Clean Technol., Volume 3, Issue 1 (March 2021) – 15 articles

Pet-coke (petroleum coke) is identified as a carbon-rich and black-colored solid. Despite the environmental risks posed by the exploitation of pet-coke, it is mostly applied as a boiling and combusting fuel in power generation, and cement production plants. It is considered as a promising replacement for coal power plants because of its higher heating value, carbon content, and low ash. A computational fluid dynamics (CFD) computational model of methane steam reforming was developed in this research. The hydrogen production system is composed from a pet-coke burner and a catalyst bed reactor. The heat released, produced by the pet-coke combustion, was utilized for convective and radiative heating of the catalyst bed for maintaining the steam reforming reaction of methane into hydrogen and carbon monoxide. This computational algorithm is composed of three steps—simulation of pet-coke combustion by using fire dynamics simulator (FDS) software coupled with thermal structural analysis of the burner lining and a multiphysics computation of the methane steam reforming (MSR) process taking place inside the catalyst bed. The structural analysis of the burner lining was carried out by coupling the solutions of heat conduction equation, Darcy porous media steam flow equation, and structural mechanics equation. In order to validate the gaseous temperature and carbon monoxide mole fraction obtained by FDS calculation, a comparison was carried out with the literature results. The maximal temperature obtained from the combustion simulation was about 1440 °C. The calculated temperature is similar to the temperature reported, which is also close to 1400 °C. The maximal carbon dioxide mole fraction reading was 15.0%. COMSOL multi-physics software solves simultaneously the catalyst media fluid flow, heat, and mass with chemical reaction kinetics transport equations of the methane steam reforming catalyst bed reactor. The methane conversion is about 27%. The steam and the methane decay along the catalyst bed reactor at the same slope. Similar values have been reported in the literature for MSR temperature of 510 °C. The hydrogen mass fraction was increased by 98.4%. Full article

Lignocellulosic biomass feedstocks are promising alternatives to fossil fuels for meeting raw material needs of processing industries and helping transit from a linear to a circular economy and thereby meet the global sustainability criteria. The sugar platform route in the biochemical conversion process is one of the promising and extensively studied methods, which consists of four major conversion steps: pretreatment, hydrolysis, fermentation, and product purification. Each of these conversion steps has multiple challenges. Among them, the challenges associated with the pretreatment are the most significant for the overall process because this is the most expensive step in the sugar platform route and it significantly affects the efficiency of all subsequent steps on the sustainable valorization of each biomass component. However, the development of a universal pretreatment method to cater to all types of feedstock is nearly impossible due to the substantial variations in compositions and structures of biopolymers among these feedstocks. In this review, we have discussed some promising pretreatment methods, their processing and chemicals requirements, and the effect of biomass composition on deconstruction efficiencies. In addition, the global biomass resources availability and process intensification ideas for the lignocellulosic-based chemical industry have been discussed from a circularity and sustainability standpoint. Full article

As the power output of direct drive generators increases, they become prohibitively large with much of this material structural support. In this work, implicit modeling was coupled to finite element analysis through a genetic algorithm variant to automate lattice optimization for the rotor of a 5 MW permanent magnet direct drive generator for mass reduction. Three triply periodic minimal surfaces (TPMS) were chosen: Diamond, Schwartz Primitive, and Gyroid. Parameter and functionally graded lattice optimization were employed to reduce mass within deflection criteria. Inactive mass for the 5 MW Diamond, Schwartz Primitive, and Gyroid optimized designs was 10,043, 10,858, and 10,990 kg, respectively. The Schwartz Primitive rotor resulted in a 34% reduction in inactive mass compared to a 5 MW baseline design. Radial and axial deflections were below the critical limit of 0.65 and 32.17 mm, respectively. The lowest torsional deflection was seen in the Schwartz Primitive TPMS lattice at 3.89 mm. Based on these designs, hybrid additive manufacturing with investment casting was used to validate manufacturability in metal. A fused deposition modeling (FDM) TPMS topology was printed for validation of the FEA results. Comparison between digital image correlation of the FDM printed design and FEA design resulted in a 6.7% deformation difference for equivalent loading conditions. Full article

The electric power characteristic of solid oxide fuel cells (SOFCs) depends on numerous influencing factors. These are the mass flow of supplied hydrogen, the temperature distribution in the interior of the fuel cell stack, the temperatures of the supplied reaction media at the anode and cathode, and—most importantly—the electric current. Describing all of these dependencies by means of analytic system models is almost impossible. Therefore, it is reasonable to identify these dependencies by means of stochastic filter techniques. One possible option is the use of Kalman filters to find locally valid approximations of the power characteristics. These can then be employed for numerous online purposes of dynamically operated fuel cells such as maximum power point tracking or the maximization of the fuel efficiency. In the latter case, it has to be ensured that the fuel cell operation is restricted to the regime of Ohmic polarization. This aspect is crucial to avoid fuel starvation phenomena which may not only lead to an inefficient system operation but also to accelerated degradation. In this paper, a Kalman filter-based, real-time implementable optimization of the fuel efficiency is proposed for SOFCs which accounts for the aforementioned feasibility constraints. Essentially, the proposed strategy consists of two phases. First, the parameters of an approximation of the electric power characteristic are estimated. The measurable arguments of this function are the hydrogen mass flow and the electric stack current. In a second stage, these inputs are optimized so that a desired stack power is attained in an optimal way. Simulation results are presented which show the robustness of the proposed technique against inaccuracies in the a-priori knowledge about the power characteristics. For a numerical validation, three different models of the electric power characteristic are considered: (i) a static neural network input/output model, (ii) a first-order dynamic system representation and (iii) the combination of a static neural network model with a low-order fractional differential equation model representing transient phases during changes between different electric operating points. Full article

Mist evaporation cooling (MEC) is increasingly used as a low-energy means to improve thermal comfort in hot environments. However, the thermal sensation votes (TSV) often overshoot values of Predicted Mean Vote (PMV) models. Evaluations of MEC may be affected by an expectation that mist feels cool or the “good subject” effect. Here, subjects are exposed to a misting fan and an identical fan without mist and asked which fan feels cooler. Unknown to the subjects, the misting fan has almost no cooling effect (about 0.4 K reduction in air temperature) and a hidden heater increased the temperature of the misting fan air flow, making it up to 1.6 K warmer than the fan without mist. Supplemental experiments told the subjects about the heater. Surveys of over 300 subjects when varying this misted air temperature showed a bias above random chance that people vote that a misting fan airflow was cooler, even when it was the same temperature or slightly warmer than the non-misting fan. It is possible that the expectation of cooling or good subject effect influences evaluations of mist. This effect should be considered in thermal comfort evaluations of mist cooling and in the deployment of MEC systems. Full article

Billions of litres of wastewater are produced daily from domestic and industrial areas, and whilst wastewater is often perceived as a problem, it has the potential to be viewed as a rich source for resources and energy. Wastewater contains between four and five times more energy than is required to treat it, and is a potential source of bio-hydrogen—a clean energy vector, a feedstock chemical and a fuel, widely recognised to have a role in the decarbonisation of the future energy system. This paper investigates sustainable, low-energy intensive routes for hydrogen production from wastewater, critically analysing five technologies, namely photo-fermentation, dark fermentation, photocatalysis, microbial photo electrochemical processes and microbial electrolysis cells (MECs). The paper compares key parameters influencing H₂ production yield, such as pH, temperature and reactor design, summarises the state of the art in each area, and highlights the scale-up technical challenges. In addition to H₂ production, these processes can be used for partial wastewater remediation, providing at least 45% reduction in chemical oxygen demand (COD), and are suitable for integration into existing wastewater treatment plants. Key advancements in lab-based research are included, highlighting the potential for each technology to contribute to the development of clean energy. Whilst there have been efforts to scale dark fermentation, electro and photo chemical technologies are still at the early stages of development (Technology Readiness Levels below 4); therefore, pilot plants and demonstrators sited at wastewater treatment facilities are needed to assess commercial viability. As such, a multidisciplinary approach is needed to overcome the current barriers to implementation, integrating expertise in engineering, chemistry and microbiology with the commercial experience of both water and energy sectors. The review concludes by highlighting MECs as a promising technology, due to excellent system modularity, good hydrogen yield (3.6–7.9 L/L/d from synthetic wastewater) and the potential to remove up to 80% COD from influent streams. Full article

This study reviews the available and most commonly used methods of gas deodorization. Comparing various methods of odor removal, undoubtedly biological methods of pollution degradation have an advantage over others—chemical and physical. This advantage is manifestedmainly in ecological and economic terms. The possibility of using biological methods to remove H₂S and NH₃, as the most common emitted by the municipal sector companies, was analyzed in terms of their removal efficiency. The method of bio-purification of air in biotrickling filters is more advantageous than the others, due to the high effectiveness of VOCs and odors degradation, lack of secondary pollutants, and economic aspects—it is a method competitive to the commonly used air purification method in biofilters. Full article

The burgeoning photovoltaics’ (PVs) penetration in the low voltage distribution networks can cause operational bottlenecks if the PV integration exceeds the threshold known as hosting capacity (HC). There has been no common consensus on defining HC, and its numerical value varies depending on the reference used. Therefore, this article compared the HC values of three types of networks in rural, suburban, and urban regions for different HC reference definitions. The comparison was made under balanced and unbalanced PV deployment scenarios and also for two different network loading conditions. A Monte Carlo (MC) simulation approach was utilized to consider the intermittency of PV power and varying loading conditions. The stochastic analysis of the networks was implemented by carrying out a large number of simulation scenarios, which led towards the determination of the maximum amount of PV generation in each network case. Full article

Environmental management in facilities such as wastewater treatment plants (WWTPs) allows for the implementation of the Deming cycle, and thus the constant improvement of the mitigation of the environmental impact. The correct diagnosis of the current state of functioning of the WWTPs, the identification of aspects that may have a measurable impact on the environment, and their assessment are of key importance. The article discusses the possible causes of the impact of WWTPs on the natural environment. Among other problems, such issues as energy consumption, noise and the formation of bioaerosols and odor nuisances were taken into account. Different ways of assessing the impact of wastewater treatment plants on the environment were collated, taking into account the need to assess not only the technological process itself but also the buildings during their use. The results of methods for assessing the environmental impact of wastewater treatment plants in selected countries were also compared. Full article

Electric vehicle (EV) penetration has been increasing globally and is expected to continue its exponential growth over the coming decades. Several countries have already announced plans to achieve total or partial electrification of their vehicle fleets. Such rapid transportation electrification will have a significant impact on society and businesses that support the transportation industry. Additionally, new business opportunities will be available to support this technological evolution. In this paper, the business opportunities emerging from EVs and their supporting infrastructure are reviewed. It has been observed that several businesses, such as sustainable mining and manufacturing, will need to be developed before EV growth as they provide the initial platform required for EV adoption. Other businesses such as fleet optimization, battery management, and recycling can be developed at a later stage. All of these businesses will also have social and technological impacts, which will drive policy decisions. Regional governments play a critical role in ensuring the smooth execution of a transition to transportation electrification through social programs, such as training and education for equitable growth, and legislative decisions, such as technology standardization. Full article

Pollution prevention is an approach for generating less waste using fewer toxic chemicals while conserving water and energy. Even though pollution prevention practices have been encouraged for over thirty years, many smaller businesses have not considered or adopted such techniques. This study examines the effect of a community-based approach designed to emphasize the benefits to the health and economic well-being of urban communities when source reduction practices are implemented by businesses in the community. Partnering with existing community groups in Newark and Jersey City, NJ, technical assistance was provided to small and medium-sized businesses under grant funding from Region 2 of the US Environmental Protection Agency. In this research, 32 small and medium-sized businesses were evaluated for source reduction opportunities and implementation plans were drawn up. After these businesses implemented operational changes, emission and cost savings were determined and reported back to respective small business owners as well as to the communities during community meetings designed to encourage additional participation. Based on 32 case studies, several measurable benefits were achieved, including the yearly saving of 932 pounds of hazardous waste, 3917 pounds of non-hazardous waste, 13.62 metric tons of carbon equivalent (MTCE) of greenhouse gases and $5335 USD. The initial findings suggest that community-based programs such as this can be beneficial but must be sustained over a period of time. One issue that was repeatedly observed, and is likely widely believed, is the concern of small business operators that cooperation with any group funded by a government program may lead to the assessment of fines or penalties for environmental violations. This concern limits the willingness of many smaller businesses to participate. The findings of this study suggest that a sustained community-based program may overcome that concern through demonstration of the benefit to the business and the community, and through credibility building achieved by regular community reporting and the absence of official intervention. Full article

The capability of routing power from one phase to another, interphase power flow (IPPF) control, has the potential to improve power systems efficiency, stability, and operation. To date, existing works on IPPF control focus on unbalanced compensation using three-phase devices. An IPPF model is proposed for capturing the general power flow caused by single-phase elements. The model reveals that the presence of a power quantity in line-to-line single-phase elements causes an IPPF of the opposite quantity; line-to-line reactive power consumption causes real power flow from leading to lagging phase while real power consumption causes reactive power flow from lagging to leading phase. Based on the model, the IPPF control is proposed for line-to-line single-phase power electronic interfaces and static var compensators (SVCs). In addition, the control is also applicable for the line-to-neutral single-phase elements connected at the wye side of delta-wye transformers. Two simulations on a multimicrogrid system and a utility feeder are provided for verification and demonstration. The application of IPPF control allows single-phase elements to route active power between phases, improving system operation and flexibility. A simple IPPF control for active power balancing at the feeder head shows reductions in both voltage unbalances and system losses. Full article

As Earth’s fossil energy resources are limited, there is a growing need for renewable resources such as biodiesel. That is the reason why the social, economic and environmental impacts of biofuels became an important research topic in the last decade. Depleted stocks of crude oil and the significant level of environmental pollution encourage researchers and professionals to seek and find solutions. The study aims to analyze the economic and sustainability issues of biodiesel production by a systematic literature review. During this process, 53 relevant studies were analyzed out of 13,069 identified articles. Every study agrees that there are several concerns about the first-generation technology; however, further generations cannot be price-competitive at this moment due to the immature technology and high production costs. However, there are promising alternatives, such as wastewater-based microalgae with up to 70% oil content, fat, oils and grease (FOG), when production cost is below 799 USD/gallon, and municipal solid waste-volatile fatty acids technology, where the raw material is free. Proper management of the co-products (mainly glycerol) is essential, especially at the currently low petroleum prices (0.29 USD/L), which can only be handled by the biorefineries. Sustainability is sometimes translated as cost efficiency, but the complex interpretation is becoming more common. Common elements of sustainability are environmental and social, as well as economic, issues. Full article

The substitution of fossil resources by renewable alternatives is a major challenge for our society. Kolbe electrolysis converts carboxylic acids to hydrocarbons, which can be used as base chemicals, specialty chemicals, or fuels. Carboxylic acids may be retrieved from biomass or residues and, in consequence, can be a sustainable feedstock. Since the Kolbe electrolysis has only been investigated in lab scale, this work proposes the first basic engineering design study on process development for a continuously working process. Thermophysical data, including solubility and boiling point, are used to gain insight into requirements on process equipment such as separation processes or process parameters such as operating temperature. Furthermore, Aspen Plus was used to retrieve information on acid base equilibria and azeotropes. The process development for three different feedstocks (acetic acid, valeric acid and lauric acid) was performed. The process design shows that most of the process units are rather straightforward and rely on state of the art technologies. The addition of an alkaline catalyst improves the solubility and deprotonation of the carboxylic acid but on the cost of a possibly lower product selectivity. Elevation of the operating temperature above the Krafft point is necessary for long-chain fatty acids. Kolbe electrolysis can be an interesting technology for future production processes based on carboxylic acids and electricity from sustainable sources. Full article