Effect of Gasification Operating Parameters on Quality of Syngas Produced Using Sawdust Feedstock

Effect of Gasification Operating Parameters on Quality of Syngas Produced Using Sawdust Feedstock

Chapter One

Aim and Objectives

This research work aims to investigate the effect of various gasification operating parameters, namely; equivalence ratio, reaction zone temperature, gasifying agents, and residence time on the quality of syngas produced using sawdust as feedstock and a downdraft gasifier.

Specific objectives of the research work are:

1. To collect sawdust sample from sawmill at timber market(Kasuwan Katako)Zaria in Sabon Gari Local Government Area of Kaduna State,
2. To characterize the sawdust sample using proximate and ultimate
3. To carryout gasification of the sawdust sample using air and oxygen enriched-air as gasifying
4. To carryout qualitative and quantitative analysis of gasification products, namely; CO, CO₂, CH₄, H₂and O₂ using online gas
5. To carryout MATLAB simulation of thermodynamic equilibrium model using proximate and ultimate analyses data and to compare results obtained with experimental data.

CHAPTER TWO

LITERATURE REVIEW

  Introduction

There are two main routes of converting biomass into biofuels, namely biochemical and thermochemical conversion processes. Biochemical process operates at lower temperatures and employs microbial activities on wet biomass such as molasses, starch, animal dung etc. Biomass with moisture content less than 50% can be converted to combustible gas fuel using thermal process operated at higher temperatures.

The term gasification refers to a process of conversion of any solid or liquid carbon-based material (feedstock) into gaseous fuel through partial oxidation with air, oxygen, water vapour or their mixtures. In practice gasification process converts only 60 – 90 % of  energy originally stored in the biomass into energy contained in gaseous or liquid fuel(Reed and Das, 1988).

Historical Development of Gasification

Historical records dated the earliest gasification back to 1659 as illustrated in Figure 2.1 when “carbureted hydrogen” popularly known as methane was discovered by Thomas Shirley from coal mine(Basu, 2010). The need for lighting streets became the primary motivation behind the discovery of coal-gas also known as town gas. In 1792 William Murdoch was the first to exploit the flammability of coal-gas for practical application for lighting. In 1798 Murdoch lit up the main building of the Soho Foundry (steam engine works) where he works. In 1808 Murdoch made a striking paper presentation to the Royal Society where he demonstrated the application of coal-gas for lighting. One of the major economic implications of gas lighting was the extension of working hours during the industrial revolution. Factories operated even at night especially during the winter months when nights are significantly longer. Later around 1920, town gas lighting technology crosses over the Atlantic Ocean and became widespread in the United States (Singer, 1958; Kaupp, 1984).

The period 1940–1975 saw gasification enter two fields ofapplication of synthetic fuels as internal combustion and chemical synthesis into oil and other process chemicals. During the second world war, allied bombing of Nazi oil refineries and oil supply routes greatly diminished the crude oil supply that fueled Germany‟s massive war machinery. This forced Germany to synthesize oil from coal-gas using the Fischer-Tropsch and Bergius processes.Other chemicals and aviation fuels were also synthesized from coal.

Development of gasification technology witnessed a major drawback at the end of second world war in 1946 as inexpensive gasoline from Middle East became available during the oil glut. However this technology experiences dramatic renaissance as oil supplies to the western world cuts off duringthe Arab oil embargo in 1973 which was triggered by the Yom Kippur War. On October 15, 1973, Arab members of the Organization of Petroleum Exporting Countries (OPEC) banned oil exports to the United States and other western countries, which were at that time heavily reliant on oil from the Middle East. This shocked the western economy and gave a strong impetus to the development of alternative technologies like gasification in order to reduce dependence on imported oil.Global warming and political instability in some oil-producingcountries gave a fresh momentum to gasification at the millennium.

Gasification came out as a natural choice for conversion of renewable carbon-neutral biomass into gas. The quest for energy independence and the rapid increase in crude oil prices prompted some countries to recognize the need for development of integratedgasification combine cycle (IGCC) plants. The attractiveness of gasification for extraction of valuable feedstock from refinery residue was rediscovered, leading to the development of some major gasification plants in oil refineries. In fact, chemical feedstock preparation took a larger share of the gasification market than energy production (Basu, 2010).

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CHAPTER THREE

 MATERIALS AND METHODS

  Materials and Equipment

List of materials and Equipments used in the present gasification experiment are provided as follows:(See Appendix Bfor equipment specifications).

1. Portable infrared gas analyzer
2. Gas conditioning system
3. Digital thermometer
4. Air blower
5. Mass flowmeter
6. Thermocouple probe
7. Air/oxygen cylinder
8. Silicon esealer
9. Matches sticks

Sawdust Characterization

Sawdust sample was collected in plastic bags from Sawmills at Timber Market (Kasuwan Katako), Zaria inSabon Gari Local Government Area of Kaduna State, Nigeria. Prior to characterization, the collected sample was sorted and spread in open air for about 2 weeks to reduce significant amount of its initial moisture content.

Ultimate and proximate analysis procedure published by the American Society for Testing and Material (ASTM) E870-82(2013)was used in characterization of the sawdust sample.In this analysis moisture content (M), volatile matter (VM), ash content (A), sulfur (S) content and nitrogen (N) contentof the sawdust sample were determined.However, correlation developed by Shen et al., (2010) was used to estimate percentage compositionof hydrogen (H), oxygen (O) and carbon (C)in the sawdust sample using proximate analysis data as input variables (see equation3.1 – 3.3).Moisture content was determined using ASTM E871-82designated for particulate wood analysis. In thismethod,50 grams of sawdust sample was weighed and heated in an air oven at 103°C for about 30 minutes. The sample was then removed from the ovenand weighed again after cooling. To ensure complete drying of the sample, the process was repeated until the sample weight remains unchanged. The difference in weight between the dry and the fresh sample gives the moisture content. Feedstock sample further subjectedto higher temperature of about 950^oC drives off volatile content leaving behind the fixed carbon. Table 3.1 provides summary of ASTM specification used in characterization of the sawdust sample.

CHAPTER FOUR

 RESULTS AND DISCUSSION

 Proximate Analysis Result

From proximate analysis of the sawdust sample presented in Table 4.1, it can be seen that fixed carbon content, volatile matter and ash content were found be 14.94, 71.2 and 8.06% respectively. Similar result was reported by Jigisha et al., (2004)as 25.00, 72.40 and 2.60% respectively. Kong et al., (2013) in their work observed that FC, VM and M significantly affect the HHVof biomass sample. They demonstrated that HHV improves from 15.86 – 29.49MJ/kg by pyrolysis at 773K which reduces the VC and MC of the sample used.

CHAPTER FIVE

CONCLUSIONS AND RECOMMENDATIONS

Conclusions

Inthis research work, experimental study was carried out to investigate the effect of various gasification operating parameterson quality of syngas produced in a downdraft gasifier using sawdust feedstock.Air and oxygen enriched air were used separately as gasification medium with varying equivalence ratios to determine their respective effect on reduction zone temperature, product gas percentage composition and heating value. Gasification performance was determined using Cold Gas Efficiency (CGE) and Carbon Conversion Efficiency (CCE),which are indicators evaluated at different operating condition. Within the range of parameters examined in this work, the following conclusions were drawn.

1. Levels of CO and H₂in product gas recorded peak value of 13.55 and 2.59% respectively using air as gasification medium at flow rate of 6.4 LPM.Decreasing the flow rate to 1.9 LPM however led to corresponding drop in CO and H₂levels t 5.18 and 0.82%, respectively

2. Increasing percentage oxygen in gasifying medium from 21 – 80% led to a significant increase in Equivalence Ratio (ER) from 0.152 – 0.622.Similarly average temperature of reduction zone rise from 381.17 -4°C.
3. The overall best product gas profile using oxygen enriched gasifying medium was observed at 40% oxygen enrichment where CO continue to increase up to 20 minutes and reaches peak value of 29.57% while H₂reaches 29%.
4. Lower Heating Value (LHV) of product gas rises consistently from 2.08 – 6.69MJ/Nm³as percentage oxygen in gasifying medium rises from 21–40%.
5. Cold Gas Efficiency (CGE) rises continuously from lowest value of 8.65%at 0.152 ER to a maximum value of 46.81% at 0.295 ER. The CGE was observed to decline by about 53% with further increase in ER value of 0.6225.

6. Carbon Conversion Efficiency (CCE) followed similarly trend as CGE with a maximum value of 82.04% attained at same 0.2953 ER. Thus considering overall gasification performance evaluation it can deduce that the optimum operating condition was achieved atERknee pointstated above beyond which performance falls
7. Model validation with experimental data obtained in this research revealed that CO predicted value of 8.05% best fit experimental value of 9.53% at the lowest preset temperature of17°C.
8. Root Mean Square (RMSE) value of model and experimental data comparison at six preset temperatures were found to be 5.67, 6.63, 3.51, 5.13, 10.80 and 9.35%. Consequently model comparison with lowest RMSE value (3.51%) is considered the overall best data fitting point which is obtained at a preset temperature of 454.33°C.

 Recommendations

The following recommendations were made base on the present research work carried out:

1. In this research work only one point temperature probe was employed and therefore inadequate to monitor temperatures at other points of interest at the same time. In additioninconsistent temperature profile was identified as a major  It is therefore recommended that additional temperature probe should be considered in further research.

2. The feeder system of gasifier used in this work operates in batch mode and therefore imposes constraint to continuous operation. Moreover the rotating grate system intended todischarge ash and to allowcontinual flow of fresh feedstock down the reactor end up not working properly by a way of scooping out the entire combustion zone. It is therefore recommended that a continuous feeder system reactor be design and constructed insubsequent research
3. Lack of lagging around the gasifier contributes enormously to heat loses to the environment principallyby convection and radiation. It is therefore recommended that appropriate lagging material be selected and applied according to design principle to improve stability of operating
4. Current gasifier used in this work operates under positive pressure displacement and therefore prone to active leakages. For safety reasons and accuracy of findings, it is therefore recommended that negative pressure displacement should be considered in future
5. Experimental investigation conducted using compressed air/oxygen mixture experiences significant pressure buildup inside the gasifier and hence subjects the system to potentialexplosion. It is therefore recommended that appropriate design principle be appliedindeveloping new gasifier with clear specification for ranges of operating

REFERENCE

• Ajay, K., David, D. J., & Milford, A. H. (2009). Thermochemical Biomass Gasification: A Review of the Current Status of The Technology. Journal of Energies, 2, 556-581 DOI: 10.3390/en20300556.
• Anjireddy B. and Sastry R. C. (2011, December). Biomass Gasification Processes in Downdraft Fixed Biomass Gasification Processes in Downdraft Fixed. A Review, International Journal of Chemical Engineering and Applications, 2(6), 231-245.
• Asadullah, M. (2014). Biomass Gasification Gas Cleaning For Down Stream Applications: A Comparative Critical Review. Renewable and Sustainable Energy Reviews, 40, 118–132.
• Badejo, S. O. (2005). Preliminary Study on the Utilisation of Nigeran Sawmill Sawdust for the Production of Water Proof Cement Bonded Ceiling Boards. FRIN Bulletin., p. 58.
• Barman, N. S., Ghosh, S., & Sudipta, D. (2012). Gasification Of Biomass in a Fixed Bed Downdraft Gasifier – A Realistic Model Including Tar. Bioresource Technology, 107, 505–511.
• Basu, P. (2010). Biomass Gasification and Pyrolysis: Practical Design and Theory.
• Kidlington, Oxford: Elsevier.
• Bergerson, J., & Keith, D. (2006). Life Cycle Assessment of Oil Sands Technologies. Alberta Energy Futures Project, Institute for Sustainable Energy, Environment, and Economy (ISEE). University Calgary.

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