Carbon Capture in Pulp Mills: Modelling and Process Integration Strategies

Abstract

The bioenergy industry, particularly pulp mills, holds promise for achieving carbon negativity
through the adoption of carbon capture processes. Presently, CO2 capture from flue gases poses
significant challenges due to its energy-intensive nature and the risk of solvent chemical
degradation.
This thesis conducts a screening of primary absorption technologies and models a carbon capture
process in a stand-alone pulp mill. The modeling is executed using Aspen Plus, followed by a
process integration study to identify energy source alternatives within the mill while minimizing
steam usage.
The model indicates a requirement of 3.6 MJ/kgCO2 for capture, with a feasible energy supply
strategy involving the integration of a low-pressure steam generation heat pump to utilize waste
hot water streams within the mill. Additionally, alternatives such as incorporating a new
combustion air preheater have been explored, showcasing potential electricity savings of up to 3,5
MW, although with marginal reductions in steam flow for carbon capture applications.
In conclusion, first implementing carbon capture in the lime kiln is recommended due to its smaller
column size and lower energy demand compared to the recovery boiler. Furthermore, conducting
a more exhaustive energy efficiency assessment of the mill is advised to identify additional sources
of waste heat usable by the heat pump.

Popular Abstract

This thesis examines the repercussions of introducing carbon capture processes into pulp mill
operations. Beginning with the modeling of a carbon capture process using flue gas data, I assessed
the energy requirements for the mill. Furthermore, I explored avenues for process integration,
aiming to reduce the energy footprint of the operation.
As everyone knows, the climate is changing all over the globe. One of the main drivers of this
change is the constantly increasing CO2 content in the atmosphere. Simply put, CO2 is the gas
emitted when carbon is burned. As you can imagine, most of the fuels used nowadays contain
carbon. But why is it burned? It is burned because historically it has been the easiest way to extract
the energy stored in carbon. After burning, the energy is released in the form of heat, which is then
used to heat something else, such as water to produce steam. In conclusion, every time fuels are
burned to extract energy, CO2 is emitted into the atmosphere.
The energy content of fuels is used by many industries and power plants, including cement, steel,
pulp and paper, and oil refineries. These sectors all face the same problem: they emit CO2.
However, the pulp and paper sector utilizes biomass (wood from trees) as a raw material. The trees
absorb CO2 during photosynthesis, and then that CO2 is released when burned. Hence, if that
CO2 could be captured, the net CO2 emission would be negative. This underscores the relevance
of capturing CO2 from industries that use biomass as a raw material. However, despite its
importance, it is not being done for three main reasons: the investment is high, the operation
requires a lot of energy (money), and the technology needs to be proven and accepted.
In my study, I have addressed the second problem: high energy requirements. First, I modeled the
CO2 capture process and validated that model with experimental data from other research and lab
experiments. The main outcome of this model is the size of the capture module, which gives us
an idea of the capital cost and the energy requirements of capturing that CO2. These results show
that capturing 1 kg of CO2 requires 3.6 MJ, which is similar to the energy produced by one onshore
wind turbine in one second. The case study of Montes del Plata emits 88 kg of CO2 per second,
hence 88 wind turbines spinning and producing 3.6 MJ each of energy every second that the mill
is in operation. It should be remembered that pulp mills run around 350 days per year and 24
hours. It is clear that the energy requirements are huge. This is why the second part of my study
focused on using the internal energy of the mill to satisfy the demand for the carbon capture
process.
In the final part, I have dimensioned and shown how the different waste energy streams of the
mill can be valorized. That means that energy that is being wasted can be useful again with an
energetically feasible process such as heat pumps. Additionally, I have shown that other heatexchanging
processes can be optimized, and energy can potentially be saved. The main takeaway
of this section is that carbon capturing is doable from an energetic point of view if waste heat is
used through the implementation of heat pumps. Without the utilization of heat pumps, capturing
the CO2 will cause an immense reduction in energy production.

• author: Robano, Enzo
• supervisor: Hesameddin Fatehi
• organization: Department of Energy Sciences
• course: MVKM05 20241
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• report number: ISRN LUTMDN/TMHP-24/5587-SE
• ISSN: 0282-1990
• language: English
• id: 9164184
• date added to LUP: 2024-06-19 10:56:55
• date last changed: 2024-06-19 10:56:55