Analysis and Prospect of Waste Heat Utilization from Blast Furnace Slag Flushing

Estimating the residual heat of blast furnace slag flushing in China,classifying and introducing the current proposed methods of slag flushing waste heat utilization,and listing existing cases.In order to better save energy and water in the slag flushing process of blast furnaces,an ideal comprehensive cascade utilization system scheme for annual recovery of waste heat is proposed.Based on the measured waste heat data of a steel plant,design calculations are carried out to further analyze the economic feasibility of the new scheme and provide reference for its promotion and application.

Integration of Low-level Waste Heat Recovery and Liquefied Nature Gas Cold Energy Utilization

Two novel thermal cycles based on Brayton cycle and Rankine cycle are proposed, respectively, which integrate the recovery of low-level waste heat and Liquefied Nature Gas （LNG） cold energy utilization for power generation. Cascade utilization of energy is realized in the two thermal cycles, where low-level waste heat,low-temperature exergy and pressure exergy of LNG are utilized efficiently through the system synthesis. The simulations are carried out using the commercial Aspen Plus 10.2, and the results are analyzed. Compared with the conventional Brayton cycle and Rankine cycle, the two novel cycles bring 60.94% and 60% in exergy efficiency, respectively and 53.08% and 52.31% in thermal efficiency, respectively.

Performance Analysis of Multi-Energy Hybrid System Based on Molten Salt Energy Storage

This paper briefly summarizes the current status of typical solar thermal power plant system,including system composition,thermal energy storage medium and performance.The thermo-physical properties of the storage medium are some of the most important factors that affect overall efficiency of the system,because some renewable energy sources such as solar and wind are unpredictable.A thermal storage system is therefore necessary to store energy for continuous usage.Based on the form of storage or the mode of system connection,heat exchangers of a thermal storage system can produce different temperature ranges of heat transfer fluid to realize energy cascade utilization.Founded upon the review,a small hybrid energy system with a molten-salt energy storage system is proposed to solve the problems of heating,cooling,and electricity consumption of a 1000 m2 training hall at school.The system uses molten-salt storage tank,water tank and steam generator to change the temperature of heat transfer fluid,in order to realize thermal energy cascade utilization.Compared to the existing heating and cooling system,the proposed system needs more renewable energy and less municipal energy to achieve the same results according to simulation analysis.Furthermore,by improving the original heating and cooling system,PMV has been improved.The comprehensive efficiency of solar energy utilization has been increased to 83%.

Thermodynamics of Cascaded Waste Heat Utilization from Flue Gas and Circulating Cooling Water

A detailed thermal power plant model was developed to evaluate power plant waste heat usage in terms of the operating parameters,energy consumption,water consumption,and pollutant emissions.This model was used to analyze the bypass flue gas energy cascade utilization design which provides excellent energy savings and emission reductions.This paper then presents a design to use the low-temperature waste heat and to extract water from the flue gas.The low-grade heat can be recovered from a coal-fired unit using absorption heat pumps to increase the air preheating.This method significantly reduces the turbine steam extraction in the low pressure stages which increases the turbine power and reduces the coal consumption.This design has a small heat transfer temperature difference between the air preheater and the air warmer,resulting in a smaller exergy loss.The power output of the present design was 1024.28 MW with a coal consumption savings of 3.69 g·(kWh)^(−1).In addition,the present design extracts moisture out of the flue gas to produce 46.48 t·h^(−1)of water.The main goal of this work is to provide a theoretical analysis for studying complex thermal power plant systems and various energy conservation and CO_(2)reduction options for conventional power plants.

A Comprehensive Study of a Low-Grade Heat-Driven Cooling and Power System Based on Heat Current Method

Combined cooling and power(CCP)system driven by low-grade heat is promising for improving energy efficiency.This work proposes a CCP system that integrates a regenerative organic Rankine cycle(RORC)and an absorption chiller on both driving and cooling fluid sides.The system is modeled by using the heat current method to fully consider nonlinear heat transfer and heat-work conversion constraints and resolve its behavior accurately.The off-design system simulation is performed next,showing that the fluid inlet temperatures and flow rates of cooling water as well as RORC working fluid strongly affect system performance.The off-design operation even becomes infeasible when parameters deviate from nominal values largely due to limited heat transfer capability of components,highlighting the importance of considering heat transfer constraints via heat current method.Design optimization aiming to minimize the total thermal conductance is also conducted.RORC efficiency increases by 7.9%and decreases by 12.4%after optimization,with the hot fluid inlet temperature increase from 373.15 to 403.15 K and mass flow rate ranges from 10 to 30 kg/s,emphasizing the necessity of balancing system cost and performance.

A Distributed Energy System with Advanced Utilization of Internal Combustion Engine Waste Heat

New trigeneration system consists of an internal combustion engine,a power and cooling cogeneration system and an absorption heat transformer system.The exhaust gas is recovered by the power and cooling cogeneration subsystem producing the cooling and power.The jacket water is recovered by the absorption heat transformer subsystem producing lowpressure steam.The exergy performance and the energy saving performance which is evaluated by the primary energy saving ratio of the new distributed energy system are analyzed.The effects of the ratio of the output power and cooling of the power and cooling cogeneration subsystem and the generator outlet temperature of the absorption heat transformer subsystem to the primary energy saving ratio are considered.The contributions of the subsystems to the primary energy saving ratio are quantified.The maximum primary energy saving ratio of the new distributed energy system is 15.8%,which is 3.9 percentage points higher than that of the conventional distributed energy system due to the cascade utilization of the waste heat from the internal combustion engine.

Performance improvement of a pulse tube cryocooler with a single compressor through cascade utilization of cold energy

The high-frequency pulse tube cryocooler(HPTC)has been attracting increasing and widespread attention in the field of cryogenic technology because of its compact structure,low vibration,and reliable operation.The gas-coupled HPTC,driven by a single compressor,is currently the simplest and most compact structure.For HPTCs operating below 20 K,in order to obtain the mW cooling capacity,hundreds or even thousands of watts of electrical power are consumed,where radiation heat leakage accounts for a large proportion of their cooling capacity.In this paper,based on SAGE10,a HPTC heat radiation calculation model was first established to study the effects of radiation heat leakage on apparent performance parameters(such as temperature and cooling capacity),and internal parameters(such as enthalpy flow and gas distribution)of the gas-coupled HPTC.An active thermal insulation method of cascade utilization of the cold energy of the system was proposed for the gas-coupled HPTC.Numerical simulations indicate that the reduction of external radiation heat leakage cannot only directly increase the net cooling power,but also decrease the internal gross losses and increase the mass and acoustic power in the lower-temperature section,which further enhances the refrigeration performance.The numerical calculation results were verified by experiments,and the test results showed that the no-load temperature of the developed cryocooler prototype decreased from 15.1 K to 6.4 K,and the relative Carnot efficiency at 15.5 K increased from 0.029%to 0.996%when substituting the proposed active method for the traditional passive method with multi-layer thermal insulation materials.

Experimental Study on Coal Partial Gasification Coproducing Char,Tar,and Gas

The coal partial gasification process produces a large number of chars.They have similar combustion characteristics to anthracite and can be utilized as a material manufacturing clean briquette to replace residential coal to achieve clean combustion.Moreover,the coal partial gasification produced more tar at relatively low temperature,which can be applied as naphtha or diesel after purification and hydrogenation.Herein,experiments of coal partial gasification coproducing char,tar,and gas are carried out on a bench-scale fluidized bed reactor during the temperature range of 625–762℃.The effect of equivalence ratio on the characteristics of coal partial gasification products is studied.The results show that the equivalence ratio increasing from 0.06 to 0.13 leads to a higher partial gasification temperature and lower char yield,and tar yield reaches a maximum value and the lower calorific value of gas reaches as high as 6.14 MJ/m^(3).When the gasification temperature is lower than 643℃,the increase in temperature promotes the generation of oxygen-containing functional groups and aromatic compounds in coal particles,and the microstructures of char become more disordered.The combustion stability of char is getting worse,whereas the pore structures in char become abundant at high temperatures.From the analysis of the tar chromatography column,it is observed that asphaltene and non-hydrocarbon account for 77%–88%of the total amount of tar.

Performance Analysis of a Combined Absorption Refrigeration-Liquid Desiccant Dehumidification THIC System Driven by Low-Grade Heat Source

Traditional condensing air-conditioning systems consume large amounts of energy in hot and humid areas,and it is difficult to achieve simultaneous control of temperature and humidity.A combined absorption refrigeration(AR)and liquid desiccant dehumidification(LDD)air-conditioning system based on cascade utilization of low-grade heat source is proposed.The system can realize independent control of temperature and humidity and carry out profound recovery of low-grade heat sources.Under the design conditions,the heat utilization rate C reaches 21.05%,which is 2.73 times that of the conventional absorption refrigeration reference system.A parametric sensitivity analysis is performed to optimize the system.The C increases from 9.79%to 18.55%and the coefficient of performance C O P t increases from 0.33 to 0.35 with an increase in chilled water temperature from 7°C to 15°C.With an increase in regenerant solution temperature from 60°C to 70°C,the C achieves the optimal value of 21.05%at 68°C.C decreases from 21.05%to 15.05%as the concentration of the regenerant solution increases from 36%to 40%.Under variable environmental temperature and humidity,the C the proposed system changes within a small range and stays much higher than that of the reference system with the same quality heat source,which indicates that the proposed system has a better adaptability to changing environmental parameters.

A New Cleaner Power Generation System Based on Self-Sustaining Supercritical Water Gasification of Coal

A new cleaner power generation system(IPGS) is proposed and investigated in this paper. Integrating combined cycle with supercritical water gasification of coal, the thermodynamic energy of the produced syngas is cascade utilized according to its temperature and pressure, both sensible and latent heat of the syngas can be recycled into the system, and thereby the net power efficiency can be about 6.4 percentage points higher than that of the traditional GE gasification based power plant(GEPP). The exergy analysis results show that the exergy efficiency of the proposed system reaches 52.45%, which is 13.94% higher than that of the GEPP, and the improvement in exergy efficiency of the proposed system mainly comes from the exergy destruction decline in the syngas energy recovery process, the condensation process and the syngas purification process. The syngas combustion process is the highest exergy destruction process with a value of 157.84 MW in the proposed system. Further performance improvement of the proposed system lies in the utilization process of syngas. Furthermore, system operation parameters have been examined on the coal mass fraction in the supercritical water gasifier(GF), the gasification temperature, and the gasification pressure. The parametric analysis shows that changes in coal concentration in the GF exert more influence on the exergy efficiency of the system compared with the other two parameters.

Broadband spectrum generation with compact Yb-doped fiber laser by intra-cavity cascaded Raman scattering

We experimentally demonstrate a cascaded Raman scattering continuum, utilizing a compact mode-locked Yb-doped fiber laser based on a nonlinear polarization rotation technique in the all normal dispersion regime.There is no physical filter or polarization controller in the oscillator, and a different mode-locked operation is achieved, corresponding to the extra fiber location in the oscillator. The broadband spectrum generation owes to the enhanced stimulated Raman scattering progress. The maximum output average power and peak power are14.75 n J and 18.0 W, and the short coherence light is suited for optical coherence tomography.

A simplified tunable frequency interval optical frequency comb generator using a single continuous-wave laser

We propose and demonstrate a simplified and tunable frequency interval optical frequency comb(OFC) generator based on a dual-drive Mach-Zehnder modulator(DD-MZM) using a single continuous-wave(CW) laser and low-power radio frequency(RF) driven signal. A mathematical model for the scheme is established. The 21-and 29-mode OFCs with frequency interval ranging from 6 GHz to 40 GHz are obtained under DD-MZM driven by a low-power RF signal within a maximum bandwidth of 1.12 THz. The generated OFCs exhibit spectral flatnesses of less than 0.5 d B and 0.8 d B within bandwidths of 160 GHz and 400 GHz, respectively.