- Title
- Effect of coal and microalgae biomass co-firing on CO2, SO2 and NOx emissions: An experimental evaluation
- Creator
- Magida, Nokuthula Ethel
- Subject
- Port Elizabeth (South Africa)
- Subject
- Eastern Cape (South Africa)
- Subject
- South Africa
- Date Issued
- 2021-12
- Date
- 2021-12
- Type
- Master's theses
- Type
- text
- Identifier
- http://hdl.handle.net/10948/53817
- Identifier
- vital:45984
- Description
- There is increasingly stringent legislation on the environmental impact of energy production from coal combustion, and this has led to growing pressure to reduce the emission of greenhouse gases (GHGs). Thus, there is a significant need to develop and implement clean coal combustion technologies that would reduce the environmental gas pollutants. For power generation, the co-firing of biomass fuels at conventional coal-fired power stations is recognised as one of the low-cost, low-risk options to achieve significant reductions in GHG emissions. When coal is co-utilized with biomass there is added attractiveness because the biomass is CO2 neutral, and there is interest in using waste biomass and microalgae. Thus, the co-combustion of coal and biomass for energy production results in pollutant reduction, especially in the emissions of NOx, SOx, volatile organic compounds and polyaromatic hydrocarbons. The synergistic activity observed for toxic organic emissions is not well understood and is thought to involve chemical interaction between the volatiles from each fuel coupled with possible catalytic activity from the inorganic constituents of the fuels. The characterization of co-firing products and gases emitted from coal and microalgae (particularly the Scenedesmus strain) co-combustion has received limited attention. Therefore, this study seeks to understand possible interactions occurring during co-combustion of coal and Scenedesmus microalgae (Coalgae®). Additionally, the study aims to determine the effect of co-firing coal and Scenedesmus microalgae on CO2, SO2 and NOx emissions. The term “Coalgae®” refers to the mixture of coal and microalgae biomass. The study looks at physico-thermal characteristics as well as CO2, SO2 and NOx emissions of various coal-microalgae blending ratios by mass; 100:0 (coal), 95:5 (Coalgae® 5%), 90:10 (Coalgae® 10%), 85:15 (Coalgae® 15%) and 80:20 (Coalgae® 20%). Characterization techniques carried out included proximate and ultimate analyses, Fourier-transform infrared (FT-IR) and Scanning electron microscopy and X-ray energy dispersive spectroscopy (SEM/EDS). For combustion studies two techniques were applied. Low heating rate was obtained through a Thermogravimetric-Mass spectrometer analysis (TG-MS). Other combustion experiments were performed on the five lumpy fuels (coal and Coalgae® 5% - 20%) exposed to the flame in a fixed-bed combustion reactor. The emission concentrations of CO2 (%), NOx (ppm) and SO2 (ppm) of coal and Coalgae® blends were measured during the combustion of the five materials using a Lancom 4 portable flue gas analyser. The mass reduction (g) and temperature (°C) at the reactor exit were recorded during the combustion tests to compare the combustion behaviour of the four mixtures to that of raw coal. TG-DTG curves of coal and microalgae confirmed that the combustion behaviour of these materials was different. Coal showed one reaction during the combustion process, while microalgae and the Coalgae® blends showed three reactions. A significant reduction in activation energies of 160.4 kJ/mol, 159.6 kJ/mol, 151.3 kJ/mol, and 134.2 kJ/mol for Coalgae® 5% - Coalgae® 20%, respectively, compared to coal (161.3 kJ/mol) was achieved. The lowering of activation energy could be attributed to the relative fixed carbon content. SEM morphology images of ash obtained from the combustion of coal and Coalgae® 5% - 20% confirmed changes in devolatilization and combustion behaviour of solid raw fuel. The ash of Coalgae® blends had higher fluxing elements (Fe, Ca, K and Mg) than coal and this shows possibility of slagging and fouling in combustion systems. The Coalgae® blends showed a synergistic effect due to different combustion characteristics of coal and Scenedesmus microalgae. The combustion results obtained from the fixed-bed reactor showed significant reductions in concentrations of CO2, SO2 and NOx emissions for Coalgae® blends compared to baseline coal. Microalgae reduced CO2 emissions from baseline coal by 14.9%, 19.5%, 23.5% and 31.4% for Coalgae® 5%, 10%, 15% and 20%, respectively. SO2 reductions of 1.9%, 10.6%, 15.8% and 18.2%, and NOx reductions of 22.4%, 26.1%, 24.4% and 16.9% were achieved with Coalgae® 5%, 10%, 15% and 20%, respectively. Moreover, the combustion efficiency of Coalgae® blends increased significantly by up to 14.5% from baseline coal (86.4%) to Coalgae® 20% (98.9%). Based on the above findings, the co-firing of coal and Scenedesmus microalgae biomass was necessary for the reduction of CO2, SO2, and NOx emissions. As such, Coalgae® blends can be considered as alternative fuels in any coal driven process for energy generation.
- Description
- Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2021
- Format
- computer
- Format
- online resource
- Format
- application/pdf
- Format
- 1 online resource (xxii, 162 pages)
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela University
- Rights
- All Rights Reserved
- Rights
- Open Access
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | Magida, N.pdf | 4 MB | Adobe Acrobat PDF | View Details Download |