Distillation: processes – separatory – With measuring – testing or inspecting
Reexamination Certificate
2002-04-25
2004-10-19
Manoharan, Virginia (Department: 1764)
Distillation: processes, separatory
With measuring, testing or inspecting
C062S003200, C062S238500, C159S024200, C159SDIG001, C202S176000, C202S187000, C203S022000, C203S027000, C203S087000, C203S100000, C203SDIG008, C203SDIG009, C203SDIG001
Reexamination Certificate
active
06805774
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process of purifying a liquid, particularly water, using a thermoelectric module; and apparatus of use in said process.
BACKGROUND TO THE INVENTION
Thermoelectric modules are small, solid state, heat pumps that cool, heat and generate power. In function, they are similar to conventional refrigerators in that they move heat from one area to another and, thus, create a temperature differential.
A thermoelectric module is comprised of an array of semiconductor couples (P and N pellets) connected electrically in series and thermally in parallel, sandwiched between metallized ceramic substrates. In essence, if a thermoelectric module is connected to a DC power source, heat is absorbed at one end of the device to cool that end, while heat is rejected at the other end, where the temperature rises. This is known as the Peltier Effect. By reversing the current flow, the direction of the heat flow is reversed.
It is known that a thermoelectric element (TEE) or module may function as a heat pump that performs the same cooling function as Freon-based vapor compression or absorption refrigerators. The main difference between a TEE device and the conventional vapor-cycle device is that thermoelectric elements are totally solid state, while vapor-cycle devices include moving mechanical parts and require a working fluid. Also, unlike conventional vapor compressor systems, thermoelectric modules are, most generally, miniature devices. A typical module measures 2.5 cm×2.5 cm×4 mm, while the smallest sub-miniature modules may measure 3 mm×3 mm×2 mm. These small units are capable of reducing the temperature to well-below water-freezing temperatures.
Thermoelectric devices are very effective when system design criteria requires specific factors, such as high reliability, small size or capacity, low cost, low weight, intrinsic safety for hazardous electrical environments, and precise temperature control. Further, these devices are capable of refrigerating a solid or fluid object.
A bismuth telluride thermoelectric element consists of a quaternary alloy of bismuth, tellurium, selenium and antimony—doped and processed to yield oriented polycrystalline semiconductors with anisotropic thermoelectric properties. The bismuth telluride is primarily used as a semiconductor material, heavily doped to create either an excess (n-type) or a deficiency (p-type) of electrons. A plurality of these couples are connected in series electrically and in parallel thermally, and integrated into modules. The modules are packaged between metallized ceramic plates to afford optimum electrical insulation and thermal conduction with high mechanical compression strength. Typical modules contain from 3 to 127 thermocouples. Modules can also be mounted in parallel to increase the heat transfer effect or stacked in multistage cascades to achieve high differential temperatures.
These TEE devices became of practical importance only recently with the new developments of semiconductor thermocouple materials. The practical application of such modules required the development of semiconductors that are good conductors of electricity, but poor conductors of heat to provide the perfect balance for TEE performance. During operation, when an applied DC current flows through the couple, this causes heat to be transferred from one side of the TEE to the other; and, thus, creating a cold heat sink side and hot heat source side. If the current is reversed, the heat is moved in the opposite direction. A single-stage TEE can achieve temperature differences of up to 70° C., or can transfer heat at a rate of 125 W. To achieve greater temperature differences, i.e up to 131° C., a multistage, cascaded TEE may be utilized.
A typical application exposes the cold side of the TEE to the object or substance to be cooled and the hot side to a heat sink, which dissipates the heat to the environment. A heat exchanger with forced air or liquid may be required.
Water in bulk may be purified by a number of commercial methods, for example by reverse osmosis and by distillation processes.
Reverse osmosis (R.O.) technology relies on a membrane filtration system that is operated under high pressure. While this technology is one of the two leading technologies of water purification, it suffers from the following main disadvantages:
(a) the infrastructure of the system is complex because of the operating pressure, typically 8 atmospheres, required to cause the reverse osmosis process in the membrane;
(b) the membrane is an expensive component that needs to be replaced, frequently, depending on the salinity and the purity of the source water, generally, every 4 to 6 months. Also, there is a problem of membrane fouling, if the quality of the source water is not within certain bounds. The restriction on the water quality that is inputted into the system precludes many sources of water or would necessitate the utilization of pretreatment systems;
(c) the amount of purified water is very low when compared to the amount of water that has to be pumped into the system. Therefore, the cost of pumping and discharging the rejected water (capital cost to install the required facility and the energy cost to operate and maintain it) makes this system very costly;
(d) the quality of purified water obtained by the reverse osmosis process is inferior to that of distilled water, in the sense that it leaves small microorganisms and any impurities that are small enough to go through the membrane. Also, as the membrane ages, the water quality does not remain consistent;
(e) the system is feasible from a physical and economical point of view, for only large commercial installations. The system is not amenable for use in household units or even in small commercial units; and
(f) energy, operating and maintenance costs are high for the R.O. system. The main disadvantages of distillation technologies, such as the multistage flashback evaporation systems, are:
(i) relatively large capital cost needed to assemble and install the system;
(ii) high energy costs to perform the evaporation, provide energy and equipment for the vacuum system and the condensation in, literally, three independent subsystems;
(iii) significant corrosion problems that necessitate significant pretreatment of input water and complete replacement of plant equipment as frequently as every three to four years;
(iv) the system, generally, needs to be installed only near large power plants and large bodies of water; and
(v) the disadvantages listed in item (e) and (f) hereinabove.
There is, therefore, a need to provide a means for producing a purified liquid, particularly water, in a safe, reliable, convenient, relatively cheap manner, having low energy requirements, and which either eliminates or reduces the aforesaid disadvantages.
Offenlegungsschrift DE 35 39 08 6A (Wagner Finish Tech Center GmbH) published May 7, 1987, describes apparatus for the purification of organic solvents containing paint or varnish by evaporation and condensation by use of a Peltier element which functions as both a heating and cooling element during the evaporation and condensation stages. An essential feature is the condensation of the solvent vapour solely on the cooling element.
It is known that in addition to the production of a temperature differential across the module between the ‘hot’ and ‘cold’ surfaces that heat may be beneficially “pumped” from the cold surface to the hot surface through the module. For example, latent heat of condensation of a vapour on the cold surface may be captured by the cooler element and pumped to the hot side. It is also known that the heat pumped by the cold side varies linearly with the cold side temperature.
However, in the apparatus and process described in OLS DE3539086A a balanced continuous evaporation and condensation equilibrium cannot be established by reason that the cold side of the module absorbs the latent heat which is then pumped to the hot element and, thus, very significant amounts of latent heat of the steam genera
Manelli Denison & Selter
Manoharan Virginia
Stemberger Edward J.
LandOfFree
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