Decarbonisation Technology – August 2021

Fuel oil to liquefied natural gas Most furnaces in Europe and the US have already shifted to fuel gas firing, so is there any carbon reduction advantage in these furnaces shifting to LNG?

A simple Google search of ‘Climate Change’ yields about 60,00,00,000 results in 0.80 seconds. Spending even a few minutes on the first page of the search brings forth articles on varied topics such as hurricanes affecting the American coastlines, raging wildfires ravaging large places of Australia, cloud bursts and heavy downpours disrupting life and business in the Asian sub-continent, extended stretches of drought over parts of Argentina, never-before- seen soaring summer temperatures in Europe, and so on. From these, one thing is certain – ‘climate change’ is a threat, and it is not local. And there is no scope for ‘Not in my backyard!’. ‘Climate change’ and ‘global warming’ are two sides of the same coin. Global warming due to greenhouse gas emissions is a major issue engaging the most prominent leaders and economies. Carbon emissions due to anthropogenic sources of fuel are constantly on the rise. The silver lining is that ambitious targets and roadmaps have been laid out on inter- governmental levels to curb this menace. In this critical transition toward sustainable operation, combustion equipment like furnaces in the oil and gas industry have their role to play. Traditionally, in many parts of the world, heavy fuel oil (HFO) is fired in oil refinery furnaces, prioritising operating cost over the carbon emission aspect. However, over time, cleaner fuel sources have evolved that provide better emission characteristics and may drive refinery operations towards a more sustainable future. Of late, liquefied natural gas (LNG) has gained much importance as an energy source due to enhanced production and availability from various fields. LNG is touted as the transition fuel leading the way towards a low carbon future. This article examines various common fuels Ankur Saini, Akhil Gobind and RupamMukherjee Engineers India Limited

fired in a refinery furnace on the carbon footprint yardstick. The article will traverse the carbon emissions generated from traditional HFO firing through to LNG, with lighter fuel oil (LFO) and refinery fuel gas (RFG) as pit stops in between. Furnace fuels and their carbon footprint In general, furnaces utilise fuel generated within the refinery complex for their heat demand. Fuels commonly used are HFO (Type-6 fuel oil), LFO and RFG. While the fuel oils are derived primarily from the vacuum residue and other cutter stocks, the RFG is generated from the off-gas produced from various refinery units. The composition of RFG can vary depending upon various operating and unit availability scenarios. Along with the three fuel types, a fast-emerging fourth option is LNG, exported into the refinery from the gas grid or a specific LNG source. Typical characteristics of these four fuels are noted in Table 1 . For a better and more accurate assessment, the entire range of fuel gas from minimum molecular weight to maximum molecular weight has been considered. Typical RFG composition does not remain constant and varies with parameters such as the diet of crude processed, a single unit or a group of units taken out for maintenance, availability of off-gas PSA unit, and so on. The above fuels were studied on a 46.5 GCal/ hr case study furnace operating in a 180,000 BPSD refinery. Excess air for HFO and LFO were considered as 20% in line with API recommendation. Similarly, being inherently cleaner and easier to burn, excess air for RFG and LNG was considered as 15%. The furnace employs an air preheat system for combustion air preheating. The flue gas exit temperature from the air preheater (APH) was set at approximately 150°C for all fuels to set the datum