Despite diesel engines being highly efficient, with low fuel consumption and reduced carbon dioxide emissions, they emit relatively high levels of particulate matter and oxides of nitrogen (NOx) due to high exhaust ga...Despite diesel engines being highly efficient, with low fuel consumption and reduced carbon dioxide emissions, they emit relatively high levels of particulate matter and oxides of nitrogen (NOx) due to high exhaust gas temperatures. Engine emissions show the quality and completeness of combustion. This paper aims to present the results of a study comparing exhaust emissions from a diesel and syngas powered engine. Syngas was produced from co-firing coal and biomass in a gasifier then cleaned, cooled and applied as an alternative fuel in an engine operated from 0 - 100% load. Exhaust-emissions were monitored at this load conditions. The exhaust-temperature was measured using thermocouples and the emission gases were analyzed using Testo 350. The emissions were lower and decreased as the engine load increased, except for sulphur dioxide and NOx. The study shows that levels of carbon monoxide, were higher in a range of 46.5 - 80.2%, while carbon dioxide was 3.3 - 18% higher compared to those from diesel. Hydrocarbon emissions were 480 and 1250 ppm for diesel and syngas respectively. The study reveals that the engine operates optimally at higher loads since hydrocarbons and oxides of carbon are low due to complete combustion at higher temperatures. Exhaust gas temperature was higher in the syngas fuel and increased as the engine load increased in the range of 455.83 - 480.03˚C which influenced the formation of NOx. NOx from diesel was found to be higher, ranging from 32.5 - 40.5%, compared to those from syngas with an engine load of 75%. The study observed that relative to diesel, the emissions of sulfur dioxide at 50% engine load were lower in a range of 23.7 - 57.1%. Emissions of hydrocarbons depended on the degree of substitution of diesel and engine load. The study therefore shows that, relative to diesel, emissions decreased when syngas was used with upgraded syngas from Prosporis juliflora presenting as the best alternative followed by Hyphanae compressa, and lastly rice husk. For optimal performance of the syngas fuelled engine, the study reports that the engine should be operated at engine loads above 50% with strategies on NOx emissions considered.展开更多
Radiation is considered one of the possible causes of cancer disease with natural background sources including cosmic, terrestrial and internal radiation. A number of cancer disease cases have been reported in Kargi w...Radiation is considered one of the possible causes of cancer disease with natural background sources including cosmic, terrestrial and internal radiation. A number of cancer disease cases have been reported in Kargi with their causes not properly documented. The present work characterized the radioactivity in soil and water, to find out possible causes of radiation in KARGI-KENYA by studying magnetic intensities, anomalous zones with depth to magnetic sources and delineating subsurface structures. A total of 117 soil and 14 water samples were collected from the entire area and analysed for radionuclides due to <sup>40</sup>K, <sup>232</sup>Th and <sup>226</sup>Ra. Measurement methods of proton magnetometer and gamma spectrometry employing a high purity germanium (HPGe) detector were employed basically to evaluate the magnetic survey and radiological hazard of radioactivities respectively. A total of 51 magnetic field measurements were taken on the eastern part of Kargi, a place suspected to have more concentration of radionuclides. The results showed that there could have been a fractionation during weathering period or metasomatic activity of the radioelements involvement. This study also reveals that the mining activities in the nearby study area could have affected the geologic formation causing more fracturing in rocks and pronounced subsurface structures as a result of mining that could have served as passage for leachates from pollutants as well as the level of radiation in the study area.展开更多
The main aim of investigating activity concentrations together with distribution of radionuclides naturally in soil from Kargi was to evaluate radiological health hazard together with environmental radioactivity. Rese...The main aim of investigating activity concentrations together with distribution of radionuclides naturally in soil from Kargi was to evaluate radiological health hazard together with environmental radioactivity. Research shows radionuclides as one source of exposure due to radiation with detrimental effects health wise for populations found in areas considered high background radiation. After collecting 117 soil samples from the area, analysis was done in order to measure their natural radioactivities due to <sup>40</sup>K, <sup>232</sup>Th and <sup>226</sup>Ra radionuclides. Measurements method of gamma spectrometry employing a high purity germanium (HPGe) detector was employed basically to evaluate the radiological hazard of radioactivities. For <sup>40</sup>K, <sup>232</sup>Th and <sup>226</sup>Ra, mean calculated activities were 353.19 ± 110.07, 7.98 ± 3.98 and 7.37 ± 2.60 Bq<span style="white-space:nowrap;">·</span>kg <sup>-1</sup> respectively. Mean values of absorbed and effective dose rates, external and internal hazard indices together with radium equivalent activity were 23.82 ± 6.59 nGy<span style="white-space:nowrap;">·</span>h <sup>-1</sup> and 0.14 ± 0.04 mSv<span style="white-space:nowrap;">·</span>y <sup>-1</sup>, 0.12 ± 0.03 and 0.14 ± 0.04 and 45.90 ± 12.65 Bq<span style="white-space:nowrap;">·</span>kg <sup>-1</sup> respectively. Comparing with approved global values, the values were found to be below the given global limits. Evidence of involvement of metasomatic activity of the radioelements or fractionation during weathering is seen as calculations give a higher value Th/U. Excess cancer risk, calculated from the samples showed lower values as compared to global standard values hence minimal chance of getting cancer disease. The area is safe from cancer causing radionuclides.展开更多
Water hyacinth, E. crassipes, an invasive water weed thrives in fresh water bodies causing serious environmental problems. In Kenya the weed has invaded Lake Victoria and poses great socioeconomic and environmental ch...Water hyacinth, E. crassipes, an invasive water weed thrives in fresh water bodies causing serious environmental problems. In Kenya the weed has invaded Lake Victoria and poses great socioeconomic and environmental challenges. Currently the weed is harvested from the Lake and left in the open to rot and decay leading to loss of aesthetics, land and air pollution. There is therefore need for development of value addition and economic exploitation strategies. The aim of the study is to assess the potential for utilization of the weed as a renewable energy resource for biogas production. Samples were collected from Lake Victoria, pulped and blend with cow dung at a ratio of 3:1 as inoculum. The resultant mixture was mixed with water at a ratio of 1:1 and fed into a 6 m3 tubular digester. The digester was recharged with 20 kg after every three days. The temperature, pH variations, gas compositions, upgrading and gas yields were studied. The temperature ranged between 22.8°C - 36.6°C and pH 7.4 - 8.5. Biogas was found to contain 49% - 53% methane (CH4 ), 30% - 33% carbon dioxide (CO2 ), 5% - 6% nitrogen (N2 ) and traces of hydrogen sulphide (H2S). The biogas was upgraded using solid adsorbents and wet scrubbers increasing the methane content by up to 70% - 76%. The upgraded gas was used to power internal combustion engines coupled with an electricity generator and direct heat applications. The study concludes that E. crassipes is a potential feedstock for biogas production especially in areas where it is abundant.展开更多
Thermal gasification of biomass provides a potential renewable energy resource in rural areas in Kenya. Rice husks are a key byproduct of rice production that are not considered of economic value to millers. Rice husk...Thermal gasification of biomass provides a potential renewable energy resource in rural areas in Kenya. Rice husks are a key byproduct of rice production that are not considered of economic value to millers. Rice husks obtained from Mwea, Embu County, Kenya were converted into syngas using a locally assembled modified updraft gasifier. The syngas production was produced at temperatures between 450°C and 750°C with injection of limited supply of air and purified using series of gas cleaning and cooling devices. Proximate analysis shows that rice husks have a mean content of 21.9% ± 0.3% ash, 9.5% ± 3.3% moisture, 78.8% ± 0.3% volatiles and 91.8% ± 1.3% total solids. Carbonized rice husks have mean contents of 37.8% ± 1.2% ash, 3.1% ± 0.4% moisture, 62.3% ± 1.2% volatiles and 96.5% ± 0.4% total solids. The study shows that feedstock is consumed at a rate of 25 - 32 Kg/Hr with gas generation rate of 7.76 - 7.78 m3/hr;this translates to a gas yield of 0.31 - 0.35 m3/Kg. Process water was re-circulated at a rate of 2.2 m3/hr within the plant. The total electricity consumption per hour was 1.1 - 1.3 kWh. Carbon monoxide (CO) and temperature were monitored in the working area to assess the safety of the workers and were found to be in the range of 35 - 50 ppm and 24°C - 29.5°C respectively. The two were found to be within safe limits;however, the CO concentrations increased when leakages occurred. Syngas was found to be composed of 16.5% - 17.55% CO, 14.5% - 16.1% CO2, 4.1% - 4.5% H2, 6.8% - 7.2% CH4 and 17.9% - 45.7% N2 among others. The gas was used for direct heating applications and to run modified petrol engines. Carbonized husks were used to make energy briquettes and partly applied to the rice growing pads to improve soil properties. The technology provides energy solutions and aids in the abatement of climate change mitigation and abatement since it provides a permanent carbon sink. The technology provides a value addition chain for rice growers.展开更多
Pinch Analysis is an attractive solution for reduction of thermal energy costs in thermo-chemical industries.In this approach,maximum internally recoverable heat is determined and a heat exchange network is designed t...Pinch Analysis is an attractive solution for reduction of thermal energy costs in thermo-chemical industries.In this approach,maximum internally recoverable heat is determined and a heat exchange network is designed to meet the recovery targets.The thermal performance of a heat exchanger over its lifetime is however a concern to industries.Thermal performance of a heat exchanger is affected by many factors which include the physical prop-erties of the shell and tube materials,and the chemical properties of the heat transferfluid.In this study,thermal performance of shell and tube heat exchangers designed to meet heat recovery targets in a Pinch Analysis study is simulated.The aim of this paper is to present predictions of thermal performances of shell and tube heat exchan-gers with different heat transferfluids and geometries as they undergo fouling degradation.Engineering approaches based on thermodynamic analysis,heat balance and Kern Design equations,as well as what-if simu-lation modeling are used in this work.Shell and tube heat exchangers were designed to meet internal heat recov-ery targets for three process plants,A,B and C.These targets were published in a separate paper.The effects of degradation of the tubes-due to incremental growth of fouling resistance-on thermal performance of the exchan-ger were simulated using Visual Basic Analysis(VBA).Overall,it was found that growth in fouling reduces ther-mal efficiency of shell and tube heat exchangers with an exponential relationship.An increase of 100%of fouling resistance leads to an average reduction of 0.37%heat transfer.Higher values of logarithmic mean temperature difference(LMTD)and higher ratios of external diameter to internal diameter of the exchanger tubes amplify the effect of fouling growth on thermal performance of the exchangers.The results of this work can be applied in pinch analysis,during design of heat exchangers to meet the internal heat recovery targets,especially in predicting how fouling growth can affect these targets.This can also be useful in helping operators of shell and tube heat exchangers to determine cleaning intervals of the exchangers to avoid heat transfer loss.展开更多
Rice is a grass seed from Oryza glaberrima species also known as the African rice.In Kenya,rice is mostly grown in Central(Mwea)and Nyanza(Ahero,West Kano,Migori and Kuria)areas.Milling rice produces rice husks as by-...Rice is a grass seed from Oryza glaberrima species also known as the African rice.In Kenya,rice is mostly grown in Central(Mwea)and Nyanza(Ahero,West Kano,Migori and Kuria)areas.Milling rice produces rice husks as by-products which can be sources of valuable chemical products(silica gel,sodium silicate).In trials to produce silica gel from rice husks,rice husks were charred in a combustion chamber(30 min)then ashed in a Muffle furnace(Advantec KL-420)at different temperatures.The ashes were then leached with distilled water/acids to remove metal oxides.Sixty grams(60 g)of the leached RHA(Rice Husk Ash)was mixed with 300 mL of 3 M NaOH solution in a Pyrex 500 mL beaker and boiled at 100℃(1 h).The silica gel samples were characterized using several methods.Elemental analysis was done using TXRF(Total X-Ray Fluorescence),while FTIR(Fourier-Transform Infrared Spectroscopy)was used to obtain an infrared spectrum of absorption of the silica sample.Results of the analysis conform to local and international quality standards.The rice husks had an average moisture content of 7.07%and 1.00-2.00 mm diameter.And 1.74%of the rice husk had pore sizes of about 0.710 mm.The average ash content was 22.65%.At 600℃,leaching with water yielded 98.2%silica compared with 99.1%(H2SO4)and 96.9%(HCl).At 500℃,leaching with HCl/H2SO4 causes a decrease.At 500℃,the availability of SiO2 is more for water leached samples.At 400℃,water leaching gave 98.49%silica while HCl leaching was 97.85%silica and H2SO4 was 99.41%.Silica is a precursor of silica gel.Statistical analyses imply water leaching RHA instead of acid leaching at 500℃ will produce a significant amount of silica gel.The open burn samples produced equal or better SiO2(silica gel precursor)yields compared with the incineration samples.FTIR analysis of the silica gel sample compared well with adsorption peaks of silica gel in literature.XRD(X-Ray Diffraction)analysis produced a pattern consistent with other XRD patterns of silica gel published by other researchers.展开更多
Rice growing is a popular agricultural activity in some areas in Kenya.The challenge is in the disposal of RH(Rice Husks).Rice production results in 20%RH as byproduct.Simple incineration of RH results in RH ash which...Rice growing is a popular agricultural activity in some areas in Kenya.The challenge is in the disposal of RH(Rice Husks).Rice production results in 20%RH as byproduct.Simple incineration of RH results in RH ash which is a source of valuable chemical products.The ash is 87-97%silica,highly porous and light weight,with a very high external surface area.The end product of RHA(Rice Husk Ash)after chemical treatment,sodium silicate,is a precious commodity that has myriad applications especially in detergent manufacture and soap production.The objective was to determine the best conditions to synthesize silica from agro-wastes(RH)in Kenya.The yield(%SiO2)of the HCl(Hydrochloric Acid)leached RH at 500°C was the highest at 99.2%.Overall these conditions were the best in producing silicate.Percentage(%)removal of each metal is different due to its chemical form in RH.The removal percentage of K is especially remarkable.And 0.5 M HCl leaching followed by thermal treatment of 600°C gave the best increase in%silica dioxide.The same process removed the most metallic impurities(P2O5,K2O,CaO,Mn and Zn).Leaching with 0.5 M HCl followed with thermal treatment of 500°C gave the best overall yield in%silica dioxide.An increase in temperature from 600°C slightly reduced the%silica dioxide content.The 0.5 M HCl used in these trials was able to produce 99.17%silica content from the Mwea RH.The SiO2 obtained with the water washed RH sample is 97.37%as compared 99.17%(HCl-washed)and 99.02%(H2SO4(Sulphuric Acid)-leached).The FTIR(Fourier Transform Infrared Spectroscopy)spectra indicates HCl leaching avails more silica content than H2SO4 leaching.展开更多
文摘Despite diesel engines being highly efficient, with low fuel consumption and reduced carbon dioxide emissions, they emit relatively high levels of particulate matter and oxides of nitrogen (NOx) due to high exhaust gas temperatures. Engine emissions show the quality and completeness of combustion. This paper aims to present the results of a study comparing exhaust emissions from a diesel and syngas powered engine. Syngas was produced from co-firing coal and biomass in a gasifier then cleaned, cooled and applied as an alternative fuel in an engine operated from 0 - 100% load. Exhaust-emissions were monitored at this load conditions. The exhaust-temperature was measured using thermocouples and the emission gases were analyzed using Testo 350. The emissions were lower and decreased as the engine load increased, except for sulphur dioxide and NOx. The study shows that levels of carbon monoxide, were higher in a range of 46.5 - 80.2%, while carbon dioxide was 3.3 - 18% higher compared to those from diesel. Hydrocarbon emissions were 480 and 1250 ppm for diesel and syngas respectively. The study reveals that the engine operates optimally at higher loads since hydrocarbons and oxides of carbon are low due to complete combustion at higher temperatures. Exhaust gas temperature was higher in the syngas fuel and increased as the engine load increased in the range of 455.83 - 480.03˚C which influenced the formation of NOx. NOx from diesel was found to be higher, ranging from 32.5 - 40.5%, compared to those from syngas with an engine load of 75%. The study observed that relative to diesel, the emissions of sulfur dioxide at 50% engine load were lower in a range of 23.7 - 57.1%. Emissions of hydrocarbons depended on the degree of substitution of diesel and engine load. The study therefore shows that, relative to diesel, emissions decreased when syngas was used with upgraded syngas from Prosporis juliflora presenting as the best alternative followed by Hyphanae compressa, and lastly rice husk. For optimal performance of the syngas fuelled engine, the study reports that the engine should be operated at engine loads above 50% with strategies on NOx emissions considered.
文摘Radiation is considered one of the possible causes of cancer disease with natural background sources including cosmic, terrestrial and internal radiation. A number of cancer disease cases have been reported in Kargi with their causes not properly documented. The present work characterized the radioactivity in soil and water, to find out possible causes of radiation in KARGI-KENYA by studying magnetic intensities, anomalous zones with depth to magnetic sources and delineating subsurface structures. A total of 117 soil and 14 water samples were collected from the entire area and analysed for radionuclides due to <sup>40</sup>K, <sup>232</sup>Th and <sup>226</sup>Ra. Measurement methods of proton magnetometer and gamma spectrometry employing a high purity germanium (HPGe) detector were employed basically to evaluate the magnetic survey and radiological hazard of radioactivities respectively. A total of 51 magnetic field measurements were taken on the eastern part of Kargi, a place suspected to have more concentration of radionuclides. The results showed that there could have been a fractionation during weathering period or metasomatic activity of the radioelements involvement. This study also reveals that the mining activities in the nearby study area could have affected the geologic formation causing more fracturing in rocks and pronounced subsurface structures as a result of mining that could have served as passage for leachates from pollutants as well as the level of radiation in the study area.
文摘The main aim of investigating activity concentrations together with distribution of radionuclides naturally in soil from Kargi was to evaluate radiological health hazard together with environmental radioactivity. Research shows radionuclides as one source of exposure due to radiation with detrimental effects health wise for populations found in areas considered high background radiation. After collecting 117 soil samples from the area, analysis was done in order to measure their natural radioactivities due to <sup>40</sup>K, <sup>232</sup>Th and <sup>226</sup>Ra radionuclides. Measurements method of gamma spectrometry employing a high purity germanium (HPGe) detector was employed basically to evaluate the radiological hazard of radioactivities. For <sup>40</sup>K, <sup>232</sup>Th and <sup>226</sup>Ra, mean calculated activities were 353.19 ± 110.07, 7.98 ± 3.98 and 7.37 ± 2.60 Bq<span style="white-space:nowrap;">·</span>kg <sup>-1</sup> respectively. Mean values of absorbed and effective dose rates, external and internal hazard indices together with radium equivalent activity were 23.82 ± 6.59 nGy<span style="white-space:nowrap;">·</span>h <sup>-1</sup> and 0.14 ± 0.04 mSv<span style="white-space:nowrap;">·</span>y <sup>-1</sup>, 0.12 ± 0.03 and 0.14 ± 0.04 and 45.90 ± 12.65 Bq<span style="white-space:nowrap;">·</span>kg <sup>-1</sup> respectively. Comparing with approved global values, the values were found to be below the given global limits. Evidence of involvement of metasomatic activity of the radioelements or fractionation during weathering is seen as calculations give a higher value Th/U. Excess cancer risk, calculated from the samples showed lower values as compared to global standard values hence minimal chance of getting cancer disease. The area is safe from cancer causing radionuclides.
文摘Water hyacinth, E. crassipes, an invasive water weed thrives in fresh water bodies causing serious environmental problems. In Kenya the weed has invaded Lake Victoria and poses great socioeconomic and environmental challenges. Currently the weed is harvested from the Lake and left in the open to rot and decay leading to loss of aesthetics, land and air pollution. There is therefore need for development of value addition and economic exploitation strategies. The aim of the study is to assess the potential for utilization of the weed as a renewable energy resource for biogas production. Samples were collected from Lake Victoria, pulped and blend with cow dung at a ratio of 3:1 as inoculum. The resultant mixture was mixed with water at a ratio of 1:1 and fed into a 6 m3 tubular digester. The digester was recharged with 20 kg after every three days. The temperature, pH variations, gas compositions, upgrading and gas yields were studied. The temperature ranged between 22.8°C - 36.6°C and pH 7.4 - 8.5. Biogas was found to contain 49% - 53% methane (CH4 ), 30% - 33% carbon dioxide (CO2 ), 5% - 6% nitrogen (N2 ) and traces of hydrogen sulphide (H2S). The biogas was upgraded using solid adsorbents and wet scrubbers increasing the methane content by up to 70% - 76%. The upgraded gas was used to power internal combustion engines coupled with an electricity generator and direct heat applications. The study concludes that E. crassipes is a potential feedstock for biogas production especially in areas where it is abundant.
文摘Thermal gasification of biomass provides a potential renewable energy resource in rural areas in Kenya. Rice husks are a key byproduct of rice production that are not considered of economic value to millers. Rice husks obtained from Mwea, Embu County, Kenya were converted into syngas using a locally assembled modified updraft gasifier. The syngas production was produced at temperatures between 450°C and 750°C with injection of limited supply of air and purified using series of gas cleaning and cooling devices. Proximate analysis shows that rice husks have a mean content of 21.9% ± 0.3% ash, 9.5% ± 3.3% moisture, 78.8% ± 0.3% volatiles and 91.8% ± 1.3% total solids. Carbonized rice husks have mean contents of 37.8% ± 1.2% ash, 3.1% ± 0.4% moisture, 62.3% ± 1.2% volatiles and 96.5% ± 0.4% total solids. The study shows that feedstock is consumed at a rate of 25 - 32 Kg/Hr with gas generation rate of 7.76 - 7.78 m3/hr;this translates to a gas yield of 0.31 - 0.35 m3/Kg. Process water was re-circulated at a rate of 2.2 m3/hr within the plant. The total electricity consumption per hour was 1.1 - 1.3 kWh. Carbon monoxide (CO) and temperature were monitored in the working area to assess the safety of the workers and were found to be in the range of 35 - 50 ppm and 24°C - 29.5°C respectively. The two were found to be within safe limits;however, the CO concentrations increased when leakages occurred. Syngas was found to be composed of 16.5% - 17.55% CO, 14.5% - 16.1% CO2, 4.1% - 4.5% H2, 6.8% - 7.2% CH4 and 17.9% - 45.7% N2 among others. The gas was used for direct heating applications and to run modified petrol engines. Carbonized husks were used to make energy briquettes and partly applied to the rice growing pads to improve soil properties. The technology provides energy solutions and aids in the abatement of climate change mitigation and abatement since it provides a permanent carbon sink. The technology provides a value addition chain for rice growers.
文摘Pinch Analysis is an attractive solution for reduction of thermal energy costs in thermo-chemical industries.In this approach,maximum internally recoverable heat is determined and a heat exchange network is designed to meet the recovery targets.The thermal performance of a heat exchanger over its lifetime is however a concern to industries.Thermal performance of a heat exchanger is affected by many factors which include the physical prop-erties of the shell and tube materials,and the chemical properties of the heat transferfluid.In this study,thermal performance of shell and tube heat exchangers designed to meet heat recovery targets in a Pinch Analysis study is simulated.The aim of this paper is to present predictions of thermal performances of shell and tube heat exchan-gers with different heat transferfluids and geometries as they undergo fouling degradation.Engineering approaches based on thermodynamic analysis,heat balance and Kern Design equations,as well as what-if simu-lation modeling are used in this work.Shell and tube heat exchangers were designed to meet internal heat recov-ery targets for three process plants,A,B and C.These targets were published in a separate paper.The effects of degradation of the tubes-due to incremental growth of fouling resistance-on thermal performance of the exchan-ger were simulated using Visual Basic Analysis(VBA).Overall,it was found that growth in fouling reduces ther-mal efficiency of shell and tube heat exchangers with an exponential relationship.An increase of 100%of fouling resistance leads to an average reduction of 0.37%heat transfer.Higher values of logarithmic mean temperature difference(LMTD)and higher ratios of external diameter to internal diameter of the exchanger tubes amplify the effect of fouling growth on thermal performance of the exchangers.The results of this work can be applied in pinch analysis,during design of heat exchangers to meet the internal heat recovery targets,especially in predicting how fouling growth can affect these targets.This can also be useful in helping operators of shell and tube heat exchangers to determine cleaning intervals of the exchangers to avoid heat transfer loss.
文摘Rice is a grass seed from Oryza glaberrima species also known as the African rice.In Kenya,rice is mostly grown in Central(Mwea)and Nyanza(Ahero,West Kano,Migori and Kuria)areas.Milling rice produces rice husks as by-products which can be sources of valuable chemical products(silica gel,sodium silicate).In trials to produce silica gel from rice husks,rice husks were charred in a combustion chamber(30 min)then ashed in a Muffle furnace(Advantec KL-420)at different temperatures.The ashes were then leached with distilled water/acids to remove metal oxides.Sixty grams(60 g)of the leached RHA(Rice Husk Ash)was mixed with 300 mL of 3 M NaOH solution in a Pyrex 500 mL beaker and boiled at 100℃(1 h).The silica gel samples were characterized using several methods.Elemental analysis was done using TXRF(Total X-Ray Fluorescence),while FTIR(Fourier-Transform Infrared Spectroscopy)was used to obtain an infrared spectrum of absorption of the silica sample.Results of the analysis conform to local and international quality standards.The rice husks had an average moisture content of 7.07%and 1.00-2.00 mm diameter.And 1.74%of the rice husk had pore sizes of about 0.710 mm.The average ash content was 22.65%.At 600℃,leaching with water yielded 98.2%silica compared with 99.1%(H2SO4)and 96.9%(HCl).At 500℃,leaching with HCl/H2SO4 causes a decrease.At 500℃,the availability of SiO2 is more for water leached samples.At 400℃,water leaching gave 98.49%silica while HCl leaching was 97.85%silica and H2SO4 was 99.41%.Silica is a precursor of silica gel.Statistical analyses imply water leaching RHA instead of acid leaching at 500℃ will produce a significant amount of silica gel.The open burn samples produced equal or better SiO2(silica gel precursor)yields compared with the incineration samples.FTIR analysis of the silica gel sample compared well with adsorption peaks of silica gel in literature.XRD(X-Ray Diffraction)analysis produced a pattern consistent with other XRD patterns of silica gel published by other researchers.
文摘Rice growing is a popular agricultural activity in some areas in Kenya.The challenge is in the disposal of RH(Rice Husks).Rice production results in 20%RH as byproduct.Simple incineration of RH results in RH ash which is a source of valuable chemical products.The ash is 87-97%silica,highly porous and light weight,with a very high external surface area.The end product of RHA(Rice Husk Ash)after chemical treatment,sodium silicate,is a precious commodity that has myriad applications especially in detergent manufacture and soap production.The objective was to determine the best conditions to synthesize silica from agro-wastes(RH)in Kenya.The yield(%SiO2)of the HCl(Hydrochloric Acid)leached RH at 500°C was the highest at 99.2%.Overall these conditions were the best in producing silicate.Percentage(%)removal of each metal is different due to its chemical form in RH.The removal percentage of K is especially remarkable.And 0.5 M HCl leaching followed by thermal treatment of 600°C gave the best increase in%silica dioxide.The same process removed the most metallic impurities(P2O5,K2O,CaO,Mn and Zn).Leaching with 0.5 M HCl followed with thermal treatment of 500°C gave the best overall yield in%silica dioxide.An increase in temperature from 600°C slightly reduced the%silica dioxide content.The 0.5 M HCl used in these trials was able to produce 99.17%silica content from the Mwea RH.The SiO2 obtained with the water washed RH sample is 97.37%as compared 99.17%(HCl-washed)and 99.02%(H2SO4(Sulphuric Acid)-leached).The FTIR(Fourier Transform Infrared Spectroscopy)spectra indicates HCl leaching avails more silica content than H2SO4 leaching.