Greg H. RauInstitute of Marine Sciences

University of California, Santa CruzAnd

Carbon Management ProgramEnergy and Environmental Security Div. Lawrence Livermore National Laboratory

rau4@llnl.gov

GCEP/Stanford April 15, 2008

Chemical CO2 Mitigation:An Option for the Cement Industry

Overview

The chemical reactivity of CO2 with hydroxide orcarbonate solutions can be exploited for low-cost, low-tech CO2 mitigation.

As an example, the waste metal oxidesproduced in cement manufacture (cement kilndust) can be hydrated and used as a CO2absorber, with other potential co-benefits.

The chemical reactivity of CO2 can be used forCO2 mitigation:

CO2 is a reactive compound, e.g.:

Requirements for cost-effective, safe sequestration: Low energy input Inexpensive, abundant reactants Benign, storable/useable products

CO2+ CO3

2- + H2O ---->2HCO3-

+ MO ----> MCO3

+ OH- ----> HCO3-

+ M0 + H2O ----> MCO3 + H2

Nature’s Chemical CO2 Capture and Storage:

Photosynthesis

Weathering Reactions

Ocean uptake

Atmospheric CO2

CO2 + H2O + CO32-

---> 2H+ + 2HCO3-

Silicate weathering: CO2 + Ca/MgOSiO2 ---> Ca/MgCO3 + SiO2

Carbonate weathering: CO2 + H2O + CaCO3 ---> Ca2+ + 2HCO3-

CO2 + H2O + photons ---> R-(CH2O) + O2

Nature’s own mechanisms:

Natural CO2 Sequestration: Effective but slowInstantaneous doubling of pre-industrial atmospheric CO2 content

(Caldeira and Rau, 2000)

Accelerated Weathering of Limestone (AWL) Reactor:

(Rau and Caldeira, 1999)

Analogies to Flue Gas Desulfurization:

AWL:CO2(g) + H2O(l) + CaCO3(s) ---> Ca2+

(aq) + 2HCO3-(aq)

FGD:SO2(g) + H2O(l) + CaCO3(s) ---> CaSO3(aq) + CO2(g) + H2O(l)

CaSO3(aq) + 0.5O2 ---> CaSO4(s)

Gases captured via reaction with wet limestone (at ambient temperature and pressure), and converted to benign, storable/useable liquids or solids

AWL cost: $3-$30/tonne CO2 avoided

CO2 Mitigation In Cement Manufacture:

CCAP Report 2005: CA Cement Manufacture - Current state emissions ≈ 10.5 MMT CO2/yr

Flue gas is 20-30% CO2 Est. BAU emissions in 2020 = 13.6 MMTCO2/yrMight be reduced to 11 MMTCO2/yr by 2020 at a cost <$10/tonne CO2 via:

Limestone or flyash + cement blendsAlternative fuels

But AB 32 mandates state return to 1990 emissions (CA cement, est. 7.8 MMTCO2/yr) by 2020 Therefore, current CO2 reduction path inadequate.

Chemical Composition of CKD:

Strongly alkaline waste (pH >12); highly reactive with acid gases including CO2

Quantity of waste CKD produced per tonne clinker quite variable: 0 to >25%.However, legacy CKD stockpile is massive

82,000 tonnes/yr disposed of in California alone (‘05 PCA Survey) 3.3 MMT disposed nationally in US in 1995, 4 MMT in 1990 (EPA)

US Mitigation potential: 3 MMT CKD X 50 years X 0.5 T CO2 /T CKD = 75 MMT CO2

Duchesne and Reardon, 1998

CaCO3+

sand +high heat

Kiln

alkaline cementkiln dust (CKD)

cement

<--CaCO3 recycle

CO2 and Kiln DustMitigation in Cement

Manufacture

CO2

e.g., Ca(OH)2 + 2CO2 ---> Ca2+ + 2HCO3

-

Ca2+ + 2HCO3- --->

H2O + CaCO3 + CO2

Csequestration

as CaCO3-and/or-

H2O

Aqueous CO2 + CKD contactor

Settling/precipitationreservoir(s)

Na,K,MgCarbonates

Use Highly Alkaline Waste Cement Kiln Dust for CO2 Mitigation:

pH>12

air

CaCO3+

sand +high heat

Kiln

alkaline cementkiln dust (CKD)

cement

<--CaCO3 recycle

CO2 and Kiln DustMitigation in Cement

Manufacture

e.g., Ca(OH)2 + 2CO2 ---> Ca2+ + 2HCO3

-

Ca2+ + 2HCO3- --->

H2O + CaCO3 + CO2

Csequestration

as CaCO3-and/or-

H2O

Aqueous CO2 + CKD contactor

Settling/precipitationreservoir(s)

Na,K,MgCarbonates

Air CO2 capture option:

pH>12

CO2 Air CO2

Features: Helps mitigate both CO2 and CKD, esp legacy stockpiles of

CKD Potential co-benefits

Recycle of waste Ca as CaCO3 Can include air CO2 capture Selective precipitation of other useful compounds e.g.

K, Mg, and Na carbonates, sulfates, etc. Avoid landfilling and/or reclamation of landfills

Retrofitable to existing plants Should be relatively low cost, <$3/tonne CO2

Compared to >$25/tonne using CCS Might profitable now without carbon credit/tax

Issues:

Only relevant when/where/if CKD is availableNot applicable if CKD recycled in kilnNot relevant if other uses of CKD outweigh CO2

emissions reductionWill consume water via gas or air contacting and/or

solar or waste heat evaporation.Might generate waste solutions; waste permitting

issuesWill require capital expenditure and spaceMore R&D needed to determine cost effectiveness

CKD flue gas scrubber has been demonstrated

http://www.netl.doe.gov/technologies/coalpower/cctc/cctdp/bibliography/demonstration/ia/bia_cemkiln.html

DOE conclusions:

Estimated net after-tax profit = $2.6M/yrPayout of investment in 3.2 years

However, proposals to the Portland Cement Assoc. and to Cal’s Air Resources Board where not funded:

Other Aqueous Chemistry-Based CO2 Mitigation Ideas---->

gases

solids

oil

oil

Produced Water+ Dissolved

CarbonInjection

Oil+Water+Gas Lifting

Primary separation:

Secondary separationwith CO2 addition:

gases+CO2

water storage,isolation fromair

flotationflocculationskimmingsettling

CO2 + H2O + CO32- -->

2HCO3-

CO2

Low-pressure,waste CO2

Limestone, wastecarbonates

Produced Water Re-injection with CO2 Capture + Geologic Storage:

Use of CO2 as an oxidant in an Fe fuel cell:

FeCO3 storage/outputH2O input Waste

CO2 inputWaste

Fe Waste

Fe Anodes

UsedAnodes

H2/gas collection and cleanup

Waste gasH2 output

CO2 cleanup?

Fuel CellBattery Array

Scrap Iron Processing ------------ Anode Formation

Scrap Iron input

Voltage/ CurrentProcessing ?

Hi/Lo VACoutput

FeCO3 Stripping

VDC

+

H2O cleanup?

Fe++ outputto ocean?

Used electrolyte

H2O/CO2 equilibration H2CO3 formation

CO2 cleanup?

H2O recycle

CO2 recycle

G.H. RauAug 11’03 Schematic of Fe/CO2 Fuel Cell Battery Operation:

Waste gas

Figure 1

Fe0(s) + CO2(g) + H2O(l) => FeCO3(s)↓ + H2(g)↑ + 61.2kJ

Fe/CO2 Fuel Cell Requirements, Yields, Costs

Mass in (tonnes): 1 Fe0

--> 0.79 CO2 --> 0.32 H2O -->

Mass/energy out:--> 2.07 FeCO3

--> 0.04 H2

--> 300 kWhe

Fuel cell

Cost per tonne Fe: $100 Fe0

--> $30 COM -->

Output value per tonne Fe:--> $15 CO2 avoid.(@$20/tonne)--> $60 H2 (@$1.50/kg H2)--> $15 elect. (@$0.05/kWh)

Fuel cell

Net cost = ($130-$90)/0.79 = $50/tonne CO2 mitigated?

2H+ 2OH-

0.5O2and/or

other gases H2

2H2O

2e- 2e-

Ca(HCO3)2(aq)

anodecathode

-+

saline solution level

+ -

Gaseous CO2

H2O

DCElectricitySource

proprietary

CaCO3(s)

Use renewable DC electricity to allow:

Production of air CO2 absorbingsolutions while generating “green”hydrogen.

22 tonnes CO2 absorbed pertonne H2 produced

thus, novel production ofcarbon-negative hydrogen.

Addition of alkalinity to seawaterneutralizes or offsets ocean acidity.

Electrochemical production of alkalinity for CO2

mitigation and carbon-negative H2 production

Air CO2

Experimental results - Alkalinity generated, air CO2 absorbed

Lots of assumptions, but -

Electricity Source

net $ cost/ tonne CO2

avoided

averg. electricity 2015PV 241NGCC electricity 165wind 40-80

CONFIDENTIAL March 20, 2008

7.8

8

8.2

8.4

8.6

8.8

9

9.2

0 20 40 60 80 100 120 140Elapsed Time, hrs

Solu

tion

pH

7.8

8

8.2

8.4

8.6

8.8

9

9.2

-CaCO3 +CaCO3

2.5

4.0

6.3

10.0

15.8

25.1

Solu

tion

[OH-

], um

oles

/L

Seawater+Ca(OH)2

Seawater

Seawater+Ca(HCO3)2

Atmos. CO2

H2

Limestone

+O2

H2O +electricity

For Example: Ocean-based, carbon-negative wind hydrogen

offshore

onshore

Conclusions: Continued reliance on fossil fuel energy in a carbon-

constrained world requires that multiple, cost-effectiveand safe CO2 sequestration technologies be quicklyfound and deployed.

For point source mitigation, relying solely on the captureand storage of CO2 in molecular form (CCS) isunnecessary and unwise because inherentcapture/separation costs, and local availability of safe,secure storage may delay/limit application.

A variety of chemistry-based sequestration approachesare available and/or may emerge; these need to bepursued - the cement industry is a prime example.

Let’s get going! Partners and funding sought.