Energy from biomass and the use of small direct fired gas turbine systems

This paper discusses the context for the use of biomass for electricity generation in the UK and similar markets and evaluates the possibility of using cyclonic gasification coupled to small gas turbine systems. In the UK the Government has strongly pushed for a significant increase in the use of renewable energy for electricity generation with only very modest success, nearly 3% coming from this source at present, predominantly hydro and wind. Subsidy for the early tranches of these systems came from an elevated price for generated electricity, but since attempts at price convergence with that pertaining with conventional fossil fuel generation systems has occurred the number of biomass systems being constructed and their net generating capacity has not increased in line with other technologies. Although utilisation technologies exist, and are well proven technologically in Scandinavia, when translated to markets such as the UK, give generating costs which are not competitive with other forms of renewable energy. Problems have arisen with many systems, being predominantly due to fouling/slagging, the different nature of the fuels, and elevated moisture content. In this context this paper describes an EU sponsored programme of work to develop a simple cyclone gasifier and combustor which can produce a medium calorific fuel gas for materials such as sawdust, retain up to about 80% of the total ash/residues in the system, and fire simple, low cost gas turbines for power generation. The system is shown to have a very wide operating range and can handle sawdust with significant quantities of material up to 4mm in size, whilst tolerating significant variation in moisture content and capturing very significant quantities of the ash/particulate matter as well as volatile species

Optimising the combustion of low calorific value gases by utilising transient flow phenomena in swirl burners

The aerodynamics caused by the PVC are highly complex and understanding the three dimensional phenomenon it is therefore of paramount importance. The information gained from the novel PIV system contributed substantially to the understanding of the complex flow pattern associated with the PVC. Secondary vortices have been identified reacting as closed loop feedback system to recycle and burn active combustion species. They also provides re-ignition for those combustion species and hence aids the overall flame stabilisation. The 100kW model swirl burner/furnace system was used to carry out measurements under rich operation conditions due to safety consideration of the exhaust system of the full scale rig. The CO emissions under piloted premixed conditions in this case were substantially lower than under non premixed conditions. Under premixed conditions the CO emissions were extraordinary low when compared to non premixed conditions. The NOx emissions confirm the advantages of piloted premixed or premixed operation conditions. NOx were 30% lower in case of piloted premixed and 60% lower in case of premixed operation conditions. The higher exhaust gas temperatures under non premixed and piloted premixed operation conditions compared to the premixed case were reflected in the NOx emissions. Intense turbulence caused by the PVC reduced the formation of thermal NOx. Lower outlet temperatures and lower CO emissions at the same power indicate higher e ciency due to premixed combustion conditions and subsequently utilising the PVC and its associated phenomena. Investigations on the industrial scaled 2MW swirl burner/furnace system were only carried out under lean operation conditions. Non premixed and piloted premixed fuel entry modes were compared. Under non premixed conditions a long flame extending down to the furnace exit occurred. Piloted premixed conditions required an axial pilot flame to ensure flame stability for fuel simulated calorific values less than 1.5MJ/m3. All the results clearly show that operating swirl burner/furnace systems under piloted premixed or premixed (where possible due to flame stability limits) conditions has clear advantages over the axial fuel entry mode. The resulting short and intense flame provides more e cient combustion and wider flame stability limits (under very lean operation conditions)

Influence of bulk doping type on the Li adsorption site on Si(111)-(1x1): H

The model surface Si(111)-(1x1):H is used as a substrate for the adsorption of submonolayer amounts of Li. For n-doped substrates a peak right at the conduction band minimum is found in photoemission spectra. The peak is absent if the experiment is conducted on p-type substrates. Density functional theory calculations for different adsorption sites correlate this peak in the conduction band with Li adsorption in a H3 site of the Si(111)-(1x1):H surface. Experiment and theory show that the binding energy of the spectral feature is independent of the Li coverage. The absence of the structure for p-type substrates suggests a doping dependence of the adsorption site for Li on Si(111)-(1x1):H