Supervisory control for conventional unitary air conditioning system

The Supervisory control for conventional unitary air conditioning system is conceptually designed based on Programmable Logic Control (PLC) system. The advantage of PLC system is that it allows online monitoring continually and updates or modification can be performed interactively. This supervisory mode is applied to the conventional unitary air conditioner to avoid the frequent interruption or adjustment of the fan speed or temperature set point by users normal practice which has contributed to the surge of energy consumption due to the frequent on/off of the compressor. Three experiments have been performed at different control methods to simulate user’s daily practice. The first control method is the Variable Set point with high speed fan, the second control method is the Fixed Set point with high speed fan and the third control method is a Supervisory Control; a fixed set point with variable fan speed. The experiments have been conducted for eight (8) hours and the statistic data of accumulated energy consumption based on one unitary air conditioner with capacity of 1 Horse Power are acquired and sampled at the time interval of 30 minutes for the analysis. From these experiments, the supervisory control has consumed 4.2 kWh per day which is 82.35% compared to normal consumption of 5.1 kWh. This result translated into 0.9 kWh or 17.65% of total energy saving per day. The consistency of the air compressor operation in this control method has become a major factor in achieving indoor temperature steadiness whilst improving the energy savings

Properties of Activated Carbon Prepared from Coconut Shells in Ghana

Activated carbons have applications in various industrial processes in Ghana including purification of water and gold adsorption from gold solutions. Materials commonly used for preparation of activated carbons include coal and coconut shells. Ghana generates over 30,000 tonnes of coconut shells annually from coconut oil processing activities but apart from a small percentage of the shells, which is burned as fuel, the remaining is usually dumped as waste. To increase recycling and utilisation of the coconut shells, activated carbons were prepared from the shells by carbonisation of the shells at 900oC in an inert atmosphere of nitrogen, followed by steam activation of the resulting char also at 900oC activation temperature and various durations of activation. The adsorptive properties determined for the resulting Coconut Shell Activated Carbons (CSAC) fell within the values of the reference commercial activated carbon (Norit RO 3515) commonly used by most Ghanaian mining companies. For example, the specific surface area of the CSAC reached a maximum value of 795 m2/g after 3.5 hours of activation: well within the range of 780-812 m2/g obtained for Norit RO 3515. Also, the maximum total pore and micropore volumes developed in the CSAC were 0.42 cm3/g and 0.38 cm3/g respectively compared to 0.44 and 0.39 for the Norit RO 3515

Combustible gaseous products from pyrolysis of combustible fractions of municipal solid waste

Municipal Solid Waste (MSW) sample was pyrolysed under inert atmosphere of nitrogen in a static bed pyrolysis reactor, heated at a controlled rate of 10°C min-1 to a final temperature of 700°C to recover combustible gaseous product. The yield of the combustible gaseous product was 23.01 wt%. Other pyrolysis products were 32.00 wt% char and 44.99 wt% oil. The combustible gaseous product evolved, analysed off line by gas chromatography to contain mainly CO2, CO, H2, CH4, C2H6 and C3H8 has relatively high calorific value of 18.0 MJ m-3, making the gas suitable for use as a fuel. The significance of this research is that the pyrolysis recovered combustible gas can now be stored conveniently and easily transported for various applications. This research, in addition to providing energy needs if implemented, has the capacity to stimulate regular collection of MSW to feed a pyrolysis plant thereby reducing accumulation of the waste in communities, especially in developing countries

Tillage and Fertilizer Effects on Maize Production in Northern Guinea Savanna of Ghana

Maize (Zea mays L.) is a major food crop in Ghana but grain yield is often constrained by low soil fertility and water deficits during grain fill. Response of maize to tillage and fertilizer treatments was evaluated in a field experiment from 2000 through 2002 on a sandy loam soil (Typic-plinthic Paleustalf) in Wa in the northern Guinea savanna of Ghana Tied-ridging at 4wk after planting on the flat was compared with planting on a flat soil surface without ridging and with a traditional ridging practice 4 wk after planting on the flat in combination with four fertilizer treatments (F1 = no fertilizer; F2 = 45-19-19; F3 = 64-38-38 and F4 = 90-38-38) as kg N, P O and K O ha-1. Tillage-induced differences in maize growth and yield were not 2 5 2 significant in any season. Over the years fertilizer increased maize growth and yield but this was independent of the tillage treatment. Mean grain yields with the F2, F3 and F4 treatments were 208-234, 304-413 and 391-567% greater than with no fertilizer treatment, respectively. Mean stover yield was 74-85, 147-158 and 131-141% greater respectively, with F2, F3 and F4 than with no fertilizer treatment. Economic analyses showed that the marginal rate of return in applying fertilizer ranged from 97 to 107%. The MRR for F3 was greater than that of F4 but F4 had greater net returns Further studies may be needed to establish appropriate time of tied-ridging and optimum fertilizer level for maize in the Guinea savanna of Ghana.Keywords: Maize, fertilizer, tied-ridging, savanna zone, net returns

Removal of Fluoride in Water Using Activated Carbons Prepared From Selected Agricultural Waste Materials

Water is essential to life, but many people do not have access to clean and safe drinking water and many die of water borne or water related infections. Fluoride is one of the anionic contaminants which are found in excess in both surface and groundwater due to geochemical reactions and anthropogenic sources like industrial wastewater disposal. Many methods like coagulation, precipitation, membrane processes, electrolytic treatment and ion – exchange are some of the methods used for the defluoridation of water. But the most widely used method is the adsorption process. Though various conventional and non-conventional adsorbents have been assessed for the removal of fluoride from water, this research aims to promote innovative use of local raw materials and relatively low cost techniques in the production of activated carbons for fluoride adsorption. Activated carbons were prepared from coconut shells, cocoa pod husks and palm kernel shells by carbonisation of the residues to obtain chars which were activated at 900 o C using steam as the activating agent. Analysis of fluoride was done before and after treating water with the derived activated carbons. The water treatment experiment using fluoride as a model pollutant demonstrated that activated carbons prepared from agricultural waste materials have a good potential for fluoride removal. Adsorption of fluoride was also found to be influenced by the type and concentration of other ions in the treated water. Keywords: fluoride, adsorption, carbons, waste, pH, ions, fluorosis, Langmuir isotherms

Treatment of Iron Tailings at the Forecariah Guinea Mine - Guinea Conakry

Forecariah Guinea Mine SA (FGMSA) in Guinea - Conakry mines and processes Iron ore. About 0.5 Mt of tailings material has already been generated with additional 4000 tons generated daily. This paper presents a re-treatment technology for the Iron tailings obtained from the processing plant of FGMSA. Metallurgical tests were carried out on the tailings to determine which process route gives the most satisfactory result in terms of recovery and cost. Two representative samples (FCOPD-01 and FCDOP-02), taking from the tailings, were investigated. Particle Size Distribution (PSD) and chemical composition of various size fractions of representative samples of the tailings were performed. Dense Medium Separation (DMS) and Magnetic Separation (WHIMS) were also performed on a number of size fractions. The initial chemical composition of the various size fractions shows that the highest Fe grades were present in the +1 mm fractions at 58.8% and 58.6% for FCOPD-01 and FCOPD-02 respectively. The PSD of the tailings also indicated a mass yield of 77.9% for the +1 mm fraction and 22.1% for the -1 mm fraction. Contaminant Oxides, such as Al2O3 and SiO2 tend to be higher in the finer size fractions (-1 mm) of both samples. Result from the DMS analysis performed on the (-4 +0.5) mm fraction shows an underflow mass yields of 45.98% with Fe grade of 65.55% and overflow mass yield of 53.08% with Fe grade of just 13.5%. Magnetic separation (WHIMS) results on the (-4 +0.5) mm samples also gave varied mass yield and Fe grade at different magnetic intensities (3000 Gauss, 6000 Gauss and 10,000 Gauss). However, the highest Fe mass yield and grade produced from the magnetic separation were 18.10% and 50.8% respectively. The results show that DMS technique has the potential to re-treat the tailings at FGMSA. Keywords: Treatment, Iron ore, Tailings, Magnetic separation, Dense Medium Separatio

Sorption of Heavy Metals from Mine Wastewater by Activated Carbons Prepared from Coconut Husk

A study on sorption of heavy metal ions: Lead (Pb2+), Copper (Cu2+) and Cadmium (Cd2+) from mine wastewater by activated carbons prepared from coconut husk was conducted.  The activated carbons were prepared by carbonisation of the husk at 900 ºC pyrolysis temperature, followed by steam activation of the pyrolysis derived char. Activation was also performed at 900 ºC for various durations at steam addition rate of 0.2 mol/h/g in a Gas Fired Static Bed Pyrolysis-Activation Reactor. The derived activated carbons were contacted with mine wastewater containing heavy metal ions to assess their heavy metal ions adsorption potential. The results show that the activated carbons efficiently adsorbed the heavy metal ions from solution, reducing concentrations of  Pb2+, Cu2+ and Cd2+ from 1.56 mg/L, 1.87 mg/L and 0.69 mg/L respectively to below Ghana Environmental Protection Agency (GEPA) standards of  0.10 mg/L, 1.30 mg/L and 0.03 mg/L for Pb2+, Cu2+ and Cd2+ respectively. The significances of this study are that, the conversion of the coconut husk to activated carbons provides a solution to environmental problems associated with dumping of the waste and also provides valuable products capable of reducing the effects of heavy metals in wastewater.  Keywords: Coconut Husk, Activated Carbon, Heavy Metal, Adsorptio

Recycling Waste Polyurethane as a Carbon Resource in Ironmaking

Globally, major avenues available for dealing with waste Poly-Urethane (PU) are disposal at landfill sites and incineration. However, PU contains high levels of carbon and hydrogen that can be recovered for use as reductant in metal extraction processes. In this work the use of post-consumer PU as reductant for the production of metallic iron from iron oxide was investigated in a horizontal tube furnace through the composite pellet approach. Composite pellets were formed from mixtures of iron oxide and post-consumer PU. The iron oxide-PU composites were heated from room temperature to 1200 °C and then between 1200-1600 °C in a continuous stream of pure argon and the off gas was analysed continuously using an infrared (IR) gas analyser. Elemental analyses of samples of the reduced metal were performed chemically for its oxygen content using a LECO oxygen/nitrogen analyser. The extent of reduction was then determined at two temperatures 1200 °C and 1550 °C. Gas emission studies revealed the emission of large volumes of the reductant gas CO along with CO2. It is further demonstrated that post-consumer PU is effective at reducing iron oxide to produce metallic iron with complete reduction achieved in less than 4 min at 1550 °C. Keywords: Polyurethane, Composite Pellets, Infrared gas Analyser, LECO Carbon/Sulphur Analyse

Quality Protein Maize Response to Nitrogen Rate and Plant Density in the Guinea Savanna Zone of Ghana

Field experiments were conducted in the Guinea savanna ecology of Ghana to evaluate yield response of quality protein maize (Zea mays L.) hybrid to plant density and nitrogen (N) fertilizer. The experiments were conducted at four locations on 16 farmers’ fields in 2002 and 2003. Three N rates (0, 90 and 135 kg/ha) were combined with three plant densities (50 000, 62 500 and 71 400 plants/ha) to constitute nine treatments which were tested in a randomized complete block design. Optimal N rate was not affected by plant density. There was no yield response to plant density. However, grain yield had a linear and quadratic response to N at all sites. Grain yield increases as a result of 90 kg N/ha applied over the farmers’ practice (0 kg N/ha) at Tumu, Jirapa, Kpongu and Wa were 39%, 85%, 101% and 303% in 2002, respectively. Grain yield increases for the same rate and sites in 2003 were 31%, 83%, 63% and 51%, respectively. Marginal rate of return (MMR) to 90 kg N/ha combined with 62 600 plants/ha was the highest (5564%). Increasing N rate beyond 90 kg/ha did not result in corresponding increase in yield nor net benefit to merit the extra cost that may be incurred. From the study, application of 90 kg N/ha to hybrid maize would give economic yield response and acceptable returns at low risk to farmers, regardless of plant density

Effects of Physical Activation Procedure on the Production Yield, Surface Chemistry and Surface Pores of Coconut Shells Based Activated Carbons

Activated carbons are produced either by physical or chemical activation or both. However, due to different experimental protocols used in preparing and characterising these carbons, it has been difficult in comparing their yields, surface chemistry and pore developments. In this study the effects of physical activation procedure on yields, surface chemistry and surface pore developments of activated carbons prepared by three physical activation procedures using the same protocols were compared. The results of the yields revealed that during the production of activated carbons better yields are obtained when the particle size of the precursor is reduced to the required size of the expected activated carbon prior to carbonisation and activation. The spectra produced by Fourier transmission infrared spectroscopy demonstrated shift in bands and changes in wavelength numbers and absorbance between the raw and the derived activated carbons  during pyrolysis or activation. Comparing the micrographs of the Scanning electron microscope of the derived carbons also showed an irregular and heterogeneous surface morphology with a well-developed porous structure. Keywords: porosity, micrographs, surface area, yield, activation, spectroscop