Mineral sequestration-costs

There is a considerable difference between various mineral carbonation routes, when it comes to costs but there is also a significant difference in mineral carbonation compared to other CCS related costs as can be seen from the below table.

 Although the data provided in the table is a few years old (2005), the current best case costs for (at least) mineral carbonation appears to remain within the given price range (38–77 €/CO2 net mineralized).

Cost ranges for the components of large-scale CCS systems [6] (US$ have been converted to € at the rate of  1.3 US$ = 1Euro)

The differences in cost of various CCS related process steps are significant, but mineral carbonation is by far the most expensive one. In the table below the costs of different mineral carbonation alternatives have been compared. The estimated costs do not include the cost of mining, CO2 capture or transport.To improve the economics of mineral carbonation recommended that particular focus should be placed on the carbonation degree (especially for wollastonite, due to the high ore cost) in pilot scale experiments and the required L/S ratio. Integrating mineral carbonation with CO2 capture was also recommended, as the price for CO2 capture by current means is comparatively high (ranges from 12 $ (9 €) for a new hydrogen plant to 44 $ (34 €) for a new NGCC plant, IPCC, 2005).

Another approach to CO2 sequestration by mineral carbonation was taken by Khoo and Tan, who applied the Life Cycle Assessment (LCA) on five different process alternatives. The LCA study presented by Khoo and Tan does not take into account transportation of CO2 from the power plant, but unlike the results of the cost comparison in the above table CO2 capture was taken into consideration.

The most promising CCS method consisted of CO2 capture by chemical absorption and wollastonite carbonation  followed by chemical absorption and olivine carbonation.

Cost estimates used by the proponents of mineral sequestration are $70 per tonne of CO2 sequestered if one scaled up current laboratory processes. Eliminating pre-treatment and solving the dewatering problem would reduce the cost to $30 per tonne of CO2 sequestered.

The IEA Greenhouse Gas R&D Programme estimates the cost of the current mineral sequestration processes at $60-100 per tonne of CO2 sequestered, which matches well with the proponents’ estimates. By comparison, the IEA GHG R&D Programme reports values for ocean and geologic sequestration at $1-5 per tonne of CO2 sequestered. All the above numbers are exclusive of any capture and transport costs.

The following points will give the above numbers some perspective:

• Capture and transport costs need to be added to all the above sequestration costs. A rough estimate of capture and transport costs is $50-60 per ton of CO2 avoided.
• The above sequestration costs need to be put on an avoided cost basis. If a process is energy intensive (such as pre-treatment of the ore), the cost per ton avoided could be significantly larger than the cost per ton sequestered.
• One way to reduce the cost of mineral sequestration is to integrate it with a capture process. This is what ZECA attempts to do.
• Another option being investigated to improve the economics of mineral sequestration is to find commercial uses for the process by-products.


Capital Cost Factors

• Economies of scale applying to today’s mining technology suggest a  minimum mining operation of 50,000 to 100,000 tons day–1 (Hartman, 1992), which translates into a minimum mineable volume of about 0.3 km3 for a mine with a 30 year life.
• Like in other mining operations, disposal of tailings and mine reclamation are important issues to consider.
• A life cycle analysis of the mining, size reduction process, waste disposal and site restoration calculated additional annual CO2 emissions of 0.05 tCO2/tCO2 stored.
• The grinding of the rock to particle sizes less than 100 microns; a ratio of 2.6 tons of serpentine per ton of CO2 was assumed. The cost was assessed to be about 14 US$/tCO2 stored; the capital cost being about 20% of the total.
• The conversion factor from electrical energy to CO2 emissions was 0.83 tCO2/MWh electricity. Costs were calculated on the basis of an electricity price of US$ 0.05kWh–1 electricity.
• The basic cost factors are as vague as estimates because no single power plant has yet employed this system, its difficult to predict the exact input of capital needed. So , in summary the capital expenditure by general expenditure stands at around 40-50% of the total power plant initial set up costs without CCS.


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