Design of A District Heating System Including The Upgrading of Residual Industrial Waste Heat

Abstract

This study was aimed to evaluate the feasibility of using a waste heat stream from DSM for a District Heating System. A conceptual design was carried out with emphasis on the unit for upgrading the residual waste heat. Having reviewed heat pump technology, mechanical heat pump was found to be the best option for recovering the heat from the residual waste water. This heat pump (ammonia loop) combined with a natural gas fired heater will provide the districts with the required heat. The energy that can be extracted from the waste heat from DSM (100 TJ/annum) with a mechanical heat pump represents approximately 8% of the required energy input of the total Upgrading Unit. Therefore, additional energy input will be provided by a gas fired heater as combustion, which will also serve as a back up system. Heat pump technology is a sustainable method of heating and district heating system using heat pumps is a proven and well-known technology. It is widely used in Europe, Canada and the USA. Currently there is a district heating system in Norway using ammonia in a mechanical heat pump, which includes one airport and adjacent residential buildings and the design of another facility in the future has been considered. Moreover, nowadays environmental concerns require that the flue-gas emissions resulting from the supply of energy to processes should be minimized. By using the mechanical heat pump for upgrading the heat in this specific design, 4% emissions reduction will be achieved. The outputs of the design were established based on the required plant capacity and the results of the evaluation of the demand fluctuations and heat losses in the distribution system. Thus, the Upgrading Unit was designed for 923 Tera Joules per annum in order to compensate the heat losses in the pipeline network and supply the districts with a maximum annual demand of 780 Tera Joules. This capacity corresponds to approximately 11,000 houses being supplied with heat. The Upgrading Unit will be located as close as possible to DSM site in Delft, The Netherlands. The configuration of the distribution system and pipeline lengths were estimated based on the districts listed in a previous feasibility study. The economical plant life was assumed to be at least 15 years, considering continuous operation 24 h/day, 365 days/year. The total investment is MUS$29.3 and the production costs are MUS$20.3. They were calculated with Lang’s factored estimation method aiming to achieve ± 25% accuracy. As a result of the economic evaluation of this design, a negative cash flow of MU$6.1 was found. The Upgrading Unit might be profitable if one considers the possibility of using it as a power station in addition to the normal function as a heat producing plant. Decreasing the number of connected districts or collecting more waste water or waste water with a higher energetic value would be another option.