Multiple Effect Evaporators

Multiple Effect Evaporators (MEE) are equipment used in Industry to concentrate a solution by removing the solvent (mainly water) by the application of heat (steam) and boiling it in a series of vessels with decreasing pressure levels.

Applications in Different Industries

Pharmaceuticals, chemicals and textiles

In these industries, MEEs are used for concentration of effluent water having high TDS, waste water treatment and drying of sludge. Plants obtain easy to dispose of solids, reducing the impact on the environment.

Food & beverage

MEEs play an important role in evaporative crystallization and concentration of organic/inorganic salt bearing solutions.

Process Steam Consumption

The process section consists of several multi-piece equipment, for example dyeing machines, vertical drying ranges for textiles, and reactors and dryers in pharmaceuticals and chemicals. Even under ideal conditions, the MEEs, consume 1/3rd of the total plant steam. Focusing on MEEs and SEEs(single effect evaporators), significant improvements can be made in overall plant steam consumption. Monitoring this single equipment is easier, and benefits get reflected not only at evaporator level, but also at plant level.

Conventional operating practices rely very heavily on manual intervention. Operating systems with these traditional methods can lead to excess steam consumption of as high as 24%.

Some of the associated problems leading to high steam consumption are :

Variations in inlet and outlet feed concentrations
Scaling due to temperature overshoots
Variations in feed flow rates and temperature at inlet and outlet
Steam Control Valve is manually controlled and is 100 % open for entire feed flow range
Pressure and temperature not maintained in effects
Vent line kept 100% open, leading to venting of vapours from separator vessels into the condenser
Reduced motive steam pressure for thermocompressor (TVR)
Uneven differential temperature between effects
Venting of vapours from separator vessels
High amount of reflux
Imbalance in mass and energy
Fouling

The Forbes Marshall Solution: Automation packages for Multiple Effect Evaporators

Steam Energy Factor (SEF) is a universal performance indicator that can be used freely across any steam using equipment as it compares present performance to what it should be, taking into account all process variables. It is the ratio of the actual energy consumed (Qa) to the theoretical energy consumed (Qt).

SEF = Qa/Qt

SEF helps to :

determine the gap between steam energy required and actual steam energy used.
bridge the gap between theoretical baseline and actual consumption.
identify the factors contributing to higher steam consumption.

The MeeSEF is an excellent tool to monitor the performance in terms of evaporation economy (EE), specific steam consumption (SSC) and steam energy factor (SEF). EE, SSC and SEF vary depending on input-output conditions and operating practices. The combined data, along with historical analysis, provides the calculated basis to determine the correct set points and operating practices for the process.

The meeMAC measures, monitors and controls essential process parameters like

Feed : flow rate, temperature, specific gravity
Product : flow rate, temperature, specific gravity
Steam : flow rate, temperature, pressure
Non-condensable gases line : temperature, pressure