The drying process in a rapid dryer HAZEMAG rapid dryers demonstrate the advantages of short-retention and uniflow drying in a most emphatic way, achieving an exceptional degree of effectiveness. Short retention drying in the rapid dryer is characterised by the combined effects of mechanical turbulence of the feed material by agitator paddles and the simultaneous exposure to hot gases, promoting a quick, safe, and intensive drying process. With the uniflow system, the wet (feed) material and the hot gases flow through the dryer in the same direction, the advantage being that high hot gas temperatures can be applied without any deleterious effects on the feed material. When the hot gases come into contact with the wet material, intensive moisture evaporation is coupled with a simultaneous drop in drying gas temperature.
The rapid dryer is particularly effective when used to dry wet, plastic clay or problematical „filter cake“ which has already been dewatered mechanically by belt filter, filter press, drum filter or centrifuge – flue gas gypsum, chemical gypsum, chrome hydroxide, for example. The material is broken up into small lumps, presenting a large surface area which permits intensive transfer of heat and matter. Make-up The rapid dryer housing is of welded steel construction, designed to take particular account of the thermal loads anticipated during operation. The rapid dryer is an agitator shaft dryer. The lower housing accommodates one (AS models) or two (ASS models) shafts fitted with arms to which agitator paddles are affixed. The shaft bearings at the feed end can be water-cooled if necessary. Large doors are provided in the dryer housing for easy access into the interior. Feed and discharge are effected by HAZEMAG pendulum flap gates. If the dried material is very fine, it can be discharged with the dryer off-gases. Thanks to its compact design, the rapid dryer is particularly effective in applications where space is at a premium.
Method of operation the flue gases used for drying enter the front end of the dryer above the agitator shafts; the material to be dried is fed into the dryer via a double pendulum flap gate. The agitator shafts serve to break up and disperse the feed material throughout the drying chamber. The dispersed material comes into contact with the hot gases which enter the chamber at the same time, resulting in an immediate and intensive evaporation process. The progress of the material through the dryer is effected by the agitator shafts in conjunction with the dryer gas flow. Special internals are provided in the dryer to influence the residence time of the material.
Drying gases as a rule, the drying gases are provided by a hot gas generator using oil, natural gas, coal, etc. as fuel. The hot gas temperatures can be as high as 700 or 800 °C. Versatility The rapid dryer is distinguished by its versatility. It can be used to dry a very wide range of materials, of which just some are listed below: clay, trass, blast furnace slag, limestone chippings, cement raw material, pozzolana, pyrite, aluminum hydroxide, natural and synthetic gypsum, flue gas gypsum, fluorite, bentonite, slurry coal, quartz sand, anode residue, lignite, and pit coal fly ash.
For each drying process, a mass transfer of water from the product to be dried to the drying medium (usually air) is necessary. Each kg of air can absorb a certain amount of water at a certain temperature.
The higher the temperature, the more water the air can absorb, or in other words – drying a given amount of water requires less air mass flow at a higher temperature.
The HAZEMAG rapid dryer is technically safe because it mechanically deagglomerates the material to be dried with the centrifugal shafts, which other dryers can only achieve to a limited extent or not. In a HAZEMAG rapid dryer, the product to be dried is always kept in motion and thrown into the passing air stream. This ensures that the individual particles always come into contact with the hot air all around and are dried quickly. Drying is more uniform, non-deagglomerate agglomerates with core moisture is less likely.
Basics of drying technology
Drying is an evaporation process that is used when a substance cannot be sufficiently dehydrated by mechanical treatment (e.g., filtration, centrifugation).
The drying of solid, free-flowing substances is about separating these substances from moisture. The moisture is already contained in many substances from nature. However, it can also have been added retrospectively by processes of processing technology (e.g., wet washing), so that a separation may also be necessary here.
In contrast to dewatering, where moisture separation is carried out by mechanical methods (e.g., pressure, gravity, centrifugal forces), thermal drying uses heat energy. Normally, this method is used in the removal of water (or organic solvents) from materials that have only a low liquid content (e.g., after pre-treatment with the above-mentioned methods).
Fundamental to this process is that the individual components (drying material and drying gas) have a significantly different boiling point.
Functional principle of the HAZEMAG Rapid Dryer
The HAZEMAG rapid dryer, also known as centrifugal shaft dryer in the literature, is a proven dryer design in practice and combines the advantages of convection drying and DC drying, whereby a high efficiency is achieved. Due to the mechanical turbulence of the dry material with throwing blades and simultaneous flow through with hot gas, thermally gentle drying is possible in a short time. Gas or light oil burners are usually used to heat the drying air for applications in the mineral industry. The combustion gases are mixed with a proportion of ambient air to average drying air temperatures between 800°C and 900°C.