CONTROLLED TEMPERATURE ION TRANSPORT MEMBRANE REACTOR

Abstract

The controlled temperature ion transport membrane reactor is a combustion-type ion transport membrane reactor for combusting a hydrocarbon fuel with oxygen. The reactor includes an oxygen permeable ion transport membrane for separating oxygen from air. In order to control temperature within the reactor, a thermally conductive plate is positioned between a mixing passage, where a diluent gas and the permeated oxygen are mixed, and a reaction zone. The reaction zone is in fluid communication with the mixing passage and a fuel chamber through a porous plate for combusting the hydrocarbon fuel with the oxygen.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to combustion reactors, and particularly to a controlled temperature ion transport membrane reactor including a thermally conductive plate for controlling reaction temperatures.

2. Description of the Related Art

FIG. 2 illustrates a conventional ion transport membrane reactor 100. In the example of FIG. 2, an oxygen combustion reactor is illustrated. Such reactors are typically cylindrical, including an outer cylindrical wall 114 and an inner cylindrical ion transport membrane 116 positioned coaxially therein. As shown, pressurized environmental air A (typically provided by a compressor or the like) is pumped within annular regions 126, which are defined between the cylindrical shell of the respective inner cylindrical ion transport membrane 116 and the inner surface of the cylindrical wall 114.

Gaseous hydrocarbon fuel F is pumped into a central region 124 (which often includes additional carbon dioxide, depending upon the particular application and implementation of the reactor), defined by the inner cylindrical ion transport membrane 116. The inner cylindrical ion transport membrane 116 separates O₂ from air A, allowing only O₂ to pass therethrough from the annular region 126 into the central region 124.

The gaseous O₂ is transported from the annular region 126 to the inner surface of the inner cylindrical ion transport membrane 116 for combustion with fuel F within the central region 124. This combustion results in the production of gaseous CO₂ and H₂O vapor. Combustion of the fuel F with the O₂ within reactor 100 generates heat, resulting in high temperature combustion products, which are then used to drive some external apparatus, such as a turbine or the like. Further, gaseous nitrogen (N₂), which remains after the O₂ is removed from the air A, is channeled to an external reservoir or the like.

The driving force for oxygen permeation across the membrane 116 is the oxygen potential gradient, i.e., the oxygen partial pressure. Thus, an ion transport membrane (ITM) air separation unit model must include an expression relating the local oxygen flux through the membrane to the local temperature, the oxygen partial pressures of each stream, and the membrane thickness for a given material. The “oxygen partial pressures” refer to the local values directly adjacent to either side of the membrane surface in the gaseous phase. Similarly, “temperature” refers to the local value at the membrane surface. The oxygen permeation flux J₀₂ as a function of partial pressure of O₂ on both sides (P′₀₂ and P″₀₂) and the membrane temperature is given by:

$J_{O2}=\frac{D_VK_r\left(\sqrt{P_{O2}^{\prime }}-\sqrt{P_{O2}^{″}}\right)}{2{\mathrm{LK}}_f\sqrt{P_{O2}^{\prime }P_{O2}^{″}}+D_V\left(\sqrt{P_{O2}^{\prime }}+\sqrt{P_{O2}^{″}}\right)},$

where D_v, K_r and K_f are functions of temperature and the specific properties of the membrane, and are determined by fitting experimental oxygen flux data as a function of temperatures and oxygen partial pressure gradients.

The oxygen permeation at low temperatures (˜750° C.) is limited by the rate of oxygen-ion recombination, but is dominantly controlled by bulk diffusion at high temperatures (˜950° C.). However, the oxygen permeation is very low at low temperatures. ITM systems, however, operate at relatively high temperatures; e.g., above 1000 K, and rely on a difference in O₂ chemical potential to drive the separation process. Typical ITM operating conditions consist of a membrane surface temperature between 1000 K and 1270 K, and an oxygen partial pressure difference across the membrane ranging from 0.2 to a few bars. Thermal stresses can lead to membrane cracks due to the multi-layered nature of the fabrication process, or non-uniform temperature fields inside the ITM reactor.

The local membrane temperature is a critical ITM parameter that must be monitored and controlled. Specifically, the oxygen permeation through the membrane has Arrhenius dependence on the local temperature, which, in general, is different from the bulk temperature. Further, excessive membrane temperatures must be avoided in order to avoid material failure. Thus, the heat transfer between the feed and permeate must be calculated as a function of operating conditions in order to correctly model ITM performance and operating constraints.

For separation-only ITM reactors, acceptable inlet temperatures eliminate the possibility of local excessive heating, but the local temperature must still be determined in order to calculate the local oxygen flux. However, for reactive ITM applications, the local heat transfer away from the reaction zone must be large enough to accommodate the local heat release from the chemical reactions.

For low local membrane temperature, the flux is nearly insensitive to the partial pressure gradient because of the relatively slow kinetics resulting from the Arrhenius dependence. However, in the high-temperature range, the sensitivity to partial pressure gradients is significant as the diffusive resistance becomes dominant. In other words, the Arrhenius term e^−Ea/RT included in the diffusion coefficient of oxygen vacancies in the oxygen permeation flux equation is extremely small for low temperatures. This implies that the membrane axial temperature profile must be controlled and maintained near the maximum temperature limit in order for large partial pressure differences to matter. Thus, an ITM reactor designed with the intent to exploit large partial pressure differences would only be successful if the temperature is maintained at a high level. It can be clearly seen that both oxygen partial pressures and local temperature are important in the high-performance operating regime. Thus, it would be desirable to provide an ITM reactor that takes advantage of both.

Thus, a controlled temperature ion transport membrane reactor solving the aforementioned problems is desired.

SUMMARY OF THE INVENTION

The controlled temperature ion transport membrane reactor includes a reactor housing having first and second laterally opposed ends, an upper wall, and a lower wall. An oxygen-permeable ion transport membrane is disposed within the reactor housing. An air passage is defined between the oxygen-permeable ion transport membrane and the upper wall of the reactor housing. An air inlet is formed through the first end of the reactor housing for receiving pressurized air, which passes through the air passage, and a depleted air outlet is formed through the second end of the reactor housing for expelling depleted air following removal of oxygen therefrom. A thermally conductive plate is also disposed within the reactor housing. A mixture passage is defined between the oxygen-permeable ion transport membrane and the thermally conductive plate. A diluent inlet is formed through the second end of the reactor housing for receiving a diluent gas. The diluent gas and the oxygen permeated through the oxygen-permeable ion transport membrane mix in the mixture passage.

A porous plate is disposed within the reactor housing. A reaction zone is defined between the thermally conductive plate and the porous plate. An exhaust outlet is formed through the second end of the reactor housing for expelling combustion products. The reaction zone is in fluid communication with the mixture passage. A fuel inlet is formed through the second end of the reactor housing. The fuel inlet is in fluid communication with a fuel chamber defined between the porous plate and the lower wall of the reactor housing. A hydrocarbon fuel passes through the porous plate to react with the diluent gas and the oxygen in the reaction zone to generate heat and the combustion products.

In an alternative embodiment, the controlled temperature ion transport membrane reactor includes a reactor housing having first and second laterally opposed ends, an upper wall, and a lower wall. An oxygen-permeable ion transport membrane is disposed within the reactor housing. An air passage is defined between the oxygen-permeable ion transport membrane and the upper wall of the reactor housing. An air inlet is formed through the first end of the reactor housing for receiving pressurized air, which passes through the air passage, and a depleted air outlet is formed through the second end of the reactor housing for expelling depleted air following removal of oxygen therefrom.

A thermally conductive plate is disposed within the reactor housing. A mixture passage is defined between the oxygen-permeable ion transport membrane and the thermally conductive plate. A diluent inlet is formed through the second end of the reactor housing for receiving a diluent gas. The diluent gas and the oxygen that permeates through the oxygen-permeable ion transport membrane mix in the mixture passage. In this alternative embodiment, the thermally conductive plate is divided into first and second portions. The first portion is formed from a first material and the second portion is formed from a second material. A thermal conductivity of the first material is greater than a thermal conductivity of the second material.

A fuel inlet is formed through the first end of the reactor housing. The fuel inlet is in fluid communication with a fuel chamber defined between the thermally conductive plate and the lower wall of the reactor housing. The fuel chamber is in fluid communication with the mixture passage, such that a hydrocarbon fuel entering the fuel chamber through the fuel inlet reacts with the diluent gas and the oxygen in the fuel chamber. The fuel chamber is divided into a flame zone adjacent the second portion of the thermally conductive plate and a combustion products portion adjacent the first portion of the thermally conductive plate. An exhaust outlet is formed through the first end of the reactor housing.

These and other features of the present invention will become readily apparent upon further review of the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic side view in section of a first embodiment of a controlled temperature ion transport membrane reactor according to the present invention.

FIG. 2 is a diagrammatic side view in section of a conventional oxygen transport reactor of the prior art .

FIG. 3 is a diagrammatic side view in section of an alternative embodiment of a controlled temperature ion transport membrane reactor according to the present invention.

Similar reference characters denote corresponding features consistently throughout the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, the controlled temperature ion transport membrane reactor 10 includes a reactor housing 14 having first and second laterally opposed ends, 40, 38, respectively, an upper wall 36, and a lower wall 34. An oxygen-permeable ion transport membrane 16 is disposed within the reactor housing 14. An air passage 26 is defined between the oxygen-permeable ion transport membrane 16 and the upper wall 36 of the reactor housing 14. An air inlet 12 is formed through the first end 40 of the reactor housing for receiving pressurized air A adjacent the upper wall 36, which passes through the air passage 26, and a depleted air outlet 60 is formed through the second end 38 of the reactor housing 14 for expelling depleted air following removal of oxygen therefrom. The depleted air is primarily N₂ gas.

A thermally conductive plate 20 is also disposed within the reactor housing 14. A mixture passage 24 is defined between the oxygen-permeable ion transport membrane 16 and the thermally conductive plate 20. The material forming the plate 20 is preferably selected to have a desired conductivity in order to control the required amount of heat that will reach the membrane surface. In conventional membrane reactors, the membrane surface temperature has a certain thermal limit, and once temperatures beyond this limit have been passed, the membrane will be destroyed. The controlled temperature of the present reactor 10, provided by thermally conductive plate 20, allows for avoidance of such membrane rupture.

A diluent inlet 18 is formed through the second end 38 of the reactor housing 14 for receiving a diluent gas D. The diluent gas D and oxygen permeated through the oxygen-permeable ion transport membrane 16 mix in the mixture passage 24. The diluent gas D may be pressurized carbon dioxide. The diluent gas D (sometimes referred to as a “sweep gas”) purges the oxygen in order to reduce the partial pressure of O₂, thus increasing the oxygen flux through the membrane 16.

A porous plate 30 is disposed within the reactor housing 14. A reaction zone 28 is defined between the thermally conductive plate 20 and the porous plate 30. An exhaust outlet 22 is formed through the second end 38 of the reactor housing 14 for expelling combustion products, which are primarily carbon dioxide and water vapor. The reaction zone 28 is in fluid communication with the mixture passage 24 via a channel 52 formed adjacent the first end 40.

A fuel inlet 32 is formed through the second end 38 of the reactor housing 14. The fuel inlet 32 is in fluid communication with a fuel chamber 50 defined between the porous plate 30 and the lower wall 34 of the reactor housing 14. A hydrocarbon fuel F is injected through the fuel inlet 32, into the fuel chamber 50, and passes through the porous plate 30 to react with the mixture of diluent gas D and oxygen in the reaction zone 28 to generate heat and the combustion products. The diluent gas D works in the reaction zone 28 as the energy carrier medium. The flow of the diluent gas D in the mixing passage 24, preferably at high velocity, causes more oxygen to be extracted from the air A in order to be used in the adjacent reaction zone 28 in the combustion process.

The counter-current profile of reactor 10 provides advantages over the conventional reactor design of FIG. 2. The partial pressure difference is essentially constant along the reactor length, thus providing good material stability potential by minimizing chemical expansion stress. Further, in this counter-current flow configuration, the more sensitive region where the permeate partial pressure is low coincides with the region where the feed partial pressure is low, thus providing a better match than the conventional co-current case, where the high-pressure feed matches up with the low-low pressure permeate.

In an alternative embodiment, illustrated in FIG. 3, controlled temperature ion transport membrane reactor 200 includes a reactor housing 214 having first and second laterally opposed ends 240, 238, respectively, an upper wall 236, and a lower wall 234. An oxygen-permeable ion transport membrane 216 is disposed within the reactor housing 214. An air passage 226 is defined between the oxygen-permeable ion transport membrane 216 and the upper wall 236 of the reactor housing 214. An air inlet 212 is formed through the first end 240 of the reactor housing 214 for receiving pressurized air A. The pressurized air A passes through the air passage 226, and a depleted air outlet 260 is formed through the second end 238 of the reactor housing 214 for expelling depleted air following removal of oxygen therefrom.

A thermally conductive plate 254 is disposed within the reactor housing 214. A mixture passage 224 is defined between the oxygen-permeable ion transport membrane 216 and the thermally conductive plate 254. A diluent inlet 218 is formed through the second end 238 of the reactor housing 214 for receiving a diluent gas D. The diluent gas D and oxygen permeated through the oxygen-permeable ion transport membrane 216 mix in the mixture passage 224. In this alternative embodiment, the thermally conductive plate 254 is divided into first and second portions 220, 221, respectively. The first portion 220 is formed from a first material, and the second portion 221 is formed from a second material. The thermal conductivity of the first material is greater than the thermal conductivity of the second material.

A fuel inlet 232 is formed through the first end 240 of the reactor housing 214. The fuel inlet 232 is in fluid communication with a fuel chamber 250 defined between the thermally conductive plate 254 and the lower wall 234 of the reactor housing 214. The fuel chamber 250 is in fluid communication with the mixture passage 224 via a channel 252 adjacent the first end 240, such that a hydrocarbon fuel F entering the fuel chamber 250 through the fuel inlet 232 reacts with the mixture of diluent gas D and oxygen in the fuel chamber 250.

The fuel chamber 250 is divided into a high temperature flame zone 230 adjacent the second portion 221 of the thermally conductive plate 254 and a lower temperature combustion products portion 228 adjacent the first portion 220 of the thermally conductive plate 254. An exhaust outlet 222 is formed through the first end 238 of the reactor housing 214. In reactor 200, in order to maintain the surface temperature of the membrane 216 constant along the whole reactor length, two different materials with different thermal conductivities are used to form the plate 254. The lower conductivity portion 221 is used adjacent the high temperature flame zone 230, and the high conductivity portion 220 is used adjacent the low temperature combustion product zone 228. The length of each conductive portion 220, 221 is preferably controlled according to the amount of permeated oxygen, the fuel flow, and, accordingly, the flame length, i.e., the reactor design function decides the length of each portion 220, 221 according to the flame length.

It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.

Claims

1. A controlled temperature ion transport membrane reactor, comprising:

a reactor housing having first and second laterally opposed ends, an upper wall, and a lower wall;

an oxygen-permeable ion transport membrane disposed within the reactor housing;

an air passage defined between the oxygen-permeable ion transport membrane and the upper wall of the reactor housing;

an air inlet formed through the first end of the reactor housing for receiving pressurized air, the pressurized air passing through the air passage;

a depleted air outlet formed through the second end of the reactor housing for expelling depleted air following removal of oxygen therefrom;

a thermally conductive plate disposed within the reactor housing;

a mixture passage defined between the oxygen-permeable ion transport membrane and the thermally conductive plate;

a diluent inlet formed through the second end of the reactor housing for receiving a diluent gas, the diluent gas and oxygen permeated through the oxygen-permeable ion transport membrane mixing in the mixture passage;

a porous plate disposed within the reactor housing;

a reaction zone defined between the thermally conductive plate and the porous plate, the reaction zone being in fluid communication with the mixture passage;

an exhaust outlet formed through the second end of the reactor housing for expelling combustion products,

a fuel inlet formed through the second end of the reactor housing; and

a fuel chamber defined between the porous plate and the lower wall of the reactor housing, the fuel inlet being in fluid communication with the fuel chamber;

wherein a hydrocarbon fuel injected into the fuel inlet passes from the fuel chamber through the porous plate and reacts with the diluent gas and the oxygen in the reaction zone to generate heat and the combustion products.

2. The controlled temperature ion transport membrane reactor as recited in claim 1, further comprising a channel positioned adjacent the first end of the reactor housing, the channel connecting the reaction zone with the mixture passage.

3-7. (canceled)