Browsing by Author "Said, Mahir Mohammed"

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    Analysis of a circulating fluidized bed medical waste incineration facility with air pollution control
    (University of Dar es Salaam, 2010) Said, Mahir Mohammed
    Circulating Fluidized Bed Incinerator is known to be one of the best available options for treating medical waste, particularly the pathological related waste. A proper operation of the incinerator is essential to ensure complete destruction of the waste. The combustion efficiency (one of the performance indicators) of the CFB incinerator is determined by the presence of carbon monoxide and carbon dioxide emission. In this regard, a study to investigate the relationship between variables affecting the combustion efficiency, namely temperatures, air pressure and air pollution control devices were performed using excel. Results showed that waste, combustion temperatures, air pressure and air pollution control devices contribute significantly to the combustion efficiency of the process. Two variables were used; inlet air flow rate and inlet liquid flow rate. The maximum and minimum liquid to gas ratio were between 1.9 l/m3 and 0.6 l/m3. The pressure was constant along riser. The maximum pressure drop of the CFB was 490 kPa. The combustion temperature was ranging between 700 and 970 , the constant temperature along the riser was observed when inlet air flow rate was 12 m/s. high temperature reduction was observed at heat exchanger from 350 to 90 . Approximately 75% of the flue gas heat energy was absorbed by cooling liquid; the maximum heat transfer in the heat exchanger was 60 kW. The pH of water used as scrubbing solution was changing from 6.68 to 5.57 and 6.88 to 5.72 for wet scrubber Stage 1 and 2 respectively, and the pH of 6 g/l lime concentration was changing from 12 to 6 for both stages. The combustion efficiency of the CFB with assistance of multistage wet scrubber was 99.6 %.
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    Modeling of fast pyrolysis of biomass for bio-oil production
    (University of Dar es Salaam, 2015) Said, Mahir Mohammed
    Biomass processing and use can meet the challenge of reducing fossil resources by producing a liquid feedstock that can lessen the fossil dependence and meet the increased demand via rapidly emerging thermochemical technologies such as pyrolysis. The main objective of this research work was to develop a mathematical model for fast pyrolysis of biomass for liquid fuel (bio-oil) production. Few tropical biomass types have been studied for pyrolysis and nothing has been previously studied on the effect of mixing of different varieties of biomass for production of bio-oil. This research studied the pyrolysis of six tropical biomass materials of eucalyptus, pine, mangrove, cashew-nut shells, coconut husk and rice husk. The chemical and physical properties were studied to enable to develop the model that predicts the yields of bio-oil. Good agreement of the developed model and existing models were observed for all biomass except rice husk and coconut husk whose deviations were above 10%. The validation of the model with experimental results gave a variation of less than 10% for all biomass materials. Cashew nut shells and eucalyptus produced about 0.7 wt/wt yields of bio-oil. Mangrove and pine produced about 0.6 wt/wt yields and the least bio-oil yield was observed from coconut husk and rice husk which was about 0.5 wt/wt yields. The maximum yield of mixed biomass was about 0.5 wt/wt, and the gas produced was 0.95 wt/wt. It is concluded that the model works in both forest and agricultural biomass. The model is also flexible enough to predict the yield even if the biomass is in the mixed form.