Effects of ash removal by agitated aqueous washing and sedimentation on the physico-chemical characteristics and fast pyrolysis of trommel fines

A pre-treated trommel fines feedstock (DPT) with 35.1 wt% ash content and particle size range of 0.5–2 mm was processed through two (100% distilled water and 1% surfactant in distilled water) aqueous agitated washing and sedimentation procedures for ash reduction prior to fast pyrolysis in a bubbling fluidized bed reactor. The washing process led to more than 36% reduction in the ash/inorganic contents of the DPT feedstock and yielded about 78 wt% of organic-rich feedstocks denoted as WPT1 and WPT2. Characterisation and fast pyrolysis of all three feedstocks was carried out to evaluate the effect of the washing process on their physico-chemical characteristics and yields of fast pyrolysis products. Results showed that the ash reduction led to increase in the volatile matter contents of the washed feedstocks by 20%, while reducing nitrogen contents. In addition, fast pyrolysis of the feedstocks showed improved yield of liquid and gas products, with a dramatic reduction of reaction water, indicating that the ash removal reduced the catalytic effect of the ash on water formation during the fast pyrolysis process. The major organic compounds in the liquid products included phenols and furans from biogenic fraction of the feedstock as well as aromatic hydrocarbons such as those obtained from pyrolysis of plastics. More importantly, the overall energy yields from the fast pyrolysis process increased by over 35% after washing the feedstock, with washing with only distilled water alone giving the highest energy yield of 93%. Hence, coupling the water-washing ash reduction process with fast pyrolysis appeared to be a suitable technology for valorising feedstocks with high ash contents such as trommel fines for energy and chemicals

Influence of moisture contents on the fast pyrolysis of trommel fines in a bubbling fluidized bed reactor

In this study, the effect of moisture contents [2.69 wt% (bone-dry), 5 wt% and 10 wt%] on product yields and process conversion efficiency during fast pyrolysis of a pre-treated trommel fines feedstock was investigated at 500 °C. Experiments were carried out using a 300 g h −1 bubbling fluidised bed rig. Yields of organic liquids ranged from 15.2 to 19.6 wt% of feedstock, which decreased with increasing moisture content. Hence, the bone-dry feedstock gave the maximum yield and consequently the highest process conversion efficiency of 43%. Increased moisture content also led to increase formation of unidentified gas products, indicating increased conversion of organic liquids. Due to the high ash content of the feedstocks, about 52 wt% solid residues, containing around 82% ash was recovered in the char pot in each case. Hence, to maximize oil yields during fast pyrolysis, trommel fines would require extensive drying to remove the original 46 wt% moisture as well as reducing the ash content considerably. XRF analysis of the ash in the feedstock and solid residues showed that the main elements present included Ca, Si, Fe, Pb, K, Cl and Al. Apart from the presence of Pb (which may be from the glass contents of the feedstock), the solid residues could be used for land reclamation or co-incinerated at cement kilns for cement manufacture

Energy recovery by fast pyrolysis of pre-treated trommel fines derived from a UK-based MSW material recycling facility

In this experimental study, a physically pre-treated trommel fines feedstock, containing 44 wt% non-volatiles (ash and fixed carbon) and 56 wt% volatile matter (dry basis), was subjected to fast pyrolysis to recover energy from its organic load, using a 300 g h−1 bubbling fluidized bed (BFB) fast pyrolysis rig. A physical pre-treatment method (including crushing, grinding and sieving) was used to prepare a 0.5–2 mm sized trommel fines feedstock to make it suitable for fast pyrolysis in the BFB reactor. Experimental results from the fast pyrolysis process showed that the highest yield of organic liquid was obtained at around a temperature of 500 °C. However, both char and gas yields increased dramatically at temperatures above 500 °C, as a result of enhanced cracking of organic vapours, which reduced the yield of liquid products. Overall, energy recovery from the pyrolysis products (liquid and gas products as well as char pot residues) ranged from 63 to 70%, generally increasing with temperature. A large proportion of the high ash content (36 wt%) of the feedstock was found in the char pot (>62%), while smaller proportions were found in the reactor bed and some liquid products. The char pot ash residues composed mostly of non-hazardous earth materials and may be applied in bulk construction materials e.g. cement manufacture. Although, there was no problem with the pyrolysis rig during 1 h of operation, longer periods of operation would require periodic removal of accumulated solid residues and/or char pot modification to ensure continuous rig operation and process safety

Pre-treatment of Malaysian agricultural wastes toward biofuel production

Various renewable energy technologies are under considerable interest due to the projected depletion of our primary sources of energy and global warming associated with their utilizations. One of the alternatives under focus is renewable fuels produced from agricultural wastes. Malaysia, being one of the largest producers of palm oil, generates abundant agricultural wastes such as fibers, shells, fronds, and trunks with the potential to be converted to biofuels. However, prior to conversion of these materials to useful products, pre-treatment of biomass is essential as it influences the energy utilization in the conversion process and feedstock quality. This chapter focuses on pre-treatment technology of palm-based agriculture waste prior to conversion to solid, liquid, and gas fuel. Pre-treatment methods can be classified into physical, thermal, biological, and chemicals or any combination of these methods. Selecting the most suitable pre-treatment method could be very challenging due to complexities of biomass properties. Physical treatment involves grinding and sieving of biomass into various particle sizes whereas thermal treatment consists of pyrolysis and torrefaction processes. Additionally biological and chemical treatment using enzymes and chemicals to derive lignin from biomass are also discussed