Coal gasification is a significant method for hydrogen production, particularly in regions with abundant coal reserves. However, its greenhouse gas emissions profile varies considerably depending on whether carbon capture and storage (CCS) is implemented. A comprehensive assessment must account for upstream emissions from coal mining, process emissions during gasification, efficiency penalties introduced by CCS, and potential leakage risks. Comparisons with other fossil-based methods, such as steam methane reforming (SMR), and regional adoption challenges further contextualize its environmental impact.

Coal gasification without CCS is among the most carbon-intensive hydrogen production methods. The process involves reacting coal with oxygen and steam at high temperatures to produce syngas, a mixture of hydrogen, carbon monoxide, and carbon dioxide. Subsequent water-gas shift reactions convert carbon monoxide and steam into additional hydrogen and CO2. For every kilogram of hydrogen produced, approximately 18 to 20 kilograms of CO2 are emitted. Upstream emissions from coal mining, including methane leakage during extraction and transportation, add another 1 to 3 kilograms of CO2-equivalent per kilogram of hydrogen. Methane, a potent greenhouse gas with a global warming potential 25 times greater than CO2 over a 100-year horizon, exacerbates the total emissions footprint.

Introducing CCS to coal gasification can reduce CO2 emissions by 70% to 90%, depending on system design and capture efficiency. Post-combustion capture, pre-combustion capture, or oxy-fuel combustion methods are commonly employed. However, CCS imposes energy penalties, reducing overall process efficiency. The additional energy required for CO2 compression, transport, and storage lowers the net hydrogen output by 10% to 20%. Even with CCS, residual emissions remain, typically 2 to 6 kilograms of CO2 per kilogram of hydrogen. Methane emissions from coal mining are unaffected by CCS, maintaining upstream contributions. Leakage risks from CO2 storage sites, though relatively low at well-managed facilities, present additional long-term concerns.

Comparatively, steam methane reforming (SMR) without CCS emits 9 to 12 kilograms of CO2 per kilogram of hydrogen, primarily from methane combustion and the water-gas shift reaction. Upstream methane leakage from natural gas extraction and distribution varies by region but generally adds 1 to 2 kilograms of CO2-equivalent. With CCS, SMR emissions drop to 2 to 4 kilograms of CO2 per kilogram of hydrogen, making it a cleaner option than coal gasification with CCS. Partial oxidation of hydrocarbons, another fossil-based method, falls between SMR and coal gasification in emissions intensity.

Regional adoption of coal gasification for hydrogen production is heavily influenced by resource availability, infrastructure, and policy. China, for instance, relies on coal gasification due to its vast domestic coal reserves and existing industrial base. Without widespread CCS deployment, this contributes significantly to national emissions. In contrast, regions with abundant natural gas, such as the Middle East and North America, favor SMR due to lower costs and emissions. The European Union, with stringent climate policies, prioritizes electrolysis using renewable energy, though fossil-based methods with CCS are considered transitional solutions.

The economic viability of coal gasification with CCS depends on carbon pricing and technological advancements. High capture costs and energy penalties make it less competitive than SMR with CCS in most scenarios. However, in coal-dependent economies, government subsidies and integrated gasification combined cycle (IGCC) plants may offset some disadvantages. Retrofitting existing coal plants for hydrogen production with CCS could also extend their operational life amid decarbonization efforts.

Environmental trade-offs must be carefully weighed. While CCS significantly reduces direct emissions, upstream methane leakage and land-use impacts from coal mining remain unresolved issues. Water consumption for coal gasification is another concern, particularly in water-stressed regions. In contrast, renewable hydrogen production methods, such as electrolysis powered by wind or solar, offer near-zero emissions but face scalability and cost challenges.

In summary, coal gasification without CCS is highly emissions-intensive, while the addition of CCS substantially mitigates but does not eliminate its climate impact. When compared to SMR, coal gasification with CCS is less efficient and more carbon-intensive, though regional resource availability may dictate its use. The long-term role of coal-derived hydrogen hinges on advancements in CCS technology, methane leakage reduction, and the pace of renewable hydrogen deployment. Without aggressive decarbonization measures, coal-based hydrogen risks locking in high-emission infrastructure, undermining global climate goals.

The transition to low-carbon hydrogen must prioritize renewable methods while using fossil-based production with CCS as a bridging solution. Policymakers must balance energy security, economic feasibility, and environmental integrity to ensure hydrogen contributes meaningfully to a sustainable energy future.