labs_title

Caldeira Lab Research:Energy, Global Carbon Cycle, and Climate

Reducing energy related CO2 emissions using accelerated weathering of limestone

Greg H. Rau, Kevin G. Knauss, William H. Langer, & Ken Caldeira

An investigation of the possibility of using accelerated weathering of limestone (AWL) to sequester CO2 in the atmosphere. Using AWL to reduce CO2 levels in the atmosphere seems to be a feasible way to reduce 10-20% of the CO2 created through electricity production in the US.


Rau, G.H., K.G. Knauss, W.H. Langer and K. Caldeira. Reducing energy-related CO2 emissions using accelerated weathering of limestone, Energy 32 (8): 1471-1477, 2007

Efficiency of storage following accelerated weathering of limestone: After AWL, the resulting carbonate would be injected into the deep ocean. According to the model, this would result in much less leakage of carbon dioxide into the atmosphere than would direct injection of the gas.

Changes in ocean chemistry and atmospheric CO2 concentration resulting from AWL: Using accelerated weathering of limestone before deep sea injection would greatly reduce increases in ocean acidity and atmospheric CO2 concentration that result from direct carbon injection.

Abstract

The use and impacts of accelerated weathering of limestone (AWL; reaction: CO2+H2O+CaCO3-(Ca2+)+2(HCO3) is explored as a CO2 capture and sequestration method. It is shown that significant limestone resources are relatively close to a majority of CO2 emitting power plants along the coastal US, a favored siting location for AWL. Waste fines, representing more than 20% of current US crushed limestone production (>109 tonnes/yr), could provide an inexpensive or free source of AWL carbonate. With limestone transportation then as the dominant cost variable, CO2 mitigation costs of $3-$4/tonne appear to be possible in certain locations. Perhaps 10–20% of US point–source CO2 emissions could be mitigated in this fashion. It is experimentally shown that CO2 sequestration rates of 10-6 to 10-5 moles/sec per m2 of limestone surface area are achievable, with reaction densities on the order of 10-2 tonnes CO2 m-2day-1, highly dependent on limestone particle size, solution turbulence and flow, and CO2 concentration. Modeling shows that AWL would allow carbon storage in the ocean with significantly reduced impacts to seawater pH relative to direct CO2 disposal into the atmosphere or sea. The addition of AWL-derived alkalinity to the ocean may itself be beneficial for marine biota.