Article pubs.acs.org/EF
Fate of Sulfur, Chlorine, Alkali Metal, and Vanadium Species during High-Temperature Gasification of Canadian Tar Sand Products Marc Blas̈ ing,* Kaveh Nazeri, and Michael Müller Institute of Energy and Climate Research (IEK-2), Leo-Brandt-Straße 1, 52425 Jülich, Germany ABSTRACT: Co-feed of alternative fuels, e.g., petcoke, gains increasing importance for energy conversion in not only Germany but also worldwide. An auspicious process for power generation is the integrated gasification combined cycle (IGCC). Several volatile inorganic species are of concern in IGCC power systems, because they can cause erosion, corrosion, fouling, and slagging. The aim of this work was to obtain detailed information on the influence of fuel composition of the refinery product line tar sand, bitumen, and petcoke in comparison to the standard fuel hard coal on the release of sodium, potassium, chlorine, sulfur, and vanadium species during high-temperature gasification. In addition to the pure fuels, blends of hard coal and petcoke were gasified in lab-scale experiments in a helium/oxygen atmosphere at 1500 °C. The atmospheric conditions were in an entrained flow gasifier. Hot gas analysis was performed by molecular beam mass spectrometry. Species of interest were HCl, H2S, COS, SO2, NaCl, KCl, KOH, and V. A major finding is that the dilution effect cannot satisfactorily explain the release of the sulfur species under investigation for the fuel blends on one side but can explain the release of sodium and chlorine species on the other side.
1. INTRODUCTION Co-feed of alternative fuels will be of increasing importance for energy conversion in not only Germany but also worldwide.1 Petcoke is a promising co-fuel for coal-based power conversion systems. Some advantages are its low ash content and high calorific value.2 A major disadvantage is its low reactivity, which is usually balanced by the use of a higher gasification temperature. Entrained flow gasification with temperatures up to 1600 °C is a preferable conversion technique.3 Recently, Khosravi and Khadse reviewed the available literature regarding the co-gasification of petcoke and summarized that cogasification of coal with petcoke can enhance the efficiency and profitability of the gasification of petcoke alone.3 In summary, petcoke can be co-gasified with high efficiency in large-scale power plants, e.g., integrated gasification combined cycle (IGCC) plants (using an entrained flow gasifier). It is well-accepted that alkali and alkaline earth metals have a catalytic function and enhance the reactivity of petcoke during co-gasification with coal significantly.3 Petcoke usually contains high amounts of sulfur and trace metals, especially vanadium. Coal usually contains a significant amount of alkali metals and chlorine as well as sulfur. Little is known thus far about the release of sulfur, alkali metal, chlorine, and vanadium species during gasification of petcoke and co-gasification with coal. However, the release and downstream condensation of volatile inorganic species, e.g., H2S, COS, NaCl, KCl, HCl, etc., can cause several problems in the power plant, e.g., fouling and corrosion, and reduce the efficiency significantly. Therefore, fundamental research on the release behavior of inorganics is needed. For a comprehensive picture, the research has to include the raw material basis of the petcoke, which is derived from oil refinery coker units or other cracking processes as well. In the near future, the raw material basis of refineries will shift from crude oil to bitumen, because of the declining resources of crude oil and vast resources of tar sand. By way of example, Alberta in Canada has large amounts of tar sands, which are © 2014 American Chemical Society
equal to 173 billion barrels of natural oil. However, the tar sand has to be further processed. Therefore, the tar sand is openminded and further processed to separate the tar from the sand. The product is bitumen, which can be feed to a refinery that produces petroleum products, e.g., transportation fuels, and the byproduct petcoke. An increased efficiency and a decreased amount of harmful species, e.g., Na, K, S, and Cl species, can be achieved through hot fuel gas cleaning.4 This innovative cleanup technique requires comprehensive knowledge of the release characteristics of the mentioned inorganic fuel constituents. The objective of this work was to study the fate of volatile inorganic species, especially sulfur, chlorine, vanadium, and alkali metal compounds, during high-temperature gasification of tar sand, bitumen, petcoke, and hard coal.
2. EXPERIMENTAL SECTION 2.1. Fuel Preparation and Analysis. Samples from tar sand, bitumen, petcoke, and hard coal were taken. The tar sand was mined in Alberta, Canada. The bitumen was extracted from the tar sand by ultrapure petroleum ether. The remaining solid residue was mechanically separated from the liquid phase. The liquid phase was concentrated at 60 °C to obtain the bitumen. The petcoke was produced in Canada independently from the tar sand under investigation. The hard coal was mined in Germany. The petcoke and hard coal were dried and crushed in a mill to a particle size of
