Publication: Energy and carbon reduction efficiency of ship with reformer-integrated system
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Date
2023-11-01
Authors
Law Li Chin
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Abstract
This thesis proposes reformer-integrated decarbonization system to meet the carbon reduction targets for a ship. The system included hydrogen production unit (reactor), carbon capture system (CCS) and ship propulsion engine (ICE) to achieve low-carbon operation. In addition, waste heat recovery (WHR) was integrated followed by model optimization to reduce the energy penalty of the reformer-integrated system further. The integrated system performance was gauged by energy efficiency (εo) and carbon reduction (βo) efficiency.
Three reactors and four CCS were studied. Among the reactor systems which were steam methane reforming (SMR), auto-thermal reforming (ATR) and methane pyrolysis (MPR), SMR was found to be 37.5% and 38.5% more efficient than MPR and ATR respectively. The integration of SMR with different CCS such as pressure swing adsorption (PSA), membrane (MEM), cryogenic separation (CS) and amine absorption (AA) was shown able to remove 60-70 % of CO2 emission from ship. SMR-PSA was the most efficient combination (εo = 33.4%), with 0.9-percentage points of energy penalty was contributed by PSA, whereas MEM, CS and AA had resulted in 2.8%, 7.8% and 6.0% energy penalty respectively.
The εo of SMR-PSA system was optimized with WHR networks utilizing heat recovered from high temperature streams and engine exhaust. The sensitivity of four operational parameters (factors): methane feed into furnace (XCH4), steam to methane ratio (S/C), SMR exit temperature (TSMR) and SMR pressure (PSMR) were analysed. PSMR was found to be the least significant factor. Hence, mathematical models for factors (XCH4, S/C and TSMR) and responses (εo, βo, and hydrogen production rate (αH2)) of the integrated system were developed to study the factor-response interactions. In summary, a high εo was obtained at the expense of low βo. Then, model optimization was conducted.
Finally, the optimized integrated system was applied for shipping decarbonization target. The optimum conditions were achieved at XCH4 = 24.2 %, S/C = 3.9, TSMR = 1075 °C with o= 41.8 % and o= 75.6 % which met both IMO2030 and IMO2050 carbon reduction targets. Next, the application of the proposed SMR-integrated system for ship decarbonisation was projected. Partial implementation gave the ship a promising energy efficiency, whereas the full-scale application was able to reduce about 75% of carbon emissions. Thus, it was shown that the reformer-integrated system is a potential decarbonization approach for shipping.