Next-generation IGCC Will Offer Higher Efficiencies
Next-generation IGCC Will Offer Higher Efficiencies
The following report is from Stratas Advisors’ Global Syngas Service.
Syngas is increasingly used for power generation through combustion applications. Integrated Gasification Combined Cycle (IGCC) is a technology that uses a gasifier to turn coal and other carbonaceous substances into syngas. A key advantage of syngas combustion over conventional feedstock combustion is the reduced emissions and contaminants profile of syngas.
Contaminants such as sulfur, sulfur dioxide, particulates, arsenic and mercury are removed before combustion, syngas-based power is a cleaner utilization of carbonaceous substances, including coal. Additional reactions can shift carbon monoxide to hydrogen resulting in a low carbon fuel, potentially to supply hydrogen fuel cells or drive hydrogen turbines for an ultra-clean electricity source.
Some of the produced carbon dioxide (CO2) can be sequestered in underground formations or converted, but these are largely novel and commercially unproven applications. A mature utilization of CO2 is in enhanced oil recovery schemes whereby the gas is used to coax more petroleum out of reservoirs, thus “sequestering” the CO2 beneath the unproduced oil reserves. This application requires ready access to such oilfields and/or the construction of CO2 pipelines.
The excess heat produced from syngas combustion is passed to a steam cycle to drive a steam turbine. This two-step thermal utilization approach increases the overall thermal efficiency of an IGCC plant.
According to the Energy Information Administration’s 2016 Energy Outlook, crude oil and natural gas made up 65.5% in U.S. primary energy consumption while coal contributed 67.5% to China’s primary energy use. Recent demand for emission control and reduction in China and the political drive for CO2 cap and reduction has imposed a significant challenge to coal and its value chain sector.
This creates a demand factor for cleaner technologies for utilizing coal, including gasification.
The demand for IGCC is supported on several fronts, particularly in Asia, notably:
- The water consumption profile of IGCC relative to conventional combustion;
- Efficiency considerations;
- Reduced coal consumption;
- Efficient management of lower quality coals; and
- The potential for co-product development, including high-purity hydrogen and fertilizers.
The viability of carbon capture management approaches will be crucial for the greater development of IGCC projects during the assessment timeframe.
In the U.S., IGCC needs a leap forward in managing both capital investment and performance, particularly amid newly added regulations. In August 2015, the U.S. Environmental Protection Agency (EPA) added a requirement that new coal plants in the US emit no more than 636 kilograms (kg) (1400 lb. of CO2 per MWh of gross power produced).
Gasifying coal then firing the synthesis gas using conventional combined-cycle configuration can meet EPA guidelines, according to research from Electric Power Research Institute (EPRI). However, this is only with certain gasifiers and when integrated in a plant using high-quality coal. Assuming further progress, coal gasification provides multiple pathways for achieving the standard, including gasifiers integrated with solid oxide fuel cells and novel cycle designs such as the closed Brayton Cycle.
Next-generation IGCC offers higher efficiencies, approximately 50% to 54%. Even with IGCC, typical current generations are still above the new limits, except in a case EPRI found to be within compliance: high-quality bituminous coal and the dry-feed Shell gasifier. Presumably, the heat transfer characteristics of the dry-feed gasification approach combined with high-quality coals with lower CO2 content reduces CO2 emissions on thermal conversion, albeit the benefits of slurry feeding reduce operating cost impact, an economic consideration regarding long-term project viability.
High-temperature firing in a syngas application in the range of 2,600º F to 3,100º F would also meet the standard. Pratt and Whitney developed a turbine that operated at 3,600º F, but the technology is not likely to be commercially available for another decade. Combustion at these temperatures would also meet the new standards.
EPRI also found that closed Brayton cycles, using supercritical CO2 as the working fluid are also ways to increase efficiency. The approach is more than a decade away, but the study found that coal plants integrating Brayton cycles with 100% CCS are more efficient than the latest state-of-the-art IGCC integrating 90% CCS.
EPA’s standard could be achieved using a conventional gasifier with a solid oxide fuel cell (SOFC) operating at atmospheric pressure. More stringent standards, such as those in the U.K. and Canada, could be met by using a pressurized SOFC or catalytic gasifier. An IGCC plant operating on methane-enriched syngas at elevated pressure would have a CO2 emission intensity of 430 kg/MWh. However, this technology is still at the early stages and the EPRI does not expect SOFCs to be available in MW-scale modules until after 2020.
Carbon management solutions have had some commercial development success since our July 2016 update. Just west of Houston, Petro Nova is scheduled to open the world’s largest carbon capture and storage (CCS) facility. A joint venture of NRG Energy (NRG) and JX Nippon Oil & Gas Exploration, the coal-fired plant will capture 90% of from a 240-megawatt slipstream of flue gas, sequestering 1.6 million tonnes per annum (MTPA) of greenhouse gases. The companies will inject the CO2 into mature oil fields in the Gulf Coast region. At one site, CO2 production is anticipated to boost production from 500 barrels per day (bbl/d) to 15,000 bbl/d.
Another (novel by region) concept for CCS at a coal-fired power plant was announced in India. The small-scale project will purportedly capture 60,000 tonnes of CO2 from a 10-MW coal slipstream from a plant in Chennai. This would be the country’s first foray into coal-fired carbon capture.
Projected and operational IGCC investment represents US$58.425 billion, with US$16.35 billion projected in the assessment timeframe to 2026. This includes US$4 billion in investment in Saudi Arabia, US$4.7 billion in the UK (exclusive in biomass and waste-based implementations), and US$6.1 billion in Japan. Nameplate capacity in 2026 of 41,046 megawatts thermal versus a power output of 18,440 megawatts electrical indicates a plant output through IGCC of 44.9% of feedstock thermal input.