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Investigation on the Use of Intermediate Crops for Anaerobic Digestion as a Renewable Source of Energy

Ahlberg, Ida LU and Silva Nilsson, Thais Leidiomara LU (2015) KET920 20151
Chemical Engineering
Abstract
The eminent dilemma around the relationship between the increasing world population, the need of new fuel sources and environment issues has raised great awareness in the last decades. The European Parliament has set common goals such as the reduction of the greenhouse gases by 20 % by the year of 2020, followed by the requirement of at least 10 % of the fuel has to be biofuel. An adjacent issue is the source of the biofuel, which are currently most of agricultural crop nature. However these energy crops should not compete with food crops and favourably have other features that promotes its usage. Intermediate crops are for example a promising resource since it may reduce the risk of the nutrients leaching since the crop can take up... (More)
The eminent dilemma around the relationship between the increasing world population, the need of new fuel sources and environment issues has raised great awareness in the last decades. The European Parliament has set common goals such as the reduction of the greenhouse gases by 20 % by the year of 2020, followed by the requirement of at least 10 % of the fuel has to be biofuel. An adjacent issue is the source of the biofuel, which are currently most of agricultural crop nature. However these energy crops should not compete with food crops and favourably have other features that promotes its usage. Intermediate crops are for example a promising resource since it may reduce the risk of the nutrients leaching since the crop can take up nutrients in the soil.

The aim of this thesis was to investigate the potential of six different intermediate crops (hemp, oilseed radish, white mustard, phacelia, sudangrass and hairy vetch) as energy resources under anaerobic digestion condition after 30 days. Hairy vetch showed the highest methane yield (343 m3/ t VS) followed by sudangrass (316 m3/ t VS). Sudangrass showed a slight potential to increase the methane yield (97 % of theoretical yield based on the component analysis for the sudangrass) if steam pretreatment is for instance applied. This relatively high yield result could be attributed to the relatively low lignin content of sudangrass compared to other crops (16 % of TS). An important factor taken into consideration when selecting which crop to investigate for pretreatment was also the methane yield per hectare for sudangrass which had the second highest value (995 Nm3/ ha) after oilseed radish (1217 Nm3/ ha). Other factors were also taken into account in the decision such as: total solids content, how easily the crop is managed in agriculture for example due to water content and the negative impact of shared diseases with other crops.

Based on the results and factors discussed above, the crop which had the greatest potential for methane yield improvement but also availability of ensiled material, sudangrass, was further investigated for the pretreatment effects on methane production. The ensiled sudangrass was pressed into a liquid fraction and a solid fraction, where the latter was taken forward to the pretreatment step. The pretreatment conditions studied were steam pretreatment with added catalyst (1 % acetic acid or 2 % sodium hydroxide weight percentage base on total solid of sudangrass, sprayed in the crop) and it was compared to steam pretreatment alone. Also different temperatures (180 °C, 190 °C, 200 °C and 210 °C) and retention times (5 and 10 min) were studied. The sodium hydroxide impregnated crop did not show better yield than the ensiled sudangrass. Quite the contrary: the alkaline catalyst showed in the best case scenario (190 °C and 10 min) a methane production decrease of 12 % compared to the solid fraction of ensiled sudangrass (325 m3/ t VS). On the other hand the acid treatment at 190 °C and 5 min residence time showed an 11 % increase in the same context. The acid treatment at 190 °C and 5 min showed the highest final methane yield (362 m3/ t VS).

Conclusively it could be said that all the intermediate crops have a potential for usage in methane production, assuming other aspects are optimized for its usage. Pretreatment can be with advantage be used to improve the methane yield, where there is room for improvement. The question is rather what specific combination of pretreatment conditions will yield the best enhancement and careful investigations should be made before determining the ultimate pretreatment for a specific crop (Less)
Popular Abstract (Swedish)
I detta examensarbete har sex olika mellangrödor (hampa, honungsört, oljerättika, sudangräs, luddvicker och vitsenap) undersökts för användning till biogas produktion som ett alternativ för framställning av biobränsle.

Miljöfrågor, behovet av nya bränslen och ökningen av världens befolkning har lett till uppmärksamheten för förnybara bränslen det senaste årtiondet. Den Europeiska Unionen har satt gemensamma mål att minska utsläppen av växthusgaserna med 20 % till år 2020, vilket följs av att minst 10 % av bränslena i transportsektorn ska vara förnybara. Biogas är ett av de befintliga alternativa bränslena. Dessutom är det mycket fördelaktigt om råvaran för biogasen inte konkurrerar med jordbruksareal avsedd för livsmedel. De så kallade... (More)
I detta examensarbete har sex olika mellangrödor (hampa, honungsört, oljerättika, sudangräs, luddvicker och vitsenap) undersökts för användning till biogas produktion som ett alternativ för framställning av biobränsle.

Miljöfrågor, behovet av nya bränslen och ökningen av världens befolkning har lett till uppmärksamheten för förnybara bränslen det senaste årtiondet. Den Europeiska Unionen har satt gemensamma mål att minska utsläppen av växthusgaserna med 20 % till år 2020, vilket följs av att minst 10 % av bränslena i transportsektorn ska vara förnybara. Biogas är ett av de befintliga alternativa bränslena. Dessutom är det mycket fördelaktigt om råvaran för biogasen inte konkurrerar med jordbruksareal avsedd för livsmedel. De så kallade mellangrödorna blir i kontexten ett mycket bra alternativ eftersom de förebygger kväveläckage genom att fånga upp näringsämne från jorden.

En viktig fråga är källan till biobränslet, vilket för närvarande är mest jordbruksgrödor, såsom majs och vete. Den energigröda som används till produktion av biobränsle bör dock inte konkurrera med livsmedelsgrödor utan även ha andra funktioner som främjar dess användning. Mellangrödor är ett lovande material då de bland annat kan förbättra kvalitén i jorden genom att binda näringsämnen och minska näringsläckaget till närliggande vattendrag. Mellangrödor etableras och skördas i ett intervall i grödsekvensen eller växtföljden då marken ligger oanvänd för annan odling, mellan två huvudgrödor. Huvudgrödorna kan till exempel vara potatis, höstvete eller raps.

Biogas består till största delen av metan och därefter koldioxid. När våra undersökningar gjordes på metanutbyte blev det oljerättika som gav bäst resultat per hektar, följt av sudangräs. För sudangräs ansågs det finnas utrymme för förbättringar med hjälp av förbehandling. Ensilerat sudangräs valdes därför för ytterligare undersökning. Detta utifrån bland annat beslut om att ensileringen av material blivit bra, hur lätt materialet är att hantera i jordbruket och resultat för metanutbyte per hektar. Undersökningen delades upp i två typer av förbehandlingar, en där det ensilerade sudangräset impregnerades med en syra och en där det impregnerades med en bas. Det ensilerade sudangräset sparades i en vätskefas och en fast fas. Den fasta delen av sudangräset behandlades med ättiksyra eller med natriumhydroxid. Därefter ångförbehandlades sudangräset och under ångförbehandlingen testades olika temperaturer och uppehållstider. Den förbehandling som gav högst metanutbyte var syra-katalyserad sudangräs ångförbehandlat i 190 °C och med 5 minuters uppehållstid. Undersökningen visade att sudangräs katalyserad med natriumhydroxid som bas inte gav bra resultat, då metanutbytet var lägre än både färskt material och ensilerat sudangräs.

Analyser på såväl färska mellangrödor, ensilerat material samt förbehandlat sudangräs har gjorts med avseende på komponentanalyser och undersökningar för metanutbyte. Det har tagits fram hur mycket socker, biprodukter och lignin som de olika materialen innehåller. Med analys av dessa resultat tillsammans med resultat för metanutbyte gjordes slutsatser både för färska mellangrödor och för det förbehandlade sudangräset. Slutligen kom vi fram till att syrakatalyserad ångförbehandling på sudangräs gav bättre metanutbyte än baskatalyserad. (Less)
Please use this url to cite or link to this publication:
author
Ahlberg, Ida LU and Silva Nilsson, Thais Leidiomara LU
supervisor
organization
alternative title
En undersökning av biogaspotential för färska mellangrödor och ångförbehandlad ensilerat sudangräs
course
KET920 20151
year
type
H2 - Master's Degree (Two Years)
subject
keywords
biofuels, pretreatment, acetic acid, steam pretreatment, sodium hydroxide, kemiteknik, chemical engineering, Mellangrödor, Hemp, White mustard, Oilseed radish, Sudangrass, Hairy vetch, Phacelia, energy, Intermediate crops, Biogas, Anaerobic digestion
language
English
id
5472252
date added to LUP
2015-06-16 11:21:12
date last changed
2015-06-18 14:04:26
@misc{5472252,
  abstract     = {The eminent dilemma around the relationship between the increasing world population, the need of new fuel sources and environment issues has raised great awareness in the last decades. The European Parliament has set common goals such as the reduction of the greenhouse gases by 20 % by the year of 2020, followed by the requirement of at least 10 % of the fuel has to be biofuel. An adjacent issue is the source of the biofuel, which are currently most of agricultural crop nature. However these energy crops should not compete with food crops and favourably have other features that promotes its usage. Intermediate crops are for example a promising resource since it may reduce the risk of the nutrients leaching since the crop can take up nutrients in the soil.

The aim of this thesis was to investigate the potential of six different intermediate crops (hemp, oilseed radish, white mustard, phacelia, sudangrass and hairy vetch) as energy resources under anaerobic digestion condition after 30 days. Hairy vetch showed the highest methane yield (343 m3/ t VS) followed by sudangrass (316 m3/ t VS). Sudangrass showed a slight potential to increase the methane yield (97 % of theoretical yield based on the component analysis for the sudangrass) if steam pretreatment is for instance applied. This relatively high yield result could be attributed to the relatively low lignin content of sudangrass compared to other crops (16 % of TS). An important factor taken into consideration when selecting which crop to investigate for pretreatment was also the methane yield per hectare for sudangrass which had the second highest value (995 Nm3/ ha) after oilseed radish (1217 Nm3/ ha). Other factors were also taken into account in the decision such as: total solids content, how easily the crop is managed in agriculture for example due to water content and the negative impact of shared diseases with other crops.

Based on the results and factors discussed above, the crop which had the greatest potential for methane yield improvement but also availability of ensiled material, sudangrass, was further investigated for the pretreatment effects on methane production. The ensiled sudangrass was pressed into a liquid fraction and a solid fraction, where the latter was taken forward to the pretreatment step. The pretreatment conditions studied were steam pretreatment with added catalyst (1 % acetic acid or 2 % sodium hydroxide weight percentage base on total solid of sudangrass, sprayed in the crop) and it was compared to steam pretreatment alone. Also different temperatures (180 °C, 190 °C, 200 °C and 210 °C) and retention times (5 and 10 min) were studied. The sodium hydroxide impregnated crop did not show better yield than the ensiled sudangrass. Quite the contrary: the alkaline catalyst showed in the best case scenario (190 °C and 10 min) a methane production decrease of 12 % compared to the solid fraction of ensiled sudangrass (325 m3/ t VS). On the other hand the acid treatment at 190 °C and 5 min residence time showed an 11 % increase in the same context. The acid treatment at 190 °C and 5 min showed the highest final methane yield (362 m3/ t VS).

Conclusively it could be said that all the intermediate crops have a potential for usage in methane production, assuming other aspects are optimized for its usage. Pretreatment can be with advantage be used to improve the methane yield, where there is room for improvement. The question is rather what specific combination of pretreatment conditions will yield the best enhancement and careful investigations should be made before determining the ultimate pretreatment for a specific crop},
  author       = {Ahlberg, Ida and Silva Nilsson, Thais Leidiomara},
  keyword      = {biofuels,pretreatment,acetic acid,steam pretreatment,sodium hydroxide,kemiteknik,chemical engineering,Mellangrödor,Hemp,White mustard,Oilseed radish,Sudangrass,Hairy vetch,Phacelia,energy,Intermediate crops,Biogas,Anaerobic digestion},
  language     = {eng},
  note         = {Student Paper},
  title        = {Investigation on the Use of Intermediate Crops for Anaerobic Digestion as a Renewable Source of Energy},
  year         = {2015},
}