A comparative environmental life cycle assessment of the combustion of ammonia/methane fuels in a tangential swirl burner

Ammonia has been proposed as a replacement for fossil fuels. Like hydrogen, emissions from the combustion of ammonia are carbon-free. Unlike hydrogen, ammonia is more energy dense, less explosive, and there exists extensive experience in its distribution. However, ammonia has a low flame speed and combustion emits nitrogen oxides. Ammonia is produced via the Haber-Bosch process which consumes large amounts of fossil fuels and requires high temperatures and pressures. A life cycle assessment to determine potential environmental advantages and disadvantages of using ammonia is necessary. In this work, emissions data from experiments with generating heat from tangential swirl burners using ammonia cofired with methane employing currently available technologies were utilized to estimate the environmental impacts that may be expected. Seven ammonia sources were combined with two methane sources to create 14 scenarios. The impacts from these 14 scenarios were compared to those expected from using pure methane. The results show that using ammonia from present-day commercial production methods will result in worse global warming potentials than using methane to generate the same amount of heat. Only two scenarios, methane from biogas combined with ammonia from hydrogen from electricity and nuclear power via electrolysis and subsequent ammonia synthesis using nitrogen from the air, showed reductions in global warming potential. Subsequent analysis of other environmental impacts for these two scenarios showed potentially lower impacts for respiratory organics, terrestrial acidification-nutrification and aquatic acidification depending on how the burner is operated. The other eight environmental impacts were worse than the methane scenario because of activities intrinsic to the generation of electricity via wind power and nuclear fission. The results show that generating heat from a tangential swirl burner using ammonia currently available technologies will not necessarily result in improved environmental benefits in all categories. Improvements in renewable energy technologies could change these results positively. Other means of producing ammonia and improved means of converting ammonia to energy must continue to be explored

An overview on convergence acceleration of cyclic adsorption processes

Cyclic adsorption processes are inherently dynamic where the process variables are always varying with time. The cyclic processes have no steady state. Thousands of repeated cycles may be needed before cyclic steady state (CSS) is reached. In this paper, the basic concept and characteristics of cyclic adsorption processes are first introduced, using air separation by rapid pressure swing adsorption as an example. Next, different approaches to calculate and accelerate the convergence of CSS are briefly reviewed. The computational time can be reduced by having an efficient discretisation technique and accelerators to achieve the final CSS. Hybrid methods are potentially attractive

Hybrid algorithm for acceleration of convergence to cyclic steady state

Cyclic process is inherently dynamic, thus it has no steady state. However, the process, after a sufficient number of cycles, will reach a state called Cyclic Steady State (CSS) where the process state variables at some instant within a cycle have the same value at the corresponding instant within each subsequent cycle. Depending on the nature of the cyclic process, the number of cycles needed before the process reaches CSS may vary from tens to thousands. In this study, a hybrid algorithm that aims to predict and accelerate the convergence of the CSS is developed and tested on a cyclic operation of controlled-cycled stirred tank reactor

Preparing for Shortages of Future COVID-19 Drugs: A Data-Based Model for Optimal Allocation

Drugs for the treatment of Covid-19 are currently beign tested, and those that are apporved for use are likely to be in short supply due to the global scale of the pandemic. This policy brief proposes a model for optimally allocating future Covid-19 drugs to patients to minimize deaths under conditions of resource scarcity. A linear programming model is developed that estimates the potential number of deaths that may result from Covid-19 under two scenarios: with antivirals and without antivirals. It takes into account patient risk level, the severity of their symptoms, resource availability in hospitals (i.e. hospital beds, critical care units, ventilators), observed mortality rates, and share of the Philippine population. Based on simulations, the model can make actionable recommendations on how to prioritize the allocation of the drugs

Phosphorus recovery from wastewater and sludge

Wastewater and sludge are potential resource of phosphorus (P) for fertilizer production. One method of recovering phosphorus is via chemical precipitation. In the study, phosphorus was recovered from wastewater and sludge. First, hydrolysis was carried out to release the phosphorus in the sludge by the addition of 1.0M acid (sulfuric acid) or base (sodium hydroxide) solution mixed for three hours at 200 rpm. The hydrolyzed sludge was filtered, and the pH of the solution was adjusted to 9.0. Precipitation for both wastewater and hydrolyzed sludge solution was carried out using magnesium chloride hexahydrate (MgCl2•6H2O) and ammonium chloride (NH4Cl). The mixture was stirred for an hour for crystallization. Precipitates were allowed to settle for 24 hours before it was filtered and dried in an oven at 55-58oC for 24 hours. The dried sample was grinded and characterized using Fourier transform infrared spectroscopy (FTIR), x-ray fluorenscence (XRF), and scanning electron microscope with energy-dispersive x-ray spectroscopy(SEM-EDX)

Is nitrogen fixation (once again) “vital to the progress of civilized humanity”?

The world food supply has become dependent on synthetic fertilizer from ammonia, which comes from the Haber–Bosch process. This process consumes large amounts of fossil fuels and releases large amounts of greenhouse gases. The excessive use of synthetic fixed nitrogen fertilizers has led to severe environmental effects, but fixed nitrogen is essential to the sustainability of biofuels. Nitrogen fertilizers are also required for biotic carbon capture schemes like bioenergy with carbon capture and storage (BECCS), afforestation, and soil carbon sequestration. Ammonia has been proposed as a non-carbon emitting alternative fuel that has many advantages over hydrogen. Organic agriculture and nitrogen recovery from waste streams may only partially reduce the demand for synthetic fixed nitrogen. Social solutions like population stabilization may be the best solution for the food supply problem, but ammonia is an enabling technology for alternative fuels and carbon sequestration. Alternative processes for nitrogen fixation are very early in development. This paper offers the viewpoint that alternative means of nitrogen fixation and the wise use of fixed nitrogen need to be developed quickly.© Springer-Verlag Berlin Heidelberg 2014

Effect of reactor heat capacity on the stability and start-up time of a diabatic controlled-cycled stirred tank reactor

A simple model was written to simulate a first-order exothermic reaction taking place in a diabatic controlled-cycled stirred tank reactor (CCTR) in which the reactor jacket heat capacity is not infinitely larger than the reacting fluid heat capacity. The simulations have shown tpthat including the reactor heat capacity in the model tends to stabilize oscillatory states to a unique steady state. A further result is that a smaller reactor heat capacity results in a shorter transition time to the final steady state. The study shows the possibility that reactor stability and short start-up times may be achieved by simple changes in the reactor design rather than through complex control systems. Copyright © Taylor & Francis Inc

Life cycle analysis of an alternative to the haber-bosch process: Non-renewable energy usage and global warming potential of liquid ammonia from cyanobacteria

The production of ammonia via the Haber-Bosch process consumes large amounts of fossil fuels and releases large amounts of greenhouse gases. Ammonia has many important applications including fertilizer for crops and for microalgae-derived biofuel systems. Aquatic cyanobacteria fix nitrogen from the air and have been mass-cultured for many uses. This study analyzes, on a life cycle basis, a process to culture the cyanobacterium, Anabaena sp. ATCC 33047, in open ponds; harvest the biomass and exopolysaccharides and convert these to biogas; strip and convert the ammonia from the biogas residue to ammonium sulfate; dry the ammonium sulfate solution to ammonium sulfate crystals; transport the ammonium sulfate and convert it to liquid ammonia and concentrated sulfuric acid. When compared to the ammonia produced via the Haber-Bosch process, savings of about 1.0 × 105 MJ of non-renewable energy and 3100 kg CO2 equivalent of global warming potential per 1000 kg of liquid ammonia might be possible. The results are robust and are not sensitive to the model parameters. The proposed system, if implemented, might have a significant impact on many important global issues such as global warming, fossil fuel depletion, and food security. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 618-624, 2014 © 2013 American Institute of Chemical Engineers Environ Prog