Multiple Effect Evaporation (MEE)
Every industry, be it in Textile, Paper, Tannery, Pharmaceutical, Distilleries, etc, generates effluent.
These effluents pose a serious problem if disposed into water courses or on land. Hence various pollution control boards have stringent laws to monitor the surface water quality by limiting COD, BOD, pH, Suspended solids (TSS, TDS), temperature, heavy metals etc. With water crises at its peak, government all through the country is becoming extremely conscious about the water usage of industry. The companies are being forced to comply with norms of “Zero Liquid Discharge”. This means that the industry not only has to ensure treatment of the effluents being generated by them, but is also responsible to extract reusable water from it to the extent that they generate solid waste as final reject and permeate water as main product. After treatment of effluent, which involves reduction of TSS, COD, BOD etc., the effluents as taken to membranes for reduction of volumes. Evaporation process being an expensive process running on steam and power. By extracting as high quantity of permeate from the effluent. The RO reject with high TDS, is then taken to evaporator for further reduction and then taken to a dryer/crystallizer for converting it into solid waste containing moisture below 10% level. This solid waste being baggable is then taken to a solid waste disposal site.
Unitop a chemical engineering organisation specializes in heat transfer designs for evaporation and drying makes turnkey supplies for plants connected with Zero Effluent Discharge Systems.
Design
There are various type of evaporator based on feed specifications & conditions, they are selected for each application.
Each have their own set of advantages and disadvantages & right selection of the type of evaporator for each application decides the working evaporator at optimum running & maintenance cost.
Effluent Filtration Equipment:
Effluents, if at high temperature pose problems during Effluent Treatment Plant, because of high BOD. Hence, Effluent has to be cooled. Heat Recovery System, when provided, not only cools the effluent but also produces Hot Water Suitable for Process/Boiler use.
Chemicals Recovery:
With proper studies, Effluent Containing expensive chemicals can be sent to a separate evaporation system to recover chemicals Like: Caustic Soda, Sodium sulfate, Soda Ash, Glycerin etc. With such recovery plants, not only we save Treatment: cost but also earn profits by recovering these expensive chemicals. Hence such plants have highly attractive payback periods.
Heat Recovery System:
It is necessary to clean it off any fibers/insoluble’s, so that they don’t interfere the working of the Evaporation Plant by clogging the small sized devices such as Spray Nozzles, Pump Impellers, Heat Exchanger Tubes etc.
Effluent / RO Rejects Evaporation:
In case of effluents, this is a huge uncertainty on salt conposition. There is possibility of various due to change in processes, Shock loads and treatment procedures. Presence of Bicarbonates, silica, solvent and hardness can affect smooth operation of evaporators.
At Unitop every palnt is tailor-designed to suit various process conditions like: Feed Temp, Feed Concentration, Product Concentration and Characteristics of Material like Heat Sensitivity, Flow Characteristics, Corrosion and Scaling Tendencies.
Design Basis:
Steam always enters the first heater. Vapors from the first effect are fed to the second heater and so on. The heaters transfer heat indirectly with a shell and tube heat exchanger.
The vapor liquor mixture enters the flash vessels and gets separated in 3-stage separation program and more or less pure water vapors enter the 2nd stage guaranteeing quality of condensate to be recycled. The concentrated liquor enters the 2nd heater gets heated by indirect contact with the generated vapors and the same procedures is repeated.
The overall result of such meticulous design is very encouraging in these days of high energy costs and the Processing Costs on Evaporation plants are amongst the highest in the industry.
When the liquor contains soluble organic or inorganic contents, they tend to separate out when solubility is reduced because of either increase in concentration or decrease in temperature or both.
The total characteristics of the effluent are seldom known or even if known keep changing as per the product mix. Due to this inconsistent feed quality, there are very high chances of tube fouling and maintenance operations.
If the separated solids / crystals are not taken care of properly, they will choke Evaporator, piping or Exchanger tubes. Consequent excessive scaling also would call for stoppages far cleaning.
Since Evaporation systems are susceptible to fouling as described above, there is a |imitation to the achievable concentration of the product in an evaporator. Usually most of the salts start crystallizing / scaling after about Z7P» concentration. 5o to reduce downtime and cleaning costs, it is best suggested to concentrate the effluent in the forced circulation evaporator up to a concentration depending upon the nature of effluents and then take it for further processing; Crystallization / Solidification, depending upon the nature of salt.
Why UNITOP MEE
Unitop Aquacare has earned a name in industry thanks to its super economy plant design.
Our strength Is many folds:
Process optimization.
Depending on the process conditions, we design proper circuitry to optimize the corrosion conditions and scaling tendencies Forward Feed is Selected when Concentrate at high temperature is highly Corrosive Backward Feed is selected when Concentrate is highly viscous at low Temperature. When both these requirements exist partially, selection could be: Mixed Feed.
Selective use of Material of Construction:
We supply the plant in Material of Construction which can limit the Investment while accommodating the quality and sustainable life requirement.
Flexibility in plant design:
UNITOP designs tailor-made systems to suit customer’s needs and the local conditions like fuel prices, quality of water and the space constraints. Our plant can generate hot water at such temperature that all of it can get consumed, in which case generation of hot water can recover the cost of steam supplied to evaporation plant making effluent evaporation virtually free! In case of hot water generated cannot be consumed we have options! Unitop’s unique feature – Adiabatic Evaporator Utilizes the exhaust vapor from the last stage this also reduces Steam Consumption significantly.
Optimum Number of Stages:
Depending on the plant Capacity, Material of Construction and cost factors associated with the plant operation, optimum number of effects are worked out and suggested by a computer program.
Lowest steam Consumption:
Our unique selection of parameters and steam saving innovations improve the steam economy to as high as 6:5 kg evapn/Kg of steam. This is possible because of provision of:
- Optimum number of stages.
- Multistage Condensate Flashing System.
- Feed Preheating 6ysterri.
- Thermo Compressor (TVR) When necessary
- Adiabatic Evaporator
The steam consumption is 20% – 30% lower than other manufacturer. Unbelievable but true! Optimum heat economy for every plant works out to ensure value for money.
Multistage Condensate Flashing Systems:
Condensate from each effect is flashed successively at lower pressure and the flash vapors are used for. carrying out the evaporation in the next stage
Feed Preheating Systems:
When feed is cold and has to enter the stage which is at high Temperature, a lot of steam is consumed to heat the feed up to. boiling point. In our plant feed is heated by evaporated vapors in countercurrent fashion bringing in substantial saving in steam.
Thermo Compressor (TVR):
Thermo – Vapor – Compressor is used to recycles vapors from one of the effects to the first effect calandria by using Motive force of high pressure steam thereby saving Iive steam
Condensate Quality:
Demisters provided in flash vessels ensure good quality of condensate with TDS below 100 ppm much to the liking of pollution control board.
Low Space Requirement:
Our plants are compact with low headroom requirement. AII options are from Ground Level plant can be fitted inside or above the processing house.
Forced Circulation Evaporator:
In this type of evaporator liquid is pumped through heat exchanger tubes by mixed flow pump at high velocity avoiding precipitation and creating high turbulence. Though the consume higher power than conventional evaporators this gets compensated by reduced scaling tendency Reduced Downtimes and Reduced Cleaning frequencies.
Effective Automation:
An entire Plant operation is automated and hence the plant can be monitored and controlled by a single person. Advanced plants are equipped with level, density, pH controllers operations with DAS/SCADA. Trouble shooting modules –
Types of MEE
Our installations
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