A common system for coal-fired hot water boilers

The commonly used system

Direct blowing pulverizing system: the pulverized coal is directly sent into the furnace for combustion. It is advisable to use medium speed and high speed coal grinder, which is suitable for grinding soft bituminous coal and lignite.The disadvantage is that the coal mill output and pulverized coal fineness are related to boiler load, so with the boiler load changes need to adjust the number of coal mill operation, and grinding parts are easy to wear.The direct blow pulverizing system of medium speed coal mill is divided into positive pressure type and negative pressure type.Modern large capacity boilers mostly adopt positive pressure system.

(2) intermediate silo type pulverizing system: the characteristics of the coal mill output and pulverized coal is independent of the boiler load, suitable for the use of grinding various kinds of coal hardness of the steel ball mill.The disadvantage is that the equipment is more complex than the direct blowing type, the power consumption of the coal mill is large, no load and full load when the power consumption difference is not big, so it should be kept in full load operation.

Structure classification

Pulverized coal burner is the equipment that sends pulverized coal into the furnace for combustion.

Swirl burner: the primary air with pulverized coal and the secondary air without pulverized coal are connected with the burner by different pipes.Pulverized coal and air can mix well and form a backflow zone.Each boiler can be equipped with 4 ~ 48 burners.

(2) straight flow burner: nozzle into a narrow shape, one, the secondary air in the burner are not rotating.Pulverized coal burns completely in it.

The heating surface is divided into evaporation heating surface and overheat heating surface.Modern large and medium-sized boilers are composed of water wall furnace, so the radiant heat in the water wall (heating surface) absorption furnace makes the water evaporate into saturated steam.In order to increase the radiant heating surface without increasing the furnace volume, large boilers can use double-faced water cooling wall.The overheating heating surface can be divided into the plate superheater heating surface arranged in the upper part of the furnace and the convection superheater heating surface arranged in the convection flue.The former absorbs radiant heat in the furnace;The latter absorbs convective heat.

The air preheater is installed at the end of the boiler flue to recover the residual heat of flue gas and raise the temperature of the combustion air.The boiler with high parameters and large capacity is to increase the temperature of hot air.300℃), often need to make the air preheater and economizer classification cross arrangement.