chemical co2 mitigation: an option for the cement...
TRANSCRIPT
Greg H. RauInstitute of Marine Sciences
University of California, Santa CruzAnd
Carbon Management ProgramEnergy and Environmental Security Div. Lawrence Livermore National Laboratory
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.