| Energy
By Matt Hale, International Sales & Marketing Director, HRS Heat Exchangers
Thermal hydrolysis boosts biogas production The HRS Unicus Series of scraped surface heat exchangers is well suited thermal hydrolysis he conversion of various forms of sustainable or shorter retention times). In the case of involves heating the sludge to 160-170 biomass, including food manures and sewage sludges the high °C of the sludge and a steam explosion waste, crop and processing temperatures involved also sterilise the step can be included for extra efficiency. residues, manures and feedstock, destroying any pathogens This heat treatment changes the cell sewage sludges, into biogas which may be present and opening up structure of the compounds, breaking and advanced liquid biofuels has more options for the resulting digestate, down lignin and hemi-cellulose chains to significant potential to contribute to the such as its use as a high-quality create free sugars which are easier for world’s renewable energy and carbon biofertiliser. the bacteria to digest. Consequently, reduction goals. However, many of the residence times in the digester or most sustainable feedstock materials fermenter can be reduced, and overall Although less used in waste and contain high levels of woody materials gas production improved. agricultural AD plants, hydrolysis (both known as lignin and cellulose, which are thermal and biological) is commonly used difficult to break down, limiting the overall in the water treatment industry to HRS offers patented processes for efficiency of energy production from such improve biogas production at wastewater thermal hydrolysis both with and without materials. treatment plants since the first full-scale steam explosion. Unlike some other application of thermal hydrolysis for systems, both are based around a Hydrolysis is the process of breaking up sewage sludge in Norway in the midcontinuous process using scraped of the polymers which form 1990s. It is also employed in the surface heat exchangers to avoid fouling, lignocellulosic material (such as straw production of advanced biofuels for allowing more efficient production. and woody biomass), to release lignocellulosic feedstocks. Furthermore, the systems incorporate molecules such as saccharides, energy recovery to provide a significant therefore improving the efficiency of cost reduction during operation, and the Numerous experiments have shown that processes such as anaerobic digestion technology can be retrofitted to existing increasing the temperature during and fermentation in the production of installations in order to improve their treatment can significantly improve the bioenergy and biofuels. In most cases output. sludge reduction and organic release hydrolysis utilises temperature and rapid efficiencies, and that multiple treatment decompression (thermal hydrolysis), cycles can also be beneficial, depending In the HRS process using steam chemicals such as hydrochloric acid on the nature of the treatment. The explosion, the biomass is first preheated, (chemical hydrolysis), or enzymes benefits of thermal hydrolysis include a and is then heated further at high (biological hydrolysis) to break apart the reduction in the overall ratio of volatile pressure to achieve the thermal lignin. solids, and improvements in the hydrolysis. The biomass is then passed conversion rate of total organic carbon. to a vessel for rapid de-pressurisation Thermal hydrolysis is a two-stage The higher volatile solid content of and the steam that is released from this process combining high-pressure heat sludge fed into the digestion system, and is then used in the initial preheating treatment of the feedstock followed by the higher degradation rate attained, phase, while the hydrolysed biomass is rapid decompression. This combined cause higher biogas production then cooled before being passed to the action breaks apart the chemical bonds compared to feedstock which has not digester. in the lignocellulosic material, improving been pre-treated. biodegradability and allowing the With experience of thermal hydrolysis, organisms responsible for anaerobic HRS has developed a patented process HRS is well placed to advise on the best digestion or fermentation to act on a for the continuous thermal hydrolysis of solution for a particular purpose and to greater surface area of material digester sludge using the Unicus Series deliver a tailored solution, whatever the (therefore allowing higher loading rates, of scraped surface heat exchangers. his application.
T
HRS thermal hydrolysis systems
62 |
Farming Monthly | June 2021
www.farmingmonthly.co.uk
