Low-grade Industrial Waste Heat Research Articles

Thermodynamic analysis of an ammonia-water double absorption-resorption heat transformer system

Absorption heat transformer (AHT) presents an effective solution for enhancing energy efficiency through the utilization of low-grade industrial waste heat. To reduce the high operating pressures of traditional ammonia AHT and elevate waste heat to a higher temperature level, a novel ammonia-water double absorption-resorption heat transformer (DARHT) incorporating a coupled middle absorber-generator is proposed in this paper. A thermodynamic simulation model of the system is established using MATLAB software to analyze the effects of operating pressures and temperatures on the COP, temperature lift, solution circulation ratio and bypass ratio, thereby determining the optimal operating conditions of the system. The simulation results indicate that there exist optimal PH/PL pairs and middle absorber-generator temperatures which lead to the maximum COP of the system. COP decreases with the increase of absorber and resorber temperatures while increases with the increase of generator and desorber temperatures. When PH/PL pair is 1.5/0.36 MPa, the DARHT system can provide a temperature lift exceeding 70 °C, while the working pressures are significantly lower compared to conventional AHT, thereby reducing the requirements of robust components and enhancing the operational stability of the system.

Preparation and thermal properties of zeolite/MgSO4 composite sorption material for heat storage

Thermochemical sorption heat storage based on salt hydrates offers the potential advantages such as high energy density, negligible heat loss, small volume change and flexible working modes. Magnesium sulphate (MgSO4) is a high energy density hydrated salt available for the thermochemical sorption heat storage. In this work, different types of zeolites (including 3A, 5A and 13X zeolites) have been selected as mass-transfer-enhancing and structural stabilizing materials, and a series of zeolite/MgSO4 composites have been fabricated. To investigate the thermal energy storage performance of zeolite/MgSO4 composites, the properties of the composites, such as micro-morphology, pore structure, chemical composition and sorption-desorption behavior, have been characterized and analyzed. Results indicated that the mass transfer performance of the composite materials is significantly better than that of the pure zeolites. As the mass fraction of MgSO4 in the composite sorbents increases, the specific surface area and porosity of the composite sorbent decreases, and the sorption performance has been enhanced. Compared with 3A zeolite-based and 5A zeolite-based composites, 13X zeolite/MgSO4 composite materials show the best heat storage performance. At the condition of 25 °C and 60% RH, the 13XM20 has the highest sorption capacity of 0.21 g/g, which is 24% higher than that of pure zeolite 13X. Accordingly, the maximum heat storage density is 438.4 kJ/kg, which exhibits the superior heat storage performance among of the hydrated salt sorbents. The potential of 13X zeolite/MgSO4 as sorption heat storage material in efficient utilization of solar heat and low-grade industrial waste heat has been revealed.

Charging/discharging performance and corrosion behavior of a novel latent heat thermal energy storage device with different fin plate materials

The use of low-grade industrial waste heat for building heating could facilitate the decarbonization of heat sector, which accounts for a large share of energy consumption worldwide. However, the uncontrollable fluctuation characteristics of heat source and mismatch between energy supply and demand greatly limit its large-scale application. Notably, latent heat thermal energy storage (LHTES) technology, showing remarkable advantages in terms of energy storage density, heat storage temperature (nearly constant), technology maturity and cost, could effectively solve the above problem. Hence, this work specially focused on LHTES device that utilized fin plate for improving performance of heat harvesting and reuse. Furthermore, charging/discharging performance and corrosion behavior of a novel device with different fin plate materials (brass, aluminum and stainless steel) were investigated. Results showed that temperature difference between plate surface and melting point above 10 °C effectively shortened charging time more than 45.7 %. A higher thermal conductivity of fin material contributed to a better thermal performance. Aluminum and stainless steel preferred to be used as fin plate materials of targeted hydrated salt owing to their low corrosion rate of 0.016 and 0.002 mg/(cm2·yr), respectively. This work was expected to provide a guidance on designing a LHTES device applied in building heating.

Advanced exergy analysis of a double absorption heat transformer recovering industrial waste heat for pure water production

Conventional and advanced exergy analyses are applied for a double absorption heat transformer system utilizing low-grade industrial waste heat for water purification. The conventional method provides information about the location and magnitude of inefficiencies and does not consider any interaction among components regarding the irreversibility occurring in them. The advanced exergy technique however, exposes the real origins of irreversibilities and latent potential for enhancement of each system component, along with reflecting mutual interaction between components. The simulation of the cycle is carried out with engineering equation solver software. The results show that the overall improvement potential of the cycle is only 16%. Also, the mutual interdependency between components is found to be weak as 97% of the total exergy destruction appeared as endogenous. Furthermore, considering endogenous avoidable exergy destruction, the improvement strategy of components obtained by advanced exergy method is disparate from conventional one. Results of the advanced exergy suggest this order: condenser, absorber, evaporator, absorber/evaporator assembly, generator assembly, economizer 1, and economizer 2. Additionally, a parametric investigation is performed to assess the sensitivity of splitting exergy destruction to the variation of heat source temperature for highlighting improvement opportunities. The results indicate that the condenser yields the highest amount of avoidable endogenous exergy destruction in the entire studied temperature range.

Selective CO2 deoxygenation to CO in chemically looped reverse water–gas shift using iron-based oxygen carrier

Chemical-looped reverse water–gas shift reaction was investigated using transition metal/metal oxides as oxygen carriers. Iron is identified as the only promising oxygen carrier that shows compelling CO 2 splitting reactivity. A chemically looped reverse water–gas shift reaction was developed using an iron-based oxygen carrier. Compared with conventional catalytic conversion processes, the chemical looping method has the advantage of high selectivity and cheap materials cost due to the separation of CO2 splitting and H2 oxidation half-reactions that are enabled by earth-abundant transition metal oxygen carriers. However, for such process to be economically attractive, the operation temperature should ideally be low enough such that low-grade industrial waste heat can be utilized. In other words, the reactivity of oxygen carriers toward the aforementioned half-reactions is most critical. To address the materials challenge, four transition metal-based oxygen carriers, i.e., iron, nickel, manganese, and copper, are studied using temperature-programmed techniques under H2 and CO2. Iron is identified to be the only oxygen carrier reactive toward CO2 splitting and capable of completing the redox cycle at 450 °C with 100% reverse water–gas shift selectivity. Although the thermal stability of the iron oxygen carriers shows room for improvement, our work demonstrates the great potential of a scalable and economically viable route for CO2 conversion that is compatible with current industrial processes.Graphical abstract

Energy performance assessment of a novel zeolite-water direct contact adsorptive heat pump for waste heat recovery

• The low-grade industrial waste heat can be recovered using adsorption heat pumps. • The direct contact adsorption heat pumps guarantee simple configurations. • The water inlet downward flow configuration shows excellent thermal performances. The adsorption heat pumps are a promising technology suitable for the industrial waste heat recovery. In particular, the direct contact configuration can be used to generate high pressure steam for industrial applications limiting the design complexities. In this paper, a numerical simulation of the adsorption phase of an original configuration of a direct contact water/zeolite heat pump is presented and discussed. Two different models have been developed and compared using experimental data. Different sensitivity analyses were carried out with the aim of understanding the process of steam generation. The mass flow inlet results to be one of the most relevant parameters of the process and, consequently, an innovative process configuration is proposed. A descendent inlet water flow is implemented and compared with the classical ascendent process. The simulations on this configuration demonstrated that it is possible to obtain higher steam production and better process performances doubling the generated steam mass flow.

Low-grade industrial waste heat utilization in urban district heating: Simulation-based performance assessment of a seasonal thermal energy storage system

In this study, a large-scale industrial waste heat heating system integrated with borehole thermal energy storage (BTES) and an absorption heat pump was proposed, designed, and assessed using long-term dynamic simulations. Simulations were performed with different reference combinations of storage volumes and circulation flow rates for the borehole heat exchanger, and a procedure for determining the optimal design parameters was demonstrated. The simulation results indicated that a large-scale BTES has significant potential for buffering short-term temperature variations in industrial waste heat recovery systems. The initial quasi-stable temperature of the BTES established itself gradually, and the energy input and output of the storage tended towards stability after 3–4 years of operations. The effect of increasing storage capacity tended to gradually decline with increasing circulation flow rate and storage volume after reaching a peak, becoming marginal at higher design parameter values. This result indicate that the storage volume and circulation flow rate of the system should be optimized according to an appropriate economic index, to maximize economic benefits. The simulation results emphasized the potential of large-scale seasonal BTES systems to be integrated with industrial waste heat recovery systems and district heating networks, to improve the stability of energy demand and efficiency.

Numerical investigation of melting enhancement for paraffin in an innovative finned-plate latent heat thermal energy storage unit

Latent heat thermal energy storage (LHTES) is essential for eliminating the discrepancy between energy supply and demand as well as for improving the utilization rate of low-grade industrial waste heat. This paper aims to solve the problem of long energy charge time in finned-plate LHTES device. In the present study, the LHTES unit is designed with three different orientations of the fin plates: A denotes a horizontal unit with fins; B and C denote vertical units with transverse and longitudinal fins, respectively. First, the melting process with different sizes and distributions of fins is investigated and the effect of fin thickness on the melting time is analysed. When obtaining the optimized fin parameters, two potential strengthening strategies (rippling fins and fins of non-equal length) are applied to further improve the melting performance of the device. The results show that long and thick fins can remarkably ameliorate the melting performance of paraffin, and the melting rate for the three orientations is of the order A>C>B. Compared with the finless structure, the melting rate increased by 4.52, 3.63, and 3.62 times for the three orientations of A, B, and C, respectively, for a fin length of 50 mm and fin number equal to 10. The use of rippling fins can reduce the melting time up to 4.1%, 5.4%, and 10.7% for the three orientations of A, B, and C, respectively, compared to using equal-length homogeneous fins with a thickness of 3 mm. Moreover, for orientations A and B, by adjusting fin length arrangement or using full fins, 11.4 and 46% reduction in melting time could be achieved compared with the configuration with a fin length of 50 mm and a thickness of 3 mm. The proposed innovative finned-plate LHTES device provides a useful reference and groundwork for the future large-scale utilization of the LHTES system.

Application of entransy method in heat exchanger networkoptimization for low-grade waste heat utilization

<p indent="0mm">Efficient utilization of low-grade industrial waste heat is of great significance to improve the efficiency of energy utilization and to reduce CO₂ emission. Energy system integration and corresponding heat exchanger network optimization are effective solutions. The entransy method is suitable for quantifying the irreversibility of the heat exchange process and guiding and evaluating heat exchanger network optimization. However, there are relatively few cases in which the entransy method is applied to the heat exchanger network optimization for waste heat utilization. In this study, the waste heat utilization of steam condensate in an industrial park through a heat exchanger network was analyzed based on the entransy method. By reducing the entransy dissipation of the heat exchange process of the condensate, the existing heat exchanger network was optimized, and the high-grade waste heat was utilized by an absorption chiller for local air conditioning demands. As a result, the discharge of high-grade waste heat was converted to the discharge of low-grade waste heat. The optimized heat exchanger network guided the redesign of the actual heat exchanger network. The testing results showed that the cooling effect of the developed seawater cooled absorption chiller reached <sc>3430 kW</sc>, with a coefficient of performance of 0.76. The entransy dissipation of the heat exchange process of the condensate was reduced by 57.3%. The thermal efficiency and exergy efficiency of the heat exchanger network were increased by 55.8% and 81.1%, respectively. These results demonstrate that the entransy method is valid in the application of low-grade waste heat utilization through heat exchanger network optimization.

Novel District Heating Systems: Methods and Simulation Results

Fifth-generation district heating and cooling (5th DHC) systems offer promising approaches to decarbonizing space heating, cooling and domestic hot water supply. By using these systems, clustered buildings combined with industrial waste heat can achieve a net-zero energy balance on a variety of time scales. Thanks to the low exergy approach, these systems are highly efficient. As part of the Smart Anergy Quarter Baden (SANBA) project, the thermal energy grid simulation tool TEGSim has been further developed and used to design an ultra-low-temperature district heating (ULTDH) network with hydraulic and thermal components fitted to the specific regional characteristics of the investigated case. Borehole thermal energy storage (BTES) used as seasonal storage ensures long-term feasibility. The annual discrepancy of input of thermal energy provided by space cooling and output of energy demanded by space heating and domestic hot water is supplied by an external low-grade industrial waste heat source. This paper presents the functionality of the simulation and shows how to interpret the findings concerning the design of all components and their interplay, energy consumption and efficiencies.

Fabrication of wooden thermoelectric legs to construct a generator

Herein, wooden-stick-based thermoelectric legs are introduced as a new type of thermoelectric legs. As a proof of concept, graphite- and bismuth-coated wooden sticks are fabricated with a green method, and their use as thermoelectric elements is successfully demonstrated by constructing a test thermoelectric generator. The generator based on 20 pairs of p–n legs shows a maximum power output of ∼18 nW on heating one side of the device to 70°C. The strategy can suitably be extended to other good thermoelectric materials. The approach can be promising due to the ultralow thermal conductivity of the wooden substrate pillars in contrast to other typical substrates such as glass, and hence, better thermal gradients across the device can be achieved. These environmentally friendly, non-toxic and low-cost wooden-stick-based thermoelectric devices with good thermoelectric material coatings can be conveniently used for low-grade industrial waste heat conversion applications.

A Framework for Design and Operation Optimization for Utilizing Low-Grade Industrial Waste Heat in District Heating and Cooling

In the process industry, a large amount of low-grade waste heat is discharged into the environment. Furthermore, district heating and cooling systems require considerable low-grade energy. The integration of the two systems has great significance for energy saving. Because the energy demand of consumers varies in periods, the design and operation of an industrial waste heat recovery system need to match with the fluctuations of district energy demand. However, the impact of the periodic changes on the integration schemes are not considered enough in existing research. In this study, a framework method for solving above problem is proposed. Industrial waste heat was integrated with a district heating and cooling system through a heat recovery loop. A three-step mathematical programming method was used in design and operation optimization for multiperiod integration. A case study was conducted, and the results show that the multiperiod optimization method can bring significant benefits to the system. By solving the mixed integer nonlinear programming model, the optimal operation plans of the integration in different periods can be obtained.

Design of steam-assisted temperature vacuum-swing adsorption processes for efficient CO2 capture from ambient air

Direct air capture (DAC) is an efficient, negative-carbon-emission technology that enables the capture of distributed emissions and removes location restrictions on capture facilities. However, current DAC demonstration plants are still too costly to be commercialized. In this work, a three-step steam-assisted temperature vacuum-swing adsorption (S-TVSA) cycle based on a packed column was designed for use in DAC systems, and the CO2 and H2O capacities and kinetics of the adsorbents were considered in detail. By operating the steam purge step at reduced pressures, steam at temperatures lower than 100 °C can be supplied by cheap thermal sources. In addition, the adsorption of H2O during the steam purge step can release heat for CO2 regeneration. Parameter sensitivity analysis reveals the trade-off relationship between the performance and energy consumption of DAC system with the S-TVSA cycle. The optimal case with a variational steam purge step operating at 90 °C and 0.3 bar achieves a CO2 productivity of 4.45 mol kg−1 day−1 and an energy requirement of 0.295 MJ mol−1. If the heat energy for the purge steam comes from solar energy or low-grade industrial waste heat, which represents 80.6% of the total energy consumption, the DAC system with S-TVSA cycle will be competitive with post-combustion CO2 capture technologies. Note that the productivity can be increased by up to 280% with only 32.8% of the initial energy consumption by using novel adsorbents with higher capacities and kinetics, potentially making S-TVSA cycles highly efficient for DAC systems.

Energy Storage of Low Potential Heat using Lithium Hydroxide Based Sorbent for Domestic Heat Supply

With the increasingly energy consumption and environmental degradation, the recovery of low-grade industrial waste heat and the development and utilisation of renewables have become urgent needs. At present, the recovery of waste heat is mainly at high temperature, and the recovery rate of waste heat at medium and low temperatures is low. Adsorption thermochemical energy storage (TCES) is a pivotal technology applied for long-term thermal energy storage based on the reversible gas-solid reaction at mid-to low-temperature. LiOH·H2O is a potential thermochemical material (TCM) candidate because of the high energy storage density (ESD). In this paper, the expanded graphite (EG) is used as supporting matrix to impregnate LiOH to further improve its heat and mass transfer. The water vapour adsorption properties such as sorption capacity and sorption isotherms of the consolidated composite sorbents with EG contents of 0, 5, 8, 12, and 15 wt% were tested. It was found that the samples with 5% and 8% wt% EG have superior sorption capacity and kinetics at various relative humidities (RHs), and the maximum water uptake substantially decreased with increasing temperature. The cyclability results showed 90% and 92% of the original ESDs are retained after 12 cycles for the samples with 8% and 15% wt% EG, suggesting good stability of composite sorbent. The ad/desorption isobars processes also proved the existence of the sorption hysteresis loop, and this phenomenon is more obvious at low pressure. The data fitting results revealed that the kinetics coefficient of the promising composite sorbent containing 8 wt% EG is 0.01671 s – 1 at 30 °C with 58% RH. Compared with the sensible or latent energy storage, the heating temperature produced from the sorbent is adjustable for different purposes. Considering the low emissions and pollution of LiOH-based heat production compared to the coal-fire system, i.e., 1262 kg pollutants are theoretically reduced for a household per year, it is a clean alternative for the residential heat supply.

Thermo-economic optimization of small-scale Organic Rankine Cycle: A case study for low-grade industrial waste heat recovery

This work is focused on a case study of a small-scale Organic Rankine Cycle (ORC) adopted for electricity production from low-grade industrial waste heat recovery. This kind of applications raises a great interest due to the high amount of low-grade waste heat recoverable within industrial processes, but lacks of in-depth experimental investigations on the topic. The main reason is the difficulty to reach profitable small-scale projects, so more cost-effective solutions are being explored in the literature through thermo-economic optimizations. Nonetheless, the results obtained cannot be discussed with respect to actual operating data. In light of this, this paper proposes to conduct the thermo-economic optimization on the basis of an experimental application. In this manner, a comprehensive model of the facility is developed, calibrated, and validated from actual operating data. The model is used to conduct the thermo-economic optimization, revealing the influence of the organic fluid, cycle architecture, geometric parameters of main components, or control strategy used to obtain the best cost-effective solution. The main results show that, by means of a multivariable optimization using cost-effective ratios as objective function, a cheaper and powerful solution adapted to each specific project may be designed.

Feasibility limits of using low-grade industrial waste heat in symbiotic district heating and cooling networks

Low-grade waste heat is an underutilized resource in process industries, which may consider investing in urban symbiosis projects that provide heating and cooling to proximal urban areas through district energy networks. A long distance between industrial areas and residential users is a barrier to the feasibility of such projects, given the high capital intensity of infrastructure, and alternative uses of waste heat, such as power generation, may be more profitable, in spite of limited efficiency. This paper introduces a parametric approach to explore the economic feasibility limits of waste heat-based district heating and cooling (DHC) of remote residential buildings depending on network extension. A parametric model for the comparative water–energy–carbon nexus analysis of waste heat-based DHC and Organic Rankine Cycles is also introduced, and applied to an Italian and to an Austrian setting. The results show that, for a generic 4 MW industrial waste heat flow steadily available at 95 °C, district heating and cooling is the best option from an energy–carbon perspective in both countries. Power generation is the best option in terms of water footprint in most scenarios, and is economically preferable to DHC in Italy. Maximum DHC feasibility threshold distances are in line with literature, and may reach up to 30 km for waste heat flows of 30 MW in Austria. However, preferability threshold distances, above which waste heat-to-power outperforms DHC from an economic viewpoint, are shorter, in the order of 20 km in Austria and 10 km in Italy for 30 MW waste heat flows.

Optimum Design of Shell and Tube Heat Exchangers using Modified Kinetic Gas Molecule Optimizer for the use of Low Temperature in Organic Rankine Cycles

Shell and Tube Heat Exchangers (STHEs) plays a crucial role in an effective design of Organic Rankine Cycle (ORC) power plants.The main aim of this research work is to design a cost-effective ORC in order to exploit low to medium temperature geothermal fluid or low grade industrial waste heat. In this research work, modified Kinetic Gas Molecule Optimization (KGMO) algorithm was developed forfinding the optimized parameter settings of the power plant. In modified KGMO algorithm, feedback learning stage was included for improving the fitness of individual worst particles. In addition, the proposed optimization algorithm was tested on two dissimilar fluids such asR245fa and R134a in order to show the effectiveness of proposed scheme. The experimental investigation showed that the proposed scheme effectively improved the heat exchanger performance as related to the existing schemes.The enhancement factor of proposed scheme was 2.8063 for R245fa fluid and 1.9346 for R134a fluid, which was better compared to the existing schemes; KGMO and Bell-Delaware method.

Development and Testing of Novel Applications for Adsorption Heat Pumps and Chillers

This work aims at the development and the experimental characterization of new applications for adsorption heat pumps and chillers driven by industrial waste heat or renewable sources that can provide heating and/or cooling. Adsorption technologies offer the advantage of providing heating and cooling from low temperature sources below 100 °C without using refrigerant with high Global Warming Potential and with very low electricity consumption. Therefore, the technology enables the use of large untapped heat sources, increasing the energy efficiency of the heating and cooling sector with very limited impact on the environment. Several applications were investigated numerically for Switzerland using a simplified model of an adsorption heat pump. Four scenarios were identified as interesting: (1) the valorization of low-grade industrial waste heat in district heating networks, (2) energy efficiency improvement of district heating substations, (3) an autonomous adsorption heat pump with a wood pellets burner and (4) cooling applications. These scenarios were experimentally validated with a laboratory test of a commercial silica gel/water machine. Results show that there is a gap of up to 40% between the prediction of the simplified model and the experimental results. Therefore, there is huge potential to improve the performances of this commercial unit for these applications.

Thermolytic osmotic heat engine for low-grade heat harvesting: Thermodynamic investigation and potential application exploration

The osmotic heat engine is a promising technology for harvesting low-grade heat from different heat sources. However, a better understanding of the system performance, thermodynamic efficiencies, and suitable application circumstances (type of heat sources, system energy generation capacity, etc.) is needed before the transition can be made from conceptual design to practice. Firstly, the energy efficiency (ƞth) and exergy efficiency (ƞX) of a thermolytic osmotic heat engine (NH4HCO3 solution as the working fluid) were investigated in this study. It was found that the osmotic heat engine performs better when the operating temperature (heat source temperature) is lower (323 K). Additionally, a higher draw solution concentration and a lower feed solution concentration can increase both ƞX and ƞth. Subsequently, the energy return on investment with either low-grade industrial waste heat or solar thermal energy acting as the heat source was calculated. It was found that different energy return on investment values can be obtained with different heat sources. The results show that when industrial waste heat is used as the heat source, a much higher energy return on investment value (approximately 55) can be obtained. This finding indicates that it is suitable to generate electricity from industrial waste heat using the osmotic heat engine. When solar thermal energy is used as the heat source the energy return on investment value is 1.3–2.2 because there is a large amount of embodied energy in the flat-plate solar collector. This study represents a step forward towards the practical application of the osmotic heat engine.

Energy capture from thermolytic solutions and simulated sunlight coupled with hydrogen peroxide production and wastewater remediation

A novel solar salinity energy nexus was developed by combining a photocatalytic fuel cell (PFC) and a reverse electrodialysis (RED). The hybrid cell (called a PRC) can effectively transfer the solar energy and salinity gradient energy (which is regenerated by low grade industrial waste heat) to electrical energy coupled with enhanced pollutant (Rhodamine B, RhB) degradation and H2O2 production. Energy-Environment win-win will be realized. The open circuit voltage of the PRC was the sum of those of the PFC and the RED, and the RED stack made the larger contribution to the electricity production of PRC. The bias voltage generated from the RED stack accelerated the separation of photo-induced holes and electrons on the three-dimensional TiO2 array photoanode, which enhanced RhB degradation and H2O2 production. The flow rate and concentration of the working fluids (ammonium bicarbonate) and the reaction conditions in the electrode chambers had substantial effects on the PRC performance. Under the optimal condition, the peak power density and energy efficiency of PRC reached 1500 mW m−2 and 4.21% respectively. The performance of PRC on electricity production is better than photocatalytic electrolytic cell driven by desalination(PFCD), but not good as microbial reverse electrodialysis electrolysis cell (MREC).