Steam generator for fuel cell system
A steam generator for a fuel cell system having a heat exchanger ( 34 ) with at least one internal heat exchange surface, a water inflow pipe ( 46 ), a dripper head ( 52 ) with a flow passageway fluidly connected to the water inflow pipe ( 46 ). The dripper head ( 52 ) extends inside the heat exchanger ( 52 ) above the heat exchange surface for feeding water down onto the heat exchange surface for conversion into steam. The dripper head ( 52 ) has outlet holes ( 56 ) spaced along the flow passageway and between adjacent outlet (holes 56 ) the dripper head has a stepped profile on at least its underside to prevent droplets from adjacent holes coalescing. A fuel inflow pipe can have a section mounted coaxially to a part of the water inflow pipe ( 46 ). The fuel inflow pipe's section can surround the water inflow pipe's part. In a fuel cell system with a steam generator, the steam generator can include the fuel inflow pipe and a combined steam and fuel outlet and a reformer directly or indirectly connected downstream of the steam generator.
1 . A steam generator for a fuel cell system, comprising:
a heat exchanger with at least one internal heat exchange surface,
a water inflow pipe and a fuel inflow pipe,
a dripper head comprising a flow passageway fluidly connected to the water inflow pipe, which dripper head extends inside the heat exchanger above the heat exchange surface for feeding water down onto the heat exchange surface for conversion into steam;
wherein:
the dripper head comprises a plurality of outlet holes spaced along the length of the flow passageway;
between adjacent outlet holes the dripper head has a stepped profile on at least its underside, when viewed in cross-section, to prevent droplets from adjacent holes coalescing;
each outlet hole is segregated from an adjacent outlet hole by at least one baffle that projects outwardly relative to the outlet hole;
the baffle extends at least partially around the circumference or periphery of the dripper head; and
the steam generator is configured so as to combine the fuel with the steam inside the steam generator during use.
2 . The steam generator of claim 1 , wherein the stepped profile between adjacent outlet holes comprises at least two step surfaces at different heights above the heat exchange surface.
3 . The steam generator of claim 2 , wherein the adjacent outlet holes are each provided on a step surface, with at least one step surface between those surfaces that is at a different height above the heat exchange surface.
4 . The steam generator of claim 3 , wherein the adjacent outlet holes are each provided on a step surface which forms part of a structure that projects outwardly towards the heat exchange surface below, the step surface optionally being of a selected size and shape to encourage growth of a droplet of a suitable size, and optionally wherein the adjacent outlet holes are providing in respective projecting structures formed integrally with the dripper head and separated from each other by grooves or channels.
5 . The steam generator of claim 1 , wherein the baffle extends all the way around the circumference or periphery of the dripper head.
6 . The steam generator of claim 1 , wherein each outlet hole has a respective pair of baffles associated with it, these being arranged axially along the dripper head on either side of each hole, to segregate it from an adjacent hole.
7 . The steam generator of claim 1 , wherein the baffle is an integral structure of the dripper head.
8 . The steam generator of claim 1 , wherein the baffle defines an outwardly projecting arc shaped shoulder.
9 . The steam generator of claim 1 , wherein the dripper head comprises a tubular end section, and the baffles comprise pairs of washers mounted on the tubular end section, one of each pair being proximal of its outlet hole and the other of each pair being distal of its outlet hole.
10 . The steam generator of claim 1 , wherein the dripper head is a removable or replaceable component.
11 . The steam generator of claim 1 , wherein the outlet holes are provided at spaced axial positions along the lower half or underside of the dripper head.
12 . The steam generator of claim 1 , wherein the fuel inflow pipe has a section mounted coaxially to a part of the water inflow pipe, and optionally wherein the fuel inflow pipe's section surrounds the water inflow pipe's part.
13 . The steam generator of claim 1 , further comprising a control system configured to deliver liquid water to the outlet holes at a suitable temperature and mass flow rate such that the liquid water forms droplets that drop from the dripper head under gravity, the control system optionally comprising a controller within the steam generator in operable communication with sensors and actuators.
14 . A fuel cell system comprising a steam generator according to claim 1 , optionally wherein the steam generator comprises a fuel inflow pipe and a combined steam and fuel outlet and optionally wherein a reformer is directly or indirectly connected downstream of the steam generator in the fuel cell system.
15 . A fuel cell system according to claim 14 , comprising a fuel cell stack, a fuel inflow pipe, an air or oxidant inflow pipe, and an optional reformer connected to the steam generator for providing hydrogen or syngas to the fuel cell stack, the heat exchanger of the steam generator being for taking heated fluid directly or indirectly from an outflow of the fuel cell stack, the heat thereof being used to heat the at least one internal heat exchange surface of the heat exchanger, wherein the at least one internal heat exchange surface is used to generate the steam from the water from the water inflow pipe of the steam generator via the dripper head of the steam generator.
16 . A method comprising using a steam generator according to claim 1 in a fuel cell system so as to reduce fluctuations in stack voltage due to fuel side compositional or pressure changes in an incoming fuel/steam mix to a fuel cell stack of the fuel cell system.
17 . A method of generating steam using a steam generator as defined in claim 1 , wherein water is fed through the water inflow pipe and the dripper head to the heat exchange surface and is converted to steam, and optionally, wherein concurrently fuel is fed into the heat exchanger, wherein the fuel mixes with the steam and is heated.
18 . A method of reducing pressure pulsations in a steam generator during steam generation, the steam generator comprising a heat exchanger with at least one internal heat exchange surface; a water inflow pipe and a fuel inflow pipe; and a dripper head comprising a flow passageway fluidly connected to the water inflow pipe, which dripper head extends inside the heat exchanger above the heat exchange surface for feeding water droplets down onto the heat exchange surface for conversion into steam; wherein:
the dripper head comprises a plurality of outlet holes spaced along the length of the flow passageway;
between adjacent outlet holes the dripper head has a stepped profile on at least its underside, when viewed in cross-section, the method comprising adjusting the flow rate of the water to a selected flow rate whereby the stepped profile prevents droplets from adjacent holes coalescing;
each outlet hole being segregated from an adjacent outlet hole by at least one baffle that projects outwardly relative to the outlet hole, the baffle extending at least partially around the circumference or periphery of the dripper head; and
the steam generator combines the fuel with the steam inside the steam generator during use.
19 . A method of operating a steam generator for a fuel cell system, the steam generator comprising:
a heat exchanger with at least one internal heat exchange surface,
a water inflow pipe and a fuel inflow pipe,
a dripper head comprising a flow passageway fluidly connected to the water inflow pipe, which dripper head extends inside the heat exchanger above the heat exchange surface for feeding water down onto the heat exchange surface for conversion into steam;
wherein the dripper head comprises a plurality of outlet holes spaced along the length of the flow passageway, between adjacent outlet holes the dripper head has a stepped profile on at least its underside, when viewed in cross-section, to prevent droplets from adjacent holes coalescing, each outlet hole being segregated from an adjacent outlet hole by at least one baffle that projects outwardly relative to the outlet hole, the baffle extending at least partially around the circumference or periphery of the dripper head;
the method comprising:
feeding water through the water inflow pipe to the dripper head;
dripping the water from the dripper head, via the outlet holes, as water droplets, rather than steam or a spray, the water droplets dripping onto the heat exchange surface for conversion into steam; and
the steam generator combining the fuel with the steam inside the steam generator during use.