EuroSun2008-2

Methodology for Solar Integration

The methodology to integrate solar process heat in industry follows the pathway that was developed within the IEA Task 33 SHIP, subtask B “Investigation of industrial processes”. The approach highlights the importance of energy efficiency as a first step, before an efficient solar process heat plant is designed. The energy efficiency measures include energy demand reduction by technology optimization, but as well heat recovery possibilities within the whole production process (system optimization - heat integration). Based on the reduced heat demand, an optimized energy-consumption profile of the company can be developed, which is then used to plan the practical utilization of renewable energies, especially solar process-heat, for the production. Only with this approach a real economic and efficient solar process heat plant can be designed that fits well into the energy supply system of a company. The following reasons can support this statement

[5]:

• The optimisation of the production process reduces the overall energy demand and prevents an over-dimensioning of the energy supply systems (e. g. the solar plant).

• The technological optimisation of unit operations can result in different energy demand and different temperature levels of the processes. Both parameters have a large impact on the considerations of solar process heat.

• The investigation of processes leads to detailed know-how of unit operations and their operational data (temperatures, operation schedule etc.) and gives the necessary overview to identify the ideal integration for solar process heat into the production system.

Consideration of all possibilities of heat recovery and the use of waste heat (heat integration) makes sure that no supplementary heat is introduced to the production where recovered or waste heat is available as an already existing energy source.

The following steps are taken for the considerations on the integration of a solar plant in industrial processes:

• Data acquisition of all energy data within the company (energy demand and energy availability)

• Calculation of the overall energy balance of the company

• Reviewing of possible measures for enhancing energy efficiency (technological improvements, best available technologies, reduction of heat losses etc.)

• Calculation of the (theoretical) minimal heating and cooling demand with external energy sources

• Design of a heat exchanger network (heat integration)

• Definition of the heat demand that can be sensibly covered by solar thermal applications or other renewable energy sources

• Design of the renewable heat supply system

• Economic analyses

Tools for solar integration in industry

The Matrix of Indicators: Industrial sectors vary in structure and heat demand. Therefore a systematic approach is needed to describe the processes in energetic terms. Also, the minimization of the heat demand of an industry can be achieved by several approaches: (a) applying changes in the process (application of competitive energy technologies), (b) applying changes in the energy distribution system (application of heat integration systems) and (c) applying changes in the energy supply system (application of heat pumps/co-generation systems and/or application of solar thermal systems).

Solar thermal systems, on the other hand, vary in layout and design. Therefore a classification of the different hydraulic schemes is needed to point out their suitability to be applied for the energy supply in production processes.

In order to fulfil the above issues on a theoretical level, a tool that systematically includes process engineering and energetic information of industrial sectors with a potential for application of solar thermal systems has been developed. The aim was to design a decision support system that gives the user a large information database for all crucial steps that have to be taken when designing a solar heating system for industrial processes. These steps include the overview of the processes, important parameters of the energy supply of unit operations, benchmark data on energy consumption, competitive technologies, hydraulic schemes for solar integration and successful case studies.

Heat integration: A correct way to integrate (waste) heat into a process is described by the pinch theory [Ferner, Schnitzer, 1990] that was developed by Linhoff et. al. in the 1970s. With the pinch

analysis the heat and cold demand of the whole production is plotted in one diagram that shows the energy (heating or cooling) demand of the processes and at which temperatures this energy is needed. Some very important statements can be drawn from this analysis:

• How much energy can theoretically be saved by heat recovery?

• How much external heating demand does the production process have? Which temperature level is necessary?

• How much external cooling demand does the production process have? Which temperature level is necessary?

The pinch analysis is a strong tool for a first estimation of the energy saving potential by heat recovery (which later has to be adapted due to practical and/or economic reasons). Secondly, the analysis shows at which temperature levels the demanded heat/cold is necessary - important information for a possible solar process heat plant.

In the framework of the IEA Task 33 SHIP the development of a Heat Integration Tool started that is especially suitable for low temperature applications and batch processes. This tool could already be applied and tested for the Austrian case studies.

The basis for the application of the pinch analysis is the profound knowledge on the energy demand and energy availability streams of the production system. For the Austrian case studies, this data could either be acquired directly from the company’s data information system or measurements (ultrasonic measurements of fluid flows) had to be conducted.

Solar Simulation

The implementation of solar energy can either be done into the energy supply system, but as well directly at the process. An important aspect is to integrate the solar energy in no competition to possible available waste heat available within the process. Here the storage design plays a crucial role and the load management of waste heat, solar heat, energy supply and the demand schedules. In many industrial applications storages have to be implemented to achieve an increase in the efficiency of solar heat (and waste heat).

For the design of solar plants the Computer Software T-Sol was used. This tool allows the calculation of solar yields, collector areas, storage dimension and investment cost assessments of the solar plants. Based on the energy data achieved after the energy optimisation, the decision of the integration of the solar plant was done by the process engineers and the solar experts to achieve the highest yields of solar energy and the best overall economic system.

2 Results

In Styria, 10 case studies were conducted in 2007 in order to develop concepts for energy conservation and for the implementation of solar heat. In four of these ten case studies, detailed concepts, based on extensive measurements and calculations, were developed. The suggested measures in terms of heat-integration, technological innovations and the use of solar process-heat result in savings that amount to more than 28 Mio. kWh/a for all 10 companies, implying an annual reduction of 5.830 t CO2. The economically recommended collector-area for those companies, which the solar plant was thoroughly examined, was 2.790 m2 in total for 5 of 10 companies.

The following table gives an overview of the companies, their sectors, the solution that were drawn and the savings that could be achieved.

It is important to point out that most of the solar plants designed for the companies focus on the supply of hot process water that is stored in a central hot water storage tank. Partly this hot water is directly applied for production processes (company Nr.3 and Nr. 10), partly hot water is used for the general hot water household mainly for washing and cleaning activities (company Nr.2 and 6).

In both cases hot water is first transferred to the storage and if necessary temperature is elevated by the back up system. Again it is shown in the work with the case studies that storage plays a crucial role and that simulation is needed for complex storage tanks which are in the centre of several heat demand and heat availability streams with different schedules.

Additionally the case studies highlight the importance of demand reduction first. This includes energy efficiency measures and heat integration, but as well the optimisation of industrial processes to lower temperature processes. The economics of the overall project can be strongly

improved if the solar plant can operate with higher efficiency at lower temperature levels (company Nr. 10).

Economical estimation showed that for the case studies pay back times between 1-5 years could be reached.

3 Conclusions

Several potential studies, including the in this paper presented study within the project Styrian Promise for the region of Styria, show the high potential for the integration of solar heat in industrial processes.

For the realisation of this potential it is necessary to follow a specific methodology to ensure the application of solar thermal energy in an economic and sustainable way in industrial companies. Tools for this methodology have been elaborated in the framework of Austrian national projects and within the Subtask B of the IEA Task 33 SHIP. These tools have been applied and tested during the performance of the case studies.

The case studies showed the economic feasibility of the integration of solar thermal heat in combination with a full energy efficiency concept. The methodology applied leads to clear concept based on a detailed know-how of the energy demand structures of the company.

The work with the companies showed that crucial technical questions of future research will a. o. mainly focus on

the reduction of temperature requirements of industrial processes and

complex storage simulations for heat integration and solar applications in batch processes.

References:

[1] ECOHEATCOOL (IEE ALTENER Project), www. ecoheatcool. org: The European Heat Market, Work Package 1, Final Report published by Euroheat & Power.

[2] H. Schweiger et al.: POSHIP (Project No. NNES-1999-0308) The Potential of Solar Heat for Industrial Processes, Final Report. Barcelona, 2001

[3] C. Vannoni, R. Battisti. S. Drigo: Potential for Solar Heat in Industrial Processes. Study performed within Task 33 “Solar Heat for Industrial Processes” of the IEA Solar Heating and Cooling Programme and Task IV of the IEA SolarPACES Programme. Madrid, 2008.

[4] Sachs L. (1984), Angewandte Statistik.- 6. Aufl., Berlin-Heidelberg-New York-Tokyo

[5] C. Brunner, B. Slawitsch, K. Giannakopoulou, H. Schnitzer: Industrial Process Indicators and Heat Integration in Industry. Report performed within Task 33 “Solar Heat for Industrial Processes” of the IEA Solar Heating and Cooling Programme and Task IV of the IEA SolarPACES Programme. Graz, 2008.