JPS61138526A - Tubular furnace - Google Patents

Abstract

PURPOSE:To make a furnace small size and light weight by providing a heating space wherein the combustion gas of down flame type burners provided to the ceiling surface of the heating furnace moves downward, and >=2 rows of tube groups comprising many tubes of vertically heated tubes in the heating space. CONSTITUTION:For example, combustion gas at high temp. such as 1,100-1,200 deg.C flows between many numbers of vertically heated tube groups 17 arranged to >=2 rows each aligned to a straight line, and transmits heat by mainly radiation to the heated tubes 17 from down flame burners 16 arranged to the surface of the ceiling 13 of a heating furnace 11. On one hand, feed gas for reforming which has been preheated and fed from a feed pipe 21 provided with fins connected to said heated tubes 17 is reformed to the gas having a composition suited to the final target product (e.g. NH3) while rising upward through the heated tube 17b, by the effect of heat transmitted during rising and the catalytic effect of a catalyst packed in the heated tube 17.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a tube heating furnace in which a process flow flows through a tube interior space and is chemically changed by heat supplied mainly by radiation from outside the tube.

[Technical background 1 Tubular heating furnaces are used to produce raw material gas for ammonia synthesis and methanol synthesis, hydrogenation gas in oil refining and petrochemical industries, reducing gas for metallurgy, and other uses. Gaseous mixtures based on hydrogen and carbon monoxide are produced on a large scale by steam reforming of feedstock hydrocarbons.

Since steam reforming is a high temperature reaction and the required amount of reaction heat is extremely large, it is extremely important that the energy economic performance of a tube heating furnace for steam reforming reactions be improved.

Tubular heating furnaces for steam reforming reactions are large in size and use a large amount of expensive materials with 8 refractory resistance. It needs to be downsized.

C.Object of the Invention] An object of the present invention is to provide an improved tube heating furnace for steam reforming reactions that meets these demands.

[Prior art] A heat recovery object such as a wire mesh with appropriate ventilation is installed between the object to be heated and the combustion gas outlet in the heating furnace, and the heat recovery object absorbs the amount of heat held by the combustion gas. There is a method of utilizing radiant heat from a heat recovery object heated to a high temperature for heating an object to be heated, that is, an invention disclosed in Japanese Patent Publication No. 55-25353.

[Components of the invention The above-mentioned prior art is utilized in this invention.

In this invention, a haze type burner is arranged on the ceiling surface of a heating furnace, and a heating space is provided in which the combustion gas of the haze type burner descends. Optionally, swirling flame/wall burners are also disposed on the inner surface of the furnace side walls surrounding the sides of the ha thermal space.

In the heating space, two or more rows of heating tube groups are arranged, each of which is a group of vertical heated tubes arranged in parallel on a straight line perpendicular to its axis.

A predetermined volume for the heating space is secured, and the bottom of the heating space is made of air permeable solid material, with the lower portion of each vertical heating tube passing through at a height close to the lower end of each vertical heating tube. The floorboards are installed horizontally. A waste heat recovery space within the heating furnace is defined by the bottom plate, and below the bottom plate, a waste heat recovery space is formed between the bottom plate and the bottom surface of the heating furnace. In the waste heat recovery space in the heating furnace, a plurality of finned supply pipes are arranged in parallel with each other, to which the lower ends of the vertical heated pipe groups are connected in each row.

However, if the desired amount of heat transfer can be obtained with just the tube, it is not necessary to add fins to the tube. These finned supply pipes are connected to the main supply pipe in a state where they intersect at right angles at their respective central portions.

If desired, the bottom plate of the heating space made of air-permeable solid material is provided by a portion of the periphery of the fins of the finned supply pipe or by a portion of the fin of the finned supply pipe extended as a bearing. supported. The fins of the finned supply pipe are attached to the supply pipe along the flow direction of the combustion gas in order to evenly distribute the flow of the combustion gas in the waste heat recovery space.

If desired, the bottom plate that partitions the heating space and the waste heat recovery space in the heating furnace is thickened within a limit that keeps the flow resistance of combustion gas flowing through the bottom plate within an allowable range. A heat exchanger made of thin tubes is embedded inside, increasing the rigidity of the bottom plate and ensuring the shape of the bottom plate in a high-temperature atmosphere. The constituent material of the bottom plate is a multi-layered product such as a porous molded product or a mesh made of ceramic or refractory metal, but the tube heating furnace of this invention is a large furnace, and the bottom plate is made of combustion gas dust. The danger of clogging of the booth holes is that the pressure of combustion gas that the bottom plate receives is large, so the thickness of the bottom plate should be within the range of 5 to 100I, the average diameter of the booth holes should be within the range of 0.5 to 201. This can be prevented by setting the porosity of the bottom plate within the range of 60 to 99%.

In the case of porous molded products, thin layers such as honeycombs, which have openings of the same or similar shape arranged evenly, are superimposed in multiple layers with each opening being mismatched, and are called net-like products. In this case, multiple layers or more are layered with mismatched mesh openings, and the bottom plate is designed to minimize the obstruction of gas flow and make it difficult for radiation to pass through. Ru. In addition, the bottom plate extends in a direction substantially perpendicular to the direction of flow of combustion gas, is arranged in a state in which it is difficult for radiation to pass through in the direction of flow of combustion gas, and contains heat exchange media that are parallel to each other. It can be composed of a group of tubules. In this case, in order to promote the flow of the heat exchange medium within the capillary tube group, it is preferable that the capillary tube group be given a slight inclination of 0 degrees or less.

The tube-type heating furnace of the present invention has a heating space in which gastritis-type burners are arranged on the floor by being turned upside down, and combustion gas from the gastritis-type burners rises, and two or more linear rows are arranged in this heating space. A large number of vertical heated tubes arranged in a row,
A heating space ceiling plate made of air permeable solid material extending horizontally to a height close to the upper end of each vertical heated tube and penetrated by the upper part of each vertical heated tube; Waste heat recovery space formed between the ceiling plate and the top surface of the heating furnace,
A group of finned supply pipes are arranged in parallel in the waste heat recovery space and the upper ends of the vertical heated pipes are connected in each row, and these finned supply pipes are connected at right angles to each other at the center of the pot. Of course, it can be modified to a type having a main supply pipe.

In order to further facilitate understanding, the apparatus of the present invention and its functions will be explained using figures. FIG. 1 is a vertical cross-sectional view of the entire heating furnace, in which high-temperature combustion gas of, for example, 1100 to 1200° C. is aligned in a straight line from a haze type burner 16 disposed on the ceiling surface 13 of the heating furnace 11. While flowing downward between two or more rows of multiple vertical heated tubes (groups) 17,
Heat is applied to these heated tubes 17 mainly by radiation.

On the other hand, in the heated pipe 17, preheated reforming raw material gas from a finned (reforming raw material) supply pipe 21, which will be described later, connected to these pipes rises, and the given heat and Through the catalytic action of a catalyst (not shown) filled in these heated tubes, the gas is reformed into a gas having a composition corresponding to the final target product (for example, ammour). The generated reformed gas exits each heated pipe, passes through the manifold 20, and collects in the outlet pipe 19.
It is guided to the next process equipment (for example, a second reforming furnace). The combustion gases descending between the vertical heated tubes 17 reach the breathable solid base plate 18 of the present invention disposed near the lower ends of the tubes, and while passing therethrough, The high temperature heat of, for example, 1000 to 1100°C is applied to the bottom plate, and the temperature of the combustion gas is significantly lowered. The degree of the drop is, for example, about 100° C. in the case without the bottom plate 18, but it drops even further to reach 400° C. This degree greatly depends on the properties of the bottom plate 18,
It is appropriate for the various conditions to be within the ranges mentioned above, but from a comprehensive viewpoint such as technical and economical aspects, the thickness of the bottom plate should be 10 to 30 mm, and the average diameter of the small holes should be 1 to 31 mm.
1. It is particularly desirable that the porosity be 85 to 90% and that the material be ceramic.

Under these conditions a temperature drop of approximately 200°C is obtained. Thermal sound corresponding to this temperature drop is transmitted from the bottom plate 18 to the heated tubes (group) 17 again by radiation. The combustion gas that has passed through the bottom plate 18 passes through the furnace bottom 15 and reaches the combustion gas outlet 24 while entering from the reforming raw material supply clay pipe 22 and passing through the finned supply pipe 21 to each heated pipe (group) 1.
Preheat the reforming raw material supplied to Step 7.

FIG. 2 is a horizontal sectional view of the furnace bottom 15 of FIG. 1, showing the arrangement relationship between the main reforming material supply pipe 22 and the finned supply pipe 21. The main supply pipe 22 is arranged at the center of the furnace bottom 15, and the finned supply pipes 21 connected to each row of the heated tubes 17 are branched from the main pipe 22 horizontally in a straight line to the left and right. Each fin is provided to improve heat reception by radiation from the bottom plate 18 and heat transfer from combustion gas to each supply pipe.

FIG. 3 shows a horizontal section of the bottom of the furnace when the finned supply pipe is meandering. In this case, since the branched finned supply pipe is long to each vertical heated pipe 11 connected to it,
The amount of heat transferred by the combustion gas, that is, the amount of heat recovered, increases.

FIG. 4 is a sectional view of the furnace bottom in FIGS. 2 and 3, perpendicular to the axial direction of the finned supply pipe, and shows an example of how the fins are attached and how the bottom plate 18 is supported. As a result, each fin has the effect of evenly dividing the flow of combustion gas within the furnace bottom 15.

"Effects of the Invention" The effects brought about by manufacturing the heating furnace according to the present invention and using the manufactured heating furnace are as follows.

First of all, regarding manufacturing, 1) uniform heat flux is obtained, making it possible to design with high heat flux, and 2) the exit temperature of combustion gas is lower than before, so the design conditions for gas passages are relaxed, etc. This makes it possible to design a compact, lightweight, and economical heating furnace.

The effects of use are as follows: 1) Under the same combustion conditions, more heat is given to the vertically heated tubes by radiation from the bottom plate than in the past in the furnace, so heating fuel corresponding to this amount is saved. (Improvement in basic unit) 2) By providing a breathable solid bottom plate, the flow of combustion gas in the furnace is improved in terms of heat transfer and temperature distribution than before.

3) By installing a preheater for the reforming raw material in the combustion gas furnace bottom passage, more heat can be recovered than before.

[Brief explanation of drawings]

FIG. 1 is a vertical section of the entire furnace. 11: Heating furnace (whole), 12: Behind the ceiling, 13: Ceiling surface,
14: Furnace inside, 15: Furnace bottom, 16: Burner, 1γ:
Vertical heated pipes (group), 18: Breathable solid bottom plate, 19
: Reformed gas outlet pipe, 20: Reformed gas outlet manifold,
21: Fined supply pipe, 22: Reforming raw material supply main pipe,
23: Combustion air supply pipe, 24: Combustion gas outlet, Fig. 2,
FIG. 3 is a horizontal sectional view of the bottom of the furnace. 11: Vertical heated tube (group), 21: Fined supply pipe, 22: Main reforming material supply pipe, 25: Heat insulating material (castable or ceramic). FIG. 4 is a vertical sectional view of the bottom of the furnace. 17: Vertical heated pipe(s), 18: Breathable solid bottom plate, 21: Fined supply pipe, 26: Fin, 27:
pillar,

Claims (1)

[Scope of Claims] A heating space in which descending flame type burners are arranged on the ceiling surface and the combustion gas of the flame descending type burners descends, and two or more rows or more are arranged linearly in this heating space. a group of multiple vertical heated tubes; the bottom of a heating space made of a permeable solid material extending horizontally to a height close to the lower end of each vertical heated tube and penetrated by the lower portion of each vertical heated tube; A floor plate, a waste heat recovery space formed below this bottom plate between this bottom plate and the bottom surface of the heating furnace, and a waste heat recovery space that is arranged parallel to the waste heat recovery space, with the lower ends of the vertical heated pipe groups arranged in each row. A tube heating furnace characterized by having a group of connected finned supply pipes, and a main supply pipe connected to the finned supply pipes so as to intersect at right angles at the center of each of the finned supply pipes.