Air Product’s Ted Foster speaks to gasworld about an innovative oxygen separation method that could change the face of gas infrastructure.
Ion Transport Membrane technology uses a ceramic membrane - a complex metal oxide which, under pressure and temperature, ionises and separates oxygen molecules from air.
It is being developed by Air Products as a viable alternative to conventional cryogenic air separation, as no external power source is required in the process, and the technology has the potential to produce large quantities of oxygen.
ITM technology is patented by Air Products. The company began its exploratory research back in 1988, and has worked with the US Department of Energy (DOE) since 1999 in order to develop it further.
Last month, the company announced it had signed an agreement with the Electric Power Research Institute Inc. (EPRI) for furthering the development of ITM, in terms of advances towards successful deployment of the technology within the power industry, suggesting the research has taken a significant step forward.
Ted Foster, Director of Business Development for Advanced Gas Separation, spoke to gasworld about the technology, he said, “We dope the crystal structure so that some of the oxygen in the metal oxide is not there in the solid state. When high temperature oxygen ionises it jumps into the oxygen vacancies in the crystal; it then transports itself through the crystals, hopping between those oxygen ion vacancies to the other side.”
“What happens when this mechanism is activated is an ionic transport - it’s very very fast, and is only selective for oxygen ions. In one stage of membrane separation you get high purity oxygen and you get it at a very high transport rate. This all happens at about 800-900˚C.”
The process does not simply produce oxygen alone; power is co-produced, and in an alternate process configuration, synthesis gas can be produced.
“After extracting the oxygen, you are left with high temperature, high pressure, oxygen depleted air. This has a lot of energy in it, which you don’t want to waste. The hot pressurised air is put through an expander, out of that comes a hot gas, which is then put in a heat recovery steam generator, and power is produced from both the expander and a steam turbine.”
Foster continued, “Since you have the oxygen at 900˚C, if you want to make synthesis gas you can simply take natural gas and steam and put it on the oxygen product side of the membrane, and you’ll automatically have reforming and partial oxidation reactions taking place, which will convert the steam and methane into hydrogen and carbon monoxide. Synthesis gas is used in the gas to liquids business to make clean fuels, and it can also be further reacted to make hydrogen, as Air Products does, or chemicals.”
Given the fact that both oxygen and power are produced from ITM technology, it is best suited to advanced power generation systems like Integrated Gasification Combined Cycle (IGCC) plants and oxyfuel combustion power systems.
“If you value the power, the cost of the oxygen compared to the commercial technology is about 30% less to make the oxygen,” Foster explains.
Conventional ASUs will not be phased out by the technology, as many companies do not require the power, and do require other gases, like argon.
“You need to find an application that not only wants large volumes of oxygen, but also one which is in a location where power is needed; also, if you want argon (as is produced from a standard ASU) this might not be your choice of technology,” Foster adds.
For those who do need the power or can integrate into high temperature and pressure processes, the technology is a “radical innovation,” as Foster puts it. A large ASU will have two or three columns in a 10x10m cold box, standing at around 40-60m tall, whereas a complete ITM unit lays vertical and is much smaller.
Foster explains, “If you took a pencil and stood it up, that’s your distillation tower, but lay it down on the ground and take a quarter of it, that would be how the ITM unit would look - it’s extremely compact.”
“The other benefit is that it’s extremely fast; the flux rate of gas going through the membrane is 10,000 times faster than any other membrane separation.”
The recent signing of an agreement between Air Products and EPRI is a significant step in ITM’s development.
“The EPRI joined us recently because they believe that this is a key enabling technology to improve the economics of gasification and oxy-fuel combustion power plants,” Foster said.
The new collaboration will help Air Products to push the technology and develop it further; in a recent press release published by the company, Vice President of Environment and Generation at EPRI said, “We expect our efforts will help accelerate ITM technology to market.”
Air Products is in phase three of a cooperative agreement formed with the US DOE in 1999. Foster explained, “The target of the phase three development is to put in a 150tpd ISTU intermediate scale test unit. This would be the first time that we have scaled up the technology to the point where we have a large array of ceramic membrane modules of full height in a separator vessel that will give commercial design and further scale up basis.”
After the 150tpd test unit is complete the company will set about creating a 2000tpd facility of sufficient scale to get the data needed for clean energy plants. This is expected in the 2013/2014 time frame.
“I think that when we roll this out in the applications where it has benefits it will be a significant factor to gain market share and to maintain and add to profitability, due to enabling economics in many end use applications,” Foster concluded.