Why Copper Mines Need Solar Thermochemistry: Hydrogen
The fastest way to commercialize solar hydrogen could be to supply hydrogen, oxygen and heat to the Australian copper mining industry using solar thermal chemistry, Christian Sattler recently told SolarPACES.
With his experience as head of solar fuel research at the German Solar Research Center at DLR, Sattler sees a synergistic connection between sulfuric acid processing in copper mining and the sulfur-based solar thermochemical process for hydrogen production; the Hybrid sulfur (HyS) Technology.
In the two-stage HyS process, the researchers use high-temperature solar heat of up to 900 ° C to break down sulfuric acid (H2SO4) by splitting water into hydrogen and oxygen. The sun’s heat comes from a solar field made up of heliostats (mirrors) that direct concentrated solar power onto a receiver on a power pole. The decomposition of H2SO4 is part of the first process step, which produces sulfur trioxide (SO2) and oxygen.
In the second step, the SO2 is fed together with water to an SO2-depolarized electrolyser (SDE), which generates hydrogen and fresh H2SO4, which is recycled in step one. Compared to conventional water electrolysis, the SDE only needs around a seventh of the electrical energy, so that the HyS can produce around 50% more hydrogen with the same solar input.
International research groups in Germany, Australia, Japan and the USA have developed and tested the components that are required for this sulfur-based high-temperature process – a solar reactor / evaporator, a heat exchanger for the SO3 decomposition, an oxygen separator for SO2 and O2. The search for materials identified a silicon carbide construction that could maintain stability under the corrosive conditions and very high temperatures required to perform thermochemistry.
Many advantages of sulfur-based solar thermal chemistry
In the open air, sulfur can be stored cheaply in a heap for a long time; like a pile of coal. In contrast to all other heat storage technologies, its stored energy can be called up at a temperature that is actually higher than that of the original heat supply and recovered at a constant temperature.
A sulfur-based thermochemical process has more than an order of magnitude larger storage capacity than today’s molten salts, which would lower the cost of reliable round-the-clock operation even further than the current storage cost of CSP, which is about a tenth the cost of Batteries. Energy storage is necessary in the manufacture of solar fuels. Like many industrial processes, hydrogen splitting requires a constant supply of heat around the clock. All solar thermochemical processes include the possibility of ensuring this constant supply by hybridizing the solar reactor or by integrating a thermal energy storage medium such as commercially proven molten salts.
“If you want to use any type of renewable energy, you need to have enough storage to provide 24/7 supply,” added Mehdi Jafarian, who conducts HyS research at the University of Australia’s School of Mechanical Engineering. contributes to Adelaide.
“This is why we believe that the HyS process has the potential to be integrated into copper processing. However, if you were using solar PV, for example, the cost of battery storage would significantly increase the net cost of decarbonizing these processes, ”he added.
How is sulfuric acid used in copper mines?
Sulfuric acid reactions are used to refine copper from ores, and in the solar reactor both hydrogen and oxygen, which are required for copper refining, can be produced from sulfuric acid.
“There are mining processes like the roasting of copper ore that produce sulfur dioxide. From this, hydrogen, oxygen and sulfuric acid can be produced in a hybrid thermal-electrical circuit, ”explains Sattler.
“Copper mines need both hydrogen and oxygen. You need the oxygen first to roast the ore because it is high in sulfur. When you roast, you convert the ore to copper oxide and then use hydrogen to reduce the copper oxide to copper. The copper ore contains the sulfur that you use to make the sulfuric acid, which you use to leach out the other impurities in the minerals. “
Win-win: Producing solar hydrogen and oxygen on site in the copper mine
Currently, due to the cost of providing hydrogen and oxygen to the mines and the cost of fossil fuels for heat for the required chemical reactions, copper mines only produce copper oxide on site and then have to pass the copper oxide on to another company for refinement into copper, so the mines lose the production of the valuable end product copper.
“This HyS technology will be able to do that on site. So anyone who can produce hydrogen and oxygen at the same location as the copper mine is independent of an external company that has to produce the gases elsewhere in order to refine the copper oxide. That increases your costs. ”Sattler explained.
“We have developed a system that allows us to incorporate HyS into copper processing,” added Jafarian.
“That is why we are working with DLR on integrating the HyS into copper processing in order to produce hydrogen and oxygen in situ for copper processing and mining. This enables us to supply copper processors with hydrogen and oxygen for around nine to ten months a year. In economic terms, it is even comparable to the most modern technologies for producing hydrogen with fossil fuels. “
As soon as solar hydrogen is produced as part of an industrial service for the copper mining industry, the benchmark for its mass production as a stand-alone energy carrier with many applications in sectors that are difficult to decarbonize, such as heavy haulage such as cargo shipping, is established.
Jafarian noted that BHP Group, the world’s largest mining company with large holdings in Australia, unveiled its green hydrogen plan last month. “If this giant wants green hydrogen, this is the fastest way for me and Australia has all the infrastructure, skills and resources to do it,” he said.
Australia is testing this sulfur-based solar thermal chemical technology
University of Adelaide solar research engineer Alfonso Chinnici agrees that Australia is the place where HyS research could first be commercialized. A private-public initiative to decarbonise heavy industry via a Cooperative Research Center (CRC) has started there and the HyS technology is about to be tested. Chinnici, who is also involved in the Australian HiltCRC program, stated that DLR is about to send a receiver to Australia for a small pilot test in the laboratory.
“And then with an on-sun test – outdoors with a solar heliostat field – probably in 2022. So it won’t take five or ten years,” he said.
“I think DLR has a pretty accelerated program because it doesn’t start from scratch; Christian’s group has generated a lot of know-how at DLR. I think you’ve been working on developing the idea and the receiver for about five years. So the background of the technology itself is already done. “
According to Jafarian, further improvements to this advanced solar technology are being tested: “We are also working on another technology to improve the way we bring solar energy into the system. We are working on a kind of solar receiver, which we call the Solar Cavity Bubble Receiver. We did a technology assessment and found that there was also potential to further reduce costs, ”he said.
“Current assessments are mainly based on the technologies developed at DLR. But we are also working in parallel on a technology that we are developing and which, in our opinion, also has great potential to further reduce the costs of hydrogen production for the copper industry. “
Globally, the copper industry must ramp up quickly to meet the growing demand from the growth of clean energy technologies, while meeting new climate goals that require fossil fuel substitution. With Bloomberg forecasting an annual supply shortfall of 4.7 million tons of copper by 2030, economical methods of refining copper that can use clean energy to provide heat are required. Australian copper companies understand this need.
As Chinnici noted, “What we are learning from working with the mining and mineral industries here is that if they have to do something, they will do it.”