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Negative Emissions Technologies and Reliable Sequestration: A Research Agenda (2019)

Chapter: Appendix E: Carbon Mineralization

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Suggested Citation:"Appendix E: Carbon Mineralization." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"Appendix E: Carbon Mineralization." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Suggested Citation:"Appendix E: Carbon Mineralization." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Page 481
Suggested Citation:"Appendix E: Carbon Mineralization." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Page 482
Suggested Citation:"Appendix E: Carbon Mineralization." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Page 483
Suggested Citation:"Appendix E: Carbon Mineralization." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Page 484
Suggested Citation:"Appendix E: Carbon Mineralization." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Page 485
Suggested Citation:"Appendix E: Carbon Mineralization." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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Page 486

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APPENDIX E Carbon Mineralization ENERGY BUDGET FOR “GENERIC” EX SITU MINERAL CARBONATION This section focuses on energy use in a general general ex situ mineral carbonation process, where the energetic and material inputs and outputs will be examined for the following steps: extraction, reactant transport, pre-processing, chemical conversion, post-processing, product transport, and disposal or reuse. Because there are a variety of alkalinity sources (rocks and industrial waste products) and a number of possible reaction conditions (e.g., elevated temperature and pressure), all calculations are pre- sented first generally and then applied to a case involving olivine carbonation at 155 and 100 bar.1 A general scheme for this process is provided in Figure E.1. Extraction, Reactant Transport, and Pre-Processing Alkalinity stored in naturally occurring silicate deposits can be made available for on- site carbonation through mining, separating, crushing to size, and delivery via truck or rail depending on distance to source.2 Because the drilling, blasting, excavation, and hauling activities associated with mineral extraction vary based on quarry location, the energetic consumption is expected to fall between similar low- and high-intensity extractions (97.0 MJ/t and 360.9 MJ/t) (Kirchofer et al., 2012). Based on electricity sourced from coal and natural gas, this results emissions of 0.02-0.08 t CO2/t CO2 pro- cessed and 0.013-0.05 t CO2/t CO2 processed, respectively.3 An additional source of alkalinity exists in the form of industrial waste by-products (e.g., cement kiln dust (CKD), steel slag, and coal fly ash (FA). Carbonation of these 1  This is in keeping with the development of ex situ mineral carbonation, which started with a single step, high-temperature, high-P(CO2) reaction in an aqueous medium with naturally occurring minerals. (contacting CO2 with dry rock was quickly shown not to work). Such processes were envisioned to use pure CO2 gas. More recently, multistage extraction processes have been put forward. Some produce Mg(OH)2 which can be reacted at lower (and possibly atmospheric) P(CO2). The distinction is important. If direct single step mineral carbonation is used then a gas purification step is needed. If a multistage extraction process is used, then it may be possible to avoid pre-gas purification. 2  It is assumed that rail transport is required for hauls more than 60 miles (one-way). 3  Assumes a material loss of 1 percent. 479

APPENDIX E FIGURE E.1  Material and energy flows for an ex situ mineral carbonation process based on a carbonation rate of 1000 tCO2 /day using and an olivine feedstock at 155 and 100 bar. SOURCE: Kirchofer et al., 2012. waste-products represents an opportunity for reliable carbon storage while also treat- ing industrial waste that would otherwise require disposal. Additionally, waste from industrial manufacturing may fill niche scenarios whereby transport of crushed olivine or serpentine proves cost-prohibitive due to distance considerations. The energy required in handling and collecting of industrial alkalinity can be approximated as 50 percent of that outlined for the natural mineral extraction case above (Kirchofer et al., 2012). Transport can be considered invariant to source and is reported as the energy re- quired to move 1 ton of reactant material over 1 mile. Using a standard diesel conver- sion of 2.68 kg CO2 per liter and assuming a 3 percent material loss during transport, transport via truck and rail freight yields 0.11 kg CO2 and 0.03 kg CO2 per ton-mile, respectively. Alternatively, in some cases ex situ mineral carbonation could be done at the source of solid reactants (mine tailings, quarry, alkaline waste site) with very low transport costs (Moosdorf et al., 2014), for example by building direct air capture plants at the source. In the final step before chemical conversion, the feedstock must be ground to reduce the input particle size (ca. 10,000 microns) to an output size suitable for efficient conversion (4 to 2000 microns). The electric work for grinding is a function of the 480

Appendix E 2 Negative Emissions Technologies and Reliable Sequestration: A Research Agenda 2 The electric work for grinding is offunction Technologies andpassing size ofgrain size A Research Agenda 80 percent passing size Emissions of the grain size (I)Reliable Sequestration: (O), in Negative a the feedstock 80 percent and desired the feedstock grain size (I) and desired grain size (O), in microns: 1 1 microns: 𝑊𝑊 = 10𝑊𝑊' − 𝑂𝑂 𝐼𝐼 The electric work for grinding is a function of the 80 percent passing size of the feedstock grain size (I) and desired grain size (O), in microns: # 1 1 where Wi is theWi is thework index4 for the#4 = 10𝑊𝑊'material (Gupta et al., 2006). Using the oliv-index 𝑊𝑊 for the − 𝑂𝑂 value, this corresponds to 2.0 and 1.0 kgCO2/t using electricity𝐼𝐼kgCO2/t from coal and natural gas fired where Bond’s Bond’s work index material (Gupta et al., 2006). Using the olivine work ine work index value, this corresponds to 2.0 and 1.0 sourced using electricity sourced plants, respectively. where Wfrom coal and natural gas4firedthe material (Gupta et al., 2006). Using the olivine work index is the Bond’s work index for plants, respectively. i value, this corresponds to 2.0 and 1.0 kgCO2/t using electricity sourced from coal and natural gas fired plants, respectively. Chemical Conversion Chemical Conversion In the conversion of carbon dioxide, alkalinity must be liberated via dissolution of of the the conversion of carbon dioxide, alkalinity must be liberated via dissolution the pre- Chemical Conversion processed feedstock, followed by heating and mixing of andreactants tothe reactants tostable carbonate. pre-processed feedstock, followed by heating the mixing of precipitate the precipi- Water consumption during this process is consumption during this process is estimated as 6.7al., 2012) estimated as 6.7 tH2O / tCO2 processed (Kirchofer et In the conversion of carbonWater alkalinity must be liberated via dissolution of the pre- tate the stable carbonate. dioxide, less 0.73 tHO / tCO 2 processed recycled from downstream processing, yielding a net water consumption tH2 2O/tCO2 followed by heating et mixing of the reactants to precipitate the stable carbonate. processed feedstock, processed (Kirchoferandal., 2012) less 0.73 tH2O/tCO2 processed recycled of 5.9 tH2O/tCO2 processed. Energy consumption to deliver and recycle water for chemical conversion is from downstream processing, yielding a net 6.7 tH consumption of 5.9 tH2O/tCO Water consumption during this process is estimated as water 2O / tCO2 processed (Kirchofer2et al., 2012) estimated at 4.66 MJ/tCO2 processed, resulting in 1.0 and 0.6 kgCO2/tCO2 processed using power sourced less 0.73processed.2 Energy consumption to deliver and recycle water for chemical water consumption tH2O/tCO processed recycled from downstream processing, yielding a net conversion from coal and natural gas, respectively. of 5.9 tHisO/tCO2 processed. Energy consumption resulting in 1.0 and 0.6 kgCO /tCO processed 2 estimated at 4.66 MJ/tCO processed, to deliver and recycle water for chemical conversion is The energy required to mix reactants is determined from the mixing power, Pm: The energy required to mix reactants determined 𝐷𝐷 𝑃𝑃, = 𝑁𝑁. 𝜌𝜌𝑁𝑁 0 2 2 2 2 estimated at 4.66 MJ/tCO2 processed, resulting in 1.0 gas, 0.6 kgCO2/tCO2 processed using power sourced using power sourced from coal and natural and respectively. from coal and natural gas, respectively. The energy required to mix reactants is is determined from the mixing power,:Pm: from the mixing power, Pm 𝑃𝑃, = 𝑁𝑁. 𝜌𝜌𝑁𝑁 𝐷𝐷 2 where Np is the power number (3.75 in this case), ρ is the0mixture density, N represents the impeller speed (0.6 rps), and D represents the impeller diameter, taken as one-third of the reactor tank diameter.5 The total energy is thus contingent on the reaction speed, where the rate of CO2 carbonation is considered power number (3.75 in this case), ρ is the mixture density, N represents the impeller where Np is the N is the power number (3.75 in this case), ρ is the mixture density, N represents speed limiting.whereit is assumed that the rate of carbonation is dependent on the alkaline feedstock dissolution Here p (0.6 rps), and D represents the impeller diameter, taken as one-third of the reactor tankas one- 5 The diameter. and not on the mass transfer (0.6 rps), and D represents the impeller diameter, taken the impeller speed of CO2 into the liquid phase. thus contingent on diameter.5 speed, where the rate of CO2 carbonation is considered total energy isof the reactor tank the reactionThe total energy is thus contingent on the reaction third input is required to bring the reactants (including water) up to reaction temperature plus any Heat limiting. Here it is assumed that the rate of carbonation is dependent on the alkaline feedstock dissolution additional energy to compensate for heat loss from theconsidered limiting. Here it is assumed from the speed, where the rate of CO2 carbonation is reactor vessels. The former is calculated and not on the mass transfer of CO2 into the liquid phase. specific that the rate of carbonation ischange required: alkaline feedstock dissolution and heat capacity and temperature dependent on the 𝑞𝑞 = 𝑚𝑚𝐶𝐶 ∆𝑇𝑇 Heat input is required to bring the reactants (including water) up to reaction temperature plus any specific heat capacity and temperature change required:. additional energy tomass transfer ofheat loss fromliquid phase. not on the compensate for CO2 into the the reactor vessels. The former is calculated from the 𝑞𝑞 = 𝑚𝑚𝐶𝐶. ∆𝑇𝑇 Heat input is required to bring the reactants (including water) up to reaction tempera- loss is calculated assuming that the heat flux (𝜙𝜙9 ) from the stainless-steel tank is equal to heat flux to the ture plus any requirement is effectively lowered because relevant reactions are exothermic.6 Heat However, this heating additional energy to compensate for heat loss from the reactor vessels. The former is calculated from the specific heat capacity and temperature change loss is calculated assuming that the heat flux (𝜙𝜙9 ) from the stainless-steel tank is equal to heat flux to the surroundings, and is calculated from: required: 𝜙𝜙 = ℎ 𝑇𝑇< − 𝑇𝑇= + 𝜀𝜀@ 𝜎𝜎(𝑇𝑇< − 𝑇𝑇= ) However, this heating requirement is effectively lowered because relevant reactions are exothermic.6 Heat C C surroundings, and is calculated from: 9 4  W = 12.00, 13.49, 13.39, 11.31, and 11.61 kWh per tonne for SS, CKD, FA, olivine and serpentine, where h and (2) for high-pressure conversion= ℎto𝑇𝑇100 bar, 2m-2diameter,− 𝑇𝑇case), 𝜀𝜀@ is the emissivity for the tank i represents the convection coefficient (20 𝑇𝑇 + 𝜀𝜀K𝜎𝜎(𝑇𝑇 Cthis m3)volume). 𝜙𝜙9 (up < − W m @ in 27 = respectively. C insulation material (0.050 for mineral fiber), 𝜎𝜎 is the Stefan-Boltzman constant, and To and Ta represent = < 5 Two reactor tanks are considered: (1) for ambient pressure conversion (10 m diameter, 785 m3 volume) -1 where h represents the convection coefficient (20 W m-2 K-1 in this case), 𝜀𝜀@ is the emissivity for the tank insulation material (0.050 for mineral fiber), 𝜎𝜎 is the Stefan-Boltzman constant, and To and Ta represent the temperature of the outer tank surface and the ambient surroundings, respectively. 481 the itemperature of the outer tank surface kWhthe ambient surroundings, olivine and serpentine, respectively. 4 W = 12.00, 13.49, 13.39, 11.31, and 11.61 and per tonne for SS, CKD, FA, respectively. 5 Two reactor tanks are considered: (1) for ambient pressure conversion (10 m diameter, 785 m3 volume) and (2) for 3

where Np is the power number (3.75 in this case), ρ is the mixture density, N represents the impeller speed where Np is the power number (3.75 in this case), ρ is the mixture density, N represents the impeller speed (0.6 rps), and D represents the impeller diameter, taken as one-third of the reactor tank diameter.5 The (0.6 rps), and D represents the impeller diameter, taken as one-third of the reactor tank diameter.5 The total energy is thus contingent on the reaction speed, where the rate of CO2 carbonation is considered total energy is thus contingent on the reaction speed, where the rate of CO2 carbonation is considered limiting. Here it is assumed that the rate of carbonation is dependent on the alkaline feedstock dissolution limiting.AHere it is assumed that the rate of carbonation is dependent on the alkaline feedstock dissolution and not onPthe mass X E PENDI and not on the mass transfer of CO2 into the liquid phase. transfer of CO2 into the liquid phase. Heat input is required to bring the reactants (including water) up to reaction temperature plus any Heat input is required to bring the reactants (including water) up to reaction temperature plus any additional energy to compensate for heat loss from the reactor vessels. The former is calculated from the additional energy to compensate for heat loss from the reactor vessels. The former is calculated from the specific heat capacity and temperature change required: 𝑞𝑞 = 𝑚𝑚𝐶𝐶. ∆𝑇𝑇 specific heat capacity and temperature change required: 𝑞𝑞 = 𝑚𝑚𝐶𝐶. ∆𝑇𝑇 loss is calculated assuming thatloss heat flux (𝜙𝜙9 ) from the stainless-steel flux (f )equal to heat flux to the loss is calculated assuming that the heat flux (𝜙𝜙9 ) from the stainless-steel tank isq equal to heat flux to the However, this heating requirement is effectively lowered because relevant reactions are exothermic.6 Heat However, this heating requirement is effectively lowered because relevant reactions However, this heating requirement is effectively lowered because relevant reactions are exothermic.6 Heat are exothermic.6 Heat the is calculated assuming that the heat tank is from the surroundings, and is calculatedequal to heat flux to the surroundings, and is calculated from: surroundings, and is calculated from: 𝜙𝜙9 = ℎ 𝑇𝑇< − 𝑇𝑇= + 𝜀𝜀@ 𝜎𝜎(𝑇𝑇<C − 𝑇𝑇= ) stainless-steel tank is from: C C 𝜙𝜙9 = ℎ 𝑇𝑇< − 𝑇𝑇= + 𝜀𝜀@ 𝜎𝜎(𝑇𝑇< − 𝑇𝑇= ) C where h represents the convection coefficient (20 W m-2 K-1 in this case), 𝜀𝜀@ is the emissivity for the tank represents the convection coefficient (20 W m-2 K-1 in this case), 𝜀𝜀@ case), e1 is the emis- insulation material (0.050 for mineral fiber), 𝜎𝜎 is the Stefan-Boltzman constant, and To and Ta represent sivity for the tank insulation fiber), 𝜎𝜎 is the for mineral fiber), σ is the Stefan-Boltzman where h where h represents the convection coefficient (20 W m-2 K-1 in this is the emissivity for the tank insulation material (0.050 for mineralmaterial (0.050Stefan-Boltzman constant, and To and Ta represent the temperature of the outer tank surface and the ambient surroundings, respectively. the temperature ofand outer tank surface and the ambient surroundings, respectively. and the constant, the To and Ta represent the temperature of the outer tank surface ambient surroundings, respectively. 4 4 Wi = 12.00, 13.49, 13.39, 11.31, and 11.61 kWh per tonne for SS, CKD, FA, olivine and serpentine, respectively. Wi = 12.00, 13.49, 13.39, 11.31, and 11.61 kWh per tonne for SS, CKD, FA, olivine and serpentine, respectively. 5 5 Two reactor tanks are water demand, mixing of reactants, and reactiondiameter, 785 mmainte- and (2) for Considering considered: (1) for ambient pressure conversion (10 m temperature 3 volume) conversion (10 m diameter, 785 m3 volume) and (2) for Two reactor tanks are considered: (1) for ambient pressure 3 high-pressure conversion (up to 100 bar, 2 m for chemical volume). nance, the total energy requireddiameter, 27 m 3conversion of olivine at 155 is 3.185 GJ/ high-pressure conversion (up to 100 bar, 2 m diameter, 27 m volume). 6 6 The standard processed, or 0.70 tCO and is –179 kJ/mol for industrially-sourced alkalinity, power tCO2 heat of reaction for carbonation is –179 kJ/mol for industrially-sourced alkalinity, –88 kJ/mol for The standard heat of reaction for carbonation 0.43 tCO2 of additional emissions based on –88 kJ/mol for 2 olivine and –35coal and natural gas, respectively. from kJ/mol for serpentine. olivine and –35 kJ/mol for serpentine. Post-Processing, Product Transport, and Reuse or Disposal After conversion, the solid carbonate product must be clarified to remove and re- cover water, then separated via liquid cyclone, centrifugal filtration, or a combination in series. Following separation, the product is transported for reuse as an aggregate material or disposed of as mine back-fill. In post-processing, a material loss of 5 percent is assumed. Energy requirements are calculated assuming a processing train of clarification, liquid cyclone separation, and centrifugal filtration. In the first step, 75-80 vol.% water is clarified from the product mixture of 0.1-35 wt% solids. Clarification power is calculated from: Pcl = ccl D2 where the coefficient ccl is taken as 0.0045 and the tank clarifier tank diameter D is taken as 25 m,7 and the volumetric flow rate is assumed to be 0.20 m3/s. 6  The standard heat of reaction for carbonation is –179 kJ/mol for industrially-sourced alkalinity, –88 kJ/mol for olivine, and –35 kJ/mol for serpentine. 7  Typical values for c range from 0.003 to 0.006, with typical clarifier tank diameters from 2–200 m. cl 482

Appendix E After clarification, the product mixture is fed to the liquid cyclone process to produce a 30-50 wt% solid mixture. The power requirement for this step is a function of the volumetric flow rate qv: Plc = ccl qv where the coefficient clc is taken as 2008 and is 0.075 m3/s. This mixture is passed for additional processing in the centrifugal filter to produce an 80-95 wt% solid mixture. The power requirement in this step is a function of the solids input rate, qm (kg/s): Pcf = ccf qm where the coefficient ccf is taken as 16.5 and the volumetric flow rate is 0.076 m3/s. The collective power requirement for post-processing is 8 MJ / tCO2 carbonated, which results in a negligibly small carbon footprint in comparison to other steps in the carbonation chain. Product transport is similar to reactant transport and energy requirements are cal- culated using the same fuel economies presented in the reactant transport section. However, the total product weight is greater than the total reactant weight per tCO2 carbonated (ca. 44% more weight in the case of olivine carbonation); thus, the level- ized emissions from product transport are expected to be greater than those reported for reactant transport. If the processed material is reused, it is necessary to quantify the emissions saved in the displacement of an aggregate product. Here, the life cycle energy associated with medium-intensity mining and extraction of crushed limestone serves as a general representation of the energy saved in reuse of carbonate as an aggregate material (Kirchofer et al., 2012). This equates to an energy credit of 97 MJ/t, or 21 and 13 kgCO2 for coal and natural gas, respectively. If, instead, the processed carbonate heads for open mine disposal as back-fill, the energy cost can be assumed as 50 percent that of low-intensity mining. The total cost for an ex situ mineral carbonation system is an order of magnitude larger than that observed for in situ systems (Table E.1). A previous National Acad- emies of Sciences, Engineering, and Medicine (NASEM) study examined the cost of mineral carbonation based on the exampled presented in Kirchofer et al., 2012 and obtained a similar result of $1,000 /t CO2 reliably stored (NASEM, 2015). The domi- nant capital factor involves the reactor vessels that house the chemical conversion of CO2 into stable mineral form, while the dominant operating cost involves delivery of 8  Typicalvalues for clc range from 100 to 300; values for ccf range from 3-30, while values for qv range from 0.002 – 0.015 kg/s. 483

APPENDIX E alkalinity to the facility. This latter cost can be mitigated if the ex situ facility is posi- tioned to take advantage of local alkalinity resources. Though a thorough life cycle analysis on treatment of industrial waste products has shown that these processes are far more carbon intensive than those involving the mining, transport, and grinding of natural silicate minerals (i.e., 200-500 tonnes less avoided per 1000 tonnes CO2 reliably stored), these processes may garner more public support by virtue of waste treatment (Kirchofer et al., 2012). TABLE E.1  Economic Costs Associated with Reliable Storage via Ex Situ Mineral Carbonation CAPEX Cost ($M) Comment Grinding 44 Estimate scaled from Huijgen et al. (2007) assuming two grinders operated in succession: (1) cone crusher and (2) ball mill to achieve particle size of ca. 10 microns. Reactor vessels 2,700 Estimate scaled from Huijgen et al. (2007) assuming type a reactor tank (see Kirchofer et al., 2012), 780 m3 capacity, and ~150 tanks required to process volume of material necessary to reliably store 2,778 tCO2/d. Filtration system 30 Estimate scaled from Huijgen et al. (2007) assuming rotating vacuum tumble filter with 50 m2 filter area collects 8.8 m3 filtrate/day. CAPEX Subtotal 2,774 Annualized Capital 313 Assumes a plant life of 30 years and fixed charge factor of Payment ($M/y) 0.11278 (Rubin et al., 2007). OPEX Cost Comment ($M/y) Maintenance 83 Range calculated as 0.03 of total capital requirement. Labor 25 Range calculated as 0.30 of maintenance cost. 484

Appendix E TABLE E.1 Continued Total fuel (coal, natural gas, 140 Collective energy cost for all steps including mining, pre- and electricity) post-processing, chemical conversion, transport, and disposal. Excludes energy costs associated with capture, compression, and transport of CO2. Excludes petroleum cost for alkalinity transport, which is assumed into the delivery cost. Assumes $3/GJ for natural gas, Appalachian medium-sulfur coal, cost of $50/t, and higher heating value (HHV) of 31 GJ/t (Rubin et al., 2007), and $60 MWh electric cost. Alkalinity delivery 250 Assumes alkalinity delivery cost of $250/tCO2 fixated. Cost reflects mining and transport via trucking. Rail costing may be cheaper for greater distances (>100 km) or where the mineral carbonation site exists at a railhead. Capture, compression, and 40-70 Reflects cost of capture, compression and transport via pipeline delivery of pure CO2 (assumes 250 km) (Rubin et al., 2015). Range exists for various point sources (e.g., supercritical pulversized coal (SCPC) vs natural gas combined cycle (NGCC), average value of 55 used in total. OPEX Subtotal 553 Levelized Cost ($/tCO2 866 yr-1)a Avoided Cost ($/tCO2 1170 yr-1)b a Levelized basis = 1Mt CO2. b Levelized basis = 0.74 Mt CO2 (Kirchofer et al., 2012). 485

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To achieve goals for climate and economic growth, “negative emissions technologies” (NETs) that remove and sequester carbon dioxide from the air will need to play a significant role in mitigating climate change. Unlike carbon capture and storage technologies that remove carbon dioxide emissions directly from large point sources such as coal power plants, NETs remove carbon dioxide directly from the atmosphere or enhance natural carbon sinks. Storing the carbon dioxide from NETs has the same impact on the atmosphere and climate as simultaneously preventing an equal amount of carbon dioxide from being emitted. Recent analyses found that deploying NETs may be less expensive and less disruptive than reducing some emissions, such as a substantial portion of agricultural and land-use emissions and some transportation emissions.

In 2015, the National Academies published Climate Intervention: Carbon Dioxide Removal and Reliable Sequestration, which described and initially assessed NETs and sequestration technologies. This report acknowledged the relative paucity of research on NETs and recommended development of a research agenda that covers all aspects of NETs from fundamental science to full-scale deployment. To address this need, Negative Emissions Technologies and Reliable Sequestration: A Research Agenda assesses the benefits, risks, and “sustainable scale potential” for NETs and sequestration. This report also defines the essential components of a research and development program, including its estimated costs and potential impact.

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