Pitch
Renewable (and perhaps nuclear) energy sources can best replace fossil sources by developing liquid renewable fuels as energy carriers.
Description
Summary
California currently derives the majority (about 60%) of its electric power from natural gas. This is a relatively clean fuel, but even so electric power generation is a major contributor to GHG pollution. The proposed strategy aims to eliminate this pollution in two stages: First, continue to use natural gas as an energy source, but decarbonize it by converting to a carbon-free fuel while sequestering the carbon-bearing residue; Second, replace natural gas as an energy source with renewable (and perhaps nuclear) sources. Investment in infrastructure to enable the first stage also enables the second stage. An initial analysis of this strategy has been carried out. Further studies to evaluate costs and feasibility (technical and financial) are needed. MIT alumni can help to carry out this analysis.
What actions do you propose?
California currently derives the majority (about 60%) of its electric power from natural gas. This is a relatively clean fuel, but even so electric power generation is a major contributor to GHG pollution. The proposed strategy aims to eliminate this pollution in two stages:
- First, continue to use natural gas as an energy source, but decarbonize it by converting to a carbon-free fuel while sequestering the carbon-bearing residue;
- Second, replace natural gas as an energy source with renewable (and perhaps nuclear) sources.
Investment in infrastructure to enable the first stage also enables the second stage. An initial analysis of this strategy has been carried out, reported in three papers cited below. Further studies to evaluate costs and feasibility (technical and financial) are needed. MIT alumni can help to carry out this analysis.
Natural gas can be converted to a carbon-free fuel such as hydrogen or ammonia for use in the electric power sector. To attain commercial viability we must retain as much of the existing infrastructure as possible, with minimal modification. For this reason ammonia is preferred to hydrogen as an energy carrier [see endnote].
A two-step strategy can completely decarbonize the electric power sector by 2100, with significant near-term reduction in carbon footprint to help meet California’s 2050 goals. The first step is to continue to use natural gas as an energy source, but to de-carbonize it by conversion to ammonia with carbon capture and sequestration (CCS). The second step is to cease entirely using natural gas as an energy source, replacing it with renewable (and perhaps nuclear) sources. In this second step, the renewable fuel ammonia would continue to be used as an energy carrier and storage medium. Note that the second phase depends on the infrastructure modifications done in the first. These make it commercially viable for renewable fuels to be introduced into the energy system.
In the first phase, natural gas is decarbonized by converting it to a carbon-free fuel and capturing and sequestering the carbon. This is done at the sites where natural gas is produced, distributed throughout Western North America from Alberta to Texas. Very large ammonia production plants will be located near the well-heads in the gas production fields. As a by-product of ammonia production, a carbon dioxide stream results. This will be re-injected into nearby mature gas fields (exploited in former decades, now nearly depleted). In effect, CH4 has been taken out of the ground, 2H2 stripped off and replaced with O2, and the resulting CO2 returned underground. The net change is merely to replace one gas with another. The same underground storage chamber which has proven its geologic stability by holding the first gas for millions of years can be relied on to do the same for the second. The carbon-free liquid fuel NH3 is produced. This is transported via pipeline to California, where it is distributed to power plants. Perhaps 10 large plants for production of NH3 with CCS would supply 1000 power plants. It is reasonable to expect that concentrating CCS at a few locations yields economies of scale to offset costs incurred for infrastructure modification. This is required to enable transport, storage, and utilization of ammonia in place of natural gas.
An important investment goal in the first phase is to build an infrastructure that can support the second phase: the transition to 100% renewable (and perhaps nuclear) energy by the end of the century. In this second phase, ammonia serves as an energy storage medium as well as an energy carrier. In its storage role it definitively solves the problem of variable (both cyclic and stochastic) renewable energy sources. As an energy carrier, ammonia can be conveniently shipped not only over land but also over oceans. This makes it an essential complement to electric power as a medium for global energy trade. Ammonia will have a role not only at the transmission level, but also at the distribution level, as its use with distributed generation enables combined cooling heat and power (CCHP) district services with their attendant extremely high energy utilization efficiencies.
Three papers which develop these ideas in more detail are listed below. Further studies to evaluate costs and feasibility (technical and financial) are needed. MIT alumni can help to carry out this analysis.
References
1. W. L. Ahlgren, “The Dual-Fuel Strategy: An Energy Transition Plan.” Proceedings of the IEEE 100, 3001-3052 (2012).
2. W. L. Ahlgren, “Fuel Power Density.” Journal of Pressure Vessel Technology 134, 054504 (2012).
3. W. L. Ahlgren, “Planning for Hundred-fold Increase in Global Ammonia Production.” Ammonia Plant Safety and Related Facilities, Vol. 54, pp. 81-90 (American Institute of Chemical Engineers, 2013).
ENDNOTE
Ammonia can serve as fuel for electric power generation and other large stationary applications, and in some mobile (transportation) applications. Several very significant transportation applications will require carbon-based energy carriers. To qualify as renewable fuels, these must use atmospheric carbon dioxide as their feedstock. These liquid renewable fuels include methanol, dimethyl ether (DME), and methyl-derived fuels (MDFs, which are relatively complex gasoline-like substances). Possibly, renewable methane (e.g. biogas) might also find a market niche where existing infrastructure favors gaseous over liquid fuels. Please to the reference documents cited above for further information.
By:
Pacific Rim
