Opportunities for solar process heat integration and heat recovery in the South African fishmeal industry

[摘要] ENGLISH SUMMARY: Solar thermal renewable energy is a promising alternative heat source capable of providing a large portion of the South African industrial heat demand. The major energy demand within the energy intensive South African industrial sector is process heat, furthermore, industrial process heat constitutes approximately 30% of the national annual energy consumption. Most of this heat is currently supplied by fossil fuels, which is a challenge to the future sustainability of the industrial sector since the cost of fossil fuels is expected to increase indefinitely, and their use impacts negatively on the environment.Two South African fishmeal factories were studied with the aim of determining the feasibility of integrating solar thermal heat into existing production processes within the industrial sector. The fishmeal production process is energy intensive as it requires the evaporation of large amounts of water.Base case processes were established, based on actual production data collected from the factories, in order to determine the energy and fuel requirements of the factories. Opportunities for heat recovery and solar heat integration were identified, and their effects on the energy demand quantified. The total potential for solar heat (in terms of total collector area) was established and two systems proposed: 1) with an area that minimised the difference between solar heat demand and supply, and 2) with an area that resulted in no excess heat production. A preliminary economic analysis was performed to quantify the economic viability of the proposed systems.Factory A produces fishmeal from lean-fish processing by-products using a single dryer, with heavy fuel oil as fuel source. Preheating of the raw material stream presented an opportunity for both solar heat integration and heat recovery. A 384 m2 solar heat system was the most profitable option investigated with a net present value of R 3.3 million and levelized cost of heat of R 0.79. Heat recovery from the condensate stream exiting the dryer was also economically viable, however, it was less profitable and resulted in lower fuel savings.Factory B produces fishmeal and fish oil from pelagic fish species using the wet-pressing method, with coal as fuel source. Solar thermal heat could be used to preheat the entering raw material and boiler make-up water streams and to heat the stickwater concentrate prior to drying. Heat recovery from the fish oil stream could only supply a very small fraction of the heat required. Due to the large capital costs of the solar thermal systems and the low cost of coal, none of the proposed systems were economically viable.The cost of the fuel being replaced and the heat demand throughout the year were found to be major factors affecting the economic viability of the solar thermal heat systems. It is recommended that the energy requirements and production schedules determined in this study, be used to simulate the solar heat systems and obtain more accurate values of the solar thermal system efficiency and output. This will aid the specific factories to obtain implementable solutions.

[发布机构] Stellenbosch University