This invention relates to solid fuel fired heating apparatus.

Known heating apparatus comprise a furnace, which may be fired by oil, gas or solid fuel, and a heat exchanger. In a known shell boiler, for example,- there is an inner cylindrical furnace co-axial with an outer shell, the space between the furnace and the shell incorporating the heat exchanger and containing a plurality of heat exchanging tubes through which hot combustion gas from the furnace is directed. The direction of gas flow usually has to change between the furnace and the heat exchanger and the tubes may have one or more passes requiring the airflow to change from one direction to the opposite direction. With relatively clean gases from gas and oil fired boilers the reversal of the gas causes few problems, but with coal fired furnaces the hot gas contains particles of ash and unburnt coal which can cause severe erosion of the boiler tube ends and tube bores. As a result the boiler tubes have to be frequently replaced. Further¬ more, to increase the efficiency of the heat exchanger it is common to install a larger number of smaller ^^USE

bore tubes, or insert retarders, such as coils, within the tubes. However, with a solid fuel fired unit, small bore tubes or tubes with retarders would become clogged and eroded by the particles in the gas. This results in solid fuel fired boilers having a greater physical size and consequently being more expensive than gas or oil fired boilers of comparable duties.

Other kinds of heating apparatus, for example so- called "water-tube" or "composite" boilers may have the same problems as discussed above.

For many years attempts have been made to solve the problems associated with solid fuel fired heating apparatus, both to increase their efficiency and permit a reduction in the size of the apparatus and to increase their versatility of application, that is to make them more suitable for a wider range of applications, part¬ icularly in industry. One such attempt has been made to increase the efficiency of a solid fuel fired boiler. In such a boiler the furnace is surrounded by outer water tubes and the heated water from the. tubes and the exhaust gases from the furnace both pass to a second stage heat exchanger. Such a boiler does not, however, operate entirely satisfactorily.

The aim of the present invention is to provide a solid fuel fired heating apparatus which overcomes the above-mentioned problems.

In accordance with the invention, there is provided a heating apparatus comprising a furnace, a heat exchanger to which exhaust gases can pass from the furnace, and a particle separating means which is arranged to separate particles from the exhaust gas stream passing from the furnace to the heat exchanger.

Preferably, the particle separating means is a cyclonic separator designed to operate at the high temperatures of furnace exhaust gases.

Some forms of solid fuel fired heating apparatus the invention will now be described

by way of example, with reference to the accompanying drawings, in which:-

Figures 1 to 3 are respectively diagrammatic views of the different forms of apparatus. The forms of heating apparatus shown in Figure 1 comprises a solid fuel fired furnace 1, having an out¬ let 2 for hot exhaust gases which can flow to an inlet 3 of a separate heat exchanger 4. Interposed between the furnace 1 and the heat exchanger 4 is a particle separator or gas cleaning device 5. The separator 5 is arranged so that hot gas from the furnace outlet 2 is cleaned, the cleaned gas passing through the heat exchanger inlet 3. Separated particles, which are of ash, soot and unburnt coal, pass through a bottom outlet 6 of the separator 5 and can be discarded as waste or returned to the furnace 1 for reburning.

In figure 2 there is shown an apparatus comprising a shell boiler having an internal furnace 10 of cylindrical shape and surrounded by a co-axial cylind- rical outer shell 11. In the space 12 between the furnace 10 and the shell 11 is the heat exchanger 13 which comprises a plurality of small bore convector tubes 14 which are located in the space 12.

Attached to an end face of the shell 11 is a particle separator 15. Exhaust gases from the furnace 10 pass through an outlet tube 16 to the separator 15 and the cleaned gas is directed to the tubes 14 of the heat exchanger. The tubes 14 direct the gas through one or more passes of the exchanger, the direction of gas flow being changed by a reversal chamber (not shown), which may form part of the separator 15. As in the previously described form of separator, particles separ¬ ated from the furnace exhaust gas stream are collected from an outlet 17 of the separator 15. Figure 3 illustrates how the invention can be applied to a heating apparatus in the form of a water

tube or composite boiler. In such a boiler, a furnace 20 is connected to a heat exchanger 21, of fire tube or water tube design, through the intermediary of a high temperature convection surface or superheater 22. In order to ensure that clean gases are passed to the superheater 22 and heat exchanger 21 a particle separator 23 is located between the furnace 20 and the superheater 22.

It will be appreciated that the invention can be applied to process heating in which clean gases are required for dryers, furnaces or other heating processes. Also, existing gas or oil fired boilers could be readily converted to operate on solid fuel by replacing the existing burner or furnace by a solid fuel grate in combination with a high temperature separator.

In each of the above-described forms of apparatus,' the particle separator is preferably a cyclonic device which is designed to operate at high temperatures. Generally, the cost of incorporating such a device would be balanced by the reduced cost of the heat exchanger, reduced maintenance costs and the elimination of costly tube replacement. Furthermore, the use of the separ¬ ator between the furnace and the heat exchanger permits greater versatility of design since the heat exchanger does not have to cope with substantial exhaust particles.