Search

This paper is written in response to the paper “How green is blue hydrogen?” by R. W. Howarth and M. Z. Jacobson. It aims at highlighting and discussing the method and assumptions of that paper, and thereby providing a more balanced perspective on blue hydrogen, which is in line with current best available practices and future plant specifications aiming at low CO2 emissions. More specifically, in this paper, we show that: (i) the simplified method that Howarth and Jacobson used to compute the energy balance of blue hydrogen plants leads to significant overestimation of CO2 emissions and natural gas (NG) consumption and (ii) the assumed methane leakage rate is at the high end of the estimated emissions from current NG production in the United States and cannot be considered representative of all-NG and blue hydrogen value chains globally. By starting from the detailed and rigorously calculated mass and energy balances of two blue hydrogen plants in the literature, we show the impact that methane leakage rate has on the equivalent CO2 emissions of blue hydrogen. On the basis of our analysis, we show that it is possible for blue hydrogen to have significantly lower equivalent CO2 emissions than the direct use of NG, provided that hydrogen production processes and CO2 capture technologies are implemented that ensure a high CO2 capture rate, preferably above 90%, and a low-emission NG supply chain.

This report evaluates post-capture CO2 management options for the cement industry. A number of possible CCU products are evaluated according to metrics such as the energy demand, the technology readiness level and the market size. Six scenarios were proposed and evaluated in this report, in order to illustrate of the options available for the reference CEMCAP cement plant. 1) CCS1: CO2 capture from a cement plant in Belgium and injection in a saline aquifer in the Dutch continental shelf is estimated to cost 114 €/ton CO2 avoided. 2) CCS2: CO2 capture from a cement plant in costal Germany and injection in a saline aquifer in the Norwegian continental shelf is estimated to cost 153 €/ton CO2 avoided. The difference between these two scenarios show the impact of the transportation mode and the distance between source and sink on the CO2 cost. 3) CCS3: mineralization to MgCO3 is expected to between 150 and 400 €/ton CO2 avoided. The process efficiency, the transportation of rock and MgCO3, as well as the heat demand, play an important role in the final cost. Further process developments and an optimized chain can bring the costs significantly down; 4) CCS1+U1: blue ethanol production using 3,1% of the emitted CO2 requires 50 MW excess renewable power. The remaining fraction of the captured CO2 (86,9%) is sequestered using CCS1. The total CCUS cost is 111 €/ton of CO2 avoided (3% reduction as compared to CCS1) when blue ethanol replaces green ethanol from sugarcane. In case of replacement of green ethanol from wheat, the cost drops to 96 €/ton of CO2 avoided (16% reduction as compared to CCS1). 5) CCS1+U2: by using 7,5% of the emitted CO2, 288 kt/y of blue polyol are produced. 82,5% of the CO2 is stored via CCS1. This configuration may lead to a positive business case, depending on the spread between the polyol market price and that of propylene oxide. If both prices are set as 1400 €/ton (zero spread), the CCUS chain leads to a profit of 18 €/ton CO2 captured. 6) CCS1+U3: purifying 6,5% of the emitted CO2 to food-grade (blue CO2) and placing it in the food market lowers the integrated CCUS cost as long blue CO2 replaces fossil-derived CO2: in that case, the cost drops to 108 €/ton CO2 captured. If green CO2 is available (e.g. from fermentation), the CCUS option actually leads to a higher cost than CCS1: 120 €/ton CO2 avoided. Polyol and ethanol are representative of other CO2 utilization routes, and the overall conclusions derived for these processes can be extended to high value specialties and fuels, respectively. CO2 utilization should always be considered in combination with storage. The fraction of the CO2 that is utilized in a full scale CCUS implementation in a cement plant is expected to be lower than 10%. High added-values products may lead to positive business cases. However. the number of cement plants that could benefit from this option will be strongly limited by the product’s market. The utilization of CO2 to replace CO2 intensive raw materials or products (e.g. ethanol from wheat or propylene oxide) lead to improved costs when the basis of calculation is CO2 avoided. LCA should be conducted for the different technological routes, in order to take this important factor into consideration., This work was supported by the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number 15.0160