Fluid handling – Processes
Reexamination Certificate
2000-01-14
2001-08-28
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Processes
C137S179000, C137S181000, C137S187000, C137S396000
Reexamination Certificate
active
06279593
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention.
The invention relates generally to devices used to remove condensate (liquid created from the condensation of a gas or vapor) from steam lines and/or equipment or volatilized liquid lines and/or equipment, and more particularly to a steam trap system that has electronic sensors for monitoring the condensate level within the steam trap, an electronic control system for both monitoring steam trap performance as well as adjusting the opening of a condensate discharge valve to maintain condensate level within a control band, a flashing utility which permits reuse of high temperature condensate, and an electronic temperature/pressure sensing device that will constantly monitor temperature and pressure variables in the individual condensate lines to verify the integrity of the individual condensate lines that are going into a single manifold of a steam trap.
2. Description of the Related Art.
In a steam system, a boiler or steam generating unit is supplied feedwater (water which has cycled through the steam system or makeup/city water) which is heated to the saturated liquid state, vaporized to the saturated vapor state (steam), and then superheated. The steam produced may be used to transfer heat to a process. The steam leaves the boiler via the main steam line and enters the main steam header. From the main header, piping directs the steam to the steam heating equipment. As the steam performs its work in manufacturing processes, turbines, building heat, etc. (collectively, Process), the steam transfers its heat. As the steam releases this heat, it is cooled and reverts back to a liquid phase called condensate.
If condensate backs up in the steam system, much inefficiency will occur. The heat transfer rate to the Process is greatly reduced. Also, condensate backed up inside of the steam system piping cools the tubes that carry the steam to the Process. When this sub-cooled condensate is suddenly replaced by hot steam, the expansion and contraction of the tubes stress the tube joints. Constantly repeating this cycle causes premature failure. Finally, water hammer may result. Water hammer may occur where an accumulation of condensate (water) is trapped in a portion of horizontal steam piping. The velocity of the steam flowing over the condensate causes ripples in the water. Turbulence builds up until the water forms a solid mass, or slug filling the pipe. This slug of condensate can travel at the speed of the steam and will strike the first elbow in its path with a force comparable to a hammer blow. This force may be strong enough to break the pipe.
To solve these problems, steam traps have been long used in steam piping and in steam operated equipment to prevent the build-up of condensate formed by the condensation of steam in lines from the boiler. The goal of these steam traps is to drain the condensate as well as discharge air and non-condensable gases without permitting the steam to escape. If steam is allowed to escape, heat that should have been transferred to the Process will be lost. Steam traps are located after the main steam header throughout the system. Multiple pipes conducting steam to the Process may connect to a single manifold which conducts condensate to the steam trap. The condensate passes through the condensate return line and is collected and directed back to the boiler to repeat the water to steam process. Removing the condensate prevents damage to steam lines, steam turbines, steam pistons and other equipment that is operated and/or powered by the energy contained within the steam. Additionally, condensate removal, in some cases, may prevent water damage to the goods being manufactured.
Steam traps commonly used fall into four categories: mechanical steam traps, thermodynamic steam traps, thermostatic steam traps, and electronic steam traps.
Mechanical steam traps work on the principal of differentiating between the density of steam and condensate. The inverted bucket is a type of mechanical steam trap. In the mechanical steam traps, a valve opens and closes depending on the level of condensate in the steam trap bowl. For instance, in the inverted bucket steam trap, condensate enters the steam trap chamber from the bottom. As the level of condensate rises, the inverted bucket rises until it actuates a mechanical valve which allows the condensate to be blown by steam pressure into the condensate recovery lines. In the presence of steam only, the inverted bucket/float does not become buoyant, but sits securely over the orifice to close the steam trap.
The thermostatic steam traps operate by sensing the temperature of the condensate. As steam condenses, the condensate so formed is at steam temperature, but as it flows to the steam trap, it loses temperature. When the temperature has dropped to a specified value below the steam temperature, the thermostatic steam trap will open to release the condensate. For instance, this type of steam trap might have a bellows filled with a fluid that boils at steam temperature. As the fluid boils vapors expand the bellows to push the valve closed. When the temperature drops below steam temperature, the bellows contract to open the valve and discharge condensate. The bimetallic steam trap is an example of a thermostatic steam trap.
Thermodynamic steam traps operate on the principal of the difference between the flow of steam over a surface compared to the flow of condensate. Steam flowing over a surface creates a low-pressure area thus these steam traps are designed to open when the condensation of steam within the steam trap causes a change in pressure.
Electronic steam traps have also been developed to remove condensate from steam lines. Examples of electronic steam traps include Green, Rasmussen, Koch, Bridges, and Lin.
U.S. Pat. No. 3,905,385, Sep. 16, 1975 (Green) illustrates what appears to be the first use of an electronic sensor in the steam trap. Green shows the use of a condensate sensor connected directly to a condensate discharge valve. When the condensate level reaches the level of the discharge sensor, a circuit will be completed which will actuate the solenoid and open the condensate discharge valve.
U.S. Pat. No. 5,469,879, Nov. 28, 1995 (Rasmussen). This steam trap removes condensate on demand similar to a mechanical steam trap with the difference being that a electrical sensing probe extends into the condensate collection chamber and senses the high and low levels of condensate. When the condensate reaches the sensing probe an electric current causes a valve to open and the condensate is purged from the steam trap chamber. Once the condensate level falls below a preset level the valve will close until condensate again accumulates in the steam trap. This system also discloses an alarm circuit, which will indicate lack of valve opening or unusually high or low levels of condensate within the steam trap chamber.
A third example is described in U.S. Pat. No. 4, 974,626, Dec. 4, 1990 (Koch). Koch discloses an electronic-controlled steam trap that also uses an electrical sensor to control a discharge valve. In addition to Rasmussen's high and low level sensors, Koch also has a timedelay circuit. The upper sensor or the high-level sensor will actuate the discharge valve. The valve will stay open until a specified time-delay after the condensate level has reached the low-level sensor. Thus, the steam trap will drain the level of condensate past the low-level sensor. The purpose of the time delay is to insure that steam trap drains completely and that the flashing of condensate within the steam trap chamber during drainage does not prevent complete drainage of the steam trap.
U.S. Pat. No. 4,505,427, Mar. 19, 1985 (Bridges) provides a fourth example of an electronic steam trap. This steam trap is designed to prevent the steam trap from becoming locked by a bubble of steam around the electronic probe. The circuit includes a timing circuit that is reset each time the valve opens. If the condensate discharge valve does not open after a predetermined time then th
Frost Brown Todd LLC
Michalsky Gerald A.
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