JPH0633372B2 - City gas production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an improvement in a city gas production method.

(b) Conventional Technology City gas has various components depending on the manufacturing method, raw materials, etc. Natural gas, LP
It is a mixed gas of G (liquefied petroleum gas) and air, and other petroleum decomposition gas.

The composition of the petroleum decomposition gas includes hydrogen, carbon dioxide, carbon monoxide and the like. This is because the composition of the gas was like this in the era when gas was produced from coal in the early days of city gas supply, so it is inherited as it is even after the current raw material is changed to petroleum-based. Of.

The most widely used method for producing this petroleum-decomposed gas is the low-pressure cyclic method. In this method, a petroleum-based material is decomposed with steam to produce a gas. Since this decomposition reaction is an endothermic reaction, the amount of heat necessary for the reaction must be given. In order to supply this amount of heat, a heating period for heating the reaction furnace and a making period for producing gas are alternated. Therefore, gas production is intermittent, and since there is a purge period as an intermediate period, it is more efficient than continuous production (efficiency here means the total calorific value of the raw material and the total calorific value of the manufactured gas). Is bad).

Apart from this, there is a manufacturing method called continuous partial combustion method (usually called continuous partial combustion) that falls in the same category of petroleum decomposition gas, and it has been partially used for the production of city gas. With the recent conversion of raw materials from naphtha to LPG,
Since it has become possible to improve drivability and produce high-quality gas,
Recently, this method has been re-evaluated and is on the rise. This is because the amount of heat required for the endothermic reaction in gas production is obtained from the combustion reaction with oxygen in the air supplied simultaneously with the raw materials. That is, at the same time as the reforming reaction, a part of the raw material is burned in the same reaction furnace and used as fuel.
Therefore, the amount of heat used is less wasteful and more efficient than the cyclic type, and the difference is usually 6 to 10%.

The gas according to this method has a high specific gravity because the nitrogen gas contained in the air as the oxygen source is mixed, and the combustion range (to be described later) is 4A, 4B, 5 having a slow burning rate.
Many belong to A, 5B, etc.

Also, in order to improve efficiency recently, LP is added to the manufacturing gas (the gas on the outlet side of the raw material decomposition reaction furnace, not the final supply gas).
A process called heat quantity adjustment for mixing raw gas of G (liquefied petroleum gas) and air is provided after the conventional manufacturing process. Conventionally, since the calorific value of the manufacturing gas is low, the LPG is only used to increase the calorific value to a predetermined value.
However, the heat amount adjustment is to adjust the heat generation amount by mixing LPG in an amount equal to or more than a predetermined heat generation amount and by mixing air therein. This is because when a large amount of raw gas of LPG is mixed, the LPG itself does not react and remains in the supply gas as it is, and considering only that, the efficiency is 100%, which improves the efficiency. The greater the amount of LPG mixed, the higher the efficiency. However, in order to mix a large amount of LPG without significantly changing the properties of the gas, the specific gravity of the gas must be made smaller than in the past. This is because the specific gravity of LPG and air is larger than that of the production gas, so that the specific gravity of the supply gas becomes large.

As described above, the petroleum decomposition gas contains carbon monoxide due to its generation reaction. This is very harmful to the human body and causes so-called gas poisoning. Therefore, it can be said that the supplier's mission is to reduce the concentration of carbon monoxide as much as possible. Currently, most gas companies are equipped with carbon monoxide shift converters in their production facilities to reduce the concentration of carbon monoxide in the production gas through shift reactions. However, it is impossible to completely remove carbon monoxide or reduce it to the extent that it does not affect the human body, and it is currently impossible because of the balance between the cost for reduction and the gas charge. It is said that the concentration in the supply gas should be less than 6%.

However, even at this level, toxicity is still sufficient and it is still dangerous.

Under the circumstances as described above, the following points are requested of the gas company.

(1) We want to improve efficiency and reduce manufacturing costs.

Where there is a cyclic type manufacturing facility, we would like to switch the manufacturing method to a highly efficient continuous combustion system.

I want to increase the amount of LPG mixed as much as possible, regardless of the manufacturing method.

(2) From the viewpoint of preventing gas poisoning, we want to reduce the concentration of carbon monoxide as efficiently as possible.

(c) Problems to be Solved by the Invention In response to the above-mentioned demand, since the low-pressure cyclic system has low efficiency, it is necessary to be able to change to a highly efficient continuous part combustion, but this is impossible for the following reason. .

Among petroleum-decomposed gases, there is a large difference in the burning rate due to the difference in the components, and it is difficult to completely burn them in the proper state with the same gas appliance. Therefore, gas appliances
Each is manufactured exclusively and the usable gas is specified. The properties of gas are divided into several groups (called combustion range) by a constant coefficient, 4A and 4A, respectively.
The names are given as B, 5A, 5B, 6C, etc. This name is specified on each gas appliance and indicates whether it can be used. Then, each gas company clearly specifies the combustion range of its own supply gas, and each household uses a gas appliance suitable for it. Of course, it is very dangerous to use something that does not fit this. Therefore, changing this combustion range should be avoided as much as possible because all gas appliances in each home must be replaced or adjusted.

Recently, major city gas companies tend to switch from conventional petroleum-decomposed gas to natural gas, but in this case conversion and adjustment of household appliances and the like takes considerable expense and time.

However, even if the majority of the gas companies in Japan are almost impossible to change the normal production equipment or change the gas composition a little, the combustion range is not changed.

Therefore, it is not possible to change the equipment from low-pressure cyclic system with different combustion range to continuous combustion.

Regarding the increase in the amount of LPG mixed during the heat amount adjustment, as described above, increasing the amount of LPG increases the specific gravity and changes the flammability, so it cannot be introduced beyond the current level. Especially when the manufacturing method is not changed, it is completely impossible. This is a problem that is common to all types regardless of the cyclic system, the continuous part combustion system, and the like.

That is, it is impossible to reduce the specific gravity of the production gas unless the production method is changed. However, it is conceivable to reduce the specific gravity of the gas before mixing LPG, not the specific gravity of the production gas. For example, reducing carbon dioxide in the gas, reducing nitrogen if it is included, and adding hydrogen.

None of these methods are very costly and very impossible with current gas rates.

Next, regarding the gas poisoning of (2), it is necessary to reduce carbon monoxide as much as possible by a shift reaction.

However, this carbon monoxide converter causes the following metamorphic reactions, which are exothermic reactions (9.8 kcal /
mol).

CO + H ₂ O → CO ₂ + H ₂ Furthermore, it is said that its operation is very difficult because the catalyst is weak at high temperature. Also, the catalyst is often damaged. That is, the operation is performed according to the designed value, and if the temperature of the catalyst layer exceeds the allowable value, the catalyst is damaged and the operation must be stopped, and the cost is considerable. Therefore, the transformation rate is lowered a little and the temperature at the outlet side of the transformer is suppressed to operate. As described above, at present, very few places are completely operating with the capacity as designed. In particular, a low-temperature carbon monoxide shift converter using a copper-based catalyst can reduce the concentration of carbon monoxide on the outlet side, but its temperature control is difficult, and it is hardly used in city gas production facilities.

This low-temperature carbon monoxide transformer can reduce the carbon monoxide concentration on the outlet side to 1% or less, but when high-concentration carbon monoxide is introduced, the reaction heat is large and the heat generation in the transformer is high. Will damage the catalyst. Therefore, if it is used to further reduce the concentration of carbon monoxide, it usually must be passed through a high temperature carbon monoxide transformer, reduced in concentration to some extent, and then introduced into the low temperature transformer. Therefore, there is a drawback that the equipment cost becomes high and the operation becomes more complicated.

(d) Means for Solving Problems In view of such a situation, in order to improve the gas properties after production, the present inventor, in the carbon monoxide shift converter, decomposes methanol at the same time as the carbon monoxide shift reaction. The present invention has been completed, focusing on the fact that it suffices to cause the hydrogen generation reaction by the method described above.The feature of the present invention is that in a city gas production facility, methanol is added on the upstream side of the carbon monoxide shift converter. There is a point to introduce.

Here, the city gas production equipment is equipment for producing gas to be supplied as city gas, and it does not matter what kind of system it is. For example, various types such as a low pressure cyclic system and a continuous partial combustion system are conceivable.

Further, the carbon monoxide shift converter may be any one as long as it causes a so-called shift reaction in which carbon monoxide and steam react to form carbon dioxide and hydrogen.

Methanol having any purity may be introduced in any state.

When the catalyst layer of the shift converter has a multi-stage structure, it may be introduced in the intermediate portion or in both. Further, where there are multiple transformers, they may be upstream of any transformer.

(e) Operation Next, the operation when methanol is introduced on the upstream side of the carbon monoxide shift converter will be described. Methanol causes the following reaction by the carbon monoxide conversion catalyst.

CH ₃ OH + H ₂ O → CO ₂ + 3H ₂ This reaction is an endothermic reaction (11.8 kcal / mol). This reaction and the above-mentioned carbon monoxide conversion reaction occur at the same time, exchanging heat with each other, and both do not adversely affect others. In addition, since a large amount of hydrogen is produced by this methanol decomposition reaction, the gas at the outlet of the shift converter has a high hydrogen concentration as a whole, the specific gravity is lowered, and the properties are improved. Of course, it does not generate any components that must not be mixed as city gas.

In other words, the transfer of this amount of heat consumes the surplus amount of heat generated by the shift reaction by the methanol decomposition reaction,
This means that the temperature rise is prevented, and it is possible to make the temperatures of the carbon monoxide inlet and outlet exactly the same. Therefore, it can be operated throughout at the temperature where the efficiency is highest in calculation or experience (transformation rate and reaction rate).

Of course, it is not necessary to strictly control the temperature in such a manner, and the conventional drawbacks can be greatly reduced by mixing an appropriate amount of methanol. In this way, the mixing of methanol has the unique advantages of improving the properties of gas and facilitating the operation of the carbon monoxide shift converter.

(f) Example FIG. 1 is a schematic flow sheet showing an example of the present invention. Methanol (3) is mixed at the outlet side of the reaction furnace (2) of the continuous-part combustion type production apparatus (1) using butane as a raw material, and the mixture is introduced into the carbon monoxide shift converter (4). The gas on the outlet side of the shift converter (4), that is, the shift gas, is heated by mixing LPG in the enrichment box (5), and then air is mixed in the mixer (6) to adjust the calories, and the gas holder ( (Not shown).

Table 1 shows the properties of the produced gas on the outlet side of the reactor in this example. Furthermore, the gas properties after this production gas was transformed by a carbon monoxide shift converter (transformation rate is 70%), the post-transformation gas was heated with butane to a prescribed heating value (here 4500 kc
The property of the gas adjusted to al / Nm ³ ) (the amount of heat is not adjusted by mixing air as described above) is also shown. Table-
2 shows the properties of the gas on the outlet side of the shift converter and the heat-up gas when methanol was introduced before the carbon monoxide shift converter in an amount such that the heat amounts of the carbon monoxide shift reaction and the methanol decomposition reaction were balanced.

Further, FIG. 2 shows various combustion ranges, and as is clear from the figure, the combustion range is WI and CP.
It is decided by. The WI and CP are calculated by the following equations.

Here, H, CO, CmHn, and CH ₄ are the mole fractions of hydrogen gas, carbon monoxide gas, hydrocarbons other than methane, and methane gas, respectively. K is a coefficient determined by the oxygen concentration, and is set to 0.99 when oxygen is 0 (zero) and 1.14 when it is 5%.

Then, WI and CP are calculated, plotted on FIG. 2, and if a certain combustion range is entered, the gas is properly burned by the gas appliance for that combustion range.

(g) Effects of the Invention In the cyclic manufacturing method described above, most of the places where the supply gas calorie is 4500 kcal / Nm ³ are 5C,
It is not possible to supply the gas (indicated by point P ₁ ) by continuous combustion without changing the combustion range. However, if the gas of the method of the present invention for introducing methanol shown in Table 2 is:
It has a small specific gravity and is well within the range of 5 C (P ₂ ). That is,
This means that the manufacturing method can be changed from the cyclic method to the highly efficient continuous combustion method without changing the conventional combustion range of 5C.

Of course, the present invention is not limited to 5C, and it is possible to change from a cyclic type manufacturing gas having a small specific gravity to a continuous part combustion type manufacturing gas having a large specific gravity. Therefore, it is possible to change the manufacturing method from the cyclic method to the continuous combustion without changing the combustion range.

In addition, as is clear from Table 1 and Table 2, the specific gravity of the gas on the outlet side of the transformer is reduced by about 10%. For this reason, the amount of LPG mixed becomes larger than before,
Will be satisfied.

Further, regarding the problem (2) of the amount of carbon monoxide, since the carbon monoxide transformer can be operated easily, the carbon monoxide transformer can be operated at its full capacity, which can be greatly reduced.

Further, it is possible to easily operate a low-temperature carbon monoxide transformer which is difficult to operate at present and is not provided. Conventionally,
Although carbon monoxide could not be reduced to 1 to 3% unless a high temperature carbon monoxide transformer and a low temperature carbon monoxide transformer were used together, according to the present invention, only a low temperature carbon monoxide transformer can be operated. This is because the disadvantage that the temperature control of the low temperature transformer is difficult is solved.

According to this method, the required cost is low, the concentration of carbon monoxide can be reduced, and the requirement (2) is satisfied.

As described above, the present invention is a very useful invention that solves the matters currently requested by city gas companies.

[Brief description of drawings]

FIG. 1 is a schematic flow sheet showing one embodiment of the present invention, and FIG. 2 is a graph showing a combustion range. 1 …… Continuous section combustion type manufacturing equipment 2 …… Reactor 3 …… Methanol 4 …… Transformer 5 …… Enrich box 6 …… Mixer

Claims (3)

[Claims] 1. A method for producing city gas, characterized in that in the city gas production facility, methanol is introduced upstream of the carbon monoxide shift converter. 2. The method for producing city gas according to claim 1, wherein the city gas production facility is of a low pressure type. 3. The method for producing city gas according to claim 2, wherein the city gas production facility is of a continuous partial combustion system.