Steam generator for fuel cell systems

Abstract

A steam generator for a fuel cell system comprises: a heat exchanger (34) with at least one internal heat exchange surface, a water inlet pipe (46), and a dripper (52) having a flow channel fluidly connected to the water inlet pipe (46). The dripper (52) extends inside the heat exchanger (52) and above the heat exchange surface for supplying water downward to the heat exchange surface for conversion into steam. The dripper (52) has outlet orifices (56) spaced apart along the flow channel, and between adjacent outlets (orifices 56), the dripper has a stepped profile at least on its underside to prevent droplet coalescence from adjacent orifices. The fuel inlet pipe may have a section coaxially mounted with a portion of the water inlet pipe (46). This section of the fuel inlet pipe may surround that portion of the water inlet pipe. In a fuel cell system with a steam generator, the steam generator may include a fuel inlet pipe and combined steam and fuel outlets, as well as a reformer directly or indirectly connected downstream of the steam generator.

Description

Technical Field

[0001] The present invention relates to a steam generator for a fuel cell system, a fuel cell system including the steam generator or a steam fuel heater, and a method of using the steam generator to generate steam or heated steam and fuel. Background Technology

[0002] A fuel cell system typically includes a fuel cell stack, a reformer for fully or partially reforming the inlet fuel (to supply hydrogen or syngas (reformate) to the fuel cell stack), and a steam generator that supplies steam and fuel to the reformer. Once the reformate, along with the oxidant, is supplied to the fuel cell stack on either side of the electrochemically active layer within the fuel cell stack, it undergoes an electrochemical reaction to generate heat (hot effluent gas) and electricity.

[0003] In many fuel cell systems, the heat generated is used to operate both the steam generator and the reformer via a heat exchanger.

[0004] In some fuel cell systems, there is no separate reformer—reforming occurs within the fuel cell stack. Summary of the Invention

[0005] The amount of electricity generated from a fuel cell stack needs to be controllable. To increase electrical output, more fuel or reformate needs to be supplied to the fuel cell stack, or the operating conditions within the stack need to be changed (e.g., to improve stack efficiency). For the former approach, it is important to ensure that the fuel or reformate is supplied without excessive pressure pulsations, a consistent fuel-to-steam ratio, and large temperature variations. Furthermore, it is preferable that the reformate or fuel is supplied at a controllable rate, adjustable as needed, with minimal time lag. To achieve this, if a reformer is present, it needs to be supplied with heated fuel and steam with minimal pressure pulsations and no time lag. Therefore, the present invention relates to an improved steam generator for achieving controlled and uniform delivery of the fuel / steam mixture to the reformer or fuel cell stack, thereby best achieving minimal fluctuations in stack voltage due to changes in fuel composition or pressure.

[0006] According to the present invention, a steam generator for a fuel cell system is provided, the steam generator comprising:

[0007] A heat exchanger having at least one internal heat exchange surface;

[0008] Water flows into the pipe;

[0009] A dripper, comprising a flow channel fluidly connected to the water inlet pipe, the dripper extending inside the heat exchanger and above the heat exchange surface for supplying water downwards to the heat exchange surface for conversion into steam;

[0010] The dripper includes a plurality of outlet holes spaced apart along the length of the flow channel; and

[0011] Specifically, when viewed in cross-section, the dropper has a stepped profile at least on its underside between adjacent outlet orifices to prevent droplets from adjacent orifices from coalescing.

[0012] The phrase "having a stepped profile at least on the lower side of the dropper" refers to having a stepped surface at different heights on at least the lower half of the dropper. The stepped surface or step (e.g., a horizontal line defined by a corner or shoulder) promotes a surface tension effect that prevents the droplet from spreading beyond the stepped surface—for example, when a droplet is held in place by surface tension, it will resist the surface tension effect due to the pull of gravity and will not tend to rise.

[0013] The corners or shoulders may include convex corners or shoulders, and are preferably sharp corners or shoulders. They may be formed by the intersection of two (preferably flat) surfaces, which are a lower surface (the outer surface in the radial direction) and an ascending surface (e.g., an "upward" extending surface—a surface extending from the lower surface toward the axis of the droplet, which, due to gravity, will not tend to climb but rather tend to remain on the lower surface).

[0014] The lower surface can have an inner shoulder (closest to the aperture) and an outer shoulder (opposite to the aperture). The lower surface can then have two convex corners. Water droplets will form against the inner shoulder as they leave the aperture and can grow on the lower surface before reaching the outer shoulder. However, because the rising surface extending upwards from the outer shoulder forms this forward gravitational barrier, the droplets will not tend to spread too far beyond the outer shoulder.

[0015] In other embodiments, the hole may be in the lower surface, whereby a single convex shoulder may be present on the side of the lower surface (opposite to the hole). The single convex shoulder may be annular around the hole, or the single convex shoulder may be one of a pair of shoulders spaced apart on both sides of the hole along the axis of the dropper.

[0016] While in practice the convex intersection, or each convex intersection, corner, or shoulder, may be rounded, it is preferred that it be substantially angular, i.e., sharp. However, the intersection may be more or less rounded. The angle or sharpness of the intersection (i.e., corner or shoulder) can be defined by the radius of curvature of the intersection / corner / shoulder in the cross section or by the perceived sharpness of the intersection / corner / shoulder—that is, (in the cross section) it appears as an intersecting line rather than a curved corner. Ideally, where it can be perceived as having a radius, it will still have a radius of less than 0.5 mm in the cross section. However, it is alternatively possible to provide more rounded intersections, corners, or shoulders, for example, with a radius (in the cross section) up to half the diameter or longest width of the hole associated with the intersection, corner, or shoulder.

[0017] Alternatively, it can have a radius of up to 40% of the height of the step, as measured perpendicular to the axis of the dripper (or parallel to the axis of the hole). However, more preferably, the radius of the intersection, corner, or shoulder will not exceed 20% of the height, or even 10% or 5% of the height.

[0018] The stepped surface can have selected dimensions and shapes to allow droplets to grow to a suitable size to control vapor generation and respond accordingly, while simultaneously preventing excessively large droplet sizes, thereby preventing or minimizing any possibility of coalescence between droplets from adjacent orifices. This can also be controlled by requiring a selected range of water flow rates and a selected orifice size.

[0019] In use, the orifice is preferably positioned laterally along the dropper or selectively within the heat exchanger above the corresponding heat exchange surface on which the droplet is to be dropped, i.e., the orifice is positioned such that the heat exchange surface is below the orifice, so that the droplet can drip directly onto the heat exchange surface.

[0020] An orifice is provided to allow water droplets to fall, and therefore typically has a diameter of at least 0.2 mm, and more preferably at least 0.3 mm. The resulting droplets will be larger than the diameter of the orifice, and therefore typically at least 0.5 mm wide, as the droplets fall from the orifice(s) under gravity onto the heat exchange surface to convert into vapor, and more commonly at least 1 mm wide. The droplets are not an atomized water spray. Nor are the droplets droplet vapor. (The head with the outlet orifice is, after all, a dripper, not an atomizer or spray nozzle, so that water drips from the dripper as a liquid rather than a gas under the influence of gravity, and drips from the dripper as a drop rather than a spray.)

[0021] The stepped profile between adjacent outlet holes may include at least two stepped surfaces at different heights above the heat exchange surface. Typically, adjacent outlet holes are respectively disposed on stepped surfaces, wherein at least one stepped surface between these surfaces is at a different height above the heat exchange surface. Alternatively, adjacent outlet holes are respectively disposed on stepped surfaces at the same height on the heat exchange surface.

[0022] In addition to convex intersections, corners, or shoulders, concave corners or intersections may also exist, defining an upper surface extending generally parallel to the axis of the dropper between adjacent holes. Concave corners can also be sharp, angled, or rounded, similar to convex intersections, corners, or shoulders, or have the same angle or radius in cross-section as adjacent convex intersections, corners, or shoulders, or have a different radius or angle in cross-section. However, preferably, it falls within a similar radius range.

[0023] In most examples, the length of the upper surface spans across the opposite rising surfaces of adjacent steps in the dropper. This span defines the gap between the opposite rising surfaces of adjacent steps (typically >2 mm or >3 mm).

[0024] The upper surface may include one or more planar surfaces, or the upper surface may be curved about the axis of the dropper.

[0025] Preferably, the height of each step is measured vertically (perpendicular to the axis of the dropper) from the upper surface of the step to the lower surface of the step. If the upper or lower surface is curved around the axis of the dropper, the height is measured through the sagittal plane of the dropper, which extends through the centerline of the corresponding orifice. Preferably, the height is greater than the diameter of the orifice. More preferably, the height is at least two or three times the diameter of the orifice.

[0026] The length of the gap between opposite rising surfaces of adjacent steps of adjacent holes, measured at a midpoint height of the rising surface (midway between the upper and lower surfaces) parallel to the axis of the dripper, is preferably equal to or greater than the height of the shorter of the two steps at the end of the gap; however, preferably, the two steps have the same height. If the surface has curvature around the axis of the dripper, this can again be measured in the sagittal plane. More preferably, the gap is at least two or three times the height of the shorter of the two steps at the end of the gap.

[0027] Using these step dimensions, the profile and spacing between the step-shaped surfaces will tend to minimize or eliminate droplet coalescence between adjacent orifices. Therefore, in use, droplets will tend to fall vertically downwards from the dropper to below the orifice.

[0028] Typically, the dropper is elongated and has a flow channel that includes orifices spaced axially along the length of the dropper.

[0029] In one embodiment, the adjacent outlet orifices are respectively disposed on a stepped surface forming part of a structure that protrudes outward and downward from the heat exchange surface. The stepped surface may optionally have selected dimensions and shapes to facilitate the growth of droplets of appropriate size.

[0030] The structure may include a small channel that extends laterally away from the flow channel and leads to an outlet hole on the stepped surface. This small channel may be threaded to receive a hollow screw with a drilled hole of a selected diameter, thereby providing a desired cross-section and thus providing flow. Therefore, the hole size can be changed or selected by using a specific hollow screw.

[0031] The adjacent outlet holes can be provided in corresponding protruding structures, which are integrally formed with the dripper and separated from each other by grooves or channels.

[0032] Alternatively, the structure can be a nail—that is, a cylindrical shape with a generally flat bottom, a hole in the bottom, and a shoulder around the edge of the bottom.

[0033] Alternatively, each outlet orifice is separated from the adjacent outlet orifice by at least one spacer that protrudes outward relative to the outlet orifice. The term spacer is used to refer to a protruding structure or (e.g., a lateral) divider that restricts the flow of liquid, for example, to prevent liquid from spreading in a particular direction. The spacer can be a narrow or wide structure or a divider with a corner / shoulder as defined above.

[0034] By using a spaced arrangement of adjacent orifices, the droplets supplied to the heat exchanger from the outlet orifice can have a controlled size and be positioned correctly (above the heat exchange surface), all within acceptable parameters, to ensure that the evaporation of water flowing onto the heat exchange surface occurs in a continuous and stable manner, thereby reducing or minimizing pressure pulsations in the steam-fuel flow output from the heated steam (and optionally fuel gas) outlet port of the heat exchanger.

[0035] As previously described, the size of the controlled water droplet is preferably at least 0.5 mm wide (i.e., the preferred minimum droplet size) because the droplet falls toward the heat exchange surface under the influence of gravity, and more preferably at least 1 mm wide—that is, having a diameter of at least 0.5 mm or more preferably at least 1 mm (at the widest point of the droplet).

[0036] Preferably, each outlet orifice is separated from the adjacent orifice by a corresponding pair of associated spacers arranged axially on both sides of each orifice along the dropper. These spacers are preferably spaced apart to define a gap of at least 2 mm between them, in which water can accumulate to form droplets.

[0037] In embodiments where the outlet orifices are sufficiently closely spaced, the dripper may include outlet orifices and spacers or steps arranged alternately along the dripper at spaced axial intervals, such that only a single spacer or step is provided between adjacent orifices. Preferably, although there are two spaced-apart spacers between adjacent orifices to form a series of steps, spaces or gaps are formed between adjacent spacers and between orifices. This further helps prevent droplets from adjacent outlet orifices from pooling together or otherwise interacting with each other to form a liquid pool within the heat exchanger—water will evaporate more slowly if it can accumulate, which can lead to a delayed response in the steam flow rate from the steam generator under transient inlet flow conditions. It can also cause droplets to drip away from the intended heat exchange surface. It can also allow water to accumulate during or after a shutdown event, as water does not evaporate easily in advance, which can cause difficulties when restarting the fuel cell system, or even lead to localized oxidation or deposition (after evaporation), resulting in maintenance problems. Therefore, the aim is to ensure a steady drip from each outlet, rather than water pooling at the drip tip between adjacent outlet orifices, which could lead to irregular or uncontrolled dripping and thus excessive buildup on the heat exchanger, instead of the desired controlled water droplets.

[0038] If buildup occurs at the base of the heat exchanger (where hot gases first enter the heat exchanger), it can be particularly problematic because it can cause unstable water boiling, resulting in undesirable and significant pressure pulsations in the steam outflow. Therefore, avoiding large water droplets is important. This is especially true in this case, where any unboiled water will naturally accumulate at the base of the heat exchanger due to gravity.

[0039] The protruding structure, partition, or step that projects outward relative to the outlet orifice can be an integral or mating structure. It preferably defines a shoulder (e.g., arcuate) that is laterally spaced from the outlet orifice. It can be formed by a flange or gasket, or by a groove in the wall of the dripper, wherein the outlet orifice is positioned within a recess formed by the groove.

[0040] The dropper head can be machined, and thus the groove can be cut into the wall of the dropper head, or the structure can be manufactured onto the dropper head or integrally formed on the dropper head.

[0041] The structure can extend partially around the periphery or outer circumference of the dropper, or it can extend all the way around the dropper. Extending all the way around the dropper provides a low probability of water accumulating across multiple outlet orifices, because each droplet is contained vertically and horizontally.

[0042] The outlet orifice preferably extends radially relative to the longitudinal axis of the dripper. Ideally, the outlet orifice points downward.

[0043] The dripper can be a removable or replaceable component—preferably threaded to the end of the water inlet pipe, or threaded to a connector at the end of the water inlet pipe.

[0044] A dripper typically includes two or more outlet holes spaced apart axially along the dripper, wherein each outlet hole is separated from adjacent holes by a corresponding pair of associated separators arranged axially on both sides of each hole, such that at least two separators are provided between adjacent holes. By providing two separators between adjacent holes, water will not accumulate on and beyond the outer edge of the separator in a manner that interacts with corresponding accumulations from adjacent holes—the gap between adjacent separators separates any such accumulations.

[0045] The heat exchange surface can be a plate-like or tubular surface of the heat exchanger. Heat sinks or other non-flat components may be additionally provided, extending within the heat exchanger and typically from the plate-like or tubular surface within the heat exchanger. For example, a spear-shaped, offset arrangement of heat sinks may be present within the heat exchanger. These help to avoid any straight-through paths within the water / steam passage of the steam generator. Thus, as water decreases, even if it is not rapidly evaporated upon impact with the heat exchange surface directly below the outlet orifice, multiple locations and surfaces within the heat exchanger serve to transfer heat to the water, allowing evaporation to occur before accumulation at the base of the heat exchanger.

[0046] Preferably, the steam generator also includes a fuel inlet pipe for allowing fuel to be supplied to the steam generator to mix with steam, so that the outflowing steam is a heated steam-fuel gas suitable for supplying to a reformer or directly to a fuel cell stack. Preferably, the gaseous fuel is supplied to the steam generator together with water. It may surround the water inlet pipe.

[0047] Droplets from the dripper form at a desired or controllable rate from the outlet orifice. The droplets can be controlled by the supply water pressure or a flow control valve—which is variable, allowing for different steam supply rates from the steam generator. The water is still liquid when it reaches the outlet orifice—meaning there is active control over the conditions to prevent premature steam formation (i.e., before it drips from the dripper nozzle onto the heat exchange surface). This invention aims to provide a controlled drip of a certain regularity and size from the dripper's outlet orifice to achieve the desired steam output from the steam generator. Thus, water arrives at the outlet orifice as liquid water and leaves the dripper as liquid water droplets, allowing the droplets to fall onto the heat exchange surface below the dripper under gravity. Therefore, this invention does not discharge steam or atomized spray from the dripper or outlet orifice, but rather drips droplets that fall under the influence of gravity.

[0048] The outlet orifices are located at spaced-out axial positions along the lower half or underside of the dropper. Therefore, gravity helps to prevent droplets from accumulating between the outlet orifices.

[0049] The partition structure on both sides of the outlet orifice can form a gap around the entire periphery of the dripper—preferably, this gap is an annular gap.

[0050] At least one of the partition structures can have a ring-like form surrounding the dropper.

[0051] The partition structures on both sides of at least one outlet orifice in the outlet orifice can have an annular form surrounding the dripper.

[0052] The partition structure may have a height that extends radially outward relative to the longitudinal axis of the dropper, and this height is greater than the width of the partition structure.

[0053] The partition structure or baffle may include a separate component mounted on the dripper.

[0054] The dripper may include a tubular end section, and the separation structure may include a pair of gaskets mounted on the tubular end section, one gasket being proximal to the outlet orifice relative to the tubular end section, and the other gasket being distal to the outlet orifice relative to the tubular end section. This simple structure is very cost-effective.

[0055] Preferably, the gasket is press-fitted onto the tubular end section. This minimizes the gap between the outer side of the tubular end section and the inner side of the gasket, thereby minimizing the chance of water leakage between the outer side of the tubular end section and the inner side of the gasket, which could promote water accumulation between adjacent outflow holes.

[0056] Preferably, the pair of separating structures are integrally formed with the tubular end section, for example, as an integral flange or shoulder.

[0057] This structure can define parallel sidewalls between which water is supplied from its outlet orifice during the use of the steam generator.

[0058] In some embodiments, the parallel sidewalls are perpendicular to the longitudinal axis of the nozzle.

[0059] Typically, only one outlet hole is provided between each pair of parallel sidewalls.

[0060] In some embodiments, the dripper is a one-piece structure.

[0061] To allow water to be supplied through the dripper, the dripper has a central bore that fluidly connects to both the water inlet pipe and the outlet orifice. Since the end is preferably not the outlet orifice, the dripper generally has a closed distal end.

[0062] When the structure is formed by a transverse cut or groove on one side of the dropper and the outlet hole is at the base of the transverse cut or groove, the separator can define arcuate shoulders on both sides of the outlet hole.

[0063] The sidewalls do not need to be parallel—in some embodiments, the sidewalls taper outwards to widen at the outer side.

[0064] The dripper may have a hexagonal cross-section along at least a portion of its length, and preferably has a threaded hole at the proximal end of the dripper to facilitate attachment of the nozzle to the end of the water inlet pipe.

[0065] Preferably, the steam generator has a steam outlet that is connected to the reformer of the fuel cell system.

[0066] Preferably, the steam outlet is located at or near the bottom of the heat exchanger, and the dripper is installed inside the heat exchanger, at or near the top of the heat exchanger.

[0067] Preferably, the fuel and steam are combined in a steam generator.

[0068] In some embodiments, the steam generator is a combination of a steam generator and a fuel heater for a fuel cell system (e.g., a steam fuel heater in which steam and fuel are mixed and heated).

[0069] Preferably, the fuel cell system is a solid oxide fuel cell system. Preferably, the fuel cell system has at least one fuel cell stack. Preferably, at least one fuel cell stack is formed of a metal-supported solid oxide fuel cell. Solid oxide fuel cells or their stacks can be as described in WO2015136295, the entire contents of which are incorporated herein by reference only.

[0070] In some embodiments, the fuel inlet pipe has a section coaxially mounted to a portion of the water inlet pipe. Preferably, this section of the fluid (fuel) inlet pipe surrounds that portion of the water inlet pipe. Preferably, this arrangement is positioned at the point where the two pipes enter the steam generator.

[0071] This section and portion may be located on or near the outer wall of the heat exchanger, or it may extend the flow of fuel and water through the outer wall of the heat exchanger. Typically, the water inlet pipe is installed perpendicular to the outer wall of the heat exchanger. Similarly, the fuel inlet pipe is typically installed perpendicular to the outer wall of the heat exchanger.

[0072] The combination of fuel and water inflow allows for a preferred arrangement.

[0073] According to this aspect of the invention, a steam generator for a fuel cell system is provided, the steam generator comprising:

[0074] A heat exchanger having at least one internal heat exchange surface;

[0075] Water flows into the pipe;

[0076] Fuel inlet pipe; and

[0077] A dripper, fluidly connected to the water inlet pipe, extends inside the heat exchanger and above the heat exchange surface for supplying water downwards onto the heat exchange surface to be converted into steam;

[0078] The fuel inlet pipe has a section that surrounds a portion of the water inlet pipe at or near the outer wall of the heat exchanger and extends through the outer wall of the heat exchanger, such that the section of the fuel inlet pipe and the fuel located in the section of the fuel inlet pipe during use are used to thermally insulate the surrounded portion of the water inlet pipe from the heat exchanger.

[0079] The steam generator may also have the same features as the steam generator of the first aspect of the present invention.

[0080] The present invention also provides a fuel cell system comprising a fuel cell stack; a fuel inlet pipe; a water inlet pipe; and an air or oxidant inlet pipe; a steam generator and a fuel heater connected to a combination of the fuel inlet pipe and the water inlet pipe; an optional reformer connected to the combined steam generator and fuel heater for supplying hydrogen or syngas to the fuel cell stack; and a heat exchanger for directly or indirectly obtaining heated fluid from the effluent of the fuel cell stack, the heat being used to heat at least one internal heat exchange surface of the heat exchanger, wherein the at least one internal heat exchange surface is used to generate steam from water via a dripper from the water inlet pipe, the combined steam generator and fuel heater being a steam generator as defined above, the steam generator including the fuel inlet pipe and the water inlet pipe, and wherein fuel is mixed with and heated in the steam generator.

[0081] The heated fluid can be fuel electrode gas or air electrode gas from the battery stack.

[0082] According to another aspect of the invention, the use of the above-described fuel cell system is disclosed, which is used to minimize fluctuations in the stack voltage caused by changes in the composition or pressure of the fuel / steam mixture entering the fuel cell stack of the fuel cell system.

[0083] The present invention also provides a method for generating steam using the steam generator as defined above, wherein water is supplied to a heat exchange surface through a water inlet pipe and a dripper, where the water is converted into steam. Optionally, the method minimizes pressure pulsations in the generated steam by controlling the droplet size from the dripper using the dripper as defined above.

[0084] Furthermore, this can be achieved by using (for example, by selective positioning) a dropper with a stepped profile on its underside to position water droplets above the heat exchanger surface.

[0085] According to the invention, a method for minimizing pressure pulsations in a steam generator during steam generation is also provided, the steam generator comprising: a heat exchanger having at least one internal heat exchange surface; a water inlet pipe; and a dripper including a flow channel fluidly connected to the water inlet pipe, the dripper extending inside the heat exchanger and above the heat exchange surface for supplying water droplets downward to the heat exchange surface for conversion into steam; wherein the dripper includes a plurality of outlet orifices spaced apart along the length of the flow channel; and wherein, when viewed in cross-section, the dripper has a stepped profile at least on its underside between adjacent outlet orifices, the method comprising adjusting the flow rate of water to a selected flow rate, whereby the stepped profile (e.g., together with a selected orifice size) prevents droplet coalescence from adjacent orifices.

[0086] A stepped profile can have corners or shoulders as defined above.

[0087] When the dropper has a longitudinal axis, the cross-section of the stepped profile passes through the vertical sagittal plane of the dropper and extends through the longitudinal axis.

[0088] The stepped profile provides a rising surface that water droplets do not tend to rise to, so water droplets on adjacent rising surfaces do not interact with each other, and therefore the water droplets do not coalesce.

[0089] Preferably, the orifice of the dropper is located vertically above the corresponding heat exchange surface of the heat exchanger, so that the droplet evaporates rapidly when it lands on those heat exchanger surfaces.

[0090] Optionally, fuel is simultaneously supplied through a fuel inlet pipe and to a heat exchanger, where the fuel is mixed with and heated by steam in the heat exchanger.

[0091] In another aspect, a steam generator for a fuel cell system is provided, the steam generator comprising:

[0092] A heat exchanger having at least one internal heat exchange surface;

[0093] Water flows into the pipe; and

[0094] A dripper, fluidly connected to the water inlet pipe, extends inside the heat exchanger and above the heat exchange surface for supplying water downwards onto the heat exchange surface to be converted into steam;

[0095] The dripper includes a plurality of transverse outlet holes spaced apart along the axial direction of the dripper, each hole being separated from an adjacent hole by at least one structure protruding outward relative to the transverse outlet holes.

[0096] In another aspect, a steam generator for a fuel cell system is provided, the steam generator comprising:

[0097] A heat exchanger having at least one internal heat exchange surface;

[0098] Water flows into the pipe;

[0099] A dripper, comprising a flow channel fluidly connected to the water inlet pipe, the dripper extending inside the heat exchanger and above the heat exchange surface for supplying water downwards to the heat exchange surface to be converted into steam;

[0100] The dripper includes a plurality of outlet holes spaced apart along the length of the flow channel; and the steam generator is configured to allow water to appear from the outlet holes of the dripper as water droplets rather than steam or spray during use, the water droplets falling onto the heat exchange surface under gravity to be converted into steam.

[0101] Specifically, when viewed in cross-section, the dropper has a stepped profile at least on its underside between adjacent outlet orifices to prevent droplets from adjacent orifices from coalescing.

[0102] Water droplets from the dripper fall under the influence of gravity, while steam, as a gas or atomized spray (which acts like a gas due to the tiny size of the particles and the gas accompanying the spray particles), tends to remain suspended or be powered by the jet force from the outlet orifice (i.e., the flow of gas accompanying the spray), rather than being primarily affected by gravity.

[0103] The present invention also provides a method for operating a steam generator for a fuel cell system, the steam generator comprising:

[0104] A heat exchanger having at least one internal heat exchange surface;

[0105] Water flows into the pipe;

[0106] A dripper, comprising a flow channel fluidly connected to the water inlet pipe, the dripper extending inside the heat exchanger and above the heat exchange surface for supplying water downwards onto the heat exchange surface to be converted into steam;

[0107] The dropper includes a plurality of outlet holes spaced apart along the length of the flow channel, and when viewed in cross-section, the dropper has a stepped profile at least on the underside of the dropper between adjacent outlet holes to prevent droplet coalescence from adjacent holes.

[0108] The method includes:

[0109] Water is supplied to the dripper through the water inlet pipe; and

[0110] The water is dripped from the dripper through the outlet hole as a water droplet rather than steam or a spray, and the water droplet falls onto the heat exchange surface to be converted into steam.

[0111] In some embodiments, a steam generator forms part of the fuel cell system and generates steam, which is supplied to the fuel cell inlet within the fuel cell system.

[0112] The method of this invention aims to ensure that the water remains liquid when it reaches the outlet orifice and when it drips onto the heat exchange surface. Therefore, the method in the preferred embodiment actively controls the conditions upstream of the dripper to avoid premature steam formation. For example, the steam generator may include a control system configured to deliver liquid water to the outlet orifice at a suitable temperature and mass flow rate, causing the liquid water to form droplets that fall under gravity. This could include, for example, a controller within the steam generator that communicates operatively with sensors (e.g., temperature / pressure / flow sensors) and actuators (e.g., control valves and / or mass flow controllers) to achieve this purpose. Thus, the invention achieves controlled dripping with preferred regularity and size: the liquid water reaches the outlet orifice as liquid water and exits the dripper as a series of liquid water droplets falling under gravity onto the heat exchange surface, where it is then converted into steam by heat at the heat exchange surface. Therefore, the invention prevents water from exiting the dripper as steam. The present invention also prevents water from exiting the dropper as an atomized spray (e.g., tiny water droplets that do not fall due to gravity).

[0113] The inventors have realized that the dripper should supply water droplets formed discontinuously on the dripper, which then grow until they are large enough to fall or drop under the influence of gravity. This differs from steam, and also from atomized sprays, in which tiny droplets appear continuously in a gas stream as a fine mixture of water particles and a supporting gas stream, suspended in the gas stream (typically air) and therefore not falling under the influence of gravity.

[0114] The method of this invention uses several parameters to ensure the formation of droplets. First, the outlet orifice is configured as a drip orifice, rather than a spray orifice, and therefore has a suitable size and shape for dripping rather than spraying. Furthermore, the dripper is operated such that water pressure (mass flow rate), water temperature, the temperature and pressure of the surrounding heat exchanger air work together to generate water droplets that fall under gravity. Thus, the method avoids the generation of water spray atomized by air, and also avoids premature vapor formation in the dripper and water inlet pipe, preventing liquid water from evaporating before it has a chance to fall from the dripper as droplets. Attached Figure Description

[0115] These and other features of the invention will now be described in more detail by way of example only with reference to the accompanying drawings, in which:

[0116] Figure 1 A fuel cell system including a steam generator according to the present invention is schematically illustrated;

[0117] Figure 2 A first embodiment of a steam generator for a fuel cell system is schematically illustrated.

[0118] Figure 3 An alternative dripper arrangement connected to the steam generator is shown;

[0119] Figure 4 Showing more details Figure 3 The arrangement of drippers;

[0120] Figure 5a and Figure 5b It is a schematic partial cross-sectional view through two alternative steam generators, showing the drippers and details of the water and fuel supply;

[0121] Figure 6 and Figure 7 Another dripper arrangement is shown; and,

[0122] Figure 8a It shows Figure 7 The perspective view and cross-sectional view of the dropper, and Figure 8b and Figure 8c It shows Figure 8a The corresponding view of the variant of the dropper. Detailed Implementation

[0123] First refer to Figure 1 The diagram schematically illustrates a basic fuel cell system, such as a solid oxide fuel cell system. It can be seen that the fuel cell system 10 includes a stack 12 of fuel cells 14.

[0124] The fuel cell has an electrochemical active layer, and the stack has fuel and oxidant flow paths on either side of the electrochemical active layer to allow electrochemical reactions to occur on the electrochemical active layer, thereby generating both electricity 16 and heat from the cell and thus from the stack. The heat is in the form of heated exhaust gas 18, which is a combination of fuel electrode gas and air electrode gas leaving the stack's exhaust device.

[0125] The heated exhaust gas 18 can be used in the fuel cell system 10 for a variety of purposes. One of these purposes is to preheat the oxidant (typically air 27) supplied to the fuel cell stack 12 using an air heater (first heat exchanger 20). Although the oxidant is typically air, other oxidant gases, such as oxygen-enriched gases, can also be used. Typically, for a temperature of 400... o C and 600 o In a solid oxide fuel cell operating at temperatures between C and [other temperatures], the oxidant 27 is heated by the first heat exchanger 20 to approximately 300 [temperatures]. o C to 500 o Output at C. As shown in the figure, this can be achieved using a high level of heat from the cathode (oxidant) exit gas 18a after the cathode (oxidant) exits the battery stack 12.

[0126] The heated exhaust gas 18 can also be used to preheat fuel 26 and water 28 to produce a heated steam and fuel mixture 30. In other words, after losing some heat in the first heat exchanger 20, the cathode (oxidant) exit gas 18b can then transfer a lower level of heat to fuel 26 and water 28. The resulting heated steam and fuel mixture 30 is typically supplied to reformer 24, although in some fuel cell systems, reforming takes place in the stack 12. The reforming process may take place partly in reformer 24 and then continue in stack 12 because the effluent from reformer 24 is typically only partially reformed into syngas 25 (hydrogen and carbon monoxide), which is also mixed with unreformed fuel and steam.

[0127] For the purpose of generating a steam and fuel mixture 30, a steam generator 22 (second heat exchanger 34) is provided. This second heat exchanger 34 receives both fuel 26 and water 28 at its inlet. The water 28 is converted into steam in the steam generator 22, and the fuel 26 is either entrained in or mixed with the steam and heated, so that the mixture 30 can be output as a heated steam and fuel gas mixture 30. For a temperature of 400°C... o C and 600 oFor solid oxide fuel cells operating at temperatures between C and [other temperatures], the steam and fuel mixture is heated by a second heat exchanger 34 to approximately 200 [temperatures]. o C to 500 o Output in C, usually in the range of 250. o C to 350 o The heated steam and fuel gas mixture 30 is then supplied to a reformer 24, which can also be heated by the exhaust gas 18. The reformer 24 then outputs a reformate or syngas 25 containing at least hydrogen and carbon monoxide. This syngas, along with heated air 32 from the first heat exchanger 20, can then be supplied to the fuel cell stack 12 to undergo electrochemical processing by the fuel cells 14 in the fuel cell stack 12.

[0128] Instead, in some fuel cell systems, steam is generated first, and then the fuel is mixed separately within the fuel cell system, possibly in a reformer or in a separate mixing chamber (which may have an additional heat exchanger).

[0129] In a typical fuel cell system, fuel is supplied in the form of methane, propane, or ethanol.

[0130] Furthermore, the water supplied for generating steam can be tap water, or more preferably distilled water, because distilled water will form less sediment when it evaporates.

[0131] The above is only one arrangement of heat exchangers in a fuel cell system. The heated anode exit gas can also travel through a heat exchanger to transfer heat to the incoming gas, and heat exchangers can be arranged in other orders. Additional heat exchangers can even be present in the fuel cell system to ensure that the heated air and syngas are supplied to the stack at suitable temperatures, and similarly ensure that the heat supplied to the first and second heat exchangers is suitable for the operation of the air heater from the steam generator, and also suitable for the reformer.

[0132] Next reference Figure 2 A schematic example of a steam generator 22 is shown. It can be seen that the steam generator 22 includes a second heat exchanger 34 having inlet and outlet ports. These ports include a combined fuel and water inlet port 36, a heating fluid inlet port 38, a heating fluid outlet port 40, and a heated steam and fuel gas outlet port 42.

[0133] The fuel and water inlet port 36 of this assembly can be attached to the side of the second heat exchanger 34 via a manifold, preferably using an insulating gasket to prevent leakage through the joint and to provide thermal shielding from the second heat exchanger 34 to the manifold. The gasket can be a high-temperature thermoulite gasket.

[0134] Upstream of the combined fuel and water inlet port 36, this embodiment features a T-shaped connector 44 with a direct-flow water inlet pipe 46 and a fuel inlet pipe 48 with a side port. Due to this T-shaped connector, the water and fuel inlets can be merged into a single inlet port 36—as will be described in further detail with reference to the following embodiments.

[0135] As shown in the figure, the second heat exchanger 34 is a counter-current heat exchanger. This is a preferred arrangement. In the illustrated arrangement, the fuel and water inlet ports 36 are mounted towards the top of the second heat exchanger 34, and the heated steam and fuel gas outlet ports 42 are positioned towards the bottom of the second heat exchanger 34, so that liquid water enters at the top of the heat exchanger section and exits as steam from the bottom of the second heat exchanger 34; while the heating inlet port 38 is located at the bottom of the second heat exchanger 34, and the heating outlet port 40 is located at the top of the second heat exchanger 34. This counter-current heating, with the flow direction opposite to that of the water and steam products, provides efficient operation of the heat exchanger function within the second heat exchanger 34.

[0136] Next reference Figure 3 and Figure 4 (Enlarged view) An alternative dripper arrangement for the steam generator 22 is shown. In this embodiment, the T-shaped connector 44 with a fuel inlet pipe 48 having a side port is located further upstream of the steam generator, such that a longer length of the water inlet pipe is surrounded by a concentric outer fuel inlet pipe 48. The second heat exchanger 34 can still have the same counter-current arrangement, with the ports in the same positions as before, and the drippers at the top of the steam generator. However, the figures also show the internal heated plates 50 of the second heat exchanger 34, which are heated by direct current from the heated exhaust gas 18. These internal heated plates 50 provide the initial heat exchange surface inside the second heat exchanger 34, onto which water 28 supplied to the second heat exchanger 34 via the combined fuel and water inlet ports 36 can be supplied (typically by dripping).

[0137] from Figure 4As can be seen, the dripper 52 is located at the distal end of the water inlet pipe 46. This dripper 52 extends into the second heat exchanger 34 to position the outlet orifice 56 (which will be seen more clearly in a later embodiment) above the plate 50 so that water drips onto the plate 50. In this embodiment, the outlet orifice extends laterally—perpendicular to the axis of the dripper. To allow the dripper 52 to be installed in the steam generator 22 in this way, the plate 50 has an orifice 54 through which the dripper 52 is inserted. However, the dripper 52 can simply be installed above the top wall of the plate 50.

[0138] As can be seen, in this embodiment, the size of the orifice 54 in the plate 50 is set larger than that of the dripper 52 to facilitate insertion and prevent direct contact between the plate 50 and the dripper 52. Such direct contact would allow conductive heat transfer from the plate 50 to the dripper 52, which could lead to overheating of the dripper 52 and consequently, boiling of the water within the dripper 52 before it drips from the outlet orifice 56 of the dripper 52. This could then result in a cessation of water flow through the dripper 52, and consequently, pressure changes in the steam output from the steam generator 22, and the possibility of internal deposits within the dripper (due to evaporation of water in the enclosed space), which could eventually accumulate on the dripper and clog it. All of these symptoms are undesirable. Therefore, the arrangement of the present invention is designed to minimize the occurrence of such overheating. This then minimizes the risk of clogging and minimizes any pressure changes or pressure peaks or troughs (because the cessation of water flow will reduce pressure, while the resumption of flow can lead to an excess of water in the system, resulting in a surge in steam pressure).

[0139] The present invention seeks to supply liquid water to a plate (or other heated heat exchange surface, if possible) by attempting to ensure that water remains as a liquid (i.e., not steam) until it enters the heat exchanger and drips from the dripper.

[0140] In this embodiment, the dropper 52 has a closed distal end and outwardly projecting structures on both sides of the outlet orifice 56. These outwardly projecting structures separate the two downward-facing outlet orifices 56 to prevent or minimize the risk of water pooling as it drips from the outlet orifices 56 onto the plate 50 below them. Therefore, water will tend to fall directly as controlled droplets onto the plate 50 located below each respective outlet orifice 56.

[0141] In this embodiment, there are two plates 50 and two outlet holes 56. Other embodiments may have more plates than holes, for example, if not every plate is used to receive the supply of water droplets. Preferably, the holes are selectively positioned relative to the internal heat exchange surface of the steam generator to optimize steam generation.

[0142] Next reference Figure 5a and Figure 5b These figures are schematic partial cross-sectional views depicting two alternative drippers 52 inserted into the top of the second heat exchanger 34 of the steam generator. Each figure shows only a partial cross-section of the second heat exchanger 34, and the two heated plates 50 can again be seen. Furthermore, the drippers 52 are visible, with the outlet orifice 56 now clearly visible on the lower half of the elongated dripper.

[0143] The outlet orifice 56 is fluidly connected to the internal channel 58 of the water inlet pipe 46, allowing the inflowing water 28 to be supplied from the water supply device through the internal channel 58 of the water inlet pipe 46 to the outlet orifice in the dripper 52 and onto the plate 50. Since the plate 50 is hot, upon landing on it, the water will begin to heat and evaporate to form steam, and this steam (and any liquid water) will flow downwards through the second heat exchanger 34 and toward the heated steam and fuel gas outlet port 42 (not shown in the figure). During its journey downwards through the second heat exchanger 34, the water or steam may travel over fins or other interlaced or non-flat components 60, preferably with multiple interruptions and changes in flow direction due to the internal fins, to increase the heat exchange area for evaporation, which ultimately promotes a fully mixed outlet flow. These components 60 or fins will also be hot—typically from the plate 50 to which they are connected. Therefore, this arrangement ensures a large contact area for water evaporation and thus ensures rapid steam formation. This arrangement also provides a consistent maintenance of steam pressure within the steam generator, so that any pressure fluctuations that occur due to water dripping onto the heated surface can be kept at a low level at the steam outlet port 42.

[0144] This preferred swirling flow path arrangement, and the preferred method of dripping water onto the plate (or other such heat exchange surfaces within the heat exchanger section) from orifices located at selected positions relative to such plates (e.g., directly above), optimizes the ability of the steam generator 22 to rapidly and easily change its steam production rate instantaneously. This can be achieved simply by altering the flow rates of water (and fuel) entering the heat exchanger, while ensuring that the water still completely evaporates through the outlet port 42.

[0145] Furthermore, the heat sinks or non-flat components 60 within the second heat exchanger 34 cause the steam to expand in multiple directions as it is generated, thereby equalizing any pressure variations within the second heat exchanger 34 and again contributing to providing low pressure pulsations. This is beneficial because high pressure pulsations within the second heat exchanger 34 would cause the reformer 24 to receive fluctuating steam / fuel mixtures—potentially with unevenly mixed steam and fuel—which would affect the efficiency of the reformer 24. This, in turn, could also affect the operation of each fuel cell.

[0146] Therefore, the present invention seeks to provide low pressure pulsation to produce a uniform and consistent steam and fuel output from the steam generator 22 to the reformer 24. After all, the outflow to be received by the fuel reformer 24 should be a superheated steam-fuel mixture free of liquid water.

[0147] The dropper 52 is designed to drip uniformly onto the plate 50, rather than forming pools or large droplets. To this end, the dropper has a stepped profile between adjacent holes, with sharp corners between the steps (i.e., steps of different heights). This construction allows surface tension to prevent droplet coalescence from adjacent holes. Specifically, structures can be provided on both sides of each outlet hole 56 of the dropper 52 to separate the different outlet holes from each other. Figure 5a In one embodiment, the structure includes an outwardly extending flange 62. The outwardly extending flange 62 is integrally formed on the dripper 52, which in turn is integrally formed on the water inlet pipe 46.

[0148] Flange 62 is a continuous annular flange extending around the (entire) perimeter (or circumference) of the water inlet pipe 46. Flange 62 is axially spaced from outlet orifice 56 by approximately the diameter of the outlet orifice, although other distances are possible. Flange 62 also extends laterally outward from outlet orifice 56 by a distance between one and two times the diameter of the orifice, although other lengths are possible.

[0149] exist Figure 5b In one embodiment, the structure further includes an outwardly extending flange 62 integrally formed on the dropper 52, which in turn is integrally formed on the water inlet pipe 46. However, in this embodiment, these structures extend only around the lower portion of the periphery of the water inlet pipe 46. With the orifice only located on the lower side of the dropper, the effects of gravity and surface tension mean that the partially flanged structure may be all that is needed to constrain the droplet, while the orifice located on the upper half of the dropper may require a continuous annular structure for constraint.

[0150] exist Figure 5a and Figure 5bIn the embodiments shown, two such flanges 62 are provided for each outlet hole 56, and there are two such outlet holes 56. Therefore, there are four such flanges 62. Moreover, the flanges 62 extend perpendicular to the central axis of the water inlet pipe 46, or more specifically, perpendicular to the central axis of the dripper 52. In this embodiment, the flange 62 closest to the distal end of the dripper 52 is spaced apart from that distal end.

[0151] Outside the second heat exchanger 34, surrounding the water inlet pipe 46 is a T-shaped manifold 64. This T-shaped manifold 64 covers a portion of the water inlet pipe 46 and can be attached to the outer wall of the second heat exchanger 34 by any conventional means, although it is preferred to attach it to the outer wall of the second heat exchanger 34 using gaskets to provide a tight seal between them. The gaskets can be insulating gaskets, such as high-temperature gullet gaskets, thereby minimizing conductive heat transfer from the side of the second heat exchanger 34 to the T-shaped manifold 64.

[0152] The T-manifold 64 has an internal passage with a diameter larger than that of the water inlet pipe 46 (or the portion of the water inlet pipe 46 that extends through the T-manifold 64). This creates an annular gap between the inner wall of the T-manifold and the outer wall of that portion of the water inlet pipe 46. This annular gap provides a flow passage for the fuel 26. The fuel 26 enters the T-manifold 64 via a side branch 66. With this arrangement, the fuel can enter the second heat exchanger 34 as a (concentric) coating surrounding the water inlet pipe 46, and subsequently mix with the steam generated within the second heat exchanger 34.

[0153] Covering the water inlet pipe 46 with fuel 26 has the effect of suspending the water inlet pipe away from any solid surface near the heat exchanger—the water inlet pipe can be attached only to the far left. This prevents heat from being directly conducted from the structure of the second heat exchanger 34 into the water inlet pipe 46. All of this helps to keep the water in the water inlet pipe 46 in a liquid state until it drips from the dripper 52, because the heat from the second heat exchanger 34 needs to raise the temperature of the fuel 26 before it can raise the temperature of the water 28 in the water inlet pipe 46, but when the steam generator 22 is in operation, the fuel 26 is kept refreshed from the cooler fuel supply. Thus, with this arrangement, water leaving the outlet port 56 during the operation of the steam generator 22 will tend to drip from the outlet port 56 rather than expel steam, thereby minimizing the occurrence of steam blockage in the water inlet pipe 46 or the dripper 52 (which would otherwise occur—leading to pressure fluctuations). This arrangement also reduces or eliminates evaporation deposits that occur in the dripper 52 or the water inlet pipe 46, which are difficult to remove and could potentially cause malfunctions in the steam generator 22. The connection point (i.e., the starting point of the gas coating) can be connected to the preceding... Figure 3 The difference is, for example, shown in the example where a longer length is covered.

[0154] With this arrangement of the steam generator 22, water 28 and fuel 26 are unmixed before entering the second heat exchanger 34, but become mixed inside the second heat exchanger 34 as the water boils and turns into steam. This can be advantageous compared to pre-mixing fuel and water—the relatively dry fuel gas flowing through the same channels of the heat exchanger helps evaporate water into the gas stream.

[0155] Next reference Figure 6 This illustrates another embodiment of the invention. Although similar to... Figure 5a In this embodiment, instead of a single flange 62, pairs of gaskets 72 are fitted onto the pipe to be positioned on either side of each downward-facing outlet hole 56. Between the pairs of gaskets is a recessed section 78 that forms a recessed section relative to the gasket. These gaskets 72 can be pushed to engage with the free end of the water inlet pipe 46.

[0156] As in Figure 6 As can be seen, as water flows out of the outlet orifice 56, it forms droplets 74 due to surface tension. These droplets 74 are held in the gap between adjacent gaskets 72 on both sides of the outlet orifice 56 and diffuse around that gap. Specifically, the surface tension effect means that the droplets do not diffuse around the protruding outer shoulders (sharp corners) of the gaskets into the adjacent recessed sections 78. However, without the gaskets 72, the droplets 74 could diffuse along the water inlet pipe 46, where the gaskets 72 retain the droplets 74 and position them locally within the outlet orifice 56. Furthermore, since the droplets in adjacent outlet orifices 56 are kept separate and do not combine or mix, the size of these droplets can be controlled. As a result, the water droplets 74 cannot combine to form larger droplets, which, if the water is located on the exchange surface of the heat exchanger instead of evaporating steadily, could tend to create increased pressure pulsations within the steam generator. Furthermore, by ensuring that the droplets grow in a desired position relative to the heat exchange surface below, this prevents the droplets from falling in a random manner; for example, the droplets might fall to the side of the plate and thus land on different parts of the heat exchange surface, and (if large enough) potentially discharge downward through the heat exchanger to the base of the heat exchanger, thereby creating the possibility of large pressure pulsations toward the outlet of the second heat exchanger 34 or the outlet port 42 of the heated steam and fuel gas (because the hottest part is at the bottom—where the heated fluid enters the heat exchanger).

[0157] Although the non-flat components 60 or heat sinks within the second heat exchanger 34 will tend to resist such liquid accumulation, the avoidance of large water droplets from the dripper 52 remains an important feature of the invention because water accumulation can subsequently be substantially eliminated, thereby resulting in an ideal low-pressure pulsation within the steam generator.

[0158] Next reference Figure 7 Another embodiment of the dripper 52 is shown. In this embodiment, the dripper 52 is a replaceable dripper that can be fitted onto the end of the water inlet pipe 46. This is achieved through the threaded end of the water inlet pipe 46 and the internal threaded hole at the proximal end of the dripper 52. To facilitate screwing the dripper 52 onto the thread, the cross-section of the dripper 52 can be hexagonal, similar to a nut, at least at a portion of the dripper (here, at the proximal end of the dripper). The hexagonal cross-section allows a wrench to screw the nozzle onto the water inlet pipe 46.

[0159] In this embodiment, the outlet orifice 56 is again located on the underside of the dropper head, and each outlet orifice has a structure on both sides thereof, which in this embodiment is an arc-shaped flange 76 with sharp corners. The dropper head 52 can be manufactured by cutting off a portion of its sidewall or by molding. The shoulders on both sides of the outlet orifice 56 are thus configured to receive water droplets and resist lateral diffusion. In this embodiment, the flange does not extend continuously around the periphery of the dropper head 52, but the flange still performs the same function of preventing droplets from adjacent outlet orifices 56 from combining, such as... Figure 6 As shown in the diagram.

[0160] In this embodiment, additional transverse cuts are provided—one transverse cut between the two outlet holes 56 to form a recessed section 78 between the two arcuate flanges 76 located between the outlet holes 56; and two additional transverse cuts on the outer sides of the other two “outer” arcuate flanges 76 to define the outer sides of the arcuate flanges 76.

[0161] Four arcuate flanges 76 are located in pairs on either side of a corresponding outlet hole in the outlet hole 56, thus having a recessed section 78 between the pairs of arcuate flanges 76. The gap inside helps to ensure that water droplets between adjacent outlet holes do not merge together as they bridge the gap.

[0162] Next reference Figures 8a to 8c These figures illustrate three alternative embodiments of the dropper, each including a perspective view taken from the left side of the underside of the dropper, and a cross-sectional view taken from the right side (rotated 180 degrees) of the dropper in the operating direction with the orifice facing down. Figure 8a Dropper 52 is shown, as per reference. Figure 7As described, the dropper 52 has an outlet hole 56, each outlet hole 56 having a structure on both sides thereof, which in this embodiment is an integrally formed arcuate flange 76.

[0163] Figure 8b Another dropper 152 is shown, which is a reference. Figure 7 and Figure 8a A variation of the described dropper 52. Droppers 52 and 152 are substantially similar, and only the differences are described. Instead of an arcuate flange, this variant of the dropper 152 is provided with a transverse tube section 176 located away from the main fluid channel. An outlet orifice 56 is provided at the end of each transverse tube section. Each transverse tube section 176 extends downward relative to the dropper 152 in a transverse or radial direction to a depth similar to the depth of the arcuate flange 76 of the dropper 52. The ends of the transverse tube sections 176 are much larger than the diameter of the outlet orifice, presenting a step with a recess between the tube sections or a flat end surface protruding from the section 178, or a step with a sharp corner. The flat end surface on which droplets form can be selected to have a suitable size to support the growing droplets, while the effects of gravity and surface tension prevent the droplets from spreading laterally around the sharp corners, and thus prevent the coalescence of adjacent droplets bridging the gap and in the (higher) recessed section 178. The transverse tube section 176 is shown with a circular cross-section, but other cross-sections, such as square, pentagonal or hexagonal, may also be used.

[0164] Figure 8c A view of another dropper 252 is shown, which is a variation of dropper 52. Droppers 52, 152, and 252 are substantially similar, with only differences described. Instead of an arcuate flange, this variation of dropper 252 has an integral curved or arcuate surface 276 on its underside, having an arcuate vertical edge surface 277 defining a sharp corner. The downward-facing arcuate surface 276 may be a continuation of the generally cylindrical periphery of the sidewall of dropper 252, and can be formed by cutting off the periphery of the sidewall of dropper 252 or by molding. Again, a transverse side channel away from the main channel leads to an outlet orifice 56 provided in the arcuate surface 276, on which droplets can be formed. Therefore, the outlet orifice 56 is again located in the downwardly projecting arcuate surface 276 of the dropper 252, which is defined by a sharp corner and is again separated by a recessed (higher) section 278, which prevents water droplets from adjacent outlet orifices from bridging the recessed section 278 and converging together by the effects of gravity and surface tension.

[0165] like Figure 8cAs shown, the outlet orifice 56 of the dripper 252 has a larger diameter compared to the diameters of drippers 52 and 152. This larger diameter facilitates customization of the dripper 252 using screw threads 57 disposed in the outlet orifice 56. The screw threads 57 allow for customization of the dripper's outlet orifice by inserting a flat-head screw and drilling a hole, the size of which can be customized to control the flow rate. Similarly, screw threads can be used to add a pipe section similar in shape and function to pipe section 176 for positioning and adjusting the diameter of the outlet orifice 56. Alternatively, the outlet orifice 56 of the dripper 252 can be similar to... Figure 8a and Figure 8b The outlet holes shown have holes of similar diameter.

[0166] Therefore, the invention has been described above by way of example only. Detailed modifications can be made to the invention within the scope of the appended claims.

[0167] Figure label:

[0168] 10 Fuel Cell System

[0169] 12 battery stack

[0170] 14 fuel cells

[0171] 16 electrical outputs

[0172] 18 Heated exhaust gases

[0173] Flow path of 18a emission gas

[0174] 20 First heat exchanger

[0175] 22 Steam generator

[0176] 24-Reformer

[0177] 25 Syngas

[0178] 26 fuels

[0179] 27 air

[0180] 28 water

[0181] 30 Heated steam and fuel mixture

[0182] 32 Heated air

[0183] 34 Second heat exchanger

[0184] 36 water inlet ports

[0185] 38 Heating Inlet Ports

[0186] 40 heating outlet ports

[0187] 42 Heated steam and fuel gas outlet port

[0188] 44T-shaped connector

[0189] 46 Water flows into the pipe

[0190] 48 Fuel Inlet Pipe

[0191] 50 internal heating plate

[0192] 52 droppers

[0193] 54-hole

[0194] 56 outlet holes

[0195] 57 screw thread

[0196] 58 Internal Channel

[0197] 60 Non-flat components

[0198] 62 flange

[0199] 64T manifold

[0200] 66 lateral branches

[0201] 72 gasket

[0202] 74 water droplets

[0203] 76 arc-shaped flange

[0204] 78 Depression Section

[0205] 152 droppers

[0206] 176 lateral pipe section

[0207] 178 Depression Section

[0208] 252 droppers

[0209] 276 curved surface

[0210] 277 curved edge

[0211] Section 278.

Claims

1. A steam generator for a fuel cell system, the steam generator comprising: A heat exchanger having at least one internal heat exchange surface; Water flows into the pipe; A dripper, comprising a flow channel fluidly connected to the water inlet pipe, the dripper extending inside the heat exchanger and above the heat exchange surface for supplying water downwards to the heat exchange surface to be converted into steam; The dripper includes a plurality of outlet holes spaced apart along the length of the flow channel; and Specifically, when viewed in cross-section, the dropper has a stepped profile at least on its underside between adjacent outlet orifices to prevent droplets from adjacent orifices from coalescing.

2. The steam generator according to claim 1, wherein, The stepped profile between adjacent outlet holes includes at least two stepped surfaces at different heights above the heat exchange surface.

3. The steam generator according to claim 2, wherein, The adjacent outlet holes are respectively disposed on the stepped surfaces, wherein at least one stepped surface between these stepped surfaces is located at a different height above the heat exchange surface.

4. The steam generator according to claim 3, wherein, The adjacent outlet holes are respectively disposed on a stepped surface that forms part of the structure of the heat exchange surface protruding outward and downward.

5. The steam generator according to claim 4, wherein, The stepped surface has a selected size and shape to facilitate the growth of droplets of appropriate size.

6. The steam generator according to claim 4, wherein, The adjacent outlet holes are disposed in corresponding protruding structures, which are integrally formed with the dripper and separated from each other by grooves or channels.

7. The steam generator according to claim 1, wherein, Each outlet hole is separated from the adjacent outlet hole by at least one spacer that protrudes outward relative to the outlet hole.

8. The steam generator according to claim 7, wherein, Each outlet orifice has a corresponding pair of spacers associated with it, the pair of spacers being arranged axially on both sides of each orifice along the dripper to separate the outlet orifice from the adjacent orifice.

9. The steam generator according to claim 8, wherein, The pair of partitions includes parallel sidewalls.

10. The steam generator according to any one of claims 7 to 9, wherein, The baffle is an integral part of the dripper.

11. The steam generator according to any one of claims 7 to 9, wherein, The partition extends partially around the periphery or outer circumference of the dropper.

12. The steam generator according to claim 11, wherein, The partition defines an outwardly protruding, curved shoulder.

13. The steam generator according to any one of claims 7 to 9, wherein, The baffle extends around or around the periphery of the dropper.

14. The steam generator according to any one of claims 7 to 9, wherein, The baffle includes a separate component mounted on the drip head.

15. The steam generator according to claim 14, wherein, The dripper includes a tubular end section, and the spacer includes a pair of gaskets mounted on the tubular end section, one gasket in each pair being located proximal to the outlet orifice of the tubular end section, and the other gasket in each pair being located distal to the outlet orifice of the tubular end section.

16. The steam generator according to any one of claims 1 to 9, wherein, The dripper is a removable or replaceable component.

17. The steam generator according to any one of claims 1 to 9, wherein, The outlet hole is located at a spaced-out axial position along the lower half or lower side of the dripper.

18. The steam generator according to any one of claims 1 to 9, further comprising a fuel inlet pipe, wherein the steam generator is configured to combine fuel with the steam inside the steam generator during use.

19. The steam generator according to claim 18, wherein, The fuel inlet pipe has a section that is coaxially mounted to a portion of the water inlet pipe.

20. The steam generator according to claim 19, wherein, The section of the fuel inlet pipe surrounds the portion of the water inlet pipe.

21. A steam generator for a fuel cell system, the steam generator comprising: A heat exchanger having at least one internal heat exchange surface; Water flows into the pipe; Fuel inlet pipe; and A dripper, fluidly connected to the water inlet pipe, extends inside the heat exchanger and above the heat exchange surface for supplying water downwards onto the heat exchange surface to be converted into steam; The fuel inlet pipe has a section that surrounds a portion of the water inlet pipe at or near the outer wall of the heat exchanger and extends through the outer wall of the heat exchanger, such that the section of the fuel inlet pipe and the fuel located in the section of the fuel inlet pipe during use are used to thermally insulate the surrounded portion of the water inlet pipe from the heat exchanger.

22. A steam generator for a fuel cell system, the steam generator comprising: A heat exchanger having at least one internal heat exchange surface; Water flows into the pipe; Fuel inlet pipe; and A dripper, fluidly connected to the water inlet pipe, extends inside the heat exchanger and above the heat exchange surface for supplying water downwards onto the heat exchange surface to be converted into steam; The fuel inlet pipe has a section that surrounds a portion of the water inlet pipe at or near the outer wall of the heat exchanger and extends through the outer wall of the heat exchanger, such that the section of the fuel inlet pipe and the fuel located in the section of the fuel inlet pipe during use are used to thermally insulate the surrounded portion of the water inlet pipe from the heat exchanger. The steam generator is further described in any one of claims 1 to 9.

23. A fuel cell system comprising a steam generator according to any one of claims 1 to 22.

24. The fuel cell system according to claim 23, wherein, The steam generator includes a fuel inlet pipe and a combined steam and fuel outlet, and in the fuel cell system, a reformer is connected directly or indirectly downstream of the steam generator.

25. The fuel cell system according to claim 23 or 24, wherein, The fuel cell system is used to minimize fluctuations in the stack voltage caused by changes in the composition or pressure of the fuel / steam mixture entering the fuel cell stack of the fuel cell system.

26. A fuel cell system, comprising: Fuel cell stack; fuel inlet pipe; water inlet pipe; And air or oxidant flow into the pipe; Steam generator; And a heat exchanger for directly or indirectly obtaining heated fluid from the effluent of the fuel cell stack, the heat of the heated fluid being used to heat at least one internal heat exchange surface of the heat exchanger, wherein the at least one internal heat exchange surface is used to generate steam from water flowing from the water inlet pipe via a dripper, the steam generator being a steam generator as defined in any one of claims 1 to 22.

27. The fuel cell system according to claim 26, wherein, The fuel cell system includes a reformer connected to the steam generator to supply hydrogen or syngas to the fuel cell stack.

28. The fuel cell system according to claim 26, wherein, The fuel cell system is used to minimize fluctuations in the stack voltage caused by changes in the composition or pressure of the fuel / steam mixture entering the fuel cell stack of the fuel cell system.

29. A method for generating steam using a steam generator, said steam generator being a steam generator as defined in any one of claims 1 to 22, wherein, Water is supplied to the heat exchange surface through the water inlet pipe and the dripper and is converted into steam.

30. The method according to claim 29, wherein, Simultaneously, fuel is supplied to the heat exchanger, where the fuel is mixed with the steam and heated.

31. The method according to claim 29, wherein, The steam generator forms part of the fuel cell system and generates steam, which is supplied to the fuel cell inlet within the fuel cell system.

32. A method for minimizing pressure pulsations in a steam generator during steam generation, the steam generator comprising: A heat exchanger having at least one internal heat exchange surface; Water flows into the pipe; A dripper, comprising a flow channel fluidly connected to the water inlet pipe, the dripper extending inside the heat exchanger and above the heat exchange surface for supplying water droplets downwards to the heat exchange surface for conversion into steam; wherein the dripper comprises a plurality of outlet orifices spaced apart along the length of the flow channel; and wherein, when viewed in cross-section, the dripper has a stepped profile at least on its underside between adjacent outlet orifices, the method comprising adjusting the water flow rate to a selected flow rate, whereby the stepped profile prevents droplets from adjacent orifices from coalescing.

33. The method according to claim 32, wherein, The steam generator forms part of the fuel cell system and generates steam, which is supplied to the fuel cell inlet within the fuel cell system.

34. A method of operating a steam generator for a fuel cell system, the steam generator comprising: A heat exchanger having at least one internal heat exchange surface; Water flows into the pipe; A dripper, comprising a flow channel fluidly connected to the water inlet pipe, the dripper extending inside the heat exchanger and above the heat exchange surface for supplying water downwards to the heat exchange surface to be converted into steam; The dropper includes a plurality of outlet holes spaced apart along the length of the flow channel, and when viewed in cross-section, the dropper has a stepped profile at least on the underside of the dropper between adjacent outlet holes to prevent droplet coalescence from adjacent holes. The method includes: Water is supplied to the dripper through the water inlet pipe; and The water is dripped from the dripper through the outlet hole as a water droplet rather than steam or a spray, and the water droplet falls onto the heat exchange surface to be converted into steam.

35. The method according to claim 34, wherein, The steam generator forms part of the fuel cell system and generates steam, which is supplied to the fuel cell inlet within the fuel cell system.

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