JPH0240280B2 - - Google Patents

Description

[Detailed description of the invention]

A. Object of the Invention A. Field of Industrial Application The present invention relates to a method for producing low-calorie city gas from raw material hydrocarbons through a low-temperature steam reforming reaction. B. Prior Art The conventional method for producing low-calorie city gas from raw material hydrocarbons is a high-temperature steam reforming method, that is, a production method at 650° C. or higher. This production method is a violent endothermic reaction due to the high temperature reaction, and to promote the reaction, heat is supplied to the reactor from the outside by a direct method or a heat storage method. The direct method is a direct external heating method with a medium-high pressure, i.e., 2 Kg/cm ² G or more, and a reaction temperature of 650 to 800°C, and the heat storage method is a discontinuous method with a low pressure, i.e., 2000 mmH ₂ O or less, and a reaction temperature of 650 to 800°C. (usually called the cyclic method). On the other hand, the conventional low-temperature steam reforming method produces high-calorie city gas whose main component is methane, i.e.
The purpose is to produce city gas of 11,000 kcal/Nm ³ . The present invention deals with low-temperature steam reforming reaction, that is, reaction temperature
This is a method for producing low-calorie city gas at 550 to 450°C.It is a method of reforming the raw material gas by giving the necessary heat for the reaction from the outside using an indirect continuous heating method. Even when converting gas to high-calorie city gas, equipment can be easily repurposed. C. Problems to be solved by the invention As mentioned above, in the conventional method for producing low-calorie city gas, the reaction is at a high temperature of 650°C or higher.
In the case of direct external heating method, the reactor contains HK-40,
It is necessary to use high-grade materials such as Inconel,
In the case of the cyclic method, the reactor must be lined with high-temperature refractory bricks. These high-grade materials require complicated operation management, maintenance management, etc., resulting in the problem of increased costs. Furthermore, the gas produced by the conventional production method contains 4 vol% or more of carbon monoxide, which is harmful to the human body. Furthermore, if we switch to producing high-calorie city gas using low-temperature steam reforming in the future, it will be impossible to repurpose the high-temperature reaction city gas production equipment.
New manufacturing equipment will need to be installed. Furthermore, since the cyclic production method uses low pressure, a pressure transfer machine is required to supply city gas to consumers, and there are problems such as the power cost of this machine occupies a large proportion of the gas production cost. The purpose of the present invention is to reduce the material cost and management cost of the reactor, reduce the carbon monoxide concentration to 2 vol% or less, and facilitate the conversion to high-calorie city gas production in the future. B. Structure of the Invention A. Means for Solving the Problems The present invention is a method of converting feedstock hydrocarbons such as methane, LPG, and naphtha into 3600~
A method for producing low-calorie city gas of 5000 kcal/Nm ³ , which includes a hydrodesulfurization step, a mixed gas of desulfurized raw material gas and water vapor, and a predetermined temperature, predetermined pressure, and predetermined supply rate. The process consists of a low-temperature steam reforming process in which the reformed gas is reformed by giving the same gas, a heat recovery process in which the heat of the reformed gas is recovered to a predetermined temperature, a dehydration process, a heat amount adjustment process, and the like. The hydrodesulfurization step includes a hydrogenation step in which a gas containing hydrogen is mixed with the feedstock hydrocarbon, and the sulfur compounds contained in the feedstock hydrocarbon are hydrogenated to hydrogen sulfide, and the hydrogen sulfide in the feedstock hydrocarbon is It consists of a hydrogen sulfide removal process in which hydrogen sulfide is removed by adsorption, and the raw material hydrocarbon is desulfurized and becomes a raw material gas through the hydrodesulfurization process. For hydrogenation of sulfur compounds in the hydrogenation process in the first half of the hydrodesulfurization process, nickel, molybdenum or cobalt
A catalyst containing molybdenum is used. For example, NiO−MoO ₃ −Al ₂ O ₃ , CoO−
MoO ₃ -Al ₂ O ₃ etc., and is reduced during normal use. In addition, when mixing the produced gas through the recycling line, it is necessary to increase the hydrodesulfurization activity,
In order to suppress the methanation reaction between carbon monoxide, carbon dioxide and hydrogen, it is desirable to sulfurize the catalyst with hydrogen sulfide, carbon dioxide, etc. before use. The reaction temperature in the hydrodesulfurization step is 450°C or lower, preferably 410 to 250°C. At temperatures above 450°C, the rate of methanation reaction of carbon monoxide and carbon dioxide with hydrogen is large, resulting in a large temperature rise in the catalyst layer, causing a half-melting phenomenon of the catalyst. This may lead to problems with precipitation.
Further, if the temperature is lower than 250°C, the hydrodesulfurization activity is not sufficient. In order to particularly increase the hydrogenation activity of thiophene among sulfur compounds, the temperature is maintained at 300°C or higher, preferably 350°C or higher. As a method for removing sulfur compounds after hydrodesulfurization,
Any known method can be used. Examples include methods using solid adsorbents such as ZnO, Fe ₂ O ₃ , CuO, and activated carbon. The amount of hydrogen required to hydrogenate the sulfur compounds in the raw material hydrocarbon is sufficient if it is 0.08 to 0.25 moles or more per mole of hydrogen, and the necessary amount can be supplied from the production gas in the recycle line. The feed rate of the raw material in the hydrogenation step is preferably 0.5 to 200 h ^-1 in terms of space velocity (LHSV). If the space velocity is less than 0.5, the amount of catalyst used is large and it is uneconomical, while if it exceeds 200 h ^-1 , the hydrogenation activity will not be sufficient. The pressure in the hydrodesulfurization step may be 1 to 30 kg/cm ² G, but is not particularly limited. The higher the pressure, the higher the proportion of carbon monoxide and carbon dioxide methanation as side reactions. Next, the low temperature steam reforming process will be explained. As an example of the catalyst for causing the desulfurized raw material gas to undergo a reforming reaction with steam, it is preferable to use a catalyst containing a nickel-based or noble metal-based catalyst. For example, NiO
_-Al2O3 , NiO-La- _{Al2O3 , Ru} - _{Cr2O3 ,} etc., and are reduced during normal use. The ratio of water vapor and hydrocarbons is determined based on chemical equilibrium, firstly to prevent carbon precipitation, and secondly, under conditions that satisfy the calorie and combustibility of the city gas product. The weight ratio to carbon is preferably in the range of 1.0 to 5.0. The reforming reaction of hydrocarbons by steam is represented by the following three equations, among which the outlet composition is determined by the equilibrium of the equations. CmHn＋mH ₂ Om→mCO＋(m+n/2)H ₂ ……
(Thermal decomposition reaction) CO + H ₂ OCO ₂ + H ₂ ... (Shift reaction) CO + 3HCH ₄ + H ₂ O ... (Methanation reaction) The above reaction is a reversible reaction, and the lower the temperature, the more it progresses to the right. In order to obtain relatively low-calorie city gas, it is necessary to increase the hydrogen concentration in the gas to be reformed. Furthermore, the chemical equilibrium in the above equation is expressed by the following equation. PCO・PH ₂ O／PCO ₂・PH ₂ = Kps (-) ... PCO・(PH ₂ ) ³ / PCH ₄・PH ₂ O=Kpm (atm ² ) ... Therefore, to increase the hydrogen concentration, the pressure should be as low as possible. It is advantageous to increase the water vapor ratio. Regarding the reaction pressure in the operating conditions, there is no need to particularly consider it, since it is necessarily determined by the production gas delivery pressure in view of the relationship with operating costs. In the conventional high-temperature steam reforming method, the _H2 concentration is increased by setting the steam ratio to the lowest level that does not affect the activity of the catalyst and keeping the reaction temperature at a high temperature. ℃, and the water vapor ratio is controlled according to the need for H ₂ concentration. Normally, increasing the steam ratio reduces the thermal efficiency of the equipment and becomes uneconomical, but in the present invention, it can be sufficiently compensated for in the subsequent heat recovery process, and the thermal efficiency is equivalent to that of the high-temperature reforming method. can get. Also, in this temperature range, the carbon monoxide concentration is 2 vol%.
The following is true. The preferred inlet temperature for the low temperature steam reforming process is 550
~500℃. If the temperature exceeds 600℃, a melting phenomenon will occur due to the heat resistance of the catalyst, which is highly active in the low temperature range.
At temperatures below ℃, the ratio of water vapor to hydrocarbons becomes large and thermal efficiency decreases, making it uneconomical. The pressure may be 1 to 30 kg/cm ² G, but is preferably around 10 kg/cm ² G in relation to the delivery pressure. The mixed gas supply speed is at maximum load condition.
4800-10000Kg/ ^m2hr is preferred. Next, the dehydration process will be explained. In the dehydration process, moisture contained in the produced gas is removed by known water cooling, a freezing method using a refrigerant, a method using the cold energy of LPG used to adjust the amount of heat, or a combination thereof. Next, the heat amount adjustment process will be explained. The calorific value adjustment process reduces the calories of the produced gas.
Air or LPG to keep it below 5000kcal/ ^Nm3
You can use a mixture of gas and air as a calorie diluent and adjust it to the final calorie requirement. Next, the decarbonation gas step will be explained. In the decarbonation gas step, carbon dioxide is removed using any of the known carbon dioxide absorption liquids such as MEA (monoethanolamine), DEA (diethanolamine), potassium carbonate, and the like. B. Examples of the Invention Next, the present invention will be explained with reference to Examples, but the present invention is not limited thereto. Flowcharts of examples are shown in FIGS. 1 to 4, and data of examples are shown in Table 1. [Example 1] In Fig. 1, LPG1, which is a raw material hydrocarbon
After being pressurized to 9 kg/cm ² G by the raw material pump 2 and mixed with the recycled gas 9', it enters the heat recovery section 7, where it is preheated and evaporated to produce the necessary gas for the hydrogenation process.
The hydrogenation tower 3a of the hydrodesulfurization tower 3 is heated to 380°C.
to go into. The sulfur compounds (10 ppm) in the raw material gas 1a that entered the hydrogenation tower 3a are hydrogenated (hydrogen sulfide) by a hydrogenation reaction with the hydrogen in the recycled gas 9', and the sulfur content is reduced to 0.2 ppm in the next desulfurization tower 3b. The following will be removed. A cobalt-molybdenum catalyst and a zinc oxide catalyst were used as catalysts for the hydrogenation tower 3a and the desulfurization tower 3b, respectively. The raw material gas 1a that has exited the hydrodesulfurization process enters the next low-temperature steam reforming process, where steam 4 is converted into the raw material gas 1a.
The mixed gas 1b is mixed with carbon at a weight ratio of 3.0, and heated to 520°C in the next raw material heater 5.
and enters the reforming tower 6. In the reforming tower 6, the mixed gas 1b has an outlet composition of 29.11 vol% hydrogen and carbon monoxide due to a steam reforming reaction.
0.80vol%, carbon dioxide 19.98vol%, methane
The reformed gas 1c was 50.11vol%. The pressure in the reforming tower 6 at this time is 6.7 Kg/cm ² G. Under this condition, the steam reforming reaction is a slight endothermic reaction and there is no heat input from the outside (adiabatic reaction), so the outlet temperature The temperature reached 479℃. Note that a NiO-La-Al ₂ O ₃ system was used as the reforming catalyst. The reformed gas 1c that has exited the reforming tower 6 enters the next heat recovery step, where it is passed through a second raw material preheater 7a, a process gas boiler 7b, a boiler feed water preheater 7c, a first raw material preheater 7d, and a decarburization reboiler 7e. , water preheater 7
f, process gas cooler 7g, process gas
The heat is recovered to 40° C. in a heat recovery section 7 consisting of a KO drum 7h, and becomes reformed gas 1c'. Next, the reformed gas 1c' enters a dehydration process and is cooled to 3°C in a dehydration equipment 8 that uses a freezing method.
Moisture is separated and preheated to 25°C in a gas-gas heat exchanger, resulting in manufactured gas 9 with a total calorific value of 5673 kcal/Nm ³ . This is mixed with dilution air 11 in a heat adjustment mixer 10 in the next heat adjustment process to make city gas 13 of 5000 kcal/Nm ³ and supplied to consumers. In addition, in addition to air 11, LPG is used in the heat adjustment process.
Table 1 shows the properties when city gas with a total calorific value of 4500 kcal/Nm ³ was produced by mixing No. 12. In order to produce city gas 13 with properties that meet the demands of consumers, various combinations of processes are required in addition to the above embodiments. The following embodiments address this need. [Example 2] The outlet gas of the reforming tower 6 in the flow of Example 1 was heated again in the second heating furnace 14 and then heated in the second stage reforming tower 1.
5, the hydrogen concentration in the reformed gas 1c could be increased and the methane concentration could be reduced. The data of the examples are shown in Table 1. [Example 3] In order to improve the combustibility of city gas, a decarbonation equipment 16 that performs a decarbonation process after the flow heat recovery section 7 is provided in Example 1, and carbon dioxide in the reformed gas 1c is removed. Remove. The MEA method was adopted as the decarbonation method. The carbon dioxide in the reformed gas 1c' is released from the top of the absorption tower.
Carbon dioxide is removed from the top of the column by countercurrent contact with a 15 wt% MEA solution. Example data is shown in Table 1. [Example 4] In order to improve city gas combustibility, a decarboxylation equipment 16 is installed in the flow of Example 2 to remove carbon dioxide. The MEA method was adopted as the decarbonation method. Example data is shown in Table 1.

【table】

【table】 [Brief explanation of drawings]

FIG. 1, FIG. 2, FIG. 3, and FIG. 4 are system diagrams showing the flow of the embodiment. 1... Raw material hydrocarbon, 1a... Raw material gas, 1b
...Mixed gas, 1c...Reformed gas, 2...Material pump, 3...Hydrodesulfurization tower, 3a...Hydrogenation tower, 3b
... Desulfurization tower, 4 ... Steam, 5 ... Raw material heater,
6... Reforming tower, 7... Heat recovery section, 8... Dehydration equipment, 9... Production gas, 9'... Recycle gas,
10... Heat control mixer, 11... Air, 12...
LPG, 13... city gas, 14... second heating furnace,
15...Two-stage reforming tower, 16...Decarboxylation equipment.

Claims (1)

[Scope of Claims] 1. Hydrocarbons are heated to 3600~
In a city gas production method for producing low-calorie city gas of 5000 kcal/Nm ³ , the raw material hydrocarbon and hydrogen-containing gas are mixed as a raw material gas,
The sulfur compounds in the raw material gas are reduced to 450% in the presence of a catalyst.
A hydrodesulfurization process in which hydrogenation is carried out at ~250°C to adsorb and remove hydrogen sulfide, and water vapor is added to the raw material gas from the hydrodesulfurization process at a weight ratio of 1.0 to 5.0 with respect to carbon in the raw material gas. A low-temperature steam reforming reaction step in which the mixed gas is reformed by a reforming reaction at a temperature of 550 to 450°C and a pressure of 1 to 30 Kg/cm ² G in the presence of a nickel or noble metal catalyst; A dehydration step to remove moisture in the reformed gas obtained by reforming the mixed gas through a quality reaction step, and a heat amount consisting of air or LPG to make the produced gas, which is obtained by dehydrating the reformed gas through the dehydration step, to the final required heat amount. A method for producing low-calorie city gas from hydrocarbons, characterized by including a calorific value adjustment step of mixing with a regulated gas. 2. The low-calorie city gas from hydrocarbons according to claim 1, wherein carbon dioxide contained in the produced gas can be removed by bringing the produced gas into contact with a carbon dioxide absorption liquid. Manufacturing method. 3. The carbonization method according to claim 1 or 2, wherein a part of the production gas is recycled so that it can be mixed with the raw material hydrocarbon for hydrodesulfurization of the raw material hydrocarbon. A method for producing low-calorie city gas from hydrogen.