Queens University Belfast Valorisation of Lignocellulosic Waste and the Potential of Supercritical Water and Wet Air Oxidation PART 2 Dr. Stephen Glover Workshop - Technology Foresight Conference, Cologne University of Applied Science Campus Gummersbach, April 23rd to 25th 2013
Part 2 Supercritical Water (SCWO) and Wet Air Oxidation (WAO) of tree bark and derived products + + = Part 1Part 2 Valorisation of Lignocellulosic Waste 2
Overview of Currently Proposed Process A catalytic / chemical process on tree bark leaving a lignocellusioc material, followed by a Wet Air and / or a Supercritical Water Oxidation process Part 1 Part 2 Option 3
The Waste for WAO and / or SCWO The waste to be processed by WAO and / or SCWO is the liquid and solid Lignocellulosic material by products of the catalytic / chemical treatment of bark Bark itself and intermediate compounds between bark and Lignocellulosic may also be processed by WAO and SCWO at specific pressures and temperatures in or approaching these conditions Lignocellulosic contains aromatics, carbohydrates and fatty acids and we seek to recover the catalyst metals and potentially small organics plus other in the WAO and / or SCWO processes 4
The Objectives of the Investigative Work From WAO and / or SCWO To investigate the use of WAO and SCWO in terms of the operating regions to determine what and how efficiently can be recovered from the bark / Lignocellulosic waste At different Supercritical pressure and temperatures At different Subcritical pressure with Supercritical temperatures In the two phase region To potentially investigate other wet air oxidation and supercritical oxidation media other than water CO2?, Other? 5
Properties of Water for WAO and SCWO Pressure / Enthalpy Diagram for Water Critical Point of 220 Bar & 374 C SUPERCRITICAL WET AIR OXIDATION 6
Properties of Water for WAO Subcritical Liquid water is a polar solvent at subcritical conditions Dipole dipole molecular attraction Helping molecules form ions, dissolving in solution Water will react chemically in the hydrolysis of carbohydrates, esters, etc. reducing the polymer sizes Polar components of biomass will dissolve and react in WAO If metals are retained from chemical processing they may assist in catalytic WAO reactions 7
Properties of Water for SCWO Supercritical Supercritical water behaves more like a non polar solvent at supercritical conditions due to the density decrease or molecular proximity weakening dipole to dipole bonding As a result, non polar compounds such as most hydrocarbons including the non polar components of biomass and gases (e.g., O2, N2) are more soluble in supercritical water and polar compounds such as inorganic salts are insoluble in supercritical water and precipitate out of solution A complete reversal of water s subcritical behaviour 8
WAO and SCWO What are they? Both WAO and SCWO use water as a medium to promote the solubility of materials to facilitate the oxidation of organic compounds. SCWO results in total oxidation to CO2, water and energy, WAO is incomplete and leaves small organics Water also, very importantly, provides a uniform thermal environment that provides stable conditions at reduced peak temperatures that facilitiates specific and controllable reactions 9
WAO and SCWO What are they? SCWO was developed to destroy hazardeous compounds such as nerve agents as it gives complete oxidation There is significnat interest in SCWO and is an obvious choice for aqueous waste with water already there 10
WAO and SCWO What are they? WAO being at lower temperatures has much lower reaction rates, lower solubility and lower transport properties giving slower less complete reactions Catalyst are often used to assist WAO SCWO has 99.9999 % complete oxidation reactions with organic compounds to water and carbon dioxide With SCWO precious metals are precipitated as metal oxides which is a more easily handled form for re processing SCWO is a relatively mature but is not yet a commercialised technology due to non commercially resolved engineering issues 11
The Main Problems with SCWO SCWO has advantages over WAO in terms of reaction rate and the completeness of the reaction It has great potential on its own or after a WAO process as will be investigated in this research work The problems with SCWO as a flow or batch process are related to : High Pressures with high temperatures Presents a significant engineering challenge Precipitation of salts in the process can block pipes Acids and electrolytic corrosion destroying the reactor 12
A Generic SCWO Plant Layout Generic SCWO plant 13
The Potential of WAO and SCWO in Processing Tree Bark Water in WAO or SCWO provides a mechanisms and a medium that stabilises and facilitates control of reaction conditions Given this, WAO and SCWO at specific pressure, temperature and concentration conditions, with the possible addition of other reactants, have the potential to facilitate a series of controlled extraction processes for value products from tree bark QUB will map the WAO and SCWO operating regions and investigate tree bark and tree bark derivative reactions with various applied reactants 14
QUB Batch Tester High Pressure Batch Reactor with Laminar Flame Speed, Internal Condition and Sample Analysis Experimental Capability Main Specification Maximum operating pressure: 270 bar Maximum vessel temperature: 400 600 C Internal diameter: 175 mm Volume: 2.8 litres Required bolt load: 2 MN (200 tonnes) (approximately) Ø 35 mm Will add a stirrer or agitator (eg. bubble N2) Ports and Instrumentation 1 absolute WC pressure transducer 1 dynamic WC pressure transducer 2 thermocouples 2 ionisation probes 2 spark igniter probes 2 top inlet ports 1 top sampling/exhaust port 1 top burst disc 1 base sampling/drain ports 15
Questions for Workshop Why water? green, clean, cheap and abundant Why not water +220 bar and 374 C are difficult to reach and maintain. Is the very high pressure necessary? Does it contribute to the reaction we want Is there any other medium other than water? Analysis of tank captured product stream samples, who, when and where? Transport of samples? Could analysis be at QUB with stakeholder assistance / equipment? 16
Thank You for Your Attention 17
Additional Information 18
Properties of Water Water Solvation or density properties Most supercritical fluids have a density (or solvating power) closer to that of a liquid but mass transport properties (such as viscosity and diffusivity) closer to that of a gas Non Polar behaviour And at 250 bar 19
Properties of Water Liquid water is a polar solvent at subcritical conditions Dipole dipole molecular attraction Helping molecules form ions, dissolving in solution Polar Salt dissolved in water 20