JPS6033407A - Method of maintaining fluidization in fluidized-bed boiler - Google Patents

Abstract

PURPOSE:To increase the efficiency of a boiler, by keeping a fluidization in fluidized-bed without increasing the air ratio, by flowing part of exhaust gas from the boiler into combustion air, passing through a bypass passage, at the time when loading to the fluidized-bed boiler is low. CONSTITUTION:A part of an air duct 1 on the upstream side of a forced draft fan 2 is connected to a part of an exhaust gas duct 7 on the downstream side of an induced draft fan 8 by a bypass dust 9. When loading to a boiler 3 is decreased, a controlling damper 11 is opened, at the same time the flow rate of exhaust gs duct 7 is throttled by operating a controlling damper 10 to the closing direction in accordance with the decrease of loading. Then part of exhaust gas is to be mixed with the combustion air flowing through the air duct 1, by way of the bypass duct 9, and the rate of mixed flow of combustion air and exhaust gas which is to be supplied to the boiler 3 is able to be kept as equal as the rate of combustion air in the normal operating time. Accordingly, a fluidized-bed 6 can be kept fluidiezed at the time of low loading without heightening the air ratio, so that the efficiency of the boiler at the time of low loading can improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for maintaining fluidization in a fluidized bed in a fluidized bed boiler.

In the fluidized boiler, the supplied combustion air combusts the fuel and fluidizes the bed material forming the fluidized bed.

However, in such a fluidized bed boiler, when the load is lowered with the air ratio constant, the amount of combustion air decreases with the load.
The flow of the fluidized bed deteriorates.

Therefore, it is necessary to provide an amount of air necessary for flow even in a low load state, which causes the air ratio to increase and become excessive, resulting in a problem of deterioration of boiler efficiency.

The present invention has been made in view of the above circumstances, and is designed to bypass a part of the boiler exhaust gas to the combustion air when the fluidized bed boiler is under low load, thereby reducing the air ratio to - [ensuring fluidized bed flow without evaporation. The purpose of this is to improve boiler efficiency.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of the present invention, in which combustion air is supplied to a lower wind box 4 of a fluidized bed boiler 3 via an air duct 1 and a forced draft fan 2, and is charged onto an air distribution plate 5. After the bed material is fluidized to form a fluidized bed 6 for heating and burning the fuel supplied as appropriate, the combustion becomes exhaust gas, which is sent to a chimney (not shown) via an exhaust gas duct 7 and an induced draft fan 8. It is meant to be guided.

In the above configuration, the upstream position of the forced draft fan 2 in the air duct 1 and the downstream position of the induced draft I! I8 in the exhaust gas duct 7 are connected by a bypass duct 9, and the exhaust gas duct An adjustment damper 10 is provided at a position further downstream of the connection portion of the bus/child bus duct 9 at 7, and an adjustment damper 11 is provided in the middle of the bypass duct].0.Although omitted in the drawing,
An air preheater, energy saver, dust collector, etc. may be provided.

Under normal boiler operating conditions, the regulating damper 10 is open and the regulating damper 11 is closed, so that all of the exhaust gas is guided to the chimney on the downstream side.

When the load on the boiler 3 decreases from the above state, the adjustment damper 10 is operated in the closing direction accordingly, and the exhaust gas duct 7 is closed.
At the same time, the adjustment damper 11 is opened. Then,
A part of the exhaust gas passes through the bypass duct 9 to the air duct 1.
The boiler 3 will be mixed with the combustion air.
It becomes possible to maintain the air/exhaust gas mixed flow 1 supplied to the engine to be equal to the combustion air amount under normal conditions. Therefore, fluidization of the fluidized bed 6 can be ensured without increasing the air ratio at low loads, thereby improving boiler efficiency at low loads.

FIG. 2 shows the exhaust gas take-off point, which was downstream of the induced draft IJ8 in FIG.
This shows the case where the exhaust gas recirculation fan 13 is installed in the bypass duct 1-9 via the mechanical precipitator 12, and a part of the exhaust gas is forced into combustion air. I'm trying to mix it up. This method also has the same effect as the case of FIG. 1, except that driving power for the exhaust gas recirculation fan 13 is required.

Note that the present invention is not limited to the above-mentioned embodiments, and the adjustment damper or the exhaust gas recirculation fan may be operated manually by an operator or automatically according to the boiler load. It goes without saying that various changes can be made within the scope of the invention without departing from the gist of the invention.

According to the above-described fluidized bed boiler method of the present invention, by mixing a part of the boiler exhaust gas into the combustion air when the fluidized bed boiler is under low load, the fluidized bed can be fluidized without increasing the air ratio. Since the boiler efficiency is ensured, the boiler efficiency can be improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one example of an apparatus for carrying out the method of the present invention, and FIG. 2 is an explanatory diagram showing another example. 1 is an air duct, 3 is a fluidized bed boiler, 6 is a fluidized bed, 7 is an exhaust gas duct, 9 is a bypass duct, 10.11 is a regulating damper, 12 is a mechanical precipitator, and 13 is an exhaust gas recirculation fan. 5-

Claims (1)

[Claims] 1) A method for maintaining fluidization in a fluidized bed boiler, which comprises: ensuring fluidization in the fluidized bed by mixing part of the boiler exhaust gas into combustion air supplied to the fluidized bed boiler when the fluidized bed boiler is under low load.