MORRIS, Minn. — The University of Minnesota’s West Central Research and Outreach Center has been producing nearly carbon-free ammonia fertilizer at its unique pilot wind to nitrogen plant since 2013. They are now ready to take small-scale green nitrogen production to the next level.
Ammonia fertilizers, such as anhydrous ammonia and urea, use large amounts of the methane from natural gas to obtain the hydrogen required to produce the widely used fertilizers. The nitrogen is manufactured from the atmosphere as a by-product of making hydrogen. The two elements are separated from their original material, methane and air, using the Haber-Bosch process developed by German chemists Fritz Haber and Carl Bosch. Then the process combines the nitrogen and hydrogen, using a catalyst along with very high heat and pressure, to form ammonia.
The process of making ammonia fertilizer, as it is conventionally done, requires immense amounts of energy. Roger Ruan, University of Minnesota Professor of Biorefining, estimates that ammonia fertilizer production uses “around one to two percent of the world’s total energy supply”.
Mike Reese, Director of Renewable Energy at the WROC, says conventional ammonia fertilizer production also is generally done in large, capital-intensive industrial facilities far from where its end use will be. That’s because the necessary high pressure and intense heat which are required generally are best suited to large industrial facilities.
“Most of the anhydrous ammonia we use in this area comes from plants on the Gulf Coast or Canada,” Reese said.
The idea for the ammonia production facility at WROC came when it was realized the the University’s two wind generators, which generate 5,400 kilowatt-hours annually, had more generating capacity than what was immediately needed.
Now, using about 10 percent of the electricity from the wind generators, the small plant at WROC is able to replace natural gas with water as a source for hydrogen. That hydrogen is then fused with atmospheric nitrogen to make ammonia.
“We are able to use electrolysis to separate the hydrogen and oxygen that make up water,” Reese said.
Once the hydrogen has been captured from water, the Haber-Bosch process can proceed as usual using electricity from the research station’s wind generators. The result has been that WCROC, for a number of years, has been supplying a local cooperative it’s locally made-from-the-wind anhydrous ammonia.
University researchers had made their point. Ammonia fertilizer could be made on a small scale using wind-generated electricity and carbon-free water as its source of hydrogen.
“Even though the renewable ammonia pilot plant has capacity to produce 28 tons per year, we wanted to demonstrate that this could be done locally and scaled up on a farmers cooperative scale,” Reese said. “We imagined farmers from two or three counties getting together and building one of these plants.”
“We wanted to demonstrate that this could be done locally on a farmers’ cooperative scale,” Mike Reese said. “We imagined farmers from two or three counties getting together and building one of these plants.”
But the conventional Haber-Bosch system has inefficiencies. It’s similar to refining gasoline from crude oil. Neither system is efficient but both are necessary to sustain our way of life so we accept these inefficiencies, Reese says. Producing ammonia on a small scale, using electricity to separate the hydrogen from water, is even more inefficient.
The restless minds of the University’s engineers and researchers found that level of efficiency to be unacceptable. So, they’ve spent a number of years experimenting and testing more efficient methods of making ammonia fertilizer. They’ve developed a system in the laboratory that is much more efficient and that require less pressure. Because the pressure requirements are less, it’s expected that small scale ammonia production facilities, using the new process, may be feasible.
The new process is called “Absorbent Enhanced Ammonia Production” and it was developed by professors Ed Cussler, Lanny Schmidt, and Alon McCormick in the Department of Chemical Engineering and Material Science.
The U.S. Department of Energy, which is helping fund the project through its REFUEL program, describes the process as follows:
“The University of Minnesota will develop a small-scale ammonia synthesis system using water and air, powered by wind energy. Instead of developing a new catalyst, this team is looking to increase process efficiency by absorbing ammonia at modest pressures as soon as it is formed. The reactor partially converts a feed of nitrogen and hydrogen into ammonia, after which the gases leaving the reactor go into a separator, where the ammonia is removed and the unreacted hydrogen and nitrogen are recycled. The ammonia is removed completely by selective absorption, which allows the synthesis to operate at lower pressure. This reduced pressure makes the system suitable for small-scale applications and more compatible with intermittent energy sources. The success of preliminary experiments suggests that this new approach may be fruitful in reducing capital and operating costs of ammonia production.”
The absorbent is an ordinary salt called magnesium chloride. Reese says that the magnesium chloride had some inefficiencies itself — because it wasn’t stable and needed to be replaced too often.
“The absorbent isn’t stable unless it’s supported by being combined with an inert substance like sand” he said.
The researchers have developed a way to make the salt last and they will be ready to start operating their new pilot plant in April.
Reese says moving the process from the laboratory to a pilot plant involves a lot of unknowns. He calls the period of time between the successful laboratory process to the successful and prolonged operation of a pilot plant “Death Valley.”
If Reese and the research team can make it across Death Valley with the new process, they are imagining more than just small to medium-sized wind to ammonia plants locally producing fertilizer.
“We are converting a diesel tractor to run partially on ammonia,” Reese said.
But, he points out, when looking at the total energy required to produce corn, tractors and transportation aren't actually major users of carbon fuels on the farm. Grain drying is. Reese and the research team are also looking at a system to substitute propane and liquid natural gas with home-grown ammonia fuel to dry corn.
The possibilities, it seems, are nearly unlimited.