Search Results (34)

This work presents the thermodynamic design and performance assessment of an integrated process line for the separation, liquefaction, storage, and valorization of carbon dioxide (CO₂) and nitrogen (N₂) from flue gas streams. The proposed system aims to combine carbon capture with cryogenic energy storage by exploiting the thermophysical properties of the main flue gas constituents. A representative flue gas derived from complete methane combustion (9.5% CO₂, 71.5% N₂, and 19% H₂O by volume) is considered as the feed stream. The process is developed and simulated in DWSIM v9.0.5, adopting a steady-state mass and energy balance framework coupled with rigorous thermodynamic modeling of phase equilibria and unit operations. The plant configuration is based on sequential cooling, compression, and expansion stages, enabling the selective condensation of H₂O, CO₂, and N₂ at different temperature levels. The system integrates heat exchangers, compressors, pumps, turboexpanders, phase separators, and cryogenic storage tanks, while a portion of the liquefied CO₂ is reused as an energy carrier through vaporization and expansion in a dedicated turbine. The results demonstrate that the process achieves a CO₂ capture ratio of 81.7%, with a specific electric consumption (SEC) of 10.44 kWh/kg_CO2 and 1.71 kWh/kg_N2. The overall net electric demand is 1.29 kWh/kg of treated flue gas, while the round-trip efficiency (η_RT,CO2) is 18.6%. A significant amount of energy can further be recovered from the “waste” exhaust water stream (12.94 kg_L-H2O/kg_flue-gas, at 91 °C and 1.2 bar) up to 800 Wh/kg_flue-gas, improving the performance of the entire process (SEC_CO2: 3.86 kWh/kg_CO2, η_RT,CO2: 69.8%). The study confirms the thermodynamic feasibility of the proposed configuration and identifies nitrogen liquefaction as the dominant energy-intensive step. Future optimization efforts should therefore focus on reducing exergy destruction in the deep cryogenic section through improved heat integration, enhanced cold-energy recovery, optimized compression–expansion staging, and reduced pressure losses. Full article

In industrial production, flue gas heat exchangers are often affected by the low-temperature condensation of industrial flue gas due to the influence of the working environment, resulting in serious ash deposition and corrosion. In order to solve this problem, in this study, we developed an ash deposition and corrosion monitoring system to compare the ash deposition prevention performance and corrosion resistance of different materials, as well as its influence on the heat transfer performance of different materials in the same environment. The following coatings were selected for the experiment (values in parentheses are the concentrations of the added compounds): ND, Q235, 316L, Ni-Cu (0.4 g/L)-P, Ni-P-SiO₂ (40 g/L), Ni-Cu (0.4 g/L)-P-SiO₂ (20 g/L), Ni-Cu (0.4 g/L)-P-SiO₂ (40 g/L), and Ni-Cu (0.4 g/L)-P-SiO₂ (60 g/L). The results show that the Ni-Cu (0.4 g/L)-P-SiO₂ (40 g/L) coating has excellent corrosion resistance, while the Ni-Cu (0.4 g/L)-P-SiO₂ (60 g/L) coating shows excellent antifouling performance. Through the comparative analysis of polarization curves, impedance spectra, and coupled corrosion experiments, the test materials were ranked as follows based on their corrosion resistance: 316L > Ni-Cu-P-SiO₂ (40 g/L) > Ni-Cu-P-SiO₂ (20 g/L) > Ni-P-SiO₂ > Ni-Cu-P-SiO₂ (60 g/L) > Ni-Cu-P > ND > Q235. It was also demonstrated that the new coated pipes were able to reduce the exhaust temperature below the dew point and maximize the recovery of energy from the exhaust gas. The acid–ash coupling mechanism of the coating in the flue gas environment was further analyzed, and an acid–ash coupling model based on Cu and SiO₂ is proposed. This model analyzes the effect of the coating under the acid–ash coupling mechanism. Using coated tubes in heat exchangers helps to recover waste heat from coal-fired boilers, enhance heat exchange efficiency, extend the service life of heat exchangers, and reduce costs. Full article

District heating systems in northern China predominantly rely on coal-fired heat sources, necessitating sustainable alternatives to reduce carbon emissions. This study investigates a biomass combined heat and power (CHP) system integrated with cascaded absorption heat pump (AHP) technology to recover waste heat from semi-dry flue gas desulfurization exhaust and turbine condenser cooling water. A multi-source operational framework is developed, coordinating biomass CHP units with coal-fired boilers for peak-load regulation. The proposed system employs a two-stage heat recovery methodology: preliminary sensible heat extraction from non-saturated flue gas (elevating primary heating loop (PHL) return water from 50 °C to 55 °C), followed by serial AHPs utilizing turbine extraction steam to upgrade waste heat from circulating cooling water (further heating PHL water to 85 °C). Parametric analyses demonstrate that the cascaded AHP system reduces turbine steam extraction by 4.4 to 8.8 t/h compared to conventional steam-driven heating, enabling 3235 MWh of annual additional power generation. Environmental benefits include an annual CO₂ reduction of 1821 tonnes, calculated using regional grid emission factors. The integration of waste heat recovery and multi-source coordination achieves synergistic improvements in energy efficiency and operational flexibility, advancing low-carbon transitions in district heating systems. Full article

This paper deals with combustion air humidification for application with a biomass boiler and a spray flue gas condenser. The use of a combustion air humidifier increases the dew point temperature of the flue gas, thereby increasing the potential for heat recovery in the flue gas condenser and increasing the amount of heat supplied to the thermal system. The air humidification process in a counter current spray humidifier was experimentally analysed under conditions corresponding to the use before a biomass boiler with a flue gas condenser. For air heating and humidification, temperature factor values of up to 0.90 can be obtained; this value is mainly influenced by the ratio of the spray water and humidified air flow rates. The volumetric heat transfer coefficient is significantly affected by the humidified air velocity, although this velocity is negligible compared to the counter current spray water velocity. The volumetric heat transfer coefficient reaches higher values at higher spray water temperatures and therefore higher air heating. The whole process is also affected by the saturation of the incoming air, where the dew point temperature of the air drawn in from the surroundings is lower than its temperature. These results can be used as basic information for the design of combustion air humidifiers, for the selection of their operating parameters, and for a basic balancing of the energy contribution of the combustion air humidifier before a more detailed design of the whole system. Full article

The combustion of gaseous fuels in condensing boilers contributes to the greenhouse gas and toxic compound emissions in exhaust gases. Hydrogen, as a clean energy carrier, could play a key role in decarbonizing the residential heating sector. However, its significantly different combustion behavior compared to hydrocarbon fuels requires thorough investigation prior to implementation in heating systems. This study presents experimental and theoretical analyses of the co-combustion of natural gas with hydrogen in low-power-output condensing boilers (second and third generation), with hydrogen content of up to 50% by volume. The results show that mixtures of hydrogen and natural gas contribute to increasing heat transfer in boilers through convection and flue gas radiation. They also highlight the benefits of using the heat from the condensation of vapors in the flue gases. Other studies have observed an increase in efficiency of up to 1.6 percentage points compared to natural gas at 50% hydrogen content. Up to a 6% increase in the amount of energy recovered by water vapor condensation was also recorded, while exhaust gas losses did not change significantly. Notably, the addition of hydrogen resulted in a substantial decrease in the emission of nitrogen oxides (NOx) and carbon monoxide (CO). At 50% hydrogen content, NO_x emissions decreased several-fold to 2.7 mg/m³, while CO emissions were reduced by a factor of six, reaching 9.9 mg/m³. All measured NO_x values remained well below the current regulatory limit for condensing gas boilers, which is 33.5 mg/m³. These results highlight the potential of hydrogen blending as a transitional solution on the path toward cleaner residential heating systems. Full article

As China continues to adjust its energy structure in order to address energy security and environmental crises, changes in centralized heating technology and energy saving are gradually being promoted. Flue gas waste heat recovery from traditional gas boilers has the potential to play a significant role in the promotion of low-carbon heating, energy saving, and emission reduction. This study took the Beijing Baoneng Heating Plant as its research object. We designed a flue gas deep-condensation waste heat recovery system based on the combination of absorption heat pump technology and stepped waste heat recovery technology. We determined that 40 °C is the target temperature for flue gas: At this point, the condensate in the flue gas is precipitated by approximately 60%. This results in a 12.18% efficiency improvement in the boiler. Subsequently, experimentation demonstrated that the recovered flue gas heat was able to fulfill the heating requirements of the Baoneng plant and that it was able to enhance the heating capacity of the heat source plant by utilizing the flue gas waste heat without increasing energy consumption. This represents a mutually beneficial scenario for environmental and economic considerations. Full article

The possibility of applying the organic Rankine cycle (ORC) to further recycle the low-grade waste heat efficiently is studied in the present work. The energy, exergy, and economic models of the ORC system are established, and the isobutane, isopentane, and their mixtures are selected as the organic working mediums (OWMs). Due to the slip characteristics of mixed OWM, four operational conditions of the ORC system are proposed, and then the contrastive analysis of energy, exergy, and economic performances under the four operational conditions are conducted. Finally, the optimal mixture mass fraction and crucial parameters of the ORC system are separately determined through the bi-objective optimization. The results show that the ORC system using the mixed OWM can achieve a larger net power output and exergy efficiency by comparing the pure OWM when the condensing temperature is set as the saturated vapor temperature during the condensation process. The electricity production cost first rises and then decreases with the rising mass fraction of isobutane in mixed OWM, and the ORC system using the isopentane can achieve the smallest electricity production cost. By taking the low-grade flue gas of 433.15 K as the ORC heat source, four operational conditions have the same optimal ORC crucial parameters, namely the evaporating temperature of 393.15 K, condensing temperature of 308.15 K, and superheat degree of 0 K. The pure OWM of isobutane can achieve better overall performance by setting the condensing temperature as the saturated liquid temperature. Full article

Limestone-gypsum wet flue gas desulfurization (WFGD) played a key role in SOx removal and clean emissions. However, it would also affect the condensable particulate matter (CPM) removal and compositions. The effects of the WFGD system on the removal of CPM and the contents of soluble ions in CPM were investigated in a spray desulfurization tower at varied conditions. The results indicate that the emission concentration of CPM decreased from 7.5 mg/Nm³ to 3.7 mg/Nm³ following the introduction of cold water spray and hot alkali droplet spray systems. This resulted in a CPM reduction rate of approximately 51%, reducing the percentage of CPM in total particulate matter and solving the problem of substandard particulate matter emission concentrations in some coal-fired power plants. The concentrations of NO₃⁻, SO₄²⁻, and Cl⁻ among the soluble ions decreased by 41–66.6%. As the liquid-to-gas ratio of the cold water spray and hot alkali droplet spray increased, CPM came into contact with more spray, which accelerated dissolution and chemical reactions. Consequently, the CPM emission concentration decreased by 17.4–19%. The liquid-to-gas ratio has a great effect on the ion concentrations of NO₃⁻, SO₄²⁻, Cl⁻ and NH₄⁺, with a decrease of 28–66%. The temperatures of the cold water spray and the hot alkali droplet spray primarily affect the ionic concentrations of SO₄²⁻ and Ca²⁺, leading to a decrease of 32.3–51%. When the SO₂ concentration increased from 0 mg/Nm³ to 1500 mg/Nm³, large amounts of SO₂ reacted with the desulfurization slurry to form new CPM and its precursors, the CPM emission concentration increased by 57–68.4%. This study addresses the issue of high Concentration of CPM emissions from coal-fired power plants in a straightforward and efficient manner, which is significant for enhancing the air quality and reducing hazy weather conditions. Also, it provides a theoretical basis and technical foundation for the efficient removal of CPM from actual coal-fired flue gas. Full article

To achieve the goals of carbon peaking and carbon neutrality, the retrofitting of existing coal-fired power plants is crucial to achieving energy-saving and emission reduction goals. A conventional recovery system of waste heat typically occurs downstream of the air preheater, where the energy quality in flue gas is low, resulting in limited coal-saving benefits. This study proposes a scheme involving a flue gas exchanger bypassing the air preheater and low-temperature economizers, which is used to transfer the waste heat from flue gas to primary and secondary air (System I). Additionally, a heat pump can be introduced to provide supplementary energy for primary and secondary air, as well as the condensate from the steam turbine (System II). The coal consumption rate and exergy efficiency are used to evaluate the two schemes. The results show that both waste heat recovery systems can increase the power output of the coal-fired unit by recovering waste heat. System II can boost power output by approximately 13.98 MW. The power increase in both waste heat recovery systems show a declining trend as the unit load decreases. This increased power is primarily attributed to the medium- and low-pressure cylinders, while the contributions from ultra-high-pressure and high-pressure cylinders are negligible. The increased power output for the medium-pressure cylinder ranges from approximately 3.49 to 3.58 MW, while the low-pressure cylinder has an increased power output of around 10.10 to 10.19 MW. The coal consumption rate is decreased from 250.3 g/(kW·h) to 247.5 g/(kW·h) under a full load condition for both systems, which can be augmented at lower load conditions. System II outperforms System I at 30% load condition, achieving a reduced coal consumption rate of 3.36 g/(kW·h). System I has an exergy efficiency of 40%, while System II shows a higher efficiency of 44%. Full article

A flue gas condenser (FGC) system recovers heat from exhaust flue gases in energy production and chemical plants, reducing air pollution due to dust, SOx, and HCl. An FGC system is divided into indirect contact condenser (ICC) and direct contact condenser (DCC) types. In an ICC, the exhaust gases do not mix with the working fluid, and a water film is formed during flue gas condensation for partial SOx removal. In a DCC, direct mixing of the exhaust flue gas with the cooling fluid (mainly water) occurs, with simultaneous absorption of SOx. In this study, we investigated the SO₂ removal efficiency and heat recovery of an ICC, a DCC, and a DCC–ICC hybrid system, and compared the results of the hybrid system with those obtained for a single DCC type at the same liquid-to-gas (L/G) ratio. The SO₂ removal characteristics of the hybrid system were examined based on the L/G ratio and absorbent-to-SO₂ molar ratio. In the reference ICC-type FGC system, the exit temperature of the mixed gas was 28 °C, with the condensed water ratio and heat recovery efficiency being 80.9% and 93.4%, respectively. At an L/G ratio of 1.5–3.5, the SO₂ removal efficiency of a single DCC was 31.5–65.9%, whereas that of the hybrid FGC system (with packing material) increased from 47.1% to 72.3%, which further increased to ~90% upon the addition of NaOH at a molar ratio of 0.7 and an L/G ratio of 1.5. Full article

The global energy crisis, forced by fossil fuel shortages and supply chain disruption, stimulates EU policymakers to find alternative energy replacement. Modifying the present polyisoprene footwear production plant into a hybrid system by combining different energy sources raises energy efficiency. The proposed hybrid system incorporates classical and solar-based technology, resulting in energy optimization by utilizing waste heat recovery. By installing an economizer for feeding water preheating using flue gas recovery, it results in the volume of the flue gases lowering from ${\mathrm{v}}_{{\mathrm{FG}}_{\mathrm{P}}}=1.7969{{ \mathrm{m}}^3}_{\mathrm{FG}}/{\mathrm{kg}}_{\mathrm{P}}$ to ${\mathrm{v}}_{{\mathrm{FG}}_{{\mathrm{ECO}}_{\mathrm{P}}}}=1.597 {{\mathrm{m}}^3}_{\mathrm{FG}}/{\mathrm{kg}}_{\mathrm{P}}$, or by 11.13%, while the flue gases’ temperature is lowered from 204 °C (477.15 K) to 50.99 °C (324.14 K). Further improvement in combining feed water and air preheating results in natural gas savings of 12.05%, while the flue gases’ exhaust temperature is decreased to 30.44 °C (303.59 K). The third option, using condensate heat recovery and feeding water preheating using flue gases, showed natural gas savings as much as 17.41% and exhaust flue gases cooling to 112.49 °C (385.64 K). The combination of condensate heat recovery, combustion air and feed water preheating results in the volume of the flue gases being lowered by 20.42% and natural gas savings by 20.24%, while the flue gases’ temperature is reduced to 45.11 °C (318.26 K). The proposed solar application in polyisoprene production predicts the hybrid system showing fuel savings ranging from 77.96% to 87.08% in comparison to the basic process. The greatest fuel savings of 87.08% is shown in a solarized polyisoprene footwear production plant with combustion air and feed water preheating combined with the condensate return system. Integrating the solar heat into the regular industrial process of polyisoprene production showed great potential and showed environmental sustainability through energy optimization in polyisoprene production. Full article

Pyrolysis is a recognized alternative for the sustainable management of contaminated organic waste, as it yields energy-rich gas, oil, and a carbon-rich biochar product. Low-volatility compounds, however, such as heavy metals (HMs; As, Cd, Cu, Cr, Ni, Pb, and Zn) typically accumulate in biochars, limiting their application potential, especially for soil improvement. The distribution of HMs in pyrolysis products is influenced by treatment temperature and the properties of both the HMs and the feedstock. There is a significant knowledge gap in our understanding of the mass balances of HMs in full-scale industrial pyrolysis systems. Therefore, the fate of HMs during full-scale relevant pyrolysis (500–800 °C) of seven contaminated feedstocks and a clean wood feedstock were investigated for the first time. Most of the HMs accumulated in the biochar (fixation rates (FR) >70%), but As, Cd, Pb, and Zn partly partitioned into the flue gas at temperatures ≥ 600 °C, as demonstrated by FRs of <30% for some of the feedstocks. Emission factors (EFs, mg per tonne biochar produced) for particle-bound HMs (<0.45 µm) were 0.04–7.7 for As, 0.002–0.41 for Cd, 0.01–208 for Pb, and 0.09–342 for Zn. Only minor fractions of the HMs were found in the condensate (0–11.5%). To investigate the mobility of HMs accumulated in the biochars, a novel leaching test for sustained pH drop (at pH 4, 5.5 and 7) was developed. It was revealed that increasing pyrolysis temperature led to stronger incorporation of HMs in the sludge-based biochar matrix: after pyrolysis at 800 °C, at pH 4, <1% of total Cr, Cu, Ni, and Pb and < 10% of total As and Zn contents in the biochars were leached. Most interestingly, the high HM mobility observed in wood-based biochars compared to sewage-sludge-based biochars indicates the need to develop specific environmental-management thresholds for soil application of sewage-sludge biochars. Accordingly, more research is needed to better understand what governs the mobility of HMs in sewage-sludge biochars to provide a sound basis for future policy-making. Full article

This article outlines the design and performance of a flue gas condensation system integrated with a biomass combustion plant. The system comprises a biomass plant fuelled by wood chips, generating flue gases. These gases are condensed via a double heat exchanger set-up, extracting water and heat to reduce concentrations of CO, CO₂, and NO_x while releasing gases at a temperature close to ambient temperature. The 100 kW biomass plant operates steadily, consuming 50 kg of wood chips per hour with fuel energy of 18.98 MJ/kg. Post combustion, the gases exit at 430 °C and undergo two-stage cooling. In the first stage, gases are cooled in a high-temperature tube heat exchanger, transferring heat to air. They then enter the second stage, a flue gas/water heat exchanger, recovering sensible and latent thermal energy, which leads to water condensation. Flue gas is discharged at approximately 33 °C. Throughout, parameters like the flue gas temperatures, mass flow, fuel consumption, heat carrier temperatures, and water condensation rates were monitored. The test results show that the system can condense water from flue gas at 75 g/min at 22 °C while reducing pollutant emissions by approximately 20% for CO₂, 19% for CO, 30% for NO, and 26% for NOx. Full article

Decarbonizing fossil-fuel usage is crucial in mitigating the impacts of climate change. The burning of fossil fuels in boilers during industrial process heating is one of the major sources of CO₂ in the industry. Electrification is a promising solution for decarbonizing these boilers, as it enables renewable energy sources to generate electricity, which can then be used to power the electric boilers. This research develops a user-driven simulation model with realistic data and potential temperature data for a location to estimate boilers’ current energy and fuel usage and determine the equivalent electrical boiler capacity and energy usage. A simulation model is developed using the Visual Basic Application (VBA)^® and takes factors such as current boiler capacity, steam temperature and pressure, condensate, makeup water, blowdown, surface area, and flue gas information as input. Random numbers generate the hourly temperature variation for a year for discrete-event Monte Carlo Simulation. The simulation generates the hourly firing factor, energy usage, fuel usage, and CO₂ emissions of boilers for a whole year, and the result compares fossil-fuel and electrical boilers. The simulated data are validated using real system data, and sensitivity analysis of the model is performed by varying the input data. Full article

In this study, it is proposed to generate electrical energy by recovering the waste heat of an annealing furnace (AF) in an iron and steel plant using combined cycles such as steam Rankine cycle (SRC), organic Rankine cycle (ORC), Kalina cycle (KC) and transcritical CO₂ cycle (t-CO₂). Instead of releasing the waste heat into the atmosphere, the waste heat recovery system (WHRS) discharges the waste heat into the plant’s low-temperature oxygen line for the first time, achieving a lower temperature and pressure in the condenser than conventional systems. The waste heat of the flue gas (FG) with a temperature of 1093.15 K from the reheat furnace was evaluated using four different cycles. To maximize power generation, the SRC input temperature of the proposed system was studied parametrically. The cycles were analyzed based on thermal efficiency and net output power. The difference in SRC inlet temperature is 221.6 K for maximum power output. The proposed system currently has a thermal efficiency and total power output of 0.19 and 596.6 kW, respectively. As an environmental impact, an emission reduction potential of 23.16 tons/day was achieved. In addition, the minimum power generation cost of the proposed system is $0.1972 per kWh. Full article