Waste-to-Energy : ORCs and heat pumps to recover heat from waste incineration plants

ORC technology and heat pumps allow recovering heat from waste incineration plants, such as household waste incineration plants, or sludge incinerators in water treatment plants, to convert it into valuable energy: electricity or upgraded heat

ORCs can recover heat from incineration furnace fumes to convert it into electricity. A heat recovery heat exchanger is installed to cool down the fumes. When such a system is already installed and the fumes are cooled by a circuit with air coolers, the air coolers can be bypassed, and the hot water is diverted to the ORC evaporator. 

Sometimes a steam turbine is already installed to recover the heat, but there may still be some available heat at a lower temperature, e.g., 150°C or 200°C. ORC technology is fully adequate to recover this lower-grade heat and can complement the electricity production from the steam turbine. 

If heat is used during the winter in a district heating network, and only available in the summer, the ORC can be switched off part of the year and turned on when heat is in surplus. ORC is also flexible enough to handle the fluctuations of the available heat, which depends on the fluctuations of quantity and quality of the wastes.

Heat pumps can also contribute to incineration plants energy efficiency. When a steam turbine is installed, low-grade heat at the outlet of the steam turbine can be recovered using a heat pump, and upgraded heat produced by the heat pump may be used to provide heat to a district heating network. In such configuration, existing steam air-cooled condensers are partially bypassed towards a water condenser, and low-temperature heat from the water loop is used as the heat source for the heat pump. 

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