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Gasification

 

 

 

 

 

 

 

 

Introduction to Thermochemical Processes

The figure below represents the basic concept of our areas of research on the thermochamical conversion of bio-waste into 2nd generation fuels, chemicals and biochar.

thermo

Gasification

Biomass gasification differs from pyrolysis in that a limited amount of oxygen is allowed, either via the addition of air, oxygen or steam. Gasification processes tend to provide a smaller range of products than pyrolysis processes and are geared more towards the production of combustible (e.g. hydrogen, carbon monoxide, methane, ethylene, etc) or reformable gases. Temperature, and the particular architecture of the gasifer employed, affect the distribution of these products. These gases can be used directly for energy or catalytically reformed into valuable chemicals for industry or transport.

Gasification occurs best under higher temperatures (>1000 oC) and in less oxygen restricted conditions than pyrolysis. Since the formation of the gas from gasification is endothermic, the necessary temperature is attained via the oxygen burning of approximately 25% of the feedstock. Where air is used to supply the oxygen the resulting gas is termed a producer gas. The use of air is only a viable option for gasification technologies where electricity production is the target. The catalytic processes required for the synthesis of biofuels and chemicals require a much cleaner gas. Hence, oxygen or steam are used and the resulting gas is termed a synthesis gas (or syngas). The general formula for the oxygen-fuelled gasification of carbohydrates is included below:

C6H1206 + 3/2 O2         ->        6 CO + 3 H2 + 3 H2O

Many potential products (such as Fischer-Tropsch diesels, alcohols, olefins, acetic acid etc.) can be synthesized from these gases with the synthesis depending on the ratio of carbon monoxide to hydrogen in the syngas. The amount of hydrogen (and hence carbon dioxide) produced can be increased via the water gas shift reaction (at conditions of approximately 300 oC and 15-25 bar]) which involves mixing steam with the syngas, since insufficient water vapour is usually released from the biomass.

Providing the syngas can be cleaned and contaminants such as tars and inorganic components effectively removed, the catalytic mechanisms for subsequent chemical synthesis from biomass-derived syngas should be the same as those employed on a large scale for the syngas produced from fossil fuels. The production of biomethanol from syngas (ideal H2:CO ratio of 3:1), via copper/zinc based catalysts at conditions of 220-300 oC and 50-100 bar, is probably the easiest route and several Swedish companies are considering commercial systems that can upgrade the black liquor from pulp and paper mills. However, methanol is no longer considered suitable as a major transport fuel but can be converted to viable transport fuels and platform chemicals, using the Methanol to Gasoline (MTG) process.

Ethanol Production from Syngas

There are several companies considering commercialising the production of ethanol from syngas. One route involves the production of a mixture of alcohols, including ethanol, butanol, and methanol using either a modified copper methanol catalyst or a molybdenum sulfide catalyst with a modification of the catalyst or of the conditions influencing the composition of the product stream. A research project in the USA aims to have a pilot plant utilising this technology operational by 2012 and is targeting the production of ethanol, at a cost of $1.01 per US gallon, via the conversion of forest residues. This project uses a moly-sulfide-based (MoS2) catalyst system, promoted with cobalt and alkali metal salts, because of its ability to produce linear alcohols (as opposed to branched), and its potential for higher ethanol selectivity. It considers that, by the end of 2012, the current problems associated with the catalysts, which include poor selectivity and stability, will be overcome. Range Fuels are said to be preparing a biomass to syngas to ethanol facility that they claim will produce 38 m litres of ethanol and about 8 m litres of methanol per year. The company also says that the process can work efficiently at high moisture contents (40%-50%), and that massive economies of scale are not required.

Biocatalytic Synthesis

For about 20 years there has been research into the biocatalytic synthesis of chemicals, including ethanol, from syngas. Autotrophs use C1 compounds, such as CO, CO2 and methanol, for their carbon source and hydrogen as their energy source while unicarbonotrophs use C1 compounds alone for both these purposes. These microorganisms also utilise metals such as cobalt and nickel (which are contained in their enzymes) for the conversion of C1 compounds into value added products such as ethanol, but they are less sensitive to many of the gas contaminants, such a sulphur, that poison metal-based catalysts. Also, the adjustment of the H2:CO ratio via the water gas shift reaction is not necessary where biological catalysts are employed and synthesis conditions can be much milder.

Fischer Tropsch Synthesis

The Fischer-Tropsch (FT) synthesis of a mixed range of linear hydrocarbons from syngas is a complex, highly exothermic, process that may require that many of the products are recycled in order to achieve satisfactory yields. It has been used, for about 50 years, in South Africa where the technology was developed in order to synthesise chemicals and fuels from coal when oil supply was limited. A H2:CO ratio of 2:1 is best for FT and process temperatures and catalysts (iron or cobalt) can be manipulated according to the particular hydrocarbons desired. The products of this process are not yet comparable to diesel fuels and are typically waxes that can be hydrocracked to produce a diesel that is suitable as a transport fuel (although it does suffer from a reduced lubricity and density) as well as naptha and kerosene as co-products.

Problems in Biomass Gasification

Various components in biomass feedstocks cause problems in the gasification and catalytic synthesis stages. Firstly, it is generally required for the biomass to be relatively dry, otherwise some of the syngas will need to be utilised for drying purposes. Costs rise rapidly once moisture contents rise above 50%; hence such feedstocks are not currently considered suitable for the gasification platform. Regarding catalysts, methanol synthesis catalysts can be poisoned by sulphur compounds, and Fischer Tropsch catalysts are highly sensitive, particularly to tars, carbon dioxide, halides and alkalis. Catalysts can also be deactivated by ash. Indeed, the amount and composition of ash is also a very important consideration in gasification schemes. A study estimated that, for mixed alcohol synthesis from forest residues, the minimum selling price for ethanol rises by approximately 50% (from $1.01 to $1.50 a gallon) when the ash content is increased from 1 to 15%. Issues relating to ash slagging and sintering in the reactor are particularly problematic with the gasification of some feedstocks. Fluidised bed gasifiers, by operating at less than 1000 oC, reduce this problem, but such conditions produce more tars and methane in the syngas. It is considered that such reactors will be inappropriate at the scales needed for the economical synthesis of many chemicals. Instead it is likely that entrained flow gasifiers will be necessary for the economies of scale needed for competitive biofuel production. These operate at higher temperatures but are engineered to minimise slagging. However, they require the biomass particles to be very fine which may incur a significant energy expense.

The formation of tars, and measures to deal with their removal are big considerations in biomass gasification schemes. Catalysts have a vital role in the reforming of these tars and non-metallic calcined dolomites and nickel based catalysts have been the focus of much research. However, both have problems, and further research is needed. It is generally considered that fundamental advances in state of the art catalyst preparations will be needed in order to make large-scale biomass to liquid facilities practical. The fossil-fuel to liquid facilities that currently exist are very large; for example, a (natural) gas to liquids facility recently built in Qatar produces about 34,000 barrels of FT products a day. Such economies of scale are necessary for many gasification technologies, particularly those employing the Fischer-Tropsch mechanism. It is estimated that a minimum gasifier rating of 500MW will be necessary in order for FT biomass to liquids to be viable. Clearly, a massive quantity of biomass would be required for such a facility, and it may be necessary to source material from long distances, increasing transport costs.

Possible Solutions

Several approaches have been considered to overcome the hindrances associated with biomass gasification. One option is to convert the biomass to a more appropriate state for gasification and/or transport. The production, via pyrolysis, of a bio-oil, or a bio-oil and biochar slurry, has been studied as one means of achieving this and Dynamotive claim to have tested syngas produced from such a slurry. The bio-oil/slurry should be more suitable for utilisation in an entrained flow gasifier, and its greater density (than the original biomass material) will increase the potential radius (since transport costs will be lowered) within which biomass can be sourced for a large scale gasification facility. Hence, a network of smaller flash pyrolysis facilities could “upgrade” the biomass to a bio-oil which is then delivered to a central facility.

Torrefaction is an alternative to bio-oil production. In this, slow pyrolysis conditions at low temperatures (250-300 oC) facilitate biomass grinding at reduced energy costs, and allows biomass to be utilised effectively in an entrained flow gasifier. The Choren process consists of a slow-pyrolysis stage which produces a gas which goes to a gasifer and to a char that is ground down and injected in the lower part of the gasification chamber, facilitating a reaction with the hot gases. The syngas then feeds a Fischer-Tropsch chamber, based on a Shell Gas to Liquids process, for the synthesis of a diesel-type fuel, termed SunDiesel. A pilot plant has demonstrated the Choren technology and a 15,000 tonne capacity demonstration plant, that will process 75,000 tonnes of biomass per year, is being commissioned. Choren have claimed that commercial facilities will have an output of 200,000 tonnes per year, and current estimates are that the cost of diesel production will be in the order of 70 euro cents per litre.

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Material/Downloads

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Journal Articles

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Hayes, D. J. M. (2013) Second-generation biofuels: why they are taking so long, Wiley Interdisciplinary Reviews: Energy and Environment 2(3):304334

Click for abstract
There has been a significant degree of hype regarding the commercial potential of second?generation biofuels (2GBs; biofuels sourced from lignocellulosic materials). In 2007, ambitious targets for the mass substitution of fossil?fuel?derived transport fuels by 2GBs were put forward in the United States and similar targets exist for other countries. However, as of May 2012, no commercial?scale 2GB facilities are currently operating. The technical and financial obstacles that have delayed the deployment of these facilities are discussed, as are recent advancements in research that may help to overcome some of these. There are six commercial?scale facilities currently (May, 2012) in construction and many more are planned in the near term. The prospects for 2GBs are more promising now than in the past but the delays in getting to this point mean that the ambitious targets of several years ago are unlikely to be reached in the near term.


Bulushev,D.A. Ross,J.R.H. (2011) Catalysis for conversion of biomass to fuels via pyrolysis and gasification: a review, Catalysis Today 171(1):113

Click for abstract
A current aim of society is to produce fuels from non-food biomass and catalysis is central to achieving this aim. Catalytic steam-reforming of biomass gives synthesis gas and this can be further transformed to give transport fuels using catalysis. Biofuels and fuel additives can also be obtained by catalytic upgrading of bio-oil produced by non-catalytic pyrolysis of biomass. This upgrading can be performed by low temperature esterification with alcohols (followed by water separation) or by high temperature gasification, cracking or hydrotreating processes. Upgraded bio-oil can also be obtained by pyrolysis of biomass in the presence of catalysts. This review considers recent trends in the chemistry of these processes for biofuel production and the catalysts used.

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Posters

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Kwapinski, W. (2009) Biomass Pyrolysis and Gasification and Their Applications, IRCSET 2009 Symposium - Innovation Fuelling the Smart Society, Dublin, 25 Sep 2009
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Projects

Current Projects

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Tar Mitigation in Biosyngas Production

This project examines the way to avoid the formation of tars in the gasification of biomass.

 

 


ReUseWaste

ReUseWaste is an Initial Training Network project funded under the Marie Curie action of the EU-FP7-PEOPLE-2011 program. It brings together major EU research groups, agri-environmental technology companies and public authorities from regions of intensive livestock production in Europe. The ReUseWaste network will train a group of young researchers in developing new technologies for socially and environmentally sustainable utilisation of resources in animal waste.

 

 


Completed Projects

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Novel Catalysts for the Dry Reforming of Methane to Syngas and Hydrogen

This project examines various types of catalysts for the dry reforming of methane to produce a synthesis gas (syngas) and/or hydrogen.

 

 


Design and Operate a Pyrolysis/Gasification Unit

A laboratory scale pyrolysis/gasification unit has been designed and built. This facility will shortly be operational at Carbolea and will be used to process a variety of residues, wastes and dedicated agricultural crops.

 

 


Personnel Involved

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Senior Lecturer

An expert in analytical chemistry, biodiesel, and biomass combustion, pyrolysis, and gasification. Member of the Charles Parsons Initiative.


Lecturer Below the Bar

An expert in thermo-chemical conversion of waste materials. Is examining and upgrading products of pyrolysis (bio-char, bio-oil/vapours) and its production efficiency.


Post-Doc

Marzena is currently working in on the gasification of biomass feedstocks in the pilot scale fluidised bed gasifier


PhD Student

PhD student. He is studying methods for mitigating tars in the gasification of biomass.


PhD Student

An international PhD student, supported by China Scholarship Council and University of Limerick, is focusing on the hydrogenation of biomass derivatives to useful chemicals.


PhD Student

PhD student working on the pyrolysis and gasification of waste biomass and its efficiency.


PhD Student

PhD stduent working on the torrefaction and gasification of Biomass, and on the upgrading of the quality of the gas produced.


News Articles

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05 Sep 2011

Alen Horvat Joins Carbolea

Alen Horvat today joined the Carbolea team. He previously worked as an intern at Carbolea during the summer of 2010 and has now returned to undertake a PhD via the Earth and Natural Sciences Doctoral Study Programme. His project is entitled "Tar mitigation of biosyngas production". The reduction of tar can be achieved via different approaches. System modification related to type of gasifier, temperatures, media agent, bed material, catalyst involved, feedstock pretreatment, ... To choose right approach to tar reduction, quality and quantity of tar have to be known. A target feedstock for this in the Carbolea group is Miscanthus Agricultures residue like straw, mushroom compost, and manures can also be utilized.


30 Apr 2011

Eight Postgraduate Positions Available at Carbolea (Now FIlled)

We are happy to announce that seven PhD positions and one MSc positions are available at Carbolea. These are listed below:

PhD Projects:

The Combustion of Biofuels under Combustor Relevant Conditions (2 PhDs Available)

Click Here for More Details

Use of functionalised mesoporous silicas for pyrolysis oil upgrading (One PhD Available)

Click Here for More Details

Catalytic conversion of biomethane to methanol and higher alcohols (2 PhDs Available)

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Tar mitigation in biosyngas production (One PhD Available)

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The hydrogenation of furfural to furfuryl alcohol (One PhD Available)

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MSc Project:

The project will deal with catalytic conversion of some biomass derived intermediates to fuel additives. The student will work and be fully financially supported for 2 years by Science Foundation Ireland. For more details on this project contact Dmitri Bulushev.


11 Jan 2010

Marzena Kwapinska Joins Carbolea Team

Marzena will be responsible for operation of the fluidised bed pilot gasifier. Numerous biomass feedstocks and wastes from our project partners, e.g. residues from enzymatic processes, will be gasified. The target will be to develop novel and effective configurations; to optimize the conditions for biomass particles with favourable gas–solid mixing and contact efficiencies and finally achieve a high yield of hydrogen in the syngas.


06 Oct 2009

Research Areas Update: Pyrolysis and Gasification

The webpage explaining the background to pyrolysis and gasification, two key areas of research at Carbolea, has been expanded today. Figures have been added to illustrate these thermochemical processes and a diagram of the bench-scale slow pyrolysis unit has been included. Witold Kwpainski and JJ Leahy are the persons with most involvement in this area. More details can be found on the appropriate webpage.


05 Oct 2009

Project Update: Gasifier/Pyrolysis Reactor Design

The webpage detailing our work, on the design and construction of a pilot-scale 10kg/hr pyrolyser/gasifier here at the University of Limerick has been updated. Witold Kwpainski and JJ Leahy are the persons with most involvement in this project. More details can be found on the appropriate webpage.


26 May 2008

Successful Launch of the CPI

The Charles Parsons Initiative, of which Carbolea is a member, was officially lauched today.The launch was addressed by Minister Eamon Ryan (Department of Communications, Marine and Natural Resources), Professor Son Barry (President of the University of Limerick), and Lord Oxburgh of Liverpool (ex-chairman of Shell and chairman of D1 Oils). There were also world renowned experts in the fields of biomass, wind, biofuels, ocean energy and energy storage. The event was well attended by stakeholders from various fields.

The programme can be downloaded here and many presentations can be downloaded from the CPI website while those relating to the areas of study in Carbolea can be downloaded below:

Lord Oxburgh of Liverpool - "Some Thoughts on Biofuels..."

Daniel Hayes - "Biorefining, Work at Carbolea and the Biofine Process"

Dr. Dmitri Bulushev and Prof. Julian Ross - "Catalysis for Hydrogen and Transport Fuel Production from Biomass"

Dr. JJ Leahy and Dr. Witold Kwapinski - Thermochemical Conversion/Biomass Gasification

Prof. Austin Darragh - "Sir Charles Parsons and the Evolution of an Energy Led Economy"

Katerina Kryachko - "Bio-char and Plant Growth"


13 Apr 2008

Biomass Conversion Conference Attended in Krakow

Katerina Kryachko, Witold Kwapinski, Dmitri Bulushev and Daniel Hayes attended the ERA Chemistry workshop, entitled “Chemistry of raw material change/chemical transformation of biomass” in Krakow, Poland. This was a very useful event which involved presentations and discussions concerning numerous areas of biomass conversion. The following articles that were presented at this conference can be downloaded here:

Daniel Hayes - "An Outline of Work by Carbolea and the Biofine Process"

Dmitri Bulushev - "Some applications of bio-oil and chemicals production"

Katerina Kryachko - "Investigations of methods of recovery products from Biofine Process and their applications"




 

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