Biomass to Syngas and Liquid Fuels (BTSL)

Aims

To improve and optimise the dual fluidised bed (DFB) gasifier for steam gasification of various feedstocks to produce hydrogen-rich syngas.

A 100KWth DFB gasifier has been designed, constructed and in operation since 2007. It consists of a bubbling fluidised bed (BFB) for steam gasification and a fast fluidised bed (FFB) for combustion of solid char generated from the BFB reactor to supply heat to the gasification. Sand is commonly used as the bed material and is circulated as a heat carrier to transfer heat from the FFB to the BFB. The advantage of this gasifier is its ability to produce a high calorific value (11-14 MJ/Nm³) producer gas with high content of hydrogen (30-60% mol/mol). To improve the gasification technology, fundamental studies have been carried out including gasification kinetics studies, hydrodynamics studies and mathematic modeling of biomass gasification and co-gasification of blended biomass and coal. A cold flow model has been developed for study of flow hydrodynamics in the DFB gasifier and for optimisation of scale-up design and operation of the DFB gasifier.

Operation of the DFB gasifier has been optimised for high carbon conversion, high gas quality (low tar content) and achieving various H2 to CO ratios from 0.9 to 4.4 thus giving flexibility for syngas applications such as heat and power generation, Fischer-Trosch synthesis for liquid fuels, or hydrogen production.

Optimisation has been conducted to investigate the effects of the following parameters:

• Steam/biomass ratio
• Gasification temperature
• Catalytic bed materials including olivine, dolomite, magnetite and calcite
• Gas residence time or BFB bed height

Feedstocks for gasification in the DFB gasifier include:

• Pellets of radiate pine sawdust
• Blends of wood pellets and biosolids or dried sewage
• Pellets of blended wood and coal/lignite at various ratios
• Pellets of herbaceous crops
• Wood chips and bark

Leader

• Dr Woei-Lean Saw, Postdoctoral Research Fellow

Supervisors

• Prof Shusheng Pang, Dr Justin Nijdam (Senior lecturer)

Researchers

• Mr Ian Gilmour, Research Fellow, retired senior lecturer
• Dr Tana Levi, Technology Operation Manager, CRL Energy Ltd
• Mr Prasanth Gopalakrishnan, PhD student on modelling of biomass gasification
• Mr Qixiang Xu, PhD student on Mathematical modeling of co-gasification of biomass & coal
• Mr Ziyin Zhang, ME student graduated in 2012 on experimental investigation of co-gasification, now PhD student on gasification performance of various biomass feedstocks
• Dr Mook Tzeng Lim, PhD student graduated in 2012 on hydrodynamics of a cold model of a dual fluidised bed gasification plant, now working as a Postdoctoral Researcher in the Green Technology Research Centre, Universiti Teknologi Petronas in Malaysia

Aims

Development of gas cleaning technologies to remove impurities (tars, H2S, NH3) in gasification producer gases for different gas applications with a primary target to FT synthesis for liquid fuel.

Removal of impurities in gasification producer gases is essential in order to meet the stringent requirement of the FT synthesis process. Two gas cleaning systems have been in development. One is tar removal using integrated scrubber and stripper columns. Canola derived biodiesel is used as solvent in the system so that tars in the producer gas are firstly absorbed in a scrubber and then the tars in the loaded biodiesel are released in a stripper to hot air. The hot air with tars can be sent to the combustion column of the DFB gasifier for recovery of the tar energy.

Another gas cleaning system is catalytic removal of ammonia (NH3) and hydrogen sulphide (H2S). A reactor with simultaneous removal of NH3 and H2S has been designed and constructed for its simple design and operation with low construction and operating cost. This novel technology has a potential to remove NH3 and H2S in only one reactor instead of two or more in the current existing technologies. In the reactor, NH3 is cracked by hot catalytic decomposition reaction while H2S is adsorbed into an adsorbent. The reactor can be operated either in fixed-bed or bubbling fluidized bed regimes. Selection of catalysts/adsorbents and optimisation of operation conditions are very important to achieve high efficiency of NH3 and H2S removal. Catalysts and adsorbents investigated will include natural substances abundantly available in New Zealand, modified catalysts, and combinations of these materials. Operating parameters studied are bed temperature and gas residence time. The catalytic gas cleaning reactor will be integrated into the DFB gasifier to produce clean syngas for FT synthesis when promising catalysts and adsorbents are identified and the operating conditions are optimised.

Leader

• Dr Woei-Lean Saw, Postdoctoral Research Fellow

Supervisors

• Prof Shusheng Pang
• Dr Aaron Marshall (Senior lecturer)
• Dr Alex Yip (Lecturer)

Researchers

• Ms Janjira Hongrapipat, PhD student on Development of gas cleaning technology for removal of NH3 and H2S.
• Dr Gershom Mwandila, PhD student graduated in 2011 on development of a tar removal system for scrubbing and stripping tars in biomass gasification, now working as a senior lecturer in the Department of Chemical Engineering, Copperbelt University, Zambia.

Aims

To develop a fast pyrolysis reactor to densify loose biomass into a pyrolysis oil; to develop a new pyrolysis system for production of high quality liquid fuel; and to develop an entrained flow gasification system to gasify the pyrolysis slurry.

A lab-scale fluidised bed (FB) pyrolysis reactor has been designed and constructed with capacity of 1kg/h biomass feeding. This reactor is used to investigate densification of biomass and production of high quality liquid fuels.

Portable pyrolysis system

A portable pyrolysis system with energy self-sufficient is to be developed for densification of biomass into pyrolysis oil. Wood residue chips have a bulk density about 180kg/m³ (for dry radiata pine chips), while wood pyrolysis oil has a density of 1200kg/m³. Both of them have similar lower heating value of 18-19 MJ/kg. Therefore, conversion of wood chips to pyrolysis oil can increase the energy density by 6 times. Delivery of pyrolysis oil or slurry of pyrolysis oil and char to a bioenergy plant can thus save transport cost and storage space compared with biomass. This makes it possible to construct a large scale of bioenergy plant without significant increase in biomass transporation/storage cost.

Biomass pyrolysis is an endothermic process to thermally decompose biomass in the absence of oxygen to bio-oil, char and gas. Energy is required to raise the biomass temperature to the pyrolysis temperature and to convert the solid biomass into the reaction products. The proportion of the pyrolysis products depends primarily on the pyrolysis conditions. Fast pyrolysis with high temperature, high heating rate and short gas residence time would result in high yield of bio-oil; while slow pyrolysis would favour high char production. The lab-scale FB pyrolysis reactor with assistance of a TGA-DSC (thermo gravimetric analysis-differential scanning calorimeter) is used to investigate operating conditions which produce enough non-condensable gas to provide energy to the pyrolysis process so that it is heat self-sufficient while still producing substantial quantities of bio-oil.

High quality liquid fuels

The target is to produce a liquid fuel that can be used directly in combustion engines from biomass pyrolysis by investigating biomass pretreatment methods, pyrolysis bed materials and using a selective vapour condensation system. Fast pyrolysis will be carried out in the lab-scale of FB reactor.

Direct use of pyrolysis bio-oil in combustion engines is restricted due to the bio-oil’s well-known undesirable characteristics such as high oxygen and water content, instability, high viscosity, high organic acid content, traces of inorganic alkali and alkali earth metals (AAEMs) and entrained solids carried over from the pyrolysis reactor. Upgrading bio-oil through catalytic cracking and hydrotreating has been extensively researched but there are high treatment costs associated with the upgrading. This has led to the requirement of a new approach for producing high quality fuel from pyrolysis. The new approach is designed to integrate biomass pretreatments, catalytic FB bed material and selective condensation to improve bio-oil quality by reducing the contents of solids, alkaline metals, water, acids and oxygen in the pyrolysis oil.

Entrained flow gasification

A 20kWth atmospheric entrained flow gasifier is designed and constructed for gasification of pyrolysis oil and slurry of pyrolysis oil and char. Experiments and kinetic study will be conducted to:

• Select appropriate atomiser for spraying bio-oil and slurry respectively.
• Test the effects on producer gas composition by using different gasification agents including oxygen, steam and their combination.
• Optimise gasification conditions including gasification temperature, gasification agent ratio (O2/steam), and gasification agent to feedstock ratio for producing clean syngas with required ratio of H2 to CO.

Leader

• Prof Shusheng Pang

Supervisors

• Prof Shusheng Pang, Dr Alex Yip (Lecturer)

Researchers

• Ms Jingge Li, project engineer on portable pyrolysis system.
• Ms Tansy Wigley, PhD student on fast pyrolysis of biomass to produce high quality liquid fuel.
• Mr Fazly Abdul Patah, PhD student on entrained flow gasification of pyrolysis oil and char slurry.

Aims

to assess the feasibility of an integrated heat, power and FT liquid fuel plant; to develop a microchannel FT reactor and catalyst; and to optimise FT synthesis conditions (pressure, temperature) for higher conversion efficiency.

Traditionally Fischer-Tropsch (FT) plants are huge in scale, producing thousands of barrels a day of hydrocarbon fuels from mixtures of carbon monoxide and hydrogen. Small scale FT plants are therefore contrary to contemporary economic wisdom but essential for biomass to liquids production. Biomass has a low density and is widely distributed requiring a shift to smaller plants. Two concepts are investigated to enable this shift, firstly the use of combined heat, power and liquids plants integrated into existing wood processing facilities and secondly the development of microchannel reactors as both have advantages in reducing the negative financial effects of scale-down.

Combined Heat, Power and Liquid Fuels

The exothermic nature of the FT process, and the heat and power requirements for a sawmill create an excellent synergy. Integrating an FT plant into a sawmill allows heat from the FT process to be used for both kiln and biomass drying. Electricity can be generated from the off gas to satisfy both the FT plant requirements as well as those of the sawmill. As the off gas has a use the process can be run as a "once through" system, eliminating the need for the cost and complication of recycling, reforming and carbon dioxide removal. Our research includes the process design and modelling of combination of energy, FT and sawmill operations enabling the assessment of their economic feasibility and optimisation of operating conditions.

Microchannel Reactors

Microchannel reactors are known for having heat and mass transfer rates considerably higher than traditional reactors. This results in better catalyst utilisation and physically smaller reactors than the comparable fixed bed or slurry reactors typically used in FT processes. In our research we have developed and tested a lab scale microchannel FT reactor using cobalt catalyst wash coated onto the channel walls. Our model allows us to scale up the performance of this reactor to commercial scale and suggests a reactor capable of producing 100 barrels per day of FT liquids which would be less than a tenth the volume and a third of the cost of a slurry FT reactor, the best available of the conventional technologies.

Leader

• Dr Chris Williamson, Senior lecturer

Supervisors

• Dr Chris Williamson
• Dr Aaron Marshall (Senior lecturer)
• Prof Shusheng Pang

Researcher

• Chris Penniall, PhD student

Aims

To develop new biomass resources of purpose-grown crops, and establish an integrated system model for analysis of techno-economic feasibility from biomass to FT liquid fuels.

New biomass resources are developed by our collaborator Bioenergy Cropping Solutions Ltd. Three herbaceous crops identified to have high dry mass yield on marginal lands in New Zealand are Miscanthus grass, Jerusalem artichoke and Triticale. Protocols of the three species are in establishment through field trials with field management preferences, synchronous supply practices, and production cost for supplying feedstock to gasification/pyrolysis. Life cycle assessment (LCA) is also in progress to analyse the energy use and environmental impacts during biomass production and handling.

Techno-economic feasibility study is to provide potential investors with information for making investment decisions on construction of a feasible scale of biomass to liquid fuels plant. An integrated model for such a plant is established in UniSim Design computer environment to conduct conversion efficiency optimisation, life cycle assessment and economic analysis. The system model selects the most advanced technologies with high reliability in commercialisation for biomass processing, DFB gasification, gas cleaning & conditioning and FT synthesis. Performance of the DFB gasification is simulated with a quasi three-stage equilibrium model. The other units are simulated using both user-defined and built-in unit operations in the UniSim Design. The model development is primarily based on theoretical work and validated with experimental results, which have primarily been from our BTSL programme. The study is to compare two processing routes for converting biomass to FT liquid fuels as shown in the following diagram. Route 1 consists of biomass preparation, biomass gasification, gas cleaning and FT synthesis while Route 2 consists of biomass preparation, biomass pyrolysis, gasification of pyrolysis slurry and FT synthesis.

Leader

• Ms Jingge Li, Project Engineer

Co-leader

• Dr Rocky Renquist, Scientist and Director, Bioenergy Cropping Solutions Ltd

Supervisors

• Prof Shusheng Pang
• Ms Jingge Li

Researchers

• Dr Huub Kerckhoffs, Scientist, Bioenergy Cropping Solutions Ltd.
• Ms Nargess Puladian, PhD student on modelling and techno-economic feasibility study of systems from biomass to liquid fuels