JPS608604A - Operation of combustion device - Google Patents

Abstract

PURPOSE:To ensure an amount of gas, which is 25% of that required during maximum combustion load (called MCR) specified for safety, during starting, by a method wherein, based on measurements of O2 concentration in exhaust gas and gas in a wind box, a recirculating exhaust gas amount and an amount of the air supplied for combustion are regulated. CONSTITUTION:The flow rate of recirculating gas and flame are held through regulation of the openings of dampers 23 and 32 on a feed line for the air for combustion. During such time, O2 concentration in a wind box of gas supplied to a starter burner 11a is measured by an O2 meter 31. When O2 concentration is reduced to below a set value, the air A required by circulating gas is fed through regulation of the opening of the damper 32 to ensure combustion of the starting burner. Simultaneously, with a damper 21 opened, a part of exhaust gas is exhausted outside a system, and meanwhile, O2 concentration in exhaust gas is measured in a recirculating line 24 by a difference O2 meter 33 (or 33a) attached to an outlet for recirculating gas to detect O2 concentration in exhaust gas which is exhausted to the outside, and further the measurements are utilized as a correction value for control of O2 concentration in gas in the wind box of the starting burner 11a.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of operating a combustion device such as a boiler, and particularly to a method of operating a combustion device such as a boiler that can reduce the concentration of nitrogen oxides at the time of starting the device.

Nitrogen oxides (hereinafter referred to as "NO") emitted from various combustion devices
NOx (hereinafter referred to as NOx) is one of the air pollutants, and there is a social desire to reduce its emissions.In response to this, legal regulations have been put in place regarding the amount of NOx contained in exhaust gas. There is. For this reason, various measures are being taken to reduce the NOx value. The following is a typical method, (1
)' Means for removing NOx in the presence of NH3 by a catalyst in a denitrification device using a reducing agent such as NH, (2) Means for lowering the flame temperature to reduce the occurrence of so-called thermal nox, specifically (I) ) Improvements to the structure of the burner itself, (b) Utilization of recirculated gas, (3) Efficient combustion of most of the fuel with a reduction burner that produces prompt components (ON, OH) that function as reducing agents in the burner itself. There are improvements to the arrangement of the main burner and the inside of the furnace.

FIG. 1 is a system diagram of a conventional apparatus which supplies and uses the above means. Exhaust gas discharged from the boiler indicated by reference numeral 1 is passed through a main pipe 2 to a denitrification device 3 containing a catalyst. Dust collection equipment such as electric dust collector 4. Desulfurization equipment5. It is released into the atmosphere via the chimney 6.

Reference numeral 7 indicates a recirculation exhaust gas pipe (hereinafter referred to as pipe 7) which branches from the main exhaust gas pipe 2 and connects to each burner of the boiler and the bottom of the furnace.
), and a damper 8 and a recirculation blower 9 are provided in this conduit. Combustion air is sent from the forced air blower 10 to each wind box 12 via the air preheater 10a, and is then sent to the burner 1.
It is sent into the furnace together with fuel spray etc. from one nozzle.

Recirculated exhaust gas is similarly supplied into the furnace from the wind box 12 or around each burner. (Other fuel supply systems such as a fuel pump or a mill are not shown in the drawings.) Reference numeral 13 is an after air 7 amp which supplies air used for combustion of unburned components during denitration in the furnace and the like. Reference numeral 14 is a pump for supplying fuel (for example, light oil) to the small-capacity punch burner 5 used for starting the boiler.

Here, regarding laws and regulations, the following 02 standard NOx value calculation is prescribed.

In other words, based on the Prime Minister's Office Ordinance (for "NOx emission standards", the target standard value is calculated using the formula below.

Here is the converted concentration of C2NOx (ppm) - O8 converted value for each fuel type (gas, solid, liquid).

O = Oxygen concentration in exhaust gas (Hook O = Actual measurement value of NOx (ppm)) (New J Engineering 5KO10
4) (also referred to as raw NOx) ON: Gas = 5 Coal = 6 Night = 4 (Currently, in thermal power plants, the above C value is required to be lower than -loppm at startup.

As is clear from the above equation, when 0X (OS) in the exhaust gas increases, the C value of equation (1), which is the regulation value, becomes larger as O becomes larger with respect to the actually measured NOx value (08) value.

Normally, if the oil is burning well, the first
The 00□ value in the exhaust gas in the device shown in the figure is about 3 to 4%, and the 0♂08NOx value in the above equation (1) immediately changes to C
Therefore, low NOx control is relatively easy.

However, during boiler startup and low load, it is very difficult to reduce NOx due to the following reasons.

That is, to explain the startup time as an example, after the startup burner is ignited, at the stage where the main burner is being ignited as the startup burner, cooling gas is constantly supplied from the wind box 11a to prevent burnout of the burner while it is stopped. The structure is such that air (air, etc.) leaks into the furnace. Therefore, when using a raw burner as a starting burner, the amount of air required for combustion (
02 amount) or more leaked from the wind box and was eventually supplied, the 02 concentration O in the exhaust gas increased, and the N
The C value as an Ox value increases.

In view of the above problems, the inventors discovered that when the boiler is started, there is a large amount of 0□ in the exhaust gas at startup, which can be used as combustion gas, and that the exhaust gas is circulated to completely eliminate NOx emissions. The present invention provides a device configured to operate a burner and replenish combustion air as needed.

This invention relates to an improvement of the above-mentioned invention, and its purpose is to provide a method for securing 25% of the gas amount at maximum combustion load (referred to as MOR) specified for safety when starting a combustion device such as a boiler. be.

In short, this invention starts the recirculation fan before the burner is turned on, measures the 02 concentration of the gas supplied to the burning burner after the burner is turned on, and measures the 02 concentration in the exhaust gas at the beginning of operation. Focusing on the fact that the value is approximately 17%, the amount of recirculated exhaust gas and the amount of air supplied for combustion are determined based on the measurement results of the concentration of carbon in the exhaust gas and the gas in the wind box in order to reduce the C value in equation (1) above. The method is characterized in that it is a method of adjusting.

The present invention will be explained in detail below with reference to the drawings.

In FIG. 2, reference numeral 20 is a control box for storing memory and issuing command signals, and the control shown below is performed via this control box 20. First, prior to starting the boiler 1, the recirculation blower 9 is started to purge the flammable gas remaining in the boiler furnace. Also, if necessary, a forced air blower 1 for supplying combustion air.
0 is also activated. Normally, only the recirculation blower 9 is activated and the damper 23 of the combustion air supply pipe is kept fully closed.

The purge is performed by the damper 21 of the exhaust gas pipe line 2. Air supply pipe 22
The purge gas is carried out by opening the dampers 23 and supplying air A and air from the pipe line 2 into the furnace by the blowers 9 and 10, and discharging the purge gas to the outside through the exhaust gas pipe line 2.

Once the purge is complete, the burner is ignited next, but in this case, the burner 11 is horizontal (lateral) to the boiler 1.
There are multiple burner details arranged in multiple stages (the one shown is 4
The main burner in the lowermost stage is designated as the starting burner. This is because if the lowest burner is used as the starting burner, a sufficient length of the high-temperature exhaust gas passage can be ensured, and the temperature of the entire furnace can be raised in a short time, thereby shortening the starting time of the entire boiler. starting burner
Prior to ignition of la, dampers 21 and 23 are fully closed,
Then, the dampers 24a and 25 of the exhaust gas recirculation line 24 are opened. Correspondingly, the damper 26 of the conduit supplying recirculation gas to the starting burner lla is also opened. In this case, the dampers 27, 28, and 29 of the pipes that supply exhaust gas to the main burner that is not ignited are also left slightly open to allow the recirculated gas to leak, and the m due to the heat of the starting burner 11a is
Prevent losses. Further, at this time of startup, the boiler is required to flow gas at a flow rate of 25% of the gas flow rate at maximum load (MCR) according to domestic regulations that apply mutatis mutandis to the NFPF US regulations. This regulation was established because if the gas flow rate is small, unburned oil droplets from the startup burner will accumulate in a part of the boiler, and if the flow rate increases, it can cause an explosion inside the furnace, which is extremely dangerous. It is.

However, when starting the boiler, the fuel supply is normally M
Approximately 10% of OH, therefore the air flow rate is also approximately 10% of MOH.
is sufficient, and the conventional method cannot satisfy the flow rate stipulated by law. In this invention, the flowmeters 30a and 30b provided in the recirculation gas pipeline and the combustion air supply pipeline
The gas flow rate inside the boiler is estimated and controlled to meet the standards specified by law. That is, since the 02 concentration contained in the circulating gas for the starting burner lla changes over time, the flame is maintained along with the flow rate of the circulating gas by adjusting the opening degree of the damper 23, 32 of the combustion air supply pipe. During this time, the starting burner l
The O2 concentration in the wind box of the gas supplied to the la is measured, and when the O2 concentration drops below the set value, the amount of air A required for the circulating gas is adjusted by adjusting the opening degree of the damper 32. to ensure combustion of the starting burner. At the same time, the exhaust gas 21 is opened to discharge part of the exhaust gas to the outside of the system, but another outlet is provided at the outlet of the recirculation exhaust gas in the recirculation pipe 24. The 04 degree in the exhaust gas is measured by the 2 total 33 (or 33a), the 02 concentration in the exhaust gas to be discharged to the outside is detected, and this measurement result is activated.The 02 concentration in the gas in the wind box of the burner lla is Used as a correction value for control. In this case, if the flow meter 34 measures the flow rate of gas to the starting burner lla and the thermometer 35 measures the temperature of this gas, more precise control can be achieved.

Next, the burner that can be used as the starting burner is not limited to the lowest burner, and other burners may also be used. For this reason, in order to allow other burners to be used as starting burners, the wind boxes of the burners in other stages are equipped with 02 total.

Install a flow meter and, if necessary, a thermometer.

By carrying out this invention, N
The amount of Ox emissions can be reduced, and low pollution properties can be fully exhibited.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a conventional exhaust gas recirculation type low NOx combustion device, and FIG. 2 is a control system diagram of a boiler device for implementing the method according to the present invention. 2...Exhaust gas pipe 20...Control box 21, 23.26.2'7.28.29.32...Damper 31.33...02 total

Claims (1)

[Claims] 1. In a method for recirculating and supplying exhaust gas from a combustion device to a nozzle, a recirculation blower is started before the starting burner reaches a high temperature, and the recirculation blower is started before the starting burner reaches its maximum temperature. After the starting gas is ignited, air is sequentially mixed into the wind box in accordance with the amount of oxygen contained in the gas inside the wind box, and thereafter the oxygen content in the gas inside the wind box is A method for operating a combustion device characterized by controlling a mixing ratio of circulating exhaust gas and air in accordance with the above. 2. Claim 1, characterized in that the amount of gas supplied into the furnace upon startup is controlled such that the amount of gas supplied into the furnace is 25% of the amount of exhaust gas at the maximum combustion load of the combustion device. The combustion equipment operating method described. 3. A patent claim characterized in that the numerical value of the O1 content in the exhaust gas at the outlet of the exhaust gas to be recirculated is used as a signal, and is input as a correction value of the 02 value in the wind box to a control box that outputs a memory and command signal. A method for operating a combustion device according to scope 1. 4. Combustion according to claim 1, characterized in that the burner device is constituted by multiple stages of burner groups in which a plurality of burners are arranged in a horizontal row, and the lowest stage burner is used as a starting burner. How to operate the device. 5. Claims characterized in that a pipe line for supplying recirculated exhaust gas is connected to the burner group of each stage, and 081 is connected to each wind box, and any burner stage is used as a starting burner. The method of operating a combustion device according to item 1. 6. For burners in stages other than the starting burner membrane, the dampers of the recirculation exhaust gas supply pipes connected to each wind box should be set at a small angle so that the maximum twist IJt, C' is approximately 25% of the amount of exhaust gas when loaded. 3. The method of operating a combustion apparatus according to claim 1, wherein the amount of gas is controlled by a flowmeter so that the gas flows through the exhaust gas passage at the furnace outlet of the boiler.