Electrochemical Acceleration of Chemical Weathering & Geoengineering. Kurt Zenz House KITP Climate Physics Conference May 9 th,2008

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1 Electrochemical Acceleration of Chemical Weathering & Geoengineering KITP Climate Physics Conference May 9 th,2008

2 The extremely skewed distribution of point sources indicates the potential need for multiple strategies MT CO2/yr The 150 largest coal power plants emit ~10% of global CO2 The top 1000 stationary point sources compose ~30% of emissions The next 7000 compose ~15% The tails is extremely long with transportation and very small distributed sources composing nearly half of all emissions Number of Point Sources Source: Alliance Bernstein

3 Agenda Accelerating atmospheric CO 2 concentration The Taxonomy of climate change abatement technology The details of electrochemical weathering

4 The emissions growth rate since 2000 was greater than for the most fossilfuel intensive of the IPCC emissions scenarios developed in the late 1990s Raupach et al, PNAS (2007) Raupach et al, PNAS (2007)

5 The biggest surprise has been a reversal of the long time trend in carbon intensity (kgc/$gdp) Raupach et al, PNAS (2007)

6 The oil supply curve suggests that supply is have trouble keeping up with demand

7 Agenda Accelerating atmospheric CO 2 concentration The Taxonomy of climate change abatement technology The details of electrochemical weathering

8 Climate Change Abatement/ Mitigation Technology Long Wave Radiation Short Wave Radiation Reduce CO 2 Emissions Remove CO 2 from the air Decrease incident solar radiation Increase the Earth s Albedo Switch Energy Sources Improve Efficiency CO2 capture & storage with fossil carbon Surface albedo Cloud seeding Stratospheric Aerosols Engineered particles Biologic Schemes Chemical Schemes CCS with biomass Iron Fertilization Reforestation Solvent Regeneration loops Altering the Ocean s alkalinity

9 The sensibility of these various schemes can be visualized in risk cost space Risks Sulfur particles in the stratosphere Engineered particles in the stratosphere Mirrors in Space Iron Fertiliz ation Biomass with CCS Reduce GHG Emissions $ Cost Electrochemical Weathering Air Capture/Solvent regeneration

10 The cheapest way to remove CO2 from the air is to combust appropriately harvested biomass and capture and store the CO 2 CO 2 Biomass CO 2 + N 2 CO Power plant 2 separation N 2 Incident solar radiation ~ 300 W/m 2 X Photosynthetic efficiency ~ 0.5% = 1.5 W/m 2 X Thermal efficiency ~ 40% = 0.6 W e /m 2 1 GW e power plant would require ~1700 km 2 of land Assuming perfect land use, then offsetting 1Gt C/yr with biomass requires ~10% (~1M km 2 ) of current agricultural land If we do CO 2 with CCS, then the land requirements drops to about ~7%

11 Agenda Accelerating atmospheric CO 2 concentration The Taxonomy of climate change abatement technology The details of electrochemical weathering

12 Chemical weathering is the Earth s thermostat CaSiO3 + CO2 CaCO3 + SiO2 Can chemical weathering be accelerated? MgSiO + CO MgCO + SiO

13 The partitioning of carbon between the atmosphere and the oceans is controlled in part by the ocean s alkalinity CO2 ( g ) ATMOSPHERE ( ) K K aq + H O H + HCO H + CO % 12.5% CO Surface Ocean The ocean has a surplus of conservative positive charge Alkalinity = Na + 2 Mg + 2 Ca + K +... Cl 2 SO 4... which is primarily balanced by the carbonate system 2 Alkalinity = HCO CO

14 On long time scales, nature will solve global warming on its own (in multiple ways) + 2 ( ) ( ) 2 + CO g + H2O3 HCO33+ + H 2 ATMOSPHERE & EARTH CO g H O MgSiO HCO Mg ( ) + Alkalinity CO aq H O H HCO H CO K1 + K Surface Ocean Droplet A reacts with MgSiO 3 Adds 2HCO 3 + Mg 2+ to ocean The increase in Alkalinity shifts the partitioning toward HCO 3 Most of the additional HCO 3 remains as such Droplet B falls directly into ocean Adds HCO 3 + H + [H + ] goes up; ph goes down Shifts dissolved inorganic carbon partitioning toward CO 2 (aq)

15 If alkalinity can be added to the ocean at industrial rates, then the ocean will take up atmospheric CO Alkalinity = Na + 2 Mg + 2 Ca + K +... Cl 2 SO 4... Various scholars have considered ways to increase the ocean s alkalinity by dissolving carbonates into the ocean (e.g., Broecker, Caldeira) So I thought, perhaps we can remove conservative negative charge in order to increase the ocean s alkalinity

16 More detailed block diagram (version 1) W e HCl (aq) HCl Fuel Cell $ (small scale) Silicate Rock Source (i.e., MgSiO 3) SiO 2 H 2 (g) Cl 2 (g) W e Chloralkali Like Process MgCl 2 (aq) Atmosphere NaCl(aq) NaOH(aq) CO 2 (g) [Cl ] Surface Ocean (~NaCl (aq)) HCO 3 Mg 2+

17 Chemical steps (version 1) Step 1: electrolysis Δ G 1 =+ 212 kj/(mol NaOH) 2 NaCl( aq) + 2 H O( l) 2 NaOH ( aq) + Cl ( g) + H ( g) Step 2: HCl Fuel Cell Δ G 2 = 131 kj/(mol HCl) Cl ( g) + H ( g) 2 HCl( aq) 2 2 Step 3: Rock Dissolution Δ H 3 = 58 kj/(mol HCl) 2 HCl( aq) + MgSiO ( s) MgCl ( aq) + SiO ( s) + H O Step 4: CO 2 capture, storage Δ H 4 = 70 kj/(mol NaOH) 2 CO ( g) + 2 NaOH ( aq) 2 NaHCO ( aq) 2 3 Overall Process: Δ G = 4 kj/(mol NaOH) MgSiO () s + H O() l + 2 CO ( g) Mg + SiO () s + 2HCO

18 It turns out that halogen fuel cells have great potential for grid scale energy storage DUAL USE POTENTIAL for HCl Fuel Cell CO 2 sequestration Peak shaving / load leveling Cl 2 Cl 2 Jason Rugolo (2 nd yr Harvard GS) 2HCl

19 The net reaction is spontaneous, but a range of scenarios bounds the work that will be required kj/mol House et al, ES&T (2007)

20 Rock type matters Furthermore, secondary reactions can limit the alkalinity generated pure unit mass of the rock. For example: FeS + 2H + 2Cl + H O + 5 O FeCl + 2HSO + 2H 2 FeCl + 2H O Fe OH + 2H + 2Cl ( ) 2 2 2

21 Dissolution reaction kinetics are highly temperature dependent

22 Enhanced CaCO 3 precipitation is the ultimate fate of the additional alkalinity and carbon MgSiO () s + H O() l + 2 CO ( g) Mg + SiO () s + 2HCO HCO + Ca CaCO + CO + H O If the dissolution products are returned to the ocean, CaCO 3 is certain to precipitate quickly due to the increase in local alkalinity

23 Another way to think about this the creation of artificial soda lakes

24 The purity requirements pose a serious engineering challenge Mg Ca

25 Offsetting 1 GtC/yr with electrochemical weathering is a serious task To offset 1 GtC, ~10 14 moles of HCl would have to be produced and neutralized each year i. Volumetric flow rate of seawater equal to 6000 m 3 /sec ii. Volumetric flow rate of artificial brine from mined halite of 600 m 3 /s If basalt were used for neutralization, then 10 Gt would be required annually Our kinetic experiments indicate the rock dissolution would require ~10 7 m 3 of reaction volume (1500 Olympic swimming pools) The global weathering rate would be x10 Local alkalinity hot spots would form and potentially cause severe damage to marine biota

26 Benefits of electrochemical weathering Permanency of storage to do thermodynamics and kinetics of marine chemistry Simultaneously manage the oceans and the atmosphere particularly ocean ph Could be run off stranded power 1 large plant (~50 m 3 /sec) would offset ~5,000,000 cars

27 Conclusions Despite global awareness and the Kyoto treaty, CO 2 emissions have outpaced our most pessimistic forecast A wide variety of schemes other than decreasing CO 2 emissions have been proposed to deal with climate change Of these, biomass with CO 2 capture & storage will work, but is limited in scale to about 1 GtC/year We can accelerate weathering with electrochemistry, but it will be expensive and the rock requirements will severely limit its scale