By Lars Gullev, Managing Director, VEKS
For all of us, efficient use of the resources in the world is on top of the agenda. Only in this way can we ensure that our children and grandchildren can have the same opportunities in life that we have had. Therefore, it is important that we focus on how waste residues in one process can be a resource in another process. If we succeed, we can create a real life fairy tale!
An agreement, signed 2 December 2016 between CP Kelco and the district heating (DH) company VEKS ensures that as from Q4, 2017, a huge amount of the excess heat will be utilized in the local DH network, which VEKS is currently expanding. The recovered amount of excess heat is calculated to 150 TJ/year (42,000 MWh/year), which is 25 % of the total heat demand of Koege DH company. Extreme COP value As seen in figure 2, excess heat from the extraction process is supplied to the heat exchanger with a temperature of 75 o C (direct heating). Here, the DH return water is heated up from 47 o C to a flow temperature of 72 o C. In parts of the year, where a DH flow temperature of 85 o C is required, the additional temperature boost is done by using the heat pump which uses excess heat from the extraction process.
Such a fairy tale starts in South America where the citrus fruits grow.
Juice and oil The citrus is picked and the juice is squeezed out of the fruit flesh and citrus oil is pressed out of the peels. After juice and oil are extracted from the citrus fruits, the peels are dried and shipped to Denmark for the company CP Kelco, situated about 40 km south of Copenhagen. At CP Kelco, pectin is extracted from the peels. Pectin is a naturally occurring substance found in citrus fruits, apples and other fruit. At CP Kelco, the citrus peel goes through a comprehensive extraction process, after which the pectin is available in powder form. Pectin is used to improve texture and stability in a variety of products, especially within the food area. Pectin is e.g. the gelling agent that adds the right level of thickness to jams and jellies. Pectin is also used in e.g. dessert fillings, medicines, sweets, fruit juices and milk drinks. Excess heat The pectin extraction process requires large amounts of energy, and the excess heat has until today been lost in cooling towers (Fig. 1).
Fig. 2 - Principal diagram and construction boundary between CP Kelco and VEKS
Therefore, since it is only the last 13 o C which is boosted by the heat pump (72 o C to 85 o C), while the first 27 o C (from 45 o C to 72 o C) is heated directly with the excess heat, the overall COP (Coefficient Of Performance) of the system is about 18.5. So we are here talking about a very high system efficiency. After pectin is extracted from the peels, a by-product is left. Previously the by-product was used as feed for calves, but the farmers who produce calves have moved from the eastern to the western part of the Denmark, making transportation too expensive. Biogas plant wanted In 2008, the idea of constructing a biogas plant arose caused by the odour of decomposing seaweed at the beach of Koege Bay. The idea was to build a biogas plant that could utilise the seaweed, organic residual products, including citrus peels from CP Kelco, and animal manure, in order to produce green energy.
Fig. 1 – CP Kelco – Cooling towers
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