(703e) Southwest USA Regional CO2 Utilisation Pathways

Global energy demand continues to rise, creating pressing challenges for both resource availability and environmental management. A major concern is the widespread emission of carbon dioxide (CO2), which holds potential as an underexploited resource for creating valuable chemicals and fuels. Carbon capture and utilization not only helps in conversion of CO2 to marketable commodities such as methanol, biodiesel and concrete, but also help in net CO2 mitigation. CO2 concrete curing provides a with a potential solution for its permanent conversion to useful mineral. The CO2 curing can drastically reduce the curing time from weeks to few days, to achieve same compressive strength. Up to 40 kg of CO2 can be utilized for curing a ton of concrete. CO2 concrete curing can potentially utilize 50-100 million tons of CO2 per year in USA. Similarly, algae cultivation holds promise for transforming captured CO2 into biomass rich in lipids, which can then be processed into biodiesel. When coupled with methanol synthesis via CO2 hydrogenation, this approach can yield two highly sought-after fuels, offering the dual benefit of CO2 utilization while generating revenue streams. However, often the CO2 utilization industrial sites are not co-located with CO2 stream sites. The objective of this work is to establish how an efficient infrastructure for regional decarbonization efforts by connecting CO2 sources with utilization options. The I-WEST (intermountain-West) region in the USA (which includes New Mexico, Arizona, Colorado, Utah, Montana, and Wyoming) contributes 17.5% of the total energy production of the USA, and generates 362 million tons of CO2 annually. I-WEST can emerge as the leader in CO2 utilization to profitable products for local use and export to other regions. We have utilized the LANL developed SimCCS tool to optimally locate the CO2 utilization industry with CO2 sources. SimCCS tool optimizes the CO2 transport routing by integrating factors across the carbon capture and sequestration value chain.

We first analyzed the performance of CO2 concrete curing, as a function of feed gas composition, flowrate, residence time and humidity. One of the important parameters to characterize the performance of concrete is the compressive strength, and accordingly the net CO2 intake (carbonation) can be predicted. Predominantly, the CO2 reacts with calcium oxide (CaO) present in cement to generate calcium carbonate (CaCO₃). Initially the rate of carbonation is much faster and decreases gradually with time. This is probably because of the fresh CaCO₃ formed blocks the CaO ions to CO2 exposure, resulting in reduced rate of carbonation with time. With increase in the CO2 concentration, the net carbonation increases due to the higher CO2 exposure. Use of flue gas from natural gas combined cycle for concrete curing increase the curing time by 50%, compared to use of pure CO2. The relative humidity also plays a dominant role on net carbonation. The water molecules help the CO2 to penetrate through the CaCO₃ molecules, thereby increasing the CO2 exposure to CaO. This helps in improving the reaction kinetics. We also evaluated the effect of regional factor in deployment of CO2 based concrete curing, and concrete curing can help in mitigating around 0.75-1.22 million ton of CO2 per year in I-West. The cost of CO2 cured concrete with compressive strength of 17 MPa (residential grade) was calculated to be ~100-105 $/ton, while the costs of curing 28 MPa (commercial grade) compressive strength concrete was ~112-129 $/ton.

Algae rely on solar energy, impaired water source including brackish and sea water, and can directly utilize CO2 from flue gas. Algae, can utilize around 1.8 kg_CO2/kg_algae, and has potential to utilize up to 80% of CO2 either from flue gas or pure stream. The CO2 is injected into the algal pond and in presence of sunlight it gets converted into algae. The water stream leaving the algal pond contains algae with needs to be further processed for conversion into useful chemicals. Biodiesel can be generated from algal feedstock. This a sequential arrangement of cultivation, harvesting, extraction, reaction, and separation stages, along with the incorporation of buffer storage and recycle streams, creates a robust and efficient production system for biodiesel production. The algae cultivation medium maintains relatively dilute algae concentrations of 1-2 g/L. Following cultivation, the algal biomass concentration is increased to 100-200 g/L via harvesting and is finally dried in a drum drier. The dried algal biomass is then passed through oil press for lipid extraction. Lipid is later used for biodiesel production. Transesterification reaction is used to convert the lipids into biodiesel in a continuously stirred tank reactor. Methanol is introduced as a key feedstock for Transesterification reaction for biodiesel production. We modeled the algae and methanol production for CO2 utilization which later was be converted to biodiesel. Biodiesel diesel production requires 13 kg of algae per gallon of biodiesel. With 1.8 kg of CO2 utilization per kg of algae, then net CO2 utilization potential for biodiesel from algae is around 23.4 kg/gal. In addition, algae biodiesel requires methanol for transesterification of lipid. The net CO2 mitigation potential for methanol production is 1.38 kg/kg_methanol. Biodiesel requires around 0.45 kg of methanol/gal. Therefore, biodiesel can additionally utilize 0.6 kg of CO2 per gal. The net CO2 utilization potential for biodiesel production is 24 kg/gal. We considered three sizes of the biodiesel production plant: small (5 million gal/year), medium (50 million gal/year) and large range (150 million gal/year). With small scale biodiesel plant, around 0.12 million ton of CO2 can be utilized, while the large-scale biodiesel plant around 3.6 million ton of CO2 can be utilized. The cost of biodiesel production was calculated to be 12.4 $/gal for southern I-WEST state for New Mexico and Arizona due to close proximity with CO2 source and good solar radiation. While northern I-WEST state received low solar radiation resulting in a high biodiesel cost of >30 $/gal. Additionally by considering CO2 utilization tax credit and selling of the biodiesel byproducts, the cost of biodiesel for southern I-WEST can be reduced by up to 80%.