PTQ Q2 2023 Issue

Digital platform for intelligent operation of fired heaters An innovative web-based tool that optimises fired heater operation and reduces carbon footprint while doing so

Grandhi Srivardhan, Rupam Mukherjee and Shilpa Singh Engineers India Limited

F ired heaters account for more than 60% of the total energy consumed in refining crude oil. W ith energy prices rising continuously over the years, refiners are increasingly pressured to reduce this critical operating cost through better and more efficient management of fired heaters. A nd interestingly, fired heaters do present oppor - tunities if looked at critically. Any increase in furnace efficiency, minor or major, has a strong rate of return on operating expenditure and benefits the global commitment towards sustainable development by reducing the carbon intensity of refining operations. Digitisation in fired heater operation can lead to a mul - titude of advantages. Benefits are well defined. For exam - ple, it enables refiners to fine-tune their fired heaters in real-time. Such digitised operation addresses, monitors, and evaluates fired heaters in refineries while adapting to prevalent operating and ambient conditions, and it also directs necessary actions to maximise operating efficiency. This optimisation exercise on periodic intervals can lead to tons of fuel savings annually, translating into lucrative monetary benefits for refining operations and helping to reduce carbon emissions. In fact, a 1% increase in fuel effi - ciency of ~80 MMkCal/hr heat duty furnace in a 200,000 bpsd refinery can lead to 900 tons of fuel saved in an oper - ating year. Refinery furnaces are often operated throughout the year with a fixed set of operating parameters or with only minimal adjustments resulting from existing control loops. However, many other parameters often go unnoticed from a refiner’s perspective, which, if optimised, might lead to higher earnings. The intent of digitised operation is to focus on these seemingly benign parameters on a real-time basis and identify actions for more efficient operation against the backdrop of strong computational algorithms and estab- lished engineering practices. Why real-time optimisation? Fired heaters are well known to be the energy guzzlers in hydrocarbon processing industries, amassing as much as a two-thirds share of the energy consumption in the crude fractionation process. Interestingly, the progress of tech - nology or available options for increasing the efficiency of fired heaters has plateaued over the years. This is primarily because of the limitation posed by the sulphur dew point in

fuel, which still looms large as one of the major determining factors in heater efficiency. Balance apprehension lies in ensuring that the industry is not playing too safe on this aspect and intends to utilise the asset to its full potential. However, the question at this point is whether the fired heater engineer in charge is fully aware of the best achievable potential for the current scenario or case of operation. Or are they relying on set points and stan - dard operating procedures, which primarily apply to some other operating condition? AI-based digital tools can play a pivotal role in such situations, bridging the gap between the current operation and set operating scenarios. While opti - mising the efficiency, safety and reliability of the equipment is accorded prime importance. Quite often, the calorific value of fuel takes centre stage while talking about fired heater efficiency. While calorific value is indeed the prime character, fuel sulphur content is the dark horse of efficiency calculation. It can overturn fig - ures on paper; more so, it can damage equipment irrevers - ibly at site. But what has fuel sulphur got to do with furnace efficiency? The answer is acid corrosion due to sulphur in flue gases. Then, the focus shifts towards protecting furnace auxilia- ries from acid corrosion, which is inevitable every time the flue gas temperature in the furnace circuit goes below the sulphur dew point. To ensure equipment safety, furnace designers maintain the flue gas temperature at the system exit or, in other terms, ‘the stack temperature’ above the dew point, knowing full well that high-temperature gases going into the atmosphere are a necessary evil associated with fuel combustion in fired heaters. Fired heaters are built to operate over decades, and gov - ernmental legislature often changes over this long period of time. A classic example is the case of fuel sulphur content. Nowadays, in India, the pollution control authority mandates a maximum SOx emission of 850 mg/Nm3 from new fired heaters, which operate with 100% fuel oil. This can only be achieved when fuel oil sulphur content is limited to nearly ~0.5 wt%. Interestingly, a number of existing refinery fired heaters and auxiliaries have been built for a sulphur content of 1-1.2 wt%. Directionally, flue gases from 1.2 wt% sulphur fuel oil will have a significantly higher dew point than the 0.5 wt% sulphur-containing fuel. Thus, an inherent potential for

PTQ Q2 2023