Docket No. 67.124-027/C-3292

THREE FLUID HEAT EXCHANGER FOR FUEL CELL POWER PLANT

BACKGROUND OF THE INVENTION

This invention relates a three fluid heat exchanger for a fuel cell power plant. A typical fuel cell power plant may only be between twenty-five to forty percent efficient. The inefficiency manifests itself as heat. Typically, there are two different fluids from which the heat can be recovered and used to heat a customer fluid.

In one prior art example, an interface heat exchanger is used to transfer the heat from a higher temperature fluid, such as water from the fuel cell, to an intermediate fluid, such as glycol, which is circulated in a loop. A lower temperature fluid, such as hot gas, also transfers heat to the intermediate fluid. A customer heat exchanger receives the intermediate fluid and transfers its heat to the customer fluid. The customer fluid can be water used to provide, for example, potable hot water to a building or radiate heat to a room in the building. Accordingly, it is desirable to transfer as much heat from the fuel cell power plant to the customer fluid as possible.

What is needed is an improved heat recovery system that more efficiently transfers heat from the fuel cell power plant to the customer fluid to improve the quality of the customer fluid by achieving a higher customer fluid temperature.

Docket No. 67,124-027/03292

SUMMARY OF THE INVENTION

A heat recovery system is provided that includes a fuel cell power plant having first and second fluids. A heat exchanger receives the first and second fluids and includes a customer fluid receiving heat from the first and second fluids. First and second loops respectively carry the first and second fluids from the fuel cell power plant to the heat exchanger. The heat exchanger receives all three fluids to more efficiently transfer heat from the first and second fluids to the customer fluid.

The heat exchanger includes a housing having first, second and customer passages each having inlets and outlets. The inlets and outlets of the passages are arranged relative to one another to more efficiently transfer heat from the first and second fluids to the customer fluids. Further, portions of the passages can be shunted to minimize the heat transfer between the fluids where the passages have been shunted in order to more efficiently transfer heat.

Accordingly, the present invention provides a heat recovery system that more efficiently transfers heat from the fuel cell power plant to the customer fluid to improve the quality of the customer fluid by achieving a higher customer fluid temperature.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

Docket No. 67,124-027/C-3292

BRIEF DESCRIPTION OF THE DRAWINGS

Figure IA is a schematic view of a heat recovery system according to the present invention.

Figure IB is a schematic view of a heat exchanger shown in Figure IA. Figure 2 is a schematic view of the fluid passages within one example heat exchanger.

Figure 3 is a schematic view of the passages within another example heat exchanger.

Figure 4A is a schematic view of the passages within yet another example heat exchanger.

Figure 4B is a schematic view of the heat exchanger shown in Figure 4A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A heat recovery system 10 for a fuel cell power plant 12 is shown in Figure IA. A heat exchanger 14 is used in conjunction with the fuel cell power plant 12 to maintain a temperature range ensuring desired operation of the fuel cell power plant

12. The fuel cell power plant 12 is shown schematically including the heat exchanger 14 in the example shown by the dashed line. First and second loops 20 and 22 carry first and second fluids H and L between the fuel cell power plant 12 and the heat exchanger 14 to remove heat from the fuel cell power plant 12. A customer loop 26 passes through the heat exchanger 14 near the first and second loops 20 and 22 so that heat from the first and second fluids H and L can be transferred to a customer fluid C within the customer loop 26. The heated customer

Docket No. 67,124-027/C-3292 fluid C can then be used to reject heat to an environment 28. For example, the environment 28 may be a building space or a water heater.

Unlike prior art heat recovery systems, a single heat exchanger is used to receive all three fluids. The use of multiple heat exchangers in the prior art resulted in a low quality customer fluid with less than the desired temperature. In this manner, heat is not lost through radiation when transferring one fluid from the interface heat exchanger to the customer heat exchanger. Further, additional efficiencies may be gained from conduction and/or convection by having all three fluids in close proximity to one another. These efficiencies gained from the inventive system and heat exchanger result in an improved quality customer fluid having a higher temperature.

A housing 27 for the heat exchanger 14 is schematically shown in Figure IB. The first and second fluids H and L are shown entering the heat exchanger 14 to heat the customer fluids C passing through the heat exchanger 14. In the example shown, the first fluid H is hotter than the second fluid L. Also, the first and second fluids H and L are both hotter than the customer fluid C.

Figure 2 schematically depicts a simplified version of the inside of an example heat exchanger 29. The heat exchanger 29 shows portions of the fluid loops passing through the heat exchanger in close proximity to one another. A first passage 48 having the first fluid H includes a first inlet and outlet 36 and 42. Similarly, a second passage 50 carrying the second fluid L includes a second inlet and outlet 38 and 44. A customer passage 52 carrying the customer fluid C includes a customer inlet and outlet 40 and 46. The first, second and customer passages 48,

Docket No. 67,124-027/C-3292 50 and 52 respectively include first, second and customer heat transfer portions 30,

32 and 34 that are schematically depicted by saw tooth lines in the figures.

The inlets and outlets of the first, second and customer passages 48, 50 and

52 can be arranged relative to one another to achieve a more efficient heat transfer from the first and second fluids H and L through the customer fluids C. For example a large temperature gradient at certain locations within the heat exchanger may be desired. In one example shown in Figure 2, the first inlet 36 is arranged near the customer outlet 46, and the first outlet 42 is arranged near the customer inlet 40.

The second inlet 38 is arranged downstream of the customer outlet 46, and the second outlet 44 is arranged near the customer inlet 40.

It may be desirable to utilize different length passages to provide a more efficient heat exchanger. For example, the customer heat transfer portion 34 has a length schematically depicted by Xl, and the second heat transfer portion 32 has a length schematically depicted by X2. The length X2 is less than the length Xl since it is more efficient to transfer heat from the lower temperature second fluid L to the customer fluid C closer to the customer inlet 40.

Another example heat exchanger 53 is shown in Figure 3. The heat exchanger 53 uses shunts to selectively inhibit the heat transfer between various portions of the passages to improve the efficiency of the heat exchanger. In the example shown, a first shunt portion 54 is arranged along the first passage 48 between first heat transfer portions 30. A customer shunt portion 56 is arranged along the customer passage 52 near the customer inlet 40. The first and customer shunt portions 54 and 56 operate to encourage heat transfer between the

Docket No. 67.124-027/C-3292 first fluid when it is at its hottest and the customer fluid when its at its hottest, and the second fluid L when its at its hottest and the customer fluid C when its at its coolest.

Another heat exchanger 57 using shunts is shown in Figure 4A. In this example embodiment, the first shunt portion 54 is arranged near the first outlet 42 on the first passage 48, and the customer shunt portion 56 is arranged along the customer passage 52 with customer heat transfer portions 34 on either side. Effectively, the heat transfer between the first fluid H and the customer fluid C is the same as shown in Figure 3. However, the transfer between the second fluid L and the customer fluid C is in closer proximity to the customer inlet 40. A housing 58 for the heat exchanger 57 is schematically shown in Figure 4B. The housing 58 can be schematically broken into intermediate, first and second housing portions 62, 64 and 66. The shunting shown in Figure 4A can be schematically depicted by a tube 59 that basically passes straight through the intermediate portion 62 while inhibiting heat transfer from the first and second fluids H and L to the customer fluid C. The shunting shown in Figure 4A is also schematically depicted by the first and second fluids H and L entering the housing 58 offset from one another.

Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.