Art by Kara Tao.
Increased wildfires, heat, drought, and hurricanes are some of the devastating effects of climate change that continue to be seen across the world, and urgent action must be taken. To ensure that the Earth remains tolerable for humans to live on, environmentally friendly technologies are crucial. Over the past few years, there has been growing excitement about hydrogen fueling stations worldwide. The media portrays hydrogen fuel as a sustainable alternative to fossil fuels, with water being the only by-product.
In reality, hydrogen fuels are usually generated using fossil fuels, emitting carbon dioxide (CO2) as a by-product. Hydrogen comes from methods such as steam methane reforming, coal gasification, and electrolysis from electricity sources such as grid, solar, etc. Hydrogen fuel contributes to greenhouse gas emissions and, consequently, climate change.
But if many methods to generate hydrogen fuel either directly or indirectly contribute to greenhouse gas emissions, what can we do to mitigate its impact on the climate? The answer lies in a process called bioenergy with carbon capture and storage (BECCS), which is the process of generating energy from biomass or organic matter while capturing and storing the CO2 emitted and providing net negative greenhouse gas emissions.
In previous studies, methods such as techno-economic analysis (TEA) and life cycle assessment (LCA) were used to assess the economic feasibility and environmental impacts of BECCS. However, these studies did not consider the effect of the choice of energy supply. Moreover, previous studies rarely explored categories beyond climate impact, such as a broader range of impact indicators (e.g., human health impacts) of hydrogen as a fuel. In order to maximize the potential of BECCS, a holistic understanding of the effect of energy supply strategies and the implementation of carbon capture is crucial.
Researchers at the Center for Industrial Ecology at the Yale School of Environment wanted to assess the efficiency and impact of BECCS. “The basic idea is to evaluate the economic feasibility and environmental impacts of emerging biotechnologies,” said Na Wu, a postdoctoral researcher in the Yao Lab.
To assess its impacts, the researchers developed the techno-economic-environmental assessment (TEES) framework–a method to evaluate the environmental and economic impacts of BECCS and other similar carbon capture technologies. This framework incorporates methods used in previous studies, such as TEA and LCA, but also simulations of implementing BECCS with different possible conditions for the biorefinery, the facility that converts biomass to energy.
How It Works
This study assessed gasification-based BECCS, using leftover wood scraps and branches from logging, called forest residues, as a source of biomass for gas conversion. Their analysis focused on forest residues from the Pacific Northwest, specifically the Douglas fir and ponderosa pine, because there is a large amount of biomass present in the region, and due to wildfires, there is a need to thin the forests. This assessment was conducted using the TEES framework and is novel because it is an integrated model addressing the knowledge gaps of the biorefinery with all carbon dioxide emission sources. These simulation models integrate energy supply strategies while also taking into consideration the real-world application of these models.
“We tried to maximize the carbon capture and storage process using our simulation models and integrate that with energy supply strategies,” Wu said.
In order to simulate real-life scenarios, the researchers used a system with various components to measure and calibrate different options. They modeled eight biorefinery processes to determine which scenario is the most economically and environmentally feasible. These components include biomass preparation (such as size reduction and drying), gasification, cleaning syngas (a mixture of hydrogen and carbon monoxide), water-gas shifting, carbon capture, pressure swing adsorption, air separation, and heat power generation. This was used to simulate the conditions required to produce syngas from biomass. Additionally, they modeled the three main stages of carbon capture: capturing the CO2, transporting it, and then storing it deep underground. As the amount of biomass can affect the method’s perceived efficiency, different scales with different amounts of biomass were used.
With the appropriate boundaries established, the researchers analyzed four different scenarios. Scenario one consists of burning the syngas produced to generate heat and power simultaneously, leading to electrical self-sufficiency while trapping carbon underground (carbon capture). Scenario two is similar to scenario one but with no carbon capture, which served as a baseline to understand the effect of carbon capture implementation. Scenario three includes the same components as scenario one but uses all the syngas products for hydrogen production, leading to partial electrical self-sufficiency. Scenario four includes carbon capture technology but does not use a combined heat and power generation plant, which makes it the least self-sufficient electricity scenario.
The researchers decided which scenario was most favorable based on considerations such as the highest capital expenditure and operating expenditure. The most and least favorable scenarios varied depending on the type of expenditure examined. For instance, scenario one (fully self-sufficient) has the highest capital expenditure (CAPEX), whereas scenario two (no carbon capture) has the lowest CAPEX. This indicates that carbon capture requires a large amount of capital since scenario two is the only scenario without carbon capture included. However, scenario four (least self-sufficient) has the highest yearly operating expenditure (OPEX), whereas scenario one (fully self-sufficient) has the lowest OPEX due to the lowest utilities needed as a result of the full electrical self-sufficiency.
After calculating and analyzing the minimum selling price for hydrogen and carbon price for these four scenarios, they made two main conclusions. First, hydrogen derived from forest residues has the potential to achieve similar economic feasibility to current fossil fuel-based hydrogen with carbon capture. In fact, when the price of carbon dioxide is higher than $89 per ton of CO2, all four scenarios become more economically attractive than the current fossil fuel-based hydrogen. However, the opposite—lower economic attractiveness when the price of CO2 is lower—also applies. This leads to the second conclusion, which is that CO2 prices help determine how economically competitive the three scenarios with carbon capture can be.
To further analyze the effect of renewable energy, additional cases for scenarios one (fully electricity self-sufficient) and four (least electricity self-sufficient) were examined. Instead of using an electricity source from the current grid, solar and wind energy were used. The findings indicated that renewable energy sources make scenario four preferable to electricity self-sufficiency (scenario one). However, further research needs to be conducted to determine the optimal renewable energy design for BECCS.
These findings suggest that using BECCS has lower environmental impacts than the current hydrogen production methods and highlight the need for individuals from various sectors, including chemistry, analytics, business, engineering, and more, to successfully implement this biotechnology approach.
Limitations
There is no denying that BECCS has an immense amount of potential to be an excellent environmental solution, but it is important to acknowledge certain limitations in this study. The study did not include CO2 transportation and storage or hydrogen transportation in its model. Moreover, the study focused on the Pacific Northwest of the United States, which is only one small region in the world. Similar studies must be conducted in other regions to determine if this technology is economically feasible and has reduced environmental impacts.
Implications and Next Steps
Looking towards the future, BECCS could be used in other waste feedstocks beyond forest residues to sustainably provide energy, such as animal wastes, food wastes, etc. This could be used to reform the agricultural industry, which is responsible for much of global greenhouse gas emissions.
The findings from this study can help inform further research on other types of carbon capture and storage. Looking ahead, Wu wants to expand their study of carbon capture technologies to assess their economic and environmental impact. “BECCS is a chemical-based process, but there are more natural methods for carbon capture and storage, such as afforestation and reforestation, enhanced weathering, and biochar and soil carbon sequestration,” Wu said. Afforestation and reforestation rely on trees, enhanced weathering relies on rocks, and biochar and soil carbon sequestration rely on the soil (after CO2 is transformed into more stable carbon). “The next project I am working on is analyzing enhanced weathering carbon capture—using rocks to capture CO2 in the atmosphere. We are trying to explore the different possibilities,” Wu said.
“We can help in the decision-making of various parties, such as researchers working in the lab, and we can also provide insights to companies. For instance, we can explain if it’s a good investment by determining if it is profitable, and we can also provide insights to the environmental authorities,” Wu said. One thing is clear: an interdisciplinary team is necessary to create a more sustainable, low-carbon, and circular society. “We need different kinds of parties: authorities, companies, chemists, engineers, business people, etc. In that way, we can make sure we are heading in the right direction,” Wu said.