Comparison of a pilot scale gasification installation performance when air or oxygen is used as gasification medium 2 – Sulphur and nitrogen compounds abatement Filomena Pinto ⇑ , Rui Neto André, Helena Lopes, Carlos Franco, Carlos Carolino, Margarida Galhetas, Miguel Miranda, Ibrahim Gulyurtlu LNEG, Estrada do Paço do Lumiar, 22, 1649-038 Lisboa, Portugal article info Article history: Received 19 December 2011 Received in revised form 14 February 2012 Accepted 14 February 2012 Available online 5 March 2012 Keywords: Co-gasification Oxy-gasification Coal Wastes Nitrogen abatement abstract The release of H 2 S and NH 3 into syngas during co-gasification of two coals (German and Polish) mixed with wastes (pine, olive bagasse and polyethylene) was studied. Sulphur and nitrogen contents in feed- stock were found to have a great influence on H 2 S and NH 3 concentrations in syngas, as the highest con- tents of these elements led to the highest releases. Air/steam or oxygen/steam mixtures were used in the gasification medium, keeping constant experimental conditions, including equivalent ratio. However, when air was added instead of oxygen, higher flow rates were used, due to the introduction of nitrogen and thus lower residence times were used. Different H 2 S and NH 3 contents were obtained by changing the gasification medium. In presence of oxygen and steam higher H 2 S contents and lower NH 3 concentra- tions were obtained than those produced in presence of air and steam. However, after syngas hot treat- ment in two fixed bed reactors, the first one with dolomite and the second one with a Ni-based catalyst (G-90 B 5) these differences lost significance. On the other hand, different final compositions of H 2 S and NH 3 were obtained for different feedstocks. Those with highest sulphur and nitrogen contents led to the highest final H 2 S and NH 3 contents in syngas. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Co-gasification of coal mixed with wastes is a promising option, as it decreases fossil fuels utilization, diversifies the use of alterna- tive fuels and reduces CO 2 emissions. The use of wastes might di- lute some negative characteristics of coals, like high ashes and lower volatile matter contents. However, the use of wastes with high contents of undesirable elements, like: S, N, halogens and hea- vy metals may lead to the formation of H 2 S, HCl, NH 3 , alkali metals and particulates. Several authors have studied the formation and destruction of such compounds. Meng et al. [1] reviewed syngas desulphurization, both during gasification and for syngas cleaning. In syngas cold wet cleaning, amines are usually used for acid gases removal, by chemical absorption, physical absorption or a combi- nation of both. Physical and chemical absorption processes are highly energy demanding [2]. When syngas needs to be heated again, for further cleaning and upgrading, cold wet processes are disadvantageous. Dry hot syngas cleaning process are believed to be more efficient and cleaner, though they are still far from com- mercialization [3–7]. Thus, the interest by hot cleaning processes has increased recently. Low cost natural minerals like: limestone, olivine and dolomite, have been widely used inside the gasifier for sulphur retention and tar decomposition [1]. Different researchers have reported contra- dictory results, because natural minerals may present different compositions of several compounds that affect the performance of these materials [3]. Limestone and dolomite have high attrition and may put into danger the normal operation of gasification installations. Limestone also has the problem of incomplete con- version below the calcination temperatures, dolomite usually pre- sents a better performance and lower sintering, but due to the presence of magnesium its attrition is higher [1]. Cheah et al. [8] reviewed several types of sorbents based on Zn, Cu, Fe, Ca, Mn and Ce for syngas desulfurization. The respective metal oxides have been checked, each one with different advanta- ges and disadvantages. Thus, mixtures of oxides, to combine the best features of each one, have been checked. Zinc oxide has the best thermodynamic property for H 2 S removal, but its use is lim- ited to 600 °C, due to zinc vaporization, migration and agglomera- tion at higher temperatures. The presence of Ti, Al, Si, Zr, Co, Ni and Fe and promoters like Co, Ni, and Fe may improve significantly sul- phur retention during multiple cycles and the regeneration process 0016-2361/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.fuel.2012.02.031 ⇑ Corresponding author. Tel.: +351 21 092 4786; fax: +351 21 716 6569. E-mail address: filomena.pinto@lneg.pt (F. Pinto). Fuel 97 (2012) 770–782 Contents lists available at SciVerse ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel