JPH02157505A - Control of amount of combustion air in fluidized bed furnace - Google Patents

Abstract

PURPOSE:To grasp the operating condition of a furnace more correctly by a method wherein the amount of air, necessary for maintaining fluidized bed, which is a part of the amount of combustion air necessary for keeping the concentration of outlet port exhaust gas in constant is supplied through an air blow-off port at the lower part of the fluidized bed at all times while the amount of balanced air, fluctuating in accordance with a load, is blown into the intermediate position of a sand layer. CONSTITUTION:An oxygen concentration meter 7 is provided at the outlet port 6 of exhaust gas to measure the concentration of oxygen in the exhaust gas at all times and send a signal to an oxygen concentration controller 8 while a valve 10 is opened and/or closed by a combustion air controller 9 to control so that the amount of combustion air, necessary for keeping the concentration of oxygen in the outlet exhaust gas in constant, is supplied into a furnace. The amount of air, necessary for maintaining fluidized bed, which is a part of the necessary amount of the combustion air is supplied at all times to an air blow-out port at the lower part of the fluidized bed through a pipeline 11. The amount of balanced air, obtained by subtracting a given amount of air supplied to the air blow-off port of a wind box 3 at all times from the amount of combustion air necessary for the fluctuation in accordance with a load, is blown into the intermediate position of a sand layer 4 through the pipeline 12. According to this method, the amount of combustion air can be controlled while grasping the operating condition of the furnace correctly.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for controlling the amount of combustion air in a fluidized bed furnace used for incinerating dry sludge etc. generated from a sewage treatment plant.

(Prior Art) A fluidized bed furnace has been widely known in which a sand layer is maintained in a fluidized state by air blown from the bottom of the sand layer, and sludge and the like are burned therein. In such a fluidized bed furnace, the thickness of the fluidized bed may change due to the influx of earth and sand in the sludge or the abrasion of the media, but if the amount of air is kept constant, changes in the thickness of the fluidized bed can be prevented by the wind box. Since this appears as a change in the pressure inside the tank, it was possible to replenish or extract the medium based on the indicated pressure value.

However, in recent years, the No. 4 degree regulation has been tightened, and it has become necessary to constantly measure the oxygen concentration of the exhaust gas at the outlet of the fluidized bed furnace and supply only the amount of combustion air necessary to maintain a constant oxygen level of 4 degrees. Therefore, when the amount of lη mud input changed, the amount of air supplied to the air outlet at the bottom of the sand layer also changed significantly. For this reason, it has recently become impossible to understand the thickness of the fluidized bed inside the reactor as pressure changes in the wind box, making it extremely difficult to understand the operating status of the reactor.

(Problems to be Solved by the Invention) The present invention solves these conventional problems and can maintain a constant oxygen concentration in the exhaust gas at the outlet of a fluidized bed furnace by changing the amount of combustion air according to changes in load. In addition, to provide a method for controlling the amount of combustion air in a fluidized fluidized furnace, which allows the thickness of the fluidized bed in the furnace to be understood as a change in pressure at the air inlet at the bottom of the sand bed, thereby allowing accurate understanding of the operating status of the furnace. This is what was done.

(Means for solving the problem) The above problem is to reduce the amount of combustion air required to maintain the fluidized bed to the lower part of the fluidized bed, out of the amount of combustion air required to maintain a constant oxygen concentration in the exhaust gas at the outlet of the fluidized bed. This problem can be solved by a method for controlling the amount of combustion air in a fluidized bed furnace, which is characterized by constantly supplying air from the air inlet and blowing the remaining amount of air, which varies depending on the load, into a position in the middle of the sand layer.

(Example) The present invention will be explained in detail below along with illustrated embodiments.

In the figure, (1) is a fluidized furnace, (2) is an air distribution plate equipped with many air outlets, (3) is a wind box,
(4) is a sand layer made of a medium made fluid by the combustion air ejected from the air outlet. The sludge injected from the inlet (not shown) is heated and combusted while being vigorously stirred inside the sand layer (4), and the combustion gas is discharged from the exhaust gas outlet (6) at the upper end of the freeboard (5). .

This exhaust gas outlet (6) is equipped with an oxygen concentration meter (7), which constantly measures the oxygen concentration in the exhaust gas and sends a signal to the oxygen concentration controller (8). Control is performed by opening and closing the pulp qO so that the amount of combustion air necessary to keep the oxygen concentration of the exit exhaust gas constant is supplied into the furnace. As a result, when the amount of sludge supplied increases, the amount of combustion air also increases, and when the amount of sludge supplied decreases, the amount of combustion air also decreases, making combustion possible at a low NO3 concentration.

In conventional fluidized bed furnaces, the entire amount of combustion air required was supplied to the wind box (3), but in the present invention, the entire amount of air necessary to maintain the fluidized bed is supplied to the wind box (3). The constant amount of air corresponding to 60-70% of
Approx.
It is constantly supplied while maintaining a linear velocity of 5 g@/rrf sec or higher. In addition, the remaining amount of air after subtracting the constant amount of air constantly supplied to the air outlet of the wind box (3) from the required amount of combustion air that fluctuates depending on the load is:
It is blown into the middle position of the sand layer (4) via a pipe (12). Therefore, the amount of air blown into the sand layer (4) from the pipe Q2) is adjusted according to the load. The position where the air is blown into the sand layer (4) is preferably the sand layer (4).
The thickness is 175 to 1/2 from the top. Although the fluidized bed has very good vertical stirring effect, horizontal stirring is relatively poor, so by blowing air from the horizontal direction,
This has the effect of improving horizontal agitation. Here piping 02
) is desirably 175 to 1/2 from the top of the sand layer (4), because if it is above this, air will blow through and contribute to combustion within the sand layer (4). This is because the stirring effect in the lateral direction of the fluidized bed cannot be expected. On the other hand, if it is below this level, sufficient energy will not be given to stir the fluidized bed in the lateral direction. Furthermore, in the case of sludge incineration, water evaporates in the surface layer of the fluidized bed, but this is because the stirring effect in this area cannot be sufficiently obtained. Note that 03) is connected by pulp 04 from pipe 02) to sand layer (
4) A controller for controlling the amount of air blown into the chamber.

For example, in an incinerator that incinerates 10 sewage sludge dehydrated cakes per day, if the diameter of the furnace is 5 m and the height of the sand layer is about 1 m, the required air amount is 6000 rd/h, which is 60 to 70 m.
% of the air is supplied from the bottom of the fluidized bed, and the remaining air of about 2000 rd/h is blown into the furnace from a position in the middle of the sand bed. If the load amount is 12
On the 7th day, approximately 3000 rrf/h of air will be blown into the furnace from a position in the middle of the sand layer.

(Function) In this way, in the present invention, the oxygen concentration in the exhaust gas is constantly measured by the oxygen concentration meter (7) at the exhaust gas outlet (6),
Control is performed so that the amount of combustion air necessary to maintain a constant oxygen concentration in the outlet exhaust gas is supplied into the furnace, but of the amount of combustion air necessary for this, only the amount necessary to maintain the flow aided layer is supplied. A constant amount of air is constantly supplied to the air outlet of the wind box (3) at the bottom of the fluidized bed via piping (IQ). For this reason, the amount of air inside the wind box (3) is always constant regardless of changes in load, and changes in the thickness of the fluidized bed can be accurately understood as changes in the pressure inside the wind box (3). The medium can be replenished or withdrawn according to the indicated pressure value. In addition, in the present invention, since the remaining air amount, which varies depending on the load, is blown into the middle position of the sand layer (4), this air is also blown into the wind box (3).
It contributes to combustion together with the air blown out from the air, and sludge and the like can be reliably combusted at a preferable air ratio. Furthermore, when the load is high, the lateral stirring effect becomes large, resulting in better combustion characteristics. Therefore, according to the present invention, sludge and the like can be incinerated with a low concentration of NO, and it is also effective in preventing air pollution.

(Effects of the Invention) As explained above, the present invention is capable of keeping the oxygen concentration of the exhaust gas at the outlet of a fluidized fluidized furnace constant regardless of load fluctuations, and also allows the thickness of the fluidized bed in the furnace to be adjusted within the wind box. It is possible to accurately grasp the operating status of the reactor by recognizing it as a change in pressure, so it will greatly contribute to the development of industry as a method of controlling the amount of combustion air in a fluidized fluidized reactor that eliminates the problems of conventional methods. There is something.

[Brief explanation of the drawing]

The first section is a control system diagram showing an embodiment of the present invention. (1): Fluidized fluid furnace, (3): Wind box, (4):
Sand layer, (7): Oxygen concentration meter.

Claims (1)

[Claims] 1. Of the amount of combustion air necessary to maintain a constant oxygen concentration in the exhaust gas at the outlet of the fluidized bed, a constant amount of air necessary to maintain the fluidized bed is constantly supplied from the air outlet at the bottom of the fluidized bed. A method for controlling the amount of combustion air in a fluidized bed furnace, characterized by supplying the amount of air and blowing the remaining amount of air, which varies depending on the load, into a position in the middle of a sand layer. 2. The method for controlling the amount of combustion air in a fluidized bed furnace according to claim 1, wherein the position at which air is blown into the sand layer is from 1/5 to 1/2 from the top of the thickness of the sand layer.