Abstract:
Apparatus that uses a supply of superheated steam to heat a supply of white water and optionally one or more supplies of clean water by means of heat exchangers. The heat exchanger used to heat the white water uses baffle trays to accommodate the contaminants in the white water.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to processes or facilities that both produce superheated steam and use one or more sources of water wherein one water source has material suspended therein. More particularly, the present invention relates to capturing heat from such superheated steam and then using the energy to heat the one or more sources of water.  
           [0003]    2. Description of Related Art  
           [0004]    Many manufacturing processes require supplied water, and often it is necessary or desirable for this water to be heated. From an economic standpoint it is best to use waste heat—that is heat which is produced from the manufacturing process, as opposed to for it—to heat the water. During such manufacturing processes, the supplied water often becomes contaminated with solids or chemicals, and, notwithstanding this contamination, is reused for its original or an alternative purpose. A problem arises in using waste heat to heat supplies of contaminated water: solids in the contaminated water tend to foul (plug) certain types of heat exchanges used to effect the heating.  
           [0005]    Few attempts have been made to use an abundant supply of waste heat to heat the supply of contaminated water. (In certain fields this contaminated water is referred to as “whitewater.”) An apparatus and process for drying cellulosic and textile substances with superheated steam is taught by Curry (U.S. Pat. No. 5,105,558; 1992). The apparatus of Curry uses superheated steam as a medium to dry cellulosic goods, and contains an internal steam condenser for recapturing the energy of the steam after the steam has been used for drying the goods. While providing for an efficient method of drying pulp goods and recapturing the energy of spent steam, the Curry apparatus fails to provide a method and structure with which to use this heat energy advantageously to heat the whitewater produced in the initial stages of the molding process.  
           [0006]    A similar apparatus and method are taught by Stubbing (U.S. Pat. No. 5,711,086; 1998). The Stubbing apparatus, like that of Curry, uses superheated steam as a drying medium and has a condenser to capture heat from the spent steam. The Stubbing apparatus, like that of Curry, fails to provide for the heating of dual production liquid supplies where one of the supplies has by-product in suspension.  
           [0007]    A waste water heat recovery apparatus is taught by MacKelvie (U.S. Pat. No. 5,736,059; 1998). The MacKelvie apparatus employs a three-fluid convective heat exchanger that transfers heat from waste water to a fresh water supply indirectly via a reservoir of fresh water. Certain embodiments of the MacKelvie apparatus contain a solids separator to remove particulate matter from the waste water supply. The MacKelvie apparatus uses waste water to heat the fresh water supply for a house or other such building. Because of the paramount need to keep the supply of fresh water potable, an indirect heat exchanger is necessary; the waste water supply can never, barring the rupture of both supply pipes, come into contact with the fresh water supply. Such indirect heat exchanges, particularly those with an intermediate fluid—as is the case with the MacKelvie heat exchanger—are inherently less efficient than direct heat exchanges, i.e., heat exchanges wherein the input and output fluids mix directly.  
           [0008]    A wet/dry steam condenser is taught by Brigada et al. (“Brigada”) (U.S. Pat. No. 4,381,817; 1983). The apparatus of Brigada uses a plurality of substantially vertical pipes (“heat pipes”) and that contain a heat transfer liquid. Steam is collected and directed to the lower end of the heat pipes, causing the heat transfer liquid to vaporize within the pipes. Cooling air, and in some embodiments cooling water, carry away heat from the sealed heat pipes, causing the vaporized heat transfer liquid to condense. The step of vaporizing the heat transfer liquid removes energy from the steam, and causes the steam to condense to liquid water. The Brigada apparatus uses an indirect heat exchanger wherein the steam supply and the fluid that ultimately carries away the extracted heat energy are separated by an intermediary and enclosed fluid, and because of this the inefficiencies inherent in such heat exchanges are present. Moreover, the Brigada apparatus provides no structure with which to use the heat that is extracted from the steam; the apparatus is directed to condensing steam, and not to beneficially using the extracted thermal energy.  
           [0009]    In light of the limitations described above, what is needed therefore, is an apparatus  
           [0010]    In light of the limitations described above, what is needed therefore, is an apparatus that is capable of transferring heat from a supply of superheated steam to one or more supplies of water, where one such supply is whitewater with manufacturing by-products therein.  
         SUMMARY OF THE PRESENT INVENTION  
         [0011]    The present invention solves the problem of heating a supply of whitewater with waste heat while accommodating the manufacturing by-products in the whitewater by use of a whitewater heat exchanger that has multiple baffle trays which accommodate the manufacturing by-products in the whitewater.  
           [0012]    When superheated steam is produced in a manufacturing process and is subsequently vented unused to the atmosphere, economically valuable thermal energy that might otherwise be beneficially used is wasted. This superheated steam represents a source of energy with which to heat other fluids used in the manufacturing process. The most common among these fluids are water and “white water.” White water, as previously noted, refers to water that contains by-products of the particular manufacturing process. The problem with using this superheated steam to heat supplies of such whitewater is that the solid materials contained in the whitewater eventually plug most types of heat exchangers. The present invention solves this problem and provides for the use of waste heat contained in a supply of exhausted superheated steam to heat one or more supplies of water, one supply containing suspended material.  
           [0013]    As used herein “superheated steam” refers to steam at a pressure of about one atmosphere which is heated above the saturation temperature; “superheated steam” may also refer to any mixture of such steam with air. Furthermore, the term “freshwater” includes reference to any supply of water, whether from municipal, groundwater, or surface sources, that is suitable for a particular manufacturing process and which has not been contaminated with manufacturing by-product(s).  
           [0014]    An essential aspect of the present invention is the presence of a direct-contact heat exchanger assembly with which to heat a supply of whitewater, the “whitewater heat exchanger,” which is capable of accommodating the suspended solids of the supply of whitewater; this whitewater heat exchanger is able to function despite the presences of solid material in suspension in the whitewater. This functionality is provided by baffle trays within the whitewater heat exchanger which filter the suspended material while still allowing the superheated steam to pass through the whitewater heat exchanger.  
           [0015]    The present invention includes classes of embodiments that use only one heat exchanger, for a single whitewater supply; the present invention further includes classes of embodiments that use two or more heat exchangers, one of the heat exchangers being for a white water supply and the remaining heat exchanger(s) being for non-whitewater supplies The heat exchangers of the present invention are of the direct-contact type: the steam comes into direct contact (i.e., directly mixes) with the water and no barrier separate the two fluids. In most types of heat exchanges, a barrier is present between the fluids. This barrier is most commonly metal. However, this barrier presents a resistance to heat transfer regardless of the type of material use for the barrier. For optimum heat transfer between the steam and water, barrier walls are done away with in the present invention.  
           [0016]    Superheated steam from a steam source enters a steam inlet of the apparatus of the present invention and is directed to the whitewater heat exchanger. If it is the case that a freshwater supply is to be heated as well, there will be a forked plenum (manifold) that directs some of the superheated steam to a freshwater heat exchanger. In both types of heat exchanger, the water supply enters the heat exchanger above where the superheated steam enters (the “superheated steam inlet”) and exits below this superheated steam inlet; the superheated steam in both types of heat exchanger exits above the water inlet. This arrangement provides for optimal heat transfer between the fluids; the superheated steam rising up through the heat exchanger and being cooled by the falling water while the water is simultaneously heated as it comes into contact with the rising superheated steam.  
           [0017]    While the present invention described in the following Preferred Embodiment is directed to use in the process of making paper-pulp-goods, the scope of the present invention is not limited to that single application. Indeed, the present invention may be used in any process where (1) superheated steam as well as white water are produced, and (2) it is desired to heat such whitewater. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 shows a front view of the Preferred Embodiment of the present invention wherein a superheated steam inlet is connected to a white water heat exchanger and a fresh water heat exchanger.  
         [0019]    [0019]FIG. 2 shows a sectional side view of the white water heat exchanger of the Preferred Embodiment of the present invention.  
         [0020]    [0020]FIG. 3 shows a plan view of a baffle tray of the white water heat exchanger.  
         [0021]    [0021]FIG. 4 shows an edge view of a baffle tray. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    The following description of the Preferred Embodiment is directed to use in the production of paper pulp goods with the industrial dryer that is the subject matter of U.S. Pat. No. 5,105,558. Obviously, other sources of superheated steam may be used with the present invention. This description is by way of example and is not meant to be limit the scope of the present invention.  
         [0023]    A direct-contact steam-to-water heat exchanger in accordance with the present invention is generally represented by the reference character  10  in the figures and includes, as shown in FIG. 1, a whitewater heat exchanger  20 , a freshwater heat exchanger  30 , a freshwater sump  40 , a whitewater sump  50 , a superheated steam inlet  60 , and a steam plenum  62 .  
         [0024]    With reference to FIG. 1, a superheated steam inlet  60  distributes superheated steam from an industrial dryer (not shown) through a forked steam plenum  62  to both a whitewater heat exchanger  20  and freshwater heat exchanger  30 . Each of these heat exchangers has a generally cylindrical shape, and the superheated steam enters each heat exchanger near the bottom of the cylinder through exchanger steam inlets  24 ,  34  respectively. The superheated steam entering each heat exchanger is regulated by a damper  61   a ,  61   b  that is present between the plenum  62  and each exchanger steam inlet  24 , 34 . These dampers are typically of the electronically controlled “butterfly-valve” type.  
         [0025]    The freshwater heat exchanger  30  has a freshwater inlet  32  that feeds a freshwater spray nozzle  35 . After passing through the freshwater spray nozzle  35 , the freshwater flows downward through the freshwater heat exchanger  30  and eventually collects in a freshwater sump  40 . Between the freshwater spray nozzle  35  and the freshwater sump  40 , “packing”  36  is stacked. This packing  36 , sometimes known as “tellerettes” or “saddles,” consists of cylinder segments that have rectangular portions removed in a brick-like pattern from their surface. On this inside of these hollow cylinder segments are arched portions of metal. This packing  36  is present to increase the distance the surface area which the falling freshwater must travel on its downward path to the freshwater sump  40 .  
         [0026]    With reference to FIG. 2, the inside of the whitewater heat exchanger  20  is shown. Whitewater enters into the whitewater heat exchanger  20  through a whitewater inlet  22  which is positioned near the top of the whitewater heat exchanger  20 . The whitewater then is sprayed through a whitewater spray nozzle  18  toward an upper most baffle tray which is one of nine similar semicircular baffle trays  25 . Each baffle tray  25  is fastened along its arc to the inside wall of the heat exchanger and is made so as to cover slightly more than half of the cross sectional area of the heat exchanger  20 . The trays are positioned horizontally, though in other embodiment s they can be tilted downward (i.e., the body-spanning straight-edge lies along the lowest point) slightly. Each of these baffle trays  25  is positioned at a different height within the whitewater heat exchanger  20 , and the distance between adjacent baffle trays  25  drops from bottom to top to maintain the velocity of the superheated steam and to keep heat transfer coefficients up. The baffle trays  25  alternate in orientation: each baffle tray  25  is rotated about the vertical centerline of the whitewater heat exchanger  20  through an angle of about 180 degrees. By this arrangement any two adjacent baffle trays  25  cover the entire cross sectional are of the whitewater heat exchanger  20 . Each of the baffle trays  25  has a vertical wall, the outlet weir  17 , along its body-spanning straight-edge. Whitewater sprayed from the spray nozzle  18  pools upon the uppermost baffle tray and the baffle tray immediately below. Two rows of holes  16  which are formed through each baffle tray  25  near the outlet weir  17  allow some of this pooled water to flow downward to be caught by the next baffle tray  25 . When the flow of whitewater through the whitewater heat exchanger  20  exceeds the capacity (designed to be about 50% of designed flow through the whitewater heat exchanger) of the drain holes  16 , the water flows over the outlet weir  17  and down toward the next baffle plate  25 , and in so doing forms a continuous water curtain. At low flows when all of the water is flowing through the drain holes  16 , a water curtain still develops but in this case the curtain is not necessarily continuous. The superheated steam which is traveling upward through the heat exchanger  25  is constrained to travel through the water curtains and it is the passing of the steam through these water curtains that effects the bulk of the heat transfer within the whitewater heat exchanger  20 .  
         [0027]    With regard to the whitewater heat exchanger  20 , the superheated steam that has passed through the plenum  62  and that has been admitted by the damper  61  enters through the  5  whitewater heat exchanger steam inlet  24 . The superheated steam then rises through the whitewater heat exchanger due to a pressure gradient present between the steam inlet  24  and the steam outlet  19 . A fan (not shown) located along the exhaust pipe  70  facilitates in the creation of this pressure gradient. A chevron-type mist eliminator (not shown) is near the steam outlet  19  to reduce water carry-over to the fan. A water wash of approximately one gallon per minute (1 gpm) is placed on top of the mist eliminator to wash away any solids or deposits back down to the whitewater steam exchanger  20 .  
         [0028]    With reference to FIG. 3, a plan view of one of the baffle trays  25  is shown. Two rows, one offset from the other, of drain holes  16  are shown near the outlet weir  17 . With reference to FIG. 4, a full circumferential tray ring  47  is shown. Such a tray ring  47  is provided in the whitewater heat exchanger  20  at the position of the topmost baffle tray  25  and the lowermost baffle tray  25 . These tray rings  47  allow for, after the removal of the baffle plates  25 , packing (not shown) to be used in the whitewater heat exchanger  20  such a change is desired.  
         [0029]    With reference to FIG. 5, an edge view of one of the baffle trays  25  is shown. The outlet weir  17  is shown having a 90 degree V-notch patten across the top edge of the outlet weir  17 . This pattern facilitates the stable operation of the whitewater heat exchanger  20  at low to moderate flows.  
         [0030]    The previous description of the Preferred Embodiment is by way of example and does not define the scope of the present invention. As will be apparent to those skilled in the art, various changes and modifications may be made to the apparatus of the present invention without departing from the spirit and scope of the present invention as recited in the appended claims and their legal equivalent.