Flue Gas Heat Recovery Research Articles

Modeling and Optimization of the Flue Gas Heat Recovery of a Marine Dual-Fuel Engine Based on RSM and GA

Implementation of flue gas waste heat recovery is an effective way to improve the energy utilization of marine engines. This paper aims to model and optimize a marine four-stroke dual-fuel (DF) engine coupled with a flue gas waste heat recovery system. Firstly, the DF engine and waste heat recovery system were respectively modeled in GT-Power and Simulink environments and verified with experimental data. Then, a regression model was built using the response surface method, with the intake temperature, compression ratio, and pilot fuel injection timing as input parameters and parametric analysis was performed. Finally, multi-objective optimization of the waste heat recovery system was performed using a genetic algorithm. The result showed that the optimal solution is obtained when the intake temperature is 306.18 K, the geometric compression ratio is 14.4, and the pilot fuel injection timing is −16.68 °CA after the top dead center. The corresponding brake-specific fuel consumption was 155.18 g/kWh, reduced by 3.24%, and the power was 8025.62 kW, increased by 0.32%. At the same time, 280.98 kW of flue gas waste heat generation was obtained.

Experimental investigation of a high-temperature heat pump for industrial steam production

Low-temperature flue gas heat recovery acts as an important way for energy saving and emission reduction in industry sectors. It is difficult to reuse low-temperature heat in the industrial production process, upgrading low-temperature heat using a heat pump is a promising approach to pursue. In this work, an experimental prototype of a high-temperature compression-absorption heat pump was conducted and investigated. Driving by low-grade waste heat and a small amount of electricity, using ammonia-water as a working fluid, this heat pump experimental prototype can produce high-temperature (more than 150 °C) process steam for industrial processes. The operation strategies of the experimental system are clarified and programmed into the control system. Two hours of automatic stable operation indicates the operation strategies are suitable for this high-temperature heat pump. The temperature and pressure of the produced steam are 154 °C and 0.53 MPa, respectively. The steam heat output of the heat pump experimental prototype reaches 70.15 kW, in which the electric heating share is 18.9% and the waste heat heating share reaches 81.1%. The experimental results indicate the hybrid heat pump is capable of recovering low-temperature (less than 170 °C) flue gas heat for process steam generation. This work provides a new approach to upgrade low-temperature waste heat for process steam production.

Performance analysis of a novel double stage multifunctional open absorption heat pump system: An industrial moist flue gas heat recovery application

Rising industrial energy consumption and waste heat in moist flue gas exhausts are the key scientific issues. A potential hybrid system with efficient heat recovery technology can fulfill the industrial energy demand for dehumidification, heating and cooling applications by utilizing the waste latent heat. The main objective of this study is to present a multifunctional hybrid system for double stage open absorption cycle to recover the latent heat from the exhaust moist flue gas for heating and to dehumidify the ambient humid air for cooling applications by operating at low-grade heat source. The validated thermodynamic models for energy and exergy analysis are developed for its performance optimization and to conduct a comparison with single stage system. The operating inlet parameters are varied to analyze the performance of both systems. The parametric study results showed that the double stage system can operate for a wider moist gas humidity range such as 0.054–0.2 kg/kg at lower regeneration heat source of 96.3℃ with varying thermal performance of 1.24–2.39 as compared to the single stage system which operates for 0.118–0.2 kg/kg and at 112.3–153.8℃. Furthermore, this hybrid system is capable to provide heating effect of 280.1 kW at thermal performance of 1.73 and 9.85 kW cooling capacity while operating at 113.7℃ heat source temperature. The thermal performance of system is related to the operating pressure in low pressure generator and can be increased 8–11% when pressure is increased from 25 kPa to 35 kPa. However, the cooling capacity is found to be sensitive only to the absorbers and the dew point cooler. The exergy performance results indicate that the exergy efficiency of double stage system is 3–16% higher as compared to single stage with effect of regeneration temperature and varies from 46.2 to 58.63%. Moreover, the highest exergy destruction is found to be in regenerators which accounts for about 49–51% of overall destructed exergy.

Experimental and simulation study on heat and mass transfer characteristics in direct-contact total heat exchanger for flue gas heat recovery

Direct-contact total heat exchange with liquid desiccant produces enormous gains in both sensible and latent heat recovery of low-grade flue gas. Previous studies related to that has tended to focus on the system performance rather than the heat and mass transfer characteristics, which is equally essential to their design, simulation and operation. This paper establishes an experimental system to investigate the heat and mass transfer characteristics in direct-contact total heat exchanger for flue gas total heat recovery. Ceramic structured packing is adopted considering its corrosion and high-temperature resistances; calcium chloride aqueous solution is employed as the coolant and absorbent for its low cost and high latent heat recovery capability. Based on those, the effects of flue gas and solution inlet parameters on the performance indices, including sensible and latent heat recovery capacities, latent heat rate and total heat recovery rate, are tested and analyzed. Coupled heat and mass transfer models between flue gas and solution in this process are developed, which feature the enthalpy of dilution. By combining the models and experimental data, heat and mass transfer coefficients are calculated and fitted. In addition, the effect of packing height on total heat recovery capacity and ratio is investigated through simulations. The results show that the total heat recovery rate of 74.7% can be achieved at packing height to 1.5 m when liquid–gas ratio is 5.172.

CHISA 2021 virtually – Worldwide Chemical Engineers Meeting

CHISA 2021 virtually – Worldwide Chemical Engineers Meeting You have just accessed a special issue of Chemical Engineering & Technology which is composed of contributions presented at the 24th International Congress of Chemical and Process Engineering CHISA held virtually on March 15–18, 2021 due to the pandemic of covid-19. Despite the difficult situation for both the organizers and the participants in regard to a new conference format, I feel that a nice virtual meeting of chemical engineers from all over the world was organized. However, it is clear that face-to-face discussions and meeting others in person cannot be easily replaced. The CHISA 2021 congress addressed the full spectrum of chemical and process engineering topics, such as reaction and catalysis engineering, separation processes, fluid flow and multiphase systems, computer-aided process engineering, and pharmaceutical engineering. Many interesting lectures and talks were presented, some of which are part of this special issue. The presented topics reflect the current focus of chemical engineering research on socially relevant subjects, such as decreasing environmental pollution. Studies on this topic deal with, e.g., introducing a new technology for efficient cleaning and heat recovery of flue gas from small-scale boilers, optimizing combustion processes via plasma activation while minimizing harmful emissions or removal of VOCs using an ionic liquid membrane. Another important topic is the transition from coal to green energy sources and the utilization of energy from waste; this is covered in studies on biomass gasification/combustion and fast pyrolysis of biomass and PE waste. Also included are studies of two-phase flow CFD modeling and image analysis of flow maldistribution during boiling in parallel minichannels and the utilization of catalytic processes to produce alkanes, biofuels, or synthesis gas. This is just a small sample of studies contained in this issue and I wish every reader to find a topic of interest. I want to thank the CHISA 2021 Scientific and Organizing Committees for providing an excellent platform and I hope that the next conference in 2022 will be in the usual format, allowing us again to meet in person in Prague. Prof. Dr.-Ing. Lucie Obalová Institute of Environmental Technology, CEET, VSB-Technical University of Ostrava Lucie Obalová

Efficient Cleaning and Heat Recovery of Flue Gas from a Small‐Scale Boiler

AbstractSmall‐scale biomass boilers contribute to the emission of particulate matter (PM) to the environment. In this study, the performance of a wet‐scrubber purification system for flue gas was experimentally investigated. The experimental setup consisted of a boiler, a wet scrubber, a generator, and heat exchangers. The results showed an average PM collection efficiency of ca. 42 % for a PM size range of 0.08–10 µm over a testing period of five months. Furthermore, the results showed an improvement in the heat recovery of about 18 %. Focusing only on the heat losses through exhaust flue gases, the losses were shown to have decreased by 72 %. During the total testing period of 8.5 months, no decrease could be noticed in the absorption solution ability.

Investigation of the forced-convection heat-transfer in the boiler flue-gas heat recovery units employing the real-time measured database

Extra moistures condensation and extraction from the boiler flue-gas have been proven to be an effective measure to enhance the thermal efficiency of the boiler system. Previous researches on the condensing flue-gas heat recovery unit was based on the controlled lab condition or instant site measurement which was unable to reflect the long-term real performance of the boiler system with flue-gas heat recovery units. This research employed the real-time measurement database established between 2008 and 2019 to investigate the heat transfer at the flue-gas heat recovery unit. This solution can evaluate the long-term dynamic heat-transfer performance of the flue-gas heat recovery unit. A semi-experimental formula was established to address the relationship between the dew point temperature and heat transfer coefficient of the flue gas. It was found that the heat-transfer coefficient is sensitive to the inlet temperature of cooling water. Further, a dimensionless formula was established to address the relation among the convection heat-transfer coefficient and its other operational parameters. The all-applicable criterion equation that can judge the heat and mass transfer performance of flue-gas heat recovery units, and assess the energy saving potential of the boiler system with such a unit.

Technology for Optimizing Flue Gas Pollutant Emission Reduction in Oil Field Heating Furnace Combustion

The energy consumption of the heating furnace is an important part of the energy consumption of the oilfield gathering and transportation system. The low energy efficiency of the heating furnace will directly lead to the increase of oilfield production costs. In response to the national energy-saving and emission-reduction policy, the oilfield has implemented energy-saving practices in heating furnace load adjustment, efficient combustion, excess air coefficient control, flue gas waste heat utilization, and furnace modification. It is clear that the energy efficiency of oilfield heating furnaces is still lower than foreign advanced levels. There is an urgent need for further energy conservation and efficiency enhancement. MVR low-temperature flue gas heat recovery technology, flame shape matching technology, nanofluid heat transfer enhancement technology, solar auxiliary heating technology and other new technologies that can be used for energy saving and consumption reduction of oilfield heating furnaces provide a reference for oilfield heating furnaces to tap the potential and increase efficiency.

Experimental and numerical studies on novel airfoil fins heat exchanger in flue gas heat recovery system

• The novel airfoil fins heat exchanger was studied experimentally and numerically. • The novel airfoil fins channel has the best thermal–hydraulic performance. • The enhancement mechanism could be explained with field synergy principle. • Thermal-hydraulic correlations of novel airfoil heat exchanger were proposed. To improve the performance of waste heat recovery, a novel airfoil fins heat exchanger was applied to flue gas waste heat recovery. Two groups of experimental conditions were installed to test the heat effectiveness of the novel airfoil fins heat exchanger. The results showed that the heat effectiveness of the novel airfoil fins heat exchanger could reach more than 96%, which is higher than the conventional heat exchanger. The thermal–hydraulic performances of the novel airfoil channel, NACA 0020 airfoil channel and zigzag channel were investigated with the first and second laws of thermodynamics, which showed that the novel airfoil channel has the best comprehensive thermal–hydraulic performance among the three channels. The correlations of Nusselt number and friction factor of the novel airfoil fins heat exchanger were proposed for flue gas, whose maximum deviations were within ±5.0% and ±7.1%, respectively. The present work could provide guidance for the application of the novel airfoil fins heat exchanger in waste heat recovery.

Numerical investigation of the optimization of phase change thermal storage units with air as heat transfer fluid

Phase change thermal storage units (TSUs) that use air as heat transfer fluid (HTF) are in huge demand in the fields of building heating, solar energy utilization, and flue gas heat recovery. Researchers have developed various air-based TSUs and used different methods to optimize their structure. In the current study, the structural parameters of a novel TSU with air as the HTF are optimized using a comprehensive method that combines overall thermal resistance analysis and numerical simulation. The influence of different HTF injection methods on the natural convection of a phase change material (PCM) and the effects of different structural parameters on the TSU's charge performance were investigated. Results indicated that the heat transfer thermal resistance of the developed TSU is mostly concentrated in the PCM side. When the depth direction of the flat tube was perpendicular to the direction of gravity and the HTF adopted side injection, the phase change completion time was shortened by 20.59% compared with that in the original TSU. Thermal resistance balance was achieved in the air and PCM sides when the rib height, pitch, and thickness of the flat tube were 0.03, 0.0232, and 0.00025 m, respectively. At this moment, the compact factor and effectiveness of the novel TSU were 1.63 times and 10.52% higher than those of the original TSU, respectively.

Techno-Economic Assessment of Enamel Heat Pipe Exchanger in a Combined Heat and Power Plant With Back Pressure Turbine

Abstract The enamel heat pipe exchanger (EHPE) is a promising technology for waste heat recovery of coal-fired flue gas due to its abilities to resist acid corrosion, erosive wear, and ash deposit. This article presents a techno-economic assessment of EHPE based on an existing 135 t/h combined heat and power plant (CHP). The results indicated that over the 50–70 °C exhaust temperature range of flue gas, the application of EHPE could obviously improve the energy efficiency and slightly promote the exergy efficiency. The energy and exergy efficiencies gradually increase with the decrease in the exhaust temperature. However, the increased revenue by fuel saving could be totally offset by the decreased revenue in electricity selling. The net annual revenue would probably turn to be negative when coal price is low and electricity price is relatively high. One should pay more attention to the economic aspects for the application of EHPE.

Incorporating ash removal unit in local rice parboiling industries for flue gas cleaning and heat recovery

Local rice parboiling industries of Bangladesh are burdened with heavy emission. Despite recent modification in the rice-parboiling boiler, the amount of stack emission (especially particulate matter) from local rice parboiling industry is still considerably high to jeopardize public health and environmental sustainability. There is no provision of flue gas cleaning in these industries since flue gas cleaning often requires significant investment, complicated installation and heavy-maintenance. Therefore, a modified flue gas cleaning system, namely Ash removal unit (ARU) was designed for simultaneously and synergistically removing particulate matter (PM), SO2, NOx, CO2 and heat from flue gas of local rice parboiling industries. In this study, ARU was incorporated in a local rice parboiling industry in order to evaluate the co-removal efficiency achieved by the ARU. Installation of ARU eliminated PM from flue gas by 91.8%, while it removed 78.5% SO2, 78.3% NOx and 23.9% CO2 respectively from the emitting stack. Other than flue gas cleaning , ARU also facilitates heat exchange between flue gas and boiler feed water. Hence, flue gas temperature was dropped by 42.1%, while boiler feed water temperature was raised by 36% in 30 min. Moreover, adopting ARU also improved the ambient air quality surrounding the industrial area, since it reduced SO2, NOx, SPM, PM2.5 and PM10 level in ambient air by 81.7%, 78.2%, 21.1%, 22.9% and 43.1% respectively.

Компоновочное решение блочно-модульной котельной с установкой контактного теплоутилизатора дымовых газов

Компоновочное решение блочно-модульной котельной с установкой контактного теплоутилизатора дымовых газов

Characterization of a new total heat recovery system using CaCl2 as working fluid: Thermal modeling and physical analysis

• A new type of heat pump system is proposed. • The variation trend of three working medium in absorber is analyzed. • The rise of flue gas temperature can reduce the harmful substances by more than 50%. • The advantages of the system compared with LiBr absorption heat pump are analyzed. This paper introduces a kind of open cycle absorption heat wet flue gas heat recovery system, which use CaCl 2 as the working medium. The system will use the wet heat recovery method and combined with an efficient heat pump system for flue gas as a heat source generator. Through direct contact with the solution in the absorber, the flue gas is going to carry out gas, liquid heat transfer between heat exchanger, realization of sensible heat and latent heat step by step. As the key part of the system, absorber is established by one-dimensional steady-state heat transfer and mass transfer model. This paper uses the finite difference method to model the discrete numerical methods, and analyzes the characteristics of heat and mass transfer in the absorber. We obtain the concentration curves of the three kinds of working medium's temperature and flow along the height direction. We also analyze the influence of CaCl 2 solution parameters changes on the absorption process, parsing the reason of the temperature change by analyzing the three working medium's energy flow trend. We found that the temperature change of flue gas is non-monotonic, which decreases gradually in the range of absorption tower height 0–0.9 m, and then increases gradually. The reason for this change is that sensible heat exchange and latent heat exchange exist between flue gas and solution. Although such a change has an impact on the efficiency of the system, it prevents the "white smoke" from condensing in the air, which effectively protects the environment. Compared with conventional LiBr absorption heat pump, the system constructed in this paper has certain advantages in latent heat recovery, flue gas heat energy utilization, energy conservation and emission reduction and economy.

System integration optimization for coal-fired power plant with CO2 capture by Na2CO3 dry sorbents

For the post-combustion CO2 capture by the Na2CO3 dry sorbents, system integration of CO2 capture into an existing coal-fired power plant is of great significance, as the huge energy consumption of CO2 capture results in great efficiency penalty. By system integration optimization, nearly 80% of the low temperature energy released from the CO2 capture could be recovered to gain more power output and provide considerable heat supply for users, yielding a respective 0.6% and 34.13% increment of the net electric efficiency and coal utilization coefficient. Besides, combination with the waste heat recovery of flue gas further increases the net electric efficiency by 0.57%. Both the thermodynamic and exergy analysis results show that the optimization measures provide a promising way for system integration of the coal-fired power plant with CO2 capture. Techno-economic analysis results shows that cost of electricity and cost of CO2 avoided are obviously reduced due to the optimization measures proposed in this paper.

Efficiency improvement in thermal power plants using waste heat recovery of flue gas – simulation study.

In this paper an Organic Rankine cycle is used as waste heat recovery cycle for a 250 x 2 MW thermal power plant. The exhaust flue gas (80 to 130°C) in the thermal power plant is often released into the atmosphere as waste heat. This waste heat can be utilized as a form of heat source for the Organic Rankine Cycle. The treated flue gas form the Flue Gas Desulphurization plant will be fed to the heat exchanger where the heat transfer between the flue gas and the working fluid (e.g.: Ammonia, R245A) will take place. The working fluid will be fed to the (low pressure) turbine where the work done can obtained. After the expansion of the working fluid in the turbine, the working fluid is cooled in the condenser using water. Then this fluid is again sent to the heat exchanger using pump. The flue gas from the heat exchanger after the heat transfer will be then supplied to the stack. The cooling of the condenser water can be done using a cooling tower. As the load varies for the thermal power plant the temperature of the flue gas also changes and hence the turbine shaft output also changes this may result in tripping of the generator. In order to avoid this, a turbine governing system is designed with a step-up gear box and a torque converter. This governing system will keep the generating shaft in motion at constant speed even during low loads and high loads. This cycle will help the thermal power plants to obtain extra power output and will increase the efficiency of the plants.

Heat Transfer Characteristics of High-Temperature Dusty Flue Gas from Industrial Furnaces in a Granular Bed with Buried Tubes

Experimental heat transfer equipment with a buried tube granular bed was set up for waste heat recovery of flue gas. The effects of flue gas inlet temperature (1096.65–1286.45 K) and cooling water flow rate (2.6–5.1 m3/h) were studied through experiment and computational fluid dynamics’ (CFD) method. On the basis of logarithmic mean temperature difference method, the total heat transfer coefficient of the granular bed was used to characterize its heat transfer performance. Experimental results showed that the waste heat recovery rate of the equipment exceeded 72%. An increase in the cooling water flow rate and inlet gas temperature was beneficial to recovering waste heat. The cooling water flow rate increases from 2.6 m3/h to 5.1 m3/h and the recovery rate of waste heat increases by 1.9%. Moreover, the heat transfer coefficient of the granular bed increased by 4.4% and the inlet gas temperature increased from 1096.65 K to 1286.45 K. The recovery rate of waste heat increased by 1.7% and the heat transfer coefficient of the granular bed rose by 26.6%. Therefore, experimental correlations between the total heat transfer coefficient of a granular bed and the cooling water flow rate and inlet temperature of dusty gas were proposed. The CFD method was used to simulate the heat transfer in the granular bed, and the effect of gas temperature on the heat transfer coefficient of granular bed was studied. Results showed that the relative error was less than 2%.

Collaborative optimization of energy conversion and NOx removal in boiler cold-end of coal-fired power plants based on waste heat recovery of flue gas and sensible heat utilization of extraction steam

Abstract Based on the close relationship among the feed water heating process, Selective catalytic reduction (SCR) de-NOx and air preheating process, collaborative optimization of energy conversion and NOx removal in the boiler cold-end of coal-fired power plants is proposed in this paper. In the proposed system, recovery of flue gas waste heat and sensible heat efficient utilization of extraction steam provide engineering support for the collaborative optimization concept. The proposed system achieves optimal performance by increasing SCR de-NOx temperature and energy for air preheating. The results reveal that, based on 50% load of a typical 1000 MW coal-fired power plant, the proposed system could increase 5.4 MWe of additional output power with a 0.47% increase of thermal efficiency. The increase of SCR de-NOx temperature brings 6.5% of NOx removal efficiency increase and 28.4 mg/Nm3 of NOx emission decrease. Besides, the proposed system gains 2.27 million USD of extra annual income. In general, the proposed system achieves great energy savings, NOx removal, and economic performances.

Numerical study on operating characteristics of self-driven total heat recovery system for wet-hot flue gas

This paper proposes a self-driven wet-hot flue gas total heat recovery system according to the characteristics of the heat transfer process of flue gas condensation, which uses the sensible heat in the high-temperature section to drive the system and complete the deep waste heat recovery of flue gas. The effect of flue gas and secondary water flow rate, flue gas and secondary water inlet temperature, and flue gas moisture on system performance were investigated and analyzed. Besides, the applicability analysis of technology and economic analysis are also performed. The results show that under the rated working conditions, the flue gas outlet temperature and relative humidity are 41.39 °C and 61.25%, respectively, and the maximum heat recovery rate of the system can reach 11.6%. When the flue gas inlet temperature is increased from 350 °C to 550 °C, the heat exchange capacity of the system is increased by 46%. Besides, when the flue gas inlet parameter is 550 °C/ and 120 g/kg (a), if the expected heat recovery rate of the known project is 10%, the maximum temperature of the secondary water that can be prepared by the self-driving system is 63 °C and the payback time is 2.53 years. When the flue gas inlet temperature and the moisture content is high, the system can provide hot water with higher temperature and is more energy-efficient than the traditional scheme.

Technical-&-Economic, Financial and Environmental Feasibility Studies of Energy-Saving Activities Carried out to Use the Loop Air Heater for the Metallurgy Waste Recycling Technology

Technical-&-economic, financial and environmental feasibility studies of energy-saving activities were carried out to use the loop air heater for the metallurgy waste recycling technology developed by the State Company “UkrScience and Technology Center “Energosteel”. The developed and improved Waelz-process allows us to remedy many deficiencies peculiar for similar foreign technologies. In particular, high-priority problems dealing with the exhaust flue gas heat recovery are solved using the loop air heater with the subsequent gas cleaning. The use of the loop air heater will lift the technology developed by the “UkrScience and Technology Center “Energosteel” to a new plane of competitiveness. The main specific feature of this technology is the use of the air heater with the original structure designed for the heat recovery of flue gases and heating the air that is redelivered to the flow process. According to the technology, the Waelz-process requires a hot air and its heating by the air heater eliminates the need for the natural gas firing. The computations done show that the use of the original structure of the air heater for the heat recovery of flue gases and air heating is an urgent energy-saving technological measure. The natural gas saving is an important environmental and economic aspect because the national conception of the “Clean World for Future Generations” anticipates the dividend payment for the CO2 emission reduction.