JP5255291B2 - How to stop the reformer - Google Patents

Description

  The present invention is a reformer that generates a hydrogen-rich reformed gas by steam reforming a mixture of a raw material gas and steam in the presence of a reforming catalyst, and reforms the steam after the reformer is shut down. The present invention relates to a method for stopping a reformer provided with a pressure-holding step for sealing the inside of the reformer and maintaining the interior of the reformer at a positive pressure.

2. Description of the Related Art Conventionally, there is known a reformer that generates a hydrogen-rich reformed gas by steam reforming a mixture of a source gas and steam (hereinafter referred to as a source-steam mixture) in the presence of a reforming catalyst. The hydrogen-rich reformed gas obtained in the reformer is converted into CO ₂ by reacting residual CO (carbon monoxide) with an oxygen-containing gas in the presence of a catalyst by means of CO reduction, for example, a solid polymer electrolyte. When the reformed gas is supplied to the fuel cell, CO is reduced to several ppm level. As the source gas, hydrocarbons such as methane, aliphatic alcohols such as methanol, ethers such as dimethyl ether, city gas, and the like are used. In such a reformer, a reaction formula of steam reforming when methane is used as a raw material gas can be expressed as CH ₄ + 2H ₂ O → CO ₂ + 4H ₂ , and a preferable reforming reaction temperature is 650 to The range is 750 ° C.

  There are an external heating type and an internal heating type as a system for supplying heat necessary for the reforming reaction of the reformer. The external heating type reformer is provided with a heating unit outside, and a reformed gas is generated by reacting a raw material gas and water vapor with a heat source. The internal heating type reformer is provided with a partial oxidation reaction layer on the supply side (upstream side), and the steam reforming reaction layer disposed on the downstream side using the heat generated in the partial oxidation reaction layer is subjected to a steam reforming reaction. Heating to a temperature is performed, and a steam reforming reaction is performed in the heated steam reforming catalyst layer to generate a hydrogen-rich reformed gas.

The partial oxidation reaction can be represented by CH ₄ + 1/2 · O ₂ → CO + 2H ₂ , and the preferable partial oxidation reaction temperature is in the range of 250 ° C. or higher. A self-oxidation internal heating type reformer is known as an improvement of the internal heating type reformer. The self-oxidation internal heating type reformer has a double structure with an outer pre-reforming chamber and an inner main reforming chamber communicating with it, and the pre-reforming chamber is provided with a reforming catalyst layer. The main reforming chamber is provided with an oxidizing air supply pipe, a mixed catalyst layer in which the reforming catalyst and the oxidation catalyst are mixed, a shift catalyst layer, and the like. Note that a supply pipe for supplying oxidized air is extended to the central portion of the main reforming chamber, and an air ejection portion including a plurality of nozzles is formed in a portion where the supply pipe extends to the mixed catalyst layer.

  A steam generating means is provided for supplying steam necessary for steam reforming of the reformer. The water vapor generating means burns gaseous fuel or liquid fuel with a burner and heats water with the combustion gas to generate water vapor. The water vapor generated by the water vapor generating means and the raw material gas from the raw material gas supplying means are mixed by, for example, a mixer comprising an ejector, and the obtained raw material-steam mixture is supplied to the reformer.

  For example, when the internal heating type reformer is stopped, if the supply of the raw material gas to the reformer and the supply of oxidized air are stopped, the internal temperature of the reformer decreases, so the raw material gas remaining in the reformer However, when the high temperature of the carbon deposition temperature or higher (for example, the temperature of 200 ° C. or higher) continues, the raw material gas remaining in the reformer causes a carbon deposition phenomenon. In order to prevent the carbon deposition, for example, Patent Document 1 proposes a method of purging the raw material gas remaining inside the reformer with water vapor when the reforming system is stopped.

  The method for stopping the reforming system in Patent Document 1 is that the raw material gas remaining in the reformer is purged with steam after the supply of the raw material gas to the reformer is stopped, and then the natural gas is allowed to cool naturally. The raw material gas is sealed in the reformer when the temperature becomes lower than the carbon deposition temperature of the gas. However, in the process where the reformer is naturally cooled while steam is sealed inside the reformer, when the temperature inside the reformer falls below the dew point of the steam, the steam partially condenses and the reformer is negatively charged. There is a risk of pressure. If the inside of the reformer is left in a negative pressure state, external air is sucked in from a connection portion of a valve provided in the pipe and the catalyst is deteriorated.

  Therefore, in order to prevent the negative pressure state from continuing inside the reformer, it is necessary to appropriately supply steam to the reformer so as to compensate for the condensate. In addition, such a negative pressure prevention process performed when the reformer is stopped is referred to as a pressure holding process in the present invention.

JP 2002-151124 A

  In order to solve the negative pressure state of the reformer as described above, it is necessary to supply new steam to the reformer from the steam generating means. However, for that purpose, it is necessary to continue the operation of the steam generation means even during the stop operation of the reforming system or to start the steam generation means every time the negative pressure state is reached. Thus, even when the reformer is stopped, if the steam generating means is operated continuously or frequently to supply a large amount of steam, a corresponding amount of fuel is consumed. There arises a problem that the overall thermal efficiency including the stoppage is lowered.

  Furthermore, since the internal temperature during natural cooling of the reformer is not uniform and varies depending on the region, condensation of water vapor occurs relatively early in the region where the temperature is low. As a result, the amount of steam supplied to the reformer also increases accordingly, and the consumed heat energy also increases. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve such a problem in the conventional reformer stopping method, and to provide a new reformer stopping method therefor.

A method for stopping a reformer of the present invention that solves the above-described problem is a reformer that generates a hydrogen-rich reformed gas by steam reforming a mixture of a raw material gas and steam in the presence of a reforming catalyst. In the method for stopping the reformer in which steam is enclosed in the reformer after the operation of the reformer is stopped and the pressure holding step is performed ,
A raw material gas is mixed with water vapor used in the pressure holding step,
Prior to the pressure holding step, a steam purge step of purging the interior of the reformer with steam is performed (claim 1).

In the above reformer stopping method,
When the internal pressure of the reformer decreases during the pressure holding step, steam can be replenished inside the reformer (claim 2).

  The method for stopping a reformer according to the present invention is characterized in that a raw material gas is mixed with water vapor used in the pressure-holding step. Thus, when the raw material gas which is non-condensed gas is mixed with water vapor which is condensed gas, the dew point as a mixture is lower than the dew point when water vapor is 100%, and the condensation temperature of water vapor is lowered, so that water vapor is substantially reduced. Can be prevented from condensing.

  For example, when the raw material gas is mixed with the water vapor so that the carbon number ratio of the water vapor / the raw material gas is 2.8, the dew point of the water vapor at atmospheric pressure is 100 ° C., but the water vapor: city gas (C1.2H4. Since 4) is 3.36 (mol ratio), the water vapor partial pressure under atmospheric pressure is {3.36 / (3.61 + 1)} × 1013 = 781 hPa. This corresponds to 93 ° C. in terms of dew point (hereinafter, the dew point lowered by mixing is referred to as a real dew point in the present invention). In this example, the temperature difference between the real dew point and the dew point of only water vapor at atmospheric pressure is 7 ° C., but the condensation start time of water vapor can be delayed accordingly.

  Furthermore, since the raw material gas, which is a non-condensable gas, is mixed with the water vapor, even if a part of the water vapor is condensed in the local temperature drop region of the reformer, the water vapor is condensed in the region as much as the water vapor is condensed. The mixing ratio of the water vapor decreases, and the amount of water vapor condensing per hour thereafter is further suppressed. For these reasons, even if the reformer is subsequently replenished with steam to maintain the holding pressure, the total steam replenishment amount is reduced from the conventional method.

In the initial stage of the pressure holding process, there is a period in which the internal temperature of the reformer is equal to or higher than the carbon deposition temperature of the raw material gas. Even in such a period, the raw material gas is caused by water vapor present around the raw material gas. The carbon deposition phenomenon is substantially prevented. In addition, when the mixing ratio of water vapor in the local temperature decrease region is reduced, when viewed from the raw material gas side, it shifts to a somewhat dry state, but the region reaches a temperature at which a part of the water vapor is condensed. Since it is lowered (lower than the carbon deposition temperature), carbon deposition of the source gas does not occur.
Furthermore, since the steam purging process for purging the interior of the reformer with steam prior to the pressure holding process is provided, since the interior of the reformer is filled with steam in advance, only the source gas is added in the pressure holding process. The desired mixing of the raw material gas with respect to the water vapor can be easily set .

  In the method for stopping the reformer, as described in claim 2, when the internal pressure of the reformer decreases during the pressure holding step, steam can be supplied into the reformer. Such steam replenishment can more reliably prevent the reformer from entering the negative pressure region.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a process flow diagram of a reformer for explaining an example of the stopping method of the present invention. 1 is a reformer, 2 is a steam generating means, 3 is a mixer, 4 is a desulfurizer, 5 is a CO reducer, 6 is a facility for using reformed gas such as a fuel cell, 8 and 9 are regulating valves, a to k is a pipe.

  Although the reformer 1 shown in FIG. 1 is an example of a self-oxidation internal heating type reformer, the reformer 1 may be another type of internal heating type or external heating type. The water vapor generating means 2 generates water vapor by burning fuel such as city gas supplied from the pipe g or anode exhaust gas of the fuel cell with combustion air supplied from the pipe h. Pure water, which is a raw material of water vapor, is supplied to the water vapor generating means 2 through the pipe j. During operation of the reformer 1, a raw material gas such as city gas supplied from the pipe a is supplied to the mixer 3 through the pipe b after the sulfur content is removed by the desulfurization device 4. The mixer 3 is composed of, for example, an ejector, sucks the source gas by the suction force of the steam supplied from the pipe c, and supplies the mixture of the source gas and the steam to the reformer 1 from the pipe d. The mixing ratio of the water vapor and the raw material gas can be adjusted by adjusting the opening of the adjusting valves 8 and 9, adjusting the amount of combustion, or the like.

  The reformer 1 has an oxidation catalyst disposed therein, oxidizes part of the raw material gas with the oxidizing air supplied from the pipe i, and the reforming catalyst is brought to the reforming temperature (about 700 ° C.) by the generated oxidation heat. The temperature rises. The hydrogen-rich reformed gas generated in the reformer 1 is supplied to the CO reducer 5 from the pipe e, where CO (carbon monoxide) remaining in the reformed gas is reacted with air to, for example, the order of ppm. To reduce. At that time, the oxidizing air to be used is supplied through the pipe k. The reformed gas with reduced CO is supplied from the pipe f to the reformed gas use facility 6 such as a fuel cell. Next, a method for stopping the reformer 1 of FIG. 1 will be described.

(First embodiment)
In order to stop the operation of the reformer 1, first, the regulator valve 8 is closed to stop the supply of the raw material gas to the mixer 3, and the oxidizing air supplied from the pipe i is stopped to stop the reformer. 1 reforming reaction is stopped. At that time, the operation of the steam generating means 2 is continued as it is, and the generated steam is supplied to the reformer 1 through the path of the pipe c-mixer 3 -pipe d, and the raw material gas remaining inside the reformer 1 is supplied. Purge with steam (steam purge process).

  After the steam purge step, the internal temperature of the reformer 1 gradually decreases due to natural cooling, but the internal pressure of the reformer 1 gradually decreases accordingly. Therefore, the pressure holding process is performed so that the internal pressure does not become a negative pressure. In the pressure-holding step, for example, the regulating valve 8 and the regulating valve 9 are adjusted so that a predetermined amount of water vapor and raw material gas can be supplied from the mixer 3 to the reformer 1. The raw material gas can be supplied to the reformer 1 without going through the mixer 3, for example, directly from the desulfurizer 4 or through a pressure pump.

In the pressure holding process, the upper limit of the mixing ratio of the raw material gas to the water vapor is set within a range in which the raw material gas supplied to the reformer 1 does not cause carbon deposition in the initial stage during the pressure holding process. That is, as the ratio of water vapor to the raw material gas increases, carbon precipitation is less likely to occur, and the range can be determined by experiments or the like.
According to the experiment, when the internal temperature of the reformer 1 at the initial stage of holding pressure is 400 ° C., the carbon S / C of the steam / feed gas is set to 0.4 or more, and the real dew point is about 75 ° C. or slightly Similarly, in the case of 500 ° C., it was found that it is desirable that the water vapor / source gas carbon S / C is 1.1 or more and the real dew point is about 85 ° C. or slightly higher.

  When the internal temperature of the reformer 1 (particularly the temperature of the reforming catalyst layer) becomes equal to or lower than the carbon deposition temperature (approximately 200 ° C. or lower), the pressure holding process is terminated and the raw material gas replacement process is started. For example, pressurized source gas is supplied to the reformer 1 via the pipes ab-d, and the interior of the reformer 1 is replaced with the source gas to be in a source gas sealed state. And if necessary, the reformer 1 is kept warm by a heat-retaining heater provided around the reformer 1 so that dew condensation does not occur inside the reformer 1.

(Second Embodiment)
In the second embodiment, first, the regulating valve 8 and the regulating valve 9 are closed to stop the supply of the raw material gas and water vapor to the mixer 3, and the oxidation air supplied from the pipe i is stopped for reforming. Stop the reaction. In this state, the reformer 1 is sealed with the mixture of the raw material gas and the steam supplied immediately before the end of operation remaining.

  The reformer 1 is naturally cooled with the mixture of the raw material gas and water vapor remaining therein, and the cooling period is the same as the pressure holding step in the first embodiment. And according to the fall of the internal pressure of the reformer 1, water vapor | steam and source gas can also be replenished in a predetermined ratio. Next, when the internal temperature of the reformer 1 (particularly the temperature of the reforming catalyst layer) is equal to or lower than the carbon deposition temperature (approximately 200 ° C. or lower), the pressure holding step is terminated in the same manner as in the first embodiment, The process proceeds to the step of replacing the interior of the reformer 1 with the raw material gas.

  The method for stopping the reformed gas of the present invention can be used for a reforming system that generates a hydrogen-rich reformed gas by steam reforming the raw material gas and supplies it to additional equipment such as a fuel cell.

The process flow figure for demonstrating the stop method of the reformer of this invention.

Explanation of symbols

1 Reformer 2 Steam generation means
DESCRIPTION OF SYMBOLS 3 Mixer 4 Desulfurization apparatus 5 CO reduction device 6 Equipment used for reforming gas 8,9 Regulating valve a to k Piping

Claims (2)

A reformer that generates a hydrogen-rich reformed gas by steam reforming a mixture of raw material gas and steam in the presence of a reforming catalyst, and after the reformer is shut down, the steam is enclosed in the reformer. In the stopping method of the reformer so as to perform the pressure holding step,
A raw material gas is mixed with water vapor used in the pressure holding step,
A method for stopping a reformer comprising performing a steam purge step of purging the interior of the reformer with steam prior to the pressure holding step . In claim 1,
A method of stopping a reformer, characterized in that when the internal pressure of the reformer decreases during the pressure holding step, steam is supplied into the reformer.

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