A.V. Bridgwater

Renewable fuels and chemicals by thermal processing of biomass

Abstract Bio-energy is now accepted as having the potential to provide the major part of the projected renewable energy provisions of the future. There are three main routes to providing these bio-fuels—biological conversion, physical conversion and thermal conversion—all of which employ a range of chemical reactors configurations and designs. This review concentrates on thermal conversion processes and particularly the reactors that have been developed to provide the necessary conditions to optimise performance. A number of primary and secondary products can be derived as gas, liquid and solid fuels and electricity as well as a considerable number of chemicals. The basic conversion processes are summarised with their products and the main technical and non-technical barriers to implementation are identified.

An overview of fast pyrolysis of biomass

Biomass fast pyrolysis is of rapidly growing interest in Europe as it is perceived to offer significant logistical and hence economic advantages over other thermal conversion processes. This is because the liquid product can be stored until required or readily transported to where it can be most effectively utilised. The objective of this paper is to review the design considerations faced by the developers of fast pyrolysis, upgrading and utilisation processes in order to successfully implement the technologies. Aspects of design of a fast pyrolysis system include feed drying; particle size; pretreatment; reactor configuration; heat supply; heat transfer; heating rates; reaction temperature; vapour residence time; secondary cracking; char separation; ash separation; liquids collection. Each of these aspects is reviewed and discussed. A case study shows the application of the technology to waste wood and how this approach gives very good control of contaminants. Finally the problem of spillage is addressed through respirometric tests on bio-oils concluding with a summary of the potential contribution that fast pyrolysis can make to global warming.

Fast pyrolysis processes for biomass

Fast pyrolysis for production of liquids has developed considerably since the first experiments in the late 1970s. Many reactors and processes have been investigated and developed to the point where fast pyrolysis is now an accepted feasible and viable route to renewable liquid fuels, chemicals and derived products. It is also now clear that liquid products offer significant advantages in storage and transport over gas and heat. These advantages have caused greater attention to be paid to fast pyrolysis, leading to significant advances in process development. The technology of fast pyrolysis for liquids is noteworthy for the wide range of reactor configurations that have been developed to meet the stringent requirements for high yields of useful liquids, for use as a fuel in boilers, engines and turbines and as a source of chemical commodities. This review summarises the key features of fast pyrolysis and the resultant liquid product and describes the major reaction systems and processes that have been developed over the last 20 years.

The technical and economic feasibility of biomass gasification for power generation

Abstract This paper reviews the costs and technologies involved in an integrated system for the production of electricity from biomass in general and wood in particular. It first examines the economics of gasification, showing that the potential for this form of renewable energy lies in either processing low-cost wastes or relying on some sort of fiscal incentive, even at relatively large scales of operation and with high-efficiency processes. The paper then considers all the elements required with respect to wood handling and preparation, gasification, gas quality and gas cleaning, and establishes the criteria for their selection for delivery of a clean gas to a gas turbine or engine. Special emphasis has been placed on the technology status and key uncertainties that are considered to be crucial to the success or failure of a biomass-based IGCC system. The main conclusions are that wood handling, storage, drying, comminution and screening are well established and present no uncertainties in operation and performance. The technology of biomass gasifiers is sufficiently advanced to justify a substantial demonstration plant to prove the total IGCC concept and obtain reliable performance data. There are still areas of uncertainty, but these are relatively minor and will not be resolved until and unless a large integrated plant is built. Gas cleaning has been successfully developed in laboratories to the point where large-scale demonstration and long-term operating experience are necessary. This area can be considered the least developed and most likely to create problems in a demonstration plant. Turbine and turbine fuel specifications are imperfectly defined, although engines are known to be more tolerant of contaminated fuel gas.

Principles and practice of biomass fast pyrolysis processes for liquids

Abstract Biomass fast pyrolysis is of rapidly growing interest in Europe as it is perceived to offer significant logistical and hence economic advantages over other thermal conversion processes. This is because the liquid product can be stored until required or readily transported to where it can be most effectively utilised. The objective of this paper is to review the design considerations faced by the developers of fast pyrolysis, upgrading and utilisation processes in order to successfully implement the technologies. Aspects of design of a fast pyrolysis system include feed drying; particle size; pretreatment; reactor configuration; heat supply; heat transfer; heating rates; reaction temperature; vapour residence time; secondary cracking; char separation; ash separation; liquids collection. Each of these aspects is reviewed and discussed.

A techno-economic comparison of power production by biomass fast pyrolysis with gasification and combustion

This paper presents an assessment of the technical and economic performance of thermal processes to generate electricity from a wood chip feedstock by combustion, gasification and fast pyrolysis. The scope of the work begins with the delivery of a wood chip feedstock at a conversion plant and ends with the supply of electricity to the grid, incorporating wood chip preparation, thermal conversion, and electricity generation in dual fuel diesel engines. Net generating capacities of 1–20 MWe are evaluated. The techno-economic assessment is achieved through the development of a suite of models that are combined to give cost and performance data for the integrated system. The models include feed pretreatment, combustion, atmospheric and pressure gasification, fast pyrolysis with pyrolysis liquid storage and transport (an optional step in de-coupled systems) and diesel engine or turbine power generation. The models calculate system efficiencies, capital costs and production costs. An identical methodology is applied in the development of all the models so that all of the results are directly comparable. The electricity production costs have been calculated for 10th plant systems, indicating the costs that are achievable in the medium term after the high initial costs associated with novel technologies have reduced. The costs converge at the larger scale with the mean electricity price paid in the EU by a large consumer, and there is therefore potential for fast pyrolysis and diesel engine systems to sell electricity directly to large consumers or for on-site generation. However, competition will be fierce at all capacities since electricity production costs vary only slightly between the four biomass to electricity systems that are evaluated. Systems de-coupling is one way that the fast pyrolysis and diesel engine system can distinguish itself from the other conversion technologies. Evaluations in this work show that situations requiring several remote generators are much better served by a large fast pyrolysis plant that supplies fuel to de-coupled diesel engines than by constructing an entire close-coupled system at each generating site. Another advantage of de-coupling is that the fast pyrolysis conversion step and the diesel engine generation step can operate independently, with intermediate storage of the fast pyrolysis liquid fuel, increasing overall reliability. Peak load or seasonal power requirements would also benefit from de-coupling since a small fast pyrolysis plant could operate continuously to produce fuel that is stored for use in the engine on demand. Current electricity production costs for a fast pyrolysis and diesel engine system are 0.091/kWh at 1 MWe when learning effects are included. These systems are handicapped by the typical characteristics of a novel technology: high capital cost, high labour, and low reliability. As such the more established combustion and steam cycle produces lower cost electricity under current conditions. The fast pyrolysis and diesel engine system is a low capital cost option but it also suffers from relatively low system efficiency particularly at high capacities. This low efficiency is the result of a low conversion efficiency of feed energy into the pyrolysis liquid, because of the energy in the char by-product. A sensitivity analysis has highlighted the high impact on electricity production costs of the fast pyrolysis liquids yield. The liquids yield should be set realistically during design, and it should be maintained in practice by careful attention to plant operation and feed quality. Another problem is the high power consumption during feedstock grinding. Efficiencies may be enhanced in ablative fast pyrolysis which can tolerate a chipped feedstock. This has yet to be demonstrated at commercial scale. In summary, the fast pyrolysis and diesel engine system has great potential to generate electricity at a profit in the long term, and at a lower cost than any other biomass to electricity system at small scale. This future viability can only be achieved through the construction of early plant that could, in the short term, be more expensive than the combustion alternative. Profitability in the short term can best be achieved by exploiting niches in the market place and specific features of fast pyrolysis. These include: •countries or regions with fiscal incentives for renewable energy such as premium electricity prices or capital grants; •locations with high electricity prices so that electricity can be sold direct to large consumers or generated on-site by companies who wish to reduce their consumption from the grid; •waste disposal opportunities where feedstocks can attract a gate fee rather than incur a cost; •the ability to store fast pyrolysis liquids as a buffer against shutdowns or as a fuel for peak-load generating plant; •de-coupling opportunities where a large, single pyrolysis plant supplies fuel to several small and remote generators; •small-scale combined heat and power opportunities; •sales of the excess char, although a market has yet to be established for this by-product; and •potential co-production of speciality chemicals and fuel for power generation in fast pyrolysis systems.

Catalysis in thermal biomass conversion

Abstract The potential offered by biomass and solid wastes for solving some of the worlds energy problems is widely recognised. The energy in biomass may be realised either by direct use as in combustion, or by upgrading into a more valuable and usable fuel such as fuel gas, fuel oil, transport fuel or higher value products for the chemical industry. This paper is concerned with conversion and upgrading by thermochemical conversion. It briefly describes the technologies of gasification, pyrolysis and liquefaction of biomass with particular reference to the use of catalysts. In addition, the use of catalytic processes in upgrading primary products from thermochemical conversion to higher quality and value fuels and chemicals is included.

Developments in thermochemical biomass conversion

Volume One: Preface. Acknowledgements. Pyrolysis: Overview. Fundamentals. Laboratory Experimentation. Pilot and Demonstration. Analysis and Characterisation of Pyrolysis Liquids. Combustion of Pyrolysis Liquid. Chemicals from Pyrolysis Liquid. Upgrading Pyrolysis Products. Pretreatment. Volume Two: Preface. Acknowledgements. Gasification: Fundamentals. Laboratory Experimentation. Pilot and Demonstration. Commercial. Upgrading. Combustion: Overview. Fundamentals. Pilot and Demonstration. Environment. System Studies. Workshps. Author Index. Subject Index.

Production of high grade fuels and chemicals from catalytic pyrolysis of biomass

Abstract The potential offered by biomass and solid wastes for solving some of the worlds energy problems is widely recognised. The energy in biomass may be realised either by direct use as in combustion, or by upgrading into a more valuable and usable fuel such as fuel gas, fuel oil, transport fuel or higher value products for the chemical industry. This paper is concerned with conversion and upgrading by pyrolysis and briefly describes the technologies of fast pyrolysis with particular reference to the use of catalysts in chemicals production and the use of catalytic processes in upgrading the primary pyrolysis products to higher quality and higher value fuels and chemicals. There are natural catalysts in biomass which substantially influence the production of high yielding chemicals. Removal or reinforcement of these catalysts has a dramatic effect on product yield and composition. The pyrolysis vapours can be catalytically cracked over zeolites to give aromatics and other hydrocarbon products which can be further converted into gasoline and diesel and the condensed liquid can be hydrotreated to a naphtha like product also for upgrading into transport fuels. There is, however, considerable uncertainty over the ability of the upgrading technology to be scaled up to commercial feasibility most notably in terms of catalyst performance and life. Considerably more research and development is needed to develop and prove suitable catalyst systems. There is also considerable uncertainty over the cost of upgrading in terms of capital costs, operating costs and performance and some preliminary estimates are included.

Progress in thermochemical biomass conversion

Combustion: Co-combustion of coal and biomass wastes in fluidised bed Development of catalytic wood fired boiler The mathematical modelling of biomass pyrolysis in a fixed bed and experimental verification Operating parameters for the circulating fluidised bed (CFB) processing of biomass Combustion properties of a fuel bed - Experimental and modelling study Summary of recent parametric studies of small-scale domestic biomass combustion Combustion processes in a biomass fuel bed - Experimental results of the influence of airflow and of particle size and density Influence of the ash composition in slagging and defluidisation in a biomass fired commercial CFB boiler A new type of a boiler plant for dry and wet biofuel Gasification: Modern technologies of biomass conversion Redox process for the production of clean hydrogen from biomass Dynamic Modelling of Char Gasification in a Fixed-Bed A two stage pyrolysis/gasification process for herbaceous waste biomass from agriculture Fundamental fluid-dynamic investigations in a scaled cold model for biomass-steam gasification Biomass Power Generation: Sugar Cane Bagasse and Trash Biomass and waste to energy conversion in the Netherlands by means of (in) direct co-combustion: Status, projects and future applications in the Dutch utility sector Gasification study of biomass mixed with plastic wastes The development of methanol synthesis with biomass gasification Final report: Varnamo demonstration programme Design of a moving bed granular filter for biomass gasification Pyrolysis: Bagasse pyrolysis in a wire mesh reactor BCO/Diesel oil emulsification: Main achievements of the emulsification process and preliminary results of tests on diesel engine Overview of fast pyrolysis Production of hydrogen from biomass-derived liquids Levoglucosenone - A product of catalytic fast pyrolysis of cellulose Pyrolysis and gasification of black liquors from alkaline pulping of straw in a fixed bed reactor Thermal efficiency of the HTU process for biomass liquefaction Low-temperature pyrolysis as a possible technique for the disposal of CCA treated wood waste Mathematical modelling of the flash-pyrolysis process for wood particles Flash pyrolysis of biomass in a conical spouted bed. Kinetic study in the 400-500C range Scale up effect on plastics waste pyrolysis Research on the rotating cone reactor for sawdust flash pyrolysis Thermal desorption technology: Low temperature carbonisation of the biomass for manufacturing of activated carbon Scaling-up and operation of a flash-pyrolysis system for bio-oil production and applications on basis of the rotating cone technology Systems: Utilisation of bagasse residues in power production Barriers for the introduction of biomass in the Netherlands Assessment of the techno-economic viability of a bioelectricity demonstration plant in Spain Innovative components for decentralised combined heat and power generation from biomass gasification A role of bioenergy utilization technologies considering bioenergy supply potential and energy systems using a global energy and land use model