For the supercritical plant in Example 6-8, suppose that the CO2 from 15 such plants is piped to a saline aquifer where it is injected. The aquifer is approximately 1000 km long and 500 km wide, with an average depth of 1000 m. All of the aquifer’s volume is available for dissolution of CO2, and

Question

For the supercritical plant in Example 6-8, suppose that the CO[latex]_2[/latex] from 15 such plants is piped to a saline aquifer where it is injected. The aquifer is approximately 1000 km long and 500 km wide, with an average depth of 1000 m. All of the aquifer’s volume is available for dissolution of CO[latex]_2[/latex], and the porosity is 10%. The pressure in the aquifer is 500 kPa on average, and the temperature is 325 K. (a) If the plants function for 75 years, is there sufficient capacity in the aquifer to sequester all the CO[latex]_2[/latex] generated? (b) If the total cost per tonne CO[latex]_2[/latex] sequestered, including repayment of capital cost and all operating costs, is $25/tonne, by what percent does the cost of electricity increase?

Accepted Answer

(a) Since the full volume of the reservoir is available, there is no part that is saturated with water, and s[latex]_w[/latex] = 0. The volume of the reservoir is 5 × 10[latex]^{14}[/latex] m[latex]^3[/latex]. Therefore, using the pressure and temperature values given, the maximum number of moles is

[latex]n=\frac{\left(5 imes 10^{5} \mathrm{~N} / \mathrm{m}^{2} ight)(0.10)\left(5 imes 10^{14} \mathrm{~m}^{3} ight)}{8.314(325)}=9.25 imes 10^{15} \mathrm{~mol}[/latex]

At 44 g/g·mol for CO[latex]_2[/latex], this converts to 4.07 × 10[latex]^{11}[/latex] tonnes. From Example 6-8, the CO[latex]_2[/latex] generated per plant is 1.47 × 10[latex]^6[/latex] tonnes/year. The amount of CO[latex]_2[/latex] generated by 15 plants over 75 years is 1.66 × 10[latex]^9[/latex] tonnes. Therefore, there is adequate capacity in the aquifer.

(b) If the cost per tonne is $25.00, then the cost per year is $36.9 million. Spreading this cost among 3.07 billion kWh generated per year gives $0.0120/kWh. Since the original cost was $ 0.0353/kWh, the increase is (0.0120)/(0.0353) = 34%.

Question 7.4: For the supercritical plant in Example 6-8, suppose that the...

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