic phase being the top layer.  The next stage is the scrubber mixer-settlers, where the solvent is washed with a low pH solution to remove impurities like iron and silica.  Similarly, in the strip mixer-settler units, the Copper is stripped from the organic again, using high concentration sulphuric acid solution. This solution (electrolyte) is then pumped to the electrowinning plant to produce pure Copper cathodes.



PERISTALTIC PUMPS IN MINING

Mining operations challenge most conventional pumps. Handling abrasive and corrosive fluids typically used in mining operations presents a challenge to any pump manufacturer. High solids content and strong acidity create problems for diaphragm, centrifugal or other types of pumps where the product comes in contact with the working parts of the pump.

To overcome these problems, mine operators have had to purchase specialised pumps, often constructed from acid-resistant and wear resistant materials or put up with frequent, costly pump maintenance or replacement. Often rotors or impellers on slurry pumps last only weeks and diaphragm pumps clog, leak or fail after only a few months.

Replacing centrifugal slurry pumps with peristaltic hose pumps makes economic sense. High density thickener underflow slurries are too high to allow centrifugal pumps to deliver the correct flow rate and abrasive wear causes regular costly repairs. Because abrasives in the slurry do not affect peristaltic hose pumps, mine operators are now able to reduce downtime and achieve dependable pump operation at the required flow rate. Often peristaltic hose pumps were overlooked as being “low flow”. The AFX150 pump however has one of the highest flowrates in the world at 150m3/hr.

Because peristaltic hose pumps contain the fluid entirely within the hose, the hose is the only wearing part. The rubber hose is highly abrasion resistant and pumps can easily pump abrasive fluids like tailings, metal slurries and thickener underflow. Due to the high solids content of these slurries other types of pumps often fail because the product comes into contact with the rotors, stators, impellers and seals of the pump. In a peristaltic hose pump however, the hose never fails due to abrasion.

Unlike most rotary pumps, peristaltic pumps have no shaft seals to flush with water, coupled with the ability to handle slurries with high solids concentrations plants use much less water with peristaltic hose pumps, saving the plant considerable amounts in both maintenance and water usage. In the mining industry, water is money and the less you use the better. Flushing pump seals and diluting thickened slurries is incredibly costly to a mine because the water added has to be removed or treated.

AFX peristaltic pumps are designed to operate at slower speeds and have lower energy consumption than most traditional peristaltic hose pumps. Actual tests have seen up to 50% savings on power consumption.


CHEMICAL






GENERAL

The AMX range of agitators are designed and manufactured to suit applications throughout chemical production plants. Chemical manufacturing is a precisely controlled process, which works best with the correctly sized mechanical tools. Other than the agitator, the reactor vessel and baffle sizing are individual contributors to the completed product and if any one of these are incorrectly sized, the process will suffer with failing final products, inefficiencies and possibly increased costs.

The processes and reactions in this industry cover a broad scope of mixing requirements such as liquid-liquid, gas-liquid, liquid-solid mixing, as well as various types of batch and crystallization processing applications. Agitator tasks range from dispersion of liquids, dissolving of gases and solids, basic mixing and blending, co-current scrubbing, homogenizing as well as neutralization.


CHEMICAL INDUSTRY APPLICATIONS
  • Mixing miscible or dispersing immiscible reactants
  • Dissolving gases
  • Providing plug flow with reaction controlled conditions
  • Dispersing liquids in extraction and washing processes
  • Mixing gases in front of oxidation reactors
  • Vaporizing liquids in font of oxidation reactors
  • Homogenizing process and product streams for representative sampling
  • pH adjustment

Crystallization forms the basis for the following chemical reactions and are generally applied to bulk chemical mixing.


COMPETITIVE-CONSECUTIVE REACTION

This reaction is when insufficient mixing occurs and consecutive and competitive side reactions occur creating unwanted reactions and depleting the available solution of chemicals that are required to manufacture the primary products.

The AFX F3 axial flow hydrofoil impeller is the dynamic workhorse of AFX’s solutions in eradicating the occurrence of competitive-consecutive reactions. This impeller is suitable adjusted for the process design to ensure process guarantees. The F3 impeller is capable of producing high pumping rates at a low power draw than when deploying the commonly witnessed pitched blade turbines. The F3 impellers shear rate remains low when correctly sized and powered, offering the client an energy efficient and cost saving solution.


GAS-LIQUID REACTION

These types of reactions often require a self-inducing process or a gas sparge type installation to facilitate the dispersion of gas into the liquid.

AFX has worldwide success in many processing industries utilising its mass transfer  agitators and agitators and sparging solutions. AFX has been successfully designing and implementing scale-up solutions in this industry. The incorporation of the R&D department in developing ongoing solutions has made AFX a world leader in these applications. AFX predominantly uses its P4 mass transfer impeller and gas dispersion agitator solutions in this reaction.


SOLID-LIQUID REACTION

These solutions require a mixing process that avoids settling of the solids on the bottom of the tank, which directly effects the mixing rate. The use of baffles is normally recommended in this reaction.

AFX design engineers utilise the calculated velocities in the tank, to design solutions, that can be process guaranteed based on the client’s process data. The F3 axial flow hydrofoil impeller would most commonly be selected for these types of applications due to its robust design as well as versatility.


LIQUID-LIQUID REACTION

These reactions suffer from scale-up due to the fact that drop formation and coalescence change with scale. The scale-up problem is often remedied with over mixing and exposing the droplet to a higher concentration of reagent in the aqueous phase.

AFX has evaluated the typical problems in scale-up of this reaction type and designed solutions that do not over mix or unnecessarily increase the power draw required. The AFX design tools allow meticulous design of the mechanical solution, ensuring the required process is achieved.  

Depending on the particular solutions as well as their properties, AFX would combine various impeller solutions to ensure competent processing. This could include a combination with FS4 and F3 impellers or P3 and F3 combination.


REACTIVE CRYSTALLIZATION

When both a reaction and crystallization need to occur in the mixing process the application engineer’s design becomes more critical. In the scale-up process the design of the agitator needs to accommodate the balance between a growth-dominated process which cannot be too fast so as to cause crystal fracture coupled to the requirements of mixing fast enough for the micro-mixing effective of fast reactions.

Particular applications require low velocity movement on the floor of the reactor or they may call for solids suspension, which would result in increased power requirements. Our F3 range of impellers include various blade pitches that allow AFX to solve all the crystallization processes challenges.


PRICIPALS OF REACTOR DESIGN AND MIXING IN THE CHEMICAL INDUSTRY

The rate of mixing is determined by the chemical reaction speed. Insufficient mixing may lead to the formation of side reactions which are the impurities in the final product. The creation of side products is related to concentration differences in the tank on a micro level. If pH balancing is incorporated into the process and neutralization is required to halt a process, then inefficient mixing speed will result in a delayed neutralization event which could result in by-products being formed.

Generally speaking, four types of mixers are included in the design of mixers in the chemical industry.


The following mixer types form part of the existing pipework and take up very little space and have low running costs:


The following mixer types are commonly found in solutions that are top-entry or side-entry mixers:

  • Stirred tank

A pipe, or tubular reactor, is the most common designed reactor. Reactants are injected into one end and an obstruction that causes turbulent flow is present in the pipes. The tee-mixer is a variation on the pipe mixer, wherein two reactants are injected into the t-joint at pressure, utilizing turbulence with pressure energy. Static mixers are placed in the pipes to create obstructions that promote mixing. The stirred tank consists of the vessel and the mixing device with stirred tanks being the most versatile option for mixing.


The reactors geometry and the position of the feed point affects the reactions yield. The optimal feed point is near the tip of the impeller where maximum turbulence is present. Some designs use this principal to create multipoint feeds which allow the flow rate to be reduced without decreasing productivity.


HETEROGENEOUS REACTIONS AND REACTORS

Three main classifications occur depending on the feeding mode of the reaction, namely batch, semi batch and continuous flow. Batch flow incorporates all the chemicals at once and once the reaction is completed the tank is emptied of its contents and the intermediate or final product delivered. Semi-batch flow caters for feeds to be used to add additional chemicals during the process, normally related to time based or the concentrations of formed product present in the tank. Continuous flow processes have the inlet and outlet operational simultaneously. The process ensures the reaction is completed using time based calculations that determine the flow of the inlet to outlet as a ratio. These process are normally controlled by the inlet flow speed and the outlet flow allowed.

Slow chemical reactions are not effected as much by chemical kinetics as are fast reacting chemicals. Mixing speed is critical when fast reacting reagents are presented for mixing, as both presentation of the reacting chemicals to each other needs to occur and the concentration needs to be sufficient for the reaction to effectively convert and create the required products, whilst minimizing the by-products. In heterogeneous solutions, the time the reagents are in the tank, will determine the selection of main product and by-product created.


AFX has the expertise to ensure that the mixing will conform to the application process.


SCALE-UP IN THE CHEMICAL INDUSTRY

Some factors effect the scale-up process:

  • Shear rate and energy dissipation in the tank. Thermodynamics work logarithmically based on volume therefore cooling and heating are not extrapolated in a linear calculation using linear multipliers. This typically would result in hot spots and unwanted chemical reactions which effects the rate at which chemicals can be introduced into a tank, to ensure the correct concentrations.

CRYSTALLIZATION IN THE CHEMICAL INDUSTRY

Crystallization is essential in the development of products and mixing has a direct effect in the production process. Mixing effects crystal nucleation, growth and slurry maintenance. This makes scale-up a challenge when designing these processes. AFX’s application engineers are equipped with the knowledge and the tools to successfully design mixers for this scale-up to mass production.


AFX designs accommodate

  1. Control of the crystal size with the type, size and speed of the impellers in the mixing vessel.
  2. The quantity of nucleation occurring to avoid excess and fracturing of crystals.
  3. The occlusion of impurities due to poor mixing action and unacceptable physical properties of crystals.

EQUIPMENT

Crystallization is normally achieved in a multipurpose vessel with hydrofoil impellers like AFX’s F3. Good circulation with low shear in the tank is necessary to avoid secondary nucleation and crystal breakage. Baffles are used to ensure good mixing.


MIXING AND CRYSTAL GROWTH

A balance, in the mixing process is required, between growing crystals and not breaking them. A high mass transfer rate is required to avoid super-saturation around the crystal growth area whilst ensuring good heat transfer rates and dispersion of the additives, avoidance of settling and uniformity of the crystals in the product. Over-mixing would result in crystal breakage and secondary nucleation, which is undesirable as it is a by-product which results in reduced yield of the required product and requires removal from the main product to maintain the products purity level.


PERISTALTIC PUMPS – CHEMICAL INDUSTRY APPLICATIONS

Within the chemical industry high demands are placed upon pumps to ensure uninterrupted production and compliance with health and safety regulations. Fluid containment and chemical compatibility are essential. AFX Pumps not only provide process improvements and cost savings, but have distinct benefits over other pump types:

  • Fluid containment entirely within the hose with no seals or glands
  • Low shear pumping
  • High degree of accuracy and repeatability
  • Long pump life and low maintenance
  • Dry-running and self-priming capability

With the pumped fluid contained entirely within the pump hose, only the hose and connections need be selected to withstand any chemical attack from the process fluid, often negating the cost for expensive pump housing options or special coatings.

In environments where the atmosphere is corrosive, AFX Pumps can be supplied with stainless steel housings and support frames.

The gentle action of AFX Pumps incorporating roller technology, allows for very low shear pumping. Thus, shear sensitive products can be handled without damage to the product.

Peristaltic pumps due to their positive displacement nature are inherently suited to dosing applications. The high quality of the AFX Pump hose ensures consistent and repeatable performance with accurate levels of dosing.

Pump failure during production can be hazardous. AFX Pumps have no seals, valves, diaphragms or glands to leak, clog or corrode. Normal maintenance is limited to the hose and lubricant only. Hose failure during operation can be monitored and contained, thus controlling any potential hazard.

AFX Pumps have a clear flow path through the hose and can run dry indefinitely. They are self-priming up to 9.5 metres ensuring excellent suction capabilities. Gas locking or blockage is virtually eliminated due to the pump design and the flexibility of the pump allows for easy low cost installation with guaranteed performance.


FOOD & BEVERAGE







The food and beverage industry utilises a number of mixer types to process there products. AFX has key industry knowledge on the process involved in manufacturing and continues to engage with plant engineers to create improvements that include higher product yields and more robust products. Having interacted with these plant engineers, through the different stages, AFX was able to fully conceptualise the importance of equipment which far exceeds client’s expectations, as well as constructing a new approach for targeting their markets. By understanding the plant requirements, we are able to design and manufacture agitators and peristaltic pumps to the required specifications, adhering to the industry standards.


DAIRY INDUSTRY

The dairy industry has a number of stages involved in processing milk based products. Milk is transferred to receiving stations which require vigorous agitation of the milk followed by storage tanks that require mild agitation. AFX is able to assist with the design and supply of the required agitators throughout the dairy based products which include but are not limited to; Bottling plants, Cheese factories, Creameries, Condensories, Dry-Milk plants and Ice-Cream plants and yogurt plants.

Knowing that the majority of the agitators running in dairy processing plants form part of a complete package when purchasing mixing and storage tanks/vessels, AFX aligned it’s engineers to work closely with the tank manufacturers, thereby ensuring that the provided solution is appropriate for the process requirement.


VEGETABLE AND ANIMAL PROCESSING

The processing of vegetable and animals is intricate and specialised and most facilities host a range of equipment which takes the vegetable plant or animal matter from “raw” to the “end” product. Certain areas of the food processing utilise agitators. AFX worked closely with a food processing company, producing soya bean meal for feeds and was commissioned to design the agitator for a 15 000 litre storage tank. Certain elements of design were considered and a prominent issue was that there was a constant build-up of residue and fine particles left in the oil after the final processing. The client needed to empty the tanks monthly in order to scrape and clean the bottom of their storage tanks. This meant that they were operating inefficiently as they only had a single storage tank in commission at any one time. AFX compiled a design to suit their tanks and process thereby ensuring that the residue and fine particles did not settle on the bottom of the tanks.

Certain process stages, such as Hydrogenation, the reaction is strongly exothermic and the agitator aids in the removal heat from the reaction thereby maintaining temperature uniformity throughout the products in the agitator.

AFX specialises in providing a solution for your agitator requirements in the manufacturing process or for the storage phase.


BOTTLING INDUSTRY

The bottling industry includes a number of process which include but are not limited to syrup mixing and storage, pulp blending and suspension with fruit juices and speciality drinks and sodas. Agitators are used to ensure product uniformity and achieve process results for the desired products.

AFX fully understands the fundamental parameters that influence the sizing of the agitators from  syrups and sugars, to ensuring that the product quality in juice blending is not compromised as well as paying attention to the smaller batch mixing that occurs throughout speciality drinks and supplies a suitable agitator solution. AFX guarantees a quality product, process success whilst maintaining an energy and maintenance efficient design.

AFX has designed a hydrofoil impellerwhich has proven to be beneficial for these type of applications. AFX has the expertise to modify its designs and thereby giving the appropriate performance to its impellers.


BREWERY, WINERY AND DISTILLERY OPERATIONS

Although dating back many years, the making of alcoholic beverages has progressed and recently having improved the processing methods, including agitation, the industry has modernized, resulting in improved production yields and superior products.

Agitators are found in the following Brewery processes:

Gelatinization: With high viscosities, top entry agitators, using axial flow impellers are mostly used in this step. The design of these agitators takes into account the viscosity and the rate of grain addition along with the heat transfer requirements thereby optimising the design of the agitator.

Mash Tub: This phase is a rather delicate process requiring a high flow of the product through the vessel, ensuring that the grain is thoroughly wet down in the tub, however, through this steeping phase, the shear rates are required to remain low. AFX acquires the required product information and process parameters and designs the agitator to achieve the desired process outcome. The most commonly supplied agitator to this process is the top entry agitator which does mixing,  solid suspension and temperature and material uniformity.

Brew Kettle: This step in the process is a fairly simple step in comparison to the other steps. The process uses a side entry agitator design which acheives the desired wort and hops uniformity and temperature uniformity throughout the mix. These designs normally have a lower installed power as the wort is water like and the settling rate of the hops is mostly negligible.

Fermenters: This stage of the process initially would have been un-agitated. The more modern designs see fermenters with a side entry installation agitator. Mechanical seals are used to aid in keeping to the stringent sterility requirements. The design of these agitators provide a light gentle mix throughout the fermentation tank, acknowledging that the process requires very little shear.

Filter Aid Slurry Make Up: This process forms the final filtration process of the beer production process. The makeup of the filter aid requires very low shear as the filter aid is easily broken up. The agitator’s aim is to provide a uniform slurry. The most commonly used agitator is the top entry axial flow agitator. Once this filtration process is complete the beer moves to the bottle house for packaging.


WINERY OPERATIONS

Agitators are used for various applications throughout the wine making process, some for solids suspension and others for blending components.


Agitators may be found during in the following Wine processes:

Storage & Mixing: Agitators are used to improve filtration rates by ensuring that there is a uniform feed to the filter, as well as aiding in the juice recovery and reducing the primary fermentation time for making heavier bodied wines.

Fermenter Make Up: Agitators are used to perform blending within the fermenter tanks to provide good quality control over all components prior to fermentation.


Many of the applications in the winery and distillery operations require the design of agitators using both top and side entry designs. As production capacity and demands increase, so do the mixing vessels., This leaves room for the agitators to be adapted to suit the vessels. In the very large mixing vessels, top entry agitators may not be economical or may not be an option due to height restrictions or even weight and load limitations. Due to the mixing and blending of this type of product the use of side entry mixers has become a defacto standard in this process. The side entry units utilise less space, provide an economical solution in oversized mixing tanks and still achieve the desired process outcome.

Throughout the starch processing stage and fuel alcohol processing stage, there are numerous applications where agitators are installed. The agitators are used to ensure that there is product uniformity throughout the tank and to allow for an evenly distributed mixture as well as aid in shortening the time periods which such processes would normally require. Agitators may also be installed for solid suspension within tanks thereby avoiding sediment build up and aiding in producing homogenous mixtures. The fluid regimes required in the process are important and AFX is able to advise on agitator positioning as well as baffling designs to suit the process demands.


PERISTALTIC PUMPS – FOOD AND BEVERAGE APPLICATIONS

Peristaltic pumps are regularly used in the food and beverage industry. The low shear peristaltic action is created by compressing the hose element between 2 rotating rollers. In between each pass of a roller, the hose recovers to create a vacuum and draw in fluid. This means that the pump is self-priming and dry running. This simple dynamic effect requires no seals or valves and the fluid is totally contained within the hose, separated from the pump. No other positive displacement pump offers this unique separation of pump and fluid. Peristaltic pumps regularly outperform other pump types, such as lobe or diaphragm pumps for example, which rely on their mechanism including seals and valves to work within your product.


Peristaltic pumps may be found during in the following processes:


BREWERY PROCESSES

Yeast cropping: Yeast is easily damaged and should be pumped without shear. Traditional pumps can produce varying degrees of shear and damage to the yeast by impellers, vanes, lobes or valves. Peristaltic pumps are inherently low shear. Yeast quality is maintained, allowing accurate process control and improved finished product quality. Dependent upon the beer, yeast cropping can be bottom tank or top tank. Top tank especially can involve pumps running dy. The can be a problem for many pumps, but not for peristaltic pumps which can run dry indefinitely. Peristaltic pumps do not rely on the pumped media for lubrication, offering true dry running, improved reliability and eliminating unplanned maintenance.

Diatomaceous earth (kieselgur): the abrasive nature of the product causes premature failure of many pump types. Because peristaltic hose pumps contain the fluid entirely within the hose, the hose is the only wearing part. The rubber hose is highly abrasion resistant and where other types of pumps often fail because the product comes into contact with the rotors, stators, impellers and seals of the pump. In a peristaltic hose pump however, the hose never fails due to abrasion.


WINERY OPERATIONS

Peristaltic pumps have a wide range of applications within the wine industry. Just about anywhere a pump is required in a winery and a peristaltic pump can fit the bill.

Peristaltic pumps are able to pass significant amounts of suspended solids, in the form of grape pulp, skins and seeds without grinding or breaking any seeds, and without overly macerating the skins and thereby increasing turbidity.

Must from Destemmer to Fermenter or Press: the pumps that move the grapes and juice from the destemmer to the fermenter. Peristaltic pumps can move the destemmed grapes from the destemmer to the tank or press without macerating them or their seeds

Press Sump pumping gently minimises emulsion of the solids in the freerun.

Wine, Pomace Fermenter to Press: the design of a peristaltic pump means that the pomace isn’t subjected to shearing forces as it moves through the pump.


PULP & PAPER







The design of agitators in the pulp and paper processing industry is critical and AFX has the required expertise. AFX guarantees that the desired process performance parameters are achieved.

Paper stock slurries behave in a manner that is very different to that of other fluid slurries and as such AFX takes into account that there are specific minimum requirements for the mentioned slurries and ensures that these requirements are met with the designed and supplied agitator. The requirements, namely motion and blend time, in correlation with the effect of mixer and paper stock variables, are factors which influence power requirements of the agitator.

AFX works in close correlation with the mill’s engineers and staff thereby ensuring that final consideration is given to all the process variables. AFX has built its expertise over many years in understanding the factors and parameters for the agitators to be designed correctly.

System: AFX has the in-depth knowledge of the processes involved in this industry which include the feeds and pumps and the particle process in a chest.

Consistency: The fluid consistency plays a large role in power selection. A consistency change from 3.5% to 4% could result in a 50% increase in motor power in order to achieve the desired process performance. AFX’s knowledge of this is included in it’s design process for the agitator.

Stock type: The type of stock as well as its behaviour assist the applications engineer in knowing what the slurry’s tendencies are while being agitated. AFX has the design tools to ensure that the specific parameters are met according to the stock type.

Temperature Effects: General theory states that the higher the stock temperature, the easier it is to agitate. However the temperature does not always play a major role in the power selection, as most stocks are at a high temperature with no large variation is expected.

Time: The retention time is critical in the design of the agitator and if incorrectly designed may result in compromised consistency. If short retention times are required then the agitator would have to perform its duty in a shorter period, this ultimately results in increased power and sometimes larger impeller selections. AFX has knowledge of the standard process variables in this industry and using “standard” retention times the applications engineer designs a more cost effective agitator for the blending process.

Chest Configuration: AFX’s knowledge in this industry allows us to assist and advise on optimal sizes for chests to be built that achieve optimal agitator performance.

Using the above variables, the AFX applications engineer calculates the process factors and accordingly the design and size of the agitator, which will meet the required process requirements. Our mechanical knowledge and understanding of this industry provides our client with peace of mind whilst taking into account the importance of minimising down time during routine maintenance. AFX processes data on the client’s application requirement along with the operating environment. The applications engineer then has an indication of the type of agitator which would be suitable for the area and will then include the mechanical variations such seals and coatings.

Given the mission embarked upon by business to go green, energy conservation has been a focal point when designing suitable agitators. Our agitators are guaranteed to deliver the on process performance, as well as aid companies with their energy saving requirements. AFX designs well engineered solutions that deliver the correct mechanical sizing coupled to the best power draw for the application.

AFX’ applications engineers have an in depth understanding of the variations and various process requirements which are encountered within the pulp and paper industry, namely oversized storage tanks, controlled zone agitation, split feed forward control, bleaching, stock pulping as well as consistency control.

AFX understands that the process is a continuous operation through the pulp and paper manufacturing process, which include the blending of chemicals into stock lines. Some plants may consider the installation of static mixers, also known as in-line mixers. AFX is able to provide designs as well as technical advice regarding these specialised agitators.

AFX will provide you with the technical information, services and support for all your pulp and paper applications. AFX has numerous successful installations within this industry and we pride ourselves in evolving with the changes in the processes related to this industry.


PERISTALTIC PUMPS IN PULP & PAPER

In all sectors today, cost effective and reliable equipment is paramount.  Accurate and reliable metering of additives and colours in today’s paper industry is no exception. Peristaltic pumps have proven their way in the industry offering:

  • Accurate and repeatable dosing and metering
  • Long life and greater reliability
  • Self-priming and dry-running
  • Lowest cost of ownership with quick and easy maintenance

Whether the application is to meter dyes and chemicals or transfer duties of coatings, liquors or additives, peristaltic pumps can offer a reliable alternative to other pump types.

The features of a peristaltic pump can often have a big impact upon overall installed cost. For example, peristaltic pumps can dry run and self-prime up to 9 metres WC. Compared to alternative pump types that may require expensive dry run protection controls, or need increased civil engineering costs to install below the pumped fluid peristaltic pumps can be installed with ease.

Peristaltic pumps contain the fluid entirely within the hose, meaning there are no expensive seals or check valves to clog or block. Peristaltic pumps have only one wearing part, the hose, which means that maintenance costs are considerably lower than other pump types. Increased plant productivity and lower repair costs means pump payback is over months rather than years.

Paper colouring and tinting requires repeatable pump control for accurate addition of dyes and brighteners. Many traditional positive displacement pumps deliver varying flow rates, resulting in scrapped product and increased costs. Peristaltic pumps have a linear flow rate and are accurate across their total speed range. Less waste means increased profits.


WATER TREATMENT







WATER & WASTE WATER TREATMENT (WWTP)

This process is specific to cleansing water or making it acceptable for its intended use. Water and waste water treatment remove contaminants, in some cases the process may only reduce the contaminant concentration in order for the water to be fit for its intended use of either industrial water supply, irrigation or even safe return back into the environment.


WATER TREATMENT

Focusing on the desired out come of potable water, there are several processes both of a physical and chemical nature which ensure that water is fit for human consumption. Substances removed during treatment include bacteria, algae, suspended solids, viruses, fungi as well as iron and manganese minerals.

Physical processes or settling and filtration are accompanied by chemical processes, namely disinfection and coagulation. Water quality measures do not only account for the treatment of the water but the distribution there of. Residual disinfectants are commonly kept in treated water in order to kill any types of bacteria contamination during the distribution phase.

During the purification the following processes are encountered, pre-chlorination, aeration, coagulation for flocculation and slow-sand filtration.


WASTE WATER TREATMENT PLANTS - WWTP

WWT is either of a domestic or industrial process and it is accomplished by a process of waste water selection processes. This refers to the decision of disposal or reuse, although this is the last step, it is decided before any water is processed through the plant.

Domestic water treatment is commonly known as Sewage treatment works. WWTP commonly have the following stages, phase separation, oxidation and polishing. Phase separation is divided further into sedimentation and followed by filtration. Oxidation is too, further divided into the biochemical and chemical oxidation.

Although both water and waste water treatment industries have a vast array of process applications where agitators are installed and commissioned, only a few are highlighted, focusing in particular on problematic and difficult mixing applications, where AFX have industry proven solutions.


COAGULATION AND FLOCCULATION

Through the water treatment process, coagulation destabilizes particles through chemical reactions between colloids and coagulants. Flocculation is the transport mechanism of the destabilized particles, causing the collisions with the flocculent. Flocculation is a mixing technique which promotes agglomeration as well as assisting with particle settlement. Flocculent is sensitive and affected by mixing speed, intensity and residence time. Each of these aspects are taken into account when designing the high flow, low shear mixer for the process.


MIXING OF POLYELECTROLYTES

Polyelectrolytes are used as thickeners, emulsifiers, conditioners and clarifying agents. These are most typically used to initiate flocculent make up. These are similar to electrolytes (salts) with mixing, and similar to polymers and may often be referred to as “polysalts”. The solutions are charged and most often viscous. Mixing in these applications is rather “easy” and gentle, should all process data be provided regarding the polyelectrolytes.


AERATION TANKS AND LAGOONS

Split into surface and subsurface, aerators are commissioned to mix, dissolve or circulate air into the water. The use of the mixers assists with providing the oxygen required for bacteria to properly function and decreases the requirements and volume of chemicals which may have previously been employed.

Surface aerators commonly require flow and radial dispersion. The water is dispersed up into the air and the droplets fall back into the water thus inducing the oxygen. AFX size’s the aerators using a modified FS4 impeller, which is a combination impeller. The FS4 provides the desired radial flow as well as the requirement of dispersed water on the surface through an upward (up pumping) projection into the air.

AFX delved further into finding a more energy and process efficient solution, predominantly focused on subsurface aerators. Using a combination impeller agitator with a F3 hydrofoil impeller at the first stage and an up pumping P3 pressure impeller. Although the P3 has a variation of applications, the impeller in the up pumping configuration causes turbulence on the surface. Thus entraining air into the water and drawing it back into the tank or lagoon. The F3 impeller distributes the oxygen rich water through out the tank due to the axial flow generated.


FOULED IMPELLERS

Throughout the WWTP industry, agitators are most often seen failing, either mechanically or in a process delivery. This is due to the build up of rags and solid debris found through the process stages. This build up collects on the leading edge of the impeller and continues to grow and become more entangled throughout the constant operation. The large mass, which has fouled the impeller, restricts the flow of the liquids as well as solids. The mass created additional loads on the drive chain of the agitator which accounts for the premature mechanical failures. The collection of rags around the impeller, requires continuous maintenance and shut down, which is costly and requires a large amount of equipment and labour.

AFX have introduced a new clean edge or “ragless” impeller to their high flow range of impellers. The FCE3 was designed to eliminate commonly experienced issues of build up. It will eliminate the expensive costs involved with maintenance and shut down or even premature agitator failure. The clean edge impeller does not have a protruding leading edge which the rags would commonly catch on. The impeller, much like the F3 hydrofoil impeller, promotes axial flow for solid suspension throughout the tank. Most WWTP applications do not require air entrainment, which is required in anaerobic, anoxic and de-nitrification tanks. The FCE3 impeller provides high flow and low shear conditions, proving successful throughout the applications in WWT. The impeller, as the F3, has a low power number, which means that the power installation is significantly less than other agitators seen through similar applications.


PERISTALTIC PUMPS IN WATER & WASTE TREATMENT

All treatment plants must meet increasingly stringent levels of discharge consent, whether you are handling primary sludge, digester feed or sampling and dosing, cost effective reliability is key to the process.

Pump failures can cause major problems resulting in downtime and high cost. Peristaltic hose pumps contain the pumped medium entirely within the hose which is resistant to abrasive wear, has a clear flow path and operates without the need for seals or check valves. Fibrous and solids laden materials are handled with ease as there are no internal parts such as impellers or rotors.

All pumps require maintaining throughout their serviceable life. Pump and plant downtime can be costly, therefore simple and quick serving is highly desirable. Peristaltic hose pumps require only one component to be replaced, the hose. Hose replacement can be carried out in-situ without the need for special tools. No other pump type is able to offer such ease of maintenance, low spares inventory and lowest whole life cost.

It is common in the water and waste industries to have in ground tanks; thus to ensure a pump has a positive head, costly “dry well” chambers are constructed, increasing the civil engineering costs. This is not necessary with peristaltic hose pumps, which can dry run, self-prime and have suction lift capabilities up to 9 metres WC.

It is not uncommon in the waste water process for the viscosity and density of the pumped medium to change. Unlike many pumps, peristaltic pumps will not vary flow as a result, causing process fluctuations.

Chemical dosing such as pH control requires accurate and consistent dosing. The nature of the chemicals used demand that the pump must be able to handle conditions such as salt settlement, gassing, abrasive wear and clogging. These conditions can cause loss of performance in traditional pump types; however peristaltic pumps do not suffer from these problems giving accurate and predictable flow throughout.

Some chemicals used such as flocculants are shear sensitive and their performance can be dramatically reduced by the high velocities induced by pumps that utilise impellers, vanes and lobes. Peristaltic pumps are inherently low shear, ensuring chemical quality and performance is maintained.


PHARMACEUTICAL






GENERAL

The delicate dynamics and fine manufacturing tolerances utilized in the fine chemical/pharmaceutical processes coupled to the vast variation of products indicates the possible variations of agitator designs required to suit the specific application processes in this industry.

The majority of mixing in this industry supports a chemical reaction process and the solution stays resident in the same mixing vessel for batch or semi batch processing.


This type of mixing is used to support:

  • Homogeneous and heterogeneous mixing until complete chemical conversion has occurred.
  • The accurate adding of reagents to the vessel including gasses.
  • Productivity and flexibility by implementing impellers that have a wide scope of operational characteristics that are coupled to variable speed drives.

A number of challenges exist in the mixing of fine chemicals which include the following:

  • Uniformity of the mixture, based on a time constraint, that has an impact on by-product production and
  • Stopping the reaction at the optimum point to avoid chemical wastage and
  • Efficient mixing speeds that assist with heat transfer whilst avoiding
  • Thermal hazards related to volume production in exothermic reactions
  • The settling of fine chemicals below baffles or inconsistent suspension of solids and
  • Entrained vapours causing foaming and cavitation of the mixing process

which has led to the development of specialised solutions that scale within a given set of performance parameters.


SPECIALISED FINISHES AND COATINGS

This industry has a number of coatings that are used to protect the wetted parts and vessel from the chemicals, thereby affording chemical and wear protection. AFX has specialised knowledge of the industry standard glass lined coatings and includes the tolerances related to these coatings into the designs.


SPECIALISED IMPELLER BLADES

The following types of blades are the standard blade types used in this industry:


SUPPORT FOR SCALING APPLICATIONS

A number of lab based production designs cannot be scaled efficiently into production quality and quantity solutions, especially in multiphase processes. The industry has developed a number of methods to handle this nuance successfully by incorporating design alternates.

  • Continuous reactors

    These reactors are used when thermal heat transfer affects the production values. It is more desirable to avoid large quantities of the mixing products being together, this has an exponential heating effect on the batch. A number of solutions are used to achieve this type of reaction. Small batch mixing based

    • on a packed bed
    • fluid bed
    • trickle bed

    which allow fine control of the production output.

    Static inline mixers or tubular mixers form part of the available solution. These are highly efficient and offer good control over reaction temperatures and offer better control in constant mixing intensities and the reactions occurring.  

  • Reaction calorimetry

    Calorimetry is the heat by-product of a reaction that is used to determine the state of a reaction, which ultimately determines whether the reaction has completed and a successful product created.

    Inline mixers with invasive temperature probes have an advantage over moving impellers for high sample rate requirements. Moving impellers normally require external non-invasive measurements normally achieved with Infra-Red light. AFX can incorporate the positioning of these temperature collection probes into the design of the static mixer.


HOMOGENOUS REACTIONS

Slow acting reactions are normally fairly scalable. Reactions that are fast are normally more sensitive to the mixing variables with heat transfer being directly related to production volume. These mixing parameters are:


MIXING SENSITIVE REACTIONS

When significant conversion occurs rapidly, the concentration of by-products and the distribution need to be controlled to ensure product purity. This process directly affects the product certification or registration if impurities cannot be effectively removed downstream in the process.


PREDICTION OF MIXING SENSITIVITY

Lab based testing incorporates predicting the mixing sensitivity of a product with the focus on expanding the process to full scale production volumes. A number of steps are incorporated into this stage to determine if a potential problem exists:

  • For consecutive reactions an excess reagent is added to induce a test for the buffers and an overreaction. If no overreaction occurs, it can be determined that no pathway exists for consecutive reactions and hence scaling should not be a problem.
  • For parallel or consecutive reactions, a difference in mixing result, between different runs, should be noted for further investigation. Poor lab mixing is an indication of an inefficient process.
  • The test reaction vessel should be a cylindrical shape, with a standard turbine impeller, alloy or glass coatings and the mechanical agitator system fitted with baffles, to avoid swirl or cavitation.

SCALE-UP OF PILOT TO PRODUCTION

Scale-up in the pharmaceutical industry in considered simple in homogenous reactions in which kinetics play the dominant role of the reaction and the heat is controlled by conventional methods. Special attention is given to distribution of products in the vessel as small deviations can lead to product separation and subsequent purity issues.

The majority of these applications use  static mixersor multi stage impellers. The selection of the agitator depends on the required mixing action, the process data and the process engineer’s instruction on what the agitator is to aid in eliminating.


HETEROGENEOUS REACTIONS

Heterogeneous reaction systems are very common in the pharmaceutical industry due to the nature of mixing insoluble or partially insoluble products and their required reaction agents. These type of reactions can also be manipulated to achieve higher yields than in homogenous reactions. Furthermore, any deviations in kinetic behaviour are determined by the reaction rate, relative mass transfer rate and mixing, making the reaction more amenable to quantitate analysis and hence the formulation process developed more fully.


FINAL STAGE PRODUCT DEVELOPMENT

The final stages of product development involve purification and product isolation. A number of processes involve simultaneous extraction or crystallization during the reaction phase. The following reactions are used to promote extraction in process:


GAS-LIQUID AND GAS-LIQUID-SOLID REACTIONS
  • Gas as reagent

    The design of a hydrogenation system normally requires an excess hydrogen supply to ensure there is no limiting reaction on the catalyst. This is normally achieved with the addition of a sparge ring in the mixing vessel and on occasion assisted by pressurizing the vessel to slow the process and force reabsorption in the pressurized space.

  • Gas as a by-product

    Special design consideration is given when a reaction creates a gas by-product that is part of the reaction process. This gas needs to be kept in contact with the reaction in the appropriate concentration so as to ensure the principal product and expected yields are met. The gas is then distilled off the process once the reaction completes. Some issues arise with foaming, which normal is attributed to impurities, fine solids or a second liquid phase. AFX uses its standard F3 impeller or a specially designed rake, to remove these impurities along with Food Grade Teflon scrapers on the anchor.

  • Scale-up

    One of the key designs in operating with gas as a reagent, solids and catalysts is the power requirement to achieve equivalent mass transfer for scale-up. AFX has designed a unique impeller, the P4 impeller, which produces high mass transfer rates whilst maintaining blending and solids suspension efficiency. If the mixer energy is to low the entire effect of the flow pattern is destroyed by the gas-flow. Scale-up requires appropriate design to balance the mixing variables.


LIQUID-LIQUID DISPERSED PHASE REACTIONS
  • Reactivity

    Slow reacting reactants can have improved solubility with the addition of a third solvent, used to improve the mutual solubility between the reactants. This process is often avoided due to the requirement to separate the impurities in a downstream process. A more recognized method of attaining the required products to mix, is to create a large interfacial area of intense mixing, followed by the removal of one of the phases via distillation of the more volatile solvent and thereby combining the reactants in the remaining phase. AFX uses the F3 hydrofoil impellers throughout these various mixing processes to achieve its process guarantees.

  • Selectivity in Liquid-Liquid dispersed phase reactions

    A key process design criteria is to protect reactants and products from consecutive competitive reactions, which cause the manufacturing of undesired by-products.

    Conventional mixing in a vessel is not feasible because of rapid decomposition of the main products and hence, a static inline mixer is preferred.


SOLID-LIQUID PROCESSES
  • Solids as dissolving reagents

    Dissimilar particle sizes in both organic and inorganic reagents causes an insoluble solution under standard conditions. The process engineering normal tackles the chemical kinetics and then addresses the dissolution limitations and then decides on the mixing required.


SOLIDS AS PRECIPITATING PRODUCTS

This is normally the effect of crystallization in the vessel and impeller speed is crucial in creating the appropriate size particles. The particle size is effected by supersaturation, reaction rate, mixing and other factors that affect crystallization.

Mixing plays a key role in this process whereby a balance between circulation and shear has to occur to ensure micro-mixing and meso-mixing while avoiding shredding or crystal fracture. Having carefully combined the technology of the hydrofoil impellers with the delicate process of crystallization, AFX has become the sought after mechanical solution provider for these difficult applications.


Scale-up

Scale-up in this reaction is often characterized with power levels that are above the normal mixing in a homogenous suspension. These systems often create agglomerate and therefore an increased power is required to ensure adequate dispersion. A further critical design parameter is the layering and the creation of the films of precipitated products becoming covered by one of the solids in the vessel or second of complex three-phase liquids. This affects the mass transfer rate and could cause the reaction to prematurely end, affecting the yields. Surfactants are sometimes used to modify surface properties or prevent the creation of these separating films. AFX uses a combination of shear impellers, namely the FS4 or shear disk, with the F3 axial flow hydrofoil impellers. The turbine combination can also include a P3 or P4 impellers for viscous or high mass transfer applications.


MIXING AND CRYSTALLIZATION

The interaction during mixing and crystallization needs to be planned for in the design process. Crystallization is effected by the process of nucleation, crystal growth and the maintenance of the crystal slurry. A careful optimization is required to achieve the required mixing as one aspect of the process and the preservation of formed products as the other. This aspect creates a scale-up operation that is challenging and careful design criteria must be met to be successful.

The workhorse of this process is the AFX F3 axial flow hydrofoil turbine, which creates effective pumping but has a low shear value, giving good circulation, while avoiding the destruction of formed crystals. These vessels are almost always baffled to avoid cavitation or swirl.

Two alternative crystallization process are available, mainly fluidizing beds and impinging jets. Fluidizing beds limit nucleation and impinging jets promotes nucleation.

The aspects of crystallization effected by mixing are:

  • Nucleation

    Primary and secondary nucleation are the derived processes with secondary nucleation being of interest and the major part of the crystallization process.

    The following interactions apply during nucleation

    • Crystal-Crystal impact is defined by local micro-mixing (at shear impact between particles) and the overall macro-mixing (at tank mixing)
    • Crystal-impeller and crystal-wall impact is a function of tip speed and impact against the vessel wall.
    • The absorbed layer thickness of the solution decreases with an increase in mixing.

    These factors affect the rate of crystallization which determines the number of nuclei formed and their size. The number of nuclei formed is exponential but on scale-up a smaller particle size may result as local power dissipates. Critical factors remain as impeller speed, type of impeller and their influence in local turbulence and overall circulation in the tank. Nucleation rate is effected by concentration and variances in the tank and this makes it difficult to maintain scale-up performance in the process. Scale-up can be achieved initially by the calculated power per unit required to achieve nucleation in a calculation known as equal power per unit.

  • Growth of crystals

    Mixing affects crystal growth as follows:

    • Mass transfer rate
    • Bulk turnover rate
    • Heat transfer rate
    • Shear on crystal breakage
    • Dispersion of the reagent or anti-solvent
    • Growth rate dispersion
    • Minimizing impurity concentration at the crystal surface

    If the process relies on nucleation, AFX recommends that information be obtained, for the purpose of design, on the impeller speed, the width of the metastable region (overall tank movement) and on the impeller speed compared to the rate of nucleation.


The process of scale-up has been discussed above but there may be a requirement to have homogeneous dispersion, whilst not breaking the crystals, but at the same time avoiding settling on the bottom of the vessel, which results in encrustation.

AFX has specialised knowledge in mixing for crystallization processes. Although the industry solutions have, in the past, not up-scaled well, AFX’s team of application engineers have the tools and experience to design mechanical solutions.


AGRICULTURE







Although this industry is expansive and requires diverse solutions, many intermediate processes that form part of the solutions call for the need of agitators and peristaltic pumps. By focusing on understanding the requirements of the apparatus’ application, and having the process knowledge, AFX is able to provide you with the best solution to achieve the desired outcome.


LIQUID FERTILIZER

The manufacturing of a liquid fertilizer involves the mixing of granular / dry fertilizer into water to create the liquid fertilizer solution. The process demands that the agitator ensures complete mixing throughout the tank. Ideally, after mixing, there would be no granules or dry product still present if 100% or less saturation is achieved, otherwise a sediment is observed on the bottm of the tank or mixing vessel. Should the solution be over saturated, the agitator will keep the remaining solids in suspension throughout the solution.

Some dry fertilizers require a high shear dispersion process to break up and prevent the powder from clumping whilst ensuring that the powders are evenly distributed throughout the water. Certain applications may have a residence time which limits and specifies the allowable blending/ mixing time whilst some applications, made up from rapidly dissolving products, are simple and merely need circulation in the mixing tank/ vessel. Agitators may also be used to keep the solution from standing still and having the solids settle to the bottom of the tank.

Sizing of the AMX agitators, for any of these applications, is largely dependent on what the agitator is firstly required to do, process data and the mixing tank / vessel size. Our agitators are designed to meet your process requirements and sized according to your application needs. Agitators types vary from being designed to suit 210 liter drums, IBC bulk containers, Jojo or similar material and construction type tanks, to manufactured and fabricated stainless tanks for liquid fertilizer production plants.


WASTE EARTHEN PIT

Also known as waste storage ponds or basins, these are often placed on the farms/plots in such a way as to collect the waste and contaminated runoffs. These tank duties vary throughout the different types of farming but all have a general purpose. Most commonly experienced, these tanks are rectangular or square in shape and are excavated deep into the land, and are concrete lined, preventing seepage.

Agitators are required to keep the collected waste sludge in suspension to facilitate pumping and in some cases the agitator is designed with a shear blade running just below the fluid surface in order to entrain the caked waste material comprising of grass, animal fecal matter, fats and offal from animals or other processes happening on site. The AMX agitator is designed for solids suspension and sized to suit the pits shape. Using hydrofoil impellers which have a low power number and high pumping number, the agitator will deliver maximum pumping and flow with the minimum require power. AMX Agitators are energy efficient and cost effective solutions for your process requirements.


PERISTALTIC PUMPS – AGRICULTURE APPLICATIONS

The agriculture industry is expansive and has a diverse range of applications. Common throughout the industry however are the high demands that are placed upon pumps. Fluid containment, chemical compatibility and abrasive resistance are just some of the challenges facing pumps within the industry. AFX Pumps not only provide process improvements and cost savings, but have distinct benefits over other pump types:

  • Fluid containment entirely within the hose with no seals or glands
  • Suction lifts to 9.5m
  • Abrasive resistant
  • Long pump life and low maintenance
  • Dry-running and self-priming capability

Applications such as handling chemicals and liquid fertilizers can often result in corrosion on traditional pumps. In the AFX Pump the pumped fluid is contained entirely within the pump hose, only the hose and connections need be selected to withstand any chemical attack from the process fluid.

AFX Pumps have a clear flow path through the hose and can run dry indefinitely. They are self-priming up to 9.5 metres ensuring excellent suction capabilities. Gas locking or blockage is virtually eliminated due to the pump design and the flexibility of the pump allows for easy low cost installation with guaranteed performance.

Peristaltic pumps due to their positive displacement nature are inherently suited to dosing and transfer applications. The high quality of the AFX Pump hose ensures consistent and repeatable performance with accurate levels of dosing.

Pump failure during production can be hazardous. AFX Pumps have no seals, valves, diaphragms or glands to leak, clog or corrode. Normal maintenance is limited to the hose and lubricant only. Hose failure during operation can be monitored and contained, thus controlling any potential hazard.


PETROCHEMICAL





The petroleum industry is generally seen as limited when compared to the chemical and pharmaceutical manufacturing industry. The refinery processes are less complex than those encountered in speciality fine chemicals but only when making references to physical fluid and process conditions.

Mixing plays an important role in enhancing productivity and profitability, when considering the large volumes of petroleum. Larger petroleum companies have exceptionally integrated chemical operations with a spectrum spanning, reacting and non-reacting, single-stage and multi-stage systems.


The following process are often commonly encountered throughout refinery operations:

Emulsion make-up, absorption of CO2, crude oil-water homogenisations, sludge suspensions, de-salting, neutralisation and alkylation, pH control.


Small enhancements in mixing can yield large benefits and reduced operating costs, as well as lower the risk of losing large volumes of product.

Most petrochemical processes experience similar mixing challenges found in the chemical mixing industry.


EMULSION MAKE-UP

During the emulsion make-up process, the final product is prepared in batches by combining clay with stable water in oil emulsion. The emulsion is prepared by dispersing water in oil in agitated tanks. This final emulsion is required to be highly stable so as to avoid the solids settling out during the on-site storage periods. The emulsion storage stability is achieved by the formation of a solid protective film at the interface between water droplets and the continuous phase. The protective film is a product of the chemical reaction between PIBSA (polysiobutylene succinic acid) and polyacrylic acid. The acids are added into the oil and water phase before the emulsification process.

In order to overcome potential phase inversion, water is added slowly into the mixing vessel with the agitator operating. The impeller selection is vital for providing the required drop dispersion for the best shear thickening results. AFX are able to size and design the agitator required for such applications as well as guarantee the process.


CO² REDUCTION
THE GAS TREATING PHASE

Natural gas has a high concentration of CO2, making it unsuitable for direct use as a fuel. The concentration of CO2 is required to be less than 2%. This process conventionally requires an amine solution that the CO2 absorbs into. The absorption occurs at pressures in excess of 100Bar and with a gas liquid ration of 2:1, static mixers are favoured in these applications.


Static mixers are used in these applications, not only due to the mixing outcome, but the physical construction of the mixer that contributes to the successful use of the solution. The required plug flow is achieved with very little axial mixing which ensures great radial mixing.

Static mixers are smaller in size and weight when compared to packed bed towers and are easy to install horizontally, vertically or inclined, processing allowing. Static mixers handle foaming systems with ease and they have a high mass transfer coefficient, often 20 times higher than that of packed towers. Static mixers also require a very short resident time in achieving the target CO2 concentration.


HOMOGENISATION OF WATER IN CRUDE OIL

High demands and expectations are placed on mixers installed in these tanks. Inadequate mixing results in large losses. A 0,1% yield error can result in heavy financial losses, hence the need to have adequate mixing.

Adequate mixing ensures good dispersion of the water in oil mixture. The emulsification in this instance should not have stabilised and should not be stable in water as the water needs to separate in the storage phase. Good mixing results in high volume returns to the refiner. Ship pumps often operate on varying rates, thus being taken into consideration, the mixer sizing depends on the overall pipe length, flow pattern sections as well as pressure drop. Therefore, the mixers are not only sized for the immediate process results but are sized to handle fluctuating flow rates.

Static inlinemixers are commonly used to provide rapid mixing and adequate turbulence causing dispersion and homogenizing of the emulsion in the pipe. The internal construction and arrangement of the sequential vanes in the mixer, force the flowing fluid into different directions abruptly and several times resulting in high shear forces.

These mixers do not need to be powered externally, deriving their power via pressure and flow transfer originating from the ships or ports pumps. It is important to note that these mixers do not operate optimally with low fluid velocities. Although there are alternate mixers that can supply variable geometry and recirculation, static mixers are economical as well as superior in delivering the desired outcomes.

Consult with AFX to assist with the design and sizing of a suitable ALM in-line mixer.


SLUDGE CONTROL

In crude oil storage tanks, settling of sludge, which comprises both organic and inorganic products, requires agitation to ensure off bottom suspension thereby preventing downstream process problems and settling in the tank resulting in build-up which effects the tank capacity and the agitator’s performance. Further issues resulting from this build-up accumulation could result in errors in the pre-heat train, thereby affecting the product process controls.

Sludge build-up causes safety and environmental issues and has implications in the frequent cleaning of tanks. This is both hazardous and an environmental problem whilst reducing the storage capacity of the tank farm. The settled sludge present in the tank can also be corrosive over a period of time.

The abnormally large diameter tanks require the the use of side-entrymixers as top entry mixers are not economically viable due to the required impeller diameters. Side entry mixers are comprised of hydrofoil impellers and in most cases are belt driven. These side entry mixers are designed with shut-off devices and mechanical seals are used. Positioning is of prime importance with side entry mixers as incorrectly placed mixers will either create a vortex, resulting in solids swirling around the bottom of the tank and not being put into suspension. Side entry mixers are sized and designed to be installed at a 10-degree angle to the left when the mixer is operating in a clockwise direction.

A cluster can be installed where high energy is required due to a high or heavy solid/sludge content.


AFX has extensive expertise in side-entry mixers throughout a number of industries and have successfully designed and manufactured side entry mixers in the sludge suspension requirement processes.