JPS6333612B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for low-temperature complete combustion of fuel gas. In particular, it relates to low NOx combustion technology for fuel gases applied to air heating for food drying purposes.

That is, when drying food, NOx generates harmful pollutants, so it is desired to extremely reduce NOx in fuel exhaust gas.

Known techniques to solve this problem include:
There are methods to lower the flame temperature and eliminate local high-temperature areas within the flame through two-stage combustion, exhaust gas recirculation, etc., but NOx is usually around 50 to 100 ppm, and NOx reduction is insufficient. It is. In other words, in order to be used for the purpose of food drying, it is required that the NOx in the fuel gas before dilution during the drying process is on the order of 1 ppm on average (maintained on the order of 1 ppm), but the above-mentioned known technology This target value has not been reached.

The present invention achieves combustion by complete combustion at low temperature.
The purpose is to reduce NOx, and the fuel gas and air are completely premixed in advance to conditions close to the lower limit of flammability (fuel-lean mixture) to enable complete combustion at low temperatures. be.

The first invention of the present application separately supplies fuel gas and a large amount of combustion air for diluting the gas to conditions close to the lower limit of flammability into a mixer section equipped with a plurality of ventilates, and The mixed gas discharged from each ventilate is mixed homogeneously by a flashback prevention trap provided on the outlet side of the mixer section, and the completely mixed lean mixed gas is transferred to an office equipped with a flame stabilization device. A low-temperature complete combustion method for gas, which is characterized in that the gas is passed through a plate and supplied to a combustion chamber made of refractory material, and the combustion chamber is combusted, and the outlet of the combustion chamber is shaped like a tapered cone to stabilize combustion by utilizing radiation. provide.

The second invention of the present application relates to an apparatus for carrying out the above method, which is characterized by a mixer section having a plurality of ventilaries 8 and an orifice having a plurality of orifices 18 each equipped with a flame stabilization device 20. The mixer section includes a plate 14 and a combustion chamber 16 surrounded by a heat-resistant material provided on the outlet side of the orifice plate. There is a space between the mixer section and the orifice plate for completely stirring the mixed gas premixed by each of the ventilaries. A trap 12 for preventing backfire is provided, and fully stirred gas is jetted into the combustion chamber from multiple orifice plates for combustion.The combustion chamber has a tapered conical outlet on the opposite side from the orifice plate 14 to ensure combustion stability. The reason is that

The present invention will be explained in detail below based on illustrated embodiments.

Referring to FIG. 1, combustion air is supplied via an air inlet duct 2 to a mixer module or section 3. The mixer section 3 consists of a cylindrical container 4 having partition walls 5 and 6 facing each other at its opposite ends, and a plurality of ventilates 8 are provided between the partition walls 5 and 6. Six venturis 8 are arranged in the mixer section 3 in a ring shape around this axis at approximately equal intervals. Fuel gas passes through duct 10,
It is fed into the mixer section 3 and further enters the ventilator 8 via a hole 9 provided in the throat of each ventilator. In this case, premixing is performed by supplying air to the fuel gas at a dilute ratio close to the lower limit of the flammability limit to the ventilate 8. Note that it is very important that the ventilate 8 be made accurately so as not to cause internal upheaval, and that the inner surface be highly smooth.

The discharge side of this mixer section 3 and the combustion chamber 1
An anti-flashback trap 12 is disposed between the orifice plate 14 forming the end wall of 6. This trap 12 is used to prevent backfire and to
It has the effect of mixing and homogenizing the mixed gas ejected from.

The orifice plate 14 is provided with a number of orifices 18 through which a mixture of air and gas passes. The resulting jet of mixed gas is ignited into a refractory combustion chamber 16 on the opposite side of the orifice plate 14.
It exits the combustion chamber via an outlet 28 provided at the end of the combustion chamber 16, where it is diluted and quenched by the surrounding air, but before that it burns in the combustion chamber 16 to more than 99.5% complete combustion. In order to effectively carry out this combustion, the outlet 28 is formed into a conical shape that converges forward. This allows heat to be reflected from the orifice 18 to the burner jet, thereby improving combustion stability. The flashback prevention trap 12 also serves to prevent the possibility of light shining back into the ventilate 8.

The supply of fuel gas and air for combustion via duct 2 and duct 10 is regulated so that the gas/air
The air ratio approaches the lower flammability limit of the gas and the combustion products at the combustion chamber outlet 28 contain more than 8.5% free oxygen before being diluted with outside air.

The burner orifice 18 is designed and arranged to maintain a stable flame even when the mixture is weak at the lower end of the permissible flammability limit of the fuel gas in question.

Some of the orifices 18 incorporate flame retention or flame stabilization devices 20. The flame stabilization device 20 allows most of the mixture to pass through to the center, but a small amount passes through the tubular orifice 1.
8 wall, where it loses speed and stabilizes, providing conditions for stabilizing the main flame into itself. The combustion chamber 16 is surrounded by refractory material, and in particular the orifice plate/end wall 14 is rapidly heated;
It radiates itself into a small flame to promote stability and rapid combustion.

FIGS. 2-4 illustrate the flame stabilization device described above, which further comprises a ceramic tube inserted into an orifice plate 14 for providing multiple flame jets. It is desirable to leave sufficient space between adjacent jets to promote flame stability and to ensure space for recovery of partial combustion products which, due to the temperature at the flame base, enhances rapid ignition and combustion.

The device shown in FIG. 2 consists of a ceramic tube 22;
This is a surface that is on the same level as both end surfaces of the orifice plate 14. In FIG. 3, the ceramic tube 24 is retracted relative to the front end surface of the plate 14, while in FIG.
protrudes from the front end surface of. Additionally, although not shown, at least some of the tubes may be provided with a reduced diameter section at the upstream end to abruptly reduce velocity and thus provide stability. Different flame stabilization devices described above may be used together in a single device.

The basic burner device described above can be assembled in a variety of shapes and sizes of modules suitable for use in various types of air heaters.

Furthermore, the device can be used for controlled operation so that a section of the burner can be extinguished while the remaining sections remain in operation, yet still provide the same controlled combustion conditions at reduced heat output. can be placed.

Factors that influence the formation of nitrogen compounds are the temperature of the flame, the availability of oxygen and nitrogen, and the amount of time the fuel gas is maintained at high temperature.

According to the present invention, since air and fuel gas are premixed by the plurality of ventileries 8 and mixed again by the trap 12, even if there is a slight difference in the mixing ratio in each ventilary 8, it can be made uniform. Can be done. Therefore, a mixture of fuel gas close to the lower limit of gas flammability and a large amount of air can be made into a "completely mixed gas" (total premix), and by completely combusting this, it can be It provides a method of burning fuel gas with air, and here we will discuss 99.5% of complete combustion in the combustion chamber.
% or more of the fuel gas is combusted, which consists of introducing the combustion gas and air as a "fully mixed gas" into the combustion chamber. "Fully mixed gas" means that the fuel gas/air ratio is close to the flammability limit of fuel gas with air, so that the combustion products at the entrance of the combustion chamber before dilution with extraneous air are Contains more than 8.5% of free oxygen, Trap 12
is constant at all positions within the volume occupied by the mixture and at all constant throughputs over the entire operating range of the burner. Such a ratio is constant over the flow cross-section of the mixture and at all longitudinal positions. By ensuring that such a constant fuel gas/air ratio is maintained at all times, flame temperatures are controlled to the lowest practicable levels, the mixture does not fluctuate to rise or fall, and nitrogen oxides are reduced. Conditions similar to those described above do not create flame conditions inconsistent with those needed to minimize formation, but with known burner formats such as post-mix or nozzle mix modes, operating at the practical limit of flammability. There is nothing designed like that.

Furthermore, different combustion conditions are applied due to imperfections in the mixture proportions at the combustion point, and NOx (nitrogen oxides) levels are higher than permissible for the purpose.

The gas/air ratio is maintained at as high a level as possible. For example, for natural gas, the ratio is 1:15 or more. At the high levels of excess air used, the flame velocity is low, which results in problems with flame stability. To solve this problem, the orifice plate 14, which has a plurality of orifices 18 each equipped with a flame stability maintenance device 20, works effectively and achieves stable ignition and combustion with a lean mixture. Stable ignition and combustion are possible even with a dilute mixture of up to 20:1.

As described above, the present invention enables complete premixing of combustion gas and air to conditions close to the lower limit of flammability (fuel-lean mixture), and uses radiation in the combustion chamber to achieve low-temperature complete combustion. This has the effect of achieving low NOx combustion for food drying when the NOx concentration in the combustion exhaust gas is extremely reduced to about 1 ppm on average.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a burner device showing an embodiment of the present invention, and FIGS. 2 to 4 show various flame holding devices for selecting flame holding characteristics, each of which is a stable flame holding device. FIG. 2... Air inlet duct, 3... Mixer section, 4... Cylindrical container, 5, 6... Partition wall, 8
... Bench lily, 9 ... hole, 10 ... duct,
12... Backfire prevention trap, 14... Orifice plate, 16... Combustion chamber, 18... Orifice, 20... Flame stability holding device.

Claims (1)

[Claims] 1. A fuel gas and a large amount of combustion air for diluting the gas to conditions close to the lower limit of flammability are separately supplied into a mixer section equipped with a plurality of ventilates, and each Premixing is carried out by a ventilator, the mixed gas discharged from each ventilator is mixed homogeneously by a flashback prevention trap provided on the outlet side of this mixer section, and the completely mixed lean mixed gas is transferred to an off-loader equipped with a flame stabilization device. A method for low-temperature complete combustion of gas, which is characterized by passing through an iris plate, supplying the gas to a combustion chamber made of refractory material, and combusting it.The outlet of the combustion chamber is shaped like a tapered cone to stabilize combustion by utilizing radiation. . 2. A mixer section equipped with a plurality of ventilates 8, an orifice plate 14 having a plurality of orifices 18 each equipped with a flame stability holding device 20, and a combustion chamber surrounded by a heat-resistant material provided on the outlet side of the orifice plate. 1
6, the mixer section is equipped with an air inlet duct 2 and a fuel gas supply duct 10 connected to each ventilary, and the mixer section is equipped with an air inlet duct 2 and a fuel gas supply duct 10 connected to each ventilary, and the mixer section is equipped with an air inlet duct 2 and a fuel gas supply duct 10 connected to each ventilary, and the mixer section is equipped with an air inlet duct 2 and a fuel gas supply duct 10 connected to each ventilary, and the mixer section is equipped with an air inlet duct 2 and a fuel gas supply duct 10, which are connected to each ventilary, and the mixer section is equipped with an air inlet duct 2 and a fuel gas supply duct 10, which are connected to each ventilary. A flashback prevention trap 12 is provided between the mixer section and the orifice plate to completely stir the mixed gas premixed by each ventilate, and completely stirred gas is jetted from each of the plurality of orifices. This low-temperature complete combustion device for gas is characterized in that the outlet on the opposite side of the orifice plate 14 has a tapered conical shape in order to eject combustion into the combustion chamber and to measure combustion stability.