Efficient Waste Heat Recovery Research Articles

Modeling of fractal heat conduction of semi-coke bed in waste heat recovery steam generator for hydrogen production

With the steam obtained from the waste heat of high temperature semi-coke, the hydrogen production through gasification method is considered more commercial. In order to improve the efficiency of waste heat recovery, the fractional model for heat conduction of semi-coke bed in waste heat recovery process was established. The non-destructive CT was employed to obtain the inner morphology of semi-coke bed and the image binarization processing was used to segment the CT image. With the MATLAB program, the box-counting method was used to calculate the fractal dimension of semi-coke bed. The fractional model for heat conduction of semi-coke bed was established by the fractal theory. The results showed that, the CT image and bit binary image of semi-coke bed can really reflect the inner morphology of semi-coke bed, and the inner morphology of semi-coke bed can be regarded as a fractal medium. The fractal dimension of semi-coke bed is 1.7537, which is very close to golden mean, 1.618, this could be the optimal structure for the heat conduction of semi-coke bed under the condition of natural accumulation. The one-dimensional heat conduction fractional equation of semi-coke bed was established and it can be accurately solved by fractal complex transformation and traveling wave transformation.

A decision support system for waste heat recovery and energy efficiency improvement in data centres

Data centre sector is emerging as one of the largest and fastest growing industrial sectors, accounting for 3% of the global electricity supply and contributing to 4% of total greenhouse gas emissions. A framework for waste heat energy recovery and its accompanying decision support system is presented with the ability to evaluate the waste heat (source) and potential demand (sink) compatibility, perform exergy and temporal availability analysis, and undertake cost-benefits and environmental impact analysis of available heat recovery technologies. This four stages framework is implemented through the case study of a medium-sized commercial data centre to provide evidence of its applicability. The results demonstrated that the framework and decision support system can deliver a streamlined and optimised heat recovery strategy for reducing overall energy requirement in the data centre. About 68% of the inevitable waste heat from IT equipment can be recovered by the recommended solution, allowing the recovered waste heat in the form of warm water to be fed back into the facility for applications such as space heating, achieving about 10% improvement in data centre power usage effectiveness. The solutions given by the decision support system are generally accessible for most data centres as the technologies are readily available and often lead to short payback time and substantial energy savings.

Efficient waste heat recovery system for high-temperature solid particles based on heat transfer enhancement

A series of efficient heat recovery methods including PCHEE-A, PCHEE-K and a double-medium system is proposed in this paper, which is to provide comprehensive solutions for high temperature particle in different situations. The PCHEE-A and PCHEE-K can increase the heat transfer area and heat transfer coefficient, through extending specific area to 1000–2000 m2/m3 and inducing turbulence in the heat transfer boundary, respectively. For the double-medium system which can achieve deep heat recovery and utilization, a multi-dimensional thermal resistance model is established to conduct heat analysis. Based on the model, Pareto frontier optimization of the double-medium system is carried out, and the optimal medium arrangement as well as the heat load distribution is derived. By combing the above methods, three typical systems (single-medium vertical plate-type with PCHEE-A, double-medium vertical tube-type and horizontal-type with PCHEE-K) are established and can get heat recovery efficiency at around 80%.

Performance simulation of a low-swirl burner for a Stirling engine

A new type of gas burner for Stirling engine that can recover adequate heat from exhaust gas was designed based on the plate heat exchanger and low-swirl combustion technology, which consists of three components: a cyclone, a burner, and a circular plate heat exchanger. The circular plate heat exchanger tightly wound around the combustion chamber plays a high efficiency of heat recovery role. In consideration of the radial symmetry of the burner, a three-dimensional numerical simulation was carried out by Ansys15. The velocity distribution, temperature distribution, and pressure distribution of the combustion gas were presented respectively. Strong backflow that came from the exhaust gas around the root of the flame in the combustion chamber and a vortex below the inlet of the exhaust gas channel were found, which were beneficial for the combustion and improving the uniformity of temperature distribution. Combustion behaviors of the burner under standard operating conditions were obtained, the highest temperature was about 2200 K in burner and the exhaust gas entered the plate heat exchanger at the temperature of 1375 K and exited at 464 K, with the waste heat recovery efficiency over 65.8%. And, the air-fuel ratio and combustion power had negligible effect on the waste heat recovery efficiency.

A new approach to increasing the efficiency of the ship main engine air waste heat recovery cooling system

The efficiency of integrated cooling air at the intake of Turbocharger and Scavenge air at the inlet of working cylinders of the main diesel engine of dry-cargo ship by transforming the waste heat into a cold by an Refrigerant Ejector Chiller (ECh) as the most simple in design and reliable in operation and by complex in design but more efficient Absorption Lithium-Bromide Chiller (ACh) was analyzed. A ship power plant of cogeneration type using the relatively low-grade heat of water of a heat supply system with a temperature of about 90 °C, that significantly complicates the problem of its conversion into cold were considered. Because of the insufficiently high efficiency of transformation of the heat of hot water (low coefficient of performance) as compared with steam, the resulting cooling capacity may not be enough for cooling intake air of the turbocharger and scavenge air, that raises the problem of the rational distribution of heat loads between the Turbocharger Intake Air cooling circuit (subsystem) and Scavenge air cooling circuit and the need to use chillers of various types. This takes into account the rational parameters of cooling processes of the scavenge air in the cogeneration high-temperature stage of scavenge air cooler, in the intermediate stage of traditional cooling air with seawater, and in the low-temperature stage for deep cooling of the scavenge air by using a chiller. A new approach is proposed to improve the efficiency of integrated cooling Intake Air of the turbocharger and Scavenge Air at the inlet of the working cylinders of the ship main engine of a transport ship, which consists in comparing the required cooling capacity and the corresponding heat needs during the trade route with the available heat of exhaust gases and scavenge air of the cogeneration power plant, determining the deficit and excess cooling capacity of heat utilizing cooling machines of various types, that allows to identify and realize the reserves of improving the efficiency of cooling intake air of the turbocharger and the scavenge air of the main diesel engine through the joint use of chillers of various types.

Modeling energy flows in industry: General methodology to develop process step models

The manufacturing sector has been one of the most significant energy consuming and CO2 emitting sectors over the past three decades. Therefore, it is important to have energy flow models of manufacturing processes to identify efficiency improvement and waste heat recovery opportunities with very specific targets. One of the best methods to pinpoint such locations is by referring to manufacturing process step models. Such models can be created on a large scale per industry and on small scale per process within an industry branch. Industry level modeling provides energy saving contingency by large magnitude where the impact on the economy and environment can be observed more visibly especially when sequential trends are identified. The methodology, reviewed in this paper, describes how to model energy flows on an industry scale by deriving the connection between key energy conversion activities on the one hand – including energy purchased/sold and onsite electricity generated, and the key end uses on the other hand. Industry-level energy flow model, referred to in this work, does not assume any specific system. That feature makes it scalable and allows analysis of manufacturing at various levels starting with single processes and finishing at sector and national economy levels. A combined analysis of the procedure is described in detail for creating process step models of manufacturing processes. The availability of U.S. national databases to calibrate these models is discussed and the challenges that arise in finding and using such databases are identified and analysed. In addition to addressing generic data issues associated with energy flow models, the paper also focuses on energy and material models and presents several examples of energy-intensive manufacturing processes, producing industrial gases, textiles, pulp and paper. Finally, importance of water use in onsite energy conversion and process end uses in various industries is addressed along with the sources of where this important data can be found to complete the energy flow modeling.

Heat Recovery Systems for Agricultural Vehicles: Utilization Ways and Their Efficiency

The focus of today’s agriculture is to reduce fuel consumption and pollutant emission. More than 50% of the fuel energy is lost with the exhaust gas and coolant of diesel engines. Therefore, waste heat recovery systems are a promising concept to meet economical and ecological requirements. Agricultural vehicles have an operating cycle that is quite different from on-road trucks (higher engine load factor and less annual utilization). This has influence on the efficiency of waste heat recovery. The purpose of this paper was to analyze different waste heat recovery technologies to be used in agricultural applications. In the study, technical and economic indicators have been used. According to suggested classification, four pathways for utilization were studied. Turbocompounding, electric turbocompounding, and heating of transmission oil for hydraulic clutch gearboxes have proved to be effective for agricultural vehicles. For the economical conditions of the European Union (EU), a turbocompounding diesel engine is acceptable if agricultural tractor rated power is more than 275 kW, and combine harvester rated power is more than 310 kW. In cold climates, heat recovery transmission warm-up may be recommended. Waste heat absorption refrigerators have proven to be a viable technology for air conditioning and intake air cooling systems.

Process integration of organic Rankine cycle (ORC) and heat pump for low temperature waste heat recovery

Organic Rankine cycles (ORCs) have been a mature technology for low temperature waste heat utilization. However, the relatively low thermal efficiency and incomplete waste heat recovery limit the power output of ORC systems. The reason for the above two problems is that the temperature-enthalpy (T-H) profile of waste heat sources does not match well with the organic working fluid in an ORC system. Heat pumps may reinforce the match between the waste heat carrier and the organic working fluid of the ORC. The condensation heat released by a heat pump can be used to evaporate the organic working fluid during phase change. Thus, a better thermal match between waste heat and the organic working fluid in the ORC can be obtained. Due to the possibility to improve power output, the integration of an ORC and a heat pump is investigated in this study. Proper working fluids in ORCs and heat pumps are chosen simultaneously. The integration between ORCs and heat pumps presents significant power output increases for special cases and deserves to be popularized in practical applications. However, the integrated system does not always lead to an increase in power output. The integration is profitable only when the following pre-conditions are satisfied simultaneously: (a) poor thermal match between working fluid and waste heat for standalone ORC; (b) the evaporation temperature of the ORC is set appropriately; (c) the working fluid of the ORC has a small ratio of latent to sensible heat; (d) the COP of the heat pump is satisfactory. A systematic procedure to determine the optimal operating conditions of the system is proposed in this study. A case study adopted from literature demonstrates the potential benefits of the integration of heat pumps and ORCs. The results show that the net power output and the amount of waste heat recovered increase by 9.37% and 12.04% respectively.

Design and optimization of a novel high temperature heat exchanger for waste heat cascade recovery from exhaust flue gases

The waste heat of high temperature exhaust flue gases is widely distributed in many industrial processes. Recovery of waste heat is of great significance to energy saving and sustainability. In this paper, a novel high temperature heat exchanger with hybrid enhancement technologies is proposed to improve waste heat recovery efficiency based on the cascade recovery and utilization method. Algorithm for HTHE structural design and optimization is developed and verified according to the experimental results. Heat transfer and pressure drop performance of the proposed HTHE are estimated by using the algorithm. The results show that the effectiveness of the proposed HTHE increases as the gas temperature increases and mass flow rate decreases. Average effectiveness of the proposed HTHE and temperature of preheated air are 12.5% and 85.8 °C higher than those of traditional HTHE with additional 70.0% and 22.0% pressure drop on air and gas sides, respectively. The structural optimization of the proposed HTHE is carried out and it shows that the optimized HTHE has better heat transfer capacity and comprehensive performance under identical pressure drop, increasing effectiveness by 12.6% without enlarging pressure drop compared with the non-optimized HTHE.

Thermodynamic analysis on molten slag waste heat cascade recovery method (MS-WHCR)

Thermal energy recovery of pyrometallurgy slags is a worldwide problem that is widely concerned for decades. As chemical recovery method, molten slag cascade recovery method (MS-WHCR) is proposed in this work. As typical endothermic chemical reactions, pyrolysis, gasification, calcination and reforming reactions are applied in this method. Gasification–pyrolysis system, calcination–pyrolysis system, enhanced pyrolysis system (R-SEP) and fixed carbon gasification and sorption-enhanced pyrolysis system (CG–SEP) systems of MS-WHCR method are designed. Based on the first law of thermodynamics and second law of thermodynamics, enthalpy–exergy compass analysis method is applied to analyze the exergy efficiency, consumption of reactants and products of designed MS-WHCR method, compared with traditional water quenched (WQ) method and gravity bed waste heat recovery (GWHR) method. As calculation example, 1000kg copper slag is used in this paper. The results showed that the exergy efficiency and exergy loss of WQ method are 20.7% and −947 MJ respectively. By WQ method, energy quality of molten copper slag is discounted. Copper slag particles should be fast cooled during granulation process. Thus, lots of air is blown in to make enough heat transfer with copper slag particles, which generate some exergy loss. And exergy efficiency of GWHR method is 76.9%. Using chemical endothermic reactions, MS-WHCR method improves the exergy efficiency of molten slag waste heat recovery. There is a slight fluctuation of exergy efficiency by MS-WHCR method for four kinds of systems from 66.6 to 70.1%. Fixed carbon and combustible syngas are acquired by MS-WHCR. And enhanced pyrolysis process in proposed R-SEP and CG–SEP systems improves hydrogen contents in syngas.

Energy efficiency enhancement and waste heat recovery in industrial processes by means of the heat pipe technology: Case of the ceramic industry

This paper investigates the application of heat-pipe based heat exchanger for improving the energy efficiency of industrial processes. In particular, the case of the ceramic industry is addressed and the potential heat recovery and reduction of fuel consumption is determined. A theoretical model is constructed based on the established, proven performance characteristics of heat-pipe technologies and the performance of the ceramic process are calculated using numerical simulation. The results of the kiln numerical model are then combined to the theoretical model of the heat-pipe based heat exchanger and the heat recovery potential is evaluated as well as the reduction of fuel consumption. The combined theoretical and numerical approach demonstrates that the application of the heat pipes based heat exchanger to the cooling stack of the ceramic kiln enables to recover more than 863 MWh of thermal energy that can be used for heating up the hot air stream of the pre-kiln dryer. Thus, approximately 110,600 Sm3 per year of natural gas can be saved from the burners powering the dryer and the emission of 164 tonnes per year of carbon dioxide can be avoided. Additionally, the avoided cost due to the fuel consumption reduction amounts to more than 22,000 Euro per year. These figures support the application of the heat pipes based heat recovery to the ceramic process from the viewpoint of the improvement the energy efficiency and environmental impact and also of the economic investment.

Numerical Study on Heat Transfer to an Arc Absorber Designed for a Waste Heat Recovery System around a Cement Kiln

A numerical study on combined free convection, forced convection, and radiation heat transfers from an industrial isothermal rotating cylinder (cement kiln) is carried out in this work. The investigation is done by the study of two-dimensional (2D) incompressible turbulent flow around the kiln under steady- and unsteady-state solutions. The results of this study show that the average Reynolds and Rayleigh numbers around the cylindrical kiln are 647,812.1 and 1.75986 × 1011, respectively. A heat absorber is specifically designed around the kiln, according to the available space around the kiln, in a sample cement factory. The study investigates the effect of an added absorber on the heat transfer features, for both constant heat flux and constant temperature, on the kiln. The temperature distribution along the absorber circumference is obtained for designing an efficient thermoelectric waste heat recovery system as a future study. It is observed that the contribution of the radiative heat transfer is significant in the total heat transferred from the kiln to the absorber.

Energy analysis of a lignite predrying power generation system with an efficient waste heat recovery system

ABSTRACTLignite has been extensively used for electricity generation in many regions worldwide. However, its high water content has obviously negative effect on plant thermal efficiency. Performance of lignite-fired power plant can be improved by predrying the lignite before combustion. In addition, recovery of waste heat from the dryer and the power generation system will enhance the plant thermal efficiency further. In the present study, a new lignite predrying power generation system integrated with an efficient waste heat recovery system was proposed. Both dryer exhaust waste heat and steam turbine exhaust latent heat were recovered to heat boiler feed water. Energy analysis indicates that system performance is improved significantly. The plant thermal efficiency increases linearly with drying degree and then increases at a lower rate. The generation of unused dryer exhaust changes the variation tendency of system performance with drying degree.

Technical and economic analysis of organic flash regenerative cycles (OFRCs) for low temperature waste heat recovery

Organic Flash Cycles (OFCs) can improve the overall efficiency of waste heat recovery or geothermal systems due to a better match of the hot and cold heat transfer curves. However, the lower mean temperature difference between the heat transfer curves implies larger exchanger areas and therefore higher heat exchanger costs.In order to reduce the exchanger size, a new cycle configuration is introduced in this paper, consisting in a new type of organic flash regenerative cycle (OFRC) for heat source temperatures in the range 80–170°C. The regeneration allows to recover part of the enthalpy of the liquid phase from the flash evaporator increasing the temperature of the liquid at the exchanger inlet, thus reducing the exchanger size. The thermodynamic performance of OFRCs are practically the same as of the OFC, but the unit cost of the system per kW installed power can be 20% lower. A variety of working fluids was tested and results have shown that long molecular chain alkanes provide the best thermodynamic efficiency, but those fluids have the main drawback of a low vapor density, resulting in very large expansion devices and condensers. R601a is the working fluid featuring the best tradeoff between thermodynamic efficiency and components size in the heat source temperature range between 80°C and 170°C. The comparison of the OFRC with conventional ORCs has shown the thermodynamic superiority of the OFRC with every tested fluid. Finally the cost analysis has highlighted that OFRCs specific cost has the same magnitude as ORCs for mini and micro scale plants.

Complex and Efficient Waste Heat Recovery System in Aluminum Foundry

The study presents the evaluation of a heat recovery system in a Romanian aluminum foundry. The study was based on a thermal power balance that revealed on one side that the components of the balance is in good agreement with similar results presented in the literature and revealed on the other side the heat recovery potential from the available waste represented by exhaust gases. The proposed heat recovery from waste is capable to recover more than 25% of the total thermal power of the burners, equivalent with more than 60% of the available waste.

Design of New Type Waste Gas/Wastewater Dual - source Heat Pump Energy Cascade Recovery System in Campus Bath

With the energy shortage, environmental degradation is becoming increasingly serious, waste heat recovery has become one of the important technical means to solve the energy shortage. Campus bath as an important part of the campus building have waste heat, large flow of people, energy consumption and other characteristics. Through the basic data of the baths and water temperature of a university in Shenyang, the energy consumption of the baths in the campus was obtained. So we want to propose a new type of bathroom exhaust gas/waste water and gas dual source heat pump cascade waste heat reuse hot water system. By using the dimensionless contrast analysis method, the efficiency of waste heat recovery and the technical problems to be solved in the waste heat recovery and utilization of the bath are analyzed, and the corresponding solutions are given. The use of the dual source heat pump system can reduce fuel 40%, save operating costs 30%.

Research on a new type waste heat recovery gravity heat pipe exchanger

The industrial waste heat carrier, such as exhaust gas, mostly contains oil, particles, fibers and other impurities. If the conventional heat transfer enhancement techniques are applied in the gas side to recovery waste heat, the gas side flow channels are easily to be blocked, which not only greatly reduces the waste heat recovery efficiency but some time also makes the heat exchanger out of work. In this paper, a new type waste heat recovery heat pipe exchanger has been designed and applied to recover thermal energy in high temperature exhaust gas emitted from setting machine in the dyeing and printing industry. Its major feature is that clean air passes though fin-enhanced vertical tubes whose inner side is a condenser while dirty gas passes though inner smooth surface of horizontal tubes whose outside is an evaporator. The new type heat pipe exchanger has a big boiling chamber. The condensed water falls down to the chamber by gravity. Three-month continuous operation of recovering dirty exhaust gas waste heat shows that the new type heat pipe exchanger can save 15% natural gas without any blockage of the gas side channel.

Effects of Trace Copper on Shrinkage and Low-Temperature Co-Firing of Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are an attractive power generation due to their high energy efficiency and possibility of waste heat recovery with operating at high temperature. SOFCs were fabricated by commonly three steps with pre-sintering of anode, dip-coating electrolyte and screen printing cathode materials cause of different shrinkages. It is hard to commercialize with these high manufacturing costs of multi-step process. SOFCs have been focused on low-cost materials and process for commercializing with high efficiency and performance. 8 mol % yttria-stabilized zirconia (8 YSZ) has been considered as one of the most conventional material for SOFC electrolyte. The 8 YSZ electrolytes doped with Cu contents which used as a sintering aid leads to densify the electrolyte and increase the shrinkage and performance. So we attempted to fabricate with one step co-firing process with 8 YSZ electrolytes at low temperature as 1250 oC. First of all, we found addition of trace Cu is effective to improve the sinterability of the YSZ electrolytes. The YSZ electrolyte with 100ppm CuO shows better sinterability and ionic conductivity than the pure YSZ electrolyte. The YSZ electrolyte with 100ppm CuO was densified below 1300 oC and the increased oxygen vacancy concentration leads to have higher ionic conductivity. Furthermore, the performances of the single-layer YSZ cells with 100ppm CuO were about 1.5 times higher(0.51 W cm2) than the cell with the pure YSZ electrolyte (0.36 W cm2) at 800 oC. The GDC/YSZ (100 ppm CuO) bi-layer cells also showed higher cell performance at 700 oC which shows similar tendency to the single-layer YSZ cell tests. These show that addition of 100 ppm CuO into the YSZ electrolyte is greatly effective for improvement of SOFC performance with energy saving during sintering process. According to these results of enhancing the sinterability and ionic conductivity, co-firing process was developed by addition of 5000 ppm Cu to the YSZ electrolytes and anodes at 1250 oC which is seriously lower than conventional multi-step fabrications with the sintering temperature above 1500 oC. The sinterability of the YSZ electrolyte was significantly improved 1250 oC by the 5000 ppm Cu. The co-fired cells with one- and two-step exhibited reasonable OCV value of 1.016 V and 1.011 V, respectively. Maximum power density of two-step cell with 0.71 W cm-2 at 850 oC which was similar value compared to conventional cell but the one-step cell has low maximum power density with 0.14 W cm-2. Above 1200 oC as sintering temperatures, the LSM/YSZ cathode produces insulating phases at the interfaces and low porosity makes cathode polarization. As a result, the cathode should be improved to be stable at 1250 oC, or the co-firing temperatures should be reduced below 1200 oC.

Selection of a Waste Heat Recovery System for a Marine Diesel Engine Based on Exergy Analysis

Highly increased fuel prices and the need for greenhouse emissions reduction from diesel engines used in marine engines in compliance with International Maritime Organization (IMO) on the strict regulations and guidelines for the Energy Efficiency Design Index (EEDI) make diesel engine exhaust gas heat recovery technologies attractive. The recovery and utilization of waste heat not only conserves fuel, but also reduces the amount of waste heat and greenhouse gases dumped to the environment .The present paper deals with the use of exergy as an efficient tool to measure the quantity and quality of energy extracted from waste heat exhaust gases in a marine diesel engine. This analysis is utilized to identify the sources of losses in useful energy within the components of the system for three different configurations of waste heat recovery system considered. The second law efficiency and the exergy destroyed of the components are investigated to show the performance of the system in order to select the most efficient waste heat recovery system. The effects of ambient temperature are also investigated in order to see how the system performance changes with the change of ambient temperature. The results of the analysis show that in all of the three different cases the boiler is the main source of exergy destruction and the site of dominant irreversibility in the whole system it accounts alone for (31-52%) of losses in the system followed by steam turbine and gas turbine each accounting for 13.5-27.5% and 5.5-15% respectively. Case 1 waste heat recovery system has the highest exergetic efficiency and case 3 has the least exergetic efficiency.

Cascade utilization of exhaust gas and jacket water waste heat from an Internal Combustion Engine by a single loop Organic Rankine Cycle system

This work presents the methodology of Internal Combustion Engine (ICE) waste heat recovery by an Organic Rankine Cycle (ORC) system. Though jacket waster heat is usually ignored due to its low temperature, the contained thermal energy is roughly the same as that of exhaust gas from an ICE with certain rated loads, which makes the recovery of this energy a subject of interest. The cascade utilization of exhaust gas and jacket water heat by single loop ORC systems is here investigated and compared with a system which only recovers exhaust gas heat. System performances are evaluated through thermal efficiency, waste heat recovery efficiency and improvement of ICE efficiency. Then the calculated heat exchanger capacity is validated under different ICE load conditions. Results show that the highest thermal efficiency (21.82%) can be reached by using R141b. The full recovery of exhaust gas heat yields the highest waste heat recovery efficiency (10.19%) and improvement of the ICE efficiency (14.23%). Preheaters and evaporators operated at high evaporating pressure may have a heat exchanger capacity which is lower than the calculated heat amount under ICE part-load conditions. It is therefore essential to validate the calculated heat exchanger capacity in real operating conditions.