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Exhibit 3-13. Common Vacuum Evaporation Terminology

Bodies Also called vapor heads or flash chambers; the unit where vapor-liquid separation takes place. Also a label given to the basic module of an evaporator, comprising one heating element and one flash chamber.

Calandria The unit in which heat transfer takes place.

Compression Evaporation A process in which evaporated vapor is compressed to a higher pressure level and then condensed. The compressed vapor provides heat required for evaporation. Energy economy obtained by multi-effect evaporation can often be equalled in a compression evaporation system.

Condenser Evaporator equipment used to condense the vapor from the last effect or used as an intercondenser in multi-stage vacuum producing systems.

Cooling Water Water used in the condenser of an evaporator to condense the vapor phase that exists in the separator. Cooling water can come from cooling towers or reservoirs, or once-through process water can used.

Direct Contact Condenser Condenses vapors as they are contacted with the cooling medium. There are no heat transfer surfaces and therefore the vapor pressure drop is low. Due to contact with the process solution, the cooling water will require waste treatment.

Effect One or more bodies boiling at the same time.

Evaporator The entire system of effects, not necessarily one body or one effect.

Fouling Formation of deposits other than salt or scale.

Heat Pump A device in which a refrigerant fluid is continuously circulated through a closed cycle. The gaseous refrigerant is first compressed and then allowed to condense by giving out heat to a cooler environment. The liquid refrigerant is then throttled to low pressure, by means of an expansion valve and allowed to evaporate in another heat exchanger, drawing in heat. The vapor is then circulated to the compressor to begin another cycle.

Intercondenser A condenser within a multistage system that condenses some of the steam between stages and reduces steam consumption.

Mechanical Compression Uses a compressor driven by a mechanical drive to compress all the overhead vapors.

Mechanical Pumps One of two devices (see steam jet ejectors) used to produce a vacuum. More energy efficient than steam jet ejectors but less reliable due to the number of moving parts involved.

Precondenser A condenser that removes process vapors and permits the use of smaller vacuum pumps.

Refrigeration Systems that absorb heat not wanted or needed and reject it elsewhere. Heat is removed from the system by evaporation of a liquid refrigerant and is rejected by condensation of the refrigerant vapor.

Scaling Growth or deposition on heating surfaces of a material that is either insoluble or has a solubility that decreases with an increasing temperature.

Staging Two or more sections of a single effect evaporator operating at different concentrations.

Steam Jet Ejectors One of two devices (see mechanical pump) used to produce a vacuum. Jet ejectors usually have lower initial costs, lower maintenance costs (fewer moving parts) but higher operating costs (less energy efficient) than mechanical systems. Multistage jet ejectors (connected in series) improve thermodynamic efficiency.

Surface Condenser A condenser with a heat transfer surface on which condensing occurs. The heat transfer surface is subject to fouling, corrosion and plugging. Generally more expensive than direct contact condensers. Cooling water is not contaminated with the process solution.

Thermal Compression Uses a steam jet to compress a fraction of the overhead vapors with high pressure steam.

Thin Film Thin films of solution are created in evaporators to maximize the liquid surface area per unit volume of flow and therefore facilitate rapid evaporation.

Sources: ref: 373, 374, 423.


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