Gas Waste Heat Recovery System Research Articles

Design on a novel waste heat recovery system integrated with the bypass flue and outside primary air preheater for bitumite-fired power plants

Bitumite is widely used in coal-fired power plants. However, due to its high volatile content, the temperature of primary air to coal mills is limited to a lower value because of its high risk of spontaneous combustion. The method to reduce primary air temperature by mixing with cold air leads to irreversible loss and reduces the power generation efficiency of the power plant. To address the issue, a novel flue gas waste heat recovery system integrated with the bypass flue and outside primary air preheater for bitumite-fired power plants was suggested. The thermo- and techno-economic analysis models of the waste heat recovery system were developed, and the design parameters were optimized to maximize profit. The thermo-economic analysis shows that the exergy efficiency of the waste heat recovery system can reach 49.8 %, and the coal consumption rate can be reduced by 4.75 g (kW h)−1 by integrating the optimal waste heat recovery system. The techno-economic analysis shows that the net present value of the power plant during ten years can reach 10.6 M$, and the discounted payback period is 0.6 years. The novel waste heat recovery system can effectively improve the thermo- and techno-economic performance of bitumite-fired power plants.

Study on the process technology of energy saving and consumption reducing for municipal sludge-based biochar

Taking the production process of sludge-based biochar as the research object, based on the measured data of engineering field operation, the thermal balance models of sludge carbonization and cooling conveying system, pyrolysis gas incineration and waste heat recovery system, flue gas treatment and deodorization system were established respectively. The energy loss points in the process of operation were determined and calculated. The results show that the energy consumption loss of sludge-based biochar production process is 23550 MJ/h under the field operation conditions of feeding 2920 kg/h of dry sludge (moisture content 30 %), 19.65 kg/h of natural gas and 67 kg/h of fresh water, producing 1500 kg/h of sludge-based biochar (moisture content 4.5 %) and carbonization temperature 450 °C. Compared with the sludge drying incineration process, it can save energy and reduce consumption by 52.2 %, and the calorific value of sludge-based biochar is 7.04 MJ/kg, which is 49.6 % higher than that of dry sludge.

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.

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.

Dynamic control method of flue gas heat transfer system in the waste heat recovery process

A new flue gas waste heat recovery system and its control strategy are proposed based on the intelligent control technology and the principle of phase-change heat transfer. It is composed of flue gas heat transfer system (FGHTS) and air heat transfer systems (AHTS). The system pressure and outlet flue gas temperature are adjusted by blower frequency in the AHTS and the concentration of lithium bromide-water in the FGHTS, respectively. For FGHTS, a dynamic control method is proposed based on improved particle swarm optimization (PSO). In this method, the optimization ability and the convergence of PSO algorithm are affected by inertia weight and fitness function. The inertia weight strategy with the inverted S-shaped function (IWS-ISF) can enhance the global search ability in the initial stage and the local search ability in the later stage compared with other inertia weight strategies. Meanwhile, the integral time absolute error (ITAE) fitness function is improved by introducing overshoot into ITAE, and the improved fitness function is defined as IITAE fitness function. The improved PSO algorithm based on IITAE fitness function can reduce the overshoot of FGHTS by 66.23%. This paper can provide a theoretical basis for improving the control performance of the new system.

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.

Performance research and application of the vapor pump boiler equipped with flue gas recirculation system

To improve the boiler thermal efficiency and reduce oxynitride emissions, a novel flue gas waste heat recovery system is proposed. The vapor pump boiler equipped with a flue gas recirculation system is first applied for practical engineering. The oxidizing air is preheated and humidified before the combustion process, which causes the dewpoint temperature of the flue gas to increase. Thus, more waste heat in the flue gas can be recovered by the boiler feedback water. Heat recovery efficiency of the system can reach 82.6%, resulting in a 7–8% increase in the boiler efficiency. In addition, the increases in oxidizing air humidity and flue gas recirculation both reduce oxynitride production. As a result, oxynitride emission decreases from 129 mg/m3 to 23 mg/m3, resulting in a reduction of 82.3%. The gas-fired boiler realizes ultra-low oxynitride emission. For a 1.8 MW boiler, annual natural gas consumption can be saved by 7–8%. Given current energy prices in Beijing, the proposed system is economical with a static payback period of 1.2 years. An overall system performance is provided as evidence of the potential benefits. The proposed system is proved to have advantages in energy savings, pollutant reduction, and economic benefits.

Performance Analysis of the Technology of High-Temperature Boiler Feed Water to Recover the Waste Heat of Mid-Low-Temperature Flue Gas.

In coal-fired power plants, most of the working fluids used in a mid–low-temperature flue gas waste heat recovery system (FGWHRS) are low-temperature boiler supply air or condensate water in the flue gas condenser. This is prone to cause low-temperature corrosion, as the system temperature is lower than the acid dew point of the flue gas. In this study, an experimental apparatus was set up at the entrance of the desulfurization tower of a 330 MW unit in Xinjiang, China, which uses the technology of high-temperature boiler feed water (above 80 °C) to recover the waste heat of mid–low-temperature flue gas. The heat exchange performance of the mid–low-temperature FGWHRS was evaluated under different working conditions, and the optimal input parameters of the system for each considered working condition are given based on the analysis. It was found that the low-temperature corrosion in the system could be avoided using this technology. To eliminate low-temperature corrosion, the lowest temperature for the inlet water was predicted to be 69 °C in our study via curve fitting based on the experimental data. The results could provide a theoretical basis and engineering guidance for determining the best heat recovery strategy of mid–low-temperature FGWHRS.

Novel flue gas waste heat recovery system equipped with enthalpy wheel

Waste heat recovery from flue gas is an efficient way to increase the thermal efficiency of a gas-fired boiler. This paper proposes a novel flue gas waste heat recovery system, which comprises a condensing heat exchanger and an enthalpy wheel. The flue gas firstly flows through the condensing heat exchanger for heating boiler water, and then flows through the enthalpy wheel. The wheel, covered with desiccant material, acts as a medium for further heat and moisture transfer from the flue gas to the oxidizing air, resulting in an increase in the dew point temperature of the flue gas. Experimental results show that the average boiler efficiency reaches 106% and the average total recovery efficiency reaches 88%. The dew point temperature of the flue gas discharged from the boiler increases to around 60 °C, higher than that of conventional flue gas (around 55 °C). Consequently, more latent heat is recovered in the condensing heat exchanger by virtue of the proposed system. A mathematical model is established for further analysis based on the experimental results. The rotation speed of the enthalpy wheel and backwater temperature are key factors influencing the system performance.

Experimental Study on Operation Regulation of a Coupled High–Low Energy Flue Gas Waste Heat Recovery System Based on Exhaust Gas Temperature Control

Controlling the exhaust gas temperature (EGT) of coal–fired boilers at a reasonable value is beneficial to ensuring unit efficiency and preventing acid corrosion and fouling of tail heating surfaces in power plants. To obtain the operation regulation of coupled high–low energy flue gas waste heat recovery system (CWHRS) under a given EGT, experimental equipment was designed and built. Experiments were carried out to maintain the exhaust gas temperature under different flue gas flow, flue gas temperature and air temperature conditions. As the flue gas flows, the flue gas temperatures and air temperatures increased, and the bypass flue gas flow proportions or the water flows of the additional economizer were increased to maintain the EGT at about 85 °C. An improved low temperature economizer (LTE) and front located air heater (FAH) system were put forward. As the flow of the crossover pipe increased, the EGT and the inlet water temperature of the LTE increased. As the flow of the circulating loop increased, the EGT and the inlet water temperature of the LTE decreased. Operation regulations of LTE–FAH system under four cases were given. The operation regulations of CWHRS and LTE–FAH system can provide references for power plant operation.

Node Temperature of the Coupled High-Low Energy Grade Flus Gas Waste Heat Recovery System

Coupled high-low energy grade flus gas waste heat recovery systems (CWHRS) have been applied in power plants to improve unit efficiency. In this study, to evaluate the rationality of waste heat recovery, the energy-grade balance coefficient (EBC) of the CWHRS was derived using the theory of heat balance, exergy balance and energy grade balance. The inlet flue gas temperature (IFT) of the low-temperature economizer was defined as the node temperature of the CWHRS. The optimal node temperature (ONT) was optimal when the absolute value of the EBC was the smallest. The exergy efficiency and EBC of the system installed on a supercritical 600 MW unit were calculated and the result shows that the ONT of the system was about 115 °C, the ONT decreased from about 135 °C to about 113 °C when the IFT increased from 335 °C to 380 °C and the ONT decreased from about 144 °C to about 113 °C when the inlet air temperature increased from −10 °C to 35 °C. The node temperature is recommended as an adjusting parameter of CWHRS to ensure the effect of waste heat recovery.

Thermoelectric generator heat performance study about improved fin structures

This paper involves an exhaust gas waste heat recovery system for vehicles, which uses thermoelectric modules and a heat exchanger to produce electric power. Based on summarizing the latest research of vehicle exhaust thermo-electric generator (TEG), it presents two new fin structures for the cylindrical heat exchanger in a TEG system. It mainly studies the thermal performance of two kinds of three-dimensional cylindrical heat exchanger models including spiral-fin heat exchanger with variable pitch in a computational fluid dynamics simulation environment. In terms of interface temperature and thermal uniformity and based on an evaluation method of the temperature uniformity for the heat exchangers, the thermal characteristics of heat exchangers with different pitch angle of the twisted fins, pitch of spiral fin, fin thickness and fin height are discussed. Two new fin structures are feasible to enhance the heat transfer performance of heat exchanger.

Influence of different cooling methods on thermoelectric performance of an engine exhaust gas waste heat recovery system

Thermoelectric generators (TEGs) present good potential applications for the conversion of low level thermal energy into electrical power, especially applied to waste heat recovery systems. This paper presents an advanced mathematical model that uses multi-element thermoelectric components connected in series, and considers internal and external irreversibility and also the temperature gradients along the flow direction. A Fortran computation program was used for the numerical calculations. This paper focusses mainly on the thermoelectric performance study under four different types of cooling methods with temperature gradient modeling. The results showed that it is important in TEG system design to choose an optimal module area that is appropriate to the mass flow rate of the fluids, but this is not affected by the intake temperature of fluids. With the water cooling method, the coflow and counterflow methods did not need to be distinguished because of their small difference, but they should be distinguished for the air cooling method. The counterflow arrangement generally produced a small higher maximum power output, but needed a much larger module area compared to the coflow method.

Waste Heat Recovery from Gas Turbine Flue Gases for Power Generation Enhancement in a Process Plant

To improve on-site power generation capacity and efficiency in process facilities, the thermal coupling of an industrial gas turbine cycle with a bottoming organic Rankine cycle for power plant flue gas waste heat recovery in a process facility is investigated. Using 1,1,1,3,3-pentafluoropropane (R245fa) as heat carrier in the Rankine cycle, 5.2 MW of additional electric power is generated, enhancing on-site power generation capacity and energy/exergy efficiency by approximately 23% and 6%, respectively. The overall energy and exergy efficiencies of the waste heat recovery system are estimated at 9% and 24%, respectively. Primary energy savings of approximately 1.3 million standard cubic feet per day (MMSCFD) of natural gas, or net annual operating expenditure savings of 1.6 million USD, could be realized with the proposed flue gas waste heat recovery system based on subsidized industrial electricity tariffs in the UAE, with 457 tons of avoided CO2 emissions per year.

A novel flue gas waste heat recovery system for coal-fired ultra-supercritical power plants

Recovering flue gas waste heat is important in improving power plant efficiency. The most widely method is installing a low-temperature economizer (LTE) after the electrostatic precipitator (ESP) to heat the condensed water, thereby saving the extraction steam from the steam turbine and achieving extra work. The inlet flue gas temperature of the LTE is relatively low, so it can only heat condensed water from low-grade regenerative heaters, resulting in comparatively minor energy savings. After conducting an in-depth analysis of the conventional waste heat recovery system (WHRS), this paper proposes a novel WHRS, in which the air preheater is divided into high-temperature (HT) and low-temperature (LT) air preheaters, and the LTE can be situated between the ESP and the LT air preheater. Through system integration, higher-grade extraction steam can be saved, resulting in greater economic benefits. Results show that the net additional power output can reach 9.00 MWe and using the proposed WHRS can yield net benefits up to USD 2.60 million per year, which is much greater than those of conventional WHRS. Exergy destruction is also reduced from 34.1 MWth in the conventional WHRS to 28.5 MWth in the proposed WHRS.

Experiments and Simulations on a Heat Exchanger of an Automotive Exhaust Thermoelectric Generation System Under Coupling Conditions

The present experimental and computational study investigates an exhaust gas waste heat recovery system for vehicles, using thermoelectric modules and a heat exchanger to produce electric power. It proposes a new plane heat exchanger of a thermoelectric generation (TEG) system, producing electricity from a limited hot surface area. To investigate the new plane heat exchanger, we make a coupling condition of heat-flow and flow-solid coupling analysis on it to obtain the temperature, heat, and pressure field of the heat exchanger, and compared it with the old heat exchanger. These fields couple together to solve the multi-field coupling of the flow, solid, and heat, and then the simulation result is compared with the test bench experiment of TEG, providing a theoretical and experimental basis for the present exhaust gas waste heat recovery system.

A case study on compatibility of automotive exhaust thermoelectric generation system, catalytic converter and muffler

The power generation of an exhaust TEG (thermoelectric generator) depends on heat energy and thermoelectric conversion efficiency. However, there are compatibility problems among TEG, CC (catalytic converter) and muf (muffler). The present work tried to vary the installation position of TEG and propose three different cases. Case 1: TEG is located at the end of the exhaust system; case 2: TEG is located between CC and muf; case 3: TEG is located upstream of CC and muf. Simulation and experiment were developed to compare thermal uniformity and pressure drop characteristics over the three operating cases. From the simulation and experiment, heat exchanger in case 2 obtained more uniform flow distribution, higher surface temperature and lower back pressure than in other cases. At the same time, the CC and muf could keep normal working in case 2, providing a theoretical and experimental basis for the exhaust gas waste heat recovery system.

Experiments and Analysis on Thermoelectric Generators of Automotive Exhaust under the Multi-Field Coupling

The present experimental and analytic study reports a new thermoelectric generation (TEG) system, working with heat exchangers to produce electricity from a limited hot surface area. Results are obtained for generators using a coupling condition of heat-flow and flow-solid coupling analysis to obtain the temperature, heat, pressure field of heat exchanger. These fields couple together to solve the multi-field coupling of the flow, solid, heat, and then the simulation result is compared with the test bench experiment of TEG, providing a theoretical and experimental basis for the present new exhaust gas waste heat recovery system.

干燥塔尾气余热回收系统换热器设计

干燥塔尾气余热回收系统换热器设计

Conceptual Design and Performance Analysis of an Exhaust Gas Waste Heat Recovery System for a 10000TEU Container Ship

According to operation characteristics of the main engine 9K98ME-C7, a combined turbines-exhaust gas waste heat recovery system is proposed to recover waste heat and increase system energy efficiency. Thermodynamic models based on the first thermodynamic law and the second thermodynamic law are formulated. The superheated steam yield, the total electric power yield, the first thermodynamic law efficiency, the exergy efficiency at different exhaust gas boiler working pressure, and the variation of the exergy efficiency under different feed water temperature and different steam turbine back pressure are analyzed. Thermodynamic results indicate that the most appropriate exhaust gas boiler pressure is 0.8MPa for studied main engine and the total thermal efficiency with combined turbines arrangement has climbed up to 53.8% from 48.5%.