Exergoeconomic (Thermoeconomic) Analysis and Performance Assessment of a Gas Engine–Driven Heat Pump Drying System Based on Experimental Data

Exergoeconomic analysis has been used as a powerful tool to study and optimize various types of energy-related systems. In this study, we use the specific exergy cost (SPECO) method to calculate exergy-related parameters and display cost flows for all streams and components in a gas engine–driven heat pump drying system based on the experimental data. We analyze and evaluate the performance of the drying system components and the drying process for three different medicinal and aromatic plants from an exergoeconomic point of view. We also investigate the effect of varying dead (reference) state temperatures on exergoeconomic performance parameters for the drying system components and drying process. Although the condenser and drying chamber of the gas engine–driven heat pump dryer were significantly affected by the ambient temperature, the gas engine was slightly influenced by the ambient temperature. At low ambient temperatures, the exergy rates increased and the most effective performance obtained from this dryer was at 0°C. The performance of the drying process also increased at low ambient temperatures. This study demonstrated that exergoeconomic analysis can provide more information than exergy analysis, and the results obtained from the exergoeconomic analysis provided cost-based information, suggesting potential locations for drying system improvement.     

A Comparative Study on Exergetic Performance Assessment for Drying of Broccoli Florets in Three Different Drying Systems

This article deals with the exergy analysis and evaluation of broccoli in three different drying systems. The effects of drying air temperature on the exergy destruction, exergy efficiency, and exergetic improvement potential of the drying process were investigated. The exergy destruction rate for the drying chamber increased with the rise in the drying air temperature at 1.5 m/s, both in the tray and the heat pump dryer. The highest exergy efficiency value was obtained as 90.86% in the fluid bed dryer in comparison to the other two drying systems and the improvement potential rate was the highest in the heat pump dryer during drying of broccoli at the drying air temperature of 45°C and the drying air velocity of 1.0 m/s.     

Waste Heat Integration of Coating Paper Machine Drying Process

The paper sheet drying process consumes about 70% of the total energy required in coated papermaking, and almost all the thermal energy used in the process can be found in the exhaust air; thus, it has significant potential to recover the heat. With the aim of saving energy, the recovered energy is usually used to heat different process streams instead of steam.

This article examines the drying process of an operating coating paper machine to demonstrate an optimization method. To study the possibility of improving energy efficiency, thermodynamic analysis was conducted. The reasons why there is so much heat lost during drying were investigated. Based on the results of the energy and exergy analysis, a new waste heat integration scheme is presented. Furthermore, the performance of the proposed scheme has been evaluated. The results of the case study show an energy efficiency improvement of 7.3% and a specific energy consumption reduction of 4.6% with profitable investments.     

板式换热器及其热力系统的运行特性和高级分析

针对不同换热设备组合之间以及换热设备在系统中的分布情况进行了研究,建立了高级分析模型,将换热设备与系统的损进一步分割成不可避免性部分和可避免性部分,计算相应的损失和效率,确定换热设备与系统中能量损失的主要部位,并在有机朗肯循环（organic Rankine cycle,ORC）系统试验台中进行验证,为换热设备及其热力系统的运行优化提供科学依据。结果表明,不同的换热面积对换热设备的能效有着非常大的影响,同时常规分析和高级分析提出了不同的系统优化次序。高级分析表明,蒸发器可避免损占蒸发器损的41.2%～60.0%,冷凝器可避免损占冷凝器总损最高可达91%～97%,整个ORC系统有52.5%～66.3%的损可以避免,有很大的改造潜力,且发现不合理设计的管道也会影响ORC系统性能。     

Exergy Analysis of Drying Process: An Experimental Study in Solar Greenhouse

This article examines the exergy variation during drying in solar greenhouses. Exergy efficiencies were derived as functions of drying time and temperature of the drying air. An illustrative example is considered to verify Dincer and Sahin's model and to show the applicability of the model to actual drying processes at different drying air temperatures. This work is intended not only to demonstrate the usefulness of exergy analysis in thermodynamic assessments of drying processes but to provide insights into their performances and efficiencies. In this study, the drying performance of the passively heated solar greenhouse has been investigated. Experimental results under the meteorological conditions of Izmir, Turkey (latitude 38.24 N, longitude 27.50 E), are presented.     

Multistage Zeolite Drying for Energy-Efficient Drying

This work discusses the potential of three multistage zeolite drying systems (counter-, co-, and cross-current) with a varying number of stages. The evaluation showed that for 2–4 stages with heat recovery the efficiency of the systems ranges between 80 and 90%. Additionally, by introducing a compressor, the latent heat in the exhaust air from the regenerator is recovered and used to heat the inlet air for an additional drying stage. As a result, for the counter-current drying system and compressor pressure 1.5–2 bar, a maximum energy efficiency of 120% is achieved, which results in halving the energy consumption compared to conventional drying systems.     

Multistage Zeolite Drying for Energy-Efficient Drying

This work discusses the potential of three multistage zeolite drying systems (counter-, co-, and cross-current) with a varying number of stages. The evaluation showed that for 2-4 stages with heat recovery the efficiency of the systems ranges between 80 and 90%. Additionally, by introducing a compressor, the latent heat in the exhaust air from the regenerator is recovered and used to heat the inlet air for an additional drying stage. As a result, for the counter-current drying system and compressor pressure 1.5-2 bar, a maximum energy efficiency of 120% is achieved, which results in halving the energy consumption compared to conventional drying systems.     

Innovative Steam Drying of Empty Fruit Bunch with High Energy Efficiency

Empty fruit bunch (EFB) is one of the solid wastes from crude palm oil mills and has the lowest value for utilization compared to other solid wastes. To achieve an efficient utilization of EFB, drying is considered the first crucial process due to the high moisture content of EFB. In this study, EFB drying based on exergy recovery is proposed to achieve high energy efficiency. A fluidized bed is adopted as the main dryer. The proposed model is evaluated in terms of energy efficiency, especially regarding the influence of target moisture content and fluidization velocity. Up to 92% of the energy involved in the drying process can be recirculated. The total energy consumption for drying decreases as the target moisture content decreases, though there is no significant impact of fluidization velocity to total energy consumption. In addition, the required total length of the heat transfer tubes immersed inside the fluidized bed dryer is calculated because it relates to fluidization performance and economic issues. Lower target moisture content results in a longer heat transfer tube, and higher fluidization velocity leads to a shorter heat transfer tube.     

涤纶干燥设备的节能改造及效果

为了节约能源和降低生产成本,对干燥系统作了改造:在每套干燥系统中各加了1台列管式换热器及1台旋风分离器,利用其余热给工艺用压缩空气加热。经过改造后,不仅每套设备的实际能耗可以降低4.3 k W,5套结晶干燥设备每年共节约电量172 000 k W·h,而且可减少流程中废气对环境造成的热污染。     

Energy and Exergy Analyses of Thin-Layer Drying of Potato Slices in a Semi-Industrial Continuous Band Dryer

This article is concerned with the energy and exergy analyses of the continuous-convection drying of potato slices. The first and second laws of thermodynamics were used to calculate the energy and exergy. A semi-industrial continuous-band dryer has been designed and used for drying experiments. The equipment has a drying chamber of 2 m length and the inlet air used for drying is heated by gas power. The experiments were conducted on potato slices with thickness of 5 mm at three different air temperatures of 50, 60 and 70°C, drying air mass flow rates of 0.61, 1.22, and 1.83 kg/s and feeding rates of 2.31 × 10^?4, 2.78 × 10^?4, and 3.48 × 10^?4 kg/s. The energy utilization and energy utilization ratio were found to vary between 3.75 and 24.04 kJ/s and 0.1513 and 0.3700, respectively. These values show that only a small proportion of the supplied energy by the heater was used for drying. The exergy loss and exergy efficiency were found to be in the range of 0.5987 to 13.71 kJ/s and 0.5713 to 0.9405, respectively, indicating that the drying process was thermodynamically inefficient and much energy was vented in the exhaust air. In addition, the results showed that the feeding rate and the temperature and flow rate of the drying air had an important effect on energy and exergy use. This knowledge will provide insights into the optimization of a continuous dryer and the operating parameters that causes reduction of energy consumption and losses in continuous drying.     

Simplification and Energy Saving of Drying Process Based on Self-Heat Recuperation Technology

A simplified drying process based on self-heat recuperation (SHR), which can further reduce energy consumption compared to previous SHR drying processes, is proposed. The specific energy consumption (SEC) of the SHR drying process was evaluated at various air flow rates and compared with a mechanical vapor recompression (MVR) drying process with superheated steam. The results show that the SEC of SHR can be reduced from 474 to 147 kJ (kg-H₂O evaporated)^?1 by removing heat exchangers for preheating. The SEC of the simplified SHR process was only 1/16 of a conventional drying process with heat recovery and 3/5 of an MVR process. Exergy transfer of the process was also analyzed and summarized as exergy flow diagrams.     

EXERGY ANALYSIS FOR THE FREEZING STAGE OF THE FREEZE DRYING PROCESS

The mathematical expressions for exergy and the exergy analysis of the freezing stage of the freeze drying process are presented. The exergy analysis indicates that very substantial reductions in the magnitudes of the total exergy loss and of the exergy input due to the heat that must be removed during the freezing stage, can be obtained when the freezing stage is operated through the use of a rational distribution in the magnitude of the temperature of the cooling source. The rational distribution in the magnitude of the temperature of the cooling source should provide significant savings in the utilization of energy during the freezing stage of the freeze drying process as well as satisfactory freezing rates that form ice crystals that are continuous and highly connected and their shape and size are such that the pores of the porous matrix of the dried layer generated by sublimation during the primary drying stage, have a pore size distribution, pore shape, and pore connectivity that are appropriate to allow high rates for mass and heat transfer during the primary and secondary drying stages of the lyophilization process.     

Exergy analysis of a spray dryer: Methods and interpretations

Exergy analysis has been used to assess the intrinsic exergy efficiency of a spray drying system modeled to produce 1.25?kg s^?1 of skim milk powder. From an exergy perspective, the dryer has a low exergy efficiency of 38% (on an evaporation basis), while the efficiencies associated with the mass transfer and heat transfer are 94% (thermomechanical efficiency) and 30% (transiting exergy efficiency), respectively. The improvement potential of 575?kW, of the 722?kW energy flow in the feed, also shows that the exergy efficiencies of spray dryers are intrinsically small. Reviewing exergy efficiency factors, there appears to be no universal efficiency factor for an exergy analysis. The inevitable (INE) exergy loss method is a potential shortcut technique based on the Carnot efficiency and first law analysis. There are some limitations on using the INE method for processes that are not exclusively thermal; in those cases, an entropy balance (second law property) is more appropriate. The INE method still shows potential as a starting basis of comparison because it shows the scale and the efficiency together, which is important for targeting areas for process improvement without doing a full exergy analysis. This work is a short review of the work on dryer exergy efficiency, mainly focusing on the various factors which are used, followed by a discussion and case study testing each factor to find a potential optimization method and a discussion on each factors merits.     

Ultrasonic Convective Drying Kinetics of Clipfish During the Initial Drying Period

A hybrid drying system for high-intensity airborne ultrasound applied in convective drying was investigated for the drying of salted codfish (clipfish). Convective drying with ultrasonic assistance at 10, 20, and 30°C was compared to the same process without ultrasound. The Weibull model was used to model and investigate the drying behavior, and the effective diffusion in Fick's law was determined. The ultrasound decreased the drying time more at lower drying temperatures. The drying time was reduced by over 90% at a drying temperature of 10°C. For an industrial drying process at a temperature of 20°C, the drying time was reduced by 32.2%. The ultrasonic, convective drying of clipfish at a temperature of 20°C was faster than the same process without ultrasound at 30°C. The investigations showed a thermal effect for all products when ultrasound was applied. The specific moisture extraction ratio (SMER) in the investigated system was improved by 0.2 kg_water kWh^?1. The heat transfer coefficient in the system used was increased by 32.6% for a heating process in a separate investigation, whereas for a cooling process no increased heat transfer coefficient was determined. The thermal effect might (at least partially) explain the faster drying of ultrasonic-assisted convective drying. The results obtained demonstrate the potential of airborne ultrasound in convective drying with regard to drying time, energy consumption, and product quality. Documentation of the thermal effect should be included in future R&D on this topic.     

Improvement potential analysis for integrated fractionating and heat exchange processes in delayed coking units

A novel diagram-based representation approach is developed to analyze the thermodynamic efficiency and identify quickly the promising energy-use improvement for integrated fractionating and heat exchange processes in delayed coking units. For considering temperature dependence of heat capacity and integrating fractionating and heat exchange processes, an advanced energy level composite curve is constructed by using the simulation results and a stepwise procedure. More accurate results of exergy analysis are obtained and the interaction between different components of the integrated system can be properly revealed in an integrated figure. Then the exergy calculation is performed to validate the performance of processes and to define the targets for improvement. The avoidable exergy destruction is also analyzed by applying the concepts of avoidable and unavoidable exergy destructions for the integrated system. In a case study for a Chinese refinery, the results reveal that the heat exchange between gas oil and deethanization gasoline is the most inefficient process with the highest retrofitting potential, and the lowest exergy efficiency of component in the integration system is only 29.4%. The improvement potential and exergy efficiency for the fractionator are 38.1% and 97.3%, respectively. It is obvious that the fractionator is not the most promising component for improvement.     

Energy,exergy and economic analyses on heat pump drying of lignite

Abstract

Evaporative drying of lignite is an energy intensive process. In this study, the heat pump is integrated with a lignite drying system to decrease the energy consumption rate of lignite drying. The performance of heat pump drying is energetically and exergetically evaluated with developed models. Results show that the power consumption rates to dehydrate 1?kg of water from raw lignite in the heat pump drying system without and with lignite preheater are 660.82 and 585.62?kJ (kg H₂O)^?1, respectively. Exergetic analysis indicates that most exergy is destructed in the condenser and the evaporator in the heat pump drying. The case of lignite-to-electricity process (i.e., a lignite-fired power plant integrated with heat pump drying) is studied to examine additional benefits of heat pump drying to the downstream industrial processes that consume dried lignite. Thermodynamic and economic models are developed. Net efficiency of the lignite-to-electricity process can be increased by 1.4 and 1.57 percentage points for heat pump drying without and with lignite preheater, respectively. Preliminary economic analysis shows that the integration of heat pump drying without and with lignite preheater can earn additional 1.42 and 1.73 million USD, respectively. The influences of drying system and heat pump parameters are also analyzed.     

Forced Convective Drying of Wastewater Sludge with the Presentation of Exergy Analysis of the Dryer

The main objective is studying the fundamental aspect, by means of drying kinetics and the application of forced convective drying of wastewater sludge with the determination of the optimum drying conditions. The drying system is composed of two units; small samples of 2.5 g are dried in the first unit and a bed of sludge weighing 250 g is dried in the second unit. The experiments are performed under air temperatures varying between 80°C and 200°C. The range of the air velocity and its humidity is 1–2 m/s and 0.005–0.05 kg_water/kg_{dry air}, respectively. The experiments are performed for two different sludges: activated sludge (AS) and thermalized and digested sludge (TDS). Usually, three main drying phases are observed during drying of bed of sludge. These phases are reduced to only two for small samples. Determination of the influent parameters shows that the temperature of the drying air and sludge origin can profoundly influence the drying kinetic of the sludge. The exergy analysis of the two units of the drying system allows selecting 140°C, 2 m/s, and 0.05 kg_water/kg_{dry air} as optimum drying conditions with an exergy efficiency reaching 90%.     

Steam Drying - Modelling and Applications

The concept of steam drying originates from the mid of the last century. However, a broad industrial acceptance of the technique has so far not taken place. The paper deals with modelling the steam drying process and applications of steam drying with in certain industrial sectors where the technique has been deemed to hove special opponunities.

In the modelling scction the mass and heat transfer proceases are described along with equilibrium, capillarity and sorption phenomena occurring in porous materials during the steam drying process. In addition existing models in the literslure are presented.

The applications discussed involve drying of fuels with high moisture contcna, cattle feed exemplified by sugar beet pulp. lumber. paper pulp. paper and sludges.

Steam drying is compared to flue gas drying of biofuels prior to combustion in a boiler. With reference to a current insrallation in Sweden. the exergy losses. as manifested by loss of co-generation cupacity. are discussed. The energy saving potentid when using steam drying of sugar beet pulp as compared to other possible plant configurations is demonstrated.

Mechanical vapour recompression applied to steam drying is analysed with reference to reponed dau from industriul plsnts. Finally. environmcntul advantages when using steam drying are presented.     

A new energy efficient single-stage flash drying system integrated with heat recovery applications in industry

Abstract

A new system developed here conducts the thermal management of the flue gas from the cement industry and employs this heat for the drying of raw materials before reaching to the preheating section. As of now, an additional amount of heat is used to provide the drying section with hot air while this proposed configuration recovers the heat from the same plant and employs it for drying purpose. This approach also results in cost saving as this configuration decreases the cost of heating the ambient air to provide the drying section with hot air. The entire system is simulated using the Aspen Plus industrial software. A comprehensive thermodynamic analysis is conducted for each component of the proposed system keeping more focus on the drying section. Numerous parametric and sensitivity studies are conducted to investigate the system performance, pressure drop and raw materials drying. The energy and exergy efficiencies of the drying process are found to be 55.6% and 24.17%. On the basis of the present results achieved, one can say that this novel configuration can be proved as a benchmark for the cement industry and has the capability to reduce the cost as well.     

Convective Drying with Time-Varying Heat Input: Simulation Results

Intermittent drying aims to match the heat input rate to the drying kinetics of the material so as to avoid thermal degradation of heat-sensitive products in particular. This paper presents results of a liquid diffusion model to examine the effect of varying the rates of heat input by convection heat transfer. This is accomplished by varying the drying air velocity, varying the air temperature as well as its relative humidity over different periods of time in a sequential manner. One of the outcomes of this work is guidelines for use of a heat pump to dehumidify the drying air. While most heat pump dryers are designed to operate continuously, our results show that it is not necessary to use heat pump continuously over the entire drying period. This option saves running costs by reducing use of electrical power in the drying cycle. Furthermore, it is possible to save capital costs by utilizing a smaller heat pump for a given dry product output. Alternatively, a given heat pump system can be used to service two or more drying chambers that may dry the same or different products by simply switching the dehumidified and heated air from one chamber to the other sequentially. When the heat pump air is switched off, unsaturated ambient air maybe used to accomplish rest of the drying. It is shown that using heat pump air over only a part of the drying cycle does not increase the drying time appreciably.