Solar integration scheme
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The figure shows the classification of industrial heat consumers for the integration of solar heat for industrial applications. To find a suitable integration concept for a heat consumer that was chosen to be supplied with solar heat the level of integration has to be distinguished at first. For an integration point at supply level, a distinction is drawn between steam and liquid heat transfer media. The integration concepts for liquid heat transfer media are valid for hot water, synthetic media, or thermal oils. The different media will only lead to differences in the required heat exchanger type. In principle the integration concepts for liquid heat transfer media are also valid for air as heat transfer medium.
By using steam three different integration concepts are possible: solar steam generation (parallel integration), heating of boiler feed water and heating of make-up water (both serial integration). The parallel integration can be realized directly or indirectly (e.g. with thermal oil or pressurized water). The concepts for serial integration to heat boiler feed water or make-up water differ mainly in the respective temperature level and potential heat recovery measures that have to be considered. Besides the parallel and serial integration of solar heat in conventional heat supply systems with liquid heat transfer media there is also the possibility to heat storages or cascades that are part of the conventional heat supply system.
At process level a first distinction is drawn by the category of the heat consumer. If a process was identified to be suitable for the integration of solar heat within a feasibility assessment (e.g. based on the temperature level and load profile) it should be assigned to one of the three categories “(pre)heating of fluid streams”, “heating and maintaining temperature of baths, machineries or tanks” or “thermal separation processes”. Afterwards another distinction is drawn by the conventional way of heating. For the category “(pre)heating of fluid streams” two ways of heating are distinguished: External heat exchangers and direct steam injection. Processes assigned to the second category “heating and maintaining temperature of baths, machineries or tanks” can additionally be heated with internal heat exchangers (this includes heating jackets and coils, tube bundles, platecoil heat exchangers, electric heating elements and direct combustion). Within the third category “thermal separation processes” it is distinguished between convective- and contact dryers that cover the bulk of all drying installations as well as evaporators that are used for distillation and rectification besides general evaporation processes.
Based on the category of the heat consumer in combination with the conventional way of thermal energy supply different integration concepts for solar heat can be applied. At process level three general classes of integration concepts are distinguished. The first class is the integration of an external heat exchanger that is fed by solar thermal energy. Therefore, four integration concepts are basically possible: integration of an additional external heat exchanger for product or process medium in serial to the conventional one, solar heating of an intermediate hot water circuit, solar driven heat exchanger for external heating of baths, machineries or tanks and preheating of product or process media input streams. The second class is the integration of an additional heat exchanger surface within baths, machineries or tanks. The third class is solar generation of steam with vacuum or low pressure.
The table summarizes all solar heat integration concepts from the presented classification.A short abbreviation exists for every integration concept that includes relevant information. The first two letters define the level of integration. This can be supply level (SL) or process level (PL). For integration concepts on supply level the third letter defines the conventional heat transfer medium. This can be steam (S) or liquid media (L). On process level the third letter defines the position of solar driven HEX (E for external or Ifor internal) or that steam with reduced pressure is supplied (S). The fourth and fifth letter gives further information. E.g. the code PL_E_HBis used for an integration concept on Process Levelthat uses an External heat exchanger for Heating of Baths, machineries or tanks.
Literature:Schmitt, B., 2014. Integration of solar heating plants for supply of process heat in industrial companies (in German language), Dissertation University of Kassel, Shaker Verlag, Aachen, Germany.
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