Howard J. Herzog

Lifetime of carbon capture and storage as a climate-change mitigation technology

In carbon capture and storage (CCS), CO2 is captured at power plants and then injected underground into reservoirs like deep saline aquifers for long-term storage. While CCS may be critical for the continued use of fossil fuels in a carbon-constrained world, the deployment of CCS has been hindered by uncertainty in geologic storage capacities and sustainable injection rates, which has contributed to the absence of concerted government policy. Here, we clarify the potential of CCS to mitigate emissions in the United States by developing a storage-capacity supply curve that, unlike current large-scale capacity estimates, is derived from the fluid mechanics of CO2 injection and trapping and incorporates injection-rate constraints. We show that storage supply is a dynamic quantity that grows with the duration of CCS, and we interpret the lifetime of CCS as the time for which the storage supply curve exceeds the storage demand curve from CO2 production. We show that in the United States, if CO2 production from power generation continues to rise at recent rates, then CCS can store enough CO2 to stabilize emissions at current levels for at least 100 y. This result suggests that the large-scale implementation of CCS is a geologically viable climate-change mitigation option in the United States over the next century.

Carbon Capture and Storage from Fossil Fuel Use

Glossary Carbon sequestration: capture and secure storage of carbon that would otherwise be emitted to or remain in the atmosphere. Carbon sources: for this chapter, we are concerned with large stationary sources of CO2, e.g. fossil fueled power plants, cement manufacturing, ammonia production, iron and non-ferrous metal smelters, industrial boilers, refineries, natural gas wells. Carbon capture: the separation and entrapment of CO2 from large stationary sources. CO2 storage: the injection of CO2 into geologic or oceanic reservoirs for timescales of centuries or longer.

Economic and energetic analysis of capturing CO2 from ambient air

Capturing carbon dioxide from the atmosphere (“air capture”) in an industrial process has been proposed as an option for stabilizing global CO2 concentrations. Published analyses suggest these air capture systems may cost a few hundred dollars per tonne of CO2, making it cost competitive with mainstream CO2 mitigation options like renewable energy, nuclear power, and carbon dioxide capture and storage from large CO2 emitting point sources. We investigate the thermodynamic efficiencies of commercial separation systems as well as trace gas removal systems to better understand and constrain the energy requirements and costs of these air capture systems. Our empirical analyses of operating commercial processes suggest that the energetic and financial costs of capturing CO2 from the air are likely to have been underestimated. Specifically, our analysis of existing gas separation systems suggests that, unless air capture significantly outperforms these systems, it is likely to require more than 400 kJ of work per mole of CO2, requiring it to be powered by CO2-neutral power sources in order to be CO2 negative. We estimate that total system costs of an air capture system will be on the order of

Modeling the release of CO2 in the deep ocean

1,000 per tonne of CO2, based on experience with as-built large-scale trace gas removal systems.

Capture-ready coal plants—Options, technologies and economics

In order to better understand the mechanics of ocean disposal of CO2 captured from power plants, a comprehensive plume model was developed to simulate the dynamic, near-field behavior of CO2 released in the water column as either a buoyant liquid or vapor. The key design variables in the model that can be controlled are: (1) release depth, zo (2) number of diffuser ports, N, and (3) initial bubble or droplet radius, ro. For a CO2 stream from a 500 MW power plant with 100% capture and zo=500 m, N=10, and ro=1 cm, the model predicts that the plume will rise less than 100 m. This will result in CO2 enrichment at depths greater than 400 m. Detailed predictions of local CO2 concentrations near the plume are presented and discussed. The issue of the residence time of the captured CO2 in the ocean is also addressed. We estimate a typical residence time of less than 50 years for releases of CO2 less than 500 m deep and, for a release depth of 1000 m, a residence time from 200 to 300 years. These residence times may be increased by releasing in areas of downwelling or by forming solid CO2-hydrates, which can sink to the ocean floor.

Impacts of ocean CO2 disposal on marine life: I. A toxicological assessment integrating constant‐concentration laboratory assay data with variable‐concentration field exposure

This paper summarizes the spectrum of options that can be employed during the initial design and construction of pulverized coal (PC), and integrated gasification and combined cycle (IGCC) plants to reduce the capital costs and energy losses associated with retrofitting for CO2 capture at some later time in the future. It also estimates lifetime (40 year) net present value (NPV) costs of plants with differing levels of pre-investment for CO2 capture under a wide range of CO2 price scenarios. Three scenarios are evaluated—a baseline supercritical PC plant, a baseline IGCC plant and an IGCC plant with pre-investment for capture. This analysis evaluates each technology option under a range of CO2 price scenarios and determines the optimum year of retrofit, if any. The results of the analysis show that a baseline PC plant is the most economical choice under low CO2 prices, and IGCC plants are preferable at higher CO2 prices (e.g., an initial price of about

ECONOMIC EVALUATION OF CO2 STORAGE AND SINK ENHANCEMENT OPTIONS

22/t CO2 starting in 2015 and growing at 2%/year). Little difference is seen in the lifetime NPV costs between the IGCC plants with and without pre-investment for CO2 capture. This paper also examines the impact of technology choice on lifetime CO2 emissions. The difference in lifetime emissions become significant only under mid-estimate CO2 price scenarios (roughly between

Environmental impacts of ocean disposal of CO2

20 and 40/t CO2) where IGCC plants will retrofit sooner than a PC plant.

How aware is the public of carbon capture and storage

Feasibility studies suggest that the concept of capturing CO2 from fossil fuel power plants and discharging it to the deep ocean could help reduce atmospheric CO2 concentrations. However, the local reduction in seawater pH near the point of injection is a potential environmental impact. Data from the literature reporting on toxicity of reduced pH to marine organisms potentially affected by such a plume were combined into a model expressing mortality as a function of pH and exposure time. Since organisms exposed to real plumes would experience a time‐varying pH, methods to account for a variable exposure were reviewed and a new method developed based on the concept of isomortality. In part II of this paper, the method is combined with a random‐walk model describing the transport of passive organisms through a low pH plume leading to a Monte‐Carlo‐like risk assessment which is applied to several candidate CO2 injection scenarios.

Stakeholder Attitudes on Carbon Capture and Storage - an international comparison

This project developed life-cycle costs for the major technologies and practices under development for CO{sub 2} storage and sink enhancement. The technologies evaluated included options for storing captured CO{sub 2} in active oil reservoirs, depleted oil and gas reservoirs, deep aquifers, coal beds, and oceans, as well as the enhancement of carbon sequestration in forests and croplands. The capture costs for a nominal 500 MW{sub e} integrated gasification combined cycle plant from an earlier study were combined with the storage costs from this study to allow comparison among capture and storage approaches as well as sink enhancements.