AIR1-CT92-8006-GB Thermal Biomass Conversion and Utilisation - Biomass Information System

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AIR Cluster II - Bioenergy Conversion : Bulk Chemicals : Fine Chemicals : Liquid Biofuels and Biogas : Thermochemical Conversion

Thermal Biomass Conversion and Utilization - Biomass Information System A Bridgwater, University of Aston, UK (AIR1-92-8006-GB) This AIR Study for DGXII contains a detailed review of the science and technology of fast pyrolysis and related processes. It covers the basic scientific priciples of fast pyrolysis for producing liquids; their application to working processes with identification of the main problems; a description of the more commercially and technically advanced of these processes; and opportunities for chemicals recovery and upgrading of vapours and liquids to more valuable chemicals and transport fuels. Ref: EUR 16863 EN ISBN: 92-827-7207-1

EXECUTIVE SUMMARY

A detailed review of the science and technology of fast pyrolysis and related processes has been carried out covering the basic scientific principles of fast pyrolysis for producing liquids; their application to working processes with identification of the main problems; a description of the more commercially and technically advanced of these processes; and opportunities for chemicals and transport fuels. The contribution that has been made to the development of a Biomass Information System is described and copies of specimen data are included. Finally the conclusions summarise the current status and opportunities for each of the areas described.

INTRODUCTION

The potential offered by biomass and solid wastes for solving some of the world's energy and environmental problems is widely recoanised. The energy in biomass may be realised either by direct use as in combustion to give heat, or by conversion and upgrading into a more valuable and usable fuel such as fuel gas or fuel oil or higher value products for the chemical industry. Liquid products have significant advantages in handling, storage, transport and substitution for conventional fuels and pyrolysis is being rapidly developed for direct production of both crude liquids for direct fuel oil substitution and production of hydrocarbons for more technically demanding applications and transport fuels. There is a further advantage in electricity generation of being able to de couple fuel production from electricity generation through fuel storage which is not possible in gasification or combustion systems.

Biomass has received considerable attention as a renewable energy resource after the oil crises of the last 20 years. Pyrolysis in particular has been researched and developed for the economic production of fuel products that may be readily integrated into the energy infrastructures of both industrialised and developing countries. More recently, attention has focussed onto much higher value chemicals either as unique specialities or as substitutes for petroleum derived products.

Thermochemical Technologies

There are four thermochemical methods of converting biomass: pyrolysis, gasification, liquefaction and direct combustion. Each gives a different range of products and employs different equipment configurations operating in different modes. These are summarised in the table below.

The basis of a fuel or chemical production system is that the feedstock is converted to a useful primary energy product and either used as such, or further converted, upgraded or refined in subsequent processes to give a higher quality and higher value secondary product as shown in the figure below.

When organic materials are heated in the absence of air, they degrade to a gas, a liquid, and a solid as summarised in the figure below. It is possible to influence the proportions of the main products by controlling the main reaction parameters of temperature, rate of heating, and vapour residence time. For example fast or flash pyrolysis is used to maximise either the gas or liquid products, depending on temperature as summarised below:

• Slow pyrolysis at low temperatures of around 400°C and long reaction times (which can range from 15 minutes to days in traditional beehive kilns) maximises charcoal yields at about 30% wt.

Thermochemical Conversion Technologies and Products:

Technology	Primary Product	Typical yield. wt%	Application
Pyrolysis generally	gas	20-90 #	fuel gas
	liquid	5-80	fuel oil
	solid char	5-30	solid fuel or slurry fuel
Flash pyrolysis (lowtemp.)	liquid mostly	75	fuel oil
Flash pyrolysis (high temp.)	gas mostly	80	fuel gas & chemicals
Slow pyrolysis	solid char mostly	30	solid fuel or slurry fuel
Liquefaction	liquid	35	fuel oil
Gasification	gas	100 #	fuel gas & chemicals
Combustion	heat	heating

# based on carbon conversion

Products from Thermochemical Biomass Processing

• Flash pyrolysis at temperatures of typically 500°C; at very high heating rates and short vapour residence times of typically less than 1 second or 500 ms; maximises liquid yields at up to 85% wt (wet basis) or up to 70% dry basis.

• Similar flash pyrolysis at relatively high temperatures of above 700°C; at very high heating rates and similarly short residence times maximises gas yields at up to 80% wt. with minimum liquid and char production.

• "Conventional" pyrolysis at moderate temperatures of less than about 500°C and low heating rates (with vapour residence times of 0.5 to 5 minutes) gives approximately equal proportions of gas liquid and solid products.

This study is focussed on pyrolysis for the production of liquid fuels by the relatively novel process of fast pyrolysis, as these are currently viewed as a promising process and a promising product both in Europe and North America. The pyrolysis liquids are variously referred to as "bio oil", "bio crude oil" or even as "oil" although they share few similarities with any oil products.

In order to appreciate the scientific and technical complexities of flash pyrolysis, the development of understanding of reaction mechanisms and pathways is first reviewed which will explain some of the unusual product properties that have been reported and some of the reasons for the way the technology has developed. Modeling of the complex and interactive physical and chemical processes that occur in pyrolysis has also attracted considerable attention and this area is also reviewed to at least partly explain why technology and scale up is still largely empirical. Developments of some of the process technologies that have been promoted and scaled up are subsequently described to show the underlying principles have been applied.

Summary of Method and Contents

The project has been carried out through a detailed review of the science and technology of fast pyrolysis and related processes and a contribution to the development of a Biomass Information System. The basic scientific principles of fast pyrolysis for liquids are described and reviewed in Chapter 2 followed by a explanation in Chapter 3 of how these are applied to working processes and the main problems that have been encountered. Chapter 4 summarises the current status of fast pyrolysis and Chapter 5 describes in detail the more commercially and technically advanced of these processes. Opportunities for chemicals recovery and upgrading of vapours and liquids to more valuable chemicals and transport fuels is reviewed in Chapter 6. Chapter 7 summarises the contribution made to the BIS project and includes copies of the data suplied as an annex to that chapter. Finally Chapter 8 provides some conclusions on the current status and opportunities for each of the areas described.