Increased fuel flexibility and modulation capability of fixed-bed biomass gasifiers by means of model-based control

Project: Research project

Description

Being almost carbon-neutral, the energetic utilization of biomass became more important within the
last decades. Especially in the combustion of biomass significant development steps have been
achieved and biomass combustion systems are widely spread from small-scale applications typically
used for residential heating up to medium and large-scale applications for combined production of
heat and power. Parallel to the increase of practically implemented biomass combustion systems, a
strong focus of research and development was given to biomass gasification. The main difference
between biomass combustion and gasification is the incomplete burnout in gasification leading to a
combustible product gas. This resulting product gas gives very high flexibility in the production of heat
and power, transportation fuels, chemicals or valuable gases.
By using biomass gasification for combined heat and power production, typically autothermal,
atmospheric and air-blown gasification systems are considered. Besides fluidized-bed gasifiers or
entrained flow reactors, fixed-bed gasifiers have been successfully commercialized for small-scale
gasification systems, especially for combined heat and power production. These state-of-the-art smallscale
biomass gasification systems can be considered to be robust enough for practical application
but their limitations to very specific fuel properties, load modulation capabilities and steady state
operation are a remaining barrier on the way towards a wider market distribution.
In order to increase the gasifiers fuel flexibility and load modulation capability, an appropriate
improvement of their automation and control should be carried out. Currently, the automation and
control applied in the different small-scale gasification systems is rather simple since the main external
disturbances are avoided a priori by holding the fuel properties as well as the load demand as
constant as possible. Consequently, the control just has to keep the system in a steady state what can
be achieved by a comparatively small degree of automation and instrumentation sufficiently well. Up to
now the research in small-scale biomass gasification focused on procedural and mechanical issues in
order to bring a significant amount of plants into economically feasible, practical operation what can be
considered as achieved by several technologies. However, in terms of automation and control no
significant research has been conducted up to now in the field of small-scale biomass gasification.
The most promising approach for the control of such complex systems are model-based control
strategies which enable an explicit consideration of the couplings and nonlinear correlations between
the different process variables. The system is described by a comparatively simple but nonlinear,
mathematical model used as a basis for the controller design. The advantages of such model-based
control strategies mainly result from the explicit consideration of all couplings and nonlinear
correlations between the different variables leading to increased fuel flexibility, increased load
modulation capability, decreased maintenance effort for the operators, increased efficiency and
decreased pollutant emissions.
This project aims for developing model-based control strategies for selected processes of a fixed-bed
biomass gasification system combined with an internal combustion engine for combined production of
heat and power. The control should increase the systems fuel flexibility as well as the load modulation
capability. The development of the model-based control strategy will be done both experimentally at a
real-scale gasification system operated by Urbas Maschinenfabrik Ges.m.b.H and theoretically on the
basis of control theoretical, thermochemical or thermotechnical considerations. Finally, the modelbased
control strategies for selected processes to be developed will be implemented and
experimentally verified by means of the real-scale gasification system.
StatusActive
Effective start/end date1/03/1728/02/20