Lower Gasification Temperature Research Articles

In Situ CO2 Capture in a Dual Fluidized Bed Biomass Steam Gasifier – Bed Material and Fuel Variation

AbstractThe AER (absorption enhanced reforming) process, based on the dual fluidized bed steam gasification process, uses a bed material which, apart from its function as heat carrier, acts as a CO2 transporting agent and selectively transfers CO2 from the gasification reactor to the combustion reactor. Thus, a hydrogen‐rich gas is produced (H2 55...70 vol.‐%db, CH4 8...13 vol.‐%db, CO 5...11 vol.‐%db as well as CO2 7...20 vol.‐%db). Seven different CaO containing bed materials were tested for their principal applicability to the AER process with special focus on their influence on tar production. The amount of tars was generally found to be five times lower than with conventional gasification (at 850 °C) despite the low gasification temperatures (600–700 °C). Due to these low gasification temperatures, biomass with high alkali contents (e.g., straw), indicating a low ash melting point (< 800 °C), can be used under AER conditions. In summary, the AER process is very effective owing to the integration of the heat of the chemical reaction of CO2 with CaO and the water‐gas shift reaction, which are both exothermic, into the gasification and the internal reforming of primary and secondary tars, which cuts off the formation of higher tars.

Gasification of refuse derived fuel in a fixed bed reactor for syngas production

Steam gasification of two different refuse derived fuels (RDFs), differing slightly in composition as well as thermal stability, was carried out in a fixed-bed reactor at atmospheric pressure. The proximate and ultimate analyses reveal that carbon and hydrogen are the major components in RDFs. The thermal analysis indicates the presence of cellulose and plastic based materials in RDFs. H2 and CO are found to be the major products, along with CO2 and hydrocarbons resulting from gasification of RDFs. The effect of gasification temperature on H2 and CO selectivities was studied, and the optimum temperature for better H2 and CO selectivity was determined to be 725 degrees C. The calorific value of product gas produced at lower gasification temperature is significantly higher than that of gas produced at higher process temperature. Also, the composition of RDF plays an important role in distribution of products gas. The RDF with more C and H content is found to produce more amounts of CO and H2 under similar experimental conditions. The steam/waste ratio showed a notable effect on the selectivity of syngas as well as calorific value of the resulting product gas. The flow rate of carrier gas did not show any significant effect on products yield or their distribution.

Product Analysis and Thermodynamic Simulations from the Pyrolysis of Several Biomass Feedstocks

The pyrolysis of southern pine, red oak, and sweet gum sawdust is reported. Pyrolysis experiments were conducted under either a helium or nitrogen atmosphere at ∼371−871 °C, to determine the balance between liquid and gas products. Gas- and liquid-phase pyrolysis products were identified using gas chromatography (GC) and GC/mass spectrometry (MS). A total of 109 liquid and 40 gas compounds were identified. A total of 59 chemical compounds (35 liquids and 24 gaseous products) were quantitatively determined. The influence of the gas-phase residence time and biomass feed particle size were studied. The gas residence time determined the extent of secondary reactions. Very short residence times enhanced liquid production versus gas production. Particle sizes (d < 105 μm, 105 μm < d < 149 μm, 149 μm < d < 297 μm, and d > 297 μm) did not have a pronounced effect on either the yield or product distributions, indicating that heat-transfer limitations within the particles were negligible. The pyrolysis of pine, red oak, and sweet gum sawdust yielded similar product distributions. Simulations were conducted using the ASPEN/SP software package based on Gibbs energy minimization. At high temperatures, dominant species were hydrogen and carbon monoxide, while at lower temperatures, methane, carbon dioxide, and water were the predominant species. Above 871 °C, further increases in the temperature did not affect the product distribution. Lower gasification temperatures and higher steam/carbon ratios resulted in higher hydrogen and carbon monoxide production.

In-Situ CO2-Absorption in a Dual Fluidized Bed Biomass Steam Gasifier to Produce a Hydrogen Rich Syngas

Within the last years renewable energy sources came more and more into the public focus. Steam gasification of solid biomass yields high quality producer gases that can be used for efficient combined heat and power production (CHP) and as a renewable resource for chemical syntheses. The dual fluidized bed steam gasification technology provides the necessary heat for steam gasification by circulating hot bed material that is heated in a second fluidized bed reactor by combustion of residual biomass char. The hydrogen content in producer gas of such gasifiers is about 40vol% (dry basis). Addition of carbonates to the bed material and adequate adjustment of operation conditions in the reactors allow selective transport of CO2 from gasification to combustion zone (Absorption Enhanced Reforming – AER concept). An 8MW (fuel power) CHP plant successfully demonstrates gasification in Guessing, Austria since 2002. A process development unit (100 kW fuel power) has been recently operated to investigate the potential of the selective CO2 transport achieving a H2 content of up to 75vol% (dry basis) in the producer gas. No significant increase in tar formation occurs despite the low gasification temperatures (600-700°C). It can be shown, that the selective transport of CO2 yields high hydrogen contents in the producer gas and the possibility of operating at lower temperatures increases the efficiency of energy conversion.

An experimental study on biomass air–steam gasification in a fluidized bed

The characteristics of biomass air–steam gasification in a fluidized bed are studied in this paper. A series of experiments have been performed to investigate the effects of reactor temperature, steam to biomass ratio (S/B), equivalence ratio (ER) and biomass particle size on gas composition, gas yield, steam decomposition, low heating value (LHV) and carbon conversion efficiency. Over the ranges of the experimental conditions used, the fuel gas yield varied between 1.43 and 2.57 N m 3/kg biomass and the LHV of the fuel gas was between 6741 and 9143 kJ/N m 3. The results showed that higher temperature contributed to more hydrogen production, but too high a temperature lowered gas heating value. The LHV of fuel gas decreased with ER. Compared with biomass air gasification, the introduction of steam improved gas quality. However, excessive steam would lower gasification temperature and so degrade fuel gas quality. It was also shown that a smaller particle was more favorable for higher gas LHV and yield.

Gasification of Rice Husk in a Fluidized-Bed Gasifier without Inert Additives

A novel fluidized-bed gasifier was designed in which rice husk was fluidized and gasified without inert additives. The gas compositions of CO, CO2, H2, CH4, and O2 were determined by an online analyzer and gas chromatography. The results showed that low fluidized velocity and low gasification temperature (550−650 °C) were beneficial to the production of syngas with a high composition of CO. The composition of H2 was influenced slightly by the equivalent ratio. The average composition of H2 was almost unchangeable to different fluidized velocities. The minimal fluidized velocity vmf of rice husk without inert additives experimentally determined was 0.495 m/s, which was higher than that of the two-component system containing rice husk and sand (vmf < 0.3 m/s). The throughput of rice husk in this reactor was higher than that in a fixed bed with the same volume. This fluidized-bed reactor had a longer service term than a traditional fluidized bed for a two-component system.

Steam gasification of lignocellulosic residues in a fluidized bed at a small pilot scale. Effect of the type of feedstock

This paper discusses different biomass materials such as pine sawdust, pine wood chips, cereal straw, and thistles (Cynara cardunculus) from energetic crops gasified with steam in a 15-cm-i.d. fluidized bed reactor. The gas, tar, and char yields, the composition and heating value of the gas produced, and the conversion of carbon have been determined at temperatures between 650 and 780{degrees}C (923-1053 K) for each material. The product distribution varies with the biomass used and the gasification temperature. The differences are very marked for the H{sub 2}, CO, and CO{sub 2} contents in the gas product at low gasification temperatures. These differences decrease when the temperature increases to 780{degrees}C at which point a gas composition similar for all types of biomass tested is obtained by the achievement of equilibrium in the water-gas shift reaction.

Mechanisms of Alkali Metal Catalysis in the Gasification of Coal, Char, or Graphite

Abstract Catalytic gasification of coal is an old technology with patents dating back to at least 1884 [1]. To gasify charcoal, lignite, or subbituminous coals, these materials were mixed with the oxides, hydroxides, or carbonates of alkali metals or alkaline-earth metals, Considerably higher gasification rates or lower gasification temperatures were realized by these additives.

Catalytic gasification of doped carbon—a kinetic study

Carbons were prepared from pure and doped furfuryl alcohol, the doping being done by known additions of metal nitrate solutions. The metal within the carbon is considered to be dispersed as atoms or as small aggregates of atoms. Such dispersions of metals are catalytically active in the gasification of carbons of HTT 1123 and 1823 K, by carbon dioxide and of carbon of HTT 723 K by nitrous oxide and oxygen. The relative catalytic activities of the metal decrease in the order Ni, Co, Cu, Ag, Fe and Ca. Arrhenius plots of the temperature dependence of rate of gasification were not linear over the temperature range studied, i.e. between 773 and 1223 K, except for the pure carbon of low surface area, HTT 1823 K. The activation energies from the lower gasification temperatures are considered to be descriptive of chemical control of rate. Catalysis by iron is unusual, being effective at the higher reaction temperatures. Activation energies are lowered on increasing the concentration of nickel in the doped carbons, the pre-exponential term of the Arrhenius equation similarly decreases. These phenomena are discussed as examples of the compensation effect known to occur in heterogeneous catalytic reactions. The mechanism of catalytic gasification of carbon is briefly discussed in terms of mobility of oxygen over surfaces of the metal aggregates and the formation of C-O-M bridges at the metal-carbon interface.