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Energy efficient drying of high TDS wastewater by Sludge Dryer
Industrial wastewater is a generated from the various manufacturing processes and cleanup operations. As water is required for nearly every step of production across a multitude of industries, it can pick up a variety of contaminants that require removal to acceptable levels before discharge from an industrial manufacturing facility. Typical constituents requiring treatment may include suspended solids (TSS), dissolved solids (TDS), fats-oils-grease (FOG), pH, bacteria, selenium, heavy metals and other regulated chemicals and substances.
Typical wastewater treatment involves primary, secondary, and tertiary treatment to remove mainly contaminates, followed by concentration of high TDS stream by evaporation technique. Treatment of this concentrated stream is the last part of wastewater treatment. Sometimes concentrated stream generates directly from plant operation.
Various types of methods are used to treat concentrated wastewater. Most conventional methods operate in batch mode, which involves filtration or kettle drying. In filtration method, mother liquor has to be recycled for concentration, which involves repeated use of energy to evaporate same liquid. Also, sludge from the filter contain high amount of water, which is expensive to dispose. In kettle drying method, kettle filled with wastewater is heated indirectly with hot utility on jacket side. This technique involves high energy consumption and longer hours for drying. Also removing sludge after drying become difficult task which involves lot of manual work. This leads to unsafe and messy operation.
Commonly used continuous method is spray drying. This is direct contact drying where hot air is in direct contact with wastewater droplets. In this case, energy efficiency is low because of inefficient contact with hot medium. Also size of the plant is huge and number of equipment involve are more. Evaporated water along with flue gases discharged to outside air. Hence evaporated water cannot be recovered. This technique is not environment friendly and less energy efficient
The Technoforce Sludge dryer is example of indirect contact drying method. Agitated Thin Film Drying technology is used in this type of dryer. Sludge Dryer consists of a vertical cylinder fitted with a heating jacket. The feed material is pumped continuously to the feed nozzle on top of the equipment. By gravity it flows down and is spread uniformly to a thin film on the inner wall of the Sludge Dryer by a fast-rotating agitator. The heating jacket is heated by steam or thermal oil and transfers the heat to the evaporator. Evaporated vapors from feed film travel to an external condenser while the feed material turns into slurry, sludge, paste and finally dry powder that is collected at the bottom. For wastewater applications, the dryers are often run under atmospheric pressure. This leads to ease in powder collection.
Rotor design is crucial to be successful in the wastewater drying process. Most wastewater feeds are sticky in nature. During drying process, solids stick to the inside wall of Sludge Dryer should be removed continuously to keep surface clean. For this purpose, Zero clearance rotors having hinged blades are used. These hinge blades can touch the shell and wipe the solid built up. (Refer figure 3) Blades are sturdy in design and can handle various types of wastewater.
Figure 3: Zero clearance blade in Sludge Dryer
Agitated Thin Film Drying is highly energy efficient process. Because of the compact design, good control over operating parameters; Sludge dryer become very easy to operate and require less space. One can vary dryness of the solids from dryer based on requirement by simply changing the feed rate or heating temperature. Evaporated water can be condensed and reused.
The indirectly heated sludge dryer eliminates air pollution and gives unmatched thermal efficiency of more than 90 % which is way higher than spray dryer. Overall, 75% space saving can be achieved as compared to similar size spray drying plant.
Technoforce has two types of Sludge Dryers based on their orientation, i.e., vertical and horizontal. Sludge Dryer – Vertical suits well for feeds in the form of solutions or slurries which are pumpable. Sludge Dryer- horizontal is versatile alternative. It is suitable for solutions, dilute slurries, thick slurries, pastes or filter cakes.
Technoforce has already designed and built more than 150 Sludge Dryers for various industrial sectors. We also make Agitated Thin Film Dryers (ATFD) specially designed for product drying applications. We offer other evaporation technologies like Agitate Thin Film Evaporation, Short Path Distillation, Falling Film, Rising Film and Forced Circulation Evaporation, as well as Liquid-Liquid Extraction and Crystallization technologies. Technoforce is ISO 14001:2015, ISO 45001:2018, ISO 9001:2015 certified company with decades of experience in construction under ASME U stamp and PED/CE mark certification. Technoforce also have Pilot Plants facility in The Netherland and India. Sales office in India and Germany. For more details, visit Technoforce website www.technoforce.net