JPS5833288B2 - Combustion control method for hot stove - Google Patents

Description

[Detailed description of the invention] This invention appropriately determines the amount of heat input during the combustion period during hot blast furnace operation, especially during unsteady operation periods due to changes in air blowing temperature, thereby preventing a decrease in hot blast furnace thermal efficiency and ensuring smooth operation of the blast furnace. This invention relates to a method for controlling combustion in a hot stove.

During hot blast furnace operation, if the input heat during the combustion period is insufficient, the specified temperature cannot be maintained during the blowing period, which impedes the smooth operation of the blast furnace.Also, even if an excessive amount of heat is input, it cannot be used effectively as a blast furnace blower. Since the amount of heat is limited, the heat loss of the exhaust gas and the heat loss of the furnace body increase, reducing thermal efficiency.

Therefore, it is necessary to always appropriately manage the amount of heat input during the combustion period.

Conventional hot blast furnace combustion control consists of gas flow rate control to manage heat input and gas/air ratio control to manage combustion temperature, but setting and controlling the input heat amount during the combustion period depends on the operator's experience. In many cases, controls based on quantitative data were rarely implemented.

As a result, more gas than necessary may be burned, or the temperature or amount of heat may be insufficient.

In order to solve these problems, several methods have recently been proposed in which computers are introduced to calculate and control the amount of heat input during the combustion period.

However, all of these control methods are valid only when the hot air stove is in a steady operating state, and no consideration is given to changes in the input heat amount when the blowing temperature changes.

For this reason, effective control cannot be performed during periods of unsteady operation that involve changes in the air blowing temperature, which not only makes it impossible to maintain the specified air blowing temperature, but also has the disadvantage of causing an extreme drop in thermal efficiency.

This invention was made to solve the above-mentioned conventional drawbacks, and is a method for improving the combustion controllability of a hot air stove by improving the calculation accuracy of the input heat amount when changing the blowing temperature and finding the appropriate input heat amount. This is what we propose.

In other words, this invention is characterized by the method of determining the amount of heat to be input during the combustion period of a hot air stove, by predicting the air flow rate and air temperature before the start of combustion, and calculating the required amount of heat removal corresponding to the predicted values.
This is a method of calculating the thermal efficiency corresponding to the expected air blowing temperature when the air blowing temperature changes and the amount of excess or deficiency of heat in the hot air stove at the end of air blowing, and calculating the amount of heat that should be input this time from these values.

According to this method, it is possible to determine in advance the amount of heat input to the hot air stove that corresponds to the time when the air temperature is changed.
Even during unsteady operation periods due to changes in the air blowing temperature, the specified air blowing temperature can be maintained, and a decrease in thermal efficiency can be prevented.

This invention will be explained in detail below.

In this invention, before the hot air stove starts combustion corresponding to the time when the air blowing temperature is changed, predicted values of the blowing amount and blowing temperature in the blowing period of the hot blast stove are set, and the required amount of heat removal corresponding to the predicted values is determined.

First, when there are several hot air stoves, the expected values of the air volume and air temperature are the average values of the expected air volume and air temperature at the time when the Ai hot air stove is in its blowing period at the time when the Ai hot air stove starts combustion. It can be obtained by performing arithmetic processing to obtain .

That is, it is determined by calculation formulas (1-2) and (1-3) shown below.

However, G (N, i): Expected value of air flow rate (Nm''/min) in cycle N period of i hot air stove G (N, i): Expected value of air temperature in cycle N period of i hot air stove (' C) Vb(t): Expected value of air flow rate at future time t (N
m'/min) f'5(t): Expected value of air blowing temperature at future time t ('C) Ls: Air blowing time tss(N, i)'' j Air blowing start time tsE(N , i): Air blowing end time tNs(N, i) in cycle N period of i hot air stove: Air blowing start time tNE(N, i): Air blowing start time in cycle N period of i hot air stove tNE(N, i): Combustion end in cycle N period of i hot air stove The times tss, t8B, tNs, and tNE are the base number K of the hot air stove.
It is calculated using the following equations (1-4) to (1-7).

tss (N, 1) = Ls- to -N+Ls・(i-1)+
tO(1-4) tSE(N, 1) = Ls- to -N+Ls-10t.

(1-5) tNs (N, i) = tNE (N, 1) - LNBN (1
-6) tNE(Npi)=tss(N, i) -LNE(1
-7) However, to: Initial value (constant) I, NEN: Combustion time LNB: Combustion start time (constant) By the above calculation, at the combustion start time tNs (N, i), the expected air blowing temperature (N ,i),
The expected air blowing temperature G(N, i) is obtained.

Next, a method for determining the amount of heat and fuel gas to be input during the combustion period will be explained.

Basically, it can be determined by the following equation (4).

Fg(N, 1) = Q(N, i)/(LNEN-Pg
) (5) However, Q (N, i): i hot air stove cycle N
Required input heat amount (kcal) H (N, i): Expected heat value (kcal) without the blowing period in i hot air stove cycle N Jq (N, i): Excess/deficit amount of heat at the start of i hot air stove cycle N (kcal) ↑(N, i): Expected thermal efficiency of hot air stove cycle N Fg (N, i): Required amount of fuel gas for i hot air stove cycle N (N m'/hr) Pg: Fuel gas calories (kcal /Nm”)
The required amount of heat removal H (N
, i) are determined by the following equation (1).

Existence (N, i) = Lun (N, i)・(enemy (N, i)・ch-
Tc,'Cc)・Ls
(1) However, Ch: Hot air specific heat (kcal / N m
″-'c) Cc: Cold air specific heat (kcal/Nm3・℃)
Tc: Cold air temperature ('C) The expected thermal efficiency η(N, i) is calculated by the following equation (2) as the product of an element η(Tb) that depends on the air blowing temperature and an element η' that reflects changes over time.

? (N, i) = η(enemy (N, i))・yy'
(2) However, η(Tb)-a-Tb2+b-Tb+c
η' = Average value of η' for the past 5 cycles. However, Vb (N-1, i): i hot air stove cycle N-
Actual air blowing amount of 1 (Nm'/min) Tb (N-1, i): Actual air blowing temperature ('C) of i hot air stove cycle N-1 Tb (N-1, i): i hot air stove cycle N- 1 Actual Input Heat Amount (kcal) FIG. 1 is a chart showing the relationship between the blowing temperature Tb and the thermal efficiency η (Tb).

From this chart, the thermal efficiency η(To) is expressed as a quadratic equation of the air blowing temperature Tb, and the normal range is 1150 to 1250°C.
(%) In this invention, the change in thermal efficiency when the blowing temperature changes is formulated in advance as a quadratic or linear equation, since the thermal efficiency curve is almost a straight line. The expected thermal efficiency η(
N, i) is determined by the above equation (2).

In addition, the amount of excess or deficiency of heat Jq (
N, i) is determined by the following equation (3).

Jq(N,i)−τ−b(N,i)・(enemy(N,i
)・Ch-Th(N1.i)・Ch)・Ls However, 'rh(N-1,i): Hot air outlet temperature at the end of the previous cycle ('C) In the present invention, the hot air outlet temperature means the hot air outlet temperature. It shall mean the temperature at which the hot air leaving the furnace is just before it is mixed with the cold air.

Note that the hot air outlet temperature Th is preferably a measured value, but if there is no measured value, an estimated value using, for example, the following equation (3-1) may be used.

Th=■b″Tb″Ch Vmi・°TC″CC(31
) (Vb-Vmix) ・Ch However, Vm i x : Mixed cooling flow rate (Nrri'/min)
Next, a description will be given of an embodiment in which the present invention is applied to perform control when changing the setting of the air blowing temperature in a single air blowing system operation using four hot air stoves.

Table 1 shows the operating conditions in a steady state before changing the air blowing temperature, and Table 2 shows the changes in each characteristic value before and after changing the air blowing temperature.

The air temperature is 1200 higher than that of the second cycle NO□H8.
It is set to change from ℃ to 1220℃.

The amount of heat removed when air is blown at a temperature of 1220° C., a flow rate of 260 ON m3/min, and a blowing time of 45 minutes is calculated from the above equation (1) and becomes H=43500×103 kcal.

The thermal efficiency when the air blowing temperature reaches 1220℃ is calculated from the above (2
), η=79.0%.

In addition, since the hot air outlet temperature of NO3H8 at the end of the previous blowing was 1200°C, using the above formula (3) to calculate the difference between this temperature and the set blowing temperature, Aq = 800.
It was estimated that there was a shortage of X103kcal.

Therefore, from equation (4), the amount of heat that should be input into the second cycle NO3H8 from H2η and Aq is Q.
=56000×103kcaA.

The amount of fuel gas required at this time is 1180 kcal.
Since the combustion time is 120 minutes, Fg = 2370 ONm3/hr is calculated from equation (5), and the setting value of the gas amount controller is set to 237 at the start of combustion.
It was set at 00 Nrrl/hr.

As a result, it was confirmed that the actual blowing temperature was maintained at 1220°C, and the hot air outlet temperature at the end of blowing was about 1220°C, indicating that just the right amount of heat was being input.

For the second cycle N04H81, the third cycle N01H8, and the third cycle N02H8, the required gas amount was determined and adjusted in the same manner.

Next, in the third cycle N03H8, the required amount of heat removed H is 42,500 x 103 kca11, and the expected thermal efficiency value η is 79.
Although it remains unchanged at 0%, the hot air outlet temperature at the end of the previous time was 122
Since the temperature was 0°C, the heat excess/deficiency amount Aq was 0, and the input heat amount was sufficient at 55000 x 10"kca#, and the gas amount was readjusted to 2330 ONm"/hr.

Below, 3rd cycle NO4H8, 4th cycle N01H8
It was confirmed that a steady state was reached after the same gas amount adjustment was performed for the fourth cycle N02H8 as well.

Here, the difference between the control characteristics according to the present invention method and the control characteristics according to the conventional method will be explained.

FIG. 2a shows a pattern of control characteristics according to the conventional method, and FIG. 2a shows a pattern of control characteristics according to the method of the present invention.

In the figure, the solid line of the air blowing temperature shows the actual temperature, and the broken line shows the designated temperature.

In other words, the blowing temperature is set to 1200°C to 1220°C, for example.
In the conventional method, the thermal efficiency due to changes in air temperature
The shaded area (Sl) cannot compensate for transient excess or deficiency of heat.
As shown in the figure, if the specified temperature (1220℃) cannot be maintained and the blowing temperature is lowered, the shaded area (S2
), an excessive amount of heat is input, resulting in a decrease in thermal efficiency.

On the other hand, according to the method of the present invention, as shown in Figure 2, the necessary and sufficient amount of heat is input in advance, so it is possible to maintain the specified temperature while avoiding excessive input of heat, and there is no reduction in thermal efficiency. do not have.

[Brief explanation of drawings]

Figure 1 is a chart showing the relationship between the blast temperature and thermal efficiency of a hot air stove.
Figure 2 is a chart showing the control characteristics of hot blast stoves by the conventional method and the method of this invention, and Figure a shows the control characteristics by the conventional method;
The figure shows the control characteristics according to the method of this invention.

Claims (1)

[Claims] 1. Before the start of combustion in the hot air stove corresponding to the time of changing the air temperature, the expected values of the air flow rate and air temperature during the air blowing period of the hot air stove are set, and the required heat removal amount corresponding to the predicted values is determined. is calculated by the following formula (1), the thermal efficiency change when the blowing temperature changes is formulated in advance with a quadratic formula or a linear formula, and the thermal efficiency η is determined from the set expected blowing temperature by the following formula (2), From the difference between the actual value or estimated value of the hot air outlet temperature at the end of the previous blowing and the specified blowing temperature, the excess or deficiency amount Aq of the heat storage in the hot air furnace is determined by the following formula (3), and the required heat removal amount H1 thermal efficiency η, heat A combustion control method for a hot-blast stove, characterized in that the amount of heat Q to be input into the hot-blast stove in the current combustion period is determined by the following equation (4) from the surplus/deficiency amount aq of . Row (N, i) =? b(N, i), (intermediate(
N, i), ChTc-Cc)・Ls
(1) However, N: cycle, i: hot air blower cycle: air flow rate, enemy: air blowing temperature, Ch: hot air specific heat, Cc: cold air specific heat, Tc: cold air temperature, Ls: air blowing time ↑ (N, i) = η (enemy (N, i))・yy' (
2) However, η: An element that depends on the blast temperature Tb; η': An element that reflects changes over time; Jq=Ω(N,,i)・((N,i)・Ch−Th
(N-1,i) ・Ch) ・Ls
(3) However, Th(N-1, i): Hot air outlet temperature H+ at the end of the previous cycle, Jq Q --(4) η