Patent Application
20140004470
None.
1. Field of the Invention
The present invention relates to injection of oxygen from ion transport membranes.
2. Related Art
Air-fired glass melting furnaces has been converted to oxygen-fired technology (i.e., oxy-combustion with oxygen concentrations in the oxidant of up to 100%) primarily due to environmental regulations. Oxy-combustion is one of the most thermally efficient and cost-effective ways to enable glass manufacturers to meet NOx emissions restrictions. Compared with air-fired combustion, oxy-combustion has the potential to reduce NOx emissions by up to 85%.
Besides the reduction of NOx emissions, the oxy-combustion has several other significant advantages over traditional air-fired combustion processes:
However, economically speaking, oxygen (for use in oxy-fuel combustion) is costly for glass melting furnaces. The main cost increase is the separation of oxygen from air using a cryogenic air separation unit (ASU). This separation process requires a great deal of energy. For example, in the field of power generation nearly 15% of the production of a coal-fired power station can be consumed by the ASU.
Thus, there is a need for an alternative method of producing O2 at relatively low cost for use in oxy-combustion technology by the glass industry.
Nevertheless, oxygen generated at high temperatures has the potential to benefit oxy-combustion processes by reducing the amount of fuel needed. In comparison to ambient temperature oxy-combustion, it has been demonstrated that as much as 10% of the fuel requirement may be reduced if the oxygen is preheated to 550° C. and the natural gas fuel is preheated to 450° C. Preheating O2 to a higher temperature could provide an even greater reduction of the fuel requirement. However, handling pure O2 at a temperature higher than 650° C. is very difficult and there are very few materials that have been shown to reliably withstand such high temperatures in the O2 rich environment.
Ion transport membranes (ITMs) are fabricated from ionic and mixed-conducting ceramic oxides that conduct oxygen ions at elevated temperatures of 800-900° C. There are a wide variety of materials that are suitable for use in ITMs and their details need not be duplicated herein.
ITMs are considered desirable for integration with glass melting furnaces. Because the glass melting furnace flue gas temperature is roughly 1400° C. at the exit of the combustion chamber, the thermal energy of the hot flue gas can be partly recovered through heat transfer with compressed air, which in turn is used as the feed gas for the ITM. In operation, air is typically compressed to about 16 bars, heated to 900° C., and fed to the ITM. Hot oxygen permeates through the ITM. In order to provide a suitable driving force across the membrane, the oxygen partial pressure of the permeate must be kept low. Typically, an oxygen recovery of 50% to 80% from air is potentially possible. While the O2 product is available at 900° C., its pressure depends upon the degree of recovery from the air feed gas. The O2 product may be available at a desirably high pressure of about 2.2 bar, but at the expense of relatively low recoveries. At relatively higher recoveries, the O2 product may only be available at pressures as low as about 0.5 bar.
Glass melting furnaces operate at high temperatures and at pressures a few Pascal above the ambient pressure. O2 recovered at high temperature and at a relatively high pressure (i.e., >1.1 bar) from an ITM does not require further preheating and is suitable for injection into the glass melting furnace (via a lance or burner). If greater recoveries are desired, the resultant O2 is generated at pressures below ambient. There are difficulties experienced when attempting to inject such low pressure O2 into the furnace. Compressing O2 at 900° C. is considered undesirable due to the significant material constraints noted above. Cooling the O2 down then compressing it is another option, but such an approach will decrease the energy efficiency.
Thus, it is an object of the invention to inject oxygen from an ITM into a high temperature oxygen consuming process at relatively high recoveries without requiring compression of the oxygen. It is another object of the invention to inject oxygen from an ITM into a high temperature oxygen consuming process at relatively high recoveries without being restricted by the relatively limited selection of materials that can withstand high temperature oxygen-rich environments. It is yet another object of the invention to improve the efficiency of ITMs integrated with high temperature oxygen consuming processes.
There is disclosed a method for injecting low pressure oxygen from an ion transport membrane into an ambient or super ambient pressure oxygen-consuming process, comprising the following steps. A super ambient pressure, oxygen-containing feed gas is fed to a first ion transport membrane to produce a sub-ambient pressure first permeate stream essentially consisting of oxygen and a first non-permeate stream essentially consisting of oxygen-deficient feed gas, the ion transport membrane comprising a material that is a hybrid electron/O2− anion hybrid conductor. A high velocity gas is injected into the oxygen-consuming process from an interior of an inner tube, the high velocity gas having a velocity of at least 80 m/s. The sub-ambient pressure first permeate stream is injected into the oxygen consuming process form an annular space in between the inner tube and an outer tube concentrically disposed around the inner tube, the first permeate stream being sucked from the annular space by the relative vacuum created by expansion of the high velocity gas from the inner tube, the sub ambient pressure first permeate stream having a pressure of at least 8000 Pascal.
There is also provided a system for consuming oxygen that is received at low pressure from an ion transport membrane, comprising: a reactor adapted for consuming oxygen; a first ion transport membrane comprising a material that is a hybrid electron/O2− anion hybrid conductor, the first ion transport membrane having an inlet, a first permeate stream outlet and a first non-permeate stream outlet; a source of a gas; and an oxygen injection device comprising an outer tube concentrically disposed around an inner tube. The inner tube has an inlet and outlet, an annular space in between the inner and outlet tubes having an inlet and outlet. The inlet of the inner tube is in fluid communication with the gas source, the inlet of the annular space is in fluid communication with the first permeate stream outlet, and the outlets of the inner tube and the annular space are in fluid communication with an interior of the reactor.
Either of or both of the method and system may include one or more of the following aspects:
For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:
In this invention, sub ambient pressure oxygen that is permeated from an ion transport membrane is injected into an oxygen-consuming process from an oxygen injection device. The oxygen injection device comprises an outer tube concentrically disposed around an inner tube. The outlet of the inner tube and an outlet of an annular space in between the inner and outer tubes feed into an interior of a reactor in which the oxygen-consuming process takes place. A high velocity gas is injected into the reactor from the inner tube. Expansion of the high velocity gas at the outlet of the inner tube causes oxygen to be sucked from the annular space and, hence, sucked from the ion transport membrane.
The reactor containing the oxygen-consuming process is not limited. Typical types of reactors include oxy-combustion furnaces, oxy-combustion boilers, aluminum furnaces, cement kilns, electric arc furnaces having oxygen lances or oxy-combustion burners, industrial melting furnaces, and blast furnaces. The industrial melting furnace is typically a furnace in which glass, metal, or vitrifiable material such as a ceramic or frit.
The ion transport membrane is made of a material that includes a densified separation layer made of a hybrid electron/O2− anion hybrid conductor. The densified separation layer is otherwise gas-tight. Such materials are well known and their details need not be duplicated herein.
An oxygen-containing feed gas (that is fed to an inlet of the ion transport membrane) is similarly not limited. Typically, the feed gas is compressed air, oxygen-deficient air, or an oxygen-containing gas derived from a high temperature, industrial process such as a glass furnace or blast furnace. At least some of the oxygen from the oxygen-containing feed gas permeates through the membrane and exits the membrane at a permeate outlet. The non-permeate portion of the oxygen-containing feed gas (now termed oxygen-deficient feed gas) exits the membrane at a non-permeate outlet. The feed gas is at a temperature high enough to maintain the temperature of the hybrid O2− anion and electron conductor material so that oxygen may permeate across the membrane. Typically, the feed gas is at a temperature of about 900° C. The feed gas is also at a pressure suitably high to generate a driving force across the membrane that drives permeation of oxygen across the membrane. Typically the feed gas is at a pressure of about 16 bar.
The permeate from the membrane is at sub ambient pressure. Rather than compress the permeate in order to inject the permeate into the reactor, it is sucked into the reactor by the creation of a low pressure region adjacent the outlet of the inner tube and the outlet of the annular space that results from the expansion of the high velocity gas at the outlet of the inner tube. In this manner, oxygen that would otherwise not be able to be injected into the reactor (or injected only if it was compressed) may be injected into the reactor. As a result, higher recoveries of oxygen from the feed gas are realized. The gas pressure of the permeate should be 8000 Pascal or higher. If the pressure of the permeate is too low, it will not be able to be sucked into the reactor via the annular space.
The high velocity gas is also not limited. Typical examples include oxygen, flue gas, gaseous fuel, particulate solid fuel fluidized with a conveying gas such as air, or other industrial gas derived from a high temperature, industrial process such as a blast furnace or a partial oxidation reactor/gasifier. The high velocity gas is injected from the inner tube at a velocity sufficient to cause the oxygen to be sucked from the annular space. Typically, the velocity is at least 80 m/s or about 130-140 m/s.
The oxygen injection device may extend through a wall of the reactor so that the downstream ends of the inner and outer tubes are disposed within the reactor or their downstream ends may be flush with a wall of the reactor. The inner diameter of the outer pipe should only be a few mm larger than the outer diameter of the inner pipe in order to create the low pressure region at the outlet of the annular space. If the gap between the inner and outer pipes is too large, a high pressure zone will appear adjacent the inner surface of the outer pipe and a low pressure zone appear adjacent the outer surface of the inner pipe. In such a situation, the flue gas will recirculate at the interface of the oxygen injection device and the wall of the reactor into which it extends and the oxygen in the annular space will not be sucked into the reactor. Because the annular space is limited by the gap, the mass flow rate of oxygen sucked into the reactor is similarly limited. Therefore, a plurality of the oxygen injection devices might be necessary when a relatively large mass flow rate of oxygen needs to be sucked into the reactor from the combined annular spaces.
The suction rate (the mass flow rate of the oxygen sucked from the annular space divided by the mass flow rate of the high velocity gas) is dependent upon the velocity of the high velocity gas in the inner pipe and also upon the thickness of the gap between the inner and outer pipes. The suction rate increases when the velocity of the high velocity gas in the inner pipe increases. If the velocity of high velocity gas in the inner pipe is relatively low, the inner diameter of the outer pipe should be reduced in order to keep the same suction ratio in the gases from the outer pipe. In one embodiment, the device has seven pipe-in-pipe structures. HP O2 flows at high velocity (130-140 m/s) in the inner pipe of each structure. O2 at sub-atmosphere of ITM system connected to the outer pipes. As the HP O2 flush out of the inner pipe at high speed, a negative pressure is created at the joint area of the outer pipe and furnace wall, and thus the HT/LP O2 can be sucked into the flow stream.
The oxygen injection device can be used for a wide variety of purposes. It can be used as a burner or lance whereby the high velocity gas is oxygen. It can instead be used as a gas mixer for a high pressure gas (the high velocity gas) and a low pressure gas (the oxygen permeate at sub ambient pressure).
In one embodiment and as best shown in
In another embodiment and as best illustrated in
CFD (Computational fluid dynamics) simulations have been conducted to calculation the amount of HT/LP O2 that can be sucked in by the HT/HP O2 flow stream by a device having seven pipe-in-pipe structures. The flow rates of the O2 through the inner pipes and outer pipes, the inlet velocity of the O2 in the inner pipes, the pressure of the LP O2, and the resultant suction ratios are listed in Table 1. The suction ratio by this design is pretty high, ranging from 15% to 56.4% depending on the pressure of the LP O2. Table 2 shows the O2 suction ratio when the inner oxygen flow velocity is varied. As seen in Table 2, the O2 suction ratio increases if increasing the O2 flow velocity.
Preferred processes and apparatus for practicing the present invention have been described. It will be understood and readily apparent to the skilled artisan that many changes and modifications may be made to the above-described embodiments without departing from the spirit and the scope of the present invention. The foregoing is illustrative only and that other embodiments of the integrated processes and apparatus may be employed without departing from the true scope of the invention defined in the following claims.
