Cogeneration unit with an absorption heat pump for the district heating system

Abstract

The Imanta district heating plant began operation in 1974 as one of the main heating plants for the Riga district heating system. Until now, it has undergone several reconstructions. First, the ordinary boiler plant with steam and hot water boilers was reconstructed to be a natural gas-fueled combined cycle cogeneration plant supported with hot water boilers. Then, one of the cooling towers of the cogeneration section was replaced by an absorption heat pump/chiller, thus providing the closed cooling water circulation system and recovering 2 MWth (7 MMBTU/h) low-grade heat otherwise lost in the atmosphere. The driving force for the absorption heat pump is steam produced by the steam boiler (3 MWth = 10 MMBTU/h) already located at the boiler plant. The efficiency of the absorption heat pump is closely related to the operation of the cogeneration unit, outside temperature, and district heating water temperature regimes. The case study confirms that a more efficient energy production system reduces the fuel consumption with the same amount of the produced energy, thus lowering the expenses on energy production and reducing the amount of the polluting emissions into the atmosphere.