Studie av Karlskogas fjärrvärmenät för att sänka returtemperaturen
A district heating plant has the advantage that it can take advantage of the waste heat from industries and use of cheap fuels to produce heat. But for the long term is competitive requires that energy is also saved in district heating plants. One way to save energy in a district heating system is to increasing cooling to the return temperature. This leads to less power needed to drive the distribution pumps, and that more energy could be extracted from the same amount of fuel by an improved flue gas condensation.In Karlskoga the return temperature into the district heating plant is high. They would therefore reduce the return temperature in order to extract more energy from the flue gases. The purpose of this study is to find out how the cooling and flow looks from various facilities in the district heating system and study how it affects the return temperature. The goal of the study is to suggest how KEMAB be able to lower the return temperature.Installations flow to the energy investigated in Gothenburg district heating system, by a method called overconsumption basis. The method is a calculation that gives a cooling target for the district heating systems? facilities. The method could identify that consume high flow in relation to the cooling target. By increasing the cooling at these facilities could return temperature is lowered. The same method was used to study 148 plants in KEMAB's district heating system. Resulting became a cooling target at 41 degrees. If the ten facilities, in the district heating system, with the worst cooling would adjust after cooling the target would flow in the system to decrease by 439800 m3/year. It could well mean a lower return but also less energy to pumps etc.Two of the ten facilities according to overconsumption basis of law had the worst results were visited to investigate the reason they did not achieve the target cooling at 41 degrees. Heat exchangers k values ??were calculated by performing measurements of flow and temperature. The purpose of testing was to see if the k value had deteriorated and thus led to a poorer return temperature.It was not from the measurements on the k-value to draw conclusions about whether deposits affected the return temperature. It is thus not based on the results to see if the new heat exchanger had lowered the return temperature. However deviated k value for VVX1 from what the producer of the heat exchanger specified. In the measurement of total k-value was noted how the flow was turned on the heat exchangers. It turned out that VVX1 had been disconnected downstream and not counter which means that the return temperature can?t be lower than 55 degrees.A cooling target is not always realistic based on the facility?s need for function. Strandbadet visited had a bypass to prevent the supply line cools off when the plant is not in use. The control valve has a point value of 70 degrees. That means KEMAB can?t lower the return temperature below 70 degrees when the facility is not used if they do not follow the Swedish district heating recommendation on a flow temperature of not less than 65 degrees. A leaky control valve means unnecessarily high return temperature. A planned measurement of total flow through the control valve failed to implement because the measuring instrument did not fit.Recommendations have been submitted to KEMAB of what can be done to reduce the return temperature of the district heating system. Recommendations include checks for new installation of total domestic hot water heat exchanger and to review all round assets to reduce unnecessary leakage from the supply pipe directly into the return line.