JPS60117021A - Air-fuel ratio controlling method for combustion furnace - Google Patents

Abstract

PURPOSE:To prevent an occurrence of excess or shortage of oxygen in a combustion furnace by a method wherein a part of fuel gas is divided to flow and a supplying volume of gas containing oxygen to be supplied to the combustion furnace is controlled on the basis of the rate of inclusion of methane in the gas generated under a reaction of methanation. CONSTITUTION:Hydrogen, carbon monoxide, methane and other light hydrogen carbide are contained as major heat generating constituent and each of the rate of inclusion of each of the constituents is varied as time elapses. Fuel gas is divided to flow under a predetermined rate of divisional flow, is guided to a measuring methanation reactor and reacted there. Then, moisture is removed from the outlet gas of the reactor, a rate of inclusion of methane in the generated gas is measured. Volume of gas before and after methanation is also measured. A volume of gas including oxygen to be supplied to the combustion furnace is adjusted in anticipation of a safety factor on the basis of the measured value.

Description

DETAILED DESCRIPTION OF THE INVENTION (Purpose and Background) The present invention relates to a method for controlling the air-fuel ratio of a combustion furnace, in particular, a combustion furnace containing hydrogen, carbon oxide, methane and other light hydrocarbons as main exothermic components, and The present invention relates to a control method for maintaining an optimum air-fuel ratio in a combustion furnace using a gas whose ratio varies over time.

Examples of gases that contain hydrogen, carbon oxides, methane, and other light hydrocarbons as main exothermic components, and whose contents vary over time include refinery offgas and PSA (PressureSwing Adsor).
ption) T7 gas, etc.

When such fuel is used for combustion at a constant air-fuel ratio, in some cases there is insufficient oxygen for the fuel, resulting in incomplete combustion, and in other cases, there is an excess of oxygen for the fuel. This increases the heat loss carried away by the exhaust gases, which in both cases reduces the energy efficiency of the fuel and increases the likelihood of harmful gases such as carbon oxides or nitrogen oxides being generated.

In order to maintain optimal combustion conditions using fuel and air with a stable Mt composition, it is sufficient to measure the residual oxygen content in the combustion exhaust gas and control the air-fuel ratio to keep it at a constant value. If the composition changes significantly over time, the operation is the opposite of what is actually required. Even though the flow rate m has been increased or the fuel supply amount has been decreased, there is a possibility that the flow rate m has already changed and the required amount of oxygen has decreased. .

In such cases, the commonly considered control methods are:
The required amount of oxygen is calculated by constantly measuring the content of fuel residue components, such as H2, GO, methane, and other hydrocarbons**.If the oxygen-containing gas composition changes, the oxygen concentration is also constantly measured to optimize the The purpose is to calculate the air-fuel ratio and change the supply amount of fuel gas or nitrogen-containing scum based on the calculated air-fuel ratio. In this way, ideal control can be performed, but this method uses various expensive analytical equipment such as infrared analyzers and high-performance computers to quickly analyze the fuel composition. It is necessary to process the data and operate it without time lag. The present invention provides a method of controlling the air-fuel ratio to maintain optimal combustion conditions without using such expensive equipment.

(Structure) That is, the present invention provides a combustion furnace that uses a gas as a fuel that contains hydrogen, carbon oxide, and methane and other light hydrocarbons as main exothermic components, and discharges a gas whose content varies over time. The air-fuel ratio of the combustion furnace is controlled by controlling the amount of oxygen-containing gas supplied to the combustion furnace based on the methane content in the gas generated by diverting a part of the fuel gas and performing a methanation reaction. This is a control method.

More specifically, the present invention provides hydrogen, -carbon oxide,
Oxygen groups necessary for combustion of a gas containing methane and other light hydrocarbons as main exothermic components and whose content varies over time are caused to perform a methanation reaction on a part of the gas. The principle is that the methane in the gas produced by this process is approximately replaced by the oxygen groups necessary for combustion.Then, by controlling the air-fuel ratio based on the result, the excess oxygen in the combustion furnace can be reduced. Shortages can be prevented.

First, the principle will be explained below. It is assumed that the following reaction proceeds within the methanation reactor.

3H2+CO shout CH4+H20 (1) 4H2+CO2mcH4+2H2C) (2) (2n-
m/2) H2+CnHmmnCH4 (3) The number of moles of oxygen required to burn the composition on the left side of each equation and the composition on the right side is the same.

(1) Second left side 3H2+3/2 ・02 m3H20 Co + l/2 @ 02 mcO2 total 202 (1) Right side CH4+ 202 m C02+ 2 H20 (2) Second left side 4H2+202 m4Hz 0 (2) Second right side CHA +202 m CO 2,000 2 H20 (left side of formula 39 (2n-m/2)H2+ (n-m/4)0 2 scream
(2+1-11/2)H20CnHm+(n+m/4)
Oz m'on CO2+ (11/2) H20 people,
Shiri 10- Right-hand side of equation (3) ncH4+2 no2mncO2+2 nH2O As shown above, if the reaction proceeds completely to the right-hand side in each equation (1), (2), and (3), oxygen is required for the generated methane. The required amount of oxygen in the fuel gas can be expressed by the amount.

However, in an actual methanation reaction, a chemical equilibrium exists in each of the above equations, and hydrogen, carbon monoxide, and the like do not completely turn into methane. However, even if a small amount of hydrogen or carbon monoxide remains, the amount of oxygen corresponding to that amount is 5%, which is the oxygen excess rate usually adopted when performing combustion.
Coverage ranges from 20% to 20%. λ is determined based on the methane content in the residue produced by the f-methanation reaction, rather than determining the required amount of oxygen from chemical theory based on the methane content. This means determining the required amount of oxygen by taking into account the safety factor, including the problems of oxidation and performance of the methanation catalyst.

In order to reduce the time lag between the 4111:ii-' gas and the dregs burned in the combustion furnace, it is better to make the pipe line from the branch point to the methanation reactor for measurement as short as possible. The split flow ratio can be specified at the design stage, regardless of the capacity of the combustion furnace main body.
It is enough to make sure that you only get the following.

The fuel sludge separated in this way is led to a methanation reactor for measurement and reacted. Fill the reactor with a methanation catalyst]7. As the catalyst, any known catalyst may be used.

After removing moisture from this -III Sadakawa Reaction Apparatus 1 gas, the methane content in the produced residue was measured. The amount of residue before and after methanation is also measured. Based on this value, the amount of oxygen-containing gas supplied to the combustion furnace is increased or decreased, or the amount of fuel waste is increased or decreased, taking into account the safety factor as described above. This operation can be performed in real time by combining a methane analyzer and a computer that processes the data obtained by flow rate 1, and a flow rate regulating valve that is operated based on the calculation results.

Although the method for controlling the air-fuel ratio within a certain range in a combustion furnace has been described above, there are cases where the furnace temperature and the temperature of the heated object cannot be kept constant by this method alone. It is the fuel calorific value (K Cat
/ N m') changes, the temperature reached by the combustion scum changes and the heat transfer rate also changes, resulting in a change in the temperature of the heated body. Naturally, fluctuations in operating load also lead to changes in the temperature of the heated object. Therefore, consideration should be given to making corrections for this purpose using a computer program. This basically involves supplying waste with a certain amount of methane equivalent to the combustion furnace based on the methane content of the methane-converted waste, and controlling the temperature of the gas at the exit of the combustion furnace and the temperature of the heated object. It can be controlled by inputting it as correction information.

Example 1 A gas having the composition shown in Table 1 was obtained as a PSA off-scrap from a suiseki manufacturing process. The theoretical amount of oxygen required to burn 100 m3 of this gas was 39.9 m' (N T P,).

Table 1 Table 2 This residue was methanized at 0.3Kg/cm2G and 300℃ to remove moisture, resulting in 67 residues with the composition shown in Table 2.
．． Obtained 1m3. Gas thus obtained 67.1
The theoretical amount of oxygen required to burn methane in m' is 39
．． At 45m3 (NTP), the amount of oxygen required is 98.
9% is displayed, and there is still a margin of 4% even if the operation is carried out at the commonly used oxygen excess rate of 5%.

￥Example 2 Table 3 COG having the composition shown in Table 3 was subjected to PSA to recover hydrogen and the off-gas was used as fuel. This off-cass gold 0.3Kg/
A6 required to burn 100 tons of gas that has been methanized and dehydrated at cm2G and 300°C =)=”i++(
The fourth table shows the results of comparing A) with the oxygen required to burn only methane: 1 (B). Even when the difference is maximum (when COG is used as fuel as is), the ratio between the two is 92.6%, and if the recovery rate is within the normal range (70-80%), then the Oxygen needed to burn only methane! +:, CB) is approximately 99% of the amount of oxygen (A) required. In other words, it can be seen that the air-fuel ratio can be controlled by 19 degrees according to the law.

Table 4 (・Go jJ+, ) Below 1. As explained in detail, according to the method of the present invention, the methane content of the stubbled methane residue is simply measured, and based on that, a fuel whose composition changes over time is used to maintain optimal combustion conditions. The air-fuel ratio of the combustion furnace can be controlled. Furthermore, by roughly measuring the temperature of the combustion exhaust gas and adjusting the amount of fuel supplied accordingly, it is possible to maintain the heat generated by the combustion furnace at a constant level. Furthermore, the temperature of the heated object can be controlled to a predetermined value using the rolling load and the difference between the temperature of the heated object and the target I temperature as information.

Applicant: JGC Corporation Agent Patent Attorney Shoji Ao Asa

Claims (1)

[Claims] Mizuki, - In a combustion furnace that uses gas as fuel that contains carbon oxide, methane, and other light hydrocarbons as main exothermic components, and the content of each changes over time, a part of the fuel scum is diverted to produce methane. A method for controlling the air-fuel ratio of a combustion furnace, which comprises controlling the amount of oxygen-containing gas supplied to the combustion furnace based on the methane content in the scum produced by carrying out a chemical reaction.