DE19516879C1 - Responsive system producing gaseous fuel and steam for reforming and use in fuel cells - Google Patents

Abstract

This system produces gaseous fuel, e.g. methanol and / or steam as the source material for reforming of hydrocarbons, for use in fuel cells, e.g. for mobile use. It comprises a first heat exchanger constructed for evaporative duty, and a second heat exchanger for superheating. The feed material is at least partially evaporated before being fed by an interconnecting line from the evaporator to the superheater. In this original arrangement, the gas prodn. system (1) is thermally insulated from the surroundings, at least in the region of the interconnection (7).

Description

The invention relates to a system for generating gaseous Fuel and / or steam as a starting material for the Reforming hydrocarbons for fuel cells applications according to the preamble of claim 1.

EP 0 201 670 A2 describes a device for processing of methanol known as a hydrogen source for fuel cells, the first heat exchanger designed as an evaporator and a second heat exchanger designed as a superheater and contains a connecting line over which the at least partially Evaporated methanol from the evaporator to the superheater becomes.

In mobile applications, the gas flow may vary depending on of the adjacent fluctuate almost strongly. The problem occurs that the temperature of the escaping gaseous methanol / - Water mixture fluctuates depending on the gas flow.

However, this has negative consequences for the subsequent reform Mation of the methanol / water mixture, because this on the one hand CO production influences and secondly the implementation kinematics of the catalyst is changed.

It is the object of the invention to provide a generic gas improve the generation system so that the exiting gaseous starting material regardless of the gas flow has constant operating parameters.

The task is characterized by the characteristic features of the Claim 1 solved.  

By applying insulation, especially in the area of Connection line can ensure that the temperature of the gas mixture essentially regardless of the gas flow remains constant. The wall cools with small gas flows since the waste heat is greater than the heating effect of the flowing Gas. With large gas flows, however, the waste heat is generated by the Heating effect of the flowing gas is compensated and cooling prevents the inner tube wall. This effect can be achieved through the Insulation can be reduced or even completely eliminated.

The arrangement according to the first embodiment has the Advantage on that in addition to the required insulation effect the dead space is reduced, resulting in a verb system dynamics. At the same time, the Introducing the filler increases the flow rate. Finally, the funnel-shaped design of the one controlled entry or exit geometry Atomization of the medium.

The second embodiment in the form of double-walled Housing or pipe walls that are made of a liquid, flows through the heat transfer medium used for energy input have the advantage that not only the cooling of the Prevents walls, but even actively tempering the External walls are made, the wall temperature automatically to the Temperature of the heat transfer medium is adjusted.

The invention is described in more detail below with the aid of a drawing described, wherein

Fig. 1 is a schematic representation of a first embodiment in section and

Fig. 2 shows a schematic diagram of another embodiment example also in section.

The system in Fig. 1 products marked with 1 gas generation is composed of two series-connected heat exchangers 2, 3, which are formed exchanger in the embodiment shown as a cross-channel heat. The heat exchangers 2 , 3 consist of a cylindrical housing 4 , into which a cube-shaped heat exchanger block 5 is introduced. The diameter of the housing 4 is chosen so that the edges of the heat exchanger block 5 each touch the inner wall of the housing. At these contact surfaces, the heat exchanger block 5 is then connected gas-tight to the housing inner wall. The heat exchanger 2 , 3 are completed by floor and ceiling surfaces, not shown, which are connected gas-tight to the heat exchanger block 5 . As a result, four fluidically separate volumes are formed between the heat exchanger block 5 and the housing 4 . In the area of these volumes are then on opposite Be th of the housing 4 pipes 6-12 attached to supply or discharge of the methanol / water mixture or the heat carrier medium such that the pipes 6-12 each face one side surface of the heat exchanger block 5 against.

The heat exchanger block 5 has first channels for the methanol / water mixture and second channels for the heat transfer medium, which run essentially in the transverse direction to the first channels, the channels not being shown for reasons of clarity. Since cross-channel heat exchangers are known from the prior art, the exact structure is not further described here.

In operation, the methanol / water mixture is conveyed with the aid of a pump 13 from a storage tank (not shown) and fed via the first feed line 6 to the first heat exchanger formed as an evaporator 2 . There the methanol / water mixture flows through the heat exchanger block 5 through the first channels, the mixture being at least partially evaporated. The energy required for this is supplied via a heat transfer medium, for example a thermal oil, which flows through the heat transfer block 5 through the second channels in the transverse direction. The at least partially evaporated gas mixture is then led via a connecting line 7 to the second heat exchanger, which is designed as a superheater 3 , where it completely evaporates when flowing through the first channels of the heat exchanger block 5 and is then overheated to a predetermined temperature level. The gas mixture is then discharged from the gas generating system 1 via a further pipeline 8 and, for example, fed to a downstream but not shown reformer.

The energy required for the superheater 3 is also supplied via a heat transfer medium, for example a thermal oil. A common thermal oil system is preferably used for both heat exchangers 2 , 3 . Since the superheater 3 operates at a higher temperature level than the evaporator 2 , the thermal oil is preferably first passed through the superheater 3 and only then through the evaporator 2 . The hot thermal oil is fed to the superheater 3 via a first feed line 9 . After flowing through the heat exchanger block 5 through the second channels, the thermal oil is then discharged via an outflow line 10 , this outflow line 10 also serving as a supply line 11 for the evaporator 2 . After the thermal oil has also flowed through the heat exchanger block 5 here, it is then discharged via a further outflow line 12 .

In mobile fuel cell applications, it is important that the operating conditions for the methanol reforming are as constant as possible despite the changing load over the entire operating range. On the one hand, the temperature of the gas provided by the gas generation system 1 should be as constant as possible, since depending on the temperature of the flowing gas, the conversion kinematics of the catalyst in the reformer are established. The problem arises here that in the gas generation system 1 the heat loss to the outside is influenced by the gas flow. With a low gas flow, the pipe and housing walls cool down because the waste heat is greater than the heating effect of the flowing gas. With a large gas flow, on the other hand, the waste heat is compensated for by the heating effect of the flowing gas, so that cooling of the walls no longer occurs.

On the other hand, it should be prevented that neither methanol nor Water condenses on the pipe or housing walls, otherwise the gas flow to the reformer unwanted liquid droplets contains. This is also essentially due to the Temperature of the pipe and housing walls affected.

To solve this problem, it is proposed to isolate the gas generation system 1 and here in particular the connecting line 7 from the environment. This reduces fluctuations in the wall temperature and thus reduces the parts listed above. In principle, it is possible to apply any insulation materials to the outer walls of the connecting line 7 and, if appropriate, the heat exchangers 2 , 3 .

Another possibility is to introduce a filler 14 made of a thermally insulating material into the pipes 6-8, for example made of stainless steel, for the methanol / water mixture. For example, a temperature-stabilized plastic can be used for this. The filler 14 is inserted into the connecting line 7 and secured against slipping by clamping or positive locking. A migration of the filling member 14 in the direction of flow could lead to a partial closure of the entry surface of the heat exchanger block 5 . With this type of filler 14 , a functional separation is achieved, the stainless steel tube absorbing the mechanical forces and the filler 14 ensuring insulation from the environment. Such a filling member 14 is provided for the connecting line 7 in any case. The first feed line 6 and / or the further pipeline 8 can, however, also be provided with such a filling member 14 if required.

Another advantage of these filling elements 14 is the reduction in the dead space in the gas generation system 1 and the associated increase in dynamics. Cross-channel heat exchangers are preferably designed in a cube shape to easily separate the inlets and outlets of the two media. To square A tread of the heat exchanger block 5 out but a transition from the pipes 6-8 , which generally have a round cross section, must be created. However, in order to be able to utilize the entire heat exchanger surface, a correspondingly large cross section must be selected for the pipes 6-8 . This leads to the fact that a large dead volume is created in the entire inlet area of the heat exchanger 2 , 3 , which reduces the dynamics of the evaporation / overheating process. However, this dead volume is reduced by the filling members 14 . At the same time, however, a funnel-shaped configuration of the inlet and outlet regions of the filling elements 14 can ensure that the gas mixture is distributed uniformly over the entire inlet surface of the heat exchanger block 5 . In addition, a controlled atomization of the medium can be achieved by appropriate design of the inlet and outlet geometries.

Another advantage of this arrangement is the relatively short heating time of the system, since the stainless steel tube does not have to be heated in the starting phase. Finally, the reduction in cross section caused by the filling member 14 in the connecting line 7 leads to an increase in the flow rate. This avoids a change in the temperature of the methanol / water mixture during load changes and at the same time reduces the amount of mixture evaporated in the reduced dead space.

A further exemplary embodiment is shown in FIG. 2 , the same parts being identified with the same reference numerals as in FIG. 1. In contrast to FIG. 1, no additional insulating material is introduced here, but the heat transfer medium is used at the same time for tempering the housing wall. For this purpose, at least part of the heat exchanger housing and the connecting line 7 are double-walled, the spaces 15 formed in this way being used as a return line 10-12 for the heat transfer medium. The heat transfer medium is in turn fed via a first feed line 9 to the superheater 3 , where it flows through the heat exchanger block 5 via the second channels in a direction transverse to the gas flow direction. In the area of the volume opposite the feed line 9 , however, no discharge line 10 is now provided, but only an opening 16 through which the heat transfer medium can enter the spaces 15 of the double-walled housing.

Correspondingly, a second opening 17 is then arranged in the evaporator at the point at which the supply line 11 for the heat transfer medium was provided in FIG. 1, which connects the intermediate spaces 15 in the housing wall to the heat exchanger block 5 of the evaporator 2 . The gaps 15 in the double-walled housing are arranged such that an adequate flow connection between the first and the second opening 16 , 17 is guaranteed in all cases. The heat transfer medium is then discharged again through the discharge line 12 after flowing through the heat exchanger block 5 . The flow through the housing wall now causes it to be kept at an uncritical temperature level, regardless of the gas flow. The exact design of the spaces 15 in the housing and tube walls can be adapted to the special requirements of the respective gas generating system 1 .

Although only in the described exemplary embodiments the steam reforming of methanol was referred to, the system can also be used for other hydrocarbons Substances are used. In addition to the described benen system in which the fuel and the water as a mixture is evaporated in a common system, also for every exit a separate evaporator or superheater be provided.

Claims (6)

1. System for the production of gaseous fuel and / or water vapor as a starting material for the reforming of hydrocarbons for fuel cell applications, consisting of a first, designed as an evaporator heat exchanger and a second, designed as a superheater, the at least partially evaporated starting material via a connecting line is led from the evaporator to the superheater, characterized in that the gas generation system ( 1 ) is insulated from the environment at least in the region of the connecting line ( 7 ) by insulating means. 2. Gas generation system according to claim 1, characterized in that a filling member ( 14 ) made of a thermally insulating material is introduced at least into the connecting line ( 7 ). 3. Gas generation system according to claim 2, characterized in that a filling member ( 14 ) made of a thermally insulating material is also introduced into the first feed line ( 6 ) to the evaporator ( 2 ). 4. Gas generation system according to claim 2, characterized in that the filling member ( 14 ) in the inlet and / or outlet area to the heat exchangers ( 2 , 3 ) is funnel-shaped. 5. Gas generation system according to claim 1, characterized in that the housing ( 4 ) of the heat exchanger ( 2 , 3 ) and / or the connecting line ( 7 ) is at least partially double-walled and that a heat transfer medium is guided through the intermediate space ( 15 ) thus formed . 6. Gas generation system according to claim 5, characterized in that the heat transfer medium after flowing through the heat exchanger block ( 5 ) of the super heater ( 3 ) through the spaces ( 15 ) of the super heater ( 3 ), the connecting line ( 7 ), the evaporator ( 2 ) and then passed through the heat exchanger block ( 5 ) of the evaporator ( 2 ) itself.