Effect of different washing parameters on the fuel properties and elemental composition of wheat straw in water-washing pre-treatment. Part 1: Effect of washing duration and biomass size

Abstract

Washing pre-treatment significantly improves the fuel properties and composition of agricultural residues, though still requires further development before being applied on the industrial scale. So, to improve the efficiency of the washing pre-treatment, four basic parameters were modified in the present study, and presented in two separate and consecutive articles as Part 1: washing duration and biomass size; and Part 2: washing temperature and solid-to-liquid (S:L) ratio. In Part 1, to evaluate the effect of washing duration and sample size, three different sample sizes of wheat straw were used – 3 cm, 1 cm, and 0.05–0.08 cm, and each size was washed for 0 min, 2 min, 5 min, 10 min, 30 min, 60 min, and 180 min. The biomass composition, heating values, energy loss, and fouling and slagging propensity were evaluated for both treated and untreated samples. As a function of increasing the washing time and reducing the sample size, continuous improvements in fuel properties and fouling and slagging propensity were observed. Washing for longer durations shows best improvement in fuel properties, with a much lower fouling and slagging tendency due to the high removal of potassium (up to 68%), chlorine (up to 87%), sulphur (up to 74%), nitrogen (up to 46%), and ash (up to 39%). For biomass size, smaller sizes resulted in better washing efficiency, while larger sizes showed similar trends in washing. As shorter washing durations and a larger sample size are more favourable for industrial applicability and show considerable improvement, such cases were further modified by varying the temperature and S:L ratio (presented in Part-2).