Design and Heat Integration of an Offshore Blue Hydrogen Plant

Abstract

Dette projekt undersøger designet og modelleringen af et offshore blåt hydrogen produktionsanlæg i Nordsøen. Hydrogen er anerkendt som en vigtig brik i en dekarboniseret fremtidig energiforsyning. Hydrogen kan produceres med reducerede karbonudledninger gennem elektrolyse af vand drevet af vedvarende elektricitet, kendt som grønt hydrogen, eller fra fossile brændstoffer som naturgas med karbonfangst og -lagring, kendt som blåt hydrogen. Blå hydrogen forventes at være mest velegnet til hurtig implementering, hvorefter grøn hydrogen vil følge op, når teknologien er mere udviklet.

Det er essentielt at vurdere forskellige lokationer og produktionsmetoder af blåt hydrogen for at sikre en optimal produktion. En mulighed er offshore produktion, hvilket vil minimere eller eliminere behovet for CO2-transport, eftersom den opsamlede CO2 kan sendes til lagring tæt på hvor naturgassen udvindes. I dette projekt undersøges denne mulighed og projektet indeholder en udvælgelse af egnede enhedsoperationer, steady-state simuleringer og varmeintegration af processen.

Den anvendte proceskonfiguration omfatter omforming af naturgas med en oxygen-fyret autothermal reaktor i kombination med en gas-varmet reaktor, et CO-konvertingsanlæg for at øge koncentrationen af hydrogen og CO2, og et karbonfangst anlæg baseret på kemisk absorption med MDEA som opløsningsmiddel. Karbonfangstgrader på henholdsvis 80%, 90% og 98% er undersøgt. Derudover er produktionen af hydrogen med både høj renhed og industriel renhed undersøgt. For hydrogen med en industriel renhed varierer renhedsgraden alt efter karbonfangstgraden og er i intervallet 91,1-96,8 mol%. For at producere hydrogen med en høj renhed er tryk-svingsadsorption benyttet som et oprensningstrin, og en renhed på 99,9 mol% er opnået.

Karbonudledningerne er beregnet for hvert scenarie og inkluderer det CO2, som ikke er fanget, samt udledninger fra forsyningen af opvarmning, strøm og køling. Udledningerne er i intervallet 1,61-3,24 kg CO2 per kg H2, med de laveste udledninger for hydrogen med høj renhed og en karbonfangstgrad p ̊a 98%. De højeste udledninger er for hydrogen med industriel renhed og en karbonfangstgrad på 80%. Til sammenligning er udledningerne uden karbonfangst 8,99 kg CO2 per kg H2.

Dette studie konkludere også, at fordelene ved at producere hydrogen offshore sammenlignet med onshore kan være begrænsede. Dette er baseret på en mol balance for processen, hvor molstrømmen af hydrogen, der skal transporteres onshore, er meget større end den samlede molstrøm af det forbrugte naturgas og den producerede CO2-strøm. Dette indikerer, at det volumen, som skal transporteres for offshore produktion, vil overstige det for onshore produktion, selv hvis CO2-strømmen skal sendes tilbage offshore.

Det anbefales, at fremtidige studier fokuserer p ̊a produktion af blåt hydrogen placeret onshore, hvor optimering, livscyklusanalyse, økonomiske vurderinger og sikkerhed er vigtige faktorer, der skal inkluderes for at vurdere gennemførligheden af et produktionsanlæg.

This project investigates the design and modeling of an offshore blue hydrogen production facility located in the North Sea. Hydrogen is acknowledged as an important part of a decarbonized future energy supply. Low-carbon hydrogen can be produced through water electrolysis powered by renewable electricity, known as green hydrogen, or from fossil fuels such as natural gas with carbon capture and storage, known as blue hydrogen. Blue hydrogen is predicted to be suitable for rapid implementation while green hydrogen will follow as the technology matures.

Evaluating different locations and production methods for blue hydrogen is essential to ensure optimal production. One option is offshore production, which minimizes or eliminates the need for CO2 transportation, as the CO2 can be sent to storage close to where the natural gas is extracted. This study addresses this option, including a selection of suitable unit operations, steady-state simulation, and heat integration of the process. The selected process configuration includes reforming of natural gas with an oxygen-fired autothermal reactor in combination with a gas-heated reformer, water gas shift reactors to increase the concentration of hydrogen and CO2, and a carbon capture unit based on chemical absorption with MDEA as the solvent. Carbon capture rates of respectively 80%, 90%, and 98% are studied. Additionally, the production of both industrial-grade and high-grade hydrogen is investigated. For industrial-grade hydrogen, the purity depends on the carbon capture rate, ranging from 91.1-96.8 mol%. For high-grade hydrogen, pressure swing adsorption is added as a purification step, and a purity of 99.9 mol% is achieved.

Carbon emissions are calculated for each case study, including non-captured CO2 and utility emissions. The emissions are in the range of 1.61-3.24 kg CO2 per kg H2, being lowest for high-grade hydrogen with 98% carbon capture and highest for industrial-grade hydrogen with 80% carbon capture. For comparison, the emissions without carbon capture are 8.99 kg CO2 per kg H2.

This study also finds that the benefit of producing blue hydrogen offshore compared with onshore might be limited. This is reasoned by a mole balance of the process, where the mole flow of hydrogen being transported onshore greatly exceeds the total mole flow of consumed natural gas and produced CO2. This indicates that the transported volume required for offshore production will be larger than that for onshore production, even if the CO2 must be sent offshore again. It is recommended that future research should focus on the production of blue hydrogen onshore, where optimization, lifecycle assessment, economic evaluation, and health and safety are important factors to consider the overall feasibility of the plant.