JPH0799242B2 - Exhaust heat recovery device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a flow rate from a heating furnace group having a furnace pressure control system,
The present invention relates to an exhaust heat recovery apparatus that recovers steam from exhaust gas by providing an exhaust heat boiler in an exhaust gas system that discharges exhaust gas whose temperature fluctuates from a stack through a collecting pipe and a flue.

(Prior arts and problems) Exhaust gas whose flow rate and temperature fluctuates from a heating furnace group that has a furnace pressure control system is exhausted to an exhaust gas system that is designed to be exhausted from a stack through a collecting pipe and a flue. When recovering steam from exhaust gas by installing a boiler, if an exhaust heat boiler with ventilation capacity equivalent to the maximum exhaust gas amount of the heating furnace group is installed in the flue, the exhaust gas flow rate will fluctuate, so the boiler cannot be used effectively, In order to increase the boiler utilization rate, it is necessary to lower the ventilation capacity of the exhaust heat boiler installed in the flue than the maximum amount of exhaust gas generated by the heating furnace group. In this case, a bypass flue is installed at the exhaust heat boiler inlet / outlet flue and a damper is installed on this bypass flue to prevent damage to the exhaust heat boiler when the exhaust gas amount exceeding the ventilation capacity of the exhaust heat boiler reaches the collecting pipe. Therefore, it is necessary to open the damper and bypass the exhaust gas to the chimney, but the damper operation fluctuates the pressure in the collecting pipe and disturbs the furnace pressure control of the heating furnace. In addition, even if a steam generation amount detector is provided in the exhaust heat boiler, and the steam generation amount is controlled by operating the damper opening according to the deviation between this detection value and the set value determined by the preliminary boiler capacity. Since the pressure in the collecting pipe fluctuates, it becomes difficult to control the steam generation amount to the set value when the generated exhaust gas amount is equal to or higher than the ventilation capacity of the exhaust heat boiler.

The present invention is a flow rate from a heating furnace group having a furnace pressure control system,
Exhaust gas boilers with a ventilation capacity lower than the maximum amount of exhaust gas generated by the heating furnace group are installed in the exhaust gas system that discharges exhaust gas whose temperature fluctuates from the stack through the collecting pipe and flue, and the steam from the exhaust gas When recovering the above, the conventional defect was solved, that is, the pressure in the collecting pipe was controlled to be constant, and the generated exhaust gas amount was equal to or higher than the ventilation capacity of the exhaust heat boiler without disturbing the furnace pressure control of the heating furnace group. An exhaust heat recovery device provided with a control system capable of controlling the amount to be constant.

(Means for Solving Problems) The gist of the present invention is to provide an exhaust gas system in which exhaust gas whose flow rate and temperature fluctuate from a heating furnace group having a furnace pressure control system is discharged from a stack through a collecting pipe and a flue. In this case, a bypass flue is provided between the collecting pipe and the flue, and one flue has an exhaust heat boiler having a ventilation capacity lower than the maximum exhaust gas amount of the heating furnace, a flow control valve, and an induction blower. , A flow rate control valve is provided on the other flue, a pressure detector is provided on the collecting pipe, a steam generation amount detector is provided on the exhaust heat boiler, and a valve opening is provided on the flow rate control valve of the one flue. A detector is provided, and a controller that operates the opening of the flow control valve of the one flue according to the deviation between the pressure detection value from the pressure detector and the preset pressure setting value is provided. Based on the deviation between the detected steam amount from the mass detector and the preset steam amount set value. Based on the calculated steam flow rate operation value, the controller that operates the opening of the flow control valve of the other flue with the opening calculated based on this calculated value and the valve opening detection value of the valve opening detector. The exhaust heat recovery device is characterized by being provided.

(Operation) Hereinafter, the present invention will be described in detail.

FIG. 1 shows an example of the exhaust heat recovery device of the present invention.
Flow rate from heating furnaces 1 and 2 having a furnace pressure control system (not shown),
In an existing exhaust gas system in which exhaust gas whose temperature fluctuates is discharged from the chimney 5 through the collecting pipe 3 and the existing flue 4, a bypass flue 6 is provided between the collecting pipe 3 and the chimney 5, and the bypass smoke An exhaust heat boiler 7 having a ventilation capacity lower than the maximum exhaust gas amount of the heating furnace group is provided on the road 6 to improve the boiler utilization rate. Further, a flow rate control valve 8 and an induction blower 9 are provided in the bypass flue 6 downstream of the exhaust heat boiler 7 so that the exhaust gas ventilation amount to the exhaust heat boiler 7 can be adjusted and the exhaust gas is forcedly ventilated to the exhaust heat boiler 7. I am able to do it. A flow rate control valve 10 is provided in the existing flue 4 so that the amount of exhaust gas discharged from the chimney 5 can be adjusted. The pressure detector 11 is installed in the collecting pipe 3.
Is provided, and the valve opening of the flow rate control valve 8 is (a) based on the deviation E _o = P _S −P _set between the pressure detection value Ps from this pressure detector 11 and the preset pressure setting value P _set. A controller 12 that operates to the opening degree ko shown in the formula is provided.

The flow control valve 8 is provided with a valve opening detector 13 and the exhaust heat boiler 7 is provided with a generated steam amount detector 14. The detected steam amount Q _s from the generated steam amount detector 14 and the preliminary boiler are used. Calculation unit for calculating the steam flow rate operation value S by substituting the deviation E = Q _s −Q _set from the steam amount set value Q _{set set} from the capacity into the equation (b)
15, the steam flow rate operation value S and the detection value from the valve opening detector 13
Substituting k ₁ into the equation (C), the valve opening operation value of the flow control valve 10
The adjusting meter 17 more a calculation unit 16 for operating the valve opening degree of the flow regulating valve 10 to the valve opening operating value k ₂ is provided with computing the k _2.

The pressure inside the collecting pipe is controlled to a set value by the fluctuation of the amount of exhaust gas generated in the heating furnaces 1 and 2 by the pressure control system in the collecting pipe and the generated steam amount control system, and the adverse effect on the furnace pressure control system of the heating furnaces 1 and 2 is prevented. While preventing, when the amount of exhaust gas generated is equal to or less than the ventilation capacity of the exhaust heat boiler 7, the ventilation amount to the exhaust heat boiler 7 is manipulated to perform almost constant control to a set value determined from the boiler capacity of the exhaust heat boiler 7. When the generated exhaust gas amount is below the ventilation capacity of the exhaust heat boiler 7 and the steam generation amount is equal to or less than the set value, most of the generated exhaust gas amount is ventilated to the exhaust heat boiler 7 to improve the exhaust gas utilization rate.

Hereinafter, the concept of controlling the pressure in the collecting pipe by the controller 12 and the flow rate control valve 8 and the formulas (b) and (c) of the calculators 15 and 16 of the controller 17 will be described with reference to FIG. To do.

(1) The conditions for controlling the pressure P in the collecting pipe to be constant with respect to fluctuations in the amount of exhaust gas generated will be described.

In FIG. 2 (a), the relation among the pressure P in the collecting pipe, the generated exhaust gas amount Q, the boiler ventilation exhaust gas amount Q ₁ , and the existing flue wind exhaust gas amount Q ₂ is as follows.

Δ: Indicates a minute change amount C: Capacity coefficient Here, the minute changes in flow rate ΔQ ₁ and ΔQ ₂ are the flow control valve 8
(V ₁ ), assuming that it is proportional to the minute changes in the opening K ₁ and K ₂ of the flow control valve 10 (V ₂ ), ΔQ ₁ = αΔK ₁ (2) ΔQ ₂ = βΔK ₂ (3) α, β: Proportional constant ΔK ₁ : V ₁ can be set as a small opening change ΔK ₂ : V ₂ 〃.

Substituting equations (2) and (3) into equation (1), When the generated exhaust gas amount Q is less than the boiler ventilation capacity, it is desirable to set Q ₂ = 0 in order to recover the vapor as much as possible. Therefore, in this case, conditions for controlling the pressure P in the collecting pipe to be constant are obtained.

When βΔK ₂ = 0, equation (4) becomes Therefore, to set ΔP = 0, ΔQ−αΔK ₁ = 0 ∵ΔQ = αΔK ₁ (6) Therefore, formula (6) is used to control the pressure inside the collecting pipe when the generated exhaust gas amount Q is less than the boiler ventilation capacity. It is a condition for doing.

When the amount Q of generated exhaust gas is equal to or higher than the ventilation capacity of the boiler, the condition for controlling the pressure P in the collecting pipe to be constant is determined.

From the equation (4), to set ΔP = 0, ΔQ−αΔK ₁ −βΔK ₂ = 0 (7) The earliest time is to satisfy the condition of the equation (7). Expressions (8) and (9) are pressure control conditional expressions when Q ₂ > 0. Therefore, pressure control is always required at valve V ₁ because of the condition.

(2) When the generated exhaust gas amount Q is equal to or higher than the boiler ventilation capacity, the condition for controlling the generated steam flow rate constant while controlling the pressure in the collecting pipe constant is determined.

Q = Q ₁ + Q ₂ …… (10) Here, let Q _Bmax be the exhaust gas flow rate at which the steam flow rate can be maximally recovered, and let Q ₁ ＝ Q _Bmax …… (11), then Q ₂ ＝ Q−Q _Bmax …… ( 12) Substituting _Eqs. (11) and (12) into Eq. (10), Q = _QBmax + (Q- _QBmax ) ...... (13) Here, the amount of exhaust gas generated is ΔQ (t) at any time t. If it is increased (Fig. 2 (b)), the pressure control is performed to V _{1 first} , so Q _Bmax is Only increase. Therefore, equation (13) is Becomes However pipe between collector pipe 3～V ₁ as in FIG. 2 (b) is long, and V ₁ is operated, there is a time delay before they impact on the pressure in the collecting pipe 3. So by V ₁ As well as changes, V ₂ at the same time If it is changed, the pressure effect by V ₂ will be too early and it will be a disturbance, so it is necessary to delay the operation of V ₂ by the delay between the collecting pipes 3 and V ₁ (approximate with the first-order delay). To). In short, at the joint between the collecting pipe 3 and the bypass flue 6 and at the joint between the collecting pipe 3 and the existing flue (8), (9)
The operation of the formula is done at the same time. Therefore (1
4) is Equation (15) represents the state in which the pressure is controlled so as not to give an extra disturbance to the pressure P.

Next, the situation at t + 1 time will be explained with reference to FIG.
By The vapor flow rate is ΔQ _s (t + 1) due to the increased amount of exhaust gas.
Only increase. The t + 2 o'clock by the (second diagram (d)) for detecting a very small increment Delta] Q _s of the vapor flow rate (t + 1), the amount of exhaust gas which is increased by ΔQ _s (t + 1) Need to flow to the existing flue 4. When the pipe delay is approximated by the first-order delay, Equation (15) is the equation immediately after the pressure control at t, so Is flowing into the existing flue 4 at t + 2, and the equation (15) is as follows.

Substituting equation (16) into equation (17) here Substituting equation (8) into equation (18) Here, since it is assumed that the minute change amount of the flow rate is proportional to the minute change amount of the opening, ΔQ ₂ is Therefore, from equation (3) Therefore, equation (20) becomes the basic equation.

If the generated steam flow rate deviation in Eq. (20) is positive, it is a deviation correction term. Is positive and ΔK ₂ is positive, so V ₂ operates in the opening direction to control the steam flow rate. If the deviation of the generated steam flow rate is negative, ΔK ₁ is also small when the fluctuation in the pressure in the collecting pipe is small. Therefore, V ₂ is fully closed. When the pressure fluctuation in the collecting pipe is large, ΔK ₁ becomes large. Therefore, V ₂ operates in the opening direction.

As for the handling of, the PI control is adopted by incorporating the integral element because an offset occurs even if correction is made only with the deviation of the steam (proportional element).

The steam amount manipulated variable S calculated by the calculation unit 15 of the controller 17 from the equation (21) is determined as in the equation (b). Also (20)
The valve opening operation value K ₂ calculated by the calculation unit 16 from the above formula (C)
It is determined according to the formula.

(Example) Exhaust gas amount of the heating furnace 1; 10,000 to 60,000 Nm ³ / hr, temperature of the heating furnace 1; 250 to 400 ° C., exhaust gas amount of the heating furnace 2; 0 to 40,000 Nm ³ / h
r, temperature of heating furnace 2; 250 to 400 ° C., maximum amount of exhaust gas of heating furnace group; 100000 Nm ³ / hr, ventilation capacity of exhaust heat boiler 7; 60000 Nm ³ / h
r at 400 ℃, capacity of waste heat boiler 7 (steam flow rate); 6ton / hr,
Induction blower 9 rotations; 1195 rpm, constant of formula (a); Kp ₀
= 75, T _I0 = 30, the constant of the equation (b); Kp = 75, T ₁ = 85,
Equation (c) constant; K = 1.3, time constant; T = 4 sec, steam set value Q
_{of set} exhaust gas amount of heating furnace group, collecting pipe pressure, recovery steam flow rate, V ₁ and V ₂ opening degree in the exhaust heat recovery device shown in FIG. 1 with _set = 6 ton / hr and pressure set value P _set = −10 mAq The transition is shown in FIG. From Fig. 3, V ₂ is almost fully closed when the generated exhaust gas amount is lower than the boiler ventilation capacity, and when the generated exhaust gas amount is higher than the boiler ventilation capacity, the steam flow rate is controlled to the steam set value and excess exhaust gas is removed. It is clear that the pressure inside the collecting pipe is controlled to be constant even during the above control that is emitted from V ₂ .

In the present embodiment, the device can be controlled even if the bypass flue and the existing flue are reversed.

(Effects of the Invention) As described in detail above, according to the exhaust heat recovery apparatus of the present invention, the exhaust gas amount generated by the exhaust heat boiler is controlled without disturbing the furnace pressure control of the heating furnace group by controlling the internal pressure of the collecting pipe to be constant. When the ventilation capacity is exceeded, the steam generation amount can be controlled to be constant.

[Brief description of drawings]

FIG. 1 is an explanatory view of an exhaust heat recovery apparatus of the present invention, FIGS. 2 (a) to (d) are explanatory views of a concept of control when using the exhaust heat recovery apparatus of the present invention, and FIG. It is explanatory drawing which shows the result of the Example of invention. 1,2 …… Heating furnace, 3 …… Collection pipe, 4 …… Existing flue, 5…
… Chimney, 6… Bypass flue, 7… Exhaust heat boiler, 8…
… Flow control valve, 9 …… Induction blower, 10 …… Flow control valve, 11 …… Pressure detector, 12 …… Controller, 13 …… Valve opening detector, 14 …… Steam generation detector, 15 , 16 …… Calculator, 17
…… Controller.

Claims (1)

[Claims] 1. An exhaust gas system in which exhaust gas having a variable flow rate and temperature from a heating furnace group having a furnace pressure control system is discharged from a stack through a collecting pipe and a flue, and the collecting pipe and the stack are connected to each other. A bypass flue is provided between the flue and the exhaust heat boiler, which has a ventilation capacity lower than the maximum amount of exhaust gas generated by the heating furnace group, a flow control valve, and an induction blower. A pressure detector is provided in the collecting pipe, a generated steam amount detector is provided in the exhaust heat boiler, and a valve opening detector is provided in the flow rate control valve of the one flue. A controller for operating the opening of the flow control valve of the one flue according to the deviation between the pressure detection value and the preset pressure setting value is provided, and the steam amount detection value from the generated steam amount detector and Calculate the steam flow rate operation value based on the deviation from the set steam amount setting value, Exhaust heat recovery characterized in that a controller for operating the opening of the flow control valve of the other flue is provided with the opening calculated based on the calculated value and the valve opening detection value of the valve opening detector. apparatus.