(218c) Modeling, Simulation and Optimization of a Synergistically Mixed Blowdown Water and Produced Water Wastewater Treatment Process

Water consumption and treatment is an underlying but significant aspect within processes in the energy sector. In particular, producing cost optimum designs of wastewater treatment processes is becoming increasingly important. In thermoelectric power plants, blowdown water streams are a result of cooling tower operations. These streams are purged to remove residual contaminants within the recycled flow, and fresh water is sourced to makeup for this purge and additional evaporative losses. Within the fracking industry, produced water is a high salinity wastewater that results from the extraction process in oil and gas wells. Produced water treatment is notably expensive and thus traditionally this water is disposed of by underground injection. Under analysis of these two separately generated waters, the contaminants of each have chemically complimentary constituents and may be synergistically mixed. A combined treatment process where these two waters are mixed is an identified new approach to alleviate chemical and energy demands of the blowdown water treatment process, maximize reuse of the treated water within the cooling tower, and provide an advantageous and sustainable treatment to a portion of the produced water.

In this work, improvements to the blowdown water treatment process by introduction of produced water are assessed. Specifically, the mixed wastewater treatment design is proposed to maximize water reuse and saleable by-product generation while reducing chemical and energy costs. This treatment train is designed such that usable makeup water and 10-lb Brine are generated with supplementary production of treatment additives including sodium hydroxide, sodium hypochlorite, and chlorine. The proposed design also provides treatment units for direct integration with a thermoelectric power plant. The process flowsheet is modeled in Aspen Plus with inclusion of custom process models for water treatment unit operations not found within the software’s internal model library. Results generated from this flowsheet are evaluated in comprehensive techno-economic and sustainability analyses. Established tools in GREENSCOPE^[1] and a pollution control unit (PCU) and life cycle inventory (LCI) framework^[2] are used to quantify sustainability indicators and holistically evaluate process sustainability. The improved quality of the mixed treatment design is illustrated by the multi-objective sustainability assessment and cost optimization of the modeled process.

References

[1] Ruiz-Mercado, G. J., Smith, R. L., & Gonzalez, M. A. (2012). Sustainability indicators for chemical processes: I. Taxonomy. Industrial & Engineering Chemistry Research, 51(5), 2309-2328.

[2] Li, S., Feliachi, Y., Agbleze, S., Ruiz-Mercado, G. J., Smith, R. L., Meyer, D. E., & Lima, F. V. (2018). A process systems framework for rapid generation of life cycle inventories for pollution control and sustainability evaluation. Clean Technologies and Environmental Policy, 20(7), 1543-1561.