Aug-2021

Clean hydrogen energy from repurposed gasification plant

A former gasification plant is set to become one of the largest carbon capture and clean hydrogen production facilities in the US to date.

Bhargav Sharma and Mark Schott, Honeywell UOP
Dan Williams, Wabash Valley Resources

Article Summary

Atmospheric CO2 levels continue to climb. NOAA has reported the May 2021 monthly average to be 416 ppm.¹ This is the highest level in the last 800,000 years. The previous high was approximately 350 years ago and only reached 300 ppm. These elevated CO2 levels have already led to temperature increases and large weather fluctuations. The NASA global land-ocean temperature index has increased by approximate 1°C since 1880.1 Sea levels are rising, up about 200 mm2 in the last 120 years. However, that rate of increase has accelerated in the last 25 years to about 3.4 mm/year.²

To avoid the worst impacts of global warming, many experts have recommended the increased use of clean hydrogen (H2) across many industries. Low-carbon H2 is considered to be a significant route to decarbonise many industries, including power, steel and cement. H2 can also be a significant route to decarbonise difficult industries such as the transportation industry, especially for long-haul heavy-duty trucks. The IEA3 reported that in 2019 only 0.36 Mt/yr of low-carbon H2 was in production, with another ~1.5 Mt/yr announced. The IEA SDS plan calls for ~8 Mt/yr of low-carbon H2 to be available by 2030.

Today about 98% of 70 million tonnes of H2 comes from carbon-intensive sources. Carbon-neutral energy is receiving unprecedented attention. While green H2 is the ultimate goal of the H2 economy, blue H2 is viewed as the first step to this goal. Proven technologies combined with anticipated greater demand for H2 and government incentives like 45Q in the US are making blue H2 projects economically attractive and bankable.

Wabash Valley Resources project
The idle Wabash River gasification facility will be redeveloped by Wabash Valley Resources to produce electricity to be transferred to the network grid and provide opportunities for H2 offtakes to transportation or be used as chemical feedstock. It is anticipated to use waste products like petroleum coke and locally available biomass to generate up to 285 MW of electricity with net-zero CO2 emissions by 2024. The project will capture, liquefy and sequester the produced CO2 near the plant site in suitable underground formations of the Illinois Basin. Retrofitting the existing gasification facility reduces the technical risk and capital costs associated with the project. The Wabash gasification plant has successfully produced syngas for over 20 years, utilising petcoke as the feedstock, and the configuration selected maintains the existing plant as is with minimal modifications.

Several processes are combined in the integrated facility to produce H2 and power. Byproducts produced at the facility include CO2, sulphur and vitrified slag. The solid feedstock and biomass are milled with recycled water to produce a slurry solids concentration that varies depending on the feedstock selected. In the gasifier, the slurry is injected with a high-purity oxygen stream generated by the air separation unit. Raw syngas exiting the gasification process consists mostly of carbon monoxide, H2, CO2, water and hydrogen sulphide (H2S). The slag produced in the gasifier is quenched, crushed and removed from the unit through a continuous slag removal system. The syngas from the gasifier is cooled in a high-temperature heat recovery unit (HTHRU) that produces high-pressure saturated steam, which will be utilised in the steam turbine to produce power. The syngas from the outlet of the HTHRU is sent to a particulate removal system, where the remaining particulates consisting mostly of carbon will be recycled to the gasifier. The syngas will be directed through the existing sulphur removal process, where the H2S will be removed. The sour gas containing H2S from the sulphur removal process will be sent to the existing sulphur recovery unit (SRU). The SRU converts the H2S to elemental sulphur, a valuable byproduct of the facility. 

The syngas will be routed to the new water gas shift (WGS) process to shift the syngas to maximise H2 production. Syngas will then be routed through a new CO2 recovery system to be designed and licensed by Honeywell UOP. A dehydration unit is included to produce an anhydrous gas suitable to be sent to the new CO2 fractionation unit. The CO2 fractionation unit will then separate the CO2 from the H2, producing a high-purity liquid CO2 stream. The liquid CO2 stream will be pumped to the battery limits for permanent underground sequestration. The H2 gas stream will then be sent to a PolyBed pressure swing absorption unit (PSA) for purification. The product H2 stream from the PSA will be sent to a H2 turbine to produce electricity. The CO2 from the PSA unit will then be recycled to the CO2 fractionation unit to ensure minimal emissions of greenhouse gases (GHG). 

Since Wabash Valley Resources is investigating blending in biomass feedstocks, it has the potential to achieve negative carbon intensity H2 product while sequestering 1.65 million t/y of CO2. The project is expected to be one of the largest carbon sequestration initiatives in the US to date. Figure 1 shows the overall flow scheme.

CO2 capture system
Wabash evaluated a number of technologies for the CO2 capture process, including conventional physical and chemical solvents, as well as generic and licensed solvent-based processes, before choosing the configuration offered by Honeywell UOP. The dehydration, CO2 capture and H2 purification units are integrated into one overall system to minimise capital and operating expenses. The process equipment can be constructed as modular prefabricated units, which shortens project schedules, lowers construction costs, and improves quality and HSE performance. Higher levels of shop fabrication minimise constructability risks and allow site activities to run in parallel with module fabrication. The modular approach provides Wabash with the capability to maximise its overall project integration from restarting an existing facility while integrating new state-of-the-art carbon capture technology.

Advantages
Some of the key advantages of the Honeywell UOP CO2 capture system compared to conventional solvent systems for this plant are shown below:
- Lower Capex
- Lower Opex
- No steam integration needed with existing plant, thereby maximising electricity generation
- Dry system (no solvent storage, handling, and so on)
- Main consumables are adsorbents, and typical replacement life is >10 years, thereby requiring less planned downtime
- Commercially proven technologies
- Efficiency: single supplier for technology and equipment allows for less handoff
- Bankability: well recognised in the market for both technology licensing and modular equipment
- Faster modular execution
- Parallel on-site and module fabrication execution
- High-quality shop-fabricated equipment