Issue link: https://geospatial.trimble.com/en/resources/i/1415432
56 Spring 2019 product owner and no combustion byproducts, these projects can be technically complex and more capital-intensive. Conversely, combustion systems offer process flexibility and versatility but generate byproducts such as carbon dioxide (CO 2 ), carbon monoxide (CO), and NO X . Marine bulk distribution facilities utilise both types of technology; however, vapour combustion is more commonly applied in the US market, and this trend is expected to continue as crude oil export operations expand. Unsurprisingly, significant increases in product throughput yield higher pressure on environmental permitting. Terminal operators typically have emissions restrictions for VOC, CO, and NO X – oftentimes both annual and hourly targets – that must be met. When vapour combustion end control devices are utilised, designing systems to achieve extremely high VOC destruction efficiencies and low rates of CO production can be achieved with traditional technologies in order to offset volumetric throughput growth. Decreasing NO X to a substantial extent, however, is quite difficult to accomplish and cannot be achieved with long-standing vapour combustion technologies. Given that NO X participates in photochemical reactions, which lead to smog formation, it is ever more important to source new combustion technology to meet market demands of both high volumetric throughput and low NO X formation. Problem of NO X in terminal applications Low NO X vapour destruction in a petroleum products terminal setting presents broad technical challenges. A variety of techniques often employed in ultra-low NO X process burner design cannot be utilised in vapour combustion service. For example, in contrast to process burners, the waste gas in vapour combustion service tends to be available at very low pressure, resulting in low potential for mixing energy. Additionally, the flow rate and composition of the waste gas can vary considerably. In terminal service, hydrocarbon vapours can fluctuate from very lean to very rich, they may have an inert balance gas or air as a balance gas (non-inert), and they may span an extremely wide range of flow rates. Having high turndown capabilities from a low NO X vapour combustion system is imperative. As crude oil export facilities seek to push ship load-out rates to higher and higher levels, the turndown ratio, which must be handled by the end control device(s), must scale in kind. Generally, the end control device must process vapours generated from a slow, gravity-fill scenario at beginning of load (a lean composition, often at just a few thousand bbl/hr) all the way up to a peak load-out rate at end of load ( a rich composition, sometimes at 100 000 bbl/hr or more). Accommodating all of the aforementioned operational scenarios at high destruction efficiency rates and low NO X and CO production rates is the challenge that John Zink Co. LLC faced in the development phase of its vapour combustion technology. Combatting NO X formation The three primary sources of NO X formation in combustion systems are thermal NO X , prompt NO X , and fuel-bound NO X . Thermal NO X , the largest contributor in combustion systems, is formed by the Zeldovich mechanism – a reaction of the nitrogen and oxygen in 'hot spots' of the combustion zone. Prompt NO X is generated by the Fenimore mechanism – a reaction of hydrocarbon radicals with nitrogen present in the atmosphere at the flame front, typically occurring at lower combustion temperatures. Lastly, fuel-bound NO X (also generated by the Fenimore mechanism) involves a nitrogen-containing fuel molecule that, when oxidised, can form a cyano-compound intermediate which leads to NO X formation. Recognising the need for a low NO X , high capacity, high turndown combustion solution that is safe and flexible, John Zink conducted an analysis to reduce Figure 2. US exports of crude oil (source: US EIA). 4 Figure 3. NOxSTAR TM vapour combustion systems in crude oil ship loading service.