Energy and Heat Balance Optimization for CHP Plants with CO2 Capture: Modeling and Sensitivity Analysis

Abstract

This thesis investigates how the integration of post-combustion carbon capture (PCC) systems would affect combined heat and power (CHP) plant performance, using DWSIM, an open- source process simulation tool. A case study on a CHP plant in southern Sweden was conducted, with models simulated for both baseline and CCS-integrated operation. DWSIM proved accurate within a relative error of under 3 % for key components such as turbines and condensers, demonstrating its potential as a cost-effective alternative to commercial simulators.
Two carbon capture strategies were analyzed using steam extracted before the high-pressure (HP) turbine: the Split Stream Path (SSP) with a constant reboiler heat demand of 3.7 MJ/kg CO2, and the Separation Rate Path (SRP) with a variable duty of 3.3–3.7 MJ/kg CO2. SRP showed reduced steam use at partial capture rates but at 90 % capture, both strategies performed similarly due to equal reboiler demand.
Different steam extraction points for supplying reboiler heat to the CO2 capture system were also analyzed. Four different steam extraction points were evaluated: before the HP turbine, after the HP turbine and condenser, before the HP condenser, and after the low-pressure (LP) turbine. To reach suitable steam conditions for the reboiler, auxiliary units like compressors and coolers were added. A sensitivity analysis assessed power and heat losses, impacts on district heating, and technical trade-offs.
An economic analysis was conducted to compare different steam extraction points based on trade-offs between electricity and heat revenue losses, CO2 savings under the EU ETS, and CO2 transport and storage costs. All cases were evaluated under a 90 % capture rate. Among the four extraction strategies, Case 3 proved the most economically favorable, achieving the shortest payback time of 12.1 years due to its lower electricity revenue loss, despite slightly higher heat losses. This highlights the importance of selecting the right extraction point to maximize economic performance.
Different technologies with lower reboiler duties from literature showed potential to reduce steam extraction and cut energy losses significantly. Integrating CCS in CHP plants requires changes like optimized steam extraction, turbine adjustments, and condensate return. Overall, CCS integration is feasible with targeted modifications, and DWSIM is a reliable tool for such modeling.

Popular Abstract

Our world urgently needs effective solutions to reduce greenhouse gas emissions and tackle climate change. Combined Heat and Power (CHP) plants, which generate electricity and heat simultaneously, are already highly efficient. However, they still emit significant amounts of carbon dioxide (CO₂), contributing to global warming. Integrating carbon capture and storage (CCS) technologies into CHP plants could significantly reduce these emissions, making CHP an even greener solution.
Carbon capture and storage involves capturing CO₂ from power plant emissions, transporting it, and storing it safely underground to prevent its release into the atmosphere. This thesis focuses on understanding how integrating CCS technology would impact the performance of CHP plants. Specifically, this thesis explores how capturing CO₂ after combustion (known as post-combustion capture) affects plant efficiency, energy output including heat for district heating, and economic feasibility. A computer simulation using the software DWSIM was used to model a real CHP plant located in southern Sweden, investigating different ways of extracting steam required for the carbon capture process.
Two methods for capturing CO₂, the Split Stream Path (SSP) and the Separation Rate Path (SRP), were analyzed. The SRP was more advantageous, especially at lower CO₂ capture rates, as it utilized steam more efficiently. Subsequent energy and heat balance analyses at different capture rates using both methods revealed that both electricity generation and heat production for district heating decreased as the capture rate was reduced, where SRP showed lower losses compared to SSP.
Several steam extraction points were examined in detail:
• Before the high-pressure (HP) turbine, causing significant energy loss due to bypassing the turbine.
• After the low-pressure (LP) turbine, requiring substantial additional power for steam compression.
• After the HP turbine but before the HP condenser, resulting in minimal power loss and efficient heat utilization.
• After the HP condenser but before the LP turbine, which offered balanced performance in terms of electricity and heat generation.
Among these options, extracting steam after the HP turbine but before the HP condenser showed the lowest energy loss and provided the shortest economic payback period, around 12 years.
Further analysis highlighted new technologies capable of significantly reducing energy demands for CO₂ capture, potentially decreasing the required steam by up to 46% and considerably lowering power and heat losses. By optimizing steam extraction points and adopting advanced capture technologies, the plant’s efficiency and economic performance could be notably improved.
Overall, this thesis demonstrates that integrating CCS into CHP plants is technically and economically viable, especially when carefully choosing steam extraction points and leveraging advanced technologies. Such strategies can substantially contribute to sustainable energy systems, significantly lowering the carbon footprint of energy production and aiding global climate goals.

• author: Gounesher, Melisa
• supervisor: Marcus Thern; Meher Sanku; Laura Malek
• organization: Department of Energy Sciences
• course: MVKM05 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Carbon Capture & Storage (CCS) technologies, Combined Heat and Power (CHP), DWSIM, Modelling
• report number: ISRN: LUTMDN/TMPH-25/5646-SE
• ISSN: 0282-1990
• language: English
• id: 9205976
• date added to LUP: 2025-06-26 09:41:25
• date last changed: 2025-06-26 09:41:25