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Development and fluid dynamic evaluation of novel circulating fluidised bed elements for low-temperature adsorption based carbon capture processesZaragoza Martín, Francisco Javier January 2017 (has links)
A methodology for the thermodynamic-kinetic evaluation of circulating systems as TSA carbon capture processes is developed and used in the assessment of a novel CFB configuration against a benchmark (co-current riser). The novel CFB features a counter-current adsorber, a counter-current regenerator and a riser, the latter element playing a double role of solids conveyer and co-current adsorber. The advantages sought by using a counter-current adsorber are not only the more efficient gas-solid contact mode with respect co-current, but also a low pressure drop derived from operation at lower gas velocities and hydrostatic head partially supported on the contactor internals. Knowledge of the adsorption equilibrium alone is sufficient to realise the much higher sorbent circulation rates required by co-current configurations –compared to counter-current– to meet the stringent carbon capture specifications of 90% recovery and 95% purity. Higher solids circulation rates imply higher energy requirements for regeneration, and therefore research and development of co-current gas-solid contactors cannot be justified in terms of searching for energy-efficient post-combustion carbon capture processes. Parallel experimental investigation in the operation and fluid dynamics of cold model CFB rigs is carried out with the purposes of: 1) providing information that may impact the process performance and can be fed into the mathematical model used in the theoretical assessment for more realistic evaluation, and 2) determine gas and solids residence time distributions (RTDs), which are used for the estimation of axial dispersion and comparison with published results in similar systems. Gas RTD data is generated using a tracer pulse injection-detection technique, whereas RTD for the solid phase is studied using positron emission particle tracking (PEPT). The PEPT technique proved to be adequate for the identification of flow regimes in the novel design of the counter-current adsorber, featuring inclined orifice trays. At low gas velocities the particles flow straight down through the tray holes, whereas at higher velocities the particles flow down in zig-zag, increasing the residence time of the particles and reducing the particle axial dispersion, both beneficial in terms of separation efficiency.
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Evaluation of fluidised-bed reactors for the biological treatment of synthol reaction water, a high-strength COD petrochemical effluent / by Katharine Gaenor Aske SwabeySwabey, Katharine Gaenor Aske January 2004 (has links)
Reaction water, a high-strength COD (chemical oxygen demand) petrochemical effluent,
is generated during the Fischer-Tropsch reaction in the SASOL Synthol process at
SASOL SynFuels, Secunda, South Africa. Distillation of the reaction water to remove
non- and oxygenated hydrocarbons yields approximately 25 - 30 ML/d of an organic
(carboxylic) acid-enriched stream (average COD of 16 000 mg/L) containing primarily
C2 – C5 organic acids, light oils, aldehydes, ketones, cresols and phenols. Together with
the Oily sewer water (API) and Stripped Gas Liquor (SGL) process streams, this process
effluent is currently treated in ten dedicated activated sludge basins. However, the
successful operation of these activated sludge systems has proven to be difficult with low
organic loading rates (3.5 kg COD/m3.d) low COD removal efficiencies (<80 %) and
high specific air requirements (60 - 75 m3 air/kg CODrem). It is hypothesised that these
operational difficulties can be attributed to organic shock loadings, variation in
volumetric and hydraulic loadings, as well as variations in the composition of the various
process streams being treated. Due to the fact that the Fischer-Tropsch (Synthol) reaction
water constitutes 70 % of the COD load on the activated sludge systems, alternative
processes to improve the treatment cost and efficiency of the Fischer-Tropsch acid stream
are being investigated. Various studies evaluating the aerobic and anaerobic treatment of
Fischer-Tropsch reaction water alone in suspended growth wastewater treatment systems
have proven unsuccessful. High rate fixed-film processes or biofilm reactors, of which
the fluidised-bed reactors are considered to he one of the most effective and promising
processes for the treatment of high-strength industrial wastewaters, could he a suitable
alternative. The primary aim of this study was to evaluate the suitability of biological
fluidised-bed reactors (BFBRs) for the treatment of Fischer-Tropsch reaction water.
During this study, the use of aerobic and anaerobic biological fluidised-bed reactors
(BFBR), using sand and granular activated carbon (GAC) as support matrices, were
evaluated for the treatment of a synthetic effluent analogous to the Fischer-Tropsch
reaction water stream. After inoculation, the reactors were operated in batch mode for 10
days at a bed height expansion of 30% and a temperature of 30 ºC to facilitate biofilm
formation on the various support matrices. This was followed by continuous operation of
the reactors at hydraulic retention times (HRTs) of 2 days. While the COD of the
influent and subsequent organic loading rate (OLR) was incrementally increased from 1
600 mg/L to a maximum of 20 000 mg/L and 18 000 mg/L for the aerobic and anaerobic
reactors, respectively. Once the maximum influent COD concentration had been
achieved the OLR was further increased by decreasing the HRTs of the aerobic and
anaerobic reactors to 24h and 8h, and 36h, 24h and 19h, respectively. The dissolved
O2 concentration in the main reactor columns of the aerobic reactors was constantly
maintained at 0.50 mg/L.
Chemical Oxygen Demand (COD) removal efficiencies in excess of 80 % at OLR of up
to 30 kg COD/m3.d were achieved in the aerobic BFBRs using both sand and GAC as
support matrices. Specific air requirements were calculated to be approximately 35 and
41 m3 air/kg CODrem for the BFBRs using sand and GAC as support matrices,
respectively. The oxygen transfer efficiency was calculated to be approximately 5.4 %.
At high OLR (> 15 kg COD/m3.d) significant problems were experienced with plugging
and subsequent channelling in the BFBR using GAC as support matrix and the reactor had
to be backwashed frequently in order to remove excess biomass. Despite these backwash
procedures, COD removal efficiencies recovered to previous levels within 24 hours. In
contrast, no significant problems were encountered with plug formation and channelling
in the BFBR using sand as support matrix. In general the overall reactor performance
and COD removal efficiency of the aerobic BFBR using sand as support matrix was more
stable and consistent than the BFBR using GAC as support matrix. This BFBR was also
more resilient to variations in operational conditions, such as the lowering of the
hydraulic retention times and changes in the influent pH. Both aerobic reactors displayed
high resilience and COD removal efficiencies in excess of 80 % were achieved during
shock loadings. However, both reactors were highly sensitive to changes in pH and any
decrease in pH below the pKa values of the volatile fatty acids in the influent (pKa of
acetic acid = 4.76) resulted in significant reductions in COD removal efficiencies.
Maintenance of reactor pH above 5.0 was thus an essential facet of reactor operation.
It has been reported that the VFA/alkalinity ratio can be used to assess the stability of
biological reactors. The VFA/alkalinity ratios of the aerobic BFBRs containing sand and
GAC as support matrices were stable (VFNalkalinity ratios of < 0.3 - 0.4) until the OLR
increased above 10 kg/m3.d. At OLRs higher than 10 kg/m3.d the VFA/alkalinity ratios
in the BFBR using sand support matrix increased to 4, above the failure limit value of 0.3
- 0.4. In contrast the VFA/alkalinity ratios of the BFBR using GAC support matrix
remained stable until an OLR of 15 kg/m3.d was obtained, where the VFA/alkalinity
ratios then increased to > 3. Towards the end of the study when an OLR of
approximately 25 kg/m3.d was obtained the VFA/alkalinity ratios of both the BFBRs
using sand and GAC as support matrices increased to 9 and 6 respectively, indicating the
decrease in reactor stability and acidification of the process. Total solid (TS) and volatile
solid (VS) concentrations in the aerobic BFBRs were initially high and decreased over
time. While the total suspended solids (TSS) and volatile suspended solids (VSS)
concentrations were initially low and increased over time as the OLR was increased, this
is thought to be as a result of decreased HRT leading to biomass washout.
The anaerobic BFBR using sand as support matrix never stabilised and COD removal
efficiency remained very low (< 30 %), possibly due to the high levels of shear forces.
Further studies concerning the use of sand as support matrix were subsequently
terminated. An average COD removal efficiency of approximately 60 % was achieved in
the anaerobic BFBR using GAC as a support matrix at organic loading rates lower than
10 kg COD/m3.d. The removal efficiency gradually decreased to 50 % as organic loading
rates were increased to 20 kg COD/m3.d. At OLRs of 20 kg COD/m3.d, the biogas and
methane yields of the anaerobic BFBR using GAC as support matrix were determined to
be approximately 0.38 m3 biogas/kg CODrem (0.3 m3 biogas/m3reactor vol.d), and 0.20 m3
CH4/kg CODrem (0.23 m3 CH4/m3reactor vol.d), respectively. This value is 57 % of the
theoretical maximum methane yield attainable (3.5 m3 CH4/kg CODrem). The methane
yield increased as the OLR increased, however, when the OLR reached 8 kg/m3.d the
methane yield levelled off and remained constant at approximately 2 m3 CH4/m3reactor vol.d.
Although the methane content of the biogas was initially very low (< 30 %), the methane
content gradually increased to 60 % at OLRs of 20 kg COD/m3.d. The anaerobic BFBR
using GAC as support matrix determined that as the OLR increased (>12 kg/m3.d), the
VFA/alkalinity ratio increased to approximately 5, this is indicative of the decrease in
stability and acidification of the process. The anaerobic BFBR using GAC as support
matrix experienced no problems with plug formation and channelling. This is due to the
lower biomass production by anaerobic microorganisms than in the aerobic reactors. The
TS and VS concentrations were lower than the aerobic concentrations but followed the
same trend of decreasing over time, while the TSS and VSS concentrations increased due
to decreased HRTs. The anaerobic BFBR was sensitive to dramatic variations in organic
loading rates, pH and COD removal efficiencies decreased significantly after any shock
loadings.
Compared to the activated sludge systems currently being used for the biological
treatment of Fischer-Tropsch reaction water at SASOL SynFuels, Secunda, South Africa,
a seven-fold increase in OLR and a 55 % reduction in the specific air requirement was
achieved using the aerobic BFBRs. The methane produced could also be used as an
alternative source of energy. It is, however, evident that the support matrix has a
significant influence on reactor performance. Excellent results were achieved using sand
and GAC as support matrices in the aerobic and anaerobic BFBRs, respectively. It is
thus recommended that future research be conducted on the optimisation of the use of
aerobic and anaerobic BFBRs using these support matrices.
Based on the results obtained from this study, it can be concluded that both aerobic and
anaerobic treatment of a synthetic effluent analogous to the Fischer-Tropsch reaction
water as generated by SASOL in the Fischer-Tropsch Synthol process were successful
and that the application of fluidised-bed reactors (attached growth systems) could serve
as a feasible alternative technology when compared to the current activated sludge
treatment systems (suspended growth) currently used.
Keywords: aerobic treatment, anaerobic treatment, biological fluidised-bed reactors,
petrochemical effluent, Fischer-Tropsch reaction water, industrial wastewater. / Thesis (M. Omgewingswetenskappe)--North-West University, Potchefstroom Campus, 2004.
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Evaluation of fluidised-bed reactors for the biological treatment of synthol reaction water, a high-strength COD petrochemical effluent / by Katharine Gaenor Aske SwabeySwabey, Katharine Gaenor Aske January 2004 (has links)
Reaction water, a high-strength COD (chemical oxygen demand) petrochemical effluent,
is generated during the Fischer-Tropsch reaction in the SASOL Synthol process at
SASOL SynFuels, Secunda, South Africa. Distillation of the reaction water to remove
non- and oxygenated hydrocarbons yields approximately 25 - 30 ML/d of an organic
(carboxylic) acid-enriched stream (average COD of 16 000 mg/L) containing primarily
C2 – C5 organic acids, light oils, aldehydes, ketones, cresols and phenols. Together with
the Oily sewer water (API) and Stripped Gas Liquor (SGL) process streams, this process
effluent is currently treated in ten dedicated activated sludge basins. However, the
successful operation of these activated sludge systems has proven to be difficult with low
organic loading rates (3.5 kg COD/m3.d) low COD removal efficiencies (<80 %) and
high specific air requirements (60 - 75 m3 air/kg CODrem). It is hypothesised that these
operational difficulties can be attributed to organic shock loadings, variation in
volumetric and hydraulic loadings, as well as variations in the composition of the various
process streams being treated. Due to the fact that the Fischer-Tropsch (Synthol) reaction
water constitutes 70 % of the COD load on the activated sludge systems, alternative
processes to improve the treatment cost and efficiency of the Fischer-Tropsch acid stream
are being investigated. Various studies evaluating the aerobic and anaerobic treatment of
Fischer-Tropsch reaction water alone in suspended growth wastewater treatment systems
have proven unsuccessful. High rate fixed-film processes or biofilm reactors, of which
the fluidised-bed reactors are considered to he one of the most effective and promising
processes for the treatment of high-strength industrial wastewaters, could he a suitable
alternative. The primary aim of this study was to evaluate the suitability of biological
fluidised-bed reactors (BFBRs) for the treatment of Fischer-Tropsch reaction water.
During this study, the use of aerobic and anaerobic biological fluidised-bed reactors
(BFBR), using sand and granular activated carbon (GAC) as support matrices, were
evaluated for the treatment of a synthetic effluent analogous to the Fischer-Tropsch
reaction water stream. After inoculation, the reactors were operated in batch mode for 10
days at a bed height expansion of 30% and a temperature of 30 ºC to facilitate biofilm
formation on the various support matrices. This was followed by continuous operation of
the reactors at hydraulic retention times (HRTs) of 2 days. While the COD of the
influent and subsequent organic loading rate (OLR) was incrementally increased from 1
600 mg/L to a maximum of 20 000 mg/L and 18 000 mg/L for the aerobic and anaerobic
reactors, respectively. Once the maximum influent COD concentration had been
achieved the OLR was further increased by decreasing the HRTs of the aerobic and
anaerobic reactors to 24h and 8h, and 36h, 24h and 19h, respectively. The dissolved
O2 concentration in the main reactor columns of the aerobic reactors was constantly
maintained at 0.50 mg/L.
Chemical Oxygen Demand (COD) removal efficiencies in excess of 80 % at OLR of up
to 30 kg COD/m3.d were achieved in the aerobic BFBRs using both sand and GAC as
support matrices. Specific air requirements were calculated to be approximately 35 and
41 m3 air/kg CODrem for the BFBRs using sand and GAC as support matrices,
respectively. The oxygen transfer efficiency was calculated to be approximately 5.4 %.
At high OLR (> 15 kg COD/m3.d) significant problems were experienced with plugging
and subsequent channelling in the BFBR using GAC as support matrix and the reactor had
to be backwashed frequently in order to remove excess biomass. Despite these backwash
procedures, COD removal efficiencies recovered to previous levels within 24 hours. In
contrast, no significant problems were encountered with plug formation and channelling
in the BFBR using sand as support matrix. In general the overall reactor performance
and COD removal efficiency of the aerobic BFBR using sand as support matrix was more
stable and consistent than the BFBR using GAC as support matrix. This BFBR was also
more resilient to variations in operational conditions, such as the lowering of the
hydraulic retention times and changes in the influent pH. Both aerobic reactors displayed
high resilience and COD removal efficiencies in excess of 80 % were achieved during
shock loadings. However, both reactors were highly sensitive to changes in pH and any
decrease in pH below the pKa values of the volatile fatty acids in the influent (pKa of
acetic acid = 4.76) resulted in significant reductions in COD removal efficiencies.
Maintenance of reactor pH above 5.0 was thus an essential facet of reactor operation.
It has been reported that the VFA/alkalinity ratio can be used to assess the stability of
biological reactors. The VFA/alkalinity ratios of the aerobic BFBRs containing sand and
GAC as support matrices were stable (VFNalkalinity ratios of < 0.3 - 0.4) until the OLR
increased above 10 kg/m3.d. At OLRs higher than 10 kg/m3.d the VFA/alkalinity ratios
in the BFBR using sand support matrix increased to 4, above the failure limit value of 0.3
- 0.4. In contrast the VFA/alkalinity ratios of the BFBR using GAC support matrix
remained stable until an OLR of 15 kg/m3.d was obtained, where the VFA/alkalinity
ratios then increased to > 3. Towards the end of the study when an OLR of
approximately 25 kg/m3.d was obtained the VFA/alkalinity ratios of both the BFBRs
using sand and GAC as support matrices increased to 9 and 6 respectively, indicating the
decrease in reactor stability and acidification of the process. Total solid (TS) and volatile
solid (VS) concentrations in the aerobic BFBRs were initially high and decreased over
time. While the total suspended solids (TSS) and volatile suspended solids (VSS)
concentrations were initially low and increased over time as the OLR was increased, this
is thought to be as a result of decreased HRT leading to biomass washout.
The anaerobic BFBR using sand as support matrix never stabilised and COD removal
efficiency remained very low (< 30 %), possibly due to the high levels of shear forces.
Further studies concerning the use of sand as support matrix were subsequently
terminated. An average COD removal efficiency of approximately 60 % was achieved in
the anaerobic BFBR using GAC as a support matrix at organic loading rates lower than
10 kg COD/m3.d. The removal efficiency gradually decreased to 50 % as organic loading
rates were increased to 20 kg COD/m3.d. At OLRs of 20 kg COD/m3.d, the biogas and
methane yields of the anaerobic BFBR using GAC as support matrix were determined to
be approximately 0.38 m3 biogas/kg CODrem (0.3 m3 biogas/m3reactor vol.d), and 0.20 m3
CH4/kg CODrem (0.23 m3 CH4/m3reactor vol.d), respectively. This value is 57 % of the
theoretical maximum methane yield attainable (3.5 m3 CH4/kg CODrem). The methane
yield increased as the OLR increased, however, when the OLR reached 8 kg/m3.d the
methane yield levelled off and remained constant at approximately 2 m3 CH4/m3reactor vol.d.
Although the methane content of the biogas was initially very low (< 30 %), the methane
content gradually increased to 60 % at OLRs of 20 kg COD/m3.d. The anaerobic BFBR
using GAC as support matrix determined that as the OLR increased (>12 kg/m3.d), the
VFA/alkalinity ratio increased to approximately 5, this is indicative of the decrease in
stability and acidification of the process. The anaerobic BFBR using GAC as support
matrix experienced no problems with plug formation and channelling. This is due to the
lower biomass production by anaerobic microorganisms than in the aerobic reactors. The
TS and VS concentrations were lower than the aerobic concentrations but followed the
same trend of decreasing over time, while the TSS and VSS concentrations increased due
to decreased HRTs. The anaerobic BFBR was sensitive to dramatic variations in organic
loading rates, pH and COD removal efficiencies decreased significantly after any shock
loadings.
Compared to the activated sludge systems currently being used for the biological
treatment of Fischer-Tropsch reaction water at SASOL SynFuels, Secunda, South Africa,
a seven-fold increase in OLR and a 55 % reduction in the specific air requirement was
achieved using the aerobic BFBRs. The methane produced could also be used as an
alternative source of energy. It is, however, evident that the support matrix has a
significant influence on reactor performance. Excellent results were achieved using sand
and GAC as support matrices in the aerobic and anaerobic BFBRs, respectively. It is
thus recommended that future research be conducted on the optimisation of the use of
aerobic and anaerobic BFBRs using these support matrices.
Based on the results obtained from this study, it can be concluded that both aerobic and
anaerobic treatment of a synthetic effluent analogous to the Fischer-Tropsch reaction
water as generated by SASOL in the Fischer-Tropsch Synthol process were successful
and that the application of fluidised-bed reactors (attached growth systems) could serve
as a feasible alternative technology when compared to the current activated sludge
treatment systems (suspended growth) currently used.
Keywords: aerobic treatment, anaerobic treatment, biological fluidised-bed reactors,
petrochemical effluent, Fischer-Tropsch reaction water, industrial wastewater. / Thesis (M. Omgewingswetenskappe)--North-West University, Potchefstroom Campus, 2004.
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Powered addition as modelling technique for flow processesDe Wet, Pierre 03 1900 (has links)
Thesis (MSc (Applied Mathematics))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The interpretation – and compilation of predictive equations to represent the general
trend – of collected data is aided immensely by its graphical representation. Whilst,
by and large, predictive equations are more accurate and convenient for use in applications
than graphs, the latter is often preferable since it visually illustrates deviations
in the data, thereby giving an indication of reliability and the range of validity of the
equation. Combination of these two tools – a graph for demonstration and an equation
for use – is desirable to ensure optimal understanding. Often, however, the functional
dependencies of the dependent variable are only known for large and small values
of the independent variable; solutions for intermediate quantities being obscure for
various reasons (e.g. narrow band within which the transition from one regime to
the other occurs, inadequate knowledge of the physics in this area, etc.). The limiting
solutions may be regarded as asymptotic and the powered addition to a power,
s, of such asymptotes, f0 and f¥ , leads to a single correlating equation that is applicable
over the entire domain of the dependent variable. This procedure circumvents
the introduction of ad hoc curve fitting measures for the different regions and subsequent,
unwanted jumps in piecewise fitted correlative equations for the dependent
variable(s). Approaches to successfully implement the technique for different combinations
of asymptotic conditions are discussed. The aforementioned method of powered
addition is applied to experimental data and the semblances and discrepancies
with literature and analytical models are discussed; the underlying motivation being
the aspiration towards establishing a sound modelling framework for analytical and
computational predictive measures. The purported procedure is revealed to be highly
useful in the summarising and interpretation of experimental data in an elegant and
simplistic manner. / AFRIKAANSE OPSOMMING: Die interpretasie – en samestelling van vergelykings om die algemene tendens voor te
stel – van versamelde data word onoorsienbaar bygestaan deur die grafiese voorstelling
daarvan. Ten spyte daarvan dat vergelykings meer akkuraat en geskik is vir
die gebruik in toepassings as grafieke, is laasgenoemde dikwels verskieslik aangesien
dit afwykings in die data visueel illustreer en sodoende ’n aanduiding van die betroubaarheid
en omvang van geldigheid van die vergelyking bied. ’n Kombinasie van
hierdie twee instrumente – ’n grafiek vir demonstrasie en ’n vergelyking vir aanwending
– is wenslik om optimale begrip te verseker. Die funksionele afhanklikheid van
die afhanklike veranderlike is egter dikwels slegs bekend vir groot en klein waardes
van die onafhanklike veranderlike; die oplossings by intermediêre hoeveelhede onduidelik
as gevolg van verskeie redes (waaronder, bv. ’n smal band van waardes
waarbinne die oorgang tussen prosesse plaasvind, onvoldoende kennis van die fisika
in hierdie area, ens.). Beperkende oplossings / vergelykings kan as asimptote beskou
word en magsaddisie tot ’n mag, s, van sodanige asimptote, f0 en f¥, lei tot ’n enkel,
saamgestelde oplossing wat toepaslik is oor die algehele domein van die onafhanklike
veranderlike. Dié prosedure voorkom die instelling van ad hoc passingstegnieke
vir die verskillende gebiede en die gevolglike ongewensde spronge in stuksgewyspassende
vergelykings van die afhankilke veranderlike(s). Na aanleiding van die
moontlike kombinasies van asimptotiese toestande word verskillende benaderings
vir die suksesvolle toepassing van hierdie tegniek bespreek. Die bogemelde metode
van magsaddisie word toegepas op eksperimentele data en die ooreenkomste en verskille
met literatuur en analitiese modelle bespreek; die onderliggend motivering ’n
strewe na die daarstelling van ’n modellerings-raamwerk vir analitiese- en rekenaarvoorspellingsmaatreëls.
Die voorgestelde prosedure word aangetoon om, op ’n elegante
en eenvoudige wyse, hoogs bruikbaar te wees vir die lesing en interpretasie van
eksperimentele data.
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Optimisation of co-firing of high moisture biomass with coal in a bubbling fluidised bed combustorAkram, Muhammad January 2012 (has links)
The work presented in this thesis was carried out with a particular view of enhancing the of coal fired fluidised bed hot gas generator (HGG) at the Cantley factory of British Sugar. It covers combustion of coal and biomass and their blends also called co-firing in a fluidised bed combustor. Particularly it focuses on the effect of introduction of moisture as part of fuel or injection of water into the bed on the reduction of excess air to get a stable bed temperature. Although this thesis is focused on increasing the throughput of the HGG, the study has a broad application and can be beneficial in utilising relatively cheap, poor quality, unprepared biomass materials. The results of this study can be helpful in devising systems to deal with wastes from different industries in co-combustion with a fuel of higher calorific value such as coal. Thus the study will have dual impact on the industry; addressing waste management issues on one hand and producing useful energy on the other. This may contribute towards meeting the targets of Kyoto Protocol by reducing emissions of carbon dioxide (COi) as biomass is thought to be COa neutral. The fluidised bed at Cantley is used to dry animal feed and has a design capacity of 40 MW but due to limitations of flow of fluidising gases caused by high flow resistance through sparge pipes, the combustor is running under capacity. Consequently, some of the animal feed has to be dried by using expensive oil fired drier. In any combustion system excess air is used to control combustion temperature. In fluidised bed combustion excess air is used to control bed temperature. If the bed is cooled by other means the requirement of excess air can be reduced. This is the basic idea behind this study which is aimed at enhancing the capacity of the HGG by cooling the bed and thus reducing excess air requirements. The excess air thus spared can be used to combust more coal in the bed and thus will reduce dependence on oil fired dryer and will have financial benefits for British Sugar. Different fuels including wood pellets, wood chips and sugar industry by-products such as vinasse, raffinate and pressed pulp were fired/cofired with Thoresby coal in a fluidised bed test rig installed at the University of Glamorgan. The blends of wood chips and pressed pulp with coal are co-fired at different moisture contents. The tests were conducted at different thermal inputs at a wide range of excess air levels. Most of the work is focusedon the combustion of blends of coal and pressed pulp in different proportions. It was found that the maximum proportion of the pressed pulp in the blend with coal which could be burned successfully in the fluidised bed is 50%. During combustion of different coal-pulp and coal-wood chips blends it was found that excess air requirement is reduced by around 20% in comparison to coal only firing, over the range of the operating conditions tested. Because of the presence of potassium in pressed pulp, which could cause agglomeration during combustion in fluidised beds, longer term tests were carried out with 50/50 blend of coal and pulp. No signs of agglomeration were observed when the rig was fired for 8 days for almost 7 hours a day. However, Scanning Electron Microscopy (SEM) analyses of bed samples taken at the end of every day have shown the accumulation of potassium in the bed up to 1%. For comparison purposes tests were also carried out by co-firing coal with raffiante and vinasse and then it was observed that the bed defluidised relatively quickly, within 40 minutes of co-firing. Post experiment SEM analysis confirmed the accumulation of potassium in the bed which was found to be around 8% for raffinate and around 10% for the vinasse experiment. It was found that the pulp is difficult to deal with and particularly its feeding into the fluidised bed could be a potential problem. Therefore, injection of water into the bed, a relatively cheaper and adaptable option, was also investigated. It was found that emissions of carbon monoxide due to incomplete combustion or water gas shift reaction would not be a problem as long as the bed temperature is controlled above 800 °C. It was found that the injection of water at a rate of 4.5 1/h into the bed fired at 17 kW reduced the air flow requirement by around 7.5 m3/h which corresponds to a reduction of almost 20% which agrees with the finding with coal-pulp blends co-firing. This excess air can be used to burn around 5 kW equivalent of more coal and thus result in an increase in the thermal capacity by around 30%. Therefore, it may be possible to enhance the thermal capacity of the HGG at Cantley by 30% by injecting water into the bed or by co-firing coal and pulp.
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Oxygen carrier and reactor development for chemical looping processes and enhanced CO2 recoveryHaider, Syed Kumail January 2016 (has links)
This thesis’s main focus is a CO2 capture technology known as chemical looping combustion (CLC). The technology is a novel form of combustion and fuel processing that can be applied to gas, solid and liquid fuels. By using two interconnected fluidised-bed reactors, with a bed material capable of transferring oxygen from air to the fuel, a stream of almost pure CO2 can be produced. This stream is undiluted with nitrogen and is produced without any direct process efficiency loss from the overall combustion process. The heart of the process is the oxygen carrier bed material, which transfers oxygen from an air to fuel reactor for the conversion of the fuel. Oxygen carrier materials and their production should be of low relative cost for use in large-scale systems. The first part of this research centres on development and investigative studies conducted to assess the use of low-cost materials as oxygen carriers and as supports. Mixed-oxide oxygen carriers of modified manganese ore and iron ore were produced by impregnation. While copper (II) oxide supported on alumina cement and CaO have been produced by pelletisation. These oxygen carriers were investigated for their ability to convert gaseous fuels in a lab-scale fluidised bed, and characterised for their mechanical and chemical suitability in the CLC process. The modified ores and pelletised copper-based oxygen carriers’ mechanical properties were enhanced by their production methods and in the case of the modified iron ore, significant oxygen uncoupling was observed. The copper-based oxygen carriers particularly those containing alumina cement showed high conversion rates of gaseous fuels and improved mechanical stability. The second part of this research thesis focuses on the design philosophy, commissioning and operation of a dual-fast bed chemical looping pilot reactor. Based on the operational experience, recommendations for modifications to the CLC system are discussed. In support, a parallel hydrodynamic investigation has been conducted to validate control and operational strategies for the newlydesigned reactor system. It was determined that the two fast bed risers share similar density and pressure profiles. Stable global circulation rate is flexible and could be maintained despite being pneumatically controlled. Reactor-reactor leakage via the loop-seals is sensitive to loop seal bed-height, and inlet fluid velocity but can be maintained as such to ensure no leakage is encountered.
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Sinkkivälkkeen leijukerrospasutuksen stabiilisuusMetsärinta, M.-L. (Maija-Leena) 11 November 2008 (has links)
Abstract
Zinc production has been known since 200 BC. Fluidised bed roasting is the first process stage of the electrolytical zinc production process, was developed in the 1940s.
The raw material for zinc is usually sphalerite concentrate. This sulphide concentrate is oxidised in a roaster. Oxidation reactions produce energy, which is removed as steam, and sulphur dioxide, which is used as the raw material of sulphuric acid.
During recent decades sphalerite concentrates have contained more and more impurities and at the same time they have become more fine-grained. Impurities cause problems during fluidised bed roasting. As a consequence, production capacity decreases, there are breaks in production. Starting up and shutting down a process during production breaks cause the environmental emissions. In order to be able optimise production, the oxidation mechanisms of impure sphalerite and methods for controlling them have to be known.
The hypothesis of this work was as follows: In addition to temperature, the impurity content and particle size of the feed and oxygen coefficient also have an effect on the stability of fluidised bed roasting. Diverse concentrates require different oxygen coefficients and temperatures. The basic target of this work was to develop a method to help find the required conditions and to control them in industrial roasters. This study was restricted to considering the effects of the iron, copper and lead contents in sphalerite concentrate.
A review was made of earlier roasting studies and experiences. This study also evaluated the thermodynamic background of roasting. The oxidation mechanisms were also studied in the laboratory using a fluidised bed roaster and horizontal tube furnace. The results were validated in an industrial roaster.
On the grounds of these studies the different sphalerite concentrates really do require diverse roasting temperatures and oxygen coefficients. Foremore, the same kinds of concentrates require a different roasting temperature and oxygen coefficient, if their particle size distributions are different. Controlling the concentrate feed particle size may help to control the stability of the roasting bed and the temperature of the upper part of the furnace.
The impurities increase the forming of direct bond sintering and thus the forming of sulphide liquid phases. Oxides and sulphates may also form liquid phases. These kinds of liquid phases cause problems in the fluidised bed. Continuous control of the oxygen coefficient and bed temperature and the use of a unique oxygen coefficient and temperature range for every concentrate mixture would make it possible to minimise problems in the furnace.
Laboratory and industrial scale tests have verified the variables and methods for controlling conditions in the roaster bed. / Tiivistelmä
Sinkin valmistus on ollut tunnettua ajalta 200 eKr. Leijukerrospasutus, joka on ensimmäinen prosessivaihe elektrolyyttisessä sinkin valmistusprosessissa, otettiin sekin käyttöön jo 1940-luvulla.
Sinkin raaka-aineena käytetään sfaleriittirikastetta, joka hapetetaan pasutuksessa. Hapetusreaktiot tuottavat energiaa, joka otetaan talteen höyrynä, ja rikkidioksidia, josta tuotetaan rikkihappoa.
Viime vuosikymmeninä sfaleriittirikasteet ovat tulleet epäpuhtaammiksi ja samalla partikkelikooltaan hienommiksi. Epäpuhtaudet aiheuttavat ongelmia leijupetiin. Tämän seurauksena uunien kapasiteetti laskee, tulee tuotannon seisauksia. Näiden seisauksien yhteydessä tapahtuvat prosessin ylös- ja alasajot aiheuttavat päästöjä. Tuotannon optimoimiseksi täytyy tuntea epäpuhtaiden sfaleriittirikasteiden hapetusmekanismit ja tavat niiden hallitsemiseksi.
Tämän työn hypoteesi oli: Leijukerrospasutuksen stabiilisuuteen vaikuttaa lämpötilan lisäksi epäpuhtauksien määrä syötteessä ja syötteen partikkelikokojakauma sekä happikerroin. Erilaiset rikasteet vaativat erilaisen happikerroin- ja lämpötila-alueen. Työn tavoite oli kehittää menetelmä,jolla saadaan vaaditut olosuhteet syntymään ja hallittua. Tutkimuksissa rajoituttiin tarkastelemaan sfaleriittirikasteiden sisältämän raudan, kuparin ja lyijyn vaikutusta.
Työssä tutustuttiin epäpuhtaiden sfaleriittirikasteiden pasutuksen alueelta aiemmin tehtyihin tutkimuksiin ja eri pasutoilla saatuihin kokemuksiin sekä selvitettiin pasutuksen termodynaaminen tausta. Laboratoriotutkimuksilla selvitettiin hapettumismekanismeja leijukerrosreaktorissa ja pelleteillä kvartsilaivassa putkiuunissa. Tulosten todentaminen tehtiin koeajoilla teollisessa tuotantolaitoksessa.
Johtopäätöksenä näistä tutkimuksista voidaan todeta, että erilaiset sfaleriittirikasteet edellyttävät kullekin rikasteelle ominaista pasutuslämpötilaa ja happikerrointa. Lisäksi samantyyppistenkin rikasteiden vaatima pasutuslämpötila ja happikerroin voivat vaihdella, jos rikasteen partikkelikokojakauma vaihtelee. Syötteen partikkelikokoa säätäen voidaan ohjata pedin stabiilisuutta ja uunin yläosan lämpötilaa.
Epäpuhtaudet lisäävät suorasidossintrautumien syntyä ja siten sulfidisulafaasien muodostumista. Sulafaaseja voivat muodostaa myös tietyt oksidit ja sulfaatit. Tästä seuraa ongelmia leijupedissä. Happikertoimen jatkuva seuranta ja säätö kullekin rikasteelle ominaisella alueella, samoin kuin lämpötilan seuranta ja säätö, mahdollistavat ongelmien minimoinnin.
Tähän työhön liittyvissä laboratoriotutkimuksissa ja teollisen mittakaavan tutkimuksissa todennettiin muuttujat ja keinot olosuhteiden hallitsemiseksi.
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Využití spalin pro zplyňování biomasy / The use of flue gas for the biomass gasificationŠvácha, Filip January 2019 (has links)
The aim of this thesis is to describe the process of biomass gasification using gas simulating the composition of flue gas – a mixture of oxygen, carbon dioxide and water vapor. In the research part of the thesis the issue of gasification with the focus on fluidized bed gasification and the effect of the gasification medium used on the gasification process is discussed. In the practical part the thesis deals with the design, realization and evaluation of the experiment on a real device. The aim of the experiment is to determine the effect of the exact composition of the mixture of these three media on the gasification process and on the quality of the gas generated. The aim is to find the optimum composition for obtaining gas with the highest possible lower heating value, which contains as little tar as possible. At the end of the work, the results from the experiment are presented and described.
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Synthèse des ferrates (VI) de métaux alcalins en utilisant le chlore comme oxydant / Synthesis of alkaline metal ferrates (VI) by using chlorine as oxydantOstrosi, Etleva 15 October 2007 (has links)
Ce travail est focalisé sur la synthèse par voie sèche des ferrates de métaux alcalins (A2FeVIO4, A = K, Na) en utilisant le chlore comme oxydant. Les ferrates (VI) sont des composés qui contiennent du fer sous son état d’oxydation +6. Leur importance s’avère grandissante dans le traitement des eaux et des effluents industriels du fait de la nature multifonctionnelle du FeVI. Bien que l’existence de ferrates alcalins soit citée depuis un siècle, ceux-ci n’ont pas fait l’objet d’un nombre considérable d’études. Ceci est principalement du à leur instabilité et aux difficultés concernant les méthodes de préparation. La synthèse de ferrates alcalins dans le réacteur rotatif a été réalisée à température ambiante et la réaction totale de synthèse fut exothermique. Pour les expériences effectuées, des quantités de réactants solides (sel de fer + AOH) allant de quelques dizaines de grammes jusqu’à 400 grammes ont été utilisées. Les effets de différents paramètres sur le déroulement de la synthèse ont été étudiés. Afin d’améliorer le processus de synthèse et appliquer l’extrapolation industrielle, la synthèse de ferrates a été réalisée au sein d’un réacteur à lit fluidisé. Le procédé consiste premièrement, à mélanger préalablement l’hydroxyde de sodium (NaOH) avec le sulfate ferreux (FeSO4?H2O) et deuxièmement, à fluidiser le mélange obtenu en présence du chlore dilué. L’application de ce procédé permet d’atteindre un rendement en FeVI d’environ 56 %. Les résultats obtenus témoignent d’un processus propre et innovant et d’un faible coût pour la synthèse des ferrates de métaux alcalins à plus grande échelle / This work is focused on the dry method synthesis of alkaline metal ferrates (A2FeVIO4, A = K, Na) by using chlorine as oxidant. The ferrates (VI) are compounds which contain iron under its oxidation state +6. They gain growing importance in the industrial effluent and water treatment because of multipurpose nature of FeVI. Although the existence of alkaline ferrates has been mentioned for one century, the alkaline ferrates were not the subject of a considerable number of studies. This is mainly due to their instability and difficulties concerning the methods of preparation. The alkaline ferrate synthesis in the rotary reactor was carried out at room temperature and the whole reaction of synthesis was exothermic. For the realized tests of synthesis, solid quantities of (iron salt + AOH) of a few tens of grams up to 400 grams were used. The effects of various parameters on the synthesis process were studied. In the perspective of improving the process of synthesis and applying the industrial extrapolation, the synthesis of ferrate was realised in a fluidized bed reactor. The proceeding occurs by two successive steps: the first consisting in mixing beforehand the sodium hydroxide with ferrous sulphate and the second to fluidize the mixture obtained in the presence of diluted chlorine. The application of this process makes possible to attain a yield in FeVI of about 56 % and the results obtained show a clean and innovative process of low cost for the synthesis of alkaline metal ferrates on a large scale
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Investigation of multiphase reactor hydrodynamics using magnetic resonance imagingRice, Nicholas Paul January 2019 (has links)
This thesis presents an investigation on multiphase reactor hydrodynamics using magnetic resonance imaging (MRI). The study demonstrates experimental techniques by which computational and quasi-analytical fluid models may be validated. Three types of industrially-important multiphase reaction vessels are considered: a co-current upflow gas-liquid-solid bed, a co-current downward trickle bed (gas, liquid, solid), and a gas-solid fluidised bed. These reactors were selected as they commonly demonstrate local hydrodynamic anisotropy which affects the global performance of industrial units. MRI was used to obtain 2D velocity images of the gas and liquid phases in the packed beds, and of the gas and the solid phases in the fluidised bed. This study reports the first spatially resolved velocity measurements of both the gas and liquid phases in a co-current upflow bed, and the gas and solid phases of an isolated bubble in a fluidised bed. The experimental vessels were: 52 mm in diameter using 5 mm glass spheres in the upflow bed at 8 bara, 27 mm with 5 mm glass spheres in the trickle bed at 6.75 bara, and 52 mm using 1.2 mm poppy seeds as the fluidised particles at 8.5 bara. The experiments were conducted at a laboratory temperature of 25.0 ± 3.0 °C. In the upflow bed, time-averaged velocity images were acquired over a 2.5 h experimental time. This was done to capture the steady state behaviour of the vessel operating in the pulsing flow regime. The temporally-stable trickle flow state in the trickle bed was imaged over 15-100 minutes. In both packed beds, severe spatial anisotropy in the distribution of flow between pores was revealed. Furthermore, the data were used to determine classical design features such as catalyst wetting and liquid holdup which compared well with literature models. The trickle bed data were further analysed using a morphological algorithm which unambiguously identified the gas-liquid and liquid-solid interfaces. The interfacial flow fields were found to be similar to the bulk flow, with most voxels exhibiting static behaviour. The amount of interaction between the phases was found to be minimal, which is typical of the low interaction regime. A single bubble injection system was employed in the fluidised bed which allowed the injection of isolated bubbles into the incipiently fluidised bed. It also enabled the triggered acquisition of NMR data at precise time intervals. The bubble was found to be an indented ellipsoidal shape, which rose with atypical behaviour which caused it to collapse. Rise velocity was found to be consistent with theory, and the injected bubbles were sufficiently spatially reproducible to acquire 2D velocity images using single-point imaging. These velocity images showed flow behaviour characteristic of a 'fast' rising bubble, with a gas recirculation cloud 37 mm in diameter. The particle field was shown to have very high flow in the bubble wake, revealing the mechanism of bubble collapse. The flow data were compared to classical two-phase fluidisation theory, which revealed noteworthy differences in the division of flow between the particulate and bubbling regions.
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