Hydrothermal carbonisation of primary sewage sludge was carried out using a batch reactor. The effect of temperature and reaction time on the characteristics of solid (hydrochar), liquid and gas products, and the conditions leading to optimal hydrochar characteristics were investigated. The amount of carbon retained in hydrochars decreased as temperature and time increased with carbon retentions of 64-77% at 140 and 160°C, and 50-62% at 180 and 200°C. Increasing temperature and treatment time increased the energy content of the hydrochar from 17 to 19 MJ/kg but reduced its energy yield from 88% to 68%. Maillard reaction products were identified in the liquid fractions following carbonisations at 180 and 200°C. Theoretical estimates of the methane yields resulting from the anaerobic digestion of the liquid by-products are also presented and optimal reaction conditions to maximise these identified.
Experiments show that the simple paddle stirred cell provided an oil drop dispersion that was as monosized as that produced by the controlled shear device, if not better.An analysis indicated that only the section of the membrane close to the radius of the highest shear under the paddle stirred membrane produced oil drops. The membranes used in the experiments contained a regular array of non-tortuous pores uniformly spaced and provided oil injection rates up to 1000 l m -2 h -1 , which is much higher than reported fluxes for the alternative tortuous pore channel membranes made by sintering.keywords emulsification, rheology, sieve-membrane, force balance
• This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Industrial and En-
AbstractWater-in-oil and oil-in-water emulsions were generated using 30 μm pore diameter surface membranes to investigate the factors influencing drop size, and the degree of uniformity of drop size distribution, using a stirred cell employing a simple paddle mounted above a circular disc membrane. The importance of the transitional radius, which is the radius at which the vortex around the unbaffled paddle stirrer changes from a forced vortex to a free vortex and the shear stress at the membrane surface below the stirrer is at its greatest, is demonstrated.Monosized emulsions were produced, with drop size distribution coefficient of variation values of 10% for o/w emulsions and 13.5% for w/o emulsions. These tests demonstrated that a membrane of reduced annular operating area (ringed membrane) produced a more mono-sized o/w emulsion than a membrane where the full area was used to generate the emulsion, without affecting the mean drop size. The improved size distribution was achieved whilst the transitional radius was located within the ringed annular section of the membrane.The force balance model, applied to drops formed at the surface of the membrane during emulsification, predicted the droplet diameter provided further drop break up -1 -within the stirred cell did not occur. Drop break up occurred at Reynolds numbers below 300 for both oil in water and water in oil dispersions. Therefore, for Reynolds numbers greater than this, an annular radial ring membrane can be designed to produce monosized droplets using the stirred cell at known continuous phase viscosities with predictable mean droplet size. This knowledge can be used as a design tool to produce monosized droplets of a specified size for various applications using simple stirred cell emulsification. keywords emulsification, sieve-membrane, force balance
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