Exhaust Flue Gas Research Articles

Energy, exergy, exergo-economic and exergo-environmental analysis of waste heat-based convective dryer

Food drying is a widely used method of food preservation worldwide, and the utilization of waste heat from exhaust flue gas presents a significant opportunity to reduce the energy consumption of industrial drying processes. This study thoroughly examines the energy and exergy efficiency, sustainability indicators, and various exergo-environmental and exergo-economic parameters to assess the performance of a waste heat-based convective dryer (WHCD). The study found that drying at 70 °C performed the best (among 50 °C, 60 °C and 70 °C) for the overall drying process, with a maximum overall exergetic efficiency of 4.89 %. The results of exergo-economic analysis revealed that the drying chamber exhibited the highest exergy destruction cost at US$0.01193 per hour, and it was determined that improving the drying chamber was of paramount importance. An exergo-environmental assessment indicates that the proposed dryer effectively mitigates 14.15 tons of CO2 over a 20-year lifespan. Sensitivity analysis of the proposed system reveals that the energy efficiency is more sensitive to the food drying temperature than the exergy efficiency. A 33 % increase in drying temperature increases the exergy efficiency by 19.37 % while reducing the energy efficiency by 37.54 %. Hence, adopting the proposed system in industrial settings could significantly enhance energy-efficient and sustainable food drying processes.

The Catalytic Mechanisms and Design Strategies of Noble Metal Catalysts for Selective Reduction of NOx with CO

AbstractThe selective catalytic reduction of NOx by CO (CO‐SCR) is a viable method for simultaneously mitigating NOx and CO emissions in motor vehicle exhaust and industrial flue gases. Extensive research has been conducted on noble metal catalysts because of their superior catalytic activity and stability compared to non‐noble metals. Noble metal catalysts demonstrate efficient NOx conversion and high selectivity for N2. However, achieving high conversion, selectivity, and stability over a wide temperature range in the presence of excess O2, H2O, and SO2 remains a significant challenge. This review summarizes recent advancements in CO‐SCR over noble metal catalysts, providing insights for the development of CO‐SCR catalysts. This paper first examines the reaction mechanisms of CO‐SCR, followed by a discussion on the design and optimization strategies of noble metal catalysts, with a focus on composition and structural effects. This includes creating active metal sites, selecting appropriate supports, integrating catalytic additives, choosing monometallic nanoparticles, alloying, and using single‐atom catalysts. Finally, remaining challenges and potential avenues for future research have been suggested. The discovery of negatively charged noble metal single‐atom‐site catalysts presents new research opportunities.

Numerical Modelling of Phase Transformations of Water Droplets for Efficient Heat Recovery from Biofuel Flue Gas

The phase transformations of water droplets in the humid air flow for water injection into the flue gas in biofuel combustion technology under typical boundary conditions have been simulated. The numerical study was performed in two stages. The first one defines the influence of radiation on the thermal state of the water droplets and on the cycle of phase transformation modes. It is shown that the influence of radiation in a flue gas flow of 150℃→200℃ temperature on the thermal state of quantitatively injected water droplets is not significant, but it induces qualitative changes in the temperature field and influences phase transformations cycle of the droplets. In the second step, the cycling of the droplet phase transformation modes for water injection into the exhaust flue gas prior to a condensing economiser under typical boundary conditions was numerically investigated. It was justified that for efficient cooling and humidification of the flue gas before the condensing economiser it is necessary to inject water heated above the dew-point temperature by dispersing it into fine droplets.

Proposal and comparison of two heat recovery measures for the coal-based Allam cycle: Double expansion and lower turbine backpressure

Improving the thermodynamic efficiency of the coal-fired semi-closed supercritical CO2 cycle (coal-based Allam cycle) can be achieved by implementing self-heat recuperative coal drying and recompression with more syngas heat integrated with the efficient power cycle. To prevent the heat exchanger from overtemperature during syngas heat recovery, two measures are considered: double expansion and lower turbine backpressure. For the double expansion, a portion of the recycle CO2 is fed into an expander and the exhaust is mixed with the flue gas in the main recuperator to raise the recycle flow rate. For the lower turbine backpressure, the turbine backpressure is decreased to reduce exhaust flue gas temperature. Thermodynamic analysis indicated that self-heat recuperative coal drying and recompression could enhance the net efficiency by 4.28 % points compared to the basic cycle, but the heat exchanger for raw syngas heat recovery faces overtemperature problem with the cold stream exceeding 777 °C. Both the measures proposed above can effectively reduce the temperature to 730–760 °C with slightly decreased efficiencies of 46.93 %∼47.68 % for double expansion and 47.12 %∼47.81 % for lower turbine backpressure. Furthermore, economic assessment shows that compared to the basic cycle, the cost of electricity decreases by 2.49 % and 5.04 % for the schemes with double expansion and lower turbine backpressure, respectively. Therefore, the proposed design with lower turbine backpressure demonstrates advantages in both thermodynamic and economic performance.

ANALYSIS AND CREATION OF NEW ENERGY-SAVING DESIGNS OF INSTALLATIONS FOR ENVIRONMENTALLY COMBUSTION OF LIQUID FUEL IN OIL FACTORY FURNACES USING THE HEAT OF OUTLET COMBUSTION PRODUCTS

The article analyzes the installations and methods used at oil refineries for recycling the heat of exhaust flue gases in order to increase the efficiency of fuel use in tube furnaces and accompanying reduction in pollutant emission into the air basin. Recommendations on rational type selection of waste heaters for furnace units of oil refining industries are given.The authors present fundamentally new installations for burning liquid fuel in the form of oil-water emulsions using the heat recovery of emitted combustion products of furnace installations for heating the oil-water emulsion and its further environmentally friendly combustion, i.e. reduction of harmful emissions. The proposedoriginal installations differ from well-known analogues in the novelty of their design, a fairly high environmental effect and relatively low material costs.

Waste heat recovery from exhaust gases using porous metal fins: a three-dimensional numerical study

Abstract The objective of this study is to investigate the impact of different porous metal samples on the hydro-thermal characteristics of a single cylinder with porous fins using computational fluid dynamics. Commercially used porous samples with pore densities of 10, 20, and 40 PPI were used in this study for heat recovery from exhaust flue gas. The three-dimensional computational domain with porous aluminium fins attached to a tube over which high-temperature exhaust gas flows in a crossflow arrangement mimics a waste heat recovery system. Computations were performed at Reynolds number of 6000-9000, using the realisable κ-ϵ turbulence model. Three fin diameter to tube diameter ratios (Df/D = 2, 2.5, and 3) were considered. The local thermal non-equilibrium model is implemented for energy transfer, as it is more accurate for a high-temperature gradient scenario in a waste heat recovery system. The foam sample with the highest pore density was observed to have the highest pressure drop due to low permeability. A maximum heat transfer and Nusselt number were achieved for a 40 PPI foam sample due to a reduced flow rate inside the porous zone. The overall performance of metal foam samples at varying fin diameters was evaluated based on the area goodness factor (j/f) and a heat transfer coefficient ratio to pumping power per unit heat transfer surface (Z/E). Analysis of these two parameters suggests using 20 PPI foam at Df/D = 2.

Power Augmentation of Gas Turbine Using Exhaust Flue Gas Operated Vapor Absorption Machine

Industrial gas turbines (GT) that operate at constant speed are constant-volume-flow combustion machines. As the specific volume of air is directly proportional to the temperature, an increase in air density results in a higher air mass flow rate at low air ambient temperatures. This results more mass of air is now passes through same volume gas turbine space. Consequently, the gas turbine power output increases proportionally with the increase in air mass flow rate. For geographic regions where warm and humid months are predominant throughout the year, significant power loss occurs during these months, and a higher rate of expensive fuel is fired at reduced power output. A gas turbine inlet air cooling technique is a useful option to enhance GT output. One of the innovative options for power augmentation of gas turbine is inlet air conditioning using a vapor absorption machine (VAM). Using VAM for GT intake air conditioning has the advantage over other systems in that it can be operated from waste heat. Many gas turbine machines, particularly natural gas pumping stations, are operated without heat recovery steam generator (HRSG) or heat recovery option. Valuable heat energy is escaped with exhaust flue gas in these systems. This paper demonstrates how GT exhaust waste heat can be utilized for its own power generation enhancement. In this study, a flue gas-based vapor absorption machine is selected for cooling the inlet air of a 26 MW gas turbine, which is used to drive the booster compressor of a natural gas pumping station. The capacity of the VAM for the required cooling effect has been calculated. The expected GT power enhancement from intake air gas conditioning has also been estimated in this paper.

A novel solar-aided lignite-fired power generation system with calcium looping CO2 capture, lignite pre-drying and feedwater preheating

Integrating solar heat and calcium looping (CaL) process into the existing lignite-fired power generation system is a promising technology to control CO2 emission. However, the heat released from carbonation process led to the temperature increase of exhaust flue gas together with heat losses in boiler. To recover the waste heat from the exhaust flue gas, this paper proposed a solar-aided lignite-fired power generation system with CaL process CO2 capture, lignite pre-drying and feedwater preheating (i.e., design III). Besides, design I without waste heat recovery and design II with only lignite pre-drying were simulated for comparison. Through the case study based on a solar-aided 330 MW lignite-fired power generation system, thermal and techno-economic performance of design III was the best on the design condition. Its standard coal consumption rate was 374.44 g/kWh, which was 61.12 g/kWh and 8.24 g/kWh lower than design I and design II, respectively. With the new design, the annual net profit of design III is $18.2924 M, with $0.5652 M higher than design II. The sensitivity analysis indicated that the thermal performance of design III was also the best under various conditions of CO2 capture efficiency and integrated solar heat.

Thermoeconomic analysis of a novel cogeneration system for cascade recovery of waste heat from exhaust flue gases

In low-grade waste heat recovery scenarios, an absorption refrigeration cycle (ARC) or organic Rankine cycle (ORC) can be used because of its widespread acceptance in combined cooling and power applications. This paper introduces a cogeneration configuration employing a cascade waste-heat recovery architecture (including an ARC, ORC, and intermediate heating loop) to harness waste heat from the flue gas of a gas turbine (GT). The results demonstrated that the first-law efficiency and total power generation were largely influenced by the ARC, whereas the second-law efficiency and total available energy were primarily affected by the ORC. When the ARC generation temperature difference and ORC evaporation temperature were adjusted, the first- and second-law efficiencies exhibited divergent trends, suggesting the absence of a unified strategy to enhance both efficiencies simultaneously in the current system. The system achieved its highest first-law efficiency of 54.84 % and maximum total power generation of 1866.10 kW at an ORC evaporation temperature of 145 °C and a heat-source inlet temperature of 160 °C. Furthermore, at an ORC evaporation temperature of 150 °C and a heat-source inlet temperature of 200 °C, the system reached its highest second-law efficiency of 34.57 % and maximum total available energy of 1233.3 kW. The case study revealed that the GT system (including air compressor, air preheater, combustion chamber, and gas turbine) accounted for the highest level of irreversibility, comprising 74 % of the overall system. Specifically, the combustion chamber in the GT system produced a significant irreversibility due to chemical reactions. Compared with traditional combined cooling and power systems, the proposed system can increase the first-law efficiency and lower the unit energy cost of the output.

Energy analysis of waste heat-powered absorption cooling system for sustainable cooling

Energy wastage from power plants, which typically dissipates into the atmosphere, poses a significant challenge. The environmental consequences of such wasteful practices are manifold, contributing to climate change and resource depletion. The inefficient use of this waste heat contributes to economic and environmental concerns. Harnessing waste heat through integrating heat recovery systems with power plants effectively repurposing untapped energy. Addressing this issue optimizes energy utilization and aligns with the growing need for sustainable practices in the power generation sector. This study aims to harness the available waste heat by integrating an absorption cooling system (ACS) from the flue gas exhaust of a pressurized pulverized combined cycle power plant. Additionally, the thermodynamic performance of ACS with a cooling capacity of 30 tons has been examined. Using waste heat for cooling purposes offers a sustainable and efficient solution, reducing energy consumption and environmental impact. The working fluid used in the ACS is a binary mixture comprised of ammonia and water. Modelling and simulation were conducted using cycle tempo software, followed by energy analyses to assess the ACS's thermodynamic performance. The thermodynamic analysis discloses that the ACS achieves a coefficient of performance (COP) of 0.595. Additionally, variations in the temperatures of the generator, absorber, condenser, and evaporator significantly impact the COP of the ACS. This promising COP indicates the effectiveness of the ACS in harnessing waste heat for practical cooling applications, marking a substantial step towards sustainable energy utilization.

Analysis of Kalina Cycle for Recovering Waste Heat from Flue Gas Exhaust in Pressurized Pulverized Combined Cycle

Analysis of Kalina Cycle for Recovering Waste Heat from Flue Gas Exhaust in Pressurized Pulverized Combined Cycle

Analysis of Kalina cycle for recovering waste heat from flue gas exhaust in pressurised pulverised combined cycle

Analysis of Kalina cycle for recovering waste heat from flue gas exhaust in pressurised pulverised combined cycle

Experimental Research on Effects of Combustion Air Humidification on Energy and Environment Performance of a Gas Boiler

Abstract To increase the waste heat recovery (WHR) efficiency of gas boiler and decrease NOx emissions, a flue gas total heat recovery (FGTHR) system integrating direct contact heat exchanger (DCHE) and combustion air humidification (CAH) is put forward. The experimental bench and technical and economic analysis models are set up to simulate and evaluate the WHR performance and NOx emissions in various operation situations. The results show that when the air humidity ratio elevates from 3 g/kgdry air to 60 g/kgdry air, the dew point temperature increases by 7.9 °C. When the flue gas temperature approaches the dew point temperature, the rate of improvement of the FGTHR system's total heat efficiency notably rises. With spray water (SW) flowrate and temperature of 0.075 kg/s and 45 °C, the WHR efficiency relatively increases by up to 8.4%. The maximum sensible and latent heat can be recovered by 4468 w and 3774 w, respectively. The flue gas temperature can be reduced to 46.55 °C, and the average NOx concentration is 39.6 mg/m3. Compared with the non-humidified condition, the NOx and CO2 emissions relative reduction of the FGTHR system are 61.2% and 8.7%. The payback period of FGTHR system is 2 years. Through simulation, it can be concluded that the decrease in exhaust flue gas temperature and velocity, as well as the increase in exhaust flue gas humidity, has a negative impact on the diffusion of NOx in the atmosphere.

Modeling for on-line monitoring of carbon burnout coefficient in boiler under partial load

Combustion stability of boiler deteriorates under low load, making carbon burnout coefficient decrease, further reducing boiler thermal efficiency. The online monitoring methods of carbon burnout coefficient and boiler thermal efficiency can track energy efficiency levels of boiler in real-time under low loads. It is of great practical significance to optimize and adjust combustion conditions of boilers and upgrade boiler real-time energy efficiency. Nevertheless, extremely difficult challenge for online monitoring technology of carbon burnout coefficient seriously restricts the online monitoring of boiler thermal efficiency.In this background, an innovative theoretical model between excess air coefficient and carbon burnout coefficient is derived according to incomplete combustion equation inside furnace. Calculation method of excess air coefficient is proposed with a brand new perspective on energy balance of economizer. Subsequently, on-line monitoring model of carbon burnout coefficient and boiler thermal efficiency is constructed and verified.The online monitoring results of a 600 MW unit indicate, lower carbon burnout coefficient magnifies the degree of virtual height of calculation results and calculation error from traditional methods of national standard for calculating excess air coefficient. This operating mode results in a significant shortage of actual air flow into boiler under partial load.Carbon burnout coefficient, showing an upward trend with unit load increasing, is as high as 0.99 with unit load of 489 MW. As unit load decreases to 161 MW, carbon burnout coefficient decreases to 0.80. Additionally, combustion conditions fluctuation is greatly influenced by changing in coal quality. Under partial load, volatility in carbon burnout coefficient increases with electrical load below 300 MW. Combustion stability and combustion efficiency of boiler under low load significantly decrease. The variation in exhaust flue gas heat loss of boiler with unit load changes is relatively small due to opposite effect by exhaust gas temperature and excess air coefficient. Actually, changing trends and fluctuation degree of boiler thermal efficiency are mainly influenced by carbon burnout coefficient with a variation in load. Overall, boiler thermal efficiency, affected by heat loss of incomplete solid on combustion, fluctuates greatly at low loads. The implementation of online monitoring for carbon burnout coefficient provides a quantitative basis for improving boiler energy efficiency under low load conditions.

Эффективность трубчатой печи в процессе стабилизации углеводородного конденсата на Астраханском газоперерабатывающем заводе

One of the most important and promising areas of Russia's development for the coming decades is the in-troduction of energy-efficient and energy-saving technologies. designated by the President of the Russian Federation. Currently, in Russia, various types of technological tubular furnaces with natural thrust are widely used at many gas processing plants and refineries. The bulk of tubular furnaces are operated by personnel without any automation systems and regulation of the supply of both fuel and air. The article discusses the issues of efficient operation of a tubular furnace during stabilization of hydrocarbon condensate with acidic components at the Astrakhan Gas Processing Plant. When designing a tubular furnace, various options for efficient operation with the utilization of the thermal energy of exhaust flue gases are considered. It is established that the maximum efficiency of a tubular furnace is obtained not only when the flue gas temperature at the outlet of the chimney is minimal, but depends on a number of factors that are discussed in more detail in this article.

An innovative renewable energy–based tri-generation system for electricity, LNG regasification and hydrogen production

Waste incineration is a potent technique, that deals with the waste generated in a sustainable way to properly manage and reduce the generated waste and produce useful energy simultaneously. However, the waste-to-electrical efficiency of incineration plants is less (20–22) % because of the high moisture content of waste and flue gas heat losses. In the present study, a tri-generation system consisting of a solar parabolic trough collector integrated with a waste-to-energy plant, a liquefied natural gas (LNG), and a hydrogen production system is proposed and thermodynamically investigated. Parabolic trough collectors serve as a secondary heating source to the steam coming out of the incineration boiler. The useful heat collected by the parabolic trough solar field is provided to the fluid exiting the incineration boiler and entering into the steam turbine to improve the steam condition, while LNG is vaporized by the energy of exhaust flue gas and produces power for the PEM electrolyzer. Waste-to-energy incineration facility is capable of operating with a feed rate of 350 tons/day, producing 6.3 MW of power at an inlet temperature of 400 °C of the turbine. However, the net power produced is increased to 7.72 MW with increase in turbine inlet temperature to 515 °C. Results of the study conclude that the energetic and the exergetic efficiencies of the incineration plant are found to be 27.93 % and 26.51 %, respectively. In addition, both the first and second law efficiencies are observed as 21.51 % and 25.74 %, respectively, while the rate of hydrogen production is 7.72 kg/h. The cumulative exergy destruction rate of the system is 29.3 MW and the WtE boiler shares the maximum portion (58.14 %) of the exergy destruction.

Improved Waste Heat Management and Energy Integration in an Aluminum Annealing Continuous Furnace Using a Machine Learning Approach.

Annealing furnaces are critical for achieving the desired material properties in the production of high-quality aluminum products. In addition, energy efficiency has become more and more important in industrial processes due to increasing decarbonization regulations and the price of natural gas. Thus, the current study aims to determine the opportunities to reduce energy consumption in an annealing continuous furnace and the associated emissions. To this end, the heat transfer phenomenon is modeled and solutions for the decreasing fuel consumption are evaluated so that the overall performance of the process is enhanced. A heat transfer model is developed using the finite difference method, and the heat transfer coefficient is calculated using machine learning regression models. The heat transfer model is able to predict the heat transfer coefficient and calculate the aluminum temperature profile along the furnace and the fuel consumption for any given operating condition. Two solutions for boosting the furnace exergy efficiency are evaluated, including the modulation of the furnace temperature profiles and the energy integration by the recycling of exhaust flue gases. The results show that the advanced energy integration approach significantly reduces fuel consumption by up to 20.7%. Sensitivity analysis demonstrates that the proposed strategy can effectively reduce fuel consumption compared with the business-as-usual scenario for a range of sheet thicknesses and sheet velocities.

Economic feasibility of retrofitting blowdown heat recovery system using steam dryer to lignite-fired power plant for reduced fuel consumption

Blowdown is responsible for heat losses in boiler systems. The main objective of this paper is to propose a system to recover blowdown heat using steam dryer. The system consists of a flash tank, a steam dryer, and an air preheater. The flash tank is used to produce flash steam that is supplied to the steam dryer. Fuel moisture is removed in the steam dryer, resulting in fuel with lower moisture content and exhaust vapor. Exhaust vapor is supplied to the air preheater to increase air temperature before combustion. Due to lower fuel moisture content and higher air temperature, exhaust flue gas temperature can be decreased by adding air heater area. An analysis was performed to determine the payback period for the investment cost of the proposed heat recovery system. It was demonstrated that retrofitting a power plant with this system led to increased energy efficiency of the power plant. A case study of 250-MW existing power plant operating at the boiler pressure of 12.34 MPa was considered. Simulation results indicate that the power plant retrofitted with this blowdown heat recovery system consumes 0.87% less fuel than the power plant without this system. The payback period or the investment in this system is 7 years.

Comparative life cycle energy, water consumption and carbon emissions analysis of deep in-situ gasification based coal-to-hydrogen with carbon capture and alternative routes

In order to clarify the competitiveness of deep in-situ gasification based coal-to-hydrogen (deep IGCtH) in the context of carbon-constrained development, based on simulation results, the energy, water consumption and carbon emissions were quantitatively assessed and compared with large-scale fossil energy based routes, using life cycle assessment model from feedstock to hydrogen that covers process energy production and utilization. The results indicate when producing 1 kg of hydrogen, deep IGCtH requires 349.55 MJ of external primary fossil energy input and generates 30.47 kg CO2-eq of emissions, which are 24.88% and 16.32% lower than 465.34 MJ and 36.41 kg CO2-eq of Lurgi surface gasification based coal-to-hydrogen (Lurgi SGCtH), and also 7.38% lower than 377.39 MJ of coke-oven gas-to-hydrogen (COGtH). Furthermore, deep IGCtH can not only reduce coal consumption by 19.7% compared with Lurgi SGCtH, but also reduce oil consumption required to obtain process energy by 81.84%, which also reaches 80.09% compared with COGtH. Due to the high methane content, the exhaust gas and flue gas of deep IGCtH contributes 9.78 kg and 8.84 kg of CO2 emissions, and under the CO2 capture rate of 80%, the carbon emissions adopting exhaust gas and flue gas simultaneous capture reach 25.88 kg CO2-eq, higher than the 23.1 kg CO2-eq adopting exhaust gas single capture, of which waste gas only contributes 3.87 kg of emissions, but electricity consumption causes 15.11 kg CO2-eq of emissions, indicating the key to adopting such scheme to achieve further emissions reduction lies in reducing emissions caused by electricity consumption.

Volatilization characteristic and solidification of Pb, Zn, Cd and as during cement kiln co-processing of solid waste

Cement kiln co-processing always became one of the predominate approaches to dispose hazardous solid waste containing heavy metals. The volatilization and morphology of heavy metals should be paid to more concern during the cement production due to the environmental risk of heavy metals. In this study, the volatilization characteristics and the solidification effect of heavy metals (Pb, Zn Cd and As) during cement kiln co-processing were explored by the lab and pilot scale experiments. At same experimental conditions, the volatilization rate followed as As > Pb > Cd > Zn. Both limestone and cement raw meal have been demonstrated the capability to mitigate the rates of heavy metal volatilization. Notably, cement raw meal displays a more pronounced effect compared to limestone in suppressing volatilization processes. Over 50% of heavy metals were transformed into residual state at 1400 °C, and Cd, As and Zn were easy to be solidified than Pb. A pilot scale experiment proved that more than 80% of heavy metals was solidified, and Zn reached nearly 100%. Moreover, around 80% of Cd, As and Zn were remained in clinker and the rest was distributed in kiln dust particles, only very few amount was released into the exhaust flue gas. This study provides a comprehensive and extensive understanding of the volatilization characteristics and migration patterns of heavy metals in the cement kiln environment. It offers theoretical support for the control of heavy metals during the co-processing of hazardous solid waste in cement kilns.