火力發電廠中使用石灰岩與使用鈣鈦改質材料於鈣迴路程序之生命週期評估

Life cycle assessment of calcium looping with limestone and Ca/Ti modified material in coal fired power plant

鄭竹軒(Chu-Hsuan Cheng)

指導教授 ： 劉雅瑄

共同指導教授 ： 闕蓓德(Pei-Te Chiueh)

國立臺灣大學/理學院/地質科學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201903074

摘要

鈣迴路程序(Calcium looping)為新一代的碳捕獲技術，利用價格低廉且取得容易的石灰岩作為載體，在兩座高溫的流體化床中不斷地循環進行碳酸化/鍛燒反應來捕捉二氧化碳。然而在捕碳過程中，石灰岩會因高溫燒結使得活性快速衰退，需要消耗大量的石灰岩以維持系統的捕碳效率，連帶影響了系統的耗電量與耗煤量，使得改善材料的反應活性成為改良鈣迴路程序的重要研究主題之一。本研究以氣膠自組裝系統(aerosol-assisted self-assembly system, AASA system) 合成高穩定性的鈣鈦(CaTi)材料作為載體捕捉二氧化碳。藉由X光繞射分析（XRD）可發現CaTi材料中主要含有氧化鈣(CaO)與鈦酸鈣（CaTiO3）之特徵峰，而BET分析下材料比表面積在10-16m2/g，最後利用熱重分析（TGA）進行二氧化碳吸附測試，其結果顯示鈣鈦莫爾比為5的CaTi材料，能在第20次的反應，仍保持良好的活性(0.38g-CO2/g-sorbent)。通過鈣迴路程序的模擬可發現，相較於天然石灰岩，使用鈣鈦材料能有效地減少鈣迴路程序中鈣基吸附材、煤炭與電能的消耗量。
本研究針對火力電廠中的鈣迴路系統使用天然石灰岩與CaTi材料，以Simapro7.18軟體進行生命週期評估(Life cycle assessment)，採用ReCiPe衝擊評估方法量化這兩種案例的環境衝擊來進行比較。LCA結果顯示使用了CaTi材料的鈣迴路系統，雖然材料耗損遠低於石灰岩，但仍在多項環境衝擊中高於使用了石灰岩的鈣迴路系統，尤其是海洋生態毒性、人體毒性以及氣候變遷的衝擊項目。其衝擊來源主要來自於CaTi材料所使用的原料中的硝酸鈣。未來將針對CaTi材料所使用的原料與合成流程做修正，使CaTi材料能成為更環境友善的材料。

關鍵字

碳捕獲 ； 鈣迴路程序 ； 燒結 ； 氣膠自組裝系統 ； 生命週期評估

並列摘要

Calcium looping is a new generation of carbon capture technology, which involved limestone, a cheap and accessible sorbent for carbon capture by multicyclic carbonation/calcination in high temperature twin fluidized bed. However, there lays a problem with limestone as sorbent, the reactivity would decrease dramatically after just a few cycles due to the sinister effect, which means a great amount of fresh limestones must be put into the system to maintain the the carbon capture efficiency. The fresher limestones as the make up flow, the more coals have to be consumed for keeping the heat balance of the system. This makes modifying the calcium sorbents for improving the reation ratio and slow down the decay rate to be an important key to improve the calcium looping system.
In this study, we synthesize a modfied material, CaTi material with aerosol-assisted self-assembly (AASA) system as the sorbent for carbon capture. In X-ray Powder Diffraction (XRD) the peak of CaO and CaTiO3 can be observed, the BET analysis shows that the specific surface areas of CaTi materials is around 10-16 m2/g and in the Thermogravimetric analysis (TGA) we test the CO2 capture capacity of CaTi material, the result shows in the case of Ca/Ti molar ratio were 5, the CaTi material could maintain high reactivity even in the twentieth cycle(0.38g-CO2/g-sorbent). In the calcium looping process modeling we found out that using CaTi material could reduce the comsumption of the sorbent,coal and energy while comparing to natural limestone.
In this study, we applied life cycle assessment by using Simapro 7.18 and ReCiPe impact assessment model to compare the environmental impact of capturing CO2 from the flue gases in a subcritical coal fired power plant with calcium looping, involving two different sorbents, limestone and CaTi material. The result shows though the scenario used CaTi material has much lower consumption, the overall environmental impacts were still higher than using natural limestone, especially in the marine ecotoxicity, human toxicity and climate change catagories.The main contributor of the environmental impact in CaTi material is calcium nitrate used while synthesize. In the future work, we would try to change the formula of the material to improve the evironmetal performance of CaTi material in calcium looping process.

並列關鍵字

Carbon capture ； Caclium looping ； Sinister effect ； Aerosol-assisted self-assembly(AASA) ； Lifecycle assessment(LCA)

參考文獻

Abanades, J. C., & Alvarez, D. (2003). Conversion limits in the reaction of CO2 with lime. Energy & Fuels, 17(2), 308-315.

Abanades, J. C., Anthony, E. J., Lu, D. Y., Salvador, C., & Alvarez, D. (2004). Capture of CO2 from combustion gases in a fluidized bed of CaO. AIChE Journal, 50(7), 1614-1622.

Abanades, J. C., Anthony, E. J., Wang, J., & Oakey, J. E. (2005). Fluidized bed combustion systems integrating CO2 capture with CaO. Environmental Science & Technology, 39(8), 2861-2866.

Abu-Zahra, M. R. M., Sodiq, A., & Feron, P. H. M. (2016). Commercial liquid absorbent-based PCC processes. In Absorption-Based Post-combustion Capture of Carbon Dioxide (pp. 757-778). Woodhead Publishing

Aihara, M., Nagai, T., Matsushita, J., Negishi, Y., & Ohya, H. (2001). Development of porous solid reactant for thermal-energy storage and temperature upgrade using carbonation/decarbonation reaction. Applied Energy, 69(3), 225-238.