• Energy Research

Abstract Agriculture is one of mankind's most ecologically impactful activities, representing 70% of society's water usage and 13% of greenhouse gas emissions along with direct impacts on ecologies through land usage, habitat destruction and fertilizer runoff. Global population and per capita demand for food are both growing steadily, so it can be expected that agriculture's ecological impacts will continue to escalate rapidly. Intensive farming techniques are needed, not only to increase crop production but also to manage ecological damage. Greenhouse temperature is instrumental in determining crop yields and water usage, while active ventilation has been shown to contribute significantly to evaporative water losses. It follows that passive methods of greenhouse temperature management are crucial to affordable and efficient agriculture, particularly in developing nations. This research uses continuous temperature logging in small experimental greenhouse units to better understand their thermal interaction with the ground and to evaluate possible modifications in terms of their thermal effects. It is found that partial burying of greenhouses is an effective means of temperature stabilization in hot climates. The analysis showed energy savings of up to 13% and water savings up to 8% are possible, with a payback period of less than a month. This demonstrates that partial burying is both environmentally and financially favourable.

A brief idea

Transport emissions account for around a quarter of all CO2 emissions and so, automotive fuels are a key area of research for combating climate change. Widespread adoption of bio-ethanol fuel blends has been the first step in this direction. However, the economic and environmental viability of bio-ethanol usage is hampered by inefficiencies in its production, resulting in a need for significant improvements. The gasoline pre-blending method is a recent advancement that shows great promise in minimizing the separation energy required for bio-ethanol recovery by circumventing full purification and using gasoline’s phase equilibrium properties to eliminate water from a partially purified fermentation product. This paper models all possible gasoline pre-blending processes incorporating ethanol, butanol or both. It is found that butanol is highly suitable for gasoline pre-blending and that high recovery can be achieved even when starting with dilute concentrations. In addition, the presence of even small amounts of butanol is effective at drawing ethanol into the fuel phase, improving the overall alcohol recovery. Energy savings of up to 19% have been shown using a case study while a graphical methodology for preliminary design and synthesis of any gasoline pre-blending process has been developed, allowing for rapid flowsheet development and performance prediction. The authors would like to thank the Institute for the Development of Energy for African Sustainability (IDEAS) and the National Research Foundation of South Africa for providing financial support for carrying out this work. Dr M.J. Fernandez-Torres thanks the visiting researcher programme, at the University of South Africa, for financial support.

This article presents a quantitative model that envisions a greenhouse as a bioreactor converting power station flue gas into biomass. Through the use of this model, power‐generating capacity is correlated with greenhouse growing output and the potential benefits of such a setup are examined in terms of CO2 elimination and water recovery. It is well established in existing literature that elevated CO2 increases greenhouse plant yield by as much as 20% for suitable crop species. Our quantitative model reveals further that suitable flue gas can supply as much as 45% of the water content of plants grown in a greenhouse. Quantitative modeling indicates that for a simple flue gas‐fed greenhouse without separation or storage of flue gas, attached to a gas‐fired power station with a load factor of 35%, each 1 MW of name‐plate power producing capacity corresponds to a greenhouse growing capacity of 3.39 tons per day of plant material, with 1.64 tons per day of CO2 emissions eliminated and 1.34 tons per day of water recovered from the flue gas stream. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 1774–1780, 2018

With over 20 billion gallons of bio-ethanol produced annually, optimization of bio-ethanol production processes is a major priority for sustainability research. Recent research has made great strides toward improving the efficiency of bio-ethanol production through the development of gasoline pre-blending processes which use liquid–liquid phase separation to eliminate excess water with minimal energy input. This paper investigates the effects of process parameters on the performance and efficiency of this class of processes, offering a design basis for engineers developing new processes along with a broader understanding of their potential performance and economic value. Also explored are a range of process modifications capable of improving process performance. It has been found that blending ratio and initial alcohol concentration are the key parameters in determining ethanol recovery, with the number of liquid–liquid contact stages and the temperature also being significant. It has also been shown that temperature-swing decanting can significantly improve alcohol recovery, reducing ethanol losses by as much as 33% in a typical gasoline pre-blending setup.

Abstract Waste tyres are a particularly problematic pollutant; persistent, highly toxic, flammable, and difficult to process or store. However, waste tyres need not be viewed solely as a waste material, as they also offer promising properties as an energy material. Waste tyres have a higher energy density than coal, as well as lower ash content and favourable quantities of carbon and hydrogen. Extensive experimental research has demonstrated that thermochemical valorisation pathways including pyrolysis and gasification are viable for producing valuable chemical products from waste tyre. Despite this, there is as yet no established technology for waste tyre conversion. In this paper, fundamental thermodynamic and economic analysis is used to evaluate a range of process pathways to determine their economic favourability and environmental impact. The process performance targets derived in this way can serve as a basis for preliminary process design and provide estimates for the commodity value of waste tyre, informing long-range planning in both corporate and legislative settings. A range of pyrolysis and gasification pathways have been evaluated in terms of the fundamental thermodynamic metrics of carbon efficiency, atom economy, e-factor and chemical potential efficiency, and also their market-related revenue potential. It was found that pyrolysis pathways perform better in terms of thermodynamic efficiency and carbon footprint than gasification processes, which lose about 45% of the carbon feed to carbon dioxide. However, the gasification routes offer higher potential revenue, yielding as much as $625 per ton of waste tyre as compared to $205 from the pyrolysis route.

Abstract The production and demand for plastic products is set to only increase in the near future, despite efforts to curtail this demand. This increased demand and production comes with an increase in plastic waste, which already sees millions of tonnes discarded into landfills every year. Growing concern over the effects of this waste on the world's ecosystems has led to urgent interest in technologies for chemically converting waste plastic into other products. This manuscript uses process synthesis techniques to analyse and compare the relative performance of two commonly used chemical conversion processes: polyethylene pyrolysis and polyethylene gasification. This analysis technique is unique in that energy forms the basis of the analysis but also allows environmental and economic concerns to be considered simultaneously. It was found that pyrolysis processes are more in line with the goal of a cyclic economy for waste plastic, but that gasification processes can offer higher revenue through the production of alternate chemical products. The potential profits generated from these waste plastic processing strategies was found to be between 50 and 360 USD/ton of polyethylene, demonstrating a high economic value on what is, at present, a waste product.