Download Overview

INSTATIONARITY AS A LIMITING FACTOR FOR THE USE OF INDUSTRIAL WASTE
HEAT IN HEATING-NETWORKS
Kraussler Alois, University of Applied Sciences JOANNEUM, (43 3862) 33600 83 70, [email protected]
Theissing Matthias, University of Applied Sciences JOANNEUM, (43 3862) 33600 83 82, [email protected]
Theissing-Brauhart Ingrid, Engineering Consultant, (43 316) 812994, [email protected]
Wanek Michael, University of Applied Sciences JOANNEUM, (43 3862) 33600 83 66, [email protected]
Overview
[t/h]
In Austria and Europe an increase of heat supply to the consumer with district heating systems is an aim in (environmental)
policy. By using district heating systems, CO2-emissions for heating demand can be reduced, especially when regenerative
energy sources or industrial waste heat are used for heat supply. For a lot of industrial processes high temperatures are
necessary (e.g. for melting of metals), but up to now the generated waste heat has mostly/usually been an undesirable byproduct. For environmental reasons and because of the considerable share of energy-costs in the operation costs, the companies
try to recover this lost heat by industrial waste heat utilisation.
However, the integration of industrial waste heat in district heating systems is difficult because of its unsteady character
(fluctuations in mass flow, temperature and pressure level), which normally is incongruent with the heat demand of a district
heating system. For that reason, the amount of industrial waste heat which is supplied to district heating networks is presently
rather low.
Industrial waste heat is predominantly instationary as you can see in figure 1. This figure refers to a typical steam supply caused
by an industrial process and illustrates the considerable
60
instationarity of this energy source. It shows the
fluctuating steam supply in [t/h] over two days. Thus
50
utilisation of industrial waste heat in district heating
40
systems is constrained.
30
Furthermore there is a lack of methods for technological
and economic assessment, which take into consideration
20
both industrial waste heat supply and heat demand in
10
district heating systems. In this context tools as well as
0
methods are necessary which can be used regarding the
0
100
200
300
400
integration of industrial waste heat into (district) heating
[min]
systems. Finally a data base and an evaluation
methodology (benchmarks) are essential to support
Figure 1: Typical steam supply from industrial processes
increased utilisation of this energy source.
Source: Internal data
Methods
Concerning the discussed problems the following methods were applied to the project:
1. Investigation: First a data base which covers technological and economic aspects of waste heat utilisation was set up (e. g.
classification of industrial waste heat, technologies for waste heat utilisation and integration, costs, heat demand in
district heating systems).
2. Assessment: Development of a method for technological and economic assessment of waste heat utilisation and integration
in district heating systems. Thus a comprehensive basis for evaluation and planning for the corresponding prospective
customers could be established.
3. Demonstration: Evaluation of assessment method by application examples.
The project was carried out in cooperation with target groups (several big industry enterprises with a significant waste heat
potential and big district heating companies in Austria) to follow an open innovation approach so that application oriented
results could be guaranteed.
Results
pusher type furnance
15
walk beam furnance
batch-process
10
[MW/min]
In the industrial area reasonable and useable waste heat sources
that could be recovered are waste heat from flue gas streams,
cooling of heat treatment components, batch-processes and
cooling of products and aggregates. These different sources have
different characteristics. In this context the recovered energy
mostly varies depending on the production amount. Thus mass
flow, temperature, pressure and finally the power are very
unsteady. To be used efficiently the waste heat delivery must be
adusted. The following have been identified as reasonable
possibilities for the adjustment of industrial waste heat: passive
5
walk beam f.
0
pusher
type f.
-5
-10
batch-p.
-15
0
100
200
[min]
300
400
Figure 2: Power gradients of different waste heat sources
Source: Internal data
relative frequency [-]
approaches by the amount of production, parallel connection of several similar waste heat sources, components protection in
the production plants (leak air), active adjustment by exhaust-gas bypass flaps, active homogenization of the wast heat profile
by storage-devices as well as parallel connection of a firing plant, heat pump utilisation, possibilities for influencing power
gradients and buffering in internal heating as well as cooling networks. Useful technologies for the uncoupling of waste heat are
recuperators and regenerators in combination with storages and other heat sinks.
Furthermore, power gradients of different waste heat sources were analysed (see figure 2). You can see that due to the
discontinuous production process, batch-processes have the biggest spread in gradients, whereas the waste heat deliveries from
walking beam furnaces show the smallest power gradients because of track cooling.
To gain more detailled information of each waste heat source the frequency distribution of power gradients was determined. In
figure 3 a typical distribution of a walking beam furnace is illustrated. With a
0.16
probability of about 55 % a waste heat delivery gradient from -0.075 to
+0.075 [MW/min] can be expected. By contrast the gradient of a pusher-type
0.12
furnace has a probability of typically 60 % to be between -0.5 and +0.5
0.08
[MW/min].
Another important tool which was developed to identify the waste heat
0.04
quality is the stability-factor. This index refers to the average waste heat
delivery. The bigger the dimension of deviation from the average delivery the
0.00
smaller the factor. In general, a waste heat source with a smaller stability-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3
factor is hard to integrate and thus the price to be obtained from waste heat
[MW/min]
utilisation has to be smaller, too.
Figure 3: Frequency distribution of power
Besides the used integration technologies and the typical characteristics of the
gradients caused by a walking
waste heat sources, the absorbing capacity of the supplied heating network
beam furnace
has a considerable influence on heat integration. Thus formulas to be used in
Source: Internal data
different heating networks have been developed.
Finally, several other necessary tools and benchmarks have been developed. Due to the huge number of different waste heat
sources and the corresponding different characteristics these methods are very important for evaluation and essential in order to
increase the use of industrial waste heat.
Conclusions
Because of political and ecological aims (e.g. Kyoto) the amount of district-heating in final-energy-consumption must be
raised. Due to the small fossil energy proportion of industrial waste heat this source is proper for achieving the given aims. The
utilisation of industrial waste heat can complement the generation-portfolio of district heating very well.
Waste heat is a by-product of many industrial processes. Thus the process is preferred, which leads to considerable
instationarities and finally to utilisation-restrictions especially for the integration in heating networks. Additionally a lot of
different waste heat sources and corresponding different characteristics exist with respect to the integration and utilisation. This
causes operation-problems that can only be prevented by according amounts of energy-reserves. Therefore an adequate price
for the extraction of waste heat is hard to identify. If a waste heat utilisation had been considered at the design of the
production-process, the technological and economical benefits of waste heat could be raised significantly.
Thus methods and tools need to be found to identify the possibilities of integration, the quality of the source as well as the right
price to be achieved. Useful exemplary tools / indices are power gradients, frequency distributions and the stability-factor.
These developed tools support the integration of industrial waste heat into heating-networks significantly.
This project was subsidised within the research and technology program `factory of tomorrow´. This program is
conducted by `The Austrian Research Promotion Agency´ (FFG) for `The Austrian Federal Ministry of Transport,
Innovation and Technology´.
References
SCHRAMEK E.-R.; “Taschenbuch für Heizung und Klimatechnik“, 71. Auflage, Oldenburg Industrieverlag, München, 2003
VDI Gesellschaft Energietechnik 2000: VDI-Energietechnik; „Energietechnische Arbeitsmappe“, 15. Auflage, Springer Verlag,
Heidelberg, 2000
VDI Gesellschaft für Verfahrenstechnik 2002: VDI Gesellschaft für Verfahrenstechnik und Chemieingenieurwesen; „VDIWärmeatlas“, 9. überarbeitete und erweiterte Auflage, Springer Verlag, Heidelberg, 2002
BAEHR H. D., STEPHAN K.; „Wärme- und Stoffübertragung“, 4. Auflage, Springer Verlag, Heidelberg, 2004
BECKMANN G., GILLI P.V.: „Thermal Energy Storage“, Springer Verlag, 1984
KUGELER K., PHILLIPPEN P. W.: „Energietechnik-Technische, ökonomische und ökologische Grundlagen“, 2. Auflage,
Springer Verlag, 1993
STEINMANN W. D.: „Thermische Speicherkonzepte für den Mitteltemperaturbereich“, Institut für Technische
Thermodynamik Stuttgart