Decarbonisation Technology - November 2021

Figure 2 AMETEK Land Cyclops L pyrometer

There are two main sources of CO 2 emissions from SMRs - the CO 2 produced alongside hydrogen in the reforming reaction in the primary reaction furnace and the

section. A wide variety of fuels and feedstocks can be utilised, including naphtha, butane, propane, and ethane. Flue gas temperatures are recorded continuously from contact thermocouples, whilst thermocouples also provide coil outlet temperatures (COTs) that indicate cracking severity. Tube metal temperatures (TMTs) are gathered periodically and manually using an infrared pyrometer, and a process engineer analyses the data. Coke is deposited on the inside surface of coils which can cause plugging, overheating, and ultimately failure. This is a well-understood phenomenon, but it is not closely monitored in many cases because decoking (where coke is gasified by passing steam and/or air through the radiant coils) is scheduled on frequent, planned intervals. Excessive decoking cycles can lead to a loss in ethylene production, reduced tube life due to thermal cycling, high maintenance spending, and increased particulate release to the atmosphere. Visual inspections and temperature data collection are periodic, so these deposits may go unnoticed and unplanned decoking may be required. The layer of coke forms a layer of insulation between the hot furnace atmosphere and the comparatively cooler reaction gas, which impairs heat transfer. Therefore, the prevention and reduction of coke formation is a key priority from a maintenance, throughput, energy efficiency, and environmental perspective. Reducing coke formation also reduces energy input and potentially increases the availability of the furnace by extending run lengths. Temperature measurement and furnace monitoring To achieve a reduction in CO 2 emissions, process adjustments are being made, including reducing oxygen setpoints and increasing the hydrogen content in fuel stocks. These trends increase the need for closer visual and temperature monitoring inside both a steam cracker and SMR. Flue gas and surface temperatures may be hotter, new flame behaviours may be observed, and burner nozzles, tiles, and insulation could deteriorate

CO 2 produced by combustion of the fuel. The process of capturing CO 2 is relatively simple and low cost for the reformed gas, but

capturing CO 2 post-combustion is more expensive because it needs to be separated from nitrogen. Traditional grey hydrogen production may capture CO 2 from one of these sources, whereas blue hydrogen production is assumed to capture CO 2 from both. SMRs can achieve a conversion efficiency of 74% (HHV) and a CO 2 capture rate of up to 90%. Autothermal reformers (ATR) can also produce blue hydrogen when used together with CCUS, and technology licensors claim conversion efficiencies of 84% (HHV) with CO 2 capture rates of 95%. The natural gas feed is combusted to produce heat for the reforming reaction, so no separate fuel source is needed, as with SMRs. This process means ATRs can achieve higher conversion efficiencies and CO 2 capture rates than SMRs as there is only a single CO 2 stream. In the new, highly competitive landscape where efficiency and CO 2 capture are critical to a plant’s profitability, SMR operators must improve their efficiency to stay competitive. 2 Steam cracking for ethylene production The cracking reaction in a steam cracker takes place in sets of tubes (known as coils) that hang in huge fired radiant sections, usually in a single or twin cell layout with a common convection

Figure 3 AMETEK Land portable furnace thermal imaging system