Heat Recovery Unit Research Articles

IMPROVEMENT OF PERFORMANCE OF HEAT RECOVERY UNITS BY USING MAGNETIC NANOFLUID

Waste heat recovery units are systems that are widely used in the preheating of clean air, which is needed in industrial and waste heat facilities, without contact with polluted air, especially during the pandemic period. In this study, it is aimed to increase the operating temperature range by improving the performance of a heat exchanger consisting of a heat pipe bundle and an integrated heat recovery unit. The originality of the work is in the use of NiFe<sub>2</sub>O<sub>4</sub>/water, ZnFe<sub>2</sub>O<sub>4</sub>/water, and CoFe<sub>2</sub>O<sub>4</sub>/water nanofluids as the working fluid in the heat pipes and the improvement rates in the heat recovery unit's thermal performance were determined compared to pure water, which is the basic fluid. The turbulence of the flows in the channel prevented the establishment of a linear relationship between the Reynolds number and the thermal improvement in performance. However, by using nanofluids instead of pure water, thermal performance improvement was achieved for all Reynolds numbers. According to the results obtained it is seen that higher performances are obtained in the case of using nanofluids compared to pure water. The average performance values are 14%, 18%, 19%, and 20% for water, NiFe<sub>2</sub>O<sub>4</sub>, ZnFe<sub>2</sub>O<sub>4</sub>, and CoFe<sub>2</sub>O<sub>4</sub> nanofluids, respectively, according to the Re number on the cold fluid side, while the average performance improvement rates of NiFe<sub>2</sub>O<sub>4</sub>, ZnFe<sub>2</sub>O<sub>4</sub>, and CoFe<sub>2</sub>O<sub>4</sub> nanofluids compared to the base fluid (pure water) are 29%, 38%, and 44%, respectively. When the Re number in the hot air flow channel is taken into account, it is seen that the average performance values are 13%, 19%, 20%, and 22% in the same order, while the improvement rates are 48%, 57%, and 72%. Therefore, according to the average performance and improvement values, the CoFe<sub>2</sub>O<sub>4</sub> nanofluid was found to be a more suitable fluid than the others.

INCREASING THE EFFICIENCY OF FUEL-FIRED PLANTS WITH DUSTY WASTE GASES

The results of a set of thermal calculations of the air-heating heat exchanger of the dusty waste gases of the thermal disposal of household waste are given. The initial data for the calculations were taken in the practical range when incinerating 1t/h of household waste from the experience of using the specified installations. The heat-recovery unit is designed to heat air for combustion by recovering the heat of the exhaust gases leaving after the turbine of this installation. Its design solution is characterized by the possibility of cleaning work surfaces from deposits of technological dust. The thermal indicators (temperatures of coolants and heat productivity) of the proposed heat-recovery unit under the conditions of its use for waste incineration plants were investigated. Calculations were performed in different modes of operation of the heat-recovery unit during the year, namely: at inlet temperatures of air and exhaust gases in the range from -20 to +20 ºС and from 200 to 300 ºС, respectively, the coefficient of excess air in waste gases from 1.5 to 2, 5 and different levels of dust on the heating surface. The influence of dustiness on the thermal parameters was characterized by the coefficient k, which determined the level of reduction in the thermal efficiency of the heat exchanger as a result of dust deposits on the specified surface and varied in the range from 1 to 0.5. Under the considered conditions was established, that use of the proposed air heater it provides heat output of 72 ÷ 263 kW, cooling of flue gases to a temperature of 107 ÷ 245 °С and heating of air to 96 ÷ 220 °С. At such levels of flue gas cooling, the efficiency of the thermal disposal of household waste increases by 2 ÷ 5%. In the case of a decrease in the heat-recovery capacity of the heat-recovery unit to technologically unacceptable levels, it is necessary to carry out its forced cleaning with compressed air, as provided for in the technical solution of such an air heater.

Поєднання енерго-ресурсозберігаючих та екологічно безпечних технологій в проєктах ДП «ГИПРОКОКС»

DOI: 10.31081/1681-309X-2024-0-1-21-26 Specialty 161. U.D.C. 621.311 COMBINATION OF ENERGY-SAVING, RESOURCE-SAVING AND ENVIRONMENTALLY FRIENDLY TECHNOLOGIES IN THE PROJECTS OF THE SE "GIPROKOKS" © T.F. Trembach, M.V. Mezentseva, I.O. Radychuk (STATE ENTERPRISE "STATE INSTITUTE FOR DESIGNING ENTERPRISES OF COKE OVEN AND BY-PRODUCT PLANTS'' (SE "GIPROKOKS''), 61002, 60 Sumska str., Kharkiv, Ukraine) The article deals with the issues of energy efficiency and implementation of environmental technologies in coke production, which is one of the most energy-intensive and environmentally hazardous, but at the same time has a great potential of fuel and energy resources. The experience and achievements of SE GIPROKOKS in the use of modern technologies aimed at reducing energy and resource consumption, as well as ensuring environmental safety, are reflected. Particular attention is paid to innovative approaches to the development, design and implementation of environmentally friendly technologies in production, which help reduce emissions and negative impact on the environment. The article analyses the application of organisational, technical, design, technological and other energy saving measures in the projects of SE “GIPROKOKS” for metallurgical and coke-chemical enterprises. The most effective of these are technological: improving the quality of coke, what, when used in the blast furnace process, leads to a reduction in energy consumption; using less energy-intensive technologies and secondary energy resources. These technologies primarily include the coal charge stumping technology. Flue gas heat from the coke oven battery heating system has a significant energy potential that is released into the atmosphere, leading to irreversible heat losses and causing a negative impact on the environment. The use of a heat recovery unit with thermal flue gas treatment will significantly reduce emissions of harmful components in flue gases into the atmosphere. In its projects, SE “GIPROKOKS” pays considerable attention to the use of secondary resources generated in coke production processes, which is a vivid example of combining energy-saving, resource-saving and environmentally friendly technologies. Keywords: coke production, secondary products, utilisation, energy saving, resource saving, environmental safety, technological measures. Corresponding author: T.F. Trembach, e-mail: ozos@giprokoks.com

Математическое моделирование, оптимизация структуры и режима работы оборудования конденсационных котлов

One of the priority areas of the development of science, technology, and engineering in the Russian Federation is energy saving issues. One of the promising areas to solve the problem of energy saving is to reduce waste heat losses of power plants. The designs of condensing heat exchangers used in industry and energy sector allow both to reduce waste heat losses and to significantly reduce moisture losses. Despite the substantial number of scientific publications on this issue and the positive experience of using the developed designs of condensing heat exchangers, most gas boiler houses and thermal power plants currently continue to operate without deep heat recovery units. To a great extent, it is due to the lack of the universal methods to calculate and optimize heat exchanger modes. Thus, to effective selection of the optimal structure and operating mode of the equipment, the development of mathematical models of power plants with condensing heat exchangers and software packages for their computer implementation is an urgent task. To design a model of a condensing boiler, equations of energy and mass balances are used. To solve the problem of optimal choice of structure and operating mode of the equipment, mathematical programming methods are used. A model and a method to solve the problem of choosing the optimal structure and operating mode of condensation heat exchangers have been developed. As a target optimization function, it is proposed to use the amount of fuel required to provide pre-set heat load. A computer program has been developed for optimal distribution of load between operating units. Analysis of the results obtained has showed an adequate description of real equipment model and the possibility to generate computer mode maps. Application of these maps allows significant savings of energy resources due to the optimal choice of mode and load distribution between operating equipment. The proposed approach allows us to formulate and solve inverse problems of diagnosing the state of condensing heat exchangers.

Performance boost of a commercial air-to-air plate heat recovery unit by mesh-net insert; thermal-frictional, economic, and effectiveness-NTU analysis

This research proposes, tests, and comprehensively investigates the application of mesh-net to increase the efficiency of any air-to-air plate heat exchanger (mainly as a building heat recovery unit). The idea is tested through a commercial heat-recovery unit and all parameters including Nusselt number, pressure drop, friction factor, thermal performance factor, effectiveness, number of thermal units, pumping power and economical profitability are comprehensively investigated and reported with and without mesh-net insert. In economic evaluation the price of electricity and type of building heating system (resistance heater, heat pump and so on) are considered. In the maximum air flow rates, the overall heat transfer coefficient is enhanced from 24 to 36 W/m2K. Nusselt number increases up to 75 % depending on air flow rate. The economic results were found very interesting, and even by paying further fan power due to the higher pressure drop, the economic profitability is positive when the building heating system is resistance heater or heat pump with lower coefficient of performance. The profitability of the mesh net insert is higher for the region with higher electricity price. This means the gained recovered heat overcomes the further energy required for pumping power. Nonetheless, final decision making from pure economic viewpoint depends on the desired supply air flow rate, type of heating system and local price of electricity.

Performance study of a thermochemical energy storage reactor embedded with a microchannel tube heat exchanger for water heating

Thermochemical energy storage (TCES) provides a promising solution to addressing the mismatch between solar thermal production and heating demands in buildings. However, existing air-based open TCES systems face practical challenges in integrating with central water heating systems and controlling the supply temperature. To overcome these limitations, a novel water-based TCES-HEX-HRU system is proposed in this study, which integrates a water-to-air microchannel tube heat exchanger (HEX) and an air-to-air heat recovery unit (HRU). A comprehensive evaluation of the TCES-HEX-HRU system is conducted numerically using a COMSOL model, including a comparative assessment for different TCES system configurations. The results demonstrate that the TCES-HEX-HRU system achieves an overall thermal efficiency of 82.35 %, marking a substantial 69 percentage points improvement over the TCES-HEX system. Although slightly lower than the typical air-based TCES system without HEX and HRU by 15.44 percentage points, the TCES-HEX-HRU system can be a practically promising and viable choice for applications in central heating systems. Numerical investigations indicate that the thermal performance of the system is influenced by the inlet conditions of airflow and waterflow. Moreover, increasing the number of water channels in the HEX of the TCES-HEX-HRU system enhances heat transfer but reduces the amount of heat released by TCES composite materials, resulting in a maximum overall thermal efficiency of 92.09 % with 35 channels and a peak outlet water temperature of 33.67 °C at with 30 channels. However, further increases in the number of channels lead to a decline in overall thermal efficiency and outlet water temperature. Changes in the width of water channels in the HEX have a minor impact on the highest outlet water temperature and overall thermal efficiency, while affecting the volume of the TCES composite materials.

Exploiting district cooling network and urban building energy modeling for large-scale integrated energy conservation analyses

Research effort in analyzing the energy consumption of buildings in districts or cities is increasing as new paradigms of distributed energy production and sharing are spreading. In this work, the Urban Building Energy Model of the Quad, an area of the University of California Davis campus, is presented, validated, and analyzed for possible actions to reduce the district cooling energy consumption. Energy conservation measures involve buildings' air handling units and district chilled water generation. To investigate this system, a district cooling networks module has been developed in EUReCA, the Urban Building Energy Modeling tool used for the analyses. The model has been validated with energy demand and temperature data from 2018 to 2020, resulting in a district cooling demand deviation lower than 7% for 2018 and 2019. Normalized Root Mean Square Error is lower than 35% for each building, proving the reliability at the hourly time scale. Systems energy reduction actions like heat recovery units' installation and heuristic control of the air supply cooling temperature are beneficial in reducing the cooling demand, and they allow a more efficient discharging of the chilled water storage, reducing the average electricity price by load shifting during peak demand.

Performance enhancement of compound parabolic concentrating vaporized desalination system by spraying and steam heat recovery

This paper employs the compound parabolic concentrator to heat the thermal conduction oil as working fluid to a higher temperature. The feed water is sprayed and obtains heat from the working fluid in evaporation chamber. The spraying of feed water enhances heat and mass transfer and increases the vaporization intensity. The latent heat of steam is recovered to preheat the feed water which improves energy utilization. Multivariate orthogonal experiments were conducted to obtain the optimized nozzle arrangement in the evaporation chamber. Numerical simulations were performed to evaluate the effect of nozzle parameters on liquid film thickness and water production performance. In system performance experiments, the heat loss, heat recovery performance, fresh water production and gain output ratio in sunny weather were achieved. The daily fresh water production of the system was 15.1 kg with a maximum rate of 4.32 kg/h. The nozzle group arrangement optimization increases the fresh water production by 28.12 % and the maximum rate was 8.48 %. The heat recovery unit increases fresh water production by 13.18 %, with an average heat recovery efficiency of 0.85.

Performance analysis and multi-objective optimization of a novel poly-generation system integrating SOFC/GT with SCO2/HDH/ERC

The SOFC-based poly-generation system is an effective and environmental-friendly technology. To further improve energy efficiency of poly-generation system, a novel poly-generation system is developed based on solid oxide fuel cell/gas turbine (SOFC/GT) as the prime mover and supercritical carbon dioxide (SCO2) Brayton cycle, humidification and dehumidification (HDH) desalination and ejector refrigeration cycle (ERC) as the waste heat recovery units to produce power, cooling and freshwater. In the proposed system, a novel configuration of combining the SCO2 cycle with HDH is applied to recover the waste heat of SOFC/GT hybrid system. A mathematical model is developed to explore the system performances from the energy, exergy and economic perspectives. The effects of key parameters such as fuel flowrate, fuel utilization factor, SOFC operating pressure and temperature, and desalination top temperature on system performances are investigated. Multi-objectives optimization is conducted to obtain the optimal design parameters of the poly-generation system. The results show that the system net power output, cooling capacity and freshwater production are 273.769 kW, 12.997 kW and 24.23 g/s with the total cost being 14.01 $/h under the given condition, respectively. The electrical and exergy efficiencies and total gained output ratio of the system are 68.35 %, 67.23 % and 85.25 %, respectively. The parametric analysis indicates that an appropriate increase in fuel flowrate, fuel utilization factor and SOFC operating pressure and temperature can improve the electrical and exergy efficiency. The optimization results demonstrate that the system exergy efficiency and total cost are 67.48 % and 13.94 $/h.

Development of a hybridized small modular reactor and solar-based energy system for useful commodities required for sustainable cities

The current study develops a hybridized small modular nuclear reactor and solar-based system designed specifically for sustainable communities in metropolitan areas to meet their power, heat, clean fuel, fresh water and food requirements. Both floating-type and bifacial-type photovoltaic arrays are integrated with a high-temperature gas-cooled small modular reactor. In the integrated system, a Rankine cycle subsystem for power generation, a solid oxide electrolyzer for hydrogen production, a pressure swing adsorption unit with ammonia reactor for nitrogen and then ammonia production, a multi-effect desalination unit for freshwater generation, and heat recovery units in order to provide heating to residential area, food drying facility, greenhouse, and fish farm facilities. For both floating and bifacial PV options, the 120 MWp PV modules are considered and integrated with two small modular reactor units at 250 MWth capacities each, 500 MWth in total. A thermodynamic analysis, which is based on energy and exergy approaches, is carried out. The time-dependent analyses are carried out for floating-type PV and bifacial-type PV options for the cities of Istanbul in Turkey; Barcelona in Spain; Los Angeles (LA) in the United States; Tokyo in Japan; and Toronto in Canada by using their hourly meteorological data, source and load capacities in a typical meteorological year. Among ten cases, between 112835 and 146180 tonnes of ammonia are generated in a typical year while meeting the heating and power requirements of sustainable communities in metropolitan areas. Among ten cases, the average overall energy and exergy efficiencies are found as 41.04% and 46.88%, respectively. The hybridization of such nuclear and solar systems achieves unique advantages by preventing intermittencies compared to the renewable-alone systems, reducing carbon emissions compared to fossil-based systems, and lowering the levelized costs of energy compared to the nuclear energy-alone systems.

Next generation of heat pumps for buildings based on thermoelectricity integrated with smart grids

This paper proposes a HVAC system that integrates a novel thermoelectric heat pump with a double flux ventilation system and a sensible heat recovery unit able to provide heating, cooling and ventilation to a 74.3m2 pilot passive house in Pamplona (Spain). The heat pump has been previously prototyped and analysed in the laboratory, showing COPs ranging 1.5-4 for heating and 0.5-2 for cooling. This study investigates the energy performance of the combined system (heat pump and ventilation unit) and the comfort conditions of the dwelling one year long, showing the advantages of this technology and the potential integration with PV based building-level smart-grids.

Thermodynamic analysis of a novel combined heating and power system based on low temperature solid oxide fuel cell (LT-SOFC) and high temperature proton exchange membrane fuel cell (HT-PEMFC)

Low-temperature solid oxide fuel cell (LT-SOFC) and high temperature proton exchange membrane fuel cell (HT-PEMFC) have attracted significant attention due to outstanding advantages over traditional fuel cells. To increase the energy utilization ratio of LT-SOFC and solve the fuel supply problem of HT-PEMFC, a new combined heating and power (CHP) system mainly composed of a LT-SOFC unit, gas processing unit, HT-PEMFC unit and waste heat recovery (WHR) unit is proposed. For the CHP system, LT-SOFC can not only be used as power generation system, but also as fuel source of HT-PEMFC and heat source of WHR unit. Moreover, the influences of the recirculation percentage, fuel utilization and operating temperature of LT-SOFC on the system performance are revealed. Under typical conditions, the net electric power and total output power of the CHP system are 1002.7 kW and 1388.6 kW, and the net electric efficiency and the total energy efficiency are 62.5% and 86.5%, respectively. The superior performance of CHP system compared with other relevant systems proves its feasibility, and the analysis results also provide theoretic foundation for LT-SOFC based cogeneration systems.

Performance of a BAPVT modules coupled TEHR unit fresh air system based on micro heat pipe array

Energy consumption for heating and cooling fresh air has become a major component of building energy consumption, and there is a growing focus on highly-efficient and energy-conserving fresh-air treatment technology. This paper presents a new fresh-air system based on a high-efficiency heat transfer element, the micro heat pipe array (MHPA). It consists of a novel air-cooled building attached to a photovoltaic/thermal module (MHPA-BAPVT) and a thermoelectric heat recovery unit (MHPA-TEHR). The system uses solar energy, photovoltaic power generation, and waste heat for fresh air preheating. A series of fresh-air systems were designed, constructed, tested, and analyzed. The results reveal that on sunny winter days, the temperature of fresh air flowing through MHPA-BAPVT modules can increase by 22.15 °C. The average thermal and electric efficiency of the MHPA-BAPVT modules was 12.16% and 7.10%, respectively, and MHPA-TEHR could exceed the upper limit of passive heat recovery technology, which could generate 1.25 kW of heat per 1 kW of input electric power. The maximum ratio of total heating power to the total power consumption of the fresh-air system reached 14.94. During a typical day in the winter season, solar preheating exceeded the fresh air heat requirement by 24.34%, and the excess heat provided 292.92 MJ for building heating demand. Comparing the electric heating fresh-air unit with conventional heat recovery, the former achieved nearly zero energy consumption during the winter season. During the transitional season, the system could provide 711.82 MJ of solar energy, which improved the indoor temperature. Finally, using the experimental data and meteorological parameters of Zibo, the annual heat and electricity benefits and reduced carbon dioxide emissions of the fresh-air system were calculated. The fresh-air system in this study can fully utilize solar energy for heat collection and power generation to reduce building energy consumption and can be applied widely.

Performance investigation on a precision air conditioning system with a condensation heat recovery unit under varying operating conditions

The precision air conditioner is usually used in many occasions where the temperature and humidity are required to be constant. To guide the performance optimization of the precision air conditioners, the experimental investigation on the performance of a precision air conditioning system with condensation heat recovery was carried out. The influences of four vital parameters which are the compressor frequency, air volume and cooling water flow on the system performance were tested and analyzed respectively. It results that the cooling capacity is increased (approximately 33 %↑) while the coefficient of performance (COP) gradually decreases from 4.98 to 2.26, when the compressor frequency ranges from 120 Hz to 240 Hz. With the circulating air volume increases from 490 m3/s to 1141 m3/s, the cooling capacity and COP are both elevated, by 35.6 % and 42.6 %, respectively. Moreover, with the increase of cooling water temperature (Tw), the cooling capacity is increased at Tw ∈ [289 K, 295 K] but decreased at Tw ∈ [295 K, 301 K], gradually. It can be concluded that the phenomenon of performance variation in the precision air conditioner is relatively complex for the influence of the condensation heat recovery.

Energy efficiency in hospitals: comparative analysis of different HVAC configurations

ABSTRACT The characteristics of health facilities e.g. the need to operate 24 h a day, strict cleaning procedures and indoor environmental parameters made these building-type energy-intensive. The huge potential that can be exploited in terms of energy savings is evident, mainly regarding the HVAC system refurbishment. From literature emerges that there are poor systematic analyses concerning all the possible HVAC retrofit scenarios, considering solutions currently on the market or renewable sources. To fill the research gap pointed out, the present paper proposes a rigorous analysis of the possible generation subsystems available on the market that can be implemented in an HVAC retrofit for a hospital. A real case study of 88,000 m3, represented by a hospital in southern Italy, has been used. Different technologies, such as the photovoltaic system, electric heat pump, absorption heat pump driven by solar energy, cogeneration are analysed from the energy and environmental point of view, with the introduction of the Imported Energy Level Index (IELI). The best retrofit measures is the installation of an absorption heat pump driven by solar thermal collectors and cogeneration, with a primary energy saving of 20%. Considering the installation of a heat recovery unit, the saving is up to 43%.

Multi objectives optimization and transient analysis of an off-grid building with water desalination and waste heat recovery units

In this study, an off-grid apartment of a five-story building with a 150 m2 area, is considered. Building is considered in a remote area; therefore, all occupants' requirements are provided without using electricity and gas from the grid. For producing water, reverse osmosis (RO) desalination system is used. HVAC system is optimized for achieving the lowest CO2 emission and the best occupant’s thermal comfort simultaneously. Also, the use of two different sources, waste heat of diesel generator and solar collector, to provide domestic hot water for the building were investigated and compared. The roof-mounted PV panel is considered for supplying building's energy consumption. Due to the limited available area of the rooftop for each flat, the diesel generator is considered a backup power supplier for the building. Produced power is stored in the battery. Results show that the optimal scale factor of the heat pump is 0.9, and the cooling capacity of the heat pump should be 5.35 kW to supply thermal comfort. Regarding the results of optimization, the annual CO2 emission production of the diesel generator is 4.79 tons and PPD is 12.4%.

Thermodynamic performance analysis of air-to-air hybrid heat recovery unit driven by pump combined with booster

The air conditioning energy consumption for fresh air handling in buildings increases yearly, especially in low energy buildings. This energy consumption can be greatly reduced when exhaust air is recovered for preheating or precooling fresh air. Then, significant savings in the total energy consumption in buildings will be achieved, which in turn helps achieve the carbon peak in the building field. In this paper, a booster/pump coupled energy recovery ventilator is proposed for energy recovery in buildings. The system performance, which depends on the loop number and combination strategies were analyzed and compared through model simulations. Results indicate that the heat transfer rate of different coupling systems increases with the temperature difference. In summer, the pump/booster driven dual-loop system has the highest average temperature effectiveness of 47.3% and average heat transfer rate of 4.97 kW. The booster/booster-driven dual-loop system has the highest average heat transfer rate of 5.07 kW and average temperature effectiveness of 47.1%. The average temperature effectiveness of the pump/booster/booster driven triple-loop system reaches up to 45% and average heat transfer rate of 4.73 kW. The booster/booster/booster-driven triple-loop system has the highest average heat transfer rate of 4.82 kW and average temperature effectiveness of 44.7%. In winter, the maximum average heat transfer rate and temperature effectiveness of the pump/booster driven dual-loop system are 8.54 kW and 44.44%, respectively. The maximum average heat transfer rate and temperature effectiveness of the pump/booster/booster driven triple-loop system are 7.90 kW and 41.5%, respectively. Throughout the year, the best coupling scheme of the dual-loop system is the pump/booster driven dual-loop system, and its average heat transfer rate and temperature effectiveness are 6.755 kW and 45.85%, respectively. The best coupling scheme of the triple-loop system is the pump/booster/booster-driven triple-loop system, and its average heat transfer rate and temperature effectiveness are 6.315 kW and 43.25%, respectively.

Solid oxide fuel cell energy system with absorption-ejection refrigeration optimized using a neural network with multiple objectives

The present study focuses on modeling the solid oxide fuel cell power plant combined with an absorption-ejection refrigeration cycle. First, a comparison is made between the absorption chiller refrigeration cycle and the absorption-ejection chiller to connect the superior cycle to the solid oxide fuel cell as an auxiliary cycle. Then, the solid oxide fuel cell cycle, the combustion of the output product, the heat recovery unit combined with the refrigeration cycle, and freshwater production are modeled. Next, the sensitivity analysis is presented in order to study the effect of the design parameters on objective functions, which simplifies the justification of the optimization results based on the genetic algorithm. In order to perform optimization, machine learning methods have been employed to reduce computational time and cost. The optimization of this cycle shows that the exergy efficiency is enhanced up to 68%, whereas the overall cost rate is in within 9.7–10.4 dollars per hour.

Thermal effectiveness and NTU of horizontal plate drain water heat recovery unit - experimental study

The operating characteristics of plate heat exchanger in horizontal drain water heat recovery unit for domestic shower system were investigated in an experimental study. Based on test data the thermal effectiveness (ε) and number of heat transfer units (NTU) were calculated. The tests were carried out in simulated real-world conditions in three shower water flow rates (water consumption levels) for 4, 8 and 12 l/min, and two primary and secondary flows configurations (balanced and unbalanced), as a reflection of the three shower intensity standards and water temperature range of 30–50 °C covering the usual user-specific shower conditions. The least favorable test results (ε = 18.6% and NTU = 0.24) were obtained for the drain water temperature of 26.6 °C and cold water / drain flow rate at 12/12 l/min. The most beneficial results (ε = 50.0% and NTU = 0.99) were obtained for the sewage temperature of 50.8 °C and 4/12 l/min. It has been shown that the higher the flow on the drain water side and lower on the cold water side, the better the effectiveness. For a system with equal and low flows on both sides, the drain temperature change has a negligible effect on the effectiveness (4% growth with a drain temperature increase of 25.4 °C for 4/4 l/min). The paper presents developed easy-to-use charts of the variability of the effectiveness and NTU with the drain water temperature relates to a different set of primary and secondary flows in horizontal, plate, compact drain water heat recovery exchanger. The results of effectiveness obtained in the research were compared to the values presented in the literature for other drain water heat recovery units, both in vertical and horizontal applications.

A new biomass-based hybrid energy system integrated with a flue gas condensation process and energy storage option: An effort to mitigate environmental hazards

The development of biomass-fueled cogeneration plants can be fruitful to achieve the sustainable development goals, due to the crises of fossil energy-fueled ones. Additionally, biomass fuels can offer higher reliability and more sustainable energy compared to the two more well-known renewables (i.e., solar and wind energies) due to the no dependence on environmental and weather conditions. The present article provides a comprehensive assessment (thermodynamic-design, exergoeconomic and environmental) and optimization of a new biomass-driven cogeneration plant cascaded with a heat recovery unit. The planned plant is based on a biomass gasification process, some thermodynamic power generation cycles based on steam and gas turbines (i.e., Rankine cycle, Brayton cycle, and organic Rankine cycle (ORC)), and flue gas condensation process. Besides, a compressed air energy storage system (CAESS) as an energy storage process is integrated with the considered plant to establish a balance between production and demand and reduce electricity costs. To achieve optimal performance, a multi-objective optimization (based on a genetic algorithm) is applied. The findings showed that by considering the multi-objective optimization techniques, the plant's exergy efficiency could improve by about 15%. At the same time, the exergy cost rate is reduced by almost 17.3%. Avoiding the payment of carbon tax and the high electricity production level in the on-peak consumption period are unique and competitive features of the proposed biomass-driven power plant. It was also found that the LCOE and the payback period were 13.27 USD/GJ and 2.03 years, respectively, therefore, the proposed power plant exhibits reasonable economic feasibility.