Rotary dryer

Last updated
Single shell rotary drum dryer Single Shell Rotary Drum Dryer.jpg
Single shell rotary drum dryer

A rotary dryer is a type of industrial dryer used to reduce or minimize the moisture content of the material it is handling by bringing it into contact with a heated gas. [1] The dryer is made up of a rotating cylinder ("drum" or "shell"), a drive mechanism, and a support structure (commonly concrete posts or a steel frame). The cylinder is inclined slightly with the discharge end is lower than the material feed end so that material moves through the dryer under the influence of gravity. Material to be dried enters the dryer and, as the dryer rotates, the material is lifted up by a series of fins (known as flights) lining the inner wall of the dryer. When the material gets high enough, it falls back down to the bottom of the dryer, passing through the hot gas stream as it falls.

Contents

Applications

Rotary Dryers have many applications but are most commonly seen in the mineral industry for drying sand, stone, soil, and ore. [2] They are also used in the food industry for granular material such as grains, cereals, pulses, and coffee beans.

Design

A wide variety of rotary dryer designs are available for different applications. Gas flow, heat source, and drum design all affect the efficiency and suitability of a dryer for different materials.

Gas flow

The stream of hot gas can either be moving toward the discharge end from the feed end (known as co-current flow), or toward the feed end from the discharge end (known as counter-current flow). The direction of gas flow combined with the inclination of the drum determine how quickly material moves through the dryer.

Heat source

The gas stream is most commonly heated with a burner using gas, coal or oil. If the hot gas stream is made up of a mixture of air and combustion gases from a burner, the dryer is known as "directly heated". Alternatively, the gas stream may consist of air or another (sometimes inert) gas that is preheated. Where burner combustion gases do not enter the dryer, the dryer is known as "indirectly-heated". [3] Often, indirectly heated dryers are used when product contamination is a concern. In some cases, a combination of direct-indirect heated rotary dryers are also used to improve the overall efficiency.

Drum design

Double Shell Rotary Drum Dryer Double Shell Rotary Drum Dryer.jpg
Double Shell Rotary Drum Dryer
Triple Shell Rotary Drum Dryer Triple Shell Rotary Drum Dryer.jpg
Triple Shell Rotary Drum Dryer

A rotary dryer can consist of a single shell or several concentric shells, though any more than three shells is not usually necessary. Multiple drums can reduce the amount of space that the equipment requires to achieve the same throughput. Multi-drum dryers are often heated directly by oil or gas burners. The addition of a combustion chamber at the feed end helps ensure efficient fuel usage, and homogenous drying air temperatures.

Combined processes

Some rotary dryers have the ability to combine other processes with drying. Other processes that can be combined with drying include cooling, cleaning, shredding and separating.

See also

Related Research Articles

<span class="mw-page-title-main">Spray drying</span>

Spray drying is a method of changing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals, or materials which may require extremely consistent, fine particle size. Air is the heated drying medium; however, if the liquid is a flammable solvent such as ethanol or the product is oxygen-sensitive then nitrogen is used.

<span class="mw-page-title-main">Boiler</span> Closed vessel in which fluid is heated

A boiler is a closed vessel in which fluid is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central heating, boiler-based power generation, cooking, and sanitation.

<span class="mw-page-title-main">Water heating</span> Thermodynamic process that uses energy sources to heat water

Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature. Typical domestic uses of hot water include cooking, cleaning, bathing, and space heating. In industry, hot water and water heated to steam have many uses.

<span class="mw-page-title-main">Recuperator</span>

A recuperator is a special purpose counter-flow energy recovery heat exchanger positioned within the supply and exhaust air streams of an air handling system, or in the exhaust gases of an industrial process, in order to recover the waste heat. Generally, they are used to extract heat from the exhaust and use it to preheat air entering the combustion system. In this way they use waste energy to heat the air, offsetting some of the fuel, and thereby improve the energy efficiency of the system as a whole.

The Buell dryer, also known as the "turbo shelf" dryer, is an indirect heated industrial dryer once widely used in the Cornwall and Devon china clay mining industry. The Buell dryer was introduced to the china clay industry by English Clays Lovering Pochin & Co. Ltd for their china clay drying plants in Cornwall and Devon, as part of the mechanization and modernization of the industry, which up to that point had been using the same primitive processing methods for almost 100 years.

<span class="mw-page-title-main">Thermal power station</span> Power plant that generates electricity from heat energy

A thermal power station is a type of power station in which heat energy is converted to electrical energy. In a steam-generating cycle heat is used to boil water in a large pressure vessel to produce high-pressure steam, which drives a steam turbine connected to an electrical generator. The low-pressure exhaust from the turbine enters a steam condenser where it is cooled to produce hot condensate which is recycled to the heating process to generate more high pressure steam. This is known as a Rankine cycle.

<span class="mw-page-title-main">Air preheater</span> Device designed to heat air before another process

An air preheater is any device designed to heat air before another process (for example, combustion in a boiler With the primary objective of increasing the thermal efficiency of the process. They may be used alone or to replace a recuperative heat system or to replace a steam coil.

A pulverized coal-fired boiler is an industrial or utility boiler that generates thermal energy by burning pulverized coal that is blown into the firebox.

Economizers, or economisers (UK), are mechanical devices intended to reduce energy consumption, or to perform useful function such as preheating a fluid. The term economizer is used for other purposes as well. Boiler, power plant, heating, refrigeration, ventilating, and air conditioning (HVAC) uses are discussed in this article. In simple terms, an economizer is a heat exchanger.

<span class="mw-page-title-main">Rotary-screw compressor</span> Gas compressor using a rotary positive-displacement mechanism

A rotary-screw compressor is a type of gas compressor, such as an air compressor, that uses a rotary-type positive-displacement mechanism. These compressors are common in industrial applications and replace more traditional piston compressors where larger volumes of compressed gas are needed, e.g. for large refrigeration cycles such as chillers, or for compressed air systems to operate air-driven tools such as jackhammers and impact wrenches. For smaller rotor sizes the inherent leakage in the rotors becomes much more significant, leading to this type of mechanism being less suitable for smaller compressors than piston compressors.

<span class="mw-page-title-main">Rotary kiln</span>

A rotary kiln is a pyroprocessing device used to raise materials to a high temperature (calcination) in a continuous process. Materials produced using rotary kilns include:

<span class="mw-page-title-main">Rotary vacuum-drum filter</span>

A Rotary Vacuum Filter Drum consists of a cylindrical filter membrane that is partly sub-merged in a slurry to be filtered. The inside of the drum is held lower than the ambient pressure. As the drum rotates through the slurry, the liquid is sucked through the membrane, leaving solids to cake on the membrane surface while the drum is submerged. A knife or blade is positioned to scrape the product from the surface.

<span class="mw-page-title-main">Cement kiln</span> High temperature rotating oven used for producing clinker

Cement kilns are used for the pyroprocessing stage of manufacture of portland and other types of hydraulic cement, in which calcium carbonate reacts with silica-bearing minerals to form a mixture of calcium silicates. Over a billion tonnes of cement are made per year, and cement kilns are the heart of this production process: their capacity usually defines the capacity of the cement plant. As the main energy-consuming and greenhouse-gas–emitting stage of cement manufacture, improvement of kiln efficiency has been the central concern of cement manufacturing technology. Emissions from cement kilns are a major source of greenhouse gas emissions, accounting for around 2.5% of non-natural carbon emissions worldwide.

For environmental remediation, Low-temperature thermal desorption (LTTD), also known as low-temperature thermal volatilization, thermal stripping, and soil roasting, is an ex-situ remedial technology that uses heat to physically separate petroleum hydrocarbons from excavated soils. Thermal desorbers are designed to heat soils to temperatures sufficient to cause constituents to volatilize and desorb from the soil. Although they are not designed to decompose organic constituents, thermal desorbers can, depending upon the specific organics present and the temperature of the desorber system, cause some organic constituents to completely or partially decompose. The vaporized hydrocarbons are generally treated in a secondary treatment unit prior to discharge to the atmosphere. Afterburners and oxidizers destroy the organic constituents. Condensers and carbon adsorption units trap organic compounds for subsequent treatment or disposal.

A regenerative heat exchanger, or more commonly a regenerator, is a type of heat exchanger where heat from the hot fluid is intermittently stored in a thermal storage medium before it is transferred to the cold fluid. To accomplish this the hot fluid is brought into contact with the heat storage medium, then the fluid is displaced with the cold fluid, which absorbs the heat.

A single-ended recuperative (SER) burner is a type of gas burner used in high-temperature industrial kilns and furnaces. These burners are used where indirect heating is required, e.g. where the products of combustion are not allowed to combine with the atmosphere of the furnace. The typical design is a tubular (pipe) shape with convoluted pathways on the interior, closed on the end pointed into the furnace. A gas burner fires a flame down the center of these pathways, and the hot combustion gases are then forced to change direction and travel along the shell of the tube, heating it to incandescent temperatures and allowing efficient transfer of thermal energy to the furnace interior. Exhaust gas is collected back at the burner end where it is eventually discharged to the atmosphere. The hot exhaust can be used to pre-heat the incoming combustion air and fuel gas (recuperation) to boost efficiency.

<span class="mw-page-title-main">Thermal wheel</span> Type of energy recovery heat exchanger

A thermal wheel, also known as a rotary heat exchanger, or rotary air-to-air enthalpy wheel, energy recovery wheel, or heat recovery wheel, is a type of energy recovery heat exchanger positioned within the supply and exhaust air streams of air-handling units or rooftop units or in the exhaust gases of an industrial process, in order to recover the heat energy. Other variants include enthalpy wheels and desiccant wheels. A cooling-specific thermal wheel is sometimes referred to as a Kyoto wheel.

A belt dryer is an apparatus which is used for continuous drying and cooling of woodchip, pellets, pastes, moulded compounds and panels using air, inert gas, or flue gas.

<span class="mw-page-title-main">Flights (rotary dryer)</span>

Flights, also commonly referred to as "material lifters" or "shovelling plates" are used in rotary dryers and rotary coolers to shower material through the process gas stream. Fixed to the interior of the rotary drum, these fin-like structures scoop material up from the material bed at the bottom of the drum and shower it through the gas stream as the drum rotates. This showering creates a curtain of material spanning the width of the drum, helping to maximize the efficiency of heat transfer.

<span class="mw-page-title-main">Industrial furnace</span> Device used for providing heat in industrial applications

An industrial furnace, also known as a direct heater or a direct fired heater, is a device used to provide heat for an industrial process, typically higher than 400 degrees Celsius. They are used to provide heat for a process or can serve as reactor which provides heats of reaction. Furnace designs vary as to its function, heating duty, type of fuel and method of introducing combustion air. Heat is generated by an industrial furnace by mixing fuel with air or oxygen, or from electrical energy. The residual heat will exit the furnace as flue gas. These are designed as per international codes and standards the most common of which are ISO 13705 / American Petroleum Institute (API) Standard 560. Types of industrial furnaces include batch ovens, vacuum furnaces, and solar furnaces. Industrial furnaces are used in applications such as chemical reactions, cremation, oil refining, and glasswork.

References

  1. "Rotary Dryers". feeco.com. Feeco International Inc. Retrieved 17 February 2021.
  2. "Rotary Dryers". www.thyssenkrupp-industrial-solutions.com. Thyssenkrupp Industrial Solutions. Retrieved 17 February 2021.
  3. "Rotary Dryers". mitchelldryers.co.uk. Mitchell Dryers. Retrieved 17 February 2021.