Gas turbine combustor with integrated ash removal for fine particulates

This paper examines the performance of a novel design of combustor for utilising variable calorific value fuel gases as produced by many biomass gasification processes. An integral ash removal system is incorporated into the combustor to reduce the need for subsequent hot gas or other cleanup systems. The combustor is of cyclonic design with tangential inlets for air, start-up fuel and gasification products. Flame stability for low calorific value gases can be enhanced via the use of ceramic/refractory lined sections if required, with the system operating under lean combustion at all times to minimise NOx. Pressure drop of the cyclonic system is minimised by the use of a tangential outlet, as are combustion instabilities, as large central recirculation zones are avoided and associated instabilities like the precessing vortex core. Ash removal from the system is important to minimise damage to turbine components. Two regions are used for particle removal. The first is the base of the unit of a conventional hopper design, and the other, a unique vortex collector pocket (VCP) carefully positioned by the tangential off-take to take advantage of the accelerating tangential flow into the off-take. This paper focuses on the use of CFD to optimise the combustion performance of the combustor run under different operating conditions as well as the removal of coarse and fine material from the flow

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

Experimental and theoretical investigation of the effect of rotating circular cylinder speed on the lift and drag forces

Flow past a circular cylinder is a problem for understanding flow around bluff bodies. This flow has been studied both experimentally and numerically of laminar infinite flow of viscous incompressible fluid around a rotating circular cylinder at Reynolds number 80,120,160 and dimensionless rotation rate, α , (ratio of cylinder surface speed to the free stream velocity) varying from 0 to 6 has been carried out. Navier–Stokes and continuity equations were solved numerically by using finite volume technique is conducted with ANSYS CFX 15 package program. High Speed Photography and LDV, present new experimental results for correlation purposes, captured the flow profile. Rotation can be used as a drag reduction technique. Comparison with previous studies showed good agreement

Coherent structure impacts on blowoff using various syngases

Swirl stabilized combustion is one of the most successful technologies for flame and nitrogen oxides control in gas turbines. However, complex fluid dynamics and lean conditions pose a problem for stabilization of the flame. The problem is even more acute when alternative fuels are used for flexible operation. Although there is active research on the topic, there are still various gaps in the understanding of how interaction of large coherent structures during the process affect flame stabilization and related phenomena. Thus, this paper approaches the phenomenon of lean premixed swirl combustion of CH4/H2/CO blends to understand the impacts of these fuels on flame blowoff. An atmospheric pressure generic swirl burner was operated at ambient inlet conditions. Different exhaust nozzles were used to alter the Central Recirculation Zone and observe the impacts caused by various fuel blends on the structure and the blowoff phenomenon. Methane content in the fuel was decreased from 50% to 10% (by volume) with the remaining amount split equally between carbon monoxide and hydrogen. Experimental trials were performed using Phase Locked PIV. The Central Recirculation Zone and its velocity profiles were measured and correlated providing details of the structure close to blowoff. The results show how the strength and size of the recirculation zone are highly influenced by the fuel blend, changing stability based on the carbon-hydrogen ratios. Nozzle effects on the shear flow and Re numbers were also observed. Modelling was carried out using the k-ω SST CFD model which provided more information about the impact of the CRZ and the flame nature close to blowoff limit. It was observed that the model under-predicts coherent structure interactions at high methane fuel content, with an over-prediction of pressure decay at low methane content when correlated to the experimental results. Thus, complex interactions between structures need to be included for adequate power prediction when using very fast/slow syngas blends under lean conditions

Flashback Avoidance in Swirling Flow Burners

AbstractLean premixed combustion using swirling flows is widely used in gas turbines and combustion. Although flashback is not generally a problem with natural gas combustion, there are some reports of flashback damage with existing gas turbines, whilst hydrogen enriched fuel blends cause concerns in this area. Thus, this paper describes a practical approach to study and avoid flashback in a pilot scale 100kW tangential swirl burner. The flashback phenomenon is studied experimentally via the derivation of flashback limits for a variety of different geometrical conditions. A high speed camera is used to visualize the process and distinguish new patterns of avoidance. The use of a central fuel injector is shown to give substantial benefits in terms of flashback resistance. Conclusions are drawn as to mitigation technologies

High momentum flow region and central recirculation zone interaction in swirling flows

‘Fuel-flexible’ gas turbines will be required over the next 20 years at least. However, this contrasts with recent experiences of global operators who report increasing emissions and difficult combustion dynamics with even moderate variations in the fuel supply. Swirl stabilized combustion, being the most widely spread technology to control combustion in gas turbines, will be a technology needed for dynamic stabilization of the flow field. However, the features of the recirculation zone are highly complex, three dimensional and time dependent, depending on a variety of parameters. A high momentum flow region inherent to swirling flows has attracted the attention of several groups interested in blowoff and stretch flame phenomena. Therefore, this study focuses on experimental results obtained to characterise the relation between the central recirculation zone and the high momentum flow region under moderate swirl levels using a well-studied tangential swirl burner for power generation applications. As to be expected the recirculation zone and the high momentum flow region rotate together about the central axis. Moreover, the interaction between them produces high, intense local velocities. This region of High Momentum (shearing flow) also presents a complex geometry that seems to be based on the geometrical features of the burner, different to previous findings on the burner where the system was thought to have a unique shearing flow region. The high three dimensional interaction of these structure is confirmed at the point where the precessing vortex core losses its strength