Automatic control system and method for low-nitrogen combustion of heat-conducting oil furnace

Abstract

The invention provides an automatic control system and method for low-nitrogen combustion of a heat-conducting oil furnace, and the method comprises the steps: building a relational expression between the opening degree of a central gas valve and the gas flow, and a relational expression between the opening degree of a flue gas return valve and the gas flow, which meet the requirements of combustion stability and flue gas emission; and the fuel gas proportion of the center gun and the peripheral gun and the flue gas recirculation amount of the FGR are determined through the two relational expressions, so that the low-nitrogen combustor gives consideration to the balance of the combustion stability and the low NOx effect in the full-load section, and meanwhile the production and environmental protection requirements are met.

Description

Technical Field

[0001] The invention belongs to the technical field of low-nitrogen combustion automatic control, and in particular relates to a low-nitrogen combustion automatic control system and method for a thermal oil furnace. Background Art

[0002] In recent years, low-nitrogen burners have been used more and more widely. Gas-fired graded low-nitrogen burners combined with flue gas recirculation systems (FGR) can meet the NOx emission concentration of gas boilers below 50 mg / m 3 Even 30 mg / m 3 The prerequisite is to control the ratio of gas sent to the central gun and the peripheral gun of the burner and the amount of flue gas recirculation of FGR. Only with a good configuration and control system can the low nitrogen burner give full play to its advantages.

[0003] Due to the complexity of the combustion process and the influence of the burner load, the traditional PID algorithm is used to control the central gun gas volume or gas pressure, and the flue gas recirculation volume of the FGR system or the oxygen content after the air and flue gas are mixed. After multiple project verifications, the results are not ideal. Therefore, it is necessary to develop a new control method to balance the combustion stability and low NOx effect of the low nitrogen burner in the full load section, while meeting production and environmental protection requirements. Summary of the invention

[0004] In order to overcome the deficiencies in the prior art, the inventors have conducted intensive research and provided a low-nitrogen combustion automatic control system and method for a thermal oil furnace. By establishing a relationship between the opening of the central gas valve and the gas flow rate, and a relationship between the opening of the flue gas reflux valve and the gas flow rate that meet the requirements of combustion stability and flue gas emission, the two relationship formulas are used to determine the gas ratio of the central gun and the peripheral gun and the flue gas recirculation amount of the FGR, so that the low-nitrogen burner can strike a balance between combustion stability and low NOx effect in the full load section, while meeting production and environmental protection requirements.

[0005] The technical solution provided by the present invention is as follows:

[0006] In a first aspect, a low-nitrogen combustion automatic control system for a thermal oil furnace includes a gas combustion unit and a control unit;

[0007] The low-nitrogen burner of the thermal oil furnace in the gas combustion unit is provided with a combustion-supporting air inlet, a peripheral gun gas inlet and a central gun gas inlet. A flow meter and a flow regulating valve are provided on the gas supply pipe, and the gas supply pipe is divided into two routes to enter the peripheral gun gas inlet and the central gun gas inlet; a central gas regulating valve is provided on the central gun gas pipe to distribute the proportion of the gas volume entering the central gas gun and the peripheral gas gun under each load; an induced draft fan and a flue gas reflux regulating valve are provided on the flue gas return pipeline of the gas combustion unit, and part of the flue gas is sent back into the burner from the combustion-supporting air inlet through the induced draft fan, and the amount of recirculated flue gas entering the low-nitrogen burner under each load is controlled by the flue gas reflux regulating valve;

[0008] The control unit obtains the gas flow data from the flow meter, and uses the relationship between the central gas valve opening and the gas flow rate, and the relationship between the flue gas return valve opening and the gas flow rate that meet the requirements of combustion stability and flue gas emission to automatically adjust the opening of the central gas regulating valve and the opening of the flue gas return valve under different gas flow rates to achieve optimal low-nitrogen combustion control of the burner.

[0009] In a second aspect, a method for automatically controlling low-nitrogen combustion in a thermal oil furnace comprises:

[0010] A combustion-supporting air inlet, a peripheral gun gas inlet and a central gun gas inlet are arranged on the low-nitrogen burner of the thermal oil furnace, a flow meter and a flow regulating valve are arranged on the gas supply pipe, and the gas supply pipe is divided into two routes to enter the peripheral gun gas inlet and the central gun gas inlet; a central gas regulating valve is arranged on the central gun gas pipe to distribute the proportion of gas entering the central gas gun and the peripheral gas gun under various loads; an induced draft fan and a flue gas reflux regulating valve are arranged on the flue gas reflux pipeline, part of the flue gas is re-sent into the burner from the combustion-supporting air inlet through the induced draft fan, and the amount of recirculated flue gas entering the low-nitrogen burner under various loads is controlled by the flue gas reflux regulating valve;

[0011] The control unit obtains the gas flow data from the flow meter, and uses the relationship between the central gas valve opening and the gas flow rate, and the relationship between the flue gas return valve opening and the gas flow rate that meet the requirements of combustion stability and flue gas emission to automatically adjust the opening of the central gas regulating valve and the opening of the flue gas return valve under different gas flow rates to achieve optimal low-nitrogen combustion control of the burner.

[0012] According to the present invention, a low-nitrogen combustion automatic control system and method for a thermal oil furnace has the following features:

[0013] Beneficial effects:

[0014] (1) The present invention provides a low-nitrogen combustion automatic control system and method for a thermal oil furnace. By satisfying the requirements of combustion stability and flue gas emission, the relationship between the opening of the central gas valve and the gas flow rate, and the relationship between the opening of the flue gas return valve and the gas flow rate, the opening of the central gas regulating valve and the flue gas regulating valve are adjusted steplessly and smoothly, thus avoiding furnace shutdown due to unstable combustion state.

[0015] (2) The present invention provides a thermal oil furnace low-nitrogen combustion automatic control system and method, which adopts an automatic control method of a control unit. There is no need to set a pressure transmitter or a flow transmitter on the central gas pipe, nor is there a need to set a flow transmitter on the flue gas return pipe or an oxygen transmitter after the mixing point of the flue gas and air, thereby saving costs.

[0016] (3) The present invention provides a thermal oil furnace low-nitrogen combustion automatic control system and method, in which the interpolation points are flexibly set. If the low NOx effect near some interpolation points is not ideal or the combustion stability deteriorates after a period of operation, the system can be re-debugged and new parameters can be set according to the combustion conditions of the point without affecting the effects near other interpolation points. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the pipeline connection of the gas combustion unit;

[0018] Figure 2 is the gas flow-center gas valve opening fitting curve;

[0019] Figure 3 It is the gas flow-flue gas reflux valve opening fitting curve. DETAILED DESCRIPTION

[0020] The following detailed description of the present invention will make the features and advantages of the present invention more clear and explicit.

[0021] The word “exemplary” is used exclusively herein to mean “serving as an example, example, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0022] The present invention provides a low nitrogen combustion automatic control system for a thermal oil furnace, such as Figure 1As shown, it includes a gas combustion unit and a control unit. The low-nitrogen burner 1 of the thermal oil furnace in the gas combustion unit is provided with a combustion-supporting air inlet 2, a peripheral gun gas inlet 3 and a central gun gas inlet 4. A flow meter 5 and a flow regulating valve 6 are provided on the gas supply pipe. The gas supply pipe is divided into two routes to enter the peripheral gun gas inlet 3 and the central gun gas inlet 4. A central gas regulating valve 7 is provided on the central gun gas pipe to distribute the proportion of gas entering the central gas gun and the peripheral gas gun under each load. For the low-nitrogen burner with a flue gas recirculation system, an induced draft fan 8 and a flue gas reflux regulating valve 9 are also provided on the flue gas reflux pipeline. The induced draft fan 8 is used to send part of the flue gas from the combustion-supporting air inlet back into the burner to further reduce the generation of nitrogen oxides. The flue gas reflux regulating valve 9 is used to control the amount of recirculated flue gas entering the burner under each load.

[0023] The control unit obtains the flow data of the flow meter 5, and automatically adjusts the opening of the central gas regulating valve 7 and the opening of the flue gas return valve 9 to complete the optimal low-nitrogen combustion control of the burner.

[0024] The specific implementation method of the control unit automatically adjusting the opening of the central gas regulating valve 7 and the opening of the flue gas return valve 9 is as follows:

[0025] For the low-nitrogen burner 1, the central gas valve opening and the flue gas return valve opening under different gas flow rates are selected from low load to high load of the gas flow rate to form interpolation points; by monitoring the NOx (nitrogen oxide) content in the flue gas and observing the stability of the flame, determine whether the gas flow rate, the central gas valve opening and the flue gas return valve opening at the interpolation point match; if the NOx content in the flue gas is lower than the required value and the flame is stable, the gas flow rate, the central gas valve opening and the flue gas return valve opening match, and the interpolation point is a qualified interpolation point, otherwise the interpolation point is re-drafted and tested. Then, the full-load section is linearly fitted with each qualified interpolation point to obtain the relationship between the central gas valve opening and the gas flow rate under the full-load section, and the relationship between the flue gas return valve opening and the gas flow rate. After the burner is running, the central gas valve and the flue gas return valve are switched to the "tracking control" mode, which is automatically controlled by the control unit, that is, the central gas valve opening and the flue gas return valve opening are directly obtained from the current gas flow rate according to the aforementioned interpolation fitting line segment, and finally the optimal low-nitrogen combustion control of the burner is completed.

[0026] In the control system, the flow meter 5 and the gas flow regulating valve 6 form a PID control loop, which can adjust the gas flow entering the burner according to the process requirements. The central gas regulating valve 7 and the flue gas return regulating valve 9 both include manual control and tracking control modes. Manual control refers to manually inputting the opening data of the two valves into the control unit, and tracking control refers to automatically controlling the opening of the two valves through the control law of the control unit (the relationship between the opening of the central gas valve and the gas flow, and the relationship between the opening of the flue gas return valve and the gas flow).

[0027] The tracking control adjustment scheme of the central gas regulating valve 7 and the flue gas return regulating valve 9 is as follows:

[0028] (1) setting multiple groups of interpolation points including gas flow, central gas valve opening, and flue gas return valve opening, such as 11 groups of interpolation points;

[0029] Table 1 Low nitrogen interpolation parameter settings

[0030]

[0031] Among them, x0 <x1<……<x 10 .

[0032] (2) Determine the flue gas NOx content and the combustion conditions of the burner corresponding to each group of interpolation points. If the NOx content in the flue gas is lower than the required value and the flame is stable, the gas flow rate, the central gas valve opening, and the flue gas return valve opening match, and the interpolation point is a qualified interpolation point. Otherwise, re-draft and test the interpolation point.

[0033] Then, the full load section is linearly fitted with each qualified interpolation point to obtain the relationship between the central gas valve opening and the gas flow rate, and the relationship between the flue gas return valve opening and the gas flow rate under the full load section, as shown in Figure 2 and Figure 3 .

[0034] (3) When the central gas valve and the flue gas return valve are in tracking control mode, they are automatically controlled by the control unit, that is, the central gas valve opening y and the flue gas return valve opening z are directly obtained from the current gas flow according to the above-mentioned interpolation fitting line segment, and finally the optimal low-nitrogen combustion control of the burner is completed.

[0035] Assume that the gas flow rate measured by the current flow meter 5 is x, the central gas valve opening to be calculated is y, and the flue gas return valve opening to be calculated is z. The opening control formula is shown in Table 2.

[0036] Table 2 Opening control formula

[0037]

[0038]

[0039] The present invention also provides a method for automatically controlling low-nitrogen combustion of a thermal oil furnace, comprising:

[0040] A combustion-supporting air inlet, a peripheral gun gas inlet and a central gun gas inlet are arranged on the low-nitrogen burner of the thermal oil furnace, a flow meter and a flow regulating valve are arranged on the gas supply pipe, and the gas supply pipe is divided into two routes to enter the peripheral gun gas inlet and the central gun gas inlet; a central gas regulating valve is arranged on the central gun gas pipe to distribute the proportion of gas entering the central gas gun and the peripheral gas gun under various loads; an induced draft fan and a flue gas reflux regulating valve are arranged on the flue gas reflux pipeline, part of the flue gas is re-sent into the burner through the induced draft fan, and the amount of recirculated flue gas entering the low-nitrogen burner under various loads is controlled through the flue gas reflux regulating valve;

[0041] The control unit obtains the gas flow data from the flow meter, and uses the relationship between the central gas valve opening and the gas flow rate, and the relationship between the flue gas return valve opening and the gas flow rate that meet the requirements of combustion stability and flue gas emission to automatically adjust the opening of the central gas regulating valve and the opening of the flue gas return valve under different gas flow rates to achieve optimal low-nitrogen combustion control of the burner.

[0042] The method of obtaining the relationship between the central gas valve opening and the gas flow rate, and the relationship between the flue gas return valve opening and the gas flow rate, and automatically adjusting the opening of the central gas regulating valve and the opening of the flue gas return valve under different gas flow rates by using the relationship between the central gas valve opening and the gas flow rate, and the relationship between the flue gas return valve opening and the gas flow rate is the same as above and will not be repeated here.

[0043] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

[0044] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A low nitrogen combustion automatic control system for a thermal oil furnace, characterized in that: It includes a gas combustion unit and a control unit; The low-nitrogen burner of the thermal oil furnace in the gas combustion unit is provided with a combustion-supporting air inlet, a peripheral gun gas inlet and a central gun gas inlet. A flow meter and a flow regulating valve are provided on the gas supply pipe, and the gas supply pipe is divided into two routes to enter the peripheral gun gas inlet and the central gun gas inlet; a central gas regulating valve is provided on the central gun gas pipe to distribute the proportion of the gas volume entering the central gas gun and the peripheral gas gun under each load; an induced draft fan and a flue gas reflux regulating valve are provided on the flue gas return pipeline of the gas combustion unit, and part of the flue gas is sent back into the burner from the combustion-supporting air inlet through the induced draft fan, and the amount of recirculated flue gas entering the low-nitrogen burner under each load is controlled by the flue gas reflux regulating valve; The control unit obtains the gas flow data from the flow meter, and uses the relationship between the central gas valve opening and the gas flow rate, and the relationship between the flue gas return valve opening and the gas flow rate that meet the requirements of combustion stability and flue gas emission to automatically adjust the opening of the central gas regulating valve and the opening of the flue gas return valve under different gas flow rates to achieve optimal low-nitrogen combustion control of the burner.

2. The low nitrogen combustion automatic control system for thermal oil furnace according to claim 1 is characterized in that: The relationship between the central gas valve opening and the gas flow rate, and the relationship between the flue gas return valve opening and the gas flow rate are obtained by the following method: For the low-nitrogen burner, the central gas valve opening and the flue gas return valve opening under different gas flow rates are selected from low load to high load to form interpolation points; By monitoring the nitrogen oxide content in the flue gas and observing the stability of the flame, determine whether the gas flow rate, the central gas valve opening and the flue gas return valve opening at the interpolation point match; If the nitrogen oxide content in the flue gas is lower than the required value and the flame is stable, the gas flow, central gas valve opening, and flue gas return valve opening match, and the interpolation point is a qualified interpolation point, otherwise the interpolation point is re-drafted and tested; The full load section is linearly fitted with each qualified interpolation point to obtain the relationship between the central gas valve opening and the gas flow rate under the full load section, and the relationship between the flue gas return valve opening and the gas flow rate.

3. The low nitrogen combustion automatic control system for thermal oil furnace according to claim 1 is characterized in that: The gas flow is x, when x i <x≦x i+1 When the central gas valve opening y=(xx i )*(y i+1 -y i ) / (x i+1 -x i )+y i ; where x i is the gas flow rate at the i-th interpolation point, y i The central gas valve opening in the i-th interpolation point is i=0,1,2…,N, and there are N+1 interpolation points in total.

4. The low nitrogen combustion automatic control system for thermal oil furnace according to claim 1 is characterized in that: The gas flow is x, when x i <x≦x i+1 When the flue gas return valve opening z=(xx i )*(z i+1 -z i ) / (x i+1 -x i )+z i ; where x i is the gas flow rate at the i-th interpolation point, z i is the opening of the flue gas recirculation valve at the i-th interpolation point, i = 0, 1, 2…, N, and there are N+1 interpolation points in total.

5. A method for automatically controlling low nitrogen combustion in a thermal oil furnace, characterized in that: include: A combustion-supporting air inlet, a peripheral gun gas inlet and a central gun gas inlet are arranged on the low-nitrogen burner of the thermal oil furnace, a flow meter and a flow regulating valve are arranged on the gas supply pipe, and the gas supply pipe is divided into two routes to enter the peripheral gun gas inlet and the central gun gas inlet; a central gas regulating valve is arranged on the central gun gas pipe to distribute the proportion of gas entering the central gas gun and the peripheral gas gun under various loads; an induced draft fan and a flue gas reflux regulating valve are arranged on the flue gas reflux pipeline, part of the flue gas is re-sent into the burner from the combustion-supporting air inlet through the induced draft fan, and the amount of recirculated flue gas entering the low-nitrogen burner under various loads is controlled by the flue gas reflux regulating valve; The control unit obtains the gas flow data from the flow meter, and uses the relationship between the central gas valve opening and the gas flow rate, and the relationship between the flue gas return valve opening and the gas flow rate that meet the requirements of combustion stability and flue gas emission to automatically adjust the opening of the central gas regulating valve and the opening of the flue gas return valve under different gas flow rates to achieve optimal low-nitrogen combustion control of the burner.

6. The method for automatically controlling low nitrogen combustion in a thermal oil furnace according to claim 5, characterized in that: The relationship between the central gas valve opening and the gas flow rate, and the relationship between the flue gas return valve opening and the gas flow rate are obtained by the following method: For the low-nitrogen burner, the central gas valve opening and the flue gas return valve opening under different gas flow rates are selected from low load to high load to form interpolation points; By monitoring the nitrogen oxide content in the flue gas and observing the stability of the flame, determine whether the gas flow rate, the central gas valve opening and the flue gas return valve opening at the interpolation point match; If the nitrogen oxide content in the flue gas is lower than the required value and the flame is stable, the gas flow, central gas valve opening, and flue gas return valve opening match, and the interpolation point is a qualified interpolation point, otherwise the interpolation point is re-drafted and tested; The full load section is linearly fitted with each qualified interpolation point to obtain the relationship between the central gas valve opening and the gas flow rate under the full load section, and the relationship between the flue gas return valve opening and the gas flow rate.

7. The low nitrogen combustion automatic control method of the thermal oil furnace according to claim 5 is characterized in that: The gas flow is x, when x i <x≦x i+1 When the central gas valve opening y=(xx i )*(y i+1 -y i ) / (x i+1 -x i )+y i ; where x i is the gas flow rate at the i-th interpolation point, y i The central gas valve opening in the i-th interpolation point is i=0,1,2…,N, and there are N+1 interpolation points in total.

8. The method for automatically controlling low nitrogen combustion in a thermal oil furnace according to claim 5, characterized in that: The gas flow is x, when x i <x≦x i+1 When the flue gas return valve opening z=(xx i )*(z i+1 -z i ) / (x i+1 -x i )+z i ; where x i is the gas flow rate at the i-th interpolation point, z i is the opening of the flue gas recirculation valve at the i-th interpolation point, i = 0, 1, 2…, N, and there are N+1 interpolation points in total.

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