Unique Rotating Dryer Design is Perfect for Forest and Agricultural Products

The exclusive technology DRYER ONE, developed by Belgium company Technic One, enables the precise drying and processing of a large range of forest and agricultural products, in addition to the recovery of waste materials.

It operates bu loading the material to be dried onto a rotating plate through which passes a hot air flow. After a 360° rotation, the partially dried material is transferred onto a second plate where it is rotated again, thereby completing the drying process. Various control processes are used to ensure the good working and to reach the desired moisture content of the product.

Typical drying applications are wood waste, wood shavings, sawdust, maize, coffee grounds, brewer's grain, corn, soy, seeds, rice, and barley.

A visual understanding of the dryer operation is explained below:

1. IN - The lower rotating plate is loaded with the material to be dried.
2. LOWER LEVEL DRYING - The material is rotated by 360°.
3. UP - The material to be dried is transferred towards the upper plate by a bucket elevator or a vertical screw conveyor.
4. HIGHER LEVEL DRYING - The material is rotated 360° by the upper rotating plate, moving in the opposite direction to that of the lower level plate. This exclusive technology ensures better distribution of heat and greater efficiency than other hot air drying techniques.
5. OUT - The dried material is exited towards the packaging or storage area.
6. HOT AIR FLOW - The hot air is sucked from the top to the bottom creating a counter current. It successively crosses the higher and lower level plates.
7. RETRIEVAL AND EXPULSION OF AIR SATURATED WITH MOISTURE - After passing through the two plates the saturated air is pushed upwards for expulsion. If necessary, filters suitable for residual particles can be installed at the final stage of the process.

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1. Hot water is brought from a cogeneration unit.
2. The heat exchanger transfers the heat from the hot water into ambient air. The heated air is then drawn into the dryer.
3. Cooled water evacuation after exchange.
4. The incoming air is dry and hot (60-90°C)(140-194°F).
5. The reverse counter-current air flow (moving from the top to the bottom of the dryer) presses through material laying on the rotating plates, this largely prevents dust dispersion.
6. The outgoing cooled air (25-30°C)(77-86°F), almost completely saturated with moisture, is evacuated via the central chimney.
7. The first rotating plate gradually and partially evaporates the moisture.
8. Material is transferred from the lower plate to the higher plate via a bucket elevator or a vertical screw conveyor. During the transfer, the material is rotated and mixed, providing better quality and even drying.
9. The second rotating plate completes the drying process and allows the hot air to absorb residual moisture.

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1. ROTATION OF MATERIAL - Each drying plate is equipped with a screw conveyor which thoroughly rotates and mixes the material to be dried. This process provides more even and better quality drying.
2. ROTATION SYSTEM - Each rotating plate is driven by a gearmotor, which ensures a constant rotation speed with complete reliability.
3. PLATE COVERINGS - The rotating plates are covered with a highly resistant synthetic grooved surface or stainless steel perforated sheeting. The load loss of the material to be dried is lower than that of the covering, leading to better diffusion of the hot air flow across the whole surface. Moisture can be extracted gradually, without thermal shock. The more even humidity level is one of the main advantages of DRYER ONE™. The coverings can easily and quickly be replaced.
4. ROTATING METAL PLATES - The rotating plates have a stainless steel grated structure with a planarity much greater than that of conveyor belts. They have high resistance to load stress and corrosion. The grated structure is divided into segments of equal size, making it much easier to carry out maintenance work or replacements in the space of just a few minutes.

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For more information on the Dryer One system, contact Process Systems & Design by calling (410) 861-6437 or visiting https://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.

Safe, Efficient, and Clean Operation of Belt Conveyors

Belt conveyors are among the most commonly used piece of equipment at mineral processing operations. A conveyor, and the associated transfer points, can generate significant quantities of hazardous debris and respirable dust. Operations must control these emissions by containing, suppressing, or collecting the dust and debris mechanically, either before or after it spills or becomes airborne, giving special attention to transfer points.

A conveyor belt consists of many different parts as seen in Figure 1.

Figure 1 - Basic components of a conveyor belt. 

There are three primary root causes for hazardous debris or fugitive dust emissions associated with conveyor belts: spillage, carryback, and airborne dust (Figure 2). Control of all three primary dust sources is necessary to eliminate hazardous debris and fugitive dust emissions.

Fig. 2 - Types of fugitive dust emissions and debris from conveyor belts 

Controlling Material Spillage

Material spillage from a conveyor belt is caused by a lack of material control, either at a transfer point or along the transfer route. Spillage along the transfer route is generally associated with carryback.

Carryback

Material that sticks or clings to a conveyor belt after passing over the head pulley is called carryback. Carryback tends to fall from the belt as it passes over return idlers. This creates piles of material that require clean-up, which can increase worker dust exposure. Also, respirable portions of carryback can become airborne and increase fugitive dust exposure levels. The goal is to remove carryback before it is released into the air and becomes a source of contamination to the workers or creates piles of material that require clean-up.

The primary means of controlling carryback is to clean the belt as it passes over or past the head pulley (i.e. shortly after material is discharged from the belt). The two most common means of cleaning a conveyor belt of carryback are to mechanically "scrape" the belt via scrapers or brushes or to wash the belt.

Water Sprays for Prevention of Airborne Dust

Wet spray systems, the use of water to control dust, may be classified into prevention applications and suppression applications. When properly designed and installed, water sprays are a cost-effective method of controlling dust from conveyors. The most common and effective practice for conveyor sprays is to wet the entire width of product on the belt.

To discuss this topic in greater detail, contact the experts at Process Systems & Design. They'll be happy to share their decades of experience and knowledge with you.

www.processsytems.com
info@processsystemsdesign.com
(410) 861-6437