Waste Heat Utilization Efficiency Research Articles

Experimental study on dynamic characteristics of organic Rankine cycle coupled vapor compression refrigeration system with a zeotropic mixture

The organic Rankine cycle coupled vapor compression refrigeration system is an attractive refrigeration technology that converts low-grade thermal energy into cooling capacity to improve waste heat utilization efficiency. Due to the inevitable change in ambient temperature and cooling demand, the dynamic characteristics of the combined system are worth studying. In this paper, a small experimental apparatus with a common condenser is designed and developed. The dynamic characteristic experiments under different disturbances are carried out to understand the response characteristics of operating parameters and the variation of system performance. The results show that the maximum response time of the system under different disturbances ranges from 493 s to 694 s. The impact of throttle opening on the response characteristics of refrigeration subsystem parameters is significantly higher than that of the organic Rankine cycle. The mass flow rate of organic Rankine cycle has the fastest response to pump frequency, while the compressor inlet temperature changes rapidly with the cooling water temperature. Under a step cooling water temperature, it is important to control the compressor inlet temperature to avoid liquid droplets in its inlet. In addition, the mass flow rate of organic Rankine cycle should be controlled reasonably to achieve the maximum coefficient of system performance. The cooling capacity of the system is mainly affected by the cooling water temperature and the throttle valve opening. During the experiment, the maximum cooling capacity and performance coefficient of the system are 3.75 kW and 0.275, respectively. This work can provide guidance for the design of the control strategy of the combined system.

Thermal performance simulation and numerical analysis of a fuel cell waste heat utilization system for automotive application

To recover the waste heat generated by proton exchange membrane fuel cells, an onboard fuel cell waste heat utilization system used for cockpit heating was constructed in this study. The heat transfer numerical model of the system was established, and experimental data validated the feasibility of the model. Additionally, the thermal performance of the onboard fuel cell waste heat utilization system was analyzed under various operational conditions. The results indicate that the air temperature and heat transfer coefficient of the heat exchanger are positively correlated with the thermal performance of the cockpit heating, while the radiator inlet air velocity and pump speed show a negative correlation with the system’s performance. Under other steady conditions, the stabilized temperature of the cockpit is increased by 150 % when the air temperature increases from 0 °C to 40 °C, and the cockpit temperature is reduced by 20 % when the water pump speed accelerates from 100 to 300 r/min. Furthermore, under 20 °C ambient temperatures and with an inlet air velocity of 3 m/s, water pump speed of 500 r/min, and a heat exchange coefficient of 5,000 W·m−2·K−1, the fuel cell waste heat utilization system achieves an optimal waste heat utilization efficiency of 50.8 % underrated working conditions. In summary, this study offers theoretical guidance for designing and numerically evaluating a vehicular waste heat utilization system using fuel cells.

Thermodynamic and economic analysis of a novel design for combined waste heat recovery of biogas power generation and silicon production

A novel hybrid system based on a combination of a gas turbine cycle, a supercritical carbon dioxide cycle, and an organic Rankine cycle is devised for power generation. Based on the joint layout proposed in this study, the collaborative and efficient utilization of biogas from anaerobic digestion and flue gas from industrial silicon production can be realized. The clean biogas harvested from anaerobic digestion is exploited by a gas turbine, and the resulting hot exhaust gas is then combined with the flue gas from industrial silicon production to power the supercritical carbon dioxide cycle. Addition, the organic Rankine cycle is added as the bottom cycle in the supercritical carbon dioxide cycle to further improve the waste heat utilization efficiency. Energy, exergy, and economic analysis are performed to assess the system's performance and feasibility, the energy and exergy efficiencies are calculated as 43.61 % and 51.07 %, only 4.09 years are needed to recoup the initial investment of the design, and the net present value is as high as 136,864.14 k$.

Application of Opposition-Based Learning Jumping Spider Optimization Algorithm in Gas Turbine Coupled Cooling System

A gas turbine cooling system is a typical multivariable, strongly coupled, nonlinear system; however, the randomness and large disturbances make it difficult to control the variables precisely. In order to solve the problem of precise process control for multi-input and multi-output coupled systems with flow, pressure, and temperature, this article conducts the following research: (1) Designing a secondary circuit for waste hot water and establishing a water-circulating gas turbine cooling system to improve the efficiency of waste heat utilization. (2) Identifying the coupled system model and establishing a mathematical model of the coupling relationship based on the characteristic data of input and output signals in the gas turbine cooling system. (3) Designing a coupled-system decoupling compensator to weaken the relationships between variables, realizing the decoupling between coupled variables. (4) An Opposition-based Learning Jumping Spider Optimization Algorithm is proposed to be combined with the PID control algorithm, and the parameters of the PID controller are adjusted to solve the intelligent control problems of heat exchanger water inlet flow rate, pressure, and temperature in the gas turbine cooling system. After simulation verification, the gas turbine cooling system based on an Opposition-based Learning Jumping Spider Optimization Algorithm can realize the constant inlet flow rate, with an error of no more than 1 m3/h, constant inlet water temperature, with an error of no more than 0.2 °C, and constant main-pipe pressure, with an error of no more than 0.01 MPa. Experimental results show that a gas turbine cooling system based on the Opposition-based Learning Jumping Spider Optimization Algorithm can accurately realize the internal variable controls. At the same time, it can provide a reference for decoupling problems in strongly coupled systems, the controller parameter optimization problems, and process control problems in complex systems.

System Performance and Pollutant Emissions of Micro Gas Turbine Combined Cycle in Variable Fuel Type Cases

This study focuses on an investigation of the operating performance and pollutant emission characteristics of a micro gas turbine combined cycle using biomass gas, replacing natural gas. The models of both recuperative cycle micro gas turbines with a waste heat utilization system and a micro gas-steam turbine combined cycle system are established. When the gas turbine works at 100 kW and the same types of fuel are burnt, the recuperative cycle system consumes less fuel than the gas-steam combined cycle system. The electric efficiency of the recuperative cycle system can reach more than 29%, which is higher than 24% of the gas-steam combined system. The combined cycle thermal efficiency of the recuperative system is as high as 66%, with 36% waste heat utilization efficiency. The electrical efficiency of the recuperative cycle system in the biomass gas case decreases, while that of the gas-steam combined cycle system undergoes little change. When the gas turbine power output increases from 50 kW to 100 kW, the electrical efficiency and combined cycle thermal efficiency increases, but the thermal efficiency of waste heat utilization of recuperative cycle decreases, the NOX and SO2 emissions gradually rise. Under the same working conditions, the NOX emissions of the recuperative cycle system are greater than that of the steam-gas combined cycle system.

Viability of waste heat capture, storage, and transportation for decentralized flowback and produced water treatment

The use of waste heat has been proposed to reduce the energy footprint of membrane distillation for flowback and produced water (FPW) treatment. However, its feasibility has not been fully understood for FPW treatment. Accordingly, this study performs systematic assessments through thermodynamic modelling of waste heat capture, storage, and transportation for decentralized FPW treatment at well pads located in the Denver-Julesburg Basin. A wide range of sensible, phase-change, and thermo-chemical storage materials were assessed for their effectiveness at the utilization of waste heat from on-site hydraulic fracturing engines and natural gas compressor stations, in order to overcome the temporal or spatial mismatch between waste heat availability and FPW generation. Our results show that the type of storage material being used can have a high impact on the efficiency of waste heat utilization and the treatment capacity of membrane distillation. Sensible storage materials only utilize sensible heat capacities, while phase-change materials have improved performance because they are able to additionally store latent heat. However, sensible and phase-change storage materials lose 11–83% of heat due to conversion inefficiencies caused by their changing temperatures. Thermo-chemical materials, on the other hand, have the highest potential for use because they collect and release heat at constant temperatures. We identified three thermo-chemical storage materials (magnesium sulfate, magnesium chloride, and calcium sulfate) with the best efficiencies due to their elevated discharge temperatures which reduce the energy consumption of membrane distillation. In addition, these materials have high volumetric energy storage density, which enables capture and transportation of waste heat from remote locations such as natural gas compressor stations to the well sites, yielding up to 70% reduction in transportation costs relative to moving FPW to centralized treatment facilities at natural gas compressor stations. Our study, for the first time, demonstrates the importance of selecting appropriate energy storage material for leveraging low-grade thermal energy such as waste heat to power membrane distillation for decentralized wastewater treatment.

Numerical analysis of oxidation performance of basalt fiber bundle thermal flow-reversal reactor

• Using low-dimensional devices and mixed runners to enhance heat transfer. • Reducing the self-sustained concentration to 0.1%. • Gas processing capacity per unit volume increased by 1.03–2.5 times. • The benefit of carbon emission reduction is increased by at least 1.95. • The efficiency of waste heat utilization is increased by 2.5 times. This paper uses Ansys Fluent software to conduct a two-dimensional numerical study on the oxidation performance of basalt fiber bundle thermal flow-reversal reactor (TFRR). The influence of inlet methane concentration, inlet flow rate and circulation period on the oxidation performance of TFRR is analyzed. The results show that the maximum temperature in the reactor increases significantly with the increase of inlet concentration and flow rate. At the same time, the lower limit of the concentration that can be handled by the reactor was studied, and it was found that the basalt fiber bundle TFRR can completely treat the gas with the concentration of 0.1%, under the operating parameters of t c = 80 s, v in = 0.65 m/s or t c = 60 s, v in = 1.0 m/s. In addition, the device was compared with the honeycomb ceramic TFRR in terms of economic efficiency. It was found that the clean development mechanism(CDM) emission reduction benefit of the former was 1.95 times than that of the latter, and the economic benefit of waste heat utilization was 2.5 times than that of the latter.

Experimental study on the influence of bionic channel structure on waste heat utilization equipment

AbstractIn this paper, in order to improve the efficiency of waste heat utilization, based on the movement type and shape of the snake, snake bionic surfaces with different structures were designed, and CuO–H2O nanofluids were used instead of traditional working fluids, and they were coupled together and applied to waste heat utilization equipment. The main work is to experimentally study the effects of nanofluids mass fraction (w = 0.1 wt%, 0.3 wt%, 0.5 wt%), amplitude of bionic channel structure (A = 1 mm, A = 2 mm, A = 3 mm), angular frequency of bionic channel structure (ω = 20 rad/s, ω = 25 rad/s, ω = 30 rad/s), phase shift of bionic channel structure (α = 0°, 90°, 180°), and Reynolds number (Re = 1,300–1800) on the flow and heat transfer characteristics of working fluid. It was found that the heat transfer capacity of nanofluids increases with nanofluids mass fraction, angular frequency, amplitude and phase shift. Finally, the comprehensive performance of the whole experimental system was studied, and it was found that the greater the angular frequency, amplitude and phase shift, the better the comprehensive performance of the heat exchanger.

Experimental study of flue gas condensing heat recovery synergized with low NOx emission system

To improve overall thermal efficiency while simultaneously reducing the NOx emissions of gas boilers, a novel flue gas condensation heat recovery and low NOx emission system that integrates a direct contact heat exchange unit with a combustion air humidification unit is proposed. A well-designed experimental system was established and a test bench was set up to study the effects of variable multi-factor operating conditions on the waste heat recovery and NOx emission properties. The synergistic enhancement principle between the flue gas waste heat recovery process and low nitrogen emission is described in detail. The dew point temperature of the flue gas is improved significantly by humidifying the combustion air, which contributes to both low nitrogen emission and full waste heat recovery. The experimental results show that when the combustion air humidity ratio increased from the zero-humidification condition to 49.0 g/kgdry air, the dew point temperature of the flue gas increased by 6.4 °C. At a spray water flow rate of 0.83 m3/h and with a heat supply network return water temperature of 45 °C, the flue gas waste heat recovery efficiency and the waste heat utilization efficiency of the heat supply network increased by up to 12.2% and 6.9%, respectively, and the average NOx emissions decreased to 50.0 mg/m3. In the NE mode, with a spray water flow rate of 1.03 m3/h, the combustion air humidity ratio is increased to 101.2 g/kgdry air, the NOx emission reduction procedure is more effective and can be reduced to 23.3 mg/m3. The experimental system offers advantages in terms of energy savings, environmental protection, and economic benefits, and also outperforms other competing systems with respect to these issues.

Heat Transfer and Energy Utilization of Waste Heat Recovery Device with Different Internal Component

Steel industry is high energy-consuming industry, and its waste heat recovery is critically important for energy utilization. In this study, pipeline bundle is used to enhance heat transfer in waste heat recovery device, and associated gas-solid heat transfer and energy utilization performance with different pipeline arrangement, pipe diameter and shape of internal component are further analyzed. The temperatures of gas and particle in device with pipeline bundle periodically fluctuate in horizontal direction, and those in staggered system distribute more uniformly than those in paralleled system. Compared with paralleled device, exergy and waste heat utilization efficiency of staggered device have been improved, and they are both higher than those without pipeline. As pipe diameter increases, exergy and waste heat utilization efficiency first increases and then decreases, and they reach the maxima with optimal pipe diameter. As the width of internal component keeps constant, influence of its shape on heat transfer is very little.

Techno-economic analysis on a new conceptual design of waste heat recovery for boiler exhaust flue gas of coal-fired power plants

Recovering waste heat from boiler exhaust flue gas is an effective way to improve energy utilization efficiency and reduce coal burning pollution of coal-fired power plant (CFPP). The low-pressure economizer (LPE) is the most widely employed in waste heat recovery from boiler exhaust flue gas. However, there is a contradiction in LPE between maximizing waste heat recovery rate and maximizing waste heat utilization efficiency. This research improves waste heat utilization efficiency without reducing recovery rate by converting recovery heat. The recovery heat conversion is realized through organic fluid cycle integrating organic Rankine cycle (ORC) with high temperature heat pump (HTHP). The organic fluid cycle acts as a medium between flue gas and feedwater, which makes recovery heat match higher parameter low-pressure heater (LPH) flexibly. Based on exergy analysis, the upper limit for elevating energy-saving effects by converting recovery heat is given. For calculations and analyses, thermodynamic models are built and simulated in MATLAB together with REFPROP software based on a case study. The results show that using the proposed waste heat recovery system could produce 5361.98 kW additional net power output and electricity revenue of $1220.04 k, which are approximately 409.19 kW and $127.2 k greater than LPE respectively. The proposed system could save 5699.36 t standard coal and $854.9 k coal cost per year, which are nearly 595.5 t and $89.32 k larger than LPE. The maximum of recovery heat utilization efficiency of proposed system reaches 17.35% and the maximum efficiency improvement compared to LPE touches 3.48%.

INCREASE IN CHELYABINSK HEATING SYSTEM EFFICIENCY BY UTILIZATION OF LOW-GRADE WASTE HEAT

We consider the possibility of improving the heat supply system in Chelyabinsk through the introduction of heat pump technology for the disposal of low-grade waste heat. The paper analyzes the problems of the heat supply system in Russia. The majority of consumers in large cities of the central Russia are supplied with heat energy through the centralized heat supply system. This approach is largely outdated and inapplicable to the modern energy system. We propose the method for increasing the efficiency of centralized heating using heat pumps. This paper makes the evaluation of the effectiveness of the use of this method, namely performs a calculation study, the final result of which is estimation of efficiency of low-grade waste heat utilization in the Chelyabinsk heat supply system. For this purpose, we have previously analyzed the sources of information on the ways of utilization of waste thermal energy, the principles of the heat pumps operation, and the classification of urban sources of waste heat. The first stage of this study is the development of a calculation technique that makes it possible to estimate at varying initial parameters of the heat supply system objects. The developed technique allows estimating the efficiency of using heat pumps for each category of municipal sources of waste heat energy: energy (CHP, boilers, heating networks) and non-energy (residential, public and production facilities) ones. The second stage is the application of this technique to Chelyabinsk. As a starting point for this stage, we take the data which characterize the climatic features, energy parameters of the sources of centralized heating supply, as well as data on the population, economy and industrial facilities in Chelyabinsk. The result of the study is the numerical value of the efficiency of waste heat utilization in Chelyabinsk.

Techno-economic comparison of different cycle architectures for high temperature waste heat to power conversion systems using CO2 in supercritical phase

Bottoming thermodynamic systems based on supercritical carbon dioxide as working fluid (sCO2) are a promising technology to tackle the waste heat to power conversion at high temperature levels and that might outperform the conventional power units based on Organic Rankine Cycles. In fact, CO2 is an inexpensive, non-toxic, non-flammable, thermally stable and eco-friendly compound. Moreover, CO2 in its supercritical state shows an extreme increase in density that allows turbomachinery downsizing and a high cycle efficiency due to the reduced work required by the compression stage. In addition, supercritical CO2 permits a better temperature glide matching within the heat source which increases the overall efficiency of waste heat utilization. With the aim of identifying pro and cons of different sCO2 cycle layouts, this paper investigated four design Joule-Brayton configurations at increasing complexity: simple regenerative, with recompression, with reheating and with recompression and reheating. The research methodology is based on 1st and 2nd laws thermodynamic analyses and includes correlations to estimate the investment costs of the equipment. With reference to a high temperature industrial waste heat source, performance, costs and exergy losses in the different cycle layouts are compared. Furthermore, a parametric analysis regarding the effects of the cycle pressure ratio on net power output and back work ratio is carried out.

Multi-objective optimization design of condenser in an organic Rankine cycle for low grade waste heat recovery using evolutionary algorithm

The optimum design of a condenser is significant in an organic Rankine cycle to achieve higher waste heat utilization efficiency. Based on the mathematical model of a condenser using plate heat exchanger (PHE), some key geometric parameters on the total heat transfer surface area and pressure drop of the condenser are examined. In order to obtain geometric parameters of a plate heat exchanger, a multi-objective optimization of the condenser in organic Rankine cycle is conducted to achieve the optimal geometry design. The total heat transfer surface area and pressure drop are selected as two objective functions to minimize both total heat transfer surface area and pressure drop under the constant heat transfer rate and LMTD conditions. The plate width, plate length and plant distance are selected as the decision variables. Non-dominated sorting generic algorithm-II (NSGA-II) which is an effective multi-objective optimization method is employed to solve this multi-objective optimization design of PHE. The results show that an increase in channel distance or plate width increases the total heat transfer surface area and decreases pressure drop in the condenser. It is noted that the plate length of PHE has a positive effect on the optimization design of PHE. By multi-objective optimization design of the PHE, a Pareto optimal point curve is obtained, which shows that a decrease in total heat transfer surface area of a condenser can increase the pressure drop through the condenser.

The Feasibility Analysis of Ice Making System Driven by Liquid Nitrogen Engines and Heat Source is Diesel Exhaust

Based on the liquid nitrogen type lang Ken cycle and refrigeration circulation to analyse Ice Making system Driven by liquid nitrogen engines and Heat source is Diesel exhaust. Puts forward the evaluation method of diesel exhaust waste heat utilization efficiency, The simulation results of Matlab show that this system has Practical value, can be used in the Small and medium fishing boat.

Influence of heat recuperation in ORC power plant on efficiency of waste heat utilization

Influence of heat recuperation in ORC power plant on efficiency of waste heat utilization The present work is devoted to the problem of utilization of the waste heat contained in the exhaust gases having the temperature of 350 °C. Conversion of the waste heat into electricity using a power plant working with organic fluid cycles is considered. Three Organic Rankine Cycle (ORC) power plant solutions are analysed and compared: a solution with the basic, single thermodynamic conversion cycle, one with internal heat recuperation and one with external heat recuperation. It results from the analysis that it is the proper choice of the working fluid evaporation temperature that fundamentally affects the maximum of the ORC plant output power. Application of the internal heat recuperation in the plant basic cycle results in the output power increase of approx. 5%. Addition of the external heat recuperation to the plant basic cycle, in the form of a secondary supercritical ORC power cycle can rise the output power by approx. 2%.

97/02113 Renewal wood fuel: fuel feed system for a pulverized coal boiler

Recovering waste heat from boiler exhaust flue gas is an effective way to improve energy utilization efficiency and reduce coal burning pollution of coal-fired power plant (CFPP). The low-pressure economizer (LPE) is the most widely employed in waste heat recovery from boiler exhaust flue gas. However, there is a contradiction in LPE between maximizing waste heat recovery rate and maximizing waste heat utilization efficiency. This research improves waste heat utilization efficiency without reducing recovery rate by converting recovery heat. The recovery heat conversion is realized through organic fluid cycle integrating organic Rankine cycle (ORC) with high temperature heat pump (HTHP). The organic fluid cycle acts as a medium between flue gas and feedwater, which makes recovery heat match higher parameter low-pressure heater (LPH) flexibly. Based on exergy analysis, the upper limit for elevating energy-saving effects by converting recovery heat is given. For calculations and analyses, thermodynamic models are built and simulated in MATLAB together with REFPROP software based on a case study. The results show that using the proposed waste heat recovery system could produce 5361.98 kW additional net power output and electricity revenue of $1220.04 k, which are approximately 409.19 kW and $127.2 k greater than LPE respectively. The proposed system could save 5699.36 t standard coal and $854.9 k coal cost per year, which are nearly 595.5 t and $89.32 k larger than LPE. The maximum of recovery heat utilization efficiency of proposed system reaches 17.35% and the maximum efficiency improvement compared to LPE touches 3.48%.