MEE Forced Circulation
MEE Forced Circulation
Forced Circulation Evaporators are normally used for liquids which are prone to fouling, scaling, and crystallizing or for those which are inversely soluble or while concentrating thermally de-gradable materials. Here high re-circulation rate allows high liquor velocities through the tubes which help to minimize the buildup of deposits or crystals along the heating surface. The universal type, preferably used for concentration of solutions containing encrusting substances, hardening agents and un-dissolved solids, and for viscose solutions; also suitable for evaporative crystallization.
The liquid is circulated through the calandria by means of a circulation pump, where it is superheated at an elevated pressure, higher than its normal boiling pressure. Since liquid circulation is maintained, the flow velocity in the tubes and the liquid temperature can be controlled to suit the product requirements independently of the pre-selected temperature difference.
Energy Efficiency:
Energy Efficiency of Paramount Evaporators and Crystallizers is a crucial consideration during the design of each customer’s specific application. Energy efficient systems utilize waste heat, multiple effects, mechanical vapour recompression (MVR) and / or thermal vapour recompression (TVR).
Multiple Effect Operation :
The evaporation duty is separated into stages operating at different temperatures. External heat drives the first effect of the evaporator, with subsequent effects being driven by vapor generated from the previous higher temperature effect. Product may be passed through the evaporator in forward, back or mixed flow configurations. Additional efficiency is achieved with the use of regenerative heaters, condensate heaters, and vapour heaters.
Thermal Vapour Recompression, TVR :
Multiple effect evaporation plants save steam by repeatedly using the same quantity of heat from effect to effect. The vapours from the first effect are compressed to a higher pressure by the thermocompressor, and these compressed vapours are the heating medium for the subsequent effect. Vapours from the final effect are condensed, heat is recovered and supplemented by the cooling water if required.
Mechanical Vapour Recompression, MVR:
MVR technology yields the greatest energy efficiency for an evaporator and requires low cooling water. An MVR evaporator may be coupled with TVR and multiple effects.
Evaporation plants with mechanical vapour recompressors normally require very low live steam and shifts the necessary energy to electric energy.
MVR can be either high pressure fans or centrifugal compressor types depending on the application.Single-effect centrifugal compressors are frequently used. For high pressure increases, multi-stage compressors are provided. To supply the power to the compressor, either electric power or combustion engines are used where heat is available from the cooling water and exhaust gases. If high pressure steam is available, a steam turbine may be installed for high total energy efficiency.
Fields of application :
Liquids with a high tendency for fouling, highly viscous liquids, as the high concentration step in multiple-effect evaporation plants.Forced circulation evaporators are optimally suited as crystallising evaporators for saline solutions.
FEATURES OF COMP FORCED CIRCULATION EVAPORATORS –
• Suitable for a widest variety of evaporator applications.
• Ideal for crystallizing operation.
• High heat transfer coefficients.
• Positive circulation.
• Freedom from salting, scaling and fouling.
• Suitable for corrosive and viscous solutions.
CRITICAL DESIGN FEATURES OF FORCED CIRCULATION EVAPORATORS –
• Optimum tube velocities
• Type of vapour head used with the forced circulation evaporators is chosen to suit the product characteristics.
TYPICAL APPLICATIONS –
• Effluent Treatments Plants
• Chemical Industry
• Salt Solutions
These shell and tube type evaporators outperform other tubular evaporators when used for water with dissolved salts or organics with a tendency to foul the evaporator tubes.
How they work :
This is a tubular evaporator having heating media on the shell side and the process liquid in the tubes. It has circulation loop equipped with high flow circulation pump.
The feed is introduced into the loop at the bottom. The high flow recirculation pump (Axial Flow Pump) forces the liquid through tubes. It picks up the heat from the shell side steam and flashes in the separator. The flashed vapour moves upward to vapour nozzle of the separator while the concentrate flows down to concentrate nozzle. The concentrate is re-circulated in the loop with high flow. A part of concentrate overflows out from the separator. The liquid height is engineered to avoid the nucleate boiling within evaporator tube bundle. The high flow circulation helps solids to remain in suspension and suppresses fouling.
Features :
• Reduced scaling, ideal for materials with precipitation or crystallization tendency
• Concentration values more than the limits of conventional tubular evaporators when handling feed with dissolved salts
• Multiple effect arrangement provides steam economy
• Equipped with axial flow pumps having high capacity with minimum power
Applications :
• Pre-concentration of scale prone liquids before drying
• Evaporative crystallization
• Wastewater concentration for volume reduction
• Concentration of organic and inorganic salt solutions
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