Article pubs.acs.org/EF
Updraft Gasification at Pilot Scale of Hydrolytic Lignin Residue N. Cerone, F. Zimbardi,* L. Contuzzi, E. Alvino, M. O. Carnevale, and V. Valerio Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), Research Center of Trisaia, Rotondella 75026, Italy ABSTRACT: Autothermal gasification of lignin-rich residues was carried out to evaluate the performances of a pilot plant with a feeding rate of 20−30 kg h−1 of feedstock. The facility was based on an updraft gasifier and a gas cleaning train composed of a biodiesel scrubber and coalescence filters. The tests were performed with solid residues of ethanol production starting from straws or canes. Air at a low equivalence ratio was used as gasification medium. The autothermal processing and the lignin-rich feedstock made it possible to highlight a sequence of exothermic and endothermic reactions by measuring the heating rates along the reactive bed. The CO2 production was proportional to the ash content. The average production of raw syngas was 1.94 kg per kg of dry residue, of which H2 and CO were 27.2 and 696 g, respectively. The efficiency of energy conversion from solid to cold gas was 64% and reached about 81% including the contribution of the condensable organic fraction.
1. INTRODUCTION Under the recommendation and sponsorship of government bodies to incentivize the use of second-generation fuels in the automotive and aviation sectors, the availability of some byproducts at low cost will become more and more attractive. If the target of biofuel incorporation at 10% of the energetic content will be pursued by 2020, the quantity of lignin-rich residues will be substantial. As a reference point, considering a stable consumption of fuel in the European Union at the current rate of 12.8 EJ/year , the availability of solid residues will be 22−60 Gkg/year assuming that, in commercial plants, the ethanol yield is between 0.20 and 0.33 kg per kg of typical feedstock, such as stover or wood.1 Moreover, the development of processes based on the principle of green chemistry and focused on the exploitation of polysaccharides can be another source of lignin-rich residues. The hydrolytic lignin is a byproduct of second-generation ethanol production or similar bioprocesses that exploit carbohydrates and leave most of the lignin as solid residue that can be recovered by filtration. Generally, the obtained cake has a dry matter below 50% and contains unconverted fibers and residues from the previous steps, such as enzyme fragments, yeasts, nutrients, and free sugars. In order to use this residue for energy production, a detailed analysis of its chemical and physical properties is required. Combustion in boiler furnaces coupled with steam turbines is the most common solution to obtain steam and power from lignocellulosic biomass and lignin-rich solids. Gasification and the direct use of the resulting syngas in internal combustion engines (ICEs) or turbines can be exploited at medium small scale to avoid the steam cycle; however, syngas is more difficult to burn in gas turbines and produces lower efficiencies in ICE. Thus, it is more challenging and there is a great area of opportunity to improve these systems with syngas.2 Updraft gasifiers are thermally efficient, easily scalable, and flexible for the feedstock that can be used; in particular, it is possible to feed materials with high moisture content, which is generally not possible for other kinds of gasifiers. To reduce to 10% the moisture content of the solid fermentation residue, a © 2014 American Chemical Society
thermal energy corresponding to about 10−15% of his low heating value (LHV) has to be used. On the other hand, updraft gasification is known for producing a gaseous stream having a relatively high percentage of organic volatiles. Few types of machinery, such as externally fired combustion chambers and gas turbines, are able to operate with primary producer gas.3 For most applications, the condensation of tars in the part with the lowest temperature of the plants is a drawback as it causes plugging of the piping and failure and shortens the life of internal combustion engines and turbines. Strategies for tar reduction in fuel gases and synthesis gases from biomass gasification are widely investigated and used in all commercial applications.4 The cleaning technologies are classified according to the gas temperatures exiting the cleanup device and are defined as hot (T > 300 °C), cold (T ∼ 100 °C), and warm gas cleaning regimes. The updraft gasifiers can rely on relatively mature techniques available for cold gas cleanup uses, which are highly effective, although they often generate wastewater streams and may have energy inefficiencies.5 The majority of these techniques are based on wet scrubbers. Water has been used as a cheap scrubbing liquid, but the method suffers from drawbacks, such as the cost of wastewater disposal and the impervious separation of highly soluble tar, particularly phenol acids, aldehydes, and ketones. Highly toxic polycyclic aromatic hydrocarbons are not soluble and can be easily separated from the water, but accordingly with this property, they are not efficiently removed from the producer gas. Some advantages are obtained using more expensive organic compounds, as it is possible to achieve higher efficiency of removal for most organic volatiles. Moreover, the condensed species can serve as feedstock in many carbon conversion processes, recycled to the gasifier, or burnt in ancillary equipment for optimal energetic exploitation.6 The scrubbing of syngas with oil is the basis of one of the most tested gas cleaning technologies developed by the Energy Research Received: April 8, 2014 Revised: May 29, 2014 Published: May 29, 2014 3948
dx.doi.org/10.1021/ef500782s | Energy Fuels 2014, 28, 3948−3956
Energy & Fuels
Article
Figure 1. Scheme of the PRAGA plant for updraft gasification and gas cleaning: (1) gasifier; (2) screw feeder; (3) scrubber; (4) biodiesel tank; (5) filter; (6) pump; (7) high-temperature coalescence filter; (8) low-temperature coalescence filter; (9) blower; (10) flare. On the right, details of the gasifier: (1a) air inlet; (1b) grate; (1c) layer of expanded clay; (1d) heating lamp; (1e) thermocouples multipoint system; (1f) gas outlet; (1g) biomass inlet.
Table 1. Characteristics and Composition of the Fermentation Residues, Dry Matter Basis FR1 bulk density, kg m−3 particle density, kg m−3 HHV, MJ kg−1 LHV, MJ kg−1 fix carbon, % volatile, % ash, % hexosans, % pentosans, % lignin (Klason), % lignin (Klason), ac sol. % C, % H, % N, % O, % Cl, % S, % Si, % Al (ppm) Fe (ppm) Ca (ppm) K (ppm) Mg (ppm) Na (ppm) P (ppm) Ti (ppm) Ni (ppm) Cr (ppm) Mn (ppm) Zn (ppm) Pb (ppm) V (ppm) Cu (ppm) Mo (ppm) Co (ppm) Cd (ppm) a
382 710 18.5 17.9 21.6 64.7 13.73 33.5 4.1 45.1 2.2 48.0 5.4 2.7 34.9 0.075 0.14 3.32 13 500 9000 9000 6300 1900 1350 1350 780 390 230 150 76.8 34 24 22.6 8.6 6.2
