WO2009017478A1

WO2009017478A1 - Immiscible fluid propelling water in fuel cell power plant

Info

Publication number: WO2009017478A1
Application number: PCT/US2007/017097
Authority: WO
Inventors: Ryan J. Balliet
Original assignee: Utc Power Corporation
Priority date: 2007-07-31
Filing date: 2007-07-31
Publication date: 2009-02-05

Abstract

The water outlet (68) of fuel cell stack (37) is connected to suction inlet (200) of an eductor (202) having a primary flow of pressurized (208) immiscible fluid. The fluid mixture is applied to an inlet (240) of a separator (231); the immiscible fluid (and gas originally entrained with the water) passes through a porous hydrophobic medium (242) to a first outlet (244) of a separator (231 ) to return to the pump; and the water passes from the inlet through a porous hydrophilic medium (247) to a second outlet (248), for return to the stack; the gas is vented (212). A deionizer (175) is located either upstream or downstream of the separator.

Description

Immiscible Fluid Propelling Water in Fuel Cell Power Plant

Technical Field

[0001] Water, such as in a fuel cell power plant, is suctioned through an eductor driven by an immiscible fluid. Water is separated from the immiscible fluid by hydrophilic and hydrophobic media, and is returned to the fuel cell stack; the immiscible fluid is pumped back to the eductor.

Background Art

[0002] In evaporatively cooled fuel cell stacks, water passageways provide water to reactant gas flow passages wherein the water is evaporated in proportion to the waste heat generated in the cells; the water condensed from the exhausted reactant gas is returned to the water passageways. One such system is prescribed in patent publication US 2006/0141331 A1.

[0003] Referring to Fig. 1, a fuel cell power plant 36 of said publication includes a stack 37 of fuel cells 38 which are shown disposed vertically, although they may be disposed horizontally.

[0004] In this example, fuel from a source 41 is provided to a fuel inlet 42 and flows to the right in a first fuel pass, as indicated by the hollow arrow 43, to a fuel turn manifold 44. The fuel gas then flows downwardly and into a second fuel pass of the fuel flow fields, wherein the fuel gas flows to the left as indicated by the hollow arrow 45. From a fuel outlet 47, the fuel may flow through a recycle pump 48 (perhaps with valves not shown) back to the fuel inlet 42, and may be periodically purged to ambient through a valve 49. Single pass, triple pass or other fuel flow configuration may be used.

[0005] In Fig. 1 , air is provided by a pump 52 to an air inlet 53, and the air flows upwardly through the oxidant reactant gas flow channels of the fuel cells 38, as indicated by the solid arrow 54. As described more fully in the aforementioned patent publication, the fuel and oxidant reactant gas flow field plates are porous, hydrophilic and adjacent to water passageways 67. Water evaporates into the oxidant gas (air), thus cooling the stack 37. From an air outlet 57, the air flows over a conduit 58 to a condenser 59, which in a vehicle may be a conventional radiator. The condensate from the condenser 59 may be conducted directly or in a conduit 63 for accumulation in a reservoir 64, which is connected by a water return conduit 65 to a water inlet 66. The exit air is passed through an exhaust 62.

[0006] The water flows through fluid conduits, typically minute passageways 67, into each of the fuel cells 38; the passageways 67 terminate in a water outlet 68. Removal of gas from the passageways is provided by a pump 89 drawing some fraction of the water through a conduit 69a, a check valve 176, a conduit 69b, and a deionizer 175 (also known as a demineralizer); the water then returns to the reservoir 64. Some of the water flow may bypass the deionizer 175 by controlling a conventional bypass valve (not shown) around the deionizer 175. A deionizer may instead be connected, typically with by-pass flow control, to the outlet of the condenser, in some embodiments. It is also possible to maintain the water flow concept without the deionizer if small water circulation is desired for other purposes, such as gas removal. [0007] The check valve 176 is optional, and is provided so as to prevent, when the fuel cell power plant is shut down, water which is stored within the coolant channels inside the stack from "drooping" into the reactant gas flow field channels, through the hydrophilic porous plates (commonly referred to as "water transport plates") within which the water passageways and reactant gas flow field channels are formed. Water may be drained from passageways and the condenser at shut down in cold climates, if desired.

Summary

[0008] The system just described is sometimes referred to as "natural water management". Evaporative cooling, using barely the evaporative amount of water in the stack (that is, with no excess water) may dramatically reduce the system water volume. However, it has been determined that, over time, gas is ingested into the water. When the circulating coolant fluid contains a certain proportion of gas, the porous, hydrophilic reactant gas flow field plates (water transport plates) may experience gas breakthrough, allowing fuel on one face of the plates to mix with air on the opposite face of the plates. This should be avoided for safety reasons. It also wastes fuel, lowering efficiency, and reduces power. The gas breakthrough may also reduce coolant flow through the stack, increasing fuel cell temperature.

[0009] It has also been determined that only a small amount of water circulating external to the cell stack is required in order to remove the ingested gas so that it does not build up within the cell stack assembly. It has been found that between about 5cc/min/celt and about 10cc/min/cell of external water circulation is adequate to remove sufficient gas to prevent gas breakthrough at the water transport plates. This amounts only to between about 2 lpm and 4 lpm for a 75 kilowatt fuel cell power plant, for instance.

[0010] In many fuel cell applications, the fuel cell may be shut down in cold ambients which will cause water in the fuel cell stack or its external plumbing to freeze. One aspect of dealing with freezing water is to avoid having water contacting moving parts which become immobilized when water therein is frozen, and which may be damaged as a result of the expansion of freezing water.

[0011] To avoid water contacting moving parts of a pump, the water is mixed with a pressurized immiscible fluid which propels the water through a deionizer and optionally a heater, after which the water and immiscible fluid are separated. After the fluid is separated from water, gas entrained in the fluid escapes to exhaust, and the immiscible fluid returns to a pressurizing pump; water is returned to the stack. [0012] Separation of the water from the immiscible fluid and gas is achieved with a separator in which the mixture enters space surrounded by a porous, hydrophobic medium; in one embodiment, the hydrophobic medium is shaped as an annulus. At the downstream end of the space, there is a porous, hydrophilic medium, which may be shaped as a plug. The immiscible fluid and gas will pass through the hydrophobic medium while water alone will pass through the hydrophilic medium at the end of the annulus, so long as a sufficient, minimal bubble pressure is maintained. This arrangement avoids moving parts in contact with water; bubbles are removed with a minimal volume of water external to the fuel cell stack; typical immiscible fluids, being incompressible and retaining liquidity below 20⁰C, provide system efficiency and simple and robust water handling at freezing temperatures.

[0013] Other variations will become apparent in the light of the following detailed description of exemplary embodiments, as illustrated in the accompanying drawings.

Brief Description of the Drawings

[0014] Fig. 1 is a simplified, stylized block diagram of an evaporatively cooled fuel cell power plant disclosed in the aforementioned patent publication.

[0015] Fig. 2 is a simplified, stylized schematic illustration of an evaporatively cooled fuel cell power plant using immiscible fluid to propel external water for gas removal.

[0016] Fig. 3 is a top plan view of a separator for separating water from the immiscible fluid.

[0017] Fig. 4 is a sectioned, side elevation view taken on the line 4-4 of

Fig. 3.

[0018] Fig. 5 is a simplified, stylized schematic illustration of an alternative fuel cell power plant using immiscible fluid to propel external water for gas removal.

Mode(s) of Implementation

[0019] Referring to Fig. 2, the suction inlet 200 of an eductor 202 (also known as an ejector) is connected to the water outlet 68 of the fuel cell stack 37 by a conduit 69a. The primary inlet 205 of the eductor 202 receives a primary flow of immiscible fluid under pressure, such as 3M

HFE-7500 or GE SF-96 silicon fluid, over a conduit 206 from a pump 208.

The pump receives immiscible fluid over a conduit 210 from a reservoir

211 which has a gas vent 212.

[0020] A mixture of water, immiscible fluid, and gas is emitted through an outlet 217 of the eductor 202 and is provided over a conduit 220, both to the deionizer 175 as well as to a bypass valve 221 , which may optionally be utilized to control the amount of combined fluid that flows through the deionizer, in response to control signals from a controller 223. A plurality of conduits interconnect the outlets of the deionizer 175 and the valve 221 with inlets of the heater 227 and a bypass valve 228, both also controlled by the controller. The heater can optionally be used to heat up the combined flow in the conduit 226 to assure that the water is liquid, and thereby can be separated when applied to a separator 231 by conduits 232.

[0021] The separator 231 separates the immiscible fluid and gas, into a conduit 234 which provides it to the reservoir fluid 211. It also provides water in a conduit 237 which joins the conduit 65 and returns the water to the water reservoir 64.

[0022] Referring to Fig. 3, the separator 231 has an inlet 240 which comprises a frustoconical center of a porous, hydrophobic medium in the form of an annulus 242 which is interconnected with the conduit 234 by an outlet 244. The frustoconical inlet 240 is also in fluid communication with a central porous hydrophilic medium in the form of a plug 247 which is in fluid communication with an outlet 248 connected to the conduit 237. The porous sections 242, 247 are joined together by a solid annulus 250. [0023] Under pressure provided by the pump 208, the gas and immiscible fluid will pass through the porous hydrophobic medium 242 into the conduit 234, and the water will pass through the porous hydrophilic medium 247 into the conduit 237. The hydrophilic medium 247 is flooded (completely wetted with water) which prevents the gas from passing therethrough, much the same as in a water transport plate. [0024] The hydrophobicity of the porous hydrophobic medium 242 and the hydrophilicity of the porous hydrophilic medium 247 may be provided of materials and using processes such as those described in U.S. patent No. 6,780,533. The bubble pressure of the porous hydrophilic medium 247 may similarly be controlled by selecting pore sizes which will support the pressure of the gas and immiscible fluid, without allowing them to break through.

[0025] Fig. 5 illustrates embodimental alternatives which may be selected if desired. For instance, with sufficient pressure of air from the air pump 52 and sufficient pressure of immiscible fluid from the pump 208, the water can be separated from the immiscible fluid prior to passing through the deionizer. All that is required is that a suitable pressure balance be achieved such that there is sufficient pressure in the separated water to pass through the deionizer 175 adequately, while the pressure is sufficiently low so as to not permit breakthrough of the gas and immiscible fluid, through the porous hydrophilic medium 247.

[0026] Fig. 5 also illustrates that the heater may be employed directly in the conduit 69a to achieve greater heating efficiency. Sensible heat transfer will occur between the water and the immiscible fluid once they are mixed in the eductor 202. On the other hand, the deionizer 175 may remain downstream of the separator 231 with the heater 227 located in the conduit 220, rather than in the conduit 69a, if desired in any implementation.

[0027] The inlet 240 of the porous hydrophobic annulus 242 need not be frustoconical; it may instead be cylindrical or even of a rectangular cross section. In other words, the annulus need not be round; in fact, the porous, hydrophobic medium need not be an annulus. What is important is that the fluid entering the separator 231 be presented to both the hydrophobic portion that leads to one outlet for immiscible fluid and gas as well as being presented to the hydrophilic portion which leads to a distinctly different outlet for water.

[0028] Although the embodiment herein has been described with respect to an evaporatively cooled fuel cell stack of the type disclosed in the aforementioned publication, the arrangements described may equally well be used with fuel cell stacks having larger amounts of water flowing through the water channels, such as is utilized when cooling is achieved by sensible heat exchange with water. The point of the arrangement, having no external water in communication with moving mechanical parts, is well suited to a variety of systems.

[0029] The separator may have several distinct hydrophobic portions and several hydrophilic portions; such portions may be interspersed, or not. In some cases, suitable manifolding of several outlets for each fluid may have to be provided. [0030] It also should be understood that the separator disclosed in Figs. 3 and 4 may find use in other than the external water arrangements of a fuel cell power plant. The separator may be used, for instance, in fuel cell power plants employing direct antifreeze solutions within the stack, to continually restore the coolant to desired strength, and for other purposes.

Claims

1. A method comprising conducting immiscible fluid from an inlet (240) having a mixture of immiscible fluid and water through a porous, hydrophobic medium (242) to a first outlet (244), and conducting water from said inlet through a porous, hydrophilic medium (247) to a second outlet (248).

2. A method comprising flowing a mixture of water and immiscible fluid into an inlet (240) (a) which is in fluid communication with a first fluid outlet (244) through a porous hydrophobic medium (242), and (b) which is in fluid communication with a second fluid outlet (248) through a porous, hydrophilic medium (247).

3. A method comprising: conducting liquid water in an environment near or below the freezing temperature of water by suctioning liquid water from a water utilizing element (37) by means of a suction inlet (200) of an eductor (202) having a primary flow of immiscible fluid under pressure, thereby mixing the water with the immiscible fluid; and separating the water from the immiscible fluid and returning the separated water to the water utilizing element.

4. A method according to claim 3 further comprising: returning separated immiscible fluid to a pump (208), which provides the primary flow of immiscible fluid under pressure to the eductor (202).

5. A fluid separator (231) comprising: an inlet (240); a porous hydrophobic medium (242) in fluid communication between said inlet and a first fluid outlet (244) configured to receive fluid that passes through said porous hydrophobic medium; a porous hydrophilic medium (247) in fluid communication between said inlet and a second fluid outlet (248) configured to receive fluid that passes through said porous hydrophilic medium.

6. A fuel cell power plant (36) comprising: a stack (37) of fuel cells (38); a plurality of water passageways (67) in said stack extending between a water inlet (66) and a water outlet (68);

5 an eductor (202) having a suction inlet (200) in fluid communication with said water outlet, said eductor having a primary inlet (205) in fluid communication with a pressurized source (208, 211 ) of immiscible fluid; and a separator (231) in fluid communication with an outlet (217) of said0 eductor and configured to separate the immiscible fluid from water, the immiscible fluid provided by said separator being returned (234) to said pressurized source, the water provided by said separator being returned to the water inlet of said stack.

7. A fuel cell power plant (36), comprising: a stack (37) of fuel cells (38) each fuel cell including fuel reactant gas flow fields connected between a fuel inlet (42) and a fuel outlet (47), and oxidant reactant gas flow fields connected between an air inlet (53) and an S air outlet (57), at least one of said oxidant reactant gas flow fields and said fuel reactant gas flow fields comprising a hydrophilic, porous plate; a plurality of water passageways (67), said at least one hydrophilic, porous plate in each fuel cell being in fluid communication with one of said water passageways, said water passageways extending between a water0 inlet (66) and a water outlet (68); an eductor (202) having a suction inlet (200) in fluid communication with said water outlet, said eductor having a primary inlet (205) in fluid communication with a pressurized source (208, 211 ) of immiscible fluid; and 5 a separator (231) in fluid communication with an outlet (217) of said eductor and configured to separate the immiscible fluid from water, the immiscible fluid provided by said separator being returned (234) to said pressurized source, the water provided by said separator being returned to said stack.

8. A fuel cell power plant (36) according to claim 7 further characterized by: a deionizer (175) located downstream of said outlet (217) of said eductor (202).

9. A fuel cell power plant (36) according to claim 7 further characterized by: a deionizer (175) disposed in fluid communication either (a) between said outlet (217) of said eductor (202) and said separator (231), or (b) between said separator and said water inlet (66).

10. A fuel cell power plant (36), comprising: a stack (37) of fuel cells (38) each fuel cell including fuel reactant gas flow fields connected between a fuel inlet (42) and a fuel outlet (47), and oxidant reactant gas flow fields connected between an air inlet (53) and an air outlet (57), at least one of said oxidant reactant gas flow fields and said fuel reactant gas flow fields comprising a hydrophilic, porous plate; a plurality of water passageways (67), said at least one hydrophilic, porous plate in each fuel cell being in fluid communication with one of said water passageways, said water passageways extending between a water inlet (66) and a water outlet (68); an eductor (202) having a suction inlet (200) in fluid communication with said water outlet, said eductor having a primary inlet (205) in fluid communication with a pressurized source (208, 211 ) of immiscible fluid; and a separator (231 ) having an inlet (240) in fluid communication with an outlet (217) of said eductor and configured to separate the immiscible fluid from water, the immiscible fluid provided by said separator being returned (234) to said pressurized source, the water provided by said separator being returned to said stack, said separator comprising a porous hydrophobic medium (242) in fluid communication between said inlet and a first fluid outlet (244), said first fluid outlet in fluid communication with said pressurized source, and a porous hydrophilic medium (247) in fluid communication between said inlet and a second fluid outlet (248), said second fluid outlet in fluid communication with said water inlet.