Evaporator multi-effect

Because the number of evaporators represents an integer-valued variable, and because many engineers use tables and graphs as well as equations for evaporator calculations, some of the methods outlined in Chapters 9 and 10 can be applied for the optimization of multi-effect evaporator cascades. 

The separated liquor, which is very dark, is known as black liquor. It is concentrated in multi-effect evaporators to 60-65 percent... 

The glycol plant feed along with any high aldehyde EO bleeds from the EO purification section are sent to the glycol reactor (9) and then to a multi-effect evaporation train (10, 11, 12) for removal of the bulk of the water from the glycols. The glycols are then dried (13) and sent to the glycol distillation train (14, 15, 16) where the MEG, DEG and TEG products are recovered and purified. 

Ignore the size of a process unit and multiple process units of the same type in series, such as the number of evaporators for multi-effect evaporation or the number of Continuously Stirred Tank Reactors (CSTRs). 

Ramakrishna, P. Estimate optimum number of effects for multi-effect evaporation. Chem. Eng. 1987, 94, 82. 

The heat recovery evaporator is a multistage, multi-effect evaporator which is different from conventional multiple effect evaporator or multistage flash evaporator. Asahi Chemical s heat recovery evaporator can concentrate the catholyte from 21% to about 40% without steam by utilizing heat generated during electrolysis. To obtain product caustic soda of 50% concentration, a small amount of steam is supplied to the finishing evaporator. 

Fig. 7.48 Multi-effect evaporator for tomato concentration with a side-stream...

Operating Pretturet The proper operating pressures within single-effect and multi-effect evaporators must be maintained to enhance thermal efficiency and capacity. The pressures can be affected by loss of vacuum and line restrictions. As frictional pressure drops or vapor pressure within each effect increases, the boiling point of the liquor is higher and additional steam at a higher pressure is needed to maintain capacity and the achievable heat transfer AT s of each effect. 

Vapor Compression The vapor exiting the evaporator contains significant heating value as latent heat of vaporization. This energy can be recovered by heat-recovery techniques or multi-effect evaporation. The vapor can also be reused in the same unit If the temperature and pressure of the vapor stream are increased to the conditions existing at the time in the steam chests. The methods for reusing a fraction of this vapor are ... 

The advantage of the falling-film evaporator over the climbing-film evaporator is that of a moderate pressure drop. Thanks to the low pressure drop, it is very suitable for a multi-effect evaporator or for plants with vapour recompression. 

SMART desalination plant incorporates the falling film multi-effect evaporation with horizontal tubes and a steam jet ejector (thermal vapour compressor). The desalination unit is designed with a plant life of 30 years, performance ratio of 19.6, acid cleaning to be performed once in 12 months, maximum brine temperature of 65°C, and the supplied seawater temperature of 33°C. Thermal vapour compressor is introduced to improve thermal efficiency of the process steam. The advantages of this design are high heat transfer coefficients and a relatively simple operation system. The performance ratio of desalination plant, one of the most important coupling parameters, was optimized based on the sensitivity analysis of water production cost and on the requirements to the SMART desalination plant. 

The integrated SMART desalination plant consists of 4 units of MED combined with thermal vapour compressor (MED-TVC) as shown in Figures 1-9 and I-10. Each unit can produce 10,000 m /day of distilled water in 24-hour operation at the maximum brine temperature of 65°C and the supplied seawater temperature of 33°C. MED process coupled with the SMART incorporates the falling film, multi-effect evaporation with horizontal tubes and steam jet ejector. 

Chained processes on the other hand possess a fixed division in sections. The division is dictated by the constmction of the equipment. The best-known example is a tray column. Also combinations of serially connected unit operations can be seen as a chained process. Examples are multi-effect evaporators, coimected extractor-separator combinations or a chain of reactors. 

At Searles Lake, the brine is concentrated in a multi-effect evaporator, from which NaCl is recovered. The process liquor is fractionated further to yield a KCl-borax concentrate and burkeite, a double salt of Na2C03 and Na2S04, which is processed still further to yield soda ash and salt cake (Na2S04) as products. 

---