ENK5-2001-00545 A New Approach for the Production of a Hydrogen-Rich Gas from Biomass: An Absorption Enhanced Reforming Process - AER-GAS

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EESD (Energy, Environment and Sustainable Development) : Thermochemical Conversion

Proposal No:	ENK5-2001-00545
Date Prepared:	February 2004
Source:	European Bio-Energy Projects (EUR 20808)

Introduction

The main characteristic of the proposed process for efficient and low cost conversion of biomass is the CO₂ removal in the reaction zone of the gasifier. Due to the shifting of the reaction equilibrium the hydrogen concentration increases significantly. Therefore, the single step generation of a product gas with high hydrogen content for fuel cell applications is achievable. As the CO₂ absorption is a highly exothermic reaction, the realised heat is integrated directly into the endothermic gasification/reforming process.

The spent absorbent has to be regenerated in a subsequent process step. The main advantages of the AER process are summarised as follows:

• product gas with a hydrogen content higher than 80 vol. %,
• complete CO₂ removal from the product gas,
• in situ heat supply for the endothermic biomass conversion process (thermally selfsustaining conversion process),
• easy CO cleaning for fuel cell applications of the product gas, and
• simple conversion technology.

For the realisation of the proposed technology, a fluidised bed reactor will be employed containing a CO₂ absorbent, e. g. dolomite. The development of a catalytic absorbent material with high tar cracking efficiency is also a key aspect of the AER process. Therefore, the ongoing project work is focused on the investigation of different natural and synthetic absorbent materials with regard to their CO₂ absorption capacity, chemical and mechanical stability under real process conditions with repeated absorption - regeneration steps.

The process parameters defined in a fixed bed and in a fluidised bed reactor will be applied to a circulating fluidised bed system (Fast Internally Circulating Fluidised Bed, FICFB reactor), that allows a continuous production of hydrogen parallel to absorbent regeneration.

Project structure

The project is co-ordinated by the Centre for Solar Energy and Hydrogen Research, Stuttgart, Germany (ZSW). There are four work packages (WP) which address the technical and economic objectives.

• WP 1 concentrates on the development and improvement of a catalytic absorbent material which is a core component of the AER process. Natural materials (dolomite marble litter, raw dolomite, olivine) and synthetic materials (chemically modified absorbents, e.g. by addition of silica, alumina or zirconia) are investigated as CO₂ absorbents mainly by thermal gravimetric Analysis. The catalytic activity of the investigated bed materials is characterised by dependence on their physical (morphology and surface area) and chemical (bulk and surface) properties. The performance of the bed material is determined applying a fixed bed AER reactor. Pre-selected materials are provided to the partners of the WP 2 and WP 3.
• WP 2, in this activity the AER process is investigated in fluidised bed (FB) reactors. The main goals are the determination of the mechanical stability of the bed materials as well as the definition of optimal operation conditions for fluidised bed operation (temperature, residence time, etc.) to provide a product gas with a high hydrogen and a low tar content.
• The activities in WP 3 are concentrated on the realisation of the AER process in a pilot scale FICBF reactor with continuous operation of the reforming and regeneration steps. The regeneration of the spent absorbent will be carried out using the heat released in the combustion of char residues. Both process steps, the reforming and the absorbent regeneration are connected in terms of material flow and heat transfer.
• WP 4 deals with the techno-economic assessment of the gas and electricity production costs based on the experimental AER gasification results of WP 1, 2 and 3. A design of a 1 MW and a 50 MW unit including the required additional units for industrial applications and for CHP (Combined Heat and Power) generation from the AER-gas will be carried out. Furthermore, the market potential of this new technology will be estimated.

Progress to date

• A synthetic/improved CO₂ absorbent material with high cycle stability for fluidised bed (FB) applications was developed.
• An improved catalyst for tar (phenol) reforming/ cracking with excellent performance has been produced.
• A test facility to characterise bed materials under FB conditions was built and different types of dolomites have been characterised in terms of mechanical and chemical stability.
• In a first experiment with biomass gasification in an AER FB reactor hydrogen concentration higher than 60% has been achieved.
• The integration of the new process in the pulp production was identified as a promising application of the process.

Impact and Exploitation

The AER process is an innovative gasification technology which enables an efficient conversion of biomass into a hydrogen rich gas. As the product gas is expected to be a clean gas with low tar and CO_x content, various applications can be considered (e.g. PEM fuel cells, fuel synthesis, CHP). The AER process is applicable to a wide range of biomass feedstock.