Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor
Reexamination Certificate
2001-04-09
2002-07-23
Griffin, Steven P. (Department: 1754)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
C422S175000, C422S206000, C422S223000, C165S004000, C165S909000, C165SDIG009, C165SDIG003, C165SDIG004, C165SDIG009
Reexamination Certificate
active
06423275
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to methods and devices for processing fluids in energy conservation and environmental pollution control applications using regenerative techniques.
DESCRIPTION OF THE PRIOR ART
Regenerative systems have long been used in energy conservation and environmental equipment. One of the best known examples of the use of a regenerative system in energy conservation is the use of regenerators in open-hearth steel furnaces. In such regenerators, two stationary beds of heat transfer and storage material are used. Dampers are provided at the inlet and outlet of each bed to alternately allow hot furnace exhaust gas and cold ambient air to flow through each bed. The heat in the hot exhaust air is therefore transferred to the colder heat-transfer material during the first part of the cycle. The ambient air then cools the hot heat-transfer material during the second part of the cycle. Thus the ambient air recovers heat which would otherwise be wasted from the hot furnace exhaust gas. Other examples are regenerators in blast-furnace stoves for the production of pig-iron and regenerator systems for by-product coke ovens which follow a similar operating principle. Another type of a regenerative heat-exchanger is the Ljungstrom wheel which is widely used in commercial HVAC and power plant applications. The standard design of the Ljungstrom wheel has a moving disc of heat transfer and storage material which is alternately moved between hot and cold air streams to transfer the heat from the hot air to the cold air Detailed description of these regenerative heat-exchanger systems is given in literature such as Perry's Chemical Engineering Handbook, Fifth edition.
Another form of the regenerative heat-exchanger is described in the Steam Handbook by Babcock and Wilcox. It is similar to the Ljungstrom wheel but has a stationary wheel with revolving inlet and outlet plenums for the entry and exit of the hot gases and cold gases into the heat-exchanger core. Thus in this design, the heat transfer media remains stationary while the hot and cold air streams are moved through various sections of the heat-transfer media to transfer heat from the hot gases to the cold gases.
The regenerative heat-exchanger concept has been widely adopted for conserving energy in processes which clean polluted gas streams by oxidation of the pollutants in a furnace. Such equipment is commonly known as Regenerative Thermal Oxidizers. Currently two types of Regenerative Thermal Oxidizers are commercially available. The first type uses the principle of the regenerators as described above for steel furnace regenerators and is herein referred to as a dampered conventional Regenerative Thermal Oxidizer. Thus such Regenerative Thermal Oxidizers use at least two beds which contain regenerative heat-transfer materials. The hot oxidized cleaned air and the relatively colder polluted air is alternately passed through each bed to transfer the heat from the hot clean oxidized gas to the cold process gas. The second type of Regenerative Thermal Oxidizer uses the stationary bed principle of the Ljungstrom wheel as described in the Steam Handbook and is herein referred to as a rotary valve Regenerative Thermal Oxidizer. In this system, a plurality of beds containing heat-transfer materials are arranged in a radial manner. A rotating valve mechanism selectively allows the cold polluted air and the hot oxidized air to alternately pass through each bed to transfer heat from the hot air to the cold air.
Examples of conventional dampered Regenerative Thermal Oxidizers are described in U.S. Pat. Nos. 5,098,286 and 5,026,277 to York. Examples of the rotary valve Regenerative Thermal Oxidizers are described in U.S. Pat. No. 5,460,789 to Wilhelm, U.S. Pat. No. 5,016,547 to Thomason, and U.S. Pat. No. 4,280,416 to Edgerton.
Regenerative methods which use adsorption mechanisms and/or chemical reactions to effect the cleaning of polluted air streams have also been used in environmental control processes. A common example of such a regenerative method is the adsorption of Volatile Organic Compounds (VOCs) by granulated activated carbon (GAC) or specialized zeolites or specially modified resins. Such systems are generally used for concentrating very-low concentration VOC-containing process air-streams prior to their final recovery or disposal. Systems using granulated activated carbon generally operate using the bed principle while systems using zeolites generally use the Ljungstrom wheel principle. An example of a granulated activated carbon adsorption system is the multiple bed adsorption system sold by Calgon Corporation and other vendors. An example of the zeolite wheel adsorption system is the Ecopure(TM) system sold by Durr Environmental.
Regenerative techniques are also used with reversible chemical reactions. An example of a regenerative process which utilizes a reversible chemical reaction for cleaning polluted air is described in an article titled “A Sorbent Regenerator Simulation Model in Copper Oxide Flue Gas Cleanup Processes” published in Environmental Progress, volume 17, no.2. This article describes a method of using copper oxide for the simultaneous removal of sulfur oxides and nitrogen oxides from flue gas. In the initial step, the copper oxide reacts with sulfur dioxide and oxygen in the flue gas to form copper sulfate. The copper sulfate and the copper oxide then act as catalysts for the reduction of oxides of nitrogen by ammonia. The copper oxide is then regenerated by reduction with methane.
Each of the regenerative process configurations described above have inherent design, constructional and operational problems. For example, conventional dampered Regenerative Thermal Oxidizers require fast-acting dampers to minimize the direct bypassing of the polluted air to the atmosphere during the time-interval in which the regenerators' control-damper blades are moving from an open to a closed position or vice-versa during the switching of the regenerator from the hot clean air to the cold polluted air or vice-versa. Fast acting dampers generally have severe maintenance problems especially on large units because the damper blade has to be moved rapidly. The inertia of the moving damper blade is difficult to control generally causing the damper blade to slam on the damper seals causing them to deteriorate rapidly. Thus frequent replacement of damper blades and seals is often required on such units. The inertia of the damper blades and the need for large quantities of motive fluids such as hydraulic fluid or compressed air to operate the dampers also requires that the dampers be opened and closed at long intervals. Thus short cycle times of less than a minute are difficult to achieve in such units which makes it difficult to reduce the quantity of the heat-transfer materials used in such heat-exchanger beds.
The problems of conventional dampered Regenerative Thermal Oxidizers are well described in the above-referenced prior patents for rotary valve Regenerative Thermal Oxidizers. While rotary valve Regenerative Thermal Oxidizers utilizing the Ljungstrom wheel principle have been used to try to overcome these problems, they suffer from cross-leakage and capacity limitations. The gaps between the moving and stationary parts of the heat-exchanger are difficult to seal because the beds generally have to be wedge-shaped to fit radially in a circular array within a cylindrical shell. Therefore, complicated radial, longitudinal, and peripheral sealing mechanisms, which require accurately machined parts, are needed to keep cross leakage of the polluted air from the oxidized air. Such sealing is difficult to achieve especially for the radial, longitudinal, and peripheral moving parts that exist within such units. Thus increased leakage of polluted air into the cleaned air occurs which reduces the destruction and removal efficiency of rotary valve Regenerative Thermal Oxidizers compared to conventional dampered Regenerative Thermal Oxidizers. Therefore rotary valve Regenerative Thermal O
D'Souza Melanius
Griffin Steven P.
Vanoy Timothy C.
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