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Process Utility Performance Evaluation and Enhancements in the Traditional Sugar Cane Industry
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.ORCID iD: 0000-0001-8091-8767
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The need to achieve sustainable development has led to devising various approaches for the efficient utilization of natural resources. Renewable energy technology and energy efficiency measures feature prominently in this regard, and in particular for industries such as sugar production:  the sugar cane industry’s eponymous feedstock is a renewable resource, and mills have potential for increased energy savings via improvements to cogeneration units, electric drive retrofitting, and other measures.  The overall objective of this research work is to investigate different approaches of efficiency improvements for enhancing sugar cane conversion, thereby increasing the services obtained including surplus electric power delivery. Traditional sugar cane mills, i.e. those that lack modern components such as high-performance boilers and electric drives, are the focus of this investigation. 

System simulations show that modern mills generate more electrical power as compared to traditional mills, with power-to-heat ratios nearly one order of magnitude higher (i.e. 0.3-0.5).  Comparison of the thermodynamic performance of three retrofits showed that such modifications could raise the performance of traditional mills to approach those for their modern counterparts. Results for a base case traditional plant show that losses related to mechanical prime movers are high, since the mills and shredder are driven by steam and generate excess mechanical power. When considering press mill stoppages, steam is wasted during the ensuing fuel oil-fired start-up period. CO2emission for such transient conditions can be decreased owing via bagasse drying and storage. 

 

In studying both energy and water impacts, a comparison of four technological improvements demonstrates benefits outside the crushing season for three scenarios: recovery of excess wastewater for enhanced imbibition; recovery of waste heat for thermally-driven cooling; and pelletization of excess bagasse. The fourth option, involving upgrading of the mill’s cogeneration unit, is advantageous for continuous surplus power supply.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. , p. 120
Series
TRITA-ITM-AVL ; 2019:21
Keywords [en]
Sugar cane, energy saving, heat loss, steady state, transient state, CO2 emission; absorption chiller, pellet, bagasse drying, energy perfor-mance, traditional mills, modern mills, waste water, surplus power
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
URN: urn:nbn:se:kth:diva-251736ISBN: 978-91-7873-231-9 (print)OAI: oai:DiVA.org:kth-251736DiVA, id: diva2:1316636
Public defence
2019-08-20, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Sida - Swedish International Development Cooperation AgencyAvailable from: 2019-05-24 Created: 2019-05-20 Last updated: 2019-05-24Bibliographically approved
List of papers
1. Energy performance comparisons and enhancements in the sugar cane industry
Open this publication in new window or tab >>Energy performance comparisons and enhancements in the sugar cane industry
2018 (English)In: Biomass Conversion and Biorefinery, ISSN 2190-6815, E-ISSN 2190-6823Article in journal (Other academic) Published
Abstract [en]

In this study, energy-related operational parameters for modern and traditional (conventional) sugar mills are analyzed, with the goals of identifying improvements in energy efficiency and potential for surplus electricity export. Results show that the power- to-heat ratio of modern and traditional mills is clearly distinct, lying in the ranges of 0.3–0.5 and 0.04–0.07, respectively. Modifications under consideration for the traditional mills include the following upgrades: electric drives and higher capacity back-pressure turbine (case 1); high-pressure boiler, condensing extraction steam turbine and electric drives (case 2); and improvements in case 2 plus bagasse drying (case 3). The thermodynamic impact of these modifications shows that more power is generated as the modification becomes more advanced. Case 1 exhibits a modest increase in cogeneration efficiency (4%) as compared to the base case, while the cogeneration efficiency increase is more marked for cases 2 and 3 (21% and 31%, respectively). Surplus power was studied in a regional context, where it was found that the contribution of 19 retrofitted sugar mills in nine Brazilian regions could supply 30% or more power as compared to current installed power capacity. The economic analysis showed that levelized cost of electricity (LCOE) was lowest for case 1 (11 USD/MWh) and highest for cases 2 and 3 (58 USD/kWh).

Keywords
Sugarcane . Traditional mills . Modern mills . LCOE . Energy performance . Model
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-207111 (URN)10.1007/s13399-018-0349-z (DOI)
Note

QR 20190401

Available from: 2017-05-16 Created: 2017-05-16 Last updated: 2019-05-20Bibliographically approved
2. Assessing the potential of energy saving in a traditional sugar canemill during steady state and transient conditions: part I: basecase plant model
Open this publication in new window or tab >>Assessing the potential of energy saving in a traditional sugar canemill during steady state and transient conditions: part I: basecase plant model
2015 (English)In: Biomass Conversion and Biorefinery, ISSN 2190-6823Article in journal (Refereed) Published
Abstract [en]

Sugar cane mills are energy intensive industries andalso have a large potential of providing surplus energy interms of heat or power. Identification of heat and mechanicallosses in sugar mills is one approach in indicating energysaving potential in sugar mills, especially in traditional mills.Such assessment of the energy flows in sugar mills needs to bedone both in steady state and transient conditions (where suddenstoppages occur). In this paper, such an approach is consideredwhere a base case plant is modeled for steady state andtransient state operations. For the transient state study, a typicalstoppage is chosen and three different scenarios aremodeled. Heat loss calculations are done for major cogenerationunits and for the amount accumulated of the surplus bagassewhen the steady state operation is estimated. The resultsof the models show that during steady state operation, thelosses related to mechanical prime movers is on the higherside as the mills and shredder are driven by steamand generatemechanical power higher than what is needed by the mills andthe shredder equipment themselves. In the transient statescenarios, where fuel oil is introduced during press mill stoppage,there is steam wasted (steam that could have been usedfor mechanical power generation) starting from the periodwhere the fuel oil is introduced until the power required duringthe stoppage is reached. The CO2 emission during the use offuel oil is also quite significant during the stoppage.

Place, publisher, year, edition, pages
Springer, 2015
Keywords
Sugar cane, Heat loss, Sudden stoppage, Transient, Model
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-185729 (URN)10.1007/s13399-015-0179-1 (DOI)000377398800010 ()2-s2.0-84978024364 (Scopus ID)
Funder
Sida - Swedish International Development Cooperation Agency
Note

QC 20160512

Available from: 2016-04-25 Created: 2016-04-25 Last updated: 2019-05-20Bibliographically approved
3. Upgrading of a traditional sugar cane mill to a modern milland assessing the potential of energy saving during steady stateand transient conditions: part II: models for a modifiedcogeneration unit
Open this publication in new window or tab >>Upgrading of a traditional sugar cane mill to a modern milland assessing the potential of energy saving during steady stateand transient conditions: part II: models for a modifiedcogeneration unit
2016 (English)In: Biomass Conversion and Biorefinery, ISSN 2190-6823, Vol. 6, no 2, p. 233-245Article in journal (Refereed) Published
Abstract [en]

It is known that there is a significant amount ofthermal energy used for the sugar cane industry for the purposeof power production and for use in the sugar or ethanolprocessing in cane sugar industries. Likewise, it is understoodthat there are substantial amounts of waste heat that is notbeing recovered, in particular for traditional sugar mills. Regardlessof this, energy conservation is given less considerationas compared to operational convenience due to the factthat sugar mills are self-sufficient in energy (heat and power).The identification of such potential heat loss areas (especiallyduring transient conditions) suggests the sugar mills play avital role in energy saving. In this study, a modified setup ofthe base case plant considered in part I of this paper is assessedfor its energy potential and possible major heat losses duringsteady state and transient conditions where 2-h stoppage of themill presses are considered to occur. For the modified setup,there are two major scenarios considered having two subscenarioseach. The result of the assessment showed that thesteady state assumption scenario of the modified plant (wherebagasse drying is not considered) indicated a 20 % reductionin the losses considered which resulted in a 57 % power generationincrease as compared to the steady state model of thebase case plant. It is also possible to save excess bagasse bydrying the bagasse for later use during unexpected stoppage.The carbon dioxide emission (amounting 29 t/day in case 2aof this study) that occurs during the use of fuel oil during suchstoppages will thus be avoided. The simple economic analysisshowed that it is only in case 2a where fuel oil cost is includedin the operation cost that resulted in a negative NPV. Since therest of the scenarios use bagasse as a fuel which is free, theNPV for all was positive. For the electricity price of 0.04 US$/kWh and discount rate of 15 %, the minimum paybackperiod attained is about 3 years (case 1b) where the bagassemoisture content is 30 % whereas the maximum payback periodis 6 years (case 1a) where there is no bagasse dryingconsidered.

Place, publisher, year, edition, pages
Springer, 2016
Keywords
Sugar cane, Bagasse drying, Steady state, Transient state, Heat loss
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-185730 (URN)10.1007/s13399-015-0180-8 (DOI)000377398800011 ()2-s2.0-84978024580 (Scopus ID)
Funder
Sida - Swedish International Development Cooperation Agency
Note

QC 20160512

Available from: 2016-04-25 Created: 2016-04-25 Last updated: 2019-05-20Bibliographically approved
4. A Comparison of Various Technological Options for Improving Energy and Water Use Efficiency in a Traditional Sugar Mill
Open this publication in new window or tab >>A Comparison of Various Technological Options for Improving Energy and Water Use Efficiency in a Traditional Sugar Mill
Show others...
2016 (English)In: Sustainability, ISSN 2071-1050, E-ISSN 2071-1050, Vol. 8, no 12, article id 1227Article in journal (Refereed) Published
Abstract [en]

This study is a comparison of four technological improvements proposed in previous works for the Cuban sugar mill Carlos Balino. These technological options are: (1) utilization of excess wastewater for enhanced imbibition; (2) utilization of waste heat for thermally driven cooling; (3) utilization of excess bagasse for pellets; and (4) modification of the cogeneration unit for maximum electric power generation. The method used for the evaluation of the technological options involves using criteria such as energy saving, financial gains, and CO2 emission saving potential. The results of the analysis show that the first three technological improvement options are attractive only during the crushing season. On the other hand, the last technological improvement option can be attractive if a year round generation of surplus power is sought. The first technological improvement option leads to only minor changes in energy utilization, but the increase in sugar yield of 8.7% leads to attractive profitability with an extremely low payback period. The CO2 emissions saved due to the fourth technological improvement option are the highest (22,000 tonnes/year) and the cost of CO2 emissions saved for the third technological improvement option (lowest) amount to 41 USD/tonne of CO2 emissions saved. The cycle efficiencies of the third and fourth technological improvement options are 37.9% and 36.8%, respectively, with payback periods of 2.3 and 1.6 years. The second technological improvement option is the least attractive alternative of the group.

Place, publisher, year, edition, pages
MDPI AG, 2016
Keywords
sugar cane bagasse, Carlos Balino, energy efficiency, wastewater reuse, imbibition, CO2 emission, absorption chiller, pellet, electricity, energy saving, payback period
National Category
Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-199509 (URN)10.3390/su8121227 (DOI)000389317100018 ()2-s2.0-85007346954 (Scopus ID)
Note

QC 20170117

Available from: 2017-01-17 Created: 2017-01-09 Last updated: 2019-05-20Bibliographically approved

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