A Leading Authority on E-Liquid Manufacturing Equipment

As an alternative to smoking tobacco, inhaling vaporized liquids containing nicotine, flavors and vegetable glycerin has become very popular. The name this new industry has been given is “Vaping” and the products used in electronic vaporizers is referred to as E-Liquid. E-Liquids are heated to vapor, then inhaled, and the various compounds (such as nicotine) are adsorbed by the mouth, nose and lungs.

Because of the obvious health concerns of inhaling flavor compounds, stabilizers, and other E-Liquid constituents,  FDA (Food and Drug Administration) oversight is acute. Considering this, the E-Liquid industry must be prepared to implement strict cGMP manufacturing processes that include all aspects of production - from storage and blending, flow of ingredients, and finished product - with strict FDA record-keeping compliance.

Since the E-Liquid/Vaping industry is relatively new, companies considering a move into producing and selling E-Liquids are finding it difficult to find experienced, qualified equipment designers and consultants. Not only are their few qualified vendors, but the legislative constraints on the industry seem to change frequently. The right equipment partner needs to not only have the technical know-how to build safe, reliable, and efficient equipment, but they also must be on top of FDA and other governmental factors.

Process Systems & Design, located in Westminster, MD is one of the world’s leading experts in E-Liquid manufacturing. PS&D developed the first FDA compliant, safe, accurate, automated, and self-contained e-Liquid compounding system for the e-liquid/vaping industry.  You can lean more about Process Systems & Design at http://www.processsystemsdesign.com/e-liquid or by calling (410) 861-6437.

Gypsum Processing for Cement, Plaster and Wallboard

Gypsum is calcium sulfate dihydrate (CaSO4 2H2O), a white or gray naturally occurring mineral, and is used as a commercial and generic term for all calcium sulfate materials. Raw gypsum ore is processed into a variety of products such as a portland cement additive, soil conditioner, industrial and building plasters, and gypsum wallboard.

Gypsum ore, from quarries and underground mines, is crushed and stockpiled near a plant. As needed, the stockpiled ore is further crushed and screened to about 50 millimeters (2 inches) in diameter. If the moisture content of the mined ore is greater than about 0.5 weight percent, the ore must be dried in a rotary dryer or a heated roller mill. Ore dried in a rotary dryer is conveyed to a roller mill, where it is ground to the extent that 90 percent of it is less than 149 micrometers (100 mesh). The ground gypsum exits the mill in a gas stream and is collected in a product cyclone. Ore is sometimes dried in the roller mill by heating the gas stream so that drying and grinding are accomplished simultaneously and no rotary dryer is needed. The finely ground gypsum ore is known as landplaster, which may be used as a soil conditioner.

In most plants, landplaster is fed to kettle calciners or flash calciners, where it is heated to remove three-quarters of the chemically bound water to form stucco (CaSO4 1⁄2H2O). Calcination occurs at approximately 120° to 150°C (250° to 300°F) and 0.908 megagrams (Mg) (1 ton) of gypsum calcines to about 0.77 Mg (0.85 ton) of stucco.

In kettle calciners, the gypsum is indirectly heated by hot combustion gas passed through flues in the kettle, and the stucco product is discharged into a "hot pit" located below the kettle. Kettle calciners may be operated in either batch or continuous mode. In flash calciners, the gypsum is directly contacted with hot gases, and the stucco product is collected at the bottom of the calciner.

At some gypsum plants, drying, grinding, and calcining are performed in heated impact mills. In these mills hot gas contacts gypsum as it is ground. The gas dries and calcines the ore and then conveys the stucco to a product cyclone for collection. The use of heated impact mills eliminates the need for rotary dryers, calciners, and roller mills.

Gypsum and stucco are usually transferred from one process to another by means of screw conveyors or bucket elevators. Storage bins or silos are normally located downstream of roller mills and calciners but may also be used elsewhere.

In the manufacture of plasters, stucco is ground further in a tube or ball mill and then batch-mixed with retarders and stabilizers to produce plasters with specific setting rates. The thoroughly mixed plaster is fed continuously from intermediate storage bins to a bagging operation.

In the manufacture of wallboard, stucco from storage is first mixed with dry additives such as perlite, starch, fiberglass, or vermiculite. This dry mix is combined with water, soap foam, accelerators, and shredded paper or pulpwood in a pin mixer at the head of a board forming line. The slurry is then spread between two paper sheets that serve as a mold. The edges of the paper are scored, and sometimes chamfered, to allow precise folding of the paper to form the edges of the board. As the wet board travels the length of a conveying line, the calcium sulfate hemihydrate combines with the water in the slurry to form solid calcium sulfate dihydrate, or gypsum, resulting in rigid board. The board is rough-cut to length, and it enters a multideck kiln dryer, where it is dried by direct contact with hot combustion gases or by indirect steam heating. The dried board is conveyed to the board end sawing area and is trimmed and bundled for shipment.

The VIPER Automated, FDA Compliant, Self-contained e-Liquid Compounding System

PS&D's Viper is the first FDA compliant, safe, accurate, automated, and self-contained e-Liquid compounding system for the e-liquid vaping industry.

The production system is integrated with a flexible batch management system that provides a platform for automatic control and electronic record-keeping to comply with FDA regulations 21 CFR 210, 211, and 11. Proven products from Rockwell Automation provides the core of control and information management system. It provides the authorized operator with a secure tool for designing flexible recipes that combine operator-entered and automatic data collection into a single work flow. In-process weights are collected automatically and used to manage the flow of ingredients and finished products between storage and blending vessels. System components, including motors and automatic valves are sequenced according to the recipes’ logic. Data are stored in a relational database management system for long-term storage and reporting. PS&D supports the information technologies associated with the recipe management and data collection processes through secure cloud-based computing and network communications platforms.

For more information, visit http://www.processsystemsdesign.com/e-liquid or call (410) 861-6437.

From Biomass to Biofuel

Biomass converted to gasoline (image courtesy of epa.gov)

Biomass resources run the gamut from corn kernels to corn stalks, from soybean and canola oils to animal fats, from prairie grasses to hardwoods, and even include algae.

In the long run, we will need diverse technologies to make use of these different energy sources. Some technologies are already developed; others will be. Today, the most common technologies involve biochemical, chemical, and thermochemical conversion processes.




Ethanol, today’s largest volume biofuel, is produced through a biochemical conversion process. In this process, yeasts ferment sugar from starch and sugar crops into ethanol. Most of today’s ethanol is produced from cornstarch or sugarcane. But biochemical conversion techniques can also make use of more abundant “cellulosic” biomass sources such as grasses, trees, and agricultural residues.

Researchers develop processes that use heat, pressure, chemicals, and enzymes to unlock the sugars in cellulosic biomass. The sugars are then fermented to ethanol, typically by using genetically engineered micro- organisms. Cellulosic ethanol is the leading candidate for replacing a large portion of U.S. petroleum use.

A much simpler chemical process is used to produce biodiesel. Today’s biodiesel facilities start with vegetable oils, seed oils, or animal fats and react them with methanol or ethanol in the presence of a catalyst. In addition, genetic engineering work has produced algae with a high lipid content that can be used as another source of biodiesel.

Algae are a form of biomass which could substantially increase our nation’s ability to produce domestic biofuels. Algae and plants can serve as a natural source of oil, which conventional petroleum refineries can convert into jet fuel or diesel fuel—a product known as “green diesel.”

Researchers also explore and develop thermochemical processes for converting biomass to liquid fuels. One such process is pyrolysis, which decomposes biomass by heating it in the absence of air. This produces an oil-like liquid that can be burned like fuel oil or re ned into chemicals and fuels, such as “green gasoline.” Thermochemical processes can also be used to pretreat biomass for conversion to biofuels.

Another thermochemical process is gasification. In this process, heat and a limited amount of oxygen are used to convert biomass into a hot synthesis gas. This “syngas” can be combusted and used to produce electricity in a gas turbine or converted to hydrocarbons, alcohols, ethers, or chemical products. In this process, biomass gasifiers can work side by side with fossil fuel gasifiers for greater flexibility and lower net greenhouse gas emissions.

In the future, biomass-derived components such as carbohydrates, lignins, and triglycerides might also be converted to hydrocarbon fuels. Such fuels can be used in heavy-duty vehicles, jet engines, and other applications that need fuels with higher energy densities than those of ethanol or biodiesel.

Batch Processing vs. Continuous Manufacturing in Pharmaceuticals

Not much has changed in pharmaceutical manufacturing over the last 50 years. While technological advancements in creating new drugs have been made, the pharmaceutical industry still relies heavenly on traditional step-by-step batch processing.

Alternatively, continuous manufacturing, which is the preferred manufacturing process in automotive, food & beverage, and refining industries – has been slow to gain acceptance in pharmaceutical production, largely because of high startup costs.

Comparisons

Batch Manufacturing:

All materials are charged before the start of processing and discharged at the end of
processing.

• Examples: Bin blending, lyophilization, some reactions

Continuous Manufacturing

Material is simultaneously charged and discharged from the process

• Examples: Petroleum refining, much of food processing

VARIATIONS

Semi-Batch (Fed-batch)Manufacturing

Materials are added during processing and discharged at the end of processing.

• Examples: Wet granulation, fermentation

Semi-Continuous Manufacturing

Like continuous manufacturing, but for a discrete time period.

• Examples: Roller compaction, tablet compression

Although reliable, batch processing is viewed a slower manufacturing method for pharmaceuticals, and also less safe because of higher risk for contamination and errors between steps. Pharmaceutical manufacturers have no choice but to continually evaluate and implement the best possible production processes. Considering an estimated $50 billion per year is wasted on on inefficient processes in the pharmaceutical industry, it makes great sense to migrate toward continuous manufacturing.

Continuous manufacturing is faster, more efficient, and inherently safer. Improved safety is derived from rigid quality control requirements in continuous manufacturing. Considering this, the concern over large plant and equipment outlays looses is impact. Many experts maintain that continuous manufacturing is ultimately a far less costly production process (considering efficiency and safety), once the initial plant, equipment, and training costs are amortized.

Portland Cement Manufacturing

Cement plant.

Portland cement is a fine powder, gray or white in color, that consists of a mixture of hydraulic cement materials comprising primarily calcium silicates. More than 30 raw materials are known to be used in the manufacture of portland cement, and these materials can be divided into four distinct categories: calcareous, siliceous, argillaceous, and ferrifrous. These materials are chemically combined via pyroprocessing and subjected to subsequent mechanical processing operations to form gray and white portland cement. Gray portland cement is used for structural applications and is the more common type of cement produced. White portland cement has lower iron and manganese contents than gray portland cement and is used primarily for decorative purposes.

Portland cement, which consists of a mixture of the hydraulic cement minerals, calcium silicates, aluminates and aluminoferrites, and calcium sulfates, accounts for 95 percent of the hydraulic cement production in the United States. The balance of domestic cement production comprises primarily masonry cement. Both of these materials are produced in portland cement manufacturing plants.

The production of both portland and masonry cement can be divided into the following primary components: 

• Raw materials acquisition and handling
• Kiln feed preparation
• Pyroprocessing
• Finished cement grinding

Raw Materials Acquisition and Handling

Typically, these raw materials are obtained from open-face quarries, but underground mines or dredging operations are also used. Raw materials vary from facility to facility. The materials found in some quarries that supply raw materials for portland cement have a high degree of calcinated limestone, whereas the material from other limestone quarries must be blended with "cleaner" limestone to produce an acceptable product. In addition, pockets of pyrite, which significantly increase emissions of sulfur dioxide (SO2), can be found in deposits of limestone, clays, and shales used as raw materials for portland cement. Because a large fraction (approximately one third) of the mass of this primary material is converted to carbon dioxide (CO2) in the kiln, portland cement plants are located in close proximity to a raw material source whenever possible. Other metallic elements included in the raw feed mix are silicon, aluminum, and iron. These materials are obtained from ores and minerals such as sand, shale, clay, and iron ore. Again, these materials are most commonly extracted via open-pit quarries or mines, but they may be dredged or excavated from underwater deposits.

Either gypsum or natural anhydrite, both of which are forms of calcium sulfate, is introduced to the process during the finish grinding operations described below. These materials are also excavated from quarries or mines. However, they are generally purchased from an external source, rather than obtained directly from a captive operation by the cement plant. In addition, the portland cement manufacturing industry is relying increasingly on replacing virgin materials as described above with waste materials or byproducts from other manufacturing operations, to the extent that such replacement can be implemented without adversely affecting plant operations or product quality. Materials that have been used include fly ash, mill scale, and metal smelting slags.

Kiln Feed Preparation

The second step in portland cement manufacture is preparing the raw mix or kiln feed for the pyroprocessing operation. Raw material preparation includes a variety of blending and sizing operations that are designed to provide a feed with appropriate chemical and physical properties. The raw material processing operations differ somewhat for wet and dry processes, as described in the paragraphs below.

Cement raw materials are received with an initial moisture content varying from 1 to more than 50 percent. If the facility uses dry process kilns, this moisture is usually reduced to less than 1 percent before or during grinding. Drying alone can be accomplished in impact dryers, drum dryers, paddle- equipped rapid dryers, air separators, or autogenous mills. However, drying can also be accomplished during grinding in ball-and-tube mills or roller mills. While thermal energy for drying can be supplied by exhaust gases from separate, direct-fired coal, oil, or gas burners, the most efficient and widely used source of heat for drying is the hot exit gases from the pyroprocessing system.

Materials transport associated with raw milling systems can be accomplished by a variety of mechanisms, including screw conveyors, belt conveyors, drag conveyors, bucket elevators, air slide conveyors, and pneumatic conveying systems. The dry raw mix is pneumatically blended and stored in specially constructed silos until it is fed to the pyroprocessing system.

In the wet process, water is added to the raw mill during the grinding of the raw materials in ball or tube mills, thereby producing a pumpable slip or slurry of approximately 65 percent solids. The slurry is agitated, blended, and stored in various kinds and sizes of cylindrical tanks or slurry basins until it is fed to the pyroprocessing system.

Pyroprocessing

The heart of the portland cement manufacturing process is the pyroprocessing system. This system transforms the raw mix into clinkers, which are gray, glass-hard, spherically shaped nodules that range from 0.32 to 5.1 centimeters (cm) (0.125 to 2.0 inches [in.]) in diameter. The chemical reactions and physical processes that constitute the transformation are quite complex, but they can be viewed conceptually as the following sequential events:

1. Evaporation of free water; 
2. Evolution of combined water in the argillaceous components; 
3. Calcination of the calcium carbonate (CaCO3) to calcium oxide (CaO); 
4. Reaction of CaO with silica to form dicalcium silicate; 
5. Reaction of CaO with the aluminum and iron-bearing constituents to form the liquid phase; 
6. Formation of the clinker nodules; 
7. Evaporation of volatile constituents (e.g., sodium, potassium, chlorides, and sulfates); and 
8. Reaction of excess CaO with dicalcium silicate to form tricalcium silicate. 

This sequence of events may be conveniently divided into four stages, as a function of location and temperature of the materials in the rotary kiln.

1. Evaporation of uncombined water from raw materials as material temperature increases to 100 deg. C (212 deg. F); 
2. Dehydration as the material temperature increases from 100 deg. C to approximately 430 deg. C (800 deg. F) to form oxides of silicon, aluminum, and iron; 
3. Calcination, during which carbon dioxide (CO2) is evolved, between 900 deg. C (1650 deg. F) and 982 deg. C (1800 deg. F), to form CaO; and 
4. Reaction of the oxides in the burning zone of the rotary kiln to form cement clinker at temperatures of approximately 1510 deg. C (2750 deg. F). 

Rotary kilns are long, cylindrical, slightly inclined furnaces that are lined with refractory to protect the steel shell and retain heat within the kiln. The raw material mix enters the kiln at the elevated end, and the combustion fuels generally are introduced into the lower end of the kiln in a countercurrent manner. The materials are continuously and slowly moved to the lower end by rotation of the kiln. As they move down the kiln, the raw materials are changed to cementitious metal oxides by the direct heat exchange. The most commonly used kiln fuels are coal, natural gas, and occasionally oil. Many cement plants currently burn coal, but use of supplemental fuels such as waste solvents, scrap rubber, and petroleum coke has expanded in recent years.

Five different processes are used in the portland cement industry to accomplish the pyroprocessing step: the wet process, the dry process (long dry process), the semidry process, the dry process with a preheater, and the dry process with a preheater/precalciner. Each of these processes accomplishes the physical/chemical steps defined above. However, the processes vary with respect to equipment design, method of operation, and fuel consumption. Generally, fuel consumption decreases in the order of the processes listed above. The paragraphs below briefly describe the process, starting with the wet process and then noting differences in the other processes.

In the wet process and long dry process, all of the pyroprocessing activity occurs in the rotary kiln. Depending on the process type, kilns have length-to-diameter ratios in the range of 15:1 to 40:1. While some wet process kilns may be as long as 210 m (700 ft), many wet process kilns and all dry process kilns are shorter. Wet process and long dry process pyroprocessing systems consist solely of the simple rotary kiln. Usually, a system of chains is provided at the feed end of the kiln in the drying or preheat zones to improve heat transfer from the hot gases to the solid materials. As the kiln rotates, the chains are raised and exposed to the hot gases. Further kiln rotation causes the hot chains to fall into the cooler materials at the bottom of the kiln, thereby transferring the heat to the load.

Dry process pyroprocessing systems have been improved in thermal efficiency and productive capacity through the addition of one or more cyclone-type preheater vessels in the gas stream after the rotary kiln. This system is called the preheater process. The vessels are arranged vertically, in series, and are supported by a structure known as the preheater tower. Hot exhaust gases from the rotary kiln pass countercurrently through the downward-moving raw materials in the preheater vessels. Compared with the simple rotary kiln, the heat transfer rate is significantly increased, the degree of heat utilization is more complete, and the process time is markedly reduced owing to the intimate contact of the solid particles with the hot gases. The improved heat transfer allows the length of the rotary kiln to be reduced. The hot gases from the preheater tower are often used as a source of heat for drying raw materials in the raw mill. Because the catch from the mechanical collectors, fabric filters, and/or electrostatic precipitators (ESP's) that follow the raw mill is returned to the process, these devices are considered to be production machines as well as pollution control devices.

Additional thermal efficiencies and productivity gains have been achieved by diverting some fuel to a calciner vessel at the base of the preheater tower. This system is called the preheater/precalciner process. While a substantial amount of fuel is used in the precalciner, at least 40 percent of the thermal energy is required in the rotary kiln. The amount of fuel that is introduced to the calciner is determined by the availability and source of the oxygen for combustion in the calciner. Calciner systems sometimes use lower-quality fuels (e.g., less-volatile matter) as a means of improving process economics.

Preheater and precalciner kiln systems often have a bypass system between the feed end of the rotary kiln and the preheater tower to remove the undesirable volatile constituents. Otherwise, the volatile constituents condense in the preheater tower and subsequently recirculate to the kiln. Buildup of these condensed materials can restrict process and gas flows. In a bypass system, a portion of the kiln exit gas stream is withdrawn and quickly cooled by air or water to condense the volatile constituents to fine particles. The solid particles, which are removed from the gas stream by fabric filters and ESP's, are then returned to the process.

The semidry process is a variation of the dry process. In the semidry process, the water is added to the dry raw mix in a pelletizer to form moist nodules or pellets. The pellets then are conveyed on a moving grate preheater before being fed to the rotary kiln. The pellets are dried and partially calcined on the moving grate through which hot kiln exhaust gases pass.

Regardless of the type of pyroprocess used, the last component of the pyroprocessing system is the clinker cooler. This process step recoups up to 30 percent of the heat input to the kiln system, locks in desirable product qualities by freezing mineralogy, and makes it possible to handle the cooled clinker with conventional conveying equipment. The more common types of clinker coolers are (1) reciprocating grate, (2) planetary, and (3) rotary. In these coolers, the clinker is cooled from about 1100 deg. C to 93 deg. C (2000 deg. F to 200 deg. F) by ambient air that passes through the clinker and into the rotary kiln for use as combustion air. However, in the reciprocating grate cooler, lower clinker discharge temperatures are achieved by passing an additional quantity of air through the clinker. Because this additional air cannot be utilized in the kiln for efficient combustion, it is vented to the atmosphere, used for drying coal or raw materials, or used as a combustion air source for the precalciner.

Finished Cement Grinding

The final step in portland cement manufacturing involves a sequence of blending and grinding operations that transforms clinker to finished portland cement. Up to 5 percent gypsum or natural anhydrite is added to the clinker during grinding to control the cement setting time, and other specialty chemicals are added as needed to impart specific product properties. This finish milling is accomplished almost exclusively in ball or tube mills. Typically, finishing is conducted in a closed- circuit system with product sizing via air separation.

Process Systems & Design are dry bulk material handling experts and can assist you in any sand, gravel, cement, or concrete handling requirement. Contact them at (410) 861-6437 or visit their website at http://www.processsystemsdesign.com.

Sand and Gravel Processing

Sand and Gravel Processing

Deposits of sand and gravel, the unconsolidated granular materials resulting from the natural disintegration of rock or stone, are generally found in near-surface alluvial deposits and in subterranean and subaqueous beds. Sand and gravel are siliceous and calcareous products of the weathering of rocks and unconsolidated or poorly consolidated materials. Such deposits are common throughout the country.

Construction Sand and Gravel

Sand and gravel typically are mined in a moist or wet condition by open pit excavation or by dredging. 

Open pit excavation is carried out with power shovels, draglines, front end loaders, and bucket wheel excavators. In rare situations, light charge blasting is done to loosen the deposit. Mining by dredging involves mounting the equipment on boats or barges and removing the sand and gravel from the bottom of the body of water by suction or bucket-type dredges. After mining, the materials are transported to the processing plant by suction pump, earth mover, barge, truck, belt conveyors, or other means.

Although significant amounts of sand and gravel are used for fill, bedding, subbase, and basecourse without processing, most domestic sand and gravel are processed prior to use. The processing of sand and gravel for a specific market involves the use of different combinations of washers, screens, and classifiers to segregate particle sizes; crushers to reduce oversized material; and storage and loading facilities.

After being transported to the processing plant, the wet sand and gravel raw feed is stockpiled or emptied directly into a hopper, which typically is covered with a "grizzly" of parallel bars to screen out large cobbles and boulders. From the hopper, the material is transported to fixed or vibrating scalping screens by gravity, belt conveyors, hydraulic pump, or bucket elevators. The scalping screens separate the oversize material from the smaller, marketable sizes. Oversize material may be used for erosion control, reclamation, or other uses, or it may be directed to a crusher for size reduction, to produce crushed aggregate, or to produce manufactured sands. Crushing generally is carried out in one or two stages, although three-stage crushing may also be performed. Following crushing, the material is returned to the screening operation for sizing.

The material that passes through the scalping screen is fed into a battery of sizing screens, which generally consists of either horizontal or sloped, and either single or multideck, vibrating
screens. Rotating trommel screens with water sprays are also used to process and wash wet sand and gravel. Screening separates the sand and gravel into different size ranges. Water is sprayed onto the material throughout the screening process. After screening, the sized gravel is transported to stockpiles, storage bins, or, in some cases, to crushers by belt conveyors, bucket elevators, or screw conveyors.

The sand is freed from clay and organic impurities by log washers or rotary scrubbers. After scrubbing, the sand typically is sized by water classification. Wet and dry screening is rarely used to size the sand. After classification, the sand is dewatered using screws, separatory cones, or hydroseparators. Material may also be rodmilled to produce smaller sized fractions, although this practice is not common in the industry. After processing, the sand is transported to storage bins or stockpiles by belt conveyors, bucket elevators, or screw conveyors.

Industrial Sand and Gravel

Industrial sand and gravel typically are mined from open pits of naturally occurring quartz-rich sand and sandstone. 

Mining methods depend primarily on the degree of cementation of the rock. In some deposits, blasting is required to loosen the material prior to processing. The material may undergo primary crushing at the mine site before being transported to the processing plant.

The mined rock is transported to the processing site and stockpiled. The material then is crushed. Depending on the degree of cementation, several stages of crushing may be required to achieve the desired size reduction. Gyratory crushers, jaw crushers, roll crushers, and impact mills are used for primary and secondary crushing. After crushing, the size of the material is further reduced to 50 micrometers or smaller by grinding, using smooth rolls, media mills, autogenous mills, hammer mills, or jet mills. The ground material then is classified by wet screening, dry screening, or air classification. At some plants, after initial crushing and screening, a portion of the sand may be diverted to construction sand use.

After initial crushing and screening, industrial sand and gravel are washed to remove unwanted dust and debris and are then screened and classified again. The sand (now containing 25 to 30 percent moisture) or gravel then goes to an attrition scrubbing system that removes surface stains from the material by rubbing in an agitated, high-density pulp. The scrubbed sand or gravel is diluted with water to 25 to 30 percent solids and is pumped to a set of cyclones for further desliming. If the deslimed sand or gravel contains mica, feldspar, and iron bearing minerals, it enters a froth flotation process to which sodium silicate and sulfuric acid are added. The mixture then enters a series of spiral classifiers where the impurities are floated in a froth and diverted to waste. The purified sand, which has a moisture content of 15 to 25 percent, is conveyed to drainage bins where the moisture content is reduced to about 6 percent. The material is then dried in rotary or fluidized bed dryers to a moisture content of less than 0.5 percent. The dryers generally are fired with natural gas or oil, although other fuels such as propane or diesel also may be used. After drying, the material is cooled and then undergoes final screening and classification prior to being stored and packaged for shipment.

Process Systems & Design are experts in the processing of sand and gravel. Visit http://www.processsystemsdesign.com or call (410) 861-6437 with any inquiries or questions you may have.