Combustion and explosion characteristics of pulverised wood, valorized with mild pyrolysis in pilot scale installation, using the modified ISO 1 m(3) dust explosion vessel

Featured Application Design of explosion safety measures for torrefaction installations and design of pulverized-fired burners for biocoal. Biomass is a renewable energy source with great potential worldwide and in the European Union. However, valorization is necessary to turn many types of waste biomass into a tradable commodity that has the potential to replace coal in power plants without significant modifications to firing systems. Mild pyrolysis, also known as torrefaction, is a thermal valorization process of low-quality biomass that could be suitable for such a purpose. In this work, typical Spruce-Pine-Fir residues from a sawmill were tested in terms of the explosion and flame propagation properties. The ISO 1 m(3) dust explosion vessel was used, with a modified and calibrated dust dispersion system that could cope with very coarse particles. The deflagration index, K-st, was higher for the torrefied sample, with a peak at 36 bar m/s compared with 27 for the raw biomass. The peak flame speeds were similar for both samples, reaching 1 m/s. The peak P-max/P-i was between 7.3 and 7.4 bar for both untreated and torrefied biomass. The mechanism for coarse particle combustion is considered to be influenced by the explosion-induced wind blowing the finer fractions ahead of the flame, which burns first, subsequently devolatilizing the coarser fractions.Web of Science1224art. no. 1292

Glycerol and Glycerol/water Gasification for the Decarbonisation of Industrial Heat

This research is aimed at using Gaseq equilibrium flame chemistry modelling, to demonstrate that wet waste crude glycerol could be air gasified to produce a Biomass Gasification Gas (BGG) for direct applications as a burner fuel for the decarbonisation of industrial heat. Glycerol is a typical biomass fuel in its composition and it is similar to the distillery waste pot ale (PA), which is about 87% water and 13% pot ale syrup (PAS). Both of these low-cost waste bio-fuels are not easy to burn in conventional burners due to their high viscosity, high boiling point and high water content. There is much agricultural waste and other industrial bio-liquid wastes that are also high in water content, including distillery waste draff, spent grains from the barley malting process and farming manure. Draff is typically 75% water. Consequently, this work investigated the influence of water on BGG composition for wet bio-waste, using glycerol/water mixtures as the demonstration of wet bio-waste. Gasification of biomass can be aided by adding steam to the air gasifier, due to the water gas shift reaction that reacts with steam and CO to produce more hydrogen. However, if the steam generator is a separate plant there are energy efficiency problems. In the present work, the gasifier is heated directly by an inline burner operating very lean and this will vaporise the water in the biomass and produce steam. The burner temperature controls the gasifier operating temperature and the yield of CO and H2, as well as moving the peak energy content of the BGG to richer gasification equivalence ratio. Water in the fuel up to 60% was predicted to still achieve gasification, but the impact on equilibrium hydrogen was only a small increase with a larger decrease in CO. With BGG gas combustion in a boiler it would be possible to recover the heat of vaporisation of water through flue gas condensation and recovery of the heat using burner inlet air cooling

Renewable Energy from Whisky Distillery By-products

Whisky distillery by-products draff and pot ale (PA) have an energy content that potentially can be used to decarbonize distillery heating. Draff consists of wet grains which are the residue of the first stage of whisky production. PA is the liquid residue that results from the first stage of the distillation at malt distilleries. The yearly production of distillery by-products was estimated to have increased by 27,000 tonnes (dry) in 2014. It is not feasible to store distillery by-products because of their bio-chemical nature and high volumes. Therefore, distillery by-products need to be removed from the site as they are produced. The most economical way to dispose of distillery by-products is by using them as feed stock for bioenergy. Some distilleries send draff and pot ale to AD plants, but to be useful they have to be dried and the use of fossil fuels for this makes the process uneconomical and the carbon emissions have to be deducted from any green biogas that is produced. This work showed for the first time that distillery draff could be air-gasified. The restricted ventilation Cone calorimeter method was used. An FTIR that was calibrated for 60 species was used to carry out the speciation of the product gases. The experimentally determined optimum gasification equivalence ratio (Ø) and gasification thermal efficiency for the gasification of draff were 4.5 and 90% respectively. Keywords : Draff, gasification, decarbonisation, equivalence ratio

Effects of obstacle separation distance on gas explosions: the influence of obstacle blockage ratio

Obstacle separation distance (pitch) has received little systematic study in the literature. Either too large or small spacing between obstacles would lead to lesser explosion severity. Therefore, an optimum value of the pitch that would produce the highest flame acceleration and hence overpressure is needed. It was the aim of this work to investigate the influence of obstacle blockage ratio on the obstacle spacing in gas explosions. The explosion tests were performed using methane-air (10% by vol.), in an elongated vented cylindrical vessel 162 mm internal diameter with an overall length-to-diameter, L/D of 27.7. Double 20-40% blockage ratio, BR orifice plates were used as obstacles. The spacing between the obstacles was systematically varied from 0.5 m to 2.75 m. The 40% BR produced the highest explosion severity in terms of overpressure and flame speeds when compared to 30% and 20% BR. However, the worst case obstacle spacing was found to be shorter with increase in obstacle blockage. In general, similar profiles of overpressures and flame speeds were obtained for all the obstacle blockages. This trend was equally observed in the cold flow turbulence intensity profile generated behind a grid plate by other researchers. In planning the layout of new installations, the worst case separation distance needs to be avoided but incorporated when assessing the risk to existing set-ups. The results clearly demonstrated that high congestion in a given layout does not necessarily imply higher explosion severity as traditionally assumed. Less congested but optimally separated obstructions can lead to higher overpressures

Steam exploded pine wood burning properties with particle size dependence

Power generation using waste material from the processing of agricultural crops can be a viable biomass energy source. However, there is scant data on their burning properties and this work presents measurements of the minimum explosion concentration (MEC), flame speed, deflagration index (Kst), and peak pressure for pulverised pine wood and steam exploded pine wood (SEPW). The ISO 1 m3 dust explosion vessel was used, modified to operate on relatively coarse particles, using a hemispherical dust disperser on the floor of the vessel and an external blast of 20 bar compressed air. The pulverized material was sieved into the size fractions <500 μm, <63 μm, 63–150 μm, 150–300 μm, 300–500 μm to study the coarse particles used in biomass power generation. The MEC (Ø) was measured to be leaner for finer size fraction with greater sensitivity of explosion. The measured peak Kst was 43–122 bar m/s and the maximum turbulent flame speeds ∼1.4–5.4 m/s depending on the size distribution of the fraction. These results show that the steam exploded pine biomass was more reactive than the raw pine, due to the finer particle size for the steam exploded biomass

Improved model for the analysis of the Heat Release Rate (HRR) in Compression Ignition (CI) engines

The accuracy of the Heat Release Rate (HRR) model of Internal Combustion Engines (ICEs) is highly depended on the ratio of specific heats, gamma (γ). Previous γ models were largely expressed as functions of temperature only. The effects of the excess air ratio (λ) and the Exhaust Gas Recirculation (EGR) rate on γ were neglected in most of the existing γ functions. Furthermore, previous HRR models were developed for stoichiometric or near – stoichiometric air - fuel mixtures in an engine condition. However, Compression Ignition (CI) engines operate over a wide range of λ. No work has been done to model the HRR of CI engines under non – stoichiometric conditions. Also, no work has been done to investigate the accuracy of existing γ functions specifically with respect to the modelling of the HRR of CI engines for non – stoichiometric conditions. The aim of this work was to develop an improved HRR model for the analysis of the HRR of CI engines for non – stoichiometric conditions (λ>1). In this work, a modified γ(T,λ), was used to model the HRR of a 96 kW, multiple fuel injection, Euro V, Direct Injection (DI) engine. The modified HRR model (Leeds HRR model) predicted the fuel consumption of the engine with an average error of 1.41% confirming that the accuracy of the HRR model of CI engines is improved by using γ(T,λ). The typical average error in the prediction of the other models was 16%. The much improved HRR model leads to more accurate prediction of fuel consumption, which enables the development of and enhances better fuel consumption management strategies for engines and fuels. It was also ascertained in this work that EGR has insignificant effect on the HRR of CI engines at low and medium loads

Biomass explosion testing: Accounting for the post-test residue and implications on the results

This work uses the ISO 1 m3 dust explosion equipment to study the explosion properties and combustion characteristics of pulverized biomass dust clouds. An unreported feature of this apparatus is that in rich concentrations only about half the dust injected is burned in the explosion, while the overpressures remain high. This work was undertaken to try to understand the mechanisms of these phenomena, through the accounting of the debris at the end of the explosion, some of which was found in the form of impacted “cake” against the vessel wall. One possible explanation is that the residue material was biomass dust blown ahead of the flame by the explosion induced wind, impacted on the walls where then the flame side underwent flame impingement pyrolysis and the metal (wall) side material was compacted but largely chemically unchanged. The results also show that the heat transfer insulation provided by the powder wall layer contributes to the higher observed pressures. The risk of explosion with significant overpressures remains at 100% in very rich environments (equivalence ratios of up to 6) although these environments are leaner than thought due to material sequestration within the “cake”. There was little indication that a rich combustion limit was approached, this was determined in standard testing equipment that has been modified and calibrated to handle larger quantities of powder than normal

Fluorinated halon replacement agents in explosion inerting

The US Federal Aviation Administration (FAA) observed during explosion tests that at a low concentration of agent, some candidate halon replacement agents increased the explosion severity instead of mitigating the event. At UTC Aerospace Systems a test program was developed to assess the behaviour of alternative agents at values below inerting concentration. Two agents were selected, C2HF5 (Penta- fluoroethane, HFC-125) and C6F12O (FK-5-1-12, Novec™1230). Baseline tests were performed with unsuppressed C3H8 (propane)/air mixtures and C3H8/air mixtures with CF3Br (Halon 1301) and N2 (nitrogen). Using CF3Br or N2 at below inerting concentrations mitigated the explosion. C2HF5 was tested against C3H8 at stoichiometric (4 vol%) and lower explosion limit (LEL) (2 vol%). Against 4 vol% C3H8 the combustion was mitigated, proportional to agent concentration; however, low concentrations of C2HF5 with 2 vol% C3H8 enhanced the explosion. Tests with N2 against a volatile mixture of C3H8 with C2HF5 showed that N2 mitigated the events. Final tests were performed with low concentrations of C6F12O against C3H8/air mixtures. This showed similar behaviour to that observed with the C2HF5 tests. Normally during qualification tests for new agents the stoichiometric concentration of a fuel is deemed to be the worst case scenario and the baseline against which agents are tested. The above described test results show that this assumption may need to be reconsidered. This work shows that contrary to common assumption the agents investigated are unlikely to have acted chemically at the flame front, but most likely, mainly cooled the flame and changed the stoichiometry, i.e. the ratio of components of the flammable mixture

Comparison of the explosion characteristics and flame speeds of pulverised coals and biomass in the ISO standard 1 m3 dust explosion equipment

Pulverised coal has been known to pose explosion risks since the 19th century, with the advent of biomass use in coal fired power generation boilers the explosion risk may need revision. The objective of the present work was to compare the explosibility of two samples of bituminous coal used in UK power stations with two biomass fuels and to review available explosion data in the literature for pulverised coal and biomass. The 1 m3 ISO explosion vessel was used to determine the explosion characteristics: deflagration index (KSt), maximum explosion pressure (Pmax) and minimum explosible concentration (MEC). Flame speeds were also measured and these are relevant to understanding the mechanism of turbulent flame propagation in power station burners, which is related to the problem of flame flashback or blow-off. Despite the similarities in composition of both coals, the explosion reactivity of Colombian coal was much higher, with a KSt value of 129 bar m/s compared to 78 bar m/s for Kellingley coal. The main difference between the two fuels was the surface area of particles which was higher for Colombian coal. It was shown that the char burn out rate at 900 °C in air was higher for Colombian coal, due to the greater oxygen diffusion in the higher porosity of the char. Results for two biomass fuels are also presented with similar values for KSt and the literature review shows that both coal and biomass have very variable flame reactivities. There is no general trend that coal is less reactive than biomass, although this could be the case for specific coals and biomass

Effects of fire-fighting on a fully developed compartment fire: temperatures and emissions

This study evaluates the effects and consequences of fire-fighting operations on the main characteristics of a fully-developed compartment fire. It also presents data and evaluation of the conditions to which fire-fighters are exposed. A typical room enclosure was used with ventilation through a corridor to the front access door. The fire load was wooden pallets. Flashover was reached and the fire became fully developed before the involvement of the fire-fighting team. The progression of the fire-fighters through the corridor and the main-room suppression attack - in particular the effect of short, medium and long water pulses on either the hot gas layer or the fire seat - was charted against the compartment temperatures, heat release rates, oxygen levels and toxic species concentrations. The fire fighting team was exposed to extreme conditions, heat fluxes in excess of 35 kW/m2 and temperatures of the order of 250 oC even at crouching level. The fire equivalence ratio showed rich burning with high toxic emissions in particular of CO and unburnt hydrocarbons very early in the fire history and a stabilisation of the equivalence ratio at about 1.8. The fire fighting operations made the combustion temporarily richer and the emissions even higher