SunGas is the name we use for the desirable product of solar methane reforming.
The reforming of natural gas or biogas is either done with steam or with CO2. The reforming reactions are endothermic, i.e. they require energy to happen. In the EZKlein SunGas process this energy is solar energy. The solar energy “loads up” the resulting molecules and they have a higher calorific value than before, ~25% more saleable mmbtu’s. When the solar reformed gas, “SunGas,” is burned, the solar energy is released. If the SunGas is used for chemical processes (for example, in refineries or in production of liquid fuel), the added solar energy component will be in the new chemicals.
The reforming reactions are shown (1) and (2):
CH4+H2O=>3H2+CO DH=206.2 kJ/mol (1)
CH4+CO2=>2H2+2CO DH=247.3 kJ/mol (2)
Making it happen in the sun
For people from the catalyst industry or from the petrochemical industry it is not obvious what the challenges and possibilities are to perform natural gas reforming with solar energy.
Traditional catalyst systems for reforming usually contain Nickel. The catalysts require a slow ramp-up and ramp down temperature to stay intact. By definition, this cannot be expected from solar-based systems that ramp up and down daily and might typically experience intermittent cloud passages during any given day.
A different catalyst system is therefore developed. Using Ruthenium or Rhodium as the basis for the catalyst system has proven good for the solar environment. Ruthenium is currently priced at ~$100/ounce and Rhodium at ~$1500/ounce.
A Ruthenium catalyst system is highly efficient at high temperature and prevents carbon depositions on the catalyst surfaces. It also enables low (H2O and/or CO2)/CH4 ratios which is crucial for the solar reforming reaction where energy efficiency is key.
The solar reformer receiver/reactor is located on top of a tower. The reformer has an aperture which allows solar radiation to enter. The aperture is covered by a quartz window. Behind the window is the radiation absorbing surface, which is also the reaction surface for the catalytic reforming reaction. The receiver’s absorber surface is designed to both optimize heat transfer between the concentrated solar radiation and to facilitate the reforming reaction.
Pipes convey the reactants and the resulting SunGas to and from the tower. Heat conservation is a main focus for the operation as well as the ease of use.
Solar reforming: History and future
Solar reforming of methane has been analyzed and researched by research institutes across the globe since the 80’s. Some projects have been focused on the theoretical side and others have been tested in sun or in a sun simulator. All projects have been run by research institutes or universities, funded mostly by national research grants, such as the European Commission’s framework programs (FP5, FP6, and FP7). Though each project has furthered the knowledge of solar methane reforming, no one has yet built an industrial prototype.
EZKlein is focused on changing this pattern to bring solar methane reforming from the laboratory into accepted industrial application. EZKlein has filed its own IP on reforming of hydrocarbon gas. This IP in combination with the known state of the art brings us to the EZKlein SunGas plant design.
Uses for SunGas
SunGas can be used in a number of ways.
If SunGas is used as fuel for conventional combined cycle power plants the solar energy stored in the gas will be converted to electricity with an efficiency of up to 60%, this is the most efficient use of solar energy currently imaginable.
SunGas can also be used as a component in the manufacturing of liquid fuel such as methanol or biodiesel.
SunGas can go through additional reactions to maximize the hydrogen content in the gas. The hydrogen can be used for fuel for example in cars, trucks or trains.
It is also possible to not use the SunGas itself but to only use the solar heat stored in it. In a process call Methanation a second catalyst is used to drive the reaction backwards, an exothermic step, releasing the stored solar energy. The methane and CO2 can go back to the SunGas plant and be used again to create SunGas.
To view a short video explaining SunGas, click here.