Nenad Sarunac | University of North Carolina at Charlotte (original) (raw)

Papers by Nenad Sarunac

Low rank fuels contain significant quantities of water, with the moisture content of subbituminou... more Low rank fuels contain significant quantities of water, with the moisture content of subbituminous coals ranging from 15 to 30 percent and that for lignites from 25 to 40 percent. High fuel moisture causes several adverse impacts on the operation of a pulverized coal generating unit, resulting in fuel handling problems, and affecting heat rate, stack emissions, and the consumption of water used for evaporative cooling. The authors are involved in a research program to develop a process for partially drying coal before it is fed to the pulverizers, using low-grade power plant waste heat. For units with evaporative cooling towers, this process will reduce cooling tower makeup water requirements and also provide heat rate and emissions benefits. This paper describes the results of fluidized bed drying experiments carried out in a small, bench scale batch dryer with lignite and PRB coal and in a 2 ton/hour continuous pilot scale dryer with North Dakota lignite. Comparisons are made with...

Utilities in the U.S. with fossil-fired power plants are required to use continuous emissions mon... more Utilities in the U.S. with fossil-fired power plants are required to use continuous emissions monitoring systems (CEMs) to measure and report quantities such as NOx and SO2 emissions. Among its many components, the typical, most used CEM system includes a flue gas flow meter and a device referred to as a dilution extractive probe for flue gas sampling. Numerous studies have pointed to positive measurement bias errors in these devices which can be as high as 20 percent in some cases. Over-reporting represents the potential for financial losses associated with the NOx and SO2 emissions trading system in the U.S. This paper reports work performed by the Lehigh University Energy Research Center on flow measurement and dilution probe accuracy issues and describes approaches which have been developed to improve measurement performance of stack flow instrumentation and dilution extractive probes. Case studies are presented on the implementation of these approaches to utility stacks which h...

Energies, 2021

The heat transfer performance of a solar external receiver tube with guide vanes was numerically ... more The heat transfer performance of a solar external receiver tube with guide vanes was numerically studied under non-uniform heat flux conditions. Models of the smooth tube and the tube with guide vanes were built. The distributions of the temperature, velocity, turbulence intensity, and Nu predicted by these two models were compared to investigate the heat transfer enhancement and the mixing effect of the guide vanes. The effect of the Re and the α on the heat transfer enhancement was also studied. The results show that the guide vanes form spiraling flows, reduce the maximum tube and molten salt temperatures, and improve the heat transfer. In addition, a more uniform temperature distribution is achieved compared to the smooth tube, allowing the molten salt to work safely under higher heat flux conditions in the receiver tube with guide vanes. It was observed that a larger Re enhances the heat transfer on the tube wall and achieves a longer effective distance of enhanced heat transfe...

Combustion optimization of a pulverized coal-fired boiler is a complex process requiring in-depth... more Combustion optimization of a pulverized coal-fired boiler is a complex process requiring in-depth knowledge of combustion, operation of boiler firing system and other factors affecting emissions and unit performance. For best results, combustion tuning needs to be performed before combustion optimization tests are conducted. Also any, site-specific, operating constraints, such as high CO or opacity, need to be mitigated or removed. Slagging and sootblowing are important parameters that also need to be considered while performing combustion optimization since they affect steam temperatures, boiler and unit operation, performance and emissions. A comprehensive approach to performance improvement and emissions reduction of a tangentially-fired unit is described in this paper. Technical approach to combustion tuning and combustion optimization and achieved results are described and discussed on Part 1 of the paper. Part 2 deals with Electrostatic Precipitator (ESP) performance improveme...

Slagging and fouling of furnaces and boilers' convective pass top the list of costly coal pla... more Slagging and fouling of furnaces and boilers' convective pass top the list of costly coal plant O & M problems. Although sootblowing is a tried and true solution, running sootblowers too often can erode boiler tubes. Lehigh University's Energy Research Center has developed an 'expert' sootblowing system that has outperformed experienced operators' 'seat of their pants' sootblowing procedures on two head-to-head field tests. 7 figs., 2 tabs.

Utilities in the U.S. with fossil-fired power plants are required to use continuous emissions mon... more Utilities in the U.S. with fossil-fired power plants are required to use continuous emissions monitoring systems (CEMs) to measure and report quantities such as NOx and SO2 emissions. Among its many components, the typical, most used CEM system includes a flue gas flow meter and a device referred to as a dilution extractive probe for flue gas sampling. Numerous studies have pointed to positive measurement bias errors in these devices which can be as high as 20 percent in some cases. Overreporting represents the potential for financial losses associated with the NOx and SO2 emissions trading system in the U.S. This paper reports work performed by the Lehigh University Energy Research Center on flow measurement and dilution probe accuracy issues and describes approaches which have been developed to improve measurement performance of stack flow instrumentation and dilution extractive probes. Case studies are presented on the implementation of these approaches to utility stacks which ha...

Fuel

Abstract The energy optimization modeling work described here was performed to determine efficien... more Abstract The energy optimization modeling work described here was performed to determine efficiency improvements that could be achieved for existing coal-fired power plants to retrofit a partial CO2 capture from the post-combustion flue gas for carbon sequestration through thermal integration. The work presented includes optimization of the mono-ethanol amine (MEA)-based post-combustion CO2 capture to reduce energy requirements that could be achieved at existing power plants by thermal integration of the steam turbine cycle, boiler, CO2 compression train and post-combustion CO2 capture process to offset efficiency and capacity losses that would be incurred by retrofit or implementation of post-combustion CO2 capture. Partial CO2 capture, involving treatment of less than 100% of the flue gas leaving the plant and modular design of the CO2 scrubbing system, was also investigated. Thermal integration of the steam turbine cycle with boiler and CO2 compression train improved cycle and plant performance and offset, in part, the negative effects of post-combustion CO2 capture. The best-analyzed integration options improved gross power output by 5% and net unit efficiency by 1.57%, relative to the conventional MEA process. Operating with 40% CO2 capture increased gross power output by 11.6–14% (depending on the MEA thermal integration option), relative to the conventional MEA integration and 90% CO2 capture. The improvement in net unit performance is larger compared to the improvement in turbine cycle performance because of the CO2 compression work, which is also reduced by partial CO2 capture.

International Journal of Heat and Mass Transfer

Abstract A two-dimensional steady-state natural convection heat transfer from a bundle of closely... more Abstract A two-dimensional steady-state natural convection heat transfer from a bundle of closely spaced isothermally heated cylinders in the in-line arrangement was investigated in this study for a laminar flow regime using numerical analysis. It was determined that flow patterns and heat transfer are strongly affected by the transverse and longitudinal cylinder-to-cylinder spacing ST and SL, Rayleigh number, and thermo-physical properties of the heat storage fluid. Performance maps in the form of contour diagrams for the average Nusselt number Nu and dimensionless heat transfer volumetric density q , and corresponding correlations are presented for an in-line bundle of 9 × 5 horizontal cylinders immersed in a molten solar salt. The variation of the heat transfer enhancement for the in-line bundle of horizontal cylinders shows that there is an optimal cylinder spacing resulting in the highest heat transfer enhancement. The heat exchanger geometry was optimized by determining the optimal set of the tube (cylinder) spacings SL/D and ST/D in the bundle resulting in the maximum volumetric heat transfer rate q , and smallest size and lowest cost of a heat exchanger. A set of correlations were developed for the maximum and optimum dimensionless heat transfer volumetric densities as functions of the Rayleigh number RaD. The analyzed geometries are important in the solar heating and storage technology, nuclear reactor safety, and waste heat recovery applications.

Journal of Energy Storage

Abstract A two-dimensional steady-state natural convection heat transfer from a single row of clo... more Abstract A two-dimensional steady-state natural convection heat transfer from a single row of closely spaced isothermally heated cylinders was investigated in this study for a laminar flow regime. A few previous studies investigated the natural convection heat transfer from a single row of isothermally heated cylinders. However, no correlations or performance maps were developed for the average Nusselt number N u ¯ D for a single row of horizontal cylinders. Using the correlations proposed for natural convection heat transfer from a single cylinder results in large errors in predicting the heat transfer for multiple cylinders. Thus, numerical and statistical modeling were performed in this study to propose correlations for the average Nusselt number N u ¯ D for a single row of horizontal cylinders immersed in molten solar salt as functions of Rayleigh number R a D and dimensionless cylinder-to-cylinder spacing ( ST/D ) . The analyzed geometries are important in the solar heating and heat storage technology, nuclear reactor safety and waste heat recovery applications.

Sustainability

The analysis and optimization of an organic Rankine cycle (ORC) used as a bottoming cycle in the ... more The analysis and optimization of an organic Rankine cycle (ORC) used as a bottoming cycle in the Brayton/ORC and steam Rankine/ORC combined cycle configurations is the main focus of this study. The results show that CO2 and air are the best working fluids for the topping (Brayton) cycle. Depending on the exhaust temperature of the topping cycle, Iso-butane, R11 and ethanol are the preferred working fluids for the bottoming (ORC) cycle, resulting in the highest efficiency of the combined cycle. Results of the techno-economic study show that combined Brayton/ORC cycle has significantly lower total capital investment and levelized cost of electricity (LCOE) compared to the regenerative Brayton cycle. An analysis of a combined steam Rankine/ORC cycle was performed to determine the increase in power output that would be achieved by adding a bottoming ORC to the utility-scale steam Rankine cycle, and determine the effect of ambient conditions (heat sink temperature) on power increase. For...

ABSTRACT This report is the result of an evaluation of an invention by John Hunter of Edinburgh, ... more ABSTRACT This report is the result of an evaluation of an invention by John Hunter of Edinburgh, Scotland, which was submitted to the Department of Energy for evaluation under Section 14 of the Federal Nonnuclear Energy Research and Development Act of 1974. The invention is based on the use of a rotating fluidized bed for coal conversion. No working models of the invention have been built to date. As part of the evaluation process, Lehigh University's Energy Research Center was asked by DOE to conduct an engineering analysis of the invention and make comparisons with alternative power generation systems. Power generation cycle efficiencies were computed, component sizes were specified, cost data were gathered and relative cost comparisons were made between the Hunter power generation systems and some alternatives. Finally a review of the operational characteristics of the Hunter concepts was carried out. The major unknown quantities were identified and a list of future development needs was specified.

Low rank fuels contain significant quantities of water, with the moisture content of subbituminou... more Low rank fuels contain significant quantities of water, with the moisture content of subbituminous coals ranging from 15 to 30 percent and that for lignites from 25 to 40 percent. High fuel moisture causes several adverse impacts on the operation of a pulverized coal generating unit, resulting in fuel handling problems, and affecting heat rate, stack emissions, and the consumption of water used for evaporative cooling. The authors are involved in a research program to develop a process for partially drying coal before it is fed to the pulverizers, using low-grade power plant waste heat. For units with evaporative cooling towers, this process will reduce cooling tower makeup water requirements and also provide heat rate and emissions benefits. This paper describes the results of fluidized bed drying experiments carried out in a small, bench scale batch dryer with lignite and PRB coal and in a 2 ton/hour continuous pilot scale dryer with North Dakota lignite. Comparisons are made with...

Utilities in the U.S. with fossil-fired power plants are required to use continuous emissions mon... more Utilities in the U.S. with fossil-fired power plants are required to use continuous emissions monitoring systems (CEMs) to measure and report quantities such as NOx and SO2 emissions. Among its many components, the typical, most used CEM system includes a flue gas flow meter and a device referred to as a dilution extractive probe for flue gas sampling. Numerous studies have pointed to positive measurement bias errors in these devices which can be as high as 20 percent in some cases. Over-reporting represents the potential for financial losses associated with the NOx and SO2 emissions trading system in the U.S. This paper reports work performed by the Lehigh University Energy Research Center on flow measurement and dilution probe accuracy issues and describes approaches which have been developed to improve measurement performance of stack flow instrumentation and dilution extractive probes. Case studies are presented on the implementation of these approaches to utility stacks which h...

Energies, 2021

The heat transfer performance of a solar external receiver tube with guide vanes was numerically ... more The heat transfer performance of a solar external receiver tube with guide vanes was numerically studied under non-uniform heat flux conditions. Models of the smooth tube and the tube with guide vanes were built. The distributions of the temperature, velocity, turbulence intensity, and Nu predicted by these two models were compared to investigate the heat transfer enhancement and the mixing effect of the guide vanes. The effect of the Re and the α on the heat transfer enhancement was also studied. The results show that the guide vanes form spiraling flows, reduce the maximum tube and molten salt temperatures, and improve the heat transfer. In addition, a more uniform temperature distribution is achieved compared to the smooth tube, allowing the molten salt to work safely under higher heat flux conditions in the receiver tube with guide vanes. It was observed that a larger Re enhances the heat transfer on the tube wall and achieves a longer effective distance of enhanced heat transfe...

Combustion optimization of a pulverized coal-fired boiler is a complex process requiring in-depth... more Combustion optimization of a pulverized coal-fired boiler is a complex process requiring in-depth knowledge of combustion, operation of boiler firing system and other factors affecting emissions and unit performance. For best results, combustion tuning needs to be performed before combustion optimization tests are conducted. Also any, site-specific, operating constraints, such as high CO or opacity, need to be mitigated or removed. Slagging and sootblowing are important parameters that also need to be considered while performing combustion optimization since they affect steam temperatures, boiler and unit operation, performance and emissions. A comprehensive approach to performance improvement and emissions reduction of a tangentially-fired unit is described in this paper. Technical approach to combustion tuning and combustion optimization and achieved results are described and discussed on Part 1 of the paper. Part 2 deals with Electrostatic Precipitator (ESP) performance improveme...

Slagging and fouling of furnaces and boilers' convective pass top the list of costly coal pla... more Slagging and fouling of furnaces and boilers' convective pass top the list of costly coal plant O & M problems. Although sootblowing is a tried and true solution, running sootblowers too often can erode boiler tubes. Lehigh University's Energy Research Center has developed an 'expert' sootblowing system that has outperformed experienced operators' 'seat of their pants' sootblowing procedures on two head-to-head field tests. 7 figs., 2 tabs.

Utilities in the U.S. with fossil-fired power plants are required to use continuous emissions mon... more Utilities in the U.S. with fossil-fired power plants are required to use continuous emissions monitoring systems (CEMs) to measure and report quantities such as NOx and SO2 emissions. Among its many components, the typical, most used CEM system includes a flue gas flow meter and a device referred to as a dilution extractive probe for flue gas sampling. Numerous studies have pointed to positive measurement bias errors in these devices which can be as high as 20 percent in some cases. Overreporting represents the potential for financial losses associated with the NOx and SO2 emissions trading system in the U.S. This paper reports work performed by the Lehigh University Energy Research Center on flow measurement and dilution probe accuracy issues and describes approaches which have been developed to improve measurement performance of stack flow instrumentation and dilution extractive probes. Case studies are presented on the implementation of these approaches to utility stacks which ha...

Fuel

Abstract The energy optimization modeling work described here was performed to determine efficien... more Abstract The energy optimization modeling work described here was performed to determine efficiency improvements that could be achieved for existing coal-fired power plants to retrofit a partial CO2 capture from the post-combustion flue gas for carbon sequestration through thermal integration. The work presented includes optimization of the mono-ethanol amine (MEA)-based post-combustion CO2 capture to reduce energy requirements that could be achieved at existing power plants by thermal integration of the steam turbine cycle, boiler, CO2 compression train and post-combustion CO2 capture process to offset efficiency and capacity losses that would be incurred by retrofit or implementation of post-combustion CO2 capture. Partial CO2 capture, involving treatment of less than 100% of the flue gas leaving the plant and modular design of the CO2 scrubbing system, was also investigated. Thermal integration of the steam turbine cycle with boiler and CO2 compression train improved cycle and plant performance and offset, in part, the negative effects of post-combustion CO2 capture. The best-analyzed integration options improved gross power output by 5% and net unit efficiency by 1.57%, relative to the conventional MEA process. Operating with 40% CO2 capture increased gross power output by 11.6–14% (depending on the MEA thermal integration option), relative to the conventional MEA integration and 90% CO2 capture. The improvement in net unit performance is larger compared to the improvement in turbine cycle performance because of the CO2 compression work, which is also reduced by partial CO2 capture.

International Journal of Heat and Mass Transfer

Abstract A two-dimensional steady-state natural convection heat transfer from a bundle of closely... more Abstract A two-dimensional steady-state natural convection heat transfer from a bundle of closely spaced isothermally heated cylinders in the in-line arrangement was investigated in this study for a laminar flow regime using numerical analysis. It was determined that flow patterns and heat transfer are strongly affected by the transverse and longitudinal cylinder-to-cylinder spacing ST and SL, Rayleigh number, and thermo-physical properties of the heat storage fluid. Performance maps in the form of contour diagrams for the average Nusselt number Nu and dimensionless heat transfer volumetric density q , and corresponding correlations are presented for an in-line bundle of 9 × 5 horizontal cylinders immersed in a molten solar salt. The variation of the heat transfer enhancement for the in-line bundle of horizontal cylinders shows that there is an optimal cylinder spacing resulting in the highest heat transfer enhancement. The heat exchanger geometry was optimized by determining the optimal set of the tube (cylinder) spacings SL/D and ST/D in the bundle resulting in the maximum volumetric heat transfer rate q , and smallest size and lowest cost of a heat exchanger. A set of correlations were developed for the maximum and optimum dimensionless heat transfer volumetric densities as functions of the Rayleigh number RaD. The analyzed geometries are important in the solar heating and storage technology, nuclear reactor safety, and waste heat recovery applications.

Journal of Energy Storage

Abstract A two-dimensional steady-state natural convection heat transfer from a single row of clo... more Abstract A two-dimensional steady-state natural convection heat transfer from a single row of closely spaced isothermally heated cylinders was investigated in this study for a laminar flow regime. A few previous studies investigated the natural convection heat transfer from a single row of isothermally heated cylinders. However, no correlations or performance maps were developed for the average Nusselt number N u ¯ D for a single row of horizontal cylinders. Using the correlations proposed for natural convection heat transfer from a single cylinder results in large errors in predicting the heat transfer for multiple cylinders. Thus, numerical and statistical modeling were performed in this study to propose correlations for the average Nusselt number N u ¯ D for a single row of horizontal cylinders immersed in molten solar salt as functions of Rayleigh number R a D and dimensionless cylinder-to-cylinder spacing ( ST/D ) . The analyzed geometries are important in the solar heating and heat storage technology, nuclear reactor safety and waste heat recovery applications.

Sustainability

The analysis and optimization of an organic Rankine cycle (ORC) used as a bottoming cycle in the ... more The analysis and optimization of an organic Rankine cycle (ORC) used as a bottoming cycle in the Brayton/ORC and steam Rankine/ORC combined cycle configurations is the main focus of this study. The results show that CO2 and air are the best working fluids for the topping (Brayton) cycle. Depending on the exhaust temperature of the topping cycle, Iso-butane, R11 and ethanol are the preferred working fluids for the bottoming (ORC) cycle, resulting in the highest efficiency of the combined cycle. Results of the techno-economic study show that combined Brayton/ORC cycle has significantly lower total capital investment and levelized cost of electricity (LCOE) compared to the regenerative Brayton cycle. An analysis of a combined steam Rankine/ORC cycle was performed to determine the increase in power output that would be achieved by adding a bottoming ORC to the utility-scale steam Rankine cycle, and determine the effect of ambient conditions (heat sink temperature) on power increase. For...

ABSTRACT This report is the result of an evaluation of an invention by John Hunter of Edinburgh, ... more ABSTRACT This report is the result of an evaluation of an invention by John Hunter of Edinburgh, Scotland, which was submitted to the Department of Energy for evaluation under Section 14 of the Federal Nonnuclear Energy Research and Development Act of 1974. The invention is based on the use of a rotating fluidized bed for coal conversion. No working models of the invention have been built to date. As part of the evaluation process, Lehigh University's Energy Research Center was asked by DOE to conduct an engineering analysis of the invention and make comparisons with alternative power generation systems. Power generation cycle efficiencies were computed, component sizes were specified, cost data were gathered and relative cost comparisons were made between the Hunter power generation systems and some alternatives. Finally a review of the operational characteristics of the Hunter concepts was carried out. The major unknown quantities were identified and a list of future development needs was specified.