Sulphur content
After long operation, reasonably old heate r with efficiency E2
New heater design with fuel e ciency E1
Fuel properties
Ideal excess air
Current fuel sulphur
C apex investments, if required
Re-evaluation of performance
Re-adjustments of parameters
Fuel characteristics
Air for mixed fuel ring
Operate at best achievable e ciency
Continuous monitoring
Figure 1 Need for real-time optimisation
increasing the flue gas heat recovery exists within such fired heaters, which can be tapped to increase efficiency effectively (see Figure 1 ). In fact, actual sulphur content in fuel oil has come down to 0.10-0.25 wt% sulphur in the majority of cases wherever oil firing is still practised. In contrast, original operating instructions or limitations of maintaining a high stack temperature consistent with 1 wt% sulphur fuel oil still hold well in the standard operating procedures of the plant. To bridge this gap, the proprietary EngRT-Htr digital platform has been created. Considering the worldwide focus on net zero, it may not be prudent to put furnace ‘optimisation’ activity on standby until a fully-fledged revamp or makeover is undertaken. Optimisation of opera- tion and increase in efficiency is the first step ‘towards’ the desired goal. Many other parameters often go unnoticed from a refiner’s perspective, which, if optimised, might result in lucrative returns (such as the re-setting air requirement for the exact mix of fuel firing). Digital interventions can focus and identify actions for more efficient operation (see Figure 2 ). Inertia effect in fired heater operation In any fired heater designer’s tenure, they encounter many styles of furnace operation depending on the user’s choice of comfort and confidence. But considering the criticality of
this equipment, operators seldom choose to deviate from the furnace’s instructions. Although most installations face sig- nificant changes in fuel specifications, limitations in identify- ing or quantifying efficiency improvement potential arising from these changes bring some inertia to being too flexible. Thus, bringing digital interventions to such robust equip- ment takes time. Numerous interactions, feedback, and data evaluations warrant a gradual transition. A conversation with one of the plant managers went as follows: “Hello, Sir; indeed, the hot oil heater is operated very effi- ciently. However, we feel there is room for improvement.” “Why do you say that? The heater is being operated as per the designer’s documents only. The datasheet states that the flue gas temperature at the APH exit should be 155°C, and we are maintaining exactly that through bypassing of air. Designer parameters are supposed to recommend the best efficiency and safety, right?” “That is true, sir. However, the parameter stated in the datasheet is for fuel oil sulphur content of 1 wt%, which is the worst-case scenario. However, for the past year, your fuel oil sulphur has never breached 0.3 wt% sulphur. You could have lowered the flue gas exit temperature without compromising safety. That would have enhanced your effi- ciency by 0.7-0.9%.” “How would we know that? This information is not speci- fied in the operating manual. Moreover, our fuel specification changes frequently. There should be a tool that evaluates and guides us to operate the fired heaters for the current operating condition.” Similar conversations are commonplace for many other parameters. In many parts of the world, ambient tempera- tures rise during the height of summer and plummet during winter. A long discussion with a refinery technical services department in one such location on fixing the flue gas out- let temperature based on ambient conditions ended with the words, “How can we know of these adjustments? We cannot reach out to the original equipment manufacturers (OEM) repeatedly? In another case, the user was confident that their fired heater was operating on the tightest excess air. On closer evaluation of the operating parameters, it was recom- mended to cut on the air. An evaluation revealed that the heater was being operated on a combination of fuel oil
Fuel sulphur content
Ambient conditions
Excess air
Excess air is generally indicated for speci c fuels and operation fully dependent on oxygen analyser. Generally, this parameter is left un-adjusted for changing fuel combination percentages of heat liberated between gas and oil.
Heat loss in the cold ue gas circuit depends on
Heaters are originally designed for worst fuel conditions.
the ambient temperature.
Necessary adjustments can d o ne to utilise maximum bene t of higher ambient temperature.
Current operation is carried out with a cleaner fuel to suit environmental legislations.
Figure 2 Parameters that often go unnoticed
76
PTQ Q2 2023
www.digitalrefining.com
Powered by FlippingBook