Methods for evaluating the potential to power industrial processes with geospatially and temporally varying renewable energy resources

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2018-12

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Aminfard, Sam

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Abstract

One pathway to decarbonizing global energy systems is to replace fossil fuels with renewable forms of energy such as solar and wind. However, the geo-spatially and temporally variant nature of these energy sources makes their integration into conventional electric grids a technically and economically onerous effort. By identifying processes compatible with intermittent renewable energy sources, energy-intensive industries can displace the need for fossil fuels globally while circumventing many of the barriers to integrating these energy sources into electricity grids. This dissertation assessed the techno-economic feasibility of utilizing wind and solar resources to meet the energy demands of desalination facilities, as well as electrified pneumatic control systems at oil and gas production sites. The first study in this dissertation developed a method for assessing the technical and economic viability of using these renewable forms of energy to power brackish groundwater desalination facilities. The method relies on a multi-layered, spatial model that incorporated multiple variables such as depth of water resource, salinity levels, magnitude of local renewable energy resources, distance to water infrastructure, and, for comparative purposes, the local price of water. To illustrate this method, it was applied to 1,445 site locations on state of Texas lands owned by the General Land Office that overlay brackish aquifer resources. Using this approach, 193 potentially economically viable sites were identified that have estimated renewable desalination water production costs lower than local municipal water prices. The results of this analysis showed that using wind to power a desalination facility is economically preferable to solar power at 145 of the 193 sites; solar was preferable at the remaining 48 sites. Solar and wind resources are both abundant in Texas; however, the particularly high capacity factors for wind across much of the state helps wind deliver electricity costs that are often lower than those provided by solar. The second study sought to assess the technical and economic viability of using variable renewable energy to power electrified well site pneumatic control systems. Conventional pneumatic control systems vent methane-containing well gas during their operation. Electrifying these systems can avoid the venting of methane, which is a potent greenhouse gas. Under this study, two different strategies were considered for replacing pneumatic systems powered by well gas. One option is to exchange all components controllers, actuators and pumps to equipment that is directly powered by electricity. This scheme is referred to as the electric configuration. The second option, referred to as the electro-pneumatic configuration, is to retain the pneumatic system, but power its components with instrument air, which is ambient air that has been compressed by an electrically-driven compressor. This option thus replaces the emission of methane with ambient air. First, an energy simulator was developed to serve as a screening tool to determine the temporally-varying power demands incurred by switching a standard pneumatic system to an electrified one. The tool uses a comprehensive set of user inputs to simulate site-specific single-day power loads for the electric and electro-pneumatic configurations of well site control systems based on specifications from controllers, valve actuators, and chemical pumps commonly used at well sites. To assess the viability of meeting well site power loads with intermittent renewable energy, electric and electro-pneumatic systems were modeled with solar photovoltaic (PV) power generation and electric battery storage during one year of typical conditions at sites located near Midland, Texas (Permian Basin), Nacogdoches, Texas (Haynesville Shale), and Edmonton, Canada (Kaybob-Duvernay Formation) using a time-resolved energy flow model. The electro-pneumatic model included a thermodynamic analysis to simulate storage of energy as compressed air in addition to electric battery storage. Of the two configurations, the all-electric option was found to be cheaper than the electro-pneumatic option while potentially supplying power to the system more reliably. An electric battery with a capacity of 1-2 kWh can deliver 100% reliability under typical meteorological conditions for the all-electric configuration utilizing a 200-250 W solar panel for sites located in Texas, resulting in a methane abatement cost of $190-$200 per ton of avoided methane emissions. The solar-powered electric system could potentially be employed at a well site in Alberta, Canada. However, because its solar resource is less abundant than in Texas, ensuring a high level of reliability would be 14% more costly. Other forms of on-site power generation such as geothermal energy might be more viable, or could possibly be used in conjunction with solar PV to ensure reliable operation during the winter when insolation levels are considerably lower. The higher power demands required by the electric air compressor in the electro-pneumatic design require larger PV generation capacity to achieve high levels of reliability. However, if the electro-pneumatic design is implemented, well-gas could potentially be used as a back-up to the air compressor to achieve equivalent reliability of the systems currently used in the field without the PV/battery system providing meet 100% of energy demands. While it is technically and economically feasible for electro-pneumatic systems to utilize compressed air tanks as the primary energy storage medium, electric batteries are the more viable option due to their energy density, stability and relative affordability. For new well sites, the all-electric option will be more cost-effective. However, if electrification is performed as a retrofit, the electro-pneumatic configuration might be more cost effective if installing the electric system requires more than a week of downtime. Together, these studies illustrate methods that can be used to assess the techno-economic viability of integrating variable forms of renewable energy into carbon and energy-intensive industries.

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