JPH03214567A - Method for starting fuel modifier - Google Patents

Abstract

PURPOSE:To steam reform higher and unsaturated hydrocarbon series crude oil at a low S/C by oxidating and exhausting carbons educted onto a catalyst layer, and thereafter sending the fuel to a reforming pipe together with steam. CONSTITUTION:When a fuel reformer 1 to make steam reforming of a crude fuel 6 of hydrocarbon series such as naphtha is operated with frequent start and stop, hydrogen is generated in a catalyst layer in a reformer pipe 4 and also carbon eduction is made owing to secondary reactions. This educted carbon is oxidized by an oxidator gas into CO or CO2 by sending the oxidator gas into the reformer pipe 4 at a certain temp. appropriate for oxidation of carbon at the temp. rise time of catalyst layer to be made when the fuel reformer 1 is started, and the CO or CO2 gas thus produced can be removed. The steam carbon ratio (S/C) under driving can thus be lessened by removing the educted carbon from the catalyst layer when the fuel reformer 1 is started.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a fuel reformer for reforming hydrocarbon-based raw fuel such as naphtha into hydrogen-rich gas, and in particular for converting the reformed gas into a fuel. This article concerns how to start up the fuel reformer that supplies the fuel to the battery. [Prior art] Hydrocarbons typically represented by methane. The steam reforming reaction uses a Ni-based catalyst with a reaction rate of about 600 to 900
It is carried out at ℃. Ideally, the reaction formula is as shown below.
It seems like. m CmH. + n H. O-on Go + (n +
-)H, ―■2 n C O + n H * O - n C O t
+ n H * −−−−−−−■m C * H s + 2 n H t O →n C
O t + (2 n +) H t −・・■
2 In the above reaction, ■ is an endothermic reaction, ■ is an exothermic reaction, and ■, which is the total of the reactions of ■ and ■, is an endothermic reaction. Therefore, as the temperature of the catalyst rises, the hydrocarbon decomposition reaction (Equation 2) proceeds to the right, the CO transformation reaction proceeds to the left, and Equation 2 proceeds to the right. Based on such reactions, the following method is used to reform hydrocarbon raw fuels such as naphtha into hydrogen-rich gas. In other words, a reforming tube filled with a reforming catalyst is placed in a furnace vessel equipped with a burner, raw fuel is passed through the reforming tube along with steam, and the reforming tube is heated by the heat medium generated by combustion in the burner. The temperature of the catalyst layer consisting of the Kaiga catalyst inside the reforming tube is raised, and the raw fuel is steam-reformed. The reformed gas that has undergone steam reforming is supplied to the fuel cell. By the way, when attempting to steam reform raw fuel containing higher hydrocarbons with a large number of carbons or large amounts of unsaturated hydrocarbons, the following carbon precipitation reaction may occur in the actual reaction within the catalyst layer. It can occur as a side effect. m CaHm −4n C ” Hx −・
-■2 When the carbon precipitation reaction occurs in this way, the pressure loss in the catalyst layer increases, and the equilibrium of reaction (2) shifts to the left, suppressing the decomposition of hydrocarbons. In more extreme cases, the catalyst layer becomes blocked by carbon, making operation impossible. In order to avoid this situation, in the steam reforming of high-grade hydrocarbons or hydrocarbons containing a large amount of unsaturation, the proportion of steam supplied in excess (usually the number of moles of water molecules per mole of carbon atoms) is The steam carbon ratio S/C (referred to as the ratio S/C) is increased to a larger excess, and the reaction intermediate between water and hydrocarbons. This increases the chance of reaction with carbon and suppresses carbon precipitation. In addition, decoking, or decoking, is used to oxidize and burn off the carbon deposited during periodic maintenance of the entire plant using various oxidizing agents. [Problems to be Solved by the Invention] When trying to obtain H gas to be used in the fuel cell body by steam reforming from the above-mentioned higher-grade hydrocarbon raw fuel containing a large amount of unsaturation, S/C needs to be 71.5 to 2.5 times larger than when the raw fuel is pure methane. On the other hand, in the case of a fuel cell power generation system consisting of an on-site fuel cell and a fuel reformer, etc., the efficiency of the system is improved by having the ability to supply more high-temperature waste heat as a cogeneration system. It is tied to By the way, steam for steam reforming uses the waste heat from a fuel cell power generation system, and requires the highest temperature and the largest amount of heat. Therefore, the large amount of excess steam required for reforming means that the exhaust heat cannot be supplied to the outside. In addition, the steam for reforming in particular is generated by using the energy of the exhaust heat of the fuel cell itself from the pressurized cooling water of the fuel cell body, so it is possible to supply steam that exceeds the exhaust heat energy of the battery body. This requires a separate power source, which necessitates the use of an electric heater, etc. for startup, which poses the problem of reducing the efficiency of the entire fuel cell power generation system. Furthermore, when performing decoking during regular maintenance, equipment and utilities are required for this purpose, which raises the problem of increased equipment and maintenance costs. The purpose of the present invention is to convert higher-grade unsaturated hydrocarbon raw fuels such as naphtha into as low S/C ratio as possible.
The purpose of the present invention is to provide a method for starting a fuel converter that allows steam reforming and does not require decoking. [Means for Solving the Problems] In order to solve the above problems, according to the present invention, a hydrocarbon fuel such as naphtha is passed together with steam through a reforming tube having a catalyst layer filled with a reforming catalyst. In the startup method of a fuel reformer, in which the reformer tube is heated by a heat medium generated by combustion in a burner and reformed into hydrogen-rich gas, the oxidizer gas is After air is sent to the reforming tube to oxidize and discharge the carbon deposited on the catalyst layer, the fuel is sent to the reforming tube together with steam. [Operation] A fuel reformer that steam-reforms hydrocarbon raw fuel such as naphtha is often activated. When the system is stopped and operated, hydrogen is generated in the catalyst layer in the reforming tube by the reactions of formulas 1 to 2 above, and at the same time, carbon is deposited by the side reaction of formula 2. This precipitated carbon can be removed by oxidizing gas by feeding the oxidizing gas into the reforming tube at a predetermined temperature suitable for oxidizing carbon when the temperature of the catalyst layer is raised when starting the fuel reformer. It can be oxidized into Co or Cot gas and removed. In this way, by removing precipitated carbon from the catalyst layer when starting up the fuel reformer, the S/C during operation can be reduced. Note that the smaller the S/C, the easier carbon will precipitate, so consider the operating pattern of the fuel reformer and ensure that the precipitated carbon does not interfere with the operation of the fuel reformer or the fuel cell power generation system equipped with this reformer. S/ so as not to cause any trouble.
Determine C. For example, an on-site fuel cell power generation system starts up at the beginning of the week, rises in temperature, shuts down on the weekend, and operates continuously at night during that time. In this case, the S/C can be lowered to around 4.0, depending on the naphtha composition. [Examples] Examples of the present invention will be described below based on the drawings.
FIG. 1 is a system diagram of a fuel reformer when performing a fuel reformer startup method according to an embodiment of the present invention. In the figure 1
is a fuel reformer, which is a reforming raw material supply system that supplies raw fuel such as a cape, which is made up of a burner 2 and a furnace vessel 3 filled with a reforming catalyst, to a reforming tube 4 together with steam; It is equipped with a raw fuel supply system 6 that supplies raw fuel and a steam supply system 7 that supplies steam to be mixed with the raw fuel. Note that 8.9 is a valve. 10 is a steam reformed gas supply system that supplies steam reformed gas from the reforming pipe 4 to a fuel cell (not shown); 11 is an off-gas discharge system that supplies off-gas containing unused hydrogen from the fuel cell to the burner 2; It is a system. Bypass system 14 connects steam reformed gas supply system 10 and off-gas discharge system 11
is provided. Note 13, 18. 19 is a valve. 15 is a fuel supply system that supplies auxiliary fuel for startup to the burner 2; 16 is a combustion air supply system that supplies combustion air to the burner 2; and 17 is an exhaust gas system that discharges combustion exhaust gas. Reference numeral 20 denotes an exhaust gas supply system that connects the exhaust gas system 17 and the reforming material supply system 5 and supplies combustion exhaust gas to the reforming pipe 4, and is equipped with a valve 21. Reference numeral 22 denotes an exhaust gas exhaust system connected to the steam reforming gas supply system 10 and discharging the combustion exhaust gas that has passed through the reforming pipe 4 to the outside, and is equipped with a valve 23. The method for starting the fuel reformer according to the present invention will be explained with reference to the system diagram in FIG. 1 using the flowchart for starting the fuel reformer shown in FIG. 2 with such a system configuration. Figure 1. In Fig. 2, the fuel reformer is started (valve 8, 9,
13.18, 19.21.23 are closed fi) is performed as follows. In step 31, air is first supplied from the combustion air supply system 16 to the combustion chamber in the furnace vessel 3 of the fuel reformer 1, and the fuel is ignited and combusted by the excess combustion air from the combustion air supply system. The combustion exhaust gas containing residual oxygen that does not contribute to combustion is discharged from the exhaust gas system 17 to the outside. In step 33, the temperature of the catalyst layer in the reforming tube 4 is raised by the combustion gas produced by the combustion in the burner 2. When the temperature of the catalyst layer exceeds 500° C. in step 34, the valve 21 is opened to allow the combustion exhaust gas containing residual oxygen to flow back to the catalyst layer of the reforming tube 4 via the exhaust gas supply system 20 in step 35. Start. Incidentally, the combustion exhaust gas discharged from the catalyst layer is discharged through the valve 23.
The exhaust gas is discharged to the outside from the open exhaust gas exhaust system 22. Then, in step 36, the temperature of the catalyst layer is controlled to be between 500°C and the operating temperature of the fuel reformer. In this state, in step 37, the pressure loss when the combustion exhaust gas flows through the catalyst layer is the same as the initial value of the pressure loss of the catalyst layer at the time of initial filling of the reforming catalyst, which was measured in advance. The flow of the combustion exhaust gas is conducted through the catalyst layer, and in step 38, the flow of the combustion exhaust gas is terminated by closing the valve blunt when the pressure loss becomes the same as the initial value z1. Next, in step 39, the valve 9 is opened and steam is sent from the steam supply system 7 to the catalyst layer in the reforming tube 4 to steam purge the remaining combustion exhaust gas. The steam that has passed through the catalyst layer is discharged from the exhaust gas discharge system 22. After completing the steam purge, the valve 23 is closed, the valve 8 is opened, raw fuel such as naphtha is supplied from the raw fuel supply system 6, and the steam supply system 7
It is supplied to the reforming tube 4 along with steam from the catalytic converter to start reforming and raise the temperature of the catalyst layer. At this time, the steam reformed gas containing unreformed raw fuel is not sent to the fuel cell, and the valve 13
is supplied to the burner 2 through an open bypass pipe 14,
Used as fuel. Then, in step 41, the temperature of the catalyst layer is increased, and when the temperature of the catalyst layer reaches a predetermined temperature suitable for steam reforming, the startup of the fuel reformer is finished. In this way, when the fuel reformer is started, the combustion exhaust gas containing residual oxygen is passed through the catalyst layer at a predetermined temperature when the temperature of the catalyst layer is increased, and the precipitated carbon is oxidized, resulting in CO, CO, The carbon is discharged to the outside, and the carbon is removed from the catalyst layer. Although combustion exhaust gas is used as the oxidizing gas in the above embodiment, the same effect can be obtained by using air diluted with nitrogen gas as the oxidizing gas. [Effects of the Invention] As is clear from the above description, according to the present invention, when the fuel reformer is started and the temperature rises, the oxidant gas is passed through the catalyst layer in the reforming tube at a predetermined temperature and deposited on the catalyst layer. By oxidizing and removing the carbon that is produced, S/C can be lowered even when steam reforming raw fuel containing higher grade unsaturated hydrocarbons, so the amount of steam is reduced. The amount of heat used to heat the fuel is reduced, and even in the case of a fuel cell power generation system, for example, more waste heat can be supplied to the outside. Additionally, since there is no need to install utilities or equipment for decoking, equipment and maintenance costs are reduced, and the time required to remove precipitated carbon is shorter than for decoking operations, which also improves plant efficiency. effective.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a fuel reformer when applying the method for starting a fuel reformer according to an embodiment of the present invention, and FIG. 2 shows the procedure for starting the fuel reformer shown in FIG. FIG. 1: Fuel reformer, 4: Reforming pipe, 20: Combustion exhaust gas Figure 1 Figure 2

Claims (1)

[Claims] 1) A hydrocarbon fuel such as naphtha is passed together with steam through a reforming tube having a catalyst layer filled with a reforming catalyst,
In a fuel reformer startup method that heats a reforming tube with a heat medium generated by combustion in a burner to reform the gas into hydrogen-rich gas, the oxidizing gas is reformed at a predetermined temperature when the reformer is started and the temperature rises. A method for starting a fuel reformer, comprising: supplying air to a pipe to oxidize and discharge carbon deposited on a catalyst layer, and then supplying the fuel together with water vapor to a reforming pipe.