Asphaltene fluidised bed combustion

Transcription

1 Asphaltene fluidised bed combustion Jaqueline Saavedra Rueda 1 and Toni Pikkarainen 2 1 Ecopetrol, 2 VTT VTT beyond the obvious 1

2 Background and motivation What is asphaltene? Why fluidized bed combustion? Experimental work Test rig and fuels Test matrix Results Burning times Sulphur release/capture Summary 2

3 ECOPETROL & Business Group 4 th Latin American Petroleum 40 th world production 9000 employees Ecopetrol & business group includes 19 companies: exploration, production, transportation, refining, petrochemical, commercial, corporate Ecopetrol is the largest company in Colombia and is an integrated company in the oil chain. In addition to Colombia, where it generates more than 60% of national production, it has a presence in exploration and production activities in Brazil, Peru and the United States (Gulf of Mexico). Ecopetrol has the largest refinery in Colombia, most of the pipeline and pipeline network in the country and is significantly increasing its participation in biofuels. 3

4 VTT impact from excellence VTT Technical Research Centre of Finland Ltd is one of the leading research, development and innovation organizations in Europe. We help our customers and society to grow and renew through applied research. The business sector and the entire society get the best benefit from VTT when we solve challenges that require world-class know-how together and translate them into business opportunities. Established in M Net turnover and other operating income (VTT Group 2017) 2,368 Total of personnel (VTT Group ) SODANKYLÄ KAJAANI OULU Owned by Ministry of Economic Affairs and Employment 36% from abroad (VTT Group 2017) 27% Doctorates and Licentiates (VTT Group 2017) KUOPIO JYVÄSKYLÄ TAMPERE 4 RAJAMÄKI VIHTI ESPOO OUTO- KUMPU LAPPEEN- RANTA

5 Background and motivation What is asphaltene? Why fluidized bed combustion? 5

6 What is asphaltene? The deasphalting process, developed by ECOPETROL SA, has as main objective the processing of heavy and extra-heavy oil loads for the partial improvement of its transport properties. Main streams from the process are deasphalted crude oil (DAO) and a solid intermediate stream, composed of asphaltenes and resins precipitated during the process. The solids, composed mostly of asphaltenes, correspond to the heaviest fraction of the crude oil and once removed, they become an undesirable product because they are classified as highly contaminant. 6

7 Why fluidized bed combustion? Ecopetrol was searching technological alternatives to utilize asphaltenes as a fuel in generation of steam and/or electricity in their oil production fields. Advantages of circulating fluidized bed combustion technology: The widest fuel flexibility (with a single design) Sulphur capture in furnace (typically FGD not needed) Very low NO x levels due to low and uniform temperature level High combustion efficiency due to long residence time and high mixing The viability of fluidized bed combustion technology was evaluated by bench scale testing carried out by VTT. The bench and (on-going) pilot scale tests with techno-economic assessment will give a valuable knowledge of the behavior of the fuel and that information can be taken into account when designing the boiler for a certain fuel, protects investment and minimizes environmental impacts. Source: Valmet 7

8 Experimental work Test rig and fuels Test matrix 8

9 Bench scale BFB VTT beyond the obvious 9

10 Fuels asphaltene and petcoke Both the fuels have low ash content, high sulphur content, quite high nitrogen content and high heat value. Asphaltene contains significantly more volatiles than petcoke whereareas fixed carbon content of petcoke is higher. Based on fuel analyses it can be expected that asphaltene is much reactive (shorter combustion time) than petcoke and achieving of low SO 2 and NO emissions would be challenging for both the fuels. Analysis Unit Asphaltene Petcoke Moisture w-% a.r Ash (815ºC) w-% dry Ash (550ºC) w-% dry 0.7 #N/A Volatiles w-% dry HHV MJ/kg dry LHV MJ/kg dry LHV MJ/kg a.r Carbon w-% dry Hydrogen w-% dry Nitrogen w-% dry Sulphur w-% dry VTT beyond the obvious Oxygen w-% dry Chlorine w-% dry #N/A

11 Test matrix Test matrix of batch feed tests included 8 tests: with two fuels, asphaltene and petcoke (reference fuel) at two bed temperatures, 800ºC and 900ºC without and with limestone addition (limestone calcium to fuel sulphur ratio Ca/S=3.0 mol/mol) Combustion air (100% prim. air) was diluted by N 2 to contain 10 %-vol of O 2 Each batch test was repeated 4 times to ensure repeatability VTT beyond the obvious 11

12 Results Burning times Sulphur release/capture 12

13 mass/initial mass Determination of time instants t 50% t 90% Time (s) Fuel Sulphur Times for 50% and 90% combustion (of carbon) and sulphur release were determined based on O 2 consumption and flue gas SO 2 concentration These t 50% and t 90% characterise the fuel combustion reactivity and sulphur release Also total mass of released sulphur was determined to evaluate sulphur capture by limestone addition 13

14 mass/initial mass mass/initial mass Fuel and sulphur conversion 1 1 mass/initial mass Fuel Sulphur mass/initial mass Fuel Sulphur Time (s) Time (s) Asphaltene at 800ºC Asphaltene at 900ºC Fuel 0.4 Fuel 0.2 Sulphur 0.2 Sulphur Time (s) Time (s) Petcoke at 800ºC Petcoke at 900ºC Much shorter conversion times for asphaltene than for petcoke Two combustion stages can be distinguished: 1) rapid release and combustion of volatiles and 2) slower combustion of char 14

15 Combustion reactivity 50% and 90% burning times Asphaltene is much more reactive than petcoke Increase in temperature increases the burning rate (decreases the reaction times) for petcoke The temperature has no practical effect on the reaction times for asphaltene 15

16 SO 2 formation and capture Released mass of sulphur per mass fuel combusted (expressed by columns to left y-axis) and share of captured sulphur by limestone (expressed by points to right y-axis) Sulphur capture was relatively poor by limestone for asphaltene and fair for petcoke. At 800ºC no sulphur was captured with asphaltene and ~20% with petcoke. At 900ºC a small share (~15%) of sulphur was captured by limestone with asphaltene and relatively high share (~50%) with petcoke. 16

17 Summary VTT beyond the obvious 17

18 Summary 1/2 The objective was to characterize asphaltene a residue from oil refinery fluidized combustion and emission formation and compare them with petcoke. Circulating fluidized bed combustion technology was selected based on its maturity, fuel flexibility, low emissions and high efficiency. Chemical composition of asphaltene was as expected: low ash and moisture contents, and high volatiles and sulphur contents. In contrast, petcoke have low volatile content with otherwise quite similar composition compared to asphaltene. Source: Sumitomo SHI FW 18

19 Summary 2/2 Asphaltene was characterised as very reactive compared to petcoke. The combustion time for asphaltene was some 4-times shorter than for petcoke. The short combustion time means rapid heat release and possible risk for hot spots near the fuel/air feeding locations. Sulphur capture by limestone was relatively poor for asphaltene and fair for petcoke. Achieving a good in-furnace sulphur capture efficiency with asphaltene by limestone will be challenging. For asphaltene some softening and sticky behaviour was observed even in temperatures far below 100ºC. Fuel feeding system should be carefully designed to avoid problems. 19

20 Thank you! Questions! VTT beyond the obvious 20