Secondary application of unconverted heat produced during electric power generation has the potential to improve the life-cycle fuel efficiency of the electric power industry and the sectors it serves. This work quantifies the residual heat (also known as waste heat) generated by U.S. thermal power plants and assesses the intermittency and transport issues that must be considered when planning to utilize this heat. Combining Energy Information Administration plant-level data with literature-reported process efficiency data, we develop estimates of the unconverted heat flux from individual U.S. thermal power plants in 2012. Together these power plants discharged an estimated 18.9 billion GJ(th) of residual heat in 2012, 4% of which was discharged at temperatures greater than 90 °C. We also characterize the temperature, spatial distribution, and temporal availability of this residual heat at the plant level and model the implications for the technical and economic feasibility of its end use. Increased implementation of flue gas desulfurization technologies at coal-fired facilities and the higher quality heat generated in the exhaust of natural gas fuel cycles are expected to increase the availability of residual heat generated by 10.6% in 2040.

This review identifies challenges and opportunities facing the electricity generation sector in treating flue gas desulfurization wastewater.

Forward osmosis (FO) has the potential to improve the energy efficiency of membrane-based water treatment by leveraging waste heat from steam electric power generation as the primary driving force for separation. In this study, we develop a comprehensive FO process model, consisting of membrane separation, heat recovery, and draw-solute regeneration (DSR) models. We quantitatively characterize three alternative processes for DSR: distillation, steam stripping, and air stripping. We then construct a mathematical model of the distillation process for DSR that incorporates hydrodynamics, mass-and heattransport resistances, and reaction kinetics, and we integrate this into a model for the full FO process. Finally, we utilize this FO process model to derive a first-order approximation of the water production capacity given the rejected-heat quantity and quality available at U.S. electric power facilities. We find that the upper bound of FO water treatment capacity using low-grade heat sources at electric power facilities exceeds process water treatment demand for boiler water makeup and flue-gas-desulfurization wastewater systems. ■ INTRODUCTIONProposed effluent limitation guidelines at steam electric powergeneration facilities will significantly increase the demand for on-site water treatment. 1 One opportunity to minimize the auxiliary power consumption associated with this treatment capacity is to utilize waste heat available on-site for membranebased water treatment. One potential technology is forward osmosis (FO), where the draw solution is a thermolytic salt (e.g., NH 4 HCO 3 ) ( Figure 1). 2−4 In this two-step process, feedwater is drawn across a semipermeable membrane by a difference in osmotic pressure between the feed solution and the draw solution. The dilute draw solute is then regenerated by thermal decomposition of the thermolytic salt into its constituent gases (i.e., NH 3 and CO 2 ). 5 If waste heat is available, this separation process offers significant electricity savings over reverse osmosis. 6,7 Steam electric power-generation facilities are the largest source of waste heat in the United States, 8 but the feasibility of utilizing this waste heat to drive FO separation processes has yet to be systematically assessed in the peer-reviewed literature. 5,6,9 Past modeling efforts to evaluate the feasibility of waste-heat-driven FO assumed that heat is available at desired quantities and temperatures, 7 whereas experimental demonstrations of FO processes in the peer-reviewed literature utilized electricity or fuel to generate heat. 9−11 This significant gap in the literature exists largely because robust estimates of the quantity, quality, and availability of power-plant waste heat are sparse. 12,13 Our recent work provides estimates of the quantity, quality, and spatial-temporal availability of waste heat for the U.S. power sector over the next 30 years. 14 Demonstrating the feasibility of power-plant waste-heat-driven FO requires the integration of these waste-heat estimates with heat capture, transp...

Coal-fired power plants (CFPPs) generate air, water, and solids emissions that impose substantial human health, environmental, and climate change (HEC) damages. This work demonstrates the importance of accounting for cross-media emissions tradeoffs, plant and regional emissions factors, and spatially variation in the marginal damages of air emissions when performing regulatory impact analyses for electric power generation. As a case study, we assess the benefits and costs of treating wet flue gas desulfurization (FGD) wastewater at US CFPPs using the two best available treatment technology options specified in the 2015 Effluent Limitation Guidelines (ELGs). We perform a life-cycle inventory of electricity and chemical inputs to FGD wastewater treatment processes and quantify the marginal HEC damages of associated air emissions. We combine these spatially resolved damage estimates with Environmental Protection Agency estimates of water quality benefits, fuel-switching benefits, and regulatory compliance costs. We estimate that the ELGs will impose average net costs of $3.01 per cubic meter for chemical precipitation and biological wastewater treatment and $11.26 per cubic meter for zero-liquid discharge wastewater treatment (expected cost-benefit ratios of 1.8 and 1.7, respectively), with damages concentrated in regions containing a high fraction of coal generation or a large chemical manufacturing industry. Findings of net cost for FGD wastewater treatment are robust to uncertainty in auxiliary power source, location of chemical manufacturing, and binding air emissions limits in noncompliant regions, among other variables. Future regulatory design will minimize compliance costs and HEC tradeoffs by regulating air, water, and solids emissions simultaneously and performing regulatory assessments that account for spatial variation in emissions impacts.benefit-cost analysis | coal-fired power plants | Effluent Limitation Guidelines | spatially resolved marginal damages | emissions tradeoffs