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Pretreatment technologies to increase the methane yields by anaerobic digestion in relation to cost efficiency of substrate transportation
Linköping University, The Tema Institute, Department of Water and Environmental Studies.
2011 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [sv]

Med ett växande energibehov i världen, sinande energikällor i form av fossila bränslen och en miljö som vi under en längre tid har förorenat behövs det nya energiformer som är mer långsiktiga och framförallt miljövänliga. En sådan energiform är biogas. Biogasprocessen är dock inte helt optimerad. Flera av de substrat som används idag tar lång tid att röta och bryts bara ner till viss del i processen eller innehåller onödigt mycket vatten, vilket ger höga transportkostnader. Med syfte att göra biogasprocessen mer ekonomisk lönsam utvärderas i denna rapport på uppdrag från E.ON några olika förbehandlingstekniker: Ångexplosion, extrusion, avvattning och kalkbehandling. Förhoppningen är att dessa ska kunna öka lönsamheten för storskalig biogasproduktion och kanske möjliggöra biogasproduktion från tidigare obrukbara substrat som fjädrar och halm.

 För att jämföra och utvärdera förbehandlingsteknikerna utfördes batchrötningsförsök i 330 ml flaskor med obehandlade och förbehandlade substrat. De flesta förbehandle substraten gav snabbare nedbrytning och några gav även högre metanutbyte än de obehandlade. Fjädrar och halm, som från början hade ett lågt utbyte, påverkades mest av förbehandlingen. Ångexploderade fjädrar gav efter 44 dagars rötning 141% högre metanutbyte och extruderad halm gav 22% högre metanutbyte än obehandlad.

 För ekonomiska beräkningarna användes en referensanläggning med en förutbestämd substratmix: 12500 ton majs och 11500 ton hästgödsel. Att tillgå för referensanläggningen finns dessutom fjädrar. Cambis THP-anläggning för ångexplosion visade sig vara alldeles för dyr för referensanläggningen. En THP-anläggning kräver en större biogasanläggning där en större mängd svårnedbrytbara substrat rötas för att bli lönsam. En extruder skulle kunna vara lönsam för för refernsanläggningen om hästgödseln som de har tillgång till innehåller halm som strömaterial. En investering i en extruder bara för att förbehandla majsensilage visade sig inte lönsam.

 Avvattning av gödsel gav signifikant lägre utbyte av biogas per torrvikt men signifikant högre utbyte per våtvikt. Avvattningsutrustningen från Splitvision, som testades, var för dyr för att bli lönsam. Först när gården låg 4 mil från biogasanläggningen blev det billigare att avvattna gödsel och transportera den jämfört med att transportera den obehandlad. Andra avvattningsutrustningar i studien var billigare i drift så det finns möjligheter att tekniken kan bli lönsam med någon av dessa.

Abstract [en]

The world needs new energy sources that are durable for long time and which not affect the environment negatively. Biogas fulfills those demands. The biogas process is however not completely optimized. Several of the substrates used today for biogas production are slowly degraded and only partly digested in the process. Other substrates consist of unnecessarily much water which makes transportation costly. To optimize the process and make the biogas process more profitable, several pretreatment techniques are evaluated by direction of E.ON in this report: steam explosion, extrusion, lime treatment and dewatering. The hope is that one of those could increase the profitability and hopefully also enable substrates that not are working today like feathers and straw.

To compare and evaluate the different pretreatment batch digester, experiments were carried out during 31-44 days for untreated and pretreated substrates. Most pretreated substrates were faster degraded than untreated and some also gave a higher methane yield. Chicken waste feathers and wheat straw, which had low methane yields untreated, were affected most by pretreatment. Steam exploded feathers gave after 44 days of digestion 141% higher methane yield and extruded straw gave 22% higher methane yield than untreated samples of the same substrate.

A reference plant with a substrate mixture of 12500 tonnes of maize silage and 11500 tons of horsemanure annually was used to make economical calculations. Additionally, chicken waste feathers waste could be included. Obtainable for the reference plant were also chicken waste feathers. Steam explosion appeared to be too expensive for a plant in the size of the reference plant. Its large capacity could probably make it profitable for a much larger biogas plant running on a lot of hard digestible substrates. An extruder could be a profitable investment for the reference plant if the plant gets horse manure with straw as bedding material. To just use the extruder to pretreat maize silage could not make the investment profitable.

Dewatering of manure gave significantly lower methane yield per dry weight but significantly higher methane yield per wet weight. The increase in methane yield per wet weight makes the substrate better for transportation. The dewatering equipment from Splitvision tried in this study had too high operational costs and was too expensive to make dewatering particularly profitable. Only when the farm was situated farther away than 40km from the biogas plant it was cheaper to dewater the manure before transport than to transport the manure without any pretreatment. Other dewatering equipments evaluated in this study had much lower operational costs and among those an equipment that makes dewatering profitable might therefore be found.

The world needs new energy sources that are durable for long time and which not affect the environment negatively. Biogas fulfills those demands. The biogas process is however not completely optimized. Several of the substrates used today for biogas production are slowly degraded and only partly digested in the process. Other substrates consist of unnecessarily much water which makes transportation costly. To optimize the process and make the biogas process more profitable, several pretreatment techniques are evaluated by direction of E.ON in this report: steam explosion, extrusion, lime treatment and dewatering. The hope is that one of those could increase the profitability and hopefully also enable substrates that not are working today like feathers and straw.

To compare and evaluate the different pretreatment batch digester, experiments were carried out during 31-44 days for untreated and pretreated substrates. Most pretreated substrates were faster degraded than untreated and some also gave a higher methane yield. Chicken waste feathers and wheat straw, which had low methane yields untreated, were affected most by pretreatment. Steam exploded feathers gave after 44 days of digestion 141% higher methane yield and extruded straw gave 22% higher methane yield than untreated samples of the same substrate.

A reference plant with a substrate mixture of 12500 tonnes of maize silage and 11500 tons of horsemanure annually was used to make economical calculations. Additionally, chicken waste feathers waste could be included. Obtainable for the reference plant were also chicken waste feathers. Steam explosion appeared to be too expensive for a plant in the size of the reference plant. Its large capacity could probably make it profitable for a much larger biogas plant running on a lot of hard digestible substrates. An extruder could be a profitable investment for the reference plant if the plant gets horse manure with straw as bedding material. To just use the extruder to pretreat maize silage could not make the investment profitable.

Dewatering of manure gave significantly lower methane yield per dry weight but significantly higher methane yield per wet weight. The increase in methane yield per wet weight makes the substrate better for transportation. The dewatering equipment from Splitvision tried in this study had too high operational costs and was too expensive to make dewatering particularly profitable. Only when the farm was situated farther away than 40km from the biogas plant it was cheaper to dewater the manure before transport than to transport the manure without any pretreatment. Other dewatering equipments evaluated in this study had much lower operational costs and among those an equipment that makes dewatering profitable might therefore be found.

Place, publisher, year, edition, pages
2011. , 67 p.
Keyword [en]
biogas, steam explosion, extrusion, dewatering, feathers, anaerobic digestion
Keyword [sv]
Biogas, ångexplosion, extrusion, avvattning, fjädrar, rötning
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-69755ISRN: LIU-TEMA/TBM-EX—11/001--SEOAI: oai:DiVA.org:liu-69755DiVA: diva2:432791
Subject / course
Biotechnology
Presentation
2011-02-24, Linköping, 13:15 (Swedish)
Uppsok
Technology
Examiners
Available from: 2011-10-24 Created: 2011-08-06 Last updated: 2011-10-26Bibliographically approved

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Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
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