title: Speed control of small motors through the Ćuk Converter Topology

authors: Hutchins, Michael

subjects: motor speed control

abstract: The Ćuk Converter offers simultaneous buck-boost operation, but requires careful design owing to its having a fourth-order transfer function and numerous practical design constraints. We exploit a serendipitous overlap between the converter circuit and the equivalent circuit of a dc motor to design a motor controller that can operate with supply voltage that is lower than the motor full-speed requirement. We examine the transfer function when such a topology is used to control the speed of a small motor. We conclude that the approach is relatively straightforward owing to the impact of the motor’s inductance. Measurements agree with theory.

text: Speed control of small motors through the Ćuk Converter Topology The Ćuk Converter offers simultaneous buck-boost operation, but requires careful design owing to its having a fourth-order transfer function and numerous practical design constraints. We exploit a serendipitous overlap between the converter circuit and the equivalent circuit of a dc motor to design a motor controller that can operate with supply voltage that is lower than the motor full-speed requirement. We examine the transfer function when such a topology is used to control the speed of a small motor. We conclude that the approach is relatively straightforward owing to the impact of the motor’s inductance. Measurements agree with theory.

year: 2016

title: Pyrolysis of Sawdust

authors: Sichone, Kavwa

abstract: Lakeland Steel Limited developed a pilot plant for biomass pyrolysis based on sawdust. The pilot plant was based on an auger screw design which was indirectly heated using a double pipe heat exchange configuration to prevent oxidation (combustion) of the feedstock. This thesis covers the preliminary assessment of sawdust pyrolysis for R.H Tregoweth sawmills on behalf of Lakeland Steel Limited. 
Proximate and ultimate analyses were deployed on the sawdust to determine its composition. Proximate analysis results gave a moisture content of 60%. The dry solids had an organic matter content of 99.22% with ash making the balance. Ultimate analysis was used to determine content levels of elemental carbon, hydrogen, nitrogen sulphur and oxygen. The results on a dry basis were 47.2%, 6.5%, 0.3%, 0.3%, and 44.9 % respectively. 
Drying models were also used to analyse the sawdust drying characteristics. Drying curves were obtained experimentally and four models: Newton; Page; Henderson and Pabis; and Simpson and Tschernitz, were fitted to the data and their accuracy of fit was determined using residual squared sum of errors.  Page’s model was used to describe the sawdust behaviour in the dryer design as it had the highest accuracy.
The sawdust reaction kinetics were determined using data from thermogravimetric analysis (TGA) and analysed using distributed action energy model. The kinetics were observed at three heating rates of 10, 20 and 30 °C/min with a maximum temperature of 900°C under an argon atmosphere. Sawdust was modelled as a mixture of water, hemicellulose, cellulose  and lignin. Good agreement between Gaussian distribution functions for each component and experimental data were observed. 
Pilot plant trials were performed using a three factor-three level design of experiment. The factors under investigation were; feedstock moisture content with levels at 15, 30 and 60; reaction temperature with levels at 400, 450 and 500°C; and reactor auger speed with levels at 15, 20 and 25 rpm. Experiments at 60% moisture could not be performed to completion as the auger blocked repeatedly. The other two moisture contents showed that moisture content enhanced heat exchange properties of the feedstock and this generally increased the amount of volatile organic matter released. It was observed that for 15% moisture sawdust increase of temperature did not consistently exhibit an increase in degree of devolatilisation of organic matter. However, the 30% moisture sawdust showed an increase in devolatilisation with increase in temperature.  The effects of increasing reactor auger speed had the most consistent trend with which an increase in speed showed a decrease in degree of devolatilisation thus increasing char yield.
The empirical data collected from lab scale and pilot plant experiments were used to create mass and energy balances. These were the basis of the large scale mobile pyrolysis plant which was designed to process 3.45 tonnes per hour. Due to size restrictions the large scale dryer was not fitted in the container. It was then determined that the feedstock would either be dried using an onsite kiln or the reactor would process green sawdust.

A preliminary economic feasibility assessment was performed for the base case scenario which processed pre-dried sawdust of 15% moisture content at 400°C and a retention time of 45 minutes. A sensitivity analysis based on predicted optimistic and pessimistic conditions showed that automation of the plant had the potential to increase the economic viability of the large scale process.

text: Pyrolysis of Sawdust Lakeland Steel Limited developed a pilot plant for biomass pyrolysis based on sawdust. The pilot plant was based on an auger screw design which was indirectly heated using a double pipe heat exchange configuration to prevent oxidation (combustion) of the feedstock. This thesis covers the preliminary assessment of sawdust pyrolysis for R.H Tregoweth sawmills on behalf of Lakeland Steel Limited. 
Proximate and ultimate analyses were deployed on the sawdust to determine its composition. Proximate analysis results gave a moisture content of 60%. The dry solids had an organic matter content of 99.22% with ash making the balance. Ultimate analysis was used to determine content levels of elemental carbon, hydrogen, nitrogen sulphur and oxygen. The results on a dry basis were 47.2%, 6.5%, 0.3%, 0.3%, and 44.9 % respectively. 
Drying models were also used to analyse the sawdust drying characteristics. Drying curves were obtained experimentally and four models: Newton; Page; Henderson and Pabis; and Simpson and Tschernitz, were fitted to the data and their accuracy of fit was determined using residual squared sum of errors.  Page’s model was used to describe the sawdust behaviour in the dryer design as it had the highest accuracy.
The sawdust reaction kinetics were determined using data from thermogravimetric analysis (TGA) and analysed using distributed action energy model. The kinetics were observed at three heating rates of 10, 20 and 30 °C/min with a maximum temperature of 900°C under an argon atmosphere. Sawdust was modelled as a mixture of water, hemicellulose, cellulose  and lignin. Good agreement between Gaussian distribution functions for each component and experimental data were observed. 
Pilot plant trials were performed using a three factor-three level design of experiment. The factors under investigation were; feedstock moisture content with levels at 15, 30 and 60; reaction temperature with levels at 400, 450 and 500°C; and reactor auger speed with levels at 15, 20 and 25 rpm. Experiments at 60% moisture could not be performed to completion as the auger blocked repeatedly. The other two moisture contents showed that moisture content enhanced heat exchange properties of the feedstock and this generally increased the amount of volatile organic matter released. It was observed that for 15% moisture sawdust increase of temperature did not consistently exhibit an increase in degree of devolatilisation of organic matter. However, the 30% moisture sawdust showed an increase in devolatilisation with increase in temperature.  The effects of increasing reactor auger speed had the most consistent trend with which an increase in speed showed a decrease in degree of devolatilisation thus increasing char yield.
The empirical data collected from lab scale and pilot plant experiments were used to create mass and energy balances. These were the basis of the large scale mobile pyrolysis plant which was designed to process 3.45 tonnes per hour. Due to size restrictions the large scale dryer was not fitted in the container. It was then determined that the feedstock would either be dried using an onsite kiln or the reactor would process green sawdust.

A preliminary economic feasibility assessment was performed for the base case scenario which processed pre-dried sawdust of 15% moisture content at 400°C and a retention time of 45 minutes. A sensitivity analysis based on predicted optimistic and pessimistic conditions showed that automation of the plant had the potential to increase the economic viability of the large scale process.

year: 2013

title: Processes of Pakeha change in response to the Treaty of Waitangi

authors: Huygens, Ingrid Louise Maria

subjects: Pakeha change

abstract: The sense of crisis that marks our times may be seen as a crisis for dominant groups whose once-secure hegemony is being challenged by marginalised others. It is in theorising the reply from the dominant group to the voices of the oppressed that existing Western conceptions of social change fall silent. The dominant Pakeha group in Aotearoa New Zealand has used discourses of benign colonisation and harmonious race relations to resist 165 years of communication from indigenous Māori about their oppression and a dishonoured treaty for settlement. My research documents the appearance of the Treaty of Waitangi into the Pakeha consciousness, and the now 30 year-long response by a Pakeha antiracism movement to educate their own cultural group about its agreements. Targeting government, community and social services organisations, activist educators used Freire's (1975) approach of conscientising dialogue to present a more critical view of colonisation, and to encourage participants to consider the complicity of their organisations in ongoing structural and cultural racism.

Based on my membership of local and national networks of activist educators, I was able to organise and facilitate data gathering from three sources to investigate processes of Pakeha change in: (i) unpublished material describing the antiracism and Treaty movement's historical theorising and strategies over 30 years, (ii) a country-wide process of co-theorising among contemporary Treaty educator groups about their work and perceived influence, and (iii) a collection of organisational accounts of Treaty-focused change. The collected records confirmed that a coherent anti-colonial discourse, which I have termed 'Pakeha honouring the Treaty', was in use to construct institutional and constitutional changes in non-government organisations. My interpretation of key elements in a local theory of transforming action included emotional responses to counter-cultural information, collective work for cultural and institutional change and practising a mutually agreed relationship with Māori. I concluded that these emotional, collective and relationship processes in dominant group change were crucial in helping to construct the new conceptual resources of 'affirming Māori authority' and 'striving towards a right relationship with Māori'. These counter-colonial constructions allowed Pakeha a non-resistant and facilitative response to Māori challenge, and enabled a dialogue with Māori about decolonisation. 

By examining in one research programme the genealogy and interdependencies of a new discourse, my research contributes to theorising about the production of new, counter-hegemonic discourses, and confirms the crucial part played by social movements in developing new, liberatory constructions of the social order.

My research calls for further theory-building on (i) emotional and spiritual aspects of transformational learning, (ii) processes involved in consciously-undertaken cultural change by dominant/coloniser groups, and (iii) practising of mutually agreed relationships with indigenous peoples by dominant/coloniser groups. 

My research has implications for theorising how coloniser and dominant groups generally may participate in liberatory social change and decolonisation work, and  the part played by the Western states in the global struggles by indigenous people for recognition of their world-views and aspirations.  

It remains to be seen whether counter-colonial discourses and organisational changes aimed at 'honouring the Treaty' with indigenous peoples will be sufficiently widely adopted to help transform Western dominating cultures and colonial projects. In the meantime, acknowledging and documenting these counter-colonial discourses and their constructions opens up increasing possibilities for constructing, from a history of colonisation, a different future.

text: Processes of Pakeha change in response to the Treaty of Waitangi The sense of crisis that marks our times may be seen as a crisis for dominant groups whose once-secure hegemony is being challenged by marginalised others. It is in theorising the reply from the dominant group to the voices of the oppressed that existing Western conceptions of social change fall silent. The dominant Pakeha group in Aotearoa New Zealand has used discourses of benign colonisation and harmonious race relations to resist 165 years of communication from indigenous Māori about their oppression and a dishonoured treaty for settlement. My research documents the appearance of the Treaty of Waitangi into the Pakeha consciousness, and the now 30 year-long response by a Pakeha antiracism movement to educate their own cultural group about its agreements. Targeting government, community and social services organisations, activist educators used Freire's (1975) approach of conscientising dialogue to present a more critical view of colonisation, and to encourage participants to consider the complicity of their organisations in ongoing structural and cultural racism.

Based on my membership of local and national networks of activist educators, I was able to organise and facilitate data gathering from three sources to investigate processes of Pakeha change in: (i) unpublished material describing the antiracism and Treaty movement's historical theorising and strategies over 30 years, (ii) a country-wide process of co-theorising among contemporary Treaty educator groups about their work and perceived influence, and (iii) a collection of organisational accounts of Treaty-focused change. The collected records confirmed that a coherent anti-colonial discourse, which I have termed 'Pakeha honouring the Treaty', was in use to construct institutional and constitutional changes in non-government organisations. My interpretation of key elements in a local theory of transforming action included emotional responses to counter-cultural information, collective work for cultural and institutional change and practising a mutually agreed relationship with Māori. I concluded that these emotional, collective and relationship processes in dominant group change were crucial in helping to construct the new conceptual resources of 'affirming Māori authority' and 'striving towards a right relationship with Māori'. These counter-colonial constructions allowed Pakeha a non-resistant and facilitative response to Māori challenge, and enabled a dialogue with Māori about decolonisation. 

By examining in one research programme the genealogy and interdependencies of a new discourse, my research contributes to theorising about the production of new, counter-hegemonic discourses, and confirms the crucial part played by social movements in developing new, liberatory constructions of the social order.

My research calls for further theory-building on (i) emotional and spiritual aspects of transformational learning, (ii) processes involved in consciously-undertaken cultural change by dominant/coloniser groups, and (iii) practising of mutually agreed relationships with indigenous peoples by dominant/coloniser groups. 

My research has implications for theorising how coloniser and dominant groups generally may participate in liberatory social change and decolonisation work, and  the part played by the Western states in the global struggles by indigenous people for recognition of their world-views and aspirations.  

It remains to be seen whether counter-colonial discourses and organisational changes aimed at 'honouring the Treaty' with indigenous peoples will be sufficiently widely adopted to help transform Western dominating cultures and colonial projects. In the meantime, acknowledging and documenting these counter-colonial discourses and their constructions opens up increasing possibilities for constructing, from a history of colonisation, a different future.

year: 2007