JP5248935B2 - Operation method of oxidation autothermal reformer - Google Patents

Description

  The present invention relates to an operation method of an oxidation autothermal reformer, and more particularly to an operation method of an oxidation autothermal reformer for producing a reformed gas mainly composed of hydrogen supplied to a fuel cell. It is.

  In order to supply reformed gas containing hydrogen as a main component to a fuel cell, many steam reforming apparatuses using hydrocarbons or aliphatic alcohols and steam as raw materials are used. However, the steam reforming reaction is a large endothermic reaction, and it is necessary to provide heat necessary for the reaction by an accompanying heating device such as a burner or a heater, and it is difficult to make the reformer compact and to improve the thermal efficiency.

  On the other hand, by supplying air, which is an oxidizing gas, in addition to hydrocarbon or aliphatic alcohol and water vapor, the oxidation self that can cover the heat necessary for the water vapor reforming reaction by the heat generated by the partial oxidation reaction inside the reformer The thermal reformer has a high thermal efficiency and can easily reduce the size of ancillary heating equipment (see Patent Document 1).

JP 2001-192201 A

  In recent years, in order to realize highly efficient power generation, fuel cells that have been developed are generally operated not only at a constant load at a rated load but also at a partial load that matches the demand of the electricity supplier. It's getting on. Therefore, even in the oxidation self-heat reforming apparatus for fuel cells, there is a demand for performance capable of finely controlling the flow rate of the reformed gas supplied to the fuel cells in accordance with the power generation status of the fuel cells.

  On the other hand, conventionally, as a method of changing the operating conditions at the time of load change in the oxidation autothermal reformer, it is common to simultaneously change the supply amount of hydrocarbon or aliphatic alcohol, water vapor, and oxidizing gas. Met. However, when the present inventors examined, even if it tried to change the supply amount of each of these raw materials at the same time, the difference between liquid and gas, the difference in supply equipment such as a pump and a blower, the difference in the supply pipe length of each raw material, Due to the time lag that evaporates from water to steam, etc., there is a difference in the timing when each raw material actually reaches the catalyst layer inside the oxidation autothermal reformer, and the supply amount of each raw material is lost, As a result, it has been found that there is a problem in that the flow rate of reformed gas supplied to the fuel cell is changed, which adversely affects the power generation status of the fuel cell and promotes catalyst deterioration of the oxidation autothermal reformer. .

  Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art and to balance the supply amount of hydrocarbons or aliphatic alcohols, water vapor, and oxidizing gas in changing the operation load of the oxidation autothermal reformer. An object of the present invention is to provide a method of operating an oxidation autothermal reformer that is appropriately controlled so as not to adversely affect the fuel cell and the oxidation autothermal reformer itself.

  As a result of intensive studies to achieve the above object, the present inventors have (1) first reducing the supply amount of hydrocarbons or aliphatic alcohols when reducing the amount of reformed gas produced, and (2) Next, reduce the supply amount of oxidizing gas, and (3) balance the supply amount of hydrocarbons or aliphatic alcohol, water vapor, oxidizing gas by changing the operating conditions in the order of decreasing the supply amount of water vapor. As a result, it is found that the reforming catalyst flow rate can be prevented from deteriorating due to a decrease in the reaction temperature, and the flow rate of the reformed gas supplied to the fuel cell can be suppressed, thereby completing the present invention. It came to.

That is, the operation method of the oxidation autothermal reformer of the present invention is as follows:
An operation method of an oxidation autothermal reformer for producing a reformed gas mainly composed of hydrogen by a reforming reaction using a hydrocarbon or an aliphatic alcohol, water vapor and an oxidizing gas as raw materials,
The oxidation autothermal reformer is an oxidation autothermal reformer for fuel cells,
When reducing the amount of reformed gas produced, the order of decreasing the supply amount of the hydrocarbon or aliphatic alcohol first, then reducing the supply amount of the oxidizing gas, and finally decreasing the supply amount of the water vapor It is characterized by changing the operating conditions.

In a preferred embodiment of the operation method of the oxidation autothermal reformer of the present invention, when the amount of reformed gas produced is reduced, the O ₂ / C ratio after reduction with respect to the amount before reformed gas production ( The ratio of the number of moles of oxygen molecules contained in the oxidizing gas to the number of moles of carbon contained in the hydrocarbon or aliphatic alcohol is increased.

In another preferred embodiment of the operation method of the oxidation autothermal reforming apparatus of the present invention, the operation of reducing the reformed gas generation amount is performed in a plurality of times. In this case, the upper limit value of the O ₂ / C ratio set so as not to exceed the upper limit temperature of use of the catalyst charged in the oxidation autothermal reformer or the members constituting the oxidation autothermal reformer is not exceeded. Thus, it becomes easy to perform the reduction operation of the reformed gas generation amount.

  In another preferred embodiment of the operation method of the oxidation autothermal reformer of the present invention, the oxidation property is immediately detected when the start of the catalyst layer temperature increase is detected after the supply amount of the hydrocarbon or aliphatic alcohol is reduced. Reduce gas supply.

  In the operation method of the oxidation autothermal reforming apparatus of the present invention, the oxidizing gas is preferably air.

  In the operation method of the oxidation autothermal reformer of the present invention, the hydrocarbon or the aliphatic alcohol is at least one selected from the group consisting of light oil, kerosene, gasoline, naphtha, LP gas, ethanol and methanol. It is preferable.

In the method of operating the oxidation self thermal reforming apparatus of the present invention, as the fuel cell, preferably a solid oxide fuel cell.

  According to the operation method of the oxidation autothermal reformer of the present invention, it is temporarily generated by determining the change order of the supply amount of water vapor, oxidizing gas, hydrocarbon or aliphatic alcohol when the operation load is reduced. Therefore, it is possible to prevent a decrease in the reaction temperature and reduce the damage to the reforming catalyst, and it is possible to stably operate the oxidation autothermal reformer for a long period of time. In addition, it can satisfactorily follow changes in the demand for reformed gas mainly composed of hydrogen generated from an oxidation autothermal reformer, and in particular, in the case of partial load operation in an oxidation autothermal reformer for fuel cells. It is possible to realize highly efficient operation.

The present invention is described in detail below. In the production of reformed gas mainly composed of hydrogen in the oxidation autothermal reformer to which the present invention is applied, steam reforming using hydrocarbon or aliphatic alcohol and steam as raw materials, and hydrocarbon or aliphatic alcohol A reaction combined with partial oxidation reforming using an oxidizing gas as a raw material is utilized. In the steam reforming reaction, when methane is taken as an example of hydrocarbon, the following reaction formula (I):
CH ₄ + H ₂ O → CO + 3H ₂ (I)
And is known to be a large endothermic reaction. On the other hand, in the partial oxidation reforming reaction, when methane is used as the hydrocarbon and oxygen is used as the oxidizing gas, the following reaction formula (II):
CH ₄ + (1/2) O ₂ → CO + 2H ₂ (II)
It is an exothermic reaction represented by For this reason, in the oxidation autothermal reformer, the heat generated by partial oxidation reforming and the endotherm necessary for steam reforming can be used interchangeably in the reaction field inside the device, and hydrogen can be efficiently used. It has a feature that a reformed gas having a main component can be produced.

  In steam reforming, a reformed gas is produced by determining the ratio of the amount of hydrocarbon or aliphatic alcohol and steam supplied as raw materials. In general, the molar ratio of water vapor to carbon contained in hydrocarbons or aliphatic alcohols is called the steam / carbon ratio (S / C ratio). If this ratio is small, coking (carbonaceous deposition) in the catalyst tends to occur. In addition, coking has a significant effect on catalyst performance degradation. Therefore, it is preferable to manufacture the reformed gas while controlling the S / C ratio to be a certain value or more. For example, when using city gas as the hydrocarbon, operation is often performed under conditions of S / C ratio ≧ 2.2, and when kerosene is used, it is often operated under conditions of S / C ratio ≧ 2.5. Higher S / C ratios are required the more hydrocarbons or higher aliphatic alcohols are used. On the other hand, if the S / C ratio is increased more than necessary, the risk of reducing the catalyst performance due to the occurrence of coking is reduced, but excess steam is supplied, so that extra energy is wasted to generate steam. This is not preferable because the efficiency decreases. Therefore, in steam reforming, there is an optimum S / C ratio required from the type of hydrocarbon or aliphatic alcohol used as a raw material and the characteristics and performance of the catalyst used, and the S / C ratio is stably maintained. By performing the operation, the reformed gas can be efficiently produced. Also in the oxidation autothermal reformer, since steam reforming is used, the S / C ratio needs to be stably controlled similarly.

  An oxidizing autothermal reformer to which the present invention is applied supplies an oxidizing gas in addition to a hydrocarbon or aliphatic alcohol and water vapor. As the oxidizing gas, oxygen is a typical substance, but air is preferably used from the viewpoint of availability and cost. However, since nitrogen contains nitrogen at a high concentration, the produced reformed gas contains nitrogen. Therefore, high concentration oxygen may be supplied as an oxidizing gas to the oxidation autothermal reformer by separating nitrogen and oxygen contained in the air in advance. Any gas having oxidizing properties other than oxygen can be used, and ozone or the like can also be used.

  By supplying an oxidizing gas to the oxidation autothermal reformer, a part or all of the reaction heat required for steam reforming can be covered. In an oxidation self-heating reformer attached to a heating device such as a burner or a heater, the heating device can be reduced in size or reduced by using the heat generated by the oxidizing gas, or the heating amount can be reduced. it can. Since the calorific value can be controlled by adjusting the supply amount of the oxidizing gas, if the supply amount of the oxidizing gas is increased, the oxidation self-heating reformer is operated under the condition that the attached heating equipment is not operated at all. It is also possible to produce a quality gas, and it is also possible to realize an oxidation autothermal reformer that does not involve any heating equipment.

When air or oxygen is used as the oxidizing gas, the molar ratio of the oxygen molecules supplied as the oxidizing gas to the carbon contained in the hydrocarbon or aliphatic alcohol can be expressed as an oxygen molecule / carbon ratio (O ₂ / C ratio). it can. When the supply amount of the oxidizing gas increases, the O ₂ / C ratio increases. When the supply amount of the oxidizing gas decreases, the O ₂ / C ratio decreases. Note that oxygen contained in the aliphatic alcohol is not involved in the calculation of the O ₂ / C ratio.

The steam reforming reaction proceeds in a temperature range of about 500 to 800 ° C., and hydrogen, carbon monoxide, carbon dioxide, and methane are generated as reformed gas in addition to steam. Since steam reforming is an equilibrium reaction, the concentration of each component in the reformed gas is defined by the reaction temperature if the catalytic reaction is sufficiently advanced. Generally, the higher the reaction temperature, the higher the concentration of carbon monoxide and the lower the concentration of methane. When the reaction temperature falls below the temperature range in which the catalytic reaction proceeds, except when methane is used as the hydrocarbon, that is, when a compound having 2 or more carbon atoms as the hydrocarbon or aliphatic alcohol is used as the raw material, As a result of insufficient reforming, hydrocarbons and aliphatic alcohols other than methane are mixed into the reformed gas. As the fuel gas for power generation of the fuel cell, it is not preferable that the reformed gas contains hydrocarbons or aliphatic alcohols other than methane, so it is necessary to ensure a reaction temperature at which steam reforming proceeds sufficiently. Therefore, in the oxidation autothermal reformer, although depending on the incidental situation of the heating equipment, the type and composition of the hydrocarbon or aliphatic alcohol used as a raw material, the performance of the catalyst used, the oxidation autothermal reformer There are restrictions on the lower limit of the oxidizing gas supply amount due to heat dissipation loss, raw material input temperature, reformed gas discharge temperature, and the like. That is, when air or oxygen is used as the oxidizing gas, there is a lower limit value of the O ₂ / C ratio as an operating condition, and it is necessary to operate at an O ₂ / C ratio higher than the lower limit value.

Meanwhile, when driven at high O _{2 /} C ratio than the above lower limit, the reaction temperature is preferred operating conditions for high steam reforming, the O 2 _{/ C} ratio becomes too high, the catalyst and reforming This is a problem in view of the heat resistance of the material constituting the quality device. Furthermore, since the oxidizing gas is consumed by causing a combustion reaction with some of the hydrogen, carbon monoxide, methane, and the like that should be obtained as the reformed gas, if the operation is performed at an O ₂ / C ratio higher than necessary. In addition to reducing the efficiency of the oxidation autothermal reformer, the power generation efficiency of the fuel cell system incorporating the oxidation autothermal reformer is impaired. Therefore, similar to the above-described S / C ratio, there is an optimum O ₂ / C ratio in the oxidation autothermal reformer, and the reforming is efficiently performed by operating at the O ₂ / C ratio. Gas production can be performed.

In addition, since exhaust heat is generated from the fuel cell that generates power, the exhaust heat is taken into the oxidation self-heat reforming apparatus and effectively used to reduce the amount of oxidizing gas supplied, that is, O ₂ / C. Operation under conditions with a reduced ratio becomes possible. In particular, a solid oxide fuel cell or the like that operates at a high temperature of about 700 to 1,000 ° C. has a large room for using exhaust heat, and can greatly reduce the O ₂ / C ratio of the oxidation autothermal reformer. However, since the amount of exhaust heat available from the fuel cell is finite, there is a lower limit for the O ₂ / C ratio at which the oxidation autothermal reformer can be operated.

  By the way, in recent years, there has been remarkable progress due to the development of fuel cells, but in order to realize highly efficient power generation, not only constant operation at the rated load but also partial load operation that matches the demand of the power supply destination can be performed. It is generally done. Therefore, even in the oxidation self-heat reforming apparatus for fuel cells, there is a demand for performance capable of finely controlling the flow rate of the reformed gas supplied to the fuel cells in accordance with the power generation status of the fuel cells.

  Conventionally, as a method of changing the operating conditions at the time of load change in an oxidation autothermal reformer, it has been common to change all the supply amounts of hydrocarbons, aliphatic alcohols, water vapor, and oxidizing gases at the same time. It was. For example, when the operating condition is changed from the 100% rated operating condition to the 90% partial load operating condition, all the supply amounts of hydrocarbons, aliphatic alcohols, water vapor, and oxidizing gas set under the 100% rated operating condition are set. Are simultaneously changed to the supply amount to be set under the 90% partial load operation condition. This change method is the simplest and simplest, and no problem arises if all the supply amounts of hydrocarbon or aliphatic alcohol, water vapor, and oxidizing gas can be changed instantaneously and accurately. As a result, in reality, there was a difference in the change timing of each supply amount and the followability of the supply amount change, and it was found that there was a problem. In fact, even if you try to change the supply amount of each raw material at the same time, the difference between liquid and gas, the supply equipment such as pumps and blowers, the difference in the supply route length of each raw material, the time lag that vaporizes from water As a result, there is a difference in the timing at which each raw material actually arrives at the catalyst layer inside the oxidation autothermal reformer, resulting in an imbalance in the supply amount of each raw material. It has been found that there is a problem that the flow rate of the gas is changed, which adversely affects the power generation status of the fuel cell and promotes catalyst deterioration of the oxidation autothermal reformer.

  Normally, when reducing the operating load in an oxidation autothermal reforming device for a fuel cell, first, the power generation output from the fuel cell is reduced by lowering the current value to be supplied to the fuel cell, and then the oxidation autothermal reforming device. This is dealt with by reducing the amount of reformed gas produced. Conversely, when increasing the operating load in an oxidation autothermal reformer for a fuel cell, first, the amount of reformed gas generated in the oxidation autothermal reformer is increased, and then the current value for energizing the fuel cell is increased. Increase the power generation output from the fuel cell.

As a result of studies by the present inventors, when reducing the amount of reformed gas produced by an oxidation autothermal reformer, if the timing of reducing hydrocarbons or aliphatic alcohols is slower than that of oxidizing gas, If the O ₂ / C ratio falls and falls below the lower limit of the appropriate range of O ₂ / C ratio, hydrocarbons and aliphatic alcohols other than methane will be mixed into the reformed gas and damage the fuel cell. I understood that. The influence is particularly remarkable when the oxidation autothermal reformer is operated under conditions close to the lower limit of the optimum O ₂ / C ratio for high efficiency operation. Further, when the operation load of the fuel cell is frequently changed in accordance with the power demand, the damage is accumulated quickly and the deterioration of the fuel cell is accelerated.

  Further examination revealed that when reducing the amount of reformed gas produced by the oxidation autothermal reformer, the timing of reducing the oxidizing gas is later than the timing of reducing hydrocarbons or aliphatic alcohol and the timing of reducing steam. It has been found that the cell voltage V decreases more than necessary as the period during which the amount of reformed gas produced decreases excessively increases and the fuel utilization rate Uf in the fuel cell increases. As described above, it is a problem as an operation method of the fuel cell that the power generation output is lowered more than necessary even temporarily.

  Furthermore, as a result of further investigation, not only in the steam reformer but also in the oxidation autothermal reformer, when reducing the amount of reformed gas produced, the timing for reducing the amount of hydrocarbons or aliphatic alcohol rather than steam. It was found that when the S / C ratio was slow, the S / C ratio was lowered, and when the S / C ratio was below the lower limit of an appropriate range, coking was generated on the catalyst, leading to a reduction in catalyst activity and catalyst life.

Based on the above knowledge, in the operation method of the oxidation autothermal reforming apparatus of the present invention, when reducing the amount of reformed gas produced, the supply amount of hydrocarbon or aliphatic alcohol, water vapor, oxidizing gas Rather than simultaneously reducing, deliberately shift the timing, (1) reduce the supply of hydrocarbon or aliphatic alcohol first, (2) reduce the supply of oxidizing gas, and (3) finally reduce the water vapor The operating conditions are changed in the order of decreasing the supply amount. By reducing the supply amount of each raw material in this order, the O ₂ / C ratio falls below the lower limit, the cell voltage V falls more than necessary, and the S / C ratio falls below the lower limit. The generation amount of reformed gas can be reduced so as not to adversely affect the fuel cell and the oxidation autothermal reformer itself.

  Further, although not particularly limited, when increasing the amount of reformed gas produced, the timing of the reformed gas is not intentionally increased, but the timing is deliberately shifted instead of simultaneously increasing the supply amount of hydrocarbon or aliphatic alcohol, water vapor, and oxidizing gas. More specifically, the operating conditions are changed in the order of increasing the supply amount of water vapor first, then increasing the supply amount of oxidizing gas, and finally increasing the supply amount of hydrocarbons or aliphatic alcohols. It is preferable.

The oxidation autothermal reformer can normally be operated in a range of about 20 to 120% with respect to the rated 100% load operation condition. However, in the operation method of the present invention, the operation load can be changed. The change width is not particularly limited, and may be a relatively large change width of 20% or more. One operation load change may be handled by one step operation condition change, or the operation load may be changed by subdividing into a plurality of steps. In particular, when the change width is large, when the O ₂ / C ratio temporarily rises, the upper limit temperature of use of the catalyst charged in the oxidation autothermal reformer or the member constituting the oxidation autothermal reformer is set. In this case, it is preferable to subdivide into a plurality of steps so that the change width is small. Further, in order to follow the demand for reformed gas consumption as much as possible and realize high-efficiency operation, it is preferable to finely control the variation width of 0.1 to 10%.

When changing the production amount of reformed gas, if the operating conditions of the oxidation autothermal reformer are changed at a constant O ₂ / C ratio, the operating load is higher than when the operating load is low. The reaction temperature of the oxidation autothermal reformer tends to increase. There is oxidized self thermal reforming insulation reinforced no small heat radiation loss even if the device, since it is believed that the heat radiation amount is constant substantially irrespective of the operating load, O 2 _{/ C} ratio stabilization driven at a driving load This is because the amount of heat released is relatively small with respect to the amount of heat generated by partial oxidation reforming when the value is high. Therefore, in order to operate the oxidation autothermal reformer with high efficiency, when the operating load is lowered, that is, when the amount of reformed gas generated is reduced, the O ₂ is changed from that before the change of the operating load. It is preferable to increase the / C ratio, and conversely, when the operating load is increased, that is, when the amount of reformed gas generated is increased, the O ₂ / C ratio may be decreased more than before the operating load is changed. preferable.

The use of the reformed gas generated by the implementation of the operation method of the oxidation autothermal reformer of the present invention is not particularly limited, but the operation method of the present invention is applied to an oxidation autothermal reformer for fuel cells, It is preferably applied to an oxidation autothermal reformer for high temperature operation type fuel cells, and particularly preferably applied to an oxidation autothermal reformer for solid oxide fuel cells.

  As described above, when reducing the amount of reformed gas produced in an oxidation autothermal reformer for a fuel cell, the fuel cell must be energized before changing the operating conditions of the oxidation autothermal reformer. Usually, the power generation output from the fuel cell is reduced by lowering the current value. In the fuel cell, an appropriate range of the fuel utilization rate Uf is determined as a power generation condition. In order to avoid exceeding this range, an operation for reducing the amount of reformed gas generated in the oxidation autothermal reformer is performed. Before the operation, the current value of the fuel cell is lowered to lower the fuel utilization rate Uf. Thereafter, in the oxidation autothermal reformer, when the supply amount of hydrocarbon or aliphatic alcohol is first reduced, the reformed gas flow rate is decreased and the fuel utilization rate Uf of the fuel cell is increased, resulting in a decrease in the cell voltage V. Thus, it can be grasped that the supply amount of hydrocarbon or aliphatic alcohol actually decreased. In addition, when the temperature of the reforming catalyst layer inside the oxidation autothermal reformer is monitored, it can be grasped that the supply amount of hydrocarbons or aliphatic alcohol has actually decreased even when the temperature rises. . Next, when the supply amount of the oxidizing gas is decreased, the supply amount of hydrocarbon or aliphatic alcohol is decreased, the reformed gas flow rate once decreased is increased, and the fuel utilization rate Uf of the fuel cell is decreased. It can be grasped that the supply amount of the oxidizing gas has actually decreased by the increase. When the temperature of the reforming catalyst layer inside the oxidation autothermal reforming apparatus is monitored, it can be grasped that the supply amount of the oxidizing gas has actually decreased due to the decrease in the temperature. Finally, when the supply amount of water vapor is reduced, the supply amount of the oxidizing gas is reduced and the reformed gas flow rate once increased is reduced again, and as a result, the fuel utilization rate Uf of the fuel cell rises. As a result, the cell voltage V decreases. It can be understood that the amount of steam supplied has actually decreased.

  In the present invention, it is preferable to reduce the supply amount of the oxidizing gas immediately after detecting the start of the rise in the catalyst layer temperature after reducing the supply amount of hydrocarbon or aliphatic alcohol. Here, “immediately” refers to 10 seconds or less, preferably 5 seconds or less. In this way, by reducing the time from the start of the decrease in the hydrocarbon or aliphatic alcohol supply amount to the start of the decrease in the oxidizing gas supply amount, an excessive decrease in the reformed gas generation amount can be suppressed.

In the present invention, the oxidation autothermal reformer can be operated in a range of S / C ratio of 1.5 to 4.5 and O ₂ / C ratio of 0.001 to 0.5. An operating condition range in which the C ratio is 1.8 to 4.0 and the O ₂ / C ratio is 0.002 to 0.4 is preferable, the S / C ratio is 2.0 to 3.5, and the O ₂ / C ratio is An operating condition range of 0.003 to 0.3 is more preferable.

  As hydrocarbons, hydrocarbon gases such as methane, ethane, propane, butane, LP gas, natural gas, city gas, etc., and liquid hydrocarbons such as gasoline, naphtha, kerosene, and light oil can be used. As such, methanol, ethanol, propanol or the like can be used.

  The oxidation autothermal reformer used in the practice of the present invention includes a steam reforming unit that generates a reformed gas mainly composed of hydrogen by a reforming reaction of a mixture of hydrocarbon or aliphatic alcohol and steam, and at least It is preferable that a part is filled with an oxidation catalyst, and a partial oxidation reforming unit that generates heat by oxidizing a part of the mixture or the reformed gas is provided. Here, at least a part of the steam reforming section is usually filled with a reforming catalyst, and by contacting the reforming catalyst with a mixture of hydrocarbon or aliphatic alcohol and steam, hydrogen is reformed. A reformed gas containing as a main component is produced. Further, at least a part of the partial oxidation reforming part is filled with an oxidation catalyst, and a part of the mixture or the reformed gas is oxidized to generate heat. In addition, the oxidation autothermal reforming apparatus used for carrying out the present invention is not particularly limited, and a known oxidation autothermal reforming apparatus can be adopted.

  Hereinafter, an oxidation autothermal reformer having a triple tube structure that can be suitably used in the practice of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view of an example of an oxidation autothermal reforming apparatus suitable for carrying out the present invention, and FIG. 2 is a sectional view taken along the line II-II in FIG. This oxidation autothermal reformer has a cylindrical shape as a whole, and each element is formed in an annular shape and arranged concentrically.

  The oxidation autothermal reforming apparatus 1 in the illustrated example includes a steam reforming layer 2 and a partial oxidation reforming layer 3, and the steam reforming layer 2 is located upstream of the partial oxidation reforming layer 3. Yes. The steam reforming layer 2 and the partial oxidation reforming layer 3 each have a cylindrical shape, and the steam reforming layer 2 is an inner steam reforming layer 2A positioned radially inside and an outer steam positioned radially outward. The reforming layer 2B is composed of two layers, and the partial oxidation reforming layer 3 is disposed between the inner steam reforming layer 2A and the outer steam reforming layer 2B. A triple tube structure in which the layer 2A, the partial oxidation reforming layer 3, and the outer steam reforming layer 2B are arranged in this order is formed.

  Here, at least a part of the steam reforming layer 2 is usually filled with a reforming catalyst, and at least a part of the partial oxidation reforming layer 3 is filled with an oxidation catalyst. As the reforming catalyst, a catalyst conventionally used for reforming can be used. For example, Ru, Ni, W, Co, Rh, Pt may be used alone or in plural on a support such as alumina, silica, zirconia. A supported one is used. Among these, especially when kerosene is selected as the hydrocarbon, a catalyst supporting Ru is preferable. Although a catalyst supporting Ru is generally low in oxidation resistance, it is excellent in reforming characteristics of a liquid fuel having a large number of carbon atoms. On the other hand, as the oxidation catalyst, a catalyst supporting Pt, Pd, Rh or the like which is not easily deteriorated at high temperature is preferable.

  The steam reforming layer 2 and the partial oxidation reforming layer 3 include an inner cylinder 4 and an outer cylinder 5 of the oxidation autothermal reforming apparatus 1, and two tubular partition walls 6 positioned between the inner cylinder 4 and the outer cylinder 5. (The inner partition wall 6A and the radially outer partition wall 6B) are separated from each other, and the space between the inner cylinder 4 and the radially inner partition wall 6A forms the inner steam reforming layer 2A. The space between the partition wall 6A and the radially outer partition wall 6B forms the partial oxidation reforming layer 3, and the space between the radially outer partition wall 6B and the outer cylinder 5 forms the outer steam reforming layer 2B. Yes. As shown in detail in FIG. 2, the inner cylinder 4, the radially inner partition 6 </ b> A, the radially outer partition 6 </ b> B, and the outer cylinder 5 form an annular and concentric circular tube structure. The inner steam reforming layer 2A, the partial oxidation reforming layer 3 and the outer steam reforming layer 2B, which are respectively positioned between them, form a triple tube structure.

  1 includes a raw material introduction pipe 7 for supplying raw materials to both the inner steam reforming layer 2A and the outer steam reforming layer 2B, and the partial oxidation reforming layer 3. A reformed gas discharge pipe 8 for discharging the reformed gas from the outer cylinder 5 is connected to the lower portion of the outer cylinder 5. Partition receivers 9A, 9B, and 9C are provided above the position where the raw material introduction pipe 7 is connected and below the inner steam reforming layer 2A, the partial oxidation reforming layer 3, and the outer steam reforming layer 2B. The partition receptacles 9A, 9B, and 9C allow a mixture of a hydrocarbon or an aliphatic alcohol and water vapor and a reformed gas to pass through while preventing the catalyst or the like filled in each layer from falling. A partition wall 10 is disposed below the position where the raw material introduction pipe 7 is connected and above the position where the reformed gas discharge pipe 8 is connected. The partition wall 10 is partially oxidized and reformed. An opening 11 communicating with the layer 3 is provided. Furthermore, the oxidation autothermal reforming apparatus 1 in the illustrated example includes an oxidizing gas introduction pipe 12 that penetrates the upper end portion of the outer cylinder 5 to reach the partial oxidation reforming layer 3. A tubular ring 13 provided with a plurality of oxidizing gas ejection ports is installed at the tip.

  During steady operation, the raw material containing water vapor introduced from the raw material introduction pipe 7 in FIG. 1 into the raw material flow path 14 passes through the partition receivers 9A and 9C, and the inner steam reforming layer 2A and the outer steam reforming. The layer 2B is reformed while flowing uniformly through an upflow, and becomes a reformed gas mainly composed of hydrogen. At this time, the heat required for reforming is transmitted by sensible heat due to oxidation heat generated in the partial oxidation reforming layer 3 to the inner steam reforming layer 2A and the outer steam reforming layer 2B through the partition walls 6A and 6B. Be covered.

  The raw material introduced into the oxidation autothermal reformer 1 is partly or completely reformed in the inner steam reforming layer 2A and the outer steam reforming layer 2B, and becomes a reformed gas mainly composed of hydrogen. Enters the reformed gas flow path 15. The C1 conversion at this time is usually 90% or more, although it varies depending on the type of hydrocarbon or aliphatic alcohol and the operating conditions.

  Further, the reformed gas makes a U-turn and enters the partial oxidation reformed layer 3 in a down flow. The partial oxidation reforming layer 3 is connected with an oxidizing gas introduction pipe 12 as means for supplying an oxidizing gas, and an oxidizing gas jet is blown to the tip of the oxidizing gas introduction pipe 12. A tubular ring 13 having a plurality of ports is provided. An oxidizing gas for oxidizing part of the reformed gas to generate heat is ejected from the plurality of oxidizing gas ejection ports of the tubular ring 13 through the oxidizing gas introduction pipe 12. Here, as the kind of oxidizing gas to be used, pure oxygen can be used, but it is generally preferable to use air from the viewpoint of cost.

  The partial oxidation reforming layer 3 oxidizes with hydrogen, methane, etc. in the reformed gas introduced into the partial oxidation reforming layer 3 in order to supplement the endothermic heat in the inner steam reforming layer 2A and the outer steam reforming layer 2B. It is essential to perform an oxidation reaction (exothermic reaction) with a reactive gas, and the oxidation reaction is promoted by an oxidation catalyst.

  First, the partial oxidation reforming layer 3 can be filled with a mixture of an oxidation catalyst and a reforming catalyst. Here, the reforming catalyst used for the partial oxidation reforming layer 3 is methane and / or C2 + component (component having 2 or more carbon atoms) remaining in the reformed gas led to the partial oxidation reforming layer 3. The endotherm for this reforming is provided directly from the heat generated by the oxidation reaction promoted by the mixed oxidation catalyst, as if reforming and oxidation proceed simultaneously. Created.

  Second, the partial oxidation reforming layer 3 can be filled with a mixture of an oxidation catalyst and heat transfer particles. In the partial oxidation reforming layer 3, the temperature immediately below the outlet of the oxidizing gas tends to be the highest, and the temperature decreases as it goes downstream. Therefore, by using partially heat transfer particles in the partial oxidation reforming layer 3, the temperature difference between the upstream side and the downstream side of the partial oxidation reforming layer 3 can be reduced. Here, the heat transfer particles transfer heat generated by the oxidation reaction to the entire partial oxidation reforming layer 3, and thereby the inner steam reforming layer 2 </ b> A and the outer steam adjacent to the partial oxidation reforming layer 3. On the upstream side of the reforming layer 2B, the amount of heat transfer through the tubular partition walls 6A and 6B increases, and the temperature difference between the upstream and downstream of the inner steam reforming layer 2A and the outer steam reforming layer 2B can be reduced. It becomes.

  Furthermore, the partial oxidation reforming layer 3 can be filled with a mixture of an oxidation catalyst, a reforming catalyst, and heat transfer particles. In this case, the partial oxidation reforming layer 3 simultaneously exhibits the action of the second case in the first case.

  As the reforming catalyst used for the partial oxidation reforming layer 3, it is possible to use the reforming catalyst used for the steam reforming layer 2, but since the partial oxidation reforming layer 3 is in an oxidizing atmosphere, A catalyst in which Ni or Rh is supported alone or in plural is suitable. Moreover, the material of the heat transfer particles used for the partial oxidation modified layer 3 is not particularly limited, but a material having higher thermal conductivity is preferable, and porous silicon carbide particles are preferable.

  The installation position of the tubular ring 13 for ejecting the oxidizing gas is preferably a relatively upper portion in the partial oxidation reforming layer 3, but is not particularly limited, and considering the gas flow and the direction of heat transfer, A position higher than the inner steam reforming layer 2A and the outer steam reforming layer 2B is preferable. Further, the upper and lower sides of the tubular ring 13 for ejecting the oxidizing gas can be filled with the same mixture, but different ones can also be filled.

The amount of the oxidizing gas supplied from the tubular ring 13 for ejecting the oxidizing gas to the partial oxidation reforming layer 3 varies depending on the type of raw material, but the O ₂ / C ratio is about 0.001 to 0.5. Is preferred. Thereby, the highest temperature part of the partial oxidation reforming layer 3 becomes about 650-850 degreeC. Therefore, it is not necessary to use a particularly expensive material for the oxidation autothermal reformer.

  The reformed gas partially oxidized and / or reformed in the partially oxidized reformed layer 3 passes through the partition receiver 9B, is guided to the reformed gas channel 16, and is discharged from the reformed gas discharge pipe 8. Is done. Thereafter, the discharged reformed gas can be supplied to a solid oxide fuel cell or the like as it is.

  For example, when the reformed gas is used in a solid oxide fuel cell, the generated reformed gas is supplied to the anode electrode of the solid oxide fuel cell via the anode fuel introduction line. At this time, air is supplied from the cathode air introduction line to the cathode electrode of the solid oxide fuel cell, and electric power is generated electrochemically in the solid oxide fuel cell. In the anode electrode made of Ni cermet or the like, methane contained in the reformed gas undergoes a reforming reaction, and further hydrogen and carbon monoxide are generated to become a fuel gas for power generation. This power generation usually requires that the solid oxide fuel cell be maintained at 700 to 1000 ° C. Hydrogen, carbon monoxide, nitrogen, and water and carbon dioxide generated by the power generation reaction that were supplied to the anode electrode but did not contribute to power generation are discharged from the anode exhaust gas outlet, while from the cathode exhaust gas outlet, power generation is performed. Nitrogen and residual oxygen in the air that did not contribute to air are discharged. Part of the heat required for the oxidation autothermal reformer can be provided by using high-temperature anode exhaust gas or cathode exhaust gas, or by burning hydrogen, carbon monoxide, or methane contained in the anode exhaust gas. it can.

  And, by supplying the reformed gas to the fuel cell from the oxidation autothermal reformer to which the operation method of the present invention is applied, fluctuations in the flow rate of the reformed gas supplied to the fuel cell can be suppressed. This can prevent adverse effects on the power generation status of the fuel cell.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

In the oxidation autothermal reformer for a 1 kW class solid oxide fuel cell shown in FIG. 1, steam is supplied by pumping ion exchange water to a heated evaporator, and kerosene is sent as hydrocarbons. By supplying with a liquid pump and supplying air as an oxidizing gas with a blower, the reformed gas can be produced under conditions of S / C ratio = 3.0 and O ₂ / C ratio = 0.191 during rated operation. went. As kerosene, desulfurized kerosene having a sulfur content reduced to less than 1 mass ppm in advance was used, and was supplied after mixing steam and vaporized kerosene upstream of the reforming catalyst layer. After supplying predetermined amounts of water vapor, kerosene, and air, and the reformed gas began to be stably generated, the electric heater used to raise the temperature of the oxidation autothermal reformer was turned off. The composition of the reformed gas in the rated operating state with a load of 100% is 48 mol% hydrogen, 4 mol% carbon monoxide, 6 mol% methane, 20 mol% carbon dioxide, 22 mol% nitrogen, as a dry base excluding moisture. Met.

  In the operation of reducing the amount of reformed gas generated by changing the operation load of the oxidation autothermal reformer from 100% to 95%, and further from 95% to 90%, the operation condition change order of 6 patterns shown in Table 7 is followed. The supply amount of steam, air and kerosene is changed, the temperature of the steam reforming catalyst layer and the partial oxidation reforming catalyst layer of the oxidation autothermal reformer is changed, and the current is energized at a constant current value at each operating load. The change in cell voltage of a solid oxide fuel cell (SOFC) was monitored.

Example 1
First, after reducing the value of the current applied to the solid oxide fuel cell to reduce the power generation output from 100% to 95% of the rated load, first, according to the operating conditions shown in Table 1 in the oxidation autothermal reformer, The operating load of the oxidation autothermal reformer is reduced by reducing the kerosene supply, reducing the air supply immediately after the temperature of the partial oxidation reforming catalyst layer starts to rise, and then reducing the steam supply. When reduced, as shown in the column of Example 1 in Table 7, the temperature of the steam reforming catalyst layer of the oxidation autothermal reformer does not decrease more than before the change of the operating conditions, and the solid oxide The cell voltage of the fuel cell was not significantly decreased after the change of the operating conditions, and the operating load could be changed satisfactorily. The same result was obtained when the operating load was changed from 95% to 90%.

(Comparative Example 1)
First, after reducing the value of the current applied to the solid oxide fuel cell to reduce the power generation output from 100% to 95% of the rated load, the oxidation autothermal reformer was first operated according to the operating conditions shown in Table 2. When the kerosene supply amount was reduced, the water vapor supply amount was reduced, and then the air supply amount was reduced to reduce the operating load of the oxidation autothermal reformer, As shown in the column, the temperature of the steam reforming catalyst layer of the oxidation autothermal reformer did not decrease from before the change of the operating conditions, but the cell voltage of the solid oxide fuel cell was changed A phenomenon of lowering was observed. This is considered to be due to the fact that the amount of fuel gas to the solid oxide fuel cell has decreased more than necessary for a long time. The same result was obtained when the operating load was changed from 95% to 90%.

(Comparative Example 2)
First, after reducing the value of the current supplied to the solid oxide fuel cell to reduce the power generation output from 100% to 95% of the rated load, the oxidation autothermal reformer was first operated according to the operating conditions shown in Table 3. When the air supply amount is reduced, the kerosene supply amount is then reduced, and then the steam supply amount is reduced to reduce the operating load of the oxidation autothermal reformer, the comparative example 2 of Table 7 As shown in the column, the cell voltage of the solid oxide fuel cell did not decrease after the change of the operating condition, but when the supply amount of air was reduced, the O ₂ / C ratio decreased and oxidation occurred. A phenomenon was observed in which the temperature of the steam reforming catalyst layer of the autothermal reformer decreased. The same result was obtained when the operating load was changed from 95% to 90%.

(Comparative Examples 3-5)
Further, in the oxidation autothermal reformer, when the operating load of the oxidation autothermal reformer was changed from 100% to 95% according to the operating conditions shown in Tables 4 to 6, Comparative Example 3 to Comparative Example in Table 7 As shown in the column 5, the phenomenon that the S / C ratio of the oxidation autothermal reformer becomes lower than the value before and after the change of the operation load is recognized. It was expected that the durability of the would decrease. In the procedure for changing the operating conditions of Comparative Examples 3 and 5, the temperature of the steam reforming catalyst layer of the oxidation autothermal reformer is lower than before the operating conditions are changed, or the cell voltage of the solid oxide fuel cell is changed. However, there was a phenomenon that it was lower than after the change of operating conditions. The same result was obtained when the operating load was changed from 95% to 90%.

It is the schematic of an example of the oxidation autothermal reforming apparatus suitable for implementation of this invention. It is sectional drawing which follows the II-II line | wire of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Oxidation autothermal reformer 2 Steam reforming layer 2A Inner steam reforming layer 2B Outer steam reforming layer 3 Partial oxidation reforming layer 4 Inner cylinder 5 Outer cylinder 6 Tubular partition 6A Radial inner partition 6B Radial outer Partition wall 7 raw material introduction pipe 8 reformed gas discharge pipe 9A, 9B, 9C partition receptacle 10 partition 11 opening 12 oxidizing gas introduction pipe 13 tubular ring 14 raw material flow path 15, 16 reformed gas flow path

Claims (7)

An operation method of an oxidation autothermal reformer for producing a reformed gas mainly composed of hydrogen by a reforming reaction using a hydrocarbon or an aliphatic alcohol, water vapor and an oxidizing gas as raw materials,
The oxidation autothermal reformer is an oxidation autothermal reformer for fuel cells,
When reducing the amount of reformed gas produced, the order of decreasing the supply amount of the hydrocarbon or aliphatic alcohol first, then reducing the supply amount of the oxidizing gas, and finally decreasing the supply amount of the water vapor The operating method of the oxidation autothermal reformer is characterized in that the operating conditions are changed in step (b). When the amount of reformed gas produced is reduced, the O ₂ / C ratio after reduction with respect to the amount before reformed gas production is reduced (included in the oxidizing gas relative to the number of moles of carbon contained in the hydrocarbon or aliphatic alcohol). The method of operating an oxidation autothermal reformer according to claim 1, wherein the ratio of the number of moles of oxygen molecules generated is increased.   The operation method of the oxidation autothermal reformer according to claim 1, wherein the operation of reducing the reformed gas generation amount is performed in a plurality of times.   4. The supply amount of the oxidizing gas is reduced immediately after detecting the start of an increase in catalyst layer temperature after reducing the supply amount of the hydrocarbon or aliphatic alcohol. 5. Operation method of the oxidation autothermal reformer.   The method for operating an oxidation autothermal reformer according to any one of claims 1 to 4, wherein the oxidizing gas is air.   The said hydrocarbon or aliphatic alcohol is at least one selected from the group consisting of light oil, kerosene, gasoline, naphtha, LP gas, ethanol and methanol, according to any one of claims 1 to 5. Operation method of oxidation autothermal reformer. The method for operating an oxidation autothermal reformer according to claim 1 , wherein the fuel cell is a solid oxide fuel cell.

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