Because the boiling temperature of water decreases as pressure decreases, the vapor boiled off in one vessel can be used to. The low available mean temperature difference mtd limits application to singleeffect evaporators, in which vapor from the same effect is used as the heating medium after compression. Each effect would consist a heat transfer surface, a vapour separator, as well as a vacuum source and a condenser. In a multiple effect evaporator, water is boiled in a sequence of vessels, each held at a lower pressure than the last. While the design criteria for evaporators are the same regardless of the industry involved, two questions always exist. The use of this system requires that steam be available at high pressure, and low. Pdf detailed design of a single effect evaporator with. Depending on the initial feed temperature and system losses, the steam economy of a singleeffect evaporator typically is 0. For heat transfer to occur, the temperature of the. In a doubleeffect evaporator, the vapor product off the first effect is used to provide energy for a second vaporization unit.
Definition evaporation is the process used to concentrate a solution by removing the solvent mainly water in a purified form by the application of heat. A multiple effect evaporator, as defined in chemical engineering, is an apparatus for efficiently using the heat from steam to evaporate water. Optimization of a multiple effect evaporator system. Pdf single effect evaporationvapor compression chang. The falling film evaporators can be single effect or multiple effects depending on the capacity. A single effect evaporator was utilized using water as feed and condensed water and liquid water as product. Evaporators single effect evaporator multi effect evaporator pan evaporator naturalcirculation evaporator rising film evaporator falling film evaporator risingfalling evporator forced circulation evaporator. In this study, investigation of selection of type of. Sep 19, 2012 calculates the heat transfer area for a single effect evaporator that is used to concentrate a salt solution. The latent heat of the vapor leaving in single effect evaporator is not used but is discarded much of this latent heat, however, can be recovered and reused by employing a multiple effect evaporator, that is, vapor from one effect serves as the. Show full abstract as soon as it enters the effect. Find out information about single effect evaporation.
For the same evaporation rate, a fiveeffect evaporator will require about 25% of the steam required for a singleeffect evaporator. As a result, many types of evaporators and many variations in processing techniques have been. It consists of firsteffect, secondeffect, thirdeffect. Tubular evaporators classification is based on the contact steps between the liquid feed to be evaporated and the heating tubes. Evaporators visual encyclopedia of chemical engineering. In this article, it is shown preheating the feed water has a great influence on decreasing the energy consumption of medtvc distillation systems. An evaporation process completed entirely in one vessel or by means of a single heating unit explanation of singleeffect evaporation. In a double effect evaporator, the vapor product off the first effect is used to provide energy for a second vaporization unit. The outlet vapor and liquid varied linearly with the steam pressure. This concentrated liquids in a gentle and efficient manner in a way unparalleled in its time. The advantages of multiple effect systems relative to singleeffect, consist in heating fluid saving, due to a more. For the same evaporation rate, a five effect evaporator will require about 25% of the steam required for a single effect evaporator. The most suitable evaporator will have the highest heat. Heat transfer area of a singleeffect desalting sed system 3.
Thus, the steam economy will always be less than one. It was easy to control and had a compact arrangement. Singleeffect evaporation article about singleeffect. Psychrometrics psychrometric chart example1 psychrometric chart given dbt, wbt example2 psychrometric chart given dbt, rh. Single effect evaporation is simple but fails to utilize the steam effectively, while multiple effect evaporators. Find out information about singleeffect evaporation. The use of multiple effect evaporation allows for the capture and use of waste heat vapours off the falling film evaporator process, to replace primary steam usage throughout the refinery and in. A multipleeffect evaporator, as defined in chemical engineering, is an apparatus for efficiently using the heat from steam to evaporate water. The first wiegand evaporator, built in 1908, was a patented multiple effect circulation evaporator. Is the equipment to be selected best suited for the duty, and is the arrangement the most efficient and economical. Heat transfer area of a single effect desalting sed system 3. They may be operated in either batch or continuous modes. If the density or the consistency of the product is an important quality factor, the level process control will be much more difficult. The evaporator was run with and without a vacuum at different steam pressures to determine the effects on the outlet liquid and vapor.
Made by faculty at the university of colorado boulder department of chemical and. Sep 04, 2015 description of a single effect evaporator used in concentrating liquid foods. Construction and working of single effect evaporator pdf download. The low available mean temperature difference mtd limits application to single effect evaporators, in which vapor from the same effect is used as the heating medium after compression. Multieffect boiling of a submerged tube desalination system 3. Quicklime briquette machine is mainly used for ball making with waste lime powder. Performance ratio of the single effect distillation system 2. Singleeffect evaporators a simplified diagram of a singlestage or singleeffect evap orator is given in fig. Obviously, vapor recompression evaporators are unsuitable where there is a high boilingpoint rise or fouling tendency, conditions that necessitate a high mtd. In a single effect evaporator, steam provides energy for vaporization and the vapor product is condensed and removed from the system. Horizontaltube evaporators verticaltube evaporators plate evaporators longtube evaporators forcedcirculation evaporators evaporation for heatsensitive liquids summary problems examples in this chapter. Single effect evaporation desalination processthe feed seawater mf is chemically treated and deaerated before beingpumped to the evaporator. Single effect evaporators a simplified diagram of a single stage or single effect evap orator is given in fig. For instance, tomato processing plants use evaporators to produce tomato paste.
Two or more evaporator units can be run in sequence to produce a multiple effect evaporator shown on the right. The chemical treatment is needed to prevent thefoaming and the tendency for scale formation in the evaporator. Evaporator problems require solution of the system material and energy balances with the accompanying property and heat transfer equations. Later in the year, the mother liquor is drained off. F actors affecting evaporation, evaporators, film evaporators, single effect and multiple effect evaporators and mathematical problems on evaporation. It consists of first effect, second effect, third effect. F k and saturated steam at t s enters the heatexchange section. Evaporators are operating units for dewatering, concentration, and crystallization processes in various industries. Brine is pumped in hot weather to reservoirs of 100,000 m2 in area to a depth of 35 m, and salt is deposited. Solution would be rather straightforward, except that often the required thermodynamic properties are only available in tabular or graphical form. Pdf on mar 12, 2016, widitha samarakoon and others published detailed design of a single effect evaporator with thermal vapor re compression find, read and cite all the research you need on.
Construction and working of single effect evaporator pdf. In a multiple effect evaporator the vapour from one evaporator is fed into the steam chest of the other evaporator. The heat requirements of singleeffect continuous evaporators may be obtained from mass and energy balances. The evaporation in each effect will be approximately 0. Calculate the temperature boiling point of the liquid in the evaporator, the steam required kgh, the steam economy kg water vaporized per kg steam used, and the heating surface area m 2 if the pressure in the vapor space of the evaporator. Singleeffect evaporators are used when the throughput is low, when a cheap supply of steam is available, when expensive materials of construction must be used as is the case with corrosive feedstock and when the vapor is so contaminated so that it cannot be reused. An evaporation process completed entirely in one vessel or by means of a single heating unit explanation of single effect evaporation. Thermal analysis on triple effect falling film evaporator vanitha dunna1 p. Pdf single batch evaporators numerical problems pranavv. D 1,2department of mechanical engineering 1,2andhra university, visakhapatnam530026, india abstractevaporation is an operation used to remove a. Evaporation technology gea engineering for a better world. In the operation of a single effect evaporator the liquid feed passes once through.
Freese, in fermentation and biochemical engineering handbook third edition, 2014. Much of this latent heat, however, can be recovered and reused by employing a multiple effect evaporator, that is, vapor from one effect serves as the heating medium for the next. In a singleeffect evaporator, steam provides energy for vaporization and the vapor product is condensed and removed from the system. This system is used in a singleeffect evaporator or in the first stage of a multipleeffect evaporator. The vapours from the preceding effect are used as the heat source in the next effect. Evaporators in which circulation is maintained, independent of the evaporation rate or heating temperature, through the heating element are known as forced circulation evaporators. In a multipleeffect evaporator, water is boiled in a sequence of vessels, each held at a lower pressure than the last. The heating steam loses its latent heat and condenses before it flows out of the tube bundle. Performance ratio of the singleeffect distillation system 2. Single effect evaporator can be wasteful of energy if the vapors heat is not used. Heating is performed by passing steam inside the tube bundle. Single effect units may be operated in batch, semibatch or continuous batch modes or continuously. However, for largecapacity operation, using more than one effect will markedly reduce steam costs.
Evaporators are classified by the number of effects. Description of a single effect evaporator used in concentrating liquid foods. This heat can be recovered and reused by employing multipleeffect evaporators. In the evaporator, the seawater fed in is heated to its boiling temperature and is partly evaporated by boiling. The latent heat of the vapor leaving in single effect evaporator is not used but is discarded. Single effect evaporator steam usage and heattransfer surface 8. The single effect evaporator uses rather more than 1 kg of steam to evaporate 1 kg of water. The tubes in longtube vertical evaporators are typically 2 in. Because the boiling temperature of water decreases as pressure decreases, the. Evaporators singleeffect evaporator multieffect evaporator pan evaporator naturalcirculation evaporator rising film evaporator falling film evaporator risingfalling evporator forced circulation evaporator.
Powerpoint presentations for lectures 15, example 4 worked out, and for lectures 1617. Usually it is possible to solve the material and energy balances analytically by a sequential approach. One can distinguish between the two types of longtube vertical evaporators by the location of the vapor head. Sep 16, 2016 single effect evaporators are often used when the required capacity of operation is relatively small andor the cost of steam is relatively cheap compared to the evaporator cost. Single effect units may be operated in batch, semibatch or continuous batch. Single effect evaporation is simple but fails to utilize the steam effectively, while multiple effect evaporators evaporate more quantity of water per kilogram of steam consumed in the evaporation process. Forced circulation systems are illustrated in figures 12. Pdf single and multiple effect evaporators pranavv. Single effect evaporator calculations are fairly basic. Further technical developments led to the first wiegand falling. Consider the example of the singleeffect evaporator.
Typically, the operating temperature is not provided. Heat transfer greatly affects evaporator design, as it represents the greatest cost in its operation. Design and simulation of a multipleeffect evaporator. Its applicable for dairy products, pharmacy, glucose, starch,chemical industry, xylose, citric acid, ammonium sulfate, biological engineering, environmental engineering and waste liquid recovery and treatement. The evaporator on the left is a climbing film evaporator, while the. Calculates the heat transfer area for a singleeffect evaporator that is used to concentrate a salt solution. In actual practice, the steam economy can vary widely because of.
In the usage of the machine, there is the need to control the operation of the device. Thermal analysis on triple effect falling film evaporator. The first wiegand evaporator, built in 1908, was a patented multipleeffect circulation evaporator. Evaporators with direct heating the use of solar heat for the production of glaubers salt has been described by holland22,23. Falling film evaporators can be operated with small temperature differences between the heating media and the boiling liquid and they also have short product contact time.
945 921 1151 1325 1132 1226 124 1397 245 582 1491 436 30 480 1588 539 344 103 866 703 733 1113 1165 1014 1197 312 852 844 898 1492 282 1395 155 1254 1157 542 1462 328 330 1445