JPH0686598B2 - High calorific city gas production method - Google Patents

Abstract

In the process of producing high calorie SNG type city gas from hydrocarbonic crude gas, e.g., butane, propane, naphtha etc., an elementary feed gas is produced by using hydrodesulfurization as a first step, and then secondly further methanizing the product in a column. The hydrodesulfurization uses a nimox catalyst and a zinc oxide adsorbent. The desulfurized feed gas is further methanized on an alumina group carrier supported by nickel to obtain methane-rich gas, i.e. the elementary feed gas in a combined use type column. The necessary hydrogen to be fed into the hydrodesulfurization is obtained from a methanol/water mixture. This hydrogenizing reaction tube is combined within the same column above. Inorganic salt is used as a heat transfer medium heat-sourced in an external furnace and the heat transfer medium temperature branched into two system-flows are controlled by a three-way flow rate control valve simultaneously. The above reaction temperature is about 320<o>C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing high calorific city gas using hydrocarbons such as butane, propane and naphtha as raw materials.

[0002]

BACKGROUND OF THE INVENTION In the city gas industry in Japan, 13A (11,000 kca), which uses liquefied natural gas (LNG) as a raw material, is mainly used in large cities.
The high calorific value of city gas has been rapidly promoted into combustible gas (l / Nm ³ ). In this situation, the city gas utility is
Gas with the same composition as NG, or alternative natural gas (SNG)
The reason for the need is the nationwide integration into combustible gas of 13A, adjustment of supply and demand fluctuations of supplied gas, reduction of gas production cost, diversification of raw materials, and convenience and stable supply of city gas. Is the purpose.

Therefore, the performance particularly required for the SNG manufacturing process is that the start / stop / load change of the plant can be performed immediately and easily, the gasification efficiency is high and the quality is stable, and the plant is simple. It is a necessary condition that operability and economy are good.

[0004]

2. Description of the Related Art Conventionally, the means for producing SNG from hydrocarbon raw materials such as butane, propane and naphtha has been the activation of S in the raw materials + desulfurization of the raw materials + steam reforming of the raw materials + 1-stage methanation +2 Stage methanation + wet decarbonation +
It is the mainstream to carry out in about 8 steps of gas dehydration + LPG heat regulation. In the preceding stage, 5 steps are the raw material gas manufacturing step including the pretreatment of the raw material, 2 steps are the gas refining step, and the last step is the heat quantity adjustment step by increasing heat.

According to such conventional means, only in the production of the raw material gas, the container of 5 steps, the two heating furnaces, and the recycle gas compressor for boosting the hydrogen-containing gas for desulfurization are at least necessary. At the time of start-up, the start-up heating furnace and its temperature raising piping, and the equipment and operation of these auxiliary equipment, etc. are complicated, and there are many equipment, power and heat loss are large and manufacturing cost is high, so it is not economical, especially With regard to the mobility required for SNG performance, there is a problem that it takes at least 3 days to start the plant cold, about half a day to warm and a long time of 1% 1 minute or more for load change.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and is one column for methanation of hydrocarbon raw materials such as butane, propane and naphtha and hydrogenation of methanol. In each case, hydrogen for desulfurization and methane-rich gas are obtained in only one reaction step, which simplifies the equipment and improves gasification efficiency and quality stability. Particularly important is plant start / stop / load. The purpose is to obtain a method that can be easily changed in a short time of about 15 minutes.

[0007]

[Means for Solving the Problems] The technical means taken by the present invention to achieve the above-mentioned object is a methanation reaction in the production of a raw material gas for SNG using hydrocarbons such as butane, propane and naphtha as raw materials.・ The desulfurization reaction is carried out by an external heat system using a heating medium in order to speed up the temperature keeping and temperature control which are the reaction conditions of the catalyst, and its heat transfer. Specifically, Nimox is used for hydrodesulfurization. Using a one-body heat exchange type U-shaped desulfurization tower having a reaction tube filled with a catalyst and zinc oxide, a reaction different from the above hydrocarbon raw material while maintaining a temperature of about 350 ° C by circulating a heat medium on the shell side The hydrogen-mixed raw material added with hydrogen generated in the tower is converted to hydrogen sulfide (active sulfur compound) by reacting with hydrogen and the inactive sulfur compound in the raw material in the outward Nimox layer, and then sulfurized in the zinc oxide layer on the return route. Adsorbed as zinc A heat exchange shell-tube type reaction tower with a reaction tube filled with a methanation catalyst supporting nickel on an alumina-based carrier is used to remove sulfur compounds from the inside and perform steam reforming. By butane, propane and naphtha in each case 3
While maintaining temperatures of about 20 ° C, 315 ° C, and 330 ° C, the mixture of the desulfurized raw material and steam is allowed to react isothermally under specific reaction conditions in which one step is used to increase the reaction rate in one column through a catalyst. In order to directly generate a methane-rich gas and obtain hydrogen for hydrodesulfurization, a tube for a part of the above reaction tower is filled with a hydrogenation catalyst and used as a reaction tube in a separate channel, and methanol and water are used. The mixture is isothermally reacted under the specific reaction conditions in which the reaction rate is increased by one step at the same temperature as described above to directly generate the hydrogen-rich gas, and the optimum hydrodesulfurization and steam reforming are performed. to a temperature holding and temperature control, the rate of heat transfer large NaNO ₂ -NaNO ₃ - KNO
₃ A reforming system and a shunt that circulate using a three-component inorganic salt heat medium to absorb the heat of the exothermic reaction and supply the heat of the endothermic reaction to perform rapid heat transfer and reduce the accumulated heat in the catalyst layer. The desulfurization system is controlled by two heat medium circulation systems which can be adjusted to arbitrary temperatures via valves.

Regarding the means for refining the SNG raw material gas, the application of the applicant of the present application has already been filed.
A device for removing carbon dioxide and water in a methane-rich mixed gas, which has been published and publicly known as No. 96 (continuous flow PSA
Type decarbonation / dehydration device) is used.

As described above, the operation of the SNG consisting of the production of the raw material gas, the purification of the raw material gas and the adjustment of the heat quantity is simplified, the equipment is simplified, the gasification efficiency is improved and the production cost is reduced, and the entire plant is It is possible to start, stop, and change the load of each within 15 minutes.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The SNG manufacturing method of the present invention will be described in detail below with reference to the process flow shown in FIG.
Hydrocarbons such as butane, propane and naphtha as raw materials are boosted to a reaction pressure by a raw material pump 1 and heated and vaporized by a raw material preheater 2 and a raw material evaporator 3, and then a reaction tower 8 in a raw material / hydrogen mixer 4. Is mixed with the hydrogen-rich mixed gas generated directly in the raw material, and is then adjusted to a reaction temperature of about 350 ° C by the raw material superheater 5 to activate the S content in the raw material and to adsorb the S content in a one-body desulfurization tower. sent to 6, the non-active sulfur compound is hydrogenated reaction of hydrogen and in the raw material in Nimokkusu catalyst layer of the column in the inlet side pipe, sulfur is reduced to hydrogen sulfide _{(H 2 S) (H 2} + S
= H ₂ S). Next, the raw material gas containing this hydrogen sulfide reaches the zinc oxide layer in the tower outlet side pipe from the lower part of the tower, the hydrogen sulfide in the raw material gas causes a reaction of H ₂ S + ZnO → ZnS + H ₂ O, and is adsorbed in the form of ZnS. Adsorbed in the agent ZnO, the sulfur content in the raw material is removed.

As shown in FIG. 2, the desulfurization tower 6 has a heat exchange type shell tube type fixed tube plate structure, and the upper channel is divided into a gas inlet 62 and an outlet 63 by a partition plate 61 to form a U-shaped flow. A nimox catalyst 65 is filled in the inlet side tube (outward path) 64 of the partition forming the passage, and zinc oxide 67 is filled in the outlet side tube (return path) 66. The heat medium adjusted to a temperature of about 350 ° C. in the medium heating furnace 7 is passed between the baffle plates 70 in the upward direction,
Hold the catalyst at its activation temperature. In this case, the hydrogen-mixed raw material gas sent to the desulfurization tower 6 and the catalyst filled in the desulfurization tower are both controlled by the temperature control of the heat medium heating furnace 7 → raw material superheater 5 → desulfurization tower 6 in which the heat medium having a large heat capacity flows in series. The temperature is always constant. This temperature control is advantageous not only in the steady state but also when the plant is started up and the load is changed, and is a main factor that enables immediate start-up and immediate load change of the plant.

Since the conventional means is an internal heat type operated by the heat of gas, a difference is likely to occur between the temperature of this hydrogen-mixed raw material gas and the temperature of the catalyst, and this temperature control is difficult especially at startup, and the temperature is high. If it is too low, carbon-based precipitation problems occur, and if it is too low, the desulfurization reaction is not preferable. The present invention solves this problem by means of an external heating system using a heating medium.

Next, the two devices of the prior art, the Nimox tower and the zinc oxide tower, were integrated into one unit, and the surface area could be reduced, so that it was possible to reduce the amount of heat released from the desulfurization equipment, which has a great effect on plant efficiency. .

The desulfurized raw material leaving the desulfurization tower 6 is
After being mixed with steam in the steam mixer 9, and then adjusted to a reaction temperature of about 320 ° C. by the raw material / steam superheater 10, it is sent to the reaction tower 8 for steam reforming, and a one-step reaction rate is obtained. Under specific increased reaction conditions, an isothermal reforming (decomposition) reaction and methanation reaction are carried out through a highly active catalyst in which nickel is supported on an alumina-based carrier, resulting in a low CO content and a high CH ₄ content. Convert to high calorie gas.

The reaction is very complicated. First, a part of the hydrocarbon (explained with butane) is thermally decomposed by steam on the catalyst, and the reaction of C ₄ H ₁₀ + 4H ₂ O → 4CO + 9H ₂ produces CO. And H ₂ are produced. As gasification progresses, CO and H ₂ methanation and shift reactions occur,

[Chemical 1] This synthesis reaction is carried out in one step in one tower.

As shown in FIG. 3, the reaction tower 8 has a heat exchange type shell tube type fixed tube plate structure, and the reaction tube 81 is filled with the above-mentioned methanation catalyst 82, and is outside the tube 81 on the shell side. From the lower heat medium inlet 83, the heat medium having a temperature of about 320 ° C., which is split by the heat medium splitting control valve 11, is flown in the upper direction to keep the catalyst at the active temperature.

In this case, the desulfurized vapor mixed raw material gas sent to the reaction tower 8 and the catalyst 82 filled in the reaction tower 8 are both
The heat medium branch control valve 11 → reaction tower 8 → raw material / steam superheater 10 maintains a constant temperature due to the temperature control of the heat medium having a large heat capacity that is flowed in series. This temperature control is based on the desulfurization tower 6 described above.
As in the case of (1), it works particularly advantageously not only in the steady state but also when the plant starts up and the load is changed, and it is the main factor that enables immediate startup and immediate load change of the plant.

The reaction that takes place in the catalyst layer in the reaction tube 82 is complicated as described above, but in the reforming (decomposition) reaction, the endothermic reaction and the methanation reaction are exothermic reactions.
As shown by the solid line in FIG. 4, the temperature distribution in the axial direction within 81 drops once and then rises sharply, then is cooled by the heat medium and becomes almost the same temperature as the heat medium temperature.

The reaction gas (raw material gas) in the vicinity of the outlet of the reaction tower 8 is sufficiently cooled by the low temperature heat medium entering the shell side lower heat medium inlet 83 of the reaction tower 8 so that it should be kept at a low temperature. Therefore, the CH ₄ yield can be increased. This gas has a thermodynamically equilibrium composition, and this thermodynamic equilibrium composition is obtained by theoretical calculation, and as shown in FIG. 5, the CH ₄ yield is higher at lower temperatures.

On the other hand, the heat medium is fed from the lower part of the body as described above, flows through the baffle plates 84 shown in FIG. 3 in the upward direction, absorbs the heat in the tube side exothermic reaction zone, and becomes the highest. This time it reaches the endothermic reaction zone on the tube side. Here, conversely, heat is supplied from the heat medium to the tube side and exits from the upper part of the reaction tower body side. This means that when the heat carrier is heated in the exothermic reaction zone and reaches a high temperature, it then supplies the heat of the endothermic reaction. Since the temperature difference between the heat medium and the reaction gas is large in the heat supply in the endothermic reaction section, the heat transfer rate is high and the heat absorption is sufficient. That is, the endothermic reaction can be made sufficient.

In the process of the present invention, the one-step method can be adopted because the heat carrier can absorb a large amount of heat in the exothermic reaction zone. If a large amount of heat cannot be absorbed instantaneously, a 2- to 3-stage reaction system will have to be adopted. Actually, the above-mentioned conventional means is steam reforming +
The main stage is three-stage methanation + two-stage methanation, and a cooling device is provided between these stages to cool the reaction conditions, whereas the present invention integrates them. Since the number of devices can be reduced and the surface area thereof can be reduced, there is an effect that it is possible to reduce the amount of heat radiation from the device, which has a great influence on the plant efficiency, similarly to the desulfurization tower 6.

In the process of the present invention, a small amount of hydrogen for hydrodesulfurization described above is obtained by high-concentration hydrogenation of methanol in combination with the process in order to improve plant efficiency and facilitate start-up and load change. As shown in FIG. 1, methanol is pressurized to a reaction pressure by a methanol pump 12 and mixed with water deaerated in a methanol / water mixer 13, and then the mixture is heated and vaporized in a methanol evaporator 14. After that, the temperature is raised to about 320 ° C. in the methanol superheater 15 and sent to the reaction tower 8.

This reaction tower 8 is also used as the above-mentioned reaction tower 8 for performing steam reforming, and one part of the tube is filled with the hydrogenation catalyst 85 and used as a reaction tube 86 in another flow path. , A mixture of methanol and water is subjected to an isothermal hydrogenation reaction under the specific reaction conditions in which the reaction rate is increased by one step at the same temperature as in the steam reforming through a catalyst, and the CO and CH ₄ contents are small and H ₂ is reduced. It is converted to a gas with a large content (CH ₃ OH + H ₂ O → 3H ₂ + CO ₂ ).

As shown in FIG. 3, the reaction tube 86 has one tube of a heat exchange type shell tube type fixed tube plate structure which penetrates through the upper and lower channel parts to form separate flow passages and a hydrogenation catalyst 85 in the tube. It is the same as that of the methanation reaction tube 81 described above with respect to the flow path direction of the heat medium, temperature control, and advantages of starting up the plant, changing loads, and the like.

The reaction that takes place in the catalyst layer 85 in the reaction tube is
It is a reverse reaction of tanol synthesis, and it raises the temperature and lowers the pressure.
The higher the decomposition rate or reforming rate of methanol, the higher
Decomposition reaction (CH₃OH → 2H₂+ CO) endothermic
Reaction, shift reaction (CO + H ₂O → H₂+ CO₂)
Since it is an exothermic reaction and the endothermic reaction is dominant as a whole, the reaction
The axial temperature distribution in the tube 86 is uniform as shown by the solid line in FIG.
Decrease the heat supply from the heat medium
The temperature is almost the same as the inlet temperature of the medium. This much heat
Immediate supply of catalyst prevents catalyst temperature drop
Then, the reaction with high hydrogen yield is carried out in one reaction tube in one step.
You can

In the conventional means, one of the three gasification (methanation) means described above for obtaining hydrogen for hydrodesulfurization has a high temperature for the purpose of obtaining a methane-containing gas containing a relatively large amount of hydrogen. For this purpose, a reaction tower that reacts at
After cooling the part, the pressure is increased by a recycle gas compressor and recycled to the desulfurizer as a hydrogen mixed gas. In this case, the hydrogen content is about 10%, and the temperature of nearly 10% of the total gas generation should be lowered to near room temperature to overcome the pressure loss of 70% or more of all equipment. is there.

As described above, according to the means for obtaining hydrogen of the present invention, the large reaction tower of the first stage, the recycle gas compressor, and the heat for cooling the recycled gas and raising the temperature again are not always required, and more gas than is necessary. The very large power that compresses the fuel with low efficiency is converted into the slight power of the small amount methanol booster pump by efficiently generating the high-concentration hydrogen with the methanol of this means. In addition, the start-up of the plant and the change of load can be carried out almost immediately.

As described above, in the hydrodesulfurization and steam reforming, which are the main parts of the process of the present invention, the gas (hydrogen mixed raw material gas / steam mixed raw material gas) that maintains the optimum temperature of each catalyst and each reaction is carried out.・ Water and methanol mixed gas) are operated at the optimum temperature by using external heat from the heat medium of the inorganic salt.

The heat medium is HEAT TRANSFFE.
R SALT (HTS) is a molten salt, which is a eutectic mixture of sodium nitrite, sodium nitrate, and potassium nitrate. Like this process, it is a flow tube on the shell side of a reaction tower or heat exchanger at 320 ℃ ~ 350 ℃. In the case of promptly removing heat from the side and supplying heat, HTS has a heat transfer coefficient of about 50% higher than that of an OIL type heat medium generally used at 350 ° C or lower. Therefore, this advantage is also an important factor for realizing the method.

As shown in FIG. 1, the heat medium is boosted from a heat medium storage tank 16 by a heat medium pump 17 and is divided into two systems, a desulfurization system and a reforming system, by a heat medium distribution three-way control valve 11, and one desulfurization system is used. In the system, in order to adjust the desulfurization reaction temperature to about 350 ° C. in the heating medium heating furnace 7, the temperature is raised to about 352 ° C. and the raw material superheater 5, desulfurization tower 6,
Passes through the shell side of the secondary feed water heater 23 and supplies or absorbs heat to the tube side of each device (desulfurization tower only), 321 ℃
When the temperature reaches a certain level, it returns to the heat medium storage tank 16.

On the other hand, in the reforming system in which the heat medium branching 3-way control valve 11 is used for branching, the heat medium temperature at the time of branching is 32 times the reforming reaction temperature.
The temperature is adjusted to about 0 ° C, and heat is supplied or absorbed to the tube side of each device through the shell side of the reactor 8, the raw material / steam superheater 10, the raw material evaporator 3, and the methanol superheater 15 (reactor only). ), The temperature of 321 ℃ is reached and the heat medium storage tank
Return to 16.

As described above, it is necessary to control the heat medium circulations of the two systems at different temperatures to arbitrary temperatures, and as a means therefor, a reaction heat device (reaction tower or desulfurizer) in each system is used. And heat recovery equipment (evaporator, superheater, etc.) and heater (heat medium heating furnace) are properly arranged in the circulation system as described above, and the heat medium temperature of the two systems is returned to the heat medium storage tank 16. The desulfurization tower inlet heat medium temperature and the reaction tower inlet heat medium temperature, which are arranged so that there is no difference, are detected to detect the desulfurization system flow rate and the desulfurization system flow rate are adjusted by the heat medium shunt control valve 11 based on the temperature difference. Set the two desired temperatures by changing the diversion ratio of the mass flow rate. Next, the temperature of the desulfurization tower heat medium inlet is detected, and the amount of fuel in the heat medium heating furnace 7 is changed to balance the total heat of all processes.

This method of controlling the temperature of the heating medium is important for carrying out the optimum desulfurization reaction and reforming reaction, and also enables appropriate control even at the time of immediate start and load change and enables precise control. .

Regarding the method for producing SNG from a hydrocarbon raw material such as butane, propane and naphtha according to the present invention, in order to satisfy the performance (starting and load changing characteristics) originally required for the SNG process, the above-mentioned raw materials are required. In addition to the gas production process, a continuous flow PSA has been filed and published by the applicant of the present invention for a refining process for decarboxylation / dehydration
After performing the method (see Japanese Patent Laid-Open No. 2-281096), a series of manufacturing steps in which the amount of heat is adjusted with a hydrocarbon gas is performed. The continuous flow PSA method refining process is the same as the publicly known process already described in the publication, and therefore the description thereof is omitted here.

[0035]

EXAMPLE FIG. 7 shows a process flow of one example of the production of high calorific city gas, and Table 1 shows each numerical value of each stream number in the flowchart. In addition, in FIG. 7, 27 is a heat-increasing butane evaporator.

[0036]

[Table 1]

[0037]

The present invention has the following advantages because of the above configuration. (1) Since the hydrodesulfurization of the raw material is carried out in one column and the added hydrogen directly uses the high-concentration H ₂ obtained by reforming methanol, the equipment is simple, and the heat and kinetic energy required for this are very small. (2) Hydrocarbons such as butane, propane, and naphtha are methanated by gas phase catalytic cracking reaction in the presence of a catalyst in the reaction tower to produce a methane-containing mixed gas having a high methane yield in one step of the reaction means. You can get it. (3) In order to adjust the respective reaction conditions for hydrodesulfurization and steam reforming, the reaction is carried out externally using a heat medium with a high heat transfer rate, so the plant can be easily started and the load can be changed. . (4) The gasification efficiency is high because the number of devices is small and the reaction heat can be moved rapidly and the heat can be effectively recovered. (5) If the raw material gas is purified by the continuous flow PSA method, the operation becomes simpler, and the plant start / stop / load change (change range 100%) can be performed within 15 minutes each.

[Brief description of drawings]

FIG. 1 is a process flow chart of a method for producing an SNG raw material gas according to the present invention.

FIG. 2 is a diagram showing a schematic structure of a desulfurization tower.

FIG. 3 is a diagram schematically showing the structure of a reaction tower.

FIG. 4 is a diagram showing a temperature distribution in a catalyst layer during a butane methanation reaction.

FIG. 5 is a diagram showing a correlation between a reaction temperature of butane reforming and a yield.

FIG. 6 is a temperature distribution diagram in the catalyst layer during a hydrogenation reaction of methanol.

FIG. 7: S obtained by continuous flow PSA method for decarboxylation and dehydration
NG process flow diagram.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Natsuo Kinoshita 1-17-1 Chiyo, Hakata-ku, Fukuoka-shi, Fukuoka Within Seibu Gas Co., Ltd. (72) Inventor Kei Ota 1-1-17, Chiyo, Hakata-ku, Fukuoka No. 1 in Western Gas Co., Ltd. (72) Inventor Haruji Kawasaki 1-17-1 Chiyo, Hakata-ku, Fukuoka City, Fukuoka Prefecture In West Gas Co., Ltd. (72) Inventor Akira Nishino 22-64, Kotobuki, Abiko, Chiba Prefecture

Claims (2)

[Claims] 1. A hydrocarbon raw material such as butane, propane, naphtha, etc. is hydrodesulfurized to remove a sulfur content, and steam reforming (methanation reaction) is performed to generate a raw material gas, followed by decarboxylation / dehydration. In the manufacturing process of high calorific city gas (alternative natural gas), in which the calorific value is adjusted with hydrocarbon gas after purification by
To perform hydrodesulfurization, a one-body heat exchange system U-shaped desulfurization tower having a reaction tube filled with a nimox catalyst and zinc oxide was used, while maintaining a temperature of about 350 ° C by circulating a heat medium on the shell side. The hydrogen-mixed raw material was changed to hydrogen sulfide (active sulfur compound) by reacting hydrogen with the inactive sulfur compound in the raw material in the outward Nimox layer, and then converted to ZnS in the return ZnO layer to remove the sulfur content from the raw material. In order to perform steam reforming, a shell tube type reaction tower with heat exchange method having a reaction tube filled with a methanation catalyst in which nickel is supported on an alumina-based carrier is used. While maintaining the temperature, the mixture of the desulfurized raw material and steam is subjected to an isothermal reaction under a specific reaction condition of one step in one tower through a catalyst to directly generate a methane-rich gas to obtain hydrogen for hydrodesulfurization. To the above reaction A part of the tube of the tower was filled with a hydrogenation catalyst and used as a reaction tube in a separate flow path, and a mixture of methanol and water was isothermally reacted under the same reaction temperature under the specific reaction conditions of one step through the catalyst and enriched. In order to generate the hydrogen-containing gas directly and maintain the optimum reaction temperature for hydrodesulfurization and steam reforming, the heat of the exothermic reaction is circulated by using an inorganic salt-based heat medium with a high heat transfer rate to circulate. Absorb,
A method for producing a high calorific value city gas, characterized in that the heat of the endothermic reaction is supplied and the heat is circulated in two heating medium circulation systems which can be adjusted to an arbitrary temperature. 2. The method for producing high calorific gas according to claim 1, wherein a continuous flow PSA method is used for decarbonation / dehydration in refining the raw material gas.