The Virgin Earth Challenge

One of the requirements of the Challenge was to demonstrate that the proposed method for sequestering carbon is commercially viable even without selling Carbon Credits.

Here, in selected extracts from our entry, Answers to the VEC Checklist, we demonstrate the commercial viability of our design. Around $37 per tonne is earned from fish sales for every tonne of carbon sequestered at $14 per tonne, giving a net profit of $23 per sequestered tonne.

Carbon trading is not a prerequisite for profitability.

14) Please provide an abstract of how your design captures GHGs from the atmosphere and sequesters them Deep ocean water containing the nutrients is brought to the surface by means of our Nutrient Megapump which uses superheated water (360°C) from hydrothermal vents on the seabed to drive a giant bubble pump. Slugs of wet steam are formed in the bubble pump because the superheated vent effluent boils when brought to shallower depths. These slugs of wet steam are 27,000 times more buoyant than is surface water relative to deep water, which means each litre of vent fluid can lift 27 tonnes of cold, nutrient-rich, deep-ocean water to the surface where photosynthesis can take place.

CO2 in the upper ocean (the mixed layer) is in equilibrium with the atmosphere, and so by removing CO2 from the mixed layer we are removing it from the atmosphere. Photosynthesis removes CO2 both directly, by converting it to carbohydrate, and indirectly, by reducing the acidity of the mixed layer so allowing more of the gas to dissolve.

15) Describe in more detail how your design captures GHGs from the atmosphere
The amount of carbon removed is determined by the Redfield ratio (C:N:P = 106:16:1). Some CO2 is brought to the surface with the nitrate and phosphorus and this must be subtracted in order to determine how much is taken from the atmosphere. CO2 chemistry is complicated but the calculations show that where there is adequate nutrient, e.g. in the North Pacific and South Atlantic, there is a net removal of atmospheric CO2. The process is much more efficient at lower temperatures and so works much better at temperate latitudes than in the tropics.

The world’s oceans contain enough nutrient to sequester 20,000 Gigatons of CO2 in this way.

28) Describe what resources you would require to sequester 1 tonne of carbon equivalents (for example in terms of power, machine and materials. A Nutrient Megapump is estimated to cost $100 to $500 million by comparison with the cost of offshore oil production platforms. Vent Temperature - 360°C
Vent Depth = 2500 m
Vent Power = 1 Megawatt (MW)
Vent Flux = 0.7 kg/s
Injection Depth = 200m
Gain (Potential Energy Ratio)= 27 tonne/kg
Bubble Pump Flow = 17 tonne/s.MW
Bubble Pump Flow = .000017 Sv

For a single large vent such as in the TAG field in the N. Atlantic (1.7 GW) the bubble pump flow would be 1700 times the above, i.e. 1.9 kilotonnes/s or 1.9 milli-Sverdrup.

The Sverdrup (Sv) is a unit of flow used by oceanographers.
1 Sv = 1 million m3/s.
The flow of the Amazon is about 0.5 Sv.

29) How much GHG could you realistically sequester on a yearly basis? (Please state this in terms of Carbon not CO2) Using the above figure for bubble pump gain gives:
Latitude: 40° S
Longitude: 105° W
Location: East Pacific Rise
Surface Temperature = 15° C
C Seq. Rate per kg = 93 µmole/kg
C Seq. Rate per sec. = 1.6 mole/s.MW
CO2 Mol. Weight Factor = .044 kg/mole
CO2 Seq. Rate per second = 0.07 kg/s.MW
CO2 Seq. Rate per day = 6 tonne/day.MW
CO2 Seq. Rate per year = 2.2 ktonne / year.MW
Large Vent Field Power: 1000 MW = 1 GW
Large Vent Field Rate = 2.2 Megatonne /year

30) Explain the above figure and how you came by it The total hydrothermal vent power available is estimated to be around 4 terawatt (4 million MW, i.e. 4,000 times the above figure). So the CO2 sequestration rate could be of the order of 8 Gt/year). Realistically the amount sequestered depends on the number of vent fields which can be harnessed and this depends, in turn, on the capital invested. Also about half the oceans of the may not have sufficient nutrient.

36) What is the net cost or profit of your design to sequester 1 tonne of carbon equivalents?
(Please calculate this not including potential profits from Carbon Credits.)
Profit = $23 per tonne Carbon equivalent.
37) Please explain the above figure. Capital cost for 1 GW installation = $300 million
Nominal interest rate = 5 percent
Interest = $15 million/yr
Maintenance and monitoring = $15 million/yr
Total cost = $30 million/yr
Large vent field seq. rate = 2.2 Mt/yr
Cost = $14 per tonne
Return from fish = $37 per tonne
Net profit = $23 per tonne

38) What products does your design have?
(for example, energy waste byproducts)
Fish. Fisheries. Licenses to fish would be sold by the installers. Other products such as plankton-based bio-fuels are also possible.

39) How much of these products would you produce for every tonne of carbon equivalents sequestered? Weight of fish per Sverdrup = 0.5 Mt/yr.Sv
Average wholesale price = $2600 per tonne
Return per Sv = $1.3 billion/yr.Sv
Flow per MW of vent power (Q28) = .000017 Sv
Return per MW $22100 /yr.Mw
Carbon sequestered per MW = 600 t/yr.MW
Return per Carbon Equivalent = $37 /tonne Carbon
Cost per Carbon Eq. (Q37) = $14 /tonne Carbon

Profit = $23 /tonne Carbon


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