Utilization of geopressured resources in the oxidation of organic waste in supercritical water. Phase I, Final report
Geopressured resources are geothermal reservoirs containing dissolved methane in hot brine at pressures well in excess of their in situ hydrostatic pressure. In the US, geopressured resources are primarily located in the Gulf (of Mexico) Coast. The wells in this area are characterized by typical bottomhole temperatures of 120-180 C (250-360 F) (Negus-de Wys, 1991a) and bottomhole pressures of 675-1275 bar (9,800-18,500 psia) (Negus-de Wys, 1991b). Supercritical water oxidation (SCWO) is an emerging technology for the destruction of hazardous organic waste in which oxidation is carried out in a water medium above the critical point of pure water (374 C/705 F, 221 bar/3208 psia) (Tester et al., 1992). Geopressured resources are particularly suitable as an input stream to a SCWO waste treatment process due to the near critical conditions of their hot brine. By using a Rankine-type power cycle, electric power can be generated by capturing the available thermal and hydraulic energy from the geothermal resource and the chemical energy of the dissolved methane released by the oxidation process. In addition to oxidizing the methane to convert the chemical energy to thermal energy, auxiliary fuel in the form of an organic waste can be co-oxidized to increase the energy output to commercially sustainable levels. Coupling the treatment of geopressured brine with an organic waste in a SCWO process synergistically improves power production while providing a means for treating hazardous waste. The objective of this study is to assess the feasibility of using geopressured resources to simultaneously detoxify hazardous waste and generate electric power. Our ultimate aim is to develop conceptual process designs for above-ground and fully or modified in situ approaches to co-processing organic waste with geopressured brine in supercritical water. As a preparatory step for investigating in situ approaches, a realistic above-ground conceptual design was developed in this study. In that concept, the waste, brine and oxidant (air or oxygen) are introduced into the SCWO reactor at the system pressure of 234 bar (3400 psia). The heat of oxidation raises the temperature of the system to about 600 C (1100 F). Due to the low solubility of inorganic salts in supercritical water (about 200 ppm or less) (Armellini and Tester, 1990, 1991a, 1991b), solid salt forms and falls to the lower section of the reactor, where it is cooled and quenched with water, creating a concentrated (organic-free) brine that would be mixed with brackish water and reinjected back to the geopressured well. Power is generated by the expansion of the products of the SCWO process through a series of multi-stage turboexpanden. A processing capacity of 100,000 gallons per day (gpd) was initially taken as the design basis, following some investigations carried out at the Idaho National Engineering Laboratory (Propp et al., 1990). The process was modeled using the ASPEN PLUS{trademark} process flowsheet simulator and material and energy balances were determined. Both the cases of using air and oxygen as oxidant were investigated. Toluene was chosen as the model compound to represent the organic waste. Turbine design calculations based on the volumetric flowrates obtained for a 100,000 gpd capacity resulted in unrealistically high rotor rotational speeds and small wheel pitch diameters to achieve optimum efficiencies. Higher SCWO effluent flowrates would lower rotor rotational speeds and increase wheel pitch diameters to more practical levels. Thus, a 42-fold larger design capacity of 100,000 barrels per day (bpd) was adopted as the basis for an above-ground base case. The results for the material and energy balances for a processing capacity of 100,000 bpd using air and oxygen as oxidant scale up linearly from the results for the 100,000 gpd case. The best case flowsheet corresponding to a 100,000 bpi case using oxygen as oxidant is given in Figure 1. Our conceptual design study suggests that simultaneous detoxification of hazardous waste and production of power is possible by co-processing organic waste with geopressured brine. Net power outputs of about 140 MWe and 160 MWe have been estimated for a processing capacity of 100,000 bpd using air and oxygen as oxidant, respectively.
- Research Organization:
- Massachusetts Institute of Technology, Energy Laboratory, Cambridge, MA (USA)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 896379
- Report Number(s):
- MIT-EL-92-006; TRN: US200705%%31
- Country of Publication:
- United States
- Language:
- English
Similar Records
Feasibility study: Application of the geopressured-geothermal resource to pyrolytic conversion or decomposition/detoxification processes
Properties of Geopressured Brines and Wells in the Gulf Coast and Opportunities for Industrial/Research Participation