JPH08338697A - Repair time determining method of heat exchanger for heating furnace - Google Patents

Abstract

PURPOSE: To make it possible to grasp a repair time of a heat exchanger with high accuracy by determining when to repair a multiple pipe heat exchanger for combustion air-preheating installed in an exhaust gas duct of a heating furnace based on a comparison between a stack draft force and a total of a pressure loss of an exhaust gas up to the inlet of the stack. CONSTITUTION: The pressure loss of various exhaust gases in a gas duct 24 and a stack 23 is calculated from the input of combustion gas of a heating furnace 21 under combustion load and exhaust gas pressure on the inlet and outlet sides of a combustion air preheating multiple pipe heat exchanger and exhaust gas components and the temperature of a furnace bottom 22 of the exhaust gas. Furthermore, the total of the exhaust gas pressure from the draft force of the stack 23 including the resistance in the stack 23 up to the inlet of the stack 23 is calculated based on the result of the pressure loss calculation. When the comparison between the total loss of the exhaust gas pressure up to the draft force of the stack 23 and the inlet of the stack 23 is smaller than a predetermined value, it is judged that no draft allowance exists so that the heat exchanger must be repaired. This construction makes it possible to grasp when to repair the heat exchanger 25 with high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the repair time of a multi-tube heat exchanger for preheating combustion air provided in the exhaust gas flue of a heating furnace, with the sum of exhaust gas pressure loss up to the chimney passing wind force and the chimney inlet. It is a method of determining from the ratio of.

[0002]

2. Description of the Related Art Generally, in a heating furnace, as shown in a side view of FIG. 5 and a plan view of FIG. 6, a furnace bottom 22 and a chimney 23 of a heating furnace 21 are connected by a flue 24, and a ventilation force of the chimney 23 is passed. The combustion exhaust gas of the fuel burned to heat the object to be heated is sucked and discharged.

Since the temperature of the combustion exhaust gas discharged from the furnace bottom 22 of the heating furnace 21 into the flue 24 is high and contains a large amount of heat energy, the flue 24 has an air preheater, for example, a large number. A tube-type air preheating heat exchanger 25 is installed, normal temperature combustion air is flown inside the multi-tube type air preheating heat exchanger 25, and heat is exchanged with the combustion exhaust gas flowing outside, and high temperature combustion is performed. I try to get the air for me.

In such a heat exchanger 25, when it is used for a long period of time, high temperature combustion exhaust gas causes cracks in the tubes and wind box forming the heat exchanger, and impurities in the combustion exhaust gas cause Tubes corrode, holes open, and dust in the flue gas adheres to the equipment forming the heat exchanger. In such a state, air leaks into the flue 24 from the cracks and perforations of the heat exchanger 25, and the exhaust gas flow rate in the flue 24 increases.
The pressure loss in the flue 24 increases.

Since there is no room for the wind force passing through the chimney 23 with respect to the total pressure loss in the flue 24 and the chimney 23, even when the furnace pressure adjusting damper 26 is fully opened, the furnace can be opened even when the combustion pressure is high. The internal pressure rises abnormally, making it difficult to continue combustion. That is, in this case, the heating capacity of the heating furnace is lowered. Reference numeral 27 in FIGS. 5 and 6 is a drift prevention damper for preventing uneven flow of the combustion exhaust gas entering the heat exchanger 25.

As a conventional maintenance method of the heat exchanger which deteriorates as described above, the deterioration of the tube and the wind box is visually confirmed, the inside of the flue is checked such as measuring the wall thickness of the tube, and the heat exchanger is cleaned. Is adopted.

Among the above-mentioned methods for maintaining the heat exchanger for multi-tube air preheating, the inspection of the flue and the cleaning of the heat exchanger involve the suspension of the heating furnace. It is generally performed at the time of work.

[0008]

However, the above-mentioned conventional method for maintaining the heat exchanger for multi-tube air preheating is to check the tubes other than the front row and the rear row of the air preheating tube group in the exhaust gas advancing direction. Is extremely difficult to perform, and since it is not possible to quantitatively determine the degree of deterioration of the entire equipment from the inspection results for cracks, corrosion, and dirt, proper repair cannot be performed and excessive maintenance will be performed. There is a problem.

Further, since the inspection cycle is inevitably long, if the deterioration rapidly progresses and a large-scale leak occurs, the operation of the heating furnace is stopped for repair or replacement work. It is necessary and there is also a problem that it hinders production.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and quantitatively determines the degree of deterioration of the entire heat exchanger and each pass without stopping the operation. Therefore, it is an object of the present invention to provide a method for determining the repair time of a heat exchanger for a heating furnace, which can determine the repair time.

[0011]

A method for determining a repair time of a heat exchanger for a heating furnace according to the present invention determines a repair time of a multi-tube heat exchanger for preheating combustion air provided in an exhaust gas flue of a heating furnace. It is a method of determining the exhaust gas pressure in the flue and chimney from the combustion gas input amount of the heating furnace under combustion load, exhaust gas pressure and exhaust gas components on the inlet and outlet sides of the heat exchanger, and furnace bottom temperature of the exhaust gas. The loss is calculated, and the chimney through wind force (DC) including the resistance inside the chimney and the total exhaust gas pressure loss (PT) up to the chimney inlet are calculated based on this pressure loss calculation result, and the chimney through wind force (DC) and the chimney are calculated. When the ratio A = DC / PT to the total exhaust gas pressure loss to the inlet (PT) becomes smaller than the set value, the heat exchanger is repaired because there is no ventilation margin.

[0012]

With the exception of the multi-tube heat exchanger for preheating combustion air where deterioration progresses, the pressure loss characteristics from the bottom of the heating furnace to the stack are almost determined by the design conditions of the heating furnace. Therefore, once the characteristic is actually measured or calculated, the characteristic value does not change much in the long term.

On the other hand, the leakage rate and the pressure loss of the heat exchanger change in a relatively short period of time due to cracks and dust adhesion of the heat exchange pipe of the heat exchanger. The leak rate and the pressure loss of the heat exchanger can be correctly obtained by actually measuring the exhaust gas component and the pressure on the inlet and outlet sides of the heat exchanger.

By using these characteristic values and actual measured values, and the measured values of the amount of fuel used and the average furnace bottom temperature for a certain period under arbitrary combustion conditions, the furnace bottom damper is fully opened when the furnace pressure damper is fully opened. The pressure loss of exhaust gas generated before the chimney can be calculated accurately. That is, the total amount (PT) of exhaust gas pressure loss that occurs at least before the chimney is required. Further, the ventilation force (DC) of the chimney can be obtained by using the exhaust gas temperature before the chimney and the resistance value inside the chimney obtained by calculation.

Then, from the above-mentioned ventilation force (DC) and the total exhaust gas pressure loss (PT) up to the chimney inlet, the effective ventilation force (P) that can actually be ventilated is obtained by the equation (1). .

P = DC-PT (1) The above equation (1) can be converted into equation (2).

If P = PT {(DC / PT) -1} (2) (DC / PT) = A, then equation (2) can be expressed as equation (3).

P = PT (A-1) (3) From the equation (3), when A> 1, that is, (DC / PT)
In the case of> 1, it becomes P> 0, and it can be judged that there is effective wind force. However, in the case of A <1, that is, (DC / PT) <1, P <0, and it is judged that there is no effective wind force. It

Therefore, in the present invention, when A <1, it is assumed that there is no passing wind force, and the heat exchanger is repaired before A <1.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for determining a repair time of a heat exchanger for a heating furnace according to an embodiment of the present invention will be described with reference to FIGS. 1, 2 and 3.
FIG. 1 is a side view showing the arrangement of measuring instruments used when carrying out the method for determining the repair time of this heat exchanger, and FIG. 2 is also used when carrying out the method for determining the repair time of this heat exchanger. FIG. 3 is a plan view showing the arrangement of measuring devices, FIG. 3 is a block diagram showing a method for determining the repair time of this heat exchanger, and FIG. 4 is a graph showing an outline of calculation.

In this method for determining the repair time of the heat exchanger, the thermometer 1 for measuring the furnace bottom temperature (T0) of the exhaust gas is attached to the inlet of the flue 24 that exits the furnace bottom 22, and is equipped with a dilution device. Before and after the multi-tube air preheating heat exchanger 25, exhaust gas component analyzers 2 and 3 for analyzing exhaust gas components on the inlet and outlet sides of the multi-tube air preheating heat exchanger 25 are also provided for the multi-tube air preheating, respectively. Exhaust gas pressure detectors 4 and 5 for detecting the exhaust gas pressure on the inlet and outlet sides of the heat exchanger 25 are arranged. Also,
The furnace pressure adjusting damper is of the type installed in the flue after the heat exchanger, and the fuel is an example of a gas of known composition and a furnace operating at a constant air-fuel ratio.

The procedure of the method for determining the repair timing of the heat exchanger will be described with reference to FIG. 3 as follows.

The exhaust gas component analyzers 2 and 3 analyze the exhaust gas components on the inlet and outlet sides of the heat exchanger 25 for preheating air in a tubular type.

Based on the analysis result of the exhaust gas component, the theoretical oxygen amount and the theoretical carbon dioxide gas amount on the inlet and outlet sides of the multi-tube air preheating heat exchanger 25 are calculated by the equations (4) and (5).

[0025]

[Equation 1]

[0026]

[Equation 2]

Using the calculated theoretical oxygen amount and theoretical carbon dioxide amount on the inlet and outlet sides of the multi-tube type air preheating heat exchanger 25, the air ratio on the inlet and outlet sides of the multi-tubular type air preheating heat exchanger 25 is (6 )
It is obtained by the equation and the equation (7).

[0028]

(Equation 3)

[0029]

[Equation 4]

From the air ratios m _e and m _d on the inlet and outlet sides,
The leakage rate (R) of the heat exchanger 25 for multi-tube air preheating is (8)
Calculated by the formula.

[0031]

(Equation 5)

The fuel gas input amount (V _M ) input within a predetermined time in the steady operation state is input.

The fuel gas input amount that has been input (V _M),
The combustion air amount ( _VA ) is calculated by the heat exchanger inlet air ratio (m _e ), the theoretical air amount (L _o ) shown by the equation (9), and the air moisture (Z) shown by the equation (10). ), But (1
It is calculated by the equation (1).

[0034]

(Equation 6)

[0035]

(Equation 7)

[0036]

(Equation 8)

[0037] Using the fuel gas input amount input (V _M) (12) dry exhaust gas amount obtained by the equation (V _Gd)
When asked again, since the fuel gas input amount inputted by using the (V _M) (13) the amount of water obtained by the formula (V _Gw), the net amount of exhaust gas (V _G) is, by (14) To be

[0038]

[Equation 9]

[0039]

[Equation 10]

[0040]

[Equation 11]

From the leakage rate (R) obtained in step (1) and the combustion air amount (V _A ) obtained in step (2), the leakage air amount ( _VL ) becomes
It is calculated by the equation (15).

[0042]

(Equation 12)

The furnace bottom temperature (T _O ) is measured.

Total 10 measured furnace bottom temperature (T_O)
Exhaust gas temperature before dilution (T ₁) Is T₁≒
(T_O−10) is required.

A total of 11 exhaust gas temperatures before dilution at the heat exchanger inlet (T ₁ ) are compared with the exhaust gas permissible temperature determined to protect the heat exchanger from thermal damage.

Considering the operation of the whole 12 dilution device, the assumed exhaust gas temperature before dilution (T
_{When 1} ) is higher than the allowable exhaust gas temperature, the exhaust gas temperature before dilution at the heat exchanger inlet (T ₁ ) and the net exhaust gas amount (V _G ) obtained at The amount (V _D ) of dilution air introduced from the flue 24 is calculated by the equation (16).

Otherwise, the amount of dilution air (V _D )
Is 0.

[0048]

(Equation 13)

When a total of 13 dilution air is fed, the exhaust gas temperature (T ₂ ) after dilution at the heat exchanger inlet becomes equal to the allowable exhaust gas temperature (T _Ga ). When the amount of diluted air (V _D ) is 0, T ₂ = T ₁ .

Total 14 Determined exhaust gas temperature after dilution at heat exchanger inlet (T ₂ ), leak rate (R) of shell-and-tube type air preheating heat exchanger 25 determined by and net exhaust gas amount determined by using the value of (V _G), the heat exchanger outlet exhaust gas temperature (T ₃₎ is determined in accordance with the heat exchanger performance diagram.

Maru 15 Exhaust gas temperature before chimney (T ₄ ) is T ₄
= T ₃ .

Total 16 heat exchanger inlet / outlet side exhaust gas pressure (p _i,
p _o ) is measured.

The total 17 exhaust gas pressure loss is determined as follows.

1) Upward buoyancy (D _U ) in the flue is determined by the equation (17) using the furnace bottom temperature (T _O ).

[0055]

[Equation 14]

2) The downward buoyancy (D _D ) in the flue is determined by the equation (18) using the exhaust gas temperature before dilution (T ₁ ) at the heat exchanger inlet.

[0057]

(Equation 15)

3) The flue friction resistance (P _M ) is (19)
Calculated by the formula.

[0059]

[Equation 16]

4) The eddy current resistance (P _K ) in the flue is (20)
Calculated by the formula.

[0061]

[Equation 17]

5) When the heat exchanger has a plurality of paths and is equipped with a non-uniform flow prevention damper, the non-uniform flow prevention damper resistance (P _H ) is obtained by the same equation as the equation (20).

6) The furnace pressure adjusting damper resistance (P _R ) is
It is obtained by the same equation as the equation (20).

However, the resistance referred to here is the pressure loss generated on the inlet and outlet sides of the furnace pressure adjusting damper when it is fully opened.

7) Heat exchanger resistance (P_RE), But with 16
Exhaust gas pressure (p _i,p_o),
It is calculated as the equation (21).

[0066]

(Equation 18)

8) The in-chimney resistance (P _F ) is obtained by the same equations as the equations (19) and (20).

[0068] Using the full 18 in chimneys obtained by full 17 resistance (P _F) and circle 15 in the obtained stack before the exhaust gas temperature (T _4), a chimney draft force (D _C) is, (22) Is required as.

[0069]

[Formula 19]

Total 19 The total exhaust gas pressure loss (P _T ) to the chimney inlet is P _T
= Is determined as _{(D D -D U + P M} + P K + P H + P R + P RE).

Round 20 The ratio (A) of the chimney through wind force (D _C ) obtained in Round 18 to the total exhaust gas pressure loss (P _T ) to the stack inlet determined in Round 19 is A = (D _C /
P _T ).

It is determined whether the whole 21 A is larger than the set value.

When the total 22 A is smaller than the set value, it is determined that there is no ventilation margin, and repair is performed.

When the total 23 A is larger than the set value, it is determined that there is a ventilation margin, and the operation is continued.

FIG. 4 is a heat exchanger having a constant air leak, and illustrates the state of the above calculation process. For the sake of clarity, the dilution device is not operated and the drift damper is not used. The case is shown. FIG. 4 (a) is a straight line showing the flow path of the exhaust gas from the furnace bottom to the chimney, where A is the furnace bottom, B is the heat exchanger inlet, C is the heat exchanger outlet, and D is the furnace pressure. A damper, E is a chimney inlet, and F is a smoke outlet.

FIG. 4 (b) is a diagram showing the temperature of the exhaust gas at each position of the exhaust gas outflow passages A to F shown in FIG. 4 (a). The exhaust gas temperature T0 at the bottom of the furnace is an actual measurement value, and the temperature drop (T2-T3) due to heat exchange before and after the heat heat exchanger and leakage air are obtained by calculation and actual measurement respectively, so the exhaust gas temperature T4 at the chimney inlet is accurately obtained. To be Thereby, the wind force DC at the chimney inlet is obtained by correcting the pressure loss PF in the chimney.

FIG. 4 (d) is a diagram showing the amount of exhaust gas flowing through each part of the flue (A to F) in a standard state. The increase in flow rate due to air leakage in the heat exchanger can be accurately obtained by measuring the components before and after the heat exchanger.

FIG. 4 (c) is a diagram in which the pressure loss of the exhaust gas in each portion (A to F) from the furnace bottom to the smoke outlet is added and shown. Friction and eddy current loss PM in each part of the flue,
The PK can be calculated by the shape and size of the flue and the temperature and flow rate of the exhaust gas flowing therethrough, and the time change is relatively small. The same applies to the pressure loss PR in the furnace pressure damper portion and the ventilation resistance PF in the chimney when the furnace pressure damper is fully opened. on the other hand,
The pressure loss PRE in the heat exchanger has a relatively large change, but is accurate because the measured value is used. Therefore, the total pressure loss PT, which is the sum of these, can be accurately obtained.
In an actual operating state, the furnace pressure damper is automatically controlled, and the total pressure loss is in a state of being balanced with the passing wind force, as shown by the broken line in FIG. 4 (c). Therefore, the pressure ratio A = DC / PT calculated in this way is an index that directly indicates a margin of whether or not the pressure at the furnace bottom (furnace pressure) can be maintained. If deterioration of the heat exchanger is promoted, A = 1.5, A = 1.2 ,. ． ． Since the index decreases, it is sufficient to repair the heat exchanger before A = 1.0.

Since the method for determining the repair time of the heat exchanger for the heating furnace according to the embodiment of the present invention is performed as described above, the repair time of the heat exchanger can be accurately grasped and the repair time is delayed. Therefore, there is no possibility that the heating furnace becomes inoperable and the heating furnace is shut down for a long time, or the maintenance time is too early to cause over-maintenance.

[0080]

According to the present invention, since the deterioration degree of the entire heat exchanger and each pass can be quantitatively determined without stopping the operation of the heating furnace, the repair time of the heat exchanger can be accurately determined. Therefore, it is possible to prevent the sudden shutdown of the heating furnace due to deterioration of the heat exchanger, and reduce the repair cost of the heat exchanger.

[Brief description of drawings]

FIG. 1 is a side view showing an arrangement of measuring devices used when implementing a method for determining a repair time of a heat exchanger.

FIG. 2 is a plan view showing an arrangement of measuring devices used when performing a method for determining a repair time of a heat exchanger.

FIG. 3 is a block diagram showing a method for determining a repair time of a heat exchanger.

4A is an explanatory diagram showing instrument arrangement points in an exhaust gas outflow route, FIG. 4B is a graph showing temperature at each position, FIG. 4C is a graph showing accumulated pressure loss at each position, and FIG. It is a graph which shows the exhaust gas flow rate in each position.

FIG. 5 is a side view showing the structure of a heating furnace.

FIG. 6 is a plan view showing the structure of a heating furnace.

[Explanation of symbols]

 1 Thermometer 2 Exhaust gas component analyzer 3 Exhaust gas component analyzer 4 Exhaust gas pressure detector 5 Exhaust gas pressure detector

Claims (1)

[Claims] 1. A method for deciding a repair time of a multi-tube heat exchanger for preheating combustion air, which is provided in an exhaust gas flue of a heating furnace, comprising the combustion gas input amount and heat exchange of the heating furnace under combustion load. The exhaust gas pressure loss and the exhaust gas components on the inlet and outlet sides, and the exhaust gas pressure loss in the flue and the stack are calculated from the furnace bottom temperature of the exhaust gas, and the stack wind force including the resistance in the stack is calculated based on this pressure loss calculation result. (DC) and total exhaust gas pressure loss to the chimney inlet (PT) are calculated, and the chimney through wind force (D)
When the ratio A = DC / PT between C) and the total exhaust gas pressure loss to the chimney inlet (PT) becomes smaller than the set value, the heat exchanger is repaired because there is no ventilation margin. Method for determining repair time of heat exchanger for heating furnace.