Method for producing hydrogen and/or other gases from steel plant wastes and waste heat

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No. 12/088,579 filed on Dec. 31, 2008, now abandoned, which is the U.S. national phase of PCT/IN2006/000232 filed on Jul. 4, 2006, which claims priority to Indian Patent Application NO. 900/KOL/05 filed on Sep. 30, 2005, the disclosure of which are hereby incorporated in their entirety by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates generally to a method for producing hydrogen and/or other gases from steel plant wastes and waste heat.

Description of Related Art

With the increasing use and depletion of non-renewable sources of energy, such as petroleum, natural gas and coal, hydrogen is being increasingly looked upon as a viable alternative fuel. Quite a few processes exist for separation and collection of hydrogen gas. Among these the most popular are electrolysis and the use of high temperature nuclear reactors or petroleum processing plants to split water (H₂O) into hydrogen and oxygen. These processes are expensive as they involve use of electricity or other chemicals such as sulphuric acid, hydrogen iodide, metallic zinc and zinc oxide, which need closed-loop regeneration and handling. This makes the production of hydrogen a costly process.

In the steel plant the generated wastes, like molten slag from basic oxygen converters called LD slag, at a temperature of about 1600° C. to 1700° C., are dumped into pits for removal and further processing. In the present invention, the heat of this waste material can be used for the production of a gas stream comprising hydrogen gas or hydrogen and carbon monoxide.

SUMMARY OF THE INVENTION

The main object of the present invention, therefore, is to use the heat of steel plant wastes, like molten slags, for generating hydrogen by splitting water and/or steam, or a mixture of the two in the presence of a reducing agent.

Another object of the present invention is to use the heat of steel plant waste for generating hydrogen, carbon monoxide and/or other gases by splitting water or steam or a mixture of the two in the presence of a carbonaceous material.

Water splits into hydrogen and oxygen at 1800° K, i.e., at 1527° C. In the present invention, water and/or steam can be split into hydrogen and oxygen by using heat available in steel plant wastes like molten slags.

The waste material of molten slag may comprise steel making slag, such as desulphurisation, converter, electric arc furnace (EAF), blast furnace slags, ferrochrome and ferromanganese slags from a submerged arc furnace (SAF), or a mixture of these slags.

Water and/or steam is contacted with molten slag in the presence of reducing agents in a reactor, like, for example, a carbonaceous material.

Presence of FeO and/or other reducing agents such as carbon in the form of coal, coke or refractory blocks enhance the process of hydrogen generation. At the operating temperature (above 1500° C.), it is still possible for hydrogen to recombine with oxygen to form water. However, FeO present in the slag reacts with the oxygen to form higher valence oxides such as Fe₂O₃ and Fe₃O₄.

The thermodynamic activity of oxygen in the immediate vicinity of slag is reduced, thus, reducing the chances of recombination of hydrogen and oxygen.

Presence of strong deoxidizers, such as carbon (in the form of coal, coke, or graphite blocks), enhance the kinetics of removal of oxygen, further improving the efficiency of the hydrogen generation process. Waste materials as reducing agents, like carbonaceous materials, are abundantly available in steel plants for use in this process to assist the generation of hydrogen by contacting water and/or steam with molten slag in the presence of a reducing agent in the reactor.

Thus, the present invention provides a method for producing hydrogen and/or other gases from steel plant wastes and waste heat, comprising the steps of providing molten waste from a steel plant, like molten slag, in a reactor; contacting the molten slag with water and/or steam in the presence of a reducing agent to form a stream of hydrogen and/or other gases; and extracting hydrogen and/or other gases from said stream.

BRIEF DESCRIPTION OF THE DRAWING

The invention can now be described in detail with the help of the FIGURE of the accompanying drawing in which:

FIG. 1 is a schematic representation of a system for producing a stream of gases using steel plant wastes and their waste heat in accordance with the present invention.

DESCRIPTION OF THE INVENTION

Water and/or steam is sprayed on LD slag, or other steel plant wastes having a temperature above 1600° C. The waste is either static, for example, in a static reactor or a ladle or a pot 1 or on ground or moving (e.g., being poured or in fluid motion down a slope or on a conveyor). The water sprayed through a water line 3 immediately splits when it comes in contact with the hot slag. The emanating gases are funneled through a hood 2 placed over the area and collected using a gas collection pipe 4.

The preferred temperature of the molten slag in the reactor is greater than about 1250° C. when water is sprayed into the molten slag.

The oxygen generated from splitting the water will react with the carbon present forming carbon monoxide. The gas stream comprising hydrogen and carbon monoxide can then be collected from the reactor.

In the present invention, the production of a gas stream comprises hydrogen and carbon monoxide in the volume ratio of between 1:0.2 to 1:1.

The gas stream produced in the reactor comprises at least 10 volume percent of hydrogen gas and not greater than about 15 volume percent of carbon dioxide.

In another embodiment, the extracted gas stream may comprise hydrogen and carbon monoxide in the ratio of 1:1 to about 8:1.

The water present may be extracted from the gas stream for recycling.

The water is contacted with the molten slag in the reactor by spraying water using a spray nozzle. Steam can also be injected into the molten slag in the reactor, using a lance.

The reducing agent or the carbonaceous material can be injected into the molten slag in the reactor along with the water and/or steam.

The carbonaceous material to be injected into the molten slag may comprise material selected from a group consisting of coal, coke, steel plant waste, municipal waste, and coal mine waste. The ratio of water to carbonaceous material injected may be from about 1:0.1 to 1:1.

For promoting the formation of hydrogen, a flux may be added to the molten slag and the carbonaceous material.

From the stream of hydrogen and/or other gases produced by the method of the present invention, the hydrogen and carbon monoxide can be separated.

The use of steel plant wastes and their waste heat is a cost effective method for generation of hydrogen or hydrogen and carbon monoxide. 90 million tons of LD slag produced annually can be a major source for supply of hydrogen gas worldwide.