• Energy Research

Globally, buildings are responsible for 40% of the total world annual energy consumption which is responsible for one-third of green house gas emissions around the world. A significant portion of this energy is used for lighting, heating, cooling, and air conditioning purposes in buildings. Increasing awareness of the environmental impact of green house gas emissions and CFCs triggered a renewed interest in environmentally friendly cooling, and heating technologies for buildings. Free cooling of buildings may be seen as an alternate to compressor based air conditioning systems used for the buildings. In free cooling, nighttime cold is accumulated in storage material and extracted when needed. Latent heat storage using phase change materials (PCMs) can be used for free-cooling purposes due to their high storage density. In free cooling, using PCM as storage material, cool air during night is used to solidify the PCM and the accumulated cold is extracted during the hot day times. In this article a detailed review of work conducted by different researchers on PCM based free cooling is presented. Major challenges being faced in the design of PCM based free cooling system such as phase change materials; their thermo-physical properties and the geometry of encapsulation are elaborated and discussed in detail. Also the parameters effecting the charging and discharging of PCM, effect of phase change temperature and climatic conditions on thermal performance of the free cooling system are also discussed. Potential reduction in CO2 emissions due to the applicability of free cooling systems in residential and commercial buildings is also discussed in this article. This paper also provides a comprehensive list of the PCMs currently being used and that can be used potentially for free cooling applications. At last, this paper also presents some current problems needed further research in this area.

Abstract Biomass gasification integrated with Solid Oxide Fuel Cells (SOFCs) offers a tremendous opportunity to generate highly efficient power in sustainable and environmental friendly manner. The comprehensive survey of the up-to-date literature on the influence of producer gas contaminants (particulates, alkali metals, tar, H2S and HCl) on SOFC anodes presented in this review reveals that state-of-the-art Ni/YSZ anodes are less tolerant to the contaminants and more stringent cleaning is required for them as compared to Ni/GDC anodes, while other anodes have been scarcely studied. The most striking finding is that Ni/GDC anodes seem to be rather more tolerant to the contaminants as recently understood. This remarkable opportunity needs to be further explored via detailed experiments which would lead to design the economically viable gas cleaning systems. The available gas cleaning technologies are also analysed and the most suitable cleaning options for each of the contaminant are suggested.

Abstract Tar is the main impurity derived from biomass gasification which causes environmental hazards as well as technical problems in advanced power generation applications. Removal of tar to acceptable tolerance limits for Internal Combustion (IC) engines and fuel cells is one of the major limitations and considered the main obstacle to the wide commercial power generation using biomass producer gas. If tar is not removed to the required levels, it will condense at low temperatures and result in clogging and fouling of engines. Even though physical tar removal at low temperatures has been performing effectively with the technical and economical point of view, there is still need to explore new and more efficient tar removal techniques. In this work, compression of producer gas in a compressor is introduced as a tar cleaning mechanism of biomass tar. Compressor was exposed to low tar levels in the range of 138–312 ± 31 mg Nm−3 after the cooling and pre-cleaning system. The results demonstrate the effectiveness of the compression process in reducing tar by 84.4± 1.2% and 83± 1.1% when compressed to 0.8 MPag and 0.2 MPag respectively at ambient temperature. The blue colour flare after the compression indicates the clean producer gas from tar and corresponds to the total tar levels around and below 30 mg Nm−3 with negligible particulates in the producer gas as compared to the orange flare before the compression. It was found that tar condenses inside the compressor receiver tank. A mechanism explaining the condensation of tar in the compression process is proposed.

Abstract Gasketed plate heat exchangers (PHXs) are frequently used as preheaters in thermal water desalination systems to preheat the intake seawater by recovering heat from the brine and distillate streams. The detailed design and analysis of PHXs as a preheater is not available in the desalination related studies. Rather, the heat transfer coefficients are calculated by simple empirical equations. The current study provides a comprehensive design procedure and analysis of these preheaters. In this regard, a numerical model is developed to investigate the thermal–hydraulic performance of PHXs under various operating conditions. First, the code is validated against the experimental data and then the effect of input parameters is studied. The results show that the feed flow rate and plate chevron angle are very important parameters for the heat transfer coefficient and pressure drop in PHXs. It is shown that the salinity does not affect the HX performance; however, the study also showed that the selection of fouling resistance is critical and it considerably disturbs the design parameters that govern the heat exchanger cost. Finally, the sensitivity analysis is presented to identify the most sensitive input parameters for the thermal–hydraulic performance of the heat exchanger.

Utilisation of solar energy and the night ambient (cool) temperatures are the passive ways of heating and cooling of buildings. Intermittent and time-dependent nature of these sources makes thermal energy storage vital for efficient and continuous operation of these heating and cooling techniques. Latent heat thermal energy storage by phase-change materials (PCMs) is preferred over other storage techniques due to its high-energy storage density and isothermal storage process. The current study was aimed to evaluate the performance of the air-based PCM storage unit utilising solar energy and cool ambient night temperatures for comfort heating and cooling of a building in dry-cold and dry-hot climates. The performance of the studied PCM storage unit was maximised when the melting point of the PCM was ∼29°C in summer and 21°C during winter season. The appropriate melting point was ∼27.5°C for all-the-year-round performance. At lower melting points than 27.5°C, declination in the cooling capacity of the storage unit was more profound as compared to the improvement in the heating capacity. Also, it was concluded that the melting point of the PCM that provided maximum cooling during summer season could be used for winter heating also but not vice versa.

Abstract The combination of biomass gasification with fuel cells, especially high temperature Solid Oxide Fuel Cells (SOFCs) promises sustainable and highly efficient (decentralized and modular) energy conversion systems. This review encompasses the components of biomass integrated gasification–SOFC technology including biomass characteristics, the thermochemical conversion in gasifiers and the factors affecting the gasification process, the cleaning technologies for raw producer gas and its conditioning and finally the integration of gasifier with SOFCs. The influence of impurities present in biomass producer gas such as particulates, tar, H 2 S, HCl and alkali compounds based on recent experimental studies and their tolerance limits towards SOFCs are presented. Even though analysis based on the probable tolerance limits of impurities towards SOFCs and a comprehensive overview of the cleaning technologies for producer gas impurities indicate that producer gas cleaning at various temperatures using current technologies to meet SOFC requirements is possible, more experimental studies are still needed to acquire the detailed information on the tolerance limits of impurities for SOFCs. The recent theoretical modeling and experimental studies of biomass integrated gasification–SOFC systems are also presented.

Abstract Pakistan is facing a severe electricity shortfall due to rapidly growing demand leading to 8–12 h d−1 power outages in rural areas in summer. Predominant use of imported fossil fuels for electricity generation is exerting a huge burden on the economy and causing immense damage to the environment in the form of GHG emissions. One of the best energy sources in terms of economy and emissions is biomass waste which is abundantly available in Pakistan in the forms of animal manure, poultry waste, sugarcane bagasse and kitchen waste. This paper critically analyses the potential of these largely underutilized biomass waste resources for biogas production as a Waste-to-Energy technology to overcome Pakistan's power crisis. Potential biogas production from each resource and its subsequent utilization in power generation is calculated for Bahawalpur (a division of Pakistan) as a case study and for the whole country Pakistan as well. Remarkable results come out to be 11.65 M m3 d−1 of biogas production potential which can generate 3059.7 GWh y−1 electricity for Bahawalpur division alone. The results for the whole Pakistan are 226.8 M m3 d−1 of biogas production potential and corresponding electricity generation of 59,536 GWh y−1 which accounts to be 49.4% of the total power generation for the year 2018. The most striking finding is that power generation from biogas will be enough to eliminate Pakistan’s power shortfall. There is a possible market of 12.9 B USD y-1 corresponding to total bio-fertilizer generation of 340,800 kt y-1 from anaerobic digestion (AD). Findings of this paper present the government of Pakistan a critical consideration of widespread use of biogas technology in future and draft a proper Waste-to-Energy policy accordingly. The conclusion is that the biogas production and its subsequent use in electricity generation from biomass waste is the sustainable and eco-friendly renewable energy source which could resolve power crises and environmental and waste management issues in Pakistan. Biogas as a source of energy can be an important component for sustainability transition in Pakistan. This study could be a good reference for other developing countries too.

Homogeneous charge compression ignition (HCCI) is considered an advanced combustion method for internal combustion engines that offers simultaneous reductions in oxides of nitrogen (NOx) emissions and increased fuel efficiency. The present study examines the influence of intake air temperature (IAT) and premixed diesel fuel on fuel self-ignition characteristics in a light-duty compression ignition engine. Partial HCCI was achieved by port injection of the diesel fuel through air-assisted injection while sustaining direct diesel fuel injection into the cylinder for initiating combustion. The self-ignition of diesel fuel under such a set-up was studied with variations in premixed ratios (0–0.60) and inlet temperatures (40–100 °C) under a constant 1600 rpm engine speed with 20 Nm load. Variations in performance, emissions and combustion characteristics with premixed fuel and inlet air heating were analysed in comparison with those recorded without. Heat release rate profiles determined from recorded in-cylinder pressure depicted evident multiple-stage ignitions (up to three-stage ignition in several cases) in this study. Compared with the premixed ratio, the inlet air temperature had a greater effect on low-temperature reaction and HCCI combustion timing. Nonetheless, an increase in the premixed ratio was found to be influential in reducing nitric oxides emissions.