Investigations of the suitability of activated carbon for H2S and tar product gas cleaning

Abstract

Governments around the world are currently seeking renewable alternatives to fossil fuels for the production of electricity, heat and synthetic products. The main advantage of these renewable alternatives is their low emission of greenhouse gases and global warming. Despite this, some of the most attractive energies such as solar or wind power are very fluctuating and an alternative that provides energy on a regular basis is needed. For this reason, biomass is a valid alternative to fossil fuels and is also the only carbon containing renewable energy source. Biomass gasification is one of the most promising technologies because it can produce a wide range of solid raw materials in gas product with a medium-high calorific value to produce heat and high valueadded chemicals. However, this technology needs to be improved to be competitive against the low prices of fossil fuels. One of the key areas that needs to be improved to achieve this goal is gas cleaning. One of the most viable options, and one whose interest has increased a lot recently, is activated carbon (AC). The main advantages of this material are its low cost and that it can withstand high working temperatures. In addition, activated carbon can remove different impurities from the product gas such as sulphur-containing gases as well as tars. In this thesis, a literature review of the activated carbon technique for the removal of hydrogen sulfide (H2S) and tars has been carried out. Chapter 4 deals with the mechanism of adsorption of H2S and the parameters that influence the adsorption process, differentiating the active carbons into two types, unmodified and impregnated with metals. The main conclusions drawn from the literature research is that there is a differentiation in the adsorption mechanism of unmodified ACs and those modified with metal impregnations. In addition, process parameters such as porosity, relative humidity, temperature or pressure affect differently whether the activated carbon is modified or not. On the other hand, Chapter 5 reviews the removal of tar by AC. The results shown in different articles reveal high removal efficiencies for some of the major tar compounds. However, this technique has to be further investigated with these impurities because there are other components of the tars that still show disadvantages to be removed at high temperatures and the process needs to be optimized.