Appendix A - Reference Example
Note: This analysis was done for an earlier more complex design that utilized an ocean platform and added a low pressure steam turbine; however, the thermodynamic calculations remain basically valid for the present design. Also, this analysis used 5,767 feet as the reference ocean depth, an optimum depth is estimated to be near 1,000 feet.
Following is a basic process description and supporting calculations which corroborate the concept of producing electricity and/or hydrogen gas using ocean geothermal rifts method.
Terminology and Abbreviations:
gpm Gallons per minute psi Pounds per square inch Twb Temperature of water at ocean bottom near volcanic rift Pwb Pressure of water at bottom (@ 5,767 feet) Hwb Enthalpy of water at stated pressure/temperature Tsht Temperature of steam at entrance to high pressure turbine Tslt Temperature of steam at entrance to low pressure turbine Psht Pressure of steam at entrance to high pressure turbine (@ 450 feet) Pslt Pressure of steam at entrance to low pressure turbine (@ 1 15 feet) Hsht Enthalpy of steam at entrance to high pressure turbine Hslt Enthalpy of steam at entrance to low pressure turbine Hwht Enthalpy of water at entrance to high pressure turbine Hwlt Enthalpy of water at entrance to low pressure turbine
oF Temperature in degrees Fahrenheit
Reference Conditions:
The following parameters have been chosen as reference conditions:
hot water source of 10,000 gpm
ocean depth of 5,767 feet
pressure of 2,500 psi
Process Description:
Please refer to the attached diagram, which illustrates the basic components of the process. This process, with the reference conditions given above, would produce a steam equivalent of 480,000 gallons of number 6 fuel oil per day, or 170 million gallons per year for each 10,000 gpm of hot water. It is estimated that an apparatus similar to Fig. 1 with 100 pipes 12-inch diameter would produce 5000 gpm per pipe or 500,000 gpm. This high energy water could be used to create an energy equivalent of 24 million gallons of fuel oil per day.
Calculations:
1. The parameters of state are taken from the saturated steam tables (depth = 5,767 feet):
Twb = 668 oF. (temperature of water at ocean bottom near volcanic rift)
Pwb = 2,500 psi (pressure of water at bottom - 5,767 feet)
Hwb = 731 btu/lb (enthalpy of water at 2,500 psi and 668' F.)
2. Thermodynamic conditions chosen for the higher pressure turbine (depth = 450 feet):
Tsht = 380 oF. (temperature of steam at entrance to high pressure turbine)
Psht = 195 psi (pressure at entrance to high pressure turbine - 450 feet)
Hsht = 845 btu/lb (enthalpy of steam at entrance to high pressure turbine)
Hwht = 353 btu/lb (enthalpy of water at 195 psi and 380' F.)
3. Thermodynamic conditions chosen for the lower pressure turbine using the same nomenclature (depth = 115 feet):
Tslt = 275 oF.
Pslt = 45 psi (at 1 15 feet)
Hslt = 929 btu/lb
Hwlt = 243 btu/lb
4. The pounds of water needed to flash one pound of steam at the higher pressure turbine is:
Hsht / (Hwb - Hwht) = 845 / (378)
= 2.24 lb water per lb. steam5. Ten thousand gallons of water per minute is equal to 83,500 pounds of water per minute. Therefore, the pounds of steam generated per minute will be:
83,500 / 2.24 = 37,280 lbs. steam per minute, or
2,250,000 lbs. steam / hour6. The water remaining after supplying steam to the high-pressure turbine must be replaced by the hotter water at the bottom in order to sustain a continuous process. However, this water still contains 353 btu/lb and it can be allowed to rise to a higher elevation and flash steam to supply a lower pressure turbine. At 115 feet, the pounds of water needed to flash one pound of steam will be:
Hsht / (Hwb - Hwht) = 929 + (353 - 243)
= 8.45 lb. water per lb. steam7. There are 46,220 pounds of water remaining (83,500 – 37,280), that can create 5470 pounds per minute or 330,000 pounds per hour of steam to the low-pressure turbine.
The total steam produced for the high and low-pressure turbines is 2,570,000 pounds per hour. If this were produced by a power boiler using number 6 fuel oil at 150,000 Btu per gallon and 85% efficiency, it would be equivalent to:
2,570,000 lb./hr x 1,000 btu/lb / (.85 x 150,000btu/gal)
= 20,160 gallons of fuel oil per hour
= 483,760 gallons of fuel oil per dayGPY = 176,570,000 gallons of fuel oil per year.
At 42 gallons of fuel oil per barrel, and $100 per barrel this is equivalent to saving the American economy more than $430 million per year with no air pollution.
In addition for every pound of steam produced, a pound of pure water is created. Therefore, 60 million gallons of fresh water could be made available each day.