RU2232710C1 - Hydrogen generator - Google Patents

Abstract

FIELD: production of power equipment.

SUBSTANCE: the invention presents a hydrogen generator and is dealt with the field of the power production. The hydrogen generator may be used for production of hydrogen both at the stationary power-generating plants and on the transport installations. The hydrogen generator operating at the expense of a hydrolysis of a solid reagent - aluminum has a reaction vessel, a main pipeline for delivery of an aqueous solution of sodium hydrate, a main pipeline for delivery of hydrogen. The hydrogen generator also has a container with a solid reagent - aluminum, the heat exchanger for removal of the reaction heat made out of metal resistant to action of the aqueous solution of the sodium hydrate placed inside a reaction vessel filled in with an aqueous solution of sodium hydrate and having a direct thermal contact with the solid reagent - aluminum. At that the metal, out of which the heat exchanger is made, has a much higher thermal conductivity, than the solid reagent - aluminum. The invention allows to intensify process of generation of hydrogen.

EFFECT: the invention allows to intensify process of generation of hydrogen.

2 dwg

Description

The invention relates to power equipment and can be used to produce hydrogen both in stationary installations and in transport.

The generator is a chemical reactor that produces hydrogen by hydrolysis, i.e. decomposition of water. For this, a solid reagent is used, i.e. the hydrolysis reaction is heterogeneous in nature - occurs on the surface of a solid. It is assumed that the hydrogen thus obtained is subsequently used as fuel for power plants (EC) on fuel cells (FC). In addition, hydrogen can be used, of course, in other areas, for example, in metal cutting, welding, etc.

Earlier in the latter case, acetylene was mainly used, which was synthesized in generators having a similar design [1]. A heterogeneous hydrolysis reaction was also used, and calcium carbide served as a solid reagent. This technical solution is taken as an analog. Its disadvantages include the following:

- synthesized acetylene is not suitable for oxygen-hydrogen fuel cells and needs further decomposition to hydrogen; this significantly complicates the design of the EU and reduces its efficiency; low weight hydrogen content in such generators makes them unsuitable for transport;

- during the operation of acetylene generators an insoluble precipitate (lime) is formed, the accumulation of which limits the time of continuous operation of the generator, worsens its overall weight characteristics; removal of sludge from the reactor requires additional energy consumption, complicates the design of EU, reduces its efficiency;

- a solid reagent (calcium carbide) is a material whose long-term storage is quite difficult and unsafe, because it is very hygroscopic and when it absorbs moisture from the air, it releases acetylene.

Closer in essence is a hydrogen generator designed to power a fuel cell based on a fuel cell used in an underwater vehicle [2]. This reactor also uses a hydrolysis reaction, and metal hydrides (i.e. metal compounds with hydrogen) are used as a solid reagent. The generator includes a reaction vessel into which a “chamber” with metal hydride is placed, a heat exchanger for removing heat of reaction, a device for mixing water in the reaction vessel (located inside the latter) and a line for supplying water to the reactor and removing hydrogen from the reactor. Moreover, to improve the overall weight and weight characteristics of EU, hydrides of light metals are used, which are very expensive (LiH, BeH ₂ ...). This significantly increases the cost of hydrogen produced and is a significant drawback of the generator [2], adopted in this case as a prototype.

In addition, the disadvantages of the prototype include the following:

- the solid reagent used for hydrolysis represents a significant danger from a fire point of view, since metal hydrides are prone to self-decomposition with hydrogen evolution and are hygroscopic, which also leads to their decomposition with hydrogen evolution;

- metal hydrides are expensive, and the recovery of metals obtained by hydrolysis of metal hydrates is technically difficult and energy intensive;

- the lack of design of the generator is also its inertia, which complicates its use in transport power plants.

The latter is due to the fact that for the generator to operate in stationary mode, it is necessary to maintain a certain temperature of solid and liquid reagents. If there are a lot of them, maintaining the temperature regime of the generator is technically complicated and requires significant energy consumption (for example, the operation of mixing devices). In addition, the transient modes of operation of such a hydrogen generator take a lot of time in this case, since they require changes in the temperature of large masses of substances having a relatively low thermal conductivity (water, metal hydrides). For transport tasks, this is a huge drawback.

The objective of the proposed solution is to develop a hydrogen generator with high speed. In addition, the generator must operate on cheap and common raw materials, the storage of which is safe, and use in hydrolysis does not produce insoluble sediment. The problem is solved in that in a hydrogen generator operating by hydrolysis of a solid reagent - aluminum, having a reaction vessel, a line for supplying an aqueous solution of caustic soda, a line for delivering hydrogen, a container with a solid reagent - aluminum is introduced, a heat exchanger for removing heat of reaction made from a metal resistant to the action of an aqueous solution of caustic soda, placed inside a reaction vessel filled with an aqueous solution of caustic soda and having direct thermal contact with a solid reagent - aluminum, the metal of which the heat exchanger is made has a higher thermal conductivity than the solid reagent - aluminum. Thus, aluminum and an aqueous solution of alkali (NaOH) are used as reagents for the hydrolysis reaction; as a result of the reaction, a liquid alkaline solution of sodium aluminate is formed. The speed of the hydrogen generator increases due to the intensification of thermal processes in the generator and their localization.

The essence of the proposal is as follows. The thermal processes in the proposed generator are accelerated due to the fact that the solid reagent involved in hydrolysis is a metal with high thermal conductivity (aluminum) and, in addition, is in direct thermal contact with both the starting heater and the heat exchanger to remove reaction heat. In addition, the metal of which this heat exchanger is made also conducts heat well. If its thermal conductivity is higher than that of a metal reagent (Al), the speed of the generator is limited only by the thermal conductivity of the reagent itself. As a material for such a heat exchanger, for example, copper can be used, which has a higher thermal conductivity than aluminum and is resistant to alkali.

In this heat exchanger, it is also advisable to combine two functions - the removal of reaction heat in the stationary mode of operation of the generator and the heat influx when the generator is started. Thus, the heat exchanger to remove reaction heat during the start-up of the generator can serve as a starting heater. The temperature of the coolant circulating in the heat exchanger is higher than the temperature of the liquid in the generator. Due to the high thermal conductivity of the reagent metal, the metal of which the heat exchanger is made, and their direct thermal contact, the heating of the solid reagent also occurs at an increased rate.

The performance of the proposed reactor is also increased due to the fact that the temperature control is carried out not in the entire reaction mixture (as in the prototype), but only near a solid reagent. Since hydrolysis in this case is heterogeneous and the reaction proceeds on the surface of aluminum, there is no need to maintain the temperature of the entire reaction mixture at the required level. It is enough to regulate the temperature of aluminum itself and a thin layer of liquid near its surface. Thus, localization of controlled thermal processes, i.e. The area in which heat transfer is controlled decreases. Accordingly, the mass of the substance contained in this zone is reduced.

Such a localization of the heat control zone can significantly increase the speed of thermal processes that affect the evolution of hydrogen, and, consequently, the speed of the hydrogen generator. The latter, thus, increases simultaneously due to several factors:

- use for hydrolysis of a solid reagent with high thermal conductivity (Al);

- direct thermal contact of the reagent metal with the starting heater and heat exchanger to remove reaction heat;

- high thermal conductivity of the metal, which is made of a heat exchanger to remove heat of reaction;

- localization of thermal processes responsible for the generation of hydrogen.

The scheme of the proposed generator is illustrated in figure 1, where it is indicated:

1 - reaction vessel;

2 - container with solid reagent;

3 - solid reagent - aluminum (depicted in the form of granules, but can be used in the form of a sheet, etc.);

4 - a line for supplying a liquid reagent - an aqueous solution of sodium hydroxide (NaOH);

5 - heat exchanger for removing heat of reaction and heating of aluminum when the generator starts;

6 - line for the delivery of hydrogen.

The generator operates as follows. Aluminum (in the form of granules, sheet, etc.) is placed in a container with solid reagent (2) so that the solid reagent (3), for example aluminum, has direct thermal contact with the heat exchanger (5) to remove reaction heat and heat aluminum when starting the generator. The latter is located inside the reaction vessel (1). An alkali aqueous solution, such as NaOH, is supplied to the reaction vessel (1) along the liquid reagent supply line (4), so that the container (2) with the solid reagent (aluminum) is immersed in this solution. The exothermic reaction of hydrolysis and the evolution of hydrogen begins, which is discharged along the hydrogen delivery line (6). In this case, the self-heating of the reagents occurs rather slowly, and in order to accelerate the hydrolysis, a hot heat carrier is supplied to the heat exchanger (5), which heats the aluminum and the solution located near it. Hydrogen evolution is intensified, and after reaching the required flow rate, the heat exchanger (5) is switched to the heat generated in the reaction.

The effectiveness of the proposed measures has been verified experimentally. To do this, in laboratory conditions, a glass small-scale operating model of the proposed generator was made, the operability of the proposed device and its speed were checked.

A photo of the generator is given in figure 2, where the main elements of its design are also indicated. The alkali solution is not poured into the generator.

The heat exchanger for removing the reaction heat was made in the form of a spiral from a copper tube, through which cold tap water was supplied. Depending on the performance of the generator, the temperature in it varied in the range of 40-120 ° C. At the same time, the generator’s hydrogen output was determined by the water flow rate in the cooling heat exchanger. Direct thermal contact between the heat exchanger and the metal reagent was carried out due to the fact that aluminum granules were poured directly onto the copper coil of the heat exchanger to remove the reaction heat (Fig. 2). A starting heater was not used in the tests, and the generator was started by self-heating, which took ~ 20 min.

As the experiments showed, a noticeable (several times) decrease in the productivity of the generator was achieved within 3-10 s after changing the flow rate of water in the spiral heat exchanger. It is obvious that during such a time it is practically impossible to change the temperature of the liquid in the flask (~ 0.5 L of an aqueous NaOH solution) anyway, and the quick “response” of the generator to small changes in the flow rate of cooling water is due to the high heat transfer rate through copper and aluminum and localization controlled thermal and chemical processes near the surface of the granules (A1).

Thus, this technical solution allows you to create a hydrogen generator that uses for hydrolysis cheap, common substances that do not form a solid precipitate as a result of the reaction. Moreover, the design of the generator is fast enough, which is important for its use in transport.

The performance of the proposed design is confirmed experimentally.

Sourse of information

1. Rybakov VV Textbook gas welder. M .: Mashgiz., 1956, p. 32.

2. Hydrogen generation by hydrolysis for a power plant based on underwater fuel cells. US patent No. 5372617, 1994

Claims (1)

A hydrogen generator operating by hydrolysis of a solid reagent - aluminum, having a reaction vessel, a line for supplying an aqueous solution of caustic soda, a line for delivering hydrogen, characterized in that it contains a container with a solid reagent - aluminum, a heat exchanger for removing reaction heat made of metal, resistant to the action of an aqueous solution of caustic soda, placed inside the reaction vessel, filled with an aqueous solution of caustic soda and having direct thermal contact with a solid reagent - aluminum, while The lll of which the heat exchanger is made has a higher thermal conductivity than the solid reagent - aluminum.

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