Refineries and petrochemical industry operators find themselves in an ever-changing regulatory environment, where new global strategies for carbon emissions reduction are released frequently, often setting challenging targets and recommendations.
The US government has proposed a reduction in the country’s greenhouse gas emissions by 52% of 2005 levels by 2030 – a much shorter timeframe than its previous pledges. In summer 2021, the UK government issued its low-carbon hydrogen strategy built around blue and green hydrogen, committing to net zero emissions. To meet these new economic and technical challenges, plant operators must make significant short-term improvements in efficiency, and radical changes in the longer term. The optimisation of the most carbon-intensive fired heater processes is the logical place to begin.
Fired heater processes and CO2
Steam methane reformers (SMRs), mostly used to supply hydrogen to refineries for ammonia/methanol production, and steam crackers for ethylene production, are two of the largest and most carbon-intensive refinery and petrochemical fired heaters.
It is estimated that SMRs emit around 800 million tpy of carbon dioxide (CO2), while steam crackers produce approximately 260 million tpy of CO2 emissions.
There is much focus on reducing CO2 emissions from these fired heaters by upgrading burners, changing tube/coil/refractory materials, and improving combustion efficiency. However, temperature monitoring and control can play an important role in improving process efficiency.
SMR is used to produce more than 95% of the world’s hydrogen, typically using desulfurised natural gas, refinery off-gas, LPG, or naphtha as the feedstock.
This process works by preheating the feedstock, then mixing it with steam before it enters the primary reformer. At this point, the mixtures pass over a catalyst, reacting to produce hydrogen, carbon monoxide (CO) and CO2. The CO is shifted with steam to create additional hydrogen and CO2, and then pressure swing adsorption (PSA) is used to separate hydrogen.
The hydrogen generated is known as grey hydrogen when there is no carbon capture, usage and storage (CCUS) involved; however, when CCUS is used, blue hydrogen is produced.
SMRs emit CO2 in two main ways: producing it alongside hydrogen in the reforming reaction in the primary reaction furnace, and through combustion of the fuel. For the reformed gas, capturing CO2 is a relatively simple and low-cost process. However, post-combustion CO2 capture is more expensive because it needs to be separated from nitrogen.
Grey hydrogen production typically captures CO2 from only one of these sources, but blue hydrogen production captures CO2 from both. Using this method, SMRs can achieve a conversion efficiency of 74% and a CO2 capture rate of up to 90%.
Autothermal reformers (ATRs) can also be used together with CCUS to produce blue hydrogen. Technology licensors claim conversion efficiencies of 84%, with CO2 capture rates of 95% from this method. Heat for the reforming reaction is supplied by combustion of the natural gas feed, so no separate fuel source is needed, as with SMRs.
Since there is only a single CO2 stream, using this process means that ATRs can achieve higher conversion efficiencies and CO2 capture rates than SMRs... (cont.)
Written by James Cross, AMETEK Land, UAE.
Read the article online at: https://www.globalhydrogenreview.com/special-reports/06102022/blue-h2-the-right-way/