GB2300706A - Particle segregation in pulverised fuel burner - Google Patents

Abstract

A flow divider 7 located in the primary stream of a pulverised fuel burner leads to particle segregation by size. The different streams 4 and 5 carrying the segregated fuel are directed into the optimum zones of the near burner region, for reduction of NOx and fine particles emissions depending on the burner application. This is achieved, in the case of pulverised fuel burners used in the power industry, by tapering the flow divider so that the smaller particles are fed at a greater velocity and into the centre of the recirculation zone.

Description

PULVERISED FUEL BURNER MODIFICATION TO REDUCE EMISSIONS BY SEGREGATING PARTICLES BY SIZE The invention relates to the reduction of contaminant emissions (NO, particles) from a pulverised solid fuel combustion making use of particle segregation by size.

There are a number of ways to reduce NOx emissions in pulverised solid fuels combustion systems. One of them is via burner modifications. These modifications are geared to establish the favourable conditions for low NOx production and NOx reduction to N2. Of the designs available, none of them take advantage of the dependency of the devolatilisation/combustion mechanisms on the particle size.

Many of the present day low NOx burners in use by power industry have a tangential fuel inlet into the primary tube. Subsequently, the swirl imparted to the flow is cancelled by a number of flow straighteners thus permitting the solid fuel particles to be discharged into the combustion chamber in a number of discreet streams.

An specific application of the innovation is explained making use of an example with reference to the accompanying figures in which FIGURE 1 shows an schematic of the primary tube, and FIGURE 2 illustrates the aerodynamics of the near burner region.

In reference to the drawing in Figure 1, the present innovation takes advantage of the cyclone effect that the tangential entry 1 and the shape of the head of the primary tube 2 imparts to the particles, dividing the flow at the location of the smaller diameter 3, as shown in Figure 1. In this way the smaller particles remain in the inner region of the primary tube 4 and the larger ones in the outer region 5.

By providing a smaller cross section 6 for the flow of the stream carrying the smaller particles, a greater velocity is imparted to them. By tapering the inside of the flow divider 7, the smaller particles, 11 in Figure 2, are given an angle of entry into the near burner region that induce them to populate the central region of the recirculation zone 8 of Figure 2. In this region, in the case of pulverised fuel burner in power stations, lower oxygen is available and NOx reduction reactions are encouraged The larger particles 10 are directed to the edges of the recirculation zone 8. The greater oxygen availability due to the presence of secondary air 9 will encourage the production of NO which will be reduced to N2 when encountering all radicals in the region 12 generated by the smaller particles in the centre of the recirculation zone 8.

For the case of reduction of emissions of fine solid particles, in different burner applications, the innovation presented here will induce the fine particles to agglomerate and can be handled as bigger size particles.

Claims (5)

1 A flow divider located in the primary tube of pulverised solid burners that leads to particle separation by size and its geometry, so that particles are directed into optimised locations in the near burner region.

2 The particle manipulation of Claim 1 that leads to lower NOx emissions

3 The particle manipulation as Claim 1 that leads to reduced fine particles emissions

4 The application of such a flow divider as Claim 1 with or without existent flow straighteners leading to the reduction in emissions.

5 The application of such flow divider as per Claim 1 with any geometrical variations so that the aim of lower emissions by particle size segregation is achieved.