Efficient utilization of industrial excess heat for carbon capture and district heating

Övrigt konferensbidrag, 2020

Carbon capture and storage (CCS) from fossil and biogenic (BECCS) emission sources is necessary to limit global warming to well below 2°C. The EU as well as Swedish national agencies emphasize the importance of CCS for emission intensive industries. However, the cost of implementing CCS is currently still higher than the cost of emitting CO2 via the EU ETS, for example. To incentivize rapid deployment of CCS, the concept of partial capture has been suggested, i.e. capturing only a fraction of the site emissions to reduce capture cost. Several studies have found that the utilization of excess heat from industrial processes could significantly reduce the capture cost as the heat required (~120°C) may be available in significant quantities. However, available excess heat will not be sufficient to power full capture at most industrial sites. In Sweden, many industries utilize all or part of their excess heat in heat recovery units or in combined heat and power (CHP) plants to produce electricity and deliver heat to municipal district heating (MDH) systems. A broad implementation of CCS will, thus, effect the availability of excess heat for industrial heat and power generation. The future product portfolio of industrial processes with excess heat export and CHP plants can therefore be expected to include not only heat and power production, but also climate services (CCS/BECCS) and grid services (frequency regulation due to intermittent renewables).
The aim of this work is to assess partial capture at sites that have access to low-value excess heat to power the capture process, whilst considering competition from using the excess heat for MDH delivery. The work is based on process modelling and cost estimation of CO2 capture processes using amine absorption for two illustrative case studies, a refinery and a steel mill, which both currently use excess heat for MDH. The main focus is on investigating how seasonal variations in the availability of excess heat as well as the demand of district heating impact cost-efficient design and operation of partial capture at industrial sites. A challenge when utilizing excess heat in connection to a process connected to a district heating system is that the heat source which can be used to power part of the capture process will exhibit seasonal availability, and thus may inflict extra cost for the CCS plant not running at full load, and therefore may counteract the economic motivation for partial capture. To prevent this, heat integration between CCS and municipal district heating is investigated, for example by utilizing heat from the CO2 compression so that low-pressure steam is released from MDH to provide heat to capture CO2 whilst maintaining MDH supply. The design of the amine absorption capture process will have to handle significant load changes and still maintain high separation efficiency within hydrodynamic boundaries of the absorber and stripper columns. The cost of such operation will depend on the solvent circulation flows, the number of absorber columns (including packing and liquid collectors/distributors) and capacity of solvent buffer tanks for storing unused solvent during the winter season. Assuming that a constant amount of CO2 is avoided, the avoidance cost of CCS based on excess heat with seasonal heat load variations is compared to the avoidance cost of CCS based on the use of external fuel to achieve a constant heat load to the reboiler.