Optimization of a Leaching Tank for Hydrometallurgical Recovery of Metals

The sludge wastes generated by the metal plating industries are classified as hazardous wastes because of their high concentration of heavy metals. Amongst the various routes for their treatment, the hydrometallurgical processes are highly attractive because they can be tailored to the wide compositional range of such wastes and assure its metals recovery and/or toxicity reduction. In these processes the leaching operation is paramount to the overall efficiency. In this, the mixing of the leaching solution with sludge has to be effective in order to obtain high levels of metal extraction and make the process attractive. Most of the available data refers to laboratory tests. This paper reports on the use of CFD model to optimize the operation of a pilot size leaching tank. The results regarding the velocity field were compared with experimental data and proved that such techniques can be effectively applied to improve the process. A leaching experiment, with the best configuration for the mixing, yielded a high metal extraction, suggesting that this technique can be successfully implemented for the treatment of such wastes.

Investigation of the Feasibility and Feedstock Management Strategies of a Flexible Biomass to Ethanol Plant via Process Simulation

Current US transportation sector mainly relies on liquid hydrocarbon derived from petroleum oil and about 60% of the petroleum oil consumed is from areas where supply may be disturbed by regional instability. This has led to serious concerns on global warming and energy security. To address these issues, numerous alternative energy carriers have been proposed. Among them, second generation biofuel is one of the most promising technologies. Gasification based thermo-chemical conversion can utilize a wide range of biomass wastes and residues and bring flexibility to both feedstock and production sides of a plant, thus presents an attractive technical route. In this paper, a flexible feedstock thermo-chemical ethanol production process is investigated. This research focuses mainly on the evaluation of the feasibility of the process through numerical simulation. An existing thermo-chemical ethanol production model developed by NREL has been updated to handle the cases when different biomass feedstock and feedstock combinations are used. It is found that the ethanol yield is positively proportional to the feedstock feeding rate, while the total conversion efficiency is negatively proportional to the feeding rate. To demonstrate a feedstock management strategy, a plant located near a major city with a population of 200,000 and above is considered and MSW, legume straw and wood chips are selected as potential feedstock. Simulation results indicate that with wood chips as the backup feedstock the plant can be operated under extreme conditions when legume straw availability is significantly reduced without major equipment modification.

Production of Synthetic Petroleum Fuel Through the Absorption of Atmospheric CO2

This paper describes a theoretical device called a Petroleum Synthesizer, which absorbs the greenhouse gas carbon dioxide from the atmosphere and converts it into a synthetic petroleum fuel. The device has four parts: First, a CO2 Scrubber using sodium carbonate reversibly absorbs CO2 from the atmosphere. Simultaneously, a Hydrogen Generator separates water electrolytically to produce hydrogen (H2). Third, a Carbon Monoxide Generator mixes the H2 and the CO2 over a nickel catalyst, changing the constituents into carbon monoxide (CO) and water. Finally, the CO and additional H2 are combined in a cobalt-catalyst Fischer-Tropsch (F-T) Processor to produce gaseous and liquid petroleum products. Calculations show that one watt of electricity supplied for one year would allow the Synthesizer to create 0.420 kg of petroleum products, and absorb 1.314 kg of CO2 from the atmosphere. An acre of solar voltaic panels powering Synthesizers could produce 46,000 kg, or about 14,000 gallons, of petroleum products per acre per year, and absorb 140,000 kg of CO2. By contrast, an acre of corn produces less than 400 gallons of ethanol per year.

Experimental Simulation of Solar Flash Desalination

Experimental simulations of a sustainable desalination process have been carried out using a small pilot unit at different operating conditions to enhance process analysis and modeling. The proposed desalination process, which employs solar heating and creates vacuum in an innovative passive way, has been theoretically simulated in earlier work. It entails flowing seawater through a condenser to preheat it then through a heater before flashing it in a vacuumed evaporator connected to the condenser where the flashed hot vapor is condensed by the incoming cold seawater forming fresh water. Flashing seawater at higher temperatures increases the vaporization and the production rate of fresh water. In addition, the accumulating non-condensable gases that are slowly eroding the vacuum will decrease the overall vaporization with time which reduces the production rate of fresh water.

H2S and CO2 Filtration of Biogas Used in Internal Combustion Engines for Power Generation

Currently, there is an increasing interest in connecting thousands of small electrical plants powered by renewable energy sources to national electrical grids. The use of biogas as fuel for internal combustion engines connected to an electric generator is emerging as one of the most attractive alternatives because of its very low cost benefit ratio and very high positive impact on the environment. However, the use of biogas to generate electricity has been limited by its high content of H2S (1800–3500 ppm) and CO2 (∼40%). CO2 presence reduces the energetic density of the fuel and therefore the power output of the system. The high content of H2S corrodes important components of the engine like the combustion chamber, bronze gears and the exhaust system. This work aims to design and manufacture a low-cost industrial filter for this application. Among the different available methodologies, CaO, NaOH and amines where selected as the most appropriate for a typical farm application of 100 kW electric generations. Since there is not reported data for the H2S absorbing capacity of these substances, it was proposed to measure it by means of a bubbler. It is an experimental set up where the gas stream passes through a fixed amount of the absorbing substance until it becomes saturated. The absorbing capacity is determined as the amount of substance being trapped divided by the mass of the absorbing substance being used. Results showed an absorbing capacity of 2.8, 41.4 and 124.8 g of H2S per Kg of NaOH, CaO and monoethanolamine respectively. A gas absorbing system of amines was designed and manufactured for H2S and CO2 biogas filtration. Three different types of amines were evaluated: Monoethanolamine, Diethanolamine, and methyldiethanolamine. Results show that all the amines require a ratio of amines to biogas flow of 0.7 to obtain a 95% of H2S filtering efficiency. This data represent only a 30% of H2S mass transfer efficiency of the filter when it is compared against the mass transfer expected under quasi equilibrium conditions. Work is under way to design a high efficiency amine column for biogas treatment.

Effect of a Permanent Magnet on CHS (Compost Heating System)

Effect of a permanent magnet on ventilation of an air duct through compost have been investigated numerically. Some compost yield heat over 60 Celsius in fermentation process. That exothermic reaction produces a considerable amount of heat, which could be a potential heating source. Fermentation reaction requires ventilation, abundant supply of paramagnetic oxygen gas and exhaust of metabolized diamagnetic carbon dioxide gas. Continuous and forced air supply is more efficient rather than the conventional manual turn or stirring as ventilation means. In magneto-fluid-dynamics, the magnetizing force acting on a paramagnetic oxygen gas is applied for the enhancement of air flow, heat and mass transfer. In this research, the enhancement of the air flow of various size air ducts have been numerically investigated by applying a permanent magnet on an air duct. Numerical results shows that a permanent magnet enhances the air flow. The application of a permanent magnet to an air duct is useful for CHS, a promising alternative energy system.

Hydrothermal Conversion of Cattle Manure to Biooil: Biooil Definitions

A number of researchers have reported that biooil was produced through hydrothermal conversion of different types of biomass. However, it is difficult to evaluate and compare these biooils in terms of yields and chemical properties. They applied different organic solvents to extract biooil from products after hydrothermal conversion of biomass. The purpose of this study is to assess the impact of extraction solvents on the quantity and chemical structure of biooil. Cattle manure was used as one type of biomass feedstock for biooil production. And dichloromethane (CH2Cl2), chloroform (CHCl3) and diethyl ether (C4H10O) were used for biooil extraction. Results showed that extraction solvents influenced biooil yields. The highest biooil yield of 48.78 wt% of volatile content of cattle manure was obtained when using CH2Cl2 solvent. The main components of biooil extracted by CH2Cl2 and CHCl3 were ketones and carboxylic acids, while those extracted by C4H10O were aromatic chemicals. In terms of elemental compositions and high heating values of biooil, no statistically apparent differences were caused by different solvents. The mean elemental compositions (by weight) of biooils were carbon of 73.79%, hydrogen of 8.18%, nitrogen of 4.38% and oxygen of 13.65%. And the mean high heating value of biooil was 36.74 MJ/kg.

Use of Thermodynamics, Engineering Economics and Probabilistic Risk Assessment in Evaluating Climate Change Decisions

Climate change is often considered in terms of its macroscale implications. For example, many governments and non-governmental organizations are engaged in the development of policy frameworks that could influence different societal actions and behavioral scenarios. But such macroscale policy decisions may also significantly impact the localized design of products and services in different business ecosystems. Unfortunately, products and services are generally designed only taking into account local influences. An approach that ties macroscale frameworks to localized product- or system-level design metrics is lacking. For example, the cost of upgrading the entire U.S. electrical system has been estimated to be on the order of $200 billion, and recent U.S. policy discussions in the area outline options such as “smart” grid upgrades, distributed and/or on-site renewable energy systems including solar and wind energy, infrastructural support for plug-in of electric and hybrid vehicles etc. But most existing electricity generation and thermal performance models of power generating stations or cogeneration plants fail to provide any indication of the environmental impacts associated with distributing electricity from generator to point-of-use. It is thus not intuitive how the direction of localized plant or system design should be altered given the different macro-level initiatives. This paper attempts to fill this gap by exploring a methodology that combines engineering economics, probabilistic risk assessment, and thermodynamic (2nd Law) analysis to evaluate different policy choices. Specifically, a framework that could allow quick estimation of the comparative consumption, operational power requirements, relative thermal performance and environmental footprint associated with different proposals on upgrading the grid is developed. The approach is demonstrated in the context of a representative segment of a hypothetical electrical grid distribution system located between two electric power generating stations (EPGS) facing overload as additional customer demands are projected to be integrated with renewable sources in the near-term future.

Energy Analysis of Single Effect Thermal Vapor Compression Desalination Process Based on Pressure Exchange Phenomenon

A closed loop single effect thermal vapor compression desalination process is simulated based on pressure exchange phenomenon. Here the conventional ejector is replaced by a compressor-turbine device, where the high energy primary fluid expands over the turbine that drives the compressor through an ideal drive shaft. The compressor in turn compresses the low energy secondary fluid. Both the fluids are discharged at a constant pressure in a common mixing chamber where they undergo adiabatic mixing and then are discharged at an intermediate energy level. The functionality of the compressor-turbine device is similar to that of an ejector, hence this is also known as the turbomachinery analog of an ejector. The medium of energy transfer between the two fluids in case of compressor-expander device is pressure exchange. Energy analysis of the model is performed under various operating conditions. Key functional parameter like the boiling temperature, compression ratio, compressor-expander efficiencies and primary pressure are varied and its effect on the energy consumption per unit of distillate produced is examined. The system performance is evaluated based on the standard factors that affect the cost of the distillate like, thermal performance ratio, energy performance ratio and specific flow rate of cooling water. The model takes into consideration the inlet seawater conditions and its fouling effects as well as the use of superheated primary steam and its effects on performance of the system. With increase in the analog efficiency the energy consumption and thermal performance ratio improves steadily, where as it is observed that the flow rate of the distillate produced decreases. Initial results have shown performance ratios as high as 5.5 for ideal conditions at low primary pressures and low boiling temperature.

Economical Optimization of Integrated Cooling Tower by Solar Energy

Nowadays, the visible impact of releases to the ambient has become a matter of greater concern due to the awareness of environmental degradation and protection among the society. Therefore, the contribution of renewable energies as the free and clean sources can provide environment-friendly solutions. However, little attention has been paid to the practical applications of the renewables. Cooling towers are widely used in industries and commercial buildings to dissipate waste heat to the ambient environment. During unfavorable weather conditions, the exhaust of the wet cooling tower remixes with the cooler ambient air and as it cools down the excess moisture condenses in small fog droplets, creating visible plume. The generated plume sometime can extend up to few hundred meters and causes invisibility and darkness problem. In this study, solar energy is integrated into wet cooling tower to reduce the visible plume formation. In this method, optimum solar system is achieved taking into consideration the economical analysis. Also, the operational conditions of cooling tower at various environmental states have been incorporated in targeting the optimum solar system through different scenarios. Related coding in MATLAB version 7.1 is developed for computations.