High-Pressure\nOxy-Firing (HiPrOx) of Fuels with Water\nfor the Purpose of Direct Contact Steam Generation

High-pressure\noxy-fired direct contact steam generation (HiPrOx/DCSG)\ncan be achieved by the oxy-combustion of fuels in the presence of\nwater. This process is capable of producing flue gas streams containing\napproximately 90% steam with a balance of primarily CO<sub>2</sub>. The product flue gas is suitable for processes where the purity\nof the steam is less important, such as the steam-assisted gravity\ndrainage process used for <i>in situ</i> production of bitumen\nwithin the Canadian oil sands. This study had three primary objectives:\n(1) To show that high-moisture HiPrOx/DCSG can be achieved with hydrocarbon\nfuels. For this purpose, <i>n</i>-butanol was used because\nof its high volatility and ease of handling. (2) To see if this technology\ncould be applied to fuels with lower volatilities. This was studied\nby attempting to combust a graphite–water slurry as well as\nmixtures of graphite–water slurry and butanol. (3) To determine\nthe effects of different fuel mixtures, oxygen-to-fuel ratios, and\nwater inputs on process stability and H<sub>2</sub>O partial pressure\nin the product gas. This paper describes pilot-scale combustion testing\nand process modeling of <i>n</i>-butanol, graphite–water\nslurry, and their mixtures in an atmosphere consisting of oxygen and\nwater at a pressure of 1.5 MPa­(g). Graphite/butanol mixtures were\nselected because certain combinations could represent the range of\nfixed carbon/volatiles ratios of waste fuels and indicate whether\nlow-volatile fuels will ignite in the high-water moderator environment.\nOver the butanol test periods, a steam content of around 90 mol %\nat saturation was achievable; the O<sub>2</sub> in the combustion\nproducts was between 0.08 and 3.57 mol % (wet) with an average of\n1.13 mol % (wet). The CO emissions were low (<25 ppmv wet, 3% O<sub>2</sub>) in the combustor. The CO levels indicated that high fuel\nconversion was achieved with low excess O<sub>2</sub> content in the\ncombustion products. The testing also indicated that operation with\nextremely low O<sub>2</sub> is possible for specific fuels, which\nwill minimize downstream corrosion issues and reduce the energy consumption\nand costs associated with oxygen production requirements. Low CO emissions\n(<25 ppmv wet, 3% O<sub>2</sub>) and relatively good process stability\nwere experienced for the butanol/graphite–water slurry mixtures\ncontaining ∼40% butanol. CO emissions increased and process\nstability decreased as the graphite content in the fuel mixture was\nincreased. Unassisted combustion of the graphite–water slurry\nwas achieved for a period of 20 minutes until operational problems\nwere encountered, due to burner plugging by the slurry, requiring\nthat the burner be shut off. It was found that the maximum attainable\nH<sub>2</sub>O content in the product gas increased with increasing\nhydrogen-to-carbon ratio in the fuel. H<sub>2</sub>O content was around\n80 mol % with 100% graphite–water slurry, 81 mol % with a 25%\nbutanol in graphite–water slurry mixture, and around 86.5%\nin a 40% butanol in graphite–water slurry mixture. It was also\nfound that the fuel H/C ratio, excess O<sub>2</sub>, heat loss, O<sub>2</sub> purity, and fuel volatility are important parameters when\nconsidering a DCSG system because they directly affect the process\nperformance and quality of the desired product.

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