Flue Gas Waste Heat Research Articles

On-Site Experimental Study on Low-Temperature Deep Waste Heat Recovery of Actual Flue Gas from the Reformer of Hydrogen Production

Improving the energy-saving efficiency of flue gas deep waste heat and reducing the emission of carbon dioxide and other pollutants have been two issues that need to be paid attention to in petrochemical heating furnaces. A hydrogen production reformer with high energy consumption and high carbon emissions in the petroleum refining process affects the thermal and productive efficiency of the hydrogen production, amounts of heat from flue gas are wasted with the exhausted corrosive gas of the reformer, and latent heat is not recovered. To recover the sensible and latent heat from the exhausted gas, a new anti-corrosion, high-efficiency, and low-pressure-drop flue gas condensing heat exchanger (FGCHE) with low consumption and pressure drop was developed. The energy-saving performance was evaluated through on-site measurements and theoretical analysis. The results show that the exhausted gas temperature was reduced from 161.3~175.9 °C to 33.9~38.9 °C after using the new FGCHE to recover waste heat. The energy-saving efficiency and the utilization ratio of flue gas waste heat were 12~16.1% and 74~81.9%, respectively. The latent heat accounted for 41.3~48.1% of the total recovered heat. The exergy efficiency and the total thermal efficiency of the reformer reached 73~86.8% and 95.2~96.6%, respectively. The condensation in the flue gas reduced pollutant emissions (SO2 and NOx). This paper provides a practical application reference for the technology development of waste heat recovery and the application of an FGCHE for petrochemical heating furnaces.

Effect of flue gas condensing waste heat recovery and its pressure drop on energy saving and carbon reduction for refinery heating furnace

The refinery heating furnace has high energy consuming and high carbon emission, and the flue gas condensing waste heat recovery can achieve prominent results in saving energy and reducing emissions of petrochemical industry. Based on adding a flue gas condensing heat exchanger (FGCHE) at the rail of heating furnace, this paper investigates the effects of flue gas waste heat recovery and pressure drop on the energy saving and carbon reduction through theoretical and on-site testing methods. Flue gas heat recovery and pressure-drop characteristics of the FGCHE are analyzed to achieve maximum energy saving and emissions reduction under the normal operating conditions of heating furnace. Meanwhile, the effects of flue gas temperature and pressure drop on the energy saving and carbon reduction are derived under different combustion air temperature, humidity and excess air coefficient after fuel gas complete combustion. The results show that when the flue gas temperature is reduced from 180 °C to 20–40 °C, the energy saving efficiency, utilization ratio of flue gas waste heat, condensate recovery efficiency and carbon emission reduction ratio reach 12.5–16.9%, 74.4–98.1%, 58∼89.3% and 13.7–18.3%, respectively. Reducing the flue gas pressure drop can significantly improve the flue gas waste heat utilization ratio and carbon reduction.

Design and Research of Thermoelectric Generator Simulation System for Boiler Flue Gas Waste Heat

One of the significant factors contributing to high energy consumption is the unutilized waste heat from flue gas in industrial boilers. Thermoelectric generator (TEG) technology can directly convert thermal energy into electrical energy, and has been gradually applied in the field of waste heat recovery due to its simple and reliable structure, environmental protection, and other advantages. In this paper, a thermoelectric generator simulation system of boiler flue gas waste heat is proposed. The experimental platform is designed by simulating the flue gas waste heat temperature condition of boiler, and the structure of cold end module and hot end module is optimized. During the experiment, the fixed temperature difference was set at 120 °C (hot end:150 °C~cold end: 30 °C). An analysis is conducted on the volt-ampere characteristics and output power of the TEG module. The output characteristics of the TEG system are analyzed under the conditions of variable load, constant load, different pump speed, different heat dissipation modes, and series and parallel connection method. The results show that the experimental platform can instantaneously and accurately test the output parameters of the TEG system, and ensure the intended design requirements. When the ratio of the load resistance to the internal resistance of the TEG module is approximately 1–1.15, the output power of the system reaches its maximum. In order to optimize the output power of the TEG system, a power prediction-based adaptive variable step size maximum power point tracking (MPPT) algorithm is introduced. Additionally, a corresponding mathematical model is formulated. Simulations demonstrate that the time of the improved algorithm to reach the stable maximum power point is 1.54 s faster than that of the traditional algorithm. The improved MPPT algorithm satisfies the criteria for speed and accuracy, diminishes superfluous energy waste, and enhances the overall system efficiency. The research results have certain guiding significance for the design and application of subsequent TEG system.

Promoting the synergistic removal of SO3 aerosols and particles during the flue gas condensation by combining alkali spray and turbulent agglomeration

In the condensation process of desulfurized flue gas, not only the flue gas waste heat can be recovered, but also the SO3 aerosols and particles can be removed synergistically. However, the deep purification ability of a single heat exchanger for flue gas is quite poor. In this work, a novel removal technology is proposed for the synergistic removal of SO3 aerosols and particles in the process of flue gas condensation by combining alkali spray and turbulent agglomeration. The agglomeration and capture mechanisms were analyzed by simulating the motion trajectory and calculating the capture efficiency of single alkali droplets. The removal performance of this combined technology was evaluated through experiments. The vertexes generated in the turbulent agglomeration device can promote the agglomeration or coagulation of SO3 aerosols and particles, and finally achieve the enhanced capture effect of these particles by alkali droplets. Compared with the single alkali spray or turbulent agglomeration, the combined technology can achieve better removal performance. The number removal efficiency of the combined technology is up to 78.4% and the mass removal efficiency of SO3 and particles reaches 61.8% and 94.5% respectively under typical conditions. Moreover, the mass removal efficiencies of SO3 aerosols and particles all increase with the increase of initial particle concentration, spray amount of alkaline solution, and flue gas temperature drop.

Investigation on dynamic mathematical model and control method of flue gas heat exchange system

PurposeThe purpose of this paper is to recover the waste heat of flue gas heat exchanger (FGHE) as efficiently as possible and avoid the acid dew corrosion of that.Design/methodology/approachA novel flue gas waste heat recovery system was proposed in the paper. The dynamic mathematical models of key equipment in that were established based on theory and experiment method. The proportion integration differentiation-differentiation (PID-P) cascade control method based on particle swarm optimization algorithm was used to control the outlet temperature of FGHE. The dynamic characteristics of the flue gas heat exchange system were simulated by the particle swarm optimization algorithm with different fitness functions.FindingsThe PID-P temperature controller parameters can be quickly and effectively obtained by the particle swarm optimization algorithm based on the fitness function of integral time absolute error (ITAE). The overshoot, rise time and adjusting time of the novel system are 2, 83 and 105s, respectively. Compared with the traditional two-step tuning (T-ST) method, the novel system is better in dynamic and steady-state performance. The overshoot and the adjustment time of the system are reduced by 44% and 328s, respectively. ITAE is a performance evaluation index for control system with good engineering practicability and selectivity.Originality/valueThe dynamic mathematical model of key equipment in the new flue gas waste heat recovery system is established and the system's control strategies and methods are explored.

Multi-criteria assessment of a new energy-saving and environmentally-friendly scheme for natural gas-fired power plants

Recently, natural gas-fired power plants have received wide attention for their environmental advantages. However, high-temperature waste gas causes a quantity of heat loss, and a large amount of carbon dioxide emissions exacerbate the greenhouse effect. In order to efficiently utilize the waste heat of flue gas and reduce the carbon dioxide emissions from power plants, a cascade system which combines waste heat recovery technologies, including the supercritical carbon dioxide (SCO2) cycle and trilateral organic cycle (TOC), with carbon dioxide capture device is proposed. After validating the accuracy of thermodynamic model, the optimum working fluid for the trilateral organic cycle is selected and some main factors affecting the thermodynamic performance are analyzed in detail. Finally, to test the feasibility of the design, this paper optimizes the economy performance of the cascade system and the amount of captured CO2. The results show that the maximum net output power, carbon dioxide capture and payback period of the system are 157.1 MW, 96.49 ton/h and 4.125 years. Moreover, compared with original power plant design, the net plant efficiency of the cascade system has a significantly increasing of 23.6%. Hence, the new scheme proposed in this paper is a feasible method to achieve the aim of energy conservation and emission reduction.

Study on flue gas waste heat utilization system optimization of a new 1000MW unit

In this paper, the flue gas waste heat utilization system in a new 1000MW unit was as the research object, and the numerical simulations on the flue flow field and resistance characteristics of the low-temperature economizer for four operating conditions without guiding device or with three kind guiding devices was carried out by computational fluid dynamics software, and the correctness of the numerical simulation result was verified by the guaranteed value of the low-temperature economizer manufacturer. The results show that: The simulation result was basically consistent with the guaranteed value of the low-temperature economizer manufacturer, which was shown the correctness of the simulation calculation; the flue gas flow of low-temperature economizer without guiding device was unevenly distributed, with high-speed area and ash prone area; the additional guiding devices can reduce the inlet deflection angle of the low-temperature economizer, which can effectively reduce the speed deviation and improve the flow field distribution; The effect of flow equalization and resistance characteristics of the guiding devices first decreases and then increases with the number of guiding devices; The unreasonable selection of the number and position of the guiding devices will cause the flue gas to rush on the flue and cause the risk of flue vibration. In order to promote the realization of the transformation purpose, the improvement effect of the guiding devices should be simulated and calculated before the transformation.

Research on deep utilization technology of flue gas residual heat for large-capacity coal-fired units

The utilization of flue gas waste heat is an important measure to improve the power efficiency of coal-fired units. Traditional method is to arrange the heating surface after the air preheater, which can just recover the low-grade heat, low efficiency. For the engineering practice of a 1000MW double-reheat unit, three feasible schemes are proposed, namely scheme 1 “two-stage gas cooler plus cold air heater”, scheme 2 “air preheater bypass + two-stage flue gas cooler plus cold air heating” and scheme 3 “air preheater bypass + hot primary air temperature adjustment plus two-stage flue gas cooler plus cold air heater”. For the sake of evaluating the actual effects of different schemes objectively, the thermal characteristic calculation model of the four-part rotary air preheater was established by finite difference method, and then the effect of the inlet air temperature and the share of bypass flue gas on the thermal efficiency of the boiler were studied. The equivalent enthalpy drop method was used to establish the thermal characteristic model of steam turbine, and the influence of different heat distribution modes on the heat consumption rate of steam turbine was studied.. Considering the technical economy, the optimal bypass flue gas share of this scheme is 12%, which corresponds to the reduction of coal consumption for power supply of the unit by about 3.23g/kWh. Taking into account comprehensively, scheme 3 is recommended.

Thermal economy analysis of flue gas waste heat utilization system of 1000MW secondary reheat unit

Deep utilization of flue gas waste heat is an important means to ameliorate the power generation productivity of coal-fired units. Aiming at the waste heat cascade utilization system which is composed of “air preheater bypass + two-stage low-temperature coal economizer + thermal primary air temperature regulating device” proposed in a certain project, using the energy balance method and the equivalent enthalpy drop method, the mathematical model of the impact of waste heat utilization devices at all levels on the unit economy is established from the boiler efficiency and steam engine heat rate. Combined with the rated operation data of the unit, the thermal economy of the system is analyzed. The results show that the bypass of the air preheater and the temperature regulating device of the hot primary air can effectively improve the utilization efficiency of the waste heat of the flue gas at the tail of the boiler, the coal consumption of power supply can be reduced by 3.47 g/kWh under rated working conditions.

A new integration scheme for CO2 capture in low-rank coal fired power plants with energy savings

Integration of CO2 capture process into a fossil fuel fired power plant leads to an unavoidable efficiency loss. Thus, optimization of the integration scheme is of great necessity to reduce the efficiency loss. This study proposes a new integration scheme for a low-rank coal (LRC) fired power plant with CO2 capture system of solid amine-based sorbents, specifically including a steam cycle, a CO2 capture system and a LRC pre-drying process. By suitable system integration, the low-quality heat in the CO2 capture system could be used to replace the high-quality waste heat of flue gas for LRC pre-drying, thus achieving great energy savings. Compared to the conventional integration scheme, the thermal and exergy analyses show that the new integration scheme efficiently recovers the low-quality heat in the CO2 capture system to generate more power output and the corresponding efficiency loss is reduced by 2.66%. Economic analysis shows that the economic benefits from the new integration scheme outweigh the disadvantages of the investment increase, and the cost of electricity (COE) and the cost of CO2 avoided (COA) are reduced by 5.95 $/MWh and 8.32 $/tCO2.

Experimental research on direct expansion heat pump flue gas waste heat recovery and humidification nitrogen reduction system

In order to solve the heat loss and the pollution of gas boilers, a synergistic system consisting of waste heat recovery tower and air humidification tower is proposed. Increasing in moisture content of the air can inhibit the generation of nitrogen oxides and increase the dew point of the flue gas, which is beneficial to the utilization of the waste heat from the flue gas. More heat is absorbed by the humidification water at the fin heat exchanger after the flue gas enters the waste heat recovery tower, which enhances the heat and mass exchange process in the air humidification tower. But the performance of the heat pump was found to show a downward trend, indicating a competitive relationship between nitrogen oxides reduction and waste heat recovery. Under the optimal condition, the experimental system can reduce nitrogen oxides emissions by 62.35%, and the exhaust gas temperature can be reduced to 24.46 °C. The heat pump can recover 6.94% heat while maintaining a minimum nitrogen oxides emission of 39.66 mg/m3. The heat pump makes more heat from the fuel to enter the heating network, which improves the heating efficiency of the boiler system. The system can meet the high-efficiency and clean production requirements of the energy system at the same time.

Research on a Novel Combined Cooling and Power Scheme for LNG-Powered Ship

Cold energy recovery in LNG-powered vessels can not only improve the utilization efficiency of energy, but also benefit environmental protection. This paper put forward a new cascade scheme for utilizing flue gas waste heat and LNG cold energy comprehensively. The scheme was integrated by a dual organic Rankine circulation system (ORC), a high- and low-temperature cold storage system (TCS), an air conditioning system (ACS) and a seawater desalination system (SDS). The working medium of the dual ORC system was firstly determined by considering exergy efficiency and economic index simultaneously. On this basis, the adaptive weighted particle swarm optimization algorithm was employed to enhance thermodynamic performance of the scheme with the net output power as the optimization objective. The maximum net power and annual net interest rate can reach 725.78 kW and $115,300, respectively. Furthermore, the economic benefit of the scheme was analyzed by referring to the running track and the operation condition of the target ship. The results showed that the proposed scheme is a potential large-scale cryogenic technology and can bring considerable economic benefits to ship navigation.

An Efficient Method for Heat Recovery Process and燭emperature燨ptimization

Flue gas heat loss accounts for a significant component of the overall heat loss for coal-fired boilers in power plants. The flue gas absorbs more heat as the exhaust gas temperature rises, which reduces boiler efficiency and raises coal consumption. Additionally, if the exhaust gas temperature is too high, a lot of water must be used to cool the flue gas for the wet flue gas desulfurization system to function well, which has an impact on the power plant’s ability to operate profitably. It is consequently vital to take steps to lower exhaust gas temperatures in order to increase boiler efficiency and decrease the amount of coal and water used. Desulfurization performance may be enhanced and water use can be decreased by reasonable flue gas characteristics at the entry. This study analyzed the unit’s energy consumption, investment, and coal savings while proposing four coupling strategies for regulating flue gas temperature and waste heat recovery. A graded flue gas conditioning and waste heat recovery plan was presented under the condition of ensuring high desulfurization efficiency, along with the notion of minimizing energy loss owing to energy inflow temperature difference. Numerical results show that the proposed methods improved the system performance and reduced the water consumption and regulated the boiler temperature.

Design study on the integrated utilization system of medium temperature waste heat and LNG vaporization cold energy for 200000 DWT LNG-powered vessels

The study object for this work is a 215000 ton very large crude carrier ? liquefied natural gas ? powered vessel, intending to integrate the use of medium temperature flue gas waste heat from the exhaust turbine and cold energy from liquefied natural gas vaporization. It proposes a Rankine cycle power generating system with a two stage booster and three stage lateral nesting following the principle of ?temperature matching, stepped utilization?, taking into account real demands and circumstances of the vessel. The study shows that in this tonnage vessel, through the design and optimization of the stepped utilization scheme, the cold energy released during the vaporization of liquefied natural gas fuel from the ME-GI host machine and the medium temperature waste heat from the exhaust turbine can be fully utilized, and the system structure is tight and simple. After the non-azeotropic mixed working media was optimized and the operational parameters were optimized using genetic algorithm, the system designed in this paper can reach 54.61% exergy efficiency and 187.83 kW net output of power generation. The annual income of the final designed system can reach CNY 1, 133, 240. The capital recovery cycle is expected to be 5.06 years if the system is put into operation.

Simulation Analysis of Flue Gas Waste Heat Utilization Retrofit Based on ORC System

Simulation Analysis of Flue Gas Waste Heat Utilization Retrofit Based on ORC System

Design and optimization of LNG-powered ship cold energy and waste heat integrated utilization system based on novel intermediate fluid vaporizer

Based on a novel integrated intermediate fluid vaporizer with liquefied natural gas (LNG) cold energy utilization proposed by the author's team, a full-power generation integrated system is constructed in this study. It is a two-stage cascade Rankine cycle with two-stage condensation and coupled with a trans-critical CO2 Rankine cycle. This study regards a river–sea direct transportation type of 25,000-ton LNG fuel-powered chemical ship as the application object and considers combined utilization of the medium-temperature waste heat of flue gas from the exhaust turbine power generation cycle outlet and the vaporization cold energy of LNG. Through the simulation and analysis of the scheme, circulating working fluid optimization and operation parameter optimization based on a genetic algorithm are conducted. The overall exergy efficiency of the optimized system reaches 45.1%, while the power generation of the system reaches 72.66 kW. Furthermore, economic analysis shows that the net annual income of the optimized system can reach 280,700 yuan, and the recovery cycle of initial investment cost is expected to be 6.11 years.

Performance analysis of an open absorption heat pump and thermal desalination system for heat and water recovery of coal-fired flue gas based on zero liquid discharge

An innovative combined system based on an open absorption heat pump and low-temperature multi-effect desalination system is proposed to provide fresh water and domestic hot water in order to achieve zero liquid discharge from coal-fired power plants and recover the waste heat of flue gas. This system takes into consideration the evaporation of desulfurization wastewater by flue gas. By using a 600 MW unit as an example, energy and exergy analysis is used to examine the impacts of flue gas humidity, temperature, mass, generator pressure, solution concentration, and boiler load on system performance. The findings showed that because coal-fired power plants produce a significant amount of dry flue gas, an increase in gas humidity has little effect on product supply. As a result, little variation in the combined system is caused by the desulfurization wastewater spray evaporation, which allows power plants to achieve zero liquid discharge with only a small loss in exergy efficiency of about 6%. The recovery of sensible heat rather than latent heat benefits from an increase in the bulk of dry flue gas. The recovery of heat and water benefits more from an increase in operating load or flue gas temperature than the open absorption heat pump system itself. The generator pressure and rich solution concentration have negligible effects on heat and water recovery. The open absorption heat pump system's increasing exergy efficiency trend and the boiler operating loads are also related. The exergy efficiency of the generator is the highest by about 75%, that of the desalination system is the lowest by about 29%, and the exergy destruction of the absorber is the highest by about 43%. The findings are likewise applicable to coal-fired power stations with various levels of electrical output.

Coupling of the S-CO<sub>2</sub> cycle and ORC to realize an efficient utilization scheme of flue gas waste heat for the coal-fired power generation system

<p indent="0mm">The multistage compression regeneration process can significantly improve the thermal efficiency of the supercritical carbon dioxide (S-CO₂) cycle. Because of the improvement of regeneration, when the multistage compression cycle is used for coal-fired power generation systems, the residual heat in the tail flue cannot be fully absorbed. To solve this problem, a combination of the tri-compression cycle with reheating and organic Rankine cycle (ORC) is constructed. By optimizing the energy flow process between the system and the environment, the system performance is gradually improved. First, the heat in the cooler of the S-CO₂ cycle and tail flue is partially absorbed by ORC (R123). Then, the outlet flue gas temperature (<italic>T</italic>_fg,ex) decreases, and the boiler efficiency increases. When the main vapor parameters of the S-CO₂ cycle are 620°C/<sc>30 MPa,</sc> <italic>T</italic>_fg,ex decreases from 132°C to 123°C, and the net power efficiency (<italic>η</italic>_e) increases from 47.13% to 47.24%. This combined cycle can effectively absorb the heat of flue gas at the tail flue; therefore, high boiler efficiency and net power efficiency can be obtained. Second, based on the coupling of the S-CO₂ cycle and ORC, the characteristics of the heat release process in the cooler of the S-CO₂ cycle under different temperature conditions are further analyzed. The air and ORC jointly absorb the heat in the high-temperature range of the cooler, and the net power efficiency is further improved from 47.24% to 48.90%. This study provides an effective method for residual heat absorption in the tail flue and cooler.

Performance Modulation of S-CO2 Brayton Cycle for Marine Low-Speed Diesel Engine Flue Gas Waste Heat Recovery Based on MOGA.

(1) Background: the shipping industry forced ships to adopt new energy-saving technologies to improve energy efficiency. With the timing modulation for the marine low-speed diesel engine S-CO2 Brayton cycle, the waste heat recovery system is optimized to improve fuel economy. (2) Methods: with the 6EX340EF marine low-speed diesel engine established in AVL Cruise M and verified by the bench test data, the model of the S-CO2 Recompression Brayton Cycle (SCRBC) system for the low-speed engine flue gas waste heat recovery was developed in EBSILON, and verified by SANDIA experimental data. On this basis, the effects of injection timing and valve timing parameters on the comprehensive performance of the main engine and the waste heat recovery system were investigated. By optimizing the timing modulation parameters through multi-objective genetic algorithm (MOGA) and evaluating the flue gas waste heat recovery from the perspective of thermodynamic performance and emission reduction, the research on the performance modulation method of the S-CO2 Brayton Cycle for flue gas waste heat in marine low-speed engines has been completed. (3) Results: the SCRBC with waste heat modulation will further increase the total power and efficiency, which in turn brings about a reduction in the fuel consumption rate. The efficiency of the SCRBC system with the addition of waste heat modulation increases by 2.28%, 1.04% and 2.07% at 50%, 75% and 100%, respectively. After adding the residual heat modulation, the maximum annual CO2 emission reduction of 748.51 × 103 kg·a-1 occurred at 50% load; with the exergy analysis, the cooler has the largest system exergy loss of 165 kW, with the exergy loss efficiency of 2.06% under 100% load. (4) Conclusions: the research on the performance modulation method of S-CO2 Brayton cycle for flue gas waste heat in the marine low-speed engine has been completed, which further improves the efficiency of the system and can be extended to other engines.

A trigeneration application based on compressed air energy storage integrated with organic Rankine cycle and absorption refrigeration: Multi-objective optimisation and energy, exergy and economic analysis

Compressed air energy storage (CAES) has attracted worldwide attention due to the advantages of dealing with the intermittent problem of renewable energy. However, CAES is plagued by inadequate utilisation of the compression heat and waste heat in flue gas, and requires further improvement. In this study, a combined cooling, heating, and power (CCHP) system based on the CAES, organic Rankine cycle (ORC), and absorption refrigeration system (ARS) is comprehensively investigated. From the view of thermodynamic and economic performances, a multi-objective optimisation is performed to maximise the round-trip efficiency (RTE) and minimise the total investment cost per output power (ICPP) based on the rigorous model simulated in Aspen plus. The results show that the optimal CCHP system has the advantages of high efficiency of 68.38 % RTE (increased by 3.05 %) and low cost of 0.1984 $/kWh ICPP (decreased by 2.68 %). Additionally, the impact of different working fluids is investigated. Compared with different working fluids, the results show that R601 performs better from the system efficiency perspective (68.38 % of RTE), while R600 has an advantage over ICPP of 0.1977 $/kWh. The results indicate that the decrease in combustion chamber temperature benefits the system by generating more electricity power and cooling capacity. The discharging process accounts for the largest proportion of the exergy destruction and equipment costs. This research can help explore the potential of improving system efficiency and economy, and guide practical application in the area of CCHP.