Direct-contact steam-to-water condenser

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] 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] FIG. 2 shows a sectional side view of the white water heat exchanger of the Preferred Embodiment of the present invention.

[0020] FIG. 3 shows a plan view of a baffle tray of the white water heat exchanger.

[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 61a, 61b 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.

Claims

1. An apparatus for heating a whitewater supply, said apparatus comprising:

a superheated steam inlet receiving steam from a superheated steam source; and

a whitewater heat exchanger receiving a flow of superheated steam from said superheated steam inlet, said whitewater heat exchanger also receiving a flow of whitewater; wherein said supply of whitewater receives heat directly from said superheated steam within said whitewater heat exchanger.

2. The apparatus of claim 1 wherein said whitewater heat exchanger includes:

a heat exchanger body having a longitudinal axis;

a plurality of baffle plates, each of said plurality being substantially perpendicular to said longitudinal axis;

a superheated steam inlet on said heat exchanger body;

a superheated steam outlet on said heat exchanger body;

a whitewater inlet on said heat exchanger body; and

a whitewater outlet on said heat exchanger body;

wherein said flow of superheated steam enters said whitewater heat exchanger through said superheated steam inlet and exits through said superheated steam outlet, wherein said whitewater flow enters said whitewater inlet and exits through said whitewater outlet, and wherein said whitewater flow mixes directly with said superheated steam flow and is thereby heated.

3. The apparatus of claim 2 wherein each of said plurality of baffle plates is rotated about said longitudinal axis with respect to each adjacent baffle plate of said plurality of baffle plates.

4. The apparatus of claim 3 wherein said heat exchanger body is cylindrical.

5. The apparatus of claim 4 wherein each one of said plurality of baffle plates is semi-circular with a body-spanning straight-edge.

6. The apparatus of claim 3 wherein each one of said plurality of baffle plates has a lip along said body-spanning straight-edge.

7. The apparatus of claim 6 wherein said lip is substantially parallel to said longitudinal axis.

8. The apparatus of claim 7 wherein each one of said plurality of baffle plates further comprises a first plurality apertures disposed therethrough.

9. The apparatus of claim 8 wherein said first plurality of apertures is arranged in a first row along said lip.

10. The apparatus of claim 9 wherein each of said first plurality of apertures is spaced an identical distance from an adjacent aperture of said first plurality of apertures.

11. The apparatus of claim 8 further comprising a second plurality of apertures disposed therethrough.

12. The apparatus of claim 11 wherein said second plurality of apertures is arranged in a second row parallel to said first row.

13. The apparatus of claim 2 further comprising a freshwater heat exchanger.

14. The apparatus of claim 13 wherein said freshwater heat exchanger comprises:

a freshwater heat exchanger body having a freshwater inlet disposed therethrough;

a freshwater outlet disposed through said freshwater heat exchanger body;

a superheated steam inlet disposed through said freshwater heat exchanger body; and

a superheated steam outlet disposed through said freshwater heat exchanger body,

wherein said supply of freshwater receives heat directly from said superheated steam within said freshwater heat exchanger.

15. A steam condenser comprising:

a superheated steam inlet receiving steam from a superheated steam source;

a superheated steam plenum attached to said superheated steam inlet:

a whitewater heat exchanger receiving connected to said superheated steam plenum

and receiving a first flow of superheated steam from said superheated steam plenum, said whitewater heat exchanger also receiving a flow of whitewater; wherein said supply of whitewater receives heat directly from said superheated steam within said whitewater heat exchanger; and

a freshwater heat exchanger connected to said superheated steam plenum and receiving a second flow of superheated steam from said superheated steam plenum, said freshwater heat exchanger also receiving a flow of freshwater; wherein said supply of freshwater receives heat directly from said superheated steam within said freshwater heat exchanger.

16. The apparatus of claim 15 wherein said whitewater heat exchanger includes:

a whitewater heat exchanger body having a longitudinal axis;

a plurality of baffle plates, each of said plurality being substantially perpendicular to said longitudinal axis;

a superheated steam inlet on said heat exchanger body;

a superheated steam outlet on said heat exchanger body;

a whitewater inlet on said heat exchanger body; and

a whitewater outlet on said heat exchanger body;

wherein said flow of superheated steam enters said whitewater heat exchanger through said superheated steam inlet and exits through said superheated steam outlet, wherein said whitewater flow enters said whitewater inlet and exits through said whitewater outlet, and wherein said whitewater flow mixes directly with said superheated steam flow and is thereby heated.