Author ORCID Identifier

https://orcid.org/0000-0001-8788-095X

Semester

Fall

Date of Graduation

2023

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Lian-Shin (Lance) Lin

Committee Member

Leslie Hopkinson

Committee Member

Kevin Orner

Committee Member

Fernando Lima

Committee Member

Nicholas Siefert

Abstract

Cooling of low-pressure steam and flue gas desulfurization (FGD) process at coal-fired powerplants often require large quantities of freshwater and can generate waste streams from the blowdown (BD) operations. Treating these wastewaters for reuse can offset the freshwater demand, which is beneficial especially in semiarid and arid regions. However, the traditional treatment (i.e., chemical softening and evaporation) of cooling BD water (BDW) is chemical- and energy-intensive and adds to the overall costs of water management for powerplants. Furthermore, the updated Effluent Limitation Guidelines and Standards for powerplants set forth by the U.S. Environmental Protection Agency (EPA) require a change of technology-basis for FGD effluent. Considering the freshwater demand and need of water recovery, the overarching goal of this research is to develop innovative wastewater treatment schemes that encourage zero liquid discharge (ZLD) systems with the potential to recover valuable resources (i.e., critical minerals and low-salinity water).

Taking advantage of the complementary chemistries of the BDWs and produced water (PW) from unconventional oil and gas production and their co-locations, this study assessed the feasibility of co-treatment of these wastewaters for resource recovery and reduced chemical- and energy footprints. Specifically, the high barium content in PW and high sulfate in Cooling BDW and FGD effluent offer opportunities for barite (i.e., barium sulfate) production from co-treatment of the two wastewaters and result in a reduction in chemical costs. The high total dissolved solids (TDS) of PW can be strategically exploited in the co-treatment schemes to produce high-strength 10-lb brine (i.e., saturated sodium chloride) of commercial value, which otherwise is unfeasible if PW is to be treated alone. The primary objectives of this Ph.D. research are to (i) quantify resource recovery potential and chemical savings of a previously developed co-treatment process for cooling blowdown and produced waters; (ii) design and evaluate treatment methods for managing FGD effluent and resource recovery; (iii) conduct pilot testing of FGD effluent and PW co-treatment and resource recovery; and (iv) conduct techno-economic analysis on the co-treatment of FGD effluent and PW.

In addition to an overview of treatment methods for BDWs and PW (Chapter 1), this dissertation is organized to evaluate two co-treatment schemes of BDWs and PW. The first co-treatment scheme was designed for cooling BDW and PW to recover barite and low-salinity water for reuse. It consists of mixing of cooling BDW and PW, chemical softening, activated carbon (AC) filtration, and reverse osmosis (RO). Previous studies by Golnoosh Khajouei showed that softening using sodium carbonate (Na₂CO₃) and sodium hydroxide (NaOH) removed >95% scale forming divalent ions, and the AC filtration resulted in 90% total organic carbon removal. The effluent from softening and AC treatments was conducive to downstream RO treatment, which showed high water recovery (60%) under an applied gauge pressure of 800 psi (55 bar or 5.5 MPa). Building upon Khajouei’s research, studies conducted in this research showed that a simple mixing of BDW and PW (i.e., BDW: PW = 5:1) readily generated barite (production yield: 1.92 kg/m³ of mixed water; dry density: 4.1 g/cm³) as the predominant solid. Compared to cooling BDW and PW treated separately, the co-treatment process resulted in 70% chemical savings and production of 10-lb brine from the co-treatment method. Overall, the co-treatment of cooling BDW and PW demonstrated potential for sustainable wastewater management. These results are summarized in Chapter 2.

The second co-treatment scheme was designed by Dr. Nicholas Siefert of the National Energy Technology Laboratory (NETL) of the Department of Energy (DOE) for FGD effluent and PW. This research tested the treatment process using both synthetic and field-collected FGD and PW. The FGD effluent characterization and treatment methods evaluation are summarized in Chapter 3. The treatment units consisted of chemical softening, nanofiltration (NF), and mechanical mixing followed by RO. Jar Tests of chemical softening using Na₂CO₃ indicated pH 8.5 for selective Ca precipitation as calcium carbonate (i.e., calcite). From bench scale tests, a commercial NF 270-4040 was chosen, and four elements connected in parallel were assembled for a pilot process to increase the sulfate level in the NF-concentrate. The mixing of NF-concentrate and PW resulted in white precipitates, and the SEM-EDS analysis suggests that the precipitates are primarily barite. The batch treatment of NF-permeate using six Hydranautics SWC5-LD-4040 (equivalent to FilmTecTM SW30-4040) RO elements connected in series demonstrated the potential of recovering low-salinity water and concentrating brine stream.

The technical feasibility of a pilot process constructed by integrating all individual treatment units (discussed in Chapter 3) for critical minerals and water recovery was demonstrated and evaluated in Chapter 4. The results indicate that the co-treatment generates 30 kg/m³ calcite that can be used in SO₂ scrubber processes, and 7.5 kg/m³ high-density (i.e., 4.1 g/cm³) barite that meets the American Petroleum Institute (API) specification of Grade 4.1 for uses as a weight agent in drilling. The system water recovery by RO treatment was estimated to be 64%. The low-salinity (i.e., TDS

Lastly, a techno-economic analysis (TEA) was conducted (Chapter 5) to evaluate commercial feasibility of co-treating FGD effluent and PW. In addition to estimating the total levelized cost, a sensitivity analysis was conducted to identify the most important economic parameters that impact the overall economic feasibility of the co-treatment framework. Utilizing experimental results and relevant economic data in the literature, the TEA results suggest tremendous economic potential, with a positive levelized cost ($2.87 per m³ inflow [FGD effluent plus PW flowrates]) and a high internal rate of return (24%/yr). The chemical cost for softening was identified as the principal cost component; however, the major portion (i.e., 94%) of this cost can be offset by the value of the recovered calcite and barite. In addition to the potential of barite, a significant economic return can be realized due to the PW co-treatment, which would otherwise be an economic burden for energy producers. Overall, the TEA results encourage large scale implementation of FGD effluent and PW co-treatment to promote resource recovery.

Embargo Reason

Publication Pending

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