Improving Energy Efficiency of the Inrs Mineral Carbonation Process Using Pinch Analysis

Mineral carbonation is a key solution to tackle climate change issues. The process developed at INRS proposes to directly treat industrial CO₂ emissions without capture using serpentine mining waste. The process can be summarized into three separated steps, raw serpentine mineral processing, CO₂ and serpentine dissolution and carbonate precipitation. The efficiency observed at laboratory scale has been demonstrated during pilot plant tests where a real cement plant flue gas with CO₂ content of 18% was treated at 10 bar feed pressure and 22°C. While the process offers a viable and economic way to reduce CO₂ emissions, energy efficiency remains to be addressed.

In this work, pinch analysis was used with the aim to reducing the heat demand of the INRS process by energy integration. An Aspen Plus simulation flowsheet was first prepared for a base case plant with a capacity of 200 t of raw serpentine used per hour (350 000tCO₂/year) and the process conditions mentioned above. Cooling water and natural gas combustion were considered as external cooling and heating sources respectively. Secondly, serpentine and combustion air preheating temperatures were varied as optimisation parameters. For each case, the resulting mass and energy balances were used in a pinch analysis with the Aspen Energy Analyzer. Finally, results were compared in terms of required external heating, additional capital and operating costs.

Results show that preheating serpentine using the process waste heat before heat activation has the biggest impact on the external heat required. Raising the solid temperature by 100°C reduces the operating costs by 14%. On the other hand, a similar increase in the incoming gas temperature will only result in a 5% reduction. The best trade-off between energy integration and additional costs was obtained with solid and gas preheating temperatures of 400°C and 300°C respectively. This resulted in a reduction of global heat demand of more than 40 %. It is also worth mentioning that external cooling is also required in the INRS process, which is mainly used for cooling the recycled precipitation solution. This accounts for less than 15% of the total costs.